BRPI0618693A2 - porous substrate - Google Patents

Abstract

POROUS SUBSTRATE. The present invention relates to an extrusable mixture that is provided to produce a highly porous substrate using an extrusion process. More particularly, the present invention enables fibers, such as organic, inorganic, glass, ceramic or metal fibers, to be mixed into a mass which when extruded and cured forms a highly porous substrate. Depending on the particular blend, the present invention enables substrate porosities from about 60% to about 90%, and also enables process advantages in other porosities. The extrusable mixture can use a wide variety of fibers and additives, and is adaptable to a wide range of operating environments and applications. Fibers, which have an aspect ratio greater than 1, are selected according to substrate requirements, and are mixed with binders, pore builders, extrusion helpers and fluid to form a homogeneous extrusable mass. The homogeneous mass is extruded to a green substrate. The most volatile material is preferably removed from the green substrate, which allows the fibers to interconnect and contact each other. As the curing process continues, fiber-to-fiber joints are formed to produce a structure having a substantially open pore network. The resulting porous substrate is useful in many applications, for example, as a substrate for a filter or catalyst host, or catalytic converter.

Description

Patent Descriptive Report for "POROSO SUBSTRATE".

BACKGROUND

1. RELATED REQUESTS

This application claims priority for US provisional patent application number 60 / 737,237, filed November 16, 2005, entitled "System for Extruding a Porous Substrate"; U.S. Patent Application No. 11 / 323,430, filed December 30, 2005, entitled "An Extrudable Mixture for Forming a Porous Block"; U.S. Patent Application No. 11 / 322,777, filed December 30, 2005, entitled "Process for Extruding a Porous Substrate"; and U.S. Patent Application No. 11 / 323,429, filed December 30, 2005, entitled "An Extruded Porous Substrate and Products Using the Health"; all of which are incorporated in this document in their entirety.

2. FIELD

The present invention relates generally to an extrusion process for extruding a porous substrate, and in a particular implementation to an extrusion process for extruding a porous ceramic substrate.

3. DESCRIPTION OF RELATED TECHNIQUE

Many processes require rigid substrates to facilitate and support multiple processes. For example, substrates are used in filtration applications to filter out particulate matter, separate different substances, or remove bacteria or germs from the air. These substrates may be constructed to operate in air, exhaust gases or liquids, and may be manufactured to withstand substantial chemical or environmental stresses. In another example, catalytic materials are deposited on the substrate to facilitate chemical reactions. For example, a precious metal may be deposited on a suitable substrate, and the substrate may then act to catalytically convert hazardous exhaust gases into less harmful gases. Typically, these rigid substrates operate more effectively with a higher porosity.

Porosity is generally defined as the property of a solid material defining the percentage of the total volume of this material that is occupied by open space. For example, a 50% porous substrate has half the volume of the substrate occupied by open spaces. Thus, a substrate with a higher porosity has less mass per volume than a substrate with a lower porosity. Some applications benefit from a lower mass substrate. For example, if a substrate is used to support a catalytic process, and the catalytic process operates at a high temperature, a substrate with a lower thermal mass will heat up faster to its operating temperature. In this way, the time for the catalyst to be heated to its operating temperature, i.e. heating time, is reduced by the use of a more porous and less thermally massive substrate.

Permeability is also an important feature for substrates, particularly filtering and catalytic substrates. Permeability is related to porosity, where permeability is a measure of how easily a fluid, such as a liquid or gas, can flow through the substrate. Many applications benefit from a highly permeable substrate. For example, an internal combustion engine operates more efficiently when the aftertreatment filter provides less back pressure to the engine. Low back pressure is created by the use of a highly permeable substrate. Since permeability is more difficult to measure than porosity, porosity is often used as a surrogate guide for the permeability of a substrate. However, this is not a particularly accurate characterization as a substrate can be quite porous but still have limited permeability if the pores are not generally open and interconnected. For example, a Styrofoam drinking glass is formed of a highly porous foam material, but is not permeable to liquid flow. Therefore, in consideration of the importance of porosity and permeability, the pore structure of the substrate should also be examined. In the example of the Styrofoam cup, the Styrofoam material has a closed pore web. This means that the foam contains many unconnected and / or closed pores. Thus, there are many open and empty spaces within the foam, but since the pores are not connected the fluid or gas cannot flow from one side of the foam to the other. As more channels begin to interconnect, then paths of fluid begin to form from side to side. In such a case the material is said to possess more open pore web. The more connected channels formed through the material, the higher the permeability to the substance becomes. In the case where each pore is connected to at least one other channel, and all pores take into account fluid flowing through the total wall thickness formed of the material, the substrate would be defined as having a fully open pore network. It is important to note the difference between cells and pores. Cells refer to channels that develop (generally parallel to each other, but not necessarily) through the alveolar substrate. Often, alveolar substrates are referred to in the context of how many cells they have per square inch (square centimeter). For example, a 200 cell per square inch substrate (31 cells per square centimeter) has 200 channels along the substrate start geometric axis. Pores, on the other hand, refer to gaps within the material itself, such as in the wall material separating two parallel channels or cells. Completely or most often open pore mesh substrates are not known in the filtration or catalytic industries. Instead, even the most porous available extruded substrates are an open pore and closed pore hybrid.

Thus, it is highly desirable for many applications for substrates to be formed with high porosity, and with an internal pore structure that enables similarly high permeability. Also, substrates must be formed with a sufficiently rigid structure to withstand the structural and environmental requirements for particular applications. For example, a filter or catalytic converter that is to be attached to the internal combustion engine must be able to withstand likely environmental shocks, thermal requirements, and manufacturing and use stresses. Finally, the substrate needs to be produced at a low enough cost to account for widespread use. For example, in order to affect the worldwide level of pollution from cars, a filtering substrate must be available and usable in developed as well as developing countries. Thus, the total cost structure for filter substrates and catalytic converter is a substantial consideration in the substrate design and selection process.

Extrusion has proven to be an efficient and inexpensive process to manufacture constant cross section rigid substrates. More particularly, extrusion of ceramic powder material is the most widely used process for making filter and catalytic substrates for internal combustion engines. Over the years the process of extruding pulverized ceramics has advanced such that substrates can now be extruded having porosities approaching 60%. These extruded porous substrates have had good strength characteristics, can be flexibly manufactured, can be manufactured to scale, maintain high quality levels and are very low cost. However, extrusion of pulverized ceramic material has reached a practical upper limit of porosity, and further increases in porosity appear to result in unacceptably low resistance. For example, as porosity is increased beyond 60%, the extruded ceramic powder substrate has not proven strong enough to operate in the harsh environment of a diesel particulate filter. In another limitation of known extrusion processes, it has been desired to increase the surface area in a substrate to account for more efficient catalytic conversion. In order to increase surface area, extruded ceramic powder substrates have been experimented with increasing cell density, but the increase in cell density has resulted in unacceptable motor back pressure. Thus, the extruded ceramic powder substrate does not have sufficient strength at very high porosities, and also produces unacceptable counter pressure when there is a need for increased surface area. Thus, the extrusion of ceramic powder seems to have reached its practical limits of utility.

In an effort to achieve higher porosities, filter suppliers have been trying to move to nailed ceramic papers. Using such nailed ceramic papers, porosities of about 80% are possible with very low back pressure. With such low back pressure, these filters have been used in applications such as mining where extremely low back pressure is a necessity. However, the use of nailed ceramic paper filters has been sporadic, and has not been widely adopted. For example, nailed ceramic papers have not been effectively used in harsh environments. The manufacture of nailed ceramic papers requires the use of a papermaking process that creates ceramic paper structures that are relatively weak, and do not appear to be inexpensive compared to extruded filters. Additionally, the formation of nailed ceramic papers allows very little flexibility in cell shape and density. For example, it is difficult to create a paper filter with large input channels and smaller output channels, which may be desirable in some filtering applications. Thus, the use of nailed ceramic papers has not satisfied the requirement of higher porosity filter and catalytic substrates.

In another example of an effort to increase porosity and avoid the disadvantages of nailed paper, some have constructed substrates by forming a mass with ceramic precursors and carefully processing the mass to develop monocrystalline capillary crystals in a porous pattern. . However, developing these crystals on site requires careful and precise control of the curing process, making the process difficult to scale, relatively expensive and prone to defects. In addition, this difficult process only gives a few more percentage points in porosity. Finally, the process only develops a mullite crystalline capillary crystal, which limits the applicability of the substrate. For example, mullite is known to have a large coefficient of thermal expansion, which makes crystalline mullite capillary crystals undesirable in many applications requiring a wide operating temperature range and sharp temperature transitions.

Thus, the industry has a need for a rigid substrate that has high porosity and associated high permeability. Preferably, the substrate would be formed such as a highly desirable open cell network, would be of low manufacturing cost and would be manufactured with flexible physical, chemical and reaction properties.

SUMMARY

Briefly, the present invention provides an extrusable mixture to produce a highly porous substrate using an extrusion process. More particularly, the present invention enables fibers, such as organic, inorganic, glass, ceramic or metal fibers, to be mixed into a mass which when extruded and cured forms a highly porous substrate. Depending on the particular mixture, the present invention enables substrate porosities from about 60% to about 90%, and also enables process advantages at other porosities.

The extrudable blend can use a wide variety of fibers and additives, and is adaptable to a wide variety of operating environments and applications. Fibers, which have an aspect ratio greater than 1, are selected according to substrate requirements, and are mixed with binders, pore formers, extrusion aids, and fluid to form a homogeneous extrudable mass. The homogeneous mass is extruded to a green substrate. The most volatile material is preferably removed from the green substrate, which allows the fibers to interconnect and contact each other. As the curing process continues, fiber-to-fiber joints are formed to produce a structure having a substantially open pore web. The resulting porous substrate is useful in many applications, for example, as a substrate for a filter or catalyst host, or catalytic converter.

In a more specific example, ceramic fibers are selected with an aspect ratio distribution of from about 3 to about 1,000, although more typically in the range from about 3 to about 500. Aspect ratio is the ratio. of fiber length divided by fiber diameter. The ceramic fibers are mixed with binder, pore former and a fluid in a homogeneous mass. A shear mixing process is employed to distribute the fibers more evenly in the dough. The ceramic material may be about 8% to about 40% by weight, which results in a substrate having a porosity of about 92% to about 60%. The homogeneous mass is extruded to a green substrate. The binder material is removed from the green substrate, which allows the fibers to overlap and contact each other. As the healing process continues, fiber to fiber joints are formed to produce a rigid open cell network. As used in this description, "curing" is defined to include two important process steps: 1) binder removal and 2) bonding. The binder removal process removes free water, removes most additives, and enables fiber to fiber contact. The resulting porous substrate is useful in many applications, for example, as a substrate for a filter or catalytic converter.

In another specific example, a porous substrate may be produced without the use of pore formers. In this case, the ceramic material may be by volume from about 40% to about 60% or more of the mass, which results in a substrate having a porosity of about 60% to about 40%. Since no pore former is not used, the extrusion process is simplified and cost-effective. Also, the resulting structure is a highly desirable substantially open pore network.

Advantageously, the disclosed fiber extrusion system produces a substrate having high porosity, and having an open pore network that enables associated high permeability, as well as having sufficient strength according to application needs. The fiber extrusion system also produces a substrate at a sufficiently low cost to enable widespread use of the resulting filters and catalytic converters. The extrusion system is easily scalable for mass production, and takes into account flexible chemicals and constructions to support large amounts of applications. The present invention represents a pioneering use of fiber material in an extrudable blend. This extrusable fibrous blend enables extrusion of substrates with very high porosities, in scalable production, and in a low cost manner. By enabling fibers to be used in the repeatable and robust extrusion process, the present invention enables mass production of filters and catalytic substrates for wide use worldwide.

These and other features of the present invention will become apparent from a reading of the following description, and may be realized using the means and combinations particularly set forth in the appended claims.

BRIEF DESCRIPTION OF DRAWINGS

The drawings form part of this specification and include exemplary embodiments of the invention which may be incorporated in various forms. It should be understood that in some cases various aspects of the invention may be shown to be exaggerated or extended to facilitate an understanding of the invention.

Figure 1 is a block diagram of a system for extruding a porous substrate according to the present invention.

Figure 2 is an illustration of a fibrous extrudable blend according to the present invention.

Figures 3A and 3B are illustrations of an open pore network in accordance with the present invention.

Figure 4 is an electron microscope image of an open-pore network in accordance with the present invention and a prior art closed-powder network.

Figure 5 is an illustration of a filter block using a porous substrate according to the present invention.

Figure 6 are tables of fibers, binders, dust formers, fluids and rheology useful with the present invention.

Figure 7 is a block diagram of a system for extruding a porous substrate according to the present invention.

Figure 8 is a block diagram of a system for curing a porous substrate according to the present invention.

Figure 9 is a block diagram of a fiber processing system for a porous substrate according to the present invention.

Figure 10 is a diagram for extruding a gradient porous substrate according to the present invention.

Figure 11 is a diagram for extruding a gradient porous substrate according to the present invention.

Figure 12 is a diagram for extruding a gradient porous substrate according to the present invention.

DETAILED DESCRIPTION

Detailed descriptions of examples of the invention are provided herein. It should be understood, however, that the present invention may be exemplified in various forms. Therefore, the specific details disclosed herein are not to be construed as limitations, but rather as a representative basis for showing those skilled in the art how to employ the present invention in virtually all detailed system, structure or manner.

Referring now to Figure 1, a system for extruding a porous substrate is illustrated. Generally, system 10 uses an extrusion process to extrude a green substrate that can be cured into the final highly porous substrate product. The system 10 advantageously produces a substrate having high porosity, having a substantially open pore network enabling associated high permeability, as well as having sufficient strength according to the application needs. System 10 also produces a substrate at a sufficiently low cost to enable widespread use of the resulting filters and catalytic converters. System 10 is easily scalable for mass production, and takes into account flexible chemicals and constructions to support large amounts of applications.

System 10 enables a highly flexible extrusion process and is thus capable of accommodating a wide range of specific applications. When using system 10, the substrate designer first establishes the requirements for the substrate. These requirements may include, for example, size, fluid permeability, desired porosity, pore size, mechanical and shock resistance characteristics, thermal stability, and limitations of chemical reactivity. In accordance with these and other requirements, the designer selects materials for use in forming an extrusable mixture. Importantly, system 10 enables the use of fibers 12 in forming an extruded substrate. Such fibers may be, for example, ceramic fibers, organic fibers, inorganic fibers, polymeric fibers, oxide fibers, glass fibers, glass fibers, amorphous fibers, crystalline fibers, non-oxide fibers, carbide fibers, metal fibers. , other organic fiber structures, or a combination thereof. However, for ease of explanation, the use of ceramic fibers will be described, although it should be noted that other fibers may be used. Also, the substrate will often be described as a filtering substrate or a catalytic substrate, although other uses are considered and within the scope of this precept. The designer selects the particular type of fiber based on the specific application needs. For example, ceramic fiber may be selected as a mullite fiber, an aluminum silicate fiber, or other commonly available ceramic fiber material. Fibers typically need to be processed 14 to cut the fibers to a usable length, which may include a cutting process before mixing the fibers with additives. Also, the various mixing and forming steps in the extrusion process will further cut the fibers.

According to specific requirements, additives 16 are added. These additives 16 may include binders, dispersants, pore formers, plasticizers, processing aids, and reinforcing materials. Also, fluid 18, which is typically water, is combined with additives 16 and fibers 12. The fibers, additives and fluid are mixed in an extrusable rheology 21. This mixture may include dry blending, wet blending and blending. shear. The fibers, additives and fluid are mixed until a homogeneous mass is produced which evenly distributes and arranges the fibers within the mass. The homogeneous fibrous mass is then extruded to form a green substrate 23. The green substrate has sufficient strength to hold together through the remaining process.

The green substrate is then cured 25. As used in this description, "curing" is defined to include two important process steps: 1) binder removal and 2) bonding. The binder removal process removes free water, removes most additives and enables fiber to fiber contact. Often the binder is removed using a heating process that burns the binder, but it should be understood that other removal processes may be used depending on the specific binder used. For example, some binders may be removed using an evaporation or sublimation process. Some binders and or other organic components may melt before degrading to a vapor phase. As the healing process continues fiber to fiber joints are formed. These joints facilitate overall structural stiffness as well as creating desirable substrate porosity and permeability. Thus, the cured substrate 30 is a highly porous substrate of almost all fibers joined in an open pore web 30. The substrate can then be used as a substrate for many applications, including a substrate for filtration and application applications. of catalytic conversion. Advantageously, system 10 has enabled a desirable extrusion process to produce substrates having pores of up to about 90%.

Referring now to Figure 2, an extrudable material 50 is illustrated. The extrudable material 50 is ready for extrusion by an extruder, such as a piston or screw extruder. Extrudable blend 52 is a homogeneous mass including fibers, plasticizers and other additives as required by the specific application. Figure 2 illustrates an enlarged portion 54 of the homogeneous mass. It should be appreciated that the enlarged part 54 may not be drawn to scale, but is provided as an aid to this description. Extrudable blend 52 contains fibers such as fibers 56, 57 and 58. These fibers have been selected to produce a highly porous and rigid final substrate with desired thermal, chemical, mechanical and filtration characteristics. As should be understood, substantially fibrous bodies were not considered to be extrusable since they have no plasticity of their own. However, it has been found that by appropriate plasticizer selection and process control, an extrudable blend 52 comprising fibers can be extruded. Thus, the advantages of extrusion cost, scale and flexibility can be extended to include the benefits available when using fibrous material.

Generally speaking, a fiber is considered to be a material with a relatively small diameter having an aspect ratio greater than one. Aspect ratio is the ratio of fiber length divided by fiber diameter. As used herein, the fiber 'diameter' assumes for simplicity that the sectional shape of the fiber is a circle; This simplification assumption is applied to fibers regardless of their true sectional shape. For example, a fiber with an aspect ratio of 10 has a length that is 10 times the diameter of the fiber. The fiber diameter may be 6 microns, although diameters ranging from about 1 micron to about 25 microns are readily available. It will be appreciated that fibers of very different diameter and aspect ratios can be used successfully in system 10. As will be described in more detail with reference to the following figures, there are several alternatives for selecting aspect ratios for the fibers. . It should also be noted that the shape of the fibers is in sharp contrast to the typical ceramic powder, where the aspect ratio of each ceramic particle is approximately 1.

The fibers for the extrudable blend 52 may be metallic (sometimes also referred to as small diameter metallic threads), although Figure 2 is discussed with reference to ceramic fibers. The ceramic fibers may be in an amorphous state, a vitreous state, a crystalline state, a polycrystalline state, a monocrystalline state, or a glass-ceramic state. In making the extrudable blend 52, a relatively small volume of ceramic fiber is used to create the powdery substrate. For example, extrudable blend 52 may have only about 10% to 40% by volume ceramic fiber material. Thus, after curing, the resulting porous substrate will have a porosity of from about 90% to about 60%. It should be noted that other amounts of ceramic fiber material may be selected to produce other porosity values.

In order to produce an extrusable blend, the fibers are typically combined with a plasticizer. In this way the fibers are combined with other selected organic or inorganic additives. These additives provide three key properties for the extrudate. First, the additives allow the extrudable mixture to have a proper rheology for extrusion. Second, the additives provide the extruded substrate, which is typically called a green substrate, with sufficient strength to maintain its shape and fiber position until these additives are removed during the curing process. And third, the additives are selected so that they burn in the curing process in a mode that facilitates arranging the fibers in an overlapping construction, and in a mode that does not weaken the rigid structure formed. Typically, the additives will include a binder, such as binder 61. Binder 61 acts as a means for holding the fibers in position and providing resistance to the green substrate. The fibers and binder (s) may be used to produce a porous substrate having a relatively high porosity. However, to further increase porosity, additional pore builders, such as pore builder 63, may be added. Pore formers are added to increase open space in the final cured substrate. Pore formers may be spherical, elongated, fibrous, or irregular in shape. Pore formers are selected not only for their ability to create open space and based on their thermal degradation behavior, but also to aid in fiber orientation. In this way, pore formers assist in arranging the fibers in an overlapping pattern to facilitate proper joining between fibers during the later stage of curing. In addition, pore formers also play a role in aligning fibers in preferred directions, which affects the thermal expansion of the extruded material and strength along different geometrical axes.

As briefly described above, the extrudable blend 52 may use one or more fibers selected from the many available fiber types. Additionally, the selected fiber may be combined with one or more selected binders from a wide variety of binders. Also, one or more pore formers may be added from a wide variety of pore formers. The extrudable mixture may use water or another fluid as its plasticizing agent, and may have other additives added. This flexibility in chemical formation enables the extrudable mixture 52 to be advantageously used in many different types of applications. For example, blending combinations may be selected according to required environmental, temperature, chemical, physical, or other requirements. Additionally, since the extrudable mixture 52 is prepared for extrusion, the final extruded product can be flexibly and economically formed. Although not shown in Figure 2, the extrudable mixture 52 is extruded by means of a screw or piston extruder to form a green substrate which is then cured to the final porous substrate product.

The present invention represents a pioneering use of fiber material in a batch or plastic blend for extrusion. This extrusable fibrous blend enables extrusion of substrates with very high porosities, in a scalable production, and in a low cost manner. By enabling fibers to be used in the robust repeatable extrusion process, the present invention enables mass production of filter and catalytic substrates for wide use worldwide. Referring to Figure 3A, an enlarged cured area of a porous substrate is illustrated. Substrate part 100 is illustrated after removal of binder 102 and after the curing process 110. After removal of binder 102, fibers such as fibers 103 and 104 are initially retained in position with binder material and at the same time. As the binder material burns, the fibers are exposed to an overlapping structure, but loose. Also, a pore former 105 may be positioned to produce additional open space as well as to align or arrange fibers. Since the fibers comprise only a relatively small volume of the extrudable mixture, many open spaces 107 exist between the fibers. As the binder and pore former are burned out, the fibers may adjust slightly to additionally come into contact with each other. The binder and pore formers are selected to burn in a controlled manner, as well as not to disrupt the arrangement of the fibers or to have substrate collapse in the burn. Typically, the binder and pore formers are selected to degrade or burn before forming joints between the fibers. As the healing process continues the overlapping and touching fibers begin to form joints. It should be understood that unions can be formed in various ways. For example, the fibers may be heated to allow the formation of a liquid-assisted sintered joint at the intersection or knots of the fibers. This liquid state sintering may result from the particular fibers selected, or may result from additional additives added to the blend or coated on the fibers. In other cases, it may be desirable to form a solid state sintered union.

In this case, the intercession joints form a grain structure connecting overlapping fibers. In the green state, the fibers also do not have physical joints formed with each other, but may still exhibit some degree of green resistance because of the coiling of the fibers together. The particular type of joint selected will depend on the selection of base materials, desired strength, and chemical and operating environments. In some cases, joints are caused by the presence of inorganic binders present in the mixture that hold the fibers together in a connected network. And do not burn during the healing process.

Advantageously, forming joints such as joints 112 facilitates the formation of a substantially rigid structure with the fibers. Joints also enable the formation of an open pore network having very high porosity. For example, open space 116 is naturally created by the space between fibers. Open space 114 is created as pore former 105 degrades or burns. Thus, the fiber bonding process creates a network of open pores with no or virtually no limited channels. This open pore network generates high permeability, high filtration efficiency, and allows high surface area for catalyst addition, for example. It should be appreciated that the formation of joints may depend on the desired joining type, such as solid or liquid assisted / liquid state sintering, and additives present during the curing process. For example, additives, particular fiber selection, heating time, heating level and reaction environment can all be adjusted to create a particular type of joint.

Referring now to Figure 3B, another enlarged cured area of a porous substrate is illustrated. Substrate part 120 is illustrated after removal of binder 122 and after curing process 124. Substrate part 120 is similar to substrate part 100 described with reference to Figure 3A, so will not be described in detail. Substrate 120 was formed without the use of specific pore formers, thus the total open pore network 124 resulted from the positioning of the fibers with a binder material. Thus, moderately high porosity substrates can be formed without the use of any specific pore builders, thereby reducing the cost and complexity for manufacturing such moderately porous substrates. It has been found that substrates having a porosity in the range of from about 40% to about 60% can be produced in this mode.

Referring now to Figure 4, an electron microscope image set 150 is illustrated. Image set 150 first illustrates an open pore network 152 desirably created using a fibrous extrudable blend. As can be seen, fibers have joints formed at the fiber crossing nodes, and the pore former and binders have been burned, leaving a porous web of open pores. In sharp contrast, image 154 illustrates a typical closed cell network made using known methods. The partially closed pore network has a relatively high porosity, but at least part of the porosity is derived from the closed channels. These closed channels do not contribute to permeability. Thus, an open pore network and a closed pore network having the same porosity, the open pore network will have a more desirable permeability characteristic.

The extrudable mixture and process described in general herein is used to produce a highly advantageous and porous substrate. In one example, the porous substrate may be extruded to a filter block substrate 175 as illustrated in Figure 5. Substrate block 175 was extruded using a piston or screw extruder. The extruder may be conditioned to operate at room temperature, slightly elevated temperature or in a controlled temperature window. Additionally, various parts of the extruder may be heated to different temperatures to affect the slow characteristics, shear history and gel characteristics of the extrusion mixture. Additionally, the size of the extrusion dies may also be sized in this way to adjust the expected contraction in the substrate during the heating and sintering process. Advantageously, the extrudable mixture was a fibrous extrusable mixture having plasticizer and other additives sufficient to permit extrusion of fibrous material. The extruded green block was cured to remove free water, burn additives and form structural joints between fibers. The resulting block 175 has highly desirable porosity characteristics as well as excellent permeability and high usable surface area. Also, depending on the particular fibers and additives selected, block 175 may be constructed for advantageous depth filtration. Block 176 has channels 179 extending longitudinally through the block. The inlets for block 178 may be openings left for a continuous flow process, or each opening may be fitted to produce a wall flow effect. Although block 175 is shown with hex channels, it should be noted that other patterns and sizes can be used. For example, channels may be formed with a uniformly arranged quadrangular, rectangular, or triangular channel pattern; a quadrangular / rectangular or octagonal / quadrangular channel pattern having larger input channels; or in another symmetrical or asymmetrical channel pattern. The precise shapes and sizes of channels or cells can be adjusted by adjusting the matrix design. For example, a square channel can be made to have curved corners by using EDM (EDM) to model the pins in the die. Such rounded corners are provided to increase end product strength, despite slightly higher back pressure. Additionally, the die design can be modified to extrude honeycomb substrates where the walls have different thicknesses and the coating has a different thickness than the rest of the walls. Similarly, in some applications, an external coating may be applied to the extruded substrate for final definition of size, shape, contour and strength.

When used as a continuous flow device, the high porosity of block 176 enables a large surface area for the application of catalytic material. In this way a highly effective and efficient catalytic converter can be made, with the converter having a low thermal mass. With such a low thermal mass the resulting catalytic converter has good heating time characteristics and efficiently uses catalytic material. When used in an example wall flow or wall filtration, the high permeability of the substrate walls enables relatively low backpressures while facilitating depth filtration. This depth filtration enables efficient particulate removal as well as facilitates more effective regeneration. In wall flow design, fluid flowing through the substrate is forced to travel through the substrate walls, thereby enabling a more direct contact with the fibers composing the wall. Those fibers have a high surface area for potential reactions to occur, as if a catalyst were present. Since the extrudable mixture may be formed from a wide variety of fibers, additives and fluids, the chemistry of the extrudable mixture may be adjusted to generate a block having specific characteristics. For example, if the final block is desired to be a diesel particulate filter, the fibers are selected to consider safe operation even at the extreme temperature of uncontrolled regeneration. In another example, if the block is to be used to filter a particular type of exhaust gas, the fiber and joints are selected as well as not to react with the exhaust gas over the expected operating temperature range. Although the advantages of high porosity substrate have been described with reference to filters and catalytic converters, it should be understood that many other applications exist for the highly porous substrate.

The fibrous extrudable mixture as described with reference to Figure 2 may be formed from a wide variety of base materials. Selection of appropriate materials is generally based on the chemical, mechanical and environmental conditions under which the final substrate must operate. Thus, a first step in the design of a porous substrate is to understand the final application to the substrate. Based on these requirements, particular fibers, binders, pore formers, fluids and other materials can be selected. It should also be noted that the process applied to selected materials may affect the final substrate product. Since fiber is the primary structural material in the final substrate product, selection of fiber material is critical to enable the final substrate to operate in its intended application. In this way, the fibers are selected according to the required joining requirements, and a particular type of joining process is selected. The bonding process may be a liquid state sintering, solid state sintering, or a bonding requiring a bonding agent such as glass formers, glass, clays, ceramics, ceramic precursors or colloidal solutions. The bonding agent may be part of one of the fiber constructs, a fiber coating, or a component in one of the additives. It should also be noted that more than one fiber type can be selected. It should also be noted that some fibers may be consumed during the healing and bonding process. In selecting fiber composition the final operating temperature is an important consideration, so that thermal stability of the fiber can be maintained. In another example, the fiber is selected so that it remains chemically inert and non-reactive in the presence of expected gases, liquids or solid particulate matter. Fiber can also be selected according to its cost, and some fibers may have health concerns because of their small sizes and therefore their use can be avoided. Depending on the mechanical environment, the fibers are selected according to their ability to form a strong rigid structure as well as to maintain the required mechanical integrity. It should be noted that selecting an appropriate fiber or set of fibers may involve compensatory exchanges of performance and application. Figure 6, table 1, shows various types of fibers that can be used to form a fibrous extrudable blend. Generally speaking, the fibers may be oxide or non-oxide ceramic, glass, organic, inorganic, or they may be metallic. For ceramic materials, the fibers may be in different states, such as amorphous, vitreous, polycrystalline or monocrystalline. Although Table 1 illustrates many available fibers, it should be understood that other types of fibers may be used.

Binders and pore formers can then be selected according to the selected fiber type as well as other desired characteristics. In one example, the binder is selected to facilitate a particular type of liquid state bond between the selected fibers. More particularly, the binder has a component which at a bonding temperature reacts to facilitate the flow of a liquid bond to the intersecting fiber nodes. Also, the binder is selected for its ability to plasticize the selected fiber as well as to maintain its green strength status. In one example, the binder is also selected according to the type of extrusion being used, and the temperature required for extrusion. For example, some binders form a greasy mass when overheated and can therefore only be used in lower temperature extrusion processes. In another example, the binder may be selected according to its impact on shear mixing characteristics. In this way, the binder can facilitate fiber cutting to the desired aspect ratio during the mixing process. The binder may also be selected according to its degradation or burning characteristics. The binder needs to be able to hold the fibers generally in place, and not to disrupt the fiber structure formed during burning. For example, if the binder burns too quickly or violently, escaping gases may degenerate the formed structure. Also, the binder can be selected according to the amount of residue that the binder leaves behind after burning. Some applications may be highly sensitive to such residue.

Pore builders may not be necessary for the formation of relatively moderate porosities. For example, the natural arrangement and conditioning of the fibers within the binder may cooperate to enable a porosity of from about 40% to about 60%. Thus, a moderate porosity substrate can be generated using an extrusion process without the use of pore formers. In some cases, the elimination of pore formers enables a more economical porous substrate to be manufactured compared to known processes. However, when a porosity of more than about 60% is required, pore formers may be used to cause additional air space within the substrate after curing. Pore formers can also be selected according to their degradation or burning characteristics, and can also be selected according to their size and shape. Pore size may be important, for example, to capture particular types of particulate matter, or to enable particularly high permeability. The shape of the pores may also be adjusted, for example, to aid in proper fiber alignment. For example, a relatively elongated pore shape may arrange fibers in a more aligned pattern, while a more irregular or spherical shape may arrange fibers in a more random pattern.

The fiber may be supplied from a manufacturer as a cut fiber and used directly in the process, or a fiber may be supplied in a volume format, which is typically processed before use. However, process considerations should take into account how the fiber is to be processed for its final desirable aspect ratio distribution. Generally, the fiber is initially cut prior to mixing with other additives, and then further cut during the mixing, shearing and extrusion steps. However, extrusion can also be performed with uncut fibers by adjusting the rheology to make the extrusion mixture extrusable at reasonable extrusion pressures and without causing dilatation flows in the extrusion mixture when placed under pressure on the extrusion die face. It should be noted that fiber cutting for proper aspect ratio distribution can be done at various points in the overall process. Once the fiber has been selected and cut to a usable length, it is mixed with binder and pore former. This mixing may be done first in a dry form to begin the mixing process, or it may be done as a wet mixing process. Fluid, which is typically water, is added to the mixture. In order to achieve the required level of homogeneous distribution, the mixture is shear mixed in one or more stages. Shear mixing or dispersive blending provides a highly desirable homogeneous blending process for evenly distributing the fibers in the blend as well as for additionally cutting fibers to the desired aspect ratio.

Figure 6, table 2 shows several binders available for selection. It should be understood that a single binder may be used or that multiple binders may be used. Binders are broadly divided into organic and inorganic classifications. Organic binders will generally burn at a lower temperature during curing, while inorganic binders will typically form a part of the final structure at a higher temperature. Although several binder selections are listed in table 2, it should be noted that several other binders may be used. Figure 6, table 3, shows a list of available pore formers. Pore formers can be broadly defined as organic or inorganic, with organics typically burning at a lower temperature than inorganic ones. Although several pore formers are listed in table 3, it should be understood that other pore formers may be used. Figure 6, table 4 shows different fluids that can be used. While it should be noted that water may be the most economical and frequently used fluid, some applications may require other fluids. Although Table 4 shows various fluids that can be used, it should be noted that other fluids can be selected according to specific application and process requirements.

In general, the mixture may be adjusted to have a suitable rheology for advantageous extrusion. Suitable rheology typically results from the proper selection and mixing of fibers, binders, dispersants, plasticizers, pore formers and fluids. A high degree of mixing is necessary to adequately provide fiber plasticity. Once the appropriate fiber, binder and pore former have been selected, the amount of fluid is typically final adjusted to meet the appropriate rheology. An appropriate rheology may be indicated as by one of two tests. The first test is a subjective and informal test where a drop of mixture is removed and placed between the fingers of a qualified extrusion operator. The operator is able to identify when the mixture slides properly between the fingers, indicating that the mixture is in a suitable condition for extrusion. A second, more objective test relies on measuring physical characteristics of the mixture. In general, shear strength versus compaction pressure can be measured using a confined annular rheometer (ie high pressure). Measurements are made and plotted according to a comparison of cohesion resistance versus pressure dependence. By measuring the mixture at various mixtures and fluid levels, a rheology chart identifying rheology points can be created. For example, Table 5, Figure 6 illustrates a rheology chart for a fibrous ceramic mixture. The geometric axis 232 represents cohesion resistance and the geometric axis 234 represents pressure dependence. Extrusable area 236 represents an area where fibrous extrusion is highly likely to occur. Therefore, a mixture characterized by any measurement being included in area 236 is probably a mixture for successful extrusion. Of course, it should be noted that the rheology graph is subject to many variations, and thus some variation in the positioning of area 236 is to be expected. In addition, there are several other direct and indirect tests for measuring rheology and plasticity, and it can be seen that any number of them can be employed to verify that the mixture has the right rheology to extrude it into shape. end of the desired product.

Once the appropriate rheology has been achieved, the mixture is extruded through an extruder. The extruder can be a piston extruder, a single screw extruder, or a double screw extruder. The extrusion process may be highly automated, or may require human intervention. The mixture is extruded through a die having the desired cross-sectional shape for the substrate block. The matrix has been selected to sufficiently form the green substrate. In this way a stable green substrate is created that can be handled through the curing process while maintaining its fiber shape and alignment.

The green substrate is then dried and cured. Drying can take place under ambient conditions, controlled temperature and humidity conditions (such as controlled ovens), microwave ovens, RF ovens and convection ovens. Curing generally requires the removal of free water to dry the green substrate. It is important to dry the green substrate in a controlled manner as well as not to introduce cracks or other structural defects. The temperature may then be raised to burn additives such as binders and pore formers. The temperature is controlled to ensure that additives are burned in a controlled manner. It should be noted that additive firing may require temperature cycling through various timed cycles and various heat levels. Once the additives are burned, the substrate is heated to the temperature required to form structural joints at the fiber intersection points or nodes. The required temperature is selected according to the required joint type and fiber chemistry. For example, liquid-aided synthetic joints are typically formed at a lower temperature than solid-state joints. It should also be noted that the amount of time at the joint temperature can be adjusted according to the specific type of joint being produced. The total thermal cycle can be performed in the same oven, in different ovens, in batch or continuous processes and under ambient or controlled atmosphere conditions. After the fiber joints have been formed, the substrate is cooled slowly to room temperature. It should be appreciated that the curing process can be performed in one furnace or in multiple furnaces, and can be automated in production furnaces, such as tunnel furnaces.

Referring now to Figure 7, a system for extruding a porous substrate is illustrated. System 250 is a highly flexible process for producing a porous substrate. In order to design the substrate, substrate requirements are defined as shown in block 252. For example, substrate end use generally defines substrate requirements, which may include size restrictions, temperature restrictions, resistance restrictions and chemical reaction restrictions. In addition, the cost and ease of manufacture of substrate mass can determine and drive certain selections. For example, a high throughput rate may require the generation of relatively high temperatures in the extrusion die and therefore binders that operate at an elevated temperature without hardening or gel formation are selected. In extrusions using high temperature binders, the dies and the cylinder may need to be kept at a relatively higher temperature such as 60 ° C to 180 ° C. In such a case, the binder may melt, reducing or eliminating the need for additional fluid. In another example, a filter may be designed to capture particulate matter, so the fiber is selected to remain unreactive with particulate matter even at elevated temperatures. It should be noted that a wide range of applications can be accommodated, with a wide range of possible mixtures and processes. Those skilled in the art will appreciate the compensatory changes involved in the selection of fibers, binders, pore formers, fluids and process steps. Indeed, one of the significant advantages of the 250 system is its flexibility such as for mixing composition selection and process adjustments.

Once the substrate requirements have been defined, a fiber is selected from Table 1 of Figure 6 as shown in block 253. The fiber may be of a single type, or may be a combination of two or more types. It should also be noted that some fibers may be selected to be consumed during the healing process. Also, additives may be added to the fibers, such as coatings on the fibers, to introduce other materials into the blend. For example, dispersing agents may be applied to the fibers to facilitate fiber separation and arrangement, or joining aids may be coated onto the fibers. In the case of joining aids, when the fibers reach cure temperatures, joining aids assist in the formation and flow of liquid state joints. A typical composition for porosity> 80% <table> table see original document page 28 </column> </row> <table>

A binder is then selected from Table 2 of Figure 6 as shown in block 255. The binder is selected to facilitate green state resistance as well as controlled burning. Also, the binder is selected to produce sufficient plasticity in the mixture. If necessary, a pore former is selected from Table 3 of Figure 6 as shown in block 256. In some cases, sufficient porosity can be obtained only by using fibers and binders. Porosity is achieved not only by the natural conditioning characteristics of the fibers, but also by the space occupied by the binders, solvents, and other volatile components that are released during the deglutination and curing stages. To achieve higher porosities, additional pore builders may be added. Pore formers are also selected according to their controlled burning capabilities, and can also aid in the plasticization of the mixture. The fluid, which is typically water, is selected from Table 4 of Figure 6 as shown in block 257. Other liquid materials may be added, such as a dispersant, to aid in fiber separation and arrangement. , and plasticizers and extruders to improve the flow behavior of the mixture. This dispersant can be used to adjust the electronic surface loads on the fibers. In this way, fibers can have their loads controlled to make individual fibers repel each other. This facilitates a more homogeneous and random fiber distribution. A typical mixing composition intended to create a substrate with> 80% porosity is shown above. It should be noted that the mixture can be adjusted according to target porosity, specific application and process considerations.

As shown in block 254, the fibers selected in block 252 must be processed to have an appropriate aspect ratio distribution. This aspect ratio is preferred to be in the range of from about 3 to about 500 and may have one or more modes of delivery. It should be understood that other ranges can be selected, for example, up to about an aspect ratio of 1,000. In one example, the distribution of aspect ratios may be randomly distributed over the entire desired range, and in other examples the aspect ratios may be more distinctly selected in values. It was found that aspect ratio is an important factor in defining the packaging characteristics for fibers. In this way, the aspect ratio and the distribution of aspect ratios are selected to implement a particular strength and porosity requirement. It should also be noted that processing of the fibers at their preferred aspect ratio distribution can be performed at various points in the process. For example, fibers may be cut by an external entity processor and delivered at a predetermined aspect ratio distribution. In another example, the fibers may be supplied in bulk form and processed to an appropriate aspect ratio such as a preliminary stage in the extrusion process. It should be appreciated that mixing, shear mixing or dispersive mixing, and extrusion aspects of process 250 may also contribute to the cutting and splitting of the fibers. In this way, the aspect ratio of the fibers originally introduced into the blend will be different from that of the aspect ratio in the finished final substrate. Thus, the cutting and splitting effect of mixing, shear mixing, and extrusion should be considered when selecting the appropriate aspect ratio distribution 254 introduced in the process.

With the fibers processed for proper aspect ratio distribution, the fibers, binders, pore formers and fluids are blended into a homogeneous mass as shown in block 262. This blending process may include a dry blending aspect. , a wet mixing aspect and a shear mixing aspect. It has been found that shear or dispersive mixing is desirable to produce a highly homogeneous distribution of fibers within the mass. This distribution is particularly important because of the relatively low concentration of ceramic material in the mixture. As the homogeneous mixture is being mixed, the rheology of the mixture may be adjusted as shown in block 264. As the mixture is mixed its rheology continues to change. The rheology may be subjectively tested, or may be measured to meet the desired area as shown in Table 5 of Figure 6. Mixture being included in this desired area has a high probability of extrusion. appropriate. The mixture is then extruded to a green substrate as shown in block 268. In the case of screw extruders, mixing can also take place within the extruder itself, and not in a separate mixer. In such cases, the shear history of the mixture has to be carefully managed and controlled. The green substrate has sufficient green strength to retain its fiber shape and arrangement during the curing process. The green substrate is then cured as shown in block 270. The curing process includes removal of any remaining water, controlled burning of most additives, and formation of fiber fiber joints. During the burning process the fibers maintain their tangled and crisscrossing relationship, and as the curing process proceeds, the joints are formed at the crisscrossing points or knots. It should be understood that joints may result from a liquid state bonding process or a solid state bonding process. It should also be understood that part of the joints may be due to reactions with additives provided in the binder, pore formers such as coatings on the fibers, or on the fibers themselves. After the joints have been formed the substrate is slowly cooled to room temperature.

Referring now to Figure 8, a method for curing a porous fibrous substrate is illustrated. Method 275 has a green substrate having a fibrous ceramic content. The curing process first slowly removes the remaining water from the substrate as shown in block 277. Typically, water can be removed at a relatively low temperature in an oven. After the remaining water has been removed, the organic additives can be burned as shown in block 279. These additives are burned in a controlled manner to facilitate proper fiber arrangement, and to ensure that escaping gases and debris do not interfere with the structure. Fiber As the additives burn, the fibers maintain their overlapping arrangement, and may additionally come into contact at the crossing points or nodes as shown in block 281. The fibers are positioned in these overlapping arrangements using the binder, and may have particular patterns formed through the use of pore formers. In some cases, inorganic additives may have been used which may combine with the fibers, be consumed during the bonding process, or remain as a part of the final substrate structure. The curing process proceeds to form fiber-to-fiber joints as shown in block 285. The specific time and temperature required to create the joints depends on the type of fibers used, the type of auxiliaries or joining agents used, and the type. desired joint strength. In one example, the joint may be a sintered liquid binder generated between fibers as shown in block 286. Such joints are aided by glass formers, glass, ceramic precursors or inorganic fluxes present in the system. In another example, a liquid sintered binder may be created using sintering aids or agents as shown in block 288. Sintering aids may be provided as a coating on the fibers as additives of binders of pore formers, or the chemistry of the fibers themselves. Also, the fiber-to-fiber joint can be formed by a solid state sintering between fibers as shown in block 291. In this case, the intersecting fibers exhibit grain growth and mass transfer, resulting in the formation of joints. chemicals in the nodes and in a rigid global structure. In the case of liquid state sintering, a mass of bonding material accumulates at the fiber crossing nodes and forms the rigid structure. It should be appreciated that the curing process can be done in one or more furnaces, and can be automated in a tunnel or furnace type industrial furnace.

Referring now to Figure 9, a process for preparing fibers is illustrated. Process 300 shows that bulk fibers are received as shown in block 305. Bulk fibers typically have very long fibers in a bundled and interlaced arrangement. Such bulk fibers must be processed to properly separate and cut the fibers for use in the blending process. In this way, the bulk fibers are mixed with water 307 and possibly a dispersing agent 309 to form a slurry 311. The dispersant 309 may be, for example, a pH adjuster or a charge adjuster to aid in they keep away from each other. It should be noted that several different types of dispersants may be used. In one example, the volume fibers are coated with a dispersant prior to introduction into the slurry. In another example, the dispersant is simply added to the slurry mixture 311. The slurry mixture is thoroughly blended as shown in block 314. This intense blend acts to cut and separate the bulk fibers. for a usable aspect ratio distribution. As described above, the aspect ratio for the initial use of the fibers will differ from that of the final substrate distribution since the mixing and extrusion process further cuts the fibers.

After the fibers have been cut to an appropriate appearance distribution, water is most often removed using a filter press 316 or by pressing against a filter in another apparatus. It should be understood that other water removal processes may be used, such as freeze drying. The filter press may use pressure, vacuum or other device to remove water. In one example the chopped fibers are further dried to a complete dry state as shown in block 318. These dried fibers can then be used in a dry blending process 323 where they are blended with other dry pore binders and binders as shown. in block 327. This dry initial mixture assists in the generation of a homogeneous mass. In another example, the water content of the filtered fibers is adjusted to the appropriate moisture content as shown in block 321. More particularly, sufficient water is left in the cut fiber piece to facilitate wet mixing as shown in block 325. It has been found that by leaving part of the slurry water with the fibers, further separation and distribution of the fibers can be obtained. Binders and pore formers may also be added at the wet mixing stage, and water 329 may be added for correct rheology. The dough is also shear mixed as shown in block 332. Shear mixing can also be done by passing the mixture through spaghetti dies using a screw extruder, a twin screw extruder. , or a shear mixer (such as a sigma blade mixer). The drying mixture may also occur in a sigma mixer, a high shear mixer, and within the screw extruder. The shear mixing process is desirable to create a more homogeneous mass 335 that has desirable plasticity and extrudable rheology for extrusion to work. The homogeneous mass 335 has a uniform fiber distribution with the fibers positioned in an overlap matrix. Thus, as the homogeneous mass is extruded into a substrate block and cured, the fibers are allowed to join in a rigid structure. Additionally, this rigid structure forms a network of open pores having high porosity, high permeability and high surface area.

Referring now to Figure 10, a method for producing a gradient substrate block is illustrated. Process 350 is designed to enable fabrication and extrusion of a substrate block having a gradient feature. For example, a substrate may be produced having a first material in the direction of the center of the block, and a different material in the direction out of the block. In a more specific example, a material having a lower thermal expansion coefficient is used toward the center of the block where particularly high heat is expected, while a material with a relatively high thermal expansion coefficient is used in outdoor areas where Less heat is expected. In this way a more unified expansion property can be maintained for the total block. In another example, selected areas of a block may have higher density ceramic material to provide increased structural support. These structural support elements can be arranged concentric or axially arranged in the block. In this way, specific materials can be selected according to desired gradients in porosity, pore size or chemistry according to the application requirements. Additionally, the gradient may require the use of more than two materials.

In one example, the gradient structure may be produced by providing a cylinder of a first material 351. A blade of a second material 353 is wrapped around cylinder 351 as shown in illustration 355. Thus, layer B 353. a concentric tubing is taken around the inner cylinder 351. The layered cylinder 355 is then placed in a piston extruder, air is withdrawn and the mass is extruded through a die. During the extrusion process, material will mix at the interface between material A and material B, facilitating an uninterrupted interface. Such an interface enables fiber overlap and joining between the two different types of materials, thus facilitating a stronger overall structure. Once the material has been extruded, cured and packaged, it produces a filter pack or catalytic converter 357 having a gradient substrate. More particularly, material A forms at the center of the substrate, while material B 361 forms at the outer parts. It should be noted that more than two materials can be used, and that pore size, porosity and chemical characteristics can be adjusted gradually.

Referring now to Figure 11, another process 375 is described for creating a gradient substrate. In process 375, a first cylinder 379 is provided approximately the size of the piston extrusion cylinder. In one example, outer cylinder 379 is the actual cylinder used in the piston extruder. An inner tube 377 having a smaller diameter than outer tube 379 is provided. The tubes are arranged concentrically so that the inner tube 377 is positioned concentrically within the tube 379. Pellets of a first extrusable mixing material 383 are deposited within tube 377, while pellets of a second extrusable mixing material 381 are deposited in the ring between tube 377 and tube 379. The inner tube is carefully removed so that material A is concentrically surrounded by material 381. The material arrangement is then placed in the extrusion piston, air is removed, and is extruded through a die. Once extruded, cured and packaged, a gradient substrate as described with reference to Figure 10 is produced. It should be noted that more than two concentric rings can be created, and that various types of gradients can be produced.

Referring now to Figure 12, another method of constructing a gradient substrate is illustrated. Method 400 has an extrusable mixing column 402 having alternating discs of two extrusable materials. Extrudable mixture 402 has a first material 403 adjacent to a second material 404. In one example, material A is relatively powdery, while material B is less porous. During extrusion, the material will flow through the extrusion die causing fibers from part A and part B to blend in an overlapping arrangement. In this way, each part A and B is joined together to become a fiber substrate block. Upon cure and packaging, a 406 filter is created. Filter 406 has a first part 407 having relatively high porosity and a second part 408 having less porosity. Thus, gas flowing through the filter 406 is first filtered through a high porosity area having large pore size, and then filtered through a less porous area having smaller pore size. Thus, large particles are captured in area 407, while smaller particles are captured in area 408. It should be understood that the size and number of material discs can be adjusted to suit application needs.

The fiber extrusion system offers great flexibility in implementation. For example, a wide range of fibers and additives may be selected to form the blend. Several blending and extrusion options exist, as well as curing method, time and temperature options. With the precepts revealed, those skilled in extrusion techniques will understand that many variations can be used. Alveolar substrate is a common design to be produced using the technique described in the present invention, but other shapes, sizes, contours and designs can be extruded for various applications.

For certain applications such as use in filtration devices (DPF, oil / air filters, hot gas filters, air filters, water filters, etc.) or catalytic devices (such as 3-way catalytic converters). SCR catalysts, deionizers, deodorizers, biological reactors, chemical reactors, oxidation catalysts, etc.) The channels in an extruded substrate may need to be clogged. Composite material similar to the extruded substrate is used to clog the substrate. The obstruction may be in the green state or on a sintered substrate. Most clogging compositions require heat treatment to cure and bond to the extruded substrate.

While particular preferred and alternative embodiments of the present invention have been disclosed, it will be apparent to those skilled in the art that many different modifications and extensions of the above described technology may be implemented using the precept of this invention described herein. All such modifications and extensions should be considered to be included in the true spirit and scope of the invention as discussed in the appended claims.

Claims (10)

Porous substrate, characterized in that it has a porosity in the range of from about 60% to about 90%, has a structure formed of joined inorganic fibers, and is produced by an extrusion process comprising: mixing a fiber inorganic with additives and a fluid to form an extrudable mixture; extruding the extrudable mixture to a green substrate; and curing the green substrate to the porous substrate. Porous substrate according to claim 1, characterized in that the curing step generates fiber to fiber joints that form the structure. Porous substrate according to Claim 1, characterized in that the joints are formed by sintering or forming glass, ceramic-glass or ceramic joints. Porous substrate as defined in claim 1, characterized in that the curing step generates fiber-to-fiber joints that form a network of open pores. Porous substrate according to claim 1, characterized in that the inorganic fibers have a aspect ratio of about 3 to 1,000. Porous substrate according to Claim 1, characterized in that the inorganic fibers are selected from Table 1 of Figure 6. Porous substrate according to claim 1, characterized in that at least some fiber-to-fiber contacts do not form joints. Porous substrate according to claim 1, characterized in that substantially all fiber-to-fiber contacts form joints. Porous substrate according to claim 1, characterized in that it further includes a first substrate section joint using a first fiber-to-fiber joint type, and a second substrate section using a second substrate section. fiber to fiber joint type. Porous substrate according to claim 1, characterized in that the inorganic fibers include crystalline, amorphous, glass or ceramic materials.