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Author Topic: Growing Synthetic Corrundums  (Read 2507 times)

Pasrules

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Growing Synthetic Corrundums
« on: June 21, 2023, 07:39:27 PM »
Nice to meet you all, I'm a synthetic chemist from Sydney.

I'd like to make some stones for an engagement ring.

Would anyone have any advice on growing Ruby or Sapphires?

Currently I'm doing this by plasma arc with an alumina + Cr or Ti/Fe mix, but it's early days.

I've also had a look on alibaba/aliexpress at some $300 +ship($200) faceting machines, has anybody tried buying these imports? I figure the quality would be lacking.

I'm sure I'll find something on this forum about being a beginner:
I have experience lapping mechanical valve ceramic faces but haven't faceted before, I would imagine experience running a lathe would translate to some extent... or is there a sworn by series of videos to learn from.

Cheers,
Pas

« Last Edit: June 21, 2023, 07:41:44 PM by Pasrules »

RoughCreations

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Re: Growing Synthetic Corrundums
« Reply #1 on: June 22, 2023, 09:41:31 AM »
Nice to meet you all, I'm a synthetic chemist from Sydney.
Thanks for registering on ALF
Quote
I'd like to make some stones for an engagement ring.
I like your intrepid approach, you'll fit in well here..
Quote

Would anyone have any advice on growing Ruby or Sapphires?
Currently I'm doing this by plasma arc with an alumina + Cr or Ti/Fe mix, but it's early days.
Try using your microwave, lol.
https://www.youtube.com/watch?v=ybcdRQmQcHQ
Quote
I've also had a look on alibaba/aliexpress at some $300 +ship($200) faceting machines, has anybody tried buying these imports? I figure the quality would be lacking.
Don't do it!! If you are seriously interested in faceting, get good machinery at the outset, and sell it later if it doesn't work out for you - for the same/similar price you bought it for probably.
Quote
I'm sure I'll find something on this forum about being a beginner:
I have experience lapping mechanical valve ceramic faces but haven't faceted before, I would imagine experience running a lathe would translate to some extent... or is there a sworn by series of videos to learn from.

Cheers,
Pas
There are quite a few Youtubers that show aspects of faceting. It's worth selecting 3 or 4 Channels you like, plus back it up with a good reference or two, such as "Amateur Gemstone Faceting Vol 1" by Tom Herbst.
A couple I watch:
https://www.youtube.com/@tennpikr74/videos
https://www.youtube.com/playlist?list=PLwBsvcRI6nW-igkdv6wktCq26Z8x2ZH5T
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Faceting Frank

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Re: Growing Synthetic Corrundums
« Reply #2 on: June 22, 2023, 12:50:46 PM »
Hi Pasrules,
Welcome to the forum.
Buy the Corundum rough, or even better cubic zirconia. https://www.gemcuts.com.au/synthetic-gemstone-faceting-rough Gemcuts have a good selection at competitive prices.
As RoughCreations says, buy a good second hand machine and if you don’t like faceting, then sell it.

MakkyBrown

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Re: Growing Synthetic Corrundums
« Reply #3 on: June 23, 2023, 09:57:04 AM »
Welcome Pasrules,
Very cool trying to create your own crystals.  Very interested in how you go.

Cheers
MB

Pasrules

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Re: Growing Synthetic Corrundums
« Reply #4 on: June 24, 2023, 11:35:37 AM »
I appreciate the warm welcome and advice.

A first run to test out the graphite crucible with straight alumina can be found here:
https://cdn.discordapp.com/attachments/291251122914721793/1121971765044858910/IMG_20230624_111403_409.jpg
https://cdn.discordapp.com/attachments/291251122914721793/1121975723687690260/IMG_20230624_113005_698.jpg
My apologies for no longer having access to XRD and electron microscopy equipment, so the only analytical measurement is a Mohs 9.

I noticed some bands of graphite inclusion on the underside which I believe is a method related due to path of current. Rather than grounding through the crucible I now use two graphite electrodes which brings the material to fusion within seconds.

I'm planning to do a couple runs of 0.5-3% chromium inclusion to see if ruby forms.


As for purchasing a machine, that will probably wait until I can produce some rough. I've looked at UltraTec models which run up $5k USD.... I might make a homebrew version or consider the $500AUD Chinese one and modify it.

Faceting Frank

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Re: Growing Synthetic Corrundums
« Reply #5 on: June 24, 2023, 12:35:09 PM »
Don’t buy a cheap Chinese machine, their rubbish. Buy a good second hand one, I can’t advise you on what to buy as I make my own.  But there are plenty of people on here who can advise you.

mehoose

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Re: Growing Synthetic Corrundums
« Reply #6 on: June 24, 2023, 03:55:25 PM »
Welcome Pasrules! Always interested in someone trying something for themselves!  8)
You mention this being for a 'couple' of engagement stones. My suggestion is simply to contact a Lapidary club near you seeing as you're in Sydney, there's a few around, and let them know your intention.. as in just wanting to make a couple. They might hold 'classes' that you could partake in so you can cut the couple of stones and then when you're done, see if it is something you really want to pursue further before a large outlay on equipment.
I'd also suggest as Faceting Frank did, and that is to purchase the synth rough. The clubs know the material and how they cut on their laps as opposed the material that could 'behave' differently and potentially destroy pricey laps.

As to the images.. the second one looks interesting but I'm looking at it from a cabbing view point but, in saying that, whether it's crystal clear as most folk want for faceting, this is personal and a gift from the heart and it wouldn't matter on the clarity, just that it will withstand the test of time.
Keep em comin!!!

RoughCreations

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Re: Growing Synthetic Corrundums
« Reply #7 on: June 24, 2023, 04:04:57 PM »
Don’t buy a cheap Chinese machine, their rubbish. Buy a good second hand one, I can’t advise you on what to buy as I make my own.  But there are plenty of people on here who can advise you.

Agree.
Pasrules, I get that you have the skills to modify a faceting machine, a lot of us on the Forum do this to varying degrees by tweaking sound, well designed faceting machines - and that is frustrating enough as it is! The cheap Chinese ones can be modified, but it's like putting lipstick on a pig. You will never be happy with the end result, and will either leave the hobby in disgust a year or two down the track, or end up buying a good second-hand or new machine anyway...
Quote
Currently I'm doing this by plasma arc with an alumina + Cr or Ti/Fe mix, but it's early days.
What are you using for a power supply?
Be interested to see how adding the chromium goes.
RC
« Last Edit: June 24, 2023, 05:19:03 PM by RoughCreations »
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MakkyBrown

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Re: Growing Synthetic Corrundums
« Reply #8 on: June 25, 2023, 10:48:31 AM »
Regarding machines, Ultratec's are really nice but very expensive once you pay freight and import duties.
Getting a Hall Extra or a Facetron and put an optical encoder on it would be a nice machine. I wouldn't waste your $$ on the Chinese machines. Hall Extra are $3784aud
VJ are making machines locally(not cheap at $7300aud). They are very good machines but unable to fit an encoder if you wanted to.

Link for Halls
https://unamit.com.au/
Link for VJhttps://www.vjfacet.com.au/
Hall has a waiting list that could be quite lengthy.
Cheers
MB

Pasrules

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Re: Growing Synthetic Corrundums
« Reply #9 on: June 29, 2023, 10:42:32 AM »
Before I get into the details, the Hall Extra unit is a much more reasonable price to enter the world of faceting for myself, thank you for the suggestion. As to for finding a local club which may let me test samples. The mention of destroying laps really comes to mind after testing the sample produced on common metal shop abrasives (to be expected).

Alas onto the show.

Method:
170 Inverter Arc welder with 2x carbon gouging rods (BOC), arcing between them.
Mix of 3% chromium(III) oxide and 97% calcined alumina, shipped from walker ceramics, Victoria.
Graphite crucible (1Kg) from Australian Jewelry Supplies, Sydney.

Results:
First run was powder on the bench and arcing over it:
https://cdn.discordapp.com/attachments/291251122914721793/1123128387611938846/IMG_20230627_154556_120.jpg
https://cdn.discordapp.com/attachments/291251122914721793/1123128387934892032/IMG_20230627_154142_664.jpg
https://cdn.discordapp.com/attachments/291251122914721793/1123128388194930718/IMG_20230627_154120_198.jpg
https://cdn.discordapp.com/attachments/291251122914721793/1123128388559851561/IMG_20230627_154033_570.jpg

Most of the smaller beads are very brittle with voids, the larger piece has a surface layer of ruby about 0.5-1mm thick which a black corundum substrate, again very voided and brittle.


Second run was in a crucible with 30g of mix:
https://cdn.discordapp.com/attachments/291251122914721793/1123542106082922516/IMG_20230628_180105_105.jpg
https://cdn.discordapp.com/attachments/291251122914721793/1123542105789300746/IMG_20230628_180125_503.jpg
https://cdn.discordapp.com/attachments/291251122914721793/1123542105495711856/IMG_20230628_180158_351.jpg

Attempting to reheat the solidified mass (bottom)
https://cdn.discordapp.com/attachments/291251122914721793/1123542105189535764/IMG_20230628_181940_746.jpg

Destructive analysis
https://cdn.discordapp.com/attachments/291251122914721793/1123542104635867246/IMG_20230628_182718_848.jpg
https://cdn.discordapp.com/attachments/291251122914721793/1123542104266780783/IMG_20230628_182831_887.jpg
https://cdn.discordapp.com/attachments/291251122914721793/1123542103809609769/IMG_20230628_183041_517.jpg
https://cdn.discordapp.com/attachments/291251122914721793/1123542103486627850/IMG_20230628_183049_030.jpg

Discussion:
The first test on the bench had minimal sprays to a radius of 200mm from the arc until a puddle of molten material forms which slowly accumulates. The products created are undesirable, they are very brittle and have a lot of voids, they shatter easily with pliers. This would indicate rapid cooling causing embrittlement and crystallization not occurring during the fusion.

The crucible melt of powder took about 2 minutes under arc, it formed a molten mass sitting in the center of the powder shot without touching the crucible walls. The heating process creates a brilliant light paying homage to the Stefan-Boltzmann law. No violent stress fracturing occurred and a boule of product can be seen in the images. The bottom side of this boule was crusty with pink powder. I should have cracked it open to see the depth of ruby formation, but from the bottom view we can see corundum (black) substrate present. The boule was resistant to blows from the slag chisel.

Upon remelting the solid boule, great difficulty was encountered to melt the product owing to its poor thermal conductivity. Most of the energy input created a puddle of product ontop of the boule which would re-solidify multiple times as attempts were made to heat the surrounding material. The molten material may have been conductive but no difference in performance was observed with the electrodes above or in the molten puddle. Also to note the consistency of the puddle against the rod was like pressing into wax. The welder is under powered to push enough energy into the sample, although the steel bench popped during heating which ended the run without consequence.
Inspection of the remelted boule was black corundum with a bottom of powdered pink. This new boule broke easily and could be cracked apart by hand. Inspection under magnification shows a thin 1mm layer of ruby on a corundum substrate formed. The ruby layer easily destroyed corundum emery paper abrasive and was reasonably resistant to a stone bench grinder.

The formation of corundum is under question, the following theories may account for it:
Alumina melts at ~2000°C, chromia ~2400°C, per flame Verneuli the best temperature to create synthetic corundum is as low as possible to melt the alumina then allowing the chromia to dissolve in solution. This means the welder at ~3000°C was too hot. Possibly allowing separation to occur.
Insufficient power could have kept the alumina liquid which let it settle down to dissolve cooler powder leading to pink bottoms, or the chromia being denser could have had the same effect. Where the less dense alumina forms at the top. It is difficult to tell as the remelted boule had inverted formation to its parent.
The black material may have carbon inclusions, it is unsure what effect this has, possibly owing to the blackness or mis-identification.

Going forward, the arc method is not suitable but potential improvements would include a higher power unit, inert blanketing, longer heating cycle.
A oxyhydrogen torch method similar to flame Verneuli is to be the target of new experiments.

Faceting Frank

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Re: Growing Synthetic Corrundums
« Reply #10 on: June 29, 2023, 11:35:02 AM »
Wow, you may have broken the forum record for the biggest post.
I know nothing about creating synthetic gem material, though I do know that oxidisation and rapid cooling would cause major problems.
Never used a Hall Xtra faceting machine, but have heard good reports about them.

Ghost

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Re: Growing Synthetic Corrundums
« Reply #11 on: June 29, 2023, 08:46:22 PM »
Have had my Hall X-tra for 13 years.   Love it.
You may have a longish wait for it.   Check with UNIMAT re delivery.
Keep having fun.
Regards,
Ghost.


RoughCreations

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Re: Growing Synthetic Corrundums
« Reply #12 on: June 30, 2023, 09:47:35 AM »

Alas onto the show.

Method:
170 Inverter Arc welder with 2x carbon gouging rods (BOC), arcing between them.
Mix of 3% chromium(III) oxide and 97% calcined alumina, shipped from walker ceramics, Victoria.
Graphite crucible (1Kg) from Australian Jewelry Supplies, Sydney.

Results:
First run was powder on the bench and arcing over it:
.
.
.
Going forward, the arc method is not suitable but potential improvements would include a higher power unit, inert blanketing, longer heating cycle.
A oxyhydrogen torch method similar to flame Verneuli is to be the target of new experiments.
I reckon focusing on flame Verneuli is the way to go, see if you can replicate the process yourself first, then consider variations if you see fit. Incremental improvements and all that. So the chromium III oxide is lime-green out of the box, then goes ruby-red on reaction with alumina? That's really amazing. I will have to go through my literature regarding the Verneuli method.
RC
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Aussie Sapphire

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Re: Growing Synthetic Corrundums
« Reply #13 on: June 30, 2023, 12:46:14 PM »
I've also had a look on alibaba/aliexpress at some $300 +ship($200) faceting machines, has anybody tried buying these imports? I figure the quality would be lacking.

Cheers,
Pas

I saw a video on youtube the other day on a review of a Vevor cheap faceting machine - ultimately he gave up and turned it into a flat lap:

https://www.youtube.com/watch?v=3kTw-G0VTDg

Someone further down the thread recommended a Hall Xtra from Unamit.  As I understand it, Peter is in the process of retiring - already long waiting list for machines so may not be feasible to get that one but check on this as I did not get that from the horse's mouth.

cheers
Leah
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Pasrules

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Re: Growing Synthetic Corrundums
« Reply #14 on: June 30, 2023, 09:34:42 PM »
So the chromium III oxide is lime-green out of the box, then goes ruby-red on reaction with alumina? That's really amazing. I will have to go through my literature regarding the Verneuli method.
RC

To give a quick rundown, we deal mostly with white light which I'm sure you've seen on a Pink Floyd album, can be split into the rainbow.

So we have a matrix of alumina. In a crystal "zone" such as:
Al-O-Al-O
O-Al-O-Al
Al-O-Al-O
Now to keep the quantum effects of light aside, although feel free to ask. Aluminum is a boring ion/atom as it is not a transition metal, this means it always reflects white light. When light hits the crystal some energy is absorbed and emited at certain colour bands.

Now you've already noticed that Cr2O3 is green,  which is due to it being a transition metal. It has different states (II),(III),(IV) which can vary from black, green, purple. When we introduce chromium atoms into the crystal matrix like so:
Al-O-Al-O
O-Cr-O-Al
Al-O-Al-O
Depending on the bonding energy and state of the chromium some colour will be absorbed/emited giving the characteristic ruby red. Or the range of colours you see in gems.

Now on the topic of clarity, these crystal zones have boundaries "grain" where you see imperfections in your stone due to the matrices not lining up causing like to scatter. A perfect clarity stone will be single crystal by keeping the material liquid until all the atoms can arrange themselves rather than cooling and being caught at the boundaries.
Al-O-Al-O Al-O-Al-O
O-Al-O-Al O-Al-O-Al
O-Al-O-Al Al-O-Al-O <- bad matrix/grain boundary

 

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