Absorption Coefficient of Molten Aluminum Oxide in Semitransparent Spectral Range

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.

Temperature distribution across the growth zone of sapphire (Al 2 O 3 ) and yttrium–aluminum garnet (YAG) single crystal fibers

“…The temperature measurements for sapphire were carried out with high spatial resolution. Therefore we can argue that the temperature profile doesn't contain singularities in transition area between the melt and solid crystal despite the fact that the absorption coefficient demonstrates sharp increase of the two orders in magnitude in melting process [14,17].…”

Numerical simulation of radiation in high altitude solid propellant rocket plumes

“…The first of all is the uncertainty on the spectral and temperature dependence of alumina absorption index which may strongly influence the radiation calculation. Indeed, the absorption index has been proven to strongly depend on the impurities present in the combustion produced alumina [14]. Secondly, the uncertainty and approximations made on the nozzle exit conditions would also play an important role on the results.…”

“…Considering that the size of particules in our application is about a few micrometers, Mie theory [13] is used to calculate these radiative properties. Many investigations have been made in the past decades in order to find expressions of the refractive index n and the absorption index k as functions of the temperature and the wavelength [14,15] . Strong discrepancies exist between those studies as the results for k may vary by several orders of magnitude depending on the temperature and wavelength range of the studies and the type of investigated alumina (liquid phase or crystalline phase of solid alumina).…”

Additive manufacturing of an oxide ceramic by laser beam melting—Comparison between finite element simulation and experimental results

“…Although -values are reported by Lawrence (2004) and Bityukov and Petrov (2013), variations can extend over several orders of magnitude. Alumina shows low absorption of Yb:YAG laser light, and it can be strongly modified by impurities.…”

“…Even though literature values for absorption coefficients are scarce and show a large scatter for Al 2 O 3 , the identified values are relatively close. The review conducted by Bityukov and Petrov (2013) showed that values vary from 1 mm -1 at the melting point to 60 mm -1 at boiling point for pure powders, and from 20 mm -1 to 90 mm -1 for impure powders. The value for the dense material at room temperature reported by Sola and Peña (2013) was 1 mm -1 .…”