Two items here: Re-using the quartz reactors and oil contamination in
We have our University glassblowers make new qtz tubes for us. These
have worked very well and are much less expensive than the original tubes.
High quality quartz seems to be important. I was surprised that wall
thickness doesn't seem to be an issue (given that quartz at 750 deg C is
permeable by hydrogen). We also cut the old tubes in half with a thin
bladed slow-speed saw (Buehler Isomet). If the cut is clean, we can usually
pull the sintered Cr out of the two sides. After cleaning the glassblowers
can rejoin the two halves and pull the total length by 1mm to account for
the saw cut. We have not yet tried to cut a repaired tube to remove Cr a
second time. I would not try to re-activate the Cr, since it is cheap (2 kg
2 weeks ago our numbers became very unstable. Our internal standard
was bouncing around by + - 5 per mil. After fussing with various things, I
cleaned the lower connection and pneumatic valve below the furnace. This
was full of oil. After cleaning in solvents our problem went away and our
numbers are back to normal. I can't think of any source of oil in this
system other than the Cr powder. This makes some sense since this spot is
the first cold metal the oil vapor would see. We have been buying the
normal grade of Cr (99% pure, < 100 mesh) from Alfa Aesir (US). We have
used about 2 kg so far on about 5000 samples since May of 99. I would
recommend that users keep an eye on the lower angle connection and the
valve for oil buildup.
We are considering pre-cleaning our Cr powder. Probably a simple
toluene soak, ultrasonic, rinse, and drying. Can anyone give me any
information on metal powders and oil? Is it from the grinding process, or
is it added to prevent adherence to other particles (am I in trouble if I
clean it off?)? Or am I wrong and the oil is from something else?
Thanks in advance for any info.
David Dettman [log in to unmask]
Dept. of Geosciences ph. (520) 621-4618
Univ. of Arizona FAX (520) 621-2672
Tucson, AZ 85721