Diamond creation using High Pressure High Temperature (HPHT) technology emulates the conditions under which diamonds naturally form in the earth’s mantle. By applying extreme heat and pressure, the atoms in source materials rearrange themselves into diamond’s iconic tetrahedral crystal lattice structure.
HPHT machines use presses that generate pressures between 58,000 to 60,000 atmospheres and heat around 1500 degree Celsius. These extreme conditions are close to those found at the optimal diamond forming depth of 150km inside the earth. The raw material used is usually graphite, the same allotrope of carbon that makes up the parent material for natural diamonds.
The graphite is packed into a small refractory metal capsule along with a catalyst like nickel or iron. This capsule is placed at the center of the HPHT press between the anvils. The pressure is applied slowly and increased steadily to avoid uneven stress. Electrical energy helps heat the press and initiate the diamond seeding process.
WSU shock physicist Stefan Turneaure and a team of researchers found that at 500,000 atmospheres of pressure, the crystalline structure in the form of highly oriented graphite transformed into the rare form of hexagonal diamond, which is about four times lower than previous studies had shown.
Given weeks or months under these stable conditions, the diamond crystals can grow layer by layer to considerable sizes. Temperatures must be maintained between 1100-2500 degree Celsius to provide sufficient energy for the atoms to rearrange. After the process is complete, the metal solvent is removed by acid washing, leaving raw hpht diamonds.
So in summary, mimicking the natural conditions which create diamonds underground allows graphite’s rigid tetrahedral structure to emerge through the application of meticulously controlled high pressures and temperatures in an HPHT machine. This scientific process results in lab-created diamonds physically and optically identical to natural ones.
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