Calcium hydroxide is a colorless crystal or white powder produced on a large scale by the reaction of calcium oxide with water. The process is known as slaking, and the product is slaked lime or hydrated lime. When heated to more than 580 degree Celsius, it dehydrates to form the oxide.
Physical Properties
Calcium hydroxide is a strong base and soluble in water, only in small amounts--approximately 0.2 grams per 100 cubic centimeters. Therefore, calcium hydroxide solution is weakly basic. The clear, saturated alkaline solution of calcium hydroxide is lime water, and the suspension of slaked lime in water is called milk of lime.
Chemical Properties
Calcium hydroxide compounds are available in both aqueous suspensions and solid forms, and when they are exposed to water, disintegration of calcium hydroxide takes place, making it behave like a base.
Common Uses
Calcium hydroxide cement combined with water and an aggregate of various sizes makes workable slurry, with the consistency of a thick milkshake. The binding quality of cement arises from a chemical reaction between the cement and water, which is known as hydration. In addition, calcium hydroxide is used in treating sewage, water, and industrial wastes.
Use in Construction Industry
Calcium hydroxide cement is now almost universally used for structural concrete, for uniting the surfaces of various materials, and for coating surfaces to safeguard them from chemical attack. Since it is an inexpensive alkali, calcium hydroxide has a number of commercial uses, including whitewash, mortar, and other construction materials.
Manufacture
Manufacturing calcium hydroxide cement is a complex process. The raw materials are ground together and heated until they combine to form a clinker, which is ground into a fine powder. This is done in rotary kilns more than 150 m long and 3.7 m in diameter. The raw materials are introduced into the upper end in the form of a dry rock powder or as a wet paste made of ground-up rock and water. Then, these materials are dried and heated by hot gases at the lower end. When carbon dioxide is driven off, the charge is fused at temperatures between 1,540 and 1,600 degrees. Almost six hours are needed before the material passes from one end of the kiln to another. Then, the clinker is cooled rapidly and ground up. The cement thus produced is of a very fine texture.
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