The present study suggests the use of high energy ball milling to mix (to dope) the phase MgB2 with the AlB2 crystalline structure compound, ZrB2, with the same C32 hexagonal structure than MgB2, in different concentrations, enabling the maintenance of the crystalline phase structures practically unaffected and the efficient mixture with the dopant. The high energy ball milling was performed with different ball-to-powder ratios. The analysis of the transformation and formation of phases was accomplished by X-ray diffractometry (XRD), using the Rietveld method, and scanning electron microscopy. As the high energy ball milling reduced the crystallinity of the milled compounds, also reducing the size of the particles, the XRD analysis were influenced, and they could be used as comparative and control method of the milling. Aiming the recovery of crystallinity, homogenization and final phase formation, heat treatments were performed, enabling that crystalline phases, changed during milling, could be obtained again in the final product.
Several CAD/CAM systems are available to dental prosthesis laboratories which can be used to fabricate all-ceramic copings and frameworks. The use of these systems presents low demand, due principally the high blocks ceramics cost used for theses systems. Usually, these ceramic blocks are sintered at high temperatures, between 1450 and 15500C, resulting in micrometric ZrO2 microstructure. A considerable innovation in these ceramics systems used in CAD/CAM applications was introduced by the use of nanometric-tetragonal ZrO2 blocks, which are sintered at low sintering temperatures resulting in nanometric grains morphology and improved mechanical properties. The purpose of the present work is to characterize the mechanical properties of nanoparticled zirconium oxide blocks comparing with commercial micrometric ceramic parts. XRD patterns showed that the blocks have only the tetragonal-ZrO2 as crystalline phase. The tetragonal-monoclinic transformation phase was responsible for the excellent mechanical properties. Nanometric blocks presented hardness of 13GPa, fracture toughness of 11MPam1/2 , bending strength of 1020MPa and Weibull modulus, m=14, while micrometric ZrO2 blocks similar hardness, fracture toughness 8.5MPam1/2, bending strength of 850MPa and Weibull modulus of 10.
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