Characteristics of iron corrosion scales established under blending of ground, surface, and saline waters and their impacts on iron release in the pipe distribution system

Interior scales on PVC, lined ductile iron (LDI), unlined cast iron (UCI) and galvanized steel (G) were analyzed by XRD, RMS, and XPS after contact with varying water quality for 1 year. FeCO₃, α-FeOOH, β-FeOOH, γ-Fe₂O₃, Fe₃O₄ were identified as primary UCI corrosion products. No FeCO₃ was found on G. The order of Fe release was UCI > G ? LDI > PVC. For UCI, Fe release decreased as % Fe₃O₄ increased and as % Fe₂O₃ decreased in scale. Soluble Fe and FeCO₃ transformation indicated FeCO₃ solid was controlling Fe release. FeCO₃ model and pilot data showed Fe increased as alkalinity and pH decreased.     

Microstructure and magnetic properties of HVOF thermally sprayed Fe75Si15B10 coatings

Partially amorphous Fe₇₅Si₁₅B₁₀ coatings were prepared from nanostructured feedstock powders by using high velocity oxy-fuel spraying. Scanning electron microscopy, X-ray diffraction, Vickers indenter and magnetic measurements were used to investigate microstructural, structural, microhardness and magnetic properties of the coatings. The Rietveld refinement of the X-ray diffraction patterns reveals the presence of an amorphous phase, nanocrystalline α-Fe(Si,B) structure having a lattice parameter close to 0.2841 nm and an average crystallite size of about 78-83 nm in addition to small amounts of Fe₃O₄ oxide (104 nm) and Fe₂B boride (151 nm), which disappear completely with increasing coating thickness. Coercivity and microhardness values are 15.5 Oe and 478 Hv, respectively, for 84 μm thickness.     

Photocatalytic performance of nano-photocatalyst from TiO2 and Fe2O3 by mechanochemical synthesis

Nano-particles of homogeneous solid solution between TiO₂ and Fe₂O₃ (up to 10 mol%) have been prepared by mechanochemical milling of TiO₂ and yellow Fe₂O₃/red Fe₂O₃/precipitated Fe (OH)₃ using a planetary ball mill. Such novel solid solution cannot be prepared by conventional co-precipitation technique. A preliminary investigation of photocatalytic activity of mixed oxide (TiO₂/Fe₂O₃) on photo-oxidation of different organic dyes like Rhodamine B (RB), Methyl orange (MO), Thymol blue (TB) and Bromocresol green (BG) under visible light (300-W Xe lamp; λ > 420 nm) showed that TiO₂ having 5 mol% of Fe₂O₃ (YFT1) is 3-5 times higher photoactive than that of P25 TiO₂. The XRD result did not show the peaks assigned to the Fe components (for example Fe₂O₃, Fe₃O₄, FeO₃, and Fe metal) on the external surface of the anatase structure in the Fe₂O₃/TiO₂ attained through mechanochemical treatment. This meant that Fe components were well incorporated into the TiO₂ anatase structure. The average crystallite size and particle size of YFT1 were found to be 12 nm and 30 ± 5 nm respectively measured from XRD and TEM conforming to nanodimensions. Together with the Fe component, they absorbed wavelength of above 387 nm. The band slightly shifted to the right without tail broadness, which was the UV absorption of Fe oxide in the Fe₂O₃/TiO₂ particle attained through mechanochemical method. This meant that Fe components were well inserted into the framework of the TiO₂ anatase structure. EPR and magnetic susceptibility show that Fe³⁺ is in low spin state corresponding to μ_B = 1.8 BM. The temperature variation of μ_B shows that Fe³⁺ is well separated from each other and does not have any antiferromagnetic or ferromagnetic interaction. The evidence of Fe³⁺ in TiO₂/Fe₂O₃ alloy is also proved by a new method that is redox titration which is again support by the XPS spectrum.     

Microstructure and high temperature oxidation behavior of hot-dip aluminized coating on high silicon ductile iron

High silicon ductile iron was coated by hot-dipping into an Al molten bath. The oxidation behavior of the aluminized alloy and the bare substrate was studied in air at 750 °C. The results showed that the coating layers consisted of three layers, in the sequence of Al, Fe-Al intermetallic and Si pile-up layers from the external topcoat to the substrate. The intermetallic layer was composed of outer FeAl₃ and inner Fe₂Al₅. The outer rod-shaped FeAl₃ dispersed in the aluminum topcoat, while the inner tongue-like Fe₂Al₅ formed in the metallic layer becoming the major phase in the aluminide coating layer. Those three layers of aluminum, Fe₂Al₅ and silicon pile-up layer exhibited hardness of HV 50, HV 1100 and HV 450, respectively. In this study, when the as-coated specimens were examined, Fe-Al-Si compounds could not be found. But the silicon pile-up at the interface between the substrate and the Fe-Al intermetallic layer could be seen in all the as-coated specimens. The graphite nodules were noticed in the substrate. The presence of graphite nodules in the substrate might be markers of hot-dipping. After hot-dipping in Al all the specimens contained graphite nodules in the aluminide layer.The oxidized graphite nodules resulted in cracks propagating in aluminide coating. Even though graphite nodules meant the existence of crack in the aluminide coating, the high temperature oxidation experiments indicated that the aluminide coating could prevent the oxidation of substrate effectively even at 750 °C.     

Microstructure and corrosion resistance of ceramic coating on carbon steel prepared by plasma electrolytic oxidation

Ceramic coating was prepared on Q235 carbon steel by plasma electrolytic oxidation (PEO). The microstructure of the coating including phase composition, surface and cross-section morphology were studied by X-ray diffraction (XRD), Fourier transform infrared spectroscope (FTIR) and scanning electron microscopy (SEM). The corrosion behavior of the coating was evaluated in 3.5% NaCl solution through electrochemical impedance spectra (EIS), potentiodynamic polarization and open-circuit potential (OCP) techniques. The bonding strength between Q235 carbon steel substrate and the ceramic coating was also tested. The results indicated that PEO coating is a composite coating composed of FeAl₂O₄ and Fe₃O_4. The coating surface is porous and the thickness is about 100 μm. The bonding strength of the coating is about 19 MPa. The corrosion tests showed that the corrosion resistance of Q235 carbon steel could be greatly improved with FeAl₂O₄-Fe₃O₄ composite coating on its surface.     

Direct synthesis of Fe3O4 nanopowder by thermal decomposition of Fe-urea complex and its properties

An easy synthesis route of magnetite (Fe₃O₄) nanopowder is developed by using thermal decomposition of Fe-urea complex ([Fe(CON₂H₄)₆](NO₃)₃). The formation of Fe₃O₄ is confirmed from X-ray powder diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) measurements. The morphological properties and magnetic properties of the Fe₃O₄ are characterized by transmission electron microscopy (TEM) and magnetic measurements, respectively. By an increase in reaction temperature from 200 to 300 °C, the average crystallite size of the Fe₃O₄ nanopowder increases from 37 to 50 nm. Room temperature magnetization hysteresis curves show that the Fe₃O₄ nanopowder possesses ferrimagnetic characteristics. The saturation magnetization of the Fe₃O₄ nanopowder increases from 70.7 to 89.1 emu/g when the reaction temperature increases from 200 to 300 °C.     

Magnetic properties of mechanochemically synthesized γ-Fe2O3 nanoparticles

The synthesis of mono-dispersed γ-Fe₂O₃ nanoparticles by mechanochemical processing was demonstrated for the first time, via the solid-state exchange reaction Fe₂(SO₄)₃ + 3Na₂CO₃ → Fe₂(CO₃)₃ + 3Na₂SO₄ → Fe₂O₃ + 3Na₂SO₄ + 3CO₂(g) and subsequent heat treatment at 673 K. The nanoparticles had a volume-weighted mean diameter of 6 nm and a narrow size distribution with the standard deviation of 3 nm. The particles showed a superparamagnetic nature with the superparamagnetic blocking temperature of 56.6 K. The anisotropy constant was 6.0 × 10⁶ erg/cm³, two orders of magnitude larger than the magnetocrystalline anisotropy constant of bulk γ-Fe₂O₃. The detailed analysis of the magnetic properties indicated that the γ-Fe₂O₃ nanoparticles had a core-shell structure, consisting of a ferrimagnetic core of ∼4 nm in diameter having a collinear spin configuration and a magnetically disordered shell of ∼1.2 nm in thickness.     

Effect of carbon on corrosion and passivation of iron in hot concentrated NaOH solution in relation to caustic stress corrosion cracking

Quenched Fe-C materials with up to 0.875 wt.% C were examined in 8.5 M NaOH at 100 °C to better understand the effect of carbon on caustic stress corrosion cracking (SCC) of plain steels. Carbon at contents up to about 0.23 wt.% C accelerated anodic dissolution of iron, whereas at high contents it hindered corrosion and promoted the formation of magnetite. It is suggested that carbon particles on the corroding surface form confined regions with an increased concentration of H⁺ and HFeO₂⁻, thereby favouring the formation of Fe₃O₄. Intergranular SCC can be explained by preferred anodic dissolution of grain boundary material enriched in carbon.     

Effect of alloying element segregation on the work of adhesion of metallic coating on metallic substrate: Application to zinc coatings on steel substrates

A thermodynamic model based on the ‘Macroscopic Atom’ approach is proposed to assess the effect of alloying element segregation on the adhesion of metallic coating on metallic substrate. The interfaces that occur in hot-dip galvanized steels are considered, which include: Zn/Fe, Zn/Fe₂Al₅, Zn/FeZn₁₃, FeZn₁₃/Fe₂Al₅, and Fe₂Al₅/Fe. The effect of the alloying element on the work of adhesion of these interfaces is investigated, which includes Mg, Al, Si, P, Ti, V, Cr, Mn, Fe, Ni, Zn, Nb, Mo, Sn and Bi. Among these elements, Bi, Sn and Mg are predicted to decrease the work of adhesion of the Zn/Fe interface, whereas P, Nb, Mo, V, Ti and Ni tend to enhance this adhesion. The effect of element M (M = Al, Si, Cr, Mn) is positive when it exists in the zinc coating or negative when it occurs in the iron substrate. Among these interfaces, the Fe₂Al₅/Fe interface with a value of 3.8 J m⁻² is the strongest, whereas the Zn/FeZn₁₃ interface with of a value of 1.7 J m⁻² is the weakest. Delamination of the coating upon deformation is predicted to occur along the FeZn₁₃/Fe₂Al₅ and Zn/Fe₂Al₅ interfaces. This agrees with microscopic observations of hot dip galvanized steel after tensile testing.     

Direct synthesis and characterization of mesoporous Fe3O4 through pyrolysis of ferric nitrate-ethylene glycol gel

Mesoporous magnetite (Fe₃O₄) was successfully synthesized on a large scale by direct pyrolysis of ferric nitrate-EG (EG = ethylene glycol) gel in a one-end closed horizontal tube furnace in the air without using any template, additions, and carrier gas. The as-synthesized mesoporous Fe₃O₄ were characterized by powder X-ray diffraction (XRD), infrared spectra (IR), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), Brunauer-Emmett-Teller (BET), Barrett-Joyner-Halenda (BJH), and thermal gravimetric analysis (TGA). Results from TEM showed that the as-obtained Fe₃O₄ has mesoporous structure formed by the loose agglomeration of nanoparticles with diameter of about 6 nm, which was also confirmed by small-angle XRD and nitrogen adsorption analysis. Furthermore, vibrating sample magnetometer (VSM) measurements indicated that the saturated magnetization of the as-obtained mesoporous Fe₃O₄ was ferromagnetic with the saturation magnetization (Ms) and coercivity (Hc) of 46 emu/g and 136 Oe, respectively. In addition, a possible growth mechanism of mesoporous Fe₃O₄ was also discussed.     

Phase constituents and microstructure of laser cladding Al2O3/Ti3Al reinforced ceramic layer on titanium alloy

Laser cladding of the Fe₃Al + TiB₂/Al₂O₃ pre-placed alloy powder on Ti-6Al-4V alloy can form the Ti₃Al/Fe₃Al + TiB₂/Al₂O₃ ceramic layer, which can greatly increase wear resistance of titanium alloy. In this study, the Ti₃Al/Fe₃Al + TiB₂/Al₂O₃ ceramic layer has been researched by means of electron probe, X-ray diffraction, scanning electron microscope and micro-analyzer. In cladding process, Al₂O₃ can react with TiB₂ leading to formation of amount of Ti₃Al and B. This principle can be used to improve the Fe₃Al + TiB₂ laser cladded coating, it was found that with addition of Al₂O₃, the microstructure performance and micro-hardness of the coating was obviously improved due to the action of the Al-Ti-B system and hard phases.     

Structural and magnetic properties of nanostructured Fe50(Co50)-6.5 wt% Si powder prepared by high energy ball milling

This work investigates the effects of 6.5 wt% Si addition and milling times on the structural and magnetic properties of Fe₅₀Co₅₀ powders. For this purpose, at first the elemental Fe and Co powders were milled for 10 h to produce Fe₅₀Co₅₀ alloy and then Si was added and the new product was milled again for different times. The microstructural and magnetic properties were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and vibrating sample magnetometer (VSM). The results show that the minimum crystallite size of the as-milled powders (∼12 nm) has been achieved after introducing Si and milled for 8 h (total milling time of 18 h). Also an amount of 188 emu/g has been achieved for M_s. This amount of M_s is higher than most of those which have been already reported for M_s of different Fe-Si systems.     

Structural, magnetic and Mössbauer spectral studies of nanocrystalline Ni0.5Zn0.5Fe2O4 ferrite powders

Nanocrystalline Ni_0.5Zn_0.5Fe₂O₄ powders, synthesized by a combustion method are investigated by X-ray diffraction, vibrating sample magnetometry and Mössbauer spectroscopic techniques. We adopt a strategy to systematically control the particle sizes between 4 and 45 nm simply by changing the elemental stoichiometric coefficient, Φ_e, of the combustion mixture. Curie temperature of the superparamagnetic particles of size 4 nm is higher than that of the bulk particles. Interestingly, bigger particles (45 nm) show a comparable room temperature saturation magnetization and exceptionally very high Curie temperature of 833 K, when compared to that of the bulk Ni_0.5Zn_0.5Fe₂O₄ material (563 K).     

Ultrasonic-assisted in situ synthesis and characterization of superparamagnetic Fe3O4 nanoparticles

Superparamagnetic Fe₃O₄ nanoparticles were synthesized via a modified coprecipitation method, and were characterized with X-ray diffraction (XRD), vibrating sample magnetometer (VSM), Zeta potential and FT-IR, respectively. The influences of different kinds of surfactants (sodium dodecyl benzene sulfonate, polyethyleneglycol, oleic acid and dextran), temperatures and pH values on the grain size and properties were also investigated. In this method, Fe³⁺ was used as the only Fe source and partially reduced to Fe²⁺ by the reducing agent with precise content. The following reaction between Fe³⁺, Fe²⁺ and hydroxide radical brought pure Fe₃O₄ nanoparticles. The tiny fresh nanoparticles were coated in situ with surfactant under the action of sonication. Comparing with uncoated sample, the mean grain size and saturation magnetization of coated Fe₃O₄ nanoparticles decrease from 18.4 nm to 5.9-9.0 nm, and from 63.89 emu g⁻¹ to 52-58 emu g⁻¹ respectively. When oleic was used as the surfactant, the mean grain size of Fe₃O₄ nanoparticles firstly decreases with the increase of reaction temperature, but when the temperature is exceed to 80 °C, the continuous increase of temperature resulted in larger nanoparticles. the grain size decreases gradually with the increasing of pH values, and it remains unchanged when the PH value is up to 11. The saturation magnetization of as-prepared Fe₃O₄ nanoparticles always decreases with the fall of grain size.     

Hydrothermal preparation of a protective Fe3O4 film on Fe foil

A ‘green’ hydrothermal process was used to prepare Fe₃O₄ film on bare Fe foil. X-ray diffraction and scanning electron microscopy (SEM) were employed to characterize the film. The results showed that the film was composed of fine particles with regularly truncated cubic morphology. Electrochemical properties of the coating were investigated by anodic polarization test and electrochemical impedance spectroscopy (EIS). Anodic polarization results indicated that compared with bare Fe foil, the corrosion potential of coated foil increased by 104.4 mV while its current density reduced by 0.11 mA cm^?2. EIS analysis showed that the corrosion resistance of Fe foil increased significantly after coating with Fe₃O₄ film.     

Preparation of Fe2O3/graphene composite and its electrochemical performance as an anode material for lithium ion batteries

The micro-sized sphere Fe₂O₃ particles doped with graphene nanosheets were prepared by a facile hydrothermal method. The obtained Fe₂O₃/graphene composite as the anode material for lithium ion batteries showed a high discharge capacity of 660 mAh g⁻¹ during up to 100 cycles at the current density of 160 mA g⁻¹ and good rate capability. The excellent electrochemical performance of the composite can be attributed to that graphene served as dispersing medium to prevent Fe₂O₃ microparticles from agglomeration and provide an excellent electronic conduction pathway.     

Synthesis of LiFePO4/C cathode materials through an ultrasonic-assisted rheological phase method

LiFePO₄/C active material was synthesized using an ultrasonic-assisted rheological phase method. In addition, polyvinyl butyral (PVB) was added in various concentrations to provide carbon coating on the surface of the LiFePO₄ particles for enhanced electrical conductivity. The crystal structure, morphology, and carbon coating layer of the synthesized LiFePO₄/C was analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM), respectively. The electrochemical performance of LiFePO₄/C, such as initial capacity, rate capability, cycling performance and EIS, were also evaluated. The synthesized particle had a size range of 100-150 nm and a carbon layer of about 8 nm. The LiFePO₄/C (5 wt% PVB) delivered an initial discharge capacity of 167.5 mAh/g at a 0.1 C rate. It also showed an excellent capacity retention ratio of 100% after the 50th charging/discharging. EIS results demonstrate that the charge transfer resistance of the sample decreases greatly by coating with 5 wt% PVB.     

Microstructure Characterization of the FeAl<Subscript>2</Subscript>O<Subscript>4</Subscript>-Based Nanostructured Composite Coating Synthesized by Plasma Spraying Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>/Al Powders

The microstructure of the coating prepared by reactive plasma spraying Fe₂O₃/Al composite powders was characterized by x-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The results indicated that the coating exhibited nanostructured microstructure which consisted of FeAl₂O₄, Fe or Fe solid solution, Al₂O₃ and a little FeAl. In the composite coating, spherical Fe particles (tens of nanometers to hundreds of nanometers) were distributed uniformly within the equiaxed and columnar nanograins FeAl₂O₄ matrix. There were two kinds of Al₂O₃ phases present in the composite coating. One kind was nano-sized Al₂O₃ particles uniformly dispersed within the matrix, forming eutectic structure of (FeAl₂O₄ + γ-Al₂O₃); the other was 1-1.5 μm Al₂O₃ particles embedded individually within the matrix. The composite coating had higher toughness than the conventional microstructured Al₂O₃ coating.     

Facile synthesis, magnetic and microwave absorption properties of Fe3O4/polypyrrole core/shell nanocomposite

Fe₃O₄/polypyrrole (PPy) core/shell nanocomposite, with Fe₃O₄ nanoparticle as core and PPy as shell, could be facilely synthesized via in situ chemical oxidative polymerization of pyrrole monomers on the surface of Fe₃O₄ nanoparticles. The results indicate that core/shell nanocomposite consists of Fe₃O₄ core with the mean diameter of 100 nm and adjacent PPy shell with a thickness of about 70 nm. The as-prepared Fe₃O₄/PPy core/shell nanocomposite exhibits a saturated magnetization of 20.1 emu/g and coercivity value of 368.3 Oe, respectively. The electromagnetic characteristics of Fe₃O₄/PPy core/shell nanocomposite were also investigated with a vector network analyzer in the 2-18 GHz range. The absorbing peak position moves to lower frequency with increasing the thicknesses of samples. The value of the minimum reflection loss is −22.4 dB at 12.9 GHz for Fe₃O₄/PPy core/shell nanocomposite with a thickness of 2.3 mm, and a broad peak with a bandwidth lower than −10 dB is about 5 GHz. Such strong absorption is attributed to better electromagnetic matching due to the existence of PPy and the special core/shell structure.     

Synergistic effect of Cu and Si on hot-dipping galvalume coating

The coating microstructures and thicknesses of the iron panels galvanized in galvalume baths containing 0.0, 0.1, 0.5 and 1.0 wt.%Cu for 10 s, 30 s, 60 s, 180 s, 300 s and 600 s have been studied detailedly. The results indicate that Cu can effectively control the Fe–Al reactivity by the synergistic effect with Si. The addition of Cu makes Si be enriched in the reaction region during the hot-dipping. It promotes the formation of the τ₅ phase and hinders the growth of the Fe₂Al₅ phase. The diffusion path model was introduced to studying the effects of Cu and Si in the present study. The addition of 0.5–1.0 wt.%Cu in galvalume bath forms a stable diffusion path, iron substrate/Fe₂Al₅/FeAl₃/τ₅/overlay. The violent reaction between the iron substrate and the Al–Zn liquid is under control by the compact intermetallic layer, and it decreases the thickness of the intermetallic layer.