School of Physical and Geographical
Sciences
Geography, Geology and the
Environment
Preparation of Pressed Powder Pellets for XRF
Reagent
This will be prepared by a technician.
Polyvinylpyrrolidone – methylcellulose binder
Solution A :
Add 35g Polyvinylpyrrolidone (PVP) to 175ml alcohol. Stir vigorously until all
dissolved to form a yellow solution
Solution B :
Heat 200ml distilled water to 90oC in a 1litre beaker. Remove from heat and add
slowly 20g methylcellulose with vigorous stirring until uniformly dispersed in the
liquid. Allow to cool to about 40oC
Add solution A to solution B stirring vigorously until a viscous, slightly yellow liquid is
formed. You may need to thin this slightly with ethanol before use.
Method
1.
Clean agate pestle and mortar with an alcohol-soaked tissue.
2.
Weigh out approximately 8g of rock powder and transfer to the mortar.
3.
Add up to 1ml of PVP solution and mix in using the pestle.
The amount of binder needed varies with rock composition, ultra-basic rocks
need very little whereas granites need a lot.
4.
Clean the platens and die with an alcohol-soaked tissue.
5.
Transfer the powder to the die and press to 10 tons for 20seconds.
6.
Release the pressure and remove the pellet by inverting the die, removing the
base-plate, inserting the aluminium spacer cap and pushing out the pellet using
the press.
Should the surface of the disc be cracked, grind the disc to a powder and
continue from step 3, adding a few more drops of PVP solution.
7.
Write the sample number on the outer edge of the pellet.
8.
Place the pellet on a wire support and dry in an oven at 110 oC, preferably
overnight.
9.
Store pellet in a polythene bag and label bag with your name and the job
number.
Reference
Watson, J.S. 1996; Fast, Simple Method of Powder Pellet Preparation for X-Ray
Fluorescence Analysis. X-Ray Spectrometry, 25, 173-174.