Bert
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Identifying unlabeled molecular sieves?
Long story, 6 lb. of unlabeled sieves showed up in a drawer where they have been misplaced for about 10 years. Asside from bake/microwave, weigh,
expose to water, weigh again- Can any suggest ID methods?
[Edited on 16-2-2018 by Bert]
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aga
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Chances are they were bought for water removal, so likely they're 3A.
Apart from that, not a clue.
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NEMO-Chemistry
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Any idea what the candidates are?
dehydrate them, then add to the likely culprits, i assume the choice is limited to water (3A), and maybe a couple of solvent??
Put them in the candidates, those that warm the quickest are the likely ones.
Forgot to add
Something i notices ages ago.... 3A dont get hot as quickly in just water, so instead of water use something like IPA mixed with 50% water.
Probably just told you how to suck a egg, good job you aint my granny lol
[Edited on 16-2-2018 by NEMO-Chemistry]
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battoussai114
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Have you got an electron microscope laying around? Otherwise I can't think of anything other than checking the absorption behavior of different
solvents in it.
Batoussai.
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Bert
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Quote: Originally posted by NEMO-Chemistry  | Any idea what the candidates are?
dehydrate them, then add to the likely culprits, i assume the choice is limited to water (3A), and maybe a couple of solvent??
Put them in the candidates, those that warm the quickest are the likely ones.
Forgot to add
Something i notices ages ago.... 3A dont get hot as quickly in just water, so instead of water use something like IPA mixed with 50% water.
Probably just told you how to suck a egg, good job you aint my granny lol
[Edited on 16-2-2018 by NEMO-Chemistry] |
No, it's all good.
Harry was selling some of these to be used as cores for starting to roll round stars in a star rolling machine.
He also was selling them to use for removing water from commercial acetone before use with Magnesium or high Mg alloys, chlorinated isoprene and
perchlorate for go-getters (self propelled stars). Water is bad with Mg, M'kay?
No idea if he only had one type (3 angstrom?), but he certainly had two sizes, these tiny ones about 1mm Dia., and some bigger ones, perhaps 4mm?
I will bake some and toss in some cheap acetone from a partial can. See if initial heating and weight gain after removing the aetone occur.
[Edited on 16-2-2018 by Bert]
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j_sum1
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Yeah. Experiment with them. Take a functional approach. It matters little what they are. What is important is what they do. If they do something you
want them to do then they are useful.
[Edited on 16-2-2018 by j_sum1]
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Dr.Bob
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The most common ones are 3 and 4 Angstrom, 3A works best for methanol and ethanol, 4 works best on most other solvents. Hard to tell, but both should
work for acetone. Be aware that drying acetone for too long (much more than a day) can drive the aldol reaction of it with itself forward, as that
gives off water and removing the water drives the equilibrium to the right. If you can heat them under vacuum they will dry them best.
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Bert
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Thanks for the reminder, , I do now recall an admonishment not STORE acetone over the sieves to preemptively deal with any water absorption.
I need to rebuild my vacuum pump, only working vacuum source I have right now is a water aspirator.
Any reason NOT to microwave sieves?
[Edited on 17-2-2018 by Bert]
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NEMO-Chemistry
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I could be wrong as I cant find the ref, but i got a vague memory of two data sheets on sieves. I dont think the larger ones are the same as the
smaller ones.
If you think about the process, and quick ways of separating manufactured products, then wouldnt it make sense to have them a different diameter? Sure
different diameter could have different use and be same size, but in the context of your info, I think they are likely to be different.
A quick look at some data sheets for 3A and 4A should give a external diameter, check a couple of brands. If the pyro gods are smiling on you.... Then
it could be a easy way to tell. OR that could all be bollocks!
I got to be honest, 3A sieves cost alot. The thought that you guys blow them to shit (shakes head), there is just some things you dont ever admit too,
I think blowing up 3A sieves is something to keep to yourself and close family.
Its pretty distressing reading for some of us 
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Magpie
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Presuming each bag is either 3A or 4A:
4A will absorb ethanol, 3A will not, according to Wiki.
Place some of each bag in a different hand, respectively. Pour some absolute ethanol on each. See which hand(s) warm(s), if at all.
I hope my logic is good, I am drifting in and out of sleep at present.
The single most important condition for a successful synthesis is good mixing - Nicodem
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NEMO-Chemistry
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| Quote: Originally posted by Magpie | Presuming each bag is either 3A or 4A:
4A will absorb ethanol, 3A will not, according to Wiki.
Place some of each bag in a different hand, respectively. Pour some absolute ethanol on each. See which hand(s) warm(s), if at all.
I hope my logic is good, I am drifting in and out of sleep at present. |
You do know that hurts dont you ? I tried that ONCE
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Bert
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| Quote: | | I got to be honest, 3A sieves cost alot. The thought that you guys blow them to shit (shakes head), there is just some things you dont ever admit too,
I think blowing up 3A sieves is something to keep to yourself and close family. Its pretty distressing reading for some of us |
I have rolled stars on more expensive cores. Once I used several thousand magnum pistol primers. That cost about 2 cents a star just for the core.
They were a pretty nice effect- CRAAACK! But you wouldn't want to shoot them over an audience. All those little steel cups raining from the sky...
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aga
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The risk with a microwave is that steam can be rapidly generated which can fracture/split some of the sieves.
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Dr.Bob
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They make 3 and 4 in the same size pellets and sizes, unfortunately. As stated, 3 are more rare, so most likely 4A.
You can heat them first, and then put them under vacuum while warm. I don't know if they will heat well in a microwave, if they don't absorb much
power, the microwave can overheat if left on too long.
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NEMO-Chemistry
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3A, 4A does it make much difference when you blow the shit out of them? Or is it the diameter of them that makes the difference? i guess 3A would have
the advantage of keeping stuff dry from moisture.
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Bert
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| Quote: Originally posted by NEMO-Chemistry | | 3A, 4A does it make much difference when you blow the shit out of them? Or is it the diameter of them that makes the difference? i guess 3A would have
the advantage of keeping stuff dry from moisture. |
For the purpose of star cores, only thing that matters is the diameters and consistency of sizes/density.
Other things that have been used: mustard seed, accini de pepe pasta, sand grains, small cut stars, Lead shot, primers for reloading ammunition.
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Boffis
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@Bert,
I've been doing a bit of reading and it seems that the three main types, 3, 4, and 5A molecular sieves are synthetic zeolites with different ratios of
alkali and alkaline earth metals in them. It appears that they all contain a little sodium but only the 3A type contains K and the 5A type contains
Ca. So, since zeolites are readily decomposed by hydrochloric acid, I suggest that you evaporate to dryness a couple of times a little of the powder
sieve with 1-2ml of 5M HCl to ensure the silica is rendered insoluble then repeat this process a couple of times with water to reduce the amount of
aluminium in solution by hydrolysis. Then leach with a few drops of fresh water and place a large drop on each of two microscope slides.
To the first drop add a drop of 2M sulphuric acid and to the second add a drop of 2M perchloric acid or a soluble perchlorate (eg sodium perchlorate).
Leave to stand for about an hour, make up any evaporation with fresh water and cover with a cover slip. Examine under the microscope. (1hr because
gypsum crystals form slowly).
If delicate radiating colourless monoclinic blades form in the first drop calcium is present ie you have a 5A zeolite
If small glassy plates (usually diamond shaped) form in the second then potassium is present ie you have the 3A zeolite
If no crystals form in either both calcium and potassium are absent ie you have a 4A zeolite
I would recommend running these tests on some known examples just to check that it works as there may be a little Ca in all of the say so you need to
run a comparison.
If you don't have perchloric acid or a soluble perchlorate sodium hydrogen tartarate may also work.
It also appears that the 4A type has quite strong and selective base exchange properties, particularly for ammonium ions, so you may be able to
further confirm the identity by such tests but they would require a bit more research. Such a method has been used for natural zeolites.
If no acid is added to a third drop and it is allowed to evaporate in a warm dry place and you get tiny cubes either Na or K are present but is the
second drop has already shown K to be absent then it indicates sodium. This test is less useful since it looks like all the sieves contain some
sodium.
There are numerous other tests for Na, K and Ca but its the principle here that we need to test.
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NEMO-Chemistry
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Thx, i have been reading the book! clever stuff indeed. despite the alternatives you mentioned, i cant come up with a single cheap alternative!!!
My first reaction was what a waste!!! But i guess they are actually a pretty good choice.
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