Papers by Keyword: Reaction Bonding

Abstract: TiB₂-SiC-Si composite was fabricated by reaction bonding. The influence of carbon content on the phase compositions, microstructure, density and mechanical properties was studied. The results showed that the composite consists of TiB₂, SiC and Si phases. The vol% of SiC increased with the increase of C contents, while that of TiB₂ and free silicon reduced respectively. The mechanical properties of TiB₂-SiC-Si composites are improved initially and then deteriorated with the increase in C contents of which the optimal amount is 8 %. The optimum open porosity, volume density, Vikers-hardness, flexural strength and fracture toughness of the obtained TiB₂-SiC-Si composite are 0.12 %, 3.73 g/cm³, 17 GPa, 290 MPa and 5.9 MPa·m^1/2, respectively.

Abstract: This work reports on a novel route to produce porous matrixes for fibre reinforced ceramic matrix composites. This route relies on a reaction bonding process involving an intermediary carbide phase with subsequent oxidation. A slurry was prepared by mixing mullite powder, phenolic resin and aluminium powder in ethanol, which was used to impregnate Nextel fibres 610 (3M) by dip coating under ultrasonic vibration. The composites were vacuum-dried and submitted to a thermal treatment that consisted of a reaction step at 1250°C in Ar-atmosphere to convert the phenolic resin into carbon, which reacted with aluminium, leading to a carbide phase. The samples were then oxidized at 1250°C for 1h in air and subsequently sintered at 1300°C for 2h. Mechanical properties of composites and of matrix were determined at room temperature by 3-and 4-point bending tests, respectively. The microstructure of the composites was evaluated by optical-and scanning electronic microscopy, which revealed an apparent flawless microstructure.

Abstract: Electrophoretic deposition (EPD) allows the fabrication of ceramic coatings at lower cost and higher speed than most other deposition techniques. The processing consists of powder deposition from a suspension under the influence of an electric field and subsequent consolidation of the coating by sintering. Adherent zirconia coatings with coating thicknesses up to 0.1 mm were obtained from different suspensions, one methyl-ethyl-ketone and the other ethanol based. The standard sintering temperature is 1200°C, which easily may damage or change the substrate and also means high production costs. In order to reduce the sintering temperature, suspensions with the addition of ZrN were investigated. Due to reaction bonding, sintering in air at a remarkable low temperature of 1000°C was successful. The elastic modulus of the EPD coatings has been derived from impulse excitation experiments and the thermal conductivity from laser flash analysis. The elastic modulus was about 22 GPa and the thermal conductivity between 0.4 and 0.6 W/(m•K) at room temperature, both decreasing slightly with temperature. Especially the exceptionally low thermal conductivity makes EPD coatings a promising candidate for thermal barrier coatings.

Abstract: A novel technique to synthesize mullite by the oxidation of Al-Si alloy powder was used for the manufacture of mullite via pressure molding. The mixed powder was consisted of powders of Al-Si alloy, Al2O3 and SiO2 and additives or powders of Al-Si alloy, Al2O3, SiO2 and ZrO2 and additives. Those mixed powders were milled in nonaqueous slurry in order to prevent the oxidation of Al-Si alloy. Then the green bodies were pressureless sintered in air at ≥1380 °C. The Oxidation caused an internal volume expansion, resulting in reducing shrinkage stresses during reaction- bonding of composites, which minimized the sensitivity to crack formation. Comparing with non zirconia reinforced mullite composites, the effect of the microstructure and mechanical properties of mullite composites were studied.

Abstract: Transparent AlON ceramics are prepared with single-phase AlON powder synthesized from micron-sized aluminum and nano-sized alumina. The ceramics are prepared through sintering at the temperature of 1880°C for 10, 20 and 40 hours in flowing-nitrogen atmosphere, respectively. The effects of powder and temperature holding-time on transparent ceramic preparation and microstructure and transparency are investigated. The results show that all samples are transparent and of a single-phase AlON and, with increasing holding-time, the average pore size and porosity decreases and consequently, the ceramics are dense and their transparency is improved.

Abstract: Advanced braking devices can represent a promising application for ceramic matrix composites (CMC) with functional and structural properties. If the actual advanced braking materials could be at least partially replaced by CMCs, it might become the first consumer market for these materials. CMC containing three main phases, silicon carbide, graphite and carbon fibers were prepared. A systematic analysis of the processing-structure-properties relationship of the composite is carried out. In particular, silicon carbide provides the necessary hardness, whereas graphite is used for its lubricating properties, and carbon fibers are used as reinforcement. The samples, prepared using a reactive bonding technique, exhibited adequate mechanical properties, high resistance to thermal shocks and good stability after many thermal cycles. Morphological and structural investigations have been performed to optimize the content of each component. Preliminary tribological investigations are presented.

Abstract: Since conventional production of high-temperature materials involves high investments and costly consumption of both energy and time, reaction engineering methodology combined with near-net shaping is often the answer to problems associated with the fabrication of advanced materials. Over the last decades, the number of different reaction–based processing methods for near-net-shaped ceramics has gradually increased. In this review, different reactive processing techniques and their potential for near-netshaping are treated, e.g. SHTS (self-supporting high temperature synthesis), the Lanxide method DIMEX®, reaction bonding (RB), reactive processing of Alumina-Aluminide Alloys (3A) and Al2O3-Al alloyed metal composites (3AMC). In addition to their potential for near-net shaping, other advantages to reactive processing routes are recognized to be reduced processing temperatures, reduced glassy phase formation at the grain boundaries, fine grained microstructures and improved mechanical strength. Since the exothermic reactions constitute the base for reactive processing of high quality materials in an economic way, control of these reactions is essential. The process flows are described together with characteristic features of process and materials. In addition, specific aspects of reaction-based synthesis will be illustrated with examples from own work in the area of reaction bonding of silicon nitride and alumina.

Abstract: Ceramic foams can be used as filters, dust collectors, light weight components and catalyst carriers. They can be produced by a variety of techniques. The performance of ceramic foams will be strongly improved when their mechanical properties are improved. For this reason, we produced ceramic foams both by a modified reaction bonded (RB) replica technique and by gel casting. With both methods, reticulated foam structures with enhanced mechanical strength were obtained. Zeolites are a special type of materials that are characterized by high catalytic properties. They can be brought on a structured carrier by dip and slurry coating. Nevertheless, in situ coating has as main advantage that the support is used as the base for nucleation. This results in the formation of a chemical bond between the zeolite crystals and the support. The goal of this contribution is twofold: at first we demonstrate how Al2O3 foams with improved mechanical strength can be produced both by the modified RB-alumina replica technique and by gel casting. Secondly, it is shown that these ceramic foams can be coated with (silicalite) zeolite crystals by insitu crystallization from a precursor sol. The two-layer material combinations have been characterized with FESEM, XRD, CT (computer assisted tomography), IA (Image Analysis) and by mechanical tests.

Abstract: The Ministry of Commerce, Industry and Energy has contracted with the KIER including the ceramics company to localize of the ceramic heat exchanger tubes and its components. The basic objective of this paper is to develop a ceramic formulation and process which would yield a cost-effective and long-life Si/SiC tube materials by extrusion and reaction sintering process. Thus,KIER is currently developed and localized heat exchanger tubes with 40mm out diameter, 1500mm length. This paper was tested the mechanical and thermal properties of the localized Si/SiC tubes obtained from reaction sintering. Also, the effect of energy savings of the heat exchanger after exposure to forging furnace with hot corrosive environment was investigated.