Synthetic Diamonds

It was a very exciting time when scientist found out that diamonds are nothing more than an allotrope of carbon. In other words, it was made from only carbon atoms that also happen to make up its cousin graphite. But why is diamond "hard" and has the ability to scratch any surface while its cousin graphite is "soft" and is a lubricant. The answer to that question has to do with molecular structure of the two species. The graphites molecular structure consists of sheets of carbon atoms covalently linked with other sheets of carbons. This allows the sheets of carbon atoms to slip over each other. Hence graphite is a lubricant at STP conditions. In contrast, the carbons atoms of diamond orient themselves in a tetrahedral manner forming a tetrahedral network. This network is very strong and stable and that what makes diamonds very hard. This was all interesting to scientists but what they wanted to know was: since both diamond and graphite consist of carbon atoms, is there any way to convert the cheap graphite to its valuable form diamond?




This requires the understanding of thermodynamics. Thermodynamics dictates that in order to convert graphite to diamond, a negative ΔG is required for it to happen spontaneously. Of course, the more negative ΔG is, the faster the rate. But at what conditions is this ΔG negative? Certainly not in atmospheric conditions where the pressure is 1 atm and temperature is 293 K. That is why diamonds are never formed on the Earths crust but below it where the conditions are much more harsh. These conditions supply the sufficient energy for the formation of diamonds. Therefore it requires extreme conditions to accomplish this conversion and 1950s, technology was created that could withstand those conditions and complete the conversion at a reasonable rate. The conditions of that conversion were pressure in excess of 100,000 atm and temperature about 2800 Celsius. When graphite is subjected to these conditions, the carbon atoms of graphite rearrange themselves in a tetrahedral network and diamonds are formed. The synthetic diamonds that are formed are very small and could not be formed into a gem, but they were sufficient enough for industrial use such as coating and cutting. For more extensive details, visit the following links.

• http://www.bristol.ac.uk/Depts/Chemistry/MOTM/diamond/diamond.htm


• http://www.chem.wisc.edu/~newtrad/CurrRef/BDGTopic/BDGtext/BDGDmnd.html