Papers by Keyword: Alumina

Abstract: Cermet materials is a important new engineering materials with the advantages of ceramics and metal materials. The Al₂O₃/Al cermet materials is prepared via the powder metallurgy method, the effect of sintering technology on properties of Al₂O₃/Al cermet materials is researched in this paper, which lay the base for preparing the high performance cermet materials. The results are shown through the study, the denstity of cermet is increased with an increasing moliding pressure, the sample density is 2.084g/cm³ as the pressure for 40MPa and the sintering temperature at 600¡æ, the density is higher, that is to say it is highest performance, the distribution of aluminum and alumina is most uniform. When the sintering temperature is higher, howerver, the molding pressure is lower, the lower density of the sample is shown, the aluminum is easier to overflow the surface of the sample.

Abstract: In this study the needle-less electrospinning by means of “Nanospider^TM“ (ELMARCO) as technology for the preparation of fine α-Al₂O₃ fibers with diameters of 0.5 - 1.5 µm is presented. The fabrication consists of three steps: i) preparation of spinning solution, ii) electrospinning of the prepared solution and collection of the composite fibers, iii) calcination of the composite precursor fibers. The electrospun fibers were prepared from polyacrylonitrile/N,N-dimethylformamide (PAN/DMF) polymer solution and Al(NO₃)₃.9H₂O in ratio 1/10/1. Thereafter, the precursor fibers were calcined in the furnace at 900, 1100 and 1200 °C with a rate of 5 °C/min in air. The formation of crystalline phases, surface morphology and diameters of metastable and final alumina fibers were characterized using thermogravimetric analysis, X-ray diffraction analysis, the scanning electron microscopy and transmission electron microscopy. The precursor PAN/Al(NO₃)₃ fibers were amorphous. The thermal treatment leads to the phase transition from γ-Al₂O₃ to α-Al₂O₃ accompanied by removing of polyacrylonitrile (PAN). The fine porous microfibers composed of pure α-Al₂O₃ phase were prepared after calcinations at 1200 °C.

Abstract: Alumina ceramics with good mechanical and corrosion resistance, is one of the most widely used engineering ceramics. The aluminum has a high strength, high conductivity, high plasticity, etc. than aluminum ceramics used in more and more industries. In this paper, aluminum and alumina powder as raw material, mixing, forming, sintering and a series of processes for preparing the alumina/aluminum metallic ceramic materials, through performance testing and analysis can be found in the ratio of raw materials 50wt% Al, 50wt % Al₂O₃ relatively good moldability. After sintering, after measuring the density contrast is found better density in the pressing process pressure of 20MPa and holding pressure time for 20min. By comparing the sintering process, after the interface structure by scanning electron microscopy and found help improve density through the secondary sintering metallic ceramic materials.

Abstract: Superfine alumina has various excellent performance, superfine aluminum often used in metallurgy, aerospace, microelectronics and medicine, so the study of alumina has become a hot research at home and abroad, superfine alumina powder the body needs are also increasing. In this paper, superfine alumina powder were prepared by hydrothermal method, and to study the preparation process. The results show that the fibrous alumina particles gradually becomes granular with the increase of pH of the reaction, pH value of 9 to get a uniform particle size distribution and an average size of small powder particles. As the increasing calcination temperature, the alumina particles gradually grow, the homogeneous superfine particulate alumina powders is obtained under calcination temperature at 950¡æ. The better preferred process is that alkali molar ratio of 1:3, a concentration of 0.3mol/L, the reaction temperature at 200°C, calcination temperature of 950°C.

Abstract: Milling and hydrothermal treatment of alumina powders in aqueous medium can result in surface transformations generating aluminum hydroxides. The aim of this work was to advance the understanding on these transformations. A α-alumina powder was ball milled in water at different pHs for 10 h, and then autoclaved (150 °C, 3 atm, 3 h). The powders were analyzed by transmission electron microscopy, differential scanning calorimetry simultaneously with thermogravimetry, X-ray diffraction, and infrared spectroscopy. It was observed that milling in basic medium caused the formation of doyleite [Al (OH₃)] nanoparticles, which were fully converted to boehmite (AlOOH) by hydrothermal treatment. The boehmite fraction determined by thermal analysis was 1.7 wt%. The powder milled in acid medium had no mechanochemical and hydrothermal transformations.

Abstract: Porous ceramics have certain unique properties such as high toughness and resistance to heating at elevated temperatures. These properties make them products of great interest for applications on the field of filters and biomaterials. This paper proposes a new technique, called gelatinization, for processing this class of ceramics in order to obtain materials with more controlled pore size, plus a more homogeneous distribution. In order to check the efficiency of this technique, it was used as a raw material powders of calcined alumina and titania, previously characterized, mixed with unflavored gelatin, water and dispersant for holding the ceramic conformation. Three different formulations (with 40, 50 and 55% of solids content) were investigated using alumina and titania separately. The results indicated that the most suitable composition in terms of moldability was 55% of solids. It was also observed that the use of this technique to obtain bodies of high porosity is feasible; however, more detailed studies of sintering are necessary to obtain parts after firing in a close future. Due to the high porosity obtained the green, a detailed study of the sintering conditions is crucial to obtain parts with physical integrity.

Abstract: The aluminum anodizing is a used technique used to produce decorative and protective film of high quality. This anodizing process results in a large volume of industrial sludge, containing amounts of aluminum hydroxide colloidal problematic for these industrial waste disposal due to the environmental impact. This study aims to accomplish the treatment of these residues, which were thermally sintered at temperatures of 200 °C, 1000 °C and 1400 °C. After the heat treatment, the residues were subjected to analysis of X-ray diffraction and X-ray fluorescence. In evaluating these results, there was a gradual increase of the percentage of alumina at 1400 °C to achieve 95%. With the acquisition of the ceramic high alumina content, the objective is the fabrication of refractory linings for pipes used in the oil refining process. And this study will serve to solve an environmental problem arising from the metallurgical industry and simultaneously presenting an alternative material for the industry.

Abstract: Crude petroleum storage and transportation systems suffer from constant physical stress caused by chemical attack of crude petroleum on its structure. Ceramics are materials with high chemical stability in hostile environment and therefore can be used as an inert coating material. In the present work we have produced Al2O3-Y2O3-ZrO2 composites with high mechanical strength, through thermo-mechanical processing. To evaluate the quality of materials developed and the possibility of using them as inert protective coatings, storage and transportation systems, we have studied the physic-chemical and mechanical stability of these materials in crude petroleum originated from onshore and offshore. Structural, microstructural and mechanical tests showed that 15-20wt% ZrO2 composite ceramics with 2 wt% of Y2O3 additives presented better results in terms of mechanical hardness and microstructural characteristics. The study of stability of composite ceramics in crude petroleum environment showed that ceramics did not present any additional phase except the constituent phases. Result of microscopy and Vickers hardness tests also showed that there is no visible change in these characteristics after even 90 days of submersion in crude petroleum. Thus we conclude that composite ceramics could be potential materials for inert coating in crude petroleum environment.

Abstract: Alumina has been applied in systems of protection against high speed impact due mostly to the mechanical properties, low cost and ease of processing. A new approach to this application involves the manufacture of lamellar bioinspired composites of thin plates of alumina obtained by tape casting process, and fabrics of poly (p-aramid), Kevlar ®. The aim of this study is to investigate the interaction between the ceramic and polymeric fibers fabric observing the influence of different nature adhesives to select the most suitable for further preparation of bioinspired lamellar composite for impact protection applications. The strength of adhesion is evaluated by 90° Degree Peel Test and the interaction is investigated using techniques of optical microscopy, scanning electron microscopy (SEM) and spectroscopy with Fourier transform infrared (FT-IR) to characterize the surfaces of substrates after testing. Polyurethane aqueous based adhesive presented better interaction with both materials when compared to organic solvent based adhesive.

Abstract: The oxygen permeability of polycrystalline α-alumina wafers, which served as model alumina scales formed on heat-resistant alloys, was evaluated at a temperature of 1873 K. Mass transfer along grain boundaries (GBs) in an alumina wafer exposed to a large oxygen potential gradient (dμ_O), where both oxygen and aluminum mutually diffuse along GBs, was analyzed using ¹⁸O₂ and SIMS. ¹⁸O was concentrated at GB ridges on the high oxygen partial pressure (P_O2(hi)) surface and along the GBs near the P_O2(hi) surface. ¹⁸O adsorbed on the surface diffused almost immediately to surface GBs, resulting in the formation of new alumina by reaction with aluminum diffusing outward along the GBs. Oxygen GB diffusion coefficients in the vicinity of the P_O2(hi) surface were determined from the ¹⁸O depth profile along each GB for the ¹⁸O map of the cross section of the exposed alumina wafer. The oxygen GB diffusion coefficients were comparable to the values calculated from the oxygen permeability constants assuming an electronic conductivity and were obviously lower than those of oxygen GB self-diffusion without an oxygen potential gradient.