Rice hull ash structure and bleaching performance produced by ashing at various times and temperatures

Surface areas, pore sizes, and bleaching efficiencies of rice hull ashes pr oduced under different time and temperature conditions were examined. Speci fic surface area and average pore diameter were measured by a surface area meter. Bleaching efficiencies were calculated based on the Lovibond color i ndices of sesame oil before and after bleaching by rice hull ash, Experimen tal results indicated that specific surface area and pore size increased wi th increase in ashing temperature, reached a maximum, and then decreased. S pecific surface area decreased while pore size enlarged with the increase i n ashing time. Both surface area and pore size were observed to reach a pla teau after 30 min. Bleaching efficiency increased with increasing ashing te mperature, reached a maximum, and then decreased with further increase in a shing temperature. it also in creased with ashing time and then reached a p lateau. Bleaching efficiency remained unaffected by specific surface area w hen the pore diameter was less than 50 Angstrom but varied with specific su rface area when the pore diameter was larger than 50 Angstrom.