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Melting point / freezing point

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Endpoint:
melting point/freezing point
Type of information:
experimental study
Adequacy of study:
supporting study
Study period:
12 September 2017
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
comparable to guideline study with acceptable restrictions
Qualifier:
no guideline followed
Principles of method if other than guideline:
The method aims to investigate the temperature behaviour of tungsten zirconium hydroxide oxide. A thermogravimetric (TG) analyser together with a Differential Thermal Analysis (DTA) was used for this.
GLP compliance:
not specified
Type of method:
thermal analysis
Remarks:
A thermogravimetric (TG) analyser together with a Differential Thermal Analysis (DTA) was used for this.
Decomposition:
yes
Decomp. temp.:
< 800 °C
Remarks on result:
other: A white product was obtained after the experiment.

Results:

1. One continuous weight loss of 17.64% is noticed between room temperature and 700°C. This weight loss corresponds to different processes that overlap during the thermal treatment: dehydration, dehydroxylation and removal of minor anionic impurities from processing.

2. Dehydration is an endothermic process.

3. Material crystallisation is an exothermic process, specific to this type of material demonstrated by the display of two exotherms between 500 and 650°C. Analysed batch shows a first exotherm with a maximum at 524°C and a second exotherm with a maximum at 558°C.

4. No other weight loss or phase transition occurs up to 800°C.

Conclusions:
TG/DTA scans prove that tungsten zirconium hydroxide oxide undergoes a decomposition process when heated from room temperature up to 800°C, the final product being a white powder.
Endpoint:
melting point/freezing point
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
weight of evidence
Justification for type of information:
Read across based on the available handbook data for WO3 and ZrO2. The read across justification document is attached to IUCLID Section 13.
Reason / purpose:
read-across source
Reason / purpose:
read-across source
Reason / purpose:
read-across source
Melting / freezing pt.:
> 1 000 °C
Remarks on result:
other: Based on handbook data for the melting point of WO3 and ZrO2, it can be concluded that tungsten zirconium oxide has an equally high melting point (at least > 1000°C). No precise value could be derived.
Endpoint:
melting point/freezing point
Type of information:
experimental study
Adequacy of study:
weight of evidence
Study period:
no data
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
data from handbook or collection of data
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 were the experimental methods.
GLP compliance:
not specified
Type of method:
other: no data
Melting / freezing pt.:
ca. 1 472 °C
Conclusions:
The melting point of tungsten(VI) oxide was reported to be 1472°C.
Endpoint:
melting point/freezing point
Type of information:
experimental study
Adequacy of study:
weight of evidence
Study period:
no data
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
data from handbook or collection of data
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 were the experimental methods.
GLP compliance:
not specified
Type of method:
other: no data
Melting / freezing pt.:
2 680 °C
Conclusions:
The melting point was reported to be 2680°C.
Endpoint:
melting point/freezing point
Type of information:
experimental study
Adequacy of study:
weight of evidence
Study period:
no data
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
data from handbook or collection of data
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 were the experimental methods.
GLP compliance:
not specified
Type of method:
other: no data
Melting / freezing pt.:
ca. 2 710 °C
Conclusions:
The melting point of zirconium dioxide was reported to be 2710°C.

Description of key information

Based on melting point data available for the individual substances ZrO2 and WO3, the substance tungsten zirconium oxide can be concluded to have a high melting point (> 1000°C).

Key value for chemical safety assessment

Additional information

1. Information on zirconium dioxide

Although only two values are available from peer reviewed handbooks, it can be safely concluded that the melting point of zirconium dioxide is approximately 2700°C, rendering it environmentally irrelevant.

2. Information on tungsten(VI) oxide (WO3)

The melting point of tungsten(VI) oxide was reported to be 1472°C in a peer reviewed handbook.

3. Information on tungsten zirconium hydroxide oxide

An in-house experimental study based on TG/DTA scans performed on tungsten zirconium hydroxide oxide shows that this test item undergoes a decomposition process (mainly dehydration and dehydroxylation) when heated from room temperature up to 800°C. The final product is a white powder. Therefore, no melting point can be reported for this test material. Since this study is performed on tungsten zirconium hydroxide oxide, it is assigned as supporting study. The remaining white powder after the test can be assumed to be crystalline tungsten zirconium oxide.

 

4. Conclusion on tungsten zirconium oxide

Based on information on the individual components of the substance, i.e. zirconium dioxide and tungsten(VI) oxide, the melting point of tungsten zirconium oxide could also be expected to be very high (> 1000°C). The data on zirconium dioxide and tungsten trioxide were used in a weight of evidence approach to cover the endpoint.