矿物材料现代测试技术3X荧光分析.ppt

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1、武汉理工大学资环学院 管俊芳,1,第二部分x ray Fluorescence Spectroscope(XRF)X荧光成分分析,武汉理工大学资环学院 管俊芳,2,某些物质被一定波长的光照射时，会在一定时间内发射出波长比入射光长的光，如果这个时间比较短，这种光就称为荧光。荧光由一种能发荧光的矿物 萤石(fluosrite)而得名。除了紫外光和可见光可能激发荧光外，其它的光如红外光、X射线也可能激发出荧光，因此除紫外荧光或可见荧光外，还有红外荧光、X射线荧光等。,武汉理工大学资环学院 管俊芳,3,1 方法特点2 分析原理3 仪器构成4 WDS-XRF 5 EDS-XRF6 定量分析,武汉理工大学

2、资环学院 管俊芳,4,1 方法特点（1）,XRF是一种最有效的无损成分分析手段之一。优点：(1)速度快，一般测定一种元素(定量)需10100 秒；(2)可检测固态、粉末、液态样品，以及晶质、非晶 质等样品的化学成分；(3)非破坏性测试，不损伤样品(但对于某些高分子物质，如有机物，则会引起颜色变化)；(4)是一种物理分析方法，分析元素范围F9U92，分析的浓度范围1ppm100%；,武汉理工大学资环学院 管俊芳,5,1 方法特点（2）,优点：(5)制样简单，板状样品把被照射面加工成平面即可，粉末样品经粉碎、压片即可；(6)系表面分析，一般测定深度为0.1mm范围，另外也是表面整体分析，即分析整个

3、照射面范围内的元素种类和含量；Pros:Fast Non-destructive technique Performs elemental analysis High sensitivity,detects up to 50 ppm Can detect thin single or multi-layer films and measure their thickness.,武汉理工大学资环学院 管俊芳,6,1 方法特点(3),缺点：(1)难以作绝对分析，因此定量分析时需参照标准物质进行；(2)原子序数低的元素，其检出限及测定误差都相对较大。Cons:Does not assist in o

4、btaining chemical information Not applicable to identifying the first 11 elements.Interfering x-ray lines by matrix effects can possibly complicate analysis.,武汉理工大学资环学院 管俊芳,7,1 方法特点（4）,样品要求及处理方法：,武汉理工大学资环学院 管俊芳,8,1 方法特点（4）,仪器外观：依据光源系统的不同、探测方式的不同，仪器的大小、形状有一定差异。,武汉理工大学资环学院 管俊芳,9,1 方法特点（5）,光源：X射线光源：白色X

5、射线。即具有各种波长的X射线，可分析前面所列范围的所有元素。放射性同位素光源：放射出的射线亦在X射线范围，但能量是固定的。因此只能分析部分元素。仪器的体积可以很小，最新型的相当于一个 计算器的大小。同步辐射光源：光源的能量更大，对后续的二次 射线检测很有利，所以分析精度更高，但仪 器造价很昂贵。,武汉理工大学资环学院 管俊芳,10,2 分析原理（1）,When the atoms in a sample material are irradiated with high-energy primary x-ray photons,electrons are ejected in the form

6、 of photoelectrons.This creates electron holes in one or more of the orbits,converting the atoms into ions-which are unstable.,武汉理工大学资环学院 管俊芳,11,2 分析原理（2）,To restore the atoms to a more stable state,the holes in inner orbits are filled by electrons from outer orbits.Such transitions may be accompani

7、ed by an energy emission in the form of a secondary x-ray photon-a phenomenon known as fluorescence.,武汉理工大学资环学院 管俊芳,12,2 分析原理（3）,The various electron orbits are called K,L,M,etc.,where K is closest to the nucleus.Each corresponds to a different energy level-and the energy(E)of emitted fluorescent ph

8、otons is determined by the difference in energies between the initial and final orbits for the individual transitions.,武汉理工大学资环学院 管俊芳,13,2 分析原理（4）,Characteristic x-ray emissions result in an energy spectrum that is a fingerprint of the element.So we can determine the element kinds in the sample.And

9、also the intensities of the peaks in the spectrum are roughly proportional to the concentrations of the constituent elements.,武汉理工大学资环学院 管俊芳,14,3 仪器构成（1）,波长色散型XRF：WAVELENGTH DISPERSIVE XRF(WDS-XRF)通过分析样品在入射X射线作用下产生的二次X射线(荧光射线)的波长，来定性或定量分析样品的元素组成及含量。能量色散型XRF:ENERGY-DISPERSIVE XRF（EDSXRF）通过分析样品在入射X射线作

10、用下产生的二次X射线(荧光射线)的能量，来定性或定量分析样品的元素组成及含量。,武汉理工大学资环学院 管俊芳,15,3 仪器构成（2）,WDS-XRF and EDS-XRF,武汉理工大学资环学院 管俊芳,16,4 WDS-XRF(1),Wavelength dispersive XRF uses a crystal to separate the various wavelengths:for every angle of incident radiation,the only wavelength reflected to the detector is the one that conf

11、orms to Braggs formula:n=2d sin where is the wavelength of the x-ray radiation produced by the sample;d is a constant characteristic of every crystalline substance(i.e.the x-ray crystal);and is the angle on incidence of the x-radiation on the sample.,武汉理工大学资环学院 管俊芳,17,4 WDS-XRF(2),The crystals and t

12、heir planes often used are as follow.,武汉理工大学资环学院 管俊芳,18,4 WDS-XRF(3),How to determine the wavelength:Detector is rotating when doing the wavelength determination,also the crystal is rotating by half speed.,武汉理工大学资环学院 管俊芳,19,4 WDS-XRF(4),So,by changing the angle of the crystal,you can select any wave

13、length for specific elements of interest.Different crystal can be used determine different elements.When doing measurement,we often need to change crystals for the various elements,finally we can yield results in any form desired:qualitative,ratio,quantitative,graphic,etc.,武汉理工大学资环学院 管俊芳,20,4 WDS-XR

14、F(5),The relationship between the range of analyzing element and the crystals,and the 2 theta scanning range.,武汉理工大学资环学院 管俊芳,21,4 WDS-XRF(6),Analyzing Procedure:Every element have a strongest X ray wavelength.In order to determine it,first we should measure the intensity of that wavelength.For examp

15、le,strongest Line and their 2 position for Ni,Fe,&Ru,when detected by different crystal.,武汉理工大学资环学院 管俊芳,22,4 WDS-XRF(7),Analyzing Procedure:In order to make the determination more accurate,we should also measure their accompanying peaks.,武汉理工大学资环学院 管俊芳,23,4 WDS-XRF(8),Analyzing Procedure:,武汉理工大学资环学院

16、 管俊芳,24,4 WDS-XRF(9),WDS was introduced in the early 1950s.WDS spectrometer systems employ diffraction by a single crystal to separate characteristic wavelengths emitted by the sample.IN WDS,polychromatic radiations emanating from the X-ray tube impinge on the specimen and reject K,L,level electrons

17、 from atoms of the elements present in the specimen.This results in the emission of fluorescence radiation(K,L,.series lines)which are dispersed by an appropriate crystal according to the well-known Bragg equation.,武汉理工大学资环学院 管俊芳,25,4 WDS-XRF(10),In order to measure x-rays of different energies(wave

18、lengths),the position of the diffracting crystal and detector must be mechanically changed relative to the fixed specimen to alter the angles.To cover the range of X-ray wavelength to be measured,several different diffraction crystals must be utilized.The detectors used will often be a flow-proporti

19、onal detector a gas-filled scintillator and photo multiplier tube,武汉理工大学资环学院 管俊芳,26,5 EDS-XRF(1),The second and more common method for analyzing obsidian is EDS-XRF.EDSXRF systems detect elements on the periodic table between atomic numbers 11(Na)and 92(U).Samples can be analyzed non-destructively w

20、ith little or no sample preparation in minutes and in some cases seconds.Elements in concentrations from as low as a few parts per million to 100%may be analyzed in the same sample simultaneously.Accuracy of less than one percent relative error are attainable with comparable reproducibility,武汉理工大学资环

21、学院 管俊芳,27,5 EDS-XRF(2),Analysis by EDSXRF,like WDSXRF involves use of ionizing radiation to excite the sample,followed by detection and measurement of X-rays leaving the sample that are characteristic of the elements in the sample.However,unlike the crystal(wavelength)XRF,EDSXRF spectrometer electro

22、nics digitize the signal produced by X-rays entering the lithium drifted detector,and send this information to the PC for display and analysis.The Na to U spectral data are in the 1-37 KeV range.,武汉理工大学资环学院 管俊芳,28,5 EDS-XRF(3),武汉理工大学资环学院 管俊芳,29,5 EDS-XRF(4),The high resolution lithium drifted silico

23、n X-ray detectors provide low detection limits,few spectral interferences,and accuracy over a wide range of concentrations.These detectors are able to separate the electron energy coming from the sample into elemental components,which in turn are translated into ratio,qualitative,or quantitative ele

24、mental data in spreadsheet or word processor formats.Additionally,the tube voltages on EDSXRF are quite low and the entire instrument is plugged into a standard wall socket.WDSXRF requires filtered voltage at 220 V.,武汉理工大学资环学院 管俊芳,30,5 EDS-XRF(5),Advantages:(1)NON-DESTRUCTIVEIn the vast majority of

25、cases,analyzed samples are not destroyed or changed by exposure to x-rays.They can thus be saved for future reference or used for other types of testing that may be destructive.(2)MINIMAL PREPARATION Many samples can be examined with little or no pre-treatment.Many of the alternative techniques requ

26、ire dissolution procedures that are both time-consuming and costly in terms of the acids or other reagents required.,武汉理工大学资环学院 管俊芳,31,5 EDS-XRF(6),Advantages:(3)FASTX-ray spectrometry enables chemical compositions to be determined in seconds.(4)EASY TO USEModern instruments run under computer contr

27、ol,with effective software to handle measurement set-up and results calculation.Tasks that once required the constant attention of a trained analyst can now be handled by skilled operators or even carried out by fully automated systems.,武汉理工大学资环学院 管俊芳,32,5 EDS-XRF(7),Comparing with WDS-XRF WDS-slow,

28、but accuracy is high.EDS-fast,but accuracy is low.WDS Quantitative is easier than qualitative.EDS both are same.Generally the differentiating ability of Wavelength is higher then that of Energy.,武汉理工大学资环学院 管俊芳,33,5 EDS-XRF(8),Advantages of Energy Dispersion:*simplicity of instrumentation-no moving p

29、arts*simultaneous accumulation of the entire X-ray spectrum*qualitative analysis can be performed in 30 s,or so*a range of alternative excitation sources can be used in place of high-power x-ray tubes with their large,heavy,expensive and power-consuming supplies,武汉理工大学资环学院 管俊芳,34,5 EDS-XRF(9),Advant

30、ages of Energy Dispersion:*alternative sources include,low power x-ray tubes,secondary monochromatic radiators,radioisotopes and ion beams.,武汉理工大学资环学院 管俊芳,35,5 EDS-XRF(10),Advantages of Wavelength Dispersion:*resolution is better at wavelengths longer than 0.08 nm*higher individual intensities can b

31、e measured because only a small portion of the spectrum is admitted to the detector*with multichannel analysers sensitivity for weak lines in the presence of strong lines is limited because the strongest line determines the counting time*lower detection limits are possible,武汉理工大学资环学院 管俊芳,36,6 定量分析（1

32、）,定量分析的基本原理是测定出样品所产生的2次X射线的强度，然后与标准样品所产生的2次X射线的强度比较，从而确定出样品中某种元素的含量。首先用一系列标准样品中某元素工作峰的强度作一条工作曲线。然后把实际样品中对应该元素所产生的2次X射线的强度投影到工作曲线上，即可得到样品中该元素的含量。,武汉理工大学资环学院 管俊芳,37,6 定量分析（2）,一般对于595之间的定量效果最好。95以上的往往效果不是很好。在于标准物质选取的困难。,武汉理工大学资环学院 管俊芳,38,6 定量分析（3）,选线系 一般对Nd60号以前的元素用K线作工作峰，Cd48号以后的元素用L或L线作工作峰，而Cd48Nd60之

33、间的元素则用K或L、L均可。测定方式定时计数法：测定在一定时间间隔内的总计数；定数计时法：测定达到一定计数值所需要的时间,武汉理工大学资环学院 管俊芳,39,6 定量分析（4）,标准样品的选择 所谓标准物质是指已确切知道其中某种元素的含量(化学分析数值)。标准样品与未知样品必须由相同的处理方法制成，如处理粉末样品时的碎样方法、压片方式、压片时使用的压力大小等等，必须为相同的条件；对于块状样品，则要求样品必须有一平整面，且平整面的面积、表面光洁度等必须相同。,武汉理工大学资环学院 管俊芳,40,作 业,Briefly shows the principal of XRF(WDS and EDS).Compares the WDS-XRF and XRD.,