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Please be aware that this old REACH registration data factsheet is no longer maintained; it remains frozen as of 19th May 2023.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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water solubility
Data waiving:
study scientifically not necessary / other information available
Justification for data waiving:
the study does not need to be conducted because the substance is hydrolytically unstable at pH 4, 7 and 9 (half-life less than 12 hours)

Description of key information

Water solubility [trichlorosilane]: Not relevant due to very rapid hydrolysis in contact with water

Water solubility [monosilicic acid and silanetriol]: approximately 100 - 150 mg/L SiO2/L with condensation occurring at higher concentrations.

Key value for chemical safety assessment

Additional information

The requirement to conduct a water solubility study for the submission substance is waived because in contact with water the substance hydrolyses very rapidly to form silanetriol and hydrochloric acid. Silanetriol reacts further to generate monosilicic acid and hydrogen.

Trichlorosilane reacts very rapidly with water, generating silanetriol and hydrochloric acid. Silanetriol reacts further to give monosilicic acid, which condenses at concentrations above approximately 100-150 mg/L as SiO2 to give insoluble amorphous polysilicic acid. The other product of this reaction is hydrogen.

At concentrations >100-150 mg/L as SiO2 according to published sources, monomeric silanetriol/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. Further details about the chemistry of inorganic silicic acid is given in (PFA 2015ao) attached to Section 13.


PFA (2015ao). Peter Fisk Associates, The aquatic chemistry of inorganic silicic acid generators, PFA.404.001.001