Hexagonal boron nitride ceramic（h-BN） based on the nitridation of B powders was obtained by reaction sintering method. The effects of sintering temperature on the mechanical properties and microstructure of the resu...Hexagonal boron nitride ceramic（h-BN） based on the nitridation of B powders was obtained by reaction sintering method. The effects of sintering temperature on the mechanical properties and microstructure of the resultant products were investigated and the reaction mechanism was discussed. Results showed that the reaction between B and N2 occurred vigorously at temperatures ranging from 1 000 ℃ to 1 300 ℃, which resulted in the generation of t-BN. When the temperature exceeded 1 450 ℃, transformation from t-BN to h-BN began to occur. As the sintering temperature increased, the spherical particles of t-BN gradually transformed into fine sheet particles of h-BN. These particles subsequently displayed a compact arrangement to achieve a more uniform microstructure, thereby increasing the strength.展开更多
The influence of active elements C and Hf on the interface reactions and wettability between a Ni3Albased superalloy and the ceramic mould material was studied by using a sessile drop experiment, The microstructure of...The influence of active elements C and Hf on the interface reactions and wettability between a Ni3Albased superalloy and the ceramic mould material was studied by using a sessile drop experiment, The microstructure of the alloy interface was investigated by scanning electron microscopy analysis and the phase identification was performed by X-ray diffraction analysis, The results show that interface reactions occur as C and Hf contents reach a critical value, The critical values for C and Hf to cause interface reactions are 0,12 wt% and 1,17 wt%, respectively, The reaction products contain HfO2 and 9Al2OH,Cr2O3, Adsorptions of Hf and interface reactions improve the wettability obviously,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
基金Funded by the Scientific and Technological Development Project of Yantai(2013JH020)
文摘Hexagonal boron nitride ceramic（h-BN） based on the nitridation of B powders was obtained by reaction sintering method. The effects of sintering temperature on the mechanical properties and microstructure of the resultant products were investigated and the reaction mechanism was discussed. Results showed that the reaction between B and N2 occurred vigorously at temperatures ranging from 1 000 ℃ to 1 300 ℃, which resulted in the generation of t-BN. When the temperature exceeded 1 450 ℃, transformation from t-BN to h-BN began to occur. As the sintering temperature increased, the spherical particles of t-BN gradually transformed into fine sheet particles of h-BN. These particles subsequently displayed a compact arrangement to achieve a more uniform microstructure, thereby increasing the strength.
基金financial support from the National Natural Science Foundation of China (Grant Nos. U1037601 and 51271186)
文摘The influence of active elements C and Hf on the interface reactions and wettability between a Ni3Albased superalloy and the ceramic mould material was studied by using a sessile drop experiment, The microstructure of the alloy interface was investigated by scanning electron microscopy analysis and the phase identification was performed by X-ray diffraction analysis, The results show that interface reactions occur as C and Hf contents reach a critical value, The critical values for C and Hf to cause interface reactions are 0,12 wt% and 1,17 wt%, respectively, The reaction products contain HfO2 and 9Al2OH,Cr2O3, Adsorptions of Hf and interface reactions improve the wettability obviously,
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.
