dangerous amateur
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What kind of stirrbar for viscous slurries?
Hi there,
well, see topic. What kind of shape whould you choose for your stirrbar to handle peasoup-like slurries?
I've got a commercial stirrer, very old but the magnets and motor seem to be very strong (at least compared to my previous PC-fan ghetto setup  )
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Bot0nist
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I have a big, hexagonal, thick stir bar. It works great for thick slurries. Use a slow speed. The bar is as long as my 600ml beakers are wide, and
nearly 1inch thick. They also have ones shaped like an X at a slight angle (the points are higher than the center), I assume for RBFs. I will try to
take some pics in a minute.
[Edited on 8-3-2012 by Bot0nist]
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bfesser
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For viscous slurries, an overhead stirrer is often preferred. Otherwise, as Bot0nist said, the largest stirbar you have at a low speed.
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Hexavalent
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I will have to attest with bfesser. I have a huge stirbar, but I often prefer to use an old food processor I picked up for a dollar at a yard sale.
"Success is going from failure to failure without loss of enthusiasm." Winston Churchill
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Bot0nist
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Not very chemically resistant as is, I imagine.
U.T.F.S.E. and learn the joys of autodidacticism!
Don't judge each day only by the harvest you reap, but also by the seeds you sow.
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Hexavalent
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No, probably not . . .although its stood up to everything I've used it for so far . . .
Another item that I like, for stirring general aqueous solutions, are those coffee frothers available cheaply from supermarkets . . .I suspend it in a
clamp and lower it into the liquid. Works fairly well in situations where magentic stirring is not wanted or feasible.
"Success is going from failure to failure without loss of enthusiasm." Winston Churchill
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homeslice
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Rare Earth
There are actual specific stir bars for viscous solutions.
Do a good search for Rare Earth Magnetic Spinbars. They are green. And they do spin out a lot less than just a regular white spin bar. The downside is
that they cant be used at high temperatures.
Heres a nice page for more information!
http://www.belart.com/shop/Resources/Samarium%20Cobalt_Rare%...
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AndersHoveland
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This might not always be a good idea...
http://image.shutterstock.com/display_pic_with_logo/426631/4...
[Edited on 9-3-2012 by AndersHoveland]
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dangerous amateur
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Overhead stirring is impossible.
I've got a stirrer for a drilling machine, but this is more suited for paint.
Not for acids ect.
If you can give me a source for such a thing, made from or coated in PTFE, and not for +100€ ....
I'll try to get some samarium-cobalt bars. Unfortunately they are pretty expensive - about 30€ for a 50mm bar...
Thanks for your advice.
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barley81
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Maybe you could seal a few of <a href="http://www.kjmagnetics.com/proddetail.asp?prod=D44SH&cat=167">these</a> (good to 150C) or one
of <a href="http://www.kjmagnetics.com/proddetail.asp?prod=D3X0">these</a> (max. temp 80C) in a glass tube. Then you'd have a rare-earth
magnet stir bar for about $5. Hot glue it in place to keep the magnet from rattling. Any thoughts?
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resveratrol
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I have a large egg-shaped stirbar which I would employ for situations like this, as an alternative to overhead stirring. I would have it set at a
slower speed as others have said - I would presume the larger/more mass your stirbar has, the higher the speed you can have it going at.
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Hexavalent
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No, it is quite the opposite. Firstly, the large magnets often place strain on the magnetic stir function, only allowing it to go at a somewhat slower
speed. Secondly, if the magnet does decouple, by your fault or not, if its heavy and going quickly it can easily pass through the walls of the glass,
destroying your vessel and spilling chemicals everywhere.
"Success is going from failure to failure without loss of enthusiasm." Winston Churchill
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Magic Muzzlet
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Well if you are using it in a thick slurry as the thread suggests the stirbar will simply stop, not spinning, and just wiggle a bit as the magnets in
th plate continue to spin much faster.. It's happened to me many times, I doubt it would ever go through a flask or even continue moving at all unless
you use a lower viscosity liquid. Even then, I've never had a magnet shoot away. It has always just stayed where it is but wiggle really fast, then I
stop stirring and restart. This is common with larger ones, it's actually the smaller ones that will start going around the entire inside of the flask
and go crazy.
I have found you can get better stirring for thicker mixtures using a normal hexagonal bar (with "ring" around the middle of it) instead of the egg
shaped, they do spin on RBF's if you choose the right size.
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resveratrol
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Hm. Well, I guess I was thinking the larger the stirbar you're using, the more mass it has, thus a stronger attraction and decreased likelihood of
decoupling as a result of the resistance posed by viscosity. And when it does decouple, i wouldn't expect it to break glass. I've personally never
experienced breaking glass using even higher speeds with non-viscous liquids.
Either way, it's beating a dead horse at this point. I would just run it at slow speed.
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Endimion17
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Why can't you make a stirring rod attached to a driller via thick rubber tubing? That's how it was done for the most part of history.
Most if not all drillers today employ a speed setting and a lock. Just insert a metal rod into the driller and use strong, thick piece of rubber
tubing to attach the glass stirring rod which you've modified before. And of course, fix it with a lubricated hollow cork going through the neck of
your vessel.
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Dr.Bob
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I have a bunch of odd shaped stir bars left, some are X shaped, circlular, or other patterns, designed for different special uses. Look at
Belart.com under stribar, and see which looks best to you, they make severy type imaginable. I have most of them available. Let me know. I need
to post a photo of some of the ones I have, still.
http://www.belart.com/shop/stirring-c-21.html?page=5&sor...
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