HPHT stands for High Pressure High Temperature. It is a process used in the production of lab-grown diamonds, where a diamond seed is placed in a press and subjected to high pressure and high temperature conditions that simulate the natural process of diamond formation deep within the earth’s mantle. Under these extreme conditions, carbon atoms in the seed rearrange themselves and bond together to form a larger diamond crystal. The process can take several weeks to several months, depending on the desired size and quality of the diamond.
The steps involved in the High Pressure-High Temperature (HPHT) process for growing diamonds are as follows:
- Seed crystal selection: A small diamond crystal, known as a “seed”, is selected as the starting point for the growth of the new diamond crystal.
- Preparation of the growth cell: The growth cell is prepared by placing the seed at the bottom of a metal cylinder with a carbon source and a metal catalyst, such as iron or nickel.
- Closing the cell: The cylinder is sealed and placed inside a high-pressure press that can generate pressures up to 5-6 GPa.
- Heating the cell: The cell is heated to temperatures between 1400-1600°C, similar to the temperatures found in the Earth’s mantle where natural diamonds are formed.
- Creation of the diamond: The heat and pressure cause the carbon in the cell to dissolve and settle onto the seed, creating a diamond crystal layer around it. The crystal grows layer by layer until it reaches the desired size.
- Cooling down the cell: The cell is gradually cooled to room temperature over several hours to prevent thermal shock that could cause the diamond crystal to crack.
- Removing the diamond: The metal cylinder is opened, and the diamond crystal is removed from the cell. The diamond may be rough and cloudy at this point, so it needs to be cut and polished to reveal its beauty.
- Cutting and polishing: The diamond crystal is cut and polished using traditional diamond cutting techniques to maximize its brilliance and beauty.
- Grading and certification: The finished diamond is graded and certified using the same standards as natural diamonds, including the 4Cs of diamond quality – carat weight, cut, color, and clarity.
Overall, the HPHT process is a complex and specialized process that requires high-pressure equipment, skilled technicians, and precise control of temperature and pressure. The resulting diamonds are chemically, physically, and optically identical to natural diamonds and offer a sustainable and ethical alternative to mining diamonds from the earth.