Study on the Online Analysis of Complex and Particle Industrial Materials by X-ray Fluorescence Technique

Author:Zhang Zuo

Supervisor:jia wen bao

Database:Doctor

Degree Year:2018

Download:18

Pages:142

Size:6065K

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Practices show that the real-time on-line analysis of the industrial materials composition could improve the utilization of coal resources and reduce the emission of the harmful heavy metal material.X-ray fluorescence(XRF)serves as an effective,rapid,and nondestructive method for determining the elemental composition,therefore,XRF may become the optimal choice for qualitative and quantitative online analysis of the industrial materials.However,the accuracy of online XRF measurement are affected by many factors,such as unknown and changing amounts of elements,and most importantly the distance to the uneven surface of particle industrial materials.Therefore,it’s very significant to improve the accuracy of online XRF analyzer.Two strategies have been proposed to improve the accuracy of online XRF analysis process.First,new spectrum analysis methods were developed to reduce the impact by the overlapping peaks and the sum peaks effect between elements.Second,to address the impact of particle size effect on the measurement accuracy,the theory and validity details of the dependence of XRF intensity on the distance as well as the comparison of the formula derivation and experimental verification were elaborated.Based on this,a new correction method was established.Based on the above ideas,the theoretical calculation and experimental methods were used to address these problems,such as the overlapping,the sum peaks effect and most importantly the particle size effect,to improve the accuracy in online XRF analysis process.And the main results and conclusions were summarized as follows.(1)Optimization of the online XRF experiment platform and study of the key performance.The geometry of online XRF set-up,such as the geometric angles of incidence and emergent,the distance between the source,sample and detector,was determined by a series of simulations with the Monte Carlo code MCNP to improve the efficiency of the elements detection.And then the online XRF experiment platform was finalized according to the optimized geometrical conditions.By comparison with the results by inductively-coupled plasma mass spectrometry(ICP-MS),the limits of detection,precision and accuracy of the online XRF experiment platform were discussed by online measuring the pulverized coal and cement raw meal.The limits of detection for the pulverized coal and cement raw meal were ppm(10-6)level.The relative standard deviation(RSD)for Hg,Pb,Cr,Ti,Fe and Ca in the pulverized coal by the online XRF analyzer was less than 7.74%,and the RSD for Pb,Cr,Ti,Fe,Ca and S in the cement raw meal by the online XRF analyzer was less than 10.7%.Moreover,the comparison of results indicates that high precision and good accuracy can be obtained by online XRF analyzer for Ti and Ca.The online XRF experiment platform provided the necessary scientific data to support the developing of the online XRF analysis system for complex and particle industrial materials.(2)Decomposition the overlapping peaks using wavelet analysis method combined with the subshell theory of X-ray fluorescence.The wavelet analysis method is superior on background reduction,because of reducing the manual measurement error.Based on the subshell theory of X-ray fluorescence,the Kβ/Kαand Lβ/Lαratios of As,Hg and Pb were studied by measuring the standard samples.Then a new decomposition the overlapping peaks method was proposed by using wavelet analysis method combined with shell theory of X-ray fluorescence.By comparing the results of before and after applying this method with the results by ICP-MS,the results indicate that this method was very effective in reducing the impact of overlapping peaks during online XRF analysis,therefore increase the accuracy of Hg and Pb concentration measurement significantly.(3)Study on the online XRF measurement of the coal and cement raw meal by using MCLLS approach.A new detector response function of the Silicon Drift Detector(SDD)for the single element was proposed,and an improved computed elemental spectra library method generated based Monte Carlo code.Experimental spectra showed that sum peaks were not weak,and must be taken to differentiate them from spectra due to trace elements.So based on the principles of X-ray interactions with materials,a new and suitable detector response function model of the SDD for the single element was presented by empirical formulas.A new MCNP output read code PTRAC-XRF was developed for the computed elemental spectra libraries.By comparing the results of MCLLS and peaks area method with the results of ICP-MS,indicating that the MCLLS approach can increase the accuracy of online XRF measurement.(4)A novel distance correction method for improving the accuracy of particle industrial materials online XRF analysis:Theoretical dependence,method and experimental investigation.To address the impact of the sample’s particle size(<6mm)on the measurement accuracy,a typical XRF calculation model has been built for theoretical derivation.The theory and validity details of the dependence of XRF intensity on the distance as well as the comparison of the formula derivation and experimental verification were elaborated in the present research.The expression of the relationship between the XRF intensity and the distance from XRF spectrometer to sample surface was derived,where the variation of the distance influenced five physical phenomena:absorption of X-rays by the air;irradiated surface area of the samples;changes in exit angle;changes in solid angle and absorption of X-ray fluorescence by the air.Then a novel distance correction method was established elaborated by iteration,which was based on the linear relationship between the XRF intensity and the distance within a certain range.In order to verify the effectiveness of this method,different particle size coal samples with same components have been measured by the online XRF analyzer with a laser rangefinder.After applying the distance correction method,the results showed that the accuracy of online XRF measurement was significantly increased.In conclusion,an online XRF experiment platform has been developed for complex and particle industrial materials measurement.The overlapping peaks decomposition method was achieved by using the wavelet analysis method combined with subshell theory of XRF for addressing the impact of overlapping.A new detector response function of the SDD for the single element and the MCNP output read code PTRAC-XRF was developed for the computed elemental spectra libraries,and the results indicate that the MCLLS approach could increase the accuracy of online XRF measurement.The theory and validity details of the dependence of XRF intensity on particle size effect(<6mm)were elaborated,based on this knowledge,the distance correction method was proposed.After applying above method,the results showed that the accuracy of online XRF measurement was significantly improved.