Synthesis and characterization of CoFe2O4 magnetic particles prepared by co-precipitation method: Effect of mixture procedures of initial solution

CoFe₂O₄ magnetic particles were prepared by co-precipitation method in 60 °C homogeneous aqueous solution without any subsequent heat treatment. It was found that the mixing procedure and Fe²⁺/Fe³⁺ ratio of initial solution were critical in the preparation of CoFe₂O₄ particles in particle size, magnetization characters, uniformity in particle size and even cation distribution in spinel structure. Two different procedures were used to precipitate CoFe₂O₄ magnetic particles. Evidenced by XRD, Mossbauer analyses and magnetization determination, particles in comparative uniformity average size were obtained in procedure A, denoted as normal pH regulation procedure, in which NaOH solution was dropped into the mixture solution of iron ions, and with the decreasing in Fe²⁺/Fe³⁺ ratio of initial solution, the particle size decreased, which followed the same rule of diversification in saturation magnetization. Uniformity in particle size lowered when procedure B, referred to as reverse pH regulation procedure, where ferrous and cobalt ions were dropped into alkaline solution, was used to precipitate CoFe₂O₄. In both procedures, with the decreasing in Fe²⁺/Fe³⁺ ratio of initial solution, the saturation magnetization decreased, while the magnetic coercivity decreased but increased sharply when Fe²⁺/Fe³⁺ ratio of initial solution was 0.     

Magnetic properties of Pb2Sr2PrCu3O8

The magnetic properties of Pb₂Sr₂PrCu₃O₈ were determined using X-ray absorption, inelastic neutron spectroscopy and magnetic susceptibility measurements. X-ray absorption on the Pr L₃-edge strongly indicates a trivalent oxidation state. Inelastic neutron scattering results are modeled assuming a ³H₄ ground-state multiplet split by a crystalline electric field potential similar to PrBa₂Cu₃O_x. This potential correctly predicts the value of the Curie–Weiss moment, 2.72 μB, obtained from magnetic susceptibility measurements, and so explains the reduction from the free-ion value. The very broad magnetic response found in the inelastic neutron scattering experiments indicates a strong interaction between the Pr 4f electrons and the CuO₂ bands.     

Effects of H2O2 pretreatment on surface characteristics and bioactivity of NaOH-treated NiTi shape memory alloy

The effects of H₂O₂ pretreatment on the surface characteristics and bioactivity of NaOH-treated NiTi shape memory alloy(SMA) were investigated by scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectra, Fourier transform infrared spectroscopy as well as a simulated body fluid(SBF) soaking test. It is found that the H₂O₂ pretreatment can lead to the direct creation of more Ti—OH groups and the decrease in the amount of Ni₂O₃, Na₂TiO₃ and remnant NiTi phases on the surfaces of bioactive NiTi SMA prepared by NaOH treatment. As a result, the induction period of apatite formation is shortened by dispensing with the slow kinetic formation process of Ti—OH groups via an exchange of Na⁺ ions from Na₂TiO₃ phase with H₃O⁺ ions in SBF, which indicates that the bioactivity of NaOH-treated NiTi SMA can be further improved by the H₂O₂ pretreatment.     

Wear and Friction Properties of Electrodeposited Ni-Based Coatings Subject to Nano-enhanced Lubricant and Composite Coating

This paper presents research findings on the tribological performance of electrodeposited coatings subject to nano-lubricants with the addition of nano-Al_2O_3 and graphene and Ni/nano-Al_2O_3 composite coatings. Electrodeposited coatings were produced by using a pulse electrodeposition method. Tribological experiments were conducted by using a linear reciprocating ball on flat sliding tribometer. Experimental results confirmed that the wear and friction resistance properties were significantly enhanced by doping of nano-effects in the lubricating oil and composite coating. The addition of Al_2O_3 nanoparticles in the lubricating oil showed the best tribological properties, followed by Ni–Al_2O_3 composite coatings and nano-oil with graphene. The surface morphology and microstructure of electrodeposited coatings were examined by scanning electron microscopy, energy-dispersive spectroscopy and X-ray diffraction. The wear mechanisms of these coatings subjected to tribological testing were investigated by post-test surface analyses. This research provides a novel approach to design durable nano-coatings for tribological applications in various industries such as automotive,aerospace, locomotive and renewable energy technologies.     

Preparation of nano-sized SrAl2O4 using an amorphous hetero-nucleus complex as a precursor

Nano-crystalline SrAl₂O₄ with spinel structure was successfully prepared at 700 °C using amorphous SrAl₂(diethylenetriaminepentaacetic acid (DTPA)_1.6)(H₂O)₄ as precursor. The precursor was synthesized by a simple inorganic reaction and decomposed into SrAl₂O₄ at temperatures above 500 °C, which was proved by DTA–TGA and X-ray photoelectron spectroscopy (XPS) analysis. X-ray diffraction (XRD) results illustrated that a crystalline SrAl₂O₄ phase can form at 700 °C, which is about 600 °C lower than that used in the traditional method. The crystalline SrAl₂O₄ prepared at 900 °C for 2 h had a crystal size of about 28 nm and a grain size of about 80 nm, and its BET surface area can reach 28.056 m²/g. Calcination temperature and time had a weak effect on crystal size.     

In-situ high temperature X-ray diffraction study of Ni/Al2O3 interface reactions

In-situ experiments on the Ni/Al₂O₃ interface reaction were carried out with a high temperature X-ray diffractometer capable of measuring the X-ray diffraction pattern in 1–2 s using an imaging plate. The kinetic formation processes of the interface reaction layer were measured by short-period exposure experiments with a high temperature X-ray diffractometer. NiAl₂O₄ was formed at the Ni/Al₂O₃ interface from 1468 K to 1673 K in air. The formation of NiAl₂O₄ obeyed the parabolic rate law. The value of the activation energy suggests that the diffusion of Al through NiAl₂O₄ controls the rate of formation. The results of thermal expansion coefficient measurements suggest that when a sample is cooled to room temperature, the magnitude of the stress on the Al₂O₃ owing to NiAl₂O₄ is smaller than that caused by NiO.     

C3N4 as a precursor for the synthesis of NbC, TaC and WC nanoparticles

While there already exit some routes to prepare carbides, highly efficient and facile routes are still desired to meet the increasing demand on carbides. By a facile solid-state reaction process using graphite-like phase of C₃N₄ (g-C₃N₄) as the carbonizing reagent, we synthesized three technologically important carbides including cubic NbC and TaC, and hexagonal WC nanoparticles at relatively low temperature (1150 °C). The products were characterized by power X-ray diffraction (XRD), field-emission scanning electron microscope (FE-SEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM) and high-resolution TEM (HRTEM). The results show that g-C₃N₄ is a highly efficient carbonizing reagent and the oxides Nb₂O₅, Ta₂O₅ and WO₃ are completely converted into the corresponding carbides at 1150 °C, which is significantly lower than that reported for the commercial preparation of the carbides, typically >1600 °C. The NbC, TaC and WC nanoparticles are found to have an average particle size of 4, 35 and 60 nm, respectively. An important feature of this solid-state reaction process is that g-C₃N₄ plays double roles as both efficiently reducing and carbonizing reagent.     

超级奥氏体不锈钢AL-6XN在超临界水中的腐蚀行为

研究了超级奥氏体不锈钢AL-6XN在500℃,550℃和600℃/25 MPa超临界水中的腐蚀行为,通过扫描电镜-电子能谱(SEM-EDX)、X射线衍射(XRD)和X射线光电子能谱(XPS)分析了氧化膜的显微形貌、组织结构与成分分布。结果表明,氧化膜为双层结构,氧化膜中含Fe₃O₄, Cr₂O₃,Fe₂O₃和FeCr₂O₄相。AL-6XN在超临界水中氧化膜存在脱落现象,脱落程度随温度升高而加剧。     

Characterization of anodic films formed on AZ91D magnesium alloy

Anodization of die-casted AZ91D magnesium alloy was performed in 3 M KOH+0.21 M Na₃PO₄+0.6 M KF base electrolyte with and without Al(NO₃)₃ addition. The anodic film was characterized by using X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). The corrosion resistance of the various anodized alloys was then evaluated in 3.5 wt % NaCl solution using electrochemical impedance spectroscopy (EIS) and immersion testing. The results showed that the anodic film was mainly composed of MgO. The addition of Al(NO₃)₃ into the base electrolyte results in the formation of Al₂O₃ and Al(OH)₃ in the anodic film. The maximum amount of Al₂O₃ was found in the anodic film when the alloy was anodized in the electrolyte containing 0.15 M Al(NO₃)₃. The results of EIS analysis and morphological examination showed that the MgO anodic film modified with Al₂O₃ exhibited the superior corrosiom resistance for AZ91D Mg alloy.     

铁素体-马氏体钢P91和P92在超临界水中腐蚀后氧化膜多孔性分析

用X射线衍射（XRD）和扫描电镜-电子能谱（SEM-EDX）技术研究P91、 P92在500℃/25 MPa和550℃/25 MPa超临界水中腐蚀后氧化膜的多孔性成因。结果表明,两种材料氧化膜均为双层结构,外层氧化膜为 Fe₃O₄相,内层氧化膜为Fe₃O₄和FeCr₂O₄相,P92在接近氧化膜区域的基体内存在一个内氧化区。P91和P92在超临界环境中腐蚀后氧化膜的多孔性与外层氧化膜Fe₃O₄的缺陷类型有关,富氧Fe₃O₄中的缺陷主要类型为氧空位,在超临界状态下,当氧空位浓度达到一定程度后,空位坍塌即形成小孔。     

Microstructure and properties of CVD γ-Al2O3 coatings

This work deals with the microstructures and wear properties of chemical vapour deposited γ-Al₂O₃. The γ-Al₂O₃ coatings were deposited at 800 °C on TiN and Ti(C,N) pre-coated cemented carbide substrates. The microstructures developed in the γ-Al₂O₃ coatings and the influence of the nucleation surface on the growth of γ-Al₂O₃ were characterised using transmission electron microscopy, electron energy-loss spectroscopy and X-ray diffraction. The γ-Al₂O₃ coatings were fine-grained with a high density of {1 1 1} growth twins and contained some residual sulphur. γ-Al₂O₃ was found to grow epitaxially on the investigated substrates. The mechanical properties were evaluated in metal cutting and were compared with those of κ-Al₂O₃ coated tools. As compared with the κ-Al₂O₃ coatings, the γ-Al₂O₃ coatings exhibited slightly worse adhesion and tendency for edge chipping. However, the γ-Al₂O₃ coatings showed better crater wear resistance on the rake face than κ-Al₂O₃ coatings.     

Effect of Cu on the magnetic properties and reducibility of Fe2TiO5

Ferrites have been studied for several years due to their wide use as magnetic materials for telecommunications, audio and video, power transformers and many other applications.

Equimolar mixtures of Fe₂O₃ and TiO₂ were fired in a muffle furnace at 1200 °C for 4 h. Mixed samples were prepared by replacing TiO₂ with calculated amounts of CuO (x = 0.2, 0.4, 0.6, 0.8 and 1 mol). The synthesized samples were characterized with X-ray diffraction and their magnetic properties were measured using vibrating-sample magnetometer. The microstructure of the sample was examined using reflected light microscope and scanning electron microscope. The formation of Fe₂TiO₅, Fe₅CuO₈, Cu₂TiO₃ and CuFeO₂ phases were detected whereas their magnetic properties increased with increasing the added mole ratio of Cu²⁺ ions. The isothermal reduction kinetics of synthesized nanocrystallites Ti–Cu mixed ferrite compacts were studied at 500 °C using hydrogen gas. It was found that the reduction rate and the reduction extent increased with increasing the extent of Cu²⁺ (0.2–1) whereas the maximum reduction extent (100%) was detected for pure Cu ferrite (Cu²⁺) while the minimum reduction extent (12%) was detected for pure iron titanate (Cu²⁺ = 0). The magnetic properties showed a drastic improvement upon reduction with hydrogen gas.     

A facile route to VN and V2O3 nanocrystals from single precursor NH4VO3

V₂O₃ and VN nanocrystals have been synthesized by the decomposition of the precursor NH₄VO₃ and following nitridation in an autoclave with metallic Na flux at 450–600 °C. X-ray powder diffraction (XRD) recorded the evolution process of the reaction from precursor NH₄VO₃ to hexagonal V₂O₃ and then to NaCl-type VN. In addition, the products were characterized by X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM).     

Processing, microstructure, and properties of laser remelted Al2O3/Y3Al5O12（YAG） eutectic in situ composite

Laser remelting and rapid solidification were performed in preparing the high-performance Al2O3/Y3Al5O12（YAG） eutectic in situ composite. The microstructure characteristic and solidification behavior were studied using scanning electron microscopy（SEM）, energy dispersive spectroscopy（EDS）, X-ray diffractometry（XRD） and simultaneous thermal analysis（STA）. The hardness and fracture toughness were obtained using an indentation technique. The results show that the laser remelted Al2O3/YAG composite has a homogeneous eutectic microstructure without microcrack and pore. The component phases of Al2O3 and YAG are three-dimensionally and continuously reticular connected, and finely coupled without grain boundaries, colonies and amorphous phases between interfaces. The eutectic interspacing is greatly refined with increasing the scanning rate and average is only l μm. The synthetically thermal analysis indicates that the eutectic temperature of Al2O3-YAG is 1 824 ℃, well matching the phase diagram of Al2O3-Y2O3 system. The maximum hardness reaches 19.5 GPa and the room fracture toughness is 3.6 MPa.m^1/2.     

Synthesis and properties of Ba3NaRu2O9−δ and Ba3(Na, R)Ru2O9−δ (R=rare earth) crystals

Crystals of Ba₃NaRu₂O_9−δ (δ≈0.5) and Ba₃(Na, R)Ru₂O_9−δ (R=Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm and Yb) were grown by an electrochemical method, and their crystallographic, magnetic, and electric properties were studied. All crystals have a hexagonal structure of space group P6₃mmc. Ba₃NaRu₂O_9−δ and Ba₃(Na, R)Ru₂O_9−δ (except Ce) have a negative asymptotic Curie temperature suggesting the existence of an antiferromagnetic order; however, they are paramagnetic at temperatures above 1.7 K. Ba₃NaRu₂O_9−δ has an effective magnetic moment P_eff of 0.91 μ_B, while P_eff of Ba₃(Na, R)Ru₂O_9−δ (except Ce) reflects the large free-ion moment of the rare earth ions. Ba₃(Na, Ce)Ru₂O_9−δ shows peculiar magnetic behavior that differs from the magnetism of other Ba₃(Na, R)Ru₂O_9−δ crystals. The resistivity of all crystals exhibits an activation-type temperature dependence with an activation energy in the range of 0.10.2 eV.     

Kinetics and Morphological Analysis of Silver Platinum Bimetallic Nanoparticles

Kinetics of a one-pot core–shell synthesis of bimetallic(BM) silver–platinum(Ag–Pt) nanoparticles(NPs) by simultaneous reduction of 1:1 mol fraction of precursors H2 Pt Cl6á6H2O and Ag NO3 in aqueous solution is reported.Kinetics analysis was done by plotting UV–visible absorptions versus reaction time with a first-order fitting. Recorded constants of Ag NPs(0.079 s~(-1)), Ag–Pt NPs 1:1(0.082 s~(-1)), and Pt NPs(0.006 s~(-1)) were obtained. The NPs suspension solutions were clear, free from Ag Cl precipitate, and had characteristic optical properties of 450 nm(Ag NPs), while there were no observable bands for Pt and BM NPs. Morphological analysis using transmission electron microscopy, energydispersive X-ray spectroscopy(EDX), and selected area electron diffraction(SAED) depicted spherical aggregates of Ag NPs, Pt NPs and core shell Pt–Ag NPs 1:1 of average size of 60, 2.5, and 20 mm, respectively. Presence of the Ag and Pt elemental composition in the nanoparticle suspensions was confirmed by EDX. SAED ring patterns revealed a single facecentered cubic crystalline nature of Ag NPs and showed typical Pt-based BMs randomly overlapped ring pattern with sharp diffraction spots.     

In Situ Transmission Electron Microscopy Observations of the Growth Process of Fe_3O_4–Ag Nanoparticles

The properties of nanocrystals are highly dependent on their morphology, composition and structure. To obtain full control over their properties, the behavior of nanocrystals under external stimuli, such as heat treatment, needs to be understood. Herein, to in situ observe their microstructure and morphology changes, Fe_3O_4–Ag heterodimers were selected as a model system. Their structural changes after heat treatment were investigated by in situ transmission electron microscopy. A combination of real-time imaging with elemental analysis enabled observation of the transformation of Fe_3O_4–Ag heterodimers having a loose interface configuration to those with a Janus structure at the atomic scale after heating from room temperature to 600 °C. After incubation at 600 °C for 32 min, two kinds of Janus structures could be seen, including a clear linear interface in the Fe_3O_4–Ag heterodimers and a semi-crescent-shaped interface between the Ag and Fe_3O_4 nanoparticles(NPs). These dynamic observations provide unique insights into NP growth mechanisms, which are essential for understanding and controlling the structure and morphology of nanoparticles.     

Analysis of Oxides Formed on the Surface of the Alloy 690 in Hydrogenated Supercritical Water

The oxides formed on the surface of the alloy 690 in hydrogenated supercritical water at 400℃ for 1000 h were investigated using scanning electron microscopy,transmission electron microscopy,scanning transmission electron microscopy and energy-dispersive X-ray spectroscopy.The oxides on me surface of the alloy 690 exhibited multi-layer structure:an outer layer consisted of granular crystallites(NiO and NiFe_2O_4) and a compact inner layer(spinel and Cr_2O_3).Chemical analysis indicated that the outer layer was enriched in nickel but depleted in chromium,whereas the inner layer was enriched in chromium and iron but depleted in nickel.The inner layer was also characterized as layered structure by Fe-rich spinel on top of continuous Cr_2O_3 layer.Besides,Cr_2O_3 nodules were readily observed at the oxides/alloy interface.     

Formation of Al–Y oxide during processing of γ-TiAl

While processing Y₂O₃ dispersed γ-TiAl, Y₂O₃ particles which dissolved during hot isostatic pressing (HIP’ing) were found to precipitate during the heat treatment in the form of a mixed Al–Y oxide. To understand the chemical reaction that occurs between Y₂O₃ and γ-TiAl during the heat treatment cycle, a powder mixture comprising of γ-TiAl and 10 wt.% Y₂O₃ was mechanically alloyed (MA’d) for 8 h and the milled powder was subjected to differential thermal analysis (DTA) at 1150 °C prior to analyzing it using X-ray diffraction technique. The present study clearly demonstrates that aluminum in the combined form either as γ-TiAl or Al₂O₃ reacts in a similar manner with Y₂O₃ when milled and heat treated at 1150 °C. In either case there is formation of Al₂Y₄O₉ (2Y₂O₃.Al₂O₃).     

X-ray diffraction study on formation of ErNbO4 powder

The formation of ErNbO₄ powder, prepared by calcining an Er₂O₃ (50 mol%) and Nb₂O₅ (50 mol%) powder mixture at 1100 and 1600 °C for different durations, was investigated by using X-ray diffraction. The experimental results have displayed that although the solid-state reaction had started to some extent when the mixture was pre-calcined at 1100 °C for a duration of 13 h, the two original phases Er₂O₃ and Nb₂O₅ still dominated the mixture. When the duration of the calcination reaction was increased to 120 h at the same temperature, the resultant mixture experienced a nearly complete phase transformation. Accordingly, the ErNbO₄ phase was dominant phase in the mixture. Nevertheless, a small portion of the raw powder still existed in the mixture. When the calcining temperature was elevated to 1600 °C, ErNbO₄ powder with higher purity could be obtained for a relatively much shorter duration (only up to several tens of hours). A simple formation mechanism of ErNbO₄, an elevated-temperature-assisted solid-state chemical reaction: Er₂O₃+Nb₂O₅2ErNbO₄, is suggested. In addition, the present experimental results offer important evidence for the formation of the additional phase ErNbO₄ induced in Er:LiNbO₃ crystals by vapour transport equilibration (VTE) treatment.