CryoCooling - The Phantom Menace

Paul Hubbard phubbard at POST.ITS.MCW.EDU
Tue Nov 16 20:22:28 EST 1999


Hi,

In response to all those who requested a summary of answers I have
received regarding cryo-equipment:

1)LN2 quality featured heavily in many responses. I have been witness to
this, where ice is spat at the crysal. Not nice. One person mentioned the
filters could be a problem (our system is brand new - hopefully not a
prob. in our case)

2)Tents. We tried this out last summer with our old MSC cryocooler. It
helped, but we were hoping to avoid this (we were told this isn't
necessary).

3)Washing the crystal with LN2. I have heard this before. This sounds like
a good idea for putting on crystals taken from a dewar.

4)Inverted-Phis. I had never heard of this one - where the nozzel should
be pointing up so that the cold flow hits the crystal before the warm flow
does. We've just tried this out. So far so good... I'll get back to you if
it works.

5)Still air and humidty. Yes, and kinda yes were the responses to each. I
spoke to an Oxford sales rep. at the IUCr who told me to blow out a match
where the crystal would normally be (in the absence of the cold flow -
obviously) and see how the smoke trails off. Yes, we have a slight draft -
nothing major though. We have stuck plastic bags over the vents to divert
the air away from the goniometer.

6)Suck it - Put a fan in the post-gas flow to gently suck away the spent
gas. I guess one should be sure the fan is positioned directly in the
laminar flow so as not to distort the flow - and not too powerful that
that nitrogen hasn't had chance to cool the crystal. I've just stripped
off an old computer-chip fan - i'll smack an old toilet roll tube over it
and see if that helps.

THANKS TO ALL WHO RESPONDED. I'M JUST GLAD THAT THERE ARE PEOPLE OUT THERE
WHO TAKE TIME TO REPSOND TO THESE KIND OF QUESTIONS.

Just a minute....Yup, still no ice. Its been 1.5 hours and no sign (thats
an improvement of a couple hundred percent since inverting the
cryo-nozzel).

ags

*******************************************************************************
Paul Hubbard
Department of Biochemistry
Medical College of Wisconsin
8701 Watertown Plank Rd.
Milwaukee
Wisconsin. 53226

Tel: 414-456-4305
Fax: 414-456-6510
WWW: http://141.106.40.30
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