Tsukimura Katsuhiro, Suzuki Masaya
Research Institute of Geo-resources and Environment, Geological Survey of Japan, Advanced Industrial Science and Technology, Central 7, Higashi-1, Tsukuba, Ibaraki 305-8567, Japan.
J Appl Crystallogr. 2020 Feb 1;53(Pt 1):197-209. doi: 10.1107/S1600576719017266.
Clays and soils produce strong small-angle X-ray scattering (SAXS) because they contain large numbers of nanoparticles, namely allophane and ferrihydrite. These nanoparticles are amorphous and have approximately spherical shape with a size of around 3-10 nm. The weight ratios of these nanoparticles will affect the properties of the clays and soils. However, the nanoparticles in clays and soils are not generally quantified and are sometimes ignored because there is no standard method to quantify them. This paper describes a method to quantify nanoparticles in clays and soils with SAXS. This is achieved by deriving normalized SAXS intensities from unit weight of the sample, which are not affected by absorption. By integrating the normalized SAXS intensities over the reciprocal space, one obtains a value that is proportional to the weight ratio of the nanoparticles, proportional to the square of the difference of density between the nanoparticles and the liquid surrounding the nanoparticles, and inversely proportional to the density of the nanoparticles. If the density of the nanoparticles is known, the weight ratio of the nanoparticles can be calculated from the SAXS intensities. The density of nanoparticles was estimated from the chemical composition of the sample. Nanoparticles in colloidal silica, silica gels, mixtures of silica gel and α-aluminium oxide, and synthetic clays have been quantified with the integral SAXS method. The results show that the errors of the weight ratios of nanoparticles are around 25% of the weight ratio. It is also shown that some natural clays contain large fractions of nanoparticles; montmorillonite clay from the Mikawa deposit, pyrophillite clay from the Shokozan deposit and kaolinite clay from the Kanpaku deposit contain 25 (7), 10 (2) and 19 (5) wt% nanoparticles, respectively, where errors are shown in parentheses.
黏土和土壤会产生强烈的小角X射线散射（SAXS），因为它们含有大量纳米颗粒，即水铝英石和纤铁矿。这些纳米颗粒是非晶态的，形状近似球形，尺寸约为3 - 10纳米。这些纳米颗粒的重量比会影响黏土和土壤的性质。然而，黏土和土壤中的纳米颗粒通常没有被定量，有时甚至被忽略，因为没有标准方法对它们进行定量。本文描述了一种用SAXS对黏土和土壤中的纳米颗粒进行定量的方法。这是通过从样品单位重量中得出不受吸收影响的归一化SAXS强度来实现的。通过在倒易空间对归一化SAXS强度进行积分，可以得到一个与纳米颗粒重量比成正比、与纳米颗粒和纳米颗粒周围液体之间的密度差的平方成正比、与纳米颗粒密度成反比的值。如果纳米颗粒的密度已知，就可以根据SAXS强度计算出纳米颗粒的重量比。纳米颗粒的密度是根据样品的化学成分估算出来的。已经用积分SAXS方法对胶体二氧化硅、硅胶、硅胶与α - 氧化铝的混合物以及合成黏土中的纳米颗粒进行了定量。结果表明，纳米颗粒重量比的误差约为重量比的25%。还表明一些天然黏土含有大量纳米颗粒；三河矿床的蒙脱石黏土、庄矿山矿床的叶蜡石黏土和勘珀矿床的高岭土黏土分别含有25（7）、10（2）和19（5）wt%的纳米颗粒，括号内为误差。
