A new theory on crystal formation

Researchers at Eindhoven University of Technology (TU/e), together with researchers from Germany and the USA, claim they have found the missing piece to the theory of crystal formation.

According to the existing theories, it is individual ions that group together to form crystal nuclei.

This new understanding means the existing theories no longer need to be overturned

But in 2009 chemists led by Dr Nico Sommerdijk at TU/e showed the presence of an intermediate step in the growth process of calcium carbonate crystals.

Now Sommerdijk is having second thoughts about his 2009 conclusions. Together with researchers from the Max Planck Institute in Germany and the Lawrence Berkeley National Laboratory in the USA, he looked more closely at the role of these so-called pre-nucleation clusters in the growth process of the mineral calcium phosphate.

Using a cryo-electron microscope, which makes images of deep-frozen samples, he was able to identify the precise components of the clusters and study the growth process in detail.

In their article in Nature Communications Sommerdijk concludes that the clusters do not form a clearly defined intermediate step, but instead are part of a gradual growth process. Sommerdijk refers to the formation of clusters as a ’false start’ by the ions, because the clusters already start to organise themselves step by step while still in solution, without actually forming growth nuclei.

This new understanding means the existing theories no longer need to be overturned. Sommerdijk’s team now complete the theory by describing alternative ’pathways’ along which crystals can form. Sommerdijk’s new conclusions have since been confirmed in a second study into crystal formation in the mineral magnetite, which was published online this month in Nature Materials.

In Sommerdijk’s view the most important questions about the formation of crystals have now been answered. This theoretical knowledge is important in many fields, because of the widespread occurrence of crystallization in nature and in the chemical industry.

Just a few examples are the formation of coral in the sea, the production of pharmaceuticals and the design of nanoparticles. It could for example help to make production processes less costly, faster or more energy-efficient.