Synthesis and characterization of magnesium hydroxide by batch reaction crystallization

Magnesium hydroxide with high purity and uniform particle size distribution was synthesized by the direct precipitation method using MgCl_(2) and NaOH as reactive materials and NaCl as additive to improve the crystallization behavior of the product.The particle size distribution,crystal phase,morphology,and surface area of magnesium hydroxide were characterized by Malvern laser particle size analyzer,X-ray diffraction(XRD),scanning electron microscope(SEM)and Branauer-Emmett-Teller(BET)method,respectively.The purity of products was analyzed by the chemical method.The effects of synthesis conditions on the particle size distribution and water content(filtration cake)of magnesium hydroxide were investigated.The results indicated that feeding mode and rate,and reaction temperature had important effects on water content and the particle size distribution of the product,and sodium chloride improved the crystallization behavior of magnesium hydroxide.The ball-like magne-sium hydroxides with the particle size distribution of 6.0–30.0μm and purity higher than 99.0%were obtained.This simple and mild synthesis method was promising to be scaled up for the industrial production of magnesium hydroxide.

Effect of modifying matrix microstructures and nanosized precipitates on strengthening mechanisms and ductile-to-brittle-transitiontemperature in a 1000 MPa Ni-Cr-Mo-Cu steel

A superior combination of yield strength(1001 MPa)and-20℃ impact toughness(166 J)was obtained in Nb-V-Timicroalloyed Ni-Cr-Mo-Cu steel treated by direct quenching and tempering route(DQT).The tested steels treated by DQT route and re-austenitization and tempering route(QT)were compared with each other in terms of mechanical properties and microstructures characterized by optical microscopy,transmission electron microscopy,X-ray diffraction,electron back-scattered diffraction method and so on.Strength and Vickers hardness of the tested steel treated by the above two routes vary with isothermal aging temperature(400-600℃),shown as under-aged state,peak-aged state and overaged state.All DQT specimens show higher strength and Vickers hardness than QT specimens with the same aging condition.Furthermore,the largest difference of yield strength between DQT and QT specimens was shown in DQT600 and QT600 specimens.DQT600 or QT600 specimens refers to direct quenched(DQ)or quenched(Q)specimens isothermally aged at 600℃.The main disparities in quenched microstructure between DQ and Q specimens are mainly in morphology of prior austenite grains,dislocation density of martensite matrix and solution amount of Nb and Mo elements dissolving in martensite matrix,which play key roles in affecting microstructure and mechanical properties of DQT and QT specimens.Higher dislocation density of matrix and finer average diameter of both MC(M is any combination of Nb,Mo and V)and Cu-rich particles were shown in DQT600 specimens than in QT600 specimens.Strengthening from dislocations and nanosized MC and Cu-rich particles mainly leads to the largest difference of yield strength between DQT600 and QT600 specimens.In addition,strong dislocation strengthening and precipitation strengthening in DQT600 specimen also elevated its ductile-to-brittle-transition-temperature,compared with QT600 specimen.