Friday, 7 June 2013

Much suspected by me, Nothing proved can be, Quoth Elizabeth prisoner.

another use for diamonds, this poem was written with a diamond on her window by 
Queen Elizabeth 1 whilst she was imprisoned in the gatehouse of Woodstock Manor, Woodstock, Oxfordshire.
Did you know that since the 1950's it has been possible to create diamonds in a laboratory. Once scientists discovered that diamonds were formed from pure carbon they set about trying to create diamonds from cheap carbon.
Diamonds are simply crystallized pure carbon, just as rock candy is crystallized sugar—an ordered array of atoms or molecules.
Laboratory diamonds are mostly used in industry for grinding, cutting, drilling, polishing tools and optics. Gem-quality diamonds have only been achievable for a few years and now you can have your loved one or pet turned into a memorial diamond! We are 18% carbon, I guess the bigger you are the larger the diamond.
Laboratory diamonds are made using either  CVD, Chemical Vapour Deposition or HPHT, high-pressure high-temperature diamonds. These diamonds are termed synthetic diamonds,
a quick explanation of the difference between of Synthetic and Simulation.
Synthetic - A material  that is created in a laboratory through chemical-physical processes. A synthetic diamond is a true diamond - pure carbon, crystallised in isotropic 3D form - created by a human controlled process.
Simulation - A material that imitates another one but it is not the same substance. Diamond simulations may be natural (e.g. white zircon, quartz) or synthetic  (e.g. cubic zirconium, glass) and are fairly easy to distinguish from natural or synthetic diamonds.

The HPHT method replicates the process of natural diamond creation.
Three methods of HPHT diamond synthesis are BELT, BARS, CUBIC PRESS - they all use the same principal.
A diamond seed is placed into a reaction cell along with a carbon source such as graphite. A metal solvent or “flux” either Iron or Nickel or a combination of both is used. Using a flux means lower temperatures and pressures can be used to to convert the graphite into diamond.The exact composition of the flux strongly influences the properties of the synthetic diamond. For example, aluminium will remove nitrogen atoms from the synthetic diamond. This results in the growth of a colourless diamond. Adding boron to the growth capsule will result in a blue diamond.
The cell is subjected to extremely high temperatures and pressures – to simulate the conditions of diamond formation in the earths core. This results in the graphite crystallising as diamond. A slow, well-controlled growth is essential for growing high quality diamonds. Only a few minutes are needed to convert graphite into powder sized diamond, but it takes about three days to crystallize a 1ct, rough gem-quality stone.
HPHT created diamonds
CVD is a generic term for a group of chemical processes that involve depositing a solid material from a gas or mixture of gases onto a substrate (base layer).
In the CVD process, to start the formation of a diamond nuclei or nucleation from which the diamond crystal grows, small seed diamonds are used as a substrate. The process generally takes place at below atmospheric pressure. The starting materials for diamond synthesis are hydrogen and a hydrocarbon e.g. methane. The substrate sits within a reaction chamber at a  controlled temperature between 700°C and 1,200°C, the hydrogen-hydrocarbon gas mixture flows in,  microwaves cause the gas mixture to form a plasma which builds up over the seed diamond in ripples creating a diamond.
CVD created diamonds

A  time line to summarise the development of laboratory grown diamonds.

Next time I will look at other lab grown precious stones and discuss the issues of using lab gems.