粗制氧化锌的X射线衍射全谱图拟合定量相分析探讨

采用X射线荧光光谱(XRF)半定量法或化学法分析粗制氧化锌中ZnO含量时,如存在Zn、ZnFe₂O₄等非ZnO物相,结果往往偏高,导致一些禁止进口的固体废物进入我国。为此,实验选取两种粗制氧化锌试样,先采用X射线荧光光谱半定量法测定ZnO含量,然后采用X射线衍射(XRD)分析技术和Rietveld全谱图拟合定量相分析。利用整个衍射空间的散射信息,用多个不同物理含义的模型对实验数字衍射谱进行Rietveld全谱图拟合。拟合过程采用线性最小平方拟合算法不断调节模型中参数,获得与实际谱线吻合的理论谱线(加权图形剩余方差因子R_wp＜10%),最后获得试样组成相的含量。采用在粗制氧化锌中分别加入一定量ZnO,按照上述方法进行Rietveld全谱图拟合分析,结果差值小于5.0%。结果表明:方法精修后得到粗制氧化锌中各常见物相的晶体结构参数与已报道的文献非常接近,实现了ZnO相含量的更准确测定,可用于进口粗制氧化锌的检验监管和属性鉴别。

Discussion on quantitative phase analysis of crude zinc oxide by X-ray diffraction full spectrum fitting

During the determination of ZnO content in crude zinc oxide by semiquantitative X-ray fluorescence spectrometry (XRF) or chemical analysis method, the determination results were usually higher due to the presence of non-ZnO phases such as Zn and ZnFe₂O₄. As a result, some prohibited solid wastes were imported into China. Two types of crude zinc oxide samples were selected for analysis. The content of ZnO was firstly determined by semiquantitative XRF method, and then the quantitative phase analysis was conducted by X-ray diffraction (XRD) and Rietveld full spectrum fitting. Based on the scattering information of whole diffraction space, the Rietveld full spectrum fitting of experimental digital diffraction spectrum was conducted using several models with different physical meanings. In fitting process, the parameters in model were continuously adjusted using linear least square fitting algorithm to obtain the theoretical spectral lines which were consistent with the actual lines (the residual variance factor of weighted graph of R_wp＜10%). Finally the content of composition phases in sample could be obtained. Certain amount of ZnO was added into crude zinc oxide sample for the Rietveld full spectrum fitting analysis according to the proposed method, and the difference of results was less than 5.0%. The results showed that the obtained crystal structure parameters of common phases in crude zinc oxide by proposed method were very close to those reported in the literature. The accurate determination of ZnO content was realized. The proposed method could be used for the inspection supervision and property identification of imported crude zinc oxide.