Papers by Author: Tassilo Moritz

Abstract: Planar zirconia green bodies with unidirectionally aligned pore channels were prepared by an electrophoretic deposition method using an effect which is usually disadvantageous for the EPD from aqueous suspensions: the formation of gas bubbles by electrolysis. Aqueous ZrO2 suspensions containing acetic acid to enable a sufficient gas generation were used for the EPD experiments. The influence of selected parameters – electrolyte content, applied voltage, and kind of deposition electrode – on the pore structure has been investigated. The green bodies were sintered at 1450 °C in air. Optical microscopy and X-ray computer tomography (CT) were used for characterising the porous structures. CT-investigations have the advantage of a three-dimensional characterisation of the samples by a non-destructive method. The resulting pore structure depended to a high degree on the experimental conditions of the EPD. The kind of the deposition electrode – platinum foil or platinum gauze on foil – had a strong influence on the arrangement of the pores. The EPD on Pt-foil led to randomly arranged pores, whereas very regular pore structures were obtained by the use of Pt-gauze.

Abstract: A novel shaping technique for advanced ceramic components is presented which allows manufacturing of complex ceramic components with enclosed cavities by using ice moulds or ice cores. Different suspensions of alumina and zirconia powders have been developed for this special freeze casting technique. The suspensions must meet following requirements: high solid content, the capability of flow, a freezing point between -10 and -2 °C, and a casting temperature below 0 °C. After the casting process the moulds and cores could be easily removed by sublimation. The suspension liquid was removed in the frozen state simultaneously. In this way very complicated hollow or filled structures such as metallic or ceramic components encapsulated in ceramic shells could be produced. No de-moulding was necessary, no solid core must be removed, and no liquid phase appeared as known from other lost-mould techniques. Ice mould casting is a very environmental-friendly shaping technique. Furthermore, the influence of dispersing agents, anti-freeze agents and of the freezing speed on the pore structure of the ceramic components has been investigated.

Abstract: In the dental branch much effort is undertaken for production of metal-free ceramic restoration. Because of esthetical aspects and their biocompatibility ceramics are the material of choice. Allergic reactions or toxic tissue damages can be prevented largely by application of ceramic dental products. Zirconia in its tetragonal yttria stabilized polycrystal form (TZP) and alumina toughened zirconia (ATZ) offer highest strength combined with highest toughness. Unfortunately this favourable, outstanding combination of mechanical properties leads to difficulties in conventional hard machining in the sintered state, which is too time- and costconsuming. For this reason, electrophoretic deposition of alumina toughened zirconia powder and TZP powder was used for preparation of metal-free dental crowns and bridges. The electrophoretic deposition process was carried out directly onto the plaster moulds for single crowns, three-unit and four-unit bridges. The electrophoretic deposition process was investigated concerning the deposition rate and the output of dental crowns per volume of ethanolic ceramic suspension. Furthermore, the influence of the amount of dispersing agent on the rheological properties of the ceramic suspensions was investigated.