The Effect Of Reactants Particle Sizes On The Kinetic Parameters And The Affect Interpretation In Solid-Liquid Reactions

It has been found that reducing the size of reactants can increase the reaction rate long ago and ascribed that to the increased contact area between reactants. Later, people gradually found that the reduce of reactants size not only can increases the contact area between reactants, but also can reduce the activation energy and can even change the reaction products and reaction mechanism. There are many studies on kinetics of thermal decomposition, while the study about the effect of particle size on the kinetics of solid-liquid reaction is still little and the report about the affect interpretation of particle size on the pre-exponential factor and reaction constant has not been found. Therefore, the investigation of effects of particle sizes on chemical reactions by using nanoparticles as the reactant has important theory meanings for developing physical chemistry and theoretics guidances for applying nanoparticles to chemical fields.Firstly three solids-liquid reactions having moderate reaction rate were screened through experimentation and are reactions of nano-NiO and sodium bisulfate, nano-MgO and sodium bisulfate and nano-ZnO and acrylic acid solution respectively.Then the precursor of nano-NiO was prepared with nickelous nitrate and carbamide by homogeneous precipitation and was analyzed by XRD and TG. The result shows that calcining temperature is 400℃at least. The nano-NiO crystalline can obtained by calcinating precursor and were analyzed by XRD and TEM. The results show that nano-NiO crystal is cubic structure, similar to the ball; nano-NiO of 99% purity was prepared under different experimental conditions, and the range of average particle size is 5.0-30nm; and nano-NiO diameter decrease with the increase of the ratio of reactants, with the decrease of calcination temperature and with the decrease calcination time and the yield of the precursor increase with the increase of rate of reactants.The precursor of nano-ZnO was prepared with zinc nitrate and carbamide by homogeneous precipitation and was analyzed by XRD and TG. The rusults show that the precursor is Zn5(OH)6(CO3)2 and the calcining temperature is 400℃at least. The nano-ZnO crystalline can obtained by calcinating precursor and were analyzed by XRD and TEM. The results show that nano-ZnO crystalline is hexagonal, approximately spherical particles; different average nano-ZnO were prepared by different experimental conditions and the range of average particle size is 20-50nm; and the nano-ZnO diameter decrease with the decrease of the reactant concentration, with the decrease of the reaction temperature and with the decrease of the calcination temperature; nano-ZnO yield increase with the increase of the reactant concentration, with the increase of the reactant ratio and with the increase of the reaction temperature.The precursor of nano-MgO was prepared with magnesia and salvolatile by homogeneous precipitation method. The nano-MgO crystalline can obtained by calcinating precursor and were analyzed by XRD. The results show that nano-MgO is cubic crystal system, approximately spherical particles; different average nano-MgO were prepared by different experimental conditions and the range of average particle size is 5-37nm; and nano-MgO diameter decrease with the decrease of the concentration of reactants, with the increase of the reaction temperature and with the decrease of the calcination temperature.Instantaneous pH values or ion concentrations were tested by ion analyser under different diameters and temperatures and the reaction rate of different diameters and temperatures were also obtained. The regularities of rate constant, reaction order, pre-exponential factor and apparent activation energy varied respectively with particle size were found and the effects of particle size on the kinetics parameters and affect interpretation were disscussed in solid-liquid reaction. The results show that: there are obvious effects of the reactant particle diameter on rate constants, reaction order, apparent activation energy and pre-exponential factor in the reactions; the rate constant and the reaction order increase with the decrease of the particle diameter, whereas the apparent activation energy and the pre-exponential factor decrease with the decrease of the particle diameter; the logarithm of pre-exponential factor and the apparent activation energy are linearly related to the reciprocal of the particle diameter respectively. The essentialities of influencing of the particle diameter on the kinetic parameters in the heterogeneous reaction as follows: the reaction order is influenced by the molar surface area, the apparent activation energy by the molar surface energy, the pre-exponential factor by the molar surface entropy, and the rate constant by both the molar surface energy and the molar surface entropy.