Patent Publication Number: US-8524161-B2

Title: Multiple layer substrate support and exhaust gas treatment device

Description:
This application claims the benefit of the filing date, under 35 U.S.C. §119(e), of U.S. Provisional Application for Patent Ser. No. 61/234,003, filed on Aug. 14, 2009, and is a continuation-in-part of U.S. Ser. No. 12/200,083, filed on Aug. 28, 2008, now U.S. Pat. No. 8,017,085 which claims priority from U.S. Provisional Application for Patent Ser. No. 60/967,177, filed on Aug. 31, 2007, which applications are incorporated herein by reference. 
    
    
     Disclosed is a mat or mat-pre-form hybrid for use in an exhaust gas treatment device, such as catalytic converters and diesel particulate traps that are used in automotive exhaust systems. The mat or pre-form may be used as a mounting mat to mount a fragile monolith within an outer housing of an exhaust gas treatment device or as thermal insulation in an end cone of the exhaust gas treatment device. 
     Exhaust gas treatment devices are used on automobiles to reduce atmospheric pollution from engine emissions. Examples of widely used exhaust gas treatment devices include catalytic converters and diesel particulate traps, selective catalyst reduction units, NO x  traps, and the like. 
     A catalytic converter for treating exhaust gases of an automotive engine includes a housing, a fragile catalyst support structure or substrate for holding the catalyst that is used to effect the oxidation of carbon monoxide and hydrocarbons and the reduction of oxides of nitrogen, and a mounting mat disposed between the outer surface of the fragile catalyst support structure and the inner surface of the housing to resiliently hold the fragile catalyst support structure within the housing. 
     A diesel particulate trap for controlling pollution generated by diesel engines generally includes a housing, a fragile particulate filter or trap for collecting particulate from the diesel engine emissions, and a mounting mat that is disposed between the outer surface of the filter or trap and the inner surface of the housing to resiliently hold the fragile filter or trap structure within the housing. 
     The materials comprising fragile catalyst support structures or substrates are commonly frangible or brittle materials exhibiting a high heat resistance, a low thermal expansion coefficient, and a low impact resistance. The fragile catalyst support structure typically comprises a monolithic structure manufactured from a frangible material of metal or a brittle, ceramic material such as aluminum oxide, silicon dioxide, magnesium oxide, zirconia, cordierite, silicon carbide and the like. These materials provide a skeleton type of structure with a plurality of gas flow channels. These monolithic structures can be so fragile that even small shock loads or stresses are often sufficient to crack or crush them. In order to protect the fragile structure from thermal and mechanical shock and other stresses noted above, as well as to provide thermal insulation and a gas seal, a mounting mat is positioned within the gap between the fragile structure and the housing. 
     The geometry comprising substrates typically promotes a high surface area to volume ratio. In certain embodiments, the substrate geometry comprises a plurality of elements which are thin and fragile. Without limitation, a common geometry for substrates is a monolith comprising an array of hollow rectangular prism cells defining tiny flow channels, separated by thin, fragile walls, such as in a honeycomb-type configuration. 
     Together, the geometric and material considerations for substrates commonly result in a substrate which is susceptible to impact, crushing, or other mechanical failure from small shockloads or stress, and which operates at very high temperatures. To address the problem of the fragile nature of the substrate, it is common to protect the substrate within a housing, typically a metallic housing, with a space or gap between the external surface of the substrate and the internal surface of the housing. In order to protect the substrate from thermal and mechanical shock and other stresses, as well as to provide thermal insulation, it is known to position at least one sheet of mounting material within the gap between the substrate and the housing. 
     Because exhaust gas treatment devices are designed to operate at temperatures substantially higher than ambient temperatures and are designed to cool to ambient temperatures when not operating, exhaust gas treatment devices are designed to undergo significant temperature fluctuations. The mounting of the substrate is designed to protect the substrate over the entire range of temperatures to which the device is exposed; from ambient through operating temperatures. The temperature fluctuations present a considerable challenge in designing the substrate mounting system. 
     A common means of mounting the substrate comprises inclusion of an insulating mounting mat between the substrate and the metallic housing. The mounting mat may be wrapped about the substrate and may be compressed by enclosing the housing around it. The level of compression is selected to provide an engagement force between the housing and the mat; and, the mat and the substrate, which produces mounting or holding forces both sufficiently high to secure the substrate with respect to the housing, and sufficiently low to avoid damage to the substrate. Also, a mounting mat will inherently have some resistance to heat flow and, in certain embodiments is a good insulator; the mat resists propagation of heat from the substrate to the housing and thereby lowers the steady state operating temperature of the housing for a given steady state operating temperature of the substrate. 
     Selection of a type of mounting material and the ambient temperature compression load to which to subject the mounting material to yield acceptable mounting or holding forces at all temperatures that the exhaust gas treatment device experiences continues to be a source of difficulty. Compounding this difficulty is the need for an insulative material between the substrate and the housing having a low thermal conductivity but which will not add undesirable weight or bulk to the device. 
     DESCRIPTION 
     Disclosed is a multiple layer mat comprising a first layer comprising a non-intumescent sheet of inorganic fibers having a first major surface and a second major surface opposite the first major surface; a second layer comprising a non-intumescent sheet of inorganic fibers having a first major surface and a second major surface opposite the first major surface; a microporous inorganic insulating layer positioned between said first non-intumescent layer and second non-intumescent layer. 
     Also disclosed is an exhaust gas treatment device comprising a housing; a fragile structure located within the housing; and a multiple layer mounting mat disposed between said housing and said fragile structure, said mat comprising a first layer comprising a non-intumescent sheet of inorganic fibers having a first major surface and a second major surface opposite the first major surface; a second layer comprising a non-intumescent sheet of inorganic fibers having a first major surface and a second major surface opposite the first major surface; and a microporous inorganic insulating layer positioned between said first non-intumescent layer and second non-intumescent layer. 
     Additionally disclosed is a multiple layer mat comprising a first layer comprising an intumescent sheet of inorganic fibers having a first major surface and a second major surface opposite the first major surface; a second layer comprising an intumescent sheet of inorganic fibers having a first major surface and a second major surface opposite the first major surface; a microporous inorganic insulating layer positioned between the first intumescent layer and second intumescent layer. 
     Additionally disclosed is an exhaust gas treatment device comprising a housing; a fragile structure located within the housing; and a multiple layer mounting mat disposed between said housing and said fragile structure, said mat comprising a first layer comprising an intumescent sheet of inorganic fibers having a first major surface and a second major surface opposite the first major surface; a second layer comprising an intumescent sheet of inorganic fibers having a first major surface and a second major surface opposite the first major surface; and a microporous inorganic insulating layer positioned between the first intumescent layer and second intumescent layer. 
     Additionally disclosed is a multiple layer mat comprising a first layer comprising a non-intumescent or intumescent sheet of inorganic fibers having a first major surface and a second major surface opposite the first major surface; a second layer comprising a microporous inorganic insulating layer having a first major surface and a second major surface opposite the first major surface; and a bonding means between said first layer and said second layer. 
     Additionally disclosed is an exhaust gas treatment device comprising a housing; a fragile structure located within the housing; and a multiple layer mounting mat disposed between said housing and said fragile structure, said mat comprising a first layer comprising a non-intumescent or intumescent sheet of inorganic fibers having a first major surface and a second major surface opposite the first major surface; a second layer comprising a microporous inorganic insulating layer having a first major surface and a second major surface opposite the first major surface; and a bonding means between said first layer and said second layer. 
     Further disclosed is a multiple layer mat comprising a first layer comprising an intumescent or non-intumescent sheet of inorganic fibers having a first major surface and a second major surface opposite the first major surface; a second layer comprising a microporous inorganic insulating layer having a first major surface and a second major surface opposite the first major surface; and a banding means encircling at least a portion of the exterior surfaces of said first layer and said second layer. 
     Additionally disclosed is an exhaust gas treatment device comprising a housing; a fragile structure located within the housing; and a multiple layer mounting mat disposed between said housing and said fragile structure, said multiple layer mat comprising a first layer comprising a non-intumescent or intumescent sheet of inorganic fibers having a first major surface and a second major surface opposite the first major surface; a second layer comprising a microporous inorganic insulating layer having a first major surface and a second major surface opposite the first major surface; and a banding means encircling at least a portion the exterior surfaces of said first layer and said second layer. 
     Further disclosed is a multiple layer mat comprising a first layer comprising a non-intumescent or intumescent sheet of inorganic fibers, said layer having a first major surface and a second major surface opposite the first major surface; a second layer adjacent said first layer, said second layer comprising a microporous inorganic insulating layer having a first major surface and a second major surface opposite the first major surface; and wherein said first layer and second layer are encapsulated within a polymeric bag. 
     Additionally disclosed is an exhaust gas treatment device comprising a housing; a fragile structure located within the housing; and a multiple layer mounting mat disposed between said housing and said fragile structure, said multiple layer mat comprising a first layer comprising a non-intumescent or intumescent sheet of inorganic fibers, said layer having a first major surface and a second major surface opposite the first major surface; a second layer adjacent said first layer, said second layer comprising a microporous inorganic insulating layer having a first major surface and a second major surface opposite the first major surface; and wherein said first layer and second layer are encapsulated within a polymeric bag. 
     Further disclosed is a multiple layer mat comprising a first layer comprising a non-intumescent or intumescent sheet of inorganic fibers having a first major surface and a second major surface opposite the first major surface; a second layer comprising a microporous inorganic insulating layer; and a binder disposed between said first layer and said second layer. 
     Additionally disclosed is an exhaust gas treatment device comprising a housing; a fragile structure located within the housing; and a multiple layer mounting mat disposed between said housing and said fragile structure, said multiple layer mat comprising a first layer comprising a non-intumescent or intumescent sheet of inorganic fibers having a first major surface and a second major surface opposite the first major surface; a second layer comprising a microporous inorganic insulating layer; and a binder disposed between said first layer and said second layer. 
     Further disclosed is a multiple layer mat comprising a first layer comprising an intumescent or non-intumescent sheet of inorganic fibers having a first major surface and a second major surface opposite the first major surface; a scrim layer having a first major surface and a second major surface opposite the first major surface; and a microporous inorganic insulating layer positioned between the first layer and said scrim layer. 
     Additionally disclosed is an exhaust gas treatment device comprising a housing; a fragile structure located within the housing; and a multiple layer mounting mat disposed between said housing and said fragile structure, said multiple layer mat comprising a first layer comprising an intumescent or non-intumescent sheet of inorganic fibers having a first major surface and a second major surface opposite the first major surface; a scrim layer having a first major surface and a second major surface opposite the first major surface; and a microporous inorganic insulating layer positioned between the first layer and said scrim layer. 
     Further disclosed is a multiple layer support comprising a microporous inorganic insulating layer comprising a three-dimensional pre-form; and a flexible layer wrapped about at least a portion of the perimeter of said pre-form. 
     Additionally disclosed is an exhaust gas treatment device comprising a housing; a fragile structure located within the housing; and a multiple layer support disposed between said housing and said fragile structure, said support comprising a microporous inorganic insulating layer comprising a three-dimensional pre-form; and a flexible layer wrapped about at least a portion of the perimeter of said pre-form. 
     Further disclosed is a multiple layer support comprising a three-dimensional pre-form comprising an inner layer of microporous inorganic insulating material and an outer layer applied over at least a portion of said inner layer. 
     Additionally disclosed is an exhaust gas treatment device comprising a housing; a fragile structure located within the housing; and a multiple layer support disposed between said housing and said fragile structure, said support comprising a three-dimensional pre-form comprising an inner layer of microporous inorganic insulating material and an outer layer applied over at least a portion of said inner layer. 
     Further provided is a multiple layer mat comprising: a first layer comprising a non-intumescent sheet of inorganic fibers having a first major surface and a second major surface opposite the first major surface; a second layer comprising an intumescent sheet of inorganic fibers having a first major surface and a second major surface opposite the first major surface; and a microporous inorganic insulating layer positioned between said first layer and second layer. 
     Additionally disclosed is a multiple layer mat comprising: a first layer comprising a sheet of inorganic fibers having a first major surface and a second major surface opposite the first major surface; a second layer comprising a sheet of inorganic fibers having a first major surface and a second major surface opposite the first major surface; a microporous inorganic insulating layer positioned between the first layer and the second layer. 
     Further disclosed is a multiple layer mat comprising: a first layer comprising a sheet of inorganic fibers having a first major surface and a second major surface opposite the first major surface; a second layer adjacent said first layer, said second layer comprising a microporous inorganic insulating layer having a first major surface and a second major surface opposite the first major surface; and wherein the first layer and the second layer are encapsulated within a polymeric bag. 
     Additionally disclosed is a multiple layer mat comprising: a first layer comprising a sheet of inorganic fibers having a first major surface and a second major surface opposite the first major surface; a second layer comprising a microporous inorganic insulating layer having a first major surface and a second major surface opposite the first major surface; and either: (i) a bonding means between the first layer and the second layer; (ii) a banding means encircling at least a portion of the exterior surfaces of the first layer and the second layer, such that the first layer is engaged with the second layer; or (iii) a scrim layer, wherein the second major surface of the first layer is engaged with the first major surface of the second layer, and the scrim layer is engaged with the second major surface of the second layer. 
     Additionally disclosed is a multiple layer support comprising: a microporous inorganic insulating layer comprising a three-dimensional pre-form; and a flexible layer disposed about at least a portion of the perimeter of the three-dimensional pre-form. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows an illustrative embodiment of a mounting mat for an exhaust gas treatment device. 
         FIG. 2  shows another illustrative embodiment of a mounting mat for an exhaust gas treatment device. 
         FIG. 3  shows a further illustrative embodiment of a mounting mat for an exhaust gas treatment device. 
         FIG. 4  shows a further illustrative embodiment of a mounting mat for an exhaust gas treatment device. 
         FIG. 5  shows an illustrative embodiment of a mounting mat for an exhaust gas treatment device. 
         FIG. 6  shows an illustrative embodiment of a mounting mat for an exhaust gas treatment device. 
         FIG. 7  shows an illustrative embodiment of a hybrid mat-preform for an exhaust gas treatment device. 
         FIG. 8  shows another illustrative embodiment of a hybrid mat-preform for an exhaust gas treatment device. 
         FIG. 9  shows an illustrative embodiment of an exhaust gas treatment device incorporating a hybrid mounting mat. 
     
    
    
     Provided is a substrate mounting system for mounting a fragile substrate within a housing of an exhaust gas treatment device. The substrate mounting system includes a microporous insulation layer and at least a second layer. The substrate mounting system is positioned between the exterior surfaces of a fragile catalyst support structure, such as a fragile monolithic substrate, and the inner surfaces of the housing of the exhaust gas treatment device. 
     The insulative layer of the substrate mounting system promotes the insulative character of the material between the substrate and the housing and thereby decreases the steady state operating temperature of the housing and other materials external to the insulative layer for a given steady state operating temperature of the substrate. In such embodiments, the insulation reduces the thermal strain which the materials external to the insulative layer undergo, mitigating changes in the mounting or holding forces to which the substrate is subjected. In some embodiments, the insulative layer insulates the mat from the substrate and thereby decreases the operating temperature of the mat for a given operating temperature of the substrate. In such embodiments, the thermal strain which the mat undergoes is reduced, reducing changes in the mounting or holding forces to which the substrate is subjected. In other embodiments, the insulative layer is positioned between the mat and the housing and thereby decreases the surface temperature of the housing for a given operating temperature of the substrate. In such embodiments, the thermal strain which the housing undergoes is reduced, reducing changes in the mounting or holding forces to which the substrate is subjected. 
     The exhaust gas treatment device generally comprises a fragile substrate, a housing, and a mounting system comprising a multilayer mounting mat including a microporous inorganic insulating layer. Optionally, the device may further comprise additional components. 
     A substrate is a component in an exhaust gas treatment device which modifies exhaust material. There are many kinds of exhaust gas treatment devices which may comprise a substrate. One type of exhaust gas treatment device is a catalytic converter; the active portion of a catalytic converter comprises a substrate coated or impregnated with a catalyst to promote oxidation of carbon monoxide and hydrocarbons and the reduction of oxides of nitrogen, at least partially eliminating undesired products of combustion in the exhaust stream. 
     Substrate monoliths are typically oval or round in cross-sectional configuration, but other shapes are possible. The substrate is spaced from its housing by a gap width distance which will vary according to the type and design of the device utilized, e.g., a catalytic converter, a diesel catalyst structure, or a diesel particulate trap. In some embodiments the gap can be at least about 0.05 inch (1.27 mm), and in other embodiments the gap can be up to one inch (25.4 mm) or more. This gap width may typically range from about 3mm to about 25 mm with a range of about 3 mm to about 8 mm being commercially common widths. The substrate mounting system is disposed in this space to provide both thermal insulation to the external environment and mechanical support to the ceramic monolith substrate, protecting the substrate from damage due to mechanical shock. 
     A diesel particulate filter is another type of exhaust gas treatment device. The active portion of a diesel particulate filter comprises a substrate acting as a filter. A diesel particulate trap may include one or more porous tubular or honeycomb-like structures (having channels closed at one end, however), which are mounted by a thermally resistant material within a housing. Particulate is collected from exhaust gases in the porous structure, typically until regenerated by a high temperature burnout process. 
     Another type of exhaust gas treatment device is a selective catalyst reduction unit; the active portion of a selective catalyst reduction unit comprises a substrate, coated with a catalyst to promote chemical reduction and at least partial elimination of undesired products in the exhaust stream. 
     Another type of exhaust gas treatment device is a NO x  trap; the active portion of a NO x  trap comprises a catalytic substrate comprising alkali or alkaline earth materials. The trap operates in a cyclic manner; cycling between a “sorbtion” process and a “regeneration” process. During sorbtion the substrate intakes NO x  species and traps them on the surface of the catalytic substrate as nitrate species. During regeneration, a reducing material is introduced into the NO x  trap and the nitrate species are removed from the substrate and reduced to nitrogen. 
     Non-automotive applications for the subject mounting system include but are not limited to catalytic converters for chemical industry emission (exhaust) stacks. 
     In an exhaust gas treatment device, the substrate may operate at temperatures substantially above ambient temperature. Without limitation, the operating temperature for certain embodiments of exhaust gas treatment devices is about 1000° C. Because of the substantially elevated temperatures at which it operates, the substrate typically comprises materials having excellent resistance to heat, i.e., a very high melting point, and very low thermal expansion coefficient. There are many materials which have these properties including a wide variety of ceramics, tungsten, rhenium, and more exotic materials. One group of very common materials which exhibit excellent resistance to heat is ceramics. Exhaust gas treatment device substrates typically comprise a heat resistant frangible material, such as a monolithic structure formed of a brittle, fireproof ceramic material such as, but not limited to, aluminum oxide, silicon dioxide, magnesium oxide, zirconia, cordierite, silicon carbide and the like. 
     A property of many common ceramics is their low toughness. That is, while many ceramics are hard, strong, or both hard and strong, ceramics tend to display low toughness and tend to fracture at low strain levels. This makes ceramic components prone to breakage or fracture under mechanical loading conditions typically experienced by an exhaust gas treatment device. Therefore, it is common to incorporate means to protect the substrate. 
     A housing is a hollow body which at least partially encloses the substrate. The housing protects the substrate from impact, torsion, tension, compression, or other mechanical loading which may damage the substrate. In certain embodiments. the housing comprises a thin shell. The housing comprises materials having good resistance to heat, i.e., a high melting point and high heat resistance. The materials comprising exhaust gas treatment device housings are commonly ductile materials comprising a lower heat resistance than the monolith, a higher thermal expansion coefficient than the monolith, and a higher impact resistance than the monolith. Without limitation, in certain embodiments the exhaust gas treatment device housing comprises a metal or metal alloy, such as high temperature-resistant steel. 
     The present substrate mounting system may comprise at least one microporous insulating layer, and at least one flexible, fibrous mat which when combined, form a hybrid mounting system for incorporation within an exhaust gas treatment device. The insulating layer and the fibrous mat may be combined in a variety of ways to form the present mounting system and a variety of techniques may be employed to achieve such a combination. 
     According to certain embodiments, the mounting system may be preassembled by combining the insulating layer and the second or more layers to form a multiple layer unit. Various devices and methods may be utilized to hold the insulating layer and the layer(s) together. According to certain embodiments, the layers of the mounting mat may be connected together through the use of an elongated banding means, such as a tourniquet. The tourniquet material may comprise a tape, a non-adhesive tape or a film or a combination thereof. For example, in some embodiments, the majority of the tourniquet material may comprise a non-adhesive tape with the ends of the tourniquet material secured by an adhesive tape, while in other embodiments, the entire length of the tourniquet material may comprise an adhesive tape or elastic bands. 
     Another way of holding the layers of the mounting mat together is through the use of spot bonding. For example, in some embodiments, the insulating layer may be spot bonded to the mounting mat. Typically, adhesive is applied in a spot-like manner to various areas on the mounting mat. A film wrapped insulating layer is then applied over the adhesive treated side of the mounting mat. The fibrous mat and insulating layer are then secured together by the application of pressure to form a single unit for assembly within an exhaust gas treatment device. 
     Alternatively, a two-sided tape may be employed to attach the insulating layer and the fibrous mat together. In this embodiment, the two-sided tape may be applied to either a film wrapped insulating layer or the fibrous mat. The film wrapped insulating layer is placed over the tape treated side of the fibrous mat or the fibrous mat is placed over the tape treated side of the film wrapped insulating layer. Applying pressure to the insulating layer and the fibrous mat adheres both components to each other to secure and form a single unit for assembly within an exhaust gas treatment device. 
     In addition to spot bonding and two-sided tapes, other means for bonding the insulating layer and the fibrous mat together include brush/roll application of an adhesive, applying a spray-on adhesive, or applying a hot melt to secure the two components together to form a single unit for assembly within an exhaust gas treatment device. Brush/roll adhesives, spray-on adhesives and hot melts may be applied to either a film wrapped insulating layer or the fibrous mat followed by positioning the components over one another, and securing the components together through the application of pressure in a manner similar to that described above. 
     In an alternative embodiment, the insulating layer and the fibrous mat may be encapsulated within a single polymeric bag. The encapsulation material or bag may be formed from a polyethylene polymer that is shrink wrapped or vacuum formedaround the insulating layer and the fibrous mat to form a multiple layer unit for installation within an exhaust gas treatment device. 
     According to other embodiments, the mounting system comprising the insulating layer and the fibrous mat may form a single unit through the creation of a sandwich hybrid of the two components. A sandwich hybrid typically comprises an inner sandwich layer and an outer sandwich layer. According to certain embodiments, the sandwich hybrid of the present disclosure may comprise positioning an insulating layer (the inner sandwich layer) between two flexible fibrous layers (the outer sandwich layers) or positioning a flexible fibrous layer (as an inner sandwich layer) between two insulating layers (the outer sandwich layers). Either a single flexible fibrous layer and insulating layer may be used or differing types of flexible fibrous layers and insulating layers may be used to form the sandwich hybrid. 
     Also, the sandwich hybrid may comprise multiple inner sandwich layers, multiple outer sandwich layers, several sandwich hybrid layers, or several hybrid layers of multiple inner and/or outer sandwich layers. In one such embodiment, the flexible fibrous layer and the insulating layer are held together by a scrim. The scrim functions as an outer sandwich layer which holds the insulating layer to the flexible fibrous layer. The insulating layer may or may not need to be encapsulated by a film depending upon its position within the mounting system. For example, the porosity of the scrim may necessitate the encapsulation of the insulating layer when the insulating layer is positioned between the flexible fibrous layer and the scrim. Positioning the insulating layer between two layers of flexible fibrous layer may not necessitate the encapsulation of the insulating layer due to the low porosity typically exhibited by flexible fibrous layers. Various types of scrims may be used including tea bags, aluminum foil, ethylene, and Isofrax paper (commercially available fibers from Unifrax I LLC, Niagara Falls, N.Y., under the trademark ISOFRAX®). In addition to the scrim, an adhesive may be used to aid in the formation of the multiple layer mounting system. This adhesive may be a polymer present within the flexible fibrous layer or within the scrim. 
     An alternative embodiment of the sandwich hybrid utilizes heat and pressure to bind or weld the flexible fibrous layer(s) and the insulating layer together. In one such embodiment, the insulating layer is positioned between two flexible fibrous layers. The positioning of the insulating layer between two flexible fibrous layers renders the insulating layer not visible from an exterior view of the mounting system. The insulating layer may or may not be encapsulated within a shrink wrap or wrapped within a film. An example of one such embodiment includes an insulating layer of Wacker WDS® 1000 from Wacker Chemie GmbH (Munich) sandwiched between two layers of low basis weight mounting mat, such as ISOMAX® AV1 available from Unifrax I LLC, Niagara Falls, N.Y. 
     A further alternative embodiment of the sandwich hybrid mounting system comprises application of a binder spray to adhere the insulating layer to and between two flexible fibrous layers. The binder spray functions as an adhesive and is applied on the surfaces of the insulating layer and flexible fibrous layer as necessary to secure an adequate adhesion of the individual components to form a single unit mounting system for installation within an exhaust gas treatment device. 
     In an alternative embodiment, the mounting system comprises a preformed cylinder comprising an inner layer and an outer layer that can be assembled within an exhaust gas treatment device as a single unit. One such embodiment comprises an insulating layer that is preformed as a cylinder and at least one flexible fibrous layer wrapped around the insulating layer. In this embodiment, the insulating layer is pressed into the shape of a cylinder to form the inner layer of the preformed cylinder. At least one flexible fibrous layer is then wrapped around the cylinder of insulative material forming the outer layer of the preformed cylinder. The cylindrical shape of the mounting system in this embodiment allows the mounting system to be slide wrapped over the substrate of an exhaust gas treatment device where desired. 
     Another embodiment of the preformed cylinder mounting system comprises preforming the insulative and the fibrous material layer together into a cylindrical shape as a single unit without having to separately wrap the mounting mat around the cylindrical insulating layer. The resulting preformed cylinder comprises two separate and distinct layers of insulative and fibrous mat material wherein the inner cylindrical layer comprises the insulative material and the outer cylindrical layer comprises the flexible fibrous material. 
     The insulating layer as described above is a layer of material characterized by a low thermal conductivity. As with any other design process, during design of an exhaust gas treatment device, considerations of weight savings and space savings must be balanced against cost considerations. Materials which exhibit low density or low bulk and take up little space, are desirable. In certain embodiments, the insulating layer exhibits both low density and low bulk. In certain embodiments, the stiffness of the insulating layer is between 3 MPa and 5 MPa for strains less than 0.1. For example, at strains less than 0.1, the insulating layer WDS® Flexible Contour (from Porextherm GmbH of Kempten, Germany) has a modulus of approximately 4 MPa, compared to the mounting mat alone having a modulus approaching zero (0) and the combined mounting system also having a modulus approaching zero (0). 
     Mounting support systems provide engagement forces which are developed by compression of the materials comprising the support system. While many materials are compressible, only materials which are compressible and are substantially elastic can return the energy thereby imparted to them to the system as an engagement force. Non-stiff materials will undergo large strains at low stresses and incorporate the energy causing the strain, the strain energy. Non-stiff, substantially elastic materials, will undergo large strains at low stresses, incorporate the strain energy, and return a substantial portion of the strain energy as a restoring force. This restoring force contributes to the mounting or holding force. Stiff materials will undergo small strains, at low stresses and incorporate the strain energy. Stiff, substantially elastic materials, will undergo small strains at low stresses, incorporate the strain energy, and return a substantial portion of the strain energy as a restoring force. 
     A subject mounting system incorporates one or more layers of material, all mechanically loaded at once such that all layers experience substantially identical stress. This kind of loading is “series loading”. In series loading, non-stiff layers will undergo greater strain and therefore incorporate greater strain energy than will the stiffer layers. Because there is a positive correlation between the amount of strain energy incorporated into a material during a given loading cycle and the hysteretic erosion of the material, stiffer materials may be protected from certain kinds of erosion by incorporating them in series with a non-stiff material. In certain embodiments a stiff insulating layer (relative to the mounting mat) is incorporated into the mounting system in series with a non-stiff mounting mat. 
     The insulating layer may include at least material from a class of materials available as thin, somewhat flexible sheets which exhibit low thermal conductivity and are substantially non-intumescent. According to certain embodiments, the insulating layer is a microporous inorganic insulation layer comprising a thin, flexible sheet exhibiting extremely low thermal conductivity. 
     Such microporous inorganic insulation is available as thin, flexible sheets having a thermal conductivity at 20° C. and at a density of about 350 kg/m 3  of less than about 0.021 W/mK. In certain embodiments the insulating layer is a microporous insulation comprising a thin, flexible sheet exhibiting a thermal conductivity at 20° C. and at about 350 kg/m 3  of less than about 0.021 W/mK, and having a thermal conductivity less than 0.055 W/mK for temperatures less than about 1000° C. 
     In certain embodiments, the insulating layer is a microporous inorganic insulation comprising a thin, flexible sheet exhibiting a thermal conductivity at 20° C. and at a density of about 350 kg/m 3  of less than about 0.021 W/mK, and a thermal conductivity less than 0.055 W/mK for temperatures less than 1000° C., having a bulk density between about 260 kg/m 3  and about 520 kg/m 3 . Microporous inorganic insulation having a greater density may be acceptable if sufficiently flexible to wrap around and conform to the outer surface of the substrate. In certain embodiments the insulating layer having these properties is available as thin, flexible sheets having a thickness between about 3 mm and about 20 mm. 
     In certain embodiments the insulating layer is substantially incompressible. One type of microporous inorganic insulation exhibits the compression performance shown in TABLE I at a density of about 350 kg/m 3 . In TABLE I, the listed pressures are those required to compress the material by the listed percentages at the listed temperatures. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE I 
               
               
                   
                   
               
               
                   
                 Compression 
                 20° C. 
                 400° C. 
                 800° C. 
               
               
                   
                   
               
             
            
               
                   
                 1% 
                 0.034 MPa 
                 0.028 MPa 
                 0.028 MPa 
               
               
                   
                 3% 
                 0.089 MPa 
                 0.083 MPa 
                 0.110 MPa 
               
               
                   
                 5% 
                 0.151 MPa 
                 0.144 MPa 
                 0.165 MPa 
               
               
                   
                 10%  
                 0.275 MPa 
                 0.295 MPa 
                 0.350 MPa 
               
               
                   
                   
               
            
           
         
       
     
     The microporous inorganic insulating layer comprises finely divided metal oxide and an opacifier, that is, a material that minimizes infra-red radiation; and optionally further comprises reinforcing inorganic fiber, such as glass filaments. The inorganic insulating layer, in its pre-installed form, may be sealed in a polymeric film, such as polyethylene, although the film may be selected for economy and functionality rather than composition. It is also possible that a minor amount of organic fibers or particles may be incorporated into the microporous insulating layer for processing considerations. 
     The finely divided metal oxide may comprise at least one of pyrogenic silicas, arc silicas, low-alkali precipitated silicas, silicon dioxide aerogels, aluminum oxides similarly prepared, and mixtures thereof. In one embodiment, the finely divided metal oxide comprises fumed silica. The finely divided metal oxide may have a specific BET surface area of from about 50 to about 700 m 2 /g, in particular from about 70 to about 400 m 2 /g. 
     The particle sizes of the materials in the microporous insulating layer are small enough that mechanisms of heat transfer are controlled. The particulate and fibrous material are sized to create pores which are less than about 0.1 microns in diameter, less than the mean free path of air. By limiting the quantity and motion of air in the pores, both conduction due to air and convection heat transfer is limited, thus reducing thermal conductivity. 
     The opacifier may comprise at least one of ilmenite, titanium dioxide, iron(II)/iron(III) mixed oxides, chromium dioxide, zirconium oxide, manganese dioxide, iron oxide, rutile, zirconium silicate, silicon carbide, and mixtures thereof. The opacifier may have a particle size less than about 15 microns, in certain embodiments, in the range from about 0.1 to about 10 microns. 
     The reinforcing fiber of the insulation layer may comprise a broad family of materials. The family of materials includes any inorganic fiber capable of providing the structure necessary to retain the microporous particles in a cohesive unit. The reinforcing fiber may be selected from aluminum silicate, magnesium silicate, rockwool, or combinations thereof. In certain embodiments, reinforcing fiber of the insulation layer may comprise at least one of textile glass fibers or quartz fibers, such as high-temperature-resistant fibers having an SiO 2  content of greater than 60% by weight, and in some embodiments greater than 90% by weight, silica fibers, textile fibers made from R glass, textile fibers made from S2 glass, textile fibers made from ECR glass, and fibers made from aluminum silicate. The fiber diameter may be greater than about 1.5 microns. 
     An insulating sheet commercially available from Porextherm GmbH (Kempten, Germany), comprises 55 weight % of HDK N25 highly dispersed silica (BET 280 m2/g), 40 weight % of zirconium silicate, 5 weight % of textile glass fibers (silicon content&gt;92%) having a density of 320 kg/m3 and a thickness of 10 mm. This sheet is substantially incompressible. 
     Another such microporous inorganic insulating material is WDS® Flexible Contour insulation, available from Porextherm GmbH (Kempten, Germany). WDS® Flexible Contour microporous insulation (WDS) is an exemplative material comprising about 50% silica, about 45% zirconium silicate, and about 5% of other materials, including reinforcing glass fibers, which may be used as an insulating layer that exhibits the low thermal conductivity discussed above in a low density, thin material. Without limitation, WDS® Flexible Contour is commercially produced in 3 mm, 5 mm, 7 mm, 10 mm, and 20 mm thicknesses. Similar microporous insulation material is available from Microtherm (Alcoa, Tenn.). 
     The microporous inorganic insulating layer engages the substrate either directly, or indirectly through an intermediate component, such as but not limited to, the flexible fibrous layer. The insulating layer is installed into the exhaust gas treatment device between the housing and the substrate. Placement of the insulating layer amongst other components of the exhaust gas treatment device determines which components are on the substrate side (hot side) of the insulating layer and which components are on the housing side (cold side) of the insulating layer. 
     An inorganic fibrous support or mounting mat is a substantially elastic, compressible material layer. The mounting mat is subject to heating by the substrate, and at least indirectly by the exhaust gases, and therefore may also operate at temperatures above ambient temperatures. A support or mounting mat typically comprises materials able to withstand elevated temperature environments while remaining substantially elastic and compressible. Fibrous mounting mats may comprise materials ranging from relatively inexpensive materials such as, for example, amorphous glass fibers such as S-glass, to more expensive materials such as, for example, high alumina ceramic oxide fibers. Intumescent materials as well as non-intumescent materials have been and continue to be employed in mounting mats, depending upon the application and conditions under which the mounting mats are to be used. 
     The fibrous mounting mat engages the substrate, either indirectly through an intermediate component or directly, and substantially immobilizes it with respect to the housing. At least one fibrous mounting mat is disposed in the exhaust gas treatment device between the housing and the substrate. The installed fibrous mounting mat is compressed such that it imparts a load, either indirectly through an intermediate component, or directly, on the housing and the substrate. As noted above, the amount of the compressive load is substantially proportional to the amount of compression. A friction force resulting from the normal force is also substantially proportional to the amount of compression. These forces, the compression force and the friction force, together or separately, substantially immobilize the substrate with respect to the housing. By “substantially immobilize” it is meant that the amount that the substrate may move with respect to the housing is very small, on the order of the largest elastic strain limit of the materials providing holding forces. In certain embodiments, the largest elastic strain limit of the materials providing holding forces is about 1% of the material thickness. 
     The flexible fibrous material refers to at least one sheet or layer primarily comprising high temperature resistant fiber, such as but not limited to ceramic fiber, and optionally including either within said at least one sheet or layer, or in an additional sheet or layer, intumescent material, reinforcing material, and the like. The high temperature resistant fiber, or ceramic fiber, sheet or layer may be in various forms such as paper, blanket, mat or felt, provided such form imparts the necessary thermal insulation and mechanical support. 
     In certain embodiments, the fibrous mounting mat may comprise Fiberfrax® paper available from Unifrax I LLC, Niagara Falls, N.Y. This product is made from bulk alumino-silicate glassy fiber having approximately 50/50 alumina/silica and a 70/30 fiber/shot ratio. About 93 weight percent of this paper product is ceramic fiber/shot, the remaining 7 percent being in the form of an organic latex binder. For higher substrate monolith temperatures, papers produced from Fibermax® polycrystalline mullite ceramic fibers available from Unifrax or alumina fibers may be employed. Other ceramic fibers that may be used include those formed from basalt, industrial smelting slags, alumina, zirconia, zirconia-silicates, alumino-silicates and chrome, zircon and calcium modified alumino-silicates and the like. 
     The flexible fibrous material layer may include an intumescent agent or material. The intumescent material may include at least one of unexpanded vermiculite, hydrobiotite, water-swelling tetrasilicic fluorine mica, alkaline metal silicates, or expandable graphite, and may be formed into a sheet using organic and/or inorganic binders to provide a desirable degree of wet strength. A sheet of intumescent material can be produced by standard paper making techniques as described, for example, in U.S. Pat. No. 3,458,329, the disclosure of which is incorporated herein by reference. 
     The flexible fibrous material layer may be produced in several different ways, including a conventional paper-making process, either hand laid or machine laid. A handsheet mold, a Fourdrinier paper machine, or a rotoformer paper machine can be employed to make the flexible, intumescent fibrous mounting mat. In any case, a flocculated aqueous slurry containing a number of components, as set forth below, is pressed to remove most of the water, and the mat is then dried. This process is well known to those skilled in the art. 
     In other embodiments, the flexible, fibrous mounting mat may comprise a substantially non-expanding composite sheet of high temperature resistant fibers and a binder. In certain embodiments, the mounting mat is “integral”, meaning that after manufacture the mounting mat has self supporting structure, needing no reinforcing or containment layers of fabric, plastic or paper, (including those which are stitch-bonded to the mat) and can be handled or manipulated without disintegration. By “substantially non-expanding” is meant that the sheet does not readily expand upon the application of heat as would be expected with intumescent paper. Of course, some expansion of the sheet does occur based upon its thermal coefficient of expansion. The amount of expansion, however, is insubstantial as compared to the expansion which occurs based upon intumescent properties. It will be appreciated that this type of mounting mat is substantially devoid of intumescent materials. 
     High temperature resistant fiber, including ceramic fibers which are useful in the non-expanding mounting mat include polycrystalline oxide ceramic fibers such as mullite, alumina, high alumina aluminosilicates, aluminosilicates, zirconia, titania, chromium oxide and the like. In certain embodiments, the fibers are refractory. When the ceramic fiber is an aluminosilicate, the fiber may contain between about 55 to about 98% alumina and between about 2 to about 45% silica, in certain embodiments with the ratio of alumina to silica being between 70 to 30 and 75 to 25. Suitable polycrystalline oxide refractory ceramic fibers and methods for producing the same are contained in U.S. Pat. Nos. 4,159,205 and 4,277,269, which are incorporated herein by reference. FIBERMAX® polycrystalline mullite ceramic fibers are available from Unifrax I LLC, Niagara Falls, N.Y. in blanket, mat or paper form. The fibers used in the non-expanding mounting mat may be substantially shot free, having very low shot content, generally on the order of about 5 percent nominally or less. The diameters of such fibers may be generally about 1 micron to about 10 microns. 
     The binder used in the non-expanding fibrous mounting mat is typically an organic binder which may be sacrificial in nature. By “sacrificial” is meant that the binder will eventually be burned out of the mounting mat, leaving only the fibers as the final mounting mat. Suitable binders include aqueous and nonaqueous binders, but often the binder utilized is a reactive, thermally setting latex which after cure is a flexible material that can be burned out of the installed mounting mat as indicated above. Examples of suitable binders or resins include, but are not limited to, aqueous based latexes of acrylics, styrene-butadiene, vinylpyridine, acrylonitrile, vinyl chloride, polyurethane and the like. Other resins include low temperature, flexible thermosetting resins such as unsaturated polyesters, epoxy resins and polyvinyl esters. Specific useful binders include but are not limited to HI-STRETCH V-60™, a trademark of B.F. Goodrich Co. (Akron, Ohio) for acrylonitrile based latex. Solvents for the binders can include water, or a suitable organic solvent, such as acetone, for the binder utilized. Solution strength of the binder in the solvent (if used) can be determined by conventional methods based on the binder loading desired and the workability of the binder system (viscosity, solids content, etc.). 
     Similarly, the non-expanding mounting mat can be prepared by conventional papermaking techniques. Using this process, the inorganic fibers are mixed with a binder to form a mixture or slurry. The slurry may then be diluted with water to enhance formation, and it may finally be flocculated with flocculating agent and drainage retention aid chemicals. Then, the flocculated mixture or slurry may be placed onto a papermaking machine to be formed into a ceramic paper mat. The mats or sheets may be formed by vacuum casting the slurry or mixture with conventional papermaking equipment and are typically dried in ovens. 
     Alternatively, the fibers may be processed into a mat by conventional means such as dry air laying. The mat at this stage, has very little structural integrity and is very thick relative to the conventional catalytic converter and diesel trap mounting mats. Where this alternative technique is used, the mat may be further processed by the addition of a binder to the mat by impregnation to form a discontinuous fiber composite. The binder is added after formation of the mat, rather than forming the mat prepreg as noted hereinabove with respect to the conventional papermaking technique. 
     In another embodiment, high index, crystallized, melt-formed refractory ceramic fibers are heat treated at temperatures above the mullite crystallization temperature of 980° C., such as temperatures ranging from 990° C. to about 1400° C. in a controlled manner to obtain specific amounts of crystallinity and crystallite size, thereby increasing fiber performance in the form of a catalytic converter mounting mat. In certain embodiments, such fibers will have at least about 5 to about 50 percent crystallinity as detected by x-ray diffraction, and a crystallite size of from about 50 Å to about 500 Å. When such fibers are employed, the mounting mat provides a minimum pressure for holding the fragile catalyst support structure within the housing across a wide operating temperature range normally encountered by automotive exhaust gas treatment device applications. By way of example, but not in limitation, such a mounting mat may provide a minimum holding pressure of at least one of i) at least 2 psi after at least 200 cycles and/or after 1000° C. of testing at 900° C. or ii) at least about 5 psi after at least 1000 cycles of testing at 750° C. The ceramic fibers which are useful in this embodiment are melt-formed ceramic fibers containing alumina and silica, including but not limited to melt spun refractory ceramic fibers. These include aluminosilicates, such as those aluminosilicate fibers having from about 40 to about 60 percent alumina and from about 60 to about 40 percent silica, and some embodiments, from about 47 to about 53 percent alumina and from about 47 to about 53 percent silica. The melt-formed, spun fibers are of high purity chemically and may have an average diameter in the range of about 1 to about 14 μm, and in certain embodiments, in the range of about 3 to 6.5 μm. The fibers are beneficiated as is well known in the art to obtain a greater than 90 percent fiber index, meaning they contain less than 10 percent shot, and often only about 5 percent shot. 
     In yet another embodiment, a flexible, fibrous, non-intumescent mounting mat for a substrate in a low temperature exhaust gas treatment device comprises high temperature resistant, amorphous, inorganic fibers and optionally includes a binder. The fibers may have a use temperature up to about 1260° C., a Young&#39;s Modulus of less than about 20×10 6  psi, and a geometric mean diameter less than about 5 μm. The fibers may comprise at least one of an amorphous alumina/silica fiber, an alumina/silica/magnesia fiber (such as S-2 Glass from Owens Corning, Toledo, Ohio), mineral wool, E-glass fiber, magnesia-silica fibers, such as ISOFRAX® fibers from Unifrax I LLC, Niagara Falls, N.Y., or calcia-magnesia-silica fibers, such as INSULFRAX® fibers from Unifrax I LLC, Niagara Falls, N.Y. or SUPERWOOL™ fibers from Thermal Ceramics Company. 
     The alumina/silica fiber typically comprises from about 45% to about 60% Al 2 O 3  and about 40% to about 55% SiO 2 ; and the fiber may comprise about 50% Al 2 O 3  and about 50% SiO 2 . The alumina/silica/magnesia glass fiber typically comprises from about 64% to about 66% SiO 2 , from about 24% to about 25% Al 2 O 3 , and from about 9% to about 10% MgO. The E-glass fiber typically comprises from about 52% to about 56% SiO 2 , from about 16% to about 25% CaO, from about 12% to about 16% Al 2 O 3 , from about 5% to about 10% B 2 O 3 , up to about 5% MgO, up to about 2% of sodium oxide and potassium oxide and trace amounts of iron oxide and fluorides, with a typical composition of 55% SiO 2 , 15% Al 2 O 3 , 7% B 2 O 3 , 3% MgO, 19% CaO and traces of the above mentioned materials. 
     According to certain embodiments, the flexible fibrous material layer comprises a layer, ply or sheet of biosoluble inorganic fibers. The term “biosoluble”, with regard to inorganic fibers, refers to inorganic fibers that are soluble or otherwise decomposable in a physiological medium or in a simulated physiological medium, such as simulated lung fluid. The solubility of the fibers may be evaluated by measuring the solubility of the fibers in a simulated physiological medium over time. A method for measuring the biosolubility (i.e. the non-durability) of the fibers in physiological media is disclosed U.S. Pat. No. 5,874,375 assigned to Unifrax I LLC, which is incorporated herein by reference. Other methods are suitable for evaluating the biosolubility of inorganic fibers. According to certain embodiments, the biosoluble fibers exhibit a solubility of at least 30 ng/cm 2 -hr when exposed as a 0.1 g sample to a 0.3 ml/min flow of simulated lung fluid at 37° C. According to other embodiments, the biosoluble inorganic fibers may exhibit a solubility of at least 50 ng/cm 2 -hr, or at least 100 ng/cm 2 -hr, or at least 1000 ng/cm 2 -hr when exposed as a 0.1 g sample to a 0.3 ml/min flow of simulated lung fluid at 37° C. 
     Without limitation, suitable examples of biosoluble inorganic fibers that can be used to prepare a flexible fibrous material layer for an exhaust gas treatment device include those biosoluble inorganic fibers disclosed in U.S. Pat. Nos. 6,953,757, 6,030,910, 6,025,288, 5,874,375, 5,585,312, 5,332,699, 5,714,421, 7,259,118, 7,153,796, 6,861,381, 5,955,389, 5,928,075, 5,821,183, and 5,811,360, each of which are incorporated herein by reference. 
     According to certain embodiments, the biosoluble alkaline earth silicate fibers may comprise the fiberization product of a mixture of oxides of magnesium and silica. These fibers are commonly referred to as magnesium-silicate fibers. The magnesium-silicate fibers generally comprise the fiberization product of about 60 to about 90 weight percent silica, from greater than 0 to about 35 weight percent magnesia and 5 weight percent or less impurities. According to certain embodiments, the alkaline earth silicate fibers comprise the fiberization product of about 65 to about 86 weight percent silica, about 14 to about 35 weight percent magnesia, 0 to about 7 weight percent zirconia and 5 weight percent or less impurities. According to other embodiments, the alkaline earth silicate fibers comprise the fiberization product of about 70 to about 86 weight percent silica, about 14 to about 30 weight percent magnesia, and 5 weight percent or less impurities. More information on magnesia-silica fibers can be found in U.S. Pat. No. 5,874,375, which is hereby incorporated by reference. 
     A suitable magnesium-silicate fiber is commercially available from Unifrax I LLC (Niagara Falls, N.Y.) under the registered trademark ISOFRAX. Commercially available ISOFRAX fibers generally comprise the fiberization product of about 70 to about 80 weight percent silica, about 18 to about 27 weight percent magnesia and 4 weight percent or less impurities. 
     According to certain embodiments, the biosoluble alkaline earth silicate fibers may comprise the fiberization product of a mixture of oxides of calcium, magnesium and silica. These fibers are commonly referred to as calcia-magnesia-silicate fibers. According to certain embodiments, the calcia-magnesia-silicate fibers comprise the fiberization product of about 45 to about 90 weight percent silica, from greater than 0 to about 45 weight percent calcia, from greater than 0 to about 35 weight percent magnesia, and 10 weight percent or less impurities. Typically, biosoluble calcia-magnesia-silica fibers comprise about 15% to about 35% CaO, about 2.5% to about 20% MgO, and about 60 to about 70% SiO 2 . 
     Useful calcia-magnesia-silicate fibers are commercially available from Unifrax I LLC (Niagara Falls, N.Y.) under the registered trademark INSULFRAX. INSULFRAX fibers generally comprise the fiberization product of about 61 to about 67 weight percent silica, from about 27 to about 33 weight percent calcia, and from about 2 to about 7 weight percent magnesia. Other suitable calcia-magnesia-silicate fibers are commercially available from Thermal Ceramics (Augusta, Ga.) under the trade designations SUPERWOOL 607 and SUPERWOOL 607 MAX. SUPERWOOL 607 fibers comprise about 60 to about 70 weight percent silica, from about 25 to about 35 weight percent calcia, and from about 4 to about 7 weight percent magnesia, and trace amounts of alumina. SUPERWOOL 607 MAX fibers comprise about 60 to about 70 weight percent silica, from about 16 to about 22 weight percent calcia, and from about 12 to about 19 weight percent magnesia, and trace amounts of alumina. 
     The biosoluble fibers are typically amorphous inorganic or glass fibers that may be melt-formed, are fibers of high chemical purity (greater than about 98%) and may have an average diameter in the range of about 1 to about 10 μm, and in certain embodiments, in the range of about 2 to 4 μm. While not specifically required, the fibers may be beneficiated, as is well known in the art. 
     Optionally, the non-intumescent flexible fibrous material layer includes a binder. Suitable binders include aqueous and non aqueous binders, but the binder typically utilized is a reactive, thermally setting latex which after cure is a flexible material that is stable up to at least about 350° C. About 5 to about 10 percent latex may be employed. 
     According to illustrative embodiments, the flexible fibrous material layer may include at least 25, 50, 75, 85 or 95 weight percent of the biosoluble inorganic fibers, based upon 100 percent of the total flexible fibrous material layer weight. According to certain illustrative embodiments, the flexible fibrous material layer comprises about 25 to about 100 weight percent alkaline earth silicate fibers, based upon 100 weight percent of the total flexible fibrous material layer weight. The flexible fibrous material layer may alternatively comprise about 50 to about 100 weight percent alkaline earth silicate fibers, based upon 100 weight percent of the total flexible fibrous material layer weight. According to one embodiment, the mounting mat comprises about 66 weight percent alkaline earth silicate fibers, based upon 100 weight percent of the total flexible fibrous material layer weight. 
     In certain embodiments, the flexible, fibrous material layer comprises one or more non-intumescent plies of melt-formed, amorphous, high-temperature resistant leached glass fibers having a high silica content and, optionally, includes a binder or other fibers suitable for acting as a binder. By the term “high silica content,” it is meant that the fibers contain more silica than any other compositional ingredient in the fibers. In fact, the silica content of these fibers after leaching are typically greater than any other glass fibers containing silica, including S-glass fibers, except crystalline quartz derived fibers or pure silica fibers. In one embodiment, it will be appreciated that the mounting mat may be devoid of intumescent materials, sol gel-derived glass silica fibers and/or backing or reinforcing layers. 
     Generally, the leached glass fibers will have a silica content of at least 67 percent by weight. In certain embodiments, the leached glass fibers contain at least 90 percent by weight silica, and in certain of these, from about 90 percent by weight to less than about 99 percent by weight silica. The fibers are also substantially shot free and exert a minimum holding pressure for holding said fragile structure within said housing of one of (i) at least about 10 kPa after 1000 cycles of testing at a hot face temperature of about 900° C., a gap bulk density of from about 0.3 to about 0.5 g/cm 3 , and a percent gap expansion of about 5 percent, or (ii) at least about 50 kPa after 1000 cycles of testing at a hot face temperature of about 300° C., a gap bulk density of from about 0.3 to about 0.5 g/cm 3 , and a percent gap expansion of about 2 percent. 
     The average fiber diameter of these leached glass fibers may be greater than at least about 3.5 microns, and often greater than at least about 5 microns. On average, the glass fibers typically have a diameter of about 9 microns, up to about 14 microns. Thus, these leached glass fibers are non-respirable. 
     Examples of leached glass fibers high in silica content and suitable for use in the production of a flexible fibrous material layer for a catalytic converter or other known gas-treating device include those leached glass fibers available from BelChem Fiber Materials GmbH, Germany, under the trademark BELCOTEX and from Hitco Carbon Composites, Inc. of Gardena Calif., under the registered trademark REFRASIL, and from Polotsk-Steklovolokno, Republic of Belarus, under the designation PS-23(R). 
     The BELCOTEX fibers are standard type, staple fiber pre-yarns. These fibers have an average fineness of about 550 tex and are generally made from silicic acid modified by alumina. The BELCOTEX fibers are amorphous and generally contain about 94.5 silica, about 4.5 percent alumina, less than 0.5 percent sodium oxide, and less than 0.5 percent of other components. These fibers have an average fiber diameter of about 9 microns and a melting point in the range of 1500° to 1550° C. These fibers are heat resistant to temperatures of up to 1100° C., and are typically shot free. 
     The REFRASIL fibers, like the BELCOTEX fibers, are amorphous leached glass fibers high in silica content for providing thermal insulation for applications in the 1000° to 1100° C. temperature range. These fibers are between about 6 and about 13 microns in diameter, and have a melting point of about 1700° C. The fibers, after leaching, typically have a silica content of about 95 percent by weight. Alumina may be present in an amount of about 4 percent by weight with other components being present in an amount of 1 percent or less. 
     The PS-23 (R) fibers from Polotsk-Steklovolokno are amorphous glass fibers high in silica content and are suitable for thermal insulation for applications requiring resistance to at least about 1000° C. These fibers have a fiber length in the range of about 5 to about 20 mm and a fiber diameter of about 9 microns. These fibers, like the REFRASIL fibers, have a melting point of about 1700° C. 
     By further treating either the leached glass fibers prior to formation of the flexible fibrous material layer, or flexible fibrous material layers made from these fibers after formation, the holding pressure performance of the flexible fibrous material layer can be improved sufficiently, even after cycling, to be adaptable for use in an exhaust gas treatment device. In one particular embodiment, these leached glass fibers (or the mounting mats containing them) may be heat treated at temperatures ranging from above at least about 900° C., such as from about 900° C. to about 1100° C., such that the mounting mat employing these fibers may exert the minimum required holding pressure within the exhaust gas treatment device, even after 1000 cycles of expansion and contraction. 
     The flexible fibrous material layer of this embodiment may include up to 100 percent by weight of the leached and surface treated glass fibers containing silica. However, in other embodiments, the flexible fibrous material layer may optionally comprise other known fibers such as alumina/silica fibers, or other ceramic or glass fibers suitable for use in the production of mounting mats for the particular temperature applications desired. Thus, alumina/silica fibers such as refractory ceramic fibers may be optionally employed for high temperature or wide ranging temperature applications. Other ceramic or glass fibers such as S-glass may be used with the leached glass silica fibers in similar or lower temperature applications. In such instances, however, the flexible fibrous material layer preferably includes at least 50 percent by weight of leached and surface treated glass fibers containing silica. In other words, the majority of the fiber utilized in the production of the mat will be leached and surface treated glass fibers containing silica, and in certain embodiments, at least 80 percent by weight of the fibers will be leached and surface treated glass fibers containing silica. 
     In certain alternative embodiments, fibers such as S2-glass and the like may be added to the flexible fibrous material layer in quantities of from greater than 0 to about 50 percent by weight, based upon 100 percent by weight of the total mat. In other alternative embodiments, the flexible fibrous material layer may include refractory ceramic fibers in addition to the leached glass fibers. When refractory ceramic fibers, that is, alumina/silica fibers or the like are utilized, they may be present in an amount ranging from greater than 0 to less than about 50 percent by weight, based upon 100 percent by weight of the total flexible fibrous material layer. 
     The flexible fibrous material layer may or may not include a binder. Either a single type of binder or mixture of more than one type of binder may be included within the flexible fibrous material layer. Suitable binders include organic binders, inorganic binders and mixtures of these two types of binders. According to certain embodiments, the intumescent or non-intumescent flexible fibrous material layer, include one or more organic binders. The organic binders may be provided as a solid, a liquid, a solution, a dispersion, a latex, or similar form. The organic binder may comprise a thermoplastic or thermoset binder, which after cure is a flexible material that can be burned out of an installed mounting mat. Examples of suitable organic binders include, but are not limited to, acrylic latex, (meth)acrylic latex, copolymers of styrene and butadiene, vinylpyridine, acrylonitrile, copolymers of acrylonitrile and styrene, vinyl chloride, polyurethane, copolymers of vinyl acetate and ethylene, polyamides, silicones, and the like. Other resins include low temperature, flexible thermosetting resins such as unsaturated polyesters, epoxy resins and polyvinyl esters. 
     The organic binder may be included in the mounting mat in an amount of greater than 0 to about 20 weight percent, from about 0.5 to about 15 weight percent, from about 1 to about 10 weight percent, or from about 2 to about 8 weight percent, based on the total weight of the flexible fibrous material layer. 
     The flexible fibrous material layer may include polymeric binder fibers instead of, or in combination with, the resinous or liquid binder. These polymeric binder fibers may be used in amounts ranging from greater than 0 to about 20 percent by weight, from about 1 to about 15 weight percent, and from about 2 to about 10 weight percent, based upon 100 percent by weight of the total composition, to aid in binding the heat treated fibers together. Suitable examples of binder fibers include polyvinyl alcohol fibers, polyolefin fibers such as polyethylene and polypropylene, acrylic fibers, polyester fibers, ethyl vinyl acetate fibers, nylon fibers and combinations thereof. 
     When an organic binder is used, the components are mixed to form a mixture or slurry. The slurry of fibers and binder is then formed into a flexible fibrous material layer structure and the binder is removed, thereby providing a flexible fibrous material layer containing the heat-treated silica fibers (and optionally additional fibers). Typically, a sacrificial binder is employed to initially bond the fibers together. By “sacrificial,” it is meant that the organic binder will eventually be burned out of the flexible fibrous material layer, leaving only the heat treated silica fibers (and other ceramic or glass fibers, if used) as the flexible fibrous material layer. 
     In addition to organic binders, the flexible fibrous material layer may also include inorganic binder material. Without limitation, suitable inorganic binder materials include inorganic particulate materials, colloidal dispersions of alumina, silica, zirconia, and mixtures thereof. 
     The flexible fibrous material layer may be prepared by any known techniques commonly used in the preparation of flexible fibrous material layer. For example, using a papermaking process, the fibers may be mixed with a binder or other binder fibers to form a mixture or slurry. The fibrous components may be mixed at about a 0.25% to 5% consistency or solids content (0.25-5 parts solids to 99.75-95 parts water). The slurry may then be diluted with water to enhance formation, and it may finally be flocculated with a flocculating agent and drainage retention aid chemicals. The flocculated mixture or slurry may be placed onto a papermaking machine to be formed into a ply or sheet of fiber containing paper. Alternatively, the plies or sheets may be formed by vacuum casting the slurry. In either case, the plies or sheets are typically dried in ovens. For a more detailed description of standard papermaking techniques employed, see U.S. Pat. No. 3,458,329, the disclosure of which is incorporated herein by reference. 
     In other embodiments, the fibers may be processed into a flexible fibrous material layer by conventional means such as dry air laying. The flexible fibrous material layer at this stage has very little structural integrity and is very thick relative to conventional catalytic converter and diesel trap mounting mats. The resultant flexible fibrous material layer can therefore be dry needled, as is commonly known in the art, to densify the flexible fibrous material layer and increase its strength. Heat treatment of certain fibers may occur prior to formation of the mat or after the flexible fibrous material layer is needled. 
     Where the dry air layering technique is used, the flexible fibrous material layer may be alternatively processed by the addition of a binder to the flexible fibrous material layer by impregnation to form a fiber composite. In this technique, the binder is added after formation of the flexible fibrous material layer, rather than forming the flexible fibrous material layer prepreg as noted hereinabove with respect to the conventional papermaking technique. This method of preparing the flexible fibrous material layer aids in maintaining fiber length by reducing breakage. It will be appreciated, however, that heat treatment, may occur prior to addition of any binder. 
     Methods of impregnation of the flexible fibrous material layer with the binder include complete submersion of the flexible fibrous material layer in a liquid binder system, or alternatively brushing, coating, dipping, rolling, splashing, or spraying the mat. In a continuous procedure, a flexible fibrous material layer which can be transported in roll form, is unwound and moved, such as on a conveyer or scrim, past spray nozzles which apply the binder to the flexible fibrous material layer. Alternatively, the mat can be gravity-fed past the spray nozzles. The mat/binder prepreg is then passed between press rolls, which remove excess liquid and densify the prepreg to approximately its desired thickness. The densified prepreg may then be passed through an oven to remove any remaining solvent and if necessary to partially cure the binder to form a composite. The drying and curing temperature is primarily dependent upon the binder and solvent (if any) used. The composite can then either be cut or rolled for storage or transportation. 
     The flexible fibrous material layer can also be made in a batch mode, by immersing a section of the mat in a liquid binder, removing the prepreg and pressing to remove excess liquid, thereafter drying to form the composite and storing or cutting to size. 
     It is noted that flexible fibrous material layer produced from these fibers may be too low in density for easy use in certain catalytic converter applications. Therefore, they may undergo further densification by any manner known in the art to provide a higher density. One such manner of densification is to needle punch the fibers so as to intertwine and entangle them. Additionally or alternatively, hydro-entangling methods may be used. Another alternative is to press the fibers into a flexible fibrous material layer form by rolling them through press rollers. Any of these methods of densification of the flexible fibrous material layer or a combination of these methods can be readily used to obtain a mounting mat of the desired form. 
     Regardless of which of the above-described techniques are employed, the flexible fibrous material layer may be cut, such as by die stamping, to form mounting mats of exact shapes and sizes with reproducible tolerances. The flexible fibrous material layer exhibits suitable handling properties upon densification as by needling or the like, meaning it can be easily handled and is not so brittle as to crumble in one&#39;s hand like many other fiber blankets or mats. It can be easily and flexibly fitted or wrapped around the catalyst support structure or like fragile structure without cracking, and then disposed within the catalytic converter housing. In certain embodiments, melt-formed, leached glass fibers high in silica content are subjected to a surface treatment, which results in an increase in the holding pressure performance of the flexible fibrous material layer containing a plurality of the leached, high silica containing glass fibers. 
     According to one embodiment, the exterior surfaces of the fibers may be treated by applying an inorganic particulate material to at least portions of the fiber surfaces. Useful inorganic particulate materials that may be utilized to treat the exterior of the fiber surfaces of the leached glass fibers include, without limitation, colloidal dispersions of alumina, silica, zirconia, and mixtures thereof According to one embodiment, the inorganic material used to treat the exterior surfaces of the leached glass fibers, thereby increasing the overall holding pressure performance of the mounting mat, is a colloidal dispersion of alumina. 
     At least a portion of the exterior surfaces of at least a portion of the fibers of the flexible fibrous material layer may include a continuous or discontinuous coating of colloidal alumina, silica, zirconia, and mixtures thereof The colloidal oxide may be applied to the exterior surfaces of the fibers by any suitable means, without limitation, by coating, dipping, spraying, splashing, and the like. The colloidal oxide may be applied to the exterior surfaces of the fibers in either a continuous or discontinuous pattern. Moreover, the process of applying the colloidal oxide to the exterior surfaces of the fibers may be carried out during or after manufacture of the glass fibers. 
     The flexible fibrous material layer may comprise only one or more intumescent fibrous mats, or only one or more non-intumescent fibrous mats, as well as combinations of at least one intumescent and at least one non-intumescent mat or layer within a hybrid mat. 
     Additionally, separate flexible fibrous material layer may contact either surface of the microporous insulation layer, such as, by way of example but not limitation at least one intumescent mat proximate to the substrate and at least one non-intumescent mat proximate to the housing. 
     As an exhaust gas treatment device cycles from ambient temperature to operating temperature, the components comprising the device reach their individual operating temperatures. The operating temperature for any given component in the exhaust gas treatment device may be less than the operating temperature for the device itself, because some components are insulated from higher temperature components. As components heat, they will expand in proportion to their thermal expansion coefficients. 
     This expansion produces a change in the strain state of the component. Because all components will not experience identical thermal strain, thermal strain causes component interference forces to change. That is, a change in the strain state of the component causes a corresponding change in the stress state of the component, and a resultant change in the forces between it and other components with which it is engaged. 
     In certain embodiments, the insulating layer is disposed to engage the substrate directly, a flexible fibrous material layer is disposed over the insulating layer and engages it directly, and a housing is disposed over the mounting mat and engages it directly. In other embodiments, the flexible fibrous material layer is disposed to engage the substrate directly, an insulating layer is disposed over the flexible fibrous material layer and engages it directly, and a housing is disposed over the insulating layer and engages it directly. 
     In embodiments in which an insulation layer is positioned between the substrate and the flexible fibrous material layer, the insulation layer insulates the flexible fibrous material layer, and all other components installed on the cold side of the insulating layer (cold side components), from the substrate and heat flowing from the substrate, and thereby promotes lower operating temperatures for the flexible fibrous material layer and other cold side components than the operating temperature of the substrate. 
     Because ambient temperature is lower than the operating temperature of the flexible fibrous material layer, promotion of lower flexible fibrous material layer operating temperature and other cold side components operating temperatures decreases both the amplitude of temperature change and the maximum temperature experienced by the flexible fibrous material layer and other cold side components during any given operational cycle. The decrease in the amplitude of temperature change results in a corresponding decrease in the amplitude of the change in thermal strain of the mounting mat and other cold side components. Because a change in the strain state of the component causes a corresponding change in the stress state of the component, and a resultant change in the forces between it and other components with which it is engaged, decreasing the amplitude of the change in thermal strain of a component results in a decrease in the change in the forces between it and other components with which it is engaged. 
     The substrate is held in place by mounting forces developed from compression by other components. These mounting forces are subject to an upper and lower design limit. The upper limit is the force required to cause damage to the substrate; the mounting forces are not sufficient to harm the substrate. The lower limit is the maximum displacement force which the substrate will experience in service; the mounting forces are at least sufficient to hold the substrate in place against all displacement forces experienced in service. As noted above, thermal strain can cause the actual mounting forces developed during the course of operation to fluctuate. By insulating the components which develop the mounting forces, the amplitude of the change in thermal strain of the components is decreased as is the amplitude of the change in the mounting forces between them and the substrate. By decreasing the amplitude of the change in the mounting forces between other components and the substrate, maintaining the mounting forces within their design limits is simplified. 
     In embodiments in which the flexible fibrous material layer is positioned between the substrate and the insulation layer, the insulation layer insulates the flexible fibrous material layer from the ambient environment and permits higher mounting mat operating temperatures than the alternative. In certain embodiments, the flexible fibrous material layer additionally comprises intumescent materials. In those embodiments in which the flexible fibrous material layer comprises intumescent materials, the positioning of the flexible fibrous material layer between the substrate and the insulation layer permits flexible fibrous material layer operating temperatures high enough to induce the intumescent response in the intumescent materials. 
     In certain embodiments, the multiple layer mounting system may be used as end cone insulation in an exhaust gas treatment device. According to certain embodiments, an end cone for an exhaust gas treatment device is provided. The end cone generally comprises an outer metallic cone, an inner metallic cone and end cone insulation that is disposed within the gap or space between the outer and inner metallic end cones. 
     According to other embodiments, the end cone may comprise an outer metallic cone and at least one layer of cone insulation that is positioned adjacent to the inner surface of the outer metallic cone. According to these embodiments, the end cone assembly is not provided with an inner metallic cone. Rather, the cone insulation is rigidized in some manner to provide a self-supporting cone structure that is resistant to the high temperature gases flowing through the device. 
     An exhaust gas treatment device including at least one end cone is provided. The exhaust gas treatment device comprises a housing, a fragile structure positioned within the housing, an inlet and an outlet end cone assemblies for attaching exhaust pipes to the housing, each end cone assembly comprising an inner end cone housing and an outer end cone housing; and end cone insulation comprising the multiple layer mounting system described in the various embodiments discussed herein. 
       FIG. 1  shows a first illustrative embodiment of a multiple layer mat  10 . Mounting mat  10  comprises a first layer  12  comprising a non-intumescent sheet of inorganic fibers having a first major surface  14  and a second major surface  16  opposite the first major surface. Mat  10  includes a second layer  18  comprising a non-intumescent sheet of inorganic fibers having a first major surface  20  and a second major surface  22  opposite the first major surface  20 . A microporous inorganic insulating layer  24  is positioned between said first non-intumescent layer  12  and second non-intumescent layer  18 . 
       FIG. 2  shows a multiple layer mat  30  comprising a first layer  32  comprising an intumescent sheet of inorganic fibers having a first major surface  34  and a second major surface  36  opposite the first major surface  34 . Mat  30  also includes a second layer  38  comprising an intumescent sheet of inorganic fibers having a first major surface  40  and a second major surface  42  opposite the first major surface  40 . A microporous inorganic insulating layer  44  is positioned between said first intumescent layer  32  and second intumescent layer  38 . 
       FIG. 3  shows a multiple layer mat  50  comprising a first layer  52  comprising a non-intumescent sheet of inorganic fibers having a first major surface  54  and a second major surface  56  opposite the first major surface  54 . A second layer  58  comprising a microporous inorganic insulating layer having a first major surface  60  and a second major surface  62  opposite the first major surface  60  is positioned in adjacent contact with said first layer  52 . A bonding means  64  is located between said first layer  52  and said second layer  58 . 
       FIG. 4  shows a multiple layer mat  70  that has a first layer  72  comprising a non-intumescent sheet of inorganic fibers having a first major surface  74  and a second major surface  76  opposite the first major surface  74 . A second layer  78  comprising a microporous inorganic insulating layer having a first major surface  80  and a second major surface  82  opposite the first major surface  80  is placed adjacent the first layer  72 . A banding means  84  encircles the first  72  and second  78  layers to hold them in adjacent contact. According to the embodiment shown in  FIG. 4 , adhesive tape  86  is used to join opposite ends of the banding material  84 . 
       FIG. 5  shows a multiple layer mat  90  comprising a first layer  92  comprising a non-intumescent sheet of inorganic fibers having a first major surface  94  and a second major surface  93  opposite the first major surface  94 . A second layer  96  comprising a microporous inorganic insulating layer having a first major surface  98  and a second major surface  100  opposite the first major surface  98 . The first  92  and second  96  layers are brought into adjacent contact and are encapsulated within a common polymeric bag  102 . 
       FIG. 6  shows a multiple layer mat  110  comprising a first layer  112  comprising a non-intumescent sheet of inorganic fibers having a first major surface  114  and a second major surface  116  opposite the first major surface  114 . A scrim layer  118  having a first major surface  120  and a second major surface  122  opposite the first major surface  120  is brought into adjacent contact with one of the first or second major surfaces of layer  112 . A microporous inorganic insulating layer  124  is positioned between the first non-intumescent layer  112  and said scrim layer  118 . 
       FIG. 7  shows a multiple layer support  130  comprising a microporous inorganic insulating layer comprising a three-dimensional pre-form  132 . A flexible layer  134  of a fibrous or intumescent mat material is wrapped about at least a portion of the perimeter of said pre-form  132 . 
       FIG. 8  shows a multiple layer support  140  comprising a three-dimensional pre-form comprising an inner layer  142  of microporous inorganic insulating material and an outer layer  144  applied over at least a portion of said inner layer  142 . 
     One illustrative configuration of an exhaust gas treatment device is shown as a catalytic converter, generally designated by the numeral  150  in  FIG. 9 . It should be understood that the exhaust gas treatment device is not limited to use in the catalytic converter shown in illustrative  FIG. 9 , and so the configuration is shown only to exemplify the device. In fact, the mounting mat may be used to mount or support any fragile structure suitable for treating exhaust gases, such as a diesel catalyst structure, a diesel particulate filter, or the like. Catalytic converter  150  may include a generally tubular housing  152 , typically formed of two pieces of metal, e.g. high temperature-resistant steel, held together by flange  154 . Housing  152  includes an inlet  156  at one end and an outlet (not shown) at its opposite end. The inlet  156  and outlet are suitably formed at their outer ends whereby they may be secured to conduits in the exhaust system of an internal combustion engine. 
     Device  150  contains a catalyst support structure, such as a frangible ceramic monolith substrate  160 , which is supported and restrained within housing  152  by the hybrid substrate mounting system  170  having at least one layer of microporous insulation  172  and a second layer  174 . 
     EXAMPLES 
     Two mounting mats were created according to the procedures and processes described above. The comparative mounting mat comprised a non-intumescent mat, while a subject mounting mat comprised a non-intumescent layer substantially similar to the non-intumescent mat of the comparative mounting mat, additionally comprising a layer of microporous inorganic insulation comprising microporous silica. 
     Both the comparative and subject mounting mats were placed into substantially identical catalytic converters. A thermocouple was spot welded onto the shell of each catalytic converter. The substrates of each catalytic converter were electrically wired and heated to a temperature of 750° C. over a period of 20 minutes. The substrates were then maintained at a temperature of 750° C. for a period of 30 minutes, and the temperature of the shells was recorded. The substrates were then further heated to a temperature of 1,000° C. over a period of 20 minutes, which temperature was maintained for an additional 30 minutes, after which the temperature of the shells was again recorded. The results are shown in TABLE II. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE II 
               
               
                   
                   
               
               
                   
                 Shell Temp. at 750° C. 
                 Shell Temp. at 1,000° C. 
               
               
                   
                 Substrate Temp. 
                 Substrate Temp. 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                 Comparative Mat 
                 358° C. 
                 460° C. 
               
               
                 Subject Mat 
                 316° C. 
                 376° C. 
               
               
                 Percent Reduction 
                 12% 
                 18% 
               
               
                 in Temp. 
               
               
                   
               
            
           
         
       
     
     A reduction of the temperature of the shell by 42° C. at a substrate temperature of 750° C. and by 84° C. at a substrate temperature of 1,000° C. represent 12% and 18% increases in insulative efficiency, respectively. The results show that the subject mat reduces the temperature of the shell as compared to the comparative, conventional mounting mat. Further, the insulative efficiency increases at higher substrate temperatures. 
     While the system has been described in connection with various embodiments, as shown in the various figures, it is to be understood that other similar embodiments may be used or modifications and additions may be made to the described embodiments for performing the same function. Furthermore, the various illustrative embodiments may be combined to produce the desired results. Therefore, the substrate mounting system and exhaust gas treatment device should not be limited to any single embodiment, but rather construed in breadth and scope in accordance with the recitation of the appended claims.