As good as the real thing

GRANITE takes millions of years to form naturally, but now it can be synthesised in the laboratory in a matter of days, thanks to a technique devised at the Central Glass and Ceramic Research Institute (CG&CRI), Calcutta.

The CG&CRi researchers came upon this technology almost by chance. The scientists were trying to make scratch-proof floor tiles when they observed that the ingredients had metamorphosed into a clone of natural granite.

The magic wand is a silicate mineral called garnet found in abundance on the beaches of Kerala and Tamil Nadu, which are rich in monazite - a commercially important rare earth mineral.

Public sector Indian Rare Earths Limited (IREL) uses monazite from the sand at its plants in Orissa and Kerala, while garnet is dumped as worthless.

The IREL people didn't know what to do with the garnet heaps growing in their backyards. So they had approached CG&CRI to find out if they had any use for it.

The CG&CRi has, through the Council for Scientific and Industrial Research - both are Central government bodies - applied for a patent for the synthetic granite. Once patented, the technology can be sold to an entrepreneur willing to produce granite tiles on a Commercial basis.
Synthetic recipe For manufacturing synthetic granite, the garnet sand is first ground to a particle size of about 200 microns (a micron is a millionth of a metre) and then mixed with 2 varieties of ceramic clay in equal ratio. Water is added to the sand-ceramic mixture and it is further ground till it reaches the proper fineness.

The water is then filtered out and the tiles allowed to dry. The drying process could be natural or artificial using electricity.

The tiles are then put into a kiln and sintered at temperatures of 1,100- 1,200'c. The end result is an unpolished synthetic granite tile, which undergoes the same polishing procedure as natural granite.

Says CG&CRI's G Banerjee, the principal scientist associated with the manufacture of synthetic granite, "The basic design of the tile can be modified to suit the need of the consumer. We can also control the colour by managing the quantity of additives, but we cannot make very light coloured tiles, because the iron present in garnet imparts a dark hue to it." The lightest shade of artificial granite tile comes in beige or tan.

Tiles can be made in various designs - for example, dots of a particular colour or a diamond shape can be incorporated before the tiles are sintered and do not require any additional process. "This way we can develop any number of designs and meet the requirements of the clients," says Banerjee.

The strength of these tiles, assures Banerjee, is almost the same as that of natural granite. The hard ness of garnet on Moh's scale is about 7 (Hardness scale ranges from 1 to 10 on Moh's Scale, where the hardness of talc is rated as 1, while a diamond is rated as 10).

Banerjee cautions that synthetic granite should not be confused with the artificial granite' tiles available in the market. The artificial granite tiles are made up of natural granite rubble mixed with additives and are not as sturdy as synthetic granite tiles.

The synthetic granite tiles, when manufactured on a commercial scak, would measure 1 foot (0.3048 metre) by 6 inches (0.1524 metre), the same as natural granite tiles but would be priced at about two-thirds or half the price of natural granite tiles, which range from Rs 60 to Rs 80 per square foot (about one-tenth of a sq metre).

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