Ca0.6La0.2667TiO3 ceramics were prepared by conventional and microwave sintering techniques and their sinterability, microstructure, and microwave dielectric properties were investigated in detail for comparison. Dens...Ca0.6La0.2667TiO3 ceramics were prepared by conventional and microwave sintering techniques and their sinterability, microstructure, and microwave dielectric properties were investigated in detail for comparison. Densified Ca0.6La0.E667TiO3 ceramics were obtained by microwave sintering at 1350℃ for 30 min and by conventional sintering at 1450℃ for 4 h. An unusual phenomenon was found that some larger grains (grain size range: 8-10 pan) inclined to assemble in one area but some smaller ones (grain size range: 2-4 μm) inclined to gather in another area in the microwave sintered ceramics. The microwave dielectric properties of Ca0.6La0.2667TiO3 ceramics prepared by micro- wave sintering at 1350℃ were as follows" dielectric constant (er) = 119.6, quality factor (Qf) = 17858.5 GHz, and temperature coefficient of resonant fi'equency (rf)= 155.5 ppm/℃. In contrast, the microwave dielectric properties of the ceramics prepared by conventional sintering at 1450℃ were er = 117.4, Qf= 13375 GHz, and rf= 217.2 ppm/℃.展开更多
The microstructure and melting properties of ternary Ag-Cu-In intermediate-temperature alloys (400-600 ℃) prepared by electric arc melting were investigated in this work. The melting properties, phase compositions,...The microstructure and melting properties of ternary Ag-Cu-In intermediate-temperature alloys (400-600 ℃) prepared by electric arc melting were investigated in this work. The melting properties, phase compositions, microstructure and hardness were charac- terized by differential scanning calorimetry (DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM) and micro-hardness tester, respectively. The results show that the melting properties, phase compositions, microstructure and hardness of Ag-Cu-In brazing alloys are substantially different when adding different levels of indium. Indium element could effectively reduce the melting temperatures of (Ag-Cu28)-xIn alloys, and the melting temperatures of (Ag-Cu28)-25In alloy are located at 497.86 and 617.48 ℃. When the indium content varies from 5 wt% and 10 wt%, the dominant phases in the alloys are Ag-rich and Cu-rich phases, and their granular crystals are smaller than 0.5 ktm. When the indium content is higher than 15 wt%, the phase compositions of the alloy are Ag4In and Cu11In9, and the microstructure exhibits dendritic crystals with a uniform distribution. The hardness of (Ag- Cu28)-xIn alloy decreases first and then increases with the content of indium increasing, and the highest hardness of (Ag-Cu28)-25In alloy is HV 266.0.展开更多
A rapid and facile approach was developed for the synthesis of ultrafine SmAlO_(3) powders through the combustion of stearic acid precursors.The obtained products were characterized by typical techniques including X-r...A rapid and facile approach was developed for the synthesis of ultrafine SmAlO_(3) powders through the combustion of stearic acid precursors.The obtained products were characterized by typical techniques including X-ray diffraction(XRD),Fourier Transform Infrared(FT-IR),thermogravimetric and differential thermal analysis(TG-DTA),scanning electron microscopy(SEM),and transmission electron microscopy(TEM)to analyze the phase composition and microstructure.The dielectric characteristics of SmAlO_(3) microwave ceramics,using the as-obtained products as original materials,were also studied.Compared with the conventional solid-state reaction method,the synthesis temperature was dramatically reduced to 750℃.The large-size sheet structure was composed of a number of micro/nano-scale crystallites,which were mostly irregular in shape due to the mutual growth and overlapping shapes of adjacent grains.The SmAlO_(3) ceramics with high density and uniform microstructure were obtained after sintering at 1500℃ for 4 h due to the favorable sintering activity of the as-synthesized powders.In addition,desired dielectric properties at microwave frequencies(dielectric constant ε_(r)=20.22,quality factor Q·f=74110 GHz,and a temperature coefficient of resonant frequency τ_(f)=-74.6 ppm/℃)were achieved.展开更多
High-thermally conductive AlN-based microwave attenuating composite ceramics with spherical graphite(SG) as the attenuating agent were fabricated through hot-pressing sintering. The SG maintains its three-dimensional(...High-thermally conductive AlN-based microwave attenuating composite ceramics with spherical graphite(SG) as the attenuating agent were fabricated through hot-pressing sintering. The SG maintains its three-dimensional(3D) morphology within the sintered bodies, which considerably impedes the sintering of the composites to some extent but slightly influences on the growth of AlN grains. The addition of SG reduces the strength of the composites, but provides a moderate toughening effect at the optimal addition amount(3.8 MPa·m^(1/2) at 4 wt% SG). Benefiting from the low anisotropy, high thermal conductivity, and the 3D morphology of SG, the composites exhibit a relatively higher thermal conductivity(76.82 W·m^(–1)·K^(–1) at 10 wt% SG) compared with composites added with non-spherical attenuating agent. The dielectric constant and loss(8.2–12.4 GHz) increase remarkably as the amount of SG added increases up to 8 wt%, revealing that the incorporation of SG improves the dielectric property of the composite. The composite with 7 wt% SG exhibits the best absorption performance with a minimum reflection loss of –13.9 dB at 12.4 GHz and an effective absorbing bandwidth of 0.87 GHz. The excellent overall properties of the SG/AlN microwave attenuating composites render them as a promising material for various applications. Moreover, SG has a great potential as an attenuating agent for microwave attenuating composites due to its strong attenuation upon integration, high thermal conductivity, and low anisotropy.展开更多
0.5 Ca(0.6La0.267TiO3-0.5 Ca(Mg1/3Nb2/3)O3(5 CLT-5 CMN) ceramics were prepared by a reaction-sintering process and their sintering characteristics, microwave dielectric properties were investigated in detail.With...0.5 Ca(0.6La0.267TiO3-0.5 Ca(Mg1/3Nb2/3)O3(5 CLT-5 CMN) ceramics were prepared by a reaction-sintering process and their sintering characteristics, microwave dielectric properties were investigated in detail.Without any calcination stage involved,a mixture of CaCO_3, La_2 O_3, TiO_2, MgO and Nb_2 O_5 was pressed and sintered directly. Pure phase 5 CLT-5 CMN ceramics with high density and dense microstructure can be obtained after sintered at 1400 ℃ for 4 h. Compared with those prepared by the conventional ceramic route, 5 CLT-5 CMN ceramics produced by the reaction-sintering process exhibit slightly higher dielectric constant and Q×f value. Fine microwave dielectric properties of ε_r= 56.4, Q×f= 48,550 GHz and T_f = +8.7 ppm/℃ for 5 CLT-5 CMN ceramics sintered at 1400 ℃ for 4 h are obtained, suggesting reactionsintering process is a simple and efficient method to produce pure phase 5 CLT-5 CMN ceramics as a potential candidate for the fabrication of microwave devices.展开更多
Novel ZrB_(2)-matrix composites were designed and prepared by in-situ introducing SiC and Zr_(2)[Al(Si)]_(4)C_(5) simultaneously for the first time.The obtained composites were dense and showed good mechanical propert...Novel ZrB_(2)-matrix composites were designed and prepared by in-situ introducing SiC and Zr_(2)[Al(Si)]_(4)C_(5) simultaneously for the first time.The obtained composites were dense and showed good mechanical properties,especially the strength and toughness,706 MPa and 7.33 MPa·m^(1/2),respectively,coupled with high hardness of 21.3 GPa,and stiffness of 452 GPa.SiC and Zr_(2)[Al(Si)]_(4)C_(5) constituted a reinforcing system with synergistic effects including grain refinement,grain pull-out as well as crack branching,bridging,and deflection.Besides,the oxidation results of the composites showed that the oxidation kinetics followed the parabolic law at 1600℃,and the oxidation rate constants increased with the increase of Zr_(2)[Al(Si)]_(4)C_(5) content.The formation and evolution model of the oxidation structure was also investigated,and the oxide scale of the composite exhibited a three-layer structure.展开更多
基金financially supported by A Priority Academic Program Development of Jiangsu Higher Education Institutions
文摘Ca0.6La0.2667TiO3 ceramics were prepared by conventional and microwave sintering techniques and their sinterability, microstructure, and microwave dielectric properties were investigated in detail for comparison. Densified Ca0.6La0.E667TiO3 ceramics were obtained by microwave sintering at 1350℃ for 30 min and by conventional sintering at 1450℃ for 4 h. An unusual phenomenon was found that some larger grains (grain size range: 8-10 pan) inclined to assemble in one area but some smaller ones (grain size range: 2-4 μm) inclined to gather in another area in the microwave sintered ceramics. The microwave dielectric properties of Ca0.6La0.2667TiO3 ceramics prepared by micro- wave sintering at 1350℃ were as follows" dielectric constant (er) = 119.6, quality factor (Qf) = 17858.5 GHz, and temperature coefficient of resonant fi'equency (rf)= 155.5 ppm/℃. In contrast, the microwave dielectric properties of the ceramics prepared by conventional sintering at 1450℃ were er = 117.4, Qf= 13375 GHz, and rf= 217.2 ppm/℃.
基金financially supported by the Open Project of State Key Laboratory Cultivation Base for Nonmetal Composites and Functional Materials(No.11zxfk13)the Scientific Research Fund of Sichuan Provincial Education Department(No.14ZB0103)the China Scholarship Council(CSC)
文摘The microstructure and melting properties of ternary Ag-Cu-In intermediate-temperature alloys (400-600 ℃) prepared by electric arc melting were investigated in this work. The melting properties, phase compositions, microstructure and hardness were charac- terized by differential scanning calorimetry (DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM) and micro-hardness tester, respectively. The results show that the melting properties, phase compositions, microstructure and hardness of Ag-Cu-In brazing alloys are substantially different when adding different levels of indium. Indium element could effectively reduce the melting temperatures of (Ag-Cu28)-xIn alloys, and the melting temperatures of (Ag-Cu28)-25In alloy are located at 497.86 and 617.48 ℃. When the indium content varies from 5 wt% and 10 wt%, the dominant phases in the alloys are Ag-rich and Cu-rich phases, and their granular crystals are smaller than 0.5 ktm. When the indium content is higher than 15 wt%, the phase compositions of the alloy are Ag4In and Cu11In9, and the microstructure exhibits dendritic crystals with a uniform distribution. The hardness of (Ag- Cu28)-xIn alloy decreases first and then increases with the content of indium increasing, and the highest hardness of (Ag-Cu28)-25In alloy is HV 266.0.
基金financially supported by the Natural Science Foundation of Anhui Provincial Education Department(Nos.KJ2019A0054 and KJ2018A0041)the National Natural Science Foundation of China(No.51802003).
文摘A rapid and facile approach was developed for the synthesis of ultrafine SmAlO_(3) powders through the combustion of stearic acid precursors.The obtained products were characterized by typical techniques including X-ray diffraction(XRD),Fourier Transform Infrared(FT-IR),thermogravimetric and differential thermal analysis(TG-DTA),scanning electron microscopy(SEM),and transmission electron microscopy(TEM)to analyze the phase composition and microstructure.The dielectric characteristics of SmAlO_(3) microwave ceramics,using the as-obtained products as original materials,were also studied.Compared with the conventional solid-state reaction method,the synthesis temperature was dramatically reduced to 750℃.The large-size sheet structure was composed of a number of micro/nano-scale crystallites,which were mostly irregular in shape due to the mutual growth and overlapping shapes of adjacent grains.The SmAlO_(3) ceramics with high density and uniform microstructure were obtained after sintering at 1500℃ for 4 h due to the favorable sintering activity of the as-synthesized powders.In addition,desired dielectric properties at microwave frequencies(dielectric constant ε_(r)=20.22,quality factor Q·f=74110 GHz,and a temperature coefficient of resonant frequency τ_(f)=-74.6 ppm/℃)were achieved.
基金financially supported by the Priority Academic Program Development of Jiangsu Higher Education Institutionsthe Postgraduate Research & Practice Innovation Program of Jiangsu Province (KYCX200990)+2 种基金Qing Lan Projectthe Program for Changjiang Scholars, Innovative Research Team in University (IRT1146 and IRT15R35)the Top-notch Academic Programs Project of Jiangsu Higher Education Institutions (TAPP, PPZY2015B128)。
文摘High-thermally conductive AlN-based microwave attenuating composite ceramics with spherical graphite(SG) as the attenuating agent were fabricated through hot-pressing sintering. The SG maintains its three-dimensional(3D) morphology within the sintered bodies, which considerably impedes the sintering of the composites to some extent but slightly influences on the growth of AlN grains. The addition of SG reduces the strength of the composites, but provides a moderate toughening effect at the optimal addition amount(3.8 MPa·m^(1/2) at 4 wt% SG). Benefiting from the low anisotropy, high thermal conductivity, and the 3D morphology of SG, the composites exhibit a relatively higher thermal conductivity(76.82 W·m^(–1)·K^(–1) at 10 wt% SG) compared with composites added with non-spherical attenuating agent. The dielectric constant and loss(8.2–12.4 GHz) increase remarkably as the amount of SG added increases up to 8 wt%, revealing that the incorporation of SG improves the dielectric property of the composite. The composite with 7 wt% SG exhibits the best absorption performance with a minimum reflection loss of –13.9 dB at 12.4 GHz and an effective absorbing bandwidth of 0.87 GHz. The excellent overall properties of the SG/AlN microwave attenuating composites render them as a promising material for various applications. Moreover, SG has a great potential as an attenuating agent for microwave attenuating composites due to its strong attenuation upon integration, high thermal conductivity, and low anisotropy.
基金Project supported by Anhui Provincial Natural Science Foundation(1608085ME92)
文摘0.5 Ca(0.6La0.267TiO3-0.5 Ca(Mg1/3Nb2/3)O3(5 CLT-5 CMN) ceramics were prepared by a reaction-sintering process and their sintering characteristics, microwave dielectric properties were investigated in detail.Without any calcination stage involved,a mixture of CaCO_3, La_2 O_3, TiO_2, MgO and Nb_2 O_5 was pressed and sintered directly. Pure phase 5 CLT-5 CMN ceramics with high density and dense microstructure can be obtained after sintered at 1400 ℃ for 4 h. Compared with those prepared by the conventional ceramic route, 5 CLT-5 CMN ceramics produced by the reaction-sintering process exhibit slightly higher dielectric constant and Q×f value. Fine microwave dielectric properties of ε_r= 56.4, Q×f= 48,550 GHz and T_f = +8.7 ppm/℃ for 5 CLT-5 CMN ceramics sintered at 1400 ℃ for 4 h are obtained, suggesting reactionsintering process is a simple and efficient method to produce pure phase 5 CLT-5 CMN ceramics as a potential candidate for the fabrication of microwave devices.
基金supported by the National Natural Science Foundation of China(No.51902031)the Natural Science Foundation of the Jiangsu Higher Education Institute of China(Nos.18KJB430002 and 18KJB430001)+1 种基金the Six Talent Peaks Project of Jiangsu Province(No.2018-SWYY-001)the Scientific Research Foundation of Changshu Institute of Technology(No.XZ1639).
文摘Novel ZrB_(2)-matrix composites were designed and prepared by in-situ introducing SiC and Zr_(2)[Al(Si)]_(4)C_(5) simultaneously for the first time.The obtained composites were dense and showed good mechanical properties,especially the strength and toughness,706 MPa and 7.33 MPa·m^(1/2),respectively,coupled with high hardness of 21.3 GPa,and stiffness of 452 GPa.SiC and Zr_(2)[Al(Si)]_(4)C_(5) constituted a reinforcing system with synergistic effects including grain refinement,grain pull-out as well as crack branching,bridging,and deflection.Besides,the oxidation results of the composites showed that the oxidation kinetics followed the parabolic law at 1600℃,and the oxidation rate constants increased with the increase of Zr_(2)[Al(Si)]_(4)C_(5) content.The formation and evolution model of the oxidation structure was also investigated,and the oxide scale of the composite exhibited a three-layer structure.