Chinaza Godswill Awuchi Thank you so much for your response. I have gone through the paper and thesis of provided link, but TGA graphs in both literatures are straight after weight loss.
Hi Dr Ameer Suhel . The weight gain is due to oxidation of your samples or it may react with nitrogen to form some compounds. See the following link:https://www.researchgate.net/post/What-does-it-mean-if-my-sample-weight-increases-during-TGA-analysis
On TGA analysis of calcium carbonate containing iron, at this forum: https://www.researchgate.net/post/How_would_the_addition_of_metallic_iron_to_a_sample_of_CaCO3_effect_the_TGA_and_DSC_curves_of_CaCO3