Types Of Alumina Research Articles

Experimental Investigation on Morphological Characteristics and Propulsion Performance of Typical Metals Ablated with Multipulse Nanosecond Laser

For laser ablation micropropulsion technology with metal as the target to increase the total impulse, the effective utilization and supply of a working medium is a crucial aspect. In this research, the ablation characteristics and propulsion performance of the typical metal targets, copper and aluminum, ablated via nanosecond laser ablation are analyzed. Due to the low melting point of aluminum, the protrusion characteristics in the remelted area are more prominent. Its surface morphology has characteristics for height extremum and roughness that are higher than those of copper. Affected by the anisotropy of the rough surface, the absorbed energy decreases with increasing roughness. The impulse coupling coefficient of the metal decreases and stabilizes at about 6 μN·W−1. The specific pulse of aluminum obtains a minimum value of 603.6 s at 6000 pulses and improves with increasing pulses. The propulsion parameters of copper alters slightly under various working conditions, with a maximum specific impulse of 685 s.

Thermal response of a curtain wall framing system under fire conditions

Curtain walls are the most common façade system for modern office buildings. These facade systems play an important role in containing the fire to the floor of origin, and in the case of failure, the consequences can be severe. The heat from a fire could cause key elements to fail and sections of the facade to detach and fall from the building, facilitating flame spread to upper floors. However, no tools currently exist that can reliably predict the failure of such systems. This study computationally investigates the thermal response of two curtain wall framing systems to fire exposure – the stick system and the unitized system. The model predictions were validated against experimental data and the role of the screw connector is explored. A typical curtain wall aluminium frame system is modelled. The simulation results indicate that when heated from a compartment fire, thermal degradation of the aluminium frame is very rapid, occurring within the first 15 min of fire exposure for ISO-834 standard fire. When heated from the outside, considering the Eurocode external fire, thermal degradation of the pressure plate occurred within 10 min. With the addition of thermal protection or when using steel instead of aluminium profiles, thermal degradation was not predicted within the first 40 min of heating. The findings advance our understanding of curtain wall frame fire behaviour and can help develop more effective fire strategies and more resilient systems.

Zero sintering-induced shrinkage of porous oxide ceramics

Porous oxide ceramics are widely used in extreme working conditions owing to their excellent resistance to high temperatures and corrosion. However, sintering is an inevitable process applied to ceramics, from the green body to the final product. The highly complex structures exacerbate the shrinkage-induced irregular deformation and crack formation in the sintering process. A pioneering approach is developed in this study to achieve zero shrinkage for porous alumina ceramics during multistep sintering, using a combination of active fillers - ZrAl3 and Al75Si25. The response surface method is used to optimize the material compositions and sintering process, to achieve shrinkages of less than 0.05% for the entire process. The sintering expansion mechanism is investigated by analyzing the pyrolysis and microstructures of samples at different temperatures. The combination of ZrAl3 and Al75Si25 can attain the continuous expansion of the matrix in a wide temperature range of 600–1400 °C. Furthermore, typical alumina components are fabricated and used to verify the effectiveness of the proposed approach. Owing to shrinkage suppression, the profile deviation of the samples is less than 0.1 mm, and the proportion of microcracks is reduced by 97.8%. The suggested approach shows potential applications in near-net, low-defect fabrication of complex fine ceramic components.

Investigation on Losses with Various Emerging Core and Winding Materials in a High Frequency Planar Transformer

In this work, various emerging core and winding materials suitable for a high frequency planar transformer (PT) has been analyzed and compared. Core and winding materials used in a transformer has a significant effect mostly in the core and winding losses of the transformer. Emerging core materials like amorphous and nanocrystalline cores were compared against the conventional ferrite core. The results obtained showed that core losses were reduced by around 48.14% on using amorphous or nanocrystalline cores instead of the conventional ferrite cores. Typical copper and aluminum windings were also compared with emerging materials like carbon nanotube (CNT), Cu/CNT and Al/CNT. Winding losses was found to be the lowest on using CNT windings instead of metal windings like Cu or Al, or metals composite windings like Cu/CNT and Al/CNT. A winding loss reduction of about 56.2% was seen with CNT windings. Thus, it was concluded that the best possible core and winding combination was amorphous or nanocrystalline cores with CNT windings, as they give the lowest possible core and winding losses for the PT. Finite Element Analysis was carried out on a 2-kW PT operating at 100 kHz frequency, with the software Altair FLUX for the analysis.

Non-process elements in the recovery cycle of six Finnish kraft pulp mills

In this work, the aim was to study the distribution and accumulation of the non-process elements (NPEs) in the recovery cycle of Finnish pulp mills and look at whether the geographical location (North vs. South) correlates with the current Finnish NPE levels. In addition, a comparison to older similar Finnish measurements was made with an attempt to analyze the reasons behind differences in the most typical non-process elements, aluminum (Al), silicon (Si), calcium (Ca), phosphorus (P), magnesium (Mg), manganese (Mn), chlorine (Cl), and potassium (K), taking into account the main elements in the white liquor, sodium (Na) and sulfur (S). The extensive laboratory results gained in this study are from seven sampling points at six pulp mills and present analytical data of metal concentrations. The data obtained presents an update to previous NPE studies. The levels found did not statistically differ between North and South Finland. The NPE levels, apart from phosphorus, found in Finnish pulp mills today have not changed considerably compared to the levels in earlier investigations in the 1990s. In the newest data, the phosphorus concentration was consistently higher in the as-fired black liquor, electrostatic precipitator (ESP) ash, lime mud, and green liquor than in the previous results. In addition, the levels of Al, Si, Ca, P, and Mg in recovery boiler ESP ash were consistently higher compared to the older results. As the mills start to close their systems more, a stronger accumulation of NPEs can be expected, increasing the likelihood of more operational problems in the process. Further understanding of where the NPEs accumulate and how they can be most effectively removed will be valuable knowledge in the future.

Improving the chloride binding capacity of alkali activated slag by calcium and aluminum enriched minerals

In this paper, a modified alkali activated slag with improved chloride binding capacity is proposed by introducing calcium and aluminum enriched phases in the binding system. The Ca and Al phases are added in order to promote the formation of AFm type phases in alkali activated system and then transformed into Friedel's salt (Fs) when in contact with chloride. The effects of calcium and alumina type on phase composition, chloride binding behavior, mechanical property of modified alkali activated slag binders are discussed. The results show that the addition of Ca and Al enriched minerals effectively improve the chloride binding capacity of the binder up to 44.4%. The combination of calcium hydroxide and metakaolin shows the highest binding efficiency, followed by calcium nitrite and cement. Metakaolin exhibits better modification on chloride binding capacity than nano alumina. The incorporation of Ca and Al enriched minerals together successfully promotes the formation of AFm type phases (Mc and AFm-NO2) in alkali activated system, while the addition of metakaolin increases the reaction degree and the mean chain length of C-(A)-S-H gels, contributing to the chloride binding capacity. The mechanical properties of alkali activated slag are also improved by adding calcium hydroxide, cement, and alumina enriched minerals, while calcium nitrite exhibits a slight negative effect.

Surface Properties and Microstructures of Al-SBA-15 under Different Temperature Calcinations in Relation to Adsorption Performance

In this study, the calcination temperature was adjusted to influence the properties, including surface alumina types, microstructure, and surface acidity, and then to explore their association with the performance of As(V) adsorption after preparing aluminum-modified SBA-15 (Al-SBA-15x) by the incipient wetness impregnation method. The results showed that calcination promoted the formation of aluminum oxides with different coordination environments on SBA-15 carriers, resulting in different kinds of acid sites and Al–OH groups, which were the adsorption sites for As(V). However, with the increase in the calcination temperature, the total surface acidity on the Al-SBA-15x samples gradually decreased, and the dehydration and dehydroxylation reactions of aluminum oxides occurred, which reduced the Al–OH groups and changed the acid–base environment on the samples. Besides, high-temperature calcination caused a partial collapse of mesoporous channels, which was not conducive to dispersing the active adsorption centers on the surface and further reduced the effective utilization of active adsorption centers. Therefore, the adsorption capacity of an Al-SBA-15x adsorbent for As(V) decreased with the increase of the calcination temperature. Furthermore, kinetic models were used to investigate the relationship between the microstructure and adsorption processes. Finally, recycling tests were performed to demonstrate the reusability of Al-SBA-15x samples.

Impact-abrasive wear resistance of high alumina ceramics and ZTA

In transport of raw materials abrasive wear resistance is a requirement, which can be met with alumina ceramics. At certain locations additional impact load occurs, exacerbating the wear loss. As literature on impact-abrasive wear of ceramics is scarce this topic will be researched in this work.We selected a variety of commercial alumina ceramics (90–96% Al2O3) and according to literature much more impact resistant – and substantially more expensive – Zirconia Toughened Alumina (ZTA, 20–25% Zr) used for wear resistant linings in impact dominated systems. We selected the Impeller-Tumbler test, an impact-abrasion test for wear evaluation of highly loaded ceramic edges. Two load regimes were evaluated for the abrasive, either corundum particles for severe load or steel balls for extreme load conditions. Correlation of wear results with the fracture toughness (K1C) and Vickers hardness of the materials is intended – material parameters used as measure for brittle failure of ceramics and wear resistance, respectively.The various ceramic materials showed very different wear behaviour under the impact-abrasive load. The 90% Al2O3 was least wear resistant under both load conditions. Interestingly large differences between the 92% types were found at extreme load conditions. The increase of alumina content to 95–96% showed remarkable benefits in both wear regimes. Best wear resistance against severe load was achieved by 25% ZTA, while it is comparable to the 95–96% high alumina types at extreme load.

Simulation study on the anti-penetration performance and energy absorption characteristics of honeycomb aluminum sandwich structure

This work studied the anti-penetration performance and energy absorption characteristics of the honeycomb aluminum core structure. Tests of penetrating depth were conducted. The response and deformation resistance of the aluminum sandwich structure with a regular hexagonal honeycomb were studied through numerical simulation. The effect of the face/back plate thickness ratio and the shape of the core layer unit on the performance of the aluminum sandwich structure with a regular hexagonal honeycomb were compared and analyzed with a theoretical model of equivalent target calculation. Based on the results, the aluminum sandwich structure with a regular hexagonal honeycomb has the strongest anti-penetration capability when the thickness ratio of the face/back plate is set to 2.5:1. In terms of the energy consumption, the Arrow and concave hexagonal honeycomb aluminum sandwich structures are 14.7% and 25.9%, respectively, than the aluminum sandwich structure with a regular hexagonal honeycomb. The typical hierarchical honeycomb aluminum sandwich structure has better energy absorption characteristics than the aluminum sandwich structure with a regular hexagonal honeycomb. Therefore, the anti-penetration performance of the honeycomb aluminum sandwich structure can be improved by adjusting the thickness ratio of the face/back plate and changing the shape of the core layer. The research results are of great significance in guiding the design of the honeycomb aluminum sandwich structure.

Life cycle assessment of aluminum-silicon alloy production from secondary aluminum in China

As the world's largest aluminum producer and consumer, less than 25% of China's aluminum production was obtained through the secondary aluminum production, which had far less energy consumption and greenhouse gas (GHG) emissions than primary aluminum production. It was as an effective pathway for China's aluminum industry to achieve its carbon neutrality goals by using the recycled aluminum. Therefore, this study adopted the method of life cycle assessment (LCA) to investigate the environmental impact of aluminum-silicon alloy production from recycled aluminum, based on the actual production data of the typical secondary aluminum enterprise in China. The production of 1t aluminum-silicon alloy from secondary aluminum was chosen as the functional unit for this study, which addressed the environmental aspects and potential environmental impacts throughout the systemic processes contained in the production of aluminum-silicon alloy. The LCA results showed that the remelting stage generated the highest environmental load, especially in terms of freshwater ecotoxicity and marine ecotoxicity, with normalized characters of 96.23 and 64.36 respectively. Silicon metal and natural gas were identified through sensitivity analysis as key substances for reducing the environmental burden. Then, the potential pathways to reduce the environmental burden were also discussed, such as selecting different processes for producing silicon metal and optimizing the process parameters of the remelting stage. Meanwhile, the analysis of GHG emissions showed that the carbon footprints can be significantly decreased by transferring the energy structure and deploying technologies of carbon capture, utilization and storage.

The influence of alumina type on the immobilization of Ascorbate oxidase and ascorbic acid detection

Two alumina types (trihydrate (T) and anhydrous (G)) were used for the immobilization of ascorbate oxidase (AO) by the adsorption procedure. The samples were characterized by FTIR analysis and EPR spectroscopy to confirm the presence of enzyme in the composite and the activity of immobilized enzyme. The samples of alumina with and without AO were used as modifer of carbon paste electrode and tested by Fe(CN6)3-/4-redox probe using cyclic voltammetry at different scan rates. The response of investigated electrodes toward ascorbic acid was tested in the Britton-Robinson buffer at pH range of 2 to 5. Direct detection of ascorbic acid was tested at G and G+AO electrodes and the calibration curves were constructed by square wave voltammetry under the optimized conditions. The immobilization of AO at anhydrous alumina increased the concentration range and the sensitivity from 0.00617 ?M/?A for G to 0.01693 ?M/?A for G+AO in the concentration range from 10 ?M to 200 ?M.

Study on the Effect of Radiant Insulation Panel in Cavity on the Thermal Performance of Broken-Bridge Aluminum Window Frame

Windows have a great impact on building energy consumption, and the thermal performance of window frames directly affects its energy-saving potential. In this paper, a novel method is proposed to optimize the thermal performance of commercially available broken-bridge aluminum window frames, by incorporating radiant insulation panels (RIPs) into the window frame cavity. A typical aluminum alloy window frame heat transfer model is theoretically analyzed and validated, and the effects of key design parameters on the equivalent thermal conductivity (ETC) of the cavity radiation heat transfer and the heat transfer coefficient (U-factor) of window frames are quantitatively analyzed by a finite element simulation method using the THERM software. Moreover, the RIP, the insulation material filling, and low surface emissivity on the thermal performance of the window frame are compared and analyzed. The results show that the RIP is better placed in the middle, the width and quantity of RIPs are negatively correlated with the U-factor, while the surface emissivity of RIPs is positively correlated with the U-factor. Adding RIPs in the cavity can reduce the U-factor of the window frame by more than 7.43%, slightly lower than 8.97% for the filling type, but significantly higher than 0.81% for the low-emissivity type. Inserting RIPs is a simple and effective way to reduce the U-factor of the window frame and have a great potential of use.

Fluorinated Siloxane Modified Layered Double Hydroxide Sealing Film to Enhance the Corrosion Resistance of Anodic Oxide Film of Fricition Stir Welding Joint of Aluminum Alloys.

Aluminum alloys and their welding structures have been widely used in aviation, aerospace, automobiles, ships, and other industrial fields. The non-uniform nature of welding structures of aluminum alloys causes intractable corrosion problems. Anodizing and subsequent sealing processes are common and effective methods to improve the corrosion resistance of welding structures. However, traditional sealing processes like hot water sealing and potassium dichromate sealing are criticized due to energy consumption or toxicity. In this work, a layered double hydroxide (LDH) sealing process with subsequent fluorinated siloxane modification is proposed to improve the corrosion resistance of the anodic oxide film of friction stir welding joints of typical aluminum alloys. The obtained sealing film with typical lamelliform structures of LDH grows well at the defects of oxidation film and also smoothens the sample surface. The hydrophobicity of the film can separate the corrosive medium from the sample surface and further enhance corrosion resistance. As a result, the corrosion current of the welded sample in 3.5 wt.% NaCl solution plummets about 3~4 orders of magnitude compared to the initial state without anodizing, indicating superior corrosion resistance brought by this method.

The Formation and Disintegration of Rafts from Different Aluminas and Fines

Raft formation is a frequently encountered problem during alumina feeding in the Hall-Héroult-process and will delay alumina from being dissolved into the melt. The mechanisms for the formation and disintegration of rafts are however not thoroughly understood yet. The current study investigates the dissolution behavior and raft structure from three different types of secondary alumina in a lab cell, with a particular attention to effect of fines, and involves both sampling of rafts and video recordings of the feeding. The mass loss rate was calculated to vary between −1.57 and −0.42 g min−1 for regular bulk alumina, and −1.15 and −0.06 g min−1 for fines. Rafts created from bulk alumina were flat with a distinct bulge or crater placed in the center of it, while rafts created from fines had a pellet-shaped structure and traces of undissolved alumina in the middle. The observed structure is due to the initial spreading of powder, confirmed by video recordings.

An Optimization of Particle Size and Additives of Slip Cast Alumina Samples to Reduce Warpage and Porosity

Alumina body densification using slip casting was investigated with low warpage rates. In order to optimize slurry and sintering, 1600°C has been used. As a starting material, three types of alumina were used. Alumina has been used in conjunction with PMAA, and carboxymethyl cellulose in order to prepare the slurry. It was found that warpage rates were reduced when coarser particles were included in the composition. An acid treatment of the slurry was carried out in order to improve densification of the alumina body and to reduce warpage. This study examines the microstructure of a sintered alumina body. In the investigation, it was found that preparing a dense product reduced porosity and warping rate by 1.1% and 4%, respectively.

Numerical simulation and validation of MWCNT-CFRP hybrid composite structure in lightweight satellite design

Aluminum alloy is generally used in electronic housings of satellites in space avionics due to its remarkable mechanical, thermal, electrical, and radio-frequency shielding properties. This paper proposes a design for a lightweight multi-functional electronic housing made from plastic containing multi-wall carbon nanotubes (MWCNT) composite material. The structural design of housings was validated against a set of boundary conditions and requirements of launch and space environments as prescribed by European Cooperation for Space Standardization (ECSS) standards. The proposed concept for lightweight composite housing was designed with special emphasis on reducing machining operations. The composite housing offers a mass saving of ∼25 % over a typical aluminum housing with similar mechanical performance in the three orthogonal directions. The modal frequency is greater than 100 Hz qualifying the design requirement for satellite electronic housings. Under sinusoidal vibration loads, the structure shows no noticeable excitation in acceleration response graph, indicating no resonance in low-range frequencies from 5 to 100 Hz. Maximum stresses obtained from Quasi-static and random vibration loads are within the tensile strength limit in the three orthogonal directions. In addition, maximum deflection observed in electronic printed circuit boards is within the 1 mm design requirement.

Nanomorphological changes of anodic aluminum oxide fabricated by anodizing in various phosphate solutions over a wide pH range

High-purity aluminum plates were anodized in phosphoric acid and six phosphate solutions over a wide pH range from acidic to alkaline. The current density corresponding to the growth rate of the anodic oxide was minimum when anodizing in near-neutral solutions and increased when the pH value increased or decreased. A typical porous anodic aluminum oxide (PAAO) film consisting of an outer porous layer and inner hemispherical barrier layer, which is based on the Keller–Hunter–Robinson (KHR) model, was formed in acidic solutions. At the pH values closer to the neutral region, a uniform barrier oxide film or a PAAO film with a narrow porous layer was produced owing to the low solubility of aluminum oxide. On the other hand, two types of characteristic PAAO films were formed during anodizing in alkaline phosphate solutions: one was a PAAO film consisting of an outer porous layer with feathered pore walls and inner hemispherical barrier layer, and the second was a PAAO film consisting of an outer porous layer with elongated pores and inner flat barrier layer. We showed that novel PAAO films, which are not based on the KHR model, can be prepared by anodizing aluminum in various alkaline phosphate solutions.

A Lithium-Sulfur Battery Using Binder-Free Graphene-Coated Aluminum Current Collector.

Lithium–sulfur battery of practical interest requires thin-layer support to achieve acceptable volumetric energy density. However, the typical aluminum current collector of Li-ion battery cannot be efficiently used in the Li/S system due to the insulating nature of sulfur and a reaction mechanism involving electrodeposition of dissolved polysulfides. We study the electrochemical behavior of a Li/S battery using a carbon-coated Al current collector in which the low thickness, the high electronic conductivity, and, at the same time, the host ability for the reaction products are allowed by a binder-free few-layer graphene (FLG) substrate. The FLG enables a sulfur electrode having a thickness below 100 μm, fast kinetics, low impedance, and an initial capacity of 1000 mAh gS–1 with over 70% retention after 300 cycles. The Li/S cell using FLG shows volumetric and gravimetric energy densities of 300 Wh L–1 and 500 Wh kg–1, respectively, which are values well competing with commercially available Li-ion batteries.

Experimental investigation on microgrooving characteristics of ceramics using electroplated diamond wire tools

For precision machining such as slicing and grooving of hard and brittle materials, wire tools with electroplated diamond abrasives have been widely used. Slicing with electroplated diamond wire tools, in particular, is quickly becoming a common method for machining hard materials. Many studies have been published on the machining properties of electroplated diamond wire tools. However, there are very few reports on the tool wear of wire tools. In particular, the influence of work material on the machining and wear characteristics of electroplated diamond wire tools is still unclear. Fundamental grooving experiments are used to investigate the effect of the workpiece’s material properties on the grooving characteristics and the wear characteristics of the wire tool. Two types of ceramics, alumina (Al2O3) and zirconia (ZrO2), were used as work materials in this study. The grooving experiments revealed that the workpiece material affects the machining characteristics. Alumina, which is brittle, was found to be more machinable than zirconia, which has a high toughness for the same hardness. The wear of the electroplated diamond wire tools, on the other hand, showed no significant difference.

In vitro evaluation of the effects of different particle types in toothpastes on the efficacy against enamel erosion and wear

The effects of the particle fraction in toothpastes in the context of erosion and erosive tooth wear has not been fully elucidated. Thus, aim of this study was to investigate experimental toothpastes, each with one specific particle type. Toothpastes with seven different types of silica or alumina were prepared as slurry either with or without active ingredients (NaF or F/Sn). Human enamel samples were exposed to a cyclic erosion/abrasion model, and were either treated with the respective slurries only or additionally brushed in a brushing machine. Tissue loss was profilometrically monitored. After treatment with slurries without active ingredients or with NaF, tissue loss increased significantly within groups over time (p < 0.001 each). At the end of the trial, there were minor differences between groups (not exceeding 10–20%; p > 0.05 for most comparisons). After treatment with the F/Sn slurries, tissue loss stagnated completely over time, with the exception of one silica type and alumina, but both still reduced tissue loss by 40–50% (compared to control p < 0.001 each). Relative to the type of the active ingredient, the particle type seems to be a secondary factor for the efficacy of toothpastes on erosion and erosive tooth wear in enamel.