The CaO doped 10NiO-NiFe2O4 composite ceramics were prepared by the cold isostatic pressing-sintering process, and the effects of CaO content on the phase composition, mechanical property and thermal shock resistance ...The CaO doped 10NiO-NiFe2O4 composite ceramics were prepared by the cold isostatic pressing-sintering process, and the effects of CaO content on the phase composition, mechanical property and thermal shock resistance of 10NiO-NiFe2O4 composite ceramics were studied. The results show that the samples mainly consist of NiO and NiFe2O4 when content of CaO is less than 4%(mass fraction), bending strength increases obviously by CaO doping. Bending strength of the samples doped with 2% CaO is above 185 MPa, but that of the samples without CaO is only 60 MPa. Fracture toughness is improved obviously by CaO doping, the samples doped with 2% CaO have the maximum fracture toughness of 2.12 MPa ·m1/2 , which is about two times of that of the undoped ceramics. CaO doping is bad to thermal shock resistance of 10NiO-NiFe2O4 composite ceramics.展开更多
Ni/ （10NiO-NiFe2O4） cermets were fabricated by using cold pressing-sintering method. The phase composition and effect of metallic content on the mechanical properties such as bending strength, Vickers’ hardness, fr...Ni/ （10NiO-NiFe2O4） cermets were fabricated by using cold pressing-sintering method. The phase composition and effect of metallic content on the mechanical properties such as bending strength, Vickers’ hardness, fracture toughness and thermal shock resistance were studied. The results show that the cermets consist of Ni, NiO and NiFe2O4. Within the range of metallic content from 0 to 17%（mass fraction）, the relative density decreases with the increase of metallic content and the decrease of sintering temperature, Vickers’ hardness decreases from 7097MPa to 4814MPa and the bending strength increases from 110MPa to 157MPa, and the fracture toughness reaches the optimal value of 5.11MPa·m 1/2 at the metallic content of about 10%. The residual strength after thermal shock testing falls sharply as the thermal shock temperature difference is above 200℃.The cermets samples, whose metallic content is 10% and 15%, respectively, exhibit promising property of thermal shock resistance at 960℃ with six cycles of heating and quenching testing.展开更多
An electrostatic model for the shock observed in the earth's polar region is established by deriving the 'Sagdeev potential' from the magnetohydrodynamic equations in a cylindrical coordinate system. The r...An electrostatic model for the shock observed in the earth's polar region is established by deriving the 'Sagdeev potential' from the magnetohydrodynamic equations in a cylindrical coordinate system. The results show that the shock can develop from the ion acoustic wave or ion cyclotron wave in the polar region, and can exist when the Mach number M and the initial electric field E-0 satisfy the condition of vertical bar(a/M-2-1)E(0)vertical bar = 1. Also, some features of the shock wave are discussed. The result can interpret the electrostatic shock observed in the earth's polar region.展开更多
基金Project(2005CB623703) supported by the National Basic Research Program of China
文摘The CaO doped 10NiO-NiFe2O4 composite ceramics were prepared by the cold isostatic pressing-sintering process, and the effects of CaO content on the phase composition, mechanical property and thermal shock resistance of 10NiO-NiFe2O4 composite ceramics were studied. The results show that the samples mainly consist of NiO and NiFe2O4 when content of CaO is less than 4%(mass fraction), bending strength increases obviously by CaO doping. Bending strength of the samples doped with 2% CaO is above 185 MPa, but that of the samples without CaO is only 60 MPa. Fracture toughness is improved obviously by CaO doping, the samples doped with 2% CaO have the maximum fracture toughness of 2.12 MPa ·m1/2 , which is about two times of that of the undoped ceramics. CaO doping is bad to thermal shock resistance of 10NiO-NiFe2O4 composite ceramics.
基金Project(2005CB623703) supported by the National Key Fundamental Research and Development Programof China pro-ject (50474051) supported by the National Natural Science Foundation of China project (03JJY3080) supported by the Hunan ProvincialNatural Science Foundation
文摘Ni/ （10NiO-NiFe2O4） cermets were fabricated by using cold pressing-sintering method. The phase composition and effect of metallic content on the mechanical properties such as bending strength, Vickers’ hardness, fracture toughness and thermal shock resistance were studied. The results show that the cermets consist of Ni, NiO and NiFe2O4. Within the range of metallic content from 0 to 17%（mass fraction）, the relative density decreases with the increase of metallic content and the decrease of sintering temperature, Vickers’ hardness decreases from 7097MPa to 4814MPa and the bending strength increases from 110MPa to 157MPa, and the fracture toughness reaches the optimal value of 5.11MPa·m 1/2 at the metallic content of about 10%. The residual strength after thermal shock testing falls sharply as the thermal shock temperature difference is above 200℃.The cermets samples, whose metallic content is 10% and 15%, respectively, exhibit promising property of thermal shock resistance at 960℃ with six cycles of heating and quenching testing.
文摘An electrostatic model for the shock observed in the earth's polar region is established by deriving the 'Sagdeev potential' from the magnetohydrodynamic equations in a cylindrical coordinate system. The results show that the shock can develop from the ion acoustic wave or ion cyclotron wave in the polar region, and can exist when the Mach number M and the initial electric field E-0 satisfy the condition of vertical bar(a/M-2-1)E(0)vertical bar = 1. Also, some features of the shock wave are discussed. The result can interpret the electrostatic shock observed in the earth's polar region.
