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The goniometer has 2 circles: the theta (θ) circle, which sets the sample position, and the 2θ circle, which moves the detector. The position of the X-ray tube remains fixed. The goniometer center is defined by the concentric circle axes.

Sample Holders

Sample holders for powdered XRD samples are steel or steel with a silicon or quartz spacer. The selection of a sample holder depends on the volume of sample to be analyzed.

Detector

The VANTEC-1 detector features the fastest simultaneous recording of XRD patterns within a wide 2θ angular range. For powders, measurement time is reduced by a factor of up to 100 in comparison to other detectors.

Detector Optics

• Detector window slits
• Debye slits
• Kβ filter: suppresses characteristic Kβ radiation
• Antiscatter slits: reduce primary air scatter, which influences diffraction background patterns
• Soller slits: reduce primary and secondary air scatter
• Window opening scales

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Solid samples are prepared for X-ray diffraction by grinding, which depending on the sample matrix, the size of the sample, and/or quantity of prepared material needed can be accomplished by several different methods.

Drying Samples

Freeze-dry sample(s) for at least 12 hours before grinding. If the samples still feel cold when removed from the dryer, the samples still have moisture in them and need to dry longer.
The freeze dryer is comprised of a sample "bell" chamber and a Labconco freeze-dryer. On the bell are two valves, as shown in Figure 5. Each valve has an "Open" and "Closed" position. The top valve controls the vacuum inside of the bell, and the bottom valve controls the air flow between the cooling coil and bell. A valve parallel with the tube is open and allows air flow; a valve perpendicular with the tube is closed. In Figure 5, configuration A (closed) will hold a vacuum, but configuration B (open) will not.

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This is the recommended treatment for carbonate removal. The process is slightly more involved than the HCl procedure, but far less damage is done to the mineral structure. The following steps are from Kitty Milliken (UT-Austin).

1. Place ~2 cm³ of undried sample into a 50 mL centrifuge tube. This should approximately fill the bottom cone of the tube. Then add 25 mL of a 10% acetic acid solution. Mix well and let sit until the reaction ceases; this may take a few minutes or up to an hour. The samples can sit in the acid overnight with no harm. You may need to stir the sample and break it up with a spatula a few times.
2. Periodically shake the sample until the reaction has stopped (i.e., no more bubbles).
3. In the Chemistry Laboratory, spin the sample in the centrifuge for 15 minutes at 1500 rpm
4. Decant the acetic acid solution into the sink while running water down the drain to flush the acid through the pipes.
5. Add 25 mL of DI (nanopure) water to the centrifuge tube and centrifuge again for 15 minutes at 1500 rpm.
6. Decant the water.
7. sample in  centrifuge tube with 25 ml of 10% Acetic Acid for at least 1 hour to decarbonate (it helps to place the centrifuge tubes on the agitator in the cold room) 
8. Centrifuged for 15 mins at 1500 rpm, decant and wash with 25 ml of nanno pure water (3X to remove all Acetic Acid)Repeat the "wash cycle" (Steps 4 and 5). The water wash should be done at least twice to flush out all of the acetic acid. When the sample stops smelling strongly of vinegar, you can move on to separating clay.

Hydrochloric Acid Treatment

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"Quick and Dirty" Clay Separation Method: Not for Semi-quantitative Analysis

1. Add 25 ml of 1% Borax solution to the clay plug 
2. Dismembrated sample (machine is auto set on time), to remove the >2 um clay fraction
3. Centrifuge for 4 mins at 750 rpm, decant the suspended liquid into a separate centrifuge tube (you should end up with a ~full centrifuge tube of suspended clay)
4. Repeat steps 3-5 on the remaining >2 um fraction
5. Centrifuge the <2 um fraction for 15 mins at 1500 rpm to remove the Borax solution 
6. Decanted and add 25 ml of nanno pure water
7. Centrifuged for 60 mins at 3000 rpm, the liquid decanted before loading onto a zero background silica disk
8. In centrifuge tube, mix a small amount of bulk sample (~5 mL; fresh, not dried) with 1% borax solution. Use an ultrasonic bath or dismembrator, if necessary.
9. Centrifuge the borax solution/sample mix at 1000 rpm for 5 minutes to remove the >2 µm size fraction.
10. Decant the borax solution (containing suspended clays) into a new centrifuge tube and spin it at 1500 rpm for 15 minutes to remove the remaining <2 µm clay size fraction.
11. Decant the borax solution and wash the clay residue with distilled water.
12. Spin-down again at 1500 rpm for 15 minutes. Repeat Steps 4 and 5 as necessary to remove the borax.

Preparing the Mount

Clay mounts are put onto a zero-background silicon disk that fits into a 2 mm steel sample holder (Figure 21). Only put the disks into sample holders that have a hole drilled in the bottom. The hole allows the disks to be taken out, otherwise they are stuck inside the holder. The disk should sit flush with the sample holder.. Some of the disks are at different depths, so a quartz insert disk can also be put in the bottom of a sample holder with the silicon disk on top.

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1. Remove the <2 µm size fraction by collecting the uppermost 1 cm of solution with an eye dropper (it helps to add a little isopropanol). If necessary resuspend flocculated clay particles using the dismembrator and add more borax solution.
2. If material is still very suspended, try centrifuging the samples for 4 minutes at 750 rpm. In this instance, the >2 µm size fraction will be the only fraction suspended in the liquid and all the larger grains will be packed in the bottom. Take the suspended material with an eyedropper and put it on the quartz disk.
3. Make an oriented clay mount by placing 2–3 drops (enough to cover the disk) of clay suspension directly onto the silicon disk. If the material is not spreading evenly, add a drop or two of 70% isopropanol and spread the material around with a small glass rod. Once spread, let the sample dry in the desiccator. The clay particles orient themselves as the solution dries on the disc.
Once the sample is dry, you are ready to run it through the D4. If there are additional treatments requested, continue to the sections below.

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1. Open scan (remember the QAQC parameter file Corundum QAQC continuous 20 to 130.dql ran without the anti-air scatter screen).
2. Subtract the background (do not append, just simply close background menu) (Figure 29).

Figure 29: EVA diffractogram.
The arrow points to the Background Subtract tool.

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