超声波振荡对细颗粒黄土样品粒度测量影响的实验分析

Effects of Ultrasonic Dispersion on Granulometry of Fine-grain Loess

在使用常规的前处理方法对细粒黄土(粘黄土)样品进行粒度测量时,发现结果不稳定。为了调查原因,分别选取黄土高原东南缘河南卢氏、秦岭地区陕西洛南和陕西洛川三个地点的黄土、古土壤样品,进行对比实验,分析前处理方法对细颗粒黄土样品粒度测量结果的影响。结果发现,在进行细粒黄土的粒度测量过程中,激光粒度仪上的超声波振荡分散时间对测量结果影响很大,一般应控制在2 min以上。作者用河南卢氏乔家窑黄土—古土壤剖面的连续粒度测量结果对改进后的前处理方法进行可行性验证,结果表明,采用改进后的前处理方法所得的结果,与野外地层划分及磁化率值的变化有较好的相关性,表明改进后的前处理方法更适用于细颗粒黄土样品的粒度测量。

The common pretreatment method has caused divergent results of grain size measurement of the fine loess samples. In order to understand effects of pretreated method on the fine-grain loess grain-size distribution, samples from three sits, which are located in Luochuan of central Chinese Loess Plateau, Lushi of southern margin of the Loess Plateau and Shangbaichuan of eastern Qingling Mountains in central China, were collected and pretreated under different ultrasonic dispersion conditions. The results indicate that time of ultrasonic disaggregating by the laser grain-size equipment just before measuring is very important for granulometry of the fine loess samples. On the basis of the different experiments, we recommend a new pretreatment method for the grain-size measurement for fine-grain loess samples ： over 2 minutes are required for dispersing the samples by ultrasonic of the laser grain-size equipment just before measuring. This step is neglected in the previous measurement so that the divergent results are presented in granulometry of the fine loess samples. In addition, samples from a toess-paleosol section at Qiaojiayao of the southeast Loess Plateau are measured by the traditional and the new methods, respectively. The results show that our recommended pretreatment method is more reliable to obtain grain-size distribution of the fine-grain loess deposit than that of the older one.