Drying crc powders in a microwave

Hash and Stuff Extraction
, ,
41

I do research on smectites, which is the main components of bentonites, since years…
It is a fascinating material. What I would preferentially do is freeze drying them, as I study then finely powdered and well preserved, and its the best way to avoid aggregation upon drying.

In aim of CRC use, this is not necessary, and the best and simplest method would be drying them at 105°c for 24 hours in a ventilated oven. A basic one. I would not use a vacuum oven to not mess up with the vacuum pump.

A priori, I would not use microwaves, not because it is hazardous, but because it would mess up with their nanostructure… but in case of the CRC use, this is in fact maybe what you are looking for… :thinking:

https://www.researchgate.net/publication/257026154_The_effect_of_microwave_irradiation_and_conventional_acid_activation_on_the_textural_properties_of_smectite_Comparative_study

4 Likes
42

Thats good to know, I hadn’t even considered how heat treating would affect the pore structure of the media. But it makes sense.

So water can be forced to crystallize out of the pore its adhered to? Would you be willing to explain that in a bit more detail? Would this be considered a kind of desorption?

1 Like
43

In fact I looked the paper after, and they are dealing with use of microwave during acid activation, instead of conventional heating. This is not just about drying…

But they don’t decipher much impact of the microwave on the crystalline structure, according to the basic XRD method they employed (regarding conventional heating). They don’t show the data still… at this level, we start to dwell into the little-known, and high level. It is not really my specific area (I’m more into redox stuff), but so far I did not read any clear explanation on how acid activation exactly works… so I made up my own, based on what I know.

Here hey are dealing with “pores”, more especially mesopores, but that a actually a side effect of acid activation, which partly dissolves the clay… I think others changes also occur at a much smaller scale, acid partly disrupt the clay platelets, and they expose more edges with specific properties…

But in your case, if this this is just about drying already activated clay, this may likely promotes no much changes anymore, besides removing the water.

The water is actually not in pores. It is covering the surface of the clay minerals, which you can see as stacks of platelets. It is often called “structural water” (and represents a great deal of earth water, besides the oceans…), but it is not crystallized. There are “defects” in the clay structure (in fact isomorphic substitution of cation by other of the same size, but smaller charge, mainly Mg2+ instead of Al3+/Fe3+), which provide a negative charge to the clay crystal. External cations (mainly Na+ in sodium-activated clays, but can also be more Ca2+/Mg2+ in natural bentonites) come at the surface and compensate this charge. In ambient conditions, those cations are normally hydrated, they should have like a shell of water around them. That’s the structural water and the exchangeable cations.

They are not really part of the crystal, only linked by weak forces, mainly Van Der Walls (and hydrogen bonding at the edges). Thus, when you remove the water by drying, or exchange surface cations for others (metals, colorant, etc…), desorption is indeed the right term.

3 Likes
44

The part about crystallization is what made me think that the thought train may be headed in the wrong direction.

Doesnt freeze drying take advantage of the fact that water can be forced into a solid phase by reducing the temperature? Wouldn’t the water be bound by hydrogen bonds to the surface of the media, essentially creating a hydrated mineral rather than simply holding onto the water in the form of H2O?

As a bit of support for my rationale, why doesn’t water evaporate on the surface of the moon? Its plenty cold up there and there’s no shortage of vacuum. Interesting stuff, feed me more ideas :grin:

2 Likes
45

So if I’m reading what you posted correctly, a microwave used for drying shouldn’t cause any negative changes to the powders, even if they’re activated?

46

I guess. :thinking:
There should not be much acid not water left in there at first.

You are the experimentators here.

2 Likes
47

He was saying that using a kiln like I described could negatively impact the physical composition by causing aggregates to form when the water leaves the clay.

He suggested lyophillization instead because it wouldn’t have an effect on particle aggregation which would restrict access to much of the pore network at least until the media is fully wetted with solvent.

1 Like
48

I think it’ll be fine in a pinch. Just spread it out thinly. If you see discoloration I’d prolly say something’s going on

2 Likes
49

I got that part, but at first he said avoid the microwave, then the next post said it may not have much effect after all, I think lol.

50

So one thing I’ve noticed, is I had some leftover powder and had it stored in a jar, no discoloration.

Forgot about it and several weeks later I opened it and it had a dark layer on top. Is that oxidation I’m assuming?

51

I dint see why a microwave wouldn’t work, but remember that microwaves heat up water faster than it can evaporate so you WILL see excessive heat being transferred to the clay. Which may or may not form aggregates.

I think that it would work fine but I don’t actually know lol, @Dr_Jebril has a better grasp on these things.

2 Likes
52

Honestly just trying to follow along haha.

2 Likes
53

In fact there are no clay on the moon. The moon is very dry. :frowning:

But there are plenty on Mars. It even seems that it is red (oxidised) for only few tenth of centimenter from the surface, but then is in fact all blue (reduced)… so the red planet is likely more blue inside. There is a thin atmopshere, CO2 rich, with some trace water, sometimes clouds, so the soil might by quite dry, but some water might still be there.

Freeze drying takes advantage that solid water is easier to evaporate at low temperature, by decreasing the pressure. But it needs to freeze the water, which needs quite some energy… the interest is more into preserving the associated compound, by not applying heat. In my case, this is not microstructural nor chemical changes that concerns me, but more macrostructural ones. They clay form aggregates, which are harder to powderise by hand…

Regarding your question about hydrate, I’m sorry it is a bit late for me now…
Sound a bit elusive. The negative charge is compensated by cations. Water is neutral.
Hydrates work differently. But in fact I’m not very familiar with the concepts behind.

4 Likes
54

In fact the issue with agregation occurs when you dry a slurry, or a mud.
But dealing with the “dry” free flowing powder or pellets you get from your shop, the normal ventilated oven should be perfectly ok.

Regarding microwave, I think you would need very high energy to cause damages, like using industrial fracking tools. If you use kitchen ones, it should also be ok for the structure. Maybe be a pulsed microwave with ventilation would be the ideal.

But I’m curious to see the outcome. To be honest, I never did that. Sounded bad… :laughing:

2 Likes
55

Screenshot_20200904-172545_Drive
Screenshot_20200904-172545_Drive720×1600 869 KB

This paper suggests you’re right, water doesn’t exist on the moon when vacuum and solar radiation are in contact with the minerals. The surface of the moon is anhydrous.

1 Like
56

I mircowave b80 before I load it in the crc column Everytime, saves a shitload of time and seems to work great. I do 5 minutes on full power in a pyrex dish. It does make a mess sometimes

2 Likes
57

I know b80 comes out the bag with quite a bit of water. Are you noticing any buildup of moisture inside your microwave when you do this? How long do you typically heat your b80 in the microwave? How many watts is your microwave?

How does it make a mess?

58

It gets dusty, you definitely get a fine layer of the powders in your microwave.

I’ve also seen the steam come out fast enough where it makes the powders kinda poof up and then collapse, I think that’s what he’s referring to.

And it’s a lot of moisture, I only dry like 100g or so at a time and it’s steamy in the nuker when I open the door.

1 Like
59

I’d be worried about my microwave huffing the particles. Eventually its gonna eat up the bearing on the exhaust fan, if it has one.

60

Yeah, that’s why I’m using our old one haha.