Thermal Methods

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ThermalBy: Naaimat Muhammed

Introduction

• A general accepted definition of thermal 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.

• We will confine to three of the methods, which provide primarily chemical rather than physical information about samples of matter.

Three Methods

1. Thermogravimetry (TG)

2. Differential thermal analysis (DTA)

3. Differential scanning calorimetry (DSC)

Thermogravimetric Methods

• 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). Thermogravimetry is the measurement of the mass of a sample as the temperature increases.

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

Differential Thermal Analysis (DTA)

Differential thermal analysis is the measurement of the difference in temperature between a sample and a reference as heat is applied to the system.

This method is sensitive to endothermic and exothermic processes including:

1. phase transitions2. Dehydration3. decomposition4. Redox5. solid-state reactions

Differential Scanning Calorimetry (DSC)

• Differential scanning calorimetry independently measures the rate of heat flow to a sample and a standard that are at the same temperature. Data is taken by monitoring the differential heat flow as a function of temperature.

• DSC is useful to make the same measurements as DTA and has the added capability to measure heat capacities.

Instrumentation

• Sensitive analytical balance• Furnace• Purge gas system (for providing an

inert atmosphere)• Microcomputer/microprocessor (for

instrument control and data acquisition and display).

Thermal gravimetric Furnace

Example of TGA using Weightloss vs. Time

Power vs. Temperature

Heat content vs. Temperature

References

1. http://www.chem.vt.edu/chem-ed/crossref/ac-thermal.html

2. Principles of Instrumental Analysis, Skoog, Holler, Nieman; Saunders College Pub. 5th Edition (1998)

3. http://www.ptli.com/testlopedia/subs/TGA-result.htm