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In a number of countries of the European Ceramic Union and the Council for Mutual Economic Aid the method of a linear probe of constant power, known as the hot wire method, has been adopted as the standard for determination of the thermal conductivity of refractories with % < 2 W/(m-K).At present a plan has been developed for a standard of the Council for Mutual Economic Aid including the steady method of a plate (All-Union State Standard (GOST) 12170-76) and the hot wire method (German Democratic Republic standard TC/32153-76). The higher the thermal conductivity of the sample the lower the measuring error of the first of them while the second method is the optimum for low thermal conductivity parts and materials.In the USSR the hot wire method was first used for determining the thermal conductivity of refractories by the All-Union Institute for Refractories [i]. In the Ukrainian ScientificResearch Institute for Refractories an instrument based on the hot wire method has been built for measurements of % up to 1400~ with an error of • [2]. Standardization of the instrument using certified samples of organic and quartz glasses has shown a difference from metrological data of <2%. This article considers the possibilities of the hot wire method for thermal insulation materials with different structures including lightweight, fiber, and powder refractories.* Lightweight refractories to GOST 5040-78 with low (ShL-0.4 chamotte), medium (MKRL-0.8 mullite--silica), and high (KL-I.3 corundum) thermal conductivities were used for the tests. The sample was two bricks of normal dimensions.Between the largest surfaces of the samples was placed a measuring cross of platinum--rhodium wire with a PP thermoelectric transducer welded to it. The determinations were made in a wide range of values of power (3-60 W/m) supplied to the wire.The features of the method and the equipment used are described in The absolute values and character of the temperature relationship of thermal conductivity of the investigated lightweight parts reflect features of the influence of phase composition and structure on the processes of heat transfer in dispersed systems [3]. For the most porous material, ShL-0.4, a significant increase in thermal conductivity % with an increase in temperature t, indicating a significant contribution of radiation to heat transfer at high temperatures, is characteristic.The approximation of the experimental data by a cubic parabola ,Z=0,175+0,90 9 10-m(t,+.is shown in Fig. 1 by a broken line.The thermal conductivity of ShL-0.4 samples was also measured by methods of a cylinder [4] and a plate (GOST 12170-76).In both cases two samples each were tested, one of them cut from the brick which had served as half of the sample for measurement by the hot wire method and the other from a random brick of the same lot. The reproducibility of each method for the two samples is no poorer than 5%. Both of the methods provided results agreeing with the hot wire method within the limits of instrument errors, which are • and • respectivel...

The elastic properties of ceramics form extremely important design parameters. From a practical standpoint, it is necessary to select structural materials having high values of the modulus of elasticity. In view of the fact that the components obtained from the structural ceramics often work under static loads of constant sign, it is important to know the specific features of the dependence of the static modulus of elasticity of the ceramics on the methods of obtaining them and on the factors like temperature. The dynamic methods of measuring the modulus of elasticity are based on the assumption that the experimental materials are completely homogeneous and isotropic; deviations from ideality give overestimated results.This paper deals with a study of the static modulus of elasticity of the ceramics based on partially stabilized zirconium dioxide. It is known [1] that the presence of a tetragonal phase in such ceramics improves the thermomechanical properties due to absorption of the elastic energy during the diffusionless (martensitic) tetragonal-monoclinic transformation induced in Zr(N under the action of mechanical loads. Table 1 shows the effect of the stabilizing agents used in this study, the methods of stabilization and shaping, and the heat treatment temperature on the room temperature mechanical properties of the specimens of the experimental ceramics. The specific features of the production technolo~ of the specimens and the data concerning the density, the phase composition, and the grain size were presented in a recent paper [2].The static modulus of elasticity was measured using the previously described testing machine [3] according to the procedure developed at UGNIIO (from room temperature up to 1200~ Prismatic test specimens measuring 5 • 8 x 90 mm were used. Loading of the test specimens was carried out according to the four-point pure-bending scheme.The magnitude of the static modulus of elasticity E was calculated according to the following equationwhere a is the distance between the supporting and the loading edges (points); I is the distance between the supporting edges; b and h are the width and the thickness of the specimen, respectively; P is the applied load; andfis the deflection of the specimen. The P/f ratio was determined from the P vsfplot at P ~ 0. Figure 1 shows the temperature dependence of the static modulus of elasticity of different types of ceramics and their ultimate bend strength (determined according to the previously described procedure [2]). The plots depicting the temperature dependence of 1~ are nonmonotonic in nature and have a sinusoidal shape. The minimum values of the modulus of elasticity of the 7Y and the TsI-6 grade specimens (curves 1 and 2) are observed in the 500-600~ range and the maxima are observed in the 900-1000~ range; the plot of the MgChSTs specimens (curve 3) shows inflection at 500-600~ The temperature dependence of the ultimate bend strength (curves 4 and 5) is similar to that of the modulus of elasticity.It is known that the modulus of elasticit...