The thermogravimetric analysis measures a sample’s change of mass depending on temperature and time. The sample is heated to 1000°C in a crucible made of temperature-stable and inert material (platinum or Al2O3) and the change in weight is recorded. According to requirements, up to 19 samples can be heated simultaneously either in oxidative conditions (air or oxygen) or in a nitrogen atmosphere, in order to avoid oxidation.
The reduction or increase in weight and the temperature of the change in weight can draw conclusions from the composition of an analysed sample.
Change in mass can have the following reasons:
- Mass reduction caused by physical processes (e.g. vaporization, sublimation)
- Mass reduction of a sample caused by decomposition (e.g. decomposition and formation of volatile products)
- Mass reduction caused by reaction (e.g. reduction)
- Mass increase caused by reaction (e.g. oxidation)
Thermogravimetric analysis: Application
Thermogravimetric analysis is applied inter alia for identifying the moistness respectively the water content of volatile compounds (e.g. plastics with films of oil or plasticisers), the carbonate level and the loss of ignition respectively the residue on ignition. Furthermore, e.g., the percentage of metallic iron can be identified in a combination with XRF, which analyses the total percentage of iron.
In the field of coal analytics it is possible to measure the mass percentage of volatile components and even the ash content can be quantitatively determined by the change of mass. In order to determine the moisture analyses, the sample is heated from room temperature to 110°C. Keeping this temperature for 1 minute and measuring the change of mass measures determines the moisture of the sample. Finally the sample will be dynamically heated to 900°C. By changing the used gas of the gas atmosphere from nitrogen to oxygen further oxidation of the carbon takes place. The change of mass during this reaction determines the amount of carbon in the sample.
Relevant standards for TGA
DIN 51006:2005-07 – Thermal analysis (TA) – Thermogravimetry (TG) – Principles
DIN EN 12485:2010-08 – Chemicals used for treatment of water intended for human consumption – Calcium carbonate, high-calcium lime, half-burnt dolomite, magnesium oxide and calcium magnesium carbonate – Test methods
DIN EN ISO 11358-1:2014-10 – Plastics – Thermogravimetry (TG) of polymers – Part 1: General principles