The PTCR(positive temperature coefficient of resistance) nanosized ceramic pow der was prepared by Sol-Gel process and characterized by XRD, DSC, SEM and BET techniques. The results showed that the nanopowder has an a...The PTCR(positive temperature coefficient of resistance) nanosized ceramic pow der was prepared by Sol-Gel process and characterized by XRD, DSC, SEM and BET techniques. The results showed that the nanopowder has an average crystallite si ze of 35nm with sphere-shaped, whose specific surface area is 27.80m2·g-1 and the crystal structure is abnormal cubical perovskite phase at room temperature. In addition, the nanopowder was pressed into pellets and then sintered accordin g to improved technique which was built based on the data of thermal analysis of the PTCR green-compact to yield PTCR ceramic materials with peculiar microstru cture and higher properties, which has a resistivity at room temperature of ～20 Ω·cm, a temperature coefficient of resistivity of ～19%·℃-1, a withstand v oltage intensity of >160V·mm-1 and a resistivity jump of >105.展开更多
Sr2CeO4 phosphor was synthesized by mechanical milling and reactive sintering in this work. The solid state reaction of SrCO3 and CeO2 (2∶1) started at about 850 ℃ and completed at 1 000 ℃ for about 4 h. Two types ...Sr2CeO4 phosphor was synthesized by mechanical milling and reactive sintering in this work. The solid state reaction of SrCO3 and CeO2 (2∶1) started at about 850 ℃ and completed at 1 000 ℃ for about 4 h. Two types of formation mechanism of Sr2CeO4 were proposed. When the starting powder mixture was fired above 1 000 ℃, the unstable intermediate phase SrCeO3 was developed, which then reacted with SrCO3 to form the final product Sr2CeO4, however, SrCO3 and CeO2 converted directly to Sr2CeO4 at a lower temperature. The XRD results showed the crystal structure of Sr2CeO4 was orthorhombic. The emission spectra displayed a broad band with maximum at about 465 nm. The mechanical milling of starting power mixture and the sintering temperature had no effect on this emission spectra.展开更多
文摘The PTCR(positive temperature coefficient of resistance) nanosized ceramic pow der was prepared by Sol-Gel process and characterized by XRD, DSC, SEM and BET techniques. The results showed that the nanopowder has an average crystallite si ze of 35nm with sphere-shaped, whose specific surface area is 27.80m2·g-1 and the crystal structure is abnormal cubical perovskite phase at room temperature. In addition, the nanopowder was pressed into pellets and then sintered accordin g to improved technique which was built based on the data of thermal analysis of the PTCR green-compact to yield PTCR ceramic materials with peculiar microstru cture and higher properties, which has a resistivity at room temperature of ～20 Ω·cm, a temperature coefficient of resistivity of ～19%·℃-1, a withstand v oltage intensity of >160V·mm-1 and a resistivity jump of >105.
文摘Sr2CeO4 phosphor was synthesized by mechanical milling and reactive sintering in this work. The solid state reaction of SrCO3 and CeO2 (2∶1) started at about 850 ℃ and completed at 1 000 ℃ for about 4 h. Two types of formation mechanism of Sr2CeO4 were proposed. When the starting powder mixture was fired above 1 000 ℃, the unstable intermediate phase SrCeO3 was developed, which then reacted with SrCO3 to form the final product Sr2CeO4, however, SrCO3 and CeO2 converted directly to Sr2CeO4 at a lower temperature. The XRD results showed the crystal structure of Sr2CeO4 was orthorhombic. The emission spectra displayed a broad band with maximum at about 465 nm. The mechanical milling of starting power mixture and the sintering temperature had no effect on this emission spectra.
