The Emergence of Synthetic Diamonds

In 1796, British chemist Smithson Tennant proved that diamonds are simply a form of carbon, like graphite. This discovery spurred humanity’s pursuit of creating artificial diamonds.However, it took 157 years before the key factor for successfully converting carbon into diamond was found—the use of a catalyst. In 1954, General Electric (GE) succeeded in synthesizing diamonds using high-pressure, high-temperature (HPHT) techniques, identifying iron-group metals like iron, cobalt, and nickel as essential catalysts. This method, known as the GE process, was the first reproducible method for diamond synthesis. However, it’s important to note that in 1953, Swedish company ASEA had already produced synthetic diamonds, though they did not announce their results. Some suggest it was due to the lack of practical applications, while others point to incomplete experimental data at the time.Published

Synthesis of Diamonds

Density and Pressure

The density of diamond is 3.52 g/cm³, and this high density is due to its pure carbon composition and the compact arrangement of its atoms in a crystalline structure. In contrast, graphite, another form of pure carbon, has a density of 2.25 g/cm³, with ordinary graphite materials having densities below 1.8 g/cm³. This notable difference in density between diamond and graphite confirms that diamond synthesis requires extremely high pressures, as the arrangement of carbon atoms in diamonds is much tighter and more structured than in graphite.

Thermodynamic Conversion

In 1872, Austrian physicist Ludwig Boltzmann advanced the understanding of thermodynamics by connecting the concept of entropy to the disorder of atomic arrangements. Entropy, in this context, refers to the degree of randomness or irregularity in the arrangement of atoms in a system. When temperature increases, the disorder of atomic arrangements grows, raising the system’s entropy. In contrast, applying pressure causes atoms to arrange in a more ordered structure, thereby reducing entropy.

This inverse relationship between pressure and temperature is evident in carbon-based materials. For example, applying pressure to graphite can transform it into diamond, as the high pressure forces carbon atoms into a highly ordered lattice structure. Conversely, heating a diamond can cause it to revert to graphite, as the heat increases the disorder of atomic arrangements, expanding the volume of the material. This shows that pressure tends to decrease volume, while heat causes expansion, illustrating their opposing effects on matter.

Methods of generating pressure

  1. Mechanical high-temperature pressing
  2. PVD (Physical Vapor Deposition)
  3. CVD (Chemical Vapor Deposition)
  4. Catalyst method
  5. Laser method (using CO₂ as a carbon source)
  6. Explosion method

Development of cultivated diamonds

Cultivated diamonds have a wide range of applications due to their extremely high hardness and thermal conductivity, which is five times that of copper. They hold significant industrial value. More and more countries are investing in the cultivated diamond industry, with the size and quality of production ranging from micropowder and fine grains to gem-quality diamonds as large as 34 carats. Records are continuously being broken.

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