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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:
31 Aug - 11 Nov 2015
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Reason / purpose for cross-reference:
reference to other study
Qualifier:
according to guideline
Guideline:
OECD Guideline 102 (Melting point / Melting Range)
Deviations:
no
Qualifier:
according to guideline
Guideline:
EU Method A.1 (Melting / Freezing Temperature)
Version / remarks:
adopted in 2008
Deviations:
no
GLP compliance:
no
Type of method:
differential scanning calorimetry
Atm. press.:
ca. 1 013 hPa
Decomposition:
yes
Decomp. temp.:
138 °C
Remarks on result:
other: 3 individual tests with temperature onsets of 138.1 °C, 138.3 °C and 138.0 °C

Results

1st endothermic effect at 138 °C (ranges: 1st test: 120 - 160 °C, 2nd test:110 -170 °C, 3rd test 105 - 165 °C)

2nd endothermic effect at 390 °C (ranges 1st test 380 - 410 °C, 2nd test 370 - 410 °C)

Mass loss: About 10% of mass loss was detected in all 3 tests

Substance appearance: tests conducted until 400 °C grey powder, for test conducted until 200 °C white powder.

In capillary test running up to 410 °C at approx. 155 °C test item started to discolour at 155 °C, condensate was observed at cool end of the capillary.

The 1st endothermal effect of the DSC experiments can be referred to dehydration of test item the 2nd endothermic point can be phase transition

Endpoint:
melting point/freezing point
Type of information:
experimental study
Adequacy of study:
supporting study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment
Qualifier:
no guideline followed
Type of method:
other: Scanning Calorimetry, Xray powder diffraction
Decomposition:
yes
Remarks:
Determined by DTA, mass loss 16.6%
Decomp. temp.:
800 K
Decomposition:
yes
Remarks:
Decomposition of phase formed by decomposition at 800K
Decomp. temp.:
> 1 150 - < 1 200 K

At 644 K (DTA) or 662 K (DSC) phase transition between orthorombic δ-phase and tetragonal α-phase occurs. When cooling down phase change (from α to δ-phase) is occuring at lower temperatures than for heating. This shows that the phase change is a kinetically inhibited process with high activation energy. At 800 K (DTA) the oxalate salt decomposes. This is linked with a weight loss of 16%. The potassium carbonate salt, carbon monoxide, carbondioxide and oxygen are formed. At 1200 K (DTA) the carbonate salt decomposes. All the phases were characterized by x-ray powder diffractometry.

Endpoint:
melting point/freezing point
Type of information:
experimental study
Adequacy of study:
supporting study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
data from handbook or collection of data
GLP compliance:
not specified
Decomp. temp.:
> 160 °C
Remarks on result:
other:
Remarks:
Dehydration of monohydrate

Description of key information

Substance decomposes before melting could occur. Decomposition started at ca. 138 °C (OECD 102, DSC).

Key value for chemical safety assessment

Additional information