Papers by Author: Uraiwan Leela-adisorn

Abstract: Synthesis method of Zr2Al3C5 via solid state reaction between Al, ZrC and carbon powder was studied. Al-ZrC-C compact with equivalent mol ratio of Zr2Al3C5 was heated up to 1600oC in Ar atmosphere for 1 h and 4 h but ZrC phase still existed as major phase with very small amount of Zr2Al3C5. Because ZrC started to oxidize at low temperature under very low oxygen partial pressure, the same mol ratio of Al-ZrC-C compact was heated at 1600oC in vacuum for 1 h as parallel test. After firing in vacuum, some carbon still exist with small amount of AlZrC2 occurred with Zr2Al3C5 as a main phase, but no ZrC was found. Different result from firing in Ar atmosphere and in vacuum had been discussed here. It was believed that very small amount of impurities in Ar had some effect on the formation of Al-Zr-Ccompound. The effect of very small amount of impurities in Ar was studied by thermal analysis (DTA/TG) and XRD. It was found that very small amount of impurities in Ar haseffect on the reaction between Al, ZrC and carbon by diffusion through the surface and formZr-C-O-N solid solution. This solid solution cannot differentiate from ZrC by XRD. With help ofthermal analysis method (DTA/TG), Zr-C-O-N solid solution can be differentiated from ZrC.Therefore, synthesis of Al-Zr-C compound should be done in vacuum. Zr2Al3C5 can be prepared from mixture of Al-ZrC-C with excess amount of Al at 1600oC for 1 h.

Abstract: Nickel dispersed alumina matrix nanocomposites were fabricated using a novel soaking method. Secondary particles were introduced into the nano-pores of a porous matrix grains by a soaking method, such that γ-alumina powder was soaked in nickel nitrate solution under vacuum. During pre-calcination, nickel oxide particles were created inside of the nano-pores of γ-alumina. The alumina powders were then reduced under hydrogen atmosphere to obtain nano-sized metallic nickel embedded in γ-alumina grains. The alumina-nickel composite powders were sintered by pulse electric current sintering (PECS) technique with α-alumina seeds. The maximum strength of the alumina-nickel nanocomposites was 984 MPa after sintering at 1,450 °C with α-alumina seeds, where the specimen size was 2
2
10 mm3. The maximum fracture toughness was 5.5 MPa·m1/2 after sintering at 1,350 °C with seeds measured by the single edge V-notched beam (SEVNB) method.

Abstract: Intra-type structure of ceramic matrix composites (CMCs) can improve the mechanical properties of ceramic materials. In this work, we used γ-alumina as a matrix including nano-pore for fabricating alumina/silicon carbide composites using pressure-less sintering and pulse electric current sintering (PECS) techniques. We added α-alumina as a seed in order to improve densification of this commercially available γ-alumina. The mixture was sintered from 1250 to 1450
by pressure-less sintering and PECS techniques. Densification of the specimen sintered by pressure-less sintering is very difficult and bulk density of the specimen sintered at 1450
showed lower than 3.0 g/cc. In the case of the PECS technique, the density was improved to 3.8 g/cc in seed added specimen sintered at 1450
. Maximum Vickers hardness and maximum fracture strength were obtained 17 GPa and 500 MPa for the seed added specimens sintered at 1450
, respectively.

Abstract: Zr2Al3C5 has been successfully synthesized via solid state reaction between Al, ZrC and carbon powder at 1600
in vacuum. This complex carbide has very strong bond between metal atoms and carbon atoms. Thus, this material has a potential to be utilized as structural materials. Some properties of Zr2Al3C5 powder from solid-state reaction in vacuum had been tested. It was found that this powder was completely oxidized in air at 900
1 h, and can be hydrated in moist air. These drawbacks might come from the high reactivity of the powder due to synthesis in vacuum. Zr2Al3C5 powder from solid state reaction in vacuum was sintered at various temperatures from 1500
to 2000
under vacuum with pulse electric current sintering (PECS) and pressureless sintering. Zr2Al3C5 started to sinter at 1500
and got partially dense from 1700
. Physical properties and mechanical properties of this material were investigated and discussed.