摘要
沉积物中X射线衍射(XRD)物相定量方法的选择和如何提高定量分析的精度一直是地学XRD定量研究的难点问题。本文针对沉积物中常见矿物组合特征,设计了一系列条件实验,比较了MacDiff的面积积分法(PAI法)和Highscore的强度参比法(RIR法)定量分析方法的优缺点。结果表明两种方法计算结果基本一致,但也各有优缺点。其中RIR法对衍射峰矮而宽的矿物定量更准确,PAI法则更适用于衍射峰尖锐的矿物以及含四种以上矿物、衍射峰重叠的样品,MacDiff的PAI方法分析过程不需要其他参数,误差较少,重现性好,而且全谱拟合还能部分消除择优取向的影响,可为沉积物XRD矿物相定量分析提供可靠数据。
Background, aim, and scope How to select suitable X-ray diffraction （XRD） phase analysis methods and improve the accuracy have been an important problem in quantitative analysis of sediments. Many new methods for quantitative analysis have been derived since the theory of XRD phase quantitative analysis was mature. The requirement of these methods is too high either for the standard or for sample, which make its application restricted. In recent years, in view of XRD quantitative analysis, different instrument manufacturers and researchers have also developed a series of analysis software. MacDiff has been currently widely applied in clay mineral rather than the whole rock mineral, and its precision and reliability are still unclear. In this paper, we compare the advantages and disadvantages of MacDiff with Peak Area Integration （PAI） and HighScore with Reference Intensity Ratio （RIR）, which is the most commonly used in the quantitative analysis of mineralogy, hoping to find a kind of simple calculation, high precision and universal quantitative method, so as to provide convenience for geological research. Materials and methods Considering the practice of research method, we choose common quaternary sediments of quartz （Qtz）, feldspar （Fsp）, calcite （Cal）, mica （Mca） and uncommon mineral corundum （Crn） as materials. According to four different combinations and four different mixing ratios, 16 known content experimental samples are prepared, conducted XRD testing, analyzed using the PAI and RIR quantitative analysis method, respectively. Based on the theory of powder diffraction spectrum is the diffraction stack results of countless small grain diffraction planes and diffraction intensity is proportional to the diffraction grain volume, PAl method is made by integrating all diffraction peak areas with MacDiff, and then through Normalization method to calculate all mineral contents. The key of the RIR method is the Reference Intensity RIR, which is a constant and independent of the instrument, is measured or calculated the strongest diffraction peak intensity by adding the internal standard. The mineral semi- quantitative results can be got immediately if the matched RIR value is researched in HighScore PDF database. Results The Relationship of matched value and calculated value of PAl and RIR quantitative methods （Fig.2） shows that with high crystallinity and high content, the calculated value of quartz in two methods are very close to the matched value. For poor crystallinity, high content of feldspar, the semi-quantitative results of RIR method closer to matched value, while PAI result is on the low side and the deviation increases with the known content increasing. For the low content of minerals, such as calcite and mica, PAl quantitative result is better than RIR. Low content of corundum is usually considered a standard phase, both RIR and PAl methods quantitative results are basically consist, lower than the real value. Fig.2 also shows that PAI method can show more advantages on the samples containing more than four kinds of minerals. By comparing the RIR and PAI method of five phase quantitative absolute error （Fig.3）, PAl method quantitative results of quartz, calcite, mica obtained with less error, and feldspar, in contrast, RIR method error is less. The absolute errors of corundum got with two methods are within 3%. Discussion Because of the difference of mineral crystallinity, such as Qtz and Fsp, provided that only selecting top three or five peak areas to calculate the relative content, the results deviate largely, especially when preferred orientation exists. So PAI method fitting all diffraction peaks, will greatly reduce quantitative errors leading by preferred orientation, overlapping peaks. The results are in agreement with those provided by PAI and RIR methods, and each method has its own advantage and shortage. More specifically, the PAl method is more practical in minerals with the sharp diffraction peaks and samples containing more than four minerals whose diffraction peaks are overlapped. But for mica, the PAI quantitative results are slightly on the high side cause of mica flourish bedding leading to the existence of non-plane diffraction in the actual situation. On the contrary, the RIR method is suitable for the minerals with some short and wide diffraction peaks, such as feldspar, which the diffraction peak shape is not obvious, higher peak overlaps maybe lead to inaccurate splitting peaks. Unfortunately, the RIR method is not sensitive significantly to low content （10%） or less. According to the principle of RIR method, larger RIR value （eg. RIR（mica）=l 3.8） causes lower quantitative results. So the errors of RIR method are mainly derived from the RIR value and the diffraction peak intensity, while the PAl method errors source from three aspects： inaccurate peak splitting, idealized crystal plane diffraction and O range. Conclusions Experimental results show that the PAI and RIR method on the phase quantitative analysis is the basically consist. By far, RIR method is the most commonly used phase quantitative method. Its advantage is simple, rapid, especially for bad crystalline minerals, while the disadvantage is that the selection of RIR value is restricted by PDF database, and the quantitative result of low content phase trend to less. Although the analysis process of PAl method is a little complicated, but for better crystalline materials or samples contain more mineral species, the method owns accurate quantitative results （absolute error in most cases ~〈 3%）, good reproducibility, and can partly eliminate the effect of preferred orientation. Recommendations and perspectives The PAl analysis method does not need other parameters with small error and good reproducibility, and the full pattern fitting can partially eliminate the influence of preferential orientation, therefore, PAI method can provide reliable data for mineral quantitative analysis in sediments.
出处
《地球环境学报》
CSCD
2017年第1期78-87,共10页
Journal of Earth Environment
基金
中国科学院重点部署项目(KZZD-EW-04-02)
国家自然科学基金项目(41290253
41572162)
中国地质调查局西安地质调查中心项目(水[2016](4))~~
