Abstract:
The inner surfaces of fluorescent lamp tubing are provided with a phosphor coating. The phosphor coating defines an inward-facing surface. A protective coating is deposited on the inward-facing surface of the phosphor coating. The protective coating defines an innermost surface and makes effective recombination of Hg ions possible on the innermost surface of the second coating before the Hg ions collide with the phosphor particles in the phosphor coating.

Description:
FIELD OF THE INVENTION 
       [0001]    The field of the present invention generally involves lighting, and more particularly relates to fluorescent lamps and methods of making same. 
       BACKGROUND OF THE INVENTION 
       [0002]    A fluorescent lamp operates by passing an electric discharge through mercury vapor contained within an envelope to produce short-wave ultraviolet (UV) light (generally at wavelengths of about 253.7 nm and 185 nm). The envelope bears a phosphor material which is caused to luminesce by the UV light, thereby emitting visible light. As a practical matter, many commercial fluorescent lamps may suffer from a decrease of lumen as a function of burning time. One reason for lumen decrease is the bombardment of the phosphor material by mercury ions and by 185 nm ultraviolet light from the discharge. The amount of mercury bound by the phosphor coating also increases with burning time, which may lead to a consumption of up to around half of the total amount of mercury consumed inside the lamp. This loss of mercury can also lead to lumen decrease. These effects may seriously limit the service life of the lamps. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0003]    One embodiment of the present invention includes a fluorescent lamp having a protective coating on the inwardly-facing surface of the phosphor coating of the fluorescent lamp, thus partly protecting the phosphor coating from the harmful effects of the discharge. 
         [0004]    In another embodiment of the present invention, a fluorescent lamp is made by a process that includes the step of applying a protective coating onto the inwardly-facing surface of the phosphor coating of the fluorescent lamp. 
         [0005]    The present invention also may include the step of making the phosphor coating resistant to washing (“wash-proofing”) before applying the protective coating. 
         [0006]    The present invention also may include size-enhancing the particles of the suspension that are applied to the inwardly-facing surface of the phosphor coating to form the protective coating before applying the protective coating. 
         [0007]    Those of ordinary skill in the art will better appreciate the features and aspects of such embodiments, and others, upon review of the specification. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    A full and enabling disclosure of the present invention, including the best mode thereof to one skilled in the art, is set forth more particularly in the remainder of the specification, including reference to the accompanying figures, in which: 
           [0009]      FIG. 1  shows an embodiment of a mercury vapor discharge fluorescent lamp according to the present invention with portions cut away and portions shown in cross section; 
           [0010]      FIG. 2  schematically shows in an enlarged cross sectional view, the detail circumscribed by the circular balloon designated by the numeral  2  in  FIG. 1 ; 
           [0011]      FIG. 3  schematically depicts an enlarged view of square box designated by the numeral  3  in  FIG. 2 ; 
           [0012]      FIG. 4  schematically represents embodiments of the methods of the present invention for making a mercury vapor discharge fluorescent light source; 
           [0013]      FIG. 5  schematically shows in an enlarged cross sectional view, an alternative embodiment of the detail circumscribed by the circular balloon designated by the numeral  2  in  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0014]    Referring to  FIG. 1 , a mercury vapor discharge fluorescent lamp  10  according to an embodiment of the present invention is schematically depicted with portions cut away and portions shown in cross section. Though the lamp in  FIG. 1  is linear in the shape of a right cylinder, the invention is not limited to linear lamps and may be applied. to fluorescent lamps of any shape. The exemplary fluorescent lamp  10  has a light-transmissive glass tube or envelope  12 , which has a cross-section that is circular when taken normal to the longitudinal axis of the lamp  10 . 
         [0015]    As used herein, a “fluorescent lamp” is any mercury vapor discharge fluorescent lamp as known in the art, including fluorescent lamps wherein the discharge source includes electrodes, and also electrode-less fluorescent lamps wherein the discharge source includes a radio transmitter adapted to excite mercury vapor atoms via transmission of an electromagnetic signal. 
         [0016]    Also as used herein, a “T8 lamp” is a fluorescent lamp as known in the art, desirably linear in the shape of a right cylinder, desirably nominally 48 inches in length, and having a nominal outer diameter of 1 inch (eight times ⅛ inch, which is where the “8” in “T8” derives). However, the T8 fluorescent lamp can be nominally 2, 3, 6 or 8 feet long, or some other length. Moreover, the method and apparatus disclosed herein is applicable to other lamp sizes and loadings, ranging from T12 to T1 in diameter, and including compact fluorescent lamp (CFL) types as well. 
         [0017]    As schematically shown in  FIG. 1 , the lamp  10  is hermetically sealed at each of the opposite ends of the glass envelope  12  by a base  20  attached at one of the two spaced apart opposite ends of the glass envelope  12  and another base  20  attached at the other one of the two spaced apart opposite ends of the glass envelope  12 . Embodiments of lamps such as that in  FIG. 1  include a discharge source, which may comprise at least one electrode structure  18  desirably respectively mounted on each of the bases  20  and is disposed in the interior volume of the envelope  12 . A compact fluorescent lamp for example might require only a single electrode  18 . Each of the electrodes  18  typically is formed of tungsten coils that have been coated with emission material that has a low thermionic emission temperature and thus emits electrons at relatively low temperatures. Electricity passing through each of the coils generates enough heat to attain the thermionic emission temperature of the emission material, which continuously decreases during burning. 
         [0018]    As schematically shown in  FIGS. 1 and 2 , a discharge-sustaining fill gas  22 , comprising mercury and an inert gas, is sealed within the interior volume of the glass tube  12 . The inert gas desirably is argon or a mixture of argon and krypton, but could be some other inert gas or mixture of inert gases. The inert gas and a small quantity of mercury vapor provide the low vapor pressure manner of operation. During operation, the mercury vapor desirably may have a pressure in the range of about 0.8 Pa to about 1.2 Pa. 
         [0019]    As schematically depicted in  FIG. 2 , which shows an enlarged cross sectional view of the portion of the drawing in  FIG. 1  identified by the balloon designated  2 , the glass envelope  12  has an inner surface  13  that is cylindrical and defines an interior volume of the glass envelope  12 . As schematically shown in  FIGS. 1 and 2 , the fluorescent lamp  10  has a phosphor coating layer  30  that contains one or more phosphors. As schematically shown in  FIG. 2 , this phosphor coating layer  30  can be applied directly onto the inner surface  13  of the envelope  12  of a fluorescent lamp  10  to convert UV light to visible light. Alternatively, as schematically shown in  FIG. 5 , this phosphor coating layer  30  can be applied directly onto the inner surface  25  of a barrier coating  24  that itself has been applied directly onto the inner surface  13  of the envelope  12  of a fluorescent lamp. As generally known, a “phosphor” is a luminescent material that absorbs radiation energy in a portion of the electromagnetic spectrum and emits energy in another portion of the electromagnetic spectrum. One important class of phosphors comprises crystalline inorganic compounds of high chemical purity and of controlled composition to which small quantities of other elements (called “activators”) have been added to convert them into efficient fluorescent materials. 
         [0020]    this disclosure, a convention is employed in which “inner” means “closer to the mercury discharge” and “outer” mean “further from the mercury discharge”. Therefore, for example, an “inner surface” or “innermost surface” of a phosphor coating  30  is that surface of a layer which is closer to the mercury discharge in the lamp. 
         [0021]    As schematically shown in  FIG. 2  for example, in one embodiment the phosphor coating layer  30  may be formed on a substantial portion of the inner surface  13  of the envelope  12 . The phosphor coating layer  30  can include one or more compositions of material that include one or more phosphors. 
         [0022]    As schematically shown in  FIG. 3 , one exemplary embodiment of the phosphor coating layer  30  includes phosphor particles  32 . These phosphor particles  32  may comprise any phosphor material, such as one or more of the many known phosphor materials, such as rare earth phosphors and/or halophosphors. An exemplary but nonlimiting listing of phosphors suitable for use in the phosphor composition may include one or more of the following: zinc silicate [Zn 2 SiO 4 :Mn]; strontium green-blue [Sr 5 (PO 4 ) 3 (F,Cl):Sb 3+ , Mn 2+ ]; strontium red [Sr 3  (PO 4 ) 2 :Sn 2+ ]; SECA [Sr 5-x-y Ba x  Ca y (PO 4 ) 3 Cl:Eu 2+ ]; CBT [GdMgB 5 O 10 :Ce 3+ , Tb 3+ ]; CBM [GdMgB 5 O 10 :Ce 3+ , Mn 3+ ]; BAM [BaMg 2 Al 16 O 27 :Eu 2+ ]; BAMn [BaMg 2 Al 16 O 27 :Eu 2+ ;Mn 2+ ]; magnesium fluoro germanate [3.5(MgO)*0.5(MgF 2 )*GeO 2 :Mn 4+ ]; SAE [Sr 4 Al 14 O 25 :Eu 2+ ]; SEB [SrB 4 O 7 :Eu 2+ ] and yttrium vanadate [Y(P,V)O 4 :Eu 3+ ]. 
         [0023]    The phosphor coating layer  30  may also comprise other materials, such as fine particle inorganic additive materials, such as alumina, silica, yttria, etc., which may function to increase adhesion of the phosphor particles to the glass surface  13  and to each other. Other possible components may comprise one or more of thickeners, dispersants or surfactants, as would be well understood in the industry to regulate physical properties of a suspension used to apply the phosphor coating layer  30 . As explained more fully below, water-soluble dispersants and water soluble polymeric thickeners such as polyethylene oxide may be desirable. 
         [0024]    The phosphor coating layer  30  can be applied to the inner surface  13  of glass envelope  12  (or to a barrier coating  24 ) by any effective means, including many known coating means. As schematically shown in  FIG. 5 , in many fluorescent lamps a barrier coating  24  is applied directly onto the inner surface  13  of the glass envelope  12  in order to shield the glass envelope  12  from the mercury discharge and/or to reflect part of any UV light that may leak through the phosphor coating layer  30 . A barrier coating  24  may be composed of one or more of fine particle alumina, yttria, silica, titania, water insoluble borates or phosphates, etc. If the phosphor coating layer  30  is applied to either the glass envelope  12  ( FIG. 2 ) or the barrier coating  24  ( FIG. 5 ) as a slurry, the phosphor coating  30  may be dried via any effective means, such as by forced air convection. After being dried, the phosphor coating layer  30  may baked (“lehred”) at an elevated temperature, e.g. at least 400° C. to 650° C. for about 0.5-10 minutes to burn out any organic components of the slurry. 
         [0025]    As schematically depicted in  FIG. 3  for example, the resulting the phosphor coating layer  30  defines an inwardly-facing surface  31  ( FIG. 2 ). Importantly, such surface  31  of the phosphor coating layer  30  may typically include voids  33  between adjacent phosphor particles  32 . These voids  33  may have dimensions that can range up to as large as several (e.g., ten) micrometers. Now, in the exemplary embodiment schematically depicted in  FIG. 2 , in addition to a phosphor coating layer  30 , a protective coating  14  is applied over the inwardly-facing surface  31  of the phosphor coating layer  30 , in this embodiment schematically depicted in  FIG. 2 , the protective coating  14  is applied directly on the inwardly-facing surface  31  of the phosphor coating layer  30 . Thus, the phosphor coating layer  30  desirably is disposed between the inner surface  13  of the envelope  12  (or between the barrier layer  24 ) and the protective coating  14 . 
         [0026]    The protective coating  14  generally is substantially transparent to UV light of 254 nm wavelength. It may also be substantially transparent to the whole of the visible light spectrum. Moreover, as schematically depicted in  FIG. 2 , the protective coating  14  defines an innermost surface  15 . The protective coating  14  typically is configured to inhibit collision of Hg ions with phosphor particles in the phosphor coating; that is, it has a function of mitigating the collision of Hg ions with phosphor particles in the phosphor coating  30 . One manner in which the protective coating  14  may fulfill this function, is by effecting the recombination of Hg ions at the innermost surface  15  of the protective coating before the Hg ions collide with the phosphor particles  32  ( FIG. 3 ) in the phosphor coating  30 . 
         [0027]    The protective coating  14  may comprise one or more of crystalline inorganic materials, or particulate amorphous materials; or the like. The protective coating  14  desirably can comprise one or more of the oxides, borates or phosphates of one or more of aluminum, yttrium, lanthanum, zirconium or magnesium, and combinations of two or more of the foregoing. The protective coating  14  may comprises particles  34  that possess a size such that particles  34  substantially do not enter the voids  33  between adjacent phosphor particles  32 . That is, particles  34  of the protective coating  14  have an agglomerated particle size (e.g., size of secondary or tertiary agglomerates or flocs) that is larger than the void size of the voids  33  between adjacent phosphor particles  32 . One manner in which to ensure that particles  34  possess a size such that particles  34  substantially do not enter the voids  33 , is by size-enhancing the particles  34  through flocculation and/or agglomeration, as will be explained in further detail below. To promote transparency in the protective coating  14 , as well as to promote collision with Hg ions, the particles in the protective coating may desirably have a small (e.g., nano-sized) primary particle size. However, it generally is advantageous to collect such small primary particles that compose the protective coating into aggregates (e.g., flocs) having a size sufficiently large so as to not enter or fall into voids in the phosphor coating layer. 
         [0028]    In accordance with embodiments of the present invention, methods are provided for making a light source  10  that includes a substantially transparent, hollow envelope  12  that has an inner surface  13  coated with a layer  30  including a phosphor composition. As schematically represented in  FIG. 4 , such methods desirably include a step  41  of applying a phosphor coating  30  on the inner surface  13  of the envelope  12 . The phosphor coating  30  employed in step  41  may include a suspension of phosphor particles  32  in a water soluble binder mixed with other additives as known in the art. Once this suspension is applied to the inner surface  13  of the envelope  12 , the phosphor coating  30  may be dried and baked as described above to provide an inwardly-facing surface  31  schematically shown in  FIG. 2 . As schematically represented in  FIG. 3 , the phosphor coating  30  contains voids  33  that may have dimensions in the range of from below about 1 micrometer to as large as several (e.g., 10) micrometers. Therefore, these voids  33  are present in the inwardly-facing surface  31  ( FIG. 2 ) of the phosphor coating  30 . 
         [0029]    Generally, methods in accordance with embodiments of the invention may comprise a step of applying a suspension of material that is to form the protective coating  14  onto the inwardly-facing surface  31  of a dried phosphor coating  30 . However, prior to performing this step, it may be necessary to ensure that the phosphor coating  30  does not become washed off during the step of applying a suspension. If any dried phosphor coating  30  becomes washed off during a subsequent step of applying a suspension, this may lead to unacceptable technical and aesthetic quality in the finished fluorescent tamp  10 . Therefore, preventing the washing away of the dried phosphor coating  30  can be achieved by a step of “wash-proofing” (i.e., making the phosphor coating  30  wash resistant) the phosphor coating  30  before applying any subsequent suspension. 
         [0030]    The step of wash-proofing the phosphor coating  30  can be achieved by baking the phosphor coating  30  and thus removing any dissolvable organic materials from it prior to applying the protective coating  14 . Alternatively, the step of wash-proofing the phosphor coating  30  can be achieved by using a water-resistant binder within the phosphor coating, such as a water soluble polymer that can be made water resistant by drying with forced hot air circulation. This latter method may have advantages in cost and simplicity. A suitable choice for a water soluble polymer as the binder of the phosphor coating  30  can be the ammonium salt of acrylic (methacrylic) acid/acrylic (methacrylic) ester copolymer, preferably of high molecular mass. If a coating containing such a water-resistant binder is dried (e.g., at a temperature of at least 80 degrees C.) it becomes sufficiently water resistant to survive a subsequent water based coating step without being washed off. Thus the phosphor coating  30  can be made partly water insoluble by drying a wet phosphor coating  30  with hot air at 80 degrees C. or above. As schematically shown in  FIG. 4 , the step  41  of providing a phosphor coating  30  on the inner surface  13  of the envelope  12  desirably may also include the step of wash-proofing the phosphor coating  30 . 
         [0031]    As schematically represented in  FIG. 4 , methods for making a light source  10  may include a step  42  of providing a protective coating  14  on the inwardly-facing surface  31  of the phosphor coating  30 . As schematically shown in  FIGS. 2 and 3 , the protective coating  14  defines an innermost surface  15  that may make possible the effective recombination of Hg ions on the innermost surface  15  of the protective coating  14 , to inhibit the collision of Hg ions with the phosphor particles  32  in the phosphor coating  30 . The radial thickness range of the protective coating  14  may be a value between about 0.01 micrometers and about 5 micrometers. Other thicknesses are possible. 
         [0032]    In certain embodiments, the protective coating  14  should be transparent to visible light and as transparent to 254 nm UV light as possible. Certain materials can help the coating  14  fulfill both requirements. For example, the protective coating  14  may comprise aluminum oxide particles having a primary crystalline size of below about 20 nm with secondary (aggregate) particle diameters of about 0.05 micrometers to about 1 micrometer. Of course, the particles in the protective coating  14  may also comprise a flocculated or tertiary aggregated particle size which is larger than the voids between phosphor particles. 
         [0033]    The step of providing a protective coating  14  on the inwardly-facing surface  31  of the phosphor coating  30  desirably can include a sat-gel process, in one embodiment, one may form the protective coating  14  from an aluminum oxide sol or aluminum hydroxy-oxide sol, such as boehmite sol. Such sol may be prepared under the following conditions to bring the precursor material into a form of colloidal dispersion (precursor sol): aluminum isopropoxide [Al(OC 3 H 7 ) 3 ] (or other alkoxide) was added to an amount of distilled water (molar ratio of Al to H 2 O=1:50) at 85° C. under vigorous stirring, which was maintained for half an hour. Nitric acid (HNO 3 ) then was added to peptize the hydroxide precipitate (molar ratio of Al and HNO 3 =1:0.13). The stirring was then maintained for half an hour at 85° C. to obtain a clear boehmite sol, which is termed herein the “basic sol”. After these steps, other materials (such as neutral polymers, e.g., polyvinyl pyrrolidone and/or polyethylene glycol, etc.) in a concentration of 0.05 g/100 mL to 0.5 g/100 ml solutions can be added to the basic sol to modify the properties of the basic sol and the resultant coatings. The conventional up-flush or down-flush processes then are applied to this precursor sol to obtain the liquid that is to be applied to the inwardly-facing surface  31  of the phosphor coating  30 . The liquid that is applied to form the protective coating  14  contains a substantial amount of liquid (mainly water) that must be dried and treated at high temperature to develop a ceramic protective coating  14  having a radial thickness range that desirably is between about 0.01 micrometers and about 5 micrometers. These two steps may occur in the conventional drying and the subsequent lehring steps of the conventional manufacture of fluorescent lamps  10 . 
         [0034]    We return now to the matter of the dimension of the voids in the inwardly-facing surface  31  of the phosphor coating  30 , and the particle size of the particles  34  in the protective coating  14 . As noted above, the individual particles in the dispersed phase of the protective coating  14  may have a primary crystalline size of below about 20 nanometers (0.02 micrometers) and secondary (aggregate) particle diameters of about 0.05 micrometers to about 1 micrometer. However, as shown in the schematically enlarged view of  FIG. 3 , the phosphor coating  30  generally contains voids  33  that have dimensions in the range of below 1 micrometer and can range up to several micrometers. These voids  33  are present in the inwardly-facing surface  31  ( FIG. 2 ) of the phosphor coating  30 . 
         [0035]    As schematically depicted in the enlarged view of  FIG. 3 , the phosphor particles  32  located at the inwardly-facing surface  31  ( FIG. 2 ) of the phosphor coating  30  are the ones that are the closest to the discharge and thus are most exposed to the bombardment of mercury ions during the normal discharge that occurs during operation of the fluorescent lamp  10 . The purpose of the protective coating  14  is to mitigate this. However, unless precautions are taken during the step of drying the protective coating  14 , the particles of the protective coating  14  can fail into the voids  33 . If this occurs, the protective coating  14  will fail to create a continuous protective layer over the top of the phosphor particles  32  located at the inwardly-facing surface  31  of the phosphor coating  30 . 
         [0036]    If the particles of the dispersion that is to form the protective coating  14  are to avoid falling into the voids  33  of the phosphor coating  30 , some further aggregation may be desirable, e.g., aggregation to achieve a mildly flocculated tertiary structure. As schematically shown in  FIG. 3 , this undesirable condition can be prevented by size-enhancing the individual particles of the suspension used to form the protective coating  14 . These size-enhanced particles then may then become large enough to span across the voids  33  of the inwardly-facing surface  31  of the phosphor coating  30  and thus avoid falling into these voids  33 . One may effect such size-enhancement by the controlled flocculation (decrease of the colloidal stability) of the particles that form the suspension that is applied to form the protective coating  14 . In the case of alumina particles (e.g. Aeroxide Alu C™ by Evonik), this mildly flocculated tertiary structure desirably can be achieved by using a suitable polyethylene oxide binder of high molecular mass that is capable of flocculating the aluminum oxide to the required extent (e.g. Polyox WSR N-3000™ by Dow Chemicals). Such controlled flocculation may cause colloids in the suspension to aggregate together into a size-enhanced particle  34  that exceeds the size of the voids  33  defined in the inwardly-facing surface  31  of the phosphor coating  30 . Therefore, (and by reference to  FIG. 3 ), controlled flocculation is one way to ensure that the size of the particles  34  of the protective coating  14  are larger than the size of the voids  33  defined between the phosphor particles  32  in the inwardly-facing surface  31  of the phosphor coating  30 . 
         [0037]    As schematically shown in  FIG. 4 , the step  42  of providing a protective coating  14  on the inwardly-facing surface  31  of the phosphor coating  30  may include controlled flocculation that size-enhances the flocculated particles  34  that form the suspension that is applied to form the protective coating  14 . Thus, the application of the suspension with the size-enhanced particles  34  that is applied to form the protective coating  14  may create a continuous protective layer over the top of the phosphor particles  32  located at the inwardly-facing surface  31  of the phosphor coating  30 . 
         [0038]    There are alternative sequences of steps for providing a protective coating  14  on the inwardly-facing surface of the phosphor coating  30 . For example, a chemical vapor deposition process can be used. For example, an airborne aerosol or vapor of a suitable precursor material (such as an aluminum alkoxide or trimethyl aluminum if an aluminum oxide coating is to form the protective coating  14 ) may be blown through a heated envelope  12  containing the phosphor coating  30 . On the hot wall of the envelope  12 , the precursor material undergoes a chemical reaction resulting in the required oxide coating on the phosphor coating  30 . This chemical vapor deposition of the protective coating  14  can suitably be combined with the conventional lehring step of fluorescent lamp manufacture. 
         [0039]    In an alternative formulation of the protective coating  14 , the protective coating  14  may itself comprise some phosphor particles. However, in this embodiment, phosphor particles within the protective coating  14  are provided in a much smaller percentage than are present in the phosphor coating  30 . In this embodiment, these phosphor particles may bring about the controlled flocculation that produces the size-enhancement in the mildly flocculated tertiary structure. In one exemplary embodiment, both the phosphor coating  30  and the protective coating  14  may comprise phosphors as well as alumina. In this embodiment, the alumina: phosphor ratio in the phosphor coating  30  is usually in the 0.5% to 4% range, and the protective coating  14  used 6% to 20% alumina relative to the weight of phosphor. Accordingly, the total phosphor content of the protective coating  14  was only a fraction of the total phosphor content of the underlying phosphor coating  30  (e.g., 5 weight % to 20 weight %). After lehring/baking (pyrolysing away the organics), one obtains a phosphor coating  30  composed of the same components as the protective coating  14  but having a sharp gradient in alumina distribution, the concentration of alumina being much higher in the thin protective coating layer  14 . 
         [0040]    Thereafter, as schematically represented in  FIG. 4 , the methods desirably call for the step  43  of installing a plasma discharge source in the envelope  12 , which source is capable of creating a discharge from a fill comprising mercury and inert gas. As schematically represented in  FIG. 4 , the methods desirably may comprise a step  44  of evacuating the envelope  12 . As schematically represented in  FIG. 4 , once the envelope  12  is evacuated, the methods may comprise step  45  of adding into the evacuated envelope  12 , a gas  22  that includes a mercury and an inert gas. As schematically represented in  FIG. 4 , the methods may include a step  46  of sealing the envelope  12  to produce the light source  10 . 
         [0041]    Reference has been made in detail to present embodiments of the invention, one or more examples of which are illustrated in the accompanying drawings. The detailed description uses numerical and letter designations to refer to features in the drawings. Like or similar designations in the drawings and description have been used to refer to like or similar parts of the invention. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that modifications and variations can be made in the present invention without departing from the scope or spirit thereof. For instance, features illustrated or described as part of one embodiment may be used on another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents. 
         [0042]    It is to be understood that the ranges and limits mentioned herein include all sub-ranges located within the prescribed limits, inclusive of the limits themselves unless otherwise stated. For instance, a range from 100 to 200 also includes all possible sub-ranges, examples of which are from 100 to 150, 170 to 190, 153 to 162, 145.3 to 149.6, and 187 to 200. Further, a limit of up to 7 also includes a limit of up to 5, up to 3, and up to 4.5, as well as all sub-ranges within the limit, such as from about 0 to 5, which includes 0 and includes 5 and from 5.2 to 7, which includes 5.2 and includes 7. 
         [0043]    This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other and examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.