IMPROVEMENT OF ALUMINUM ALLOY-RICE HUSK ASH WETTABILITY WITH SURFACE MODIFICATION OF RICE-HUSK ASH (RHA) BY Si_3N_4 COATING

摘要

Success in the manufacture by the liquid-state route of Al-matrix composites reinforced with rice husk-ash (RHA) strongly depends upon its suitable wetting by the aluminum alloys. Since RHA is scarcely wetted by Al alloys, development of appropriate wetting technologies is paramount. Wettability study using the sessile drop method was conducted to elucidate the effect of Si_3N_4 coating by comparing the wetting behavior by two Al alloys of SiO_2 (RHA) substrates, reagent-grade Si_3N_4 and Si_3N_4 -coated RHA substrates. Results show that at 1200 °C, in nitrogen atmosphere with high Mg content in alloy, the minimal contact angles obtained for Si_3N_4, (RHA) SiO_2 and Si_3N_4 -coated RHA substrates are 30°, 72° and 35°, respectively, revealing the beneficial effect of modifying the surface of RHA with Si_3N_4 coating.