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MB-SERIES

MERRILL-BASSETT TYPE DIAMOND CELL

Specifications:

The triangular shaped instrument, with the corners rounded, is 3 cm from the base of the triangle to the center of the curvature. The thickness, with the diamonds in place, is 1.5 cm. The weight of the cell with mounting bracket is 85 grams. The beryllium discs are 12.5 mm in diameter and 3 mm thick; the diameter of the opening is 1 mm. Each Type I diamond, with 16 pavilion facets, weighs approximately 1/6 carat (1 carat = .20 g) and has a pressure bearing surface of 0.6 mm. Type IIa anvils are used with IR.

This diamond cell has been assembled with two diamonds each weighing approximately .20 carats with 0.6 mm culets or pressure bearing surfaces. The anvils are attached to beryllium discs with epoxy cement unless annealed stainless steel discs are requested.

MB Cell Diagram

 

MB Series in use

The alignment and the parallelism have been completed by H.P.D.O., Inc. prior to shipping, therefore simply position the red markings when loading your sample. Also, check the opposition and the parallelism under a low power microscope consistently.

Diamond is the hardest and least compressible material formed in nature, however diamond will easily scratch diamond. To avoid damaging the diamond anvils certain precautions must be observed. Keep a piece of paper between the anvils when the instrument is not in use. Care must be taken when assembling the cell to prevent the damage of the diamonds.

 

CAUTION: DO NOT DEVELOP PRESSURE ON THE BARE DIAMOND ANVIL SURFACES.

The working surface can be cleaned by wiping with a Chem-Wipe or other lint free tissue. Solvents such as acetone or alcohol are used to wipe the anvil faces.

WARNING: Excessive contact of solvents to the epoxy and glue will loosen the bonding of the anvil to its mount.

The undersides of the diamond anvils are cleaned by placing a drop of acetone in the aperture and scrubbing with a round toothpick.

The diamond cell can also be attached to a guide plate in the sample compartment of FTIR spectrometer or on the stage of IR microscope.

Although a pre-drilled gasket without indentation works fine as well, a pre-indented gasket is recommended before a hole is drilled. Inconel, a metal foil 0.01" thick, is supplied as gasket material. Any burrs around the hole should be removed with a tip needle or a micro drill bit. The sample, usually a 100 micron die or less, with a pressure calibrant and pressure transmitting medium is sealed by tightening three Allen cap screws. In order to maintain the alignment and the parallelism of the anvils during the change of each pressures, it is very important to monitor the thickness for the cell. A micrometer can then be used. It is also a common phenomenon that the hole will wander around under pressures; which might result in the failure of the chamber seal if the pressure is not evenly applied to the diamond anvils. Hence, it is always a good idea to re-exam your sample under a microscope each time you have the pressure changed. The pressure range of this instrument is about 100 kbars. The pressure increase is very sensitive with the squeeze of the cell. Therefore, a good sense of very fine adjustment is necessary when tightening three screws sequentially.

Also be aware that the indented gasket won't return to the previous thickness after routinely altering the pressures.

 

INSTRUCTIONS

The Merrill-Basset type diamond anvil cell can be used to study physical properties of liquid or solid samples under measurable pressure conditions.

CAUTION: DO NOT DEVELOP PRESSURE ON THE BARE DIAMOND ANVIL SURFACES.

Store the instrument with a piece of cardboard between the two diamond anvils to prevent abrasions. Anvils should be inspected before and after each use.

CLEANING THE ANVILS

The anvils can be cleaned by wiping acetone or alcohol across the working surfaces using tissue paper twisted into a pointed tip. Do not let the solvent come into contact with the epoxy as it will eventually loosen the bond holding the diamond to its mount. The undersides of the diamond anvils are cleaned by scrubbing with a round toothpick or placing a drop of acetone into the aperture if necessary.

HIGH PRESSURE STUDIES:

  1. Clean the two diamond anvils as instructed above.
  2. Observing parallelism:
    Align the red markings and assemble two triangular plates carefully with fingers. Insert three Allen cap screws (#10-32) into the instrument and turn until firm. Do not apply pressure on anvils yet. Observe the fringe pattern with transmitted white light under magnification. (Pressure calibrants such as ruby chips should be distributed evenly around the sample for monitoring hydrostatic pressure conditions.) Carefully manipulate the three Allen cap screws until only one light fringe is seen, showing the parallelism of the diamond anvils.
  3. Measure and record the height of the three sides of the instrument with a micrometer for future reference in maintaining parallelism.
  4. Slowly disassemble the instrument.
  5. Gasket preparation:
    A pre-indented gasket is recommended prior to making the sample chamber hole. Make alignment markings on the gasket and the diamond cell with wax or nail polish for future reference when positioning the gasket (the rounded rectangular gasket, "x7/32"x0.01", and a spacer secured by a #2-56 screw are provided.) Indent the gasket to half its thickness, then drill a hole as close to the center of the indentation as possible. Remove any rough edges (burrs) around the hole with a rat-tail file or a micro drill bit. If a pre-drilled gasket is used, position the hole as close to the center of the culet as possible. Then indent the gasket and clean any rough edges with #78, #79 or #80 drill bits.
  6. Sample preparation:
    Cut soft samples into small pieces (e.g. 50 microns die). Harder samples may be polished with fine grit sandpaper and reduced by using a sharpened needle.
  7. Loading sample:
    The rounded rectangular gasket is centered on the lower anvil and held in position by a screw. Note previous alignment markings.
  8. Level the lower support and load the sample, pressure calibrant (e.g. ruby chips) and pressure transmitting medium (e.g. liquid argon) under magnification1. Several attempts may be needed when performing this step. After completing this step, proceed to step 9 immediately.
  9. Assemble the instrument and tighten the three Allen cap screws sequentially in very small increments until a moderate amount of pressure is applied to the gasket. This procedure is needed to ensure the pressure-transmitting medium has been successfully loaded.
  10. Observe the chamber hole. Under pressure, the hole will change shape slightly. However, if the hole is significantly deformed, the instrument may have lost the pressure medium. if medium loss is uncertain, apply more pressure by tightening the three Allen screws and observing the sample hole for any changes. Begin the process from step 1 if the pressure medium has been lost. Otherwise, proceed to step 11.
  11. Measure and record the height again as instructed in step 3. The parallelism can be maintained by comparing these measurements with the data obtained earlier in step 3.
  12. Pressure calibration: Ruby fluorescence can be used to calibrate the in-situ pressure. The frequency shifts of the R1 and R2 lines determine the pressure by using the following formula:

    Where Δλ and λ0 are the wavelength (in nm) change under pressure and the wavelength at ambient pressure respectively. Lower case letter b is a parameter, would be 5 or 7.665 corresponds to non-hydrostatic or quasi-hydrostatic pressure respectively. Light sources using an argon ion laser from 488 nm and 514.5 nm lines are commonly used in this technique.
  13. Record the current pressure.
  14. X-ray studies only: Attach the X-ray bracket supplied by High Pressure Diamond Optics, Inc. to the diamond anvil cell with two #2-56 screws. Position the instrument to the goniometer head. Note that the diamond anvil cell should have come with beryllium disks as diamond mounts to be used for X-ray studies.
  15. Proceed with the experiments.
  16. Altering Pressure:
    The pressures can be repeatedly altered by tightening or loosening the three Allen screws. Refer to steps 2, 3, and 11 for maintaining parallelism. The chamber hole may shift under altered pressures. Turn the Allen cap screw(s) to move the chamber hole toward the opposite direction if the hole is off center to the culet. Notice that turning the screws will change the pressure. Follow this step closely to avoid sample failure.
  17. Calibrate the pressure according to step 12, then continue experiments.
  18. Disassemble the cell by loosening the screws sequentially in small increments. Store the diamond cell as instructed.

 

1 Pressure calibrants such as ruby chips should be distributed evenly around the sample for monitoring hydrostatic pressure conditions.

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Copyright 2008 by High Pressure Diamond Optics, Inc.
Last updated: August 12, 2008