Silicide, calcium magnesium

Reactions of HCl and nitrides, borides, silicides, germanides, carbides, and sulfides take place at significant rates only at elevated (>650° C) temperatures. The products are the metal chlorides and the corresponding hydrides. The reactions most studied are those involving nitrides of aluminum, magnesium, calcium, and titanium, where ammonia (qv) is formed along with the corresponding metal chloride. 

The following metals have been suggested for this purpose magnesium, aluminium, zinc and also silicon sometimes ferro-silicon, alumino-silicon and calcium silicide are also employed. Deissler [54] was the first (1897) to recommend aluminium as a component of explosives. He was followed by Goldschmidt [55], Escales [56], von Dahmen [57] and Roth [58], In later years Kast [59] investigated military explosives which contained aluminium. 

Magnesium and zinc are readily oxidized, and are liable to undergo oxidation during the storage of mixtures containing them, hence they have not been utilized for military purposes. Apart from this, magnesium is a valuable component of various pyrotechnic mixtures such as those used in signals or for illumination, for which it is hard to find a substitute. With the exception of calcium silicide the silicon alloys burn with more difficulty and are less efficient. For this reason aluminium and calcium silicides are the most widely used. 

Silicon carbide is comparatively stable. The only violent reaction occurs when SiC is heated with a mixture of potassium dichromate and lead chromate. Chemical reactions do, however, take place between silicon carbide and a variety of compounds at relatively high temperatures. Sodium silicate attacks SiC above 1300°C, and SiC reacts with calcium and magnesium oxides above 1000°C and with copper oxide at 800°C to form the metal silicide. Silicon carbide decomposes in fused alkalies such as potassium chromate or sodium chromate and in fused borax or cryolite, and reacts with carbon dioxide, hydrogen, air, and steam. Silicon carbide, resistant to chlorine below 700°C, reacts to form carbon and silicon tetrachloride at high temperature. SiC dissociates in molten iron and the silicon reacts with oxides present in the melt, a reaction of use in the metallurgy of iron and steel (qv). The dense, self-bonded type of SiC has good resistance to aluminum up to about 800°C, to bismuth and zinc at 600°C, and to tin up to 400°C a new silicon nitride-bonded type exhibits improved resistance to cryolite. 

Fuels used include antimony sulfide (which also acts as a frictionator), gum arabic (which also acts as a binding agent), calcium silicide (which also acts as a frictionator), nitrocellulose, carbon black, lead thiocyanate, and powdered metals such as aluminum, magnesium, zirconium, or their alloys. 

Moissan, Henri. (1852-1907). A Native of Paris, Moissan was a professor at the School of Pharmacy from 1886 to 1900 and at the Sorbonne from 1900 to 1907. At the former institution, he first isolated and liquefied fluorine in 1886 by the electrolysis of potassium acid fluoride in anhydrous hydrogen fluoride. His work with fluorine undoubtedly shortened his life as it did that of many other early experimenters in the field of fluorine chemistry. He won great fame by his development of the electric furnace and pioneered its use in the production of calcium carbide, making acetylene production and use commercially feasible in the preparation of pure metals, such as magnesium, chromium, uranium, tungsten etc. and in the production of many new compounds, e.g., silicides, carbides, and refrac-... 

Procedures for the preparation of silicides are also found in other sections of this book (see Alkali Silicides p. 989 f., magnesium silicide p. 921 f., calcium silicide p. 946 f., silicides of Ti, Zr and Th. p. 1249 f.). 

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