Calcium chloride

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Author: Amelie Stahlbuhk
back to Chloride


Abstract[edit]

The different hydrate stages of calcium chloride are presented, as well as their behavior regarding solubility and hygroscopicity.

Hydrate stages[edit]

Calcium chloride monohydrate: CaCl2•H2
Sinjarite: CaCl2•2H2O
Calcium chloride tetrahydrate: CaCl2•4H2O
Antarcticite: CaCl2•6H2O

Solubility[edit]

Figure 1: Solubility of calcium chloride in water. The molality m [n(CaCl2•xH2O)•kg(H2O)-1] is plotted against the temperature.


Under standard conditions the hexahydrate of calcium chloride Antarcticite is the stable form. The salt has got a high solubility in water which increases with increasing temperatures. The dehydration steps to the calcium chloride tetrahydrate and to sinjarite take place at temperatures of 30 °C and 45 °C, respectively.

Hygroscopicity[edit]

Figure 2: Deliquescence behaviour of calcium chloride in the temperature range from -45 to 80 °C. The water activity aw is plotted against the temperature.


In the system CaCl2-H2O hydration/dehydration and crystallization/deliquescence processes can occur by changing relative humidity or temperature. At room temperature the present phase Antarcticite has got a deliquescence humidity of about 30 %. The deliquescence behavior depends on the temperature as the deliquescence humidity decreases with increasing temperature. Changing the relative humidity at 20 °C, calcium chloride tetrahydrate forms at values below 18 % RH. The dehydration to the Dihydrate (sinjarite) and the monohydrate occurs at 9 % RH and 6 % RH, respectively.


Table 1: Deliquescence and equilibrium humidities at 20 °C.
Phase transition Deliquescence or equilibrium humidity at 20°C
Antarcticite-solution 33.3 %
Antarcticite-Calcium chloride tetrahydrate 18.5 %
Calcium chloride tetrahydrate-Sinjarite 9 %
Sinjarite-Calcium chloride monohydrate 6 %


References[edit]

Literature[edit]