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Author: Subject: Issue with magnetic stirrer
stephill92
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[*] posted on 13-1-2020 at 21:23
Issue with magnetic stirrer


Don't know if this is an issue with the actual hot plate or if I'm using the wrong stir bars but I bought this same model of hot plate/magnetic stirrer about a year ago and I've always had an issue with the stir bars spinning out but mostly it was manageable. Mostly it was an issue with erelnmeyers but today was the last straw. I was trying to make sodium using the menthol catalyzed sodium hydroxide magnesium method and it will not even go the slowest possible speed without spinning out and jumping up on the side of the flask. Is this a common issue with magnetic stirrers and is there a way to fix it? Or did I just buy a piece of junk?
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j_sum1
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[*] posted on 13-1-2020 at 22:49


A lot comes down to the stir bar you use.
Experiment with different sizes, banded and unbanded and oval bars. They do not behave the same way at different speeds and with different viscosities.

(I lost my small oval one the other day which was perfect with my 500mL RBF slightly overfilled with solutions with up to 2cm of loose sediment. It never destabilised and gave me excellent control over stirring speed.)
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XeonTheMGPony
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[*] posted on 14-1-2020 at 07:41


look at the price, and guess!

way to fix it is to dismantle it, and replace the magnet with a better / stronger type, but as J sum1 suggested try a better stir bar first.

For future reference any thing less then 500w will be a head ache for any complex or largis synth.

I would advise you invest in some quality insulating blankets.

I got an old corning with the same issue, it is in large part due to an aged magnet that is weak, some point I will replace it with a neo mag, and same time get a new top plate with heater in it.

[Edited on 14-1-2020 by XeonTheMGPony]

[Edited on 14-1-2020 by XeonTheMGPony]
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stephill92
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[*] posted on 14-1-2020 at 08:15


Thanks for the replies, I'll definitely look into some new stir bars and an insulating blanket. Unfortunately for me I'm not very mechanically knowledgeable so I don't exactly know what specifications to look for in a good hot plate.

I also found the same hot plate for various prices on amazon so I probably need to do a better job of figuring out what to buy.
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G-Coupled
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[*] posted on 14-1-2020 at 19:18


There's an Indian seller who is selling some possibly decent seeming Indian made mantle/heater/stirrers at good prices in recent thread here.
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Sulaiman
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[*] posted on 14-1-2020 at 20:30


Quote: Originally posted by XeonTheMGPony  
I got an old corning with the same issue, it is in large part due to an aged magnet that is weak, some point I will replace it with a neo mag, ...

I suggest that you use either AlNiCo or SmCo magnets as they have a much higher Curie temperature than NdFeB.
(AlNiCo magnets self-demagnetise more quickly than SmCo but can be fairly easily re-magnetised)




CAUTION : Hobby Chemist, not Professional or even Amateur
(suffering from separation of me and my chemistry stuff)
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XeonTheMGPony
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[*] posted on 15-1-2020 at 04:39


Quote: Originally posted by Sulaiman  
Quote: Originally posted by XeonTheMGPony  
I got an old corning with the same issue, it is in large part due to an aged magnet that is weak, some point I will replace it with a neo mag, ...

I suggest that you use either AlNiCo or SmCo magnets as they have a much higher Curie temperature than NdFeB.
(AlNiCo magnets self-demagnetise more quickly than SmCo but can be fairly easily re-magnetised)


Thanks will look into those!
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