Evaluation of substances and finished materials by thermal analysis as a tool that paint chemists can use to help evaluate coating performance. These properties vary with temperature.
feature
Substances undergo characteristic changes when heated. Thermal analysis (TA) monitors these changes. The TA procedure is commonly used to characterize the chemical or physical changes that various substances and materials undergo when heated. Changes in these properties as a function of temperature were used to help characterize the interrelationships between the composition and properties of the coatings. The TA method or technique measures the change in the properties of a material when it is heated or cooled.
Evaluation of TA requires programmed temperature changes of small samples from a few milligrams to 100 milligrams. The resulting property changes are detected, attenuated, mapped and measured with a recording device.
The instrument consists of an analysis module, a heating or cooling source, a measurement device, and a system for reporting the results, usually as an XY diagram. Computers are used to program and control processes, and to analyze and store results.
technical method
The main techniques for coating characterization and analysis include differential scanning calorimetry (DSC), differential thermal analysis (DTA), thermogravimetric analysis (TGA), thermomechanical analysis (TMA) and dynamic mechanical analysis (DMA). We will discuss each of these steps and illustrate the information obtained from each step.
DSC measures heat flow and temperature associated with chemical transitions and reactions. Measure the difference in heat flow between samples and standards under precisely controlled conditions. It measures the amount of heat flowing into or out of a sample as an exothermic or endothermic energy change. The general operating temperature range is -180°C ~ +725°C.
DTA has been replaced by DSC. However, DTA data also resolves changes in heat flow and measures the evolution or absorbed energy in an inert reference. The accuracy of temperature detection is a bit worse than DSC, therefore, it is replaced by DSC to get better data. It can also measure the temperature excursion of the sample from -180°C to +1600°C.
TGA measures mass change as a function of temperature, time and atmosphere. Therefore, the procedure is limited to applications where quality changes occur. Since only information on mass changes was collected, nothing was revealed about the nature of the transformation. The energy involved, or whether it was absorbed or released, was not detected or indicated. TGA only measures the change in mass, usually over the ambient temperature range to 1200°C.
TMA measures the dimensional change of a material as a function of temperature and time. Both linear and volumetric changes can be determined. TMA measures the dimensional change of a sample, typically in the range of -160°C to +1200°C.
Finally, DMA is a thermal analysis technique used to measure the behavior of materials when deformed under cyclic stress. DMA employs the application of a variable sinusoidal stress and measures the resulting sinusoidal strain. Or, to put it another way, DMA is a technique that measures the modulus (stiffness) and damping (energy dissipation) properties of a material as it deforms under a periodically oscillating stress. The DMA measures the modulus and damping changes of the sample over a temperature range of -150°C to +500°C.
