Early stage sintering of nanosized SnO2 and laser fragmentation of sub-micron SnO2 powders in water

• Main Authors: Hui-Di LU, 呂蕙荻
• Other Authors: Pouyan Shen
• Format: Others
• Language: zh-TW
• Published: 2011
• Online Access: http://ndltd.ncl.edu.tw/handle/15464244522397879926

碩士 === 國立中山大學 === 材料與光電科學學系研究所 === 99 === An onset coarsening-coalescence event based on the incubation time of cylindrical mesopore formation and a significant decrease of specific surface area by 50% relative to the dry pressed samples was determined by N2 adsorption-desorption hysteresis isotherm for cassiterite SnO2 nanoparticles (rutile-type structure with bimodal size distribution). In the temperature range of 800-1100oC, the nanoparticles underwent onset sintering coupled with coarsening-coalescence without appreciable polymorphic transformation or decomposition of SnO2. The apparent activation energy of such a rapid process for SnO2 nanoparticles was estimated as 75 ± 5 kJ/mol, respectively. The minimum temperature for sintering/coarsening/coalescence of the SnO2 nanoparticles is 735oC based on the extrapolation of steady specific surface area reduction rates to null. PLA fragmentation of cassiterite SnO2 powder (rutile type, 20-50 nm in size) in water was conducted under Q-switch mode (532 nm, 400 mJ per pulse) having laser focal point fixed at 5, 10, 15 and 20 mm beneath the water level for an accumulation time of 5, 15, 20 and 30 min at 10 Hz. The 532 nm laser incidence suffered little water absorption and was effective to produce cassiterite nanocondensates as small as 5 nm in diameter and occasional nanocondensates of α-PbO2-type structure more or less in coalescence. The combined effects of nanosize, internal compressive stress and H+ and Sn2+ co-signature in the lattice may account for a lower minimum band gap.