Effect of environment upon the melting point of Al2O3

Abstract

The me ltin g point of AI, O" has bee n d e termined in vac uum . a ir. a rgon. a nd he lium utilizin)': iridium or tun ),:s te n co ntain ers. A ll me ltin g po int expe rim e nt s we re conduc ted in indu c ti on furna ces capab le of hea ti ng s ma ll sa mpl es und er b lackbody co ndition s to 3000 °C in vacuum. 2600 °C in inert at mosp he res. a nd 2400 °C in air. Temperatures we re co ntinu ous ly mo nit o red wit h a reco rding phutoe lec tri c pyrome ter whi c h has a se n sitivity of±0.2° at 1063 °C and ± 10 at 2000 0c. Meltin g points were determ in ed on s pec im ens having a purity in excess of 99.9 pe rce nt. T he data indi c at e d that th e me ltin g poin t of AI ,O" d e te rmin ed in vac uum (-6.5 X 10 -5 torr) is 2051 °C OPTS). T he overa ll maximum un ce rt a int y was es tim ate d to be ± 6 0c. Th e mea s ure me nt s th e m se lves we re prec ise within ± 1.5 0c. Vacuum trea tm e nt had leas t de t rimenta l e ffec t upon th e AI,03 spec im e ns. Eac h of the gaseous a tmo s ph e res in c lu ding air yie lded lower me lti ng point s for AI,O", p res umably d ue to a premeltin g p he nom e no n.Key Word s : A I,O". di ss ocia tion. e nvironm e nt a l e ffec ts . me ltin g po int. prc mc ltin g:.

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

“…Acoustic vibrations existed in the gas levitation method and other perturbing factors affect these parameters as well. 13,16 All this confirms once again that the peculiarities and errors of experimental methods should be taken into consideration in comparison of the physical properties data obtained by different methods.…”

“…It is up to 8-10% and may be caused by pollution with the container or capillary materials, for example MPB method, because pollution influences the alumina melting temperature, and the density at the melting or crystallization temperature changes correspondingly. 16 Nevertheless, such pollutions were absent in the pendant-drop method. Therefore another reason for these data discrepancy should be found.…”

“…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.…”

“…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.…”