This paper reviewed the effect of powder characteristics and additives including metals,rare earth oxides,and ZrO2 on nitridation of Si powder.The decrease of particle size of Si powder increased nitridation.Most of m...This paper reviewed the effect of powder characteristics and additives including metals,rare earth oxides,and ZrO2 on nitridation of Si powder.The decrease of particle size of Si powder increased nitridation.Most of metal additives inhibited nitridation,while some metal additives such as Fe,Cu,Cr,and Ca increased nitrida—tion.Otherwise,the addition of metals might lead to the degradation of physical and mechanical properties of Si3N4.All the rare earth oxides,especially CeO2 and Eu2O3,showed nitridation enhancing effect.In addition,ZrO2 with small particle size showed a stronger enhancing effect.展开更多
Since about 10 years, there is a controversy about physics and chemistry of GdN between stoichiometric (tested) large single crystals and off-stoichiometric thin films. GdN single crystals are anti-ferromagnetic for a...Since about 10 years, there is a controversy about physics and chemistry of GdN between stoichiometric (tested) large single crystals and off-stoichiometric thin films. GdN single crystals are anti-ferromagnetic for applied magnetic fields of only 10 Oe, become ferromagnetic for excess electrons and larger magnetic fields. They are semimetallic. Thin films are ferromagnetic and semiconductors. Over the time, many experiments have been performed on both systems and the physics in each system is consistent. Band structure computations either yield ferromagnetic semimetals or ferromagnetic semiconducting thin films. There seems to be two incompatible worlds, those of single crystals and those of thin films. In the present work, the author compares directly the various measurements and calculations and gives reasons for their different results.展开更多
Porous silicon nitride（Si_3N_4） ceramics were fabricated by low temperature pressureless sintering, using carbonized rice husk and α-Si_3N_4 powders as raw materials, and MgO-CeO_2 as sintering additives. The effec...Porous silicon nitride（Si_3N_4） ceramics were fabricated by low temperature pressureless sintering, using carbonized rice husk and α-Si_3N_4 powders as raw materials, and MgO-CeO_2 as sintering additives. The effects of CeO_2 concentration and sintering temperature on phase composition, microstructure, porosity and flexural strength of the sintered products were investigated by X-ray diffraction（XRD）, scanning electronic microscopy（SEM）, Archimedes＇ displacement method and three-point bending strength, respectively. The results suggested that MgO-CeO_2 was a much more effective sintering additive for Si_3N_4 than MgO alone. When CeO_2 concentration was 4 wt.%–5 wt.% and sintering temperatures were in a range of 1500 to 1550 oC, the obtained porous silicon nitride ceramics had the porosity of 45.78%–42.81% and flexural strength of 49.44–84.09 MPa. Moreover, when sintering temperature was 1550 oC and CeO_2 concentration was 5%, large elongated β-Si_3N_4 grains were well developed.展开更多
基金financially supported by Guangdong Innovative and Entrepreneurial Research Team Program ( No. 2013G061)the National Natural Science Foundation of China ( No. 51402055)
文摘This paper reviewed the effect of powder characteristics and additives including metals,rare earth oxides,and ZrO2 on nitridation of Si powder.The decrease of particle size of Si powder increased nitridation.Most of metal additives inhibited nitridation,while some metal additives such as Fe,Cu,Cr,and Ca increased nitrida—tion.Otherwise,the addition of metals might lead to the degradation of physical and mechanical properties of Si3N4.All the rare earth oxides,especially CeO2 and Eu2O3,showed nitridation enhancing effect.In addition,ZrO2 with small particle size showed a stronger enhancing effect.
文摘Since about 10 years, there is a controversy about physics and chemistry of GdN between stoichiometric (tested) large single crystals and off-stoichiometric thin films. GdN single crystals are anti-ferromagnetic for applied magnetic fields of only 10 Oe, become ferromagnetic for excess electrons and larger magnetic fields. They are semimetallic. Thin films are ferromagnetic and semiconductors. Over the time, many experiments have been performed on both systems and the physics in each system is consistent. Band structure computations either yield ferromagnetic semimetals or ferromagnetic semiconducting thin films. There seems to be two incompatible worlds, those of single crystals and those of thin films. In the present work, the author compares directly the various measurements and calculations and gives reasons for their different results.
基金Project supported by the research fund of Collaborative Innovation Center for Ecological Building Materials(GX2015304,CP201506)Jiangsu Provincial Natural Science Foundation(BK20150427)
文摘Porous silicon nitride（Si_3N_4） ceramics were fabricated by low temperature pressureless sintering, using carbonized rice husk and α-Si_3N_4 powders as raw materials, and MgO-CeO_2 as sintering additives. The effects of CeO_2 concentration and sintering temperature on phase composition, microstructure, porosity and flexural strength of the sintered products were investigated by X-ray diffraction（XRD）, scanning electronic microscopy（SEM）, Archimedes＇ displacement method and three-point bending strength, respectively. The results suggested that MgO-CeO_2 was a much more effective sintering additive for Si_3N_4 than MgO alone. When CeO_2 concentration was 4 wt.%–5 wt.% and sintering temperatures were in a range of 1500 to 1550 oC, the obtained porous silicon nitride ceramics had the porosity of 45.78%–42.81% and flexural strength of 49.44–84.09 MPa. Moreover, when sintering temperature was 1550 oC and CeO_2 concentration was 5%, large elongated β-Si_3N_4 grains were well developed.
