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Publication Type
Journal Article
UWI Author(s)
Author, Analytic
Antao, S. M.; Hassan, Ishmael
Author Affiliation, Ana.
Department of Chemistry
Article Title
Thermal analyses of sodalite, tugtupite, danalite, and helvite
Medium Designator
n/a
Connective Phrase
n/a
Journal Title
Canadian Mineralogist
Translated Title
n/a
Reprint Status
n/a
Date of Publication
2002
Volume ID
40
Issue ID
1
Page(s)
163-72
Language
n/a
Connective Phrase
n/a
Location/URL
http:; www.nrc.ca/cisti/journals/mineral/mineralogist.html
ISSN
n/a
Notes
n/a
Abstract
Differential thermal analyses (DTA) and thermogravimetric analyses (TG) were carried out on sodalite, tugtupite, danalite, and helvite using a Netzsch STA 409 EP/3/D simultaneous TGDTA apparatus. In the DTA and TG experimental run, a weighed amount of finely powdered sample was heated from 20 to 1450C at a constant rate of 5C/min. Sodalite, Na8[Al6Si6O24]Cl2, melts at 1079C. The NaCl component in the sodalite-derived melt is lost in two stages; about 4.5 wt.% of NaCl is lost slowly at about 1150C, and about 7.0 wt.% of NaCl is lost at a faster rate at about 1284C. The interpretation that the NaCl component behaves this way in sodalite is confirmed by DTA and TG analyses of halite. Tugtupite, Na8[Al2Be2Si8O24]Cl2, melts at 1029C. The NaCl component in tugtupite is lost in two main stages; about 1.8 wt.% of NaCl is first lost at about 1007C, and about 8.2 wt.% of NaCl is lost in several steps between about 1018 and about 1442C. Danalite, ideally Fe8[Be6Si6O24]S2, and helvite, ideally Mn8[Be6Si6O24]S2, undergo an oxidation of (Mn, Fe)2+ to (Mn, Fe)3+ cations. This is followed by a loss of S2(g), and then melting at about 1060C. Finally, there is another oxidation of Mn3+ to Mn4+. These oxidations occur because the samples were heated in a static air environment. The first oxidation in danalite and helvite begins at about 771 and 705C, respectively. Danalite gains 4.0 wt.%, whereas helvite gains 5.0 wt.% in the first weight-gain stage. In the weight-loss stage, danalite loses 5.7 wt.% of S2(g) from about 1029C, whereas helvite loses 4.7 wt.% of S2(g) from about 883C. The second stage of oxidation begins at about 1300C in both the danalite- and helvite-derived melts. At this stage, the weight gain in the danalite-derived melt is about 0.7%, whereas that in the helvite-derived melt is about 0.2%.....
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