Kinetics of chlorination of niobium pentoxide by carbon tetrachloride

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Studies on the kinetics of chlorination of tantalum pentoxide powder by carbon tetrachloride vapor in dilution with nitrogen have been carried out by weight-loss measurements in two temperature ranges, i.e., 698 to 773 K and 793 to 853 K. The effect of time, temperature, and partial pressure of CCl 4 (P CCl 4 ) on the kinetics of chlorination of the powder Ta 2 O 5 , (Ϫ105 ϩ 74 m) has been investigated. In both the temperature ranges, the chlorination results have been found to fit the following relationship during the "initial periods:"where ␣ is the fraction of the oxide reacted in time t and k 1 is the rate constant. In the low-and hightemperature ranges, the activation-energy (E ) values have been calculated and were found to be 145 and 71 kJ/mole, respectively. The k 1 value was found to be proportional to P 1.5CCl4 in the lowertemperature range, while in the higher-temperature range, it was found to be proportional to P 0.9CCl4 . In the "latter periods" of the chlorination of Ta 2 O 5 , the following relationship was found to be applicable in both the temperature ranges:where k 2 is the rate constant and c is another constant. However, in the latter periods of the chlorination, the activation energy in the lower-temperature range was calculated to be 31 kJ/mole, while that in the higher-temperature range was found to be 142 kJ/mole. Further, in the lower-temperature range, k 2 was found to be nearly independent of P CCl 4 , while in the higher-temperature range, it was found to be proportional to P 0.9 CCl4 , as observed in the initial periods. Based on these kinetics results, two different mechanisms for the chlorination of Ta 2 O 5 by CCl 4 vapor have been suggested for the two temperature ranges studied.It was possible to chlorinate Ͼ92 pct of Ta 2 O 5 (Ϫ105 ϩ 74 m) at 833 K in 210 minutes, by using CCl 4 at a partial pressure of 0.6 atm.

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confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Studies on the kinetics of carbon tetrachloride chlorination of tantalum pentoxide

Jena

Brocchi

Lima

2001

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Kinetics of chlorination of tantalum pentoxide in mixture with sucrose carbon by chlorine gas

Ruiz

González

Rivarola

2004

The mechanism and kinetics of ␤-Ta 2 O 5 chlorination, mixed with sucrose carbon, have been studied by a thermogravimetric technique. The investigated temperature range was 500°C to 850°C. The reactants and reaction residues were analyzed by scanning electronic microscopy (SEM), X-ray diffraction (XRD), and Brunauer-Emmett-Teller method for surface area (BET). The effect of various experimental parameters was studied, such as carbon percentage, temperature, chlorine partial pressure, and flow, use of the multiple sample method, and carbon previous oxidation. The carbon percentage and previous treatment have an effect on the system reactivity. The temperature has a marked effect on the reaction rate. In the 500°C to 600°C temperature interval, the apparent activation energy is 144 kJ/mol of oxide, while at higher temperatures, the activation energy decreases. With high chorine partial pressures, the order of reaction is near zero. The kinetic contractile plate model, X ϭ kt, considering carbon oxidation as the controlling stage, is the one with the best fit to the experimental data. A probable mechanism for the carbochlorination of ␤-Ta 2 O 5 is proposed: (1) activation of chlorine on the carbon surface, (2) chlorination of Ta 2 O 5 , (3) oxidation of carbon, and (4) recrystallization of ␤-Ta 2 O 5 .

Kinetics of low-temperature chlorination of vanadium pentoxide by carbon tetrachloride vapor

Jena¹,

Brocchi

González

2005

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Low-temperature chlorination of vanadium pentoxide by carbon tetrachloride vapor in dilution with nitrogen has been carried out. The effect of time, particle size, partial pressure of CCl 4 vapor (0.1 to 0.6 atm), and temperature (553 to 788 K) on the extent of chlorination of V 2 O 5 has been investigated. The extent of chlorination of the oxide is found to increase with a decrease in its particle size. In all cases, the reaction followed a topochemical reaction model, obeying the following relationship:where ␣ is the fraction of V 2 O 5 chlorinated in time t and k is the rate constant. The rate constant has been found to be directly proportional to the partial pressure of CCl 4 (PCCl 4 ). The activation energy values between 553 and 643 K and that between 683 and 788 K have been calculated and found to be 38.9 and 11.5 kJ/mole, respectively. Based on the kinetics results, mechanisms of reaction in the two temperature ranges have been suggested. It has been possible to chlorinate V 2 O 5 at 753 K to about 87 pct in 30 minutes, using a very low partial pressure of CCl 4 of 0.15 atm.