Several companies are offering a service to turn ashes of human remains into diamonds. Does anyone know any details about the chemical aspects of the process?
I have no idea, but suspect that the ashes are composed mostly of phosphates and oxides. Where does the carbon hide? Any carbonate would have decomposed at the creation temperature. Or does the cremation chamber has such a high $\ce{CO2}$ partial pressure that $\ce{CO2}$ from burners is captured by the $\ce{CaO}$?
How is the carbon then extracted?
Also, diamond is normally made out of graphite, which agrees with a statement on the LifeGem website.
Let's assume they can squeeze out a little $\ce{CO2}$ by heating the ashes in an oxygen stream. Then they concentrate the $\ce{CO2}$ on a molecular sieve, use the Sabatier reaction to create $\ce{CH4}$ which they decompose on a hot metal wire. Then they dissolve that in acid and get a little bit of powder rich in $sp^2$ bonds and similar to graphite. Could one make diamonds out of that?
On the other hand, the page mentioned above states that they first extract the carbon and then turn it into graphite. How do you turn a few mg of fine carbon powder into graphite?