Decomposition kinetics of CaCO3 dry coated with nano-silica

Non-isothermal decomposition kinetics of surface coated calcium carbonate (CaCO<inf>3</inf>) was investigated using different wt.% of nano-silica. The activation energy was calculated from model-free isoconversional technique using Kissinger-Akahira-Sunose method. The result indicates that CaCO<inf>3</inf> with lower wt.% (0.25% and 1.0%) of nano-silica has low activation energy than pure and 2% nano-silica coated CaCO<inf>3</inf>. This is possibly because nano-silica acts as heat receptor and creates defects inside the crystal which is dominant at lower percentage of coating. However, higher % of nano-silica coating increases resistance to CO<inf>2</inf> diffusion which increases the activation energy. The corresponding reaction model for decomposition was predicted by Málek's method. Experimental data was in good agreement with the theoretical model proposed by Šesták Breggren (SB). The parameters (m and n) in SB model and invariance of activation energy in the entire conversion range strongly signify that decomposition mechanism is single step in nature.