Thermogravimetric Analysis (TGA)

Thermogravimetric Analysis (TGA) measures the physical and chemical properties as a function of increasing temperature or time in a controlled atmosphere. TGA analysis is used in determination of the composition of materials and thermal stability at temperatures up to 1200°C. This technique can characterize materials which exhibit weight loss or gain due to decomposition, oxidation, or dehydration.

There are three types of Thermogravimetry namely

1. Static or isothermal Thermogravimetry

2. Quasistatic Thermogravimetry

3. Dynamic Thermogravimetry

Most of the studies of polymers are generally carried out with dynamic thermogravimetry. TGA curves are characteristic forgiven polymers because of the unique sequence of physicochemical reactions,

In the TGA instrument basic requirments are: a precision balance with a pan loaded with the sample, and a programmable furnace. The furnace is programmed either for a constant heating rate or for heating to acquire a constant mass loss with time.

The sample is placed in a small, electrically heated furnace equipped with a thermocouple to monitor accurate measurements of the temperature by comparing its voltage output with that of the voltage-versus-temperature table stored in the computer’s memory. A reference sample can be placed on another balance in a separate chamber. The atmosphere in the sample chamber may be purged with an inert gas to prevent oxidation or other undesired reactions. A different process using a quartz crystal microbalance has been devised for measuring smaller samples on the order of a microgram (versus milligram with conventional TGA).

The schematic principle of the TGA measurement is shown in Figure 1. The sample is heated under nitrogen or synthetic air with constant heat rate while the difference of the mass during this process is measured. A mass loss indicates that a degradation of the measured substance takes place. The reaction with oxygen from the synthetic air for example could lead to an increase of mass

• It determines water content or the residual solvents in a material.

• Analysis of reactions with air, oxygen, or other reactive gasses.

• It can be used to measure evaporation rates as a function of temperature, such as measure the volatile emissions of liquid mixtures.

• It used in the determination of curie temperatures of magnetic transitions by measuring the temperature at which the force exerted by a nearby magnet disappears on heating or reappears on cooling.

• It can identify plastics and organic materials by measuring the temperature of bond scissions in inert atmospheres or of oxidation in air or oxygen.

• It measure the weight of fiberglass and inorganic fill materials in plastics, laminates, paints, primers, and composite materials by burning off the polymer resin.

• It measures the fill materials added to some foods, such as silica gels, cellulose, calcium carbonate, and titanium dioxide.

• It determines the purity of a mineral, inorganic compound, or organic material.

• It distinguishes different mineral compositions from broad mineral types, such as borax, boric acid, and silica