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Author: Subject: Identifying unlabeled molecular sieves?
Bert
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[*] posted on 16-2-2018 at 09:45
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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[*] posted on 16-2-2018 at 10:07


Chances are they were bought for water removal, so likely they're 3A.

Apart from that, not a clue.




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[*] posted on 16-2-2018 at 10:08


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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[*] posted on 16-2-2018 at 10:21


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.



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Bert
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[*] posted on 16-2-2018 at 11:11


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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[*] posted on 16-2-2018 at 13:01


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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[*] posted on 16-2-2018 at 19:13


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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[*] posted on 16-2-2018 at 19:37


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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[*] posted on 16-2-2018 at 19:42


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 :D
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[*] posted on 16-2-2018 at 20:04


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.




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[*] posted on 16-2-2018 at 20:17


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 :D? I tried that ONCE
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[*] posted on 16-2-2018 at 22:19


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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[*] posted on 17-2-2018 at 00:24


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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[*] posted on 19-2-2018 at 18:20


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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[*] posted on 19-2-2018 at 19:06


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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[*] posted on 20-2-2018 at 00:02


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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[*] posted on 20-2-2018 at 04:24


@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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[*] posted on 20-2-2018 at 07:52


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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