Spectral emission characteristics of refractory materials used in thermal-radiation coatings

Abstract

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.