Mar 29 2004
High-quality nanopowders made of refractory ceramics are a rare and very expensive material. All known methods of their manufacturing face the same problems - scanty quantities, extensive variety of particle sizes and expensive production. Researchers from the town of Tomsk have invented and manufactured a device to produce a choice selection of particles – all particles are equal to the required size and inexpensive. The project has been funded by two foundations – the Russian Foundation for Basic Research and the Foundation for Promotion of Small-Scale Enterprises Development in Scientific and Technological Area.
Researchers of the Tomsk State University jointly with their colleagues from the MIPOR research-and-production association have designed a device and manufactured with its help pilot lots of some nanopowders, including the silicon powder and the silicon nitride and silicon carbide powders.
The action of a new device is based on the method the researchers called “self-abrasion”. In the device, the fluid jet captures the particles and brings them upwards to the separation zone at the velocity close to the transonic speed. The centrifugal separator separates off the thin fraction, i.e. the smallest particles. Heavy and large particles fall back to the pounding zone. The streams meet each other, but their velocities are different: they fly up at a high speed and fall down rather slowly, along with that the layer contains the non-ground material, which is constantly poured into the device. Microwhirlwinds originate at the “stream/non-ground material” border due to significant difference of velocities, the relative velocities of particles inside the microwhirlwinds reach 100 to 300 meters per second. The particles break to pieces blowing each other, friction polishing the particles.
First, the researchers guided by Yuri Birukov investigated the entire process with the help of the mathematical model. The researchers determined how many times each particle is to collide with others to get broken into pieces and then to get “ground” through to the required size and shape, what should be the device parameters and the gas velocity to get the nanopowder with predetermined characteristics at the output. Besides, in order to exclude milling of admixtures, the particles should not touch the walls of the device in the course of circulation.
‘Besides mathematical modelling there exists even more important physical modelling, i.e. experimental investigation, says Yu. A. Birukov. Experimental investigations of such complicated processes as obtaining nanopowders last for years. We have produced and tested hundreds of experimental plants within 30 years before achieving the above results.”
The results achieved are powders of silicon, silicon nitride and silicon carbide, of aluminium oxide, of tungsten carbide and of titanium, aluminium, copper and tungsten, their average particle size being 300 nm and 500 nm. They contain practically no admixtures, and the particles are very similar in size. They are perfectly suited to producing various refractory components, for example turbine blades.
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