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Physical & Chemical properties

Melting point / freezing point

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Endpoint:
melting point/freezing point
Type of information:
not specified
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 a peer-reviewed handbook, accepted as a reliable data source according to Chapter R.7A of REACH Guidance on information requirements and chemical safety assessment, adequate for assessment. Restrictions apply as no experimental details and purity is not specified.
Principles of method if other than guideline:
unspecified
GLP compliance:
not specified
Type of method:
other: no data
Remarks:
handbook data
Melting / freezing pt.:
ca. 770 °C
Decomposition:
yes
Executive summary:

A reference handbook provides a melting/decomposition temperature of ca 770°C for the anhydrous form of the substance.

Endpoint:
melting point/freezing point
Type of information:
not specified
Adequacy of study:
supporting study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
data from handbook or collection of data
Remarks:
Data from a secondary source, accepted as a reliable data source according to Chapter R.7A of REACH Guidance on information requirements and chemical safety assessment, adequate for assessment. Restrictions apply as no experimental details and purity is not specified.
Reason / purpose:
reference to other study
Melting / freezing pt.:
770 °C
Decomposition:
yes
Remarks on result:
other: (ref.1) supposed anhydrous form
Melting / freezing pt.:
250 °C
Decomposition:
yes
Remarks on result:
other: (ref.2) Melts when gradually heated; at 250 deg C loses its water
Melting / freezing pt.:
770 °C
Decomposition:
yes
Remarks on result:
other: (ref.3)
Melting / freezing pt.:
86.5 °C
Decomposition:
yes
Remarks on result:
other: (ref.4) Aluminum Sulphate Octadecahydrate
Executive summary:

A reference database provides different melting point values, showing that the hydrated forms loose the crystallisation water, before the anhydrous form decomposes at 770°C.

Endpoint:
melting point/freezing point
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
supporting study
Justification for type of information:
The test substance is aluminium sulphate basic, of formula Al2 (OH)0.16 (SO4)2.92, and not pure aluminium sulphate Al2 (SO4)3; however, according to the notifier, limited basicity may occur in the technical substance. Therefore, the chemical similarity (only 0.8% OH) is considered sufficient for supporting data on the hydrated form, the reference substance for the REACh registration dossier being the anhydrous form.
Reason / purpose:
read-across source
Executive summary:

From analogue, no melting (i.e. transition to liquid form) is expected up to 550°C for the 15 - 16 H2O hydrated form, but with decomposition corresponding to crystal water loss.

Endpoint:
melting point/freezing point
Type of information:
experimental study
Adequacy of study:
supporting study
Study period:
09 March 2010- 04 June 2010
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Remarks:
This study has been performed according to OECD and EC guidelines and according to GLP principles. Test substance is adequately characterised. Therefore full validation applies.
Qualifier:
according to
Guideline:
OECD Guideline 102 (Melting point / Melting Range)
Deviations:
no
Qualifier:
according to
Guideline:
EU Method A.1 (Melting / Freezing Temperature)
Deviations:
no
GLP compliance:
yes (incl. certificate)
Type of method:
thermal analysis
Remarks:
Differential Scanning Calorimetry + ThermoGravimetric Analysis
Remarks on result:
other: Melting of the test substance was not observed (under nitrogen).

Experiments were performed from 25°C (initial temperature) to 550°C (maximum end temperature). During the experiments, endothermic effects were observed between 75°C and 175°C and between 325°C en 375°C. After all experiments, a white residue remained in the sample container (original colour: white).

 

The amount of water calculated from the structural formula Al2(SO4)3x 14H2O is approximately 42%. During the preliminary test, a 45% weight loss was observed. The endothermic effects observed between 75°Cand 175°C during the main study were due to evaporation of part of the crystal water. The endothermic effect observed between 325°C en 375°C during the main study were probably due to evaporation of the remaining crystal water.

Conclusions:
Decomposition of test substance without melting up to 550°C.
Executive summary:

The melting point of aluminium sulphate basic hydrated was investigated according to OECD/EC guidelines, thermal analysis method. A preliminary assay was conducted with TGA; four main measurements were performed with DSC (varying parameters) under nitrogen. No melting (i.e. transition to liquid form) was observed up to 550°C, but weight loss and endotherms were recorded, and attributed to decomposition corresponding to crystal water loss.

Description of key information

Aluminium sulphate (anhydrous) decomposes at 770°C (literature).

Hydrated forms undergo primary decomposition corresponding to crystal water loss from ca 80°C (from literature and experiment on analogue).

Key value for chemical safety assessment

Additional information

A reliable literature source is provided for the reference substance (anhydrous form), and is considered as key data. The same result was also found in numerous commonly used handbooks or databases, despite not peer reviewed. However the value of 770°C is associated with decomposition, and therefore will not be retained as key value for purpose of CSA (no solid-liquid transition).

A single, updated, reference handbook provides a non-consistent value, but as no details are available, the usual and lower value is retained.

Supporting information on the 18 H2O and on analogue in an experimental report show that the hydrated forms undergo primary decomposition corresponding to crystal water loss from ca 80°C.