GB2055356A - Cold formed ceramic fibers - Google Patents

Abstract

Method for cold forming polymeric-bound metal oxide fibers involves the use of a slurry of metal oxide powder of the desired material, a polymeric composition, and a solvent for the polymeric composition. Polymeric-bound fibers are formed by rapid evaporation of the solvent from an extrusion of the slurry. Thereafter, metal oxide fibers are formed by sintering the polymeric-bound fibers. Products of this process include molten carbonate fuel cell tiles made by sintering or hot pressing a composite of a plurality of fibres. Suitable apparatus for extruding the slurry is described.

Description

SPECIFICATION Cold formed ceramic fibers The invention pertains to the forming of metal oxide fibers and fibers of metal oxide mixtures, particularly ceramic fibers. The ceramic fibers can be used to form ceramic tiles or other ceramic structures. More particularly, this invention relates to forming ceramic fibers for later manufacture into fibrous electrolyte tiles for molten carbonate fuel cells.

Fuel cells provide an efficient method for energy conversion from traditional fossil fuels as well as from newer synthetic fuels. Efficient energy conversion is a major advantage of the fuel cell. Secondgeneration fuel cells use molten carbonate instead of phosphoric acid as an electrolyte. The molten carbonate fuel cell can use CO and H2 gas derived from coal gasification to produce H2O, CO2, electricity, and heat. Studies have shown that a large central station power plant using molten carbonate fuel cells and s am turbines in conjunction with a coal gasifier could operate at an efficiency of 50 percent from coal to AC electricity. About 2/3 of the electric output is from the fuel cell and about 1/3 from the steam turbine.Another advantage of the fuel cell is its modular nature with little loss of efficiency for a small number of modules. Also, the molten carbonate oxidizes the fuel electrochemically instead of by combustion; thus, the NOx emissions are significantly reduced over comparable techniques.

In particular, molten carbonate fuel cells have been in operation on a small-scale for several years.

Modular stacks of cells of up to one square foot surface area and lifetimes of 15,000 hours have been achieved. Tile thicknesses of slightly less than 1.3 mm to greater than 20 mm have been used. The method of making the tiles for the prior art apparatus involves hot-pressing such materials as Awl203, K2CO2 and Li2CO3 into an electrolyte structure (tile) of high strength and conductivity as well as good electrolyte retention. However, no technique using elevated temperature processing has produced a rigid tile structure of high strength, conductivity, and electrolyte retention while maintaining commercially reasonable manufacturing costs.

One approach to further improving fuel cell efficiency has been to reduce the tile thickness. A reduction in tile thickness reduces resistive losses but must be accomplished without sacrificing mechanical strength. Imparting a filamentary or fiber-mat type structure to the tile is one answer to the strength-with-less-thickness problem, but drawing ceramics into the needed denier of filament (i.e. with a micrometer or less diameter) has led to economically prohibitive processes. Ceramic fibers can be manufactured down to the one micrometer diameter using a complete melt process or a hot rod drawing process. In each case, high temperature at or near the melting point of the ceramic must be used which leads to technical difficulty, high energy consumption, and added expense due to the additional elevated temperature processing.The factors of expense, thickness, and electrolyte retention of the tile are important in making the molten carbonate fuel cell economically competitive with other forms of energy conversion.

One object of the present invention is to form fibers of metal oxide compositions.

Another object of the present invention is to form ceramic filaments or fibers.

Another object of the present invention is to form ceramic fibers suitable for molten carbonate fuel cell tiles having good electrolyte retention.

Another object of the present invention is to form ceramic fibers with a maximum processing temperature no greater than that needed to sinterthe metal oxide fibers.

Another object of the present invention is to form metal oxide fibers with a minimal processing temperature.

Another object of the present invention is to form ceramic fibers of greater than 0.01 meter length and of substantially one micrometer (10-6m) or less diameter.

Another object of the present invention is to form ceramic fibers which can be sintered into molten carbonate fuel cell tiles with a thickness of less than 1.3 mm (0.0013 m) and having an average operating lifetime of greater than 100,000 hours.

Another object of the present invention is to form ceramic fibers for fabrication into molten carbonate fuel cell tiles which will not suffer a substantial decrease in electrolyte retention during 100,000 hours of stable operation.

Another object of the present invention is to form a composition of matter from which ceramic fibers can be formed with a diameter no greater than one micrometer by a processing temperature no greater than that needed for sintering the ceramic particulates contained in the composition.

Another object of the present invention is to form a fibrous ceramic tile composite wherein said fibres are of no greater diameter than one micrometer and which require a processing temperature no greater than needed to sinter ceramic fibers from a ceramic powder contained in the composition.

Another object of the present invention is a fiber formed from spinning a slurry composition of a polymeric material dissolved in a solvent and metal oxide powder through an orifice of less than 2 mm and greater than the metal oxide diameter.

Other objects of the invention will become readily apparent to those skilled in the art from the following description.

The present invention provides a commercially viable apparatus and method for producing ceramic fibers of greater than 0.01 meter length and a micrometer or less in diameter using temperatures no higher than those required for sintering. Also, the present invention provides a method and apparatus for producing metal composition fibers of greater than 0.01 meter in length and a micrometer or less in diameter using minimal processing temperatures.In particular, the apparatus and method for making ceramic fibers comprise providing a substantially homogeneous slurry, said slurry containing on a weight basis a mixture of 10 to 25 percent of a liquid polymeric composition, 50 to 70 percent of a solvent for said polymeric composition, and 20 to 40 percent of a ceramic powder wherein the polymeric material has a viscosity of 0.01 to 30 poise and wherein said solvent will substantially all evaporate from a one micrometer thick sample of the slurry in less than 2 seconds; providing a member with at least one orifice of a diameter less than two millimeters but greater than the diameter of the ceramic powder; extruding the slurry through one (or more) orifice(s) with a force of 3t least 3 x 104 Pa so as to form polymeric-bound fibers; and sintering the polymericbound fibers so as to form ceramic fibers.The present invention includes the above-recited composition as well as products formed by that composition.

Such products include molten carbonate fuel cell tiles.

Figure 1 is-a schematic of the apparatus for making ceramic fibers according to the present invention the apparatus including a mixing container, a mill, a member with at least one orifice, a source for forcing the slurry through the orifice, a flow shaping member, and a source for sintering.

Figure 2 is a schematic for the apparatus for making ceramic fibers according to the present invention wherein the containing member is a cylindrical con tainer with orifices spaced circumferentially about the wall of the cylinder, a spinner connected to the cylindrical container for forcing the slurry through the orifices, and a collector for containing the polymeric bound fibers.

One preferred method of making molten carbonate fuel cell tiles is to begin by sintering or hot pressing ceramic fibers into the desired tile form. Besides adding strength to the rigid tile structure, the ceramic fibers can add sites for the electrolyte to adhere in the tile due to surface tension. Mechanically, the crossings of ceramic fibers and a roughness which can be produced on the outer surface of the ceramic fibers themselves each enhance the retention of electrolyte through the surface tension force. Thus, the economical production of ceramic fibers of about a micrometer in diameter and over a centimeter in length can increase the lifetime of a molten carbonate fuel cell while maintaining the fuel cell as cost competitive with other energy conversion methods.In addition to advancing the efficiency of energy conversion through fabrication into improved molten carbonate fuel cell tiles, most other applications for ceramic tiles can incorporate ceramic fibers. The ceramic powder can include one or more metal oxides illustrated by Al2O2, ZrO2, MgAI2O4, LILO2 Y2O3, MgO, UO2, PuO2, ThO2, and others. LiAl2 is preferred for molten carbonate fuel cell tiles. Those applications which depend on tile strength are especially of interest, such as liners for inertial confinement fusion target chambers, liners for heaters and other high temperature and/or high pressure processing equipment, high temperature insulation or outer surfaces for atmospheric re-entry vehicles.There are also improved cookware, room temperature, and low temperature applications.

Figure 1 is a schematic diagram of the apparatus for forming ceramic fibers according to the presently claimed invention. A mixing container 1 contains a mixture 2 of a given amount of a solvent such as acetone, a ceramic powder 1/2 of the amount by weight of the solvent, and a liquid polymeric composition of viscosity between one centipose and 30 poise and of amount substantially tk by weight of the amount of the ceramic powder. Next the mixture is placed in a mill 5 where agglomerates in the ceramic powder are broken up to ensure substantial uniformity of the resulting slurry.The slurry is then poured into a containing member 10 which has at least one orifice 11 of a diameter less than two millimeters but greater than the diameterofthe largest particles of the ceramic powder after milling. A source of force 12 forces the slurry through at least one orifice with a pressure of at least approximately 3.4 x 104 Pa-gauge (5 pounds per square inch; 1 pound per square inch equals 6894.76 Pa and one Pa is one newton per square meter). A flow shaping device 13 changes the cross-sectional shape of the slurry flow through the orifice(s). After passing through the orifice(s), the resulting polymeric-bound fibers are placed into a sintering device 15 for sintering into ceramic fibers.

Figure 2 illustrates a specific embodiment of the presently claimed invention. The mixing container 1 contains a mixture 2 of a given amount of solvent, a ceramic powder 'k of the amount by weight of the solvent, and a liquid polymer of viscosity between one centipoise and 30 poise and of amount substantially 1/3 by weight of the amount of the ceramic powder. Next the mixture is placed in a mill 5 where agglomerates in the ceramic powder are broken up to ensure a substantially uniform slurry. The slurry is then poured into a containing member 20 which is mounted to rotate on its own axis of cylindrical symmetry, thus forcing the slurry against the walls of the containing member 20.The spinner 25 forces the containing member 20 to rotate so the slurry moves against the walls underthe influence of a radial acceleration of between 106( revolutions )2.cen minutes timeterto 1015 ( revolutions )2.centimeter. Where the minute slurry is spun against the wall, there is at least one orifice 11 through the wall the orifice being of a diameter less than two millimeters but greater than the diameter of the largest particle of the ceramic powder after milling. A flow shaping device 13 changes the cross-sectional shape of the slurry flow through the orifice(s). This change in cross-section can optimize fiber formation for a given slurry. After passing through the orifice(s), the resulting polymer-bound fibers collect in a fiber container 17 spaced 0.3 m to 0.7 m or more radially beyond the wall of the containing member 20. The diameter is chosen to allow the solvent time to evaporate so that a polymer-bound fiber is left. The polymer bound fibers are then collected and placed in the sintering device 15 for sintering into ceramic fibers.

A critical feature of the present invention is the rapid cure of the resinous or polymeric binder of the unsintered fiber. Unless the polymeric binder cures rapidly to a sufficiently tack-free, green strength, breakage and distortions of the fiber and/or adhe sion between a plurality of freshly formed fibrous product will occur. Accordingly, it is also important that the solvent not only be essentially non-reactive, but have good solvency for the polymeric composi tion (including being mutually soluble with any carrier such as water used in emulsions). The solvent for the polymer is sufficiently quick drying that it will evaporate from each fiber formed within about 2 seconds, preferably less than about 1 second at one atmosphere pressure. Solvents contemplated include the lower alkyl ketones such as acetone, methyl ethyl ketone and diethyl ketone.Other solvents include ethers such as dimethyl ether, methyl ethyl ether and diethyl ether; lower alkyl esters such as methyl formate, ethyl formate and methyl acetate.

Acetone is preferred.

Another important feature of the present invention is the requirement that the polymeric or resinous composition cure rapidly at low temperatures when the solvent is removed, as by evaporation. Preferably the polymer will cure rapidly (i.e. 2 seconds or less), at ambient temperatures without the aid of heat, or other cure acceleration, although such can be used. Examples of such suitable polymeric compositions are polyethyl acrylate and copolymers of polymethyl acrylate and polyethyl acrylate. One suitable copolymerofthe lattertype is available from Rohm and Haas Company as an acrylic emulsion polymer under the name Rhoplex B-60A.The typical properties of Rhoplex B-60A are: appearance white milky liquid solid 46 to 47% pri (initial) 9.4to9.9 weight 8.9 Ibs/gal minimum cure temperature (film) 90C viscosity (initial) 800 to 3000 centipose (No.3 spindle, 12 rpm, 25"C.) Illustrative examples of other polymeric materials are some quick drying alkyds and polyvinylbutyrol (e.g., a product available from Monsanto underthe designation of B-76). Preferred is polymethyl acrylate and polyethyl acrylate copolymer having the properties defined above.

As a change in solvent or in ceramic or metal powder takes place, weight percentages will usually vary. The constituent percent ranges, by weight, in the slurry include 10 to 25 percent of a liquid polymer, 50 to 70 percent of a solvent for the polymeric composition, and 20 to 40 percent of a ceramic or other metal powder(s). As explained above, the solvent must be a solventforthe polymeric composition and must be able to evaporate from a one micrometerthickslurry extrusion in less than 2 seconds to leave a polymeric-bound fiber of one micrometer thickness or less. Such fibers can be generated at various lengths such as one centimeter, 0.1 meter, 0.3 meters, or longer.

Although certain specific terms have been used in the discussion of the case it is to fully understood that this is for purposes of simplicity and not by way of limitation. For example, the term polymer or acrylic polymer is used although that term is intended to include liquid or fluid polymeric compositions broadly, and resins or resinous compositions having the specified curing and cured properties discussed where appropriate. In some cases, the term ceramic is used althoughthatterm includes, unless otherwise indicated, metal compositions such as metal oxides, metal oxide mixtures, or particulates of pure metals (e.g. platinum, nickel, paladium, titanium, etc. and alloys thereof).In like fashion, acetone is recited in many cases although that is to be construed as solvent(s) having the requisite properties described.

EXAMPLES Example 1: An example of the Figure 2 apparatus was used to test the presently claimed invention. To 300 grams of acetone 150 grams of Al203 powder (99.95% AT203 powder) with an average particle size of two microns was added. Next, 50 grams of liquid acrylic polymer of viscosity from 0.2 to 30 poise was added to the mixture. The liquid acrylic polymer used was B-60A which is a proprietary acrylic emulsion manufactured by Rohm and Haas Company. Then, the mixture is placed in a jar mill with ceramic balls made from Al2O2to minimize impurities in the resulting slurry. This ceramic ball jar mill is run for four hours to break up any agglomerates in the ceramic powder. If the slurry is not to be used immediately, it is drained into an air-tight container until further processing is desired.Percent composition of the slurry by weight is 60% Acetone, 30% Awl203, and 10% liquid acrylic polymer. Then, the slurry is poured onto approximately a 0.075 m diameter disc which is spinning about a vertical axis at approximately 3000 RPM. The disc has cylindrical sides rising about 1.2 centimeters above the edge of the disc, and the sides have orifices circumferentially spaced approximately every 1.2 centimeters apart and about 0.6 centimeters above the disc. The fibers are collected against a ring about 0.4 m high and approximately one meter in diameter. The ring is placed concentrically about the disc and is centered with half of the ring height above and half of the ring height below the plane of the disc. The orifices in the cylindrical sides of the disc are approximately half a millimeter diameter.At the bottom of the ring is a surface for the acrylic-bound fibers to fall on. Fiber diameter can be reduced by adding more acetone to the slurry, if desired. The acrylic-bound fibers are collected and then placed in a furnace to be fired to sintering temperatures for the ceramic powder used. For Awl203 as used above, the temperature is in the range of 1500 to 16005C. This method for the production of ceramic fibers has produced fibers as small as one micrometer in diameter and as long as 0.3 m.

Example 2: Another apparatus, which practices the presently claimed invention but without a spinning disc, uses an apparatus similar to a paint sprayer. The slurry is prepared as above for the spinning disc up to the milling stage. After milling, the slurry of 60% acetone, 30% Al2O2 and 10% liquid acrylic polymer is poured into the reservoir of the "paint" sprayer. A pressure of 1.0 x 1 to 1.4 x 105 Pa is placed on the surface of the slurry to force it up an immersed tube leading to the nozzle. The nozzle has an adjustment to change the cross-sectional shape of spray leaving the nozzle. The cross-section can change from circu larto a substantially flattened spray.The pressure substantially determines fiber production -rate; the cross-sectional shape of the spray helps to optimize acrylic-bound fiber formation. The nozzle diameter in the range of half a millimeter is not critical. The slurry sprays into a ventilated area to protect personnei from acetone fumes. The acrylic-bound fibers are collected from where they land in the ventilated area and are placed in a furnace for sintering. As above, the Awl203 sintering temperature is in the range of 1 5005C to 1 600 C. The disadvantage of the "paint" sprayer is lack of control over where the acrylic-bound fibers land while with the spinning disc apparatus the acrylic-bound fibers are projected substantially into a plane. Also, the diameter of the fibers was easier to control with the spinning disc.

The process can operate over widely varying ranges. Once the 60:30:10 ratios are substantially satisfied for the acetone, ceramic powder, and liquid acrylic polymer, respectively, the variations can include most ceramic powders such as Al2O3, ZrO2, MgAl2O4 and LILO2 and can include most liquid acrylic polymers of viscosity between one centipose and 30 poise. The ceramic balls in the mill jar are made of the same or similar ceramic powder as is in the slurry to decrease the impurities in the slurry after milling. The orifice or orifices through which the slurry is forced can have a diameter between two millimeters and the diameter of the ceramic powder.

The exact diameter of the orifice or orifices is not critical. The pressure for pushing the slurry through the orifice or orifices can vary from around 3 x 104to 4 x 105 Pa. Standard paint sprayers can provide operation within these conditions.

The spinning apparatus can include many variations as well. A way of scaling the 3,000 to 5,000 revolutions per minute range forthe approximately 7.5 centimeter diameter spinning disc is to square the angular velocity and multiply it times the radius of the disc. Thus, the range of radial acceleration to which the slurry is subjected is approximately 105 to 1015 ( revolutions )2 centimeter. Again the orifice size minute centimeter. and the orifice size between two millimeters and the diameter of with the ceramic powder is not critical. As with the paint sprayer, acetone can be added to the slurry to decrease the diameter of the acrylic-bound fibers.

Also, a flow shaper can change the cross-sectional shape of the slurry as it emerges from the orifice or orifices. Changing the cross section between a circular one and a greatly flattened one can optimize acrylic-bound fiber formation for a given slurry. The acrylic bound fibers should be given time after passing through the orifice or orifices to let the acetone evaporate. Over 0.3 m radially outward between the spinning disc and the acrylic bound fiber collector is adequate while nearer 0.6 m separation provides plenty of time for acetone evaporation. The individual fibers should be sintered to form ceramic fibers. A standard reference in the field for sintering temperatures and other materials information are the ASTM phase diagrams.For Awl203 sintering occurs in the range of 1 500"C to 1 6005C while for ZrO2 it occurs at about 1760 C.

Molten carbonate fuel cell tiles must be structurally strong and retain the electrolyte through thousands of hours of operation. The approximately micron diameter and 0.3 m long ceramic fibers from the above process can be sintered, hot pressed, or otherwise formed into fuel cell tiles. The tiles can be formed with the fibers parallel or oriented at random. The random formation provides many fiber crossings where surface tension can have an increased effect in retaining the electrolyte in the tile.

In either case however, the "shot" formed on the sides of the ceramic fibers also form such enhanced surface tension sites. The "shot" are lumps of ceramic on the sides of the ceramic fibers. The shot can range in diameterfrom about Y2 to 5 microns or more. Thus, molten carbonate fuel cells of extended life and minimized cost can be made using the presently claimed technique of producing ceramic fibers through acrylic-bound fiber formation at room temperature and then a sintering of the already formed fibers.

The various features and advantages of the invention are thought to be clear from the foregoing description. Various other features and advantages not specifically enumerated will undoubtedly occur to those versed in the art as likewise will many variations and modifications of the preferred embodiment illustrated all of which can be achieved without departing from spirit and scope of the invention defined by the following claims.

Claims (26)

1. A method for making metal composition fibers, the method comprising the steps of: providing a substantially homogeneous slurry comprised of, by weight, to 25 percent of a polymeric material, 50 to 70 percent of a solvent for the polymeric material, and 20 to 40 percent of a metal powder composition wherein the polymeric material has a viscosity of 0.01 to 30 poise and wherein the solvent will substantially all evaporate from a filamentary extrudate of the slurry having a one micrometer diameter in less than 2 seconds; providing a member with at least one orifice of a diameter less than two millimeters but greater than the diameter of the powdered metal composition to be employed; forcing the slurry through the at least one orifice with a pressure of at least 3 x 104 Pa thereby forming polymer-bound fibers; and sintering the polymer-bound fibers so as to form polymer-free metal compound fibers.

2. A method for making fibers of a metal composition wherein the polymeric material is an acrylic polymer.

3. A method for making fibers of metal compositions as in claim 1 wherein said polymeric material is a copolymer of polymethylacrylate and polyethylacrylate having the following properties: appearance white milky liquid solids 46 to 47% pH (initial) 9.4 to 9.9 weight 8.9 Ibs/gal minimum cure temperature (film) 9"C viscosity (initial) 800 to 3000 centipoise.

4. A method for making ceramic fibers as in claim 1, further including the step of adding more solvent to the slurry to decrease the viscosity and thereby the diameter of the polymer-bound fibers.

5. A method for making ceramic fibers as in claim 1, wherein the step of forcing the slurry through the at least one orifice to form filamentary extrudate is accomplished through centrifugal force.

6. A method for making ceramic fibers as in claim 4, wherein the step of forcing the slurry through the at least one orifice to form filamentary extrudate is accomplished by gas pressure on the slurry.

7. A method for making ceramic fibers as in claim 4, wherein the solvent is acetone.

8. A method for making ceramic fibers as in claim 4, wherein the ceramic powder is a member selected from the group consisting of Awl203, ZrO2, MgAI204, LILO2, Y2O2, MgO, UO2, PuO2, ThO2, and mixtures thereof.

9. A method for making ceramic fibers as in claim 4, wherein the substantially homogeneous slurry is provided by milling said mixture in a ceramic ball jar mill wherein the ceramic balls are composed of substantially the same ceramic as in the slurry.

10. An apparatus for making fibers of metal compositions comprising: a means for providing a substantially homogeneous slurry, the slurry comprised of, by weight, to 25 percent of a polymeric material, 50 to 70 percent of a solvent for the polymeric material, and 20 to 40 percent of a ceramic powder wherein the polymeric material has a viscosity of 0.01 to 30 poise and wherein the solvent will substantially all evaporate from a filamentary extrudate of the slurry having a one micrometer diameter in less than 2 seconds; a containing member with at least one orifice of a diameter less than two millimeters but greater than a diameter of the powdered metal composition to be employed; a means for forcing the slurry through the at least one orifice with a pressure of at least 3 x 104 Pa whereby polymer-bound fibers are formed;; a means for sintering the polymer-bound fibers into polymer-free metal compound fibers.

11. An apparatus as in claim 10 wherein the metal compound is a ceramic.

12. An apparatus as in claim 11, wherein the solvent is acetone.

13. An apparatus as in claim 10, further including a supply of solvent, whereby solvent can be added to the slurry in the containing member for controlling the slurry viscosity and thereby the diameter of the polymer-bound fiber.

14. An apparatus as in claim 11, wherein the means for providing a substantially uniform slurry includes a ceramic ball jar wherein the ceramic balls are composed of substantially the same ceramic as in the slurry.

15. An apparatus as in claim 10, wherein the ceramic powder is chosen from the group consisting of Awl203, ZrO2, MgAI204, Lilo2, Y203, MgO, UO2, Put2, ThO2, and mixtures thereof.

16. An apparatus as in claim 10, wherein the means for forcing the slurry through the orifice includes a spinning means for spinning the containing member such that the slurry is forced through the orifice.

17. An apparatus as in claim 16, wherein the spinning means spins the containing member at a radial acceleration of between 106 ( n3)2revolutions cen- revolutions minute minute

18. An apparatus as in claim 10, wherein the means for forcing the slurry through the orifice includes the pressure of a pressure fluid on the slurry while it is in the containing member.

19. An apparatus as in claim 18, wherein the pressure on the slurry is between 1.0 x 105 Pa to 3 x 105 Pa.

20. An apparatus as in claim 19, further including a flow shaping means for controlling the crosssectional shape of the slurry flow after leaving an orifice.

21. Metalfibersformed bythemethod method comprising: providing a substantially homogeneous slurry comprised of, by weight, 10to 25 percent of a polymeric material, 50 to 70 percent of a solvent for the polymeric material, and 20 to 40 percent of a metal powder composition wherein the polymeric material has a viscosity of 0.01 to 30 poise and wherein the solvent will substantially all evaporate from a filamentary extrudate of the slurry having a one micrometer diameter in less than 2 seconds; providing a member with at least one orifice of a diameter less than two millimeters but greater than the diameter of the powdered metal composition to be employed; forcing the slurry through the at'least one orifice with a pressure of at least 3 x 104 Pa thereby forming polymer-bound fibers; and sintering the polymer-bound fibers so as to form polymer-free metal compound fibers.

22. A molten carbonate fuel cell tile comprising: a composite of a plurality of metal composition fibers prepared according to claim 1, said fibers being heat treated at sintering temperatures or grea term form a rigid tile structure.

23. A slurry for making ceramic fibers, the slurry comprising: providing a substantially homogeneous slurry comprising, by weight, to 25 percent of a polymeric material, 50 to 70 percent of a solvent for the polymeric material, and 20 to 40 percent of a metal powder composition wherein the polymeric material has a viscosity of 0.01 to 30 poise and wherein the solvent will substantially all evaporate from a filamentary extrudate of the slurry having a one micrometer diameter in less than 2 seconds.

24. A slurry for making ceramic fibers, according to claim 23 wherein the polymeric material is an acrylic polymer.

25. A slurry for making ceramic fibers, according to claim 24 wherein said polymeric material is a copolymer of polymethylacrylate and polyethylacrylate having the following properties: appearance white milky liquid solids 46 to 47% pH (initial) 9.4 to 9.9 weight 8.9 Ibslgal minimum cure temperature (film) 9 C viscosity (initial) 800 to 3000 centipoise.

26. The method of making ceramic fibers from a composition containing: by weight, 10 to 25 percent of a polymeric material, 50 to 70 percent of a solvent for the polymeric material, and 20 to 40 percent of a metal powder composition wherein the solvent will rapidly substantially all evaporate from an extrudate of the slurry, wherein the polymeric material has a viscosity of 0.01 to 30 poise and rapidly cures at room temperature upon evaporation of the solvent.