Calcium carbonate was synthesized in a CaCl2/NaCO3 mixed solution by using ethylenediaminetetraacetic acid （EDTA） as an additive. The thermodynamics and kinetics analyses indicate that although the driving force of ...Calcium carbonate was synthesized in a CaCl2/NaCO3 mixed solution by using ethylenediaminetetraacetic acid （EDTA） as an additive. The thermodynamics and kinetics analyses indicate that although the driving force of amorphous calcium carbonate （ACC） precipitation is always less than that of calcite and vaterite precipitation, the nucleation rate of ACC is greater than that of calcite and vaterite at the initial stage of the precipitation reaction. With the increasing incubation time, vaterite and calcite particles nucleate heterogeneously by using the as-formed particles as active sites. Scanning electron microscopy images indicate that the transformation mechanism of ACC and vaterite to calcite is the dissolution-recrystallisation reaction. The presence of EDTA not only improves the stabilities of ACC and vaterite, but also leads to forming enlongated, connected rhombohedral calcite crystals after incubation 7 days in solutions. The ACC and vaterite are stabler in air than in solutions at room temperature, although the dissolution-recrystallisation reaction occurs on the surface.展开更多
A single phase of zirconium diboride （ZrB2） powder was successfully synthesized by sol-gel method in Zr-B-C-O system, using zirconium oxychloride （ZrOC12 ~ 8H20）, nano-scale boron and suerose（C12H22011）as the st...A single phase of zirconium diboride （ZrB2） powder was successfully synthesized by sol-gel method in Zr-B-C-O system, using zirconium oxychloride （ZrOC12 ~ 8H20）, nano-scale boron and suerose（C12H22011）as the starting materials and propylene oxide （PO） as complexing agent at a low temperature. Simultaneously, the experimen- tal and theoretical studies of ZrB2 synthesized by boro/carbothermal reduction from novel sol-gel technology were discussed. The results indicated that the pure rod-like ZrB2 powder without residual ZrO2 phase could be obtained with a B/Zr molar ratio of 3.5 at 1 400~C in argon atmosphere. Besides, in this study, a kinetic model for the Zr-B-C-O sys- tem producing ZrB2 by boro/carbothermal reaction was established based on thermodynamic analysis. It was also ob- served that, with the increase of reaction temperature, the reaction which produced ZrB2 powders changed from the borothermal reaction to boro/carbothermal reaction in the Zr-B-C-O system.展开更多
Carbon spheres with size of 50-300 nm were synthesized via a solvent-thermal reaction with calcium carbide and chloroform as reactants in a sealed autoclave.The morphologies and microstructures of carbon spheres befor...Carbon spheres with size of 50-300 nm were synthesized via a solvent-thermal reaction with calcium carbide and chloroform as reactants in a sealed autoclave.The morphologies and microstructures of carbon spheres before and after high temperature treatment(HTT) were characterized by X-ray diffractometry(XRD) ,scanning electronic microscopy(SEM) ,energy diffraction spectroscopy(EDS) ,and transmission electron microscopy(TEM) .The formation mechanism of carbon spheres was discussed.The results indicate that the carbon spheres convert to hollow polyhedron through HTT.Carbon spheres are composed of entangled and curve graphitic layers with short range order similar to cotton structure,and carbon polyhedron with dimension of 50-250 nm and shell thickness of 15-30 nm.The change of solid spheres to hollow polyhedron with branches gives a new evidence for formation mechanism of hollow carbon spheres.展开更多
文摘Calcium carbonate was synthesized in a CaCl2/NaCO3 mixed solution by using ethylenediaminetetraacetic acid （EDTA） as an additive. The thermodynamics and kinetics analyses indicate that although the driving force of amorphous calcium carbonate （ACC） precipitation is always less than that of calcite and vaterite precipitation, the nucleation rate of ACC is greater than that of calcite and vaterite at the initial stage of the precipitation reaction. With the increasing incubation time, vaterite and calcite particles nucleate heterogeneously by using the as-formed particles as active sites. Scanning electron microscopy images indicate that the transformation mechanism of ACC and vaterite to calcite is the dissolution-recrystallisation reaction. The presence of EDTA not only improves the stabilities of ACC and vaterite, but also leads to forming enlongated, connected rhombohedral calcite crystals after incubation 7 days in solutions. The ACC and vaterite are stabler in air than in solutions at room temperature, although the dissolution-recrystallisation reaction occurs on the surface.
基金Supported by the Fund for the Self-dependent Innovation of Tianjin University(2014)
文摘A single phase of zirconium diboride （ZrB2） powder was successfully synthesized by sol-gel method in Zr-B-C-O system, using zirconium oxychloride （ZrOC12 ~ 8H20）, nano-scale boron and suerose（C12H22011）as the starting materials and propylene oxide （PO） as complexing agent at a low temperature. Simultaneously, the experimen- tal and theoretical studies of ZrB2 synthesized by boro/carbothermal reduction from novel sol-gel technology were discussed. The results indicated that the pure rod-like ZrB2 powder without residual ZrO2 phase could be obtained with a B/Zr molar ratio of 3.5 at 1 400~C in argon atmosphere. Besides, in this study, a kinetic model for the Zr-B-C-O sys- tem producing ZrB2 by boro/carbothermal reaction was established based on thermodynamic analysis. It was also ob- served that, with the increase of reaction temperature, the reaction which produced ZrB2 powders changed from the borothermal reaction to boro/carbothermal reaction in the Zr-B-C-O system.
基金Project(2006CB600901) supported by the National Basic Research Program of ChinaProject(0991015) supported by Guangxi Natural Science Foundation,ChinaProject(200808MS083) supported by Guangxi Education Department Foundation,China
文摘Carbon spheres with size of 50-300 nm were synthesized via a solvent-thermal reaction with calcium carbide and chloroform as reactants in a sealed autoclave.The morphologies and microstructures of carbon spheres before and after high temperature treatment(HTT) were characterized by X-ray diffractometry(XRD) ,scanning electronic microscopy(SEM) ,energy diffraction spectroscopy(EDS) ,and transmission electron microscopy(TEM) .The formation mechanism of carbon spheres was discussed.The results indicate that the carbon spheres convert to hollow polyhedron through HTT.Carbon spheres are composed of entangled and curve graphitic layers with short range order similar to cotton structure,and carbon polyhedron with dimension of 50-250 nm and shell thickness of 15-30 nm.The change of solid spheres to hollow polyhedron with branches gives a new evidence for formation mechanism of hollow carbon spheres.
