the smooth, white surface of your bathroom sink hides the fact that the process of making it is a notoriously dirty and polluting one. Aluminium oxide ceramics which find applications in a range of products (from sinks to lasers) are made by dissolving aluminium oxide powder in organic solvents and using many other chemicals in the process.
Given the widespread use of these ceramics, millions of litres of these hazardous chemicals need to be disposed off safely every year. This is expensive and also potentially dangerous. Now a team of chemists from Rice University in Houston, us, have demonstrated a much cleaner way of making aluminium oxide ceramics, which does away with hazardous solvents. Andrew Barron and his colleagues are reportedly using water to make ceramics ( Science , Vol 272, No 5259).
The conventional method starts by using aluminium oxide powder. Since this does not dissolve in water, organic solvents are used to make a solution to which other organic binders are added for cohesion. This slurry is then poured into a mould and after the material has set, is fired to high temperatures (upto 1000 c).
Other more complex ceramics are made by adding the appropriate metal oxide powders to the basic aluminium oxide. This method works for bulk ceramics and a different method, called sol-gel processing must be used for thin films. This process too requires the use of expensive and potentially hazardous chemicals like caustic acids. The aluminium oxide particles are too big to dissolve in water. Barron's group has found a way of splitting the heavy aluminium oxide particles into smaller units which can dissolve in water.
They used a form of aluminium oxide powder called boehmite. The crystal structure of boehmite is such that it is made up of sheets of aluminium atoms with oxygen atoms, each sheet being bonded by weak hydrogen bonds. Using a mild, comparatively safe acid, carboxylic acid, they were successful in breaking the hydrogen bonds, resulting in tiny rod-like structures called alumoxanes. These are surrounded by carboxylic acid groups which readily bind to water molecules, resulting in a very high solubility in water. Adding more boehmite powder, they were able to get a concentrated solution which could be moulded and fired to yield conventional ceramics.
Though the method used is deceptively simple, it is still unclear whether it is commercially feasible. There are now efforts to collaborate with industry to gauge the economics of this process. If the process can be made viable on an industrial scale, it may be a step forward towards a cleaner environment.