Abstract:
A composite material having solid ingredients of finely divided ceramic powders and about 5 to 25% by weight (10 to 42 by volume) of finely divided powdered polymer such as an epoxy resin. Shaped articles can be formed using standard ceramic formulation practices while providing the advantage of very low temperature firing to fuse the articles into high strength solids.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to compositions which are used to produce high-strength ceramic/polymer composite shaped articles and to methods of producing shaped articles from those compositions. 
     Prior workers have devised procedures for making shaped articles from ceramic and polymer powders. For instance, clay compositions have been mixed with thermosetting resins such as phenolic and thermoplastic resins such as polyethylene and formed into shapes by conventional ceramic forming techniques such as slip casting and throwing on a potter&#39;s wheel. However, the strength properties of these articles have left much to be desired. 
     The present invention relates to a composition comprising about 15 to 35 wt.% (25 to 55 vol.%) aqueous phase and 65 to 85 wt.% (45 to 75 vol.%) solids, wherein the solids comprise about 5 to 25 wt.% (10 to 42 vol.%) on solids basis of finely divided epoxy resin powder and about 75 to 95 wt.% (58 to 90 vol.%) of finely divided ceramic powder. Using standard ceramic formulation practices for the above composition range, shaped articles can be made from slip and modeling clay. In any of these processes, the water remaining after the forming operation is allowed to evaporate through drying and the articles are permanently hardened by firing at low temperatures, for example, 150°-200° C. High strength articles are obtained by all forming processes. Of particular importance is that the compositions of the present invention may be made into a slip or modeling clay and the working and forming characteristics are equivalent to polymer-free ceramic compositions which are fired at high temperatures to obtain high strengths. Nor are the compositions limited to the above forming processes. For example, extruded shapes can be formed by forcing material, which contains about 15% moisture, through a die. 
     J. D. Sullivan and C. R. Austin, U.S. Pat. No. 2,288,047, issued June 30, 1942, describes slip cast ceramic bodies containing a major portion of plastic clay and 1 to 20 weight percent of a thermoset or thermoplastic resin, preferably 5 to 20 weight percent. The patentees indicate that equal flexural strengths can be obtained by using either a thermoplastic or thermosetting resin. 
     D. W. Dill, U.S. Pat. No. 3,817,897, issued June 18, 1974, describes a moist modeling clay composition consisting of water and a mixture of 75% to 90% by weight, based on dry ingredients, of a pottery clay and from 10% to 25% by weight of a powdered polymer selected from a group of high and low density polyethylenes, polypropylene, and ethylene vinyl acetate copolymer. 
     SUMMARY OF THE INVENTION 
     The present invention relates to compositions and processes for making the compositions into shaped articles which can be hardened at low temperatures, 150° to 200° C., to give excellent physical and mechanical properties resembling high-temperature fired ceramics in many ways. 
     The present invention provides new composite material compositions comprising, on a dry basis, an intimate mixture of finely divided ceramic and resin powders. 
     This invention also provides casting slip and modeling clay compositions which have excellent working properties and are capable of being fired at temperatures available in household kitchen ovens. These fired objects possess high strength, high impact resistance, and unusually high resistance to attack by moisture when cycled in a dishwasher or when immersed in boiling water. 
     The rigid ceramic/resin composite wares can be coated with air dried or low fired glazes or stains (aqueous and nonaqueous). The coatings exhibit a high degree of adherence and permanency. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The compositions of this invention comprise finely divided ceramic powders and a finely divided, powdered, low-melt viscosity, epoxy resin system comprising: 
     (a) Epoxy resins which are well known and are noted generally to consist of the reaction products if bisphenol-A and epichlorohydrin, the reaction being carried out under alkaline conditions. In general, epoxy resins having a Durrans&#39; mercury method melting point in the range of 60° to 135° C., and an epoxide equivalent weight between about 450 and 2500 are useful in the present invention. Examples of typical epoxy resins are those available from Celanese Corporation as &#34;Epi-Rez&#34; 522-C and from Shell Chemical Company under the designation &#34;Epon 1001,&#34; &#34;Epon 1002,&#34; &#34;Epon 1004&#34; and &#34;Epon 1007.&#34; The primary difference among these &#34;Epon&#34; resins is that melting point and epoxide equivalent weight increases as the identifying number increases. Thus, &#34;Epon 1001&#34; has an epoxy equivalent weight of 450-550. It has a Durrans&#39; mercury method melting point of 65°-75° C. &#34;Epon 1002&#34; has an epoxide equivalent weight of 600-700 and a Durrans&#39; mercury method melting range of 75°-85° C. &#34;Epon 1004&#34; has an epoxide equivalent weight of 875-1025 and a Durrans&#39; mercury method melting point of 95°-105° C. These epoxy resins, sometimes considered resinous polyethers, have more than one 1,2-epoxy group ##STR1## per average molecular weight of resin. Analogous results of this invention may be obtained with other normally-solid epoxy resins as produced by the reaction of epichlorohydrin or equivalent 1,2-epoxy compound with polyhydric phenols or other polyhydric compounds such as polyhydric alcohols. Also, epoxy resins may be produced by epoxidizing double bonds of unsaturated hydrocarbons, as is well known. In all cases, the epoxy resin has, on the average, more than one 1,2-epoxy linkage or oxirane oxygen group per molecule. Reference is also made to Lee and Neville, Handbook of Epoxy Resins, McGraw Hill Book Company, 1967, pages 4-59 to 4-69, for other epoxy resins having the abovenoted characteristics. 
     (b) Solid latent curing agent for epoxy resins which are unaffected by aqueous systems and are sufficiently active as a curing agent to cure the epoxy resin in the temperature range of 150° C. to 200° C. They should be stable in an aqueous media over long periods of time after the composite material composition has been prepared into a slip or modeling clay. Typical of these are nonpolymeric amides such as dicyandiamide and amine epoxy adducts. The amount required to cure the epoxide resin is about 0.75 to 1.5 active hydrogen equivalent weight per epoxide equivalent weight of the epoxide resin. 
     The epoxy resin system may also contain a latent catalyst for accelerating reaction between the epoxy resin and curing agent and which is unaffected by aqueous systems such as a tertiary amine (up to about 1 weight percent). 
     The components of the above resin system are homogeneously mixed into a one-part system by various mixing procedures such as a two-roll rubber mill, one roll of which is heated by steam to about 45° C. while the other is maintained at ambient temperatures. The mixing time is about 10 to 20 minutes after which the homogeneous mixture is sheeted off, allowed to cool to room temperature, and ground to a fine powder which is sieved through U.S. No. 80 mesh screen (177 micron particles). The mixing procedure employed is nothing more than a superficial fusing together of the solid particles into a one-part system. Other mixing procedures such as extrusion or dry blending can be employed. 
     The ceramic powders utilized in the present invention are finely divided and generally range in particle size from 0.6 micron to 177 microns (U.S. 80 mesh). 
     The ceramic powder-epoxy resin system can be shaped into any desired configuration using standard ceramic processing methods because the resin system is present in the ceramic-epoxy resin system as discrete particles which do not interfere with the working characteristics of the ceramic powder. For example, the slip compositions can be slip cast and fired in a home oven which provides a means for an amateur to produce ceramic-like articles such as vases, flower pots, etc. Such articles have high strength, high impact resistance, and unusually high resistance to attack by water when cycled in a dishwasher. Tests have shown that impact resistance of such articles is about 30% greater than similar articles made of clay/talc hobby ceramic slips fired at about 1000° C. Articles made of compositions of this invention and coated with commercially available nonfire glazes have excellent resistance to moisture attacks. For example, these coated articles can be cycled for several times in a dishwasher before the coating begins to spall off. Articles made of high fire ceramics, when coated and tested under similar conditions, begin losing their coating during the first cycle. 
     The epoxy resin powder in Examples 1-13 included 100 parts of diglycidyl ether of bisphenol-A having an epoxide equivalent weight range of 550-650 and a Durrans&#39; melting point of 75°-85° C. (Epi-Rez 522-C of Celanese Corporation), 5 parts of dicyandiamide, and 0.29 parts of DMP-30tertiary amine. These components were homogeneously mixed into a one-part system using a two-roll rubber mill, one roll of which was heated by steam to about 45° C. while the other was maintained at ambient temperature. The mixing time was 10 minutes after which the mixture was sheeted off, allowed to cool to room temperature, and ground to a fine powder which was sieved through No. 80 mesh screen (U.S.) having 180 micrometer openings. This material was then mixed with 0.25 parts of colloidal silica (CAB-O-SIL) to form a homogeneous free-flowing powder. 
    
    
     The following specific examples are intended to illustrate more clearly the nature of the present invention. 
     EXAMPLE 1 
     Slip Preparation 
     The following dry components are made into a slip in the manner described hereinbelow. 
     
         ______________________________________     Average Particle                Specific PercentComponent   Size (Microns)                    Gravity  Wt.  Vol.______________________________________Kentucky Ball Clay #4     0.6         2.50     41.3 41.0Steawhite 200 Talc        7.0         2.75     45.4 41.0Columbia-325 Mesh Supersil Silica        11.0        2.65     8.3  7.7Epoxy Resin Powder        (1)         1.2      5.0  10.3                             100.0                                  100.0______________________________________ (1) 100% finer than 177 microns (U.S 80 mesh) 60-75% finer than 44 micron (U.S. 325 mesh) 
    
     1785 g. of tap water is intimately mixed for 20 minutes with 2.17 g. of sodium carbonate and 9.45 g. of sodium silicate solution N brand (8.9 weight percent Na 2  O; 28.7 weight percent SiO 2  ; 62.4 weight percent water) in a 1-gallon stainless steel beaker in which is immersed a jiffy stirrer attached to an air motor which operates at about 700 rpm. 1446 g. of Kentucky Ball Clay #4 is slowly added to the aforementioned aqueous solution. 1590 g. of talc Steawhite 200 is slowly added followed by the addition of a preblended mixture of 289 g. of silica Supersil and 175 g. of epoxy powder. Total mixing time to this point is one hour. Running of the jiffy stirrer is continued for two hours to achieve thorough mixing. When the mixing is finished, the slip is poured into a 1-gallon plastic container which is then sealed and allowed to age at least 24 hours before testing and forming shaped bodies by slip casting with Plaster of Paris molds. 
     Slip Casting 
     1. Fifty bars are cast by pouring slip into two-part Plaster of Paris molds containing cavities measuring about 0.635 × 1.27 × 6.35 cm. The casting time is 45 minutes. The rubber bands are removed and molds opened. The bars remain in the mold cavities for 5 minutes before removal. Mold release property is noted and recorded. 
     2. Tiles are cast by pouring slip into a two-part Plaster of Paris mold containing cavities measuring about 10 × 10 × 0.635 cm. The casting time is 45 minutes. The top plate containing slip pouring holes is removed and tiles remain in the mold cavities for 5 minutes before removal. Mold release property is noted and recorded. Wet weights and the dimensions are recorded. The tiles are air-dried for at least 48 hours before obtaining dry weights and dimensions. 
     3. A vase is cast by pouring slip into a two-part Plaster of Paris mold. The casting time is 15 minutes; the mold is then drained by inverting it to pour out the slip remaining in the mold. The drainage time is 5 minutes. The rubber band is removed and mold opened. The vase remains in the mold cavity for about 5 minutes before removal. Mold release property is noted and recorded. Wet weight is recorded and after at least 48 hours the dry weight and wall thickness is recorded. 
     Firing 
     Fifty bars are air dried at least 48 hours before firing in a Blue M Electric Co. (Blue Island, Ill.) air circulating oven (Model No. POM-880G-IX-Temp. 704° C. maximum). 
     The dried bars are divided into five groups, ten bars each, in which each group is placed on setters and fired at the conditions described below: 
     
         ______________________________________Group                    Firing ConditionNumber                   Preheat   Soak______________________________________1       Refractory setter plate                    100° C.                              150° C.   (1.6 × 12.7 × 30.5 cm.)                    1 hour    1 hour   covered with a layer of   alumina setter sand2       &#34;                100° C.                              175° C.                    1 hour    1 hour3       &#34;                100° C.                              200° C.                    1 hour    1 hour4       &#34;                100° C.                              175° C.                    1 hour    16 hours5       Tin-coated steel 100° C.                              175° C.   (14.3 × 20.3 × .03 cm.)                    1 hour    5 hours______________________________________ 
    
     The tiles are divided into two groups, three tiles each. One group is fired at the condition described for Group No. 2, above, and the other group is fired on a tin-coated steel sheet at the same preheat and soak conditions described for Group No. 2, above. 
     Testing 
     The following tests were conducted: 
     1. Slip Tests 
     A. The density measurements are made by carefully weighing 250 cc. of slip, recording the weight, and calculating the density. 
     B. Viscosity is determined by utilizing a Brookfield viscometer (LVT model with helipath stand at 12 rpm). 
     C. pH is determined by utilizing a Corning digital 109 general purpose pH meter. 
     2. Casting Tests 
     A. The water of plasticity is calculated as a percentage of the weight of the dry shapes by the following formula: ##EQU1## in which T = Percent water of plasticity 
     Wp = Weight of the plastic piece 
     Wd = Weight of the dry piece 
     B. Shrinkage of the tile is calculated by: ##EQU2## 
     3. Firing Tests 
     A. Bulk density -- Bars are weighed and measured and bulk densities calculated. 
     B. Shrinkage -- The tiles are measured and percentage linear shrinkage calculated according to the following formula: ##EQU3## The average of the values is reported. 
     C. Flexural Strength -- The bars are broken on an Instron Compression Tester equipped with a suitable sample holder with knife edges 0.6 cm. radius and 2.5 cm. apart. The machine operates with a 453.6 kg. load cell and at a crosshead speed of 0.5 cm. per minute. The break load at which the specimen fails is recorded and thickness and width of each bar at the break is measured. The flexural strength is calculated by: 
     
         Flexural Strength = 3PL/2bd.sup.2 
    
     where 
     P = the breaking load 
     L = the distance between knife edges 
     b = width of bar 
     d = depth of bar 
     The average results for each group of bars fired under conditions previously described are reported. 
     4. Test results of the example are shown below: 
     
         ______________________________________Test                  Results______________________________________SLIPDensity --g/cc        1.64Viscosity --cps       1930pH                    7.3CASTINGRelease from moldsBars                  ExcellentTiles                 ExcellentVases                 ExcellentDrainageVases                 ExcellentCasting RateVases(wall thickness) 3.2 ammWater of Plasticity (%)Tiles                 26.0Vases                 28.4Shrinkage of Tile (%)Cast                  1.8Dry                   5.0Total                 6.8FIRINGBulk density -- g/cc  1.75Shrinkage -- %        .27Flexural strength --Newtons/mm.sup.2Refractory Setter150° C. -- 1 hr.                 4.62175° C. -- 1 hr.                 4.83200° C. -- 1 hr.                 6.21175° C. -- 16 hrs.                 7.93Steel Setter175° C. -- 1 hr.                 --175° C. -- 5 hrs.                 9.31______________________________________ 
    
     EXAMPLES 2-7 
     In these examples, slip compositions with the indicated components were formulated according to the procedure of Example 1, and were also tested in the manner set forth in Example 1. 
     
         __________________________________________________________________________TEST RESULTS          EXAMPLEDESCRIPTION    2      3      4      5      6           7__________________________________________________________________________SLIPDensity -- g/cc          1.63   1.57   1.53   1.50   1.47        1.43Viscosity -- cps          1500   2100   1500   2450   1925        2300pH             7.5    7.5    7.5    7.8    7.9         8.0CASTINGRelease From Molds. Bars         Excellent                 Excellent                        Excellent                               Good   Fair        V. Poor. Tiles        &#34;      &#34;      &#34;      &#34;      Poor - cracked                                                  Did not cast. Vases        &#34;      &#34;      &#34;      &#34;      Poor - some cracking                                                  &#34;Drainage. Vases        Excellent                 Excellent                        Excellent                               Excellent                                      Excellent   --Casting Rate. Vases (wall thick, mm)          3.1 mm 3.0 mm 3.4 mm 3.9 mm 4.1 mm      --Water of Plasticity (%). Tiles        --     23.5   25.4   25.1   --          --. Vases        27.2   24.4   25.9   26.4   26.4        --Shrinkage of Tile (%). Cast         1.8    1.6    1.5    1.7    cracked     --. Dry          4.5    4.1    --     3.4    cracked     --Total          6.2    5.7    --     5.1    cracked     --FIRINGBulk Density -- g/cc          1.74   1.63   1.54   1.44   1.37        1.26Shrinkage -- % .10    .14    --     .16    --          --Flexural StrengthNewtons/mm.sup.2. Refractory Setter150° C. -- 1 hr.          --     18.3   --     26.0   23.1        24.3175° C. -- 1 hr.          --     20.5   --     28.3   25.5        25.5200° C. -- 1 hr.          --     24.1   --     29.7   27.4        --175° C. -- 16 hrs.          14.71  25.9   36.5   34.8   36.5        --. Steel Setter175° C. -- 1 hr.          10.2   --     31.4   cracked                                      cracked     --175° C. -- 5 hrs.          11.7   30.7   35.0   cracked                                      cracked     --__________________________________________________________________________DRY BATCH COMPOSITIONS -- PERCENT          EXAMPLES          2       3       4       5       6       7MATERIAL       WT. VOL.                  WT. VOL.                          WT. VOL.                                  WT. VOL.                                          WT. VOL.                                                  WT. VOL.__________________________________________________________________________CERAMICKentucky Ball Clay #4          40.7              39.6                  37.0                      33.0                          34.8                              29.5                                  32.6                                      26.4                                          30.4                                              23.6                                                  28.3                                                      21.0Talc Steawhite 200          44.7              39.7                  40.6                      33.0                          38.3                              29.5                                  35.9                                      26.4                                          33.5                                              23.6                                                  31.1                                                      21.0Silica Supersil          8.1 7.5 7.4 6.2 6.9 5.6 6.5 5.0 6.1 4.4 5.6 4.0          93.5              86.8                  85.0                      72.2                          80.0                              64.6                                  75.0                                      57.8                                          70.0                                              51.6                                                  65.0                                                      46.0PolymerEpoxy Powder   6.5 13.2                  15.0                      27.8                          20.0                              35.4                                  25.0                                      42.2                                          30.0                                              48.4                                                  35.0                                                      54.0TOTAL          100.0              100.0                  100.0                      100.0                          100.0                              100.0                                  100.0                                      100.0                                          100.0                                              100.0                                                  100.0                                                      100.0SLIP COMPOSITIONS -- PERCENT          EXAMPLES          2       3       4       5       6       7MATERIAL       Wt. VOL.                  WT. VOL.                          WT. VOL.                                  WT. VOL.                                          WT. VOL.                                                  WT. VOL.__________________________________________________________________________                                                      1CERAMICKentucky Ball Clay #4          26.86              17.6                  24.4                      15.4                          23.15                              14.3                                  21.7                                      13.1                                          20.26                                              11.9                                                  18.81                                                      10.9Talc Steawhite 200          29.55              17.6                  26.9                      15.4                          25.46                              14.3                                  28.87                                      13.1                                          22.28                                              11.9                                                  20.69                                                      10.9Silica Supersil          5.38              3.3 4.9 2.9 4.63                              2.7 4.34                                      2.5 4.95                                              2.3 3.77                                                      2.0          61.79              38.5                  56.2                      33.7                          53.24                              31.3                                  49.91                                      28.7                                          46.59                                              26.1                                                  43.27                                                      23.8POLYMEREpoxy Powder   4.30              5.9 9.9 13.0                          13.31                              17.1                                  16.64                                      20.9                                          19.97                                              24.6                                                  23.30                                                      28.0AQUEOUS SOLUTIONSodium Carbonate          .04     .04     .03     .03     .03     .03Sodium Silicate (N)          .17     .16     .15     .14     .13     .12Water          33.70   33.7    33.27   33.28   33.28   33.28          33.91              55.6                  33.90                      53.3                          33.45                              51.6                                  33.45                                      50.4                                          33.44                                              49.3                                                  33.43                                                      48.2          100.0              100.0                  100.0                      100.0                          100.0                              100.0                                  100.0                                      100.0                                          100.0                                              100.0                                                  100.0                                                      100.0__________________________________________________________________________ 
    
     EXAMPLE 8 
     This example illustrates a preferred slip composition formulated according to the procedure of Example 1, and also tested in the manner set forth in Example 1. 
     
         ______________________________________       Slip Composition       Parts by        Dry Batch         Weight-  Volume   Weight                                 VolumeMaterial      Grams    %        %     %______________________________________CeramicKentucky Ball Clay #4         1400     17.18    40    38.35Talc Steawhite 200         1540     17.19    44    38.39Silica Supersil         280      3.25     8     7.25PolymerEpoxy Powder  280      7.17     8     16.01Aqueous SolutionSodium Carbonate         2.10Sodium Silicate (N)         9.10Water         1785     55.21TOTAL         5296.2   100.00   100.00                                 100.00______________________________________ 
    
     A slip made from this example is aged for six weeks and tested in the manner set forth in Example 1. Test results are shown in comparison to the freshly prepared slip. 
     
         ______________________________________          Test ResultsTest             Fresh Slip  6-Week Age______________________________________SLIPDensity -- g/cc  1.63        1.63Viscosity        2200        2390pH               7.5         7.5CASTRelease from molds-bars, tiles            Excellent   ExcellentDrainage -- vases            Excellent   ExcellentCasting rateVases (wall thick., mm)            3.4         3.2Water of plasticity (%)Vases            27.6        Not measuredTiles            28.2Shrinkage of Tile (%)Cast             1.9         Not measuredDry              4.9Total            6.8FIRINGSteel Setter PlateBulk density -- g/cc            1.71        1.71Flexural strength175° C. -- 1 hr.Newtons/mm.sup.2 20          20175° C. -- 5 hrs.Newtons/mm.sup.2 Not measured                        23.4______________________________________ 
    
     One tile each of this Example which had been fired at 175° C. for one hour was coated with the following Duncan nonfired Bisq-Stain materials (Duncan Ceramic Products); (1) Black OS476; (2) lemon pale OS434; (3) holy red OS455; and (4) bright blue OS459. Commercial ceramic tile which had been fired at cone 06 (1023° C.) was coated with the same materials. After air drying for 24 hours, the tiles were placed in a laboratory dishwasher. Temperatures rose to about 85° C. within the washer and the water blast was vigorous. After one cycle, the coatings and tiles were observed. The coatings applied to the tile of this Example showed no evidence of spalling whereas the coating on the cone 06 ceramic tile had been removed. The tile material was unaffected in both cases. 
     A small flower pot was cast using the slip made by the composition and procedure of this Example. After air drying and firing at 175° C. for one hour, this flower pot was filled with tap water and covered with a plate glass which was sealed to the top of this pot with a silicone rubber adhesive (Dow Corning RTV735 silastic sealant). A ceramic flower pot was made from this same mold using a commercial slip supplied by Ex-Cel, Inc. After drying and firing this pot at cone 05 (1062° C.) it was filled with tap water and covered and sealed in the manner described above. The cone 05 ceramic pot was dry after three days, whereas the pot made of the material of this Example had some water remaining at the end of two months. 
     EXAMPLE 9 
     This Example illustrates a slip composition containing a finely divided epoxy powder made according to the procedure of Example 1. 
     
         ______________________________________         Slip       Dry Batch         Composition                    Composition         Parts by                Vol-            Vol-         Weight-                ume     Weight  ume         grams  %       %       %______________________________________CeramicKentucky Ball Clay #4           313.00   16.67   39.13 36.75Talc Steawhite 200           344.3    16.67   43.03 36.75Silica Supersil 62.7     3.14    7.84  6.95Polymer-25 micron Epoxy Powder           80       8.88    10.00 19.55Aqueous solutionSodium Carbonate           .47Sodium Silicate (N)           2.0Water           408      54.64Total           1210.47  100.00  100.00                                  100.00______________________________________ 
    
     The slip is allowed to age 24 hours and specific gravity is 1.60 and viscosity about 1800 cps. Test bars are made by the procedure of Example 1. Casting properties are excellent. The bars are allowed to air dry for about 70 hours. Test bars of this Example are placed on tin-coated steel sheets and fired at 175° C.; one set of bars fired for one hour and the other set for 5 hours. The bars had a fired density of 1.66 g/cc. Flexural strength results are shown below: 
     
         ______________________________________Firing Condition:175° C. -- 1 hour     Newtons/mm.sup.2                    23.3175° C. -- 5 hours     Newtons/mm.sup.2                    26.3______________________________________ 
    
     EXAMPLE 10 
     The following materials were thoroughly mixed by dry blending: 
     
         ______________________________________Ingredients         Wt. %     Vol. %______________________________________White Earthenware Clay                92        84.1(Minn. Clay, Inc.,Sp. gr. = 2.60)Epoxy powder         8         15.9               100       100.0______________________________________ 
    
     26.4% by weight water is added to 100 parts by weight of dry ingredients and mixed to produce a plastic mixture suitable for throwing on a potter&#39;s wheel. A lump of modeling clay which has been hand wedged to remove the air is placed into the open area formed by laying two metal bars (45 cm. long × 2.5 cm. wide × 0.6 cm. thick) parallel to each other and spacing each end with a metal piece measuring 1.2 cm. wide × 0.6 cm. thick. After the ends are securely fastened, the clay is hand pressed and further compacted by rolling with a rolling pin. The excess clay remaining on the surface above the metal bars is cut off with a wire. The metal bars are removed and the strip of formed clay is cut into test bars measuring about 5 cm. The bars are allowed to dry at room temperature for at least 48 hours and then placed on tin-coated steel sheets and fired in a Blue M oven. Flexural strengths are measured by procedure of Example 1 and test results are: 
     
         ______________________________________             Flexural StrengthFiring Conditions Newtons/mm.sup.2______________________________________175° C. for 1 hour             15.2200° C. for 1 hour             17.2______________________________________ 
    
     A pottery shape was formed from the modeling clay of this Example. After drying for at least 48 hours, the shape was fired at 200° C. for one hour. The fired article was extremely hard and impervious to water. 
     EXAMPLES 11-13 
     In these Examples, modeling clay materials with the indicated components were formulated according by the procedure of Example 10, and were also tested in the manner there set forth. For comparison a modeling clay (S. C. Johnson &amp; Son, Inc., Racine, Wis.) marketed under U.S. Pat. No. 3,817,897 is prepared per the procedure of Example 10 and fired concurrently with these Examples. 
     The fired clay/epoxy compositions (Examples 11-12) exhibited high impact resistance, a high degree of water impermeability, and a high degree of receptivity to commercial stains and paints. 
     EXAMPLE 14 
     An epoxy resin system formulated by dry blending as indicated below: 
     
         ______________________________________Ingredients                Wt. %______________________________________EPOXIDE RESINEpi-Rez 522-C [100% finer than74 microns (U.S. 200 mesh)]                       77.2CURING AGENTEDA Adduct 870.sup.(1) [100% finer than74 microns, H-Active equiv. Wt. is185]                        22.8                      100.0______________________________________ .sup.(1) Pacific Anchor Chemical Corporation 
    
     is mixed at the 15% by weight level with 85% by weight of a White Earthenware Clay (Minnesota Clay, Inc.) 26.4% by weight water is added to 100 parts by weight of the aforementioned dry blend to form a modeling clay which is tested in the manner set forth in Example 10. Flexural test results are: 
     
         ______________________________________             Flexural StrengthFiring Conditions Newtons/mm.sup.2______________________________________175° C. for 1 hour             17200° C. for 1 hour             21______________________________________ 
    
     These data are a quantitative measure of the strength of the modeling clay composition. This clay composition is found to have high impact resistance, is impervious to water, and exhibits good adhesive properties for a variety of commercial paints, stains, and low temperature enamels. 
     
         __________________________________________________________________________MODELING CLAY COMPOSITIONS - (PERCENT)              11      12      13     U.S. Pat. No.             Wt. Vol.                     Wt. Vol.                             Wt. Vol.                                     3,817,897__________________________________________________________________________SOLIDSCeramic -- White Earthenware Clay   (Minnesota Clay, Inc.)             71.2                 49.9                     67.2                         45.6                             63.3                                 41.7POLYMEREpoxy Powder      7.9 12.0                     11.9                         17.5                             15.8                                 22.5             79.1                 61.9                     79.1                         63.1                             79.1                                 64.2AQUEOUS PHASEWater             20.9                 38.1                     20.9                         36.9                             20.9                                 35.8             100.0                 100.0                     100.0                         100.0                             100.0                                 100.0FLEXURAL STRENGTHS(Newtons/mm.sup.2)175° C. -- 1 hour             16.5                 20  16.7*           12.0200° C. -- 1 hour             21  25  19.2*           14.0__________________________________________________________________________ *Hairline cracks formed