Thermal Analysis Method

Thermal Methods of Analysis

Thermal methods of analysis is a group of techniques in which a physical property of a substance and/or its reaction products is measured as a function of temperature while the substance is subjected to a controlled temperature program.

Physical properties include mass, temperature, enthalpy, dimension, dynamic characteristics, and others, and depending on the physical properties to be measured, the techniques of thermal analysis. It is usually measured as a dynamic function of temperature and the substance is subjected to a controlled temperature program during the analysis.

Traditionally thermal analysis has been mainly employed in measurements for research and development, but lately it is used in many practical

But in this presentation,we will focus only to three of the methods, which provide primarily chemical rather than physical information about samples of matter. The Thermogravimetry Analysis (TGA) , Differential thermal analysis (DTA), and Differential scanning calorimetry (DSC).

Thermogravimetric Analysis

In thermo gravimetric analysis, the mass of a sample in a controlled atmosphere is recorded continuously as a function of temperature or time as the temperature of the sample is increased (usually linear with time).

The technique is useful strictly for transformations involving the absorption or evolution of gases from a specimen consisting of a condensed phase.

This method is useful for determining sample purity and water, carbonate, and organic content; and for studying decomposition reactions.

The basic principle is that “Thermogravimetry is a technique in which a change in the weight of a substance is recorded as a function of temperature or

A few milligrams of the sample (S) and an inert reference substance are contained in small aluminum dishes located above sample and reference thermocouples in an electrically heated furnace.

The reference material is an inert substance such as alumina, silicon carbide, ot glass beads. The digitized output voltage E, from the sample thermocouple is the input to a computer.

The computer controls the current input to the furnace in such a way that the sample temperature increases linearly and at a predetermined rate. The sample thermocouple signal is also converted to temperature T" which is used as the x-axis of the differential thermogram.

The output across the sample and reference thermocouples flE is amplified and converted to a temperature difference fl T, which serves as the y-axis of the thermogram. Generally, the sample and reference chamber in DTA are designed to permit the circulation of an inert gas, such as nitrogen, or a reactive gas, such as oxygen or air. Some systems also have the capability of operating at high and low