Sparking advanced ceramics

Ceramics are normally processed by consolidating powders using sintering at high temperatures. The time required for this process is usually measured in hours because of the slow rate of heating/cooling of the furnaces used. Spark plasma sintering (SPS), as it is commonly known, is a rapid sintering process, where the cycle can be completed in minutes. This generates the possibility of making ceramics with new microstructures and properties. Queen Mary University of London and its spin-out company, Nanoforce Technology Ltd, are working to exploit SPS technology in the UK. Spark plasma sintering has some similarities to hot-pressing, which involves applying pressure during sintering. The rapid heating rates in SPS are achieved by the direct Joule heating of the graphite dies in which the ceramics are sintered. This involves pulsed, direct current at low voltages (1,000A). The furnace at Nanoforce can achieve rates of up to 600°C/min. Because only the ceramic and die are heated, the cooling rates can be even faster because of their low thermal inertia and forced cooling.