Einfluss von Aluminiumoxid- und Titanoxid-Additiven auf die Thermoschockbeständigkeit von MgO-teilstabilisiertem Zirkonoxid

摘要

In modern steel production, ever greater demands are made on refractories with respect to thermal shock and corrosion. A group of ZrO2-spinel composite materials was therefore developed at the Institute of Ceramic Components in Mechanical Engineering at RWTH Aachen University, which combines the good corrosion resistance of ZrO2 with improved thermal shock resistance. To this end, additives i.e. alumina and titania are supplied to MgO partially stabilized zirconia (Mg-PSZ). The Mg-PSZ is partially destabilized during sintering and spinel is formed in situ. Both processes lead to local elongation, which generates internal stresses and finally a crack structure is formed that is superimposed on the existing basic porosity. The objective of this PhD dissertation is to investigate the thermal shock resistance of this group of materials as a function of the primary structure – through various ZrO2 particle sizes at constant sinter profile – and of the additive content in detail. The overall porosity shall be kept small in order to achieve corrosion resistance of ZrO2. The specimens were characterized thoroughly. The residual fracture strength on four-point bending specimens after quenching experiments at 600°C and 1000°C in water was used at room temperature as a measure of the thermal shock resistance. The major properties determining the thermal shock resistance, i.e. density, thermal expansion coefficient, Young’s modulus, thermal diffusivity, fracture toughness and fracture work, were determined and used to calculate the thermal shock coefficients (R, R´, R´´´´, Rst) familiar from the literature. The results show that an increase in residual fracture strength was achieved for all starting powders of different particle sizes after quenching at 1000°C. Arising results show that the particle size of the ZrO2 has to be limited due to the constant sinter profile so that a sufficient porosity is achieved. Furthermore, if the additive fraction is too great then the fracture strength decreases so strongly before water quenching that no usable components can be fabricated from the material. Materials with improved thermal shock resistance were developed whose porosity remains under the porosity of carbon bonded refractories, and thus possess the potential to process refractories with limited wall thickness. The thermal shock coefficients reflect the qualitative curve of fracture strength against the quenching temperature, but do not provide any information on the absolute value of the residual fracture strength.