Papers by Keyword: Alumina

Abstract: Alumina (Al₂O₃) is a technical ceramic widely selected for demanding applications due to its excellent material properties, such as high strength, corrosion resistance, and thermal stability. In this study, the effect of the sintering temperature of 3D-printed alumina to its surface characteristics and its subsequent performance as a copper-metallized ceramic substrate was investigated. Green parts of alumina samples were prepared using stereolithography (SLA) 3D printing, debound, then sintered at temperatures ranging from 1660°C to 1740°C. Surface roughness was quantified using Atomic Force Microscopy (AFM), while the copper layer's adhesion was assessed via tape and burnishing tests. Electrical conductivity was measured with a four-point probe. A non-monotonic relationship between sintering temperature and surface roughness was observed. Roughness (Ra​) decreased as temperature increased from 1660°C to 1720°C, attributed to enhanced densification. However, increasing the temperature to 1740°C led to grain coarsening and a slight increase in roughness due to excessive grain growth. Stronger copper adhesion was achieved on smoother surfaces produced at optimized sintering temperatures. Electrical conductivity was also determined with a minimum sheet resistance of 0.089 mΩ/sq achieved.

Abstract: By replacing the interface with sharp change properties with a functionally graded material with a gradually changing composition, a stable interface can be formed for mechanical and functional properties. In this study, the final goal is to functionally grade the interface between aluminum and alumina (Al₂O₃)/aluminum (Al) composites. First, the segmentation velocity of Al₂O₃ particles under gravity was measured to clarify the possibility of functional grading. The starting materials used were A356.0 Al alloy and α-type Al₂O₃ particles. The segmentation velocity obtained by the experiment was much faster than the theoretical velocity obtained by Stokes' law. It seems Stokes' law assumes that the particles are spherical and there is no interaction between particles, but the actual particle velocity was affected by the actual particle shape and interaction between particles. These factors affect the change in the segmentation velocity. The height of the mold was set to 40 mm, and an Al₂O₃ particle/Al composite with a particle size of 6.7 μm was placed on the top and an Al alloy was placed on the bottom in the mold, melted, and rapidly solidified after 12 sec., and an Al₂O₃ particle-dispersed Al alloy functionally graded composite was obtained under gravity.

Abstract: Desert soils present some issues that need improvement. Some of these are high permeability and collapsibility potential. These problems are due to the uniform particle size distribution and the lack of particle edges. Soil improvement is required to mitigate these issues. Cement is widely used for soil stabilization but has environmental issues since it is a significant source of CO₂ emissions and requires high energy consumption. In this study, the calcined shale material is utilized as a partial replacement for cement to reduce the permeability and compressibility of soils more sustainably. The study considers three cement doses of 5%, 10%, and 15% and four calcined shale percentages of 10, 30, 50, and 70%. A series of falling head permeability and one-dimensional consolidation tests were conducted to examine the performance of cement and calcined shale as stabilizers. The results of the study indicate that the addition of 30% calcined shale as a partial replacement of cement has the most significant effect on the conductivity and compressibility of the soils. An increase in cement content decreases the permeability and compressibility of the soil due to the hydration of cement. Conversely, the conductivity and consolidation of the soil are initially decreased with an increase in the calcined shale up to 30% and then start to increase. In summary, this study reveals that the presence of CS and cement has a substantial effect on the conductivity and compressibility of the soils.

Abstract: Conventional ceramic technology is a widespread technique for synthesizing a large range of materials for household use and engineering applications. However, for advanced technical ceramics different approaches should be used in order to obtain materials with unique physical properties. Despite the well-known technology for the synthesis of alumina-based ceramics, there are a lot of challenges in optimizing manufacturing conditions or integrating the newest technologies. In particular, there are still some challenges in sintering porous bulk ceramics. In this paper, we report on synthesizing mixed-phase porous α-Al₂O₃ by modernized ceramic technology method. Precursor powders for compaction were obtained by the hydrothermal method in a Teflon vessel. X-ray diffraction and scanning electron microscopy were used to characterize the synthesized samples. It was demonstrated that hydrothermal precursors with chemical residuals make it possible to synthesize porous ceramics with an open porosity of 55–80% and an apparent density of 0.76–1.80 g/cm³. The change in microstructure of sintered samples is explained by precursor powder morphology. The developed approaches can be used in modernized ceramic technology to synthesize porous oxide materials for filters of gases and liquids or refractories.

Abstract: In this study, the Al₂O₃ round bar and Al-Si12CuNi (AC8A) round bar were joined by friction welding. AC8A is a typical piston material treated by the heat treatment T6. The parameters of the joining condition are friction time and upset pressure. SEM observed the microstructure at the interface region of joined materials. 1) Judging from these photographs, the damages to the microstructures at the interface region of joined materials by upset pressure are more significant than those caused by friction time. 2) The relationship between the joint conditions and mechanical characteristics from three points of bending test results for the joint material specimens. 3) The residual stresses around the interface were measured by the Raman spectroscopy method. There is a possibility that the friction welding conditions are correlated to the residual stresses.

Abstract: Recycling of aluminium alloys is gaining significant attention due to its economic and environmental benefits. However, close loop recycled aluminium alloys can be adversely affected by impurities and alloying elements present in the recycled feedstock. In this study, the influence of three composites, namely alumina (Al₂O₃), ferric oxide (Fe₂O₃), and manganese (Mn), on the properties of recycled aluminium taldon scraps was investigated to enhance the tensile behaviour of the alloys. The effects of these composites on the mechanical properties, microstructure, and corrosion behaviour of the recycled aluminium alloys were evaluated through experimental characterization techniques. The results showed that the addition of these composites had a significant influence on the properties of recycled aluminium alloys, providing insights into the potential for improving the performance of recycled aluminium alloys through composite additions. The addition of Al₂O₃ enhanced the tensile strength by 44.18 % and the variation can be attributed to the strengthening of the dendritic zones by the formation of α-Al.

Abstract: This study investigated the effects of mixing ratio and temperature on the electrical conductivity of a GNP-Al2O3 hybrid nanofluid. The results showed that an increase in the mixing ratio reduced the electrical conductivity ratio of the nanofluid, while an increase in temperature improved the electrical conductivity ratio. Additionally, an Artificial Neural Network (ANN) was used to predict the electrical conductivity of the nanofluid based on the mixing ratio and temperature. The optimal number of neurons in the hidden layer was found to be four neurons, with a low root mean square error (RMSE) value of 0.00696. The regression plot for the training, validation, and test data exhibited high correlation coefficients, indicating the reliability of the ANN model. These findings provide valuable insights into the behaviour of hybrid nanofluids and highlight the potential of using ANN for predicting their electrical conductivity.

Abstract: Hybrid composites are gaining increasing interest in the development of aluminium metal matrix (AMCs) for various industrial applications owing to their ability to integrate multiple functionalities within a single material matrix with enhanced physio-mechanical properties as opposed to single-fibre reinforced composites. Green plantain peel ash (GPPA) is an agricultural waste with potential for reinforcement purposes. However, no study has investigated GPPA natural filler as a reinforcement for AMCs. This study, therefore, aims at assessing the influence of variations in GPPA particles and alumina as reinforcements in the fabrication of hybrid composites using Al-Mg-Si alloy as a matrix. This study also reassessed the chemical composition of the GPPA particles and investigated their mechanical properties. However, enhanced mechanical properties, including hardness, tensile strength, and ductility, were observed at varying weight ratios. Results obtained in this study suggest a promising potential application of GPPA particulates as complementing reinforcements in the production of lightweight, strong, and high-performance AMCs well-suited for engineering, aerospace, construction, and packaging applications.

Abstract: In our previous paper[6], the effects of the retainer wear failure on the friction torque were investigated. In the present paper, to research the failure of the retainers of the PEEK-alumina ball bearings tested under dry rolling contact, the upper and bottom surfaces and the sections of the retainer pockets were observed. The wear damage was found on the surface of the upper and bottom surfaces. On the sections of the pocket, the changes due to wear at the pocket edge was found. On the worn curves of the sections, large scatter of the curvature center positions were numerically calculated in both specimens. The balls moved relatively for the retainer unit to the upper or bottom sides. These results indicate that the wear changed the pocket shape, and the ball could not become to keep the position for the retainer unit. The wear of the pocket caused the failure of the retainer.

Abstract: The rolling contact fatigue of PEEK-alumina ball bearings in non-lubrication was tested under 500 N and 600 N. During the tests, the friction torque was measured. The retainers under both conditions broke during the tests, and rubbed on the upper and bottom races. The friction features were not different between 500 N and 600 N. However, the black colored surfaces on the races and retainer were identified only in the test under 600 N. The wear loss of the bearing tested under 600 N was larger than that under 500 N. From these results, the specimen under 600 N received the heavier wear damages than that under 500 N, and the worn surface was not related to the friction torque. The wear damages of the inner elements and the outer rings in the retainer were larger than those of the races and 9-alumina balls in both specimens.