CA1332499C

CA1332499C - Laminated extruded thermal shock resistant articles

Info

Publication number: CA1332499C
Application number: CA000584336A
Authority: CA
Inventors: Irwin M. Lachman
Original assignee: Corning Glass Works
Current assignee: Corning Glass Works
Priority date: 1988-03-21
Filing date: 1988-11-28
Publication date: 1994-10-18
Anticipated expiration: 2011-10-18
Also published as: JPH01249437A; DE3850959T2; DE3850959D1; EP0333957A3; EP0333957A2; EP0333957B1; KR890014226A; JP2791486B2; KR970001181B1; US5053092A

Abstract

Laminated extruded thermal shock resistant composite articles formed from sinterable particulate or powdered materials such as ceramics are disclosed. The laminated extruded composite articles have multiple discrete layers of at least a first and second sintered material, where the first and second sintered materials are different and are selected from high strength sintered particulate or powdered materials and where the layers of each of said first and second sintered materials are substantially uniformly distributed throughout the article.

Description

1332~99 LaMINATED E~rrRUDED THERMAL SHOCI~ RESISTANT ARTICLES
Backaround of the Invention This invention relates to laminated extruded thermal shock resistant articles formed from sinterable particulate or powdered materials and to the method of 5 making such articles.
Due to properties such as high strength, temperature and chemical stability, and electrical and thermal insulating properties, ceramics are widely used engineering materials. In many applications, such as 10 cookware, spark plug insulators, abrasive wheels, refractory linings, applications in the chemical process industries, heat exchangers, and high temperature automotive substrates, ceramic materials can be exposed to rapid changes in temperature or large thermal gradients.
15 To be useful, the materials should desirably exhibit good thermal shock resistance, i.e., must maintain their strength after thermal shocking.
Thermal shock resistance is usually measured by auenching from a high temperature and by measuring the 20 strength degradation (as compared to measurements made on samples not yet subjected to thermal shock). A commonly used test for thermal shock resistance is that described by Hasselman . See , e . g ., Hasselman , ~Strength Behavior of Polycrystalline Alumina Subjected to Thermal Shock, ~ J. Am.
25 Ceramic Soc., Vol. 53, No. 9, pp. 490-495, Sept. 1970, and Larson and Hasselman, ~Comparative Behavior of High-Alumina *:

- 2 - 1 332 1 ~9 Refractories Subjected to Sudden Heating and Cooling", Transactions and Journal of the British Ceramic Societv, (74) No. 2, pp. 59-65, March/April 1975. It is recognized that all ceramic materials, as they are quenched from successively high temperatures, will undergo cracking and exhibit strength degradation.
Preferably, the ceramic materials will, upon being quenched from successively higher temperatures, exhibit stable crack propagation and, thus, a gradual and predictable decrease in strength. For the purpose of this invention, materials exhibiting such properties are deemed to exhibit good thermal shock resistance. There are ceramic materials, however, which undergo rapid crack propagation after quenching from a certain temperature and exhibit what is termed a "catastrophic"
decrease in strength . As ref erence now must be made to the figures of this application, these will first be briefly described as follows:
Figures la and lb are schematic graphs of typical thermal shock test behaviour. Figure la illustrates the catastrophic decrease in strength exhibited by a material which undergoes rapid crack propagation, and Figure lb illustrates the gradual decrease in strength exhibited by a material which undergoes stable crack propagation .
Figure 2a is a schematic drawing of an end view of an extruder barrel having a typical assembly of composite bodies of f irst and second sinterable materials loaded therein prior to extrusion.
Figure 2b is a schematic drawing of an end view of an extruder barrel having a typical assembly of once-extruded composites loaded therein.
Figure 2c is an illustration of composite body shapes of f irst and second sinterable materials which can be extruded into a laminated composite article of f inal desired shape .

1332~9 - 2a -Figure 2d is a schematic drawing of an end view of an extruder barrel having a typical assembly of rods, spheres or slugs loaded therein.
Figure 2e is a schematic drawing of a cross-sectional side view of an extruder barrel having an assembly of ribbons, sheets or discs layered therein perpendicular to the barrel axis.
Figure 3 is a schematic of a magnif ied view of a portion of the walls of a honeycomb structure showing the uniformly distributed layers of first and second sinterable materials.
Figure 4 is a graph presenting the results of Hasselman thermal shock testing of Examples 1 and 2.
Figures 5, 6 and 7 are graphs presenting the results of Hasselman thermal shock testing of Bxamples 3, 4 and 5, respectively.
Figures la and lb present graphs of schematic thermal shock test results, the first graph illustrating the catastrophic decrease in strength exhibited by a material which undergoes rapid crack propagation, and the second graph illustrating the gradual decrease in strength exhibited by a material which undergoes stable crack propagation and which is thus deemed to possess good thermal shock resistance. Clearly, materials which undergo rapid crack propagation are not suited for applications in which they will be exposed to rapid changes in temperature.
Ceramic materials in general do not have particularly good thermal shock resistance because of their brittle nature, and a need exists f or methods to improve the thermal shock resistance properties of these valuable materials.

1332~99 - 2b -Summary of the Invention The present invention relates to articles of high strength sinterable materials, such as ceramics, which exhibit good thermal shock resistance. More specifically, the articles of this invention comprise high strength sintered extruded laminated bodies having multiple discrete _ 3 _ 1 3 32 4 9 9 layers of at least a first and second sintered ~aterlal, where said first and second ~intered material6 are different and are selected fro~ high strength sintered inorganic particulate or powdered materials and wherein 5 said layers of each of said first ~nd second sintered ~aterials are substantially unlformly distributed throughout the body. In the preferred embodi~ent of the invention, the ratio of either of said layers of first or second sintered materials to the other is no greater than 10 about 1.2:1. Generally, however, the ratio of either of said layers of first or second sintered materials to the other may be up to 10 :1.
This invention al60 relates to a method of producing such sintered laminated extruded articles. The 15 method of this invention comprises (a) providing first multiple bodies comprising a mixture of a first sinterable material and a plasticizing/bonding agent for said material:
(b) providing second multiple bodies comprising a mixture of a second sinterable material and a plasticizing/bonding agent for said material;
(c) interminglinq said first and second multiple bodies to form an assembly thereof and wherein said first and second multiple bodies are substantially uniformly distributed throughout the composite;
(d) passing the assembled body through a die to form an extruded laminated composite article in a desired shape: and (e) heating said extruded laminated composite article to sinter the particulate or powdered ~aterials therein.
In addition, this invention relates to the green articles which are sintered to form the high strength extruded laminated articles above-described, and to the 1332~99 method of making such green articles. The term "green"
is used in the art and in this application to refer to the state of a formed body or piece made of sinterable powder or particulate material that has not yet been fired to the sintered state. The green body may have been heated to dry it by evaporating or volatilizing plasticizing liquid or vehicle and perhaps also to burn out volatile organic or decomposable binders mixed with the sinterable powder to render it adequately plastically formable and/or sufficiently coherent (having green strength) so that the body can be handled without deformation and other damage.
Other aspects of this invention are as follows:
A high strength article comprising a sintered extruded laminated body of a coextruded composite having multiple, discrete, substantially discontinuous, interspersed layers of at least a first and second sintered material, where said f irst and second sintered materials are different and are selected from high strength sintered particulate or powdered materials and wherein said layers of each of said first and second sinterable materials are substantially uniformly distributed throughout the body, the ratio of either of said first or second sintered materials to the other being no greater than about 1. 2 :1.
A sinterable article which comprises an extruded laminated body of a coextruded composite having multiple, discrete, substantially discontinuous 3 o interspersed layers of at least a f irst and second sinterable material, where said first and second sinterable materials are different and are selected from particulate or powdered materials capable of being sintered to form high strength materials and wherein said phases are substantially uniformly distributed through said body, the ratio of either of said first or second sintered materials to the other being no greater than about 1. 2 :1.
A method of producing a sinterable extruded B laminated article comprising . .

4a (a) providing first multiple bodies comprising a mixture of a f irst sinterable material and a plasticizing/bonding agent for said material:
(b) providing second multiple bodies comprising a mixture of a second sinterable material and a plasticizing/bonding agent for said material, where said f irst and second sinterable materials are different and are selected from particulate or powdered materials capable of being sintered to form high strength materials;
(c) intermingling said first and second multiple bodies to form an assembled body in such a manner that, after coextrusion of said assembled body to produce said sinterable extruded laminated article, said first and second sinterable materials are present in said article in multiple, discrete, substantially discontinuous interspersed layers which are substantially uniformly distributed throughout said article;
(d) passing said assembled body for coextrusion through a die to form said sinterable extruded laminated composite article in a desired shape having said layers.
Tests indicate that the sintered articles of this invention exhibit good thermal shock resistance.
It is believed that this good thermal shock resistance is the result of several factors. First, the presence of the discontinuities in the sintered article resulting :

1332~99 from the presence of a plurality of phases is believed to prevent crack growth and relieve stresses. Second, it is known that microcracking enhances the thermal shock resistance of an article based on ceramics by lowering the modulus of elasticity of the article.
Microcracking is encouraged when the materials in the different phases in the articles of this invention possess different thermal expansions and firing shrinkages. Third, the plurality of phases arranged in a laminated fashion results in each of the phases being substantially discontinuous.
Detailed Description of the Invention The materials from which the extruded laminated articles of this invention are made may be any of the well-known sinterable inorganic materials capable of providing mechanical strength and good thermal properties. In the preferred embodiment, the materials are ceramic materials, but they may also be selected from cermet, metallic, glass and glass-ceramic materials.
Reference to suitable sinterable materials which can be used in this invention is made in U. S. Patents 3,112,184, 3,444,925, 3,824,196, 3,885,977, 3,919,384, 1332~39 3,963,504, 4,017,347 and ~,582,677. Examples of suitable materlals includ- glasses, such as boro-sillcates, soda-lime-silic~tes, lead-~ilicates, alumino--ilicates, alkaline earth silicates, and fused silica, ~nd oxide 5 ceramics such as alumina, alu~ ina-zirconia, thoria, spinels, titania, urania, rare earth oxides, calcium-aluminates, sillimanite, ~ullite, magnesi~, zirconia, various silicates including cordierite, steatlte, petalite, spodumene, fosterite, clay, zircon, talc and porcelain, lo various nitrides including silicon nitride, silicon oxynitrides, and aluminum nitride, various carbides including silicon carbide, boron carbide, titanium carbide and zirconium carbide, various borides, various zirconates, various titanates, various glass-ceramics, and mixtures or 15 combinations of such materials.
The sinterable materials may also be selected from glass-ceramics or from sinterable ceramic and metal mixtures, e.g., chromium and alumina mixtures, to form cermets. Also suitable are sinterable metal powders, e.g., 20 powders of Fe, Al, Cu, Ti, Zr, Ni, Cr, ~tainless steel, various other alloys and ~ixtures or combinations thereof.
Additional examples of metal powders which can be sintered to form a sintered body are disclosed in U.S. 4,649,003.
The phases or layers of sinterable materials may 2s optionally contain reinforcing whiskers, e.g., of alumina, silicon nitride or silicon carbide, or fibers, e.g., carbon fibers, as disclosed in U.s. 3,794,707 and U.S. 4,673,658.
The sinterable particulate or powdered ceramic, glass or glass-ceramic materials used in this invention may 30 also optionally contain substantial amounts of a component which causes intracrystalline and intercrystalline microcracking to occur. Ceramic materials which contain such a component, and are therefore contemplated for use within the present invention, are disclosed in U.S. Patents i 3,528,831, 3,549,400 and 3,578,471, all issued to I. M.
Lachman. A preferred ~icrocracking agent or addition to the ceramic material i- alu~inum titanate, which i8 normally incorporated into a ceramic matrix as ~ ~solid 5 solution~ with the basic ceramic material. An aluminum titanate solid solution with mullite is disclosed in U.S.
Patent 4,483,944 to Day et al.
The choice of materials from which the articles of this invention will be ~ade is not necessarily critical, 10 and the above-mentioned materials are recited solely for purposes of exemplification. As has been previously noted, it is preferred that the ~aterials of the different laminated phases have differing thermal expansion and f iring shrinkage properties to enhance microcracking .
15 Naturally, it is also preferred that the sinterable materials of the layers not be reactive with one another to a degree 80 as to diminish the integrity of the discrete layers in the article.
The choice of materials will also, of course, 20 depend upon the intended application of the article. For example, the chemical resistance of the materials is a concern when the ultimate articles are intended for use in certain chemical processing application, e.g., silicon-based materials might be avoided in chemical processes 25 utilizing reducing gases.
The sinterable 2aterials of which each layer in the article is formed are separately formed into moldable bodies by mixing the constituent materials with an additional substance that binds those materials into a 30 plasticized mass. This plasticizing/binding agent, can be any of the well-known materials commonly used in the ceramic art for such purposes. Suitable plasticizing/binding agents are disclosed in:
~ Ceramics Processing Before Firing, ~ ed. by - 8 - 1 ~32 4 99 George Y. Onoda, Jr. ~ L. L. ~ench, John Wiley ~ Son~, NeY York ~Study of Sever~l Groups of organic Binders Under Low-Pres~ure Extrusion,' C.C. Treischel ~ E.
W. Emrich, Jour. Aw. Cer. Soc., (29~, pp.
129-132, 1946 rganic (Temporary) Binders for Ceramic Systems,~ S. Levine, Cera ic Age, (75) No.
1, pp. 39+, January 1960 ~Temporary Organic Binders for Ceramic Systems,' S. Levine, Cera~ic Age, (75) No. 2, pp. 25+, February 1960 Preferred agents are methyl cellulose, polyvinyl alcohol or a silicone resin. The silicone resins preferred for use are described in U.S . Patent 3, ogo, 691 to Weyer.
The most preferred binder is methyl cellulose, available as Methocel K75 from the Dow Chemical Company.
The sinterable particulate or powdered materials are separately mixed with ~ufficient plasticizing/binding agent to form a moldable mass. Generally, about 1-20 percent by weight, based on the sinterable particulate or powdered material weight, of the plasticizing/binding agent is used. Up to about 1 percent by weight, based upon the total body weight, of surfactant or lubricant such as sodium stearate can also be used to facilitate mixing and extruding. The mixing 6tep can be performed wet or dry.
Intensive mixing such as obtained with a Littleford mixer is preferred, but other conventional mixing e~uipment can also be used. At some point in the fabrication process, usually after dry mixing, a liquid, preferably water, is added, which acts as a plasticizer. When the plasticizing/binding agent is a silicone resin, it is preferred to use isopropyl alcohol or equivalent solvent, in addition to water. Plasticizing is attained with the use of a mix muller or other commonly used shearing device.
The plasticized masses of sinterable particulate or powdered material are molded or formed into multiple ~, . . - , 1~32~99 discrete bodies such as rods, discs, spheres, cylinders, pellets, bars, ribbons or sheets. This is generally done by extrusion methods, but other methods such as tape casting, pressing, pug milling, slip casting and slurry 5 filterlng may also be used. See, e.g., Thompson, J.J., ~forming Thin Ceramics,' Ceramic Bulletin, Vol. 42, ~o. 9, page 480 (1963~; and U.S. Patents 2,966,719, 3,007,222 and 3,444,925. Such bodies of the first sinterable material (~first~ bodies) are then intermingled with bodies of the 10 second sinterable material (~second~ bodies) to form an assembly suitable for coextrusion through a die to form a composite laminated article of the desired shape. The first and second bodies of sinterable material should be substantially uniformly distributed throughout the assembly 15 and composite article. Generally it is useful that the ratio of either of said bodies to the other will not exceed about 10:1 and more desirably 3:1. Preferably, the ratio of either of said bodies to the other will not exceed about 1.2:1, and, more preferably, the ratio of either of said 20 bodies to the other is about 1:1. It is preferred that the size and shape of the first and second bodies of sinterable material be about the ~ame.
The composite article 50 formed can be of any size or shape 80 long as the first and second bodies of 25 sinterable material are ~ubstantially uniformly distributed throughout and are present therein in distinct phases and so long as the composite article can be extruded, if desired, through a die to form the article in its final desired shape. It is also to be understood that the manner 30 of forming the composite article can be of any means by which these criteria are substantially met. For example, the first and second bodies of ~interable material can be molded together into a composite article in the shape of a sausage, sphere, bar or disc which is then extruded into 35 the final monolith shape. Figure 2c illustrates a bar and a disc of first and second bodies of sinterable material, 1 A'l - lo - 1332~99 and 2, re6pectively. It i~ ~180 possible, and preferred, to intermingle the bodies directly in the inlet barrel of the extruder, thus forming an assembly vhich can be immediately extruded thereafter, as shown ln Figure 2a.
Figures 2d and 2e illu~trate how different geometrical assemblies can be oriented in the extruder barrel. Figure 2d shows how rods, spheres or slugs of first and second sinterable materials, 1 and 2, could be assembled, e.g. by axially stacking in adjacent columns, in the extruder barrel 3 80 that, after extrusion, a laminated composite article results. Figure 2e shows how discs or sheets 1 and 2 can be layered in the barrel 3 of an extruder so that the plane of the disc is perpendicular to the axis of the extruder. This method of axially stacking will produce a type of laminated extrusion, especially if thin layers are used.
In a preferred embodiment of the present invention, the plasticized masses of first and second sinterable materials are separately extruded through a die into elongated shapes, preferably of rectangular, hexagonal or circular cross-section. Preferably, the shapes and dimensions thereof are the same for each sinterable material. Also preferably, the plasticized sinterable materials are extruded as ribbons approximately 4mm thick 2 5 by 3 2 mm wide .
The extruded composite bodies are then assembled by intermingling the molded components axially or longitudinally. Most preferably, this will be done 80 that the ribbons are substantially parallel. The extruded bodies are positioned to be substantially uniformly distributed throughout the assembly. As an example, Figure 2a depicts the cross-section of an assembly of ribbons of the two phases of materials assembled longitudinally in the barrel, 3, of an extruder. First and second bodies of sinterable material, 1 and 2, respectively, are uniformly distributed through the assembly.

3 2 ~
The composlte 80 assembled i8 then itself preferably extruded through ~I rod die one or more times to reduce it~ own cross-sectional area ~nd to ef fect further distribution of the two phases therein. A typical 5 distribution of the co~nposite bodies in a die head or extruder barrel 3 prior to reextrusion is illustrated in Figure 2b. The distribution of the phases in the extruded article, e.g., the relative thicknesses of the layers, can be controlled not only by the number of extrusions lo performed but also on the initial size of the first and second bodies used to form the composite. It is convenient that extrusion be performed in a die that reduce~ the size of the cross-sectional area of the composite itself to that similar to one of the original constituent ribbons.
Ultimately, the composite is extruded through a die to form the desired shape of the final article. In one embodiment of the invention, the article so extruded is a honeycomb body or multichannel monolith having substantially parallel cells or passages extending between 20 open end faces thereof. 5ypical honeycomb monoliths, for example, have 400 sguare cells per sguare inch with a wall thickness of 7 mils, or as another example, have 200 sguare cells per sguare inch with a wall thickness of 20 mils.
Figure 3 shows an enlarged portion of a honeycomb monolith 25 formed by the extrusion of a composite a8 described above.
L~yers lb of a first sinterable material are interspersed with layers 2b of a second sinterable material, and both such layers are substantially uniformly distributed throughout the article and both are substantially 30 discontinuous. This is in contrast to the extruded monolithic catalyst supports prepared by extrusion and disclosed in U.S. 4,631,268. The articles disclosed therein were prepared by extrusion methods similar to those described above: however, the extrusion was carried out so 35 that, rather than forming laminated phases or layers, one of the sinterable materials, the catalyst-support phase, was embedded in th- second sinterable material, ~ c-ramic which formed ~ sub~t~ntially continuou~ matrix pha6~.
Although the above description was limited to the preparation of ~n ~rticle having discrete phases of two 5 sinterable material~, this invention i8 not intended to be so limited. Three or more sinterable materials may be combined using the general methods outlined above to form extruded laminated bodies according to this invention. In all cases, it is preferred that the varieties of sinterable 10 materials be substantially uniformly distributed throughout the final article.
The extruded shapes are then heated to a teDperature and for a ti~e sufficient to sinter the particulate or powdered naterials. Optionally, this 15 heating/sintering step is preceded by drying the shapes at about 100- - 120-C. It is then preferred to burn out the temporary binders in the range of 250- - 500-C. The heating/sintering step generally takes place above 800-C, although when silicone resin i8 used as ~I binder for the 20 ceramic matrix, temperatures as low as 500-C may be sufficient. The maximum firing temperature is limited by the melting points of the constituents in the compositions.
Aspects of this invention are illustrated, but not limited by, the following examples. In these examples, 25 test results were obtained using the following:
Flexural Strenqth - ASI'M Test No. C-158-84 Thermal ~xpansion - ASTM Test No. E831-81 Modulus of Elasticity - ASTM Test No. C326-82 Bulk Density - Volume computed from measurements of the physical dimensions of a bar and weighed dry for final computation of the bulk density.
Example Five laminated extruded articles were made according to this invention using the materials as set forth in Table 1. In each example, equal amounts of components A and B were used to prepare the extruded articles .

- 13 - 1332~99 ~able 1 Example Comwnent A Co~ponent B
62 . 9% alumina 96 . 0% alumina 37.1% calcium 2.7% mangane6e carbonate 1. 3% titania 2 100% alumina~ 77 . 0% alumina 19 . 0% zirconia 2 . 7% manganese carbonate 1. 3% titania 3 50. 0% alumina 96. 0% alumina 40. 0% calcined clay 2 . 7% manganese 10/0% kaolin clay carbonate 1. 8% titania 450 . 0% alumina 87 . 0% alumina 40.0% calcined clay 9.0% zirconia 10 . 0% kaolin clay 2 . 7% manganese carbonate 1. 3% titania 255 50.0% alumina 77.0% alumina 40.0% calcined clay 19.0% zirconia 10.0% lcaolin clay 2.7% manganese carbonate 1. 3% titania ~Alcoa T-61 -325 mesh; all other aluminas Alcan C-701 RGE
TM
Baker reagent calcium carbonate 111294 Fishe~nanganese carbonate M-85 35 BakerT~eagent titania ~4162 Zircoa A-grain zirconia Georgia-Kaolin Glomax-LL $~alcined kaolin clay Georgia-Raolin Hydrite-MP lcaolin clay In each example, the dry powders were mixed in a Model M5G Littleford dry blender for three minutes. The Model MSG is a plow oriented blender which thoroughly mixes the powders without chanqing particle size or increasing batch temperature due to friction. Methylcellulose (Dow K75, 4% in Examples 1 and 2, 6% in Examples 3, 4 and 5), a temporary binder, and, in Examples 1 and 2, 1% sodium stearate lubricant were ~ixed with the other dry materials.
All compositions were wet mulled using a Lancaster counter current batch mixer type PC. Water was . .~

1332~9 introduced durlng this process and all batches were mulled between 15 to 20 mlnutes for good plasticity and homogeneity of the materlal-. After mulling, the batch consistency had an appearance of crumbs to ~mall, flat chunks that were somewhat soft and plastic.
Extrusion of the amples were conducted on a 20 ton Wahlco extrusion press with a barrel diameter of 2.626 and maximum hydraulic pre6sure of 2500 psi. The fabrication process was a multi-step procedure. It involved extruding two separate compositions in the form o~
ribbon 4 mm thick by 32 mm wide (0.157~ x 1.25~). This ribbon was then alternately stacked in the barrel of the extruder and pushed into an intermediate shape of a 5 . 2 mm rod ( . 205~ diameter) . With a successive extrusion, the laminations could be reduced to a desired thickness.
Shapes extruded for this study included 8 mm rods for firinq shrinkage, flexural strength, axial thermal expansion, mercury porosity and Hasselman thermal shock testing: 5 mm x 15 mm bars for modulus of elasticity measurements; 1~ diameter, 400 cells/in2 honeycomb for laboratory thermal shoclc testing and evaluation.
All samples were dried in a steam-like atmosphere at lOO'C for three days and then fired in a Bickley gas-air furnace at the various deeignated temperatures.
Testinq of Exa~pl,es 1 and 2 Physical property results for shrinkage, strength and thermal expansion for each component of the laminated articles of Examples 1 and 2 and for the laminated articles themselves are presented in Table 2.

Table 2 Firing Flexur~l mermal Temp. C 6hrs. % Shri lk str. .Dsi EXD.
Exampl- 1 1500 -4 . 4 1770 62 . 4 1600 -2.5 1810 64.6 1650 -1. 7 2600 64 . 6 10Component A1500 4.5 5020 55.8 1650 16. 1 22 . 6**
15Component 1600 17. 1 19700 1650 17 . 2 15300 80 20Example 2 1400 1500 11.9 11300 80.5 1600 12.3 6050 81.0 1650 12 . 5 7000 80 . 5 2 5 Component A 1400 1. 6 3400 1500 4 . 2 8000 1600 6 . 4 10000 80 3 0 Component B 1400 15.7 15200 81.4 1500 17 . 1 6200 79 . 4 1600 16.9 4300 80.0 1650 16. 7 3600 78 . 1 * in./in./C, (25C-1000C) ~*Sample ~ 1650-C began to ~elt.
me data in Table 2 indicate that, in the case of 40 the calcium-aluminate laminated composition, Example 1, the firing shrinkage is actually an expansion (+2.5% ~1600-C), resulting in very low 6trengths (1800 psi ~ 1600-C).
Example 2, the extruded laminated composition with alumina and zirconia, has higher strengths (6000 psi ~ 1600-C) but 45 also higher axial thermal expansion (81.0 x 10-7 ~ 1600-C).
me samples of Example 1 and 2 were also tested for thermal shock resistance using the Hasselman test.
Samples previously fired at 1600-C for six hours were chosen for the test. The dimensions of the test samples were 1/4~ diameter Y 4~ long, and th-y were tested o~er a range Or quench temperatures, 200-C to lOOO-C, at 100-increments. Pour rods were used at each guench temperature with a new set of rods being used at each 6ucceeding 5 te~perature. Samples wer- held at temperature for fifteen minutes and then guenched in cold water. Tested rods were then dried and submitted for room temperature modulus of rupture. The strength results for the thermal shock tested 6amples are shown in Figure 4. As these data indicate, the 10 material of Example 2 has good thermal shock resistance because of its rather stable crack propagation. The material of Example 1 is much weaker and displays signs of being less stable.
Testinq of Exam~les 3. 4 and 5 Physical property results for shrinkage, strength and thermal expansion for each component of the laminated articles of Examples 3, 4 and 5 and for the laminated articles themselves are presented in Table 3.

Table 3 Firing Flexural Thermal T~C 6hrs . % Shrink Str . . psi Exp . *

Example 3 1400 4.8 69~0 73.4 1500 9 . 6 8100 68 . 2 1600 15 . 0 15000 63 . 9 1650 15.4 16733 70.0 Component A 1400 S . 0 6890 59 . 5 1500 3 . 7 5530 49 . 2 1600 6. 3 7670 46 . 3 1650 10. 2 11000 46 . 3 Component B 1600 17.1 19700 1650 17 . 2 15300 80 Example 4 1400 4 . 9 7210 69 . 6 1500 10. 8 12100 67 . 8 1600 14 . 5 18600 64 . 5 1650 14 . 5 17350 62 . 0 Component A**
Component B 1600 17. 4 4560 1650 16 . 7 2800 80 35Example 5 1400 4.7 8660 69.7 1500 10 . 6 14800 60 . 7 1600 13 . 7 27400 64 . 3 1650 14 . 0 22900 65 . 5 4 0 Component A**
Component B 1400 15.7 15200 81.4 1500 17 . 1 6170 79 . 4 1600 16.9 4250 80.0 1650 16.4 3640 78.1 *in./in./-C, (25-C-lOOO-C) 50 **Same as component A in Example 3.
Axial thermal expansion was in the range of 60 -70 x 10-7 ~ lOOO-C for all the compositions of all three examples. The laminated layers of the mullite extruded laminated series of Exa~ ples 3 - 5 fired At both 1500-C and 1650-C are very distinctive ln photomicrographs of the articles .
~As fired~ (~ 1600-C) modulus of rupture measurements were performed for the articles of Examples 3 - 5. The results are presented in Table 4 and indicate that strength~ increase ~ith the increasing percent of zirconia .
lo Table 4 Example Room Temp. MOR. psi % ZrO2 Modulus of elasticity measurements were conducted on fired bars (.110~ thick x .475~ wide x 5.0~ long) for the compositions of Exampleg 2 - 5, the composition of 20 Example 1 being too weak to test. The results, in Table 5, show rather low values indicating that microcracking has occurred. It is estimated that the examples in Table 5 would have room temperature modulus of elasticity values of 40x 106 psi or more if there were no microcracXing. The 25 results also indicate that for the mullite-alumina series (Examples 3-5) a gradual decrease in modulus of elasticity occurred as the amount of zirconia increased, vith a much lower reading for the alumina laminated sample. It is believed that increasing zirconia content would increase 30 microcracking, thereby lowering the modulus of elasticity.
Table 5 Exammle Modulus of ElasticitY. psi Bulk Densitv. c~/cm3 211.81 3.661 326.26 3.018 423 . 62 3 . 112 522 . 95 3 . 103 1332~99 The Hasselman the~al shock test was conducted on the laminated extruded rods of E~xamples 3 - S which had been fired at both 1500-C and 1650-C for 6 hours. The 5 re6ult~ are graphically lllustrated in Figures 5, 6 and 7 and make apparent the differences between th~ 1500-C and 1650-C firings. Good strength remains at the lower end of the test quench temperature (200-400-C) and then a general decrease in strength with increasing quench temperature.
10 Although the strength decrease is substantial over the whole range of the Hasselman thermal shock test, the results appear to indicate stable rather than catastrophic crack propagation.

Claims

1. A high strength article comprising a sintered extruded laminated body of a coextruded composite having multiple, discrete, substantially discontinuous, interspersed layers of at least a first and second sintered material, where said first and second sintered materials are different and are selected from high strength sintered particulate or powdered materials and wherein said layers of each of said first and second sinterable materials are substantially uniformly distributed throughout the body, the ratio of either of said first or second sintered materials to the other being no greater than about 1.2:1.

2. An article of Claim 1 wherein the ratio of either of said first or second sintered materials to the other is about 1:1.

3. An article of Claim 1 wherein said first or second sintered materials are independently selected from the group consisting of ceramics, glass-ceramics, glasses, cermets, metals, and mixtures and combinations thereof.

4. An article of Claim 3 wherein said first and second sintered materials have different firing shrinkages.

5. A sinterable article which comprises an extruded laminated body of a coextruded composite having multiple, discrete, substantially discontinuous interspersed layers of at least a first and second sinterable material, where said first and second sinterable materials are different and are selected from particulate or powdered materials capable of being sintered to form high strength materials and wherein said phases are substantially uniformly distributed through said body, the ratio of either of said first or second sintered materials to the other being no greater than about 1.2:1.

6. An article of Claim 5 wherein the ratio of either of said first or second sintered materials to the other is about 1:1.

7. An article of Claim 4 wherein said first or second sintered materials are independently selected from the group consisting of ceramics, glass-ceramics, glasses, cermets, metals, and mixtures and combinations thereof.

8. An article of Claim 7 wherein said first and second sintered materials have different firing shrinkages.

9. A method of producing a sinterable extruded laminated article comprising (a) providing first multiple bodies comprising a mixture of a first sinterable material and a plasticizing/bonding agent for said material;
(b) providing second multiple bodies comprising a mixture of a second sinterable material and a plasticizing/bonding agent for said material, where said first and second sinterable materials are different and are selected from particulate or powdered materials capable of being sintered to form high strength materials;
(c) intermingling said first and second multiple bodies to form an assembled body in such a manner that, after coextrusion of said assembled body to produce said sinterable extruded laminated article, said first and second sinterable materials are present in said article in multiple, discrete, substantially discontinuous interspersed layers which are substantially uniformly distributed throughout said article;
(d) passing said assembled body for coextrusion through a die to form said sinterable extruded laminated composite article in a desired shape having said layers.

10. The method of Claim 9 wherein the ratio of either of said first or second sinterable materials to the other is no greater than about 1.2:1.

11. The method of Claim 10 wherein the ratio of either of said first or second sintered materials to the other is about 1:1.

12. The method of Claim 9 wherein said first or second sinterable materials are independently selected from the group consisting of ceramics, glass-ceramics, glasses, cermets, metals, and mixtures and combinations thereof.

13. The method of Claim 12 wherein said first and second sinterable materials have different firing shrinkages.

14. The method of Claim 9 where a plurality of said sinterable extruded laminated composite articles are intermingled and reextruded by being passed through a die to form a second sinterable extruded laminated composite article in a desired shape.

15. The method of Claim 14 where said reextrusion step is repeated.

16. The method of Claim 9 where said sinterable extruded laminated article is fired to a high strength article.

17. The method of Claim 10 where said sinterable extruded laminated article is fired to a high strength article.

18. The method of Claim 11 where said sinterable extruded laminated article is fired to a high strength article.

19. The method of Claim 12 where said sinterable extruded laminated article is fired to a high strength article.

20. The method of Claim 13 where said sinterable extruded laminated article is fired to a high strength article.

21. The method of Claim 14 where said sinterable extruded laminated article is fired to a high strength article.

22. The method of Claim 15 where said sinterable extruded laminated composite article is fired to a high strength article.

23. A method of producing a high strength extruded laminated composite article comprising heating a sinterable extruded laminated composite article of Claim 9 to sinter the particulate or powdered materials therein.

24. A method of producing a high strength extruded laminated composite article comprising heating a sinterable extruded laminated composite article of Claim 11 to sinter the particulate or powdered materials therein.

25. A method of producing a high strength extruded laminated composite article comprising heating a sinterable extruded laminated composite article of Claim 13 to sinter the particulate or powdered materials therein.