MX2008006387A

MX2008006387A - System for extruding a porous substrate

Info

Publication number: MX2008006387A
Application number: MX/A/2008/006387A
Authority: MX
Inventors: Zuberi Bilal; G Lachenauer Robert; C Pillai Sunikumar
Original assignee: Geo2 Technologies Inc
Priority date: 2005-11-16
Filing date: 2008-05-16
Publication date: 2008-09-26

Abstract

An extrudable mixture is provided for producing a highly porous substrate wherein fibers, such as organic, inorganic, glass, ceramic or metal fibers, are mixed into a mass that when extruded and cured forms a highly porous substrate. Depending on the particular mixture the present invention enables substrate porosities of about 60%to 90%. The extrudable mixture may use a wide variety of fibers and additives and is adaptable to a wide variety of operating environments. Fibers, which have an aspect ratio greater than 1, are mixed with binders, pore-formers, extrusion aids and fluid to form a homogeneous mass which is extruded into a green substrate. The more volatile material is removed from the green substrate allowing the fibers to interconnect. As curing continues, fiber to fiber bonds form to produce a structure having a substantially open pore network. The resulting porous substrate forms a filter, catalyst host or catalytic converter.

Description

SYSTEM FOR EXTRUDING A POROUS SUBSTRATE Related Requests This application claims the priority of the US Provisional Patent Application No. 60 / 737,237, filed on November 16, 2005, and entitled "System for Extruding a Porous Substrate"; of Provisional Patent Application No. 11 / 323,430, filed December 30, 2005, and entitled "Extrudable Mixture to form a Porous Block"; US Patent Application No. 11 / 322,777, filed December 30, 2005, and entitled "Process for Extruding a Porous Substrate"; and U.S. Patent Application No. 11 / 323,429, filed December 30, 2005, and entitled "Extruded Porous Substrate and Products Utilizing the same"; which are all incorporated in their entirety to the present invention as a reference. Field of the Invention The present invention relates generally to extrusion processes for extruding a porous substrate, and in a particular implementation to an extrusion process for extruding a porous ceramic substrate. BACKGROUND OF THE INVENTION Many processes require rigid substrates to facilitate and support various processes. For example, substrates are used in filtration applications to filter matter from particulate, separate different substances or eliminate bacteria or germs from the air. These substrates can be constructed to operate on the escape of gases or liquids in the air, and can be manufactured to withstand substantial environmental and chemical stresses. In another example, catalytic materials are placed on the substrate to facilitate the reactions. For example, a precious material can be deposited on a suitable substrate, and subsequently a substrate can act to catalytically convert hazardous exhaust gases into less harmful gases. Normally, these rigid substrates operate more effectively with greater porosity. Porosity is generally defined as the property of a solid material to define the percentage of the total volume of material that is occupied by an open space. For example, a substrate with 50% porosity has half the volume of the substrate occupied by open spaces. In this form, a substrate with greater porosity has less mass per volume than a substrate with 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 an elevated temperature, a substrate with a lower thermal mass will heat up more rapidly at its operating temperature. In this way, the time for the catalyst to be heated to its operating temperature, i.e. ignition time, is reduce using a more porous and thermally less massive substrate. Permeability is also an important characteristic of substrates, particularly filtration and catalytic substrates. Permeability is related to porosity, since permeability is a measure of how easy a fluid, such as a gas or liquid, can flow through a substrate. Most applications benefit from a highly permeable substrate. For example, an internal combustion engine operates more efficiently when the filter after the treatment provides less return pressure to the engine. The low return pressure is created using a more highly permeable substrate. Since permeability is more difficult to measure than porosity, porosity is often used as a substrate guide for the permeability of a substrate. However, it is not a particularly accurate characterization, since a substrate can be very porous, and still have a limited permeability if the pores are generally not open and interconnected. For example, a Styrofoam cup of a highly porous foam material is formed, although it is not permeable for liquid flow. Therefore, considering the importance of porosity and permeability, the structure of the substrate pore should also be revised. In the example of the Styrofoam rate, the Styrofoam material has a network of pores closed. This means that the foam contains many pores connected and / or with closed ends. In this way, there are many gaps and open spaces within the foam, although since the pores are not connected, the fluid or gas can not flow from one side of the foam to the other. As they begin to interconnect more of the channels, the fluid trajectories begin to form from one end to the other. In this case, it is said that the material has a more open pore network. The greater the number of connected channels formed through the material, the greater the permeability for the substance. In the step when each pore is connected to at least one other channel, and all pores allow fluid flow through the entire thickness of the formed wall of the material, the substrate can be defined as having a fully open pore network . It is important to observe the difference between cells and pores. Cells refer to channels that run (usually parallel to each other, but not necessarily) through the honeycomb substrate. Frequently, honeycomb substrates are referred to within the context of how many cells they have per inch (cm2). For example, a substrate with 200 cells per inch (cm2) has 200 channels along the main axis of the substrate. On the other hand, the pores refer to openings within the material itself such as in the material that constitutes the wall that separates two channels or parallel cells.

No pore network substrates are completely or almost completely open in the filtration or catalysis industries. Rather, the most porous available extruded substrates are a hybrid of open pore porosity and closed pore porosity. Therefore, it is highly recommended for many applications, that the substrates are formed with high porosity, and with an internal pore structure that allows a similarly high permeability. Also, the substrates have to be formed with a structure rigid enough to support structural and environmental requirements for particular applications. For example a filter or catalytic converter has to be attached to an internal combustion engine, it must have the capacity to withstand the probable environmental shock, thermal requirements and stresses of manufacture and use. Finally, the substrate needs to be produced at a cost low enough to allow broad use. For example, in order to affect the level of global pollution from automobiles, a filtration substrate must be producible and usable in developed countries as well as in developing countries. Therefore, the overall cost structure of filter substrates and catalytic converters is a substantial consideration in the selectable process and substrate design. Extrusion has proven to be an efficient process and cost effective to manufacture rigid substrates of constant cross section. More particularly, the extrusion of a 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 to advanced in such a way that the substrates can now be extruded having porosities that reach 60%. These substrates with extruded pores have had good resistance characteristics, can be manufactured in a flexible way, can be manufactured to scale, maintain high levels of quality and are very cost effective. However, the extrusion of pulverized ceramic material has reached a practical upper porosity limit, and additional increases in appearance of porosity result in unacceptably low strength. For example, since the porosity is increased beyond 60%, the extruded ceramic powder substrate has not proven to be strong enough to operate in an arduous environment of a diesel particulate filter. In another limitation of the known extrusion processes, it has been desired to increase the surface area on a substrate, to allow a more efficient catalytic conversion. In order to increase the surface area, extruded ceramic powder substrates have tried to increase the cell density, although the increase in Cell density has resulted in an unacceptable return pressure to the motor. Therefore, the extruded ceramic powder substrate does not have sufficient strength at much higher porosities, and also produces an unacceptable back pressure when there is a need for an increased surface area. Therefore, the extrusion of the ceramic powder seems to have reached its limits of practical utility. In an effort to obtain larger porosities, filter suppliers have tried to move towards folded ceramic papers. By using said folded ceramic papers, porosities of about 80% with a very low return pressure are possible. With such low return pressure, these filters have been used in applications such as mining, where extremely low return pressure is a necessity. However, the use of lis folded ceramic paper filter has been sporadic, and has not been widely adopted. For example, folded ceramic papers have not been used effectively in harsh environments. The manufacture of folded ceramic papers requires the use of a papermaking process that creates ceramic paper structures that are relatively weak, and do not appear to be cost effective compared to extruded filters. In addition, the formation of folded ceramic papers allows very little flexibility in the shape and density of the cell. For example, it is difficult to create a folded paper filter with large input channels and smaller output channels, which may be advisable in some filtration applications. Therefore, the use of folded ceramic papers has not satisfied the requirement of filter substrates and catalytic porosity. In another example of an effort to increase porosity and avoid the disadvantages of pleated paper, some have constructed substrates by forming a mass with ceramic precursors and carefully processing the mass to grow monocrystalline whiskers on a porous paper. However, the growth of these crystals in situ requires careful and precise control of the healing process, making it difficult to scale the process, making it relatively costly and prone to defects. In addition, this difficult process only provides very few percentage points in porosity. Finally, the process only grows a mulit-like crystalline mustache which limits the application capacity of the substrate. For example, the mulito is known to have a high coefficient of thermal expansion, which makes mulit whiskers undesirable crystallites in many applications where a wide range of operating temperature and acute temperature transitions are needed. Consequently, the industry needs a rigid substrate that has high porosity and high associated permeability. Preferably, the substrate can be formed as a highly desirable open cell network, can be cost effective in its manufacture and can be manufactured with flexible physical, chemical and reaction properties. Brief Description of the Invention In summary, the present invention provides an extrudable mixture to produce a highly porous substrate using an extrusion process. More particularly, the present invention allows fibers, such as organic, inorganic, glass, ceramic or metal fibers, to be mixed in a mass which, when extruded and cured, forms a highly porous substrate. Depending on the particular mixture, the present invention allows substrate porosities of about 60% to about 90%, and also allows process advantages in other porosities. The extrudable mix can use a wide variety of fibers and additives, and can be adapted to a wide variety of operating environments and applications. The fibers, which have an aspect ratio greater than 1, are selected according to the substrate requirement, and mixed with linkers, pore formers, extrusion aids and fluids to form a homogeneous extrudable mass. The homogeneous mass is extruded on a green substrate. He More volatile material is preferably removed from the green substrate, which allows the fibers to interconnect and make contact. As the healing process continues, fiber to fiber bonds 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 housing, or catalytic converter. In a more specific example, ceramic fibers with an aspect ratio distribution between 3 and about 1000 are selected, but more usually will be within the range of about 3 to about 500. The aspect ratio is the ratio of the length of the fiber divided between the diameter of the fiber. The ceramic fibers are mixed with a linker, pore former, and a fluid in a homogeneous mass. A cutting mixing process is used to distribute the fibers more evenly in the dough. The ceramic material may have from about 8% to about 40% by volume of the mass, which results in a substrate having between about 92% and about 60% porosity. The homogeneous mass is extruded on a green substrate. The binding material is removed to the green substrate, which allows the fibers to overlap and make contact. As the healing process continues, it form a fiber to fiber link to produce an open rigid cell network. As used in the description, the term "cure" is defined to include two important process steps: 1) elimination of linker e 2) link formation. The binder removal process eliminates free water, eliminates most of the additives and allows fiber-to-fiber contact. The resulting porous substrate is useful in many applications, for example, in the form of a substrate for a filter or catalytic converter. In another specific example, a porous substrate can be produced without the use of pore formers. In this case, the ceramic material may have from about 40% to about 60% or more by volume of the mass, which results in a substrate having between about 60% and about 40% porosity. Since a pore former is not used, the extrusion process is simplified, and is more cost effective. Also, the resulting structure is a highly desirable substantially open pore network. Conveniently, the described fiber extrusion system produces a substrate having high porosity, and having an open pore network that allows a high associated permeability, as well as having sufficient strength according to the needs of the application. The fiber extrusion system also produces substrate with enough cost effectiveness to allow extensive use of the resulting filters and catalytic converters. The extrusion system is easily scalable for mass production, and allows chemical and flexible constructions to support diverse applications. The present invention represents a pioneering use of fiber material in an extrudable mixture. This fibrous extrudable mixture allows the extrusion of substrates with very high porosities, in a scalable production, and in an effective way in cost. By allowing fibers to be used in the repeatable and robust extrusion process, the present invention enables the mass production of catalytic filters and substrates for wide use worldwide. These or other characteristics of the present invention may be appreciated from reading the detailed description that follows, and may be made by means of the instruments and combinations that are pointed out in a particular manner in the appended claims. BRIEF DESCRIPTION OF THE DRAWINGS The drawings constitute a part of the present specification and include exemplary embodiments of the present invention, which may be presented in various forms. It will be understood that in some cases various aspects of the present invention may be exaggerated or expanded to facilitate understanding thereof.

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 mixture according to the present invention. Figures 3A and 3B are illustrations of an open pore network according to the present invention. Figure 4 is an electron microscope image of an open pore network according to the present invention and a closed pore network of the prior art. Figure 5 is an illustration of a filter block using a porous substrate according to the present invention. Figure 6 are fiber boards, linkers, pore formers, fluids, and rheologies 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 system for processing fibers of a porous substrate according to the present invention. Figure 10 is a diagram for extruding a porous gradient substrate according to the present invention.

Figure 11 is a diagram for extruding a porous gradient substrate according to the present invention. Figure 12 is a diagram for extruding a porous gradient substrate according to the present invention. Detailed Description of the Invention In the present invention, detailed descriptions of the examples thereof are provided. It will be understood, however, that the present invention can be exemplified in various ways. Accordingly, the specific details described herein will not be construed as limiting, but rather as a representative basis for teaching a person skilled in the art how to employ the present invention in virtually any system, structure, or detailed form. 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 a highly porous substrate end product. The system 10 conveniently produces a substrate having high porosity, having a substantially open pore network that allows a high associated permeability, as well as having sufficient strength according to the needs of the application. The system 10 also produces a substrate with sufficient cost effectiveness to allow extensive use of the resulting catalytic converters and filters. The system 10 is easily scalable for mass production and allows chemical and flexible constructions to support diverse applications. The system 10 allows a highly flexible extrusion process, so that it has the ability to adapt to a wide range of specific applications. In the use of system 10, the substrate designer first establishes the requirements for it. These requirements may include, for example, size, fluid permeability, desired porosity, pore size, mechanical strength and shock characteristics, thermal stability and chemical reactivity limitations. According to these and others, the designer selects materials to be used in the formation of an extrudable mixture. Importantly, the system 10 allows the use of fibers 12 in the formation of an extruded substrate. These fibers can be, for example, ceramic fibers, organic fibers, inorganic fibers, polymer fibers, oxide fibers, vitreous fibers, glass fibers, amorphous fibers, crystalline fibers, non-oxide fibers, carbide fibers, metal fibers, other inorganic fiber structures or a combination thereof. However, for ease of explanation, the use of ceramic fibers will be described, although it should be appreciated that other fibers can also be used. Also, the substrate will often be described as a filtration substrate or a catalytic substrate, although other uses are contemplated within the scope of this teaching. The designer selects the type of particular fiber based on the specific needs of the application. For example, the ceramic fiber may be selected in the form of a mulch fiber, an aluminum silicate fiber or other commonly available ceramic fiber material. The fibers normally need to be processed 14, to cut the fibers to a usable length, which may include a chopping process before mixing the fibers with the additives. Also, the various steps of mixing and forming in the extrusion process, will additionally cut the fibers. According to specific requirements, additives 16 are added. These additives 16 may include linkers, dispersants, pore formers, plasticizers, processing aids and strength generation materials. Also, fluid 18, which is usually water, is combined with additives 16 and fibers 12. Fibers, additives and fluids are mixed for an extrudable rheology 21. This mixing may include dry mixing, mixing with moisture and mixing with cut. The fibers, additives and fluids are mixed until a homogeneous mass is produced, which is evenly distributed and fits the fibers into the mass. The fibrous and homogeneous mass is subsequently extruded to form a green substrate 23. The green substrate has sufficient strength to be maintained along the remaining processes.

The green substrate is subsequently cured 25. As used in the description, the term "cure" is defined to include two important process steps: 1) elimination of linker and 2) bond formation. The binder removal process eliminates free water, eliminates most of the additives and allows fiber to fiber contact. The linker is often removed using a heating process that burns the linker, although it will be understood that other elimination processes can be used depending on the specific linker used. For example, part of the linker can be removed using an evaporation or sublimation process. Some linkers and other organic components can melt before degrading into a vapor phase. As the healing process continues, fiber-to-fiber bonds are formed. These bonds facilitate general structural rigidity, as well as create desirable porosity and permeability for the substrate. Accordingly, the cured substrate 30 is a highly porous substrate of almost all fibers bonded in an open pore network 30. Subsequently the substrate can be used as a substrate for many applications, including a substrate for filtration applications and conversion applications. catalytic Conveniently, the system 10 enables a desirable extrusion process to produce substrates having porosities of up to 90%.

Referring to Figure 2, an extrudable material 50 is illustrated, the extrudable material 50 is ready for extrusion by an extruder, such as a piston extruder or screw. The extruded mixture 52 is a homogeneous mass that includes fibers, plasticizers and other additives as required by the specific application. Figure 2 illustrates an elongated part 54 of the homogeneous mass. It will be appreciated that the elongated portion 54 can not be drawn to scale, although it is provided as an aid to the present disclosure. The extrudable mixture 52 includes fibers, such as fibers 56, 57, 58. These fibers have been selected to extrude a rigid, highly porous final substrate with desired thermal, chemical, mechanical and filtration characteristics. As can be seen, the substantially fibrous bodies have not been considered as extrudable, since they do not themselves have plasticity. However, it has been found that through the proper selection of plasticizers and process control, an extrudable mixture 52 comprising fibers can be extruded. In this way, the cost, scale and advantages of extrusion flexibility can be extended to include the benefits available through the use of a fibrous material. Generally, it is considered a fiber with a material with a relatively small diameter that has an aspect ratio greater than one. The aspect ratio is a ratio of the length of the fiber divided by the diameter of the same. As used in the present invention, the "diameter" of the fiber assumes for simplicity, that the sectional form of the fiber is a circle; this assumption of simplification applies to fibers regardless of their actual section shape. For example, a fiber with an aspect ratio of 10 has a length that is 10 times greater than the diameter of the fiber. The diameter of the fiber can have 5 microns, although diameters within the range of about 1 micron to about 25 microns are readily available. It will be understood that fibers of many different diameters and aspect ratios can be used successfully in the system 10. As will be described in more detail with reference to the following figures, there are several alternatives for selecting proportions of aspects for the fibers. It will also be appreciated that the shape of the fibers is in sharp contrast to the typical ceramic powder, when the aspect ratio of each ceramic particle is about 1. The fibers for the extrudable mixture 52 can be metallic (sometimes also referred to as thin diameter metal cables, although Figure 2 will be described with reference to ceramic fibers). The ceramic fibers can be in an amorphous state, a glassy state, a crystalline state, a polycrystalline state, a monocrystalline state or in a glass-ceramic state. To make the mixture extrudable 52, a relatively low volume of ceramic fiber is used to create the porous substrate. For example, the extrudable mixture 52 may have only about 10 to 40% of the ceramic fiber material by volume. In this form, after curing, the resulting substrate may have a porosity of about 90% to about 60%. It will be appreciated that other amounts of ceramic fiber material can be selected to produce other porosity values. In order to produce an extrudable mixture, the fibers are usually combined with a plasticizer. In this form, 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 its own rheology for extrusion. Second, the additives provide an extruded substrate, which is usually termed a green substrate, sufficient strength to maintain its shape and the position of the fibers 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 way that facilitates the adjustment of the fibers in an overlapping construction, in a way that does not weaken the formation of the rigid structure. Typically, the additives will include a linker, such as linker 61. The linker 61 acts as a means to maintain the fibers in position and provide resistance to the green substrate. The fibers and linker (s) can be used to produce a porous substrate having a relatively high porosity. However, to further increase the porosity, additional pore formers can be added, such as pore former 63. The pore formers are added to increase the open space in the final cured substrate. Pore formers can be spherical, elaborate, fibrous or irregularly shaped. Pore formers are selected not only for their ability to create an open space based on their thermal degradation behavior, but also for helping to orient the fibers. In this form, the pore formers help to adjust the fibers in an overlap pattern to facilitate adequate bonding between the fibers during the last stage of healing. In addition, pore formers also play an important role in the alignment of the fibers in preferred directions, which affects the thermal expansion of the extruded material and the force along the different axes. As described briefly above, the extrudable mixture 52 may utilize one or more fibers selected from many types of available fibers. In addition, the selected fiber can be combined with one or more linkers selected from a wide variety of linkers. Also, one or more can be added pore adders selected from a variety of pore formers. The extrudable mixture may use water or other fluid as its plasticizing agent, and may have other additives added. This flexibility in formation chemistry allows the extrudable mixture 52 to be conveniently used in many different types of applications. For example, combinations of mixtures can be selected according to the environment, temperature, needs, chemical, physical, or other required needs. In addition, since the extrudable mixture 52 is prepared for extrusion, the final extrudable product can be formed flexibly and economically. Although not illustrated in Figure 2, the mixture 52 is extruded through a screw or piston extruder to form a green substrate, which is subsequently cured in the final porous substrate product. The present invention represents a pioneering use of fiber material in a batch of plastic or extrusion mixture. These fibrous extrudable mixtures allow the extrusion of substrates with very high porosities, in a scalable production, and in an effective way in cost. To allow the fibers to be used in the repeatable and robust extrusion process, the present invention allows mass production of catalytic filters and substrates for wide use worldwide. Referring to Figure 3A, an area is illustrated expanded cure of a porous substrate. The substrate part 100 is illustrated after the elimination of the linker 102 and after the curing process 110. After the removal of the linker 102, the fibers, such as the fiber 103 and 104 are initially held in place with the material of bond, and as the binding material is burned, the fibers are exposed to be in an overlapping structure, albeit in loose form. Also, a pore former 105 can be placed to produce an additional open space, as well as aligning or adjusting the fibers. Since the fibers only comprise a relatively small volume of the extrudable mixture, there are many open spaces 107 between the fibers. As the linker and pore former burns, the fibers can be adjusted slightly to make additional contact with each other. The linker and the pore formers are selected to be burned in a controlled manner so as not to interrupt the adjustment of the fibers or to have a collapse of substrates in the burn. Normally, the linker and the pore formers are selected to degrade or burn before bonding between the fibers. As the healing process continues, the overlap and contact of the fibers begins to form the bonds. It will be appreciated that in the links can be formed in various ways. For example, the fibers can be heated to allow the formation of a sintered bond aided by liquids in the intersection or node of the fibers. This liquid state sintering may result from the particular fibers selected, or may result from additional additives added to the mixture or coated in the fibers. In other cases, it may be desirable to form a sintered solid state bond. In this case, the intercept links form a grain structure that connects the fibers of the overlap. In the green state, the fibers have not yet formed physical bonds with each other, but may still exhibit some degree of green resistance, due to the entanglement of the fibers with one another. The particular type of bond selected will depend on the selection of base materials, desired strength, and chemical and operating environments. In some cases, the links are caused by the presence of inorganic binders that present the mixture that holds the fibers together in a connected network. They do not burn during the healing process. Conveniently, bonding, such as links 112, facilitates the formation of a substantially rigid structure with the fibers. The bonds also allow the formation of an open pore network having very high porosity, for example, the open space 116 is created naturally by the space between the fibers.The open space 114 is created as a pore former 105 which It degrades or burns In this way, the fiber link formation process creates an open pore network virtually without channels not finished. This open pore network generates high permeability, high filtration efficiency, and allows a higher surface area for the addition of catalyst, for example. It will be appreciated that link formation may depend on the type of link desired, such as solid state sintering or aided liquid / liquid state, and the additives present during the curing process. For example, the additives, the particular selection of the fibers, the heating time, the heat level and the reaction environment, can all be adjusted to create a particular type of bond. Referring now to Figure 3B, another expanded cured area of a porous substrate is illustrated. The substrate part 120 is illustrated after the elimination of the linker 122 and after the curing process 124. The part of the substrate 120 is similar to the part 100 described with reference to Figure 3A, so that it will not be described in detail. The substrate 120 has been formed without the use of specific pore formers, so that the entire open pore network 124 has resulted from the placement of the fibers with a bonding material. In this form, substrates with a high moderate porosity can be formed without the use of any specific pore formers, thereby reducing the cost and manufacturing complexity of said substrates of moderate porosity. It has been discovered that substrates that have a Porosity within the range of about 40% to about 60% can occur in this way. Referring now to Figure 4, a group of electron microscope images 150 is illustrated. The group of images 150 first illustrates an open pore network 152 created in a desirable manner using a fibrous extrudable mixture. As can be seen, the fibers have formed bonds in the interception of the fiber nodes and the pore former and linkers have been burned, leaving a porous open pore network. In sharp contrast, illustration 154 illustrates a typical closed cell network constructed using known processes. The partially closed pore network has a relatively high porosity, although at least part of the porosity is derived from closed channels. These channels do not contribute to permeability. In this way, an open pore network and a closed pore network have the same porosity, the open pore network will have a more desirable permeability characteristic. The extrudable mixture and the process described generally will be used to produce a highly convenient porous substrate. In one example, the porous substrate can be extruded into a filter block substrate 175 as illustrated in Figure 5. The substrate block 175 has been extruded using a piston or screw extruder. The extruder can be conditioned to operate at temperature environment, slightly elevated temperature or in a temperature controlled window. In addition, various parts of the extruder can be heated to different temperatures to affect the characteristics of slowness, cutting history and gelatinization characteristics of the extrusion mixture. In addition, the size of the extrusion dies can also be designed correspondingly to adjust to the expected shrinkage in the substrate during the heating and sintering process conveniently, the extrudable mixture was a fibrous extrudable mixture having sufficient plasticizer and others additives that allow the extrusion of the fibrous material. The extruded green state block was cured to remove free water, burn additives and form structural bonds between the fibers. The resulting block 175 has highly desirable porosity characteristics, as well as excellent permeability and a superior usable surface area. Also, depending on the particular fibers and the selected additives, the block 175 can be constructed for convenient deep filtration. The block 176 has channels 179 extending longitudinally through the block. The entrances to the block 178 may be left open for a flow passage process, or each third opening may be capped to produce a wall flow effect. Although block 175 is shown with hexagonal channels, it will be appreciated that other patterns and sizes can also be used. By For example, the channels can be formed with a channel pattern with uniform square, rectangular or triangular design; a square / rectangular or an octagonal / square channel pattern that has larger input channels; or in another symmetric or asymmetric channel pattern. The precise shapes and sizes of the channels or cells can be adjusted by adjusting the design of the die. For example, a square channel can be made to have curved corners using EDM (Electronic Discharge Machining), to form the pins in the die. Such rounded corners are expected to increase the strength of the final product, despite the slightly higher return pressure. In addition, the design of the die can be modified to extrude honeycomb substrates when the walls have different thicknesses and the skin has a different thickness to the rest of the walls. In a similar way, some applications, an external skin can be applied to the extruded substrate for the final definition of shape, size, contour and strength. When used in the form of an apparatus for flow passage, the high porosity of the 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, the converter having a lower thermal mass. With said lower thermal mass, the resulting catalytic converter has good characteristics of disconnection, and efficiently uses the catalytic material. When used in a wall flow or wall filtration, the high permeability of the substrate walls enables relatively low return pressures, while facilitating deep filtration. This deep application enables the elimination of efficient particulate, as well as facilitates a more effective regeneration. In the wall-flow design, the fluid flowing through the substrate is forced to move through the walls of the substrate, thereby enabling more direct contact with the fibers covering the wall. Said fibers have a higher surface area for potential reactions to take place, such as if a catalyst will be found. Since the extrudable mixture can be formed from a wide variety of fibers, additives and fluids, the chemistry of the extrudable mixture can be adjusted to generate a block having specific characteristics. For example, if it is desired that the final block be a diesel particulate filter, the fibers are selected to encompass the safety operation even at extreme temperatures of an uncontrolled regeneration. In another example, if the block will be used to filter a particular type of exhaust gas, the fiber and bond are selected so as not to react with the exhaust gas through the expected operating temperature range. Although the advantages of high porosity substrate have been described with reference to filters and catalytic converters, it can be appreciated that there are many other applications for the highly porous substrate. The fibrous extrudable mixture as described with reference to Figure 2 can be formed from a wide variety of base materials. The selection of suitable materials is generally based on chemical, mechanical and environmental conditions in which the final substrate must operate. Therefore, a first step in designing a porous substrate is to understand the final application thereof. Based on these requirements, fibers, binders, pore formers, fluids and other particular materials can be selected. It will also be appreciated that the process applied to the selected materials may affect the final substrate product. Since fiber is the primary structural material in the final substrate product, the selection of fiber material is important to allow the final substrate to operate in its intended application. Therefore, the fibers are selected in accordance with the required link requirements, and a particular type of link processes is selected. The bonding process can be a liquid state sintering, a solid state sintering, or a bond that requires a bonding agent, such as a glass former, glass, clays, ceramics, ceramic precursors and colloidal solvents. The bonding agent can be part of one of the fiber constructions, a coating in fiber, or a component in one of the additives. It will also be appreciated that more than one type of fiber can be selected. It will also be appreciated that some fibers may be consumed during the healing and bonding process. The selection of the fiber composition, the final operating temperature is an important consideration, so that the thermal stability of the fiber can be maintained. In another example, the fiber is selected so that it remains chemically inert and not reactive in the presence of gases, liquids or expected solid particulate matter. The fiber can also be selected according to its cost, and some fibers can present health aspects due to their small sizes, and consequently, their use can be avoided. Depending on the mechanical environment, the figures are selected according to their ability to form a strong rigid structure, as well as maintain the required mechanical integrity. It will be appreciated that the selection of an appropriate fiber or group of fibers may involve negotiations between performance and application. Figure 6, table 1, shows various types of fibers that can be used to form a porous extrudable mixture. Generally, the fibers may be oxide ceramics or without oxide, glass, organic, inorganic, or they may be metallic. For ceramic materials, the fibers may be in different states, such as amorphous, vitreous, poly-crystalline or mono-crystalline. Although table 1 illustrates Many available fibers, it will be appreciated that other types of fibers can also be used. The pore linkers or chromators can be selected subsequently according to the type of fibers selected, as well as other desired characteristics. In one example, the linker is selected to facilitate a particular type of liquid state bond between the selected fibers. More particularly, the linker has a component, which at a binding temperature, reacts to facilitate the flow of a liquid link to the nodes of the intersecting fibers. Likewise, the linker is selected for its ability to laminate the selected fiber, as well as to maintain its green state resistance. In one example, a linker is also selected according to the type of extrusion being used, and the temperature required for the extrusion. For example, some linkers form a gelatinous mass when they get too hot, and therefore can only be used in low temperature extrusion processes. With extrusion processes with lower temperature. In another example, the linker can be selected according to its impact on the cutting mixing characteristics. In this form, the linker can facilitate the chopping of the fibers to the desired aspect ratio during the mixing process. The linker can also be selected according to its characteristics of degradation or burned. The linker needs to have the ability to keep the fibers generally in place, and not interrupt the formation of the fiber structure during burning. For example, if linker burns too fast or violently, the escape of gases can interrupt the formation of the structure. Also, the linker can be selected according to the amount of residue that the linker leaves after burning. Some applications can be highly sensitive to such waste. Pore formers may not be necessary for the formation of relatively moderate porosities. For example, the natural fit and packing of the fibers within the linker can cooperate to allow a porosity of about 40% to about 60%. In this way, a substrate of moderate porosity can be generated using an extrusion process without the use of pore formers. In some cases, the elimination of pore formers allows a more economical porous substrate to be manufactured compared to known processes. However, when a porosity of greater than about 60% is required, the pore formers can be used to create a space of additional area within the substrate after curing. Pore formers can also be selected according to their degradation or burn characteristics, they can also be selected from according to their size and shape, the pore size may be important, for example, to trap particular types of particulate matter, or to allow particularly high permeability. The shape of the pores can also be adjusted, for example, to aid in proper elimination of the fibers. For example, a relatively elongated pore shape can adjust fibers in a more aligned pattern, while a more irregular or spherical shape can adjust the fibers in a more random pattern. The fiber can be provided by a manufacturer in the form of an applied fiber, and be used directly in the process, or a fiber can be provided in a format by volume, which is usually processed before being used. In any way, the considerations of the process should take into account how the fiber will be processed in its distribution of desirable final aspect ratio. Generally, the fiber is minced initially before mixing with other additives, and subsequently it is minced additionally during the steps of mixing, cutting and extrusion. However, extrusion can also be carried out with non-chopped fibers by adjusting the rheology to make the extrudable extrusion mixture at reasonable extrusion pressures and without causing dilation fluxes in the extrusion mixture when they are put under pressure on the face of the die. of extrusion. It will be appreciated that the chopping of the fibers to the distribution and proportion of the Proper appearance can be done at various points during the general process. Once the fiber has been selected and chopped to a usable length, it is mixed with the binder and pore former. This mixing can first be done in a dry form to start the mixing process, or it can be done as a wet mixing process. The fluid, which is usually water, is added to the mixture. In order to obtain the required level of homogeneous distribution, the mixture is mixed with cutting through one or more stages. The mixing or slurry mixing provides a highly desirable homogeneous mixing process for uniform distribution of the fibers in the mixture, as well as additional cutting of the fibers at the desired aspect ratio. Figure 6, table 2, shows various linkers available for selection. It will be appreciated that a single linker can be used, or multiple linkers can be used. Linkers are usually divided into organic and inorganic classifications. The inorganic binders will generally be burned at a lower temperature during curing, while the inorganic binders will normally form a part of the final structure at a higher temperature. Although several linker selections are described in Table 2, it will be appreciated that various other linkers can be used. Figure 6, Table 3, shows a list of available pore formers. Pore formers can generally be defined as organic or inorganic, with the organic burning normally at a lower temperature than inorganic. Although various pore formers are described in Table 3, it will be appreciated that other pore formers can be used. Figure 6, table 4, shows different fluids that can be used. Although it may be appreciated that water may be the most economical and frequently used fluid, some applications may require other fluids. Although table 4 shows several fluids that can be used, it will be appreciated that other fluids can be selected according to the specific requirements of the application and the process. In general, the mixture can be adjusted to have a suitable speed for a convenient extrusion. Normally, the proper speed results from the selection and proper mixing of fibers, binders, dispersants, plasticizers, pore formers and fluids. A high degree of mixing is necessary to adequately provide the plasticity to the fibers. Once the proper fiber, linker and pore former have been selected, the amount of fluid is normally adjusted in a final manner to meet the proper rheology. The appropriate rheology can be indicated, with, through one or two tests, the first Test is a subjective, informal test, where an account is removed from the mix and formed between the fingers of an experienced extrusion operator. The operator has the ability to identify when the mix slips properly between the fingers, indicating that the mix is in a suitable mix for extrusion. A second more objective test depends on the measurement of the physical characteristics of the mixture. Generally, the cutting resistance versus compaction pressure can be measured using a confined annular rheometer (eg high pressure), the measurements taken and plotted according to a comparison of a cohesion resistance versus pressure dependence. By measuring the mixture in various mixtures and fluid levels, a rheology graph can be created that identifies the rheology points. For example, Table 5, Figure 6 illustrates a rheology plot for a fibrous ceramic blend. The axis 232 represents the cohesion force and the axis 234 represents the pressure dependency. The extrudable area 236 represents an area where fibrous extrusion is highly likely to occur. Therefore, it is likely that a mixture characterized by any measure falling within this area is successfully extruded 236. Of course, it can be seen that the rheology plot is subject to various variations, and that a certain variation in the position of area 236. In addition, there are several other direct tests hints to measure rheology and plasticity, and it will be appreciated that any number of them can be shown to check if the mixture has the correct rheology to be extruded in the final form of the desired product. Once the proper rheology has been reached, the mixture is extruded through an extruder. The extruder can be a piston extruder, a single screw extruder, or a twin screw extruder. The extruder process can be highly automatic, or it may require human intervention. The mixture is excluded through a die having the desired cross sectional shape for the substrate block. The die has been selected to sufficiently form the green substrate. In this way, a stable green substrate is created that can be handled through the healing process, thus maintaining its shape and alignment of the fiber. The green substrate is subsequently dried and curd. Drying takes place under ambient conditions, at controlled temperature and humidity conditions (such as in controlled ovens), in microwave ovens, RF ovens and convection ovens. Healing usually requires the removal of free water to dry the green substrate. It is important to dry the green substrate in a controlled manner, so as not to introduce cracks or other structured defects. Subsequently the temperature can be raised to burn the additives, such as linkers and pore formers. The Temperature is controlled to ensure that the additives are burned in a controlled manner. It will be appreciated that the burned additive may require the cycling of temperatures through various cycles and various programmed heat levels. Once the additives are burned, the substrate is heated to the temperature required to form structural bonds at points or intersecting nodes of fibers. The required temperature is selected according to the type of bond required and the chemistry of the fibers. For example, sintered bonds aided by liquid are typically formed at a temperature lower than the solid state bonds. It will also be appreciated that the amount of time in the bonding temperature can be adjusted according to the specific type of bond that is being produced. The entire thermal cycle can be carried out in the same furnace, in different furnaces, in batch or continuous processes, and in air or controlled atmosphere conditions. After the fibers are formed, the substrate is cooled slowly to room temperature. It will be appreciated that the curing process can be achieved in an oven or in multiple furnaces or can be automated in production furnaces, such as tunnel kilns. 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, the substrate requirements are defined as shown in block 252. For example, the end use of the substrate generally defines the substrate requirements, which may include size restrictions, temperature restrictions, restrictions of strength and chemical reaction restrictions. In addition, the cost and capacity of mass production of the substrate, can determine and direct certain selections. For example, a high production range can comprise the generation of relatively high temperatures in the extrusion die, and therefore binders are selected that operate at a high temperature without hardening or gelatinization. In extrusions using high temperature linkers, barrel dies can be maintained at a relatively high temperature, such as 60 to 180 ° C. In such a case, the linker can be melted, reducing or eliminating the need for the additional fluid. In another example, a filter can be designed to trap particulate matter, so that the fibers are selected to remain non-reactive with the particulate matter, even at elevated temperatures. It will be appreciated that a wide range of applications can be adapted, with a wide range of possible mixtures and processes. One skilled in the art will appreciate that negotiations were involved in the selection of fibers, linkers, fluid pore formers and process steps. In fact, one of the significant advantages of the system 250 is its flexibility for the selection for the composition of the mixture and the adjustments of the process. Once the substrate requirements have been defined, a fiber is selected from table 1 or from figure 6, as shown in block 253. The fiber can be of a single type, or it can be a combination of two or more types. It will also be appreciated that some fibers may be selected to be consumed during the curing process. Also, additives can be added to the fibers, such as coatings on the fibers, to introduce other materials into the mixture. For example, dispersing agents can be applied to the fibers to facilitate the separation and adjustment of the fibers, or they can be coated on the auxiliary binding fibers. In the case of bonding aids, when the fibers reach the curing temperatures, the binding aids aid in the formation and fluidity of the liquid state bonds. A typical composition to obtain > 80% porosity Density Mass (g) Volume Volum (g / cc) (ce) in (%) Mulite Reinforcer 2.7 300.0 111.1 9.2 Bentonite fiber 2.6 30.0 11.5 1.0 HPMC 0.5 140.0 280.0 23.1 (hydroxypropylmethylcellulose) Plasticizer Propylene glycol 1.1 15.0 13.6 1.1 of the PMMA bond (polymethylmethacrylate) 1.19 5000.0 420.2 34.7 Water Fluid 1 375.0 375.0 31 pore former Total 1360.0 1211.5 100.0 Subsequently, the linker of Table 2 of Figure 6 is selected, as shown in block 255. The linker is selected to facilitate the green state resistance as well as a controlled burn. Also, the linker is selected to produce sufficient plasticity in the mixture. If needed, a pore former from Table 3 of Figure 6 is selected, as shown in block 256. In some cases, sufficient porosity can be obtained through the use of only fibers and linkers. The porosity is achieved not only through the natural packing characteristics of the fibers, but also through the space occupied by the linkers, solvents and other volatile components that are released during the de-bonding and curing stages. To achieve higher porosities, additional pore formers can be added. Pore formers are also selected according to their controlled burn capabilities, and can also help to plasticize the mixture. The fluid, which is usually water, is selected from Table 4, Figure 6 as shown in block 257. Other materials may be added, such as a disperser to assist in the separation and adjustment of the fibers, and plasticizers. and extrusion aids to improve the flow behavior of the mixture. The dispersant can be used to adjust the electronic tables of the surface in the fibers. In this way, the fibers can have their charge controlled to cause the original fibers to reject each other. This facilitates a more homogeneous and random fiber distribution. A typical composition of a mixture is shown below to create a substrate with > 80% porosity. It will be appreciated that the mixture can be adjusted according to the target porosity, the specific application and the process considerations. As shown in block 254, the fibers selected in block 252 can be processed to have a suitable aspect ratio distribution. This aspect ratio is preferred to be within the range of about 3 to about 500 and may have one or more modes of distribution. It will be appreciated that other ranges can be selected, for example, up to approximately an aspect ratio of 1000. In one example, the distribution of the aspect ratios can be randomly distributed over the desired range, and in other examples the aspect ratios can be selected in values with more discontinuous modes. It has been found that the proportion of aspects is an important factor in defining the packing characteristics of the fibers. Accordingly, the aspect ratio and the distribution of aspect ratios are selected to implement a particular strength and porosity requirement. Likewise, it will be appreciated that the processing of fibers in their preferred aspect ratio distribution can be carried out at various points in the process. For example, the fibers can be chopped by a third-party processor supplied in a predetermined aspect ratio distribution. In another example, the fibers can be provided in a bulk form, and the extrusion process can be processed in a suitable aspect ratio as a preliminary step. It will be appreciated that mixing, slurry mixing and dispersion mixing and extrusion aspects of the 250 process can also contribute to cutting and chopping the fibers. Accordingly, the aspect ratio of the fibers originally introduced into the mixture will be different from the aspect ratio in the final cured substrate. Accordingly, the strong chopping effect of the mixture, cut and extrusion mixture should be taken into consideration when selecting the appropriate aspect ratio distribution 254 introduced in the process.

With the fibers processed to the appropriate aspect ratio distribution, the fibers, linkers, pore formers and fluids are blended to a homogeneous mass as shown in block 262. The blended process may include a dry blend aspect. , aspect of mixing with moisture and cutting mix. It has been found that dispersion cutting 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 the ceramic material in the mixture. As the homogeneous mixture is mixed, the rheology of the mixture can be adjusted as shown in block 262. As the mixture is mixed, its rheology continues to change. The rheology may be subjectively tested, or it may be measured to meet the desirable area as illustrated in Table 5 of Figure 6. The mixture falling within this desired area has a high probability of extrusion adequate The mixture is then extruded into a green substrate as shown in block 268. In the case of screw extruders, mixing can also occur within the extruder itself, and not in a separate mixer. In such cases, the cut history of the mixture has to be directed and controlled with care. The green substrate has enough green resistance to maintain its shape and fiber fit during the healing process. Subsequently the green substrate is cured as shown in block 270. The curing process includes the removal of any residual, burned, controlled water from most of the additives, and bonding is fiber with fiber. During the burning process, the fibers maintain their entangled and intercept relationship, and as the healing process proceeds, links are formed at the points of intersection or nodes. It will be appreciated that links can result from a liquid state or solid state link process. Also, it will be understood that some of the bonds may be due to reactions with additives provided in the linker as pore formers, in the form of coating on the fibers, or in the fibers themselves. Once the bonds have formed, the substrate is slowly used at room temperature. Referring now to Figure 8, a method for curing a porous fibrous substrate is illustrated. Method 275 has a green colored substrate having a fibrous ceramic content. The curing process first slowly removes the residual water from the substrate, as shown in block 277. Normally, the removal of water can be done at a relatively low temperature in an oven. Once the remaining water has been removed, the organic additives can be taken, as shown in block 279. These additives are burned in a controlled manner to facilitate proper adjustment of the fibers, and to ensure that the gases and residues Do not interfere with the structure of the fiber. As the additives are burned, the fibers maintain their overlap setting, and may additionally contact at intersection points or modes, as shown in block 281. The fibers have been placed in their overlap fit using the linker, and may have particular patterns formed through the use of trainers of pores In some cases, inorganic additives may be used, which may be combined with the fibers, be consumer during the bonding process, or remain a part of the final substrate structure. The curing process proceeds to form fiber-to-fiber bonds, as shown in block 2825. The specific timing and temperature to create the bonds depends on the type of fibers used, type of auxiliaries or agents used and the type of heavy link . In one example, the link can be a sintered liquid state bond generated between the fibers as shown in block 286. Said bonds are aided by glass formers, glasses, ceramic precursors and inorganic flows present in the system. In another example, a sintered liquid state bond can be created using auxiliaries or sintering agents, as shown in block 288. The sintering aids can be provided as a coating on the fibers, as additives, from linkers, from pore formers or procedures of the chemistry of the fibers themselves. Also, a fiber to fiber bond can be formed through a solid state sinterization between the fibers as shown in block 291. In this case, the intersecting fibers exhibit grain growth and mass transfer, leading to the formation of chemical bonds in the nodes and a general rigid structure. At In the case of liquid state sintering, a mass of bonding material accumulates in the intersecting nodes of the fibers as in the form of a rigid structure. It will be appreciated that the curing process can be carried out in one or more ovens, and can be automated in a tunnel kiln or industrial furnace. Referring now to Figure 9, a process for preparing fibers is illustrated. The process 300 shows that the unprocessed fibers are received as shown in block 305. The unprocessed fibers usually have very long fibers in a fit with agglomerations and tissue internally. Said unprocessed fibers can be processed to separate sufficiently and cut the fibers for use in the mixing process. Accordingly, the unprocessed fibers are mixed with water 307 and possibly a dispersing agent 309 to form a paste 311. The dispersant 309 can be, for example a pH adjuster or a charge adjuster to assist the fibers to be rejected between yes. It will be appreciated that various types of dispersants can be used. In an example, the unprocessed fibers are coated with a dispersant before the introduction into the paste. In another example, the dispersant is simply added to the paste mixture 311. The paste mixture is mixed violently as shown in block 314. This violent mixing acts to chop and separate the unprocessed fibers in a ratio distribution of Usable aspect. As it described above, for the initial use of the fibers, it will be different to the distribution in the final substrate, since the mixing and extrusion process cuts the fibers in additional pieces. Once the fibers have been cut into pieces for a proper appearance distribution, the water is almost completely removed using a filter press 316, or pressing against a filter in another type. It will be appreciated that other water removal processes, such as freeze drying, can be used. The filter press can use pressure, vacuum or other means to remove water. In one example, the chopped fibers are further selected to a full dry state, as shown in block 318. These subsequently dried fibers can be used in a dry mix process 323, where they are mixed with other dry pore binders and formers as shown in block 327. This additional dry mixing helps to generate a homogenous mass. In another example, the water content of the filtered fibers is adjusted for a suitable moisture content, as shown in block 321. More particularly, sufficient water is left in the chopped fiber pulp to facilitate mixing with moisture such as shown in block 325. It has been found that by leaving a certain amount of pulp water with the fibers, separation and distribution can be obtained. additional fiber. The pore linkers and formers can also be added in a wet mixing step and water 329 can be added to obtain the correct rheology. The dough is also mixed with cut, as shown in block 332. Cutting mixing can also be done by passing the mixture through spaghetti-shaped dies using a screw extruder, a double screw extruder, a mixer cut (such as an optical tensioning or sigma blades). Atmospheric cutting mixing can take place in a sigma mixer, a top cutting mixer, and inside the screw extruder. The cutting mixing process is desirable to create a more homogeneous mass 335 that has a desirable extrudable plasticity and rheology for extrusion to operate. The homogeneous mass 335 has a uniform distribution of the fibers, the fibers being placed in an overlapping matrix. In this form, as the homogeneous mass is extruded into the substrate block and cured, the fibers are allowed to bond in a rigid structure. In addition, this rigid structure forms an open pore network having high porosity, high permeability and a higher surface area. Referring now to Figure 10, a method for producing a gradient substrate block is illustrated. The process 350 is designed to allow the manufacture and extrusion of the substrate block having a characteristic of gradient. For example, a substrate can be produced having a first material towards the center of the block, and a different material outside the block. In a more specific example, a material having a lower coefficient of thermal expansion towards the center of the block is used, and where a particularly high heat is expected, although a material with a relatively high coefficient of thermal expansion in the areas is used. external, where less heat is expected. In this way, a more unified expansion property can be maintained for the entire block. In another example, selected areas of a block may have a higher density ceramic material to provide increased structural support. These structural support members can be adjusted concentrically or axially within the block. Accordingly, the specific materials can be selected according to the desired gradients in porosity, por size or chemistry according to the application requirements. In addition, the gradient may comprise the use of more than two materials. In one example, the gradient structure can be produced by providing a cylinder of a first material 351. A sheet of a second material 353 is wrapped around the cylinder 351 as shown in the illustration 355. In this form, the layer B 353 it becomes a concentric tube around an inner cylinder 351. The cylinder with layers 355 is placed subsequently in a piston extruder, it is evacuated with air and the mass is extruded through a die. During the extrusion process, the material will be mixed at the interface between material A and material B, facilitating an interface without joints. This interface allows the overlap and bond of the fibers between 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, the material A is formed in the center of a substrate, while the material B 361 is formed in the external parts. It will be appreciated that more than two materials can be used, and that the pore size, porosity and chemical characteristics can be adjusted in a gradient manner. Referring now to Figure 11, another process 375 is described for creating a gradient substrate. In process 375, a first cylinder 379 of about the size of the piston extrusion barrel is provided. In one example, the external cylinder 379 is the actual barrel used in the piston extruder. An inner tube 377 having a smaller diameter than the outer tube 379 is provided. The tubes are concentrically shaped so that the inner tube 377 is placed concentrically within the tube 379. Pellets of a first mixing material are placed. extrudable 383 inside tube 377, while pellets are deposited from a second extrudable mixing material 381 within the ring between tube 377 and tube 379. The inner tube is carefully removed, so that the material A is concentrically surrounded by the material 381. The material adjustment is subsequently placed on the piston of extrusion, the air is removed with vacuum, and is extruded through a die. Once extruded, cured and packed a gradient substrate is produced as described with reference to Figure 10. It will be appreciated 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 for making a substrate or gradient is illustrated. Method 400 has an extrudable mixing column 402 having alternating discs of two extrudable materials. The extrudable mixture 402 has a first material 403 adjacent to a second material 404. In one example, the material A is relatively porous, while the material B is less porous. During extrusion, the material will flow through the extrusion die causing the fibers of part A and part B to intermix in an overlap setting. In this form, each part A and B are bonded together to become a block of fibrous substrate. At the time of curing and packing, the filter 406 is created. The filter 406 has a first part 407 having a relatively high porosity and a second part 408. that has less porosity. In this form, the gas flowing through the filter 406 is first filtered through an area of high porosity having a large pore size, and subsequently filtered through a less porous area having a smaller pore size. . In this way, large particles are trapped in the area 407, while the smaller particles are trapped in the area 408. It will be appreciated that the size and number of discs of the material can be adjusted according to the application needs. The fiber extrusion system offers greater flexibility in the implementation. For example, a wide range of fibers and additives can be selected to form the mixture. There are several mixing and extrusion options, as well as options related to the curing method, time and temperature. With the teachings described, an expert in the arts of extrusion will understand that many variations can be used. The honeycomb substrate is a common design that will be produced using the technique described in the present invention, although other shapes, sizes, contours and designs can be extruded for various applications. For certain applications, such as use in filter apparatus (DPF, oil / air filters, hot gas filters, air filters, water filters, etc.), or catalytic devices (such as 3-way catalytic converters, catalysts , SCR, deionizers, deodorizers, biological reactors, chemical reactors, oxidation catalysts, etc.) channels in an extruded substrate may need to be plugged. A material of composition similar to the extruded substrate is used to cover the substrate. The capping can be done in the green state or on a sintered substrate. Most coating compositions require thermal treatment to cure and bond to the extruded substrate. Although preferred embodiments and particular alternatives of the present invention have been described, it will be understood by those skilled in the art that many of various modifications and extensions may be implemented to the technology described above, using the teachings of the invention described herein. All of said modifications and extensions are projected to be included within the spirit and actual scope of the present invention, as described in the appended claims.

Claims

CLAIMS 1. An extrudable mixture, comprising: a ceramic material consisting essentially of elongated fibers; liaison material; fluid; and wherein the elongated fibers, bonding material, and fluid are a homogeneous mass.
2. The extrudable mixture as described in claim 1, characterized in that the ceramic material has less than about 20% the volume of the homogenous mass.
3. The extrudable mixture as described in claim 1, characterized in that the extrudable mixture further comprises inorganic clays, nanoclays, colloids, glass, or ceramic precursors without fiber.
4. The extrudable mixture as described in claim 1, characterized in that the ceramic material has less than about 40% the volume of the homogenous mass.
5. The extrudable mixture as described in claim 1, characterized in that the ceramic material is within the range of about 15% to about 30% of the homogeneous mass by volume.
6. The extrudable mixture as described in claim 1, characterized in that substantially all the elongated fibers have a aspect ratio greater than about 5 and less than about 200.
7. The extrudable mixture as described in claim 1, characterized in that substantially all of the elongated fibers have a proportion of appearance within the range of approximately 10 to approximately 1000.
8. The extrudable mixture as described in claim 1, characterized in that the ceramic material includes ceramic precursors.
The extrudable mixture as described in claim 1, characterized in that the elongated fibers are ceramic fibers selected from the group identified in Table 1 of Figure 6.
10. An extrudable mixture, comprising: fibers having a proportion of aspect greater than 1; a binding material; fluid; and wherein the fibers, the bonding material, and fluid are a homogeneous mass.
The extrudable mixture as described in claim 10, characterized in that the fibers have a distribution of aspect ratios with a mode in the range of about 3 to about 1000.
12. The extrudable mixture as described in claim 10, characterized in that the fibers have a multimodal distribution of aspect ratio with both modes within the range of about 3 to about 1000.
13. The extrudable mixture as described in claim 10, characterized in that the fibers are ceramic fibers. .
The extrudable mixture as described in claim 10, characterized in that the fibers are substantially a fiber of the type selected from the group consisting of: organic fibers, polymeric fibers, inorganic fibers, metal fibers, glass fibers, fibers of ceramic-glass, oxide ceramic, non-oxide ceramic, amorphous, polycrystalline, and metallic alloy.
15. The extrudable mixture as described in claim 10, characterized in that the fibers are a mixture of a plurality of fiber types selected from the group consisting of: organic fibers, polymer fibers, inorganic fibers, metal fibers, fibers of glass, ceramic-glass fibers, oxide ceramic, non-oxide ceramic, amorphous, polycrystalline, and metallic alloys.
16. The extrudable mixture as described in claim 10, characterized in that the fibers are coated.
17. The extrudable mixture as described in claim 10, characterized in that the fibers have from about 15% up to about 30% of the volume of the extrudable mixture.
18. The extrudable mixture as described in claim 10, characterized in that the fibers have from about 8% to about 40% of the volume of the extrudable mixture.
19. The extrudable mixture as described in claim 10, characterized in that the homogeneous mass has an adjusted rheology within the area bonded through points a, b, c, and d of table 5 of figure 6.
20. The extrudable mixture as described in claim 10, characterized because the fibers are metal fibers.
21. The extrudable mixture as described in claim 10, characterized in that the fibers are ceramic fibers selected from the group identified in Table 1 of Figure 6.
22. The extrudable mixture as described in claim 10, characterized because it also includes pore formers and wherein the inorganic fibers, binding material, pore formers, and fluid are in homogeneous mass.
23. The extrudable mixture as described in Claim 22, characterized in that the pore former is selected from the group identified in Table 3 of Figure 6.
24. An extrudable mixture, comprising: a homogeneous extrudable mass comprising ceramic material, organic linkers, and fluid; wherein the ceramic material has at least about 40% of the mass volume.
25. The extrudable mixture as described in claim 24, characterized in that the ceramic material is less than about 20% the volume of the dough.
26. The extrudable mixture as described in claim 24, characterized in that the ceramic material is a polycrystalline fiber, a monocrystalline mustache or an amorphous fiber.
27. A method for making a porous substrate, characterized in that it comprises: mixing fibers of elongated ceramic materials; bonding material, and fluids in a homogeneous mass; extrude the homogeneous mass on a green substrate; and curing the green substrate on a porous substrate.
28. The method as described in the claim 27, characterized in that the mixing step includes using less than about 40% by volume of the fibers of ceramic material.
29. The method as described in the claim 27, characterized in that the mixing step includes using less than about 20% by volume of the fibers of ceramic material.
30. The method as described in claim 27, characterized in that the mixing step includes using a cutting mixer.
31. The method as described in claim 27, characterized in that the mixing step includes mixing in a pore former to form the homogeneous mass.
32. The method as described in the claim 27, characterized in that it also includes the step of selecting a plurality of linkers, with each linker selected to have a different temperature at which it is thermally degraded compared to the other linker (s).
The method as described in claim 27, characterized in that it further includes the step of selecting the linker to provide sufficient green strength to prevent deformation of the green substrate before curing.
34. The method as described in claim 27, characterized in that it further includes the step of selecting the fibers so that substantially all fibers, by volume, have an aspect ratio that exceeds 5.
35. The method as set forth in FIG. describes in the claim 34, characterized in that the ceramic material includes fine or firing material.
36. The method as described in claim 34, characterized in that the ceramic material is substantially free of fine or shooting material.
37. The method as described in claim 27, characterized in that the healing step comprises forming bonds between intersecting fiber to form the porous substrate structure.
38. The method as described in the claim 37, characterized in that substantially all intersecting fibers are linked.
39. The method as described in claim 37, characterized in that some of the intersecting fibers are not linked.
40. A method for making a porous substrate, characterized in that it comprises: forming inorganic fibers, bonding material, and a fluids in a homogeneous mass; extrude the homogeneous mass on a green substrate; and curing the green substrate on a porous substrate.
41. The method as described in claim 40, characterized in that the step of curing comprises forming bonds between the inorganic overlapping fibers to form the rigid structure of the porous substrate.
42. The method as described in claim 40, characterized in that the links are sintered solid state links; sintered links aided by liquids; or glass links, glass-ceramic, or ceramic.
43. The method as described in claim 40, characterized in that the step of curing comprises burning substantially all of the fluid and organic material.
44. The method as described in claim 40, characterized in that the organic fibers have bonds formed to create a network of open pores.
45. The method as described in claim 40, characterized in that the extrusion step further comprises pushing the extrudable mixture through a die.
46. The method as described in the claim 40, characterized in that the extrusion step further comprises pushing the extrudable mixture through a die using a piston or screw extruder.
47. The method as described in claim 40, characterized in that the extrusion step is operated at room temperature or at elevated temperature.
48. A method for making porous substrate, characterized in that it comprises: selecting a fiber material from table 1 of figure 6; selecting a linker from table 2 of figure 6; selecting a fluid from table 4 of figure 6; process the fiber material; mix the fiber, binder, and fluid material in a homogeneous mass; adjust the rheology of the homogeneous mass to be extrudable; Extrude the homogeneous mass into green substrates; and curing the green substrates in the porous block.
49. The method as described in the claim 48, characterized in that the processing step is carried out at least partially in the mixing step, so that the mixing step cuts longer fibers into shorter fibers.
50. The method as described in the claim 48, characterized in that the processing step further comprises the step of coating the fibers with organic material to aid extrusion.
51. The method as described in claim 48, characterized in that the processing step includes making a paste from the fiber and fluid material, and violently stirring the fiber material to cut longer fibers into shorter fibers.
52. The method as described in claim 51, characterized in that the dough further includes an auxiliary dispersion, an extrusion aid and an auxiliary resistance.
53. The method as described in claim 48, characterized in that it further includes the steps of: selecting additives selected from the group consisting of: pore formers, strength generating agents, opacifiers, extrusion aids, dispersants, pH modifiers, inorganic binders, clays, washing coating materials and catalysts. and mix the additives in the homogeneous mass.
54. A process for curing a green substrate in a porous block, characterized in that it comprises: removing the fluid from a green substrate; burn the organic material; form bonds between the fibers; and forming a network of fibrous open pores in the substrate.
55. The curing process as described in claim 54, characterized in that the links are sintered solid state links; sintered links aided by liquids; or glass, glass-ceramic, or ceramic links.
56. The curing process as described in claim 54, characterized in that as an organic material is burned, the fibers are readjusted in an intersecting network.
57. The healing process as described in the claim 54, characterized in that it further includes the use of an inorganic additive material to form a part of the fibrous open pore network.
58. A method for making a porous gradient substrate, comprising: forming a first extrudable mixture having a first mixture of fibers, additives, and fluids; forming a second extrudable mixture having a second mixture of fibers, additives, and fluid; adjusting the first extrudable mixture adjacent to the second extrudable mixture in an extruder; extruding the first and second extrudable mixtures on a green substrate; and cure the green substrate.
59. The method as described in claim 58, characterized in that the healing step comprises forming bonds between the intersecting fibers to form the structure of the porous substrate
60. The method as described in claim 59, characterized in that less some of the bonds are formed of one or more fibers of an extrudable mixture that intersects one or more fibers in the other extrudable mixture.
61. The method as described in claim 59, characterized in that the links are sintered solid state links; sintered links aided by liquids; or glass, glass-ceramic, or ceramic links.
62. The method as described in claim 58, characterized in that the forming and adjusting steps further comprise forming the first extrudable mixture in a cylinder shape, arranging the second extrudable mixture as a concentric layer around the cylinder.
63. The method as described in claim 58, characterized in that the steps of forming and adjusting further comprise: forming the first extrudable mixture in first pellets; forming the second extrudable mixture in second pellets; fill a tube with the first pellets; surround the tube with the second pellets; and eliminate the tube.
64. The method as described in claim 63, characterized in that it further comprises the step of evacuating air from the pellets prior to extrusion.
65. The method as described in claim 58, further comprises the steps of: forming the first extrudate in a group of first disks; forming the second extrudate of a group of second discs; and adjust the disks to form a cylinder of first and second alternating disks.
66. A process for preparing fibers for use in a extruder, characterized in that it comprises: placing unprocessed fibers in a liquid; violently mix the fibers in a liquid to chop the fibers; and extract most of the water from the mixture.
67. The process as described in claim 66, characterized in that the fibers are a ceramic fiber selected from the group described in table 1 of figure 6.
68. The process as described in the claim 66, characterized in that it also includes the step of adding a dispersing agent or liquid binding agent.
69. The process as described in claim 66, characterized in that the extraction step further comprises pressing the fibers and a liquid against a filter.
70. The process as described in claim 66, characterized in that the extraction step further comprises drying the fibers to remove most of the free liquid.
71. A porous ceramic substrate: having a porosity within the range of about 60% to about 85%; which has a structure formed of bonded ceramic fibers and the substrate produced through an extrusion process comprising: mixing fiber of ceramic material with additives and a fluid to form an extrudable mixture; extruding the extrudable mixture into green substrate; and curing the green substrate in the porous substrate.
72. A porous ceramic substrate as described in claim 71, characterized in that it further comprises sintered, glass or glass bond between the fibers.
73. A porous ceramic substrate as described in claim 71, characterized in that the cured ceramic substrate consists essentially of ceramic fibers.
74. A porous ceramic substrate as described in claim 71, characterized in that the cured porous ceramic substrate consists essentially of a network of open pores of ceramic fibers
75. A porous ceramic substrate as described in the claim 71, characterized in that the cured porous ceramic substrate has a pore network so that all pores are internally connected.
76. A porous substrate having a porosity within the range of from about 60% to about 90% and having the structure formed of bonded inorganic fibers, on substrate is produced at through an extrusion process comprising: mixing an inorganic fiber with additives and a fluid to form an extrudable mixture; extruding the extrudable mixture on a green substrate; and curing the green substrate in the porous substrate.
77. The porous substrate as described in claim 76, characterized in that the healing step generates fiber to fiber links forming a structures.
78. The porous substrate as described in claim 76, characterized in that the bonds are formed by sintering or by forming glass, glass-ceramic or ceramic bonds.
79. The porous substrate as described in claim 6, characterized in that the healing step generates fiber to fiber links forming an open pore network.
80. The porous substrate as described in claim 76, characterized in that the inorganic fibers have an aspect ratio distributed with a mode within the range of 3 to 1000.
81. The porous substrate as described in claim 76, characterized in that the inorganic fibers are selected from Table 1 of Figure 6.
82. The porous substrate as described in claim 76, characterized in that the cured substrate it has a detectable residue from the burning of the additives.
83. The porous substrate as described in claim 76, characterized in that at least part of the fiber to fiber contacts do not form links.
84. The porous substrate as described in claim 76, characterized in that substantially all fiber to fiber contacts form bonds.
85. The porous substrate as described in claim 76, characterized in that it further includes a first substrate section having a first porosity, and a second substrate section having a second porosity.
86. The porous substrate as described in claim 76, characterized in that it further includes a first substrate section having a first density and a second section of the substrate having a second density.
87. The porous substrate as described in claim 76, characterized in that it further includes a first substrate section that is bonded using a first type of fiber to fiber link and a second substrate section that uses a second type of fiber link to fiber.
88. The porous substrate as described in claim 76, characterized in that the inorganic fibers They include amorphous crystalline materials.
89. The porous substrate as described in claim 76, characterized in that the inorganic fibers are metal fibers, metal alloy fibers or ceramic fibers.
90. The porous substrate as described in claim 76, characterized in that the extrudable mixture further comprises organic fibers.
91. A porous substrate with from about 40% to about 75% porosity that has been extruded from an extrudable mixture that does not comprise any functionally effective pore-forming component.
92. An extruded porous substrate consisting essentially of bonded fibers.
93. The porous substrate as described in claim 92, characterized in that the fibers consist essentially of ceramic fibers.
94. The porous substrate as described in claim 93, characterized in that it also includes solid state, crystalline or glass bonding between the ceramic fibers.
95. The porous substrate as described in claim 94, characterized in that the bonded ceramic fibers form a network of open pores.
96. The porous substrate as described in claim 93, characterized in that the ceramic fibers they have a distributed aspect ratio with a mode within the range of 3 to 1000.
97. The porous substrate as described in claim 93, characterized in that the ceramic fibers are selected from Table 1 of Figure 6.
98. The porous substrate as described in claim 92, characterized in that it also includes parallel inlet and outlet channels in a honeycomb pattern.
99. The porous substrate as described in claim 92, characterized in that it also includes parallel input and output channels, and the input channels are larger than the output channels.
100. The porous substrate as described in claim 92, characterized in that the porous substrate is a block having random channels.
101. A filter product, comprising: an extruded substrate having an open pore network formed by bonded fibers; a housing for retaining the substrate; an inlet for receiving a fluid and an outlet for providing the filtered fluid.
102. The filter product as described in claim 101, characterized in that the fluid is a gas or an escape liquid.
103. The filter product as described in claim 101, characterized in that the filter product is an air filter of a vehicle, an exhaust filter of a vehicle or a cabin filter of a vehicle.
104. The filter product as described in claim 101, characterized in that it further comprises a catalyst placed in the extruded substrate.
105. A catalytic converter product, characterized in that it comprises: an extruded substrate having an open pore network formed by bonded fibers; a catalyst placed on the extruded substrate; a housing for retaining the substrate; an inlet for receiving fluid and an outlet for providing a filtered fluid.
106. A catalytic converter product as described in claim 105, characterized in that the fluid is a gas or an escape liquid.
107. A catalytic converter product as described in claim 105, characterized in that the filter product is an air filter of a vehicle, an exhaust filter of a vehicle or a cabin filter of a vehicle.
108. A catalytic converter product as described in claim 105, characterized in that it further comprises a catalyst placed on the extruded substrate. SUMMARY An extrudable mixture 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 in a mass which, when extruded and cured, forms a highly porous substrate. Depending on the particular mixture, the present invention enables porosities of the substrate from about 60% to about 90%, and enables the process in other porosities as well. The extrudable mix can use a wide variety of fibers and additives, and can be adapted to a wide variety of environments and operating applications. The fibers, which have an aspect ratio of greater than 1, are selected according to the requirements of the substrate, and are mixed with binders, slurries, extrusion aids and fluids to form a homogeneous extrudable mass. The homogeneous mass is extruded on a green substrate. The more volatile material is preferably removed from the green substrate, which allows the fibers to connect and contact internally. As the healing process continues, fiber to fiber bonds are formed which produce a structure having a network of substantially open pores. The resulting porous substrate is useful in many applications, for example, in the form of a substrate for a host of filter or catalyst, or catalytic converter.