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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.


Figure 5. (A) Freeze dryer bell valves in closed position. (B) Freeze dryer bell valves in open position.

To freeze-dry samples

  1. Cut open the sealed sample bags and fold the top edge over to keep the bag open.
  2. Take the top of the bell off of the dryer and arrange samples in the bell, making sure no sample bags are pinched closed.
  3. Close the vacuum valves slowly so that you do not cause a large rush of air to blow the samples around. Figure 5A shows the configuration to dry samples and Figure 5B shows the configuration for loading and unloading samples.
  4. Set the freeze dryer to resemble the settings shown in Figure 6 and flip the "On" switch located on the right side of the machine.
  5. Press the "Auto Refrigeration" button (Figure 6A) and then the vacuum button (Figure 6B). The temperature will start to drop and the vacuum pump will turn on.
    1. When the temperature drops to –40°C, the vacuum is created in the bell and the pressure drops.
    2. Expect the temperature to be between –42° and –52°C and the pressure to be ~0.350 mBar.
    3. The indicator lights (Figure 6D) show how the cooling and pressure reduction are progressing. When all indicator are lights are on the freeze dryer is at its peak performance.
    4. If there is an error the red "Alarm" light will turn on. Press the "Menu" button (Figure 6C) to view it and clear it
  6. After samples are dry, slowly open the valves to let out the vacuum in the bell. Remove the samples from the bell and store them inside the desiccator until they are ready to be ground to prevent reabsorption of moisture.


Figure 6. Freeze dryer control panel. 

Grinding Solid Samples

There are three primary ways to grind samples:

  • With an agate mortar and pestle
  • With a Spex shatterbox
  • With a Spex mixer mill (tungsten carbide, hardened steel, agate, or alumina ceramic)
  • With Retsch MM400 mill (agate)

Mortar and pestle is the most common method. Below, each method is outlined.



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.


Figure 5. (A) Freeze dryer bell valves in closed position. (B) Freeze dryer bell valves in open position.

To freeze-dry samples

  1. Cut open the sealed sample bags and fold the top edge over to keep the bag open.
  2. Take the top of the bell off of the dryer and arrange samples in the bell, making sure no sample bags are pinched closed.
  3. Close the vacuum valves slowly so that you do not cause a large rush of air to blow the samples around. Figure 5A shows the configuration to dry samples and Figure 5B shows the configuration for loading and unloading samples.
  4. Set the freeze dryer to resemble the settings shown in Figure 6 and flip the "On" switch located on the right side of the machine.
  5. Press the "Auto Refrigeration" button (Figure 6A) and then the vacuum button (Figure 6B). The temperature will start to drop and the vacuum pump will turn on.
    1. When the temperature drops to –40°C, the vacuum is created in the bell and the pressure drops.
    2. Expect the temperature to be between –42° and –52°C and the pressure to be ~0.350 mBar.
    3. The indicator lights (Figure 6D) show how the cooling and pressure reduction are progressing. When all indicator are lights are on the freeze dryer is at its peak performance.
    4. If there is an error the red "Alarm" light will turn on. Press the "Menu" button (Figure 6C) to view it and clear it
  6. After samples are dry, slowly open the valves to let out the vacuum in the bell. Remove the samples from the bell and store them inside the desiccator until they are ready to be ground to prevent reabsorption of moisture.


Figure 6. Freeze dryer control panel. 

Grinding Solid Samples

There are three primary ways to grind samples:

  • With an agate mortar and pestle
  • With a Spex shatterbox
  • With a Spex mixer mill (tungsten carbide, hardened steel, agate, or alumina ceramic)
  • With Retsch MM400 mill (agate)

Mortar and pestle is the most common method. Below, each method is outlined.

Mortar and Pestle
Choose the appropriate mortar and pestle size (large or small) and place it on the counter (Figure 8). Obtain a glass slide, a sample holder, and a scoopula (Figure 8). Clean all items after each use with isopropyl alcohol and a KimWipe.


Figure 8: Mortar and pestle sample preparation set up. 


Pour 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 good and the sample looks homogenous, you can pack the sample into a sample holder to be placed in the D4.


Mixer mill

 There are two mixer mills located in X-Ray Prep. Both mills operate very similarly but do have slight differences (Figure 9; Figure 10). The 8000 is featured on the top and the 8000M on the bottom. 


Figure 9: 8000M mixer mill. (A) Safety latch (B) Minute timer (C) Seconds timer (D) Start button (E) Pause/Stop button (F) Timer countdown LCD display.


Figure 10: 8000 mixer mill. An older simplified version of the 8000M. Featured are the safety latch, timer dial, and start/stop button in the middle of the dial.


The main difference between the two mixer mills is the timer. The 8000M timer uses 2 buttons to adjust the minutes (Figure 9B) and seconds (Figure 9C), 2 separate buttons to start (Figure 9D) and manually stop (Figure 9E), and counts down time on the LCD display (Figure 9F). To operate the 8000 mixer mill, turn the knob to the desired time and press the "Start" button in the middle. That button will also stop the mixer mill. The dial does not move automatically, so if it is turned to 5 minutes it will stay there. The dial does not need be set back to 0 to work.


Grinding Vessels
There are three types of grinding vessels available: alumina ceramic, tungsten carbide, and hardened steel (Figure 11). Tungsten carbide and steel vessels are better for more robust grinding, and alumina ceramic is better for minimizing contamination. Check with the Science Party to see which vessel type is preferred.


Figure 11: Three types of mixer mill grinding vessels.


Each grinding vessel has its own components. Parts should not be shared among the different types of vessels. Combining pieces made of different materials can cause severe damage to the pieces involved.


Below are the components for each type of vessel. The steel (Figure 12) and tungsten carbide (Figure 13) both have a vessel body with attached lid and one separate lid that is screwed on. Cross-threading is very easy with these containers, so be very careful when screwing on the lid. Also note that the steel container has an O-ring, whereas the tungsten carbide does not. The alumina ceramic vessel (Figure 14) is assembled differently than the other two vessels: two cork rings are placed inside each lid, and the lids slip onto either side of the vessel body.

 

Figure 12: Steel vessel components. (A) Lid  (B) Container (C) Steel Grinding Ball (D) O-Ring 

Figure 13: Tungsten carbide vessel. (A) Vessel container (B) Lid (C) Tungsten carbide grinding ball

Figure 14: Alumina ceramic vessel components. (A) 2 cork rings (B) Vessel body (C) Alumina ceramic grinding ball (D) 2 lids

Label the vessel with a small printed label of the sample it holds. After the sample is ground, transfer that label to an 8 or 16 mL snap cap bottle that will hold the powder.


Loading the Grinding Vessel into the Mill

Put your sample inside the vessel. The material should be approximately the size of a pea to prevent any jamming and to ensure all pieces are ground up. Place 1 to 2 grinding balls inside the container. Tungsten carbide and steel vessels can take up to 2 balls. The alumina ceramic vessel is more brittle and 1 ball is recommended. Finish assembling the grinding vessel and open the lid to the mixer mill.

Figure 15: Inside the 8000M mixer mill. Highlighted is the sample holder clamp that holds the grinding vessels, the primary lock, and the secondary lock.


Hold the grinding vessel between the sample holder clamps (Figure 15), flush against one side. Still holding the vessel, start turning the primary lock. The holder will begin to clamp down on the sample. When the vessel is secured, you can remove your hand and continue tightening the primary lock until the sample is firmly gripped. Then tighten the secondary lock until it feels firm. Check the vessel to make sure the lids are resting flat on the clamps. If the vessel is ajar inside the clamp, when the motor starts the vessel can start grinding away at itself or fly loose into the machine.

Starting the Mill
Set the timer to the desired grinding time. The time will vary depending on sample material. Start with a conservative time, 2 to 3 minutes, check the material, and add more time if the sample still feels gritty. Harder rocks can go up to 10 minutes or beyond to grind down to the right sample consistency.
When the mill finishes grinding, remove the vessel the same way as it was put into the clamp: hold the vessel firmly against one clamp while unscrewing the primary lock. Keep the vessel straight and hold it firmly. If one of the lids starts to crack open, sample material will spill into the machine. If this happens, clean up the powder with a damp towel. Any leftover powder can get into the motor and damage it.

Transferring Powder
Collect a metal tray, weigh paper (large or small), 8 or 16 mL clear snap cap bottles, a scoopula, Kim Wipes, and isopropyl alcohol. Clean all materials with isopropyl alcohol. Place a piece of weigh paper on the metal tray. Pour the sample material from the grinding vessel onto the weigh paper. Use the scoopula to scrape the sides and lids of the vessel to remove extra material. Transfer the sample from the weigh paper into the glass vial. Label the vial with a small printed label and label the cap with a permanent marker.

Cleaning the Vessels
Clean the grinding vessels with a toothbrush and DI water. In some cases the vials are still dirty or have sample stains on them. If so, take a small amount, approximately 5 mL, of silica sand and grind it in the mixer mill for ~3 minutes. Then pour out the sand and clean the vessel with DI water and a toothbrush or Greenie Meanie. Lay out cleaned vessel parts on a Kim Towel and dry with a Kim Wipe. The cork rings take a longer to dry, so collect fresh, dry rings before grinding the next sample.
Then can now pack the samples.



Retsch MM400 mill


Grinding Jar

Each grinding jar has the main jar, the lid and ball. The inside of the jar and lid are lined with agate and the ball of made of agate. Poor freeze dried soft sediment (not hard rock) sediment grains into the jar. Fill the jar half way to three-fourths of the way up with sample. Place one ( can do two) grinding balls in the jar. Clean off any of the sediment sample with a kimwipe that has gotten onto the jars threads and screw the lid on. Be mindful not to cross thread the lid to the jar.


Loading the Jar into the Grinding Mill

Place closed grinding jar horizontally in the clamps. Verify the pin is in closed potion and tighten the clamps by turning the handle until the jar is securely tighten 9 hand tight is good).


Starting the Mill


A) Preset programs. B) The shaker frequency C) The time grinder is set for D) The start and stop

Transferring Powder





Cleaning the Jars

To clean the jars rinse with DI water and kim wipes until kimwhipes come out clean. Finish cleaning by rinsing with isopropal alcohol and drying with kim wipe.

Shatterbox
Shatterbox vessels are not commonly used for powder XRD samples. Please refer to the ICP Prep User Guide for instructions for using the shatterbox.




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