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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:
key study
Study period:
May 07, 2010
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
comparable to guideline study with acceptable restrictions
Remarks:
Well performed study performed according to a method similar to EU Method A.1. Although the heating rate in the Differential Thermal Analysis was not in compliance with the test guideline, this is not considered to have influenced the outcome of the test.
Qualifier:
equivalent or similar to guideline
Guideline:
EU Method A.1 (Melting / Freezing Temperature)
Deviations:
yes
Remarks:
heating rate too high
Principles of method if other than guideline:
In addition to the thermal analysis, a preliminary test was performed by heating a sample in a test tube over a Bunsen burner to enable visual observations.
GLP compliance:
no
Type of method:
thermal analysis
Key result
Decomposition:
yes
Decomp. temp.:
ca. 60 °C

Preliminary test:

Initial heating produced condensation on sides of the test tube above the white solid substance. Further heating produced a liquid layer (most probably water) above the solid. Still further heating produced a white solid which did not change under prolonged heating. The residue (white solid) was taken for XRD analysis and concluded to be monoclinic zirconium dioxide. This confirms the decomposition of zirconium dichloride oxide to zirconium dioxide via the release of water and hydrogen chloride.

Thermal analysis:

A rapid weight loss was recorded between the starting temperature (25°C) and just below 200°C with significant weight loss starting around 60°C. The weight loss was accompanied by a large endotherm where heat was taken up by the substance with regard to the inert reference. This process was identified as the loss or release of water and hydrogen chloride from the substance as noted in the preliminary test. A subsequent weight loss from 200°C and above, represented the continued dehydration of the substance to form zirconium dioxide. Small exotherms seen between 450°C and 500°C were concluded to be typical crystallisation exotherms of zirconia. The exotherm from this DTA analysis could not be quantified due to the nature of the equipment, however the amount of heat generated was insignificant compared to the temperature of the surroundings (400-500°C) and this exotherm is always present within any routine production operation making zirconium dioxide. Due to the limited amount of material used in the test there was insufficient sample to further analyse the residue. However, as determined in the preliminary test, the residue after heating was concluded to be monoclinic zirconium dioxide.

Conclusions:
It is not possible to determine the melting point of zirconium dichloride oxide as the substance decomposes to zirconium dioxide with the loss of water and hydrogen chloride. Decomposition is indicated by a significant weight loss starting at ca 60°C.
Endpoint:
melting point/freezing point
Type of information:
experimental study
Adequacy of study:
supporting study
Study period:
no data
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
data from handbook or collection of data
Reason / purpose for cross-reference:
reference to same study
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:
no
Decomposition:
yes
Decomp. temp.:
400 °C
Conclusions:
The test substance decomposes at 400°C.

Description of key information

Zirconium dichloride oxide was concluded not to melt before it decomposes, following Differential Thermal Analysis as described in the EC Method A.1 (Bradshaw , 2010, key study). Decomposition becomes significant starting from ca. 60°C.

Key value for chemical safety assessment

Additional information

Zirconium dichloride oxide decomposes to zirconium dioxide with the loss of water and hydrogen chloride. Decomposition is indicated by a significant weight loss starting at ca. 60°C (Bradshaw, 2010). The data from Bradshaw (2010) are considered as key information. The results of this study are supported by handbook data (Lide, 2001).