Papers by Keyword: Oxide Ceramics

Abstract: Ceramic materials are suitable for use in the high temperature range. Oxide ceramics, in particular, have a high potential for long-term applications under thermal cycling and oxidising atmosphere. However, monolithic oxide ceramics are unsuitable for use in high-temperature technical applications because of their brittleness. Thin-walled, oxidation resistant, and high-temperature resistant materials can be developed by reinforcing oxide ceramics with ceramic fibres such as alumina fibres. The increase of the mechanical stability of the composites in comparison to the non-fibre reinforced material is of outstanding importance. Possible stresses or cracks can be derived along the fibre under mechanical stress or deformation. Components made of fibre-reinforced ceramic composites with oxide ceramic matrix (OCMC) are currently produced in manual and price-intensive processes for small series. Therefore, the manufacturing should be improved. The ceramic injection moulding (CIM) process is established in the production of monolithic oxide ceramics. This process is characterised by its excellent automation capability. In order to realise large scale production, the CIM-process should be transferred to the production of fibre-reinforced oxide ceramics. The CIM-process enables the production of complicated component shapes and contours without the need for complex mechanical post-treatment. This means that components with complex geometries can be manufactured in large quantities.To investigate the suitability of the injection moulding process for the production of OCMCs, two different feedstocks and alumina fibres (Nextel 610) were compounded in a laboratory-scale compounder. The fibre volume fractions were varied. In a laboratory-scale injection moulding device, microbending specimens were produced from the compounds obtained in this way. To characterise the test specimens, microstructure examinations and mechanical-static tests were done. It is shown that the injection moulding process is suitable for the production of fibre-reinforced oxide ceramics. The investigations show that the feedstocks used have potential for further research work and for future applications as material components for high-temperature applications in oxidising atmospheres.

Abstract: Ceramic Matrix Composites (CMC) offer improved mechanical properties, especially higher toughness, preferably at elevated temperatures. Fields of application are, for example, highly hot stressed components of aero engines.Processing of Ceramic Matrix Composites by powder injection molding offers attractive economic benefits, however, it represents a considerable challenge. Development of a process chain for the ceramic injection molding of Al₂O₃ short fiber CMC had started by feedstock preparation and characterization. Fiber content varied between 10 to 50 vol.% whereas for binder a well-examined system from KIT was chosen. The fiber content showed a minor effect on the rheological properties but fiber orientation depended strongly on the apparent shear profile. The sintering behavior was affected as well, i.e. higher densities were achieved.

Abstract: Nano/microfibers are already widely used as the reinforcements in various types of advanced composites for reducing weight, improving specific properties like hardness, fracture toughness and other mechanical ones. This contribution describes the preparation of the titanium dioxide nano/microfibers by needle-less electrospinning, along with a detailed characterization of the obtained polycrystalline ceramics. For spinning solutions preparation the polyvinylpyrrolidone (PVP), titanium isopropoxide (TTIP), ethanol and acetic acid were used. Influence of the ceramic precursor concentration in the spinning solution showed that decreasing the concentration of TTIP from 30 to 10 wt.% has no effect on the precursor polymer fibers shape. However, it causes deviation from the fibers oval shape (in the cross-section) up to the formation of solid ribbons or even multilayered porous ribbons. Heat treatment temperature defined the phase composition of the obtained oxide ceramics – stabile polycrystalline rutile fibers were obtained at 600 °C.

Abstract: Glyphosate (G) is a broad-spectrum systemic organophosphate herbicide being widely used to control weeds in agricultural fields and urban areas. Its safety for both human health and aquatic biomes is a subject of wide debate. This study was aimed at evaluating the removal efficiency and ecotoxicity of G based herbicide (GBH) Klinik® (Nufarm, Austria) added to the raw municipal wastewater (WW) in a lab-scale model column system. The effect of oxide ceramics as a filtering medium (treatment „B”), as well as activated sludge and nutrients (treatment „C”) was compared with the control columns, which contained only WW (treatment „A”). After 72h treatment of WW spiked with 100 mg/L G, the lowest G concentration was detected in the treatment „B”, i.e., 79.4±0.6 mg/L. Treatments „A” and „C” resulted in the remaining G concentrations of 83.3±3.8 and 89.6±3.7 mg/l, respectively. The second addition of 100 mg/L G to the columns followed by 72h incubation also showed the advantage of oxide ceramics. Most probably, this effect could be explained by coupled sorption and biodegradation processes. Experiments were accompanied by microbiological (colony forming units; biological oxygen demand) and ecotoxicological (Daphtoxkit F magna, MicroBioTests) testing. The results indicated that WW-derived microorganisms resist the presence of GBH in the tested concentration range of G, i.e., up to 300 mg/L. As for Daphnia magna, the 24-h EC₅₀ for the GBH Klinik® under standard conditions and in raw WW was found to be 22 mg/L and 6 mg/L G, respectively.

Abstract: In this study, it was tried to develop a process chain for ceramic injection molding of Al₂O₃-chopped-fiber reinforced oxide-ceramic-matrix-composite. The feedstocks are compounded at 50 Vol. % filling degree of solid (Al₂O₃ μ-powder (Taimei Chemicals Co. Ltd.) and 3,2 mm chopped fibers (3M)), in which fiber content varies from 0 Vol. % to 100 Vol. %. As binder system, PE + Paraffin Wax + Stearic Acid are used. The ingredients are compounded in a kneader (Brabender) at 125°C and after the viscosity measurement in the high pressure capillary rheometer at 160°C and certain shear rates, the feedstock is injection molded (Battenfeld) at 160°C, which is followed by debinding process, including chemical (in n-Hexane) and thermal steps, and 2h sintering at different temperatures. Flow paths in the machinery parts, rheological properties of binding system, fiber content and the fiber orientation have significant effect on the flow behavior of the feedstock, fiber -orientation, -distribution & -length, which are crucial to understand the properties of end-parts like mechanical reinforcement of the fibers. The fibers in the sintered parts are ca. 200 μm in average length. The fibers in the feedstock show different orientations depending on the part-geometry and the green bodies have different densities depending on sintering temperature, amount of dispersant and fiber orientation.

Abstract: Ceramic components are frequently used as substrates for the production of temperature sensing devices in petroleum industries, in view of their high thermal and electrical resistance and inertness in hostile ambient conditions. Complex cubic perovskite oxide ceramics have a great advantage in terms of their varied physico-chemical characteristics with the substitution of structural elements in the respective formula units. In this context, we have produced Ba2AlSnO5.5 ceramics by solid state reaction process. Structural characteristics, studied by powder x-diffraction, reveal that Ba2AlSnO5.5 ceramic has an ordered complex cubic perovskite structure. Ba2AlSnO5;5 ceramics were sintered in the form of circular discs of 10 and 15 mm diameters and 2 mm thickness, in the temperature 1200 to 14000C by normal sintering process. The microstrutural characteristics were studied by scanning electron microscopy on both polished and fracture surfaces. The SEM micrographs show homogenous surface morphology and particle size distribution. Mechanical hardness of the sintered Ba2AlSnO5.5 ceramics were studied by Vicker´s hardness tests. The results of these studies have been presented and discussed in this work

Abstract: Structural and functional characteristics of ceramic components highly depend on their microstructure and mechanical properties. In the production of such ceramics sintering plays extremely important role. Recently, we are working on the development and fabrication of temperature sensors for the petroleum wells. In this connection, we have developed a new alumina based ordered complex cubic peroviskite oxide ceramic Ba2AlWO5.5. During our study, we found that Ba2AlWO5.5ceramics compacts could not be densified by normal sintering route. To overcome this hurdle, we have utilized the liquid phase sintering process, using CuO additives. By addition of 1 to 2 wt% CuO, we succeeded to sinter this ceramic in the temperature range 1200 to 14000 C. Sintered Ba2AlWO5.5 ceramics were examined by X-diffraction and scanning electron microscopy to verify the presence of any extra phase due to CuO addition in the Ba2AlWO5.5 matrix. Our studies revealed that CuO addition did not affect the structural characteristics, but considerably modified the densification process, microstrutural characteristics and consequently mechanical properties of the Ba2AlWO5.5 ceramics.

Abstract: Directionally solidified oxide ceramic eutectic composites with superior strength, oxidation resistance, creep resistance, structural stability and low sensitivity to crack at high temperature have aroused much attention in recent years, and various preparation techniques have been developed. In situ fabrication of ceramic eutectic composites by laser rapid solidification is a cheap and quick method compared to conventional multi-step fabrication methods of fiber reinforced composites for high temperature use. In this paper, Al2O3/YAG/ZrO2 ternary eutectics are rapidly prepared from melt by directional solidification using laser zone remelting technique, the growth characteristic and fracture toughness are investigated. The results show that: (1) Laser rapidly solidified Al2O3/YAG/ZrO2 ceramic eutectic in situ composite presents a fine interpenetrating network structure, in which Al2O3, YAG and ZrO2 phases are continually interconnected and finely coupled without pores, colonies and grain boundaries between interfaces. (2) Laser scanning rate and power density strongly affect the eutectic growth. With the processing parameters adjusted properly, the eutectic shows homogeneous and coupled lamellar microstructure. The characteristic dimensions of the microstructure are around 2~3 1m for Al2O3 and YAG phases, and around 0.2~1 1m for ZrO2 phases, respectively. (3) The hardness and fracture toughness of the rapidly solidified Al2O3/YAG/ZrO2 eutectic are 16.7 GPa and 8.0 MPa.m1/2, respectively.

Abstract: In high technology industries ceramics have several uses, especially at high temperature, e.g. inert crucibles, electrodes and catalysts. We are working on production and development of new oxide ceramics, based on complex cubic perovskite structure, for fabrication of crucibles for metallurgical applications. In the present work, we have produced and studied sintering behavior of a new ordered complex cubic perovskite oxide ceramic Ba2HoWO5.5. Microstructural characteristics of the Ba2HoWO5.5, sintered between 1200 to 1400°C for 48h, were studied by scanning electron microscopy. The mechanical behavior was studied by Vickers microhardness tests. Our studies show a gradual improvement in microstructural characteristics of sintered Ba2HoWO5.5, both on polished and fractured surface. This homogeneity of grain sizes and particle size distribution increases with the increasing of the sintering temperature, which results in higher sintered density and increased mechanical hardness.

Abstract: In the present era, high technology wireless communication and mobile communication systems require advanced ceramics as high frequency dielectric resonators. In the present work we have produced Ba2MgWO6 (BMW) ceramics and studied its structural, microstructural and mechanical properties. Ba2MgWO6 (BMW) ceramics belong to the Ba2MgTaO6 (BMT) and Ba2ZnTaO6 (BZT) ceramics family, which is well known ceramic material for the communication technology. There is little information available on materials characteristics of BMW ceramics. Structural characteristics of BMW ceramics were studied by X-ray diffractometry. Microstructural characteristics were studied by scanning electron microscopy and mechanical behavior was tested by Vickers micro-hardness tests on sintered BMW bodies. This article reports these characteristics of BMW ceramics and discusses its implications on application viability.