GETTING SMALL

Diamond is the hardest, strongest, most thermally conductive substance and the ultimate fine polish. A human hair is 60 micrometers in diameter. Silica and alumina suspensions for polishing are sold in 20 nanometer particle sizes. Getting natural diamond below one micrometer (1000 nanometers) diameter is a daunting task. Swarf, waste diamond dust from gem cutting, is big business. Natural diamond dust is not rare, it is too large. How can it be crushed, and against what? Diamond pulverizing equipment suffers significant wear and its lost mass fouls the product. Diamond is to the hardest tool steel as the hardest tool steel is to butter. Exotics like titanium nitride, titanium boride, or strained superlattices are gnawed away.

An obvious answer to smaller diamond dust is for government to sponsor crash programs to make diamond dust larger. Who could afford the cost or the delay, or the perpetual calls for more studies needed from windbag academic consultants? We will have to (gasp!) think.

This is micronization, not gravel to sand. At micron dimensions diamond in water is like dandelion seeds in air - the medium is thick as molasses at scale. Stuff does not crash together and splinter. Diamond cannot be thermally shocked. Diamond has a tensile strength of ten tonnes/mm2. By what clever means will brittle failure trigger, pulling apart each diamond dust mote at its surface defects?

Chemical erosion works (nitrate/nitrite molten salt bath). Each big lump dissolves to a teeny one, then disappears entirely. Mass loss is fastest at edges and corners. Good diamond dust is not smooth-surfaced, it is all cutting edges. Whittling individual wheat grains into individual flour grains is silly.

What has enough energy/microvolume to succeed?

  1. Bulk explosives. Diamond tends to sinter or graphitize.

  2. Ultrasonic cavitation. Very high power ultrasonics maybe barely. Horrible wear problems. Ugly energy inefficiency.

  3. Attrition, other contact milling. From what do you fabricate the contact surfaces?

  4. Jet milling. Already done. Problem of the dandelion seeds. The orifices wear away as you watch.

Whatever submicronizes diamond

  1. Cannot be a solid impact surface (nothing is hard enough).

  2. Must operate at the scale of crystal flaws (or energy is wasted).

  3. Should be focused like a chisel blade or needle punch and ignore flat, unflawed surfaces.

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Pump out diamond dust hot in vacuum to desorb air, moisture, and other surface volatiles (quantify surface area with BET nitrogen adsorption). Cool. Backfill with enough nitroglycerine or ethylene glycol dinitrate vapor to fill nanovolume pits, fissures, cracks, etc. Initiate the explosive. That last is a non-trivial item.

A pulsed laser suggests itself - perhaps in the infrared where diamond is transparent (outside 2.5 - 6.67 microns, 4000 to 1500 cm-1) and the explosive is not (nitrate N=O stretch, around 6.13 and 7.81 microns, 1630 and 1280 cm-1). That would be the mid-IR (ISO 20473 scheme 3-50 microns). Kilowatt CO2 lasers output 10.64 microns, 939.85 cm-1. Er-YAG lasers output 2.94 microns, 3401.36 cm-1. In the middle are tunable CO lasers 4.8-8.3 microns, 2083.33-1204.82 cm-1.

Maybe microwave pulse it, polar explosive lossy dielectric versus non-polar diamond. Initiated explosion may propagate on its own, or it may not.

Do not make the diamond dust mass soggy. Diamond dynamite is not the object. I propose surface adsorption, tiny surface-wicked drops the size of bacteria. If it goes at all the total energy release vs. total mass must not amount to much. Local microscopic brisance is crucial. It would be millions of tiny chisels focused at pits, cracks, and other defects. Crystalline diamond is very brittle. Robust size reduction in one fell swoop generates angular shards.

If the liquid explosive wets the diamond surface, cracks and pits will specifically fill to the exclusion of flat surfaces by capillary action (negative meniscus). This creates untold numbers of shaped charges where they are desirable. If the explosive does not wet the diamond, it will be specifically excluded from cracks and pits (positive meniscus), which is very bad indeed. Know what you are doing.

Native diamond is carpeted with a skin of C-H bonds, like grease - very low surface energy. A liquid must have a lower surface energy than the surface energy of a solid to wet it. Plasma surface treatment enhances wetting by raising surface energies through oxidation. Folks who do diamond dust ought to know about surface energies and liquid contact angles, or do a good experiment to evaluate wetting feasibility directly or with suitable model compounds.

Blast one end of a compacted cylinder (in a ductile containment sleeve, preferably non-ferrous) of nitro-adsorbed coarse diamond dust with a CO2 or Nd-YAG laser pulse to pop a macroscopic fart. Microscopically you suddenly have sub-micronized diamond dust. It scales to clean industrial production. Fast cycle time, too.

Pump diamond, suck nitro, have a blast, get small!

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