| Autor: |
J. Orehotsky, Marie Kaczenski |
| Rok vydání: |
1979 |
| Předmět: |
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| Zdroj: |
Materials Science and Engineering. 40:245-250 |
| ISSN: |
0025-5416 |
| DOI: |
10.1016/0025-5416(79)90195-2 |
| Popis: |
The kinetics for reducing a static bed of MoO2 powder to molybdenum in hydrogen were investigated as a function of the reaction temperature, the bed depth, the hydrogen flow rate and the powder size. The experimental results indicate that the bed of MoO2 powder will generally reduce to molybdenum in two stages characterized by different rate-limiting mechanisms. The reduction process in both stages occurs by the movement of an MoO2Mo interface down the powder bed with increasing reduction time at constant temperature. The initial stage occurs when the moving interface is within 1 cm of the top of the bed. During this stage the interface moves down the bed with a constant velocity, resulting in a normalized weight loss that is linearly related to the reduction time: Wt/W0 = −Kt + 1 The rate constant K obeys an Arrhenius temperature dependence with an associated activation energy of 1.78 × 104 cal mol−1. The reduction kinetics for the initial stage were found to be consistent with predictions based on the shrinking unreacted core model for the reduction of oxide particles with the chemical reaction at the core-product boundary as the rate-limitting step. The reduction kinetics change when the moving interface is more than 1 cm below the top of the bed. During this second stage the velocity of the moving interface becomes progressively slower, resulting in a non-linear relation between the normalized weight loss and the reduction time. A model was developed to describe the weight loss kinetics of this second reduction stage on the assumption that the diffusion of water vapor out of the bed is the rate-limiting step. The experimental results for this reduction stage were found to be in reasonable agreement with the proposed model. |
| Databáze: |
OpenAIRE |
| Externí odkaz: |
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