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Physical & Chemical properties

Melting point / freezing point

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Reference
Endpoint:
melting point/freezing point
Type of 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:
data from handbook or collection of data
Remarks:
Data from peer-reviewed handbook or collection of data.
Justification for type of information:
1. HYPOTHESIS FOR THE CATEGORY APPROACH: The hypothesis is that properties are likely to be similar or follow a similar pattern because of the presence of a common metal ion, in this case tungstate.
2. SOURCE AND TARGET CHEMICAL(S) (INCLUDING INFORMATION ON PURITY AND IMPURITIES):
Source: Ammonium paratungstate
Target: Ammonium metatungstate
3. CATEGORY APPROACH JUSTIFICATION: See Annex 3 in CSR
4. DATA MATRIX: See Annex 3 in CSR
Reason / purpose for cross-reference:
read-across: supporting information
Principles of method if other than guideline:
Data in this peer-reviewed publication were taken from many sources, including both compilations and primary literature. Where conflicts were found, the value deemed most reliable was chosen for inclusion in the handbook. Reference sources were not provided for this parameter, nor was the experimental method.
GLP compliance:
no
Type of method:
thermal analysis
Decomposition:
yes
Decomp. temp.:
> 300 °C
Remarks on result:
other: Upon heating to 300-800 °C, ammonia and water are evolved. The decomposition becomes more complete as temperature and duration of heating are increased.
Conclusions:
On heating APT to 300-800 °C ammonia and water are evolved.
Executive summary:

Due to the similar chemical constituency and structure between the source substance (ammonium paratungstate) and the target substance (ammonium metatungstate), the physico-chemical properties would be expected to be the same or sufficiently similar such that application of read-across is appropriate for this endpoint. For more details, refer to the read-across category approach description in the Category section of this IUCLID submission or Annex 3 of the CSR.

Description of key information

No melting point data are available for ammonium metatungstate (target substance). However, data are available for ammonium paratungstate (source substance), which are used for read-across. Ammonium metatungstate is expected to decompose at temperatures above 300°C, based on read-across from ammonium paratungstate. For risk assessment purposes the maximum melting point of 500°C was used.

 

Key value for chemical safety assessment

Melting / freezing point at 101 325 Pa:
500 °C

Additional information

Due to the similar chemical constituency and structure between the source substance (ammonium paratungstate) and the target substance (ammonium metatungstate), the physico-chemical properties would be expected to be the same or sufficiently similar such that application of read-across is appropriate for this endpoint. For more details, refer to the read-across category approach description in the Category section of this IUCLID submission or in Annex 3 of the CSR.

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