Papers by Keyword: Al₂O₃

Abstract: The expansion in the application of bio-materials leads to a wide variety of forms. The current study includes the preparation of a biological material in the form of a bio-coating that is represented by the, combination of a substrate with biological properties and at the same time high mechanical properties represented by alumina and the use of a coating from a material that provides high biological properties and low mechanical properties if it compared with the substrate, which is the hydroxyapeptite . Hydroxyapeptite was prepared from the biological waste, which is the egg shells after chemically cleaning by acetone solution and drying them in air , grind for 14 hours then calcination at 850 C^o for 2hours, and reacting with phosphoric acid ,heat treatment by sintering at 1100C^o, for 3 hours to obtain the pure hydroxyapatite phase. After preparing cylindrical samples of alumina and sintering them at a temperature of 1300°C and coating them by immersion with a solution of hydroxyapeptite prepared from mixing of hydroxyapeptite with of distilled water, the immersion is done at intervals ranging from (10,30,and 50 ) minutes, sintering process for soaking sample has been done at 1200 C^o for one hours. The XRD and EDS technique showed an increase in the proportion of hydroxyapatite coatings formed and appears in calcium and phosphorous ions with an increase in the immersion time. Degradation test has been done after soaked the samples in Buffer solution for 7 days which proved increment in degradation as the soaking time increase .

Abstract: In the present investigation Aluminum matrix composites (AMMCs), Al7075 Alloy as matrix metal and Al₂O₃/SiC particles (2-8%) with an average particulate size of 20, 50 nm as strengthened material have been processed by the stir casting method. For the counter surface wear testing, a computerized pin on a wear tester was used as EN31 (58-60 HRC) steel disc and composite pin. The wear rate for the matrix metal and composites in terms of weight loss per unit sliding distance, friction coefficient, and volume loss were achieved. The composite results show better resistance to wear than matrix metal. SEM was used to investigate the microstructural characterization of worn surfaces. Sample weight loss was calculated and the change in cumulative wear loss at a sliding distance was uniform both for metal matrix as well as for composites. The wear speed for composites was also noted to be small compared to the metal matrix. In addition, experiments have shown that, with the increasing weight fraction of Al₂O₃/SiC and the coefficient of friction increases with increasing sliding velocity and weight fraction of Al₂O₃/SiC, the wear rate reduces. The wear characteristics (wear rate, coefficient of friction and wear loss) were better than those of other composites and the matrix metal with 6wt% Al₂O₃/SiC composites.

Abstract: Thermal conductivities of silicone rubber filled with Al₂O₃ were prepared. Thermal conductivity experimental results obtained were analyzed using the Nielsen and Agari models to explain the effect of Al₂O₃ filler on the formation of thermal conductive networks. Thermal conductivities increased with the adding of mixed Al₂O₃ of large and small sizes fillers. The scanning electron microscopy (SEM) showed that it is the optimum particle sizes and quantities that made the filler packing closer, which thus leads to formation of more thermal conductive chains.

Abstract: The article analyses the influence of SiO₂ and Al₂O₃ nanopowders on properties of ceramics consisting of fly ash from thermal power plants, glass waste, and clay binder. Based on studies of physical and mechanical properties of the obtained ceramics (ultimate compressive strength, ultimate three-point bending strength, wear resistance, and water absorption), the paper shows the positive influence of the nanoadditives. The optimal number of SiO₂ and Al₂O₃ nanopowders in the formulation is 0.5 wt. % that has the strongest effect on ultimate compressive strength and water absorption of the fly ash ceramics samples. The direction of further research on improving the properties of ceramic products is an application of the Al₂O₃ nanopowder as more perspective nanoadditive using clay dispersant.

Abstract: The effect of Al₂O₃ to the properties of whiteware porcelain such as water absorption, bulk density, flexural strength and crystalline phases were studied systematically. The result shows that the addition of alumina at maximum 5 wt.% in porcelain bodies increased the flexural strength of the fired bodies which can reach 55.5 MPa, 30% higher than 0.0% alumina content. However, slight decrease in the other physical and mechanical properties was observed with Al₂O₃ addition higher than 5 wt.%, which is believed to be due to increased corundum phase compared to mullite phase in porcelain body.

Abstract: In this paper, the effect of sintering temperature on the interfacial structure of the composite was investigated and three different formulation groups were used to compare the respective properties. To obtain a composite material with excellent interface, the law between reference number and performance is obtained. Through mixing, molding, sintering, sample preparation, scanning electron microscopic observation, energy spectrometer observation and analysis, the following conclusions can be drawn: As the temperature increases, the density and hardness increase. The sample melts at 1500 °C, and there is no specific data. When the temperature reaches 1450 °C, the density and hardness reach the highest. When the formulation is Fe:Al₂O₃:SiO₂=18:1:1 and the temperature reaches 1450 °C, the properties of the sample materials are optimized. The density is as high as 95% and the hardness reaches 42.9HBW.

Abstract: In this paper, the effect on the properties of alumina/aluminum cermet by changing the sintering temperature, and comparing the advantages and disadvantages of different characterization methods and their application range, it provides a reference for selecting the characterization technology suitable for alumina/aluminum composites.Through mixing, molding, sintering, sample preparation, scanning electron microscopic observation, energy spectrometer observation and analysis, the following conclusions can be drawn: the higher the vacuum sintering temperature, the more aluminum material is melted out of the body to form aluminum balls on the surface, and the green body The more severe the cracking. When the sample is sintered at a temperature of 600 °C, the density is the highest and the appearance is the best. When the molding pressure is 40 MPa and the sintering temperature is 700 °C, the microstructure of the sintered alumina/aluminum cermet is better. It can be seen from SEM and EDS analysis that the particles are continuously distributed and the larger one is metal Al, and the particles are discontinuously distributed and finer is Al₂O₃.

Abstract: In this paper, the effect of raw materaisl on the properties of coated Al₂O₃/Al cermet materials were investigated, the raw materials were prepared via different methods, which provide a reference for obtaining higher performance cermet materials. Through mixing, molding, sintering, sample preparation, scanning electron microscopic observation, energy spectrometer observation and analysis, the following conclusions can be drawn, the density of the cermet material prepared by the mechanical ball milling method (83.5%) is higher than that of the cermet material prepared by the chemical precipitation method (92.8%). It is nearly 10% lower. The alumina particles prepared by the ball milling method are agglomerated, and a large amount of agglomeration occurs in the aluminum, and the composition is very uneven. For materials prepared by the precipitation method, the aluminum oxide is uniformly distributed in the aluminum. The ball-milling powder is used to prepare materials, most of the alumina is in the form of particles, and in the precipitation method. In the powder preparation sample, the thin layer of alumina which forms the same eggshell envelops the aluminum, and the aluminum has a certain liquid phase change. the surface hardness (824HV) of the cermet material prepared by the mechanical ball milling method is lower than the surface hardness (1005HV) of the cermet material prepared by the chemical precipitation method.

Abstract: The effect of surface treatments prior to the deposition of Al₂O₃ is performed on 4H-SiC MOS capacitors and MOSFETs. 40 nm of Al₂O₃ were deposited on 4H-SiC using atomic layer deposition (ALD) as a gate dielectric. Different surface treatments were used to investigate the capacitance-voltage and current-voltage characteristics on MOS capacitors and MOSFETs respectively, including the important parameters such as interface state density, flat band voltage, threshold voltage and field-effect mobility. Forming gas annealing and rapid oxidation processes were found to be effective in reducing the interface state density and results in high field-effect mobility with peak field-effect mobility of 130 cm²Vs^-1. The experimental results obtained manifest that the surface treatment prior to Al₂O₃ deposition is critical to producing high performance of 4H-SiC MOSFETs.

Abstract: This study was conducted to investigate the effect of Al2O3 on characteristics of A356 reinforced composites. The addition of Al2O3 as reinforced varied from 2 vf-% to 15 vf-% through Stir Casting methods to obtain the optimum addition Al2O3 as reinforced in mechanical properties of composite A356 as matrix and Al2O3 as reinforcement. Magnesium with of 10 wt-% was added to improve wettability between Al2O3 particles and Al A356. Addition of Magnesium is expected to form the spinel phase MgAl2O4 in interface area between Al2O3 and Al A356.The optimum tensile strength was found at 2 vf- Al2O3 with value 131.55 Mpa. However, the value is still lower than the tensile strength of Al A356 As cast. It is caused due to the porosity and the agglomeration of Al2O3 were found in the microstructure of the composite Al A356/Al2O3. The Hardness increased from material monolithic Al A356 as cast, reached 37.43 HRB.