Varistor ceramics of ZnO Bi 2O 3 TiO 2 Sb 2O 3 system have been fabricated by introducing pre fabricated ZnO seed grains with different size distributions respectively. The results show that the varistor properties we...Varistor ceramics of ZnO Bi 2O 3 TiO 2 Sb 2O 3 system have been fabricated by introducing pre fabricated ZnO seed grains with different size distributions respectively. The results show that the varistor properties were significantly influenced by the size of introduced seed grains, and introducing larger seed grains is more advantageous to the modification of microstructure and the improvement of varistor properties. The varistor properties were considerably improved with a moderately increased sintering temperature or time, whereas degraded apparently when the sintering temperature or time was excessively increased. Compared with the sintering time, the sintering temperature plays a more critical role in determining the varistor properties. By introducing pre fabricated ZnO seed grains into the original powders, low voltage ZnO varistor ceramics possessing the desired electrical properties have been produced with a sintering temperature of about 1 210 ℃ and a sintering temperature of 2～2.5 h. [展开更多
The structures of the Mn-Zn ferrites synthesized under different sintering conditions by the sol-gel method were investigated by the X-ray diffraction （XRD） and the scanning electron microscopy （SEM） with focus on...The structures of the Mn-Zn ferrites synthesized under different sintering conditions by the sol-gel method were investigated by the X-ray diffraction （XRD） and the scanning electron microscopy （SEM） with focus on two factors： the pre-sintering treatment and the calcining time. The results show that the sintering conditions have significant effects on the structures and the particle size of the Mn-Zn ferrites. Compared with the products without pre-sintering, those pre-sintered at 500℃ have a single phase and no diffraction peaks of Fe2O3 that could be found. The effects of the pre-sintering temperature on the structures of the ferrites were also studied. As a result, 500℃ proves to be the favorite in the pre-sintering treatment. The XRD patterns of the ferrites calcined at 1 200℃ for 6 h will present diffraction peaks of pure crystallization of spinel phase while those for 2 h or 4 h will show peaks of Fe2O3. The SEM also bears witness to well-grown grains of pure Mn-Zn ferrites if calcined for 6 hours.展开更多
W–Cu refractory alloys are widely used in aerospace,aviation,electronics,power,and other fi elds.However,because of its large melting point diff erence between alloy elements,the conventional powder metallurgy method...W–Cu refractory alloys are widely used in aerospace,aviation,electronics,power,and other fi elds.However,because of its large melting point diff erence between alloy elements,the conventional powder metallurgy method required a long time of high temperature sintering is very likely to cause low density and abnormal grain size growth.Therefore,90W-10Cu refractory alloys were successfully prepared by hot oscillatory pressing(HOP)under diff erent sintering time in this work.Then the infl uence of sintering time on the microstructure,grain size,density,Vickers hardness,room-tensile property,and electrical conductivity of the W–Cu refractory alloy was systematically invested.The results showed that during the short sintering time(30–90 min),the density,Vickers hardness,tensile strength,and electrical conductivity of the W–Cu refractory alloy increased signifi cantly to 98.7%,163.29 HV 30,507.3 MPa,and 14.2%International Annealed Copper Standard with the sintering time increasing,respectively,while its grain size showed no obvious change.When the sintering time further increased to 120 min,the density was basically consistent with the sintering time of 90 min.Nevertheless,the prolonged high temperature sintering resulted in the grain growth of the samples,which caused the deterioration of the Vickers hardness,room-tensile strength,and conductivity properties of the W–Cu refractory alloy.At the same sintering time,the density,Vickers hardness,and electrical conductivity of the HOP sintered W–Cu refractory alloy were signifi cantly higher than those of the HP sintered sample.It was indicated that high density,fi ne-grain,and excellent properties W–Cu refractory alloys could be prepared by hot oscillatory pressing under appropriate sintering time.展开更多
文摘Varistor ceramics of ZnO Bi 2O 3 TiO 2 Sb 2O 3 system have been fabricated by introducing pre fabricated ZnO seed grains with different size distributions respectively. The results show that the varistor properties were significantly influenced by the size of introduced seed grains, and introducing larger seed grains is more advantageous to the modification of microstructure and the improvement of varistor properties. The varistor properties were considerably improved with a moderately increased sintering temperature or time, whereas degraded apparently when the sintering temperature or time was excessively increased. Compared with the sintering time, the sintering temperature plays a more critical role in determining the varistor properties. By introducing pre fabricated ZnO seed grains into the original powders, low voltage ZnO varistor ceramics possessing the desired electrical properties have been produced with a sintering temperature of about 1 210 ℃ and a sintering temperature of 2～2.5 h. [
文摘The structures of the Mn-Zn ferrites synthesized under different sintering conditions by the sol-gel method were investigated by the X-ray diffraction （XRD） and the scanning electron microscopy （SEM） with focus on two factors： the pre-sintering treatment and the calcining time. The results show that the sintering conditions have significant effects on the structures and the particle size of the Mn-Zn ferrites. Compared with the products without pre-sintering, those pre-sintered at 500℃ have a single phase and no diffraction peaks of Fe2O3 that could be found. The effects of the pre-sintering temperature on the structures of the ferrites were also studied. As a result, 500℃ proves to be the favorite in the pre-sintering treatment. The XRD patterns of the ferrites calcined at 1 200℃ for 6 h will present diffraction peaks of pure crystallization of spinel phase while those for 2 h or 4 h will show peaks of Fe2O3. The SEM also bears witness to well-grown grains of pure Mn-Zn ferrites if calcined for 6 hours.
基金supported by National Natural Science Foundation of China(51904277)the Open Fund of Sichuan Province Engineering Technology Research Center of Powder Metallurgy,Chengdu University(SC-FMYJ2023-02)+4 种基金Opening Foundation of Key Laboratory of Advanced Manufacture Technology for Automobile Parts,Ministry of Education(2022 KLMT05)the Open Fund of Hubei Key Laboratory of Mechanical Transmission and Manufacturing Engineering at Wuhan University of Science and Technology(MTMEOF2022B02)Fund of Key Laboratory of Advanced Materials of Ministry of Education(ADV22-20)Training Program for Young Backbone Teachers in Colleges and University of Henan Province(2020GGJS171)Fund of Zhengzhou University of Aeronautics Graduate Education Innovation Program of China(2022CX57).
文摘W–Cu refractory alloys are widely used in aerospace,aviation,electronics,power,and other fi elds.However,because of its large melting point diff erence between alloy elements,the conventional powder metallurgy method required a long time of high temperature sintering is very likely to cause low density and abnormal grain size growth.Therefore,90W-10Cu refractory alloys were successfully prepared by hot oscillatory pressing(HOP)under diff erent sintering time in this work.Then the infl uence of sintering time on the microstructure,grain size,density,Vickers hardness,room-tensile property,and electrical conductivity of the W–Cu refractory alloy was systematically invested.The results showed that during the short sintering time(30–90 min),the density,Vickers hardness,tensile strength,and electrical conductivity of the W–Cu refractory alloy increased signifi cantly to 98.7%,163.29 HV 30,507.3 MPa,and 14.2%International Annealed Copper Standard with the sintering time increasing,respectively,while its grain size showed no obvious change.When the sintering time further increased to 120 min,the density was basically consistent with the sintering time of 90 min.Nevertheless,the prolonged high temperature sintering resulted in the grain growth of the samples,which caused the deterioration of the Vickers hardness,room-tensile strength,and conductivity properties of the W–Cu refractory alloy.At the same sintering time,the density,Vickers hardness,and electrical conductivity of the HOP sintered W–Cu refractory alloy were signifi cantly higher than those of the HP sintered sample.It was indicated that high density,fi ne-grain,and excellent properties W–Cu refractory alloys could be prepared by hot oscillatory pressing under appropriate sintering time.
