GB/T 35930-2018Determination of vapor pressure of chemical products—Thermogravimetry method (English PDF)

1 Scope

This Standard specifies the method for the determination of vapor pressure of chemical products using the thermogravimetry method.

This Standard applies to all solids and liquids of saturated vapor pressure within the range of 1-10 Pa ~ 1 Pa.

Impurities in chemical products have a certain influence on vapor pressure results during measurement.

2 Principle for test method

In this Standard, thermogravimetric analysis meter is used to determine the speed of loss in mass within a certain time under relatively high temperature and indoor pressure. Under a slow inert gas flow atmosphere and temperature T (in K), the loss in mass of sample is monitored within a certain time to obtain the speed of loss in mass vT. Based on the linear relationships between vapor pressure logarithm and the speed of loss in mass, saturated vapor pressure pT at temperature T can be calculated from vT. If necessary, vapor pressure under 20°C and 25°C can be extrapolated from the regression between 1npT and 1/T.

3 Apparatus

3.1 Thermogravimetry analysis meter, which is equipped with the following devices.

3.1.1 Thermo-balance, including the following elements.

a) furnace chamber. capable of staying at a constant temperature and heating sample to 450°C at a constant speed of 5°C/min ~ 25°C/min;

b) temperature sensor. used to display the temperature of sample/furnace chamber, with a sensitivity of ± 0.1°C;

c) continuous record balance. with a sensitivity of ± 10 µg;

d) controlled inert gas atmosphere device. with a purity of inert carrier gas above 99.99% and rate of flow (0 mL/min ± 5 mL/min) ~ (100 mL/min ± 5 mL/min).

3.1.2 Temperature controller. capable of executing specific temperature programs within temperature intervals selected, with a temperature change ratio of 0°C/min ~ 25°C/min and temperature fluctuation within ± 0.5°C.

3.1.3 Recording unit. capable of recording and displaying the mass signals of sample and the changes of noise signals to temperature and noise (the TGA Curve).

3.1.4 Crucibles. their area can be measured; they will not react with sample; they can remain stable under 450°C.

3.2 Graduated micropipettes. with a capacity of 20 µL ~ 40 µL and tolerance ± 1 µL.

4 Reagents and materials

4.1 Benzoic acid. with a purity not lower than 99.9%.

4.2 Nitrogen. with a purity of 99.99% (or other inert carrier gases). It is dried using molecular sieve or silica gel.

5 Analytical procedures