Chromium trichloride

Endpoint summary

Additional information

Chromium trichloride in its anhydrous form is a crystalline violet solid, whereas the hexahydrate form is described as dark green if solid. However, in dilute aqueous solutions also the hexahydrate is violet. No odour is reported for the two forms.

Whereas chromium trichloride in anhydrous form melts at approx. 1150 °C, the hexahydrate form of chromium trichloride melts at 83 °C (presumably under loss of crystal water, which boils off leaving the anhydrous form behind at higher temperatures). In public literature no boiling point is reported but a sublimation temperature of 1300 °C of the anhydrous form.

The relative density of chromium trichloride, anhydrous is reported in two reliable peer-reviewed handbooks as 2.76 at 15 °C and 2.86 at 25 °C, respectively. The average value of 2.8 at 20 °C is sufficient for risk and hazard characterisation and is taken forward accordingly. It is noteworthy that the relative density of chromium trichloride hexahydrate in crystalline form is much lower (1.76 at 20 °C) as described in the CRC Handbook.

The test substance is provided to the EU market exclusively as an aqueous solution (typically 50%) and would have to be dried to obtain the solid test substance for testing. Because of this, application of granulometry testing on the solid test substance is not feasible as the characteristics measured would only be relevant to the material obtained specifically during the drying and grinding process described above and would not be applicable to a generic assessment of the test substance. Thus, granulometry data are not required and available.

Being an inorganic crystalline substance chromium trichloride and its hexahydrate have a negligible vapour pressure at ambient conditions. For hazard and risk assessment a worst case value of 0.001 Pa at 20 °C will be used.

Chromium trichloride in its hexahydrate form is very soluble in water (585 g/L at 25 °C) as reported within the CRC Handbook. It is typically marketed within Europe as a 50% aqueous solution in line with this information. The anhydrous form of chromium trichloride is reported being insoluble in cold water and slightly soluble in hot water. However, once in solution and converted to its hexahydrate form, solutions are stable. Significant effects on surface tension are not expected.

Chromium trichloride is not flammable, explosive or oxidising. However, chromium trichloride hexahydrate in aqueous solution was shown to be corrosive to aluminium and steel.