Author Topic: Growing alum crystals  (Read 1835 times)

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Offline MadScientist267

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Growing alum crystals
« on: March 17, 2019, 01:51:12 pm »
If you've seen the scratch thread, you probably know that I've been messing with growing alum crystals for a little while now, and I've hit something of a brick wall with what I can and actually do expect to get from what I'm using to do this.

There's basically 2 different methods out there at the hobby level, and while I know I'm sorta reinventing the wheel on this next step up, I'm thinking it's more like "it's been done but nobody is revealing their secrets" lol... So while I won't claim it'll be an instant success, it's gotta be better than what I'm doing right now, and if so, well, let the silence end here  ;D

8089-0

Little raw concept schematic as a visual, and the key... Didn't even attempt to go for anything beyond what I'd recognize with this... But basic run down is:

P = Peltier (C being cold side)
V = Flow control valve
F = Filter
H = Heating element

Present efforts use the evaporation method to keep the solution saturated, and this has numerous issues. Growth quality has been demonstrated as "potentially excellent" but the method is high maintenance and introduces inconsistencies as such. With my current setup, on average I'm able to get about a 1/8” layer of beautiful absolutely clear growth before something either naturally interrupts the process on its own, or I have to interrupt it myself to do maintenance. Every time this happens, it causes anything from cloudiness to even "trapped bubbles", and everything in between... None of which the eye likes to look at.

The other common method is supersaturation, which isn't viable for what I'm after. Crystal quality is low and singles are very difficult to isolate at that. The crystals grow very quickly, but they're disorganized and cloudy at best. I don't even use it to generate seeds. Great for demonstrating the basic concepts to kids, but when you're looking for pristine anything, nevermind singles, can hang it up.

So, I am in the process of coming up with this. It's something of a hybrid between the evaporation and supersaturation methods you might say, but leans technically more toward a "controlled supersaturation", as evaporation is not actually involved at all.

The system being sealed off from air means that in theory at least, spontaneous seeding should be minimized (ideally non existent lol) and assuming I can get the entire system completely clean at the start, no strange "slime" showing up after a little time goes by. Still not exactly sure what this is, it's somewhere between the consistency of mucous and jellyfish tentacles, and could be either some sort of flocculation, an algae or mold, or even some combination of the two. It doesn't appear to be much of a factor in the crystal's quality so far but I can see where it may eventually if it gets thick enough in the wrong place. Still looking into all that's involved with all that...

It also would eliminate the crust growth that happens at the top of the solution that is a nuisance to deal with at best. With no air present and no evaporation taking place, this can't form, and subsequently can't fall to the bottom. This would prevent the near immediate chaos that ensues, as spontaneous seeding in numbers causes a radical increase in surface area of deposition surface, rapidly stripping the solution of it's concentration. This leads to even minor temp fluctuations in the solution causing the intended seed to dissolve, which results in the clarity and "bubble" issues forming later when the lattice goes to try to repair itself.

Ok so there's the basic problem set with the existing layout... Here's how the new scheme would work, in theory lol:

Starts out with the only "charge" of alum it would ever get, and the seed... Runs until the raw alum is gone, or I just decide I don't want to grow it any bigger.

The entire thing would be contained in an insulated chamber (with an observation window of course), and operates just slightly above normal expected maximum room temp.

Growth rate is controlled by the delta between the supply and growth containers. The heating coil would be actually placed around the circumference of the jar in a spiral. The peltier regulates the growth chamber solution temp. I'm undecided at this point if the peltier should be mounted to the growth chamber itself, or to use a heat exchanger as drawn in the schematic. There are pros and cons to both as things sit in my mind. Either way, both the peltier and heating coil would be controlled by CV feedback (probably even just analog at first, if successful, a microcontroller replacing it later).

The pump keeps a steady supply of saturated solution flowing in a primary loop (from/to the supply container), the valve controls the diversion flow rate to the growth chamber, to tune the balance between temperature regulation and disturbance of the growth chamber (ideally this solution should never be disturbed at all, so only as much flow as is needed to prevent stratification and maintain temp should be allowed).

The filter is primarily to keep raw alum from reaching the growth chamber (further reducing the chance of spontaneous seeding) and to trap any slime that may make it's way thru the system. So far a standard coffee filter has proven sufficient to trap everything but the anticake agent that gets added to the alum by the manufacturer. Presently I use sedimentation to remove this; I'm thinking I'll probably actively wash it out of the raw material using something like acetone when this begins to actually take shape.

The deltaT and flow would be adjusted to provide only the amount of saturation that the crystal needs to maintain a slow steady growth. This should result in a precisely controlled, consistent, clean, slightly supersaturated solution reaching the growth chamber at all times.

Toss in a few strategically placed LEDs for lighting, because after all, this is all for the peepers.  8)

The whole thing shouldn't take more than a dozen or so Watts to run, and should give me much better results than I'm getting now.

I guess I'll be posting future crystal related things here in the mean time.

Till then...

(PS - I Was told I needed to include "croissant man and his people" in the pic of the schematic... So there he is. The female head figure as of this writing remains nameless lol)
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Offline solarnewbee

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Re: Growing alum crystals
« Reply #1 on: March 18, 2019, 09:42:34 pm »
Saw this in Banggood.com might be quick and useful and they have various models of peltier available and all manner of stuff cheap. Never let me down.

https://m.banggood.com/DIY-Thermoelectric-Peltier-Refrigeration-Cooling-System-Fan-Kit-p-1111678.html?rmmds=search

Good luck!
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