Paper Title:
A 21st. Century Perspective on Molybdenum Powder Production by Hydrogen Reduction
  Abstract

High purity molybdenum metal powder is produced commercially from hexavalent molybdenum precursors, viz.: ammonium dimolybdate (ADM) or molybdenum trioxide. One conventional process incorporates first-stage and second-stage flowsheet components, with hydrogen gas serving as reductant. This two-stage strategy is employed in order to minimize the formation of volatile molybdenum species that would otherwise be generated at the high temperature required to obtain molybdenum (Mo) in a single stage conversion of the molybdenum precursor. Although molybdenum powder has been produced commercially for over a century, a comprehensive understanding of the kinetic mechanisms and powder characteristics, e.g. oxygen content and particle morphology, is far from being definitive. In fact, it might be argued that the “art” and engineering, in a commercial context, has advanced ahead of the fine-detail science-derived metallurgical process-engineering. Theoretical contributions presented in this paper are focused primarily on the fundamentals of the conversion process associated with second-stage reduction process – MoO2 to Mo and the factors that contribute to the oxygen content of the molybdenum powder product (1000 to 100 ppm(w) O, range). Thus, equilibrium-configuration details concerning both solid and gas phases are addressed, including the volatile hexavalent molybdenum vapor complexes as well as solubility of oxygen in molybdenum. In regard to the role of a chemical vapor-transport mechanism on powder morphology in second-stage conversion of MoO2 to Mo, it is shown that the partial pressure of the prominent molybdenum hydroxide vapor-complex (MoO2(OH)2) is far too low to support such a mechanism. This contention has been corroborated by employing helium to control the partial pressures of hydrogen and water in the gas phase. Secondarily, a limited assessment of the intrinsic rate-controlling mechanisms that can contribute to the residual oxygen-content of the Mo powder product is also provided. Powder morphology, and its concomitant influence on specific surface-area of the Mo powder product, is found to correlate with the oxygen-content determination of the powder produced during second-stage reduction, and according to the processing strategy employed. Consequently, it has been found cogent to “partition” second-stage reduction into: i) a relatively high-rate Primary Reduction Sequence, and ii) a lower rate Deoxidation Sequence.

  Info
Periodical
Materials Science Forum (Volumes 561-565)
Main Theme
Edited by
Young Won Chang, Nack J. Kim and Chong Soo Lee
Pages
447-452
DOI
10.4028/www.scientific.net/MSF.561-565.447
Citation
G.P. Martins, T. Kangsadan, G. Scott, C. Wagner, J. Van Hoose, "A 21st. Century Perspective on Molybdenum Powder Production by Hydrogen Reduction", Materials Science Forum, Vols. 561-565, pp. 447-452, 2007
Online since
October 2007
Export
Price
$32.00
Share

In order to see related information, you need to Login.

In order to see related information, you need to Login.

Authors: Xiang Yang Chen, Chun Yang Bu, Xin Zhe Lan, Xin Rui Zhao
Abstract:The principle and process of producing molybdenum powder via reduction reaction of molybdenum trioxide at lower temperature in a N2-H2 system...
723
Authors: Liu Jie Xu, Shi Zhong Wei, Guo Shang Zhang, Ji Wen Li, Xiang Dong Ma, Bao Zhu Dai
Abstract:To enhance the wear resistance of molybdenum alloys, Mo-based composites reinforced by Al2O3 ceramic particles were developed. Using Al(NO3)3...
1077
Authors: Geng An
Micro/Nano Materials
Abstract:Using the specially designed mechanochemical ball-mill equipment, the ultramicro molybdenum nitride powders were prepared from pure...
945
Authors: Shi Zhong Wei, Liu Jie Xu, Guo Shang Zhang, Ji Wen Li, Bao Zhu Dai
Chapter 3: Advanced Manufacturing Technology
Abstract:Mo-based composites with Al2O3 particles were developed in order to enhance the wear resistance of molybdenum alloys....
467
Authors: Wei Huang, Li Jun Zhu, Min Ming Zou, Fu Jun Shang, Ji Hong Su, Xiao Yan Tian, Tao Zhang
Chapter 4: Trends in Materials and Manufacturing
Abstract:In this paper, the preparation technology of spherical molybdenum powder has been studied by using of continuous induction plasma powder...
298