Molybdenum disilicide （MoSi2） sheath and aluminum oxide （Al2O3） core blended powders were fabricated by spray drying. A derived coating material was produced for the application as microwave absorbers using the as...Molybdenum disilicide （MoSi2） sheath and aluminum oxide （Al2O3） core blended powders were fabricated by spray drying. A derived coating material was produced for the application as microwave absorbers using the as prepared powders by atmospheric plasma spray （APS） technology. The effects of MoSi2/Al2O3 mass ratio on the dielectric and physical mechanical properties of the composite coatings were investigated. When the MoSi2 content of the composites increases from 0 to 45%, the flexure strength and fracture toughness improve from 198 to 324 MPa and 3.05 to 4.82 MPa-m1/2 then decline to 310 MPa and 4.67 MPa-m1/2, respectively. The dielectric loss tangent increases with increasing MoSi2 content, and the real part of permittivity decreases conversely over the frequency range of 8.2-12.4 GHz. These effects are due to the agglomeration of early molten MoSi2 particles and the increase of the electrical conductivity with increasing MoSi2 content.展开更多
In order to clarify the Na/K ratios dependence of piezoelectric properties,(K_(1-x)Na_(x))TNbO_(3)cer-amics were prepared by conventional solid-state sintering at a=0.4-0.6 with a smaller com-positional interval(0.02 ...In order to clarify the Na/K ratios dependence of piezoelectric properties,(K_(1-x)Na_(x))TNbO_(3)cer-amics were prepared by conventional solid-state sintering at a=0.4-0.6 with a smaller com-positional interval(0.02 mol).The results demonstrate that the Na/K ratios have obvious effecton piezoelectric and ferroelectric properties of(K_(1-x)Na_(x))NbO_(3)ceramics.Piezoelectric and fer-roelectric properties show the maximum(d_(33)147 pc/N,k_(p)=0.40,and P_(r)=24μC/cm^(2))at=0.54,which is not consistent with conventional viewpoint.The reasons should be attributedto the existence of a phase boundary at a=0.54 mol,which is similar to the morphotropic phaseboundary in Pb(Zr,Ti)O_(3)ceramics.展开更多
In this paper,the SiC fiber-reinforced SiC matrix composites with a 0.15μm thick pyrocarbon interphase(noted as SiC/PyC/SiC) were prepared by chemical vapor infiltration(CVI).The SiCf/PyC/SiC were oxidized in air at9...In this paper,the SiC fiber-reinforced SiC matrix composites with a 0.15μm thick pyrocarbon interphase(noted as SiC/PyC/SiC) were prepared by chemical vapor infiltration(CVI).The SiCf/PyC/SiC were oxidized in air at950 "C for 50 h.The dielectric properties after this high temperature oxidation were investigated in X-band from room temperature(RT) to 700℃.Results suggested that:ε′ of the SiC_f/PyC/SiC after oxidation increased at first then decreased with temperature elevating;ε″ increased with temperature raising in the temperature range studied.展开更多
基金Project (50572090) supported by the National Natural Science Foundation of ChinaProject (KP200901) supported by the States Key Laboratory of Solidification Processing in NWPU, China
文摘Molybdenum disilicide （MoSi2） sheath and aluminum oxide （Al2O3） core blended powders were fabricated by spray drying. A derived coating material was produced for the application as microwave absorbers using the as prepared powders by atmospheric plasma spray （APS） technology. The effects of MoSi2/Al2O3 mass ratio on the dielectric and physical mechanical properties of the composite coatings were investigated. When the MoSi2 content of the composites increases from 0 to 45%, the flexure strength and fracture toughness improve from 198 to 324 MPa and 3.05 to 4.82 MPa-m1/2 then decline to 310 MPa and 4.67 MPa-m1/2, respectively. The dielectric loss tangent increases with increasing MoSi2 content, and the real part of permittivity decreases conversely over the frequency range of 8.2-12.4 GHz. These effects are due to the agglomeration of early molten MoSi2 particles and the increase of the electrical conductivity with increasing MoSi2 content.
基金supported by National Natural Science Foundation(No.10804130,No.50872107 and No.60871027)Shaanxi Provincial Natural Science Foundation(No.2009JQ1001)State Key Laboratory of Electrical Insulation and Power Equipment(EIPE10202).
文摘In order to clarify the Na/K ratios dependence of piezoelectric properties,(K_(1-x)Na_(x))TNbO_(3)cer-amics were prepared by conventional solid-state sintering at a=0.4-0.6 with a smaller com-positional interval(0.02 mol).The results demonstrate that the Na/K ratios have obvious effecton piezoelectric and ferroelectric properties of(K_(1-x)Na_(x))NbO_(3)ceramics.Piezoelectric and fer-roelectric properties show the maximum(d_(33)147 pc/N,k_(p)=0.40,and P_(r)=24μC/cm^(2))at=0.54,which is not consistent with conventional viewpoint.The reasons should be attributedto the existence of a phase boundary at a=0.54 mol,which is similar to the morphotropic phaseboundary in Pb(Zr,Ti)O_(3)ceramics.
基金supported by the National Natural Science Foundation under Grant(51072165)the fund of the State Key Laboratory of Solidification Processing in Northwestern Polytechnical University(NPU)(KP201307 and SKLSP201313)
文摘In this paper,the SiC fiber-reinforced SiC matrix composites with a 0.15μm thick pyrocarbon interphase(noted as SiC/PyC/SiC) were prepared by chemical vapor infiltration(CVI).The SiCf/PyC/SiC were oxidized in air at950 "C for 50 h.The dielectric properties after this high temperature oxidation were investigated in X-band from room temperature(RT) to 700℃.Results suggested that:ε′ of the SiC_f/PyC/SiC after oxidation increased at first then decreased with temperature elevating;ε″ increased with temperature raising in the temperature range studied.
