Technical Ceramics for High-Tech Brakes revolutionize

Lightweight brakes coated with technical ceramics may make cars more energy-efficient. Read on to find out more.

Laser cavity reflectors

Laser cavity reflectors in technical ceramics

There is one simple rule about how to make any vehicle more energy-efficient: reduce its weight. Auto manufacturers can use all manner of materials on the bodywork to cut down on the kilograms, whether it’s in standard petrol or diesel cars or even electric vehicles.

But this has rarely applied to brake rotors. These heavy components are made from heavy cast iron. Lightweight brakes do exist in high-end racing and sports cars but make little economic sense for large vehicles. This sad situation is set to change with the development of lightweight aluminium brake rotors that are coated with technical ceramics.

This invention is the fruit of a joint project between the Empa Research Institute — the Swiss Federal Laboratories for Materials Science and Technology based in Dubendorf near Zurich — and Italy’s Politecnico di Torino and the Turin-based Fiat Research Centre, Spain’s Bilbao-based Fagor Ederlan Group and Lichtenstein’s soldering enterprise, Listermann.

On their own, aluminium rotors would be far too soft to use as brake rotors, even though they are lightweight. The key is to coat them with technical ceramics. This coating provides the aluminium with some protection from melting and disperses the heat produced during the braking process.

The coating itself is only about two millimetres thick but is made up of 15 separate layers. The main component of the ceramic is aluminium oxide, commonly called alumina, a very strong compound that is both inexpensive and in abundant supply. The alumina is mixed with various layers of silicon carbide that will increase its thermal conductivity. There is a further protective top layer that is resistant to wear and tear, together with an adherent layer that is soldered to the bottom surface.

Each of the layers is first mixed with water to produce a sludge-like substance that is applied over a synthetic film. The different layers of synthetic film are subsequently compressed together and heated to a high temperature. The film burns away in the heat, leaving the ceramic layers.

But problems remain. The ceramics are applied as small tiles to avoid stress cracks. The thermal expansion of aluminium is three to four times that of the ceramics. But these tiles need to be soldered together at temperatures below 700 degrees Celsius, the melting point of aluminium. The problem is that if braking temperatures rise higher than this, the solder can fail just when brakes are most needed. The work goes on.

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