AFM and SEM characterization of iron oxide coated ceramic membranes

Alumina–zirconia–titania (AZT) ceramic membranes coated with iron oxide nanoparticles have been shown to improve water quality by significantly reducing the concentration of disinfection by-product precursors, and in the case of membrane filtration combined with ozonation, to reduce ozonation by-products such as aldehydes, ketones and ketoacids. Commercially available ceramic membranes with a nominal molecular weight cut-off of 5 kilodaltons (kD) were coated 20, 30, 40 or 45 times with sol suspension processed Fe₂O₃ nanoparticles having an average diameter of 4–6 nm. These coated membranes were sintered in air at 900 °C for 30 min. The effects of sintering and coating layer thickness on the microstructure of the ceramic membranes were characterized using atomic force microscopy (AFM), scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDS). AFM images show a decreasing roughness after iron oxide coating with an average surface roughness of ∼161 nm for the uncoated and ∼130 nm for the coated membranes. SEM showed that as the coating thickness increased, the microstructure of the coating changed from a fine grained (average grain size of ∼27 nm) morphology at 20 coating layers to a coarse grained (average grain size of ∼66 nm) morphology at 40 coating layers with a corresponding increase in the average pore size from ∼57 nm to ∼120 nm. Optimum water quality was achieved at 40 layers, which corresponds to a surface coating morphology consisting of a uniform, coarse-grained structure with open, nano-sized interconnected pores.     

Sol-gel synthesis of alumina,titania and mixed alumina/titania in the ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulphonyl) amide

In this paper we report on the synthesis of alumina, titania and mixed alumina–titania in the ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulphonyl) amide [Py_1,4]TFSA via sol-gel methods using aluminium isopropoxide and titanium isopropoxide as precursors. Our results show that the as-synthesized alumina is mainly mesoporous boehmite with an average pore diameter of 3.8 nm. The obtained boehmite is subject to a phase transformation into γ-Al₂O₃ and δ-Al₂O₃ after calcinations at 800 and 1,000 °C, respectively. The as-synthesized TiO₂ shows amorphous behaviour and calcination at 400 °C yields anatase which undergoes a further transformation to rutile at 800 °C. The as-prepared alumina–titania powders are amorphous and transformed to rutile and α-Al₂O₃ after calcination at 1,000 °C TiO₂. The obtained alumina–titania has a higher surface area than those of alumina or titania. The surface area of the as-synthesized alumina–titania was found to exceed 486 m² g⁻¹, whereas the surface areas of the as-synthesized boehmite and titania were around 100 m² g⁻¹, respectively.     

A sol–gel-derived α-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> crystal interlayer modified 316L porous stainless steel to support TiO<Subscript>2</Subscript>, SiO<Subscript>2</Subscript>, and TiO<Subscript>2</Subscript>–SiO<Subscript>2</Subscript> hybrid membranes

A homogeneous α-Al₂O₃ crystal membrane was fabricated by the sol–gel technique on 316L porous stainless steel (PSS) substrate with an average pore size of 1.0 μm. The preparation process was optimized by carefully choosing the binder, the concentrations of the casting solutions and the sintering temperatures of the membranes. Compared to methylcellulose and polyethylene glycol 20000, polyvinyl alcohol 1750 was found to be the most effective binder to fabricate a homogeneously structured Al₂O₃ membrane without defects. The concentration to prepare an uniform coverage membrane with a thickness of ~10 μm was 0.032 mol/L. When sintered at 1000 °C, γ-Al₂O₃ membrane with ~3 μm grains was obtained. When sintered at 1200 °C, γ-Al₂O₃ completely transformed into α-Al₂O₃ and the grains grew to ~5 μm. Accordingly, the process was applied to a bigger pore-sized PSS with an average pore size of 1.5 μm to fabricate an α-Al₂O₃ intermediate layer to initially modify its surface. A single α-Al₂O₃ crystal layer with a thickness of ~5 μm and an average pore size of 0.7 μm was achieved. Subsequently, TiO₂, SiO₂, and TiO₂–SiO₂ hybrid membranes were tried on the modified PSS. Defect-free microfiltration membranes with average pore sizes of ~0.3 μm were readily fabricated. The results indicate that the sol–gel method is promising to initially modify the PSS substrates and the sol–gel-derived α-Al₂O₃ crystal layer is an appropriate intermediate layer to modify the PSS and to support smaller grain-sized top membranes.     

Hydrothermal preparation of neodymium oxide coated titania composite designer particulates and its application in the photocatalytic degradation of procion red dye

Nd₂O₃ coated onto titania composite designer particulates using 1M NaOH at 250°C and P~80 bars with an experimental duration of 5–72 h were obtained under hydrothermal conditions. Different weight % of Nd₂O₃ (1–9%) was used for coating in order to reveal the role of Nd₂O₃. Characterization of the Nd₂O₃ coated titania composite designer particulates obtained was carried out using XRD and FTIR spectroscopy techniques. Photocatalytic reactivity of Nd₂O₃ coated titania composite designer particulates was evaluated by studying the degradation of procion red dye. The effect of various kinetic parameters like initial dye concentration, catalyst amount, pH of the medium, temperature of the medium, light source and catalyst reusability on the photodegradation of procion red dye has been discussed in detail. The thermodynamic parameters like energy of activation, enthalpy of activation, entropy of activation and free energy of activation were estimated.     

Fabrication of superparamagnetic hydroxyapatite with highly ordered three-dimensional pores

Hydroxyapatite (HA) with highly ordered three-dimensional pores, whose size is about 300 nm, was prepared by colloidal template method. The effect of the surface modification of silica spheres on the order degree of porous structure was investigated by field emission scanning electron microscopy (FESEM). Then, superparamagnetic Fe₃O₄ nanoparticles were fabricated via redox reaction, followed by coating with silica via a sol–gel process, in which a certain amount of TEOS was used in order to control the thickness of the silica shell. X-ray diffraction (XRD), transmission electron microscopy (TEM), and magnetometry were applied to characterize the properties. Finally, Fe₃O₄ magnetic nanoparticles coated with silica were adsorbed in the mesopores of HA with highly ordered three-dimensional pores by capillarity. The influence of dispersing agent on the adsorption results has been studied. Magnetometry was applied to characterize the magnetic properties of superparamagnetic HA. The quantities of adsorbed SiO₂/Fe₃O₄ nanoparticles with core–shell have been compared by variation of saturation magnetization before and after adsorption.     

Comparison of magnetic-nanometer titanium dioxide/ferriferous oxide (TiO<Subscript>2</Subscript>/Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>) composite photocatalyst prepared by acid–sol and homogeneous precipitation methods

Novel magnetic-nanometer titanium dioxide/ferriferous oxide (TiO₂/Fe₃O₄) composite photocatalyst was prepared using acid–sol and homogenous precipitation methods. The photocatalyst particle was made of a Fe₃O₄ core covered with nanocrystal anatase TiO₂, without a high-temperature heat-treatment step. The catalyst has been characterized by X-ray diffraction, transmission electron microscopy, differential thermal analysis measurements, and ultraviolet spectrum. The results suggested that titania was mainly presented as anatase and Fe₃O₄ did not appear on the surface of the composite particles when the molar ratio of TiO₂/Fe₃O₄ increased to 20:1 in the acid–sol method, but 5:1 in the homogeneous precipitin method. The size of the crystal was ranged from 2.4 to 3.6 nm prepared by both methods. In the catalytic test, the composite particles, which were prepared by acid–sol, had higher catalytic activity than that prepared by homogenous precipitation method due to the size difference of the composite particles.     

Nanoporous titania-coated alumina membranes: sol-gel synthesis and characterisation

In this work, nanoporous titania top layers were deposited by dip-coating process on microporous alpha-alumina substrates using the sol-gel process. The alumina substrates were synthesized by slip casting method using Taguchi optimising approach. The microporous substrate was then used to coat nanoporous titania layers by the sol-gel method. The thickness, pore size, structure and permeability of the membranes were characterised using SEM, XRD, STA and Hg-Porosimetry. The process conditions to achieve defect-free nanoporous titania layers with the average pore size of about 4 nm coated on the microporous alumina substrates with the average pore size of about 270 nm were determined.     

Processing of submicrometric CaTi0.8Fe0.2O3-δ ceramics by mechanical activation

Effects of mechanical activation of precursors in order to obtain CaTi_0.8Fe_0.2O_3-δ are reported. Mixtures of CaCO₃, TiO₂ and Fe₂O₃ were dry-grinded in Teflon or zirconia containers using planetary ball-mills at different rotations (200, 300 and 500 rpm) and for various periods of time. The perovskite is not formed just by milling and a subsequent heat treatment at 800–1,000 °C was necessary. This still represents a significant advantage over the classical ceramic route as a result of the improved reaction kinetics due to the smaller grain size (<100 nm) of the activated powders and a modification of the thermodynamic initial state. Dense ceramic samples showing a bimodal submicrometric grain-size distribution (100–200 and 250–500 nm) were obtained after sintering the activated powders at 1,150 °C TEM revealed homogeneous samples, free from inhomogeneities such as core-shell grains typically observed in ceramics obtained from non-activated precursors sintered at 1,320–1,350 °C.     

TiB2-reinforced composite coating by gas tungsten arc welding

In situ synthesized TiB₂-reinforced Fe-based coating was fabricated by gas tungsten arc welding (GTAW) on AISI-4340 steel substrate using cheaper Fe–Ti, Fe–Cr, Fe–W, Fe–B alloys and B₂O₃ powders. The effects of processing parameters on the coating were investigated experimentally. Primary dendrites of ferrite (α) phase and complex TiB₂, Fe₂B borides were detected at the coated surface. The experimental results show that either coated surface or interface microstructures were formed by the distribution of particularly boron and titanium concentration. The difference in hardness of the microstructures is specifically attributed to the type of borides. The type, dimension, and the volume concentration changes of borides were correlated with the parameters as the concentration of additives and the dilution from the base material. The surfaces were subsequently characterized by scanning electron microscopy (SEM), the energy dispersive X-ray spectrometry (EDS), X-ray diffraction (XRD), and differential thermal analysis (DTA).     

Synthesis of CNTs via ethanol decomposition over ball-milled Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> coated copper sheets

Carbon nanotubes (CNTs) were synthesized on ball-milled Fe₂O₃ coated copper sheets by the catalytic decomposition of ethanol vapor at 650°C. TEM, SEM, and EDX revealed the presence of 30–50 nm diameter multiwalled carbon nanotubes with catalytic particles at their tips. CNTs, α-Fe, and Fe₃C were detected by XRD. Raman and TG analyses show that the product is CNTs with less than 10 wt % residues. The carbon yield was the maximum at 354 wt %. The text was submitted by the authors in English.     

Synthesis of flexible magnetic nanohybrid based on bacterial cellulose under ultrasonic irradiation

Flexible magnetic membrane based on bacterial cellulose (BC) was successfully prepared by in-situ synthesis of the Fe₃O₄ nanoparticles under different conditions and its properties were characterized. The results demonstrated that the Fe₃O₄ nanoparticles coated with PEG were well homogeneously dispersed in the BC matrix under ultrasonic irradiation with the saturation magnetization of 40.58 emu/g. Besides that, the membranes exhibited the striking flexibility and mechanical properties. This study provided a green and facile method to inhibit magnetic nanoparticle aggregation without compromising the mechanical properties of the nanocomposites. Magnetically responsive BC membrane would have potential applications in electronic actuators, information storage, electromagnetic shielding coating and anti-counterfeit.     

A facile template-free approach to metal oxide spheres with well-defined nanopore structures

Nanoporous Al₂O₃ with well-defined pore structure, crystallized framework and spherical morphology has been prepared by a facile template-free approach, which involves the preparation via homogeneous precipitation and subsequent decomposition of spherical basic aluminium sulphate particles. The particle size of the spheres can be tuned by controlling the holding time from the beginning of precipitation, and a proper decomposition temperature is important to get high surface area, high pore volume and well-defined pore structures. By the similar way, nanoporous ZrO₂ and TiO₂ spherical particles can also be prepared. These nanoporous oxides all have moderately high surface area (50–70 m²/g) and well-defined nanopores of around 4–12 nm with very narrow pore size distribution. The frameworks of these oxide spheres consist of many small nanocrystallites, between which the nanopores exist. Compared with the soft and hard template routes, this decomposition strategy of sulphates for nanoporous oxides has the advantages of simplicity and low cost.     

Direct synthesis of mesoporous Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> through citric acid-assisted solid thermal decomposition

A simple and inexpensive approach to synthesizing mesoporous Fe₃O₄ is developed by using citric acid-assisted solid thermal decomposition of ferric nitrate. The structure and magnetic property of mesoporous Fe₃O₄ were characterized by XRD, FT–IR, N₂ adsorption–desorption isotherms, TEM, and vibrating sample magnetometer. It was shown that the decomposition of citric acid results in the formation of the mesoporous structure and narrow pore-size distribution. The reducing atmosphere which created by the decomposition of the ferric nitrate–citric acid complex caused the partial reduction of Fe(III) to Fe(II) and in turn the formation of Fe₃O₄. Moreover, the strength of the coordination between carboxyl group and Fe³⁺ also affected the phase composition of the iron oxides.     

Environmental stability of the YSZ layer and the YSZ/TGO interface of an in-service EB-PVD coated high-pressure turbine blade

Hot corrosion of an in-service EB-PVD coated 1st stage high-pressure turbine (HPT) blade following an interactive CaSO₄ infiltration/CMAS deposition process has produced reactive interfaces with the yttria stabilized zirconia (YSZ) top coat and the TGO layer which were investigated by analytical scanning and transmission electron microscopy (TEM). Despite complete CaSO₄ infiltration of the coating macroscopic damage of the airfoil was confined to the pressure surface close to the trailing edge. Since the bulk composition of the CaSO₄/CMAS deposits exhibited a high lime-to-silica ratio CaSO₄/CMAS/YSZ interfaces typically involved a Ca–Zr-rich layer followed by fine-grained Ca-FSZ particles enveloping rounded YSZ column tips. No interfacial reaction was observed between the YSZ column walls and the CaSO₄ pore fillings. Possible terms for the formation of this unique CaSO₄/CMAS microstructure are evaluated. Zirconia destabilization upon hot corrosion is discussed in the light of phase compatibilities in the systems CaO–Y₂O₃–ZrO₂ and CaO–ZrO₂–SiO₂ and put into perspective with previous work on both, natural and synthetic hot corrosion deposits.     

Synthesis and characterization of γ-Fe2O3 — a magnetic tape material

Acicular FeC₂O₄ · 2H₂O was precipitated from glycerol and starch media. Thermal decomposition of this oxalate in dry and moist nitrogen yielded primarily FeO and Fe₃O₄ respectively. Characterization was attempted through DTA, TG, x-ray diffraction, TEM and magnetization studies. It was found that the oxalate can be completely decomposed to Fe₃O₄ in moist nitrogen (P_{H 2}O ∼ 35 torr) at 775 K and then oxidised by dry air to acicular γ-Fe₂O₃ at 575 K. The resulting material has saturation magnetization (∼ 70 emu/g), coercive field (∼ 300 Oe) and squareness ratio (∼ 0·60–0·65), which values art comparable with those of the commercial samples.     

Preparation and characterization of porous ultrafine Fe2O3 particles

Porous ultrafine Fe₂O₃ particles were prepared by homogeneous precipitation method. Fe³⁺ and urea were chosen as starting materials and anionic surfactant as the template. It is shown that the reaction results in the precipitation of a gelatinous hydrous iron oxide/surfactant mixture, which gives ultrafine Fe₂O₃ particles after drying and calcinations. The products were characterized by XRD, TEM, TG/DTA and BET. Conventional XRD patterns show that the products are mixture of γ-Fe₂O₃ and α-Fe₂O₃ phase after being sintered at 350 °C, and γ-Fe₂O₃ transforms entirely to α-Fe₂O₃ when sintered at 650 °C. The low-angle XRD patterns indicate that the mesostructure can only exist between 350 and 400 °C. TEM results show that the Fe₂O₃ particles have diameters of about 30 nm and lengths ranging from 100 to 120 nm; in each particle, there are several vermiculate-like mesopores with diameter of about 20-25 nm. The BET surface areas in excess of 50 m²/g are obtained after calcinations at 350 °C. The BJH desorption average pore width is around 22 nm, which is in agreement with the TEM results. The results show that anionic surfactant and sintering temperature are important to obtain this special morphology.     

Calculation and experimental determinations of the residual stress distribution in alumina/Ni/alumina and alumina/Ni/nickel alloy systems

Residual stress problems encountered in joining ceramics–ceramics or ceramics–metals systems for high-temperature applications >1000 °C have been studied. A solid-state bonding technique under hot-pressing via metallic foils sheet of Ni was used for joining alumina–alumina and alumina–nickel alloy (HAYNES^? 214™). The residual stresses expected in the specimen were predicted by finite-element method (FEM) calculations using an elastic–plastic-creep model (EPC). Stress distributions in the specimen were characterized experimentally using X-ray diffraction (XRD) and Vickers Indentation Fracture (VIF) techniques. The tensile and shear stress profiles have been determined along selected lines perpendicular to the bonding interface. The results of the FEM calculation of residual stresses have been compared experimentally with the results of classical XRD and indentation methods. It was found that the tensile stress concentration showed higher values at the edge of the boundary. The residual stresses caused by the thermal expansion mismatch between alumina (Al₂O₃) and Ni-based super-alloy (HAYNES^? 214™) severely deteriorated the joints compared to Al₂O₃–Al₂O₃ joint with the same solid-state bonding parameters. The correlations between the FEM calculations and experimental results obtained by XRD and VIF method were discussed.     

Function of magnesium aluminate hydrate and magnesium nitrate as MgO addition in crystal structure and grain size control of <Emphasis Type="Italic">α</Emphasis>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> during sintering

Chemically pure reactive alumina (α-Al₂O₃) which is commercially available was used for densification study in presence of widely accepted dopant MgO as additive. MgO was added both as spinel (MgAl₂O₄) forming precursor i.e. magnesium aluminate hydrate, and magnesium nitrate. Sintering investigations were conducted in the temperature range 1500–1600°C with 2 h soaking. Structural study of sintered pellets was carried out by extensive XRD analysis. Scanning electron mode SEM images of the specimens were considered to understand the effect of both types of additions. Addition of MgO within and beyond optimum amount had some effect on development of microstructure of sintered bodies. Densification, around 99% ρ _th, with fine grain microstructure was achieved. These different types of additions caused two distinct changes in crystal structure of alumina—one small contraction and the other expansion of unit cell parameters.     

Synthesis of Fe–4.6?wt% B alloy via electro-deoxidation of mixed oxides

Fe–4.6 wt% B alloy was synthesized via electro-deoxidation of the mixed oxide precursor. The oxides, Fe₂O₃ and B₂O₃, mixed in suitable proportions were sintered at 900 °C yielding pellets with a two-phase structure; Fe₂O₃ and Fe₃BO₆. The sintered pellets, connected as cathode, were then electro-deoxidized in molten CaCl₂ or in CaCl₂–NaCl eutectic, against a graphite anode at 3.1 V. The electrolysis at 850 °C has successfully yielded a powder mixture of Fe and Fe₂B. Sequence of changes during the electrolysis was followed by interrupted experiments conducted at 850 °C. This has shown that iron is extracted quite early during the electrolysis through the depletion of oxygen from the starting oxide; Fe₂O₃, forming the other iron oxides in the process. Boron follows a more complicated route. Fe₃BO₆, the initial boron-bearing phase, was depleted in the early stages due to its reaction with molten salt. This gave rise to the formation of calcium borate. Boron was extracted from calcium borate in later stages of electrolysis, which appeared to have reacted in situ with the iron forming compound Fe₂B. An erratum to this article can be found at     

Synthesis and photoelectric property of poly(3-octylthiophene)/ferric oxide complexes

Ferric oxide was prepared by the supercritical fluid drying (SCFD) method. A conducting polymer composite, poly(3-octylthiophene)/ferric oxide (POT/Fe₂O₃) was first synthesized through the chemical method. X-ray diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), and Infrared spectroscopy (IR) show that there is a chemical interaction in the composite, which indicates that Fe₂O₃ was successfully coated by poly(3-octylthiophene) molecules. The energy gap of the poly(3-octylthiophene)/ferric oxide composite is lower at 0.448 eV, which also shows that the optical performance of the new material is far superior to POT or Fe₂O₃ separately, by Ultraviolet–Visible spectra (UV–Vis) and fluorescence spectroscopy (PL). Solar cell was sensitized by POT/Fe₂O₃. A solar-to-electric energy conversion efficiency of 0.258% was attained with the system.