日本金属学会誌

J. Japan Inst. Metals, Vol. 51, No. 4 (1987),
pp. 319-327

Effect of a Trace of Gaseous Sulphur on the Gaseous Reduction of NiO Pellets Containing MgO

Shoji Hayashi1, Yoshiaki Iguchi1 and Jiro Hirao2

1Department of Materials Science and Engineering, Nagoya Institute of Technology, Nagoya
2Emeritus Professor of Nagoya Institute of Technology

Abstract:

Experiments have been made on the reduction of NiO pellets containing MgO with H2 or CO-CO2 mixtures bearing gaseous sulphur in the temperature range from 773 to 1273 K using a thermobalance; the sulphur activity in the reducing gas ranged from the value in the coexistence of Ni and Ni sulphide to 10-2 of it.
Except the reduction of pure NiO with H2 or 99%CO-1%CO2 mixtures, a macroscopic reduction pattern of a pellet in the absence of sulphur is a homogeneous type with the formation of a dense Ni shell on the entire surface of NiO particles, and the pattern in the presence of sulphur is a topochemical type with the formation of a fine porous Ni layer.
The reduction in the former pattern is retarded following the rate equation of oxygen diffusion control through a dense metallic nickel layer, while in the latter one it proceeds without the retardation and conforms with the mixed control equation. These facts are also observed in the reduction of pure NiO with 50%CO-50%CO2 mixtures.
The phenomena mentioned above can be interpreted by a mechanism that adatoms of sulphur on the surface of metallic Ni suppress the development of the bonding between Ni and NiO.
The gas diffusion through a porous Ni layer and the mass transfer in NiO solid were discussed using some diffusion data available.


(Received 1986/7/14)

Keywords:

NiO pellet, gaseous reduction, acceleration of reduction, adsorbed sulphur, fine porous nickel, dense nickel, MgO doping


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