Effects of Ball Milling on the Kinetics and Mechanism of Solid State Reaction between BaCO₃ and Sio₂

Abstract

Effects of ball-milling en the reaction of equimolar mixtures of BaCOs and SiO2 have been studied in the temperature range between 800 and 900C by means of isothermal thermogravimetry, electron microscopy, X-ray diffraction analysis and DTA.
The main part of the reaction, which corresponds to the formation of Ba2SiOi, was best expressed by Jander's equation and the activation energywas.determined as 53 kcal/mol irrespective of the ball-milling tirne. The reaction was found to proceed in three stages:
BaCOs+SiO2= BaSiOs+CO, (1)
BaCO3 +BaSiO3 = Ba2SiO4 + CO2 (2)
Ba2SiO+SiO2=2BaSiO3 (3)
The reaction (1) was independent of CO2 partial pressure, whereas the reaction (2) was checked by CO2.The increase in the reactivity as caused by ball-milling was detected by an endothermic peak at about 7500C in DTA. This peak was found to be associated with theformation of BaSiO3 (reaction(1)).The effect of ball-milling is possibly interpreted in terms of the decrease in particle size of BaCOs in early stage of ball-milling, and of the improvement of SiO2 dispersion in later stage, respectively.