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It has a beautiful, but also an unpleasant side: crystallization determines the shape of precious stones, but also causes the lime scale in washing machines. How this comes about, has been known for a long time - or has it? Scientists at the Max Planck Institute of Colloids and Interfaces are now whittling away at the established theory, which is unable to explain numerous phenomena. The researchers investigated the crystallization of calcium carbonate, known commonly as chalk, and found that stable nanoclusters form in water with a small quantity of dissolved calcium carbonate - not how it was assumed to happen in the past. The lime scale deposits that will eventually bring a washing machine to a standstill are created from these tiny chalk particles. Previously, it was also an unknown fact that the structure of crystallized calcium carbonate depends on the alkalinity of the solution. These new findings might provide help in coping with the lime scale in washing machines, as well as help to explain the sophisticated structure of biominerals - and to better understand the role of the oceans as carbon dioxide sinks. (Science, December 19, 2008)
Calcium carbonate is ubiquitous: everyone has probably held a stick of blackboard chalk in the hand at one time or another, or railed against the deposits it forms in washing machines. It is the main constituent of marble, dolomite and many types of sediment, and it is also found in the shells of crabs, mussels, snails, sea urchins and in single-celled organisms. These biomaterials have properties that make them interesting for applications in medicine and building materials technology. The ingenious structure of their crystals at nanoscopic level makes them particularly robust. Materials scientists would like to know how organisms produce these structures, so t
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