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Vapour pressure

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Endpoint:
vapour pressure
Data waiving:
study scientifically not necessary / other information available
Justification for data waiving:
other:
Endpoint:
vapour pressure
Type of information:
experimental study
Adequacy of study:
supporting study
Study period:
from 16 NOV 2006 to 02 FEB 2007
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
guideline study with acceptable restrictions
Remarks:
Determinations performed above decomposition temperature; phase transition not accounted for.
Qualifier:
according to guideline
Guideline:
OECD Guideline 104 (Vapour Pressure Curve)
Deviations:
yes
Remarks:
For details, see below in "Principles of method if other than guideline"
Principles of method if other than guideline:
The measurement temperatures (180, 190, 200 and 210°C) were higher than those recommended in the guideline (120 to 150°C). Due to the low vapour pressure and the hygroscopic nature of the test item, relatively high temperatures had to be used in order to obtain evaporation rates that could be measured with sufficient accuracy.
GLP compliance:
yes (incl. QA statement)
Type of method:
effusion method: isothermal thermogravimetry
Key result
Temp.:
20 °C
Vapour pressure:
< 0 hPa

REFERENCE CONTROL

The evaporation rate at 20°C of hexachlorobenzene deviated by less than 10 % to the average validated values. The vapour pressure curve was thus considered to be accurate.

 

TEST SUSBTANCE

Among the seven measurements, only the second and the third were used because the observed weight losses and therefore evaporation rates were higher. Fitting the extrapolated evaporation rate at 20°C in the vapour pressure curve gave a vapour pressure of 8.17 x 10-9 hPa at 20°C. Knowing that only the measurements with highest evaporation rates were retained for calculation, the vapour pressure of the test substance was thus reported as < 8.17 x 10-9 hPa. Due to the nature of the test substance, a more accurate determination of the vapour pressure is considered to be impossible.

The vapour pressure was calculated by extrapolation from a temperature above the melting point to 20 °C (below melting point); hence this phase transition needs to be accounted for.

As the decomposition temperature of the substance is below the measuring temperature it is concluded that the vapour pressure measured is the vapour pressure of the decomposition product.

Conclusions:
The vapor pressure at 20°C by isothermal thermogravimetry was determined to be lower than 8.17E-7 Pa. As the decomposition temperature of the substance is below the measuring temperature, the vapour pressure measured represents the vapour pressure of the decomposition product.
Executive summary:

The vapour pressure at 20°C of cerium trinitrate was determined using the isothermal gravimetric effusion method, according to OECD Guideline 104.

 

Before measurement, the test substance was dried at 105°C for 960 min. Subsequently, a measuring range from 100 to 220°C with steps of 10°C for 10 minutes was used. For calculation of the vapour pressure, the evaporation rate at four temperatures (180, 190, 200 and 210°C) was used. The evaporation rate at 20°C (VT, 20) was determined by extrapolation. The VT, 20value of cerium trinitrate was compared to those from substances with known vapour pressure values at 20°C (PT, 20); using a vapour pressure curve (log PT, 20versus log VT, 20) constructed with seven validated substances.

 

This allows yielding a PT, 20value being < 8.17 x 10-9 hPa. Due to the nature of the test substance, a more accurate determination of the vapour pressure is considered to be impossible.

As the decomposition temperature of the substance is below the temperature of measurement, the vapour pressure determined represents the vapour pressure of the decomposition product.

Description of key information

The vapour pressure of the substance is too low to enable reliable measurements below its decomposition temperature. In a supporting study, the vapour pressure of the decomposition product, extrapolated to 20°C, was determined by isothermal thermogravimetry to be < 8.17E-7 Pa (Baltussen, 2007). 

Key value for chemical safety assessment

Vapour pressure:
0 Pa
at the temperature of:
20 °C

Additional information

As the vapour pressure of the substance is too low to enable reliable measurements below its decomposition temperature and the vapour pressure of the decomposition product was concluded to be < 8.17E-7 Pa, the vapour pressure of cerium trinitrate was set at the lowest value considered relevant for the chemical safety assessment (1E-6 Pa).