Ti–Zr coating on graphite through powder immersion reaction-assisted coating (PIRAC) and its oxidation kinetics at $T = 1000^{\circ}$C

[摘要] Coating of graphite with a metal alloy Ti–Zr was carried out on a block of graphite sample; the sample was initially dipped in ZrO$_2$ containing a natural starch solution and then proceeded to powder immersion reaction-assisted coating (PIRAC) after drying. Ti powder containing 4 wt% iodine was used as depositing material, and the process was carried out at 850−950$^{\circ}$C for 10 h. The characterizations include X-ray diffraction, scanning electron microscopy and the hardness test. The coating thickness is proportional to the temperature of the PIRAC process, while the percentage of Zr is inversely proportional to the temperature of PIRAC treatment. All the characterizations revealed that the coated layer was a Ti–Zr alloy with hexagonal crystalline symmetry similar to $\alpha$-Ti. An oxidation kinetic assessment at 1000$^{\circ}$C of uncoated graphite shows a burns-off mechanism, while for a coated sample reveals a reaction of Ti with oxygen produces TiO$_2$; the reaction kinetics obey a diffusional mechanism.

[学科分类] 材料工程

[关键词] Coating;graphite;Ti–Zr alloy;oxidation;diffusional mechanism.