Abstract
A critical compilation and analysis of all the available experimental data and approximation formulas for the wavelength and temperature dependences of the absorption coefficient of molten aluminum oxide in semitransparent region are presented. The main factors and the influence of physicochemical processes on the value of the absorption coefficient are considered. Special attention is focused on possible reasons for large values of absorption of the alumina melt as compared to the crystal near melting temperature. It is shown that the available data can be divided into two groups, according to the level of absorption. The first group includes the results of the research of optical properties of solid propellant combustion products, and the second group–the results of the research of single crystal melts and some other high-purity molten aluminum oxides. Along with the detailed analysis of the absorption coefficient, also a brief analysis of available data on the refractive index has been done.
Highlights
Investigation of temperature and spectral dependences of the absorption coefficient of molten aluminum oxide Al2O3 have both a scientific and practical importance
The practical importance is connected with the application in various fields of electronics, semiconductor and infrared techniques of single crystals of corundum being grown from melts, as well as with the application of aluminized solid rocket fuel, when as a result of combustion, droplets of molten aluminum oxide are formed
The results showed that absorption coefficient after melting changed significantly and after some time it reached stable values, which were different for different ambient conditions
Summary
Investigation of temperature and spectral dependences of the absorption coefficient of molten aluminum oxide Al2O3 have both a scientific and practical importance. Based on the obtained results by Rubtsov and Emelyanov (1978), Rubtsov et al (1984), and Rubtsov et al (1988), like Mularz and Yuen (1972), the conclusion was made that during melting the absorption index of Al2O3 does not change abruptly, but increases monotonously with temperature rise, and this is typical for a polycrystalline aluminum oxide, obtained by way of crystallization of molten droplets. In research by Konopka et al (1984) there are results, in the range 1700-3000 K and wavelengths from 1.3 μm to 4.5 μm, of optical properties of submicron particles (an average radius of 0.1 μm) of aluminum oxide, obtained by capturing in the combustion products of two different full-scale solid-fuel rocket motors. Particles with a cubic lattice in reference (Gosse et al, 2003) were already considered as γ-Al2O3 particles, and the amount of detectable hollow microspheres became much less
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