Scientists from Obninsk in the Kaluga reg. (Russia) have developed a ceramic with unique properties, with heat conductivity and thermoplasticity several times higher than normal ceramics. This means that items made of it, from coffee mugs to fuel pellets for atomic power stations, will serve longer and more reliably than standard ceramics.
During a competition of innovative developments under the 5th International Innovation and Investment Salon that was held 15-18 February 2005, researchers demonstrated some amazing samples.
“A distinguishing feature of our ceramic is its structure,” explains project manager and chief scientist of the Leipunsky Physics-Energy Institute Irina Kurina. “And, as a consequence, the properties are indeed unique. Heat conductivity that exceeds reference data, enhanced plasticity and thermal stability: we have succeeded in obtaining a ceramic in which all these properties are combined.”
Generally speaking, plasticity and high thermal conductivity for massive ceramic products are properties that are almost unrealistic. For example, rubber: if you strike it, individual molecules will as if to move, changing their form a little and the thing remains intact. Or, if metal is heated, surplus heat quickly spreads from the surface to the center and an ingot, say, remains completely intact, only warm. But ceramic is a brittle material: if struck it will break; if heated rapidly it will crack or even fall to pieces.
It is precisely for this reason that a special concept of stability in thermal cycling regimes is introduced for products made from it. Put simply, it is defined in advance how many times a ceramic item can be heated and cooled until it begins to crack by itself, under load or under an impact.
“Generally speaking, there are three types of component in the structure of the ceramic made under our technology: large grains of oxide material (from 50 to 100µm), fine grains (from 1 to 10µm) and a little emptiness. In other words there are pores, located in a special way, predominantly around the boundaries of the grains,” continues Kurina. “Such pores create ideal conditions for plastic deformation. And fine grains additionally soften a mechanical or thermal impact. In the mass of fine grains, the large grains become as if stuck, like cobblestones in sand. The crystalline lattice of such a ceramic is very mobile; it has many defects. In the unusual structure of such a ceramic electron tunneling is possible. This is where the high heat conductivity comes from.”
The principal basis of the technology is both simple and universal in nature. At first it is necessary obtain a powder, whereby the grains have to be of a varied, pre-set size. And there have to be an awful lot of defects in the obtained powder particles! All begins from sedimentation (precipitation): solutions of initial substances are taken, necessary reagents are added, and out comes the sediment – those very particles of the required size.
Then these oxide particles (of aluminum, magnesium and zirconium, thorium or uranium in the case of fuel components) are annealed, pressed and sintered. It is understood that the authors are not disclosing the technological parameters of these parameters and the subject of the know-how. However, all this work is extra confirmation of the fact that chemistry is not only strictly a matter of calculation, although the parameters of the new materials can be optimized with computer modeling, which is what the authors are doing. It is also an art form, the talent and intuition of the scientists who enable the achievement of what would seem to be the impossible; such as making a heat-conducting oxide ceramic, and of any kind.
Andrew Vakhliaev | alfa