Avinash Hardas, a Masters degree holder from USA, who works as a consultant industrial and ceramic engineer, has claimed that the ``chemically-bonded'' bricks have better firing properties and other features such as high cold crushing strength, better thermal shock resistance and less shrinkage.

Also, the process can be suitably used to manufacture glass tank refractories (bricks lining the wall of the container in which glass is molten), silliminite bricks and other refractories, Hardas has claimed. He is presently conducting research to confirm whether the process can be used to manufacture ramming mass (material used to wash the lining of the kilns) and whether it could have application in manufacture of other ceramic products like tiles, castables and acid resistant bricks.

Speaking to The Indian Express, Hardas said that the whilethe low grade refractory bricks (containing less than 30 per cent alumina) could be manufactured at a low temperature, the high alumina refractories (containing more than 80 per cent alumina) require temperature as high as 1400 degrees celsius to fire. To attain this high temperature, large quantity of fuel (coal and/or oil) is required. Also, to fire these high grade bricks, special kind of ovens are required, which are not easily available in the country.

He said that the most important aspect of the process developed by him is that the high alumina bricks can be fired at a comparatively low temperature of 1200 degrees celsius in a common down draught (DD) kiln.

The process involves addition of a few chemicals of choice in a suitable quantity, which lowers the baking temperature of the bricks. The addition of the chemicals also enhances the `green strength' (strength of the material before being baked) of the bricks, which ensures low breakage and rejection while handling.

The chemicals one liquidand one powder form are added to the brick composition, which is usually fire clay, grog (powder of old bricks) and aluminium oxide. A pinch of a catalytic chemical is added to trigger the reaction. The mixture is then allowed to stand for about two hours and then pressed into shapes just when it begins to harden. This process is suitable for dry as well as wet pressing.

As the baking temperature is lowered a huge amount of fuel is saved through this process. Another cost effective point is the low rejection in ``green stage'', as the material is less prone to breakage.

The addition of the chemicals also ensure better firing properties and other features as mentioned above. The chemicals used are acids and salts and oxides of certain metals.

Hardas mentioned that the method is more cost effective for the high grade alumina refractories, which cost about Rs 40 per brick. The process may not be feasible for the low grade bricks, as they are sold at a comparatively lower price.