The changes in physical characteristics of rice husk during high speed pyrolysis were examined.The pyrolysis reaction ratios (defined as the ratio of pyrolyzed mass to pyrolyzable mass) of rice husk particles prepared under different conditions were calculated by non-isothermal thermogravimetric analysis.To study the physical characteristics of rice husk/char particles

proximate and ultimate analyses

physical adsorption/desorption measurements of N2(-196℃)

mercury injection porosimetry (414 MPa) as well as visualization by scanning electronic microscopy(SEM) were performed.Appreciable differences in physical characteristics

depending markedly on the pyrolysis stage

were observed.Rough pore surface in char particles was detected clearly by SEM measurement.The release of volatile matter led to the development of pores with different sizes.Progressive increase of micropores developed with the pyrolysis process

whereas a maximum speed of micropore development occurred at the pyrolysis reaction ratio of 0.8.But macropores in char particles had different evolution characteristics.Based on the analysis result of density and porosity data

the particles shrank greatly at the first stage of high speed pyrolysis.