A method for synthesizing gem-grade colorless diamonds by seed crystal method

Abstract

The invention discloses a method for synthesizing gem-grade colorless diamonds by a seed crystal method, which comprises the following steps: (1) FeMnCo is used as a catalyst sheet, graphite is used as a carbon source, and Cu foil is used as a nitrogen removal agent; The upper end surface of the seed is flush with the upper end surface of the crystal bed, and the synthesis block is assembled; (2) Then start high temperature and high pressure synthesis, and the pressure is raised to 60~70MPa at a constant speed of 0-200s, then maintained for 2000~3000s, and then at a constant speed of 80~120s Raise to 90~100MPa; heating power rises to 2.5~3.5KW at a constant speed for 0‑400s, then maintains for 2000~3000s, and then rises to 5~6KW at a constant speed for 500~800 seconds; heat preservation and pressure to the 10,000th second power and pressure Gradually lower and then gradually increase until it returns to the highest value, the total synthesis time is 900,000 seconds to 1 million seconds, that is, a gem-quality colorless diamond with a particle size of 3~5mm is obtained.

Description

technical field [0001] The invention belongs to the technical field of diamond synthesis production, and in particular relates to a method for synthesizing gem-grade colorless diamonds by a seed crystal method. Background technique [0002] In recent years, the synthesis technology of gem-grade cultivated diamonds at home and abroad has developed rapidly, and cultivated diamond jewelry has become more and more recognized and favored by consumers; many domestic enterprises have the technical strength to industrially produce colorless diamonds, not only the particle size The synthesis of gem-quality colorless diamonds requires strict technical conditions, the most important of which involves how to control the crystal shape, crystal growth direction, growth speed, and inhibit the generation of impurity inclusions, etc.; As a key element for the synthesis of colorless diamonds by the temperature gradient method, the difference in crystal shape, size and distribution will direct...

AI Technical Summary

Problems solved by technology

[0003] According to theory combined with production experience, in the process of synthesizing gem-quality colorless diamonds by the temperature gradient method, due to the mutual dissolution and co-infiltration of carbon source and graphite and the transformation of graphite into diamond, higher energy is required in the early stage, and the power setting in the early stage is often higher. Moreover, in the growth process of colorless diamonds, the carbon source is relatively sufficient in the early stage, and the axial temperature gradient and radial temperature gradient of the crystal are relatively large. At this time, the crystal growth rate is very fast; but as the crystal grows continuously, the carbon The source gradually decreases, and the temperature gradient of the crystal axial and radial growth surfaces gradually decreases compared with the previous period, and the growth rate begins to slow down at this time.

The growth rate is closely related to the crystal synthesis process. When the growth rate is too fast, it is easy to cause incomplete nitrogen removal, yellowish crystal color, virtual crystal, incomplete crystal form, and many internal defects, impurities, and inclusions; when the growth rate is too slow, The crystal size is fine, and the synthesis process takes too long, resulting in high production costs

In the existing process, when the gem-grade colorless diamond with a particle size of 3-5mm is synthesized, the power and pressure change as follows: image 3 As shown, the pressure rises to 65MPa at a constant speed for 200s and then keeps for 2500s, and then rises to 95MPa at a constant speed for 100s; the heating power rises to 3.0KW at a constant speed for 400s, then keeps for 2500s, and then rises to 5.5 KW; in the synthesis time of 900,000 seconds, after the power and pressure rise to the highest value, the synthesis power will always be kept at W=5.5KW, and the gauge pressure P=95MPa will remain unchanged. The colorless diamond color synthesized by this synthesis method Unsatisfactory degree and clarity

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