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To enhance the bio-based synthesis of acrolein from glycerol, a hybrid approach combining in situ nonthermal plasma (NTP) with thermo-catalytic dehydration was employed. This study investigated the impact of the reaction temperature and NTP discharge field strength on glycerol conversion, acrolein selectivity, byproduct formation, and coke deposition using two catalysts of silicotungstic acid supported on mesoporous alumina and silica. The results revealed that, while the reaction temperature and NTP field strength exhibited complex interactions, the in situ application of NTP markedly improved both glycerol conversion and acrolein selectivity when optimized for specific temperature–NTP field strength combinations. Additionally, the reaction mechanisms of glycerol dehydration with the two catalysts, in the presence and absence of NTP, were systematically analyzed and discussed based on the experimental data. [ABSTRACT FROM AUTHOR]

Understanding the performance of polymer dielectrics at different temperatures is becoming increasingly important due to the rapid development of electric cars, electromagnetic devices, and new energy production solutions. Cyclic olefin copolymers (COCs) are an attractive material due to their low water absorption, good electrical insulation, long-term stability of surface treatments, and resistance to a wide range of acids and solvents. This work focused on the dielectric and electrical properties of cyclic olefin copolymer (COC)/Al2O3 composites over a wide range of temperature and frequency domains, from room temperature to cryogenic temperatures (around 125 K). Permittivity, electrical conductivity, and electrical modulus are given consideration. A composite of up to 50% Al2O3 mixed with COC was prepared via a conventional melt-blending method. The final samples were formed in sheets and processed using injection and extrusion moldings. It was found that formulations with Al2O3 concentrations ranging from 10 to 50% resulted in higher electrical conductivity while maintaining the viscosity of the composite at a level acceptable for polymer-processing machinery. Our data show that COC/alumina composites present substantial potential as materials for high-frequency applications, even at the regime of cryogenic temperatures. [ABSTRACT FROM AUTHOR]

The irregular and deep cracks induced by thermal shock in Al2O3 ceramics were repaired by applying Cu powder layer on their surface and heating at 1200 °C under an atmosphere of air. The Al-Cu-O liquid phase formed at 1200 °C by the reaction of molten Cu, oxygen, and Al2O3 phases penetrate deep into the narrow cracks, and the precipitation phases of Cu2O and CuAlO2 densely fill the crack interior. Our observation and analysis of the filled cracks and the surrounding areas of the repaired cracks, as well as the microstructural analysis results obtained through SEM-EDS and TEM observation, suggested the aforementioned crack repair mechanism. The bending strength of the coated surface after repairing the cracks is 301.8 MPa (ΔT = 300 °C), which is twice as strong as the specimen after thermal shock and 10% higher than the original strength of the base material. [ABSTRACT FROM AUTHOR]

The aim of this study is to provide tailored alumina particles suitable for reinforcing the metal matrix film. The sol–gel method was chosen to prepare particles of submicron size and to control crystal structure by calcination. In this study, copper-based metal matrix composite (MMC) films are developed on brass substrates with different electrodeposition times and alumina concentrations. Scanning electron microscopy (FE-SEM) with energy-dispersive spectroscopy (EDS), TEM, and X-ray diffraction (XRD) were used to characterize the reinforcing phase. The MMC Cu-Al2O3 films were synthesized electrochemically using the co-electrodeposition method. Microstructural and topographical analyses of pure (alumina-free) Cu films and the Cu films with incorporated Al2O3 particles were performed using FE-SEM/EDS and AFM, respectively. Hardness and adhesion resistance were investigated using the Vickers microindentation test and evaluated by applying the Chen–Gao (C-G) mathematical model. The sessile drop method was used for measuring contact angles for water. The microhardness and adhesion of the MMC Cu-Al2O3 films are improved when Al2O3 is added. The concentration of alumina particles in the electrolyte correlates with an increase in absolute film hardness in the way that 1.0 wt.% of alumina in electrolytes results in a 9.96% increase compared to the pure copper film, and the improvement is maximal in the film obtained from electrolytes containing 3.0 wt.% alumina giving the film 2.128 GPa, a 134% hardness value of that of the pure copper film. The surface roughness of the MMC film increased from 2.8 to 6.9 times compared to the Cu film without particles. The decrease in the water contact angle of Cu films with incorporated alumina particles relative to the pure Cu films was from 84.94° to 58.78°. [ABSTRACT FROM AUTHOR]

In this paper, we demonstrate a method of measuring the flexural elastic modulus of ceramics at an intermediate (~millimeter) scale at high temperatures. We used a picosecond laser to precisely cut microbeams from the location of interest in a bulk ceramic. They had a cross-section of approximately 100 μm × 300 μm and a length of ~1 cm. They were then tested in a thermal mechanical analyzer at room temperature, 500 °C, 800 °C, and 1100 °C using the four-point flexural testing method. We compared the elastic moduli of high-purity Al2O3 and AlN measured by our method with the reported values in the literature and found that the difference was less than 5% for both materials. This paper provides a new and accurate method of characterizing the high-temperature elastic modulus of miniature samples extracted from representative/selected areas of bulk materials. [ABSTRACT FROM AUTHOR]

This study investigates the fabrication, microstructural characteristics and plasma resistance of Y–Al–Si–O (YAS) glass-ceramics coated on alumina ceramics. YAS frits were initially prepared using a melt-quenching method, then homogenously milled and coated onto alumina ceramics. The melt-coating process was conducted at 1650 °C for 1 h. The composition and microstructure of the glass frits and coatings were thoroughly characterized using X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. These analyses revealed a dense microstructure with a polycrystalline structure predominantly composed of Y3Al5O12 (YAG) phase and a minor phase of Y2Si2O7. The YAS coatings on alumina revealed a dense layer with strong adhesion to the substrate. Subsequently, the coatings underwent C4F6/Ar/O2 plasma treatment for 1 h. Plasma exposure tests demonstrated that the YAS-coated alumina exhibited significantly better etching resistance compared to uncoated alumina, with minimal surface damage observed on the YAS coating, confirming its protective properties against plasma. The superior plasma resistance of YAS coatings is attributed to the predominance of its YAG phase. This research offers a more stable and cost-efficient solution for protecting ceramics in demanding plasma environments. [ABSTRACT FROM AUTHOR]

Additive Manufacturing (AM) is advancing technologically towards the production of components for high-demand mechanical applications with stringent dimensional accuracy, leveraging metallic and ceramic raw materials. The AM process for ceramic components, known as Ultraviolet Laser Stereolithography (SLA), enables the fabrication of unique parts or small batches without substantial investments in molds and dies, and avoids the problems associated with traditional manufacturing, which involves multiple stages and final machining for precision. This study addresses the need to produce reference elements or targets for metrological applications, including verification, adjustment, or calibration of 3D scanners and mid- to high-range optical sensors. Precision spheres are a primary geometry in this context due to their straightforward mathematical definition, facilitating rapid and accurate error detection in equipment. Our objective is to exploit this novel SLA process along with the advantageous optical properties of technical ceramics (such as being white, matte, lightweight, and corrosion-resistant) to materialize these reference objects. Specifically, this work involves the fabrication of alumina hemispheres using SLA. The manufacturing process incorporates four design variables (wall thickness, support shape, fill type, and orientation) and one manufacturing variable (the arrangement of spheres on the printing tray). To evaluate the impact of the design variables, dimensional and geometric parameters (GD&T), including diameters, form errors, and their distribution on the surface of the sphere, have been characterized. These measurements are conducted with high accuracy using a Coordinate Measuring Machine (CMM). The study also examines the influence of these variables in the dimensional and geometric accuracy of the spheres. Correlations between various parameters were identified, specifically highlighting critical factors affecting process precision, such as the position of the piece on the print tray and the wall thickness value. The smallest diameter errors were recorded at the outermost positions of the tray (rear and front), while the smallest shape errors were found at the central position, in both cases with errors in the range of tens of micrometers. In any case, the smallest deformations were observed with the highest wall thickness (2 mm). [ABSTRACT FROM AUTHOR]

Porous α-Al2O3 ceramics are a highly sought-after material with a multitude of applications; for example, they are used as filters, substrates, biomedicine materials, etc. Despite the availability of raw materials, a challenge associated with this technology is the high energy budget caused by sintering above 1500 °C. For the cold sintering processing (CSP) of ceramics, lowering the α-Al2O3 sintering temperature is one of the most urgent challenges in the background of its rapid development. This paper is the first to demonstrate a solution to this problem using the CSP of α-alumina ceramics in the presence of pure water as a transient liquid. The manufactured materials were examined using XRD analysis; the evolution of their microstructures during CSP was revealed by SEM; and the porosity was evaluated using the Archimedes method. Ceramics with an open porosity up to 36% were produced at 380–450 °C and 220 MPa in 30 min. An increase in the pressure was found to impede α-Al2O3 formation from γ-AlOOH. The development of the microstructure was discussed within the framework of the dissolution–precipitation model and homogenous nucleation. The results of the SEM study pointed to the coalescence of γ-AlOOH grains during CSP. [ABSTRACT FROM AUTHOR]

The bulk and surface properties of materials based on nickel and aluminum oxides and hydroxides, as such or after reduction processes, are reviewed and discussed critically. The actual and potential industrial applications of these materials, both in reducing conditions and in oxidizing conditions, are summarized. Mechanisms for reactant molecule activation are also discussed. [ABSTRACT FROM AUTHOR]

The hydroprocessing of gasoline on modified alumina catalysts makes it possible to obtain high-octane products. The implementation and development of the process have largely become possible due to the development of modified alumina catalysts that do not contain noble metals and exhibit special catalytic properties. This article discusses topical issues of petrochemistry, namely the creation of catalysts with improved characteristics for the production of high-octane gasoline with low sulfur content. New catalytic systems based on alumina and other carriers modified with transition metals, lanthanum and phosphorus were synthesized. By physico-chemical methods of analysis TPD of ammonia, TEM and XRD, we studied the acid–base and structural characteristics of the developed catalysts. The activity of the developed catalysts in the studied process of hydrotreating gasoline fractions depends on the structure and condition of the active centers. The process of hydrotreating straight-run gasoline in the presence of synthesized catalysts was carried out on a laboratory flow unit. It was shown that, during the hydrotreating of straight-run gasoline on the NiO-MoO3-La-P-HZSM-HY-Al2O3 catalyst, the octane number in the final product increased to 88.6, and the sulfur content decreased from 0.0088 to 0.001%. It was found that the minimum sulfur content in the gasoline hydrotreating product of 0.0005% was achieved on the catalyst CoO-WO3-La-P-HZSM-HY-Al2O3, which is significantly lower than for other studied catalytic systems. The obtained results of the sulfur content in the hydrotreating products fully comply with the Euro-5 standard. Thus, the efficiency of hydrotreating the gasoline fractions studied in this work was mainly determined by the nature of the carriers and modifiers used for the synthesis of catalysts and the technological parameters of the process. The synthesized catalysts showed high activity and selectivity, resulting in high-octane gasoline with a low sulfur content that meets international quality standards. [ABSTRACT FROM AUTHOR]

The use of alumina-containing nepheline raw materials as an alternative source of alumina is relevant in the context of the limited bauxite reserves in Kazakhstan. Nepheline processing can result in products such as alumina, sodium and potassium salts, silicate products and rare metals. In terms of economic value, alumina is the most important. This article considers an advanced technology for nepheline processing for the extraction of alumina that is first purified from potassium. The application of calcium sulphate and calcium oxide as additives to the nepheline raw materials is studied. The optimal conditions for two-stage leaching with calcium additives in the form of calcium sulphate and calcium hydroxide are determined. [ABSTRACT FROM AUTHOR]

This article presents the results of studies on the distribution of rare metals among the products of the alkali sulfate processing of nepheline syenites. In response to the limited reserves of Bayer bauxite in the alumina industrial production region of Kazakhstan, the feasibility of using alternative alumina-containing nonbauxite raw materials was investigated. The most promising nonbauxite raw materials in Kazakhstan are nepheline and kaolinite clays. At present, there is no effective technology for processing nepheline ores. This article describes a proposed complex technology involving nepheline processing with the associated extraction of gallium and vanadium. The technology includes the activation of raw materials, followed by two-stage leaching, where potassium is extracted in the first stage. The sludge and solution obtained from the second stage of the leaching process are utilized for calcium silicate production and two-stage carbonization, respectively. In the first stage, aluminum hydroxide is extracted, and, in the second stage, a concentration of rare metals, such as gallium and vanadium, is obtained. Vanadium is extracted from the solution via crystallization, and gallium is extracted via electrodeposition. Overall, 38.48% of the Ga2O3 and 56.12% of the V2O5 are recovered from raw nepheline syenite. A technological scheme of the developed technology is presented in this article. [ABSTRACT FROM AUTHOR]

Symmetrical as well as asymmetrical statistical models play a prominent role in describing and predicting the real-world phenomena of nature. Among other fields, these models are very useful for modeling data in the sector of civil engineering. Due to the applicability of the statistical models in civil engineering and other related sectors, this paper offers a statistical methodology to improve the distributional flexibility of traditional models. The suggested method/approach is called the extended-X family of distributions. The proposed method has the ability to generate symmetrical and asymmetrical probability distributions. Based on the extended-X family approach, an updated version of the Weibull model, namely, the extended Weibull model, is studied. The proposed model is very flexible and has the ability to capture the symmetrical and asymmetrical shapes of its density function. For the extended-X method, the estimation of parameters, a simulation study, and some mathematical properties are derived. Finally, the practical illustration/usefulness of the suggested model is shown by analyzing two data sets taken from the field of engineering. Both data sets represent the fracture toughness of alumina (Al2O3). [ABSTRACT FROM AUTHOR]

This article presents the findings of a study on oxide reduction utilizing a novel reducing plasma torch, employing greenhouse gases such as CO2 and CH4 as plasma gases. The primary aim of this investigation is to establish the viability of this approach. The innovative plasma torch was employed to reduce various oxides, including aluminum oxide, iron oxide, and titanium oxide, as well as a mixed oxide composition, employing a CO2/CH4 molar ratio of 1:1 within a spouted bed reactor. Following plasma treatment, X-ray diffraction (XRD) analysis was conducted to examine the metallic phases, notably titanium, iron, and aluminum. SEM–EDS observations were carried out to assess microstructural changes and identify elemental compositions pre- and post-plasma treatment. The results demonstrate that within the conical section of the reactor, titanium oxide experiences partial reduction, resulting in limited titanium production, while aluminum oxide and iron oxides (magnetite and hematite) undergo reduction to yield aluminum and iron, respectively. Thermodynamic calculations, performed using Factsage software version 8.3, were utilized to predict stable-phase formations following plasma treatment for each material. [ABSTRACT FROM AUTHOR]

The main groups of catalytic materials used in the conversion of methanol to dimethyl ether (the MTD process) were presented with respect to their advantages, disadvantages, and the methods of their modifications, resulting in catalysts with improved activity, selectivity, and stability. In particular, the effects of strength, surface concentration, and the type of acid sites, the porous structure and morphology of the catalytic materials, the role of catalyst activators, and others, were considered. The prosed mechanisms of the MTD process over various types of catalysts are presented. Moreover, the advantages of membrane reactors for the MTD process are presented and analysed. The perspectives in the development of effective catalysts for the dehydration of methanol to dimethyl ether are presented and discussed. [ABSTRACT FROM AUTHOR]

This study explores the impact of non-stoichiometric aluminum oxide (AlxOy) coatings applied via thermal atomic layer deposition (ALD) on carbon fiber fabrics (CFFs), emphasizing volume per cycle, FESEM analyses, color transitions, and thermal stability enhancements. Using trimethylaluminum and water at 100 °C, AlxOy was deposited across a range of 1000 to 5000 ALD cycles, with film thicknesses extending up to 500 nm. This notable increase in the volume of material deposited per cycle was observed for the 3D CFFs, highlighting ALD's capability to coat complex structures effectively. FESEM analyses revealed the morphological evolution of CFF surfaces post-coating, showing a transition from individual grains to a dense, continuous layer as ALD cycles increased. This morphological transformation led to significant color shifts from green to red to blue, attributed to structural coloration effects arising from variations in film thickness and surface morphology. Thermogravimetric analyses (TGA and dTG) indicated that the AlxOy coatings enhanced the thermal stability of CFFs, with a postponement in degradation onset observed in samples subjected to more ALD cycles. In essence, this research highlights the nuanced relationship between ALD processing parameters and their collective influence on both the aesthetic and functional properties of CFFs. This study illustrates ALD's potential in customizing CFFs for applications requiring specific color and thermal resilience, balancing the discussion between the surface morphological changes and their implications for color and thermal behavior. [ABSTRACT FROM AUTHOR]

The adsorption of ethanol and ammonia changes the basic properties of alumina, and new basic sites are created. Ethanol reacts with surface Al-OH groups, forming ethoxy group Al-O-C2H5. The substitution of Al-OH by Al-O-C2H5 increases the negative charge of neighbouring oxygen atoms, and they became sufficiently basic to react with adsorbed CO2 forming carbonate species CO32−. These carbonates were found to be monodentate and bidentate species. Preadsorption of ammonia also increases the basicity of alumina, but the mechanism is different than for ethanol adsorption. Adsorbed ammonia interacts with surface Lewis acid sites being three-coordinated aluminium atoms. This interaction is accompanied by an electron transfer from ammonia molecules to surface sites, and increases the basicity of the neighbouring oxygens, which can react with the absorbed CO2. The carbonate species formed are polydentate ones. [ABSTRACT FROM AUTHOR]

Plasma actuators have demonstrated great potential for active flow control applications, including boundary layer control, flow separation delay, turbulence control, and aircraft noise reduction. In particular, the material used as a dielectric barrier is crucial for the proper operation of the device. Currently, the variety of dielectrics reported in the literature is still quite restricted to polymers including Kapton, Teflon, poly(methyl methacrylate) (PMMA), Cirlex, polyisobutylene (PIB) rubber, or polystyrene. Nevertheless, several studies have highlighted the fragilities of polymeric dielectric layers when actuators operate at significantly high-voltage and -frequency levels or for long periods. In the current study, we propose the use of alumina-based ceramic composites as alternative materials for plasma actuator dielectric layers. The alumina composite samples were fabricated and characterized in terms of microstructure, electrical parameters, and plasma-induced flow velocity and compared with a conventional Kapton-based actuator. It was concluded that alumina-based dielectrics are suitable materials for plasma actuator applications, being able to generate plasma-induced flow velocities of approximately 4.5 m/s. In addition, it was verified that alumina-based ceramic actuators can provide similar fluid mechanical efficiencies to Kapton actuators. Furthermore, the ceramic dielectrics present additional characteristics, such as high-temperature resistance, which are not encompassed by conventional Kapton actuators, which makes them suitable for high-temperature applications such as turbine blade film cooling enhancement and plasma-assisted combustion. The high porosity of the ceramic results in lower plasma-induced flow velocity and lower fluid mechanical efficiency, but by minimizing the porosity, the fluid mechanical efficiency is increased. [ABSTRACT FROM AUTHOR]

Binder jetting is a promising 3D printing technology that employs a liquid binder to selectively attach the particles of a pulverised material to form three-dimensional objects. It is also a popular technique for fabricating ceramics, as it permits the creation of intricate geometries and customised shapes that would be hard or impossible to achieve using conventional ceramic manufacturing techniques. This study focuses on the capabilities of some of the most essential ceramic materials, such as alumina, SiC, and calcium phosphate, to construct complicated geometries with a high level of accuracy and precision when using a process called binder jetting. These ceramic components find widespread usage in a broad variety of applications, including those relating to aircraft, biomedical, and industry. [ABSTRACT FROM AUTHOR]

Silicon carbide, a third-generation semiconductor material, is widely used in the creation of high-power devices. In this article, we systematically study the influence of three crucial parameters on the polishing rate of a silicon carbide surface using orthogonal experiments. By optimizing the parameters of chemical mechanical polishing (CMP) through experiments, we determined that the material removal rate (MRR) is 1.2 μm/h and the surface roughness (Ra) is 0.093 nm. Analysis of the relevant polishing mechanism revealed that manganese dioxide formed during the polishing process. Finally, due to the electrostatic effect of the two, M n O 2 adsorbed on the A l 2 O 3 , which explains the polishing mechanism of A l 2 O 3 in the slurry. [ABSTRACT FROM AUTHOR]

The processing and characterizing of bonding Ti6Al4V to Al2O3 brazed joints using interlayer thin films was investigated. The brazing was conducted in a tubular furnace with an argon flux at 980 °C for 30 min. The brazing fillers consisted of different combinations of thin Ag/Cu and Ti films with variable thicknesses. The joint interface analysis involved using digital microscopy (DM) and optical microscopy (OM). Microstructural characterization and chemical composition were performed via scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). Mechanical properties were assessed through microhardness and shear strength tests. Brazing successfully produced interfaces with a combination of titanium films and Ag/Cu as brazing filler. The results revealed that the interface mainly comprises Ti2Cu, TiCu2Al, α-Ti, and Ti2(Cu,Ag). Some segregation of (Ag) was observed at the interfaces, but a decrease in its amount was observed when compared to joints produced using Ag/Cu fillers. The thickness of the titanium film in the brazing filler strongly influenced the integrity of the joints. The amount of (Ag) at the interface diminished as the Ti film's thickness decreased, leading to an improvement in the mechanical properties of the joints. Using a combination of Ag/Cu and Ti thin films revealed a potential approach to reduce the segregation of soft phases at interfaces, promoting a significant improvement in joining metal to ceramic materials. [ABSTRACT FROM AUTHOR]

The possibility of using microsilica in the production of mullite–silica refractories was assessed. The chemical and mineralogical compositions of the raw materials, refractory Arkalyk clay and microsilica, were studied. It has been found that primary mullite and quartz formation occurs due to dehydration of kaolinite with the formation of intermediate metakaolinite. The introduction of alumina and microsilica into the charge composition promotes the formation of secondary mullite due to the interaction of aluminum oxide and highly dispersed chemically active microsilica. Free silica in compositions undergoes polymorphic transformations with the formation of cristobalite and tridymite. Mullite–silica refractories with an open porosity of 21%, a compressive strength of 42 MPa, and a thermal deformation temperature under the load of 0.2 MPa–1350 °C were obtained. [ABSTRACT FROM AUTHOR]

Alumina (Al2O3) ceramics are interesting for low-weight and mid-high temperature applications. The addition of indium (In) and graphene nanoplatelets (GNPs) can be used to reduce the density and modify the functional properties and mechanical performance of the ceramic matrix. GNP and In-reinforced Al2O3 matrix composites were prepared by the spark plasma sintering (SPS) technique. Monolithic Al2O3 and Al2O3 matrix composites with either 5 or 10 wt.% of In and 2 wt.% of GNPs (Al2O3-5In-2GNPs and Al2O3-10In-2GNPs) were compacted into disc-shaped samples. The microstructure was studied and characterized with light-optical microscopy (LOM) and scanning electron microscopy (SEM). Hardness was determined using the Vickers technique and tribological properties were studied by the ball-on-disk method. The coefficient of friction (COF) and specific wear rates were evaluated from tribological tests. Worn surfaces were studied by SEM and confocal microscopy. Interdiffusion transition regions were formed among individual microstructural constituents (Al2O3, In, GNPs) under high sintering temperatures, which were responsible for the balanced hardness and low porosity of the produced composites. The addition of In and graphene nanoplatelets resulted in smaller COF and wear rates indicating good improvement in the tribological behavior. The prepared Al2O3-5In-2GNP and Al2O3-10In-2GNP composites represent promising nanocomposites for self-lubricating applications. [ABSTRACT FROM AUTHOR]

Dental zirconias have been broadly utilized in dentistry due to their high mechanical properties and biocompatibility. Although initially introduced in dentistry as an infrastructure material, the high rate of technical complications related to veneered porcelain has led to significant efforts to improve the optical properties of dental zirconias, allowing for its monolithic indication. Modifications in the composition, processing methods/parameters, and the increase in the yttrium content and cubic phase have been presented as viable options to improve zirconias' translucency. However, concerns regarding the hydrothermal stability of partially stabilized zirconia and the trade-off observed between optical and mechanical properties resulting from the increased cubic content remain issues of concern. While the significant developments in polycrystalline ceramics have led to a wide diversity of zirconia materials with different compositions, properties, and clinical indications, the implementation of strong, esthetic, and sufficiently stable materials for long-span fixed dental prostheses has not been completely achieved. Alternatives, including advanced polycrystalline composites, functionally graded structures, and nanosized zirconia, have been proposed as promising pathways to obtain high-strength, hydrothermally stable biomaterials. Considering the evolution of zirconia ceramics in dentistry, this manuscript aims to present a critical perspective as well as an update to previous classifications of dental restorative ceramics, focusing on polycrystalline ceramics, their properties, indications, and performance. [ABSTRACT FROM AUTHOR]

In the presented study, a novel approach for thermal atomic layer deposition (ALD) of Al2O3 thin films using plasma-activated water (PAW) as a co-reactant, replacing traditionally employed deionized (DI) water, is introduced. Utilizing ex situ PAW achieves up to a 16.4% increase in the growth per cycle (GPC) of Al2O3 films, consistent with results from plasma-enhanced atomic layer deposition (PEALD). Time-resolved mass spectrometry (TRMS) revealed disparities in CH4 partial pressures between TMA reactions with DI water and PAW, with PAW demonstrating enhanced reactivity. Reactive oxygen species (ROS), namely H2O2 and O3, are posited to activate Si(100) substrate sites, thereby improving GPC and film quality. Specifically, Al2O3 films grown with PAW pH = 3.1 displayed optimal stoichiometry, reduced carbon content, and an expanded bandgap. This study thus establishes "PAW-ALD" as a descriptor for this ALD variation and highlights the significance of comprehensive assessments of PAW in ALD processes. [ABSTRACT FROM AUTHOR]

This study uses waste materials, specifically diatomaceous earth (DE) that is rich in aluminum and silica, as a sustainable source for aluminosilicate precursors in geopolymers to replace conventional cement in mortar applications. While the use of DE shows promising results, it lacks sufficient alumina content, thereby demanding the introduction of alumina powder. However, the effectiveness of this addition is limited, as unreacted alumina particles were observed in the X-ray diffraction and SEM analyses. This could potentially impact various geopolymer properties due to the incomplete achievement of the desired silicon/aluminum (Si/Al) ratio. Achieving the appropriate Si/Al balance remains crucial for geopolymers to realize their potential as environmentally friendly alternatives to Portland cement. [ABSTRACT FROM AUTHOR]

The influence of process parameters in the three-stage purification of aluminate solution from the Bayer process and aluminum hydroxide was considered in this paper. One of the ways of purification is treating the aluminate solution in order to reduce the concentrations in the starting raw material (solution) and then treating the aluminum hydroxide at a certain temperature and time in order to obtain an alumina precursor of adequate quality. The purification process itself is divided into three phases. The first phase involves the treatment of sodium aluminate with lime in order to primarily remove Ca2+ and (SiO3)2− impurities. Phase II aims to remove impurities of Zn2+, Fe2+, and Cu2+ by treatment with controlled precipitation using specially prepared crystallization centers. In Phase III, Na+ is removed by the process of hydrothermal washing of Al2O3 ∙ 3H2O. In this work, parameters such as temperature (T), reaction time (t), and concentration of lime (c) were studied in order to remove the mentioned impurities and obtain the purest possible product that would be an adequate precursor for special types of alumina. [ABSTRACT FROM AUTHOR]

Ladder-like poly(methacryloxypropyl)-silsesquioxanes (LPMASQ) are photocurable Si-based gels characterized by a double-stranded structure that ensures superior thermal stability and mechanical properties than common organic polymers. In this work, these attractive features were exploited to produce, in combination with alumina nanoparticles (NPs), both unmodified and functionalized with methacryloxypropyl-trimethoxysilane (MPTMS), LPMASQ/Al2O3 composites displaying remarkable thermal conductivity. Additionally, we combined LPMASQ with polybutadiene (PB) to produce hybrid nanocomposites with the addition of functionalized Al2O3 NPs. The materials underwent thermal stability, structural, and morphological evaluations via thermogravimetric analysis (TGA), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDXS), Fourier transform infrared spectroscopy (FTIR), and solid-state nuclear magnetic resonance (NMR). Both blending PB with LPMASQ and surface functionalization of nanoparticles proved to be effective strategies for incorporating a higher ceramic filler amount in the matrices, resulting in significant increases in thermal conductivity. Specifically, a 113.6% increase in comparison to the bare matrix was achieved at relatively low filler content (11.2 vol%) in the presence of 40 wt% LPMASQ. Results highlight the potential of ladder-like silsesquioxanes in the field of thermally conductive polymers and their applications in heat dissipation for flexible electronic devices. [ABSTRACT FROM AUTHOR]

Heating elements in the automotive industry are currently produced by several thermal spray processes and materials. However, simpler spraying technologies such as arc spraying are investigated regarding technological suitability as a cost-effective alternative to plasma spraying in the production process of these components. Thus, several mixtures and combinations of alternative pressurizing gases and further modifications of an arc spray process were examined in this study. Consequently, coatings based on NiCr were produced, since this alloy is typical for heating elements. Coating properties were investigated by SEM, EDS, and resistivity measurements. The results demonstrate reduced oxygen content and improved morphology compared with the industrially used plasma-sprayed coatings. Additionally, the improved microstructure affects the surface quality and specific resistivity of the coatings positively. This allowed for laser texturing the arc-sprayed coatings successfully. It must be considered a drawback, though, that cracks partially appeared in the underlying coatings. In contrast, the temperature coefficients of resistance and the resistivities of the heating elements were superior to the conventional coatings, which can lay the foundation for a future industrial application. To further investigate this and to minimize the influence of potential sample preparation issues on the analysis results, different methods of cross-sectioning, i.e., in detail hot mounting, cold mounting, and ion beam polishing, were evaluated. [ABSTRACT FROM AUTHOR]

The objective of this study was to assess the effect of airborne-particle abrasion with alumina particles of various sizes (50 μm, 110 μm, 250 μm) on the surface properties of 3Y-TZP (3 mol% yttria-stabilized tetragonal zirconia polycrystals). The analysis comprised the Vickers hardness test (HV1kp), a surface roughness evaluation (Ra, Rq, Rz, Rsk, Rsm, Rt, Vo, profile displays), and SEM–EDS microanalysis (scanning electron microscopy–energy-dispersive X-ray spectroscopy). Any statistical relationships were assessed using the Kruskal–Wallis one-way analysis-of-variance-by-rank test (p = 0.05). While airborne-particle abrasion with 50 µm alumina significantly increases the Vickers hardness of 3Y-TZP (1678.8 HV1kp), 110 μm and 250 μm alumina particles do not appear to have any such effect. The surface roughness of 3Y-TZP increases with the size of the alumina particles (Ra, Rq, Rz, Rt, Vo: vertical plane and retention volume assessment); a higher Rsm (horizontal plane assessment) was noted for specimens air-abraded with 250 µm alumina particles; air abrasion with 50 μm alumina particles yielded a symmetrical surface roughness profile (Rsk). The major topographic pattern of the surface of 3Y-TZP is altered by alumina airborne-particle abrasion, with larger alumina particles causing more severe changes. Aluminum traces on the 3Y-TZP surface are observed. The shape of the alumina particles is irregular, with rough edges; the size of the alumina particles plays a significant role in the air abrasion of zirconia-based dental ceramics, affecting their morphology and properties. [ABSTRACT FROM AUTHOR]

Modern dental implantology is based on a set of more or less related first-order parameters, such as the implant surface and the intrinsic composition of the material. For decades, implant manufacturers have focused on the research and development of the ideal material combined with an optimal surface finish to ensure the success and durability of their product. However, brands do not always communicate transparently about the nature of the products they market. Thus, this study aims to compare the surface finishes and intrinsic composition of three zirconia implants from three major brands. To do so, cross-sections of the apical part of the implants to be analyzed were made with a micro-cutting machine. Samples of each implant of a 4 to 6 mm thickness were obtained. Each was analyzed by a tactile profilometer and scanning electron microscope (SEM). Compositional measurements were performed by X-ray energy-dispersive spectroscopy (EDS). The findings revealed a significant use of aluminum as a chemical substitute by manufacturers. In addition, some manufacturers do not mention the presence of this element in their implants. However, by addressing these issues and striving to improve transparency and safety standards, manufacturers have the opportunity to provide even more reliable products to patients. [ABSTRACT FROM AUTHOR]

The industrial use of nanoparticles is rapidly increasing in agricultural products, and it causes numerous effects on plant growth and seed germination. There are limited studies about the uptake, accumulation, and effect of nanoparticles on plant growth. Moreover, there are no studies that have been able to measure the biological activity of seeds' interiors under nanoparticle treatment prior to germination. Hence, in this study, the possible size-defendant effect of alumina nanoparticles on lentil (Lens culinaris) seed germination was monitored using biospeckle Optical Coherence Tomography (bOCT) at an early stage before germination. bOCT is a non-contact, non-destructive, and non-invasive image modality developed by researchers to visualize internal biological activities in vivo. Previous studies by researchers using the technique have demonstrated its potential to observe the effect of different stimuli on seed germination at an early stage before germination occurs. In the present study, the possible size-defendant effect of 200 nm and 2000 nm alumina nanoparticles (AlNPs) on lentil seed germination was examined at a concentration of 100 mg/L. The results imply that the AlNPs could enhance lentil seed germination and seedling growth compared to control treatments, and the effect is more significant as the particle size decreases. This is believed to be due to the enhancement of energy metabolism under exposure to AlNPs. [ABSTRACT FROM AUTHOR]

The surface of zirconia-based dental ceramic restorations require preparation prior to adhesive cementation. The purpose of this study was to assess the influence of airborne-particle abrasion with different sizes of alumina particles (50 μm, 110 μm, or 250 μm) on the mechanical strength of zirconia-based ceramics' frameworks and on the extent of phase transformations. A fracture resistance test was performed. The central surface of the frameworks was subjected to a load [N]. The identification and quantitative determination of the crystalline phase present in the zirconia specimens was assessed using X-ray diffraction. The Kruskal–Wallis one-way analysis of variance was used to establish significance (α = 0.05). The fracture resistance of zirconia-based frameworks significantly increases with an increase in the size of alumina particles used for air abrasion: 715.5 N for 250 μm alumina particles, 661.1 N for 110 μm, 608.7 N for 50 μm and the lowest for the untreated specimens (364.2 N). The X-ray diffraction analysis showed an increase in the monoclinic phase content after air abrasion: 50 μm alumina particles—26%, 110 μm—40%, 250 μm—56%, and no treatment—none. Air abrasion of the zirconia-based dental ceramics' surface with alumina particles increases the fracture resistance of zirconia copings and the monoclinic phase volume. This increase is strongly related to the alumina particle size. [ABSTRACT FROM AUTHOR]

With the rapid development of the electronics industry, there is a growing demand for packaging materials that possess both high thermal conductivity (TC) and low electrical conductivity (EC). However, traditional insulating fillers such as boron nitride, aluminum nitride, and alumina (Al2O3) have relatively low intrinsic TC. When graphene, which exhibits both superhigh TC and EC, is used as a filler to fill epoxy resin, the TC of blends can be much higher than that of blends containing more traditional fillers. However, the high EC of graphene limits its application in cases where electrical insulation is required. To address this challenge, a method for coating graphene sheets with an in situ grown Al2O3 layer has been proposed for the fabrication of epoxy-based composites with both high TC and low EC. In the presence of a cationic surfactant, a dense Al2O3 layer with a network structure can be formed on the surface of graphene sheets. When the total content of Al2O3 and graphene mixed filler reached 30 wt%, the TC of the epoxy composite reached 0.97 W m−1 K−1, while the EC remained above 1011 Ω·cm. Finite element simulations accurately predicted TC and EC values in accordance with experimental results. This material, with its combination of high TC and good insulation properties, exhibits excellent potential for microelectronic packaging applications. [ABSTRACT FROM AUTHOR]

The mechanical and biological behaviors of PMMA/Al2O3 composites incorporating 30 wt.%, 40 wt.%, and 50 wt.% of Al2O3 were thoroughly characterized as regards to their possible application in implant-supported prostheses. The Al2O3 particles accounted for an increase in the flexural modulus of PMMA. The highest value was recorded for the composite containing 40 wt.% Al2O3 (4.50 GPa), which was about 18% higher than that of its unfilled counterpart (3.86 GPa). The Al2O3 particles caused a decrease in the flexural strength of the composites, due to the presence of filler aggregates and voids, though it was still satisfactory for the intended application. The roughness (Ra) and water contact angle had the same trend, ranging from 1.94 µm and 77.2° for unfilled PMMA to 2.45 µm and 105.8° for the composite containing the highest alumina loading, respectively, hence influencing both the protein adsorption and cell adhesion. No cytotoxic effects were found, confirming that all the specimens are biocompatible and capable of sustaining cell growth and proliferation, without remarkable differences at 24 and 48 h. Finally, Al2O3 was able to cause strong cell responses (cell orientation), thus guiding the tissue formation in contact with the composite itself and not enhancing its osteoconductive properties, supporting the PMMA composite's usage in the envisaged application. [ABSTRACT FROM AUTHOR]

Modern industry of advanced polyolefins extensively uses Group 4 metallocene and post-metallocene catalysts. High-throughput polyolefin technologies demand the use of heterogeneous catalysts with a given particle size and morphology, high thermal stability, and controlled productivity. Conventional Group 4 metal single-site heterogeneous catalysts require the use of high-cost methylalumoxane (MAO) or perfluoroaryl borate activators. However, a number of inorganic phases, containing highly acidic Lewis and Brønsted sites, are able to activate Group 4 metal pre-catalysts using low-cost and affordable alkylaluminums. In the present review, we gathered comprehensive information on MAO- and borate-free activating supports of different types and discussed the surface nature and chemistry of these phases, examples of their use in the polymerization of ethylene and α-olefins, and prospects of the further development for applications in the polyolefin industry. [ABSTRACT FROM AUTHOR]

Two series of MCM-36 zeolites intercalated with various pillars and modified with iron were synthesized, analyzed with respect to their physicochemical properties, and tested as catalysts for the NH3-SCR process. It was found that the characteristic MWW morphology of MCM-36 can be obtained successfully using silica, alumina, and iron oxide as pillars. Additionally, one-pot synthesis of the material with iron resulted in the incorporation of monomeric Fe3+ species into the framework positions. The results of catalytic tests revealed that the one-pot synthesized sample intercalated with silica and alumina was the most efficient catalyst of NO reduction, exhibiting ca. 100% activity at 250 °C. The outstanding performance of the material was attributed to the abundance of Lewis acid sites and the beneficial influence of alumina on the distribution of iron species in the zeolite. In contrast, the active centers originating from the Fe2O3 pillars improved the NO conversion in the high-temperature range. Nevertheless, the aggregated particles of the metal oxide limited the access of the reacting molecules to the inner structure of the catalyst, which affected the overall activity and promoted the formation of N2O above 300 °C. [ABSTRACT FROM AUTHOR]

In the presented work, a probabilistic approach to fracture analysis of commercially available polyacrylonitrile butadiene styrene (ABS) and polylactide (PLA) filaments and fused deposition modeling (FDM)-printed tensile samples produced from them, as well as PLA filled with alumina (Al2O3) specimens, is discussed. The results of the analysis reveal the presence of symmetry between the stress distribution in the plastic–elastic and fracture stress regions. The value of the transition point from elastoplastic stress distribution to fracture distribution was established. It was shown that the probability density of the destruction of samples in a bound state obeys the Cauchy distribution. The resulting model well describes the stress distributions of tensile specimens, with a minimum deviation of 0.021% and a maximum deviation of 0.048% for the ceramic–polylactide (60Al2O3/40PLA) filament. [ABSTRACT FROM AUTHOR]

A classical problem with Cu-based shape memory alloys (SMAs) is brittle fracture at triple junctions. This alloy possesses a martensite structure at room temperature and usually comprises elongated variants. Previous studies have shown that introducing reinforcement into the matrix can refine grains and break martensite variants. Grain refinement diminishes brittle fracture at triple junctions, whereas breaking the martensite variants can negatively affect the shape memory effect (SME), owing to martensite stabilization. Furthermore, the additive element may coarsen the grains under certain circumstances if the material has a lower thermal conductivity than the matrix, even when a small amount is distributed in the composite. Powder bed fusion is a favorable approach that allows the creation of intricate structures. In this study, Cu–Al–Ni SMA samples were locally reinforced with alumina (Al2O3), which has excellent biocompatibility and inherent hardness. The reinforcement layer was composed of 0.3 and 0.9 wt% Al2O3 mixed with a Cu–Al–Ni matrix, deposited around the neutral plane within the built parts. Two different thicknesses of the deposited layers were investigated, revealing that the failure mode during compression was strongly influenced by the thickness and reinforcement content. The optimized failure mode led to an increase in fracture strain, and therefore, a better SME of the sample, which was locally reinforced by 0.3 wt% alumina under a thicker reinforcement layer. [ABSTRACT FROM AUTHOR]

Highly efficient and stable catalysts are among the key factors in industrial ethanol dehydration to ethylene. Among the widely studied catalysts, alumina is the most suitable for industrial application. In this study, novel gamma alumina was synthesized by solvent protection and a hydrothermal procedure. HRTEM, XRD, FT-IR, NH3-TPD, H-D exchange, and 29Si MAS NMR were employed to compare the difference in physicochemical properties between the novel gamma alumina and commercial alumina. Characterization results show that the as-synthesized novel gamma alumina mainly exposes the high-energy crystal plane (111) while the commercial alumina mainly exposes the thermostatically stable (110) crystal plane. The dominating (111) plane, according to the characterizations, endows the novel gamma alumina with a higher density of surface hydroxyl groups, higher acid content, and higher surface energy compared to the commercial alumina. The catalytic performance of the two catalysts for industrial ethanol dehydration to ethylene was studied. The novel (111) plane-exposed alumina showed a higher yield of ethylene than commercial alumina under the same reaction conditions. This could be related to the difference in atomic arrangement and the unsaturated aluminum coordination of different crystal planes. Stability testing under severe reaction conditions (450 °C, 1 MPa, 4 h−1) indicates that novel gamma alumina shows better stability (catalyst life cycle increased by 50%) and produces less acetaldehyde as a byproduct. The effects of steam treatment on the catalytic performance were further investigated. The surface acidity and the catalytic performance of novel gamma alumina present a volcanic curve with the increase in steam treatment temperature. Under the optimal water vapor treatment temperature of 650 °C, the conversion of ethanol and selectivity of ethylene were both higher than 99%. [ABSTRACT FROM AUTHOR]

Hydrodechlorination (HDC) is a reaction that involves the use of hydrogen to cleave the C−Cl bond in chlorinated organic compounds such as chlorophenols and chlorobenzenes, thus reducing their toxicity. In this study, a palladium (Pd) catalyst, which is widely used for HDC due to its advantageous physical and chemical properties, was immobilized on alumina (Pd/Al) and graphene-based materials (graphene oxide and reduced graphene oxide; Pd/GO and Pd/rGO, respectively) to induce the HDC of 4-chlorophenol (4-CP). The effects of the catalyst dosage, initial 4-CP concentration, and pH on 4-CP removal were evaluated. We observed that 4-CP was removed very rapidly when the HDC reaction was induced by Pd/GO and Pd/rGO. The granulation of Pd/rGO using sand was also investigated as a way to facilitate the separation of the catalyst from the treated aqueous solution after use, which is to improve practicality and effectiveness of the use of Pd catalysts with graphene-based support materials in an HDC system. The granulated catalyst (Pd/rGOSC) was employed in a column to induce HDC in a continuous flow reaction, leading to the successful removal of most 4-CP after 48 h. The reaction mechanisms were also determined based on the oxidation state of Pd, which was observed using X-ray photoelectron spectroscopy. Based on the results as a whole, the proposed granulated catalyst has the potential to greatly enhance the practical applicability of HDC for water purification. [ABSTRACT FROM AUTHOR]

This study aims to design novel amine-functionalized alumina nanofibers for the removal of lead (II) and mercury (II) ions from aqueous solutions. The γ -Al2O3 nanofibers were prepared by calcination of boehmite, and then functionalization with 3-(2-aminoethylamino) propyl trimethoxy silane. The characterization of the nanofibers was carried out using TEM, EDS, elemental mapping, XRD, and XPS. The effects of initial concentration, pH, contact time, and selectivity were studied. The results revealed that the nanofibers can remove 98% of Hg2+ ions and 90% of Pb2+ ions from aqueous solution at concentrations of 40 mg/L and 35 mg/L, respectively. Additionally, the optimal pH conditions for mercury and lead ion adsorption were established to be 6. It was also observed that for concentrations of 100 mg/L and 250 mg/L, the majority of ion contaminants were removed by the nanofibers within the first hour. The adsorption capacities were found to be 129 mg/g and 165 mg/g for Hg2+ and 72.3 mg/g and 111 mg/g for Pb2+ at 100 mg/L and 250 mg/L concentrations, respectively. The ion-adsorption kinetic data was best fitted to a pseudo-second-order model. High sorption capacities were also demonstrated when employed to selectively adsorb mercury (II) and lead (II) ions from aqueous solutions containing Zn2+, Mg2+, Cu4+, Sn4+, and Ni4+. Desorption tests were performed to explore the stability of the heavy metals on the nanofiber. [ABSTRACT FROM AUTHOR]

The search for inexpensive, environmentally friendly, and highly effective catalysts to activate C-H bonds in propane dehydrogenation (PDH) reactions is still a major challenge. Co-based catalysts have gained significant attention in recent years due to their excellent ability to activate C-H bonds and their high selectivity towards olefins, despite being a non-noble and environmentally unfriendly metal. However, further improvements are necessary for practical utilization, particularly in terms of activity and anti-carbon deposition capacity. In this study, we synthesized Al2O3 nanorods with abundant pentacoordinated Al3+ (Al3+penta) sites. The supported Co on the Al2O3 nanorod (Co/Al2O3-NR) exhibited higher selectivity (>96% propylene selectivity) and stability (deactivation rate 0.15 h−1) compared to Co supported on an Al2O3 nanosheet with fewer pentacoordinated Al3+ sites. Various characterizations confirmed that Co(II) mainly exists as CoAl2O4 rather than Co3O4 in the form of Co/Al2O3-NR, which inhibits the reduction of Co(II) to Co0 and accordingly improves catalyst stability. [ABSTRACT FROM AUTHOR]

Although carbon fiber-reinforced polymer (CFRP) composites have excellent intrinsic mechanical properties, they are vulnerable to impact loads because of their weak inter-laminar fracture toughness, which results in delamination damage. This study presents a novel hybrid nanofiller combination of multi-walled carbon nanotubes (MWCNT) and alumina nanoparticles (Al2O3) to determine improvements in the impact resistance of CFRP laminate. The projectile impact experimental study is carried out on 140 mm × 140 mm × 1.5 mm CFRP laminate with spherical and conical nose shape projectiles. The numerical study of the test plate consisting of six layers is performed, in which each layer is modeled using a shell element and connected through tiebreak contact. Using the Cowper–Symonds equation to determine the dynamic mechanical properties, the numerical validation is established considering the strain rate effect. The results, such as residual velocity, damage area, ballistic limit velocity and delamination obtained from numerical analysis, are compared with the experimental observations. In laminates with hybrid nanofillers, residual velocity decreased by 20% and 9% when spherical and conical projectiles were impacted, respectively. The study indicates that 0.1 wt% MWCNT + 1 wt% Al2O3 nanofiller concentration embedded CFRP offers better resistance against spherical and conical projectile impact. [ABSTRACT FROM AUTHOR]

As the microelectronic industry develops, components that can perform several different tasks receive increasingly more attention, resulting in multifunctional materials being highly sought after. Al2O3 is widely present in electronic applications as a protective coating or as an electrical and thermal insulator due to its mechanical and thermal stabilities and chemical inertness. Al2O3 is also an important dielectric material, with high resistivity and stable permittivity over a wide range of temperatures and electric fields, but its modest permittivity necessitates large effective areas or extremely thin layers when a large capacitance is desired. Composites consisting of discrete conducting phases within an insulating matrix can produce large capacitance via Maxwell–Wagner polarization. In this work, Al2O3/Al composite thick films with different volume ratios of Al were prepared using the aerosol deposition method. A relative dielectric permittivity (εr′) of 800 at 1 MHz was achieved at 27 vol% of Al, a sixty-sevenfold enhancement compared to Al2O3. On the other hand, dielectric losses, tan(δ), at 1 MHz increased from 0.01 for Al2O3 up to 0.58 for the composite with 27 vol% of Al. A finite-element model of the composites was implemented, supporting the nonlinear electrical behavior of the composites as function of vol% of Al. Our results show novel possibilities for the applications of Al2O3-based materials in the microelectronic industry, especially for temperature-sensitive applications, for which the integration strengths of aerosol deposition are valuable. [ABSTRACT FROM AUTHOR]

The fabrication of multi-dimensional nanocomposites has been extensively attempted to achieve synergistic performance through the uniform mixing of functional constituents. Herein, we report a one-pot fabrication of nanocomposites composed of carbon nanotubes (CNTs) and Al2O3 powder. Our strategy involves a synthesis of CNTs on the entire Al2O3 surface using a rotatable chemical vapor deposition system (RCVD). Ehylene and ferritin-induced nanoparticles were used as the carbon source and wet catalyst, respectively. The RCVD was composed of a quartz reaction tube, 5.08 cm in diameter and 150 cm in length, with a rotation speed controller. Ferritin dissolved in deionized water was uniformly dispersed on the Al2O3 surface and calcinated to obtain iron nanoparticles. The synthesis temperature, time, and rotation speed of the chamber were the main parameters used to investigate the growth behavior of CNTs. We found that the CNTs can be grown at least around 600 °C, and the number of tubes increases with increasing growth time. A faster rotation of the chamber allows for the uniform growth of CNT by the tip-growth mechanism. Our results are preliminary at present but show that the RCVD process is sufficient for the fabrication of powder-based nanocomposites. [ABSTRACT FROM AUTHOR]

Alumina ceramics were obtained from three different alumina sources, A1–A3, with various rare-earth dopants (La2O3–La, Nd2O3–Nd, and Y2O3–Y), concentration levels (500 and 1000 ppm) and synthesizing routes (1500 °C, 1815 °C and cold plasma-P). Absorption (A) and density (ρ in text, rho in images) were measured, resulting in a complex, multivariate database. Principal Component Analysis (PCA) was run with the aim of deducing relationships between variables (alumina source, dopant level, thermal processing route, A and ρ), observations, and between variables and observations. A total of 206 Scanning Electron Microscopy (SEM) micrographs were recorded at various scales and the corresponding images were processed to quantify the microstructural features. Two techniques of edge detection were used; Fractal Dimension (FD) was calculated for each micrograph and results were compared. Various scales of the micrographs prevented us from using any other approach, such as simply measuring the grains or obtaining shape parameters. The initial database was extended by including FDs and PCA was run again. We found that plasma processing is positively correlated to A and negatively correlated to both temperature (T) and ρ; La ceramics have an opposite behavior to Y and Nd ceramics. FD successfully explained observations being correlated, mainly, to Y, Nd and, to a lesser extent, to La. FD proved that it is a reliable and simple approach to quantifying microstructural features when comparing highly different, noisy micrographs. [ABSTRACT FROM AUTHOR]

Ten percent of patients undergoing total hip arthroplasty (THA) require revision surgery. One of the reasons for THA are wear particles released from the implants that can activate the immune defense and cause osteolysis and failure of the joint implant. The discrepancies between reports on toxicity and immunogenicity of the implant materials led us to this study in which we compared toxicity and immunogenicity of well-defined nanoparticles from Al2O3, zirconia-toughened alumina (ZTA), and cobalt chrome (CoCr), a human THP-1 macrophage cell line, human PBMCs, and therefrom-derived primary macrophages. None of the tested materials decreased the viability of THP-1 macrophages nor human primary macrophages at the 24 h time point, indicating that at concentrations from 0.05 to 50 µm3/cell the tested materials are non-toxic. Forty-eight hours of treatment of THP-1 macrophages with 5 µm3/cell of CoCr and Al2O3 caused 8.3-fold and 4.6-fold increases in TNF-α excretion, respectively, which was not observed for ZTA. The comparison between THP-1 macrophages and human primary macrophages revealed that THP-1 macrophages show higher activation of cytokine expression in the presence of CoCr and Al2O3 particles than primary macrophages. Our results indicate that ZTA is a non-toxic implant material with no immunogenic effects in vitro. [ABSTRACT FROM AUTHOR]

Developing and improving adsorbent materials for wastewater treatment have become crucial for achieving recyclable water and keeping the environment safe. Carbon materials are modified with alumina (Al2O3) using various doping ratios and a solvothermal treatment. The process aims to combine the advantages of stable carbon and alumina materials with an efficient adsorbent for methylene blue removal. Fabricated materials including carbon and carbon/alumina derivatives were characterized with TEM, SEM, EDS, XRD, and FTIR, revealing successful surface modifications. The carbon materials exhibited pore diameters between 23 and 39 µm, while the modified ones showed pore diameters between 1.68 and 6.08 µm. The alumina nanoparticles were formed on a carbon surface with a particle size between 174 nm and 179 nm. Fabricated adsorbents were applied for the removal of methylene blue by adsorption at pH 4. The equilibrium and steady state adsorption stage was achieved after 2 h of reporting fast adsorption behavior. Low ratio carbon doping with alumina improved the adsorption capacity for methylene blue removal, while the excessive doping of carbon materials with alumina led to a reduction in adsorption efficiency. The application of pseudo-first-order and pseudo-second-order kinetic models indicated a fast adsorption mechanism, which agreed with the second-order model. The adsorption capacity for methylene blue was found to be 234 mg/g. Adsorption-isotherms including the Langmuir and Freundlich models were applied to investigate the adsorption mechanism. The results indicate that the Langmuir model fits with the adsorption data, which suggests a monolayer adsorption process. [ABSTRACT FROM AUTHOR]

The one-step AM process is considered the goal many researchers seek in the field of Additive Manufacturing (AM) of high-technology ceramics. Among the several AM techniques, only Powder Bed Fusion (PBF) can directly print high-technology ceramics using one step. However, the PBF technique faces numerous challenges to efficiently be employed in the PBF of ceramics. These challenges include the formation of cracks, generated thermal stress, effective laser–powder interaction, and low acquired relative density. This study developed a new preheating mechanism for ceramic materials using two laser systems to surpass beyond these challenges and successfully print ceramics with a single-step AM method. One laser is used to preheat the powder particles before the second laser is utilised to complete the melting/sintering process. Both lasers travel along the same scanning path. There is a slight delay (0.0001 s) between the preheating laser and the melting/sintering laser to guarantee that the melting/sintering laser scans a properly preheated powder. To further facilitate testing of the preheating system, a numerical model has been developed to simulate the preheating and melting process and to acquire proper process parameters. The developed numerical model was shown to determine the correct process parameters without needing costly and time-consuming experiments. Alumina samples (10 × 10 × 6 mm3) were successfully printed using alumina powder as feedstock. The surface of the samples was nearly defect-free. The samples' relative densities exceeded 80%, the highest reported relative density for alumina produced by a single-step AM method. This discovery can significantly accelerate the transition to a one-step AM process of ceramics. [ABSTRACT FROM AUTHOR]