Calcium hydroxide
- Calcium hydroxide
- Calcium hydroxide
- Portlandite
- Slaked lime
- Marble lime
- Calcium liquor ( as aqueous solution)
- Lime water ( as aqueous solution)
- Milk of lime ( as aqueous solution)
- E 526
Colorless, odorless solid
Fixed
2.24 g · cm -3 ( 20 ° C)
Decomposition at 550 ° C
Poorly in water ( 1.7 g · l-1 at 20 ° C)
Risk
7340 mg · kg -1 ( LD50, rat, oral)
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Calcium hydroxide (also slaked lime, hydrated lime ( white) hydrated lime, hydrated lime ) is the hydroxide of calcium.
Occurrence
Calcium is found in nature as mineral portlandite.
Production and representation
Calcium hydroxide is produced under high heat (exothermic reaction) when moving calcium oxide with water. This process is also called slaking. The heat is so strong that the water is partly evaporated ( colloquially known as "Smoking " means ).
An overview of the conversion processes between different calcium compounds (technical Kalkkreislauf ) gives the following graph:
Further, the representation by the reaction of the aqueous calcium salt solutions with alkali liquors possible ( for example, calcium nitrate with potassium hydroxide ).
Calcium or calcium itself reacts with water violently to form calcium hydroxide and hydrogen.
Properties
Calcium hydroxide is a colorless powder which dissolves only slightly in water, the solution is strongly alkaline. The solubility is temperature dependent, and decreases with increasing temperature: 1860 mg / l at 0 ° C; 1650 mg / l at 20 ° C and 770 mg / l at 100 ° C. At 580 ° C it decomposes, with calcium oxide and water arise. Calcium hydroxide is of hexagonal crystals having a crystal structure of the cadmium iodide type ( a = 3.584, c = 4.896 A).
Use
The main use of calcium hydroxide is the preparation of mortar in construction. It takes place under the name of hydrated lime use (DIN 1060 ). Lime plasters consist of mixtures of calcium hydroxide and sand. The latter can also be added in the form of ground limestone.
Calcium hydroxide is also used as an intermediate for the production of chloride of lime, and sodium hydroxide from sodium carbonate.
Furthermore, it is used as a medicine in dentistry, especially for disinfection of root canals and cavities, and to stimulate dentin formation.
It is also part of the soda lime, which is used in anesthesia equipment or diving equipment with rebreathing to filter out carbon dioxide from the exhaled air.
Another use is calcium hydroxide as pesticides in fruit growing. Here it is, for example, as a fungicide ( fungal poison) used against canker of fruit trees.
The corrosivity, which also destroyed several pathogens, is the reason why earlier slaked lime for disinfecting stables (the " whitewashing " of the stables ) was used.
In the food industry, it is added as an acidity regulator and food in the EU as a food additive called E 526 no maximum limit ( quantum satis ) generally approved for food.
The slaked lime is used, among other things as an alternative to limestone in flue gas desulfurization, as it is formed with sulfuric acid calcium sulfate (gypsum). The amount used is in this case about 1.8 times lower than for limestone. The plaster thus obtained has a whiteness of 80 % and can be used commercially. Due to its high reactivity, lower consumption amounts are needed. Disadvantage is its significantly higher price compared to limestone.
Lime is also used to improve the sustainability of building. A soil with excessive water content and resulting low bearing capacity, poor compressibility can be improved by mixing in 2-4% MA lime. The lime binds some of the water and thus improves, among other things, the plasticity, the compressibility and carrying capacity. Therefore, improving the soil with lime is a method for improving the installation immediately achievable capacity and facilitate the execution of works.
Kalkwasser is the ( nearly ) saturated solution of calcium hydroxide and serves as a clear liquid for the detection of carbon dioxide.
Suspensions in water are:
- Fat lime ( slaked lime ): a creamy- rigid mass - building materials: lime mortar
- Milk of lime: a whitish, milky fluid, but segregates - lime paint, neutralization of acids, decarbonization, flue gas desulfurization
Safety
Burned ( quicklime ) lime ( calcium oxide, quicklime ) and slaked lime are irritating, contact with the eyes can cause serious eye damage. Quicklime can cause fires under water lubrication.