HIGH SCHOOL DIAMOND PROJECT

(No, folks, this is not the Devil Solvent project. Pookie pookie.)

Less than 10-carat cut gem white diamond is all but worthless. The world is awash in unregualted smuggled African "blood diamonds" plus Siberian, Australian, and Canadian production. Carat gems are swindle cut to maximize raw stones' weight yield. A FireScope exposes the crap your jeweler is pushing at up to triple wholesale price. The few honestly "ideal cut" diamonds are inferior to EightStar specs. de Beers vaults hold some 50 million carats of raw large diamond. Big diamond money is in abrasives, particulates to sintered inserts for cutting and tooling. What wears out must be replaced, razors and razor blades. Jewelry is a dead end application.

Other than the high school science project to come, there are five ways to synthesize bulk diamond from non-diamond carbon:

  1. Nature: 100+ miles under your brogans at equilibrium on the carbon phase diagram, 1500°C and 55,000 atmospheres, megayears to crystallize. A rich diamond mine is 1 gram of diamond (all types) in a million grams of kimberlite or lamproite.

  2. Tracy Hall: nature plus a carbide-forming catalyst/solvent, 1700°C and 70,000 atmospheres. Sintered abrasive comes out in 20-30 minutes. Growing a clean carat takes about a day, and that loses up to 60% when cut. Growing larger than 5-carat cut gems is not economically attractive.

  3. Brad Pate's kinetic synthesis as chemical vapor deposition, ~800°C and 0.2 atmosphere pressure at the deposition pedestal. Argon/hydrogen/methane plasma selectively deposits diamond and erodes other carbons. An entry level rig is ~100 KW. CVD diamond is expensive, polycrystalline, and slow to grow thick.

  4. Shock synthesis, 1600°C and 300,000 to a million atmospheres for a microsecond by implosion. 100 kg of RDX/shot is not unusual. Graphite gives nanometer-sized abrasive in 30-80+% yield. Residual graphite is removed by selective oxidation in molten KNO3/KOH or warmed H2O2/HNO3 mixtures. Nasty.

  5. Continuous synthesis within molten Devil Solvent at 800°C and ambient pressure, depositing 1 carat/cm2-hr and growing gem diamond to essentially unlimited size. We're playing with it.

We know from CVD that carbon atoms plus hydrogen radicals in a whole bunch of hot will kinetically deposit diamond. What would happen in a thermite reaction run as aluminum and anhydrous sodium acetate (rather than with rust to give molten iron)? Lots of WHOOSH! is pledged. Sodium aluminate, hydrogen gas, soot, and maybe aluminum carbide exit as co-products? The carbon need not appear as graphite soot. Smoky oxyacetylene flames, a hot reducing environment containing carbon atoms and hydrogen radicals, deposit some black diamond when cold-quenched.

Equipment for carbon aluminothermy is not daunting - terra cotta flowerpots, some paper or aluminum foil, and non-flammable wide open space. It's a crazy idea, but is it crazy enough? 

2H3CCOONa + 2Al  -->  2NaAlO2 + 6H2 + 4C
 82.034   26.981     mp=1650°C (1535°C for Fe)

3.04 parts anhydrous sodium acetate to 1 of aluminum by weight is stoichiometric. 100 grams of sodium acetate get you 29 g of carbon. Add 100 ppm of borax to the well-mixed charge before firing. Type IIb boron-doped diamond phosphoresces red-orange up to a minute after 254 nm UV mercury lamp excitation. It is easy to find, even (especially!) in the dark. Sodium aluminate is very soluble in hot alkaline water. Reaction mud may be no dud!

It may run so hot that diamond graphitizes even with hydrogen around (1500°C; 800-1000°C in oxygen). Dump the molten charge out the bottom hole of the flowerpot (previously blocked inside with a sheet of paper or aluminum foil) into a metal drum of water or crushed ice. Be in a foxhole when it happens. Beware the BLEVE! Do the lab work on 04 July while chanting "safe and sane." Nobody (Homeland Severity comes to mind - "one nation, under survellance") will notice.

A diluent boosts the proportionate carbon charge and lowers the reaction energy/volume to lower the temperature. Fatty acid sodium salts (traditional soap) have lower oxygen contents and are less hygroscopic than sodium acetate. They are cheaper, too. Magnesium stearate is bulk cheap, but magnesium aluminate is the insoluble refractory ceramic spinel. 

Oxidant      wt-% O  C/2(O)
-----------------------------------
Fe2O3          30.05
Fe3O4          27.64
Na acetate    39.01     1
Na butyrate   29.07     4
Na caproate   23.16     6
Na caprate    16.47    10
Na stearate   10.44    18

Abrasive diamond retails for $(US)1-5 carat and up. Given starting materials costing pennies/gram (Ivory soap flakes come to mind) and product enjoying a 100-fold markup, there is room for profit to be made. We will celebrate with fireworks and wash our hands of the whole de Beers diamond monopoly thing. When soap is declared to be a National Security risk (Congresscritters are the best totalitarian rulers money can by), switch to sugar, 

3C12H22O11 + 22Al --> 11Al2O3 + 33H2 + 36C
 342.296   26.981

1.73 parts sucrose to 1 of aluminum by weight is stoichiometric. 100 grams of sugar get you 42 grams of carbon. One loathes to anticipate the following inescapable dialog, soap or sweets,

Production monkey, "We keep getting big clear octahedra from the aluminothermy runs. We want to make abrasive diamond dust."

Management, "The spec says 'dust.' Use sledgehammers to pulverize them. I am an important man and I am planning my week's lunches. Go away unless you know how to make this spreadsheet thing work."

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