Size and shape control of alpha-alumina particles precipitated from 1,4-butanediol solution.

摘要

Phase-pure, monodispersed, hexagonal plates of single crystal {dollar}alpha{dollar}-alumina {dollar}({lcub}approx{rcub}2 mu{dollar}m wide and {dollar}{lcub}approx{rcub}0.5 mu{dollar}m thick) have been prepared via precipitation by treating an aluminum hydrous oxide precursor in 1,4-butanediol at 300{dollar}spcirc{dollar}C under autogenous vapor pressure. Present work shows that KOH is the only reagent that precipitates an aluminum hydrous oxide precursor suitable to synthesize {dollar}alpha{dollar}-alumina in 1,4-butanediol solution. In contrast, the use of NaOH or NH{dollar}sb4{dollar}OH as the precipitating reagent for the precursor material does not yield the alpha phase. The solution pH at which the precursor materials are precipitated is also a critical factor for the formation of {dollar}alpha{dollar}-{dollar}rm Alsb2Osb3.{dollar} Phase-pure {dollar}alpha{dollar}-alumina powders were also only synthesized from the aluminum hydrous oxide precursors precipitated in the pH range from 10 to 10.5. The results of X-ray diffraction and scanning electron microscopy indicate that longer reaction times promote the phase transformation from the intermediate boehmite phase to {dollar}alpha{dollar}-alumina. The complete transformation from boehmite to {dollar}alpha{dollar}-alumina requires reaction times of about 12 hr.; Current work also involves the effect of reaction conditions on the morphology of {dollar}alpha{dollar}-alumina particles. Synthesis variables including reaction time, stirring speed, amount of methanol, and solid loading have a strong effect on the size and shape of {dollar}alpha{dollar}-alumina synthesized in 1,4-butanediol solutions. {dollar}alpha{dollar}-Alumina crystals with different habits, circular platelets, hexagonal platelets, hexagonal platelets with habit modifications on the edges, dodecahedra, polyhedra with 14 faces, polyhedra with 20 faces, hexagonal prism, and hexagonal prism with habit modifications on the edges are synthesized. Also, possible growth mechanisms of {dollar}alpha{dollar}-{dollar}rm Alsb2Osb3{dollar} particles in 1,4-butanediol solution are proposed by using the computer program SHAPE{dollar}spcopyright{dollar} and ATOMS{dollar}spcopyright.{dollar} The results of this study indicate that it is possible to control the morphology of synthesized {dollar}alpha{dollar}-alumina particles by controlling the process conditions and theoretical predictions of crystal shapes can be reconciled to the morphology of the experimentally synthesized particles.; Finally, the effect of seed particles and shear rate on the size and shape of {dollar}alpha{dollar}-{dollar}rm Alsb2Osb3{dollar} particles are described in glycothermal conditions. It is demonstrated that the size of {dollar}alpha{dollar}-{dollar}rm Alsb2Osb3{dollar} platelets synthesized in 1,4-butanediol solution can be controlled from 100-200 nm to 3-4 {dollar}mu{dollar}m by varying the amount of {dollar}alpha{dollar}-{dollar}rm Alsb2Osb3{dollar} and {dollar}alpha{dollar}-{dollar}rm Fesb2Osb3{dollar} seeds. High stirring rate promotes the formation of hexagonal platelets with high aspect ratio, whereas medium and low stirring rates promote the formation of elongated platelets and polyhedra with 14 faces, respectively. This study demonstrates that the particle size of {dollar}alpha{dollar}-{dollar}rm Alsb2Osb3{dollar} particles synthesized in 1,4-butanediol solution is controlled by varying overall nucleation rate using {dollar}alpha{dollar}-{dollar}rm Alsb2Osb3{dollar} and {dollar}alpha{dollar}-{dollar}rm Fesb2Osb3{dollar} seeds. It is also demonstrated that the shape of {dollar}alpha{dollar}-{dollar}rm Alsb2Osb3{dollar} particles grown in 1,4-butanediol solution can be retained while controlling particle size.