Papers by Keyword: Alumina

Abstract: The Chemical Mechanical Planarization (CMP) process (polishing and substrate cleaning) results in defects that can be classified as mechanical (i.e., scratching), chemical (i.e., corrosion), or physiochemical (i.e., adsorbed contaminants) according to the mechanism of formation. This work will focus on the rationale design of p-CMP cleaning systems for emerging materials (silicon carbide (SiC)) that activate the cleaning chemistry via external stimuli such as megasonic energy. More specifically, using megasonic energy in the presence of supramolecular assemblies such as micelles and vesicles was employed for a “soft” (low shear force) defect removal process. Results indicate a correlation between the structure of the “soft” cleaning additives and induced megasonic energy on overall simulated defect removal. It was determined that effective particle removal was a second-order kinetic process with a concentration dependency (i.e. above and below the critical micelle concentration (CMC)) emerging as a key driver for the defect removal rate. Although, one apparent drawback is the generation of post-cleaning carbon residue due to the adsorption of the supramolecular structures to the SiC substrate.

Abstract: This paper is aimed at investigating the mechanical properties of spark plasma sintered alumina (Al₂O₃) reinforced with tungsten-carbide-cobalt (WC-12wt%Co). Pure Al₂O₃ and admixed-Al₂O₃ powders were sintered using spark plasma sintering (SPS) technique at a temperature of 1800°C, heating and cooling rates of 100 °C/min and 200 °C/min, a pressure of 48 MPa in an argon atmosphere. The density, hardness (HV) and indentation fracture toughness (K_IC) of the sintered samples were measured and compared. Between 9 and 17% increase was observed in the HV values of the additives, while the K_IC value recorded an increase between 17 and 63% for all the additive as compared to pure Al. Phase analysis and identification was carried out with X-ray diffraction and microstructure was taken with scanning electron microscope. The results obtained showed the samples potential for cutting tool applications.

Abstract: The present work aims at the preparation and characterization of ceramic layered composite prepared from fine submicron-sized Al₂O₃ with the addition of electrospun graphene-coated Al₂O₃ fibers (Al₂O₃/G-Fs) by Spark Plasma Sintering with double pressure sintering process. A layered composite containing 2.5 wt. % of Al₂O₃/G fibers in three homogeneous layers was prepared and compared with the pure monolithic Al₂O₃ material obtained under the same conditions. The microstructures of the samples were studied by optical microscopy, scanning, and transmission electron microscopy. The presence of graphene after the sintering in the final composite was proved by Raman spectroscopy. The effect of the graphene-coated fibers on the composite`s microstructure and mechanical properties was described along with the fractographic analysis. Graphene on the surface of the electrospun Al₂O₃ fibers suppressed the grain growth which dominantly takes place during the sintering of the composite, which significantly influenced the character of the fracture. While predominantly intergranular fracture occurs in the monolithic fracture surface, the fracture character becomes transgranular with the addition of layers of Al₂O₃/G-Fs. Fracture toughness improvement took place because of the presence of small pores, in order of a few nanometers, which showed high energy absorption and provided self-induced crack propagation inhibition.

Abstract: On the one hand, cermet has the advantages of metal materials, and on the other hand, it maintains the excellent properties of ceramic materials, and is a very important new engineering material. In this paper, the alumina/aluminum cermet material composite powder was prepared by ball milling, and its densification properties were characterized and studied to provide reference for the preparation of high-performance cermet materials. When the ball milling time is more than 6h, the distribution of alumina particles around the aluminum powder is relatively uniform. The research shows that: with the extension of the ball milling time, the number of pinning of Al₂O₃ particles on the surface of the Al ball first increases and then decreases; The trend of decreasing; with the increase of ball-to-powder ratio, the distribution of Al₂O₃ particles on the surface of Al balls is more uniform. Considering its cost-effectiveness, it is more suitable to prepare pinned alumina/aluminum-ceramic composite powder under the conditions of ball milling speed of 360r/min, ball-to-material ratio of 2:1 and ball milling time of 12h. When the Al content gradually decreased, the density and hardness of the cermet material also decreased gradually. When the Al content gradually decreased, the density and hardness of the cermet material also decreased gradually. When Al accounts for 75% in the sample, the microstructure is dense and the hardness is higher. When the molding pressure is 20MPa, the unevenness of the surface of the material is greatly relieved, relatively flat, and the densification effect is better. When the sintering temperature is 800°C, the fired sample is very dense, and the particles have relatively high bonding strength, but a small amount of aluminum is precipitated on the surface of the sample, forming a silver-white spherical substance.

Abstract: In this work, functionally graded materials were synthesized by centrifugal technique at different volume fractions (0, 0.5, 1, 1.5, and 2% Vf) with different rotational speed of (0, 600, 800, 1000 and 1200) r.p.m and different rotational time (0, 1, 2, 3 and 4) min. The hardness and tribological properties were characterized to study the graded and non-graded nanocomposites and the pure epoxy material. Using a pin-on-disc machine, sliding wear tests are conducted with the following parameters: rotation speed (400 rpm), normal load (30 N), filler content (0–2% Vf), and sliding distance (0.15 km). The hardness and wear parameters of graded composites were investigated and compared to those of epoxy composites with homogeneous filling. This work demonstrates that incorporating Al2O3 nanoparticles improves graded composites' hardness and sliding wear resistance. Epoxy–Al2O3 epoxy composites with a volume fraction of 2 had the lowest specific wear rate of all samples. The FGMs had superior sliding wear performance compared to homogenous composites. The maximum difference in hardness and coefficient of friction occurred at (FGM), which is loaded from the rich side of the nanoalumina at (Vf = 2%, N = 1200 r.p.m and T = 6 min), where the maximum value was 168% and 78 % as compared with neat epoxy, respectively. The wear rate of the functionally graded samples was enhanced by (87.7%) compared with neat epoxy if loaded from the alumina-rich side.

Abstract: This study investigated the influence of adding styrene-ethylene-butylene-styrene (SEBS) and stearic acid (SA) on poly (lactic) acid (PLA) with nano-alumina (Al₂O₃) filament composite for fused deposition modeling (FDM) 3D printing (3DP) application. The filament composites were produced via hot-melt extrusion using a twin-screw extruder. Materials characterization and mechanical testing were conducted to determine the effect of SEBS+SA. Fourier transform infrared spectroscopy (FTIR) illustrated the interaction of the aliphatic group of PLA and SEBS+SA. XRD data showed that the SEBS+SA has no significant effect on crystallinity, but the differential scanning calorimetry (DSC) data showed a decreasing trend. Due to the nature of SEBS+SA, the heat capacity increased to 1.222 J/g•C°. The cold crystallization, melting, and degradation temperatures were reduced by 18.34°C, 5.29°C, and 25.19°C, respectively. An increase in the developed filament composite’s processability was evident in the MFR data. The axial strain and the toughness of PLA with nanoAl₂O₃ were increased significantly by 402.54% and 48.20%, respectively. Furthermore, the SEM images revealed overlapping of intra-and interlayers of the 3D printed specimens.

Abstract: The mechanical properties of grinding-tools relies highly on adhesion between the abrasive particles and the bonding phase, generally composed of organic rubber or resin materials. The surface modification of abrasive particles represents an industrial alternative to improve the connection with the bonding phase material. However, increasing the roughness of abrasive particles is a challenging process because of their high chemical stability. In the present study, three different approaches are investigated to modify the surface of industrially used alumina abrasive particles. Chemical erosion under harsh acidic and alkaline conditions, and hydrothermal deposition of aluminium-based coatings were used for the surface modification of the abrasive particles. The chemical stability of alumina particles was demonstrated by the chemical etching while the succesufull surface deposition of AlOOH crystals modified the apparent roughness of the processed powder particles. Morphological changes after each treatment were studied by scanning electron microscopy and the phase composition was confirmed by X-ray diffraction.

Abstract: Al₂O₃ fiber has high temperature resistance, chemical corrosion resistance, and low density. It is a good thermal insulation material. Reed is one of the most widely distributed angiosperms. The short cilia of the reed have a hollow structure, which can improve the thermal insulation performance of the fiber. Using reed fibers as a biological template, Al₂O₃ fibers with a hollow structure were prepared. After the reed fibers were immersed in the precursor solution, they were dried and sintered at a high temperature to obtain Al₂O₃ hollow fibers. The fibers replicated the hollow structure and the excellent continuity of the reed fibers.

Abstract: This paper analyzes how major impurities found in raw materials affect the chemistry of primary aluminum. Alumina and prebaked anodes tend towards lower quality due to the depletion of natural sources of high-quality bauxites and using low-quality carbon to make prebaked anodes (PA). The authors analyzed the chemistry of raw materials supplied for electrolysis. The paper shows the investigated upward trends in the presence of Fe and Si impurities in alumina and prebaked anodes, which jeopardizes the aluminum production process. The increased presence of such materials worsens the chemical composition of the resulting liquid aluminum. If the finished product is to be of high quality, alumina and PA mast contain, respectively (wt.%): 0.010 and 0.024 Fe, 0.013 and 0.022 Si. The proposed idea is to categorize the alumina in storage. Alumina from different manufacturers must then be batched in such a way as to have consistent, ‘averaged’ chemistry before going to electrolysis cells.

Abstract: This article examines the influence of fly ash on corrosion resistance of refractory forsterite-spinel ceramics by molten iron as a corrosive medium. Fly ash in comparison with alumina were used as raw materials and sources of aluminium oxide for synthesis of forsterite-spinel refractory ceramics. Raw materials were milled, mixed in different ratios into two sets of mixtures and sintered at 1550°C for 2 hours. Samples were characterized by X-ray diffraction analysis and thermal dilatometric analysis. Crucibles were then made from the fired ceramic mixtures and fired together with iron at its melting point of 1535°C for 5 hours. The corrosion resistance was evaluated by scanning electron microscopy on the transition zones between iron and ceramics. Mixtures with increased amount of spinel had higher corrosion resistance and mixtures with fly ash were comparable to mixtures with alumina in terms of corrosion resistance and refractory properties.