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Please be aware that this old REACH registration data factsheet is no longer maintained; it remains frozen as of 19th May 2023.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

Administrative data

Endpoint:
hydrolysis
Type of information:
migrated information: read-across based on grouping of substances (category approach)
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Accepted, well documented publication.

Data source

Reference
Reference Type:
publication
Title:
Current considerations for the dissolution kinetics of solid oxides with silica
Author:
Löbbus M, Vogelsberger W, Sonnefeld J, Seidel A
Year:
1998
Bibliographic source:
Langmuir 14(16), 4386-4396 (American Chem. Society)

Materials and methods

Test guideline
Qualifier:
equivalent or similar to guideline
Guideline:
other: OECD 105 (water solubility)
Principles of method if other than guideline:
Development of a dissolution model for silicon oxides, taking into account Si-O bond cleavage and formation as well as protolysis of silanol groups. Three different models, pH dependent surface potential, diffuse double layer, and gel layer, are investigated.
Experiments carried out with a well-defined amorphous silica (Monospher 250 (Merck Darmstadt) included dependence on pH and NaCl concentration at 40 °C.
GLP compliance:
no

Test material

Constituent 1
Reference substance name:
Automatically generated during migration to IUCLID 6, no data available
IUPAC Name:
Automatically generated during migration to IUCLID 6, no data available
Details on test material:
Synthetic amorphous silicas:
CAS-No. 112945-52-5, CAS-Name: Silica, amorphous, fumed, crystalline-free;
CAS-No. 112926-00-8, CAS-Name: Silica gel, precipitated, crystalline-free.

Test material: Monospher 250 (Merck Darmstadt)
Radiolabelling:
no

Study design

Analytical monitoring:
yes

Results and discussion

Transformation products:
yes
Identity of transformation products
No.:
#1
Reference
Reference substance name:
Unnamed
IUPAC name:
orthosilicic acid / silicate ion
Identifier:
common name
Identity:
orthosilicic acid / silicate ion
Details on hydrolysis and appearance of transformation product(s):
see Report, Table 1 and Fig. 4 (see below: AD under attached background material)

Any other information on results incl. tables

The surface of silica may be covered by a partial hydrolysed gel layer when in contact with water (p. 4389). This layer is in equilibrium with the outer aqueous phase and constitutes a diffusion barrier for ions and water.

It is known and generally recognised that proton and hydroxide ion promoted dissolution plays a more prevailing role in the dissolution process than a simple hydrolysis of siloxane bridges (p. 4390).

The experimental part showed that there was a distinct pH dependence in the rate of dissolution, increasing with the pH increasing. However, the free dissolved SiO2 reached a maximum independent of the pH (Report, Table 1, Fig.. 4). It is concluded that the total amount of silica dissolved is relatively constant in a broad range of pH (1.1 < pH < 8.9) (p. 4393).

The level of maximum solubility was about 2.7 mmol SiO2/L (here: Monosphere, see also 4.8 Water solubility).

The degree of hydrolysis that may be involved in the dissolution process could not yet be solved.

Applicant's summary and conclusion