Synthetic Diamonds: A Brief History

 

Synthetic Diamonds: A Brief History

In the early part of the twentieth century, several attempts to synthesise diamond were conducted, and by the 1940s, the temperature and pressure parameters under which diamond is the stable phase of carbon had been established experimentally. Berman and Simon expanded on these findings. Graphite is the stable phase at normal temperatures and pressures, which is interesting. At normal temperature and standard atmospheric pressure, diamond, the ultimate gemstone, is merely meta-stable! Fortunately, converting a diamond to graphite requires a lot of energy, and in an inert atmosphere, a diamond may be safely heated to at least 1500 °C without causing harm. When the temperature rises beyond 1800 °C, however, the material quickly transforms into graphite.

Following the availability of tungsten carbide in the 1930s, serious attempts to synthesise diamond started. This exceptionally strong material enabled the development of pressure cells capable of generating pressures of up to 400 000 atmospheres at ambient temperature and up to 70 000 atmospheres at high temperatures. Percy Bridgman of Harvard University conducted the first tests. No diamonds developed in any of the room-temperature graphite trials, and diamonds refused to form even when graphite was exposed to a pressure of 30 000 atmospheres and temperatures up to 3000 °C. Bridgman simply couldn't maintain high enough pressures and temperatures at the same time to convert graphite to diamond directly. Bridgman invented the expression "graphite is Nature's finest spring" as a result of these failures.

In 1953, a team of scientists at the Allmänna Svenska Elektriska Aktiebolaget (ASEA) laboratory in Stockholm solved the difficulty of turning graphite to diamond for the first time. That early achievement, however, was not acknowledged until after GE announced on February 15, 1955, that they had successfully turned graphite into diamond. In both situations, the secret to success was dissolving the graphite with molten metal. As additional graphite is dissolved, the metal gets saturated with carbon, resulting in the formation of tiny crystals that nucleate and develop. The crystals develop as diamonds because the temperature and pressure are kept at the zone where diamond is the stable phase. It's worth noting that the French chemist Frédéric-Henri Moissan attempted similar strategy 60 years before, but was unable to attain the circumstances where diamond is the stable phase of carbon.

However, it's almost probable that the GE scientists were thinking about Moissan's theories when they attempted, after several failures, to dissolve graphite in molten metal. It is still debatable whether the metal operates exclusively as a solvent or additionally as a catalyst, therefore the term "solvent-catalyst" is commonly employed. Cobalt, nickel, and iron are transition metals that function well as solvent catalysts, and these metals or alloys are employed in most commercial systems. In industrial synthesis, typical temperature and pressure values are 1400 °C and 55000 atmospheres, respectively.