X- Ray Fluorescence Analysis

Transcription

1 TEAM 1: Ruth Dasary Ashvin Kumar Carmen Rocha Cesar Terrazas X- Ray Fluorescence Analysis MASE 6402 Fall /14/2011

2 X-Ray Fluorescence (XRF) Objective The objective of this report is to present the results of an XRF analysis performed on several samples made from stainless steel and silicon also containing other traces of elements such as Al, Cr, Ti and Ni. The analysis was carried out in a X-MET 3000TX spectrometer and the process followed is detailed in the methodology section to follow. Introduction XRF is a technique utilized in a routine analysis of various materials such as minerals powders and fluids in a non-destructive manner. The process is similar to other techniques in the sense that the specimen is bombarded with high energy radiation causing individual atoms to ionize. As the atom resolves towards relaxation, electrons will relocate from a high to a low orbital emitting photons or light radiation in the process [1]. The physical occurrence in the X-ray fluorescence process has been termed as a resulting fluorescence emission of x-radiation from the characteristic elements present in a specimen that is exposed to an incident x-radiation beam [2]. Detection systems take advantage of the fact that emitted radiation has lower energy compared to the incident source and since the emitted radiation is characteristic to specific electron transitions of individual elements, it can be utilized in detecting the chemical composition of specimens [3]. The physical phenomenon is depicted in the schematic of Figure 1 shown below. A typical XRF spectrum depicting the most representative energy lines for different elements is shown in Figure 2 Figure 1 - Schematic representation of the XRF physics. Reproduced from [4].

3 Figure 2 - Typical XRF spectrum [4] Methodology I. Experimental Procedure The experiments were performed using X-MET 3000TXVF device, depicted in the image on the right in Figure 2. The device is operated using an HP palm PDA. After the device is ready for operation, we type a name for the file. Then, select Metal Method. Select analysis time as 300 seconds. Place the sample over the window, cover with Lead arc and turn on the X-rays. After the analysis is complete the PDA displays a notification Measurements complete. It also displays an approximate data for elemental concentrations. The results file is retrieved and then analyzed using the software PyMca. This software has been developed by the Software Group of the European Synchrotron Radiation Facility (ESRF). A total of four samples, listed below and depicted in Figure 3, were analyzed using this software. SAMPLE 1: (AlCrTiNi Stainless Steel) SAMPLE 2: (CrAlTiNi Silicon) SAMPLE 3: (CrAlTiNi Stainless Steel) SAMPLE 4: (AlTiCrNi Stainless Steel)

4 Figure 3 - Specimens analyzed by XRF and the X- MET 3000TXVF device utilized in the measurements II. XRF Spectrum Analysis in PyMCA The software PyMCA provided by the ESRF research institute was utilized to analyze the data captured by the XMET 3000TX device. Following the instructions provided in various sources, it was possible to load the information and proceed to fitting the data to the best extent possible. Among the steps carried out for the proper calibration of the study was the selection of the silver peak occurring in the vicinity of channel The calibration was achieved by selecting Ag(47) from the element menu and KL3( ) from the linemenu. This was done since the source of x-rays was a silver target bombarded with electrons and a strong elastic signal will be produced for this particular element providing means of calibrating the spectrum measured. A different specimen was analyzed by each member of the team utilizing the same parameters for PyMCA. Results The fitted spectra for the specimens analyzed are shown in Figures 4 through 7 in the next page. It can be seen that PyMCA provided relatively good fits for the data even though some of the information regarding the device was missing from the configuration file. Each figure includes the spectrum, continuum, fit and pileup graphs for the four specimens analyzed in the experiment. Table 1 also summarizes the data obtained for the fitted areas of the elements in the specimens.

5 Figure 4 Spectrum for AlCrTiNi Stainless steel specimen Figure 5 Spectrum for CrAlTiN Silicon specimen Figure 6 Spectrum for CrAlTiN Stainless steel specimen Figure 7 Spectrum for AlTiCrN Stainless Steel specimen

6 Table 1- Values of fitted area and sigma for elements present in four analyzed alloy specimens. Because some of the information regarding the X-MET 3000TXVF device was not available, a relative concentration analysis of the samples was not possible. Hence, it was decided to plot the values for areas of one element against others. These charts, which compared elements against each other, were generated for this study in a total of 6 plots. As can be seen in the sequence of figures below (Figures 8 to 12), this system provided a graphical representation of the distribution of one element versus the other and it also allows to differentiate from specimen to specimen. Series in the chart denoted each by a specific color correspond to the 4 different samples analyzed. As can be seen from the series of plots A) through O) depicted in Figure 8, it appears that all samples in the stainless steel category are related to each other since their element versus element data appear very localized in the plots compared to the silicon sample. Nonetheless, if we consider only the specimens in the stainless steel category, we see a variation in the elemental composition of some of the elements which makes us hypothesize that these samples might have originated from different batches of material. This effect is seen for some of the element versus element plots in Figure 9.

7 A) B) C) D) E) F) G) H)

8 I) J) K) L) M) N) O) Figure 8 - Plots of element VS element for fitted area values in the specimens analyzed.

9 A) B) Figure 9 - Plots of some of the element VS element composition for stainless steel specimens. C) Conclusions As can be seen from the charts comparing elements among them, Aluminum was not detected in any of the specimens analyzed. This would be congruent with the specifications of the XMET apparatus as it is unable to detect the concentration of such element regardless of the sample. Furthermore, by looking at the distribution of the plotted data, we can directly conclude that specimens came from different batches of material as they do not exhibit a close correlation in the plot. This would be the case since one specimen was silicon and the other four stainless steels and hence a direct correlation among the four samples was really not possible. Furthermore, by looking at the plots in Figure 9 it becomes clear that the stainless steel samples are not related among them as they exhibit relatively different values of element versus element for some combinations such as Ti-Cr, Cr-Ni and Ni-Fe.

10 References [1] Basic Theory of X-ray Fluorescence, LearnXRF.com. n.d. Web. 2 Nov [2] Lachance, Gerald R., and Claise Fernand. Quantitative X-Ray Fluorescence Analysis Theory and Application. Chichester, England: John Wiley & Sons, Print [3] Wirth, Karl. X-Ray Fluorescence Geochemical Instrumentation and Analysis, n.d. Web. 2 Nov [4] X-Ray Fluorescence, Wikipedia, the free encyclopedia. 5 Oct Web. 2 Nov