The Split Die Technology

The belt apparatus is too bulky for making gem diamonds on one hand, and the split sphere is too complicated for making one crystal at a time. The solution is to extend the split chamber to form a longitudinal chamber that allow multiple crystal to grow simultaneously (Sung, Chien-Min, US Patent No. 7,128,547). The growth conditions of each diamond crystal can be precisely controlled by

Figure 11.8. Polished artificial diamond gems with different colors.

its own temperature monitor with real time adjustment. Because all diamond growth chambers are coaxial, their pressures are uniform.

The split chamber makes the use of a conventional design known as cubic press. The cubic presses have been used for massive production of diamond grits. Chinese produced most of such industrial grades with several thousands press in operation (Fig. 11.13).

Figure 11.9. The Gemesis process with split sphere. Only one crystal per cycle could be grown. The lower diagram showed the crystal size and weight as a function of growth time.

Figure 11.9. The Gemesis process with split sphere. Only one crystal per cycle could be grown. The lower diagram showed the crystal size and weight as a function of growth time.

The major feature of the split chamber design is that the major diamond growth directions are perpendicular to gravity so the convection in the molten catalyst would not disturb the growth rate. Consequently, all crystals will grow at the same pace to the same size with the same quality (Fig. 11.14).

The cubic press has six anvils that are moving toward the common center of the high pressure assembly. By extending four of the six anvils, an enclosure can be formed where gem diamond seeds are placed inside. The other two anvils, lying horizontally, can be

Figure 11.10. Gemsis diamonds in the rough and after polishing.

used to stroke the cavity to achieve the ultrahigh pressure required for gem diamond growth. As the diamond becomes larger, volume is reduced in the assembly so the two anvils can follow through to maintain the pressure for growth.

The split sphere of Russian design has a complicate enclosure that involves two layers of multiple anvils with complex geometries. Any component of the multiple anvils could be misaligned with the consequence of pressure and temperature instability. Moreover, the expensive components could be damaged easily

Figure 11.11. The Russian diamonds at the display.
Figure 11.12. Natural diamond gems (left) and synthetic ones (right) are indistinguishable unless very sophisticated instruments (e.g. DiamondSure™ or DiamondView™) are used to reveal characteristic fluorescence spectra.
Figure 11.13. The Chinese cubic presses used for the production of industrial diamond grits. Each year more than four billions carats (800 metric tons) of mesh sized (less than half of a millimeter) grits are produced for sawing concrete and stones.

with routing operations. In contrast, the split die takes the advantage of rapid withdraw of four anvils to expose the cylindrical cavity where diamond growth chambers may be arranged and thermocouple for temperature monitoring can be attached.

Figure 11.14. The split sphere design of the diamond growth chamber (Sung, Chien-Min, US Patent No. 7,128,547).

Consequently, the diamond production system is robust and efficient.

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