In accordance with the existing tendency toward acceleration of the process occurring in combustion chambers, there has been an increase in interest in the use of heat-protective and thermal-insulation materials with higher operating characteristics, particularly increased refractoriness.Wide use of zirconium dioxide has started. However, the radiation characteristics of ZrO 2 have been insufficiently investigated.Existing works [1][2][3][4][5] have been done in a relatively narrow range of influencing conditions of wavelengths, temepratures, etc. The spectral degree of blackness was investigated.Investigation of the reflective characteristics provides more information on the radiation properties of a body than the emissive. First, in investigation of the bidirectional reflective characteristics it is possible to obtain the angular distributions of the reflected radiation with a change in the angle of incidence.And, second, with appropriate information it is quite simple to convert from the reflective radiation characteristics to the emissive characteristics [6]. The reverse operation is difficult and therefore we investigated the characteristics of the zirconia refractory in the wavelength range from 0.75 to i0 um. The experimental unit, the method of the investigations, and the data processing were described in detail in [7]. Magnesium oxide and sodium chloride were used as the standards in investigation of radiant properties of zirconium dioxide.The first was used in the 0.75-2.5 ~m wavelength range and the second in the 2.50-I0-~m range.The refractory specimens were disks with a diameter of 20 and a thickness of 10-15 mm. The experiments were made for two types of zirconium dioxide refractory, dense with an open porosity of 0.5% and porous with an open porosity of 20%.The refractories differed primarily in grain size. The dense specimens had a grain size of 0.002 mm and the porous of 0.5 mm. In both cases CaO was used as the stabilizer.

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One has to consider the radiation characteristics when refractory materials are used. For example, elevated lining blackness sometimes considerably improves the thermal operation in industrial furnaces [i, 2]. However, most refractories are produced and used without reference to their radiation characteristics. Adequately adhering coatings can alter those characteristics, particularly the blackness in particular spectral or temperature ranges.Refractory coatings of vitreous type are the cheapest and most readily available. The problems arise mainly over choosing components, which govern the radiative characteristics either by themselves or in combination with others.An apparatus has been built to implement the relative method [3] at this institute in the Department of Heat Engineering and Metallurgical Furnace Automation, which has been used in researches on the parameters of metal oxides (Co=O 3, NiO, and Fe203) as used in refractory coating components.The measurements were made in the range of wavelengths from 0.75 to 12.0 ~m at 293 K and also during radiative heating to ii00 K at certain selected points in that IR range. The specimens were prepared by the [4] method.We found that Co203 (curve 1 in Fig. i) has high blackness E~. n in the near-IR range (0.75-2.5 um) and in the middle range (7.5 to 12.0 ~m). The peak e%, n for Co=Om specimens lay at 1.2 and 8.5 ~m and attained 0.90 and 0.0865 correspondingly.At 2.5-7.5 ~m, there was a minimum in the blackness, which was 0.715 at 5.0 ~m.We examined the blackness spectrum for NiO in the same range (Fig. i, curve 2). NiO gave somewhat lower values throughout the IR range.The maximum occurred at 9.0 ~m, where it was 0.815, and the minimum at 5.0 ~m, where it was 0.682. Fe203 (Fig. i, curve 3) differed only slightly from the previous two at 4.5-12.0 ~m, but there were obvious differences in the near-IR range. At 0.75-4.5 Dm, the selectivity of Fe203 is very pronounced, and the blackness at 0.75 um is 0.62, while at 1.5 ~m there is a minimum g%,n = 0.12. 2) NiO; 3) Fe203.Moscow Evening Metallurgical Institute.

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One of the methods of improving the thermal operation of metallurgical furnaces is increasing the emissivity of the lining [i]. The use of traditional refractory materials does not make it possible to provide this since they have a low emissivity factor SA,n in the close and medium infrared areas of the spectrum (wavelengths A = 1-4 ~m) and the maximum emissivity falls within this region in the operating temperature range [2].It is known that in service the contact layer of a refractory changes structurally and the refractorty ages, as the result of which EA, n increases somewhat.At present the method of artificial aging of refractory materials is done by application to the lining of emitting coatings (eX,n > 0.85). A basic condition of reliable operation of the coating is stability of its adhesion and radiation properties during the whole furnace campaign [3].In Moscow Evening Metallurgical Institute two types of emitting coatings with EA, n > 0.85 have been developed based on silicon carbide and iron scale.Their compositions in weight % are 70 silicon carbide, 10 iron scale, 5 Cu20, i0 chamotte, and 5 refractory clay for coating 1 and 70 iron scale, 5 Cu20, 5 CaO, 5 MnO, I0 chamotte, and 5 refractory clay for coating 2. The coatings were applied with an atomizer to the working surface of the refractories in the form of a coating (the dry mixture of powders was mixed with an aqueous solution of water glass), after which the refractory parts were placed in the furnace.The length of the tests was 0.5, I, 2, 3, 6, and 12 months. The tests showed that in the temperature range of furnaces of this type (1100-1600 K) the coatings operate stably and spalls, cracks, and other traces of failure were not observed.Investigations of the emissivity of the coatings were made in Moscow Evening Metallurgical Institute on an instrument described earlier [4]. Fragments of the working surface of refractories which had been tested were used as the specimens.The specimens were sawed in the form of disks with a diameter of 40 and a thickness of I0 mm.The relationship of the emissivity of the silicon carbide-base coating to wave length was studied in the infrared area of the spectrum (A = 0.75-11.5 ~n).It was established (Fig. I) that the time of hold in the furnace and the service conditions do not influence the spectral radiation characteristics and they are stable.The spectral distribution of