Calciumnitrit

BeschreibungCalcium nitrite has the formula of Ca(NO2)2 and the molecular weight of 132.0894 g/mol. It can be made by the usual double decomposition reaction of sodium nitrite and CaCl2. It forms a tetrahydrate that is isomorphous with the strontium and barium salts: 2Na2NO2 (aq) + CaCl2 Ca(NO2)2 (aq) + 4NaCl (aq)

VerwendenCalcium nitrite has several industrial uses: 1. Calcium nitrite has high solubility, so can be used as a solution or powder in concrete as an “anti-freeze” during winter months as needed. Using this antifreeze at negative temperature can promote the hydration of minerals in cement, and the freezing point of operative temperature can be reduced to –25°C. 2. This salt is a steel rust inhibitor: calcium nitrite can clean steel and protect it from rust, and can protect steel material in concrete used to construct buildings and structures, to extend the useful life of concrete in buildings. 3. In concrete, Ca(NO2)2 acts as a coagulator: calcium nitrite is free of chlorine and alkali, capable to reduce alkali aggregation of concrete and improve its early strength and compressive resistance. The calcium nitrite protects steel reenforcing bars from chlorideinduced corrosion. One advantage to calcium nitrite is that its protection mechanism is well defined. Data are known that show the levels of chloride to which given levels of calcium nitrite will protect. Once corrosion initiates, the rates are lower with calcium nitrite present. These results have been used to produce reinforced concrete structures with durability in excess of 50–100 years. 4. Calcium nitrite can be used as corrosion inhibitor when added to lubricating agents. 5. Calcium nitrite can also be used in pharmaceutical, dyes and metallurgy industries, as a mild reducing agent.

synthetischeIndustrially, calcium nitrite is manufactured by reacting “NOX” gas with “lime”: Ca(OH)2 + NO +NO2Ca(NO2)2 +H2O By carefully controlling calciumnitrite conditions, the selectivity on converted lime, on a molar basis, is over 95% pure. It is soluble in water (98.2 g/100 ml at 20 °C) and the solution must be evaporated at low temperature to obtain the tetrahydrate. If heated with NO2 gas, it also form the nitrate: Ca(NO2)2 + NO2Ca(NO3)2 + NO Anhydrous calcium nitrite is unstable and slowly oxidizes in air to form the nitrate. It is also soluble in alcohol at 0.97 g/100 ml at 20 °C.