Calcium and Calcium Alloys

Abstract

Calcium, Ca, a member of Group 2 (IIA) of the Periodic Table between magnesium and strontium, is classified, together with barium and strontium, as an alkaline‐earth metal and is the lightest of the three. Calcium metal does not occur free in nature; however, in the form of numerous compounds, it is the fifth most abundant element, constituting 3.63% of the earth's crust. Calcium is mainly used as a reducing agent for many reactive, less common metals; to remove bismuth from lead; as a desulfurizer and deoxidizer for ferrous metals and alloys; and as an alloying agent for aluminum, silicon, and lead. Pure calcium is a bright, silvery‐white metal, although under normal atmospheric conditions freshly exposed surfaces of calcium quickly become covered with an oxide layer. The metal is extremely soft and ductile. Calcium's usefulness as a structural material is limited by low tensile strength and high chemical reactivity. Calcium has a valence electron configuration of 4 s 2 and characteristically forms divalent compounds. It is very reactive and reacts vigorously with water, liberating hydrogen and forming calcium hydroxide, Ca(OH) 2 . Calcium does not readily oxidize in dry air at room temperature but is quickly oxidized in moist air or in dry oxygen at about 300°C. Calcium reacts with fluorine at room temperature and with the other halogens at 400°C. Calcium is an excellent reducing agent and is widely used for this purpose. Although in Western countries the aluminothermic process has completely replaced the electrolytic method, electrolysis is believed to be the method used for calcium production in the People's Republic of China and the Commonwealth of Independent States (CIS). Because of its extreme chemical reactivity, calcium metal must be carefully packaged for shipment and storage. The metal is packaged in sealed argon‐filled containers. Calcium is classed as a flammable solid and is nonmailable. Calcium metal and most calcium compounds are nontoxic. Care must be taken, however, to avoid contact with water owing to the exothermic liberation of hydrogen and the resulting explosion hazard. Direct alloying of the pure metals is normally used in the production of 80% calcium–magnesium, 70% magnesium–calcium, and 75% calcium–aluminum alloys.