Papers by Keyword: Structural Ceramics

Abstract: The paper presents the results of the studies on the phase conversions taking place during the firing of the refuse piles processing sieve residue in the Eastern Donbass, which are the promising raw materials for the production of various types of structural ceramics – common, lining and clinker bricks, high-performance ceramic stones, ceramic tiles and siding. It is established that the sieve residue is the raw material of the low-temperature baking. Depending on the degree of grinding, the raw material may belong to the group of mid-baking or high-baking raw materials. The sieve residues have a rather narrow baking interval - no more than 50 °C, which is possible to expand by increasing the content of fine fractions during the preparation of sieve residue. The main mineral phases at the firing temperature of 1000-1100 ^оС are quartz, feldspar, ferrous silicates and aluminum silicates (fayalite, hypersten, etc.), hematite. The features of the phase and mineralogical conversions allow us to recommend to fire products on the basis of sieve residue at temperatures of 1000 °C and higher.

Abstract: The availability of TiC healing agent has been evaluated in low temperature self-healing behavior of Al₂O₃ based self-healing ceramics. For this purpose, some technical issues to actualize the advanced fiber-reinforced self-healing ceramics containing TiC based interlayer as healing agent were discussed. Especially, the mechanical matching between the matrix and the interlayer was focused. Moreover, the self-healing behavior of the advanced shFRC containing the optimized TiC based healing agent was investigated. As a result, 30 vol% TiC-70 vol% Al₂O₃ interlayer was confirmed to be the optimized healing agent in the self-healing ceramics, and the self-healing ceramics was found to enable to attain the perfect healing at 600°C within 10 min. And we succeeded in prototype production of fiber-reinforced self-healing ceramics for low pressure turbine blade.

Abstract: Self healing of surface cracks is the most effective function to ensure the structural integrity for ceramic components, because even minute surface crack give rise to a large strength decrease because of its high sensitivity to flaws. The present author and coworkers succeeded that the degraded strength due to cracking can be completely recovered by self crack healing ability driven by the high temperature oxidation of silicon carbide. Then, the mechanism and the effect of the self-healing were investigated. The most attractive feature of the self healing is to be able to respond to the damage caused during service. Thus, enhancement in self healing velocity has been necessary to actualize the self healing ceramics. In the present study, nanometer sizing the disperse silicon carbide particle was attempted to achieve the purpose. Alumina composites containing various shapes of silicon carbide nanometer sized particles were synthesized from mullite, aluminum and carbon powders. From the strength recovery behaviors of these alumina/ silicon carbide composites, the following aspects were derived. Silicon carbide particles nanometer sizing can heal completely the surface cracks at lower temperature and shorter time.

Abstract: A procedure that comes being studied for the exploitation of powder waste rejected from the sanitary ware production is the incorporation in mass for red ceramics. Objective of this work is to present the results gotten in the incorporation of this rejects. The used clay was from ceramics industries of the Jundiai region, SP. Spherical bodies test samples had been conformed incorporating 1%, 5%, 10%, 20% and 30% of the powder waste in mass. These bodies had been evaluated on compression resistance after dried to 110°C and to color after burns to 950°C. The composition that presented better results had been conformed by extrusion in prismatic bodies test samples. Again, the dried to 110°C and burnt to 950°C bodies test samples had been evaluated on flexion resistance but to linear retraction too. It was measured the ceramic properties of the burnt bodies test samples. Results indicate that there is a great potential in the formula with 30% incorporation of powder waste in mass. Comparative assays were made being used a mixture without incorporation of the denominated white reject.

Abstract: In this work, it was investigated the behavior of a ceramic composition in pressing and firing process, related to its pyroplasticity, to permit the production of roof tiles in roller kiln. Experiments were realized varying the parameters of pressing, sintering and composition, adding a refractory material. With this study, it became possible to select the optimal parameters of pressing and firing, and to start the pilot industrial tests. The developed process has advantages, in the process and the final product, related with the standard process (extrusion and firing in tunnel kiln). The process is energetically more efficient, because there are no movable in the kiln. It was measured a flexural strength above 40 MPa with 12mm thickness, saving material. Also, the product has a higher quality in size, shape and dimensional precision (linear thermal shrinkage lower than 1,5%); tonality, porosity (water absorption lower than 10%), and frost resistance.

Abstract: Fatigue behaviors of conventional alumina ceramics in cyclic loading with hemisphere and cylinder punches are investigated with modified small punch (MSP) tests. Residual strengths are used to quantify the degree of fatigue damage. The dependences of the residual MSP strength on loading mode, cyclic loading magnitude, frequency, and puncher shape have been discussed in detail. Fatigue behavior studies could be very convenient and effective because MSP tests could perform the cyclic loading and then evaluate the residual strength consistently and effectively.

Abstract: Ceramics contributes to progression of civilization. Yet advancement of ceramic science and technology benefits from the improved infrastructure and productivity. This paper assesses the development of structural and optical ceramics in the last quarter century. For example, structural ceramics such as silicon carbide whisker reinforced alumina matrix and titanium carbide dispersed silicon carbide matrix composites have made possible high-speed, wear-resistant, specialty tools. Designing of the structural materials involved consideration of thermodynamic compatibility of phases during fabrication, and consideration of the initiation and propagation of fracture. Mechanisms of the observed toughening have been proposed on a scale ranging from continuum to microstructure to atomistics. Optical ceramics including translucent polycrystalline alumina have facilitated the construction of high-pressure sodium and ceramic metal halide lamps. The microstructure and properties such as transmittance and sodium resistance of polycrystalline alumina have improved. The starting powders improved in purity, particle size, and de-agglomeration. Sintering of alumina advanced through optimization of dopants and sintering atmosphere. Densification involves grain-boundary diffusion; retardation of grain growth is due to solute drag. The solid solubility of magnesia sintering aid in alumina is a function of grain size. During grain growth and sintering of magnesia-doped alumina, both the enriched dopant level at grain boundaries and the equilibrium dopant content in the lattice alter, resulting in boundary pinning and pore annihilation. Oxygen vacancies when in motion significantly influence the boundary transport, and when stationary are important to optical properties of the sintered alumina. Further development of improved and new functional ceramics involves consideration of energy and environmental renewability. Prior achievements and outstanding challenges will be discussed.

Abstract: The erosion resistance performances of high-Cr cast iron Cr15Mo3 and three kinds of structural ceramics, a-Al2O3, ZTA, Si3N4, were investigated in flowing suspensions of solid particles with a rotary disk erosion wear tester. The microcosmic failure mechanisms of their wear surfaces were analyzed. The results showed that the erosion resistance of Si3N4, ZTA, a-Al2O3 is 21.8, 8.2, 5.6 times than that of Cr15Mo3 respectively. For ceramic materials, toughness and strength are two main factors that affect erosion resistance rather than hardness. The wear rate of ceramic materials is in proportion to the strength and the biquadratic toughness. Due to erosion, Cr15Mo3 is worn out most in the whole, the erosion holes are very clear and its failure pattern is in “W” shape. The wear of ZTA and Al2O3 mainly occurs in the binding phase of the crystal boundary. Thus, the crystal grains are exposed, but without breaks and cracks. The failure pattern is in the shape of “U”. Si3N4 only loses some binding phase of the crystal boundary and the erosion surface is smooth.

Abstract: A rapid manufacturing method for fabrication of 3D ceramic parts will be presented. The structural information is printed by ink jet in powder layers of 80 µm thickness. Different granulated powders can be used, such as zirconia and alumina if they show good flow ability. After printing the structures a heating process takes place. After these the parts can be picked out from the powder bed. The manufactured parts can be impregnated with epoxy. Another option is the infiltration with ceramic slurries and glass with sintering to higher density. The sintering process has been studied and the shrinkage and material properties evaluated. The interrelationship between the raw material qualities, infiltration media and the sinter parameters as well as the material-specific properties such as density and stability will be presented. The manufacturing method is used for fabrication of moulds and cores for casting processes. Otherwise the process can be used for fast fabrication of models and prototypes. The possibilities to use these methods for implant manufacturing will be shown. A cost analysis has been performed comparing direct manufacturing of small batches of components to mould injection processes.

Abstract: The corrosion behavior of Si3N4, SiC, mullite, alumina and sapphire was investigated in supercritical water at 450 °C and 45MPa for 2 to 50h. Corrosion resistance for the ceramics was as follows in the order; Si3N4 < SiC < mullite < alumina < sapphire. Pitting corrosion with formation of amorphous layer and intergranular corrosion due to dissolution of additives were observed in PLS-Si3N4 and PLS-SiC, respectively. The corrosion behavior of mullite was characterized by dissolution of SiO2 and formation of boehmite residue layer. High purity alumina ceramics showed the highest corrosion resistance in the ceramics. Intergranular corrosion proceeded in the alumina ceramics and its corrosion rate was strongly dependent on the impurity content.