Amorphous non-intumescent inorganic fiber mat for low temperature exhaust gas treatment devices

A non-intumescent mat for providing a support structure for low temperature fragile structures in exhaust gas treatment devices, such as catalytic converters, diesel particulate traps, and like, comprising amorphous inorganic fibers. The fibers have Young's Modulus of less than about 20.times.10.sup.6 psi and a geometric mean diameter less than about 5 .mu.m. The mat is adapted to provide a holding force of at least 15 psi throughout an average mat temperature range from ambient temperature up to at least about 350.degree. C. The amorphous inorganic fibers are preferably melt formed fibers comprising the fiberization product of a melt comprising alumina/silica.

FIELD OF THE INVENTION
 The present invention is directed to a mat functioning as a support element
 for fragile structures in exhaust gas treatment devices, such as catalytic
 converters, diesel particulate traps, and the like, for the treatment of
 exhaust gases. More particularly, the present invention is directed to an
 amorphous, non-intumescent inorganic fiber mat as a support element for
 low temperature exhaust gas treatment devices.
 BACKGROUND OF THE INVENTION
 Catalytic converter assemblies for treating exhaust gases of automotive and
 diesel engines contain a fragile structure, such as a catalyst support
 structure, for holding the catalyst, used to effect the oxidation of
 carbon monoxide and hydrocarbons and the reduction of oxides of nitrogen,
 the fragile structure being mounted within a metal housing. The fragile
 structure is preferably made of a frangible material, such as a monolithic
 structure formed of metal or a brittle, fireproof 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 tiny flow channels. However, as noted
 hereinabove, these structures can be, and oftentimes are, very fragile. In
 fact, these monolithic structures can be so fragile that small shock loads
 or stresses are often sufficient to crack or crush them.
 The fragile structure is contained within a metal housing, with a space or
 gap between the external surface of the fragile structure and the internal
 surface of the housing. In order to protect the fragile structure from
 thermal and mechanical shock and other stresses noted above, as well as to
 provide thermal insulation, it is known to position at least one ply or
 layer of mounting or support material within the gap between the fragile
 structure and the housing. For example, assignee's U.S. Pat. Nos.
 4,863,700, 4,999,168, 5,032,441, and 5,580,532, the disclosure of each of
 which is incorporated herein by reference, disclose catalytic converter
 devices having a mounting or support material disposed within the gap
 between the housing and the fragile structure contained in the devices to
 protect the fragile structure and otherwise hold it in place within the
 housing.
 In low temperature catalytic converter applications, such as turbocharged
 direct injection (TDI) diesel powered vehicles, the exhaust temperature is
 typically about 150.degree. C., and may never exceed 300.degree. C. It has
 been observed in the field that catalytic converters, that are assembled
 with typical intumescent mats, fail with an unexpectedly high frequency.
 One reason for these failures is that the exhaust temperature is too low to
 expand the intumescent, typically vermiculite, particles. This has even
 been found in converters that have been pre-heated to about 500.degree. C.
 to pre-expand the intumescent particles. When subsequently used in the low
 temperature TDI application, the mats fail to provide sufficient pressure
 against the fragile structure and thus fail. It should be noted that
 converters used in gasoline engines overcome this initial loss in holding
 force as the converter continues to heat up to the final operating
 temperature, which may be as high as 900.degree. C. At temperatures above
 350.degree. C., the intumescent particles expand and increase the holding
 force of the mat against the fragile structure.
 A second reason for these failures is that organic binder systems used in
 the intumescent mat products degrade and cause a loss in the holding
 force. From room temperature to about 200.degree. C. the loss in holding
 force is gradual; however, the loss in holding force is rapid from about
 200.degree. C. to about 250.degree. C., as shown in FIG. 3.
 FIG. 2 shows the performance of prior art intumescent mats in a 1000 cycle
 test at 300.degree. C. with a gap between the fragile structure and the
 shell of about 4.0 to about 4.1 mm. All mats were preheated at 500.degree.
 C. for one hour to pre-expand the intumescent material (vermiculite). In
 the 1000-cycle test, the mat must maintain a pressure of greater than 15
 psi at all times to provide adequate holding force on the fragile
 structure. FIG. 2 shows a loss in holding force with the eventual failure
 after about 500 cycles. The data presented in this graph correlates well
 with the failures observed with converters mounted with conventional
 intumescent mounting mats used in TDI diesel applications operating at
 less than 300.degree. C. The test procedure and specific results of the
 tests of prior intumescent mats are set forth in detail below.
 Non-intumescent mat systems are known in the art. Fibers such as
 SAFFIL.RTM. (from ICI, United Kingdom) and MAFTEC.RTM. (from Mitsubishi
 Chemicals, Japan) may be used to mount fragile structures for use over a
 wide temperature range. These fiber only products contain no intumescent
 material, such as vermiculite, to increase the holding force as the
 converter is heated. These mats are composed of polycrystalline fibers
 with a high Young's Modulus (greater than 20-40.times.10.sup.6 psi) which
 function as ceramic springs to provide the required holding force against
 the fragile structure. These products provide adequate function in
 turbocharged direct injection (TDI) diesel converters.
 Historically, these products have been dry layed without the addition of
 organic binder; as a result, the thickness of these products is typically
 greater than 18 mm making them difficult to install in converters, as
 described in the patents referenced above. Further, the cost of these
 products has been prohibitively high as compared to intumescent mats.
 Recently, a new generation of these products have been provided with
 improved handling and installation by vacuum packing, or by the addition
 of organic binders and sometimes additional stitching or needling to
 achieve a thinner and more flexible mat. A thickness of less than 10 mm
 can be achieved by these means. However, testing of the new generation
 mats in the 150.degree.-300.degree. C. temperature range has shown lower
 holding force than for the first generation mats.
 The first such product of this new generation is described in U.S. Pat. No.
 5,580,532, which claims a flexible polycrystalline ceramic fiber mat for
 use in mounting catalytic converters, particularly useful in the operating
 temperature range of 750.degree. C. to 1200.degree. C. Flexibility is
 achieved by impregnating a mat with various organic binders. All of the
 binders referenced in this patent, however, yield a mat with lower
 performance in the 150.degree.-300.degree. C. operating temperature range
 of a TDI diesel converter. However, satisfactory performance may still be
 achieved due to the high Young's modulus of the fibers used in these mats.
 European Patent Application EP803643 discloses a mat product made with
 mineral fibers over a very wide composition range (0-99 wt. % Al.sub.2
 O.sub.3, 1-99.8 wt. %SiO.sub.2) bonded with a binder to produce a thin,
 flexible mat for mounting fragile structures. The fibers are further
 defined as preferably having compositions in the range of 95 wt. %
 Al.sub.2 O.sub.3, or 75 wt. % Al.sub.2 O.sub.3 --25 wt. % SiO.sub.2. The
 application states that only fibers with a high elastic modulus will
 provide sufficient holding force to support the fragile structure as the
 converter heats and cools during use. Fibers used in prior art intumescent
 mat products are stated not to be suitable. The application describes the
 use of conventional organic binders, such as acrylic latex, for
 applications where the temperature is high enough to burn-out the binder,
 such as above 500.degree. C. For low temperature applications, such as
 with diesel engines in the 220.degree.-300.degree. C. range, the
 application states that conventional organic binders thermally degrade and
 become hard. Upon thermal cycling of the converter, the hardened mat is no
 longer capable of maintaining adequate holding force on the fragile
 structure and failure results. The application states that alternative
 binders which do not harden, such as a silicone binder, may successfully
 be used in this temperature range.
 In U.S. Pat. No. 4,929,429 and 5,028,397, the comparative examples show
 that even when melt formed ceramic fibers have been treated to reduce the
 shot content to as low as 5%, these fibers still lack the requisite
 resiliency to adequately hold the fragile structure in the converter
 shell, as is described in U.S. Pat. No. 5,250,269. The U.S. Pat. No.
 5,250,269 describes how adequate resiliency can be achieved by first heat
 treating melt formed ceramic fibers, such as CERAFIBER.RTM. (Thermal
 Ceramics, Augusta, Ga.). Comparative examples of mats made with melt
 formed ceramic fibers without treatment failed in both laboratory testing
 and converter hot shake testing.
 What is needed in the industry is a mat that can function at an average mat
 temperature range from ambient temperature up to at least about
 350.degree. C. and can be installed in exhaust gas treatment devices such
 as TDI diesel catalytic converters and the like without a loss in holding
 force.
 It is an object of the present invention to provide a mat that can function
 throughout an average mat temperature range from ambient temperature up to
 at least about 350.degree. C. while maintaining a holding force of at
 least about 15 psi in exhaust gas treatment devices such as TDI diesel
 catalytic converters and the like.
 It is another object of the present invention to provide a mat that is
 sufficiently thin and sufficiently flexible to be easily handled and
 installed in exhaust gas treatment devices such as TDI diesel catalytic
 converters and the like.
 SUMMARY OF THE INVENTION
 The present invention provides a non-intumescent mat for providing support
 for a fragile structure in a low temperature exhaust gas treatment device
 comprising high temperature resistant, amorphous, inorganic fibers, said
 fibers having a Young's Modulus of less than about 20.times.10.sup.6 psi
 and a geometric mean diameter less than about 5 .mu.m, said mat optionally
 including a binder, wherein the mat is adapted to provide a holding force
 of at least 15 psi throughout an average mat temperature range from
 ambient temperature up to at least about 350.degree. C.
 The present invention also provides an exhaust gas treatment device
 containing a fragile support structure within a housing, and a support
 element disposed between the fragile support structure and the housing,
 wherein said support element comprises a non-intumescent mat comprising
 high temperature resistant, amorphous, inorganic fibers, said fibers
 having a Young's Modulus of less than about 20.times.10.sup.6 psi and a
 geometric mean diameter less than about 5 .mu.m, said mat optionally
 including a binder, and wherein the mat is adapted to provide resistance
 to slippage of the support element in the housing at a force of at least
 about 60 times the acceleration of gravity throughout an average mat
 temperature range from ambient temperature up to at least 350.degree. C.

DETAILED DESCRIPTION OF THE INVENTION
 The present invention provides a non-intumescent mat for providing a
 support structure in a low temperature exhaust gas treatment device. The
 mat comprises high temperature resistant, amorphous, inorganic fibers and
 optionally includes a binder.
 The fiber of the present invention can also be a high temperature resistant
 fiber. By high temperature resistant, it is meant that the fiber can have
 a use temperature up to about 1260.degree. C. The amorphous inorganic
 fibers of the present invention have a Young's Modulus of less than about
 20.times.10.sup.6 psi and a geometric mean diameter less than about 5
 .mu.m.
 The fiber preferably comprises 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.TM. fibers from Unifrax Corporation, Niagara Falls, N.Y.), or
 calcia-magnesia-silica fibers (such as INSULFRAX.TM. fibers from Unifrax
 Corporation, Niagara Falls, N.Y. or SUPERWOOL.TM. fibers from Thermal
 Ceramics Company).
 The alumina/silica fiber typically comprises from about 45% to about 60%
 Al.sub.2 O.sub.3 and about 40% to about 55% SiO.sub.2 ; preferably, the
 fiber comprises about 50% Al.sub.2 O.sub.3 and about 50% SiO.sub.2. The
 alumina/silica/magnesia glass fiber typically comprises from about 64% to
 about 66% SiO.sub.2, from about 24% to about 25% Al.sub.2 O.sub.3, and
 from about 9% to about 10% MgO. The E-glass fiber typically comprises from
 about 52% to about 56% SiO.sub.2, from about 16% to about 25% CaO, from
 about 12% to about 16% Al.sub.2 O.sub.3, from about 5% to about 10%
 B.sub.2 O.sub.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.sub.2, 15% Al.sub.2 O.sub.3, 7% B.sub.2
 O.sub.3, 3% MgO, 19% CaO and traces of the above mentioned materials.
 Magnesia-silica fibers typically comprise from about 69% to about 86%
 SiO.sub.2, from about 14% to about 35% MgO, and from 0% to about 7% ZrO.
 More information on magnesia-silica fibers can be found in U.S. Pat. No.
 5,874,375, which is hereby incorporated by reference.
 Calcia-magnesia-silica fibers typically comprise about 31% CaO, about 3%
 MgO, and about 65% SiO.sub.2.
 The mat provides a holding force of at least 15 psi throughout an average
 mat temperature range from ambient temperature up to at least about
 350.degree. C. The average mat temperature is the arithmetic average
 temperature across the entire mat. The holding force is provided across
 the temperature range of the mat as it is heated from ambient temperature
 up to at least about 350.degree. C.
 An amorphous fiber is defined as a fiber that is melt formed and has not
 been post processed by heat treating to either anneal or crystallize the
 fiber, so as to be substantially crystalline free, meaning that no
 crystallinity is detected by x-ray diffraction.
 Optionally, the mat of the present invention includes a binder. Suitable
 binders include aqueous and non aqueous binders, but preferably the binder
 utilized is a reactive, thermally setting latex which after cure is a
 flexible material that is stable up to at least about 350.degree. C.
 Preferably, about 5 to about 10 percent latex is employed, with about 8
 percent being most preferred. 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 (based on
 viscosity, solids content, and the like). Preferably, the binder is a
 silicone latex.
 Production of fibers of the present invention is described in U.S. patent
 application Ser. No. 09/038,243 filed Mar. 11, 1998, which is herein
 incorporated by reference, except that in the present invention, the
 fibers are not heat treated to crystallize the fiber composition, and thus
 retain their amorphous structure. Briefly, the fibers are amorphous
 inorganic or glass fibers that are melt-formed. They are preferably fibers
 of high chemical purity (greater than about 98%) and preferably have an
 average diameter in the range of about 1 to about 10 .mu.m, and most
 preferably in the range of about 2 to 4 .mu.m. While not specifically
 required, the fibers may be beneficiated, as is well known in the art, to
 obtain a greater than 60 percent fiber index, meaning they contain less
 than 40 percent shot, and preferably less than about 30 percent shot.
 Exhaust gas treatment devices include catalytic converters, diesel
 particulate traps, and the like. These devices contain similar elements.
 By way of example, a catalytic converter, as shown in FIG. 1, is described
 herein. Catalytic converter 10 includes a generally tubular housing 12
 formed of two pieces of metal, e.g. high temperature-resistant steel.
 Housing 12 includes an inlet 14 at one end and an outlet (not shown) at
 its opposite end. The inlet 14 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 10 contains a fragile catalyst
 support structure, such as a frangible ceramic monolith 18 which is
 supported and restrained within housing 12 by a support element such as
 mat 20, the present invention. Monolith 18 includes a plurality of
 gas-pervious passages which extend axially from its inlet end surface at
 one end to its outlet end surface at its opposite end. Monolith 18 may be
 constructed of any suitable refractory metal or ceramic material in any
 known manner and configuration. Monoliths are typically oval or round in
 cross-sectional configuration, but other shapes are possible.
 In accordance with the present invention, the monolith is spaced from its
 housing by a distance or a gap, which will vary according to the type and
 design of the device, e.g., a catalytic converter or a diesel particulate
 trap, utilized. This gap is filled by a support element (or mounting mat)
 20 to provide resilient support to the ceramic monolith 18. The resilient
 support element 20 provides both thermal insulation to the external
 environment and mechanical support to the catalyst support structure,
 protecting the fragile structure from mechanical shock. The support
 element 20 also possesses good handleability and is easily processed in
 the fabrication of devices utilizing its capabilities of maintaining a
 substantially stable and uniform minimum holding pressure of at least 15
 psi after undergoing 1000 mechanical cycles at a nominal temperature of
 about 350.degree. C.
 By the term "cycle" it is meant that the gap between the monolith (i.e.,
 fragile structure) and housing is opened and closed over a specific
 distance and at a predetermined rate. In order to simulate realistic
 conditions, the expansion of the gap between a housing and a fragile
 structure of a given diameter is determined by calculating the coefficient
 of thermal expansion of the conventional housing at a maximum temperature
 of 350.degree. C. Candidate support mats are characterized for their
 performance in this test versus installation density. A final mat basis
 weight is then selected which will provide a minimum holding force (Pmin)
 of greater than about 15 psi after 1000 cycles. The goal is to provide
 adequate support at the lowest cost, so the minimum basis weight that
 satisfies the greater than about 15 psi requirement is selected.
 For alumina silica fiber mats of the present invention, this typically
 translates to a minimum basis weight of at least approximately 1200
 g/m.sup.2, and generally approximately 1600 g/m.sup.2. Higher basis weight
 mats provide increased holding pressure and thus safety factors; however,
 at higher cost. Mats of the present invention typically have a green bulk
 density of at least about 0.20 g/cm.sup.3, or greater and have an
 installed density from about 0.40 to about 0.75 g/cm.sup.3. Mats of the
 present invention typically have a nominal thickness of from about 4.5 to
 about 13 mm. Nominal thickness is defined as the thickness when measured
 under a compressive force of 0.7 psi.
 A gap of 3 to 4 mm between the fragile structure and shell is normally
 sufficient to provide adequate thermal insulation and to minimize the
 tolerance differences of the fragile structure and shell. The weight per
 unit area (basis weight) of the mat required to fill this gap is bounded
 on the lower end by the minimum compression force to provide adequate
 support of the fragile structure against the exhaust gas pressure and
 axial g-forces to which it is subjected during operation, and on the upper
 end by the breaking strength of the fragile structure. Basis weight ranges
 from about 1000 to about 3000 g/m.sup.2. For a fragile structure having a
 4.66 inch diameter mounted by a tourniquet mounting process, a 3 mm gap is
 adequate. The mat of the present invention having a nominal basis weight
 of about 1600 g/m.sup.2 will result in an installed density of about 0.53
 g/cm.sup.3. For a 1600 g/m.sup.2 mat, according to the present invention,
 the mat will have a thickness of approximately 7 mm, which facilitates
 easy handling and installation during converter assembly, compared to
 traditional non-intumescent mats.
 Preferably, the mat of the present invention provides resistance to
 slippage of the support element in the housing at a force of at least
 about 60 times the acceleration of gravity. The resistance to slippage is
 provided throughout an average mat temperature range from ambient
 temperature up to at least about 350.degree. C. The mat provides
 sufficient force between the housing and the support element to resist
 slippage of the support element within the housing, thus avoiding
 mechanical shock and breakage of the support structure.
 The mounting mat or support element of the present invention can be
 prepared by any known techniques. For instance, using a paper making
 process, inorganic fibers are mixed with a binder to form a mixture or
 slurry. Any mixing means may be used, but preferably the fibrous
 components are mixed at about a 0.25% to 5% consistency or solids content
 (0.25-5 parts solids to 99.5-95 parts water). 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 paper making machine to
 be formed into a ply of inorganic paper. Alternatively, the plies may be
 formed by vacuum casting the slurry. In either case, they are typically
 dried in ovens. For a more detailed description of the standard paper
 making techniques employed, see U.S. Pat. No. 3,458,329, the disclosure of
 which is incorporated herein by reference. This method typically breaks
 the fibers during processing. Accordingly the length of the fibers are
 generally about 0.025 cm to about 2.54 cm when this method is used.
 Furthermore, the inorganic fibers may be processed into a mat or ply by
 conventional means such as dry air laying. The ply at this stage, has very
 little structural integrity and is very thick relative to the conventional
 catalytic converter and diesel trap mounting mats. The resultant mat can
 be dry needled, as is commonly known in the art, to densify the mat and
 increase its strength.
 Where the dry air laying technique is used, the mat may be alternatively
 processed by the addition of a binder to the mat by impregnation to form a
 discontinuous fiber composite. In this technique, the binder is added
 after formation of the mat, rather than forming the mat prepreg as noted
 hereinabove with respect the conventional paper making technique. This
 method of preparing the mat aids in maintaining fiber length by reducing
 breakage. Generally the length of the fibers are about 1 cm to about 10
 cm, preferably about 1.25 cm to about 7.75 cm when this method is used.
 If continuous filaments of alumina/silica/magnesia glass or E glass are
 used in the non-intumescent mat of the present invention, they can also be
 knitted or woven into a fabric.
 Methods of impregnation of the mat with the binder include complete
 submersion of the mat in a liquid binder system, or alternatively spraying
 the mat. In a continuous procedure, a inorganic fiber mat 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 mat.
 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 mounting mat 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.
 Regardless of which of the above-described techniques are employed, the
 composite can be cut, such as by die stamping, to form mounting mats of
 exact shapes and sizes with reproducible tolerances. This mounting mat 20
 exhibits suitable handling properties, meaning it can be easily handled
 and is not so brittle as to crumble in one's hand like mat made with
 binder. It can be easily and flexibly fitted around the catalyst support
 structure 18 without cracking and fabricated into the catalytic converter
 housing 12 to form a resilient support for the catalyst support structure
 18, with minimal or no flashing such as by extrusion or flow of excess
 material into the flange area 16 and provides a holding pressure against
 the catalyst support structure 18 of at least 15 psi at a normal
 temperature of 350.degree. C. after 1000 cycles of gap expansion.
 EXAMPLES
 COMATIVE EXAMPLE 1
 FIG. 2 shows the performance of prior art intumescent mats in a 1000 cycle
 test at 300.degree. C. with a gap between the fragile structure and the
 shell of about 4.0 to about 4.1 mm. All mats were preheated at 500.degree.
 C. for one hour to pre-expand the intumescent material (vermiculite). All
 mats had an initial installed density of approximately 1.0 g/cm.sup.3. The
 mat shown by the circle, solid circle at Pmax and open circle at Pmin, is
 a typical intumescent mat containing approximately 55 wt. % vermiculite,
 38 wt. % ceramic fiber, and 7 wt. % organic binder, and is a product
 called Type-100 that is manufactured by 3M under the trademark
 INTERAM.RTM.. The mat shown by the diamond, solid diamond at Pmax and open
 diamond at Pmin, is a product called Type-200, also manufactured by 3M
 under the trademark INTERAM.RTM.. Type-200 is similar to the Type-100,
 except that the temperature at which expansion of the vermiculite
 particles begins is claimed to be lower than for the Type-100 mat. The mat
 shown by the square, solid square at Pmax and open square at Pmin, is a
 product called AV2 manufactured by Unifrax Corporation under the trademark
 XPE.RTM., and comprises approximately 45 wt. % vermiculite, 48 wt. %
 ceramic fiber, and 7% organic binder. The organic binder in all three
 products is similar.
 In this test, the samples were compressed to a gap of 4.0 mm between quartz
 rams mounted in an Instron mechanical properties test machine. A furnace
 was then installed around the sample/ram assembly. While maintaining the
 4.0 mm gap, the furnace was heated to the desired temperature, in this
 case 500.degree. C., while monitoring the pressure response of the mat.
 Upon reaching 500.degree. C., the furnace temperature was held constant
 for 1 hour to remove all of the organic binders and to allow the
 vermiculite particles to fully expand. After 1 hour, the furnace was
 cooled to room temperature, while the gap remained at the initial 4.0 mm
 gap. This preconditioned sample was then re-heated to the desired test
 temperature, in this case 300.degree. C. Upon reaching 300.degree. C., the
 furnace temperature was held constant and the gap cycled at a speed of
 approximately 2 mm/minute between 4.0 to 4.1 mm, simulating the expansion
 of the gap due to shell thermal expansion in a real converter during use.
 The pressure exerted by the mat was monitored as the gap opened and
 closed. Pmax is the pressure of the mat at 4.0 mm gap, while Pmin
 corresponds to the pressure of the mat at 4.1 mm. The test was concluded
 after 1000 cycles.
 Mechanical analysis of typical catalytic converters has shown that the mat
 must maintain a minimum effective holding force of greater than 5 psi to
 prevent the fragile structure from slipping under maximum operating
 conditions. The coefficient of friction of typical mounting mats is
 approximately 0.33. Therefore, in the 1000-cycle test, the mat must
 maintain a pressure of greater than 15 psi at all times to provide
 adequate holding force on the fragile structure. FIG. 2 shows that the
 Type-100 and Type-200 mats failed to meet the Pmin&gt;15 psi requirement even
 on the first cycle. Only the AV2 mat, square symbol, was able to maintain
 holding force above the minimum 15 psi. Even this mat had a holding force
 less than 15 psi after pre-heating, which could lead to a failure
 condition. Additional testing of the AV2 mat at 150.degree. C. showed the
 measured Pmin to be less than 5 psi. The data presented in this graph
 correlates well with the failures observed with converters mounted with
 conventional intumescent mounting mats used in TDI diesel applications
 operating at less than 300.degree. C.
 EXAMPLE 2
 Simulation of a TDI diesel converter was performed by cycle testing mats at
 300.degree. C. for 1000 cycles between a gap of about 3.0 to about 3.1 mm.
 The results are shown in FIG. 4. The samples were a 1550 g/m.sup.2 of a
 competitive dry layed, needle punched ceramic (about 50% alumina/50%
 silica) fiber blanket, such as ULTRAFELT.RTM. manufactured by Thermal
 Ceramics, Augusta, Ga., (shown by an open diamond), and a 1600 g/m.sup.2
 mat of the present invention prepared with a 50% alumina/50% silica fiber
 with no binder (shown by a triangle); a silicone binder (shown by a solid
 square); and an acrylic binder that was not burned out prior to
 installation (shown by an solid circle).
 The mat with the silicone binder comprised 92% of an amorphous fiber
 comprising 50% Al.sub.2 O.sub.3 and about 50% SiO.sub.2 with a fiber index
 of 72% and 8% of a silicone latex binder (DOW CORNING #85 silicone latex
 from Dow Corning, Inc. Midland, Mich.). The resulting mat had a basis
 weight of 1600 g/m.sup.2 and was 7 mm thick. As shown in FIG. 4, the
 ULTRAFELT.RTM. and the silicone latex binder mats maintained a holding
 force greater than 15 psi.
 The mat with the acrylic binder was similar to the mat with the silicone
 binder, with the 8% silicone binder being replaced with 8% HYCAR.RTM.
 26083 acrylic latex, available from B.F. Goodrich, Brecksville, Ohio.
 Again, the sample had a basis weight of 1600 g/m.sup.2 and was about 7 mm
 thick. The binder was not preburned, and thus failed on the first cycle. A
 second sample was prepared and was pre-burned prior to testing. This
 second mat performed comparably to the mat with the silicone binder.
 EXAMPLE 3
 Testing in a Catalytic Converter
 A 4.66" diameter converter was assembled with comparative mats and tested
 in a hot shake test at 300.degree. C. with an acceleration of 60 times
 gravity (60 g's). The converter with a traditional intumescent mat,
 consisting of approximately 55% unexpanded vermiculite, 37% ceramic fiber,
 and 8% acrylic latex binder, such as INTERAM.RTM. TYPE-100 and
 INTERAM.RTM. TYPE-200, lost its holding force and the fragile structure
 slipped within the shell in less than 50 hours.
 A mat of the present invention, made with amorphous alumina/silica fiber
 and an acrylic latex binder which had been burned out prior to
 installation in the converter, was run in the hot shake test at
 300.degree. C. with an acceleration of 60 g and performed for 100 hours
 without failure. Upon inspection after testing, the fragile structure was
 found to be firmly mounted in the shell, with no relative axial movement.
 The mat was also found to be undamaged by gas erosion or other visible
 degradation.
 A mat of the present invention, made with a silicone latex binder, was run
 in the hot shake test at 300.degree. C. with an acceleration of 60 g and
 performed for 100 hours without failure.
 As demonstrated above, the present invention achieves the objects of the
 invention. The present invention therefore provides a non-intumescent mat
 comprising an amorphous, inorganic fiber that functions up to about
 350.degree. C. without a loss in holding force in catalytic converters and
 the like.
 It should be appreciated that the present invention is not limited to the
 specific embodiments described above, but includes variations,
 modifications and equivalent embodiments defined by the following claims.