Registration Dossier
Registration Dossier
Data platform availability banner - registered substances factsheets
Please be aware that this old REACH registration data factsheet is no longer maintained; it remains frozen as of 19th May 2023.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
Use of this information is subject to copyright laws and may require the permission of the owner of the information, as described in the ECHA Legal Notice.
EC number: 231-545-4 | CAS number: 7631-86-9
- Life Cycle description
- Uses advised against
- Endpoint summary
- Appearance / physical state / colour
- Melting point / freezing point
- Boiling point
- Density
- Particle size distribution (Granulometry)
- Vapour pressure
- Partition coefficient
- Water solubility
- Solubility in organic solvents / fat solubility
- Surface tension
- Flash point
- Auto flammability
- Flammability
- Explosiveness
- Oxidising properties
- Oxidation reduction potential
- Stability in organic solvents and identity of relevant degradation products
- Storage stability and reactivity towards container material
- Stability: thermal, sunlight, metals
- pH
- Dissociation constant
- Viscosity
- Additional physico-chemical information
- Additional physico-chemical properties of nanomaterials
- Nanomaterial agglomeration / aggregation
- Nanomaterial crystalline phase
- Nanomaterial crystallite and grain size
- Nanomaterial aspect ratio / shape
- Nanomaterial specific surface area
- Nanomaterial Zeta potential
- Nanomaterial surface chemistry
- Nanomaterial dustiness
- Nanomaterial porosity
- Nanomaterial pour density
- Nanomaterial photocatalytic activity
- Nanomaterial radical formation potential
- Nanomaterial catalytic activity
- Endpoint summary
- Stability
- Biodegradation
- Bioaccumulation
- Transport and distribution
- Environmental data
- Additional information on environmental fate and behaviour
- Ecotoxicological Summary
- Aquatic toxicity
- Endpoint summary
- Short-term toxicity to fish
- Long-term toxicity to fish
- Short-term toxicity to aquatic invertebrates
- Long-term toxicity to aquatic invertebrates
- Toxicity to aquatic algae and cyanobacteria
- Toxicity to aquatic plants other than algae
- Toxicity to microorganisms
- Endocrine disrupter testing in aquatic vertebrates – in vivo
- Toxicity to other aquatic organisms
- Sediment toxicity
- Terrestrial toxicity
- Biological effects monitoring
- Biotransformation and kinetics
- Additional ecotoxological information
- Toxicological Summary
- Toxicokinetics, metabolism and distribution
- Acute Toxicity
- Irritation / corrosion
- Sensitisation
- Repeated dose toxicity
- Genetic toxicity
- Carcinogenicity
- Toxicity to reproduction
- Specific investigations
- Exposure related observations in humans
- Toxic effects on livestock and pets
- Additional toxicological data
Hydrolysis
Administrative data
Link to relevant study record(s)
- Endpoint:
- hydrolysis
- Type of information:
- experimental study
- Adequacy of study:
- other information
- Reliability:
- 2 (reliable with restrictions)
- Rationale for reliability incl. deficiencies:
- study well documented, meets generally accepted scientific principles, acceptable for assessment
- Reason / purpose for cross-reference:
- reference to same study
- Reason / purpose for cross-reference:
- reference to other study
- Qualifier:
- equivalent or similar to guideline
- Guideline:
- OECD Guideline 111 (Hydrolysis as a Function of pH)
- Deviations:
- yes
- Remarks:
- different test conditions (pH, buffer, temperature range)
- 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,were investigated.
Experiments carried out with a well-defined amorphous silica (Monospher 250 (Merck Darmstadt) included dependence on pH (pH range 1.1 to 8.9) and NaCl concentration at 40 °C. - GLP compliance:
- no
- Radiolabelling:
- no
- Analytical monitoring:
- yes
- Transformation products:
- yes
- No.:
- #1
- Details on hydrolysis and appearance of transformation product(s):
- orthosilicic acid and silicates
- Remarks on result:
- not determinable
- Key result
- Remarks on result:
- not determinable because of methodological limitations
- Results with reference substance:
- not applicable
- Validity criteria fulfilled:
- not applicable
- Conclusions:
- The surface of silica may be covered by a partially hydrolysed gel layer when in contact with water. This layer is in equilibrium with the outer aqueous phase and constitutes a diffusion barrier for ions and water. For the dissolution kinetics, the cleavage and formation of Si-oxygen bonds is a rate-limiting step. Proton and hydroxide ion promoted dissolution play a more important role as compared to a simple hydrolysis of siloxane bridges.
- Executive summary:
The dissolution of a commercial available silica, Monospher 250, as function of time, pH, and sodium chloride concentrations of 0.1, 0.01, and 0.001 mol/L at 40 °C has been measured to derive a general dissolution model considering all possible rate-limiting steps and including protolysis reactions on the surface and in solution. The measured data confirm that proton and hydroxide ion promoted dissolution plays a more prevailing role in the dissolution process than a simple hydrolysis of siloxane bridges. The degree of hydrolysis that may be involved in the dissolution process could not be quantified.
- Endpoint:
- hydrolysis
- Data waiving:
- study technically not feasible
- Justification for data waiving:
- other:
Referenceopen allclose all
The surface of silica may be covered by a partial hydrolysed gel layer when in contact with water (p. 4389 in the publication). 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 (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: Monospher).
The degree of hydrolysis that may be involved in the dissolution process could not be determined.
Description of key information
Hydrolysis, the chemical breakdown due to the reaction with water, releases several silica species from the silica matrix into solution according to the simplified reaction: nSiO2 + 2nH2O <-> nSi(OH)4 and H4SiO4(s) + H2O <-> H3O+(aq) + H3SiO4- (aq). The hydrolysis process is considered a rate-limiting step in the dissolution of silica in water.
Results of dissolution tests (OECD TG 29) are reported in IUCLID section 4.8. (water solubility).
Key value for chemical safety assessment
Additional information
The surface of silica may be covered by a partially hydrolysed gel layer when in contact with water. This layer is in equilibrium with the outer aqueous phase and constitutes a diffusion barrier for ions and water. For the dissolution kinetics, the cleavage and formation of Si-O bonds is a rate-limiting step. Proton and hydroxide ion promoted dissolution play a more important role as compared to a simple hydrolysis of siloxane bridges. A certain, not yet quantifiable degree of hydrolysis is assumed to be involved in the dissolution process (cf. Löbbus M, Vogelsberger W, Sonnefeld J, Seidel A 1998: Current considerations for the dissolution kinetics of solid oxides with silica. Langmuir 14(16), 4386-4396, American Chem. Society)
Information on Registered Substances comes from registration dossiers which have been assigned a registration number. The assignment of a registration number does however not guarantee that the information in the dossier is correct or that the dossier is compliant with Regulation (EC) No 1907/2006 (the REACH Regulation). This information has not been reviewed or verified by the Agency or any other authority. The content is subject to change without prior notice.
Reproduction or further distribution of this information may be subject to copyright protection. Use of the information without obtaining the permission from the owner(s) of the respective information might violate the rights of the owner.