Vanadium oxide sulphate

Melting point / freezing point

Link to relevant study record(s)

Reference

Endpoint:

melting point/freezing point

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

comparable to guideline study with acceptable restrictions

Remarks:

no information of the precise specification of the substance (purity, batch, expiration date)

Qualifier:

equivalent or similar to guideline

Guideline:

EU Method A.1 (Melting / Freezing Temperature)

Version / remarks:

2008

Deviations:

yes

Remarks:

no information of the precise specification of the substance (purity, batch, expiration date)

GLP compliance:

not specified

Type of method:

thermal analysis

Remarks:

TG, DTA, DTG

Decomposition:

yes

Decomp. temp.:

265 °C

Sublimation:

no

Thermogravimetry (TG), Differential thermal analysis (DTA) and derivative thermogravimetry (DTG) curves of 1. VOSO₄* 2 H₂O and 2. VOSO₄ indicate dehydration and decomposition as follows:

1. VOSO₄* 2 H₂O

The TG curve indicates three clearly distinguishable steps and the DTA curve points to three endothermic effects at 423 K, 538 K and 873 K, respectively. The results from the thermogravimetric analysis (the mass loss recorded in the TG curve) and the calculations made with them were considered enough to suggest a step-wise mechanism of dehydration and decomposition, involving the following stages:

Stage I: VOSO₄ * 2 H₂O -> VOSO₄ + 2H₂O

Stage II: 2 VOSO₄ -> V₂O₄(SO₄) + SO₂

Stage III: V₂O₄(SO₄) -> V₂O₅ + SO₂ + ¹/₂O₂

Stages II and III were assumed to occur on the bases of both chemical analysis and the mechanism of thermal decomposition of other sulfates. Besides, the data from the chemical and X-ray powder diffraction analyses of the residual solid phase showed that the tested substance had oxidised and decomposed to V₂O₅. The chemical analysis shows 55.8 mass% contents of vanadium in solid residue in stage III.

2. VOSO₄

The TG curve registered by thermal treatment of VOSO₄ points to two steps and the DTA curve displays two endothermic effects at 573 K and 878 K corresponding to the decomposition in stage II and III. The X-ray powder diffraction analysis of the residual solid phase gives a pattern characteristic for V₂O₅. This indicates that the decomposition of VOSO₄ involves intramolecular oxy-reduction transformation.

Conclusions:

Vanadium oxide sulphate decomposes at 265 °C under atmospheric pressure.

Executive summary:

Vanadium oxide sulphate (dihydrate) starts to decompose at 265°C under atmospheric pressure involving the following steps:

1. Water splits off at 100-150 °C,

2. SO₂ splits off at approximately 265 °C, and

3. SO₂ and O₂ split off and V₂O₅ is formed at approximately 600 °C.

Description of key information

Vanadium oxide sulphate starts to decompose at 265 °C.

Additional information

The Thermogravimetry (TG), Differential thermal analysis (DTA) and derivative thermogravimetry (DTG) curves of VOSO₄* 2 H₂O and VOSO₄ indicate that Vanadium oxide sulphate (dihydrate) starts to decompose at 265 °C under atmospheric pressure involving the following steps:

1. Water splits off at 100-150 °C,

2. SO₂splits off at approximately 265 °C, and

3. SO₂ and O₂ split off and V₂O₅ is formed at approximately 600 °C.