Decomposition Kinetic Of Nano-CaCO₃

Calcia（CaO）is an effectively important material,which is widely used as catalyst,toxic waste remediation agent,paint,or as an important component in refractories for clean steelmaking due to its outstanding adsorption capacity on impurities in steel.Nano CaO is a kind of new nano material which is developed in last century which can be used in bactericide,adsorbent,and catalyst manufacturing.Compared with decomposition kinetics of micron CaCO₃,the decomposition kinetics of nano CaCO₃ under air and CO₂ was studied in this paper.In addition,the nano CaO preparation method though vacuum thermal decomposition of nano CaCO₃ was investigated,as well the influence of heating treatment on the microstructure,specific surface area and grain size of CaO was investigated in this work.The results show that:（1）The decomposition temperature of nano CaCO₃ was lower than that of micron CaCO₃ decomposition temperature under different heating rate and atmosphere.When the conversion rate of decomposition is about 74%,both nano CaCO₃ and micron CaCO₃ can reach the maximum CO₂ release rate.（2）The mechanism model of decomposition reaction of nano CaCO₃ can be described as phase boundary reaction,obtaining the mechanism function: G（α）= 1-（1-α）1/n.The reaction order n is 1.5 in air and 2 in CO₂ respectively.（3）The decomposition temperature of nano CaCO₃ is lower in vacuum.Grain growth of CaO was restrained due to the defects in CaO which was formed in the decomposition of nano CaCO₃ in vacuum.With the temperature increasing,the crystallization degree and average grain size of CaO preparated in air were increased,which can be attributed to the lattice distortion stress in grain gradually decreases.（4）Sintering have been occurred between CaO particles which were preparated in air.However,there are lots of crystallites and pores existing in CaO preparated in vacuum,and the CaO particles were consisted of many aggregates connected together through the sintering neck.Due to amounts of nano crystallites existing,the activity of CaO powder prepared in vacuum is much higher than that of CaO powder prepared in air.（5）The heating rate has a great influence on the structure of aggregates of CaO crystallites during heating.CaO aggregates were sintered easily when heating rate is slow.With the increment of heating rate,CaO crystallite inside aggregates was sintered.When the heating rate was controlled between 10℃/min to 20℃/min,the activity of CaO prepared in vacuum is higher.