Hull Geological Society
Mike Horne FGS
This is unfinished work that has not been edited or peer reviewed by the Society.
The preparation of samples for XRF analysis
The sample of marl, clay or chalk is dried in a
oven.
The ball mill is cleaned. The mill is put on
the scales and tared. Then 7to 8g of sample is weighed into the mill (pieces of
chalk are picked out of marl samples when possible) and the mill tightly closed.
The sample is then shaken in the mill, 5 minutes is usually enough for a marl or
chalk sample, longer is needed for an indurated sample. The powdered sample is
tipped out into a beaker. [ The mill is usually then cleaned ready for the next
sample] A binder (Moviol) is then added to the powder, 8 drops for a marl sample
and 12 for a chalk, and mixed thoroughly, so that it binds the powder but is not
sticky.
The chamber of the 30 ton press is cleaned. The
bottom platten is placed in the chamber, shiny side up, and the sample added,
evenly. The top platten is placed on top, shiny side down, and the sample gently
tamped down. After activating the extract fan in the fume hood the vacuum pump
is plugged in and switched on and the needle valve closed. The sample is then
pressed, slowly at first, up to a pressure of 15 tons. [ clean beaker for next
sample] The pressure is slowly released followed by the vacuum.
The chamber is taken out of the press,
holding the bottom in place and the chamber inverted. The pellet is then pushed
out of the chamber using the Perspex ring in the press.
Taking care to hold the pellet by the edges,
the pellet is then numbered on the edge, and placed to dry on the rack, best
side down. The pellet number and original sample number are entered in the log
book. The pellet is left to dry for about a day, and then stored in a sealed
plastic bag before the XRF analysis.
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