Standardized EDS Analysis as of 11/4/2013 by Dave Hirsch, based on work by Aiden Brehan, 2010-2013 Initial Settings: Standardized EDAX analysis of minerals requires that in the same session you are able to analyze both a mineral standard and the unknown in question. An apparatus has been fabricated for Western’s SEM to hold both the “standard block” and whatever unknown sample you are trying to analyze. Before inserting both into the SEM, make sure that both are clean and properly coated for 20 seconds with Au-Pd. Next, make sure that the stage has been calibrated and insert the holder apparatus into the center slot. Align the long edge of the standard block perpendicular to the edge of the SEM chamber door. Doing this ensures that all standards will be within the scanning range (40mm x 40 mm square) of the SEM instrument. Tighten the small allen screw at the post of the apparatus. Pump down the instrument according to procedure. Once the instrument has been pumped down, select a grain to use as a standard (it should be as similar to the unknown as possible, while containing all the elements needed to be analyzed), and manually adjust the focus of the beam using a WD (Working Distance) from 22-23mm. When the image is best in focus, double click to create a red selection box and select a section of standard grain you wish to use. A good section of a grain will show a uniform hue in the BSE image. This hue should be somewhat consistent throughout the grain; it is an analog for the composition of the grain. Observe the readings in the lower left-hand corner of the EDAX Genesis window labeled CPS and DT%. The ultimate goal for standardized analysis is to gain a CPS between 1000 and 2000 and a DT% of 20-35. Depending on the behavior of the tungsten filament that creates the electron beam, different settings will create these readings. Attaining this target reading can normally be done within this range of settings: Vega TC settings: WD (Working Distance) of 22-24mm PC (Probe Current) of 6 to 8 depending on the scope’s mood at that particular moment. 20 or 15 kV Slight adjustment of “Heating” (maximum 3-5%) in some cases for fine-tuning. EDAX Genesis settings: Select various Amp Times (top right corner, usually 102.4µs) Once you have attained these readings, allow a couple minutes for the readings to become consistent. Consistent readings should show fluctuations for CPS of about 100 and 2-5 % for DT%. Both should remain in this same range for the duration of the reading. Select “MEMORY” then “A” in the Stage Control window to commit this section of this standard grain to memory for further use. Analysis of Standard: Once optimal settings and stable CPS and DT% readings have been attained, select a 500 second count time from the top right corner of the EDAX menu. Hit collect and allow the 500 second count time to run. Once the count has elapsed, identify all elements prominent in the standard. To enter standard data, maximize the QUANT menu on the right hand side of the EDAX genesis window. Select ZAF list, then select all elements you have standard data for in the window that appears. If a warning appears, select ok. Next select the STD button. In the window that appears, select the bubbles labeled “Compound” and “element” then select the button SETUP. In the sub window below this button you will see all of the elements you labeled in your spectrum. Select each one and enter the wt.% of each element in your standard (see appendix below). Once you have entered all this data, select the button labeled RZAF, check the box for “use as compound” and hit ok. Make sure the values you entered are correct and select OK. You should be back to normal view now and your spectrum will have a blue outline. Analysis of Unknown: Once you have attained a spectrum of the standard, find the unknown that you wish to analyze. Using the same criteria as before with the analysis of the standard, obtain a selection box of a satisfactory section of the unknown. As opposed to the analysis of the standard, use a small box for a specific section of the unknown. Make sure that the settings remain the same as for the Standard. Scanning in a different section of the analysis window may also generate different CPS and DT% values. It is most important that these values remain similar for both the standard analysis and unknown analysis. Once you have attained reasonably stable agreement between the standard and unknown CPS and DT% readings, hit “COLLECT” for the same count time used for the standard (most likely 500 sec). Allow this time to elapse. Once it has, you are ready to quantify your results. Be sure your analysis Type is set to “Oxy By Diff” (right-click on the text next to the QUANT button), then hit QUANT on the right hand side of the EDAX Genesis window and you should see a new window with quantified values for the composition of the unknown based on the known composition of the analyzed standard. Save the spectrum and values to a PDF file by choosing to Print both, then choosing the PDF printer out of the list. Accuracy and Precision: [Under construction, but Aiden found uncertainties in the range of 5% relative] Appendix I: Standard Locations A-1 B-1 C-1 A-2 B-2 C-2 A-3 B-3 C-3 A-4 B-4 C-4 A-5 B-5 C-5 A-6 B-6 C-6 A-7 B-7 C-7 A-8 B-8 C-8 A-9 B-9 C-9 A-10 B-10 C-10 Standard Anorthite Anorthoclase Apatite Augite Augite (Cr) Diopside Dolomite Gahnite Garnet Hornblende Olivine Siderite Strontianite Zircon Glass A-99 Glass A Glass B Glass C Glass D Glass, IR-V Glass, IR-W Glass, IR-X Glass, Rhyolitic Reference # NMNH 137041 NMNH 133868 NMNH 104021 NMNH 122142 NMNH 164905 NMNH 117733 NMNH 10057 NMNH 145883 NMNH 87375 NMNH 143965 NMNH 111312/444 NMNH R4260 NMNH R10065 NMNH 117288-3 NMNH 113498-1 USNM 117218-4 NMNH 117248-1 NMNH 117218-2 USNM 117218-3 USNM 117083 NMNH 117084 NMNH 117085 USNM 72854,VG568 Comments Very fine Table 1: Location, name and reference number of each mineral with comments pertinent to successful application of each standard. Standard block is catalogued as columns A, B and C from left to right. From the bottom (end with no empty holes) rows are numbered 1, 2, 3, 4, etc.