Papers by Keyword: Alumina

Abstract: This study was undertaken to compare chemically identical nanoparticles that have been synthesed by different methods. The methodology applied allows the identification of different characteristics in the structure and surface parameters of nanoparticles. The study shows that the structural parameters of nanoparticles are to a great extend related to the conditions in which nanoparticles are formed. This is demonstrated through the comparison of three oxides and their different methods of synthesis. The results show that the method of synthesis defines the structure of the nanoparticles; the surface and qualitative and quantitative parameters of the crystaline phases, energy shifts and changes in the internal electron levels. The examples of nanoliquids and the associated polymer strength identify that the interaction of nanoparticles with the environment is also depends on the synthesis method. It is proposed that a fractal dimension may be used as a basic parameter to classify nanoparticles and predict the properties in their interaction with various media.

Abstract: Bioinert ceramics in use today are the result of more than 60 years of continuous development. Early studies were concentrated on alumina that in the late 1960s was the most advanced ceramic, and on pyrolytic carbon. After tests in orthopedic bearings, pyrolytic carbon found clinical applications in artificial heart valves, where it is in clinical use so far. After 1970 zirconia-toughened ceramics (YTZP, ZTA, ATZ) were investigated in view of their use as biomaterials in orthopedics. Especially the introduction of YTZP in clinics in the 1990s gave a new momentum to the use of inert bioceramics. So far, zirconia-toughened ceramics are replacing alumina because of their outstanding mechanical properties leading to high reliability in ceramic components. The behavior of ZTAs and ATZs are exploited in several innovative devices. Especially metal-free devices are of interest, because of the increasing number of patients sensitized to metals. Using zirconia-toughened ceramics were achieved remarkable development in ceramic knee replacements, a field pioneered by Japanese researchers, because the behavior of these materials allow the production of devices similar in size to the metallic ones. In dentistry, a number of manufacturers are marketing metal-free dental implants, as well as machinable zirconia blanks for the production of crowns, bridges, copings by CAD/CAM. Besides oxides, that in todays’ orthopedics and dentistry are the state-of-the-art bioinert ceramics, silicon nitride has found application in spinal surgery, and investigations in view of its use in joint replacement bearings are in progress.

Abstract: Mullite-based ceramics were prepared by utilizing agriculture by-product called as rice husk ash (RHA) from untreated rice husk (RH) and commercial alumina powdermixtures. Various samples were prepared accordingly with the mullite stoichiometric composition and subjected to the uniaxial hydraulic press. The green bodies, then were sintered to various temperatures at 1200 °C, 1300 °C, 1350 °C, 1400 °C, 1450 °C and 1500 °C in an electric furnace. Physical and microstructural characterization were done such as bulk density (BD), linear shrinkage (LS), X-ray fluorescence (XRF), X-ray diffraction (XRD) and field emission scanning electron microscope (FESEM). The sample M1, which composed the slightest RHA (40 %) was considered the optimum composition which produced the highest densification, 3.101 g/cm3 and the lowest linear shrinkage, 8.62 % which compareswith the theoretical mullite density. Besides, it is supported by the evidence of the presenceof mullite in the samples sintered 1300 °C (shown as elongated shape) as primary mullite and continued to grow at higher temperatures at 1400 °C (shown as equiaxed shape) as secondary mullite. The sintered samples showno evidence of mullite inearly at 1200 °C due to insufficient energy to diffuse for mullitization. As the sintering temperature increased, mullitization increased while decreasing the distribution of glassy phase and voids. The results revealed the high dependency of bulk density and linear shrinkage on the Al2O3 content and the values were gradually increased with the increase of sintering temperature. These findingsmay lead to the extended study ofthermal insulationmaterials as mullite ceramic is an excellent candidate for this application due to its properties.

Abstract: Aluminum dross residue is a by-product produced at secondary re-melt plants where aluminum scraps are recycled. In this study, aluminum dross residue was utilized as a major component in the fabrication of unglazed ceramics for wall tile applications. The use of this by-product can reduce the landfill and environmental problems. The amount of aluminum dross residue used in the ceramic compositions varied in the range 50-90 wt.%. Other components utilized in the ceramic compositions included recycled glass alumino-silicate based clays. Firing was carried out between 1140 and 1200°C with 4h holding time which resulted in strong ceramic samples. Alpha-alumina, α-Al₂O₃ was the main crystalline phase found in all sintered ceramic samples. The appearance of mullite phase, Al₆Si₂O₁₃ was evident in all fired samples. Overall, the synthesized ceramics had excellent densification characteristics when the amount of aluminum dross residue was less than 70 wt% in the ceramic composition.

Abstract: Metal-free implantology with zirconia devices is a relatively new technology. Nevertheless, more and more patients demand this kind of implant in place of the ones made out titanium due to the better aesthetics, lower risk of perimplantitis, concerns about metallic ions release. This paper analyze concisely the present situation of zirconia dental implants, and overviews the developments in progress on devices made out alumina/zirconia composites that will likely replace zirconia in the next future. Besides ceramics, Polyetheretherketone (PEEK) is now proposed for metal-free dentistry, the ceramic-loaded formulation of this high-performance polymer are especially interesting for dental implantology.

Abstract: In this study, α-Al₂O₃-CeO₂ core-shell nanoparticles were synthesized from the cerium acetate and the commercial α-Al₂O₃ nanoparticles as the starting materials via a wet chemical method. Poly (acrylic acid) (PAA) as an additive compound was used for the surface modification of alumina nanoparticles. Also, the effects of PAA content, pH value and calcination temperature on the synthesis behavior of α-Al₂O₃-CeO₂ nanoparticles were investigated. The formation of core-shell structure was investigated using X-ray diffraction (XRD) and field-emission scanning electron microscopy (FE-SEM) equipped with energy dispersive X-ray spectroscopy (EDS). The results indicated that at the PAA=1.5 wt. %, pH=6 and calcination temperature=1150°C (as optimal conditions), the core-shell nanoparticles with alumina core and ceria shell and homogeneous size distribution were synthesized successfully.

Abstract: In recent times, it could be observed that metal matrix composites receive considerable importance on account of improved properties compared to unreinforced alloys which includes high specific strength, specific modulus, damping capacity and good wear resistance. Interest in composites containing low density and low cost reinforcements has been since growing. Among various discontinuous particulate, silica is one of the most inexpensive and low density reinforcement available in large quantities. Hence, composites with aluminium oxide as reinforcement after the in-situ reaction of aluminium and silica are likely to overcome the cost barrier for wide spread applications in automotive and small engine applications. It is therefore expected that the incorporation of aluminium oxide particles in aluminium alloy will improve the mechanical properties of base material that will see increased usage in aircraft application due to reduced weight. In this research an effect on aluminum matrix composite reinforced with nano sized silica particles with different weight percentage was carried out. From the results it was found that the composites with 4 to 6wt% particle volume fraction to be the best with good tensile strength, yield stress and percentage elongation.

Abstract: In this study, the characteristics of the production process of cemented carbide-alumina composite material made using the wet-shaping process were investigated. The production process in this study produced a green compact of composite material by repeating the wet-shaping process for the molding of each material, and it made possible the sintering of plural materials with varying sintering conditions at the same time, a process that was difficult until now. By using wet-shaping and ultra-fine powder, which have superior sintering characteristics, sintering conditions were found in which it was possible to sinter cemented carbide and alumina at the same time, with a sintering temperature of 1723 K and a sintering time of 5.4 ks. With these sintering conditions, the relative densities of the sintered compact of cemented carbide and alumina were 99.0 % and 98.9 %, respectively. It is clear that the characteristics of sintered compact made with these sintering conditions are superior. When the cemented carbide slurry and the alumina slurry were layered by repeating the wet-shaping process, a composite material was able to be produced by inserting an active brazing filler metal in the interface to improve the bondability of the cemented carbide and the alumina during the sintering. However, it was observed that the active brazing filler metal and the cobalt in the cemented carbide flowed out from the interface between the cemented carbide and the alumina in the sintered compact of the composite material.

Abstract: We have obtained ceramic composites containing graphene structure, where homogenization process of powdery composite was improved. At first, α-alumina was obtained from local row, which is cheap and available. The obtaining method was developed by our group. Graphene oxide was synthesized from natural graphite. Homogenization was carried out in nanomill with organic binder, which provides for equal distribution and separation of graphene oxide layers (Organic binder behaves as “scotch tape”) during grinding. Some characteristics of ceramic materials have been improved.

Abstract: The alumina hollow fiber membranes were prepared by spinning and then sintering method. The dope solution was fabricated by using 1-methyl-2-pyrrolidone (NMP), dimethylsulfoxide (DMSO), dimethylacetamide (DMAc), and triethylphosphite (TEP) as solvents, which have different interaction rate with non-solvent. SEM analysis showed that the alumina hollow fiber membranes have different pore structure. In particular, the hollow fiber membranes prepared with DMSO, DMAc and NMP had finger structures. In contrast, when it was made with TEP, the membrane had a sponge structure. The gas permeability and the contact angle of each hollow fiber membranes were measured. The fabricated hollow fiber membranes were applied to the membrane contact process for the carbon dioxide absorption. The hollow fiber membranes prepared with TEP is had the highest carbon dioxide absorption characteristics. A higher carbon dioxide absorption activity of hollow fiber membranes prepared with TEP was suggested to be due to its gas permeability and hydrophobicity. In conclusion, it was confirmed that the higher gas permeation due to pore structure of the membrane had a favorable effect on the absorption performance.