Tomsk Scientific Center (SB RAS) is working on new and improved ways to get carbides, nitrides, and borides of titanium and zirconium. These materials are highly demanded in aerospace and atomic power industries as well as in making high temperature equipment.
The work led by professor Yury Maksimov is funded by Russian Foundation for Basic Research.
‘These compounds are not easy to make – one crucial requirement is high temperatures (above 1500 °C). High-temperature furnaces are energy guzzlers. A lot of heat energy is wasted on heating both the furnace and the material itself. This is the reason why alternative approaches to making this type of materials such as self-propagating high-temperature synthesis are a viable option here. Combustion of thermites is relatively cheap and beneficial from the point of view of the materials you can get.’ says Alexander Avramchik the staff scientist of the laboratory of new metallurgical process.
The work on this project is focused around metallothermic reduction and its basic principles of use. Reducing metals ‘squeeze out’ less active metals from the compounds while providing the required heat. Conventionally one of the most powerful ergo most widely used reducing agents is calcium. However sometimes the heat it produces is simply not enough to get a desired compound (as in the case with reduction of uranium and other rare metals).
According to Alexander Avramchik a possible solution that does not imply external sources of heat could be introducing exothermic additives. One such additive to bring the synthesis of high-melting point compounds to the next level is calcium iodate mixed with calcium metal.
‘Calcium iodate is a compound occurring naturally in a mineral called lautarite. This fact is essentially relevant since it proves that calcium iodate can sustain its stability under environmental conditions for a prolonged period of time.’ Alexander explains.
When high temperature is applied calcium iodate decomposes releasing gaseous iodine and oxygen thus activating reduction reactions. In Russia the application of such additives and the possibilities it holds has not been previously studied.
The scientists at the Scientific Center have run the thermodynamic simulations to look into the core of the synthesis process assisted by calcium iodate. Now they have evidence of how it transforms when heated; combustion temperatures have been calculated and the reaction products have been studied.
Using this knowledge the scientists managed to break the threshold of 1000 °C, keeping in mind that usually such reactions are carried out at 1500 and above. Being able to synthesize high-melting point compounds at not that high temperatures grants a lot of opportunities. In particular softer process conditions allow for powders with different properties and grain sizes as well as reduced thermal stress to a material.