How HPHT Diamond grown in Lab

What is HTHP Diamond

Human have created several methods to produce diamonds, high pressure high temperature is one of them. Scientist studied various processes and performed so many experiments. Finally they built new pressure chambers and began to experiment with different temperature. HPHT is a scientific procedure which is
performed inside laboratory where temperature and pressure is raised to produce genuine facsimile mined diamonds. The price of lab grown diamonds is fairly
comparable with natural one. It shows the same optical and chemical property.

There are specific designs templates which provide prescribed parameter for the pressure and temperature to produce synthetic diamonds are:

1. The belt press
2. The cubic pressing
3. The split sphere (BARS)

Process:

Diamond seeds are placed at the bottom of the press. The internal part of the press is heated above 1400C which melts the solvent metal. The high purity carbon source which dissolve s the molten metal which is then transported to small diamond seed and precipitates which result into a large synthetic diamond.

The belt press:

The belt press has an upper and lower anvil which is used to supply the pressure load to the cylindrical cell. The internal pressure is confined radially by the pre-stress steel bands. The anvil also functions as the electrode which provides electric current to the compressed cell. A variation of the belt press uses hydraulic pressure, rather than the steel belts, to confine the internal pressure.

The cubic press:

The cubic press has six anvils which provide pressure simultaneously to all the six faces. A cubic press is usually smaller then the belt press which is beneficial in achieving high pressure and temperature necessary to create the synthetic diamond. Cubic press cannot be easily scale up to larger volumes, the pressurized volume can be increased by using the large anvils but simultaneously it increases the amount of forced applied on the anvils to match the same pressure. Again if we decreases the surface area to volume ratio of the pressurized volume, by using the more anvils to converge upon a higher-order platonic solid, such as a dodecahedron.

The split sphere (BARS):

The BARS is the most compact, efficient and economical among all the diamond-producing press. In the center of the BARS there is one cylindrical synthetic capsule of 2cm 3 size. The cell is placed in to the cube of pressure-transmitting material such as pyrophyllite ceramics which is pressed by the inner anvils made from cemented carbide. The outer octahedral cavity is pressed by 8 steel outer anvils. After mounting the whole assembly is locked in a disc type barrel with diameter about 1 meter. The barrel is filled with oil, which is then pressurizes upon heating, and the oil pressure is transferred to the central cell. The synthetic capsule is heated up by a coaxial graphite heater and the temperature is measured with a thermocouple.

That's all. Looks simple but actually is much difficult than you think. Lets learn another process which is CVD in next article.