Blast glass

a group of researchers from the Central Glass and Ceramic Research Institute, Kolkata, has developed a process to obtain glass ceramic material from the blast furnace slag generated in iron and steel plants.

The innovation holds good potential for the cookware industry as the new class of materials has an ultra-low thermal expansion coefficient and uses low cost raw materials.

"The low coefficient of thermal expansion means that the material does not expand when heated, which in turn means that it is more resistant to thermal shock and more durable,' said Swapan Kumar Das, head of the Clay and Traditional Ceramics Division of the institute and one of the authors of the paper, which was published in the Bulletin of Materials Science (Vol 28, No 5, August, 2005). He added that the new material can mean cheap glass ceramic utensils, which the common person can easily afford.

It is not the first time that such research has been conducted on ceramic material from waste products. But earlier attempts by scientists to utilise sewage sludge ash from municipal solid waste have not been as successful. This is because the complex composition of sewage deterred the formation of a crystalline structure, which is essential to the manufacture of glass.

To develop this material, the scientists used quenched (cooled) and granulated blast furnace slag, pyrophillite, which is an alumino-silicate material, and titanium oxide as the nucleating agent. "Unlike boro-silicates (commonly used to make transparent glass), this material is not transparent. Boro-silicates are transparent because they are completely amorphous but this material is opaque because of its semi-crystalline structure, which also makes it stronger,' explained Das.

He also said the selection of the various additives (type and amount) has to be carefully done to control the composition of the glass, since it is the glass composition that determines the crystalline structure. The use of pyrophillite in the blend is instrumental not only in controlling the amount of silicon and aluminium oxides but also in lowering the glass melting temperature. "This can be a crucial point for the industry because this means that the raw material that needs to be melted to produce glass can be melted at a lower temperature (using less energy),' said Das.

High potential The researchers are now initiating product development from the material so that its commercial potential can be leveraged further. "Not just for utensils, this kind of material also holds potential for the electronics industry, especially for items that are exposed to thermal shock but cannot afford expansion or contraction,' said Das.

However, the real implications of this innovation still need to be seen. "Although this is interesting, we need to find more voluminous uses of this material to actually utilise the huge heaps of blast furnace slag,' said Vikram Jayaram, professor at the department of metallurgy of Bangalore-based Indian Institute of Science.

Das and others at the Central Glass and Ceramic Research Institute now aim to reach zero thermal expansion coefficient through subsequent research.