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Physical & Chemical properties

Melting point / freezing point

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Reference
Endpoint:
melting point/freezing point
Type of information:
experimental study
Adequacy of study:
key study
Study period:
2010-04-12 to 2010-06-11
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
test procedure in accordance with generally accepted scientific standards and described in sufficient detail
Qualifier:
no guideline followed
Principles of method if other than guideline:
The pigment melting point was estimated by consulting phase diagrams that included the characteristic pigment crystalline phase, which as far as possible had the same composition.
GLP compliance:
no
Type of method:
thermal analysis
Remarks:
Differential Thermal Analysis
Melting / freezing pt.:
> 1 300 °C

The DTA test identified several thermal phenomena in the range 100 - 1000 °C. Transitions, centered at 252 °C and 343 °C, are proposed to correspond to dehydroxylation. An endothermic process begins at 650°C which might suggest pigment fusion. However, phase diagram no. 111 in reference 1 allows the inference that Pb2Sb2O7 has an incongruous melting point at about 1300 °C which rules out that interpretation.

It is highly likely taht the process that begins at 650 °C corresponds to the fusion of some of the impurities contained in the sample, possibly due to the xistence of a low-temperature eutectic. it may be noted in this sense that the PbO melting point, a small quantity of Pbo being present in the sample, is reached at 887 °C.

Conclusions:
The DTA test identified deveral thermal phenomena in the range 100 -1000 °C. Transitions, centered at 252 °C and 343 °C, are proposed to correspond to dehydroxylation. An endothermic process begins at 650 °C which might suggest pigment fusion.
Inference utilizing existing phase diagrams lead to an estimated melting point of >1300 °C.

Description of key information

The melting point of pyrochlore is >1300 °C.

Key value for chemical safety assessment

Additional information