Preparation of Pressed Powder Samples for XRF Analysis

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 110oC, 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.