Channel: Research Letter http://www.jim.org.cn EN-US http://www.jim.org.cn/EN/1000-324X/current.shtml http://www.jim.org.cn 1000-324X http://www.jim.org.cn/EN/10.15541/jim20200265 High strength SiC porous ceramic with reticular pore structure is assembled by cross-lamination of layers comprised by aligned SiC nanowire (SiCNWs) struts printed through direct ink writing. SiCNWs networks exhibit a structure with highly interconnected porosity and an architecture formed by aligned SiCNWs struts. The effects of sintering temperature on the structures, phase evolutions and mechanical properties were studied. The high aspect ratio of SiCNWs was kept well at sintering temperature lower than 1900 鈩�. The bulk density, porosity and median pore diameter of aligned SiCNWs porous ceramics sintered at 1850 鈩� were 1.49 g/cm³, 54.6% and ~1 渭m, respectively. Due to the effect of orientation and high strength of SiC nanowire struts, compressive strength of (245.5卤0.7) MPa is achieved.

]]> http://www.jim.org.cn/EN/10.15541/jim20200211 Si₃N₄ ceramics with improved and tailorable dielectric constant are desirable for microwave dielectric substrate application in harsh environment. Effect of BaTiO₃ addition on the mechanical and dielectric properties of the hot-pressed Si₃N₄ ceramics with Al₂O₃ and Nd₂O₃ as sintering additives were investigated. Relative density, flexural strength and Vickers鈥� hardness of Si₃N₄ ceramics all decreased, while indentation fracture toughness increased monotonically with the increase of BaTiO₃ content. Flexural strength of Si₃N₄ ceramics was higher than 600 MPa and dielectric constant of Si₃N₄ ceramics increased to 9.26-11.50 when 5wt%-20wt% of BaTiO₃ was added. The dielectric loss was at the level of 10^-3. The improvement of dielectric constant was attributed to the formation of TiN during hot pressing, as crystalline BaTiO₃ was not detected in the sintered samples. These findings can make a significant contribution to the new applications of Si₃N₄ ceramics.

]]> http://www.jim.org.cn/EN/10.15541/jim20200395 The present study focuses on the construction of HA nanoceramics with excellent mechanical property and osteogenic activity, and the correlation between HA precursor powders and resulting ceramics. Three precursor powders were used, i.e. HA-40 synthesized at 40 鈩�, HA-40PEG synthesized at 40 鈩� with PEG as a template, and HA-80 synthesized at 80 鈩�. The results showed that grain sizes of three HA ceramics prepared by HA-40, HA-40PEG, and HA-80 precursors were (217.87卤57.53), (123.22卤20.16), and (316.65卤68.91) nm, respectively. It demonstrated that compared with HA-40 and HA-80, HA-40PEG was more beneficial for fabricating HA nanoceramics. Among three resulting ceramics, HA-40PEG displayed the highest comprehensive strength (~300 MPa). In addition, the nano-scale HA-40PEG ceramics promoted better cell spreading and proliferation than those of submicro-scale HA-40 and HA-80 ceramics. These findings suggest that the preparation of HA precursor powders plays an important role in fabricating HA nanoceramics with simultaneous improvement of mechanical and biological properties.

]]> http://www.jim.org.cn/EN/10.15541/jim20200286 Zircaloy coating is one of the crucial technical ways to improve the accident tolerance of nuclear fuel cladding, which enables the zirconium-water reaction problems to be solved. Zr₂Al₃C₄ coating is one type of candidate solutions to improve the high-temperature oxidation resistance of zirconium claddings. However, little study has been performed on the synthesis of Zr₂Al₃C₄ coatings on zirconium alloy substrates due to the inter-diffusion, as well as the difference of the thermal expansion coefficients between the Zr₂Al₃C₄ coating and the substrates. In this study, Zr₂Al₃C₄ coatings were prepared through room-temperature magnetron sputtering and post annealing on zirconium alloy (ZIRLO) substrates with magnetron-sputtered Al/Mo-C interlayers. The effects of Al/Mo-C interlayers on phases and microstructures of Zr-Al-C coatings after annealing were studied by different methods. It is found that the coatings without interlayer are broken and no Zr₂Al₃C₄ phase is formed due to significant interdiffusion between the Zr-Al-C coating and the substrate during annealing at 800 鈩� for 3 h. The Al/Mo-C interlayers prevented elemental diffusion between Zr-Al-C coatings and substrates during the post-annealing process. The Al/Mo-C interlayers act as diffusion barriers and greatly reduce the stoichiometric deviations from Zr₂Al₃C₄ phase, which facilitates the formation of the Zr₂Al₃C₄ phase in the final coating. Moreover, this diffusion-barrier layers contribute to eliminating cracks induced by the difference of the thermal expansion coefficients between the Zr₂Al₃C₄ coatings and substrates. At the same time, the adhesions between Zr-Al-C coatings with Al/Mo-C interlayers and substrates were improved after annealing, with their strength exceeding 30 N.

]]>