Bidirectional reflecting properties of corundum refractory

Abstract

In high-temperature industrial metallurgical furnaces heat transfer occurs mainly by radiation. In carrying out heat calculations in such equipment is necessary to know the radiation characteristics (coefficients of radiation and reflection) of all the components of the working space, and in the first case of the refractory lining materials. However, existing information on the thermal radiation properties of refractories is very limited, and the data on spectral characteristicsof infrared reflection is practically completely lacking.This article deals with an experimental investigation of the reflecting properties of industrial corundum in the IR spectrum both at room temperatures and also when heated to 1500~ with subsequent cooling in air. The spectral relationship with the coefficients of reflection for these materials was obtained from spectrophotometric measurements, and the heating of the specimens was carried out by focusing the thermal radiation of an optical furnace. The plan of the experimental equipment is shown in [I]. Using the IKS-21 spectrometer we measured the intensities I, and l,p of the reflected radiation respectively from the surface of the standard (magnesium oxide and sodium chloride) and the specimens being studied. The ratio (19 and I,)/R, -rA, where R, is the reflecting capacity of the standard, enable us:to determine the coefficient of reflection (bidirectional reflective capacity) rA for different angles of incidence e' and reflection e in the wavelength range A from 0.75 to 6 ~m.The objects of the investigation were specimens of corundum refractory produced by the Podolsk refractories factory. The chemical composition of the refractories (OST 14-46-79), % was: A1203 97, Ti02 1.5, SiO 2 0.5, FezO 3 0.1; the porosity reached 21%. To clarify the possible changes in the optical properties of the surface of the refractories under the action of prolonged heating we studied corundum specimens obtained from the Volgograd Red October Factory which had been used in a heat-treatment furnace at a working temperature of 1500~ for 1.5 h. Figure 1 shows spectral curves for the reflection coefficients for the original and worked material obtained at room temperature with an angle of incidence and angle of reflection close to the normal. The coefficient of reflection of corundum refractory possesses a clearly expressed selectivity. In the close IR region of the spectra (A up to 2.3 ~m) we observe an increase in r A. Further scanning over the spectrum showed that with increase in the wavelength there is a sharp reduction in the coefficient of reflection with the formation of a minimum on the spectral curves when A -3.5 ~m and a slight increase in the region of = 4-5 ~m~In the entire spectral range studied the levels of r A of the used material in absolute values were lower than in the original material, although the qualitative character of the spectral curves was the same. This is connected with the irreversible changes in the surface roughness of the worked refractory. Measurements of this factor ca...