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wbastz
CogumeloHobby



Registered: 12/08/08
Posts: 162
Loc: Brazil
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Demagnetization of a magnetic stirring bar by heat
#12751206 - 06/16/10 07:48 AM (13 years, 8 months ago) |
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Hello all,
Could anyone tell me for sure if a magnetic stirring bar (Teflon coated) of the type used in magnetic stirrers may be demagnetized during autoclaving , or even lose some of its magnetic force due to the heat ?
Cheers,
Wilson
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mycoelf
Agent Of Chaos



Registered: 06/26/09
Posts: 555
Loc: hyperspace
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Re: Demagnetization of a magnetic stirring bar by heat [Re: wbastz]
#12751244 - 06/16/10 08:07 AM (13 years, 8 months ago) |
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Hey,
As a retired metal smith and mycologist I couldn't imagine how that could happen, Sterilization temp is so far below where metal begins to really move, the scenario in my mind would be something like you autoclave at 900 F and remove and quench, and that is not even considering the thermal barrier that the Teflon would present.
I have found however that when LC technique comes into play, the bigger the bar the better it works, the ones I use are from brew supply, and are in the neighborhood of 2".
I hope this helped, good luck
Mycoelf
-------------------- Mycoelf Sterility is a process that can be likened unto infinity, which is a long walk, the closer to the end you start before beginning, the more achievable the goal of infinity becomes. Remember, cleanliness in next to goddessness
      
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lazy bones
Stranger


Registered: 04/22/10
Posts: 250
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Re: Demagnetization of a magnetic stirring bar by heat [Re: mycoelf]
#12751389 - 06/16/10 08:58 AM (13 years, 8 months ago) |
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Like Mycoelf said, it should not hurt them. Back in college, we autoclaved them all the time.
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wbastz
CogumeloHobby



Registered: 12/08/08
Posts: 162
Loc: Brazil
Last seen: 5 years, 9 months
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Re: Demagnetization of a magnetic stirring bar by heat [Re: mycoelf]
#12751827 - 06/16/10 10:49 AM (13 years, 8 months ago) |
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Hi Mycoelf ,
Please tell me why a big magnetic bar works better than a small one ?
How does this affect the development of the mycelium ?
Cheers,
Wilson
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wbastz
CogumeloHobby



Registered: 12/08/08
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Loc: Brazil
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Re: Demagnetization of a magnetic stirring bar by heat [Re: lazy bones]
#12751846 - 06/16/10 10:51 AM (13 years, 8 months ago) |
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Hi Lazy Bones,
Thanks for this info.
Cheers,
Wilson
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RogerRabbit
Bans for Pleasure


Registered: 03/26/03
Posts: 42,214
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Re: Demagnetization of a magnetic stirring bar by heat [Re: wbastz]
#12757099 - 06/17/10 08:00 AM (13 years, 8 months ago) |
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Heat destroys the magnetic properties. They usually come back after cooling though.
Anyone can test this well-known phenomena by heating a magnet on the stove and then touching it to metal. It will only have a small fraction of the original force until it cools. RR
-------------------- Download Let's Grow Mushrooms semper in excretia sumus solim profundum variat "I've never had a failed experiment. I've only discovered 10,000 methods which do not work." Thomas Edison
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wbastz
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Registered: 12/08/08
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Loc: Brazil
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Re: Demagnetization of a magnetic stirring bar by heat [Re: RogerRabbit]
#12757130 - 06/17/10 08:14 AM (13 years, 8 months ago) |
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Hi RR,
Thanks for this info too.
Wilson
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mycoelf
Agent Of Chaos



Registered: 06/26/09
Posts: 555
Loc: hyperspace
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Re: Demagnetization of a magnetic stirring bar by heat [Re: wbastz]
#12759640 - 06/17/10 07:06 PM (13 years, 8 months ago) |
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Hello, To answer your question regarding my preference for the large bars, I would say it has to do with the fact that a small 1cm bar will whip the shit out of a culture at high speed, and is not as thoroughly "engaging" as the larger bar when at lower speed. I have also found the small bar to be unstable in the magnetic well. If a stir bar spins out to the side you will lose the culture from asphyxiation in short time. This has happened to me before and I was not around to save the work. I do a shit ton of LC and when I got my first stir tables there were little 1cm bars included. I set them up side by side and played with water in the flask to find a setting I thought was optimal. I have test run flask with water with a large bar at @ 100 rpm and it ran for weeks flawlessly. I feel as if a funnel shape in the LC is ok, and the whole body of the LC should be moving uniformly, but not having any air beat into the LC. Hyphae are fragile, so you want movement, not violence.
I do have a 5 second video of a stir table with a live LC that demonstrates what I feel is proper motion. I am posting hope it works
I think that Stametes says in the big black book that 100 rpm with vigorous gas exchange is the ideal.
Peace Mycoelf
-------------------- Mycoelf Sterility is a process that can be likened unto infinity, which is a long walk, the closer to the end you start before beginning, the more achievable the goal of infinity becomes. Remember, cleanliness in next to goddessness
      
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RogerRabbit
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Registered: 03/26/03
Posts: 42,214
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Re: Demagnetization of a magnetic stirring bar by heat [Re: wbastz]
#12760766 - 06/17/10 10:06 PM (13 years, 8 months ago) |
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Quote:
wbastz said: Hi RR,
Thanks for this info too.
Wilson
Unfortunately, I learned this the hard way. I had the bright idea to attach a rare-earth magnet to the outside of the oil filter on my airplane, thinking it would catch any metal flakes in the oil to stop them from circulating. Well, it did. Until it had a nice blob of shavings that let loose in flight over Texas on a 100F day when the engine got really hot. They clogged up the oil lines, causing the engine to seize up in flight.  RR
-------------------- Download Let's Grow Mushrooms semper in excretia sumus solim profundum variat "I've never had a failed experiment. I've only discovered 10,000 methods which do not work." Thomas Edison
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Sci-Fi
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Registered: 02/28/10
Posts: 1,232
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Re: Demagnetization of a magnetic stirring bar by heat [Re: wbastz]
#12760945 - 06/17/10 10:35 PM (13 years, 8 months ago) |
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I have autoclaved mine many times and not seen any loss from the heat.
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