Papers by Keyword: Al₂O₃-ZrO₂

Abstract: The improvement on the development of porous ceramic materials has leaded to new technologies in thermal insulation, for example, composite materials for better performance of pressure vessels in rocket engines. Within this context, the present work aims to evaluate the ability of a refractory ceramic base alumina/zirconia through the processes of co-precipitation and replica method in an organic fiber template. The green body was burnt-out and sintered at 1200-1600°C to obtain the continuous porous ceramic fibers. In the FEG-SEM analysis, an interconnected porous structure with small grains was observed. The crystalline phases were determined by X-ray diffraction and compared to micro-Raman results regarding the crystalline structure confirms that there present in the material zirconia is composed of more than one phase. Porosity was calculated through a mercury porosimeter as 77.9%, and the Laser Flash method gave a thermal conductivity value of 1.61 K W.m⁻¹.K⁻¹ for the Al₂O₃-ZrO₂ fibers.

Abstract: Functional ceramic nanopowders with emphasis on biomedical applications were engineered by gas-phase condensation using the CO₂ laser vaporization (LAVA) technique. Europium doped strontium aluminate nanoparticles (NP) were prepared from a SrO/α-Al₂O₃/Eu₂O₃ powder mixture. Excited with ultraviolet radiation (UV), the as-prepared amorphous NP revealed red photoluminescence emission. After annealing in reductive atmosphere crystalline SrAl₂O₄:Eu²⁺ nanopowder was obtained showing strong green emission at UV excitation. Ferrimagnetic iron oxide (Fe_xO_y) nanopowders were prepared starting from α-Fe₂O₃ powder. In oxygen-free condensation atmosphere γ-Fe₂O₃ NP were obtained. Oxygen as condensation gas yielded γ-and ε-Fe₂O₃ NP. Superparamagnetic NP were prepared starting from α-Fe₂O₃/SiO₂ mixtures. Depending on the mixing ratio γ-Fe₂O₃ nanocrystallites embedded in a SiO₂ glass matrix or γ-Fe₂O₃-SiO₂ Janus NP were obtained. These NP provide a reactive SiO₂ interface for subsequent functionalizing. The co-vaporization of α-Al₂O₃ as the main proportion and t-ZrO₂ yielded zirconia-toughened-alumina NP. Reinforcing effects of Al₂O₃-ZrO₂ dispersion ceramics will be increased using NP with an intraparticle dispersion of these phases. Future applications of the LAVA prepared NP include biological fluorescence labeling, and drug targeting, magnetic resonance imaging, and hyperthermic cancer therapy, as well as sintering of load bearing ceramic implants, respectively.

Abstract: A series of Al₂O₃-ZrO₂ (AZ-X) composite oxides with different ZrO₂ contents were prepared by a chemical precipitation method. Ni-P/AZ-X catalysts were prepared by temperature-programmed reduction. The supports and catalysts were extensively characterized by X-ray diffraction (XRD) and BET. The effects of support composition and P/Ni molar ratios on the catalytic performance of the catalysts were investigated by thiophene hydrodesulfurization (HDS) and pyridine hydrodenitrogenation (HDN). In comparison with Al₂O₃, Al₂O₃-ZrO₂ (20 wt% ZrO₂) composite oxide supported Ni-P catalyst exhibited higher activity and the activities of HDS and HDN increased by 7.5 % and 11.1 %, respectively. Studies of Ni-P/AZ-X catalysts with varying initial P/Ni molar ratios indicated that oxidic precursors with molar ratios of P/Ni = 2/1 yielded catalyst containing phase-pure Ni₂P which exhibited optimal activity.

Abstract: A group of new composite antibacterial agent was prepared by ion adsorption method, in which silver ion is the main active ingredient, with alumina and zirconia as the carriers. The influence of mixing time, content of zirconia, silver ion content and calcination temperature on the antibacterial properties of the composite powder are discussed in this paper. The results show that when the content of ZrO₂ is 4%, Ag⁺ content is 4%，mixing temperature is 70°C，mixing time is 4h, the composite antibacterial agent has a good property. ZrO₂ can be loaded in the large hole of Al₂O₃ as a second carrier; it can keep a larger surface area-based carrier, suitable pore structure, and also play an important role on antibacterial properties at high temperature.

Abstract: The investigation of ceramic filler on the properties of denture base materials made from PMMA filled with Al2O3/ZrO2 was carried out. The amount of Al2O3/ZrO2 filler was fixed at 5 wt%. However, the ratios of Al2O3 to ZrO2 added were varied from 0 to 100. Samples were prepared for fracture toughness and flexural test. The findings were analyzed using scanning electron microscopy (SEM). The findings were recorded that the Al2O3/ZrO2 ratios show higher fracture toughness and flexural properties than PMMA matrix. SEM micrographs indicate that distribution of Al2O3 and ZrO2 in the PMMA matrix is fairly homogeneous. The mixing method was good between reinforcement particles and PMMA matrix. Therefore, addition of six ratios of Al2O3/ZrO2 with PMMA and this mixture is able to improve the mechanical properties of this denture base material.

Abstract: Powder precursors of the Al2O3-ZrO2 system were synthesized by the sol-gel method. Dispersity of the powders depended on synthesis and drying conditions. Differential Scanning Calorimetry, X-Ray diffraction, and method of adsorption–desorption isotherms were used to characterize the interrelations between particle size and phase transition in the Al2O3-ZrO2 system. It was revealed that azeotropic drying under overpressure is quite effective for obtaining well-dispersed powder precursors synthesized by the sol-gel method. In contrast to bulk materials, tetragonal, cubic, and monoclinic phases were found to exist in a wider temperature-composition range. It was shown that the existing phase symmetry in the well-dispersed powders correlates with the crystallite size.

Abstract: Novel continuously porous alumina (25%monoclinic-Zirconia) (Al2O3-(m-ZrO2)) and tetragonal Zirconia (t-ZrO2) composites were fabricated with concentric multilayer shells of Al2O3-(m-ZrO2) and t-ZrO2 by the multi-pass extrusion process. Nanocrystaline Al2O3-(m-ZrO2)/ t-ZrO2 powders and graphite powder as a pore forming agent were mixed with polymer in extrudable form. The microstructure was tailored in the green bodies by the extrusion process with high flexibility of control. The green body was burnt-out and sintered to obtain the continuously porous ceramics. The pore diameter and pore frame thickness were around 198±10.5 μm and 158.5±10.2 μm, respectively. The pore frame region was furnished with 9 alternating shells of Al2O3-(m-ZrO2) and t-ZrO2 with uniform thickness of about 17.6±1.1 μm. The interfaces of the alternate layers were designed corrugated shape. The detailed microstructure of the porous bodies was characterized by SEM techniques.