[Dallier]

Theoretically if I combined the following  Al2O3 + Cr2O3 + MoO3(MOLYBDENUM TRIOXIDE)
placed the solution in a sealed container. Then using a furnace to achieve a temperature of approximately 1400°c... would this conceive a 'RUBY' and any idea of how long it would take ?

Also.. would I simply use water to create a solution of the chemicals used?

maybe i'm on the completely wrong track, but any help would be great! thank you !

[Arkcon]

I don't know why you need molybdenum trioxide, as I understand it, ruby is just aluminum oxide with a trace of chromium oxide.

I'd seen a Nova program on gemstones, and a pair of women do make synthetic rubies using these raw materials, and some sort of flux, which is proprietary.  But yse slowly cooled in a furnace, is the basic idea behind crystal growth from a melt.

The compounds aren't water soluble, so no they can't be grown that way.  Although you can grow insoluble salts from soluble compounds in water.  Using a gel to slow diffusion allows crystals to form.

[Enthalpy]

Isn't the difficult part to make a single crystal instead of an amorphous thing?

Ruby grown for lasers is obtained by Bridgeman or Czochralsky methods if memory serves. It takes time (weeks, months) and special procedures, similar to semiconductors.

For sure, the furnace that doesn't pollute the melt at 1400°C is non-trivial. Traces of pollutants change the colour.

http://en.wikipedia.org/wiki/Ruby#Synthetic_and_imitation_rubies

[Dallier]

Thanks for the feedback & good points! 

this is where I got the idea http://www.ncbi.nlm.nih.gov/pubmed/15080667

maybe you can make more sense of what he means by "heating a mixture of solute (Al2O3 + 0.5 mass% Cr2O3) and flux (MoO3)"

I'm slightly confused about the way the word 'flux' is used. is it referring to a container, solvent or stabilizer?
and one last question, every source I find seems to give a different idea about the amount of time it should be heated (5hours - 2weeks) maybe this is something that effects the quality & size of the crystal, perhaps avoiding a complicated method & heating only for 5hours would create something amorphous as 'Enthalpy' mentioned.

thanks again!

[Borek]

I would expect "flux" to mean "substance that facilitates melting". So what they did was they heated the mixture of solids in a crucible till it melted.

[Enthalpy]

That's how I believe to understand the abstract you linked
http://www.ncbi.nlm.nih.gov/pubmed/15080667

0.5% Cr₂O₃ in Al₂O₃ is what makes the final product, ruby. Cr makes the colour centers that give the colour or possibly lase.

Instead of melting (or dissolving if possible) the ruby constituents, then solidifying it, the authors added a flux that helps melting at a lower temperature, and chose MoO₃ because it evaporates easily. Upon evaporation of the flux, ruby is no more a liquid at the chosen temperature but a solid - it crystallizes. Well done.

The authors did not control the crystallization at all, so many small (1.7mm) crystals formed spontaneously. A slower evaporation of the flux (or more usually, cooling of the pure ruby melt) would let pass the liquid-to-solid transition more gently, hence have fewer seeds from which crystals grow, and this would produce bigger crystals.

Some uses desire single crystals of high quality (lasers, particle detectors, semiconductors) and these don't rely on random seeds. The process provides a seed and lets the crystal grow in one direction under controlled conditions, generally a temperature gradient. These are the Bridgeman and Czochralski methods.

Alternately, the crystal can begin spontaneously at the coolest end of the target part, pass through a narrow point that selects one crystal from the many spontaneous seeds, the proceed with the desired shape. This is done for gas turbine blades of nickel alloy, presently single-crystal, which reduces creeping at heat.

Among these possibilities, I see Czochralski that could be adapted to the vaporizing flux to make big crystals of ruby and more.

[crzycdn]

I read somewhere, that something similar can be done but for *diamonds*.. I cannot seem to find the particular article I had read previously.                                                                                                                                               

Looking forward to replies especially if someone does find the article I am referring to which had photos, and more detailed information.                                                                 

[Enthalpy]

Hi crzycdn, can you be more specific? Because diamond growth has been the subject of much research, is presently rather common in the industry, and articles with photos are not exceptional.