Clay could hold the key to effective electromagnetic shielding, say scientists at Aristotle University of Thessaloniki, Greece.

The team here is developing cost-effective building bricks and roof tiles made from metallurgical wastes that can be built into the structure of a building as a protective shield. Led by Dr. Costas Sikalidis, the method involves using mill scale and other metallurgical wastes as admixtures to make a product that absorbs rather than reflects electromagnetic radiation.

With the ever-increasing use of electronic devices, concerns are frequently raised about adverse health effects that could be caused by a round-the-clock exposure to the electromagnetic fields of mobile phone stations or radio and television transmitters.

Interference of wireless (particularly, radio frequency) devices with digital devices is another issue. A number of studies have been carried out over recent years, aiming to develop cement based electromagnetic shielding and absorbing materials containing wastes. However, Sikaldis claims that few studies have been conducted regarding construction of absorbing materials, especially in the field of ceramics.

The benefits of using specially mixed bricks as a shield are twofold, says Sikaldis. ‘Firstly, the protection from electromagnetic radiation and secondly, the transformation of environmentally problematic industrial wastes into useful raw materials for ceramic building products.’

‘The bricks are prepared in the same way as common bricks,’ says Sikaldis. ‘The only difference is that particle size mill scale waste is added as an admixture together with the red clay.’

The red clay forms the ceramic matrix, while the waste admixture creates the brick’s shielding function. During the thermal treatment, the iron forms existing within the wastes are transformed into hematite and magnesioferrite, giving the bricks increased shielding efficiency from electromagnetic radiation.

The work investigated the possible effects of non-thermal levels or conditions in which physiological temperature can be maintained in the presence of normally thermalising specific absorption rates. ‘Studies on human perception indicate that the greatest cutaneous sensitivity to microwave heating is at frequencies with wavelengths comparable to or smaller than the thickness of skin, the millimetre wave range,’ says Sikaldis. At frequencies between 1 to 10 GHz, with wavelengths equal to or greater than the human body, much energy is absorbed below the superficial dermis. In this range, the threshold temperature for cellular injury (about 42°C) is below the threshold for pain (about 45°C).

Sikaldis says that this is a cause for concern because cutaneous perception of radio frequency energy may therefore not be a reliable response, which normally protects against potentially harmful levels of radio frequency radiation at the lower microwave frequencies.

Mill scale and other metallurgical wastes such as electric arc and ladle furnace dust are wastes that carry handling costs for the steel manufacturers, says Sikaldis. ‘By offering this waste to a heavy clay ceramics manufacturer, this cost can be eliminated while the manufacturer will have a low cost raw material,’ he says. ‘Furthermore, a brick and roof tile that can protect from electromagnetic radiation will gain better prices in the market, because it has added value.’

With pilot plants already in production, Sikaldis hopes that the prepared bricks and roof tiles could be used in buildings for more sensitive groups such as children or the elderly, or those who are heavily exposed to electromagnetic radiation, ‘such as hospitals, school, care homes or houses under electricity transfer lines.’