A facile and cheap method for the fabrication of WC-Al2O3composite powder was proposed.Thermodynamic calculations indicate that aluminothermic reduction of WO3in WO3:xAl:(4-1.5x)C mixture is accompanied by a great dea...A facile and cheap method for the fabrication of WC-Al2O3composite powder was proposed.Thermodynamic calculations indicate that aluminothermic reduction of WO3in WO3:xAl:(4-1.5x)C mixture is accompanied by a great deal of heat,so carbothermic reduction reaction(endothermic)becomes activated in the system.By substitution of aluminum with carbon,the formation of unwanted W2C phase can be prevented because of less thermodynamic stability at lower temperatures.For the verification of the proposed reaction mechanism,various WO3:xAl:(4-1.5x)C mixtures(1.1≤x≤2)were heat-treated in a domestic microwave oven.The results showed that the type of reaction is self-propagating high temperature synthesis(SHS)when1.4≤x≤2.Lower amount of Al in WO3:xAl:(4-1.5x)C mixtures results in a higher formation of WC.A W2C-free WC-Al2O3composite was obtained by continuation of microwave heating in an isolated atmosphere,after the occurrence of SHS reaction in a mixture containing1.4mol of Al.Results also showed that when x≤1.3,type of reaction becomes gradual,which in turn brings about the incompleteness reaction and residue of initial reagents.展开更多
Pure Ca-SiAlON:Eu2+ was synthesized by microwave sintering method at a relatively low temperature of 1550℃.Photoluminescence intensity of the resultant phosphor was higher than those of the samples synthesized by con...Pure Ca-SiAlON:Eu2+ was synthesized by microwave sintering method at a relatively low temperature of 1550℃.Photoluminescence intensity of the resultant phosphor was higher than those of the samples synthesized by conventional gas-pressure sintering technique at 1750℃.When it was excited at 450 nm,the as-prepared yellow Ca-SiAlON:Eu2+ sample had an external quantum efficiency of 42%,comparable to the sample synthesized at 1750℃ under 0.5 MPaN2 gas pressure by the GPS method reported in reference.The experimental results demonstrated that the microwave sintering method was also an interesting approach for synthesizing nitride phosphors,which promises lower firing temperature than those by carbothermal reduction and nitridation (CRN) methods,higher heating rate and shorter duration time compared with those by gas-pressure sintering.展开更多
文摘A facile and cheap method for the fabrication of WC-Al2O3composite powder was proposed.Thermodynamic calculations indicate that aluminothermic reduction of WO3in WO3:xAl:(4-1.5x)C mixture is accompanied by a great deal of heat,so carbothermic reduction reaction(endothermic)becomes activated in the system.By substitution of aluminum with carbon,the formation of unwanted W2C phase can be prevented because of less thermodynamic stability at lower temperatures.For the verification of the proposed reaction mechanism,various WO3:xAl:(4-1.5x)C mixtures(1.1≤x≤2)were heat-treated in a domestic microwave oven.The results showed that the type of reaction is self-propagating high temperature synthesis(SHS)when1.4≤x≤2.Lower amount of Al in WO3:xAl:(4-1.5x)C mixtures results in a higher formation of WC.A W2C-free WC-Al2O3composite was obtained by continuation of microwave heating in an isolated atmosphere,after the occurrence of SHS reaction in a mixture containing1.4mol of Al.Results also showed that when x≤1.3,type of reaction becomes gradual,which in turn brings about the incompleteness reaction and residue of initial reagents.
基金supported by the National Natural Science Foundation of China(51102252 and 51272259)the Special Foundation for Young Scientists of Zhejiang Province(R12E020005)
文摘Pure Ca-SiAlON:Eu2+ was synthesized by microwave sintering method at a relatively low temperature of 1550℃.Photoluminescence intensity of the resultant phosphor was higher than those of the samples synthesized by conventional gas-pressure sintering technique at 1750℃.When it was excited at 450 nm,the as-prepared yellow Ca-SiAlON:Eu2+ sample had an external quantum efficiency of 42%,comparable to the sample synthesized at 1750℃ under 0.5 MPaN2 gas pressure by the GPS method reported in reference.The experimental results demonstrated that the microwave sintering method was also an interesting approach for synthesizing nitride phosphors,which promises lower firing temperature than those by carbothermal reduction and nitridation (CRN) methods,higher heating rate and shorter duration time compared with those by gas-pressure sintering.
