A technology for producing SiAlON filters for metal melts has been proposed at TSC SB RAS

Scientists at Tomsk Scientific Center of the Siberian Branch of the Russian Academy of Sciences are developing optimal compositions and technology for producing oxide-nitride ceramics (SiAlON) via SHS nitriding. Being able to filter out various inclusions from metal melts, such products are in high demand in the metallurgy industry. The research is supported by the Russian Science Foundation (project No. 24-79-00117).

– The advantages of SHS nitriding lie in its speed, simplicity of equipment, and energy efficiency. The idea of producing SiAlON this way was proposed 30 years ago, but for a long time, only amorphous ceramic sinters could be obtained via the SHS method, which required grinding into powders and further processing before we could get the final product. So, there is no doubt today about the relevance of this advanced technology for obtaining ready-to-use porous ceramic products that do not require additional mechanical or thermal processing, – explained project leader Anton Reger, a researcher at the Laboratory of New Metallurgical Processes.

The first step of the research project is pinpointing optimal compositions for multi-stage production of pure silicon nitride, free from foreign impurities. This silicon nitride is formed as a result of chemical reactions between silicon, aluminum, silica, and nitrogen.

Next comes the preliminary structuring of the powder preform, which can be compared to clay molding. To achieve the desired structure of the future product, a special liquid mass known as a slip is formed. This slip contains a silicon nitride powder mixture, an alkaline aqueous solution necessary for varying the pore size of the future product, as well as liquid glass and fiber that reinforce the porous framework of the preform.

As the alkaline solution interacts with the initial powder mixture containing aluminum and silicon, it releases gas, forming a porous structure – at this point the strength of the future product is being built. Ultimately, a fragile “skeleton” is produced, which must be carefully removed from the mold and dried.

The next stage is SHS nitriding in a special reactor: after passing through the combustion wave at temperatures ranging from 1600 to 1800 °C, the “skeleton” preform is transformed into a finished porous product with the necessary physicochemical properties. Everything goes “without a hitch” if two conditions are met: the optimal composition of the powder mixture and the conditions for nitriding during combustion. Otherwise, simply put, it will burn to a crisp: since all processes in aggressive SHS conditions happen very fast, leading to the formation of cracks and melting.

First, 8 by 8 cm cubic shape samples will be obtained in a small laboratory reactor, followed by larger samples in a pilot-scale reactor. The scientists also face another important task: learning how to impart a porous structure to the products, which can be of two types – cellular and honeycomb. As the project leader explained, the characteristics of the filter’s porous structure directly influence the efficiency of metal melt filtration. Therefore, the scientists will have to assess the properties of the obtained materials and study the effect of slip compositions on pore size.