Service and radiation properties of refractory coatings

Abstract

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