Analysis of a mixture of calcium and magnesium carbonates:

A typical TG curve of a mixture of calcium and magnesium carbonates is display in Figure. You can notice that a significant mass loss occurs before 210° C. This is due to the moisture present in the mixture. Another mass loss at about 480° C is because of the following reaction:

MgCO ₃ (s) → MgO (s) + CO₂ (g)

Previously we mentioned that CaCO₃ decomposes at about 800 °C. In Figure mass loss between about 600 °C and 900 °C can be interpreted because of decomposition of CaCO₃.

CaCO₃ (s) → CaO (s) + CO₂ (g)

Portion of the curve ab represents a mixture of MgO and CaCO₃ and cd represents a residue of the mixture of MgO and CaO. Both these plateaus ab and cd represent weight m₁ and m₂, respectively. In fact mass m1 is due to CaCO₃ + MgO.

Figure: TG curve of mixture of calcium and magnesium carbonate

Thus, m₁ - m₂ is the loss of CO₂ between 500° C and 900° C due to the decomposition of CaCO₃. Using TGA curve we could associate the mass of different components formed during TGA experiment.