Production of ZrO2 reinforced mullite ceramics by spark plasma sintering and isothermal reaction

Mullite-ZrO2 reinforced ceramics have been prepared by a two step method. The first step involves the sintering at 1420 degreesC by Spark Plasma Sintering (SPS) of a mixture of alumina and zircon. The second step allows nearly full reaction in the body by an Isothermal Reaction (IR) treatment at 1550 degreesC for 120 min in an electric furnace. After the SPS process the sample reaches 99.5 % relative density, but only 24 % mullitization. The IR treated sample achieves 98.5 % relative density and 90 % mullitization. Am expansion of 9.22 % during mullite formation results in microcracking of the sample when IR treatment is carried out. However, the fracture toughness of the final product is 4.36 MPa.m(1/2), which is an improvement with respect to the values obtained for mullite-ZrO2 ceramics in other works by a two step method. Therefore, if a mullite-ZrO2 reinforced ceramic with high density > 98 % and full reaction is prepared, higher fracture toughness can be obtained.