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Freeze-dry sample(s) for at least 12 hours before grinding. If the samples still feel cold when removed from the freeze dryer, the samples still have moisture in them and need to dry longer. There is one freeze-dryer in the Thin Section Lab. If broken, use the freeze-dryer of the Chemistry Lab.
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 1. 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 1, configuration A on the left (closed) will hold a vacuum, but configuration B on the right (open) will not.
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- Cut open the sealed sample bags and fold the top edge over to keep the bag open.
- Take the top of the bell off of the dryer and arrange samples in the bell, making sure no sample bags are pinched closed. Close the top valve of the bell chamber (Figure 1A).
- Open the vacuum valve (bottom valve) slowly so that you do not cause a large rush of air to blow the samples around. Figure 1A shows the configuration to dry samples and Figure 1B shows the configuration for loading and unloading samples.
- Flip the "On" switch located on the right side of the Freeze Dryer located in the Thin Section Lab.
- Press the "Auto Refrigeration" button (Figure 2, arrow A) and then the vacuum button (Figure 2, arrow B). The temperature will start to drop and the vacuum pump will turn on.
- When the temperature drops to –40°C, the vacuum is created in the bell and the pressure drops.
- Expect the temperature to be between –42° and –52°C and the pressure to be ~0.350 mBar.
- The indicator lights (Figure 2, arrow D) show how the cooling and pressure reduction are progressing. When all indicator are lights are on the freeze dryer is at its peak performance.
- If there is an error the red "Alarm" light will turn on. Press the "Menu" button (Figure 2, arrow C) to view it and clear it if necessary.
- After samples are dry, close the bottom (vacuum) valve to stop the air flow between the cooling unit and the bell. Slowly open the top valve to release the vacuum in the bell. Remove the samples from the bell and store them inside the desiccator (located in the X-Ray Lab) until they are ready to be ground to prevent reabsorption of moisture.
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Choose the appropriate mortar and pestle size (large or small) and place it on the counter. Obtain a glass slide, a scoopula, and a sample holder (Figure 3). Sample The sample holder shown in Figure 3 is a frontloading sample holding holder for the D4 Bruker XRD.Clean all items after each use with isopropyl alcohol and a Kimwipe to avoid cross-contamination.
Figure 3. Mortar and pestle sample preparation set up to grind soft sediment.
Pour freeze-dried sample into the mortar and grind the sample with the pestle. When finished, the sample should be the consistency of talc powder. Test the sample by taking a pinch and rubbing it on your skin. If the sample feels gritty, it needs to be ground more. If the texture is talc powder like and the sample looks homogenous, you can pack the sample into a sample holder to be placed in the Bruker or Aeris XRD sample area.
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The 8000 mixer mill (Figure 4) is located in the X-Ray Preparation area of the Thin Section Lab.
Figure 4. Spex 8000 Mixer Mill. Featured are the safety latch, timer dial, and start/stop button in the middle of the dial.
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Each grinding jar for the Retsch mixer mill (Figure Mixer Mill (Fig. 11) has a main jar, a lid, a ball, and a white a white teflon spacer. Use the Teflon spacer to avoid damaging the agate (Figure 12). The inside of the jar and lid are lined with agate and the ball is of made of agate.
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Pour the freeze dried soft sediment (not hard rock) grains into the jar (Figure 12, step #1). Fill the jar half way to three-fourths with sample. Place one grinding ball in the jar (Figure Figure 12, step #2). Clean off any of the sediment sample with a kimwipe Kimwipe that has gotten onto the jars threads and screw the lid on. Be mindful not to cross thread the lid to the jar.
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Place closed grinding jar horizontally in the clamps clamps with the pin in open position. Verify Verify the pin is in closed position (Figure 13) and tighten the clamps by turning the handle until the jar is securely tighten (hand tight is good). After the grinding jars are secured in the clamps, the pin is in the closed position and the clear cover is closed it is time to select grinding settings (Figure 13). Close lid and select desired program to run.
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Figure 13. Retsch jar clamp
Starting the Mill
Press "PROG" to go through the list of programs already created (Figure 14, arrow A). Program 1 (A) is currently set for 12 min at 25 1/s. This setting is good for clay rich material. Softer sediments such as CaCO3 typically need less time. It is important to only grind soft sediments in the agate jars and hard material should be ground in the shatter box (see XRD Sample Preparation Hard Rock). Press "START" to start a program (Figure 14, arrow D). After grinding cycle has completed turn knob counter clockwise and pull pin up and into its open position (Figure 13). Unscrew clamp and open jar to verify grind size. If sediment is still too coarse regrind.
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Figure 14. A. Preset programs. B. The shaker frequency. C. The time grinder is set for. D. The start and stop.
To create a program, press "PROG" and choose a program number (you can create up to 9 different programs) (Figure 14, arrow A). When ready, press "SET" (Figure 14, arrow A), and numbers on screen start flashing. Select a frequency (Figure 14, arrow B) and a time (Figure 14, arrow C) by pressing "-" or "+". Press "SET" to save your program, flashing stops. Then press "START" to run the program just created (Figure 14, arrow D).
Transferring Powder
After grinding is complete, rotate clamp counterclockwise and pull the pin up into the open position (Figure 13). When the pin is in the open position, unscrew the black knob until grinding jar is loose enough to remove from clamps. Pour powder onto weigh paper or directly into clean and labeled sample bag or sample vial.
Cleaning the Jars
To clean the jars and grinding ball rinse with DI water and kim wipes until kimwhipes come Kimwipes until the Kimwipe comes out clean. Finish cleaning by rinsing with isopropal isopropyl alcohol and drying with kim wipeKimwipes. Use the bent metal spatula to pry out the white teflon Teflon spacer, we have spares but those can be reused many times.
Shatterbox
Shatterbox vessels are not commonly used for sediment XRD samples. Please refer to the XRD Sample prep for hard rock samples for instructions for using the shatterbox.
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