Surface Of Alumina Particles Research Articles

Highly effective organometallic‐mediated radical polymerization of vinyl acetate using alumina‐supported Co(acac)2 catalyst: A case study of adsorption and polymerization

ABSTRACTAn alumina support system for cobalt(II) acetylacetonate (Co(acac)2) catalyst was studied for the cobalt‐mediated radical polymerization (CMRP) of vinyl acetate (VAc). We report a simple but efficient technique to produce this supported catalysts through the adsorption of Co(acac)2 on the surface of alumina particles. Moreover, kinetic and thermodynamic study of Co(acac)2 adsorption on the alumina support were conducted and the influence of effective parameters were investigated. It was found that using alumina‐supported Co(acac)2 for radical polymerization of VAc yields polymers with controlled molecular weight, narrow molecular weight distribution, and high purity. For the alumina‐supported CMRP, changing the polymerization mechanism and domination of termination pathway compared to degenerate transfer pathway resulted in a 2.5 times increase in polymerization rate (kap) and a drop in induction time while maintaining a good control of the VAc polymerization. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46057.

Generation of Hydrogen through the Reaction between Plasma‐Modified Aluminum and Water

AbstractOne of the main challenges related to hydrogen energy technologies is hydrogen storage in a safe and economically reasonable way. A promising solution could be related to the use of aluminum or its alloys to reduce water to form hydrogen when needed. The aluminum–water reaction is thermodynamically favorable, but does not proceed due to the passivation of the aluminum surface by the protective aluminum oxide layer, which prevents water molecules from coming into direct contact with metal particles. Herein, the surface of aluminum particles was modified by using a low‐temperature plasma‐activation approach. Such a modification induces a hydrophilicity effect and the modified aluminum powder sinks instantly in water, whereas unmodified powder floats on the top of the water. The plasma‐based activation technology is also discussed in detail. The structure and morphology of the samples were characterized by using SEM, energy‐dispersive X‐ray spectroscopy, and XRD. BET surface area analyses were also performed. The elemental composition on the nanoscale level and formation of polar groups were experimentally investigated by using X‐ray photoelectron spectroscopy. Amounts of oxygen/hydrogen were measured by using the inert‐gas fusion method. Tests show that hydrogen production starts after 1 min of aluminum powder immersion into slightly alkaline water and continues for up to 20 min. The reaction by‐product is environmentally friendly and could be used for the production of aluminum oxide.

Synthesis of ceramic composites using three-dimensional nanostructuring (reinforcement) of alumina matrix with TiN and SiC nanostructures and study of their mechanical properties

The paper considers a new 3D nanostructuring technology of next-genergtion ceramic composites based on a ceramic matrix reinforced with titanium nitride (TiN) gnd silicon carbide (diC). Research data are reported on the formation of TiN and diC nanostructures on the surface of disperse alumina during successive gas chemisorption of organic Ti(N(CH3)2)4 (tetrakis-dimethylamino-titanium, TDMAT) and ammonia NH3 in the first case and Cl2Si(CH3)2 and methane CH4 in the second. Such chemisorption increases the number of surface-attached Ti-N groups crystallized on annealing at 1100°C with the formation of a TiN or a SiC nanoparticle layer. According to X-ray diffraction and electron microscopy, TiN nanoparticles with an average size of about 40 nm are formed on the surface of alumina particles after TDMAT and NH3 treatment for 2 h and subsequent annealing at 1100°C. The mechanical properties of compacted α-A12O3-based ceramics reinforced with TiN and SiC nanoparticles excel the properties of the best ceramic materials provided by different manufacturers.

Performance analysis of magnetorheological fluid-assisted electrical discharge machining

ABSTRACTIn this study, a newly developed method of electric discharge machining has been proposed, which uses magnetorheological (MR) fluid instead of conventional oil like kerosene. The paper aims to reveal the process parameters that affect the material removal rate (MRR) during newly developed EDM process. This hybrid machining process showed dual advantage of high-quality machined surface with improved cutting efficiency. The viscoelastic nature of MR fluid is found to give polishing effect as well as high material removal resulting in more stable processing and improved EDM performance. The experimentation has been performed to determine effect of duty cycle, discharge current, pulse on time, percentage concentration of alumina particles surface roughness, and MRR. It has been found that MRR and surface finish improved significantly. The experimental results demonstrated that the EDM process combined with MR fluid resulted in an increase in MRR and surface finish significantly under a certain limit of carbonyl iron percentage (CIPs) in MR fluid.

Dielectric relaxation in energy condensed systems on the basis of polyefirretane elastomer. I. Frequency dependence

This paper describes the experimental study of dielectric relaxation in energy condensed systems based on ether urethane rubber plasticized by glycerin trinitrate and ammonium perchlorate, HMX, and aluminum powders in the frequency range of the electric field from 40 to 1.2 · 109 Hz. Depending on the field frequency, it was possible to determine relaxation processes caused by dipole polarization, the bulk electrical conductivity of a polymer binder, and the influence of the surface of aluminum particles.

CoMoB/Al2O3 catalysts for hydrotreating of diesel fuel. The effect of the way of the boron addition to a support or an impregnating solution

CoMoB/Al2O3 catalysts with up to 2wt.% of B have been synthesized by two different methods an introduction of boron into γ-Al2O3 support during the kneading of the paste or by the impregnating of γ-Al2O3 extrudates by the solution of Mo and Co compounds, citric and boric acids. It is shown that the activity in HDS and HDN of diesel fuel increases with increasing boron content in catalysts. The growth of the activity is associated with the increase in CoMoS phase content, Co dispersity, an average slab length of sulfide active component particles and an average number of slabs per 1000nm2. The positive effect of boron is much more pronounced for catalysts prepared by the introduction of boron to the solution, since boron is located preferentially on the surface of alumina particles.

The preparation of Al/Fe composite powders by electroless plating

ABSTRACTThe core–shell Al/Fe composite powders were synthesised by electroless plating. The effects of concentration of FeSO4·7H2O, pre-treatment method of aluminium powders, and secondary plating on the preparation of core–shell Al/Fe composite powders were studied. The composite powders were analysed by the X-ray diffraction, a scanning electron microscope, and an energy-dispersive spectrometer. The results indicate that the content of iron in the composite powders could be effectively controlled by adjusting the concentration of FeSO4·7H2O in the plating solution. The pre-treatment of the raw aluminium powders is also a key factor to form a uniform iron layer on the surface of aluminium particles. Furthermore, the density and iron content of the composite powders prepared by secondary plating have been improved.

Temperature induced gelation of non–aqueous alumina suspension using oleic acid as dispersant

Abstract A novel temperature induced gelation method for alumina suspension using oleic acid as dispersant is reported. Non–aqueous suspension with high solid loading and low viscosity is prepared using normal octane as solvent. Influence of oleic acid on the dispersion of suspension was investigated. There was a well disperse alumina suspension with 1.3 wt% oleic acid. Influence of gelation temperature on the coagulation process and properties of green body was investigated. The sufficiently high viscosity to coagulate the suspension was achieved at −20 °C. The gelation temperature was controlled between the melting point of dispersant and solvent. The gelation mechanism is proposed that alumina suspension is destabilized by dispersant separating out from the solvent and removing from the alumina particles surface. The alumina green body with wet compressive strength of 1.07 MPa can be demolded without deformation by treating 53 vol% alumina suspension at −20 °C for 12 h. After being sintered at 1550 °C for 3 h, dense alumina ceramics with relative density of 98.62% and flexural strength of 371±25 MPa have been obtained by this method.

Effects of Milling pH and Hydrothermal Treatment on Formation of Nanostructured Boehmite Binder for Alumina Extrusion

The in situ formation of nanostructured aluminum hydroxides on the surface of alumina particles, which can work as inorganic binder, was reported in this paper. The effect of the suspension pH during milling of alumina powder and subsequent hydrothermal treatment for the hydroxide formation and microstructure was depicted. Under acidic pH condition, the formation of hydroxides was not observed. When the pH of suspension changed from acidic to basic during milling, bayerite [Al(OH)3] nanoparticles were formed, but only a fraction of this hydroxide was converted to boehmite (AlOOH) during subsequent hydrothermal treatment. The aluminum hydroxide and oxyhydroxide formed in this condition improved the smoothness of extruded rods and the strength of presintered segments. For the powder milled under basic pH condition, the mechanochemically formed bayerite was completely converted into boehmite nanoparticles during the hydrothermal treatment. The presence of boehmite nanoparticles contributed to improving plasticity during extrusion, which allowed the reduction of organic binder and increased the strength of presintered alumina rods.

Application of PAP-2 aluminum powder to produce powdered composite materials: The features of technology, structure, and physicomechanical properties of composites. Part I. Process approaches providing the formation of composite materials and applied procedures for determining their physicomechanical properties

Composites Al/Al2O3 (lamellar cermet matrix)–filler (discrete metallic fibers, duralumin chips, graphite particles, fused corundum grains, and technical alumina spherulites) are fabricated. To form the lamellar cermet matrix, industrially produced PAP-2 aluminum powder was used. This powder consists of scaled particles with stearin coating (the specific surface of the powder is 4.1322 m2/g, and its particle size varies from 0.03 to 10 μm). In order to form the composites, the following main process operations were used: heat treatment of the PAP-2 powder in air to burn out stearin from the particle surface and replace it with a passivating alumina film, mixing of the thus formed powder product with a filler, and compaction and reaction sintering of powder billets in the filtration burning mode in air. To fabricate the Al/Al2O3–C composite, a new approach based on the saponification chemical reaction of stearin is proposed. This reaction runs between stearin on the surface of aluminum particles and caustic soda, which is the product of hydrolysis of the diluted liquid glass introduced into initial powder. The reaction products (sodium stearate and glycerol) are decomposed during the subsequent heat treatment in air with the formation of a coke residue on the particle surface. The physicochemical properties of the composites were determined using standard and conventional procedures.

The use of PAP-2 aluminum dust to fabricate powder composite materials: the features of technology, structure and physicomechanical composites. Part 1. Manufacturing approaches that provide the creation of composite materials and applied procedures for de

Composites Al/Al2O3 (lamellar cermet matrix)–filling agent (discrete metallic filaments, duralumin chips, graphite particles, fused corundum grains, kaolin filaments, and technical alumina spherolites) are fabricated. Industrially produced PAP-2 aluminum powder, which consists of scaled particles with stearin coating (specific surface of the powder is 4,1322 m2/g, its particle sizes vary from 0,03 to 10 μm), was used to form the lamellar cermet matrix. In order to form the composites, the following production operations were used: heat treatment of PAP-2 powder in air to burn-out stearin from the particle surface and substitute it by alumina film, mixing the formed powder product with the filling agent, pressing, and reaction sintering the powder billets in a filtration burning mode in air. A new approach based on the chemical reaction of stearin saponification is proposed to fabricate the Al/Al2O3 composite. In this reaction, stearin on the surface of aluminum particles reacts with caustic soda resulted from the hydrolysis of diluted liquid glass introduced into initial powder. The reaction products (sodium stearate and glycerin) decompose during subsequent heat treatment in air with the formation of coke residue on the particle surface. Physicochemical properties of composites were determined using standard and generally accepted procedures.

Aluminum pigments encapsulated with hybrid silica film with carboxyl groups and their stability and dispersibility in aqueous media

Aluminum pigments encapsulated with hybrid SiO2 film with carboxyl (–COOH) groups were prepared through a sol‐gel process of tetraethoxysilane (TEOS) and vinyl triethoxysilane (VTES), followed by radical copolymerization of methyl methacrylate (MMA) and acrylic acid (AA) with the vinyl group of VTES. The composite aluminum pigments were characterized by means of Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and X‐ray photoelectron spectroscopy (XPS). Their stability in acid media as well as dispersibility in water were also evaluated. It was found that VTES and TEOS could simultaneously hydrolyze and condense with hydroxyl groups on the surface of aluminum particles to form inorganic‐organic hybrid films, and copolymerization of MMA and AA could provide the film surface with –COOH groups. This helps the composite aluminum pigments disperse better in water than raw aluminum pigments (raw Al) counterparts. Compared with the serious corrosion problem of raw Al, which generated about 113 mL H2 in acid media of pH=1 in 30 days, the composite aluminum pigments showed much better anticorrosion performance (with only about 0.5 mL H2). The waterborne coatings made with this composite aluminum pigments showed great improvements on adhesive performance and stability in 0.1 mol/L H2SO4 or NaOH media.

Преимущества Clean & POROUS TM нового технологического метода обработки поверхности дентальных имплантатов

The purpose of this study was a comparative analysis of the surfaces of dental implants treated with technological methods SLA and RBM to identify their positive and negative characteristics. Based on these results to develop a new process Clean & Porous surface treatment of dental implants to obtain highly, rough and porous surface, which is characteristic for the technology SLA, and absolutely clean surface characteristic of technology RBM, without their disadvantages (unwarranted complete removal of abrasive particles SLA case and the absence of a clear structure of the surface topography in the case of RBM).The structure and purity of the implant surface Straumann, Alfa-Bio, DIO, Finish Line. studied in micrographs obtained by an electron microscope (SEM) at the University of Technion (increase 500,2000,3000). To study the chemical properties of the samples, the method of X-ray energy dispersive spectroscopy (EDS), based on an analysis of its X-ray emission energy spectrum.Comparative analysis of the implant surfaces treated with the methods and RBM SLA showed that despite the reliability of these methods, each of them has certain disadvantages (contamination cases alumina particle surface with sufficient structural SLA and craters on the surface organized RBM). Developed by Finish Line Materials and Processes Ltd new technology of surface treatment of dental implants Clean & PorousTM, combining the best characteristics of the methods of SLA and RBM, possible to obtain a well-structured and absolutely clean surface.The proposed new original method Clean & PorousTM treatment of dental implants meet the criteria (roughness, porosity and surface finish of the implant), which provide an ideal osseointegration. Since osseointegration is a key issue in modern implantology it enables to obtain reliable primary fixation of the implant in the bone. From a clinical point of view it reduces the healing of the implant, as well as creating conditions accelerate the start of prosthetics.

Electrodeposition mechanism of Ni–Al composite coating

Ni–Al composite coatings were electrodeposited from a modified Watts solution. The electrochemical behavior of the coatings was studied by means of zeta potential analysis, voltammetry and electrochemical impedance spectroscopy (EIS). It was found that the zeta potential of Al particles was −4 mV which is very close to that of Al2O3. Moreover, addition of conductive Al particles into the electrolyte shifted the polarization curve to more negative potentials and loop size of EIS curve increased. It was also demonstrated that the co-deposition behavior of Ni–Al composite coatings obeys the Guglielmi's model. The results indicate that conductive Al particles behave as the inert particles and confirm the existence of a thin aluminum oxide layer on the surface of aluminum particles.

Processing of alumina–zirconia composites by surface modification route with enhanced hardness and wear resistance

Zirconia toughened alumina (ZTA) materials are frequently used in mechanical engineering and biomedical applications due to their enhanced toughness, strength and wear resistance compared to monolithic alumina. In this study, a submicron size alumina powder was modified via wet chemical route: the alumina particles surface was coated with zirconium chloride, to yield 10vol% zirconia by subsequent thermal treatment. From this powder, several ZTA materials were produced by slip casting, sintered at different temperatures from 1475 to 1575°C. In all materials, a full characterization of their mechanical properties, microstructure and phase composition was carried out, together with wear tests carried out in a linear-reciprocating mode using a Y-TZP ball counterpart under environmental conditions.The results show low wear at sintering temperatures below 1525°C and high wear at higher sintering temperatures, which can be well correlated to the hardness, microstructure and phase evolution. The microstructure of the materials is initially extremely homogeneous and fine grained. The grain size increases moderately both for the zirconia and alumina components with the sintering temperatures considered. The grain shape of alumina gradually changes from isometric to elongated. Up to 1525°C, the size of zirconia grains stays below 400nm. The zirconia transformability was evaluated and it was observed that the zirconia dispersion remains vastly untransformable up to that sintering temperature. In this condition, the alumina matrix is under compressive hydrostatic stress and fracture resistance is moderate. At higher sintering temperatures, grain growth induces higher zirconia transformability and fracture resistance but at the expense of hardness and wear resistance. The simultaneous evolution of tabular morphology in matrix grains also contributes to toughness but facilitates grain breakout and disruption of the surface during final machining and under tribological load.

Spectral and kinetic analysis of heterogeneous gas discharge plasma in the flow of an Al, H2O, and Ar mixture

Plasma excited by a longitudinal pulse-periodic discharge in a mixed flow of a buffer gas (Ar), oxidizer (H2O), and aluminum dust is studied. The salient features of its kinetics are the atomic and molecular electronic channels of Al atom transformation, which were not taken into account earlier. They accelerate not only the oxidation process but also aluminum vaporization because the excitation and ionization energies are finally released on the surface of aluminum particles. This work is devoted to experimental and theoretical analysis of these channels.

Heterogeneous Uptake and Adsorption of Gas-Phase Formic Acid on Oxide and Clay Particle Surfaces: The Roles of Surface Hydroxyl Groups and Adsorbed Water in Formic Acid Adsorption and the Impact of Formic Acid Adsorption on Water Uptake

Organic acids in the atmosphere are ubiquitous and are often correlated with mineral dust aerosol. Heterogeneous chemistry and the uptake of organic acids on mineral dust particles can potentially alter the properties of the particle. In this study, heterogeneous uptake and reaction of formic acid, HCOOH, the most abundant carboxylic acid present in the atmosphere, on oxide and clays of the most abundant elements, Si and Al, present in the Earth's crust are investigated under dry and humid conditions. In particular, quantitative adsorption measurements using a Quartz Crystal Microbalance (QCM) coupled with spectroscopic studies using Attenuated Total Reflection Fourier Transform Infrared (ATR-FTIR) spectroscopy are combined to allow for both quantification of the amount of uptake and identification of distinct adsorbed species formed on silica, alumina, and kaolinite particle surfaces at 298 K. These oxides and clay particles show significant differences in the extent and speciation of adsorbed HCOOH due to inherent differences in surface -OH group reactivity. Adsorbed water, controlled by relative humidity, can increase the irreversible uptake of formic acid. Interestingly, the resulting layer of adsorbed formate on the particle surface decreases the particle hydrophilicity thereby decreasing the amount of water taken up by the surface as measured by QCM. Atmospheric implications of this study are discussed.

Preparation of the Gold Nanoparticles and its Activity for Single-Step Amination of Benzene to Aniline

Gold nanoparticles (AuNPs) were attached to the surface of alumina particles by an in-situ immobilizing method. SEM and XPS analysis showed that the coverage of alumina particles by AuNPs increased as the amount of alumina decreased; AuNPs onto alumina particles by the conventional colloidal deposition method were also prepared, whose TEM showed that the coverage of AuNPs was evidently smaller than that in the case of modified colloidal deposition method，although the AuNPs were spread almost uniformly over the surface of alumina particles. Au-immobilized alumina particles were subsequently utilized as the catalysts for direct amination of benzene with NH3H2O as an aminating agent and H2O2 as an oxidant under mild conditions. The reaction conditions were optimized: when catalyst amount was 2.0 g, reaction temperature was 50 °C, NH3H2O amount was 60 mL, H2O2 amount was 30 mL, and reaction time is 2 h, Au-immobilized alumina particles showed the highest aniline yield (1.96 mg) for 25 mL benzene.

Controlling protein–particle adsorption by surface tailoring colloidal alumina particles with sulfonate groups

In this study, we demonstrate the control of protein adsorption by tailoring the sulfonate group density on the surface of colloidal alumina particles. The colloidal alumina (d50=179±8nm) is first accurately functionalized with sulfonate groups (SO3H) in densities ranging from 0 to 4.7SO3Hnm−2. The zeta potential, hydrophilic/hydrophobic properties, particle size, morphology, surface area and elemental composition of the functionalized particles are assessed. The adsorption of three model proteins, bovine serum albumin (BSA), lysozyme (LSZ) and trypsin (TRY), is then investigated at pH 6.9±0.3 and an ionic strength of 3mM. Solution depletion and zeta potential experiments show that BSA, LSZ and TRY adsorption is strongly affected by the SO3H surface density rather than by the net zeta potential of the particles. A direct correlation between the SO3H surface density, the intrinsic protein amino acid composition and protein adsorption is observed. Thus a continuous adjustment of the protein adsorption amount can be achieved between almost no coverage and a theoretical monolayer by varying the density of SO3H groups on the particle surface. These findings enable a deeper understanding of protein–particle interactions and, moreover, support the design and engineering of materials for specific biotechnology, environmental technology or nanomedicine applications.

Direct Coagulation Casting of Alumina Suspension by High Valence Counter Ions Using Ca(IO3)2 as Coagulating Agent

A new direct coagulation casting of aqueous alumina suspension was developed via controlled release of high valence counter ions from calcium iodate with increase in the temperature from 55°C to 70°C. The influence of calcium iodate on the rheology of alumina suspension was investigated. A small amount of calcium iodate increased the viscosity of the concentrated alumina suspension at high temperature and finally transformed it into a wet‐coagulated body. The mechanism of coagulation is proposed such as that the solubility of calcium iodate increases with increase in temperature. The high valence Ca2+ ions diffuse into the double electrical layer of alumina particles surface through electrostatic attraction, reduces the zeta potential, hence decreases repulsive force between particles. Also reaction between Ca2+ and citrate leads to insufficient dispersant coverage on the particle surface. Both factors contribute to the coagulation of the suspension. The coagulation time was from 1 to 4 h by maintaining the temperature in the range of 55°C–70°C. The wet‐coagulated bodies prepared from 50 vol% alumina suspension showed a high compressive strength of 2.6–3.2 MPa with uniform microstructure. The relative density of sintered sample is 99.4% at 1550 °C for 2 h with perfect microstructure.