Studies on kinetics of low-temperature chlorination of ZrO{sub 2} by gaseous carbon tetrachloride

Journal Article · Sat Apr 01 04:00:00 EST 1995 · Metallurgical Transactions, B

OSTI ID:42839

Jena, P K; Brocchi, E A; Villela, T F ^[1]

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1. Catholic Univ. of Rio de Janeiro (Brazil). Dept. of Material Science and Metallurgy

Studies on the kinetics of chlorination of ZrO{sub 2} powder by carbon tetrachloride vapor in mixture with nitrogen in a low-temperature range of 650 to 825 K at different periods and partial pressures of carbon tetrachloride were carried out. The chlorination results of 650 and 675 K seem to follow a diffusion-controlled reaction model of Jander`s type: [1 {minus} (1 {minus} R){sup 1/3}]{sup 2} = k{sub 1}t where R is the fraction of ZrO{sub 2} chlorinated in time t and K{sub 1} is the rate constant. The approximate activation energy of the process was calculated from k{sub 1} values at the previously mentioned two temperatures and found to be 278 kJ/mole. For the chlorination in the temperature range of 700 to 750 K, the topochemical reaction model 1 {minus} (1 {minus} R){sup 1/3} = k{sub 2}t was followed. The rate constant, k{sub 2}, was found to be proportional to the partial pressure of carbon tetrachloride. The activation energy of this reaction was calculated to be 154 kJ/mole. In the temperature range of 775 to 825 K, the rate of chlorination was found to be directly proportional to the time of chlorination following Langmuir`s Adsorption Isotherm. Because of the very high rate of chlorination and thermodynamic possibility of decomposition of CCl{sub 4} above 773 K, the rate-controlling step has been suggested to be the decomposition of the adsorbed complex formed by ZrO{sub 2} with carbon and chlorine atoms, obtained from the decomposition of CCl{sub 4} vapor. The activation energy of the process was 54 kJ/mole. In view of nearly complete chlorination of ZrO{sub 2} by CCl{sub 4} in a very short period of about 15 minutes, at a temperature around 800 K and lesser possibility of formation of toxic product gases, the process is recommended for commercial application.

• OSTI ID: 42839
• Journal Information: Metallurgical Transactions, B, Journal Name: Metallurgical Transactions, B Journal Issue: 2 Vol. 26; ISSN MTTBCR; ISSN 0360-2141
• Country of Publication: United States
• Language: English

Related Subjects

40 CHEMISTRY
ACTIVATION ENERGY
CARBON TETRACHLORIDE
CHEMICAL REACTION KINETICS
CHLORINATION
MATHEMATICAL MODELS
NITROGEN
ZIRCONIUM OXIDES