A THERMAL-ANALYSIS AND VERY HIGH-TEMPERAT URE AL-27 NMR-STUDY OF THE SOLIDIFICATION BEHAVIOR IN CONTACTLESS CONDITIONS OF LIQUID ALUMINA - EFFECTS OF THE MELT TEMPERATURE AND OXYGEN PARTIAL-PRESSURE

Authors
COUTURES JP RIFFLET JC FLORIAN P MASSIOT D
Citation
Jp. Coutures et al., A THERMAL-ANALYSIS AND VERY HIGH-TEMPERAT URE AL-27 NMR-STUDY OF THE SOLIDIFICATION BEHAVIOR IN CONTACTLESS CONDITIONS OF LIQUID ALUMINA - EFFECTS OF THE MELT TEMPERATURE AND OXYGEN PARTIAL-PRESSURE, Revue Internationale des Hautes Temperatures et des Refractaires, 29(4), 1994, pp. 123-142
Citations number
32
Categorie Soggetti
Material Science, Ceramics
Journal title
Revue Internationale des Hautes Temperatures et des Refractaires → ACNP
ISSN journal
00353434
Volume
29
Issue
4
Year of publication
1994
Pages
123 - 142
Database
ISI
SICI code
0035-3434(1994)29:4<123:ATAVHU>2.0.ZU;2-6
Abstract
In contactless conditions, i.e. without heterogeneous nucleation, the degree of undercooling of millimetric liquid alumina droplets is relat ed to the oxygen potential of the melting atmosphere. Under oxygen, th e undercooling is around 275 degrees C, but varies between 175 and 50 degrees C under agron. This lower undercooling observed under argon an d as shown by Al-27 NMR is due to metallic aluminium atoms, their conc entration increases with the melt temperature. At 2350 degrees C the A l degrees population is around 2.5% and they act as nucleating agents. Solidified droplets obtained under oxygen are porous with a dendritic type crystallisation behavior and are more dense with crystals of lar ger size under argon.