Magnesia graphite production

Typically, Be-containing alloys and intermetallic phases have been prepared in beryllia or alumina crucibles Mg-containing products have been synthesized in graphite, magnesia or alumina crucibles. Alloys and compounds containing Ca, Sr and Ba have been synthesized in alumina , boron nitride, zircon, molybdenum, iron , or steel crucibles. Both zircon and molybdenum are satisfactory only for alloys with low group-IIA metal content and are replaced by boron nitride and iron, respectively, for group-IIA metal-rich systems . Crucibles are sealed in silica, quartz, iron or steel vessels, usually under either vacuum or purified inert cover gas in a few cases, the samples were melted under a halide flux . 

The cell which holds the molten salt and metal can be made of a variety of materials, such as iron, graphite, fire brick, alumina, magnesia, molybdenum or tantalum. The cathode is usually molybdenum, tantalum or tungsten and sometimes iron, cobalt or nickel. The choice of the cell and cathode materials will depend on the product desired. Graphite is almost always the choice for the anode because it is relatively inert to the halide gases (F2 or CI2) or oxygen liberated at this electrode. 

Excessive reaction between the container material and the products or reactants must be avoided, and this may impose a limit upon the peak temperature which is allowable, or upon the materials of reactor construction. Reactors take different forms and are made from or lined with a variety of refractory materials. Lime, magnesia, electrically fused dolomite, calcium fluoride, nickel, stainless-steel, molybdenum, tantalum, niobium or graphite have all been used, for different purposes. 

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