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Hydrolysis

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Reference
Endpoint:
hydrolysis
Type of information:
experimental study
Adequacy of study:
key study
Study period:
June 2009
Reliability:
1 (reliable without restriction)
Reason / purpose for cross-reference:
reference to other study
Qualifier:
no guideline followed
Principles of method if other than guideline:
Company data. No guideline indicated. For details on method see IUCLID6 materials and methods section.
GLP compliance:
no
Remarks:
Company data.
Specific details on test material used for the study:
Details on properties of test surrogate or analogue material (migrated information):
not indicated
Radiolabelling:
no
Analytical monitoring:
not required
Details on sampling:
10 g disodium disilicate (delta-crystalline) in 100 ml water were stirred for 5 days at 30°C and then stored in a drying oven at 30°C over the weekend. Subsequently the solution was further stirred for 3 days at 30°C. Afterwords the solution was filtered through a 0.2 µm membrane filter. The filtrate was evaporated at 90°C and the residue was dried at 200°C until constant weight. The undissolved product was dried at approx. 70°C for 2 h.
Buffers:
not applicable
Estimation method (if used):
not applicable
Details on test conditions:
A saturated solution of disodium disilicate (delta-crystalline) in water was prepared. After filtration of the undissolved material the aqueous solution was evaporated to dryness and subsequently dried at 200°C. The crystalline modification of the dry residue was analysed by powder diffratometry. The results of disodium disilicate (delta-crystalline) were compared with commercial available amorphous sodium disilicate.
Duration:
10 d
pH:
7
Temp.:
30 °C
Initial conc. measured:
104 g/L
Number of replicates:
1
Positive controls:
no
Negative controls:
no
Statistical methods:
not applicable
Preliminary study:
no preliminary study
Test performance:
no remarks on test performance
Transformation products:
yes
No.:
#1
No.:
#1
Details on hydrolysis and appearance of transformation product(s):
The powder diffractogram of the dissolved and subsequently dried disodium disilicate (delta-crystalline) doesn't show any crystalline structures but only signals of amorphous silicate. The SiO2/Na2O ratio of the dried material is comparable to the composition of commercial available amorphous sodium disilicate. Therefore, it can be concluded that the crystalline structure of layered delta-sodium disilicate is completely destroyed by dissolution in water yielding an aqueous solution which is identical to a solution of amorphous sodium disilicate (CAS No. 1344-09-8).
Remarks on result:
not measured/tested
Other kinetic parameters:
not applicable
Details on results:
not indicated
Validity criteria fulfilled:
not applicable
Conclusions:
It can be concluded that the crystalline structure of disodium disilicate (delta-crystalline) is completely destroyed by dissolution in water yielding an aqueous solution which is identical to a solution of amorphous sodium disilicate (CAS No. 1344-09-8).
Executive summary:

The powder diffractogram of the dissolved and subsequently dried disodium disilicate (delta-crystalline) doesn't show any crystalline structures but only signals of amorphous silicate. The SiO2/Na2O ratio of the dried material is comparable to the composition of commercial available amorphous sodium disilicate. Therefore it can be concluded that the crystalline structure of layered delta-sodium disilicate is completely destroyed by dissolution in water yielding an aqueous solution which is identical to a solution of amorphous sodium disilicate (CAS No. 1344-09-8).

Upon dilution of concentrated commercial amorphous sodium silicate solutions with water, the highly cross-linked polysilicate ions depolymerize rapidly to monosilicate ions. The resulting water glass is identical to naturally occuring silicate. Thus, it can be concluded that disodium disilicate (delta-crystalline) is degraded hydrolytically to a naturally occuring substance, which is widespred in nature.

Description of key information

Based on the present study and basic textbook knowledge it can be concluded that the crystalline structure of disodium disilicate (delta-crystalline) is destroyed by dissolution in water yielding an aqueous solution which is identical to a solution of amorphous sodium disilicate (CAS No. 1344-09-8).

Key value for chemical safety assessment

Additional information

The powder diffractogram of the dissolved and subsequently dried disodium disilicate (delta-crystalline) doesn't show any chrystalline structures but only signals of amorphous silicate. The SiO2/Na2O ratio of the dried material is comparable to the composition of commercial available amorphous sodium disilicate. Therefore it can be concluded that the crystalline structure of layered delta-sodium disilicate is completely destroyed by dissolution in water yielding an aqueous solution which is identical to a solution of amorphous sodium disilicate (CAS No. 1344-09-8).

Upon dilution of concentrated commercial amorphous sodium silicate solutions with water, the highly cross-linked polysilicate ions depolymerize rapidly to monosilicate ions. The resulting water glass is identical to naturally occuring silicate. Thus, it can be concluded that disodium disilicate (delta-crystalline) is degraded hydrolytically to a naturally occurring substance, which is widespread in nature.

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