1. Rotor care and handling are of the highest importance!
A. The inside edges and surface of the ceramic rotor are the most
critical. NEVER use metal tools to pack, empty, or clean a rotor. If
plastic tools are not effective, then use solvent, acid, or an ultrasonic
bath to remove the sample.
B. Never use a rotor that has been dropped on a hard surface.
Microcracking cannot always be detected. Use a padded covering on the
bench and floor where rotors are cleaned and packed. Inspection with
penetrating UV dye is the best way to check suspect rotors. Marking the
rotor with ink and then removing the ink to inspect for ink deposited in
cracks can be useful, but high magnification is required - your eye and a
magnifying glass typically aren't good enough.
C. Yellow Zirconia rotors are inferior to the more modern white variety.
Silicon Nitride is better than white zirconia.
D. Never spin a rotor or cap more than its rated maximum speed.
E. Clean the outside of the rotor before inserting it in the probe. Dirt
and oils can accumulate on the bearings.
2. Packing is also important.
A. Powder should be ground and sieved to ensure uniform particle size.
B. Pack in small layers to avoid pockets. Add powder and tamp; add powder
and tamp; etc. Try to tamp with uniform pressure.
C. Spin-packing works, but results in less signal. Spin-packed samples
must be handled very carefully to avoid shifting.
D. Vibration-packing also works with the same limitations as spin-packing.
Any vibration to settle powder should be applied gently and vertically.
This works best for coarse materials.
E. Permanently packed standard samples should be stored in a dessicator.
F. Leave room for the cap, so it is not pushed off by the sample. Pack a
small amount of sample in hollow caps before assembly.
G. Caps must fit tight. Super-glue or Magic Marker can help if the cap is
loose. Acetone will dissolve both.
H. Worn caps should be discarded. Imbalance or slow speed can result from
bad caps.
I. Hard materials, such as ceramics, should not be tamped, because the
sample itself can score the rotor wall.
F. Dense materials should be mixed with a filler. If the sample is more
dense than ~1.5, you must deratee the maximum speed of the rotor.
3. Always test the spinning performance of every sample before running to
full speed.
A. A benchtop spinning unit or a spare probe is useful to save both
instrument time and risk exposure during spinning tests.
B. If the spinning rotor whines or changes sounds, it's not spinning -
it's rattling! A well-spinning rotor emits only a whirr.
C. If it won't spin well, there are several thing to try: clean the
rotor, turn the cap 90 degrees, change caps, repack (or depack) the sample.
D. Spin at 1-2KHz for 5-10 minutes before going to higher speed. This
helps the sample to settle into a balanced position.
E. Do not override the automatic function of the spin controller. If it
doesn't work, it's because there is a problem that should be corrected
before proceeding..
F. Clean air is essential. The tolerances and small air passages in the
probe will not tolerate dirty air.
Thanks again for all of the help.
Happy spinning,
Jerry
>Date: Mon, 22 Feb 1999 10:48:46 -0500
>To: AMMRL
>From: Jerry Hirschinger <hirsch@purdue.edu>
>Subject: Solids rotor packing
>
>Hello AMMRL,
>I need some advice from those of you with experience in solids sample
packing. We had a couple of costly rotor accidents in a solids probe
recently that prompt me to ask: What procedures do you suggest be
followed to ensure that the rotor packed with powder doesn't explode at
several thousand rpm?
>Thank you,
>Jerry
===+++===
Jerry Hirschinger, NMR Instrumentation Engineer
Purdue University Interdepartmental NMR Facility
1393 Wetherill Labs, rm. 365A
West Lafayette, IN 47907-1393
Phone: (765) 494-5288
FAX: (765) 494-0239
email: hirsch@purdue.edu