Al2 O3 Research Articles

Metal-polymer composites with ultra-and nanodisperse particles

The results of studies of the structure, mechanical and tribological properties of composite materials based on polytetrafluoroethylene (PTFE) and simple (Al2 O3, Cr2 O3, ZrO2) and complex (spinels CoAl2 O3 and MgAl2 O4, and cordierite 2MgO · 2Al2 O3 · 5SiO2) oxide nanopowders, as well as amorphous polyvinyl chloride (PVC) with heat stabilizers and elastomeric additives, are presented.

Separation and determination of alkyl sulfate surfactants in wastewater by capillary electrophoresis coupled with contactless conductivity detection after preconcentration by simultaneous adsorption using alumina beads

The aim of the present study is to determine four anionic alkyl sulfate (AS) surfactants with different alkyl chains, namely, C8, C10, C12, and C14, in wastewater by CE with capacitively coupled contactless conductivity detection (CE-C4 D). The conditions effective for the separation of the four AS surfactants were systematically optimized and found to be in a Tris-His (50mM/20mM) BGE solution at a pH of 8.95, using a separation voltage of +15kV, hydrodynamic injection by siphoning using a 20cm injection height and an injection time of 20 s. The LODs for C8, C10, C12, and C14 were 2.58, 2.30, 2.08, and 3.16mg/L, respectively. The conditions used to achieve the simultaneous adsorption and preconcentration of the AS surfactants using Al2 O3 beads were pH of 3 and 0.1mM NaCl. The adsorption efficiencies were found to be 45.6, 50.8, 81.7, and 99.9%, while the desorption efficiencies reached 66.1, 70.4, 83.9, and 100.0% for C8, C10, C12, and C14, respectively. The concentrations of the AS surfactants in wastewater samples were quantified by CE-C4 D after preconcentration by simultaneous adsorption using Al2 O3 beads. The results obtained from the proposed method were consistent with those obtained by HPLC-MS/MS, with a deviation of less than 15%. Our results indicate that the CE-C4 D performed after preconcentration by an adsorption technique using Al2 O3 beads is a new, inexpensive, and suitable method for quantifying AS surfactants in wastewater samples.

Organic-Free Synthesis of Zeolite Y with High Si/Al Ratios: Combined Strategy of In Situ Hydroxyl Radical Assistance and Post-Synthesis Treatment.

Zeolite Y, with a high SiO2 /Al2 O3 ratio (SAR), plays an important role in fluidized catalytic cracking processes. However, in situ synthesis of zeolite Y with high SARs remains a challenge because of kinetic limitations. Here, zeolite Y with an SAR of 6.35 is synthesized by a hydroxyl radical assisted route. Density-functional theory (DFT) calculations suggest that hydroxyl radicals preferentially enhanced the formation of Si-O-Si bonds, thus leading to an increased SAR. To further increase the SAR, a dealumination process was carried out using citric acid, with a subsequent second-step hydrothermal crystallization, giving an SAR of up to 7.5 while maintaining good crystallinity and high product yield. The resultant zeolite Y shows good performance in cumene cracking. Introduced here is a new strategy for synthesizing high SAR zeolite Y, which is widely used in commercial applications.

Hot deformation behaviour of bimodal sized Al2 O3 /Al nanocomposites fabricated by spark plasma sintering.

The deformation behaviour of bimodal sized Al2 O3 /Al nanocomposites were investigated by hot compression tests conducted in the temperature range 350-500°C and strain rates of 0.001, 0.01 and 0.1 s-1 . The dynamic recrystallisation behaviour of the nanocomposites strongly depended on the forming parameters. The bimodal sized Al2 O3 particles played a crucial role in the recrystallised microstructure. The addition of bimodal sized Al2 O3 particles led to a significant increase of activation energy of plastic deformation, corroborating the enhanced resistance of the nanocomposite to hot deformation. This was also reflected by the increased compressive yield strength in the nanocomposite due to both dislocation strengthening caused by n-Al2 O3 and preventing the grain growth due to the presence of μ-Al2 O3 at grain boundaries. It was found that with the decrease of Z values, local strain induced by deformation was released and the grain size of aluminium matrix gradually increased, indicating that the main softening mechanism of the bimodal sized Al2 O3 /Al nanocomposites was dynamic recrystallisation (DRX). The lower the Z value was, the easier the DRX occurred. The highly beneficial role of the bimodal sized Al2 O3 reinforcement in improving the high-temperature performance of aluminium matrix nanocomposite was discussed.

Mechanical Properties and Structure of Fly Ash Modified Basic Oxygen Furnace Slag Based Geopolymer Masonry Blocks

The objective of this research was to investigate the effect of Fly ash as a source of Si and Na on the mechanical performance of the Basic Oxygen Furnace Slag based (BOFS) geopolymer. BOFS has the lowest SiO2, Al2 O3, Na2 O content compared to other aluminosilicate sources (fly ash, metakaolin, granulated blast furnace slag and mine tailings); which have been used to effectively in geopolymer synthesis. SiO2 and Al2 O3, contents of BOFS are respectively 5-7 times and 6-8 times lower than those of fly ash, metakaolin and granulated furnace slag (GBFS). This study evaluated the potential use of fly ash as a source of Si and Al to improve the mechanical performance of a BOFS based geopolymer. The influence of varying amount of Coal Fly Ash (FA) (10–50%) on UCS was studied. The effects of several factors on the UCS of BOFS geopolymer were also investigated. The test variables were molarities of sodium hydroxide (NaOH) (5 M, 10 M and 15 M); the solid to liquid ratio (20 %, 25 % and 30 %); and the curing temperature (20°C, 40°C, 80°C and 100°C). It was established that most favorable conditions for the geopolymer synthesis were FA was 10% of the mixture, 5M NaOH and 80°C curing temperature. Attempts has been made to relate the microstructure of BOFS/FA based composite with properties of geopolymer. Aggregation was identified as the main particulate process as established by the evolution of the particle size distribution (PSD) and its derived moments during the geopolymerisation process. The morphology of the particles appeared flaky and fluffy. The developed composite met the minimum requirement of ASTM C34-13 for a structural clay load bearing non exposed masonry and load bearing exposed side construction masonry.

The high energy density and efficiency of PVDF-based composites with double-shell Nd-BaTiO3 particles as fillers

Flexible dielectric capacitors are becoming shining stars in modern electronic devices. Ceramic particles with large dielectric constants and benign compatibility are attractive candidates to enhance the energy storage density of pristine polymer capacitors while guaranteeing their flexibility. In this work, double-shell structure of Al2O3 (AO) and dopamine (PDA) were successively coated on the Nd-doped BaTiO3 (NBT) particles and then introduced into the Poly(vinylidene fluoride) (PVDF) matrix. Obvious enhancement in dielectric constants was observed while the dielectric loss remained nearly constant. For the composite films with 1–4[Formula: see text]vol.% NBT@AO@PDA NPs, the maximum energy density of 9.1[Formula: see text]J/cm3 and energy efficiency of 65% was achieved at 430[Formula: see text]MV/m in the sample with 1[Formula: see text]vol.% filling ratio, which are 1.4 and 1.3 times larger than those of pristine PVDF at 450[Formula: see text]MV/m. The finite element simulation reveals the effective relief of the electric field concentration in the composite film induced by the AO and PDA layers. The greater improvement in the energy storage performance could be anticipated if the dispersity of NBT@AO@PDA NPs was further improved.

Zeta potential of inorganic fine particle-Na-bentonite binder mixture systems.

The zeta potential of single and multi-inorganic fine particle mixtures (hematite and gangues, i.e., SiO2 + Al2 O3 ) with Na-bentonite was investigated to understand and properly control the mineral surface properties relevant to pelletization of low-grade fine iron ores. The zeta potential of hematite-bentonite mixture showed more negative charge up to 1wt.% bentonite dosage and became constant. In the multiparticle mixture systems with bentonite, the SiO2 amount in the system controlled the changes in zeta potential due to its high negative charge (-54.9mV at natural pH) and the bentonite attachment on its surface based on the electrostatic interaction while Al2 O3 had no effect due to its negligible surface charge (-1.6mV at natural pH). This article reports the new insight into the characterization of surface chemistry of inorganic/mineral mixture systems to understand their surface charge properties in relation to fine mineral particle processing, and to show a direction toward the elucidation of particle dispersion/aggregation mechanism in complex ore systems aiming for their beneficiations.

Al2 O3 -Assisted Confinement Synthesis of Oxide/Carbon Hollow Composite Nanofibers and Application in Metal-Ion Capacitors.

Hollow micro-/nanostructures are widely explored for energy applications due to their unique structural advantages. The synthesis of hollow structures generally involves a "top-down" casting process based on hard or soft templates. Herein, a new and generic confinement strategy is developed to fabricate composite hollow fibers. A thin and homogeneous atomic-layer-deposition (ALD) Al2 O3 layer is employed to confine the pyrolysis of precursor fibers, which transform into metal (or metal oxide)-carbon composite hollow fibers after removal of Al2 O3 . Because of the uniform coating by ALD, the resultant composite hollow fibers exhibit a hollow interior from heads to ends even if they are millimeter long. V, Fe, Co, and Ni-based hollow nanofibers, demonstrating the versatility of this synthesis method, are successfully synthesized. Because of the carbon constituent, these composite fibers are particularly useful for energy applications. Herein, the as-obtained hollow V2 O3 -C fiber membrane is employed as a freestanding and flexible electrode for lithium-ion capacitor. The device shows an impressive energy density and a high power density.

Seawater reverse osmosis membrane fouling causes in a full scale desalination plant; through the analysis of environmental issues: raw water quality

Background: Membrane clogging is one of the most important problem for desalination plant operators in Iran, therefore, this study was conducted to investigate the main causes of this problem using field analysis. Methods: In this study, six continuous membranes in a reverse osmosis (RO) pressure vessel under the 33-month service period (April 2017 to November 2019) were selected. The membranes were analyzed through visual evaluation of the outer and inner membrane surface, analyzing the damages and physical harms, oxidative stress tests, iron spot test, fouling chemical analysis using loss on ignition (LOI) tests, X-ray fluorescence (XRF), and Fourier-transform infrared (FTIR) spectroscopy. Results: Particle size distribution in raw seawater (EC = 55 000 µs/cm, turbidity = 11 NTU) was 66.4% smaller than 1 µ and 28.3% between 1 to 1.9 µm. Physical damages were not seen on the membranes but telescopic damages were observed which was due to membrane fouling. Removal efficiencies of turbidity and silt density index (SDI) were 84% and 18%, respectively. Membrane oxidation was also seen. Most of the sediments compositions on the membranes were SiO2 , Al2 O3 , MgO, and Fe2 O3 . Biological fouling was detected on the membranes surface. Conclusion: Inaccurate use of chlorine neutralizer caused the residual chlorine to be present in the membrane entering water, which damaged the membrane. Accumulation of clogging agents on membrane surface showed malfunction of pretreatment function, therefore, revision of design and operation of units is necessary. Biological fouling is due to non-effective pre-chlorination of drinking water. Metallic compounds sedimentation on the membrane is due to improper use of anti-fouling chemicals. High SDI in the influent shows the need to change the cartridge filters.

Structural evolution and high-temperature tribological properties of AlCrON coatings deposited by multi-arc ion plating

AlCrON coatings were deposited on plasma nitrided steel substrates by multi-arc ion plating under different oxygen flow rates. The surface morphology, structure, composition, mechanical properties, and tribological behavior were investigated systematically. The coating surface roughness increases with increasing oxygen flow rate. The structural analysis show as-deposited coatings exhibit B1 NaCl like solid solution phases, transformed from fcc-(Cr, Al)N to fcc-(Cr, Al)ON followed by fcc-(Cr, Al)2O3 phase structure for coating deposited at the oxygen flow rate of 300 sccm. The hardness and elastic modulus of the coating decrease with increasing oxygen content due to phase transformation. The minimum friction coefficient of 0.52 and the lowest wear rate of 1.57 × 10−16 m3/(N∙m) at 600 °C are obtained for the coating deposited at 150 sccm, which is attributed to the excellent adhesion and thermal stability.

A Garnet-Type Solid-Electrolyte-Based Molten Lithium-Molybdenum-Iron(II) Chloride Battery with Advanced Reaction Mechanism.

Solid-electrolyte-based molten-metal batteries have attracted considerable attention for grid-scale energy storage. Although ZEBRA batteries are considered one of the promising candidates, they still have the potential concern of metal particle growth and ion exchange with the β"-Al2 O3 electrolyte. Herein, a Li6.4 La3 Zr1.4 Ta0.6 O12 solid-electrolyte-based molten lithium-molybdenum-iron(II) chloride battery (denoted as Li-Mo-FeCl2 ) operated at temperature of 250 °C, comprising a mixture of Fe and LiCl cathode materials, a Li anode, a garnet-type Li-ion ceramic electrolyte, and Mo additive, is designed to overcome these obstacles. Different from conventional battery reaction mechanisms, this battery revolutionarily synchronizes the reversible Fe-Mo alloying-dealloying reactions with the delithiation-lithiation processes, meaning that the porous Mo framework derived from Fe-Mo alloy simultaneously suppresses the growth of pure Fe particles. By adopting a Li anode and a Li-ion ceramic electrolyte, the corrosion problem between the cathode and the solid electrolyte is overcome. With similar battery cost ($12 kWh-1 ), the theoretical energy density of Li-Mo-FeCl2 battery surpasses that of a Na-FeCl2 ZEBRA battery over 25%, to 576 Wh kg-1 and 2216 Wh L-1 , respectively. Experimental results further prove this cell has excellent cycling performance (472 mAh gLiCl -1 after 300 cycles, 50 mg active material) and strong tolerance against the overcharge-overdischarge (3-1.6 V) and freezing-thawing (25-250 °C) incidents.

Supported Cobalt Catalysts for Acceptorless Alcohol Dehydrogenation.

The acceptor-less dehydrogenation of 2-octanol was tested over cobalt supported on Al2 O3 , C, ZnO, ZrO2 and various TiO2 substrates. The catalysts were characterized by ICP, XRD and TGA-H2 . For Co/TiO2 P25, the effects of passivation, aging (storage at room temperature), and in situ activation under H2 were investigated. The catalysts must be tested shortly after synthesis in order to prevent deactivation. Cobalt supported on TiO2 P25 was the most active and 69 % yield of 2-octanone was obtained, using decane as a solvent. Selectivities for 2-octanone were observed in the range of 90 % to 99.9 %. Small amounts of C16 compounds were also formed due to aldol condensation/dehydration reactions. The catalysts exhibited higher conversion in the dehydrogenation of secondary alcohols (65-69 %), in comparison to primary alcohols (2-10 %). The dehydrogenation of 1,2-octanediol led to 1-hydroxy-2-octanone, with a selectivity of 90 % and 69 % for Co/TiO2 P25 and Co/TiO2 P90, respectively.

A Bottom-Up Strategy for the Synthesis of Highly Siliceous Faujasite-Type Zeolite.

High-silica zeolite Y is a desired catalytic material for oil refining and the petrochemical industry. However, its direct synthesis remains a symbolic challenge in the field of zeolite synthesis, with a limited improvement of the framework SiO2 /Al2 O3 ratio (SAR) from ≈5 to 9 over the past 60 years. Here, the synthesis of highly siliceous zeolite Y with tunable SAR up to 15.6 through a cooperative strategy is reported, which involves the use of FAU nuclei, a bulky organic structure-directing agent (OSDA), and a gel system with low alkalinity (named NOA-co strategy). A series of quaternary alkylammonium ions is discovered as effective OSDAs based on the NOA-co strategy, and the relevant crystallization mechanism is elucidated. Moreover, the high-silica products are demonstrated to have greatly improved (hydro)thermal stability, high concentration of strong acid sites, and uniform acid distribution, which lead to superior catalytic performance in the cracking of bulky hydrocarbons. It is anticipated that this synthetic strategy will benefit the synthesis and development of zeolitic catalysts in a wide range of reaction processes.

High-Loading Single-Atom Copper Catalyst Supported on Coordinatively Unsaturated Al2 O3 for Selective Synthesis of Homoallylboronates.

Single-atom catalysts (SACs) as a bridge between hetero- and homogeneous catalysis have attracted much attention. However, it is still challenging to generate stable single atoms with high metal loadings, and the application of SACs in traditionally homogeneous catalytic reactions is highly desirable. Herein, a Cu SAC with a high Cu loading of 8.7 wt % supported on coordinatively unsaturated Al2 O3 was prepared and used in the amine-free synthesis of homoallylboranes. Up to 99 % conversion, 95 % 1,4-selective boration of the enals, and 48-68 % isolated yields of homoallylboranes were achieved, equaling the results of reported homogenous catalysts, and the system was more efficient and stable than nano Cu/γ-Al2 O3 . Mechanistic investigation indicated that Cu-Bpin species are the active intermediates of selective boration. The superior catalytic and recycling performance of Cu SAC paves an efficient and green path toward selective synthesis of homoallyborane fine chemicals.

Origin of the Threshold Voltage Shift in a Transistor with a 2D Electron Gas Channel at the Al2O3/SrTiO3 Interface

AbstractA transistor is fabricated with a 2D electron gas (2DEG) channel at the Al2O3 (AO)/SrTiO3 (STO) interface. The threshold voltage (Vth) shift of the 2DEG channel in the Pt/AO/2DEG/STO stack induced by negative bias stress is investigated. Two‐terminal current–voltage and capacitance–voltage characterization through the gate and the source reveals that the metallic 2DEG channel turns into a semiconducting channel when the negative bias stress is applied. Transfer curve measurement with various stress conditions on the 2DEG field‐effect transistor is performed to evaluate the effect of the negative bias stress. The Vth becomes positive, and the channel conductance decreases after the application of negative bias stress. These variations are promoted by large stress bias and temperature. Electron energy loss spectroscopy analysis via scanning transmission electron microscopy reveals that the chemical state of the interface changes from oxygen‐deficient to stoichiometric. Therefore, the change in the channel state from metallic to semiconducting originates from the decrease of oxygen vacancy concentration at the interface.

Memristive Behavior Enabled by Amorphous-Crystalline 2D Oxide Heterostructure.

The emergence of memristive behavior in amorphous-crystalline 2D oxide heterostructures, which are synthesized by atomic layer deposition (ALD) of a few-nanometer amorphous Al2 O3 layers onto atomically thin single-crystalline ZnO nanosheets, is demonstrated. The conduction mechanism is identified based on classic oxygen vacancy conductive channels. ZnO nanosheets provide a 2D host for oxygen vacancies, while the amorphous Al2 O3 facilitates the generation and stabilization of the oxygen vacancies. The conduction mechanism in the high-resistance state follows Poole-Frenkel emission, and in the the low-resistance state is fitted by the Mott-Gurney law. From the slope of the fitting curve, the mobility in the low-resistance state is estimated to be ≈2400 cm2 V-1 s-1 , which is the highest value reported in semiconductor oxides. When annealed at high temperature to eliminate oxygen vacancies, Al is doped into the ZnO nanosheet, and the memristive behavior disappears, further confirming the oxygen vacancies as being responsible for the memristive behavior. The 2D heterointerface offers opportunities for new design of high-performance memristor devices.

CATALYTIC TECHNOLOGIES FOR INCREASING QUALITY OF MOTOR FUELS

The aim of the work was to study the process of hydrodearomatization and alkylation of gasoline fractions under increased hydrogen pressure. It has been used Rh-Pt (9:1)/Al2 O3 catalyst in the work. It has been studied the hydrogenation of three gasoline fractions of «Atyrau Oil Refinery» LLP and Pavlodar Petrochemical Plant LLP. Technological parameters of the process of hydrodearomatization for the production of environmentally friendly fuels, containing no benzene and low in aromatic hydrocarbons have been worked out (pressure, temperature). Data on group composition of organic substances in gasolines demonstrate that after catalytic hydrogenation benzene in final samples of two fractions is absent. For hydrogenizate, the aromatic content decreased from 11.12 weight % to 2.20 weight %. For stable catalysate, the amount of aromatics decreased from 51.5 weight % to 10.96 weight %. Catalytic systems based on zeolites ZSM5 and Y modified with Mg, La, and Ce were tested during the alkylation of 2 gasoline fractions of Atyrau Oil Refinery LLP. It was established that benzene fractions was removed by 30–37% from gasoline and the content of aromatic hydrocarbons, toluene and cumene decreased by 6–10%.The catalysts were studied by BET, porometry and EM methods, which established a uniform formation of nanoscale particles on the catalyst surface.

ASSESSMENT OF VARIOUS SURFACE TREATMENTS ON PULL OFF OF POLYETHERETHERKETONE ANTERIOR CROWN

ABSTRACT Objectives: to assess the pull off of Polyetheretherketone (PEEK) anterior crown after various surface treatments. Materials& Methods: Twenty Polyetheretherketone (PEEK) full coverage crown were constructed on prepared human maxillary central incisors. All of the crowns (n=20) were divided into four groups according to the surface treatment used group I ) Control , 2) 98% Sulphric acid, 3) 9.5% Hydrofluoric acid (HF ) 4) Air Abrasion with 50 μm AL2 O3 .( n=5 in each ) Afterwards, each crown specimens were cementeded to corresponding abutments using self-adhesive resin cement RelyX U200. Then, subjected to thermo cycling (5°C - 55°C,5000 cycles,). A universal testing machine was used to assess pull-off test. Data were collected, tabulated and statistically evaluated. Results: The mean pull off values were ranked as follows: group II (253.81±7.67 N) > group IV (221.18±3.91N) ≥ group III (203.20±8.23N) > group I (135.91±9.92N). The highest and lowest Pull off values was obtained in group II (253.81±7.67 N) and group I (135.91±9.92N), respectively. Conclusions: 98% sulphric acid PEEK surface treatment is recommended to achieve high retentive strength.

Demantoid from the Telyansky Klyuch deposit (Middle Urals) – is the place of the first discovery in the Urals

The relevance of the work is due to the need to study the Ural gems, including those discovered in the Urals. This is important not only from a scientific point of view, but for the history of science and the development of geological tourism in our region as well. Purpose of the work: study of the chemical composition of demantoid from the Telyansky Klyuch deposit, which is the site of the first find of this gem in the Urals. Research methodology. Demantoid (green jewelry andradite) was washed by the author in the Telyansky Klyuch gold placer; the quantitative analysis of the chemical composition of garnet was performed using the JXA-733 X-ray electron probe microanalyzer. Results. A historical study of the sites of finds of demantoids in the Middle Urals was carried out. It was established that precious garnet was found not in placers of the Bobrovka river located south of Nizhny Tagil, but in the gold placer of the Telyansky Klyuch to the north of Nizhny Tagil. Microprobe analysis of individual demantoid crystals showed that garnets with different green color saturation according to the main components are andradites with average contents: CaO – 33,18%; Fe2 O3 – 30,74%; SiO2 – 35,02% (for 6 analyzes). The feature of the chemical composition of Telyansky demantoids is the absence or insignificant amount of aluminum impurity in them – not more than 0.02% Al2 O3 , which is practically at the level of microprobe analysis sensitivity for this element. The amount of chromium varies from 0.02% Cr2 O3 in a light green demantoid to 0.5–0.74% Cr2 O3 in green and bright green andradites. Conclusions. The place of the first find of low-impurity and chromium-containing andradites in the Urals with the name of “diamantoite” (proposed by N. G. Nordenskiöld ) is the Telyansky Klyuch gold deposit on the East Tagil dunite-harzburgite massif in the Middle Urals

Heat Transfer Enhancement of Car Radiator Using Al₂ O₃ / Water Nanofluid in the Presence of Electric Field; an Experimental Study

In this experimental study, Aluminums Oxide (Al2O3) in Pure Water (PW) as nanofluid was used for heat transfer enhancement in car radiator together with electric field. Electric field with different voltage 8, 11, 14 kV and nanofluids with volume concentrations of 0.08%, 0.5% and 1% were investigated. From the experiments, it was found that the unit with electric field pronounced better heat transfer rate, especially at low fan speed. In addition heat transfer coefficient and heat transfer rate in engine cooling system increased with the usage of nanofluids Al2O3/PW compared to Pure Water alone. With the use of nanofluid with concentration of 1% and electric field for fan speed 600 and 1200 rpm, thermal performance factors were in a range between, 1.8–3.2 and 1.6–1.74, respectively. Thermal performance factor is more than 1 in all of cases, and it can be concluded that this technique can be used in car radiators to improve heat transfer.