Studies on kinetics of low-temperature chlorination of ZrO 2 by gaseous carbon tetrachloride
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I.
INTRODUCTION
Z I R C O N I U M tetrachloride is very often the intermediate compound in the process of producing zirconium sponge from its oxide. The tetrachloride is generally produced by chlorination of zirconium dioxide by chlorine in presence of carbon in briquetted or powder form. 1~,21 The chlorination temperature is around 1223 K. In order to minimize the energy consumption and the cost of chlorination facilities, various efforts are being made to bring down the chlorination temperature. Landsberg et a l . 131 have claimed to bring down the chlorination temperature of ZrO2 with C12 by 200 ~ by using carbon monoxide in p/ace of carbon. In the process of various efforts made in this direction, a good number of studies 14,5,61 have been reported by different investigators on the kinetics of chlorination of Z r O 2 by chlorine in the presence of a reducing agent. However, very little information has been reported in the literature for producing zirconium tetrachloride from zirconium oxide by other chlorinating agents such as carbon tetrachloride. Thermodynamically, the chlorination of ZrO2 by CC14 is P.K. JENA, Senior Visiting Professor, Department of Material Science and Metallurgy, Catholic University of Rio de Janeiro, RJ, Brazil, is President, Natural Resources Development Foundation, Bhubaneswar 751002, India. E.A. BROCCHI, Associate Professor and Head, and T.F. VILLELA, Doctorate Student, are with the Department of Materials Science and Metallurgy, Catholic University of Rio de Janeiro, RJ, Brazil. Manuscript submitted January 21, 1993.
METALLURGICAL AND MATERIALS TRANSACTIONS B
highly probable, even at very low temperatures, as shown in the following equation: 17,81 ZrO2 + CC14 = Z r f l 4 q- CO2, AG ~ = - 6 2 , 3 7 8 + 21.59T log T - 275.7T J/mole
[l]
Jena e t a / . t9] have carried out the chlorination of anatase by carbon tetrachloride in the temperature range of 523 to 673 K. At 673 K, about 90 pct of the anatase could be chlorinated during a period of 60 minutes. Recently, the authors have made some exploratory studies on chlorination of zirconium and titanium oxides by carbon tetrachloride vapor at low temperatures. I1~ From these experiments, it was found that both the metal oxides could be chlorinated substantially at low temperatures by carbon tetrachloride. It was further observed that the rate of chlorination could be markedly enhanced by increasing the chlorination temperature to a little above 773 K. For example, in 15 minutes at 673 K, only 18 pct of ZrO2 was chlorinated, whereas at 825 K, nearly 90 pct of the oxide was chlorinated in the same period under similar experimental conditions. The purpose of the present work is to study in detail the chlorination of zirconium oxide by carbon tetrachloride vapor in the low-temperature range of 650 to 825 K, in order to obtain sufficient information on the kinetics and mechanisms of the chlorination processes.
VOLUME 26B, APRIL 1995--235
II.
Fractions of ZrO2 (e) Chlorinated by CCl4 at 650 K Using Pcct~ of 0.6 atm
Table I.
EXPERIMENT
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