Hardness and toughness of aluminum porcelains measured by the indentation test S.R. Bragança and C. P. Bergmann Federal University of Rio Grande do Sul LACER/UFRGS Keywords: porcelain, hardness, toughness Abstract Triaxial porcelains for utilization in electric applications use in its composition alumina replacing quartz in order to improve mechanical strength. This property is a critical parameter for the application of this product. As a consequence of that, in this work, it was evaluated the mechanical strength, analyzing porcelain hardness and toughness by the indentation test, a fast way for measurement of strength. It was studied the different models used in the measurement of these parameters found in literature. It was verified which procedures are better for this type of material, comparing to values of toughness obtained by the method of Fracture Mechanics using notched samples. It is also presented technical characterization and photomicrographs of the analyzed samples. Introduction In the development of electrical porcelain such as high tension and low tension insulators, the body composition usually contains alumina replacing partially or totally quartz. The mechanical strength of quartz porcelain is significantly lower than that of alumina porcelain, a stronger but more costly filler material. The presence of residual quartz causes cracking in the matrix, as a consequence of thermal expansion mismatch between the two phases, what decreases significantly porcelain final strength. This has been demonstrated in several works. Microcracks around quartz particles were reported by Mattyasovszky-Zsolnay [1], Warshaw and Seider [2], Kobayashi et al. [3], Carty and Senapati [4], Ohya and Takahashi [5], and Ece and Nakagawa [6]. This is not so critical with alumina filler which has a thermal expansion coefficient closer to the matrix coefficient. Generally, high-tension and large insulators are made with high alumina content ∼40%, and low-tension insulators with lower contents ∼20%. This type comprises small, dust- pressed pieces such as switch, fuse blocks, knobs and so on [7]. There seems to be a need for a fast control and measurement of the properties of this conventional triaxial porcelain. In this work, it was evaluated the mechanical strength of alumina-low content porcelain, analyzing porcelain hardness and toughness by the indentation test, a fast way for measurement of strength. It was analyzed the parameters and limitations of this method, comparing to values of toughness obtained by the method of notched samples. Materials and methods The raw materials were prepared by dry mixing. The weight proportion of the raw materials was typical of alumina-low porcelain: 50% kaolin, 25% alumina and 25% feldspar. The forming of the pieces was made by dust pressing. The samples were dried for 48h in air and then for 24h in an electric muffle at 110ºC. They were fired in laboratory electric oven with rate of 150ºC/h until the peak temperature of 1360ºC, remaining in this temperature per 60 minutes and cooling occurred along the natural cooling rate of the furnace.