Jiaochun Zheng,Mao Deng,Yang Shi,Zhangyi Huang,Haomin Wang
The cold sintering process, a novel technique for low-temperature ceramic processing , effectively removes interparticle pores via dissolution and re-precipitation. However, it often triggers grain growth, especially in nanocrystalline ceramics. To address this issue, the present study proposed an innovative two-step cold sintering process with an initial step at 1.5 GPa/RT (room temperature) for 10 min, followed by a subsequent step at 300 MPa/250 °C for 45 min. This method yields ZnO nanocrystalline ceramics with 97.5 % relative density and a 39 nm average grain size (from 30 nm powder). The initial high-pressure step significantly enhances the pressure gradient and particle solubility, leading to very high supersaturation and the occurrence of homogenous nucleation during pressure release. Subsequently, the formation of the crystal nuclei in the interparticle voids can dramatically improve the density of the compact by the additional pore filling and avoid recrystallization-induced grain growth during the second-step cold sintering process.
Ming Xiang,Youfu Zhou,Wentao Xu,Decai Huang,Kun Wang,Wei Pan
Aluminum nitride (AlN) nanopowders have been synthesized by a novel method which combines the hydrothermal and carbothermal techniques. The phase of the nitridation products can be controlled through adjusting the carbon content of precursor by adding different amount of urea (U). The nitridation product synthesized from the precursor (U/Al=2) was comprised of spherical and well-distributed particles with sizes ranging from 50 to 100 nm. The nitridation procedure was investigated in detail with TG/DSC, XRD, and TEM measurements. It was found that the core-matrix structured Al 2 O 3 /C mixture presents after pyrolysis, favoring the nitridation completed at low temperature, and brings in temperature independency for AlN grain size. Finally, the additive-free AlN ceramic with 99.08% relative density has been achieved by pressureless sintering at 1850°C.
Yuxin Lin,Xuyang Shang,Keke Hou,Changqing Cao,Hongtao Zeng,Leijie Zhao,Yanhui Wang,Jun Lin
Yttrium hydride (YH x ) has recently attracted considerable attention as a highly promising candidate for the development of compact reactors. This is primarily attributed to its exceptional thermal stability and superior hydrogen storage capacity, which are particularly advantageous under high-temperature conditions. YH x samples were fabricated by spark plasma sintering (SPS) with systematically varied process parameters. Results reveal that the microstructure of sintered YH x exhibits significant variations under different sintering processes. SPS process promotes the densification of sintered YH x monoliths, and the co-evolution of microstructure and grain growth behavior optimizes phonon transport pathways, thereby enhancing the thermal conductivity. The thermal conductivity of sintered YH x decreases with increasing temperature. Optimized under the conditions of 1000°C/65 MPa/5 min, the sintered YH x achieved a relative density of 99.14% and hydrogen content of 1.91 wt.%, exhibiting a maximum thermal conductivity of 67.8 W/(m K) at 300 K. This study conducted an in-depth analysis of the mechanisms influencing thermal conductivity variations and established more comprehensive sintering process-microstructure-thermal conductivity relationships for YH x .
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