The effect of vacuum on the reflectivity of alumina ceramics under conditions of melting by concentrated laser radiation and subsequent free cooling

Peculiarities of crystallization of alumina, yttria and rare-earth element oxides of yttria subgroup in an optical furnace

“…26 Though, as abovementioned, the oxygen presence in the medium influences both the composition of fused alumina and the peculiarities of melting and crystallization processes. 16,20 The deficiency or excess of oxygen is the most possible reason for the influence. Therefore, the first task of this work was the direct observation of gas release upon the crystallization of alumina melt and examination of the gas composition.…”

“…10,15 The influence of gas medium on melting and crystallization processes has been described. 13,[16][17][18][19][20][21] Some authors did not observe any influence of the gas composition on the density of small alumina drops (<100 mg). 13 In some works the effect of gas medium on the alumina surface tension did not exceed the measurement error, 21 whereas in others the influence of gas composition on the properties of liquid and crystallized alumina had been found.…”

“…uum or air). 17,20 The ingots obtained in an oxidizing medium were white, while those obtained in argon (argon or vacuum) were grey. Nucleation in alumina melt depends on the oxygen partial pressure.…”

“…13 In some works the effect of gas medium on the alumina surface tension did not exceed the measurement error, 21 whereas in others the influence of gas composition on the properties of liquid and crystallized alumina had been found. [16][17][18][19][20] It has been shown that melting temperature of alumina is changing with the composition of gas medium (vacuum, air, argon or helium) by up to 6 • C. 16 The reflection power of melted alumina depends on the composition of gas medium (vac- * Corresponding author. Tel.…”