电子探针定量分析测定FeO和Fe_2O_3含量常用方法的评定

Evaluation of the Methods for Quantitative Determination of FeO and Fe_2O_3 by Electron Probe Microanalysis

直接测氧法测定矿物中FeO和Fe2O3含量,在其众多影响因素中,经测量不确定度评定发现,超轻元素氧的影响显著。一方面受电子探针仪器因素和基体校正精度的限制,氧的电子探针定量分析值的准确度很低;另一方面氧对FeO和Fe2O3含量的不确定度灵敏系数分别为8.981、9.981,将氧的测量不确定度再扩大近10倍。可见直接测氧法测定FeO和Fe2O3含量,仅因超轻元素氧的测量不确定度传递就会使其误差范围过大,效果不是很理想。而利用Fe的Lα、Lβ谱线强度比的价态效应推测矿物中FeO和Fe2O3含量,由于Lβ/Lα强度比与Fe2+/Fe3+比值之间关系曲线的确定,需要对矿物进行大量的系统性研究,甚至是否必然存在这种对应都还缺乏理论依据,可见此法也并不可靠。相对而言,常用的电价差值法和剩余氧计算法仍为优选方案。

On the basis of the evaluation for measurement uncertainty, it is found that oxygen, as a super light element, affects the determination results of FeO and Fe2O3 observably when direct oxygen measurement method is used. On the one hand, the accuracy of quantitative electron probe microanalysis for oxygen is poor due to the limitations from the measurement instrument stability and the poor precision from matrix correction. On the other hand, the measurement uncertainty of oxygen would be expanded 10 times approximately again, because uncertainty sensitivity coefficients for FeO and Fe2O3, derived from super light element oxygen, are 8. 981 and 9.981 respectively. Thus it can be seen that the direct oxygen measurement method is not suitable for FeO and Fe2O3 measurements because of the transfer of oxygen measurement uncertainty. The valence state method, based on Lα and Lβ spectral intensity ratio of Fe, is also unreliable for FeO and Fe2O3 measurements, because it is very hard to establish the relationship between Lβ/Lα （spectral intensity ratio） and Fe^2＋/Fe^3＋ （content ratio）.Relatively, the＂ charge difference method and the surplus-oxygen method are still the most favorable methods.