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Influencing Factors of Thermogravimetric Analyzer


Influencing factors of thermogravimetric analyzer

1. Number of samples and sample tray

For thermogravimetric determination, the sample amount is small, generally 2 to 5 mg. On the one hand, the sensitivity of the instrument balance is very high. On the other hand, if the sample volume is large, the greater the mass transfer resistance, the greater the temperature gradient inside the sample, and even the thermal effect of the sample will cause the sample temperature to deviate from the linear heating program, thereby changing TG curve. The finer the particle size, the better. If the particle size is large, the decomposition reaction will shift to high temperature.
The material of the sample tray should be high temperature resistant and inert to the sample, intermediate products, products and the atmosphere, that is, it cannot have reactivity and catalytic activity. Commonly used sample pans include platinum, ceramics, quartz, glass, aluminum and so on. It is important to note that different samples should use sample pans of different materials, otherwise the sample pan will be damaged. For alkaline samples, such as sodium carbonate, aluminum, quartz, glass and ceramic sample pans should not be used for testing. The platinum sample pan is not suitable for polymer samples containing phosphorus, sulfur, and halogens because it is active against hydrogenated or dehydrogenated organic compounds.

2. Heating speed

The faster the thermogravimetric analyzer heats up, the more serious the temperature hysteresis. For example, if the heating speed is fast, the resolution of the curve will be reduced, and the information of some intermediate products will be lost. For example, if the heating speed is slow, some intermediate products that gradually lose water can be detected.

3. Atmosphere influence

The change of the atmosphere around the thermobalance has a significant effect on the TG curve. The TG curve of CaCO3 in vacuum, air and CO2 atmosphere differs by nearly 600°C, because CO2 is a decomposition product of CaCO3. The presence of CO2 in the atmosphere will inhibit the decomposition of CaCO3 and increase the decomposition temperature. The weight gain of polypropylene in the air at 150-180°C is the result of the oxidation of polypropylene, which is not the case in N2. The wind speed is generally 40ml/min, and the high flow rate is conducive to heat transfer and overflow gas diffusion.

4. Condensation of volatiles

The decomposition products of the thermogravimetric analyzer volatilize from the sample and often re-condensate at low temperatures. If they condense on the suspended wire sample pan, the measured weight loss will be very low. When the temperature rises further, the condensed water volatilizes again, which will cause false weight loss and deform the TG curve. The solution is to increase the gas flow rate so that the volatiles leave the sample pan immediately.
5. Buoyancy

The change in buoyancy is due to the thermal expansion of the gas surrounding the sample, which causes the relative density and buoyancy to decrease, and the apparent weight of the sample increases.

 

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