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Please be aware that this old REACH registration data factsheet is no longer maintained; it remains frozen as of 19th May 2023.

The new ECHA CHEM database has been released by ECHA, and it now contains all REACH registration data. There are more details on the transition of ECHA's published data to ECHA CHEM here.

Diss Factsheets

Physical & Chemical properties

Water solubility

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Description of key information

Water solubility (substance): Not relevant

Water solubility (monosilicic acid): approximately 100 - 150 mg/l SiO2/l with condensation occurring at higher concentrations.

Key value for chemical safety assessment

Water solubility:
150 mg/L

Additional information

The requirement to test the substance for water solubility is waived because in contact with water the substance rapidly (violently) hydrolyses to form initially silanediol and hydrochloric acid. With further reaction of the Si-H bonds and loss of hydrogen, monosilicic acid is formed.

At concentrations >100 -150 mg/l as SiO2 according to published sources, monomeric silanediol/monosilicic acid condense rapidly into a highly cross-linked network (gel) or colloidal particles of polysilicic acid. The condensation rate is dependent on temperature, concentration, and acidity or alkalinity of the system. A dynamic equilibrium is established between monomer, oligomers and insoluble amorphous polysilicic acid.

A water solubility of 1E+06 mg/l at 20°C for silanediol and monosilicic acid estimated using a QSAR estimation method shows that the substance is very hydrophilic. The method has not been validated for inorganic substances and does not take into account the condensation reaction.

Further details are given in a supporting report (PFA 2015ao) attached in Section 13 of the IUCLID dataset. PFA, 2015ao, Peter Fisk Associates, The aquatic chemistry of inorganic silicic acid generators, PFA.404.001.001