PowerPoint PresentationWhat’s the point?Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26UW- Madison Geology 777Electron Probe MicroAnalysisRevised 3/30/2014What’s the point?If it don’t fit in the machine, you ain’t gonna get any numbers. If it ain’t polished right nice and purdy, you ain’t going be able to trust the numbers like you want.If your epoxy ain’t cured nice and solid, it’s gonna bubble and degas inside the probe and make John real unhappy.If it ain’t conductive, it will charge and your numbers will be in the toilet.UW- Madison Geology 777UW- Madison Geology 777It does make a difference: Proper sample preparation can be critical to the Proper sample preparation can be critical to the success of your EPMA work. success of your EPMA work. A successful experiment (creating diffusion couple, achieving multiphase equilibrium, locating critical rock specimen, etc) can be result in unsuccessful EPMA results if the proper sample mounting and polishing is not done. Don’t be hesitant about asking questions.UW- Madison Geology 777 What is your goal? What are the “issues” with your samples? Make sure your sample preparation is appropriate. Do some “dry run” preps before you waste your precious experimental materials. There are several different ways to prepare samples for the probe. Generally people follow in the footsteps of those before them, which is many times correct – but not always. You can learn new tricks from others (I have). Sometimes “normal” sample preparation (usually the polishing aspect) yields a poor result for the type of EPMA the user desires, whereas for another user, they could “make do” with it. An example is a hard brittle material in epoxy. First, cutting rapidly with high speed saw (in a hurry?) fractures the material. Then normal polish (with loose abrasive) easily polishes the softer epoxy and makes rounded edges of the material (the little that is left). This sample would yield lousy diffusion profile data–but you could maybe get a few data points out of the center where the curvature is slight.GoalsUW- Madison Geology 777Specimen size - mount size - holder size - probe shuttle size:Shuttle: the base we insert into the probe. We have 2 shuttles, both the same size. There are 2 slots along the edges and a hole at the ‘south’ end, all for the insertion rod.Holder: this is the thing we insert into the shuttle; we have many different styles of bases (thin sections, 1”, 1 1/4” and 2” rounds, but they all have the same outside dimensions to fit into the shuttle. It is held in the shuttle by 4 screws.Mount: this is the thing you bring to the lab; your specimen is attached somehow, either embedded in plastic or epoxy, or glued to a glass slide. Round mounts are held in place with set screws; thin sections are held in place with springs. They are top referenced (pushed up from below against a stop) and therefore the complete top must be flat and smooth.SizesShuttleHolderThis is the sample holder for six 1” diameter mountsUW- Madison Geology 777 90% of the samples used in EPMA are 1” (outside diameter) rounds, smaller plugs mounted in brass 1” diameter holders, or geological thin sections. The 1” diameter rounds can have the specimens mounted with epoxy inside a 7/8” high phenolic ring forms (e.g., Buehler 20-8151) or 1” diameter compression mounts. There are a few other sample sizes that can be accepted by the probe; ask if you have questions.XSample MountsDo not use the (usually red) soft plastic pipe end covers for molds; they deform (epoxy is exothermic) and yield improper angles.UW- Madison Geology 777Many people need to mount crystals or grains. Typically like this:1.Separate out the grains to be probed2.Determine what size holder they will need to be mounted in3.Place he grains on a sticky tape, within the required perimeter4.Place the round holder over them, sticking firmly to the tape5.Pour the epoxy over the grains, without creating air bubbles. This can be difficult if using the very small (1/4”) mounts.6.Wait for hardening7.Remove and polish (itself a whole other procedure).Mounting grainsIn 2014, we have come upon an important improvement in step 3. Before, we used regular double-sided sticky tape, which has a tendency to pull up in the middle upon hardening, making it hard to have all small grains polished to the same extent. Now there is Kapton Tape. Much better.UW- Madison Geology 777If they are slightly greater, they can be unknowingly forced into the chamber, but they are impossible to remove, and the chamber must be vented to remove them manually. See image to right, view of shuttle upside down, showing mount bottom extending above/ beyond the shuttle bottom surface.Mounts cannot be more than 7/8” maximum heightUW- Madison Geology 777Mounting MediaMost samples need to be encapsulated for ease of mounting in the probe or SEM and for polishing; encapsulants are normally either compression mounts, curing at 3-4000 psi, 150°C, using Phenolics or Epoxies or Acrylics or castable (cold), using Epoxies or AcrylicsDo not use epoxies you purchase at a hardware store. Only use ones created for metallographic/microscopic applications (high vacuum, low degassing). There are several suppliers, with Buehler being one commonly used (higher price but excellent product).UW- Madison Geology 777Epoxy EvaluationsThe SIMS lab at Edinburgh has a web page where they give the results on a variety of tests of various epoxies used possibly for SIMS work. This is exactly relevant to the needs of an electron microprobe or SEM (vacuum outgassing, beam damage, etc).http://www.geos.ed.ac.uk/facilities/ionprobe/EpoxyResins/Also valuable sample preparation information from the Stanford SHRIMP lab:http://shrimprg.stanford.edu/Sample%20Preparation.htmUW- Madison Geology 777Mounting Media - comparisonOn this and the next slide are 2 tables from the Buehler (online) catalog, reprinted here to give you a feel of the different important parameters to consider in choosing mounting media.UW- Madison Geology 777UW- Madison Geology 777Mounting Media - devil in the details• Epoxy mixing and curing: it is very critical to get some things right: fresh epoxy —old is no good; if not sure, mix up a small
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