Xuyang Shang,Yuxin Lin,Keke Hou,Yajuan Zhong,Changqing Cao,Yanhui Wang,Hongtao Zeng,Jun Lin
Yttrium hydride (YH x ) is a highly promising neutron moderator material for nuclear reactors, known for its exceptional thermal stability and high hydrogen content. This study investigated the sintering mechanism and microstructural evolution of YH x monoliths processed by spark plasma sintering (SPS), with the effects of temperature, duration, and pressure. The results indicate that the sintering process can be divided into five stages: formation of sintering necks, rapid densification, anti-densification, recrystallization, and grain growth. The anti-densification behavior is attributed to hydrogen desorption, phase transformation-induced volumetric contraction, and vacancy coalescence from hydrogen migration, leaving residual pores and lattice defects. Furthermore, increasing the sintering temperature and duration promotes recrystallization and grain growth, whereas elevated pressure effectively suppresses grain boundary migration. This research establishes fundamental processing-structure correlations critical for optimizing YH x moderators in nuclear applications.
Keke Hou,Shiqi Sun,Xuyang Shang,Changqing Cao,Yajuan Zhong,Jun Lin
In recent years, yttrium hydride has garnered significant attention due to its remarkable thermal stability and potential for high hydrogen density. It is regarded as one of the most promising metal hydrides for use as a neutron moderator in microreactors . In this study, yttrium hydride monoliths were synthesized using yttrium hydride powder obtained through direct hydrogenation, facilitated by Spark Plasma Sintering (SPS) at temperatures ranging from 800 to 1200 ℃. The effects of SPS temperatures on the phase composition, microstructure, density, and mechanical properties of yttrium hydride monoliths were studied. The results show that the sintering temperature markedly impacts the hardness, pore evolution, grain size and precipitation of α-Y and Y 2 O 3 phase. Notably, the hardness of the samples escalates significantly with an increase in sintering temperature below 1000 ℃, influenced by a reduction in both the number and size of pores. The occurrence of twin crystals, distribution of grain size and the phase-transformed particles of α-Y within the sintered sample may contribute to an increase in hardness. The procedures described herein affect developing important microstructure-property relationships, as well as correlations in the sintering parameters and mechanical properties.
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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