During the last war, with the increased demand for magnesium metal and the general disregard for costs, a number of plants were constructed for the production of magnesium by vacuum metallurgical methods. (Both the Carbothermic Process and the Pidgeon Ferrosilicon Process employ vacuum systems for the production of metallic Mg.)
At the close of the war several of the government built plants were forced to suspend operations because of the economic impossibility of producing magnesium in competition with the Dow Chemical Company. It was with the availability of these plants in mind that experimentation with the possibilities of producing metallic Zn (from a sphalerite concentrate) under reduced pressure was undertaken.
The retorts used in the Pidgeon Process are of a high chrome, high nickel steel ( 28Cr, l5Ni, 1.5Si, 1.25Mn, and .3C) and the process involves runs of approximately 9 1/2 hours at a temperature of about 1150⁰C and a pressure ranging from 1000 microns (Hg) at the start of the process to 45 microns at the conclusion.
The equipment used in this experiment produces conditions that closely approximate those obtainable with the equipment used for the Pidgeon Process. Although many runs were made at pressures lower than those obtained industrially it is believed that, except for a slight increase in yield at reduced pressures, the results obtained at a pressure of 1 micron are substantially the same as those that would be obtained at a pressure of 500 microns or even higher”--Introduction, pages 2-3.
Materials Science and Engineering
Missouri School of Mines and Metallurgy
24 Jan 1949
Fuqua, John H. and Magruder, William H., "A Report on the Reduction of Sphalerite under Reduced Pressure" (1949). Missouri School of Mines and Metallurgy Reports. 4.