The advancement of science and technology provides more possibilities and convenience for beautifying people's lives. The development of artificial crystal technology has provided more and cheaper materials for the market, and the improvement of identification technology has played a role in monitoring and maintaining the market and consumption. Synthetic diamonds, especially synthetic colored diamonds, allow beauty lovers to enjoy the decorative beauty of colored diamonds at a lower cost.
Synthetic diamonds are artificially synthesized in the laboratory and have essentially the same physical properties, chemical composition and crystal structure as natural diamonds. At present, the methods for synthesizing gem-quality diamonds mainly include high temperature and high pressure synthesis (HPHT synthesis) and chemical vapor deposition (CVD).
High temperature and high pressure method (HPHT) synthetic diamond
The principle of high temperature and high pressure synthetic diamond
At present, the equipment of high temperature and high pressure synthetic diamonds popular in the world mainly has two sides (belt, mainly popular in Europe and America), six sides (special in China) and a split ball (Russ) or a modified split ball (Gemesis).
The high temperature and high pressure synthesis method is also called the seed crystal catalyst method. Graphite is a low pressure stable phase and diamond (the mineralogical name of the diamond) is a high pressure stable phase. The conversion of graphite directly to the diamond requires high pressure and temperature conditions, typically requiring pressures and temperatures above 10 GPa and above 3000 °C. If there are metal catalysts involved (such as Fe, Ni, Mn, Co, etc. and their alloys), the temperature and pressure conditions required for graphite to become diamond will be greatly reduced, so the current high temperature and high pressure synthetic diamonds have metals. Catalyst participation. The metal catalyst as a solvent is between a carbon source (generally graphite) and a diamond seed crystal. The carbon source is at the high temperature end and the seed crystal is at the low temperature end. Since the solubility of the carbon source at the high temperature end is greater than the solubility at the low temperature end, the difference in solubility caused by the temperature difference becomes the driving force for the carbon source to diffuse from the high temperature end to the low temperature end. The seed crystal gradually precipitates and the diamond crystal grows. Since the driving force for crystal growth is caused by the temperature difference, this method is also referred to as a temperature difference method.
Basic characteristics of high temperature and high pressure synthetic diamond
HTHP synthetic diamonds are often in the form of cubes, octahedrons and both; the color is often yellow, yellowish brown, and the interior is often characterized by ribbons and metal inclusions. The unmelted metal inclusions are needle-like, flaky, and small. Or an irregular appearance with a metallic luster that makes the synthetic diamond magnetic.
Synthetic diamonds usually have no fluorescence under long-wave ultraviolet rays. They often have yellow, green-yellow, and orange-yellow fluorescence under short-wavelength. Synthetic diamonds have characteristic banding under ultrashort-wave ultraviolet or cathode rays. Different growth zones show different colors of fluorescence. band.
Application of high temperature and high pressure synthetic diamond
High temperature and high pressure synthetic diamonds are mainly used for drilling (from oil, deep drilling of the crust to drilling holes in the teeth), cutting (from cutting marble to cutting gems), aerospace (from cabin window to space probe), electronics industry (from electronic instruments) To supercomputer chips), heat exchange (from large boilers to kitchen utensils) and jewellery and many other fields.
The advancement of science and technology provides more possibilities and convenience for beautifying people's lives. The development of artificial crystal technology has provided more and cheaper materials for the market, and the improvement of identification technology has played a role in monitoring and maintaining the market and consumption. Synthetic diamonds, especially synthetic colored diamonds, allow beauty lovers to enjoy the decorative beauty of colored diamonds at a lower cost.
Synthetic diamonds are artificially synthesized in the laboratory and have essentially the same physical properties, chemical composition and crystal structure as natural diamonds. At present, the methods for synthesizing gem-quality diamonds mainly include high temperature and high pressure synthesis (HPHT synthesis) and chemical vapor deposition (CVD).
Chemical vapor deposition (CVD) synthetic diamond
CVD synthetic diamond
The principle of CVD synthetic diamond
Chemical vapor deposition (CVD) is usually carried out under the action of high temperature plasma, the carbon-containing gas is dissociated, and carbon atoms are deposited on the substrate as a diamond film. The substrate can be a non-diamond material, but single crystal diamonds are typically formed by depositing carbon atoms on a diamond substrate. Carbon-containing gas generally refers to a mixed gas containing nitrogen, methane and hydrogen. Methane is a source of synthetic diamond carbon atoms, nitrogen can increase the growth rate, and hydrogen can inhibit the formation of graphite. Usually CVD synthetic diamonds are carried out under low pressure and high temperature conditions, the pressure is generally less than one atmosphere, and the temperature is about 1000 degrees.
Basic characteristics of CVD synthetic diamonds
Most of the CVD synthetic diamond single crystals are plate-shaped, and occasionally small octahedral faces and rhombohedral dodecahedrons can be seen at the edges. Early CVD synthetic diamonds were mostly dark brown or light brown in color, and recently discovered CVD synthetic diamonds have been shown to undergo high-temperature heat treatment at a later stage, so the color is colorless or nearly colorless. CVD synthetic diamonds have fewer internal inclusions, and individual needle-like, black irregular inclusions are visible. However, it cannot be used as a basis for distinguishing between natural diamonds and HTHP synthetic diamonds. Metal inclusions do not appear in CVD synthetic diamonds and therefore are not magnetic.
Early CVD synthetic diamonds exhibit orange to orange-yellow fluorescence, short-waves are stronger than long-waves; recently discovered CVD synthetic diamonds have yellow-green fluorescence, short-waves are stronger than long-waves, and mostly have phosphorescence. Under the ultra-short-wave UV lamp, CVD synthetic diamond has a typical layered growth structure and is the main identification feature of CVD synthetic diamond.
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