Use of cryotongs: freezing & storing a crystal

• Established a ‘standard’ pin length that will keep the crystal in the right place in the cryotongs
• Ensure that all your pins and top hats conform to the standard length
• Stream freeze a crystal onto the magnetic base on the goniometer
• When you are ready to store the crystal, label a cryovial
• Fill a 2 litre intermediate Dewar with liquid nitrogen and label a cryocane
• Fill a glass sample handling Dewar with liquid nitrogen
• Place the labelled vial in the vial holder and submerge them both in the liquid nitrogen. Also place the cryotongs in the glass sample handling Dewar. Put on a pair of cryogloves
• Bring the small Dewar and vial holder and the vial as close to the goniometer as possible. Inside the generator housing is ideal
• Bring the cold cryotongs up to the crystal. Separate the cryotongs and clasp the top hat and crystal in them. Move the cryotongs sideways to break the magnetic hold of the magnetic base on the top hat
• As soon as the top hat and sample are held in the cryotongs, immerse the tongs and sample in the glass sample handling Dewar
• Transfer the crystal to the magnetic wand by placing the wand in the Dewar and letting it cool down. Bring the wand up to the base of the top hat and release the tongs carefully. Remove the tongs from the Dewar
• Bring the vial holder and vial up underneath the pin and top hat. Locate the top hat into the top of the vial
• Move the wand SIDEWAYS to break the magnetic hold between the top hat and wand
• As soon as the top hat and sample are inside the frozen vial, return the vial holder and vial to the glass sample handling Dewar so that the vial and sample are fully submerged in liquid nitrogen
• It is important to note that if a lid is to be placed on the vial, a blowhole should be drilled in the lid before it is used. It is recommended that the lid is placed on the vial if canes with lateral extrusions (to rest the vial base on) are to be used
• Next, bring the vial holder up so that the top of the vial just breaks the surface of the liquid nitrogen. Put the lid on the end of the lid opener and screw the lid on the vial. Do NOT screw the lid on too tightly as vial lids sometimes freeze on and can be very hard to get off
• Immerse the whole vial and lid in the liquid nitrogen until the surface of the liquid nitrogen goes flat and equilibrium is reached
• Lift the vial holder and vial from the glass sample handling Dewar and remove the vial. Put the vial holder down
• With the free hand lift the pre-labelled cane out of the 2 litre Dewar and place the vial on it at the next free position, working from the bottom of the cane upwards
• Make a note of the crystal shape, the marking on the vial and cane and the date. When the canes are full, transfer them to the main storage Dewar all at the same time. This avoids opening and closing the storage Dewar unnecessarily, preventing ingress of moisture from the air. Note that the tongs should be warmed up and dried after each use to stop them freezing together
  

Next page >

< Back to LMB Guide Home