Fe Al2O3 Research Articles

Wear-Resistant Cr–Fe–Al2O3 Coating Deposition on Steel 35 Using Aluminum Oxide Powder

Wear-Resistant Cr–Fe–Al2O3 Coating Deposition on Steel 35 Using Aluminum Oxide Powder

Synthesis of Fe-Al catalysts to boost CNTs formation from polymer wastes via the improved two-stage system

Carbon nanotubes (CNTs) has been considering as a high-value product from polymer wastes via the coupled thermal-catalytic technology, and how to improve the yield and quality of CNTs is the key to the further industrialization. Herein, a series of Fe-Al catalysts with different Fe-loading and calcination temperature were prepared and expected to boost CNTs formation from low-density polyethylene (LDPE) in the improved two-stage reaction system. The fresh and spent Fe-Al catalysts were characterized in detail by SEM-EDX, XRD, N2 physisorption, NH3-TPD, H2-TPR, TG-DSC, Raman, and TEM to explore the effects of Fe-loading (5–20%) and calcination temperature (450–650 °C) on the physicochemical properties of Fe-Al catalysts as well as the quantity and quality of CNTs. An increase of Fe-loading generated more active sites for CNTs growth while intensified the competition for the carbon source, promoting the yield while reducing the length of CNTs. A decrease of calcination temperature reduced the interaction between Fe sites and Al2O3 support, promoting both the yield and the length of CNTs. This work provided a promising strategy for optimizing Fe-Al catalysts to boost CNTs production from polymer wastes.

Iron-alumina composites: From discrete iron particles to interconnected iron network. Powder synthesis, spark plasma sintering, microstructure and mechanical properties

The aim is to prepare Fe–Al2O3 ceramic-matrix composites with a high Fe content in order to benefit from a high degree of toughening. Fe–Al2O3 powders with different Fe contents (14.2–47.4 vol%) are prepared by selective reduction in H2 of the corresponding amorphous Al2-2xFe2xO3 oxides, themselves prepared by decomposition in air of the mixed oxalates. Dense samples are prepared by Spark Plasma Sintering. The samples are investigated by thermal analysis, scanning electron microscopy and X-ray diffraction. The microhardness, fracture strength and toughness are discussed with respect to the composition and the microstructure, i.e. a dispersion of discrete Fe particles or a continuous Fe network into the alumina matrix. The latter samples are significantly thougher than the former ones (about 14 and 8 MPa m1/2, respectively).

Aluminum‑yttrium oxides supported iron for effective catalytic reforming of toluene: Promotion roles of yttrium

A facile Fe-based catalyst (FYA) was developed for tar reforming by using the Y–Al oxides as catalyst support. Toluene was used as a tar model compound to evaluate the steam reforming (TSR) activity and stability of the catalyst. By adding Y to the Fe/Al2O3 (FA), the toluene conversion efficiency was significantly improved (76% vs. 20% at 850 °C). The yttrium prevented the iron and aluminum from forming an inactive spinel phase (FeAl2O4), thus maintaining the redox activity of iron. The Fe2+/Fe3+ couple instead of metallic iron was most likely the main active phase for tar reforming. Yttrium reduced the number of surface oxygen vacancies and weakened the lattice oxygen activity to suppress the over-reduction of the iron species on FA, which maintained the composition of active FeOx for TSR. Additionally, the anti-sintering and anti-coking properties were improved significantly after Y modification causing the enhanced stability of the catalyst. The increased basic sites, especially those with medium- and high-strength, on the FYA surface are beneficial to reducing the carbon deposits (1.61 vs. 17.58 mg-C/(gcat·h)) and keeping the surface active sites exposed to the reactants during the reactions.

Development of a high-performance green Fe–Al2O3 composites using Bayan Obo minerals: Enhancement effects of CeO2

With the deepening understanding for the concept of sustainable development, the utilization of minerals is no longer limited to the traditional way. In this study, an environment friendly method for preparing Fe–Al2O3 composites by using natural minerals was investigated. Additionally, the effects of CeO2 on the properties of composites were studied. The mechanical properties of Fe–Al2O3 composites prepared by natural minerals are affected by the brittleness of glass phase. The strength and toughness of the glass phase in the composite are improved successfully by using rare earth oxides, indicating that the natural rare earths in Bayan Obo minerals have an enhanced influence on the properties of composite materials. The results show that the properties of glass phase can be significantly improved by addition of CeO2. At the optimal addition of 3 wt% CeO2, the composite achieves the density of 4.21 g/cm3, flexural strength of 401 MPa, Vickers hardness of 13.07 GPa and fracture toughness of 6.58 MPa⋅m1/2. The composite has excellent mechanical properties, which can be used in engineering as a cheap structural material. This study aims at reducing waste emissions, improving energy efficiencies and avoiding waste of rare earth resources during the preparation of composite materials.

Catalytical enhancement on hydrogen production from LiAlH4 by Fe–Fe2O3 addition

Hydrogen storage technology plays an important role on the development of hydrogen fuel cell and lithium aluminum hydride is a powerful candidate for solid-state hydrogen storage materials. However, the high stability and slow dehydrogenation kinetics of LiAlH4 hinder its application. In this paper, the two-step thermal decomposition properties of LiAlH4 with and without Fe–Fe2O3 catalysts are investigated. According to the master plots, the model of mample power law (Pn) and nucleation and growth (An) are the optimal mechanism functions for the two-step decomposition of LiAlH4, respectively. After doping catalysts, the activation energies decrease significantly. The theoretical and optimized kinetic method are consistent with each other on activation energy. And the latter can also yield other kinetic parameters for a more comprehensive kinetic modelling of LiAlH4 decomposition. Furthermore, Fe–Al2O3 and Fe–Al intermetallics generated during dehydrogenation might significantly improve the hydrogen release properties of LiAlH4.

Promoted Ni–Co–Al2O3 nanostructured catalysts for CO2 methanation

15 wt.%Ni-12.5 wt.%Co–Al2O3 catalysts promoted with Fe, Mn, Cu, Zr, La, Ce, and Ba were prepared by a novel solid-state synthesis method and employed in CO2 methanation reaction. BET, XRD, EDS, SEM, TPR, TGA, and FTIR analyses were conducted to identify the chemicophysical characteristics of the prepared samples. The addition of Fe, Mn, La, Ce, and Ba was effective to improve the catalytic performance of the 15 wt%Ni-12.5 wt%Co–Al2O3 due to the higher CO2 adsorption capacity of the promoted catalysts. Among the studied promoters, the Fe-promoted catalyst possessed the highest catalytic activity (XCO2 = 61.2% and SCH4 = 98.87% at 300 °C). Also, the effect of calcination temperature, feed composition, and GHSV on the performance of the 15 wt%Ni-12.5 wt%Co-5wt%Fe–Al2O3 catalyst in CO2 methanation reaction was assessed. The outcomes confirmed that the 15 wt%Ni-12.5 wt%Co-5wt%Fe–Al2O3 catalyst with the BET area of 122.4 m2/g and the highest pore volume and largest pore diameter had the highest catalytic activity. Also, the catalytic performance in the methanation of carbon monoxide was studied, and 100% conversion of carbon monoxide was observed at 250 °C.

SiO2-promoted growth of single-walled carbon nanotubes on an alumina supported catalyst

Developing supported catalyst and elucidating the catalyst activation mechanism are of significant importance for large scale synthesis of single-walled carbon nanotubes (SWNTs). In the work, we designed an alumina-supported iron (Fe–Al2O3) catalyst for catalytic growth of carbon nanotubes by CO chemical vapor deposition (CVD). In the temperature range of 800–1000 °C, the prepared powder catalyst only affords the growth of carbon fibers or multi-walled carbon nanotubes. In contrast, when placing the powder catalyst on flat SiO2 substrates, such as SiO2/Si and quartz, SWNTs were observed to grow at the catalyst-substrate interface, highlighting the contributions of the SiO2 substrate in SWNT synthesis. Systematic characterizations on both the catalysts and carbon nanotubes revealed that the SiO2 substrate promotes the reduction of iron oxide in the adjacent Fe–Al2O3 catalyst, facilitating the generation of small Fe particles at the catalyst-substrate interface, which act as the active phase for the subsequent growth of SWNTs. This work opens a new avenue for growing SWNTs from supported catalyst and sheds light on enhancing SWNT growth efficiency by tuning catalyst reduction behaviors.

Preparation of Iron- and Nitrogen-Codoped Carbon Nanotubes from Waste Plastics Pyrolysis for the Oxygen Reduction Reaction.

A novel method for the preparation of iron- and nitrogen-codoped carbon nanotubes (Fe-N-CNTs) is proposed, based on the catalytic pyrolysis of waste plastics. First, carbon nanotubes are produced from pyrolysis of plastic waste over Fe-Al2 O3 ; then, Fe-CNTs and melamine are heated together in an inert atmosphere. Different co-pyrolysis temperatures are tested to optimize the electrocatalyst production. A high doping temperature improves the degree of graphite formation and promotes the conversion of nitrogen into a more stable form. Compared with commercial Pt/C, the electrocatalyst obtained from pyrolysis at 850 °C shows remarkable properties, with an onset potential of 0.943 V versus RHE and a half-wave potential of 0.811 V versus RHE, and even better stability and anti-poisoning properties. In addition, zinc-air battery tests are performed, and the optimized catalyst exhibits a high maximum power density.

Effect of reduction temperature on the structure and catalytic performance of mesoporous Ni–Fe–Al2O3 in oxidative dehydrogenation of ethane

The effects of reduction temperature on the structure and catalytic performance of mesoporous Ni–Fe–Al2O3 are investigated for the first time.

Investigation of sulfide precipitates on microstructure and properties of Fe–Al2O3 composites fabricated by carbothermal reduction of iron concentrate

Iron–alumina (Fe–Al2O3) composites were prepared by pressureless sintering, using Bayan Obo iron concentrate and alumina as the main raw materials; activated carbon was added as the reducing agent. The effects of different carbon/oxygen ratios (C/O ratios) on the phase composition, the mechanical and the corrosion-resistant properties of the materials were investigated. Due to the presence of pyrite, sulfide precipitate takes place around the iron particles, and it is transformed from FeS to MnS with increasing C/O ratio. It was found that crack propagation can be effectively hindered by MnS. The results indicate that the orientation relationships between the Fe and MnS are Fe (100) ‖ MnS (002). However, there is no specific orientation relationship between Fe and FeS. It was found that the phase interface between Fe and MnS is coherent interface since the misfit between Fe (100) and MnS (002) was 2.1%. The performance of sample with C/O ratio of 3:1 were found to be favorable, with flexural strength was 301 MPa, Vickers hardness was 13.12 GPa, the acid resistance was 93.40% and the alkali-resistance was 98.20%.

Interaction of Pure Alumina Refractory with FeO–SiO2 and FeO–SiO2–CaO Slags Relevant to the Novel Flash Ironmaking Technology

Interaction of alumina (Al2O3) refractory with FeO–SiO2 and FeO–SiO2–CaO slags relevant to the flash ironmaking technology (FIT) is investigated in this work. It is shown that for slags relevant to FIT, the interaction process can be described by a kinetic model based on counter diffusion of only Fe2+ and Al3+ cations through hercynite (FeAl2O4) formed as a result of the interaction. The diffusion of Si4+ and Ca2+ ions through FeAl2O4 can be neglected, and the only effect these cations have is that they affect the activity of iron oxide (FeO) at the slag–FeAl2O4 boundary. Analyses of reacted samples using X‐ray diffraction (XRD), scanning electron microscopy–energy dispersive X‐ray spectroscopy (SEM–EDX), and electron probe microanalyzer (EPMA) show that the proposed model appropriately describes the growth of FeAl2O4 with the parabolic rate law being obeyed for both FeO–SiO2 and FeO–SiO2–CaO slags in the temperature range of 1200–1400 °C. The values of effective diffusivity () are calculated independently from experiments with FeO–SiO2 and FeO–SiO2–CaO slags agreed with each other, with the activation energy values in the two cases being 246 and 253 kJ mol−1, respectively. These values of and activation energy are in good agreement with the corresponding values obtained previously from Fe–Al2O3 and FeO–Al2O3 systems.

Interaction of ferrous oxide with alumina refractory under flash ironmaking conditions

Abstract A novel flash ironmaking technology (FIT) has been developed at the University of Utah based on the direct reduction of iron ore concentrate by a reducing gas such as hydrogen, natural gas, coal gas or a mixture thereof. In this work, the interaction of ferrous oxide (FeO) with alumina (Al2O3) refractory under flash ironmaking conditions has been studied. A thermodynamic basis for the interaction process has been developed by considering the Fe–Al–O system and a kinetic model based on solid-state diffusion is formulated to describe the growth of the hercynite (FeAl2O4) spinel formed as a result of the interaction between FeO and Al2O3. Experiments were conducted with FeO powders and pure Al2O3 refractory in the temperature range 1200–1400 °C under gas atmospheres relevant to FIT. The analyses of reacted samples using XRD, SEM-EDX and EPMA techniques confirmed the formation of the hercynite (FeAl2O4) spinel under FIT conditions and results showed that the proposed kinetic model appropriately describes the growth of the hercynite spinel layer, which obeyed the parabolic rate law at all the three temperatures. Furthermore, using the kinetic model, expressions for the parabolic rate-constants ( k 1 ) and the effective diffusivity ( D e f f ¯ ) were obtained and their respective values at the experimental temperatures were determined. The values of D e f f ¯ calculated in this study agreed closely with those obtained independently by the authors from experiments on Fe–Al2O3 interaction thereby corroborating the interaction mechanism and the associated reaction scheme. The solid-state diffusion was temperature-dependent, with an activation energy value of 268 kJ/mol.

Fabrication of Fe–Al2O3 Composite Layer on the Surface of Carbon Steel via Gas Tungsten Arc Cladding

In this study, Fe–Al2O3 composite cladding is fabricated on the carbon steel AISI 1040 (CK40) substrates by the cost-effective process of gas tungsten arc welding. For this purpose, after milling, Fe–Al2O3 composite powders were placed on the steel surface through the sodium silicate binder. After the surface was dried, under a constant voltage and current in a range of 110 to 180 A, the melting and the fabrication of the surface composite were carried out. For non-destructive investigations, samples were analyzed by radiographic testing which showed that there are no cracks in the surface layer created and Al2O3 particles are distributed uniformly in the surface layer. Microstructural examinations by optical microscopy, scanning electron microscopy, energy-dispersive spectroscopy, and X-ray diffraction proved the presence of a pure Fe–Al2O3 phase in the surface layer. Microscopic images showed coaxial fine grains in the weld metal, which can be caused by a thermal gradient between the weld metal and substrates and rapid solidification. Increasing the current due to enhanced input heat leads to a reduction of the grain size and an increase of dramatic micro hardness that leads to agglomeration of Al2O3 particles and reduction of the quality of the cladding layer. The purpose of this research is to achieve optimal parameters of claddings to attain specific objectives of engineering by using steel via an inexpensive supplementary method.

Investigation on synthesis and characterization of Fe-doped Al2O3 nanocrystals by new sol–gel precursors

Pure aluminum oxide (Al2O3) and Fe-doped Al2O3 nanoparticles (NPs) with impurities of 1%, 2%, and 4% were synthesized by the sol-gel method with AlCl3 and FeSO4 new precursors in the presence of CTAB stabilizer and NaBH4 reduction agent. To study the structural, optical, and magnetic properties of the samples, they were exposed to heat treatment at 1000 °C. The structural results of XRD analysis showed that the sample had a crystalline γ-alumina phase in pure state, and with the increase of Fe dopant up to 1% and 2%, the δ-alumina phase appears in the sample. The novelty of this work is that, with an increase in dopant to 4%, the crystalline structure of the sample changes into α-alumina at constant temperature. The results of the FESEM analysis showed that the sample uniformity and porosity increases with increasing Fe impurities. EDX analysis also showed that Al content increased with an increase in Fe dopant from 63.39 wt% to 67.21 wt%, indicating a change in the crystalline phase of the sample to α-alumina structure. The results of the TEM analysis showed that the size of the NPs decreased through increasing the 4% Fe dopant. The Al–OH vibrations were characterized by FTIR analysis in the vibrational frequencies of 1332 and 1419 cm−1. It was also found in this analysis that the absorption in the frequencies of 580 cm−1 and 802 cm−1 increased, which is related to the sites of octahedral AlO6 and tetrahedral AlO4, suggesting the phase change into the state α-alumina in the 4% dopant. In the UV-DRS analysis, it was found that the band gap decreased with an increase in the Fe dopant from 4.20 eV for a pure Al2O3 to 3.50 eV for a sample with a 4% dopant which is less than the band gap energy of 6–8 eV obtained by many researchers. Finally, the VSM analysis showed that with increasing dopant, the magnetic behavior of the sample changes to a ferromagnetic state. Saturation magnetization and coercivity are also obtained at 0.145 emu g−1 and 127 G for the 4% dopant, respectively. The results of this study showed that in the formation of Fe–Al2O3 NPs, the structural change into the α-alumina phase is carried out with a 4% increase in the Fe dopant at 1000 °C.

Structural and Magnetic Properties of Fe–Co/Al2O3 Nanocomposite Powder Produced by Mechanical Alloying

The effect of milling time and addition of elements on the microstructure, magnetic and mechanical properties of the Fe–xCo (x = 0, 5, 10, and 20 wt.%) matrix nanocomposite reinforced with 40 wt.% Al2O3 during mechanical alloying is examined. Fe–Al2O3 and Fe–Co–Al2O3 alloys are milled for 5, 15, 20, and 30 h and 20 h, respectively. The balance between the welding and fracturing and a steady-state situation is found out in the Fe–Co–40 wt.% Al2O3 nanocomposite after 20 h, due to the Co introduction into the Fe matrix, but not in the Fe–Al2O3 nanocomposite. After 30 h of milling, the average crystallite size was 5 nm in the Fe matrix. The lattice strain increased to ~0.64% in the Fe matrix after ≤30 h of milling and in the binary Fe–20 wt.% Co matrix after 20 h of milling; the average crystallite size was 3 nm. The lattice strain increased to ~0.56% for the Fe–20 wt.% Co matrix after ≤20 h of milling. The coercive field (Hc) increased from 6.407 to 82.027 Oe, while the saturation magnetization (Ms) decreased from 20.732 to 15.181 emu/g in the Fe matrix during milling. The Hc and Ms are maximum for the binary matrix (20 and 10% Co, respectively).

New doping process mode to synthesize in situ N-MWNTs in novel coaxial nanostructure

Nitrogen-doped MWNT “N-MWNT” have gained an increasing interest because particularly of their electronic properties allowing their use in specific applications such as catalysis, sensors, nano-electronics and energy storage.In this investigation, novel coaxial structures consisting of concentric shells of pure carbon MWNT cores with external nitrogen-doped carbon walls (N-MWNT) were produced using a catalytic CVD process, with ethane and ammonia as carbon and nitrogen sources over Fe–Al2O3 support. In order to optimize the growth conditions of such N-MWNT nanostructures, we investigate the influence of different key parameters, i.e., ammonia injection moment in two doping process modes “Instantaneously doping and Mid-doping”, growth temperature (750 and 850°C) and the presence of H2 as reducer gas in the reaction environment. A strong correlation between ammonia injection duration (60, 90 and 120min) and nitrogen content (from 0.4at.% to 2.2at.%) incorporated in the nanotube products was observed and different coordination between C and/or O atoms have been described by XPS. These functionalized MWNTs were characterized using HR-TEM, FESEM, XPS, BET, TG analyses and Raman spectroscopy in order to determine their structural characteristics (graphitization and crystallinity) in quantitative and qualitative ways.

STATIC CORROSION BEHAVIOR OF IN-SITU NANOCRYSTALLINE Al2O3/Fe(Al) COMPOSITES

In this work, the static corrosion behaviors of Fe(Al), and 20 wt.% Al2O3/Fe(Al) composites with and without 4 wt.% Cr produced by mechanical alloying (MA) and plasma activated sintering (PAS) were investigated. The results showed that the main corrosion failure mode was pitting, and Fe(Al) had higher static corrosion resistance than those of Al2O3/Fe(Al) composites. The second phase Al2O3 addition resulted in an increase in phase interface and a large difference of the electron density between the Fe(Al) matrix and Al2O3 reinforcement. All these made the phase interface become the corrosion weaknesses. With 4 wt.% Cr addition, the static corrosion weight loss rate reduced by about 20% because Cr element could improve the stability of Al2O3 passivation film on the composite surface.

Oxygen-promoted catalyst sintering influences number density, alignment, and wall number of vertically aligned carbon nanotubes.

A lack of synthetic control and reproducibility during vertically aligned carbon nanotube (CNT) synthesis has stifled many promising applications of organic nanomaterials. Oxygen-containing species are particularly precarious in that they have both beneficial and deleterious effects and are notoriously difficult to control. Here, we demonstrated diatomic oxygen's ability, independent of water, to tune oxide-supported catalyst thin film dewetting and influence nanoscale (diameter and wall number) and macro-scale (alignment and density) properties for as-grown vertically aligned CNTs. In particular, single- or few-walled CNT forests were achieved at very low oxygen loading, with single-to-multi-walled CNT diameters ranging from 4.8 ± 1.3 nm to 6.4 ± 1.1 nm over 0-800 ppm O2, and an expected variation in alignment, where both were related to the annealed catalyst morphology. Morphological differences were not the result of subsurface diffusion, but instead occurred via Ostwald ripening under several hundred ppm O2, and this effect was mitigated by high H2 concentrations and not due to water vapor (as confirmed in O2-free water addition experiments), supporting the importance of O2 specifically. Further characterization of the interface between the Fe catalyst and Al2O3 support revealed that either oxygen-deficit metal oxide or oxygen-adsorption on metals could be functional mechanisms for the observed catalyst nanoparticle evolution. Taken as a whole, our results suggest that the impacts of O2 and H2 on the catalyst evolution have been underappreciated and underleveraged in CNT synthesis, and these could present a route toward facile manipulation of CNT forest morphology through control of the reactive gaseous atmosphere alone.

Effect of height to diameter (h/d) ratio on the deformation behaviour of Fe–Al2O3 metal matrix nanocomposites

The present paper reports the effect of height to diameter (h/d) ratio on the deformation behaviour of Fe–Al2O3 metal matrix nanocomposites (MMNCs) during bulk processing. Sintered compacts were machined to the required size with different h/d ratios. Test specimens were subjected to deformation at room temperature under three different interfacial friction conditions such as dry, solid and liquid lubrications. Deformed specimens show a significant improvement in the density and hardness. Results also revealed the formation of a nanosize iron aluminate phase due to reactive sintering, which in turn contributes to grain refinement. Experimental density of the specimens was also verified with the theoretical density using the standard equations. It is expected that the present work will be useful in designing and developing MMNC products with better quality at competitive cost.