Thermogravimetry (TGA)

Question 1

What are the basic principles of TGA?

Answer 1

A thermal technique in which the mass of the sample is monitored against time or temperature (while the temperature, in a specified atmosphere, is programmed).

Question 2

What are the instruments used in TGA?

Answer 2

1. Thermobalance (sensitive to μg)
2. Furnace
3. Temperature programmer
4. Temperature sensor
5. Sample holder
6. Pure gas sample (inert or reactive)

Question 3

What are important properties of the balance?

Answer 3

1. sensitive in order of 1 μg.
2. sample weight up to 20 mg.
3. Operate in inert (nitrogen) or oxidative (air or oxygen) atmosphere.

Question 4

What kind of balance equipment is preferred and why?

Answer 4

Electromagnetic balances:
1. insensitive to vibrations
2. high sensitivity (0.1 μg)
3. thermal stability

Question 5

How does the balance work?

Answer 5

1. Beam displaced from equilibrium, when sample added.
2. Detected by photocell
3. Electric torque motor starts
4. Beam’s position restored

• The force restoration is proportional to the change in weight.

Question 6

What are important properties of the furnace?

Answer 6

1. Operate at 1100 C
2. Where the balance is stored in
3. sample remains in the same heating zone of the furnace
4. Protects the balance from radiant heat and corrosive gases evolving from the sample

Question 7

What materials are used for the pans for TGA, and at what temperatures?

Answer 7

At T < 600 C:
1. aluminum

At T > 600 C:
2. platinum
3. silica
4. alumina

Question 8

What are the factors affecting TGA analysis?

Answer 8

1. heating rate
2. sample size
3. particle size
4. packaging of sample
5. crucible shape
6. Gaseous atmosphere
7. Buoyancy (density of gas changes with temperature)

Question 9

How does the crucible type affect TGA analysis?

Answer 9

It will influence the decomposition temperature.
- More open: allow evolved gases to be readily removed
- More restricted: Will delay decomposition.

Question 10

What are the applications of TGA?

Answer 10

1. Thermal stability
2. Material Characterization
3. Analysis of composition
4. Industrial Processes
5. Kinetic studies
6. Corrosion studies

Question 11

How does TGA apply to thermal stability?

Answer 11

Materials compared at elevated temperatures under required atmosphere.

Helps to separate decomposition mechanisms.

Question 12

How does TGA apply to material characterization?

Answer 12

To fingerprint materials for identification or quality control.

Question 13

How does TGA apply to Analysis of composition?

Answer 13

To Analyse materials/mixtures by removing their components.

Question 14

How does TGA apply to industrial processes?

Answer 14

Thermobalance furnace used as mini-reactor, mimicking the conditions in industrial reactors.

Question 15

How does TGA apply to kinetic studies?

Answer 15

Analyze kinetic features by weight loss or gain.

Question 16

How does TGA apply to corrosion studies?

Answer 16

To study oxidation, or reactions with reactive gases or vapors.