Thermogravimetric analysis (TGA) measures the change in mass of a substance as it is heated. In TGA, a sample is heated at a controlled rate in a furnace while its weight is continuously monitored using a microbalance. The weight change is plotted against temperature or time to produce a thermogram. Factors like heating rate, furnace atmosphere, sample weight and particle size can affect the TGA curve. TGA is used to study processes like decomposition, oxidation, and moisture loss that cause weight changes in materials when heated.

1. THERMOGRAVIMETRIC
ANALYSIS
LECTURE 3
BY HAMU NDWABE, ( M PHARM, B PHARM HONS)

3. Introduction
•Thermogravimetric analysis (TGA) is a thermoanalytical technique where a thermo-balance (a
combination of an electronic microbalance with a furnace and appropriate temperature
controller) measures changes in sample mass.
•This technique can be use to study the material weight loss due to e.g. decomposition,
oxidation, or loss of volatiles, such as moisture in a set temperature range, giving typically a
temperature (or time)/mass (or mass percentage) plot.
•Thermogravimetric Analysis is a technique in which the mass of a substance is monitored as a
function of temperature or time as the sample specimenis subjected to a controlled
temperature program in a controlled atmosphere.

4. Principle
• In thermogravimetric analysis, the sample is heated in a given environment (air, N2, CO2, He, Ar,
etc.) at controlled rate. The change in the weight of the substance is recorded as a function of
temperature or time. The temperature is increased at a constant rate for a known initial weight
of the substance and the changes in weights are recorded as a function of temperature at
different time interval. This plot of weight change against temperature is called
thermogravimetric curve or thermogram, this is the basic principle of TGA

6. EXAMPLE 2

7. Instrumentation

8. Instrument
•Instrument used for thermogravimetry is “Thermobalance”. Data recorded in form of curve
known as ‘Thermogram’
•The furnace can raise the temperature as high as 1000°C which is made of quartz.
• The auto sampler helps to load the samples on to the microbalance.
•The thermocouple sits right above the sample.
•Recorder: A recorder records the change in weight in y axis and w.r.to temperature on the x-axis.
We get a thermogram

9. Factors affecting the TG curve
The factors which may affect the TG curves are classified into two main groups.
(1) Instrumental factors
(2) Sample Characteristics

10. Instrumental factors
• Furnace Heating rate: The temperature at which the compound (or sample) decompose
depends upon the heating rate. When the heating rate is high, the decomposition temperature
is also high. A heating rate of 3.5°C per minute is usually recommended for reliable and
reproducible TGA.
• Furnace atmosphere: The atmosphere inside the furnace surrounding the sample has a
profound effect on the decomposition temperature of the sample. A pure N2 gas from a cylinder
is passed through the furnace which provides an inert atmosphere.

11. Sample characteristics
(a)Weight of the sample: A small weight of the sample is recommended using a small weight
eliminates the existence of temperature gradient throught the sample.
(b) Particle size of the sample: The particle size of the sample should be small and uniform. The
use of large particle or crystal may result in apparent, very rapid weight loss during heating

12. Applications of TGA Analysis
•Determines temperature and weight change of decomposition reactions, which often allows
quantitative composition analysis.
•May be used to determine water content or the residual solvents in a material.
•Allows analysis of reactions with air, oxygen, or other reactive gases (see illustration below).
•Can be used to measure evaporation rates as a function of temperature, such as to measure the
volatile emissions of liquid mixtures.