Materials with dynamic thermal control
Introduction
Thermal analysis is a branch of materials science where the properties of materials are studied as they change with temperature. Several methods are commonly used, distinguished from each other by the property being measured:.
Simultaneous thermal analysis (STA) generally refers to the simultaneous application of thermogravimetry (TGA) and differential scanning calorimetry (DSC) to the same sample in a single instrument. The test conditions are perfectly identical for TGA and DSC signals (same atmosphere, gas flow rate, vapor pressure of the sample, heating rate, thermal contact with the crucible and the sample sensor, radiation effect, etc.). The information collected can even be improved by coupling the STA instrument to an Evolved Gas Analyzer (EGA) such as Fourier transform infrared spectroscopy (FTIR) or mass spectrometry (MS).
Other, less common methods measure the emission of light or sound from a sample, or the electrical discharge of a dielectric material, or the mechanical relaxation in a stressed sample. The essence of all these techniques is that the sample response is recorded as a function of temperature (and time).
It is common to control the temperature in a predetermined manner, either by a continuous increase or decrease in temperature at a constant rate (linear heating/cooling) or by a series of determinations at different temperatures (step isothermal measurements). More advanced temperature profiles have been developed that use an oscillating (usually sine or square wave) heating rate (Temperature Modulated Thermal Analysis) or modify the heating rate in response to changes in system properties (Sample Controlled Thermal Analysis).
In addition to controlling the temperature of the sample, it is also important to control its environment (for example, the atmosphere). Measurements can be performed in air or under an inert gas (for example, nitrogen or helium). Reducing or reactive atmospheres have also been used and measurements are even carried out with the sample surrounded by water or other liquids. Reverse gas chromatography") is a technique that studies the interaction of gases and vapors with a surface. Measurements are often made at different temperatures so these experiments can be considered to be under the auspices of thermal analysis.
Atomic force microscopy uses a fine optical pen to map the topography and mechanical properties of surfaces at high spatial resolution. By controlling the temperature of the heated tip and/or sample, a form of spatially resolved thermal analysis can be performed.