中文摘要：

利用40kHz超声波清洗机,设计不同的超声功率和超声时间,对火山碎屑物发育土壤进行分散处理;再用湿筛-吸管法测定土壤颗粒含量,对测定结果进行分析。研究表明：增大超声功率能促进土壤颗粒的分散,但80w和140w超声功率引起的土壤各粒级含量变化不大,均小于3.00%;延长超声时间对火山碎屑物土壤分散效果影响显著,对于粗颗粒为主的样品各粒级含量变化均很小,对于细颗粒为主的火山碎屑物土壤样品,以粉粒和黏粒含量变化更大;建议火山碎屑物发育土壤的颗粒分散采用（NaPO_3）_6-超声波联合分散法,超声条件设定为：频率40kHz,功率140w,震荡时间25min。

英文摘要：

Soil developed from volcanic tephra was dispersed at different ultrasonic power and time with the 40 kHz ultrasonic machine. And then soil particles were determined by wet sieving-pipette method. Increase in ultrasonic power promoted the dispersion of soil particles, but change in dispersion effect was with less than 3.00% at 80 w or 140 w ultrasonic power. Increase in ultrasonic time could result in further dispersion for the soil samples containing mainly silt and clay particles, while the dispersion effect was less effective for the soil with more coarser particles. In this context, for the particle composition analysis of soils developed from volcanic tephra it was suggested to use the method of（NaPO_3）_6 combined with ultrasonic parameters of 40 kHz ultrasonic frequency, 140 w ultrasonic power and25 minutes ultrasonic time.