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Author: Subject: Stainless steel in microwave oven
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[*] posted on 10-8-2010 at 11:16
Stainless steel in microwave oven


From what I read around it seems like almost everyone agrees on not putting metals in a microwave oven. but what if stainless steel is the only material suitable for the reaction and you want to use microwave heating? what would you do?
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Satan
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[*] posted on 10-8-2010 at 11:55


Give more details. Like what you are going to make, and why stainless...
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[*] posted on 10-8-2010 at 11:57


Quote: Originally posted by denatured  
but what if stainless steel is the only material suitable for the reaction and you want to use microwave heating?

Curious. Which reaction works only in highly reactive steel and not say in high-T annealed corundum (or ZrO or MgO)? These materials take some beating. Have you checked for alternative crucible materials in Brauer's? There must be an alternative to steel.
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[*] posted on 10-8-2010 at 12:10


Chitin deacetylation: 100°C or more, 50-60% NaOH, duration varies (from 15 minutes to 3 hours, 600-900 Watts). I use 316 steel when using conventional heating, glass is out of question and even if there is some kind that can stand it, it will be very expensive.

Do I have to get a specialty ceramic to have this resistance against hot concentrated NaOH? or any ceramic I can get will hold?

Thanks
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[*] posted on 10-8-2010 at 12:27


Quote: Originally posted by denatured  
I use 316 steel when using conventional heating, glass is out of question and even if there is some kind that can stand it, it will be very expensive.
Oh, "... and cheap". You didn't mention that in your first post. It would be possible to make a custom microwave oven that used a stainless steel vessel as the oven, but you'd need to learn some microwave engineering to do it. It would likely need some kind of closed-loop power supply control for the magnetron not to overheat the reaction vessel (or itself). None of this is cheap, certainly in time, likely in materials.

So my next question is how much better is microwave heating than what you're doing now? In other words, where's the break even point for effort and resources?

The really cheap answer is that you can sometimes just stick metal into ovens without a problem, but only certain ovens (top feed is best) and only certain shapes of metal (those without sharp points and corners). Even then you'd need to have some feel for microwave physics to get it right. And you still might blow out your oven.
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[*] posted on 10-8-2010 at 12:33


Quote: Originally posted by watson.fawkes  


The really cheap answer is that you can sometimes just stick metal into ovens without a problem, but only certain ovens (top feed is best) and only certain shapes of metal (those without sharp points and corners). Even then you'd need to have some feel for microwave physics to get it right. And you still might blow out your oven.


In which case you run across the street to the junk shop to get another second hand microwave oven!

Most bowl-like steel vessels shouldn't spark, IMHO...
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[*] posted on 10-8-2010 at 12:47


Quote: Originally posted by denatured  
Chitin deacetylation: 100°C or more, 50-60% NaOH, duration varies (from 15 minutes to 3 hours, 600-900 Watts).

Oh, that's quite mild. ;) Many ceramics will take that without problems, but they're expensive. My first try would be a Teflon autoclave with thick walls. BTW: I've achieved over 1000°C in a 700W kitchen microwave. Careful!

Edit: If Teflon is compatible with microwave ovens, that is. No idea.

Edit2: Why microwave? Every cheap kitchen oven can do 200°C and temperature control is so much easier - just put a thermometer in there.

[Edited on 10-8-2010 by turd]

[Edited on 10-8-2010 by turd]
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[*] posted on 10-8-2010 at 16:08


It will not work at all if your intent is to have the Microwaves reach the reactants since they will reflect and absorb off of the steel never reaching whats inside. However as long as there are not sharp corners for break out of the charge built up in the Stainless material you MIGHT get away with it. As it stands however it seems useless to use a microwave over conventional heating in this case.




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[*] posted on 10-8-2010 at 16:53


On this same topic, would it be a good idea to put a magnet inside of a microwave? The idea would be to make a reflux apparatus with stirring inside a microwave, using as stirrer a computer fan with magnets and a soup dish upside down to protect it, and a teflon coated magnet inside the flask one would need to stir with the condersor coming out of the top part of the microwave. The mixture to be nucked would be a biphasic one (one of the phases being aqueous)
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[*] posted on 10-8-2010 at 20:35


100 C isn't very hot. Hot NaOH will attack glass, but I don't know that it will dissolve away the walls of a beaker entirely. At least, not in the time period you are suggesting.

Sacrifice a beaker. True, it'll never be the same. It won't be pretty anymore.

But, you will have a dedicated, ugly beaker, always on hand, for heating caustics.
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[*] posted on 10-8-2010 at 23:36


Quote:

Sparking and Metallic Samples
Many alloys interact with microwave energy and will heat sufficiently to melt plastic vessels; others accumulate
large electrical discharge potentials. One case, involving a large alloy sample melting through a container, has been
related to the authors. Several types of ferrous alloys were tested in which spark discharges were quite spectacular.
Discrete pieces (> 1 mm) of metallic samples should be avoided, because electrical arcs may occur between
individual sample pieces or between these alloys and the microwave cavity's metallic devices including the walls.
The formation and intensity of electrical sparks depend on the composition of the alloy and other conditions such as
electric field strength. Electrical arcs from inadequately grounded thermocouples constructed of 316 stainless steel
have been found to be sufficiently energetic to puncture 1/16 in Teflon(tm) PFA (39, 40). It has also been noted that
some concentrated solutions also exhibit sparking. Concentrated sodium hydroxide, copper nitrate, and nitric acid
have all been observed to discharge electrically within the solution.

Check if teflon coatings are available in your country, its one of possibilities to coat glass with it.
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[*] posted on 2-12-2020 at 17:43


Quick question:
can I decompose magnesium/calcium carbonate to oxide? Using a microwave
I saw a video about melting glass in microwave! https://m.youtube.com/watch?v=xwEQZw3KPWg
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[*] posted on 2-12-2020 at 21:23


The original poster might have succeeded with a glass or pyrex container, lined with HDPE or some other plastic. Not sure.

You want to do something that requires a lot more heat. Now, you can possibly achieve the heat.

But, what Microwavable Crucible will take that heat, and resist hot CaO?

Not impossible to displace the CO2 and H2O, by refluxing in Methanol or Ethanol. Leaving you with Magnesium Methoxide Etc... Or, Calcium Methoxide. Which on hydrolysis would leave you with Ca(OH)2
or Mg(OH)2. But, it seems like an awful lot of work to get
something your can buy at the hardware store.

Ooops! I see you are in Tunisia. I have no idea what reagents you can obtain in Tunisia.

[Edited on 3-12-2020 by zed]

[Edited on 3-12-2020 by zed]
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