Has anybody ever attempted the Verneuil process here?
This for anyone that doesn't know, involves a vibrating powder dispenser, supplied with O2, and a H2 feed lower down, ignition, of course, to give an
oxy-hydrogen flame. The dispenser shakes down small quantities at a time of for instance, Al2O3, which one would dope with various transition metal
traces, to make synthetic gemstones, the material falling onto a rod of some extremely refractory material (molybdenum? tungsten?) and slowly
withdrawn.
Anybody got any idea about the power supply needed to supply the H2 and O2 from H2O at a sufficient level to provide enough gas pressure for this
application? making synthetic gemstones out of alumina sounds like money for little expenditure. And, well, I'm poor and need a source of topped up
income. Synthetic gemstones sounds like a fun project too. Anyone done it before?wg48 - 19-2-2017 at 04:45
Years ago I made a crude attempt with sand using an oxy acetylene torch. It was obvious a carefully designed chamber was needed to keep the heat in
and control the gas flow so the molten sand would arrive at the right place.
To make gems very pure materials and gases will be needed and which insulation do you use?
As to the power required to generate your H2 and O2: If your not storing them then you will need an electrical power that is about twice the heating
power you require. So if you need 1kW heating that’s 2kW electrical to power a very large electrolysis unit. For one cell that’s 400A !!!
It is doable it was done a 100years ago but it would be a big project.
tsathoggua1 - 19-2-2017 at 05:11
Well pure alumina is available easily enough is it not, for chromatography purposes. Might be ideal, considering it should be available in very fine
grades.
Did you manage to melt the sand?PHILOU Zrealone - 19-2-2017 at 06:20
I did some rubies pearls (2-3 mm diameter) from butane/N2O torch Al2O3 and Cr2O3...you need to go higher than 2000°C even 2100°C to melt aluminia.
The main problem with this process is that a lot of the powder is sprayed away by the hot burning gas blow...also hard to avoid bubble inclusions.
I have a source in Paris that sells Verneuil's saphires some pictures of my collection are here
There exist some muffle furnaces for lab purpose that can go as high as 2500°C...with that no problem of bubble inclusion...you simply need to add a
substance (melting flux) to allow for an easier eutectic melting...then slow cooling and crystallization.
I had seen that an american lab was specialized in making such synthetic corundum/saphires for optical use/lenses...it was like a candy store full of
colored transparent candies.
The price of their gemstones was 1/20th of the price of natural occuring one. To identify them, they had introduced a doping stuff to allow for a
specific fluorescence/spectra.
Edit:
The flow of gas and heat generated must be proportionnal to the size of the pearls and sticks you want to grow...so this can be high for large
specimens as the one you intent to do (to get money return on your investment)...for this you will need a generator than can decompose at least 1
water mole/minute --> 18 g (genarating 2g of gaseous H2 (22,41 L) and 16g of gaseous O2 (11,205 L))
[Edited on 20-2-2017 by PHILOU Zrealone]markx - 26-2-2017 at 23:42
Direct electrolytic generation of the gases at a rate needed for successful operation of the Verneuil device might prove problematic for several
reasons. One of which is the trouble arising from the noncomplete separation of H2 and O2 in the generator device (or rather their tendency for
partial mixing in the electrolyser). At high current densities the gases at the electrodes evolve as very tiny bubbles that have a profound residence
time and tendency to move around with the slightest convectional currents of the electrolyte. Unless one uses efficient membrane to keep the gases
separated, there arises a great risk of the whole thing blowing the lid off. Running an eletrolyser without separating membrane at high current
densities will sooner or later result in explosive gas mix, despite intricate measures to avoid electrolyte convection. Don't ask how I know!
In light of this venture being undertaken for the sake of profit I would suggest to go for the bottled option of gas supply. Much more stable, safe
and way less complicated. In the long run this saves one a lot of time, trouble and financial loss. tsathoggua1 - 27-2-2017 at 14:21
What about using a divided cell, with separate compartments serving as anode and cathode, each with a separate feed line. Would dramatically reduce
risk of explosion for one thing, and allow proper separation of the gases.wg48 - 27-2-2017 at 15:36
Well pure alumina is available easily enough is it not, for chromatography purposes. Might be ideal, considering it should be available in very fine
grades.
Did you manage to melt the sand?
No I failed to melt the sand in to a blob. Dropping the sand in into an approximately 45deg down pointing flame did blow the sand along the flame but
most of the sand was scattered as it dropped out a long the bottom of flame length. Finer sand would have helped.
As I said you need something like the system below (from wiki)
This seems a tad easier, a bit more backyard friendly
That's very similar to what I tried. It did not work for me.. Fine particles tend to flow with the flame and heat up but larger particles drop
through the flame on to a cold bolus and don’t have time to heat up. .The flame needs to be directed on to the bolus. The vertical set up solves
both problems and insulation saves gas and keeps the bolus hot.tsathoggua1 - 20-3-2017 at 04:21
Couldn't using a colloidal solution through a fine-bore needle and charged bolus (plated if needs be by refractory metals, Ir, Mo, W, Os, Rh etc.)
help circumvent particle size issues?
And what, if anything, speaks against using a horizontal arc passed axially to the boule growth platform and a longtitudinal flame oxyhydrogen flame
or plasma torch 'flame' such as an inert xenon plasma (given Xe has a low ionization potential compared to most elements for greater ease of forming a
sustained arc)Bezaleel - 18-4-2017 at 03:05
One thing that speaks against using arcs is that they tend to be dirty. Contamination of the ruby is your big enemy.
There exists no materials which are completely resistant to an electric arc emerging from them. Internally cooled tungsten electrodes are relatively
solid state for producing arcs. But even these will burn up sooner or later. (Ask a TIG welder why he needs new electrodes once in a while.) phlogiston - 18-4-2017 at 06:45
@tsath, xenon is about 12 times less abundant in air than krypton, and about 100,000 times less abundant than argon.
Using Xe would probably be cost-prohibitive
However, perhaps with Argon?
An ICP torch uses argon and because the plasma is not in physical contact with electrodes or any other metal, it can be highly pure, as evidenced by
the fact that ICP-MS is capable of quantifying metals at extremely low concentrations (ppt levels are routine).Melgar - 30-4-2017 at 04:04
