Reduction Kinetics of Ag 2 MoO 4 by Hydrogen
- PDF / 391,271 Bytes
- 8 Pages / 593.972 x 792 pts Page_size
- 40 Downloads / 252 Views
TRODUCTION
HYDROGEN reduction of mixed oxides enables the formation of an alloy containing a low melting metal (e.g., Au) with a high melting metal (e.g., Co). For example, in the reduction of cobalt aluminate (CoAl2O4) by hydrogen,[1] to form cobalt with Al2O3 particles, indications were obtained that at temperatures higher than 1273 K, part of the alumina was reduced and the produced aluminum formed a binary Al-Co alloy. Similarly, in the reduction of ZnWO4 with hydrogen, a new W-Zn phase was obtained.[2] The reduction of MoO3 with hydrogen has been subject of numerous investigations[3–7] with contrasting opinions on the kinetics of the reduction of MoO3 to Mo. For example, Hawkins et al.[3] studied the reduction of molybdenum oxide by hydrogen in the temperature range 573 to 723 K and found intermediate suboxides between MoO2 and MoO. Orehotsky et al.[4,5] separately investigated the kinetics of hydrogen reduction of static powder beds of MoO3 to MoO2 and MoO2 to Mo at temperature ranges of 732 to 877 K and 686 to 1083 K, respectively. The activation energies reported for both processes were approximated to 70 kJ/mol. Arnoldy et al.[6] investigated the reduction of MoO3 and MoO2 by varying parameters such as heating rate, sample size, H2O content of the reducing mixture (H2/Ar), and precalcination temperature. In this study, the reported activation energy values ranged J.C. JUAREZ, Researcher, formerly with the Instituto de Investigaciones Metalu´rgicas, UMSNH, is with Universidad Autonoma del Estado de Hidalgo, Pachuca 42180, Mexico. R. MORALES, Professor, is with the Instituto de Investigaciones Metalu´rgicas, UMSNH, Morelia, Mexico. Contact e-mail: [email protected] Manuscript submitted August 20, 2007. Article published online September 16, 2008. 738—VOLUME 39B, OCTOBER 2008
from 80 to 405 kJ/mol. Du Sichen and Seetharaman[7] carefully analyzed the hydrogen reduction of MoO3 and MoO2 by using thin pellets of the oxides placed in crucibles with relatively high walls. The activation energies reported by these authors were 211 kJ/mol for the reduction of MoO3 to MoO2 and 85 kJ/mol for MoO2 to Mo. On the other hand, there does not appear to be much information in the literature on the kinetics of the reduction of Ag2O by hydrogen. This may be due to the fact the Ag2O starts decomposing at about 473 K. Indeed, the kinetics of the thermal decomposition of Ag2O has received large attention.[8] Silver alloys and silver composites find application as electrical contacts due to their high thermal and electrical conductivity. To ensure high electrical conductivity and strong wear resistance, the properties of silver are combined with those of other materials. Powder metallurgy provides a suitable route for the production of refractory alloys especially when the components of refractory alloys have greatly differing melting temperatures, limited mutual solubility, and different densities. Moreover, the powder metallurgy processing route is highly economically competitive. On the synthesis of Ag-Mo base materials, only one
Data Loading...
