Casting Method For X-ray Fluorescence Analysis

Characterization is one of the core point in materials field,and sample preparation for characterization is also a research focus in materials field.X-ray fluorescence spectrometry（XRF）is a powerful method to qualitatively and quantitatively determinate the sample composition.The accuracy of its results depends largely on sample preparation,and there are two commonly used XRF sample preparation methods,the fusion bead method and the pressed pellet method.The fusion bead method has good uniformity but it requires expensive equipment and a complicated process,rather time-consuming.The pressed pellet method is convenient and simple but it cannot eliminate the matrix effect which would bring in an unacceptable error in the measurements.In this thesis,a rapid and more reliable XRF sample preparation approach for powder samples as referred to the casting method,was proposed,using an organic liquid as a“flux”to disperse and fix the sample powder through organic liquid solidification.Organic materials mainly contain light elements such as C,H,O,etc.,and have a small fluorescence yield and X-ray absorption which will not affect the fluorescence intensity of the measuring element.So organic materials used as“flux”will considerably reduce the matrix effect,compared to the pressed pellet method in which the serious matrix effect is caused by the aggregation of the samples.In addition,sample powder is much easier to be dispersed in an organic liquid.Moreover,by solidification of organic liquid at ambient temperature,problems such as ablation of the sample at a high temperature as in the fusion bead method can be avoided.In this thesis,Si O₂was chosen as the sample powder and epoxy/hardeners were selected as the carrier dispersion system for the powder samples.The viscosity variation of the system was investigated.The effect of hardener type and powder sample content on the viscosity of the system and the effect of hardener type on the homogeneity of the samples were studied.Bisphenol A epoxy resin（E-51）was chosen as the carrier and DMP-30 as the curing agent,and curing was carried out at room temperature.The system viscosity changed with hardener and sample content.The viscosity of the system increases with the increase of sample content（1-10%）,and the effect of DMP-30 on the viscosity of the system were relatively small.From the comparison of curing agents with different curing time and different viscosity,it can be seen that the sample powder in the system has a significant settlement when a long curing time,low viscosity curing agent was used.The cast method was used for XRF analysis for validation.The uniformity and repeatability of the casts were evaluated and uncertainty in the application of the cast method to XRF analysis was assessed.Small standard deviations of homogeneity test indicated that Si O₂was well dispersed in cast.The high R²value（>0.99）showed linear response for Si O₂levels varying from 1-5%,and the Si O₂contents with higher recoveries and low errors suggest the method’s performance is good.A comprehensive assessment of the uncertainty in the implementation of the method was carried out,and the expanded uncertainty（k=2）was small than 0.1%.The above results indicate that the casting method is a reliable method for XRF sample preparation.It has verified that the casting method is a reliable sample preparation method.We have applied it in some kind of important field to verify its wide applicability.Cement is an essential building material for production and life,XRF was the mostly applied technique in routine analysis in cement manufacturing and it has unique advantages.In this experiment,we used XRF to investigate Ca O,SO₃and Si O₂of two kind of ordinary Portland cement with the castingmethod.The high R²（>0.98）indicates good linearity of the calibration curve,and the high recoveries（>99%）of testing results of reference materialsdemonstrate high precision and accuracy of the calibration curve and theresults are in good agreement with the values given by factory,indicating that the casting method was reliable and workable as a sample preparation method for XRF in the investigation of component content in cement.Selective catalytic reduction（SCR）is one of the widely used anddeveloping NOx reduction technologies.The casting method was used in the sample preparation for the determination of active ingredients of SCR Catalyst.Homogenous casts with RSDs in the range of 0.26～1.52%were gotten by the casting method.The higher R²values（>0.98）show good linearity of thecalibration curves for V₂O₅,Mo O₃or WO₃contents.Analytical results of five real commercial catalysts lie in the typical composition range of commercial SCR catalysts.Close results were observed compared to the fusion beadmethod.These indicate the casting method as a sample preparation method for XRF in the determination of active ingredients of SCR catalysts is feasible and performs well.