State the applications and limitations of TGA?

Thermogravimetry is the technique in which change in the weight is recorded as the function of temperature Or time. The phenomenon is used for qualitative as well as quantitative analysis.

Following are the applications of TGA:

1) With TGA we can have quantitative analysis. e.g. The thermal curve of 125.70 mg. of a substance contains mixture of $Ca{C}_2{O}_4.H_{2}O$ (Mol. wt. = 146.12) and thermally stable salt had a loss in the mass of 6.98 mg. At Tonset 140°C. We can find out the % of Ca-oxalate. $$Ca{C}_2{O}_4.H_{2}O\underrightarrow{140C}Ca{C}_2{O}_4+H_{2}O\uparrow$$ This indicates 146.12 gm of $Ca{C}_2{O}_4{H}_{2}O$ will lose 18 gm of $H_{2}O$.

Therefore x gm of $Ca{C}_2{O}_4{H}_{2}O$ is loosing 6.98 gm of $H_{2}O$ $$\therefore x=\frac{146.12\times 6.98}{18}=56.7gmofCa{C}_2{O}_4{H}_{2}O$$ That is $\therefore x=\frac{56.7\times 100}{125.7}=45\mathrm{\%}ofCa{C}_2{O}_4{H}_{2}O$

2) TGA curve gives the information regarding chemical kinetics.

3) As the Tonset is characteristic property so from Tonset, we can have qualitative analysis.

4) With the help of TGA curve, we can find out the energy of activation of the chemical reaction.

5) For any compound, the products formed at various temperatures can be found from TGA curve.

6) The amount of water present in the clay and soil can be determined.

7) Mechanism of polymer can be studied.

8) The correct drying and ignition temperature in gravimetry can be determined.

9) Thermal decomposition of organic, inorganic and polymeric compounds can be studied.

10) We can find out purity and thermal stability of primary and secondary standards can be determined in titrimetry.

Limitations:

1) TGA is applicable to solid compounds only.

2) As thermocouple is kept very close to sample but not in contact with the sample. Therefore exact temp. of the sample cannot be detected.