The effect of pseudoboehmite additions to conventional stoneware porcelain is investigated. Green compacts were formed by slip casting of stabilized aqueous suspensions and then sintering at 1,150 oC, 1,200 oC and 1,250 oC. The phase evolution was followed by XRD, the densification degree was calculated from densities and the microstructures were studied by SEM. Hardness, H and fracture toughness, KIC were measured by Vicker's indentation. When vitrification occurs the presence of the pseudoboehmite leads to a extra mullitization, which has two consequences: a volume expansion resulting in a high porosity and a decrease of the amount of liquid which causes problems with the densification, by these facts the pseudoboehmite particles decrease the fracture toughness of the bodies.

Keywords: Mechanical properties, Indentation, Mullite, Pseudoboehmite.