Numerical simulation and experimental verification of axial-directional crystallization purification process for high-purity gallium

A transient numerical model was applied to simulating the axial-directional crystallization purification(ADCP) process of gallium(Ga) raw material at different coolant temperatures(Tc), and the evolutions of melt/crystal(m/c) interface shape, temperature distribution and thermal stresses were simulated and analyzed. The results showed that the m/c interface shape, temperature distribution, and thermal stress in the Ga material were determined by the Tc in the crystallizer during the ADCP process. The temperature gradient and thermal stress in the grown Ga crystal increased with decreasing Tc. At Tc=15 ℃, the m/c interface shape was flat, and the temperature gradient was ideal. Therefore, the Ga materials with lower thermal stresses and suitable m/c interface shape, and an ideal efficiency of impurity removal were obtained. The purity of Ga reached 6 N standard by using ADCP process repeated 6 times at Tc of 15 ℃. The results of the simulation showed good agreement with the experimental results.

Fabrication, microstructure, friction and wear properties of SiC3D/Al brake disc-graphite/Si C pad tribo-couple for high-speed train

The friction and wear properties of interpenetrating phase composites(IPC) SiC3D/Al sliding against graphite/SiC(G/SiC) composites were investigated using a sub-scale brake dynamometer. The testing conditions included a braking pressure of 1.25 MPa and an initial braking speed(IBS) of 200-350 km/h in a braking process of high-speed train according to the scale-conversion rules. The tribo-couple materials were characterized using scanning electron microscopy(SEM), X-ray diffractometry(XRD), and energy-dispersive X-ray spectrometry(EDS). It is found that the matching tribo-couple features low friction surface temperature, reliable friction factor, and high durability. The continuous lubricating mechanically-mixed layer(MML) forms gradually on the worn surfaces of ring in the friction process. The MML is heterogeneous, which greatly controls wear rate and coefficient of friction(COF) of the composites. The wear mechanism of SiC3D/Al is typically abrasive wear at an IBS of 200-300 km/h. When the IBS increases to 350 km/h, oxidation wear and delamination are observed. The friction behavior of the tribo-couple predicted using Solidwork simulation software agrees well with the experimental results. The tribo-couple meets the requirement of emergency braking of high-speed train.