TG-DSC joint test focus

Test Principles

Thermogravimetric-Differential Scanning Calorimetry (TG-DSC) is a technique that simultaneously performs TG and DSC tests on a specimen under a programmed temperature control and a certain atmosphere, where the same specimen is utilized for the same measurement to simultaneously obtain the relevant information about the specimen's mass and thermal effect.

Test purpose and significance

Synchronous thermal analyzer (TG-DSC) can provide TG and DSC signals synchronously, through a single measurement can obtain two kinds of information of mass change and thermal effect.TG signals are used to study the mass change of materials, composition analysis, thermal stability, oxidation/reduction, decomposition behavior, corrosion studies, decomposition kinetics analysis, etc. DSC signals are used to study the melt/crystallization, solid phase transformation, crystallinity, glass transition, oxidation resistance, etc. of materials. DSC signal is used to study melting/crystallization, solid phase transition, crystallinity, glass transition, oxidation resistance, etc. According to whether a certain thermal effect corresponds to a mass change or not, the physical and chemical processes corresponding to the thermal effect can be judged (e.g., distinguishing melting peaks, crystallization peaks, phase transition peaks from decomposition peaks, oxidation peaks, etc.). It can track the change of sample mass with temperature/time in real time, and accurately calculate the heat of phase change and heat of reaction. Widely used in a variety of organic, inorganic, polymer materials, metal and alloy materials, ceramic materials, medicine, food, energy-containing materials and other fields.

Figure 1. TG-DSC thermal analyzer equipment

Important parameters to confirm before sample testing

1. How to prepare the sample?

• Sample state: can be powder, block samples
• powder samples prepared about 20 mg, block sample size is not greater than the diameter of 3 mm, 2 mm high.
• If the sample halogen samples and energy-containing materials need to pay attention to the content, there will be explosive and instrument sensor contamination.

2. Test temperature and rate: room temperature -1500 ℃;

   The test process requires insulation or unconventional heating rate (such as 15 K/min, 25 K/min) need to redo the baseline, the conventional 5-20 ℃ / min;

3. Test atmosphere: conventional nitrogen, air, argon.

Sample Testing Risks

1. Halogen samples and energy-containing materials need to pay attention to the content, there will be explosive and instrument sensor contamination and other risks;

2. Samples containing low boiling point metal components, easy to contaminate the sensor;

3. insulation samples, generally not recommended for high temperature insulation, easy to damage the instrument;

Frequently Asked Test Questions

1. During the TG-DSC test, the DSC curves were not separated for two neighboring weightless platforms?

• The heating rate is too fast, so that the DSC peak shape is large, the characteristic temperature is shifted to a high temperature, the separation ability of adjacent peaks or weightlessness steps decreases, in principle, the slower the rate of heating, the better, the maximum rate is recommended to be no more than 10K/min, the faster the rate, the higher the sensitivity, the lower the resolution;
• The sample size is too large, the temperature gradient within the sample is large, the gas product diffusion is also slightly worse, in general, the test sample as little as possible is preferred.

2. What is the difference between combined TG-DSC and single TG and single DSC?

   The purpose of DSC is to measure the heat, heat transfer there are heat conduction, thermal radiation and thermal convection in three ways, only the first is able to accurately measure the latter two ways to try to avoid, in order to achieve this purpose, a separate DSC is an aluminum dish containing samples with a lid and mold pressed to try to avoid the sample is too thick and there is a temperature gradient, the crucible of aluminum can also be effective in preventing thermal radiation and thermal convection.

   In order to take into account the thermogravimetric signal and to do high temperature, the sample can not be pressed in the aluminum dish at all, but only scattered in the alumina crucible, so its calorimetric signal is very much worse than that of individual DSC. In order to effectively reduce high-temperature heat radiation, synchronous heat will add a Pt lid (with small holes), but this will prevent the timely overflow of the decomposition products, so the thermogravimetry in the synchronous heat will also be a little biased.

3. Why is sample recovery not recommended?

   Because the samples of TG-DSC have been volatilized or pyrolyzed at high temperature during the testing process, and the quality and structure of the samples have been greatly changed after the testing is completed, so the samples are generally not recycled.

4. How much sample size is needed for testing?

   Generally 3-10mg of sample, if the sample size is small (less than 2mg), it may be greatly affected by the airflow, resulting in large deviations in the results.

5. Can we keep the test warm at high temperature?

   Generally, high temperature can't keep the test warm, it is too dangerous and damaging to the instrument.

6. What kind of crucible is used for testing?

   Generally aluminum oxide crucible (corundum crucible), platinum crucible (less).

7. The DTG curve is not smooth, burrs and other phenomena of the analysis?

   DTG is a differential curve of TG, and the corresponding temperature range of the weight loss process of many substances is quite wide, which makes it difficult to identify unknown compounds by TG method, especially when the decomposition temperature ranges of two compounds are close to each other.

   This problem can be solved by using the micro-commercial thermogravimetric method. The DTG curve represents the rate of change of mass with time (dm/dt) as a function of temperature (or time), i.e. the maximum value of the rate of weight loss; the number of peaks on the DTG curve corresponds to the number of steps on the TG curve, i.e. the number of times of weight loss.

   In the course of the test, the DTG curve of some samples will appear to be not smooth.

Figure 2. Example of DTG unsmoothed curve

This situation may be the sample decomposition reaction is intense, suddenly produce a large number of bubbles or burst phenomenon caused, and in the operation of the instrument, if there are external influences lead to vibration of the equipment, will also make the curve is not smooth, usually can be smoothed curve can be dealt with.

8. Why is the DSC baseline of TG-DSC test not flat?

   When the temperature is high, there will be thermal radiation can not be avoided, DSC curve is possible to drift, when the sample signal is weak you can see the baseline drift, when the sample signal is strong, it is ignored.