According to [1, 2], alkaline-earth modified lanthanum chromite with n-type conductivity can be used to make resistance heater elements capable of operating in an oxidizing medium up to 1800-1850~In our work on the manufacture of heaters, we used fused material obtained by a procedure developed in the Lebedev Physical Institute, Academy of Sciences of the USSR [3, 4] and described in [5]. The mixture for synthesis of calcium oxide-modified lanthanum chromite contained lanthanum oxide of LaO-1 grade according to TU 48-4-184-72 (purity not less than 99.849 wt.%), calcium oxide of OKhM-1 grade according to GOST 2912-73 (Cr20 a content 98 wt.%), and CaCO 3 of analytical reagent grade according to GOST 4530-66.The fused block was subjected to x-ray phase, petrographic, quantitative x-ray spectral, and x-ray structural analysis. The diffraction patterns of specimens from different sectors of the block show considerable redistribution of the intensities of the principal reflections in comparison with the distribution in the standard (Fig. 1). This indicates the presence of microstresses in the lattice of the solid solution obtained, or of impurities in the material; this is improbable.Petrographic analysis revealed a certain nonuniformity of the solid solution, noted during dark-field analysis and indicating the nonequilibrial state of the material. This is apparently due to incomplete homogenizatton of the melt during fusion and subsequent crystaUization, and to quenching of high-temperature

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deformation in the steady stage of creep (%'h -I) which sets in only after 350-400 h soaking. Hence, for the stated parameters, when testing for creep, for the stabilization of the structure in the refractories being studied we require a time for the order of several hundred hours. CONCLUSIONSThe creep curves for porous refractories under monoaxial compression can be described by the Andrade equation, the parameters of which depend on the nature of the macroscopic structural changes in the material.With significant densification or embrittlement of the specimens in the testing procedure during deformation the degree factor in the equation e = 8TP + q[, p ~ 89 if the structure of the specimen does not undergo marked changes then the degree factor is close to the classic value (p = 1/3). LITERATURE CITEDi. S. N.

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