Abstract:
An improved alumina-chrome refractory composition having increased strength at both ambient and high temperatures has been prepared comprising the following ingredients: 
     
       Tabular Alumina         70-96% 
     
     Calcined Alumina -325 mesh                   0-10%Milled Zircon -325 mesh 1-10%Chromic Oxide Refractory GrainsGround to -10 mesh with at Least70% +200 mesh           3-10%Bentonite               0-4%Water                   0-10%Phosphate Compound      0-18%

Description:
BACKGROUND OF THE INVENTION 
     An alumina-chrome refractory brick composition has been prepared by the prior art which contains the following composition: 
     
         Tabular Alumina         65-90%Calcined Alumina        0-10%Chromic Oxide (-325 mesh)                   1-25% 
    
     Such a product has been useful as refractory brick composition for use in the ferrous and non-ferrous industries. Although this prior art refractory product possesses high strength, it is desirable to produce a refractory composition which has a higher modulus of rupture at both ambient and high temperatures. 
     SUMMARY OF THE INVENTION 
     It has been discovered that the refractory composition of the prior art refractory product comprised of alumina and pigment grade chromic oxide (-325 mesh) may be improved considerably by employing chromic oxide refractory grains which are present in the fused or sintered form. This fused or sintered chromic oxide refractory grains should be ground to -10 mesh with at least 70`% +200 mesh, as opposed to the prior art method which employs pigment grade chromic oxide 70is 100% -325 mesh size. 
     The refractory composition produced by the instant invention comprises the following: 
     
         Tabular Alumina         70-95%Calcined Alumina        0-10%Milled Zircon           1-10%Chromic Oxide Refractory GrainsGround to -10 mesh      3-10%with at Least 70% +200 meshBentonite               0-4%Water                   0-10%Phosphate Compound      0-18% 
    
     The mixture is then formed and fired at 350° to 1750°C. for 2 to 8 hours if desired. 
     If phosphates are not employed then the firing temperature should fall within the range from 1400° to 1750°C. 
     If a ramming or plastic mixture is to be produced, the mixture itself is used directly without forming and firing for the customers use. In the case of preparing a plastic mixture, from 1% to 4% bentonite is also added to the mixture. 
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In preparing the refractory composition of the instant invention it is important to have present in the mixture a variety of sizes of the various ingredients employed. Tabular alumina may be used as the only source of alumina, but it is preferred to have a mixture of tabular and calcined alumina. 
     The tabular alumina should be employed in various sizes. All of the -1/4 inch +325 mesh alumina should be employed in the tabular form and in addition, with respect to the -325 mesh alumina, from 1/4 to all of the -325 mesh alumina should be present in the tabular form. If calcined alumina is used, it should be -325 mesh in size. 65% to 95% of the alumina should be -1/4 inch to +325 mesh in size, while the remainder of the alumina should be ground to -325 mesh. 
     The chromic oxide refractory grains should be ground to -10 mesh in size with at least 70% +200 mesh, and should be obtained from either previously fused or sintered chromic oxide. 
     It is preferred that zircon be employed in amounts from 1% to 10%, preferably from 3% to 7%. The size of the zircon should be -325 mesh. 
     In preparing the refractory composition of the instant invention, the alumina raw material, the ground refractory grains of chromic oxide, and the milled zircon are mixed together, and are formed into shapes which are then fired to form the desired refractory product. The mixture is fired at temperatures from 350°C. to 1750°C. for 2 to 8 hours to form the refractory composition. When phosphates are not employed the mixture should be fired at temperatures from 1400°C. to 1750°C. 
     The refractory composition of the instant invention possesses increased modules of rupture at both ambient and high temperatures. Although an increased modulus of rupture at ambient temperature is desirable, it is more preferable to have an increased modulus of rupture at high temperatures such as that mentioned above. 
    
    
     In order to describe the instant invention more fully, the following examples are presented: 
     EXAMPLE 1 
     The following ingredients were added to form a refractory mixture: 
     
         Tabular Alumina      -8+65 mesh, Kg.                              44Tabular Alumina      -65+325 mesh, Kg.                              22Tabular Alumina      -325 mesh, Kg.                              19Calcined Alumina     -325 mesh, Kg.                              5Chromic Oxide RefractoryGrains -10 mesh with at Least 70%+200 mesh Kg                       7Zircon               -325 mesh, Kg.                              3 
    
     The mixture was then tempered with lignin liquor and formed into bricks 9 in. × 41/2 in. × 3 in. and the bricks were then fired at 1560°C. for 5 hours. After cooling to room temperature, the bricks were analyzed to determine their strengths which are listed as follows: 
     
         Modulus of RuptureAmbient Temp.    High Temp. (1480°C.)______________________________________8777             5122______________________________________ 
    
     EXAMPLES 2-3 
     The procedure of Example 1 was repeated except that various amounts of zircon were added to the mixture in Examples 2 and 3. Bricks having properties similar to those obtained in Example 1 were produced. 
     The operational details and the results obtained are recorded in Table I along with those of Example 1. 
     For comparison, a series of control runs were made with various compositions. 
     CONTROLS A-C 
     In these runs no chromic oxide was employed. Run A contained no zircon. Runs B and C contained zircon. 
     The results of these runs indicateed that modulus of rupture at both ambient temperature and at 1480°C. were unsatisfactory. 
     The results are recorded in Table II. 
     CONTROLS D-F 
     In these runs pigment grade chromic oxide was employed instead of coarse chromic oxide refractory grains and the results were inferior to those obtained in Examples 1-6. 
     The results are also recorded in Table II. 
     It has been discovered that the use of coarse chromic oxide refractory grains increases the bond strength at higher temperature over that retained when finely divided chromic oxide is employed. 
     EXAMPLES 4-5 
     In these examples aluminum phosphate was used in Example 4 while phosphoric acid was employed in Example 5. The results are also recorded in Table I. 
     It should be noted that the modulus of rupture results at both ambient and 1480°C. temperatures were high and in addition the porosities were reduced and the bulk densities were increased over those produced in Examples 1-3. 
     The phosphates when employed are added to develop a ceramic body which possesses high strength at reduced temperatures i.e. above 350°C. Phosphates are also added to reduce the porosity and increase the bulk density which results in reduced penetration when the ceramic body is in contact with molten metals on slags. 
     While this invention has been described and illustrated by the examples shown it is not intended to be strictly limited thereto, and other variations and modifications may be employed within the scope of the following claims. 
     
                                           TABLE I__________________________________________________________________________                       EXAMPLESMATERIAL           MESH     1      2      3      4      5__________________________________________________________________________Tabular Alumina    Kg. -8+65                       44     44     44     44     44Tabular Alumina    Kg. -65+325                       22     22     22     22     22Tabular Alumina    Kg. -325 19     17     19     19     19Calcined Alumina   Kg. -325 5      3      5      5      5Milled Zircon      Kg. -325 3      7      3      3      3Aluminum Phosphate Kg.      0      0      0      5      0Phosphoric Acid    Kg.      0      0      0      0      5Lignin Liquor      Kg.      2.5    2.5    2.5    0      0Water              Kg.      2      2      2      0      0Chromic Oxide Refractory Grains              -10 mesh with                       7      7      0      7      7 Sintered          80%+200 meshChromic Oxide Refractory Grains              -10 mesh with                       --     --     7      --     -- Fused             88%+200 meshChromic Oxide (Pigment Grade)                -325   --     --     --     --     --Silica               -325   --     --     --     --     --Modulus of Rupture, Ambient 8777   8668   8144   8767   7344Modulus of Rupture, 1480°C.                       5122   5011   3349   5204   4925Porosity %                  16.0   --     14.3   12.2   11.1Bulk Density g/cc           3.22   --     3.23   3.30   3.31__________________________________________________________________________ 
    
     
                                           TABLE II__________________________________________________________________________                      CONTROLSMATERIAL          MESH     A     B     C     D     E     F__________________________________________________________________________Tabular Alumina   -8+65 Kg.                      48    48    48    48    48    48Tabular Alumina   -65+325 Kg.                      24    24    24    24    24    24Tabular Alumina   -325 Kg. 20    20    18    18    18    14Calcined Alumina  -325 Kg. 8     5     3     3     --    --Milled Zircon     -325 Kg. --    3     7     --    3     7Lignin Liquor              2.5   2.5   2.5   2.5   2.5   2.5Water                      2     2     2     2     2     2Chromic Oxide Refractory Grains             -10 mesh with Sintered         80%+200 mesh                      --    --    --    --    --    --Chromic Oxide Refractory Grains             -10 mesh with Fused            88%+200 mesh                      --    --    --    --    --    --Chromic Oxide (Pigment Grade)             -325     --    --    --    7     7     7Modulus of Rupture, Ambient                      5395  6906  6085  7111  7070  7351Modulus of Rupture, 1480°C.                      644   1835  --    2367  2658  2142__________________________________________________________________________