Preparation and application of an ultraviolet curable coating containing nanoscale α‐aluminum oxide

This study focuses on the preparation of an organic–inorganic ultraviolet (UV) curable coating containing the nanoscale α‐aluminum oxide (α‐Al₂O₃) powder and UV curable resin. This developed coating can form a protection film on the poly(vinyl chloride) (PVC) plastic tile surface. Thus, the abrasion resistance of the PVC plastic tile surface is improved. Besides, the adhesion between this UV cured film and the PVC plastic tile surface is well. After treatment with the UV curable coating that contains 6 wt % α‐Al₂O₃, the abrasion resistance of the PVC plastic tile surface can be improved up to 57%. From the result of a scanning electron microscopy (SEM) mapping photograph, it shows that the nanoscale α‐Al₂O₃ powder is well dispersed in the cured coating film. Under the wavelength of the visible light in the range of 400–800 nm, the degree of transparency for the coated film on poly(ethylene terephthalate) (PET) sheet is about 82–90%. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5747–5752, 2006     

Thermal Reaction of Cristobalite in Nano‐SiO2/α‐Al2O3 Powder Systems for Mullite Synthesis

Nanoscaled cristobalite and α‐Al₂O₃ powders were used as the starting materials for synthesizing mullite by solid‐state reaction. The thermal reaction of the cristobalite with α‐Al₂O₃ during the thermal treatment was examined. Cristobalite powder with a D₅₀ value of 430 nm was adopted to mix with α‐Al₂O₃ powders with a D₅₀ values of 230, 310, and 400 nm in a stoichiometric composition of 3Al₂O₃?2SiO₂ (71.8 wt% α‐Al₂O₃ and 28.2 wt% SiO₂). Samples for thermal reaction were prepared using uniaxial pressed from the three mixtures that showed various particle number ratios of SiO₂/Al₂O₃ due to the different particle sizes of α‐Al₂O_3. Examinations were performed by differential thermal analysis, X‐ray diffraction, scanning electron microscopy, energy‐dispersive X‐ray spectroscopy, and transmission electron microscopy techniques. The results showed that cristobalite particles amorphized during the thermal treatment, and then reacted with the α‐Al₂O₃ particle to form mullite via nucleation and growth. The amorphization temperature can be reduced by using finer‐sized α‐Al₂O₃ powders, thus leading to a lower temperature for mullite formation. Mullite crystals with a multidomain structure were observed in the α‐Al₂O₃ particle matrixes. The crystal orientation of the mullite was controlled by the α‐Al₂O₃ matrix, that is, [001] α‐Al₂O₃ → [001] mullite. These results indicate that the amorphization of cristobalite may trigger the reaction of SiO₂ with α‐Al₂O₃, initiating the nucleation of mullite. The α‐Al₂O₃ particles act as the hosts for mullite formation and determine the size of the mullite particles.     

Disperse Equiaxed α‐Al2O3 Nanoparticles Without Vermicular Microstructure

Nanocrystalline microstructure is regarded as a strategic approach to overcome the brittleness of alumina ceramics, and the preparation of disperse equiaxed α‐Al₂O₃ nanoparticles is an essential step for the preparation of nanocrystalline alumina ceramics. In this work, disperse equiaxed α‐Al₂O₃ nanoparticles were prepared using α‐Fe₂O₃ as seed and isolation phase. At first, the composite of α‐Al₂O₃ nanoparticles embedded in α‐Fe₂O₃ matrix was obtained by calcining the precursor powder containing γ‐AlOOH and Fe(OH)₃ (Fe³⁺/Al³⁺ mole ratio of 5) at 770°C for 2 h. Then disperse equiaxed α‐Al₂O₃ nanoparticles with a mean size of 12 nm and a size distribution from 2 to 40 nm without vermicular microstructure were obtained by removal of α‐Fe₂O₃ and other impurities in the composite through acid corrosion.     

Selective Corrosion Preparation and Sintering of Disperse α‐Al2O3 Nanoparticles

Disperse fine equiaxed α‐Al₂O₃ nanoparticles with a mean particle size of 9 nm and a narrow size distribution of 2–27 nm were synthesized using α‐Fe₂O₃ as seeds and isolation via homogeneous precipitation‐calcination‐selective corrosion processing. The presence of α‐Fe₂O₃ acting as seeds and isolation phase can reduce the formation temperature to 700°C and prevent agglomeration and growth of α‐Al₂O₃ nanoparticles, resulting in disperse fine equiaxed α‐Al₂O₃ nanoparticles. These α‐Al₂O₃ nanoparticles were pressed into green compacts at 500 MPa and sintered first by normal sintering to study their sintering behavior and finally by two‐step sintering (heated to 1175°C without hold and decreased to 1025°C with a 20 h hold in air) to obtain nanocrystalline α‐Al₂O₃ ceramics. The two‐step sintered bodies are nanocrystalline α‐Al₂O₃ with an average grain size of 55 nm and a relative density of 99.6%. The almost fully dense nanocrystalline α‐Al₂O₃ ceramic with finest grains achieved so far by pressureless sintering reveals that these α‐Al₂O₃ nanoparticles have an excellent sintering activity.     

Surface‐Functionalized White Sapphire α‐Al2O3 Platelets as Nanofillers for Vinylester Composites and Heavy Duty Anchoring Systems

Synthetic α‐Al₂O₃ platelets, also referred to as corundum and white sapphire, represent attractive fillers improving the mechanical properties of vinylester‐based chemical anchoring systems. Even in the absence of coupling agents, as verified by scanning electron microscopic (SEM) analyses of fracture surfaces, α‐Al₂O₃ platelets of 200 nm thickness and 5–10 µm size are uniformly dispersed in vinylester resins which are cured by free radical polymerization at room temperature. With increasing content of ultrahard α‐Al₂O₃ platelets (0–40 wt%) the Young's modulus of α‐Al₂O₃ platelet/vinylester composites increases from 3200 to 9000 MPa. However, 1–5 wt% 3‐methacryloyloxypropyl‐trimethoxysilane (MPS) as coupling agent, added to the vinylester resin or preferably used to functionalize α‐Al₂O₃ surfaces in a filler pretreatment step, improves elongation at break (+50%) without sacrificing high stiffness and strength. The X‐ray photoelectron spectroscopy (XPS) analysis confirms the successful surface‐functionalization of α‐Al₂O₃ platelets by using pretreatments with MPS in toluene, acidified ethanol/water or tetrahydrofuran, respectively. The MPS filler pretreatment simultaneously enhances tensile strength (+22%), elongation at break (+50%), and Young's modulus (+12%) as compared to composites containing unmodified filler. According to SEM analyses of composite fracture surfaces, MPS‐mediated functionalization affords significantly improved interfacial adhesion between α‐Al₂O₃ platelets and the polymer matrix.

     

Acrylonitrile‐butadiene‐styrene nanocomposites filled with nanosized alumina

A polymer nanocomposite was produced by acrylonitrile‐butadiene‐styrene (ABS) and α‐alumina was prepared through sol‐gel process using aluminum nitrate and citric acid. The particle size was analyzed by X‐ray diffraction and scanning electron microscopy (SEM) studies. The nanocomposites were characterized through tensile strength, Young's modulus, strain% at break, flexural strength, flexural modulus, and impact strength. The ABS/Al₂O₃ nanocomposites are found to have slightly higher Young's modulus, but lower tensile strength, strain% at break, flexural and impact strength than the virgin ABS. But its flexural modulus increases with increasing Al₂O₃ content in ABS matrix. The d‐spacing was calculated in nanocomposites to evaluate the interaction between Al₂O₃ and ABS. The particle distributions in nanocomposites were studied by SEM. The fractured surfaces of tensile test samples were also examined through SEM and show that the ductile fracture of ABS is converted to brittle fracture with addition of Al₂O₃. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers     

Low Temperature Synthesis of Needle‐like α‐FeOOH and Their Conversion into α‐Fe2O3 Nanorods for Humidity Sensing Application

In this study, we report template and surfactant‐free, low temperature (70°C) synthesis of needle‐like α‐FeOOH and its conversion at 400°C into α‐Fe₂O₃ nanorods using Fe(+2) and Fe(+3) chlorides and urea as a hydrolysis‐controlling agent. The isolated needle‐like α‐FeOOH indicates asparagus‐type growth pattern having length ca. 600 nm with 80 nm diameter at base and apex diameter of around 10 nm. The sample on heating (α‐Fe₂O₃) shows nanorod‐like morphology. The samples were characterized using various physicochemical characterization techniques such as XRD, Raman spectroscopy, UV‐Vis spectroscopy, particle size distribution analysis, Field Emission Scanning Electron Microscopy (FE‐SEM), and humidity sensing performance. The humidity sensing behavior of both α‐FeOOH and α‐Fe₂O₃ was studied. The α‐FeOOH shows quicker (10 s) and higher response toward change in humidity from 20%RH to 90%RH as compared with α‐Fe₂O₃ (60 s). Their typical morphology and crystalline structure plays an important role in humidity sensing behavior.     

α‐Al2O3 improves the properties of gel polyacrylonitrile nanocomposite electrolytes used as electrolyte materials in rechargeable lithium batteries

In this investigation, a series of gel polyacrylonitrile (PAN)/α‐Al₂O₃ nanocomposite electrolyte materials that incorporate various fractions of PAN, α‐Al₂O₃ inorganic powders, propylene carbonate and ethylene carbonate as cosolvents, and LiClO₄ were prepared. X‐ray diffraction revealed that the gel nanocomposite electrolyte materials contained amorphous PAN in which was uniformly dispersed α‐Al₂O₃. The gel PAN/α‐Al₂O₃ nanocomposite electrolytes had lower glass‐transition temperatures (as determined by dynamic mechanical analysis) and higher conductivity than a similar electrolyte prepared in the absence of α‐Al₂O₃. The conductivity of the PAN/α‐Al₂O₃ nanocomposite films was inversely proportional to the size of the α‐Al₂O₃ particles and directly proportional to (I) the amount of α‐Al₂O₃ (up to 7 wt %), (II) the F value [LiClO₄/CH₂CH(CN) ratio], and (III) the amount of plasticizer (propylene carbonate/ethylene carbonate = 1 : 1). Cyclic voltammetry revealed that adding α‐Al₂O₃ significantly increased the electrochemical stability of the composite electrolyte system. A rechargeable lithium battery prepared using this gel nanocomposite electrolyte system exhibited good cyclability and a stable capacity. The coulombic efficiency for the recharge/discharge process was approximately 75%, even after 100 cycles. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Statistical Optimization of the Biodiesel Production Process Using a Magnetic Core‐Mesoporous Shell KOH/Fe3O4@γ‐Al2O3 Nanocatalyst

A magnetic core‐mesoporous shell KOH/Fe₃O₄@γ‐Al₂O₃ nanocatalyst was synthesized using the Fe₃O₄@γ‐Al₂O₃ core‐shell structure as support and KOH as active component. The prepared samples were characterized by X‐ray diffraction (XRD), field‐emission scanning electron microscopy (FE‐SEM), energy‐dispersive X‐ray spectroscopy (EDS), Fourier transform infrared (FTIR), Brunauer‐Emmett‐Teller (BET), and vibrating sample magnetometry (VSM) techniques. Transesterification of canola oil to methyl esters (biodiesel) in the presence of the magnetic core‐mesoporous shell KOH/Fe₃O₄@γ‐Al₂O₃ nanocatalyst was investigated. Response surface methodology (RSM) based on the Box‐Behnken design (BBD) was employed to optimize the influence of important operating variables on the yield of biodiesel. A biodiesel yield of 97.4 % was achieved under optimum reaction conditions. There was an excellent agreement between experimental and predicted results.     

Simultaneously enhanced mechanical properties and thermal properties of ultrahigh‐molecular‐weight polyethylene with polydopamine‐coated α‐alumina platelets

Polydopamine (PDA) was employed to modify micrometric Al₂O₃ platelets to improve the interfacial compatibility between α‐Al₂O₃ powder and ultrahigh‐molecular‐weight polyethylene (UHMWPE). The structure of PDA‐coated Al₂O₃ and UHMWPE composites was investigated via Fourier transform infrared spectroscopy, scanning electron microscopy and X‐ray photoelectron spectroscopy. The thermal stability and mechanical performance of the samples were also evaluated. It is clear that UHMWPE/PDA‐Al₂O₃ composites exhibit better mechanical properties, higher thermal stability and higher thermal conductivity than UHMWPE/Al₂O₃ composites, owing to the good dispersion of Al₂O₃ powder in the UHMWPE matrix and the strong interfacial force between the macromolecules and the inorganic filler caused by the presence of PDA. The tensile strength and the tensile elongation at break of UHMWPE/PDA‐Al₂O₃ composite with 1 wt% PDA‐Al₂O₃ are 62.508 MPa and 462%, which are 1.96 and 1.98 times higher than those of pure UHMWPE, respectively. The thermal conductivity of UHMWPE/PDA‐Al₂O₃ composite increases from 0.38 to 0.52 W m^?1 K^?1 with an increase in the dosage of PDA‐Al₂O₃ to 20 wt%. The results show that the prepared PDA‐coated Al₂O₃ powder can simultaneously enhance the mechanical properties and thermal conductivity of UHMWPE. © 2018 Society of Chemical Industry     

Examination of the Dye‐Fixing Ability of Porous χ‐Alumina Flake Powders

Porous χ‐Al₂O₃ is a new material for fabricating coated inkjet printing paper. Paper coated with χ‐Al₂O₃ powders has excellent water fastness. This study investigated the dye‐fixing ability of χ‐Al₂O₃ powders through measurements of adsorption isotherms. The variations in zeta potential, pore volume, pore size distribution, and specific surface area of χ‐Al₂O₃ powders during the dye‐fixing process were also examined. The results show that χ‐Al₂O₃ powders have a strong affinity to dye colorants. The adsorption isotherm is classified as HA‐type and the adsorption data fit the Langmuir model. In addition to the positive‐charged surface of χ‐Al₂O₃ provides cationic sites for fixing dye colorants via electrostatic interaction, the porous structure on the surface of χ‐Al₂O₃ particles plays an indispensable role in trapping the colorant.     

Physical properties and enzymatic hydrolysis of poly(L‐lactide)–TiO2 composites

Amorphous poly(L ‐lactide) (PLLA) composite films with titanium dioxide (TiO₂) particles were prepared by solution‐casting using methylene chloride as a solvent, followed by quenching from the melt. The effects of surface treatment, volume fraction, size, and crystalline type of the TiO₂ particles on the mechanical properties and enzymatic hydrolysis of the composite films were investigated. The tensile strength of the PLLA composite films containing TiO₂ particles except for anatase‐type ones with a mean particle size of 0.3–0.5 μm was lowered and the Young's modulus became higher with increasing the content of TiO₂ particles. The tensile strength of the composite films containing anatase‐type TiO₂ with a mean particle size of 0.3–0.5 μm at contents of 20 wt % or less was almost the same as that of the pure PLLA film. The enzymatic hydrolysis of PLLA matrix was accelerated by the addition of the hydrophilic anatase‐type TiO₂ particles (nontreated or Al₂O₃ treated) with a mean particle size of 0.3–0.5 μm at relatively high contents such as 20 wt %. On the other hand, the enzymatic hydrolysis of PLLA matrix was inhibited by composite formation with the hydrophobic rutile‐type TiO₂ particles (Al₂O₃‐stearic acid treated, or ZrO₂‐Al₂O₃‐stearic acid treated). These results suggest that the mechanical properties and enzymatic hydrolyzability of the PLLA can be controlled by the kind and amount of the added TiO₂ particles. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 190–199, 2005     

Oxidation Resistance of AlPO4 Bonded Ceramic Coating Formed on Titanium Alloy for High‐Temperature Applications

AlPO₄ based coatings were prepared on Ti‐6Al‐2Zr‐1Mo‐1V titanium alloy using aluminum phosphate as a binder and Al₂O₃/Cr₂O₃ based mixing particles as the fillers. The microstructure, phase and chemical composition of the coatings were analyzed by SEM, XRD and EDS techniques. The high temperature infrared emissivity values of coated and uncoated titanium samples were tested. The results show that the coating had a higher infrared emissivity value (>0.8) than titanium substrate (0.15–0.3) in the wide wavelength range of 5–20 mm, which is attributed to the uniform dispersion of high emissivity Al₂O₃ and Cr₂O₃ particles in the AlPO₄ binder matrix. The coated titanium samples exhibited excellent oxidation resistance performance with significantly decreased oxidation rates at 600 and 800°C. The mass gain of the coated sample kept at a low and stable constant of 0.15 mg/cm², significantly lower than that of titanium substrate (0.54 mg/cm²) when oxidized at 600°C up to 100 h.     

Nano‐engineered nickel catalysts supported on 4‐channel α‐Al2O3 hollow fibers for dry reforming of methane

A nickel (Ni) nanoparticle catalyst, supported on 4‐channel α‐Al₂O₃ hollow fibers, was synthesized by atomic layer deposition (ALD). Highly dispersed Ni nanoparticles were successfully deposited on the outside surfaces and the inside porous structures of hollow fibers. The catalyst was employed to catalyze the dry reforming of methane (DRM) reaction and showed a methane reforming rate of 2040 Lh^?1gNi^?1 at 800°C. NiAl₂O₄ spinel was formed when Ni nanoparticles were deposited on alpha‐alumina substrates by ALD, which enhanced the Ni‐support interaction. Different cycles (two, five, and ten) of Al₂O₃ ALD films were applied on the Ni/hollow fiber catalysts to further improve the interaction between the Ni nanoparticles and the hollow fiber support. Both the catalyst activity and stability were improved with the deposition of Al₂O₃ ALD films. Among the Al₂O₃ ALD coated catalysts, the catalyst with five cycles of Al₂O₃ ALD showed the best performance. © 2018 American Institute of Chemical Engineers AIChE J, 64: 2625–2631, 2018     

Preparation and properties of nano‐Al2O3 particles/polyester/epoxy resin ternary composites

This article presents the results of an experimental study on the preparation and properties of new ternary composites composed of nano‐Al₂O₃ particles, polyester, and epoxy resin. The ternary composites were prepared by the addition of the nano‐Al₂O₃ particles in a binary matrix, with elevated viscosity, of the epoxy resin modified by the polyester. The nano‐Al₂O₃ particles were previously located and dispersed in the polyester phase. The study showed that the ternary system was a type of nanoscale dispersed composite with high strength and toughness as well as modulus, combined with excellent dielectric and heat‐resistance properties. All related properties of the composites were remarkably superior to those of both the binary matrix and the unmodified epoxy resin. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 70–77, 2002     

Development of Al2O3 Film on Diatomite for Treating Wastewater Containing Anionic Polyacrylamide

To efficiently treat anionic polyacrylamide (APAM) with a linear structure in wastewater, an Al₂O₃ film on the surface of diatomite was prepared via the hydrolysis reaction of AlCl₃. The Al₂O₃‐coated diatomite was characterized by FT‐IR, XRD, and SEM. The results show that the Al₂O₃ film can be coated on diatomite. The resulting Al₂O₃‐coated diatomite was utilized to treat wastewater (pH = 7) that contained APAM of 60 mg L^–1 and suspended solids of 90 mg L^–1. Results show that after wastewater was treated using Al₂O₃‐coated diatomite, the content of APAM and suspended solids in the filtrate can meet the standard for wastewater recycling. Therefore, Al₂O₃‐coated diatomite can be used in treating wastewater containing APAM.     

On the Mechanism of Low Temperature Oxidation for Aluminum Particles down to the Nano‐Scale

The oxidation of Al‐particles down to nano‐scale was investigated by TG, SEM and in‐situ X‐ray diffraction. Al particles are usually coated by a 2–4 nm layer of Al₂O₃ which can be derived from the degree of weight increase on complete oxidation by TG‐curves. The low temperature oxidation of Al particles occurs at least in two steps. The first step builds a layer of 6 to 10 nm thickness composed of crystallites of the same size independent on the initial particle size. This reaction is dominated by chemical kinetics and converts a substantial fraction of the particle if the particle sizes decrease below 1 μm, an effect carefully to be taken into account for nano‐particles because of safety reasons. The second step combines diffusion and chemical reaction and proceeds therefore slowly, the slower the bigger the particles are. The kinetic parameters of these two steps can be obtained by a model taking into account both reaction steps, chemical kinetics and diffusion for spherical particles when fitting it to TG‐curves. X‐ray diffraction shows that particles smaller than 1 μm build γ‐ and θ‐Al₂O₃ in the first step with nano‐crystalline structures which are then transformed to α‐Al₂O₃.     

Degradation of Nextel™ 610‐based oxide‐oxide ceramic composites by aluminum oxychloride decomposition products

Nextel? 610 alumina fibers and alumina‐YAG (yttrium‐aluminum garnet) matrices were used to make oxide‐oxide ceramic matrix composites (CMCs) with and without monazite (LaPO₄) fiber‐matrix interfaces. Twelve sequential aluminum oxychloride (AlOCl) infiltrations with 1 hour heat treatments at 1100°C and a final 1 hour heat treatment at 1200°C were used for matrix densification. This matrix processing sequence severely degraded CMC mechanical properties. CMC tensile strengths and interlaminar tensile (ILT) strengths were less than 10 MPa and 1 MPa, respectively. Axial fracture of Nextel? 610 fibers was observed after ILT testing, highlighting the extreme degradation of fiber strength. Extensive characterization was done to attempt to determine the responsible degradation mechanisms. Changes in Nextel? 610 fiber microstructure after CMC processing were characterized by optical microscopy, SEM, and extensively by TEM. In AlOCl degraded fibers, grain boundaries near the fiber surface were wetted with a glass that contained Y₂O₃/SiO₂ or Y₂O₃/La₂O₃/P₂O₅/SiO₂, and near‐surface pores were partially filled with Al₂O₃. This glass must also contain some Al₂O₃ and initially some chlorine. AlOCl decomposition products were predicted using the FactSage^® Thermochemical code, and were characterized by mass spectrometry. Effects of AlOCl precursors on monazite coated and uncoated Nextel? 610 fibers tow and filament strength were evaluated. A mechanism for the severe degradation of the oxide‐oxide CMCs and Nextel? 610 fibers that involves subcritical crack growth promoted by release of chlorine containing species during breakdown of intergranular glasses in an anhydrous environment is proposed.     

Quantitative Determination of ε‐phase in polymorphic HNIW using X‐ray Diffraction Patterns

An X‐ray diffraction method was applied for the quantitative determination of the ε‐Hexanitrohexaazaisowurtzitane (HNIW) in polymorphs of HNIW. The XRD patterns of four polymorphs illustrate the unique nonoverlapping peak at 19.9° which belongs to ε‐HNIW. The intensity ratio of the peak at 19.9° of ε‐HNIW to the peak at 79.6° of α‐Al₂O₃ is proportional to the weight ratio of standard ε‐HNIW to the internal standard of α‐Al₂O₃, which enables the internal standard method. When the particle size of the sample is less than 10 μm, the content of ε‐HNIW ranging from 70 to 100 wt.‐% can be determined with an absolute error below 2.0%.     

Interfacial microstructure evolution of glass‐based coating on IC10 superalloy with a Ni3Al bond‐coat at 1050°C

A glass‐based composite coating incorporating YSZ, corundum, and Ni₃Al was prepared on IC10 superalloy with a sputtering Hf‐modified Ni₃Al bond‐coat. Sealing effect of the glass‐based top‐coat and reactive elemental effect of Hf facilitated the formation of columnar α‐Al₂O₃ at 1050°C. Furthermore, a discontinuous gahnite interlayer formed at the α‐Al₂O₃/top‐coat interface due to interfacial reactions. However, because of the discontinuous microstructure of gahnite, the α‐Al₂O₃ suffered durative attack by the active glass matrix, which caused severe internal oxidation of Hf and Al within the bond‐coat. In addition, the oxygen barrier ability of the top‐coat changed with its microstructure evolution.