Drying Kinetics Of Magnesium Hydroxide Powders And Molecular Dynamics Simulation Of Water

Magnesium hydroxide has a wide application foreground in the industrial field. Magnesium hydroxide can be used as desulfurizer of flue gas, environment protecting neutralizer ofindustrial wastewater, removal agent of heavy metal and so on. High purity and superfine magnesium hydroxide as flame-retardant has become research focus. Basing on MgC12.6H2O as the raw material, NaOH and NH3.H2O as the mixed precipitants,magnesium hydroxide powder,the average grain diameter of which is2um, were synthesized by direct precipitation method. The drying curves and drying rate curves were obtained by drying kinetics experiments of magnesium hydroxide powders at different levels of drying medium temperatures and wet material laver thicknesses. After curve fitting and analvsis of the wxperimental data with Weibull distribution function model,the drying kinetics equation and drying kinetics parameters of magnesium hydroxide powders were derived to consider the inflrencing factors of drying kinetics parameters.The analysis results indicate that, the dry process is divided into accelerating rate,constant rate and decelerating rate drying period.The Weibull distribution function model can be used to describe the drying kinetics equations of magnesium hydroxide powders. The drying equation of magnesium hydroxide powders isMR=exp[-(t/α)β],which is reliability function of weibull distribution function. The drying rate equation is-dt-dMR/dt=β/α(t/α)β-1exp[-(t/α)β],which correspond to density function of Weibull distribution function. The scale parameterα=exp[RT-E1+RTC4L/RT]/A is related to drying medium temperatures and material layer thicknesses. With the increase of drying medium temperatures of the decrease of material layer thicknesses,the scale parameter and the drying rate increase, but the shape parameter is approximately identical. Other drying kinetics parameters are listed below that Interface evaporation activation energyEV=20.68kJ/mol pre-exponential factor a=64.12min-1, length constantC1=153.29m-1and temperature constantCT=2487.5KBasing on SPC model as water model, and every atom of water molecule as statistical object, molecular dynamics simulations were performed to study the vapor-liquid interface haracteristics of water and analyse the distribution rules. The study shows indicate that,the density of vapor and the interface thickness increase as the temperature increases, but the density of liquid, the surface tension, and the well depth of potential energy show opposite tendency. With the increase of the water molecular and the cut-off radius, the density of liquid and the interface thickness increase.