Preparation And Thermal Decomposition Kinetics Of Monodisperse Micro And Nano Powders Of Magnesium Oxide

Micro and nano powder of magnesium oxide is a new type of high functional fine inorganic material,has showed different optical,electic,thermal and chemical aspects compare to the row material in low temperature agglomeration,microwave asorbtion and catalysis.Scientists have reaerched micro and nano powder of magnesium oxide since it is applied into medication,spaceflight and catalysis successfully.The inorganic precursor is prepared with magnesium chloride hexahydrate as row material,with ethanol and distilled water as solvent,with ammonia and sodium hydroxide as precipitator,with PEG as protactant;micro powder of magnesium oxide is prepared by calcining magnesium hydroxide as precipitator;at the same time,kinetics of micro powder of magnesium hydroxide is researched with integral and romero methods.The organic precursor is prepared with sodium oleate and magnesium chloride hexahydrate as row material,with normal hexane and ethanol and distilled water as solvent;nano powder of magnesium oxide is prepared by pyrolysis with magnesium oleate as precipitator.In this paper,I studied the prepared conditions of precipitators,researched the influence of calcining temperature and calcining time.XRD,SEM,FT—IR and TG/DSC techniques were used to characterize the samples.The optimum processing conditions in preparation of magnesium hydroxide: V(ethanol):V(distilled water)=3:1,n(ammonia):n(sodium hydroxid)=5:4,reaction temperature 25℃and agitation velocity 1000r/min.Under these conditions,average crystalline diameter of magnesium hydroxide is 2μm.The optimum processing conditions in preparation of magnesium oxide:calcining temperature 400℃,calcining time 3h.Under these conditions, the particle size distribute of magnesium oxide is uniform,and average crystalline diameter is 4μm.The research of thermal decomposition kinetics of inorganic precursor is found that the thermal decomposition processes of magnesium hydroxide conclude two steps.In rapid decomposition moment of magnesium hydroxide,the rate-controlling mechanism is three dimensional diffusion,integral function is G(α)=[(1+α)^1/3-1]²,apparent activation energy is 177kJ/mol;In slow decomposition moment,the rate-controlling mechanism is nucleation and development,integral function is G(α)=[-ln(1-α)]⁴,apparent activation energy is 38kJ/mol.The processing conditions in preparation of organic precursor is:reaction temperature 70℃,reaction time 2h.Under these conditions,configuration of magnesium oleate accord with Bidentate model.The optimum processing conditions is:reaction temperature 300℃,reaction time 2h.Under these conditions,the particle size distribution of magnesium oxide is uniform,and average crystalline diameter is 200nm.