Enhanced thermal stability of amorphous aluminum alloys through microalloying

Amorphous aluminum alloy powders with compositions of Al₈₅Y₇Fe₈, Al₈₃Y₇Fe₈Ti₂, and Al₇₉Y₇Fe₈Ni₃Ti₂Nd₁ were synthesized with crystallization temperatures of 342 °C, 446 °C, and 457 °C, respectively. In-situ high-temperature synchrotron diffraction results were correlated with differential scanning calorimetry studies to investigate the structural evolution during the crystallization. The results show that, through microalloying, the onset-of-crystallization temperature was increased by 115 °C, and the resulting crystalline products changed from a mixture of fcc-Al and an intermetallic phase in the case of Al₈₅Y₇Fe₈ to only intermetallic phases.     

Preparation of Mo2C@a-C core-shell powders via carburization of Mo particles by 1-chlorobutane and hexachlorobenzene

Mo₂C@a-C core-shell powders were prepared by reacting Mo powders with gaseous 1-chlorobutane or hexachlorobenzene at 1173 K. The chlorinated reactants acted as the source of carbon for the carburization of Mo and the source of chlorine, which assists the etching of Mo to reduced particle sizes.     

Synthesis of carbon micro-rods via a solvothermal route

Novel carbon micro-rods with regular and uniform shape have been synthesized in high yield by magnesium acetate and n-butyl alcohol as the precursors via a solvothermal route. The resulting products were characterized by combined techniques including X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray (EDX) and Raman spectroscopy. The carbon micro-rods exhibit diameters ranging from 500 nm to 1 μm and up to 5-10 μm in length. We have found that the optimal reaction conditions for the growth of the carbon micro-rods were 500 °C and 12 h.     

Simultaneous doping of aluminum and fluorine on zinc oxide nanopowder using a low-cost soft chemical route

Simultaneous doping of aluminum (Al) and fluorine (F) on ZnO nanopowder was successfully achieved by a soft chemical method. The strong X-ray diffraction peaks revealed the high crystallinity of the synthesized nanopowder and the XRD profiles showed that the material has hexagonal wurtzite structure. EDAX results confirmed the presence of Al and F and from the quantitative analysis it was observed that there was a systematic increase in both dopants in the final product as they were included in the starting solution. The SEM images showed that the ZnO:Al:F powders have nanorod structure with hexagonal cross section. The simultaneous doping enhanced the carrier concentration of the ZnO nanopowders indicated by the higher IR reflectivity.     

化学镀法制备核壳型银-铜双金属粉

为改善超细铜粉的高温抗氧化性能,通过热力学数据理论上分析了液相还原反应取代置换反应的可行性,并以水合肼作还原剂,银以稳定性适中的银氨络合物存在,采用化学镀法制备银包覆超细铜粉的新技术,利用SEM、XRD等手段对双金属粉的形貌和晶相组成进行了分析.研究表明,一次包覆铜粉基体表面银的包覆率为40.22%,二次包覆银的包覆率可达94.98%,在铜粉表面形成了连续的银膜,可以认为是表面包覆结构,拓展了超细铜粉的应用领域.     

Cold compaction of silicon powders without a binding agent

We report on a novel process for the fabrication of silicon compacts, from low-cost powders, without the need for a binding agent and which avoids the inclusion of native oxides and high-temperature processing. Various types and grades of silicon powder are conditioned to produce particulates with a hydrogen-terminated surface before subjecting to uniaxial mechanical compression, at pressures between 100 MPa and 1000 MPa, at room temperature. The evolution of silane gas on initial exposure of the compacts to air indicates breaking of weak silicon-hydrogen bonds and silicon-silicon bonds during compaction. The silicon compacts have an inherent macro-porosity, with densities > 75% of solid silicon, depending on the size range of compacted particles. Enhancement in direct silicon-silicon bonding results in electrical continuity of compacted samples which are also chemically stable in HF.     

Additive-free and time-saving microwave hydrothermal synthesis of hollow microspheres structured boehmite

In this study, by using Al₂(SO₄)₃ aqueous solution and urea as raw materials, hollow microspheres structured boehmite was successfully synthesized only after 30 min reaction time at 180 °C via an additive-free and time-saving microwave hydrothermal route. The final products were characterized by techniques of X-ray diffraction (XRD), transmission electronic microscope (TEM), scanning electron microscope (SEM) and Fourier transform infrared spectrometry (FTIR). To investigate its crystal form and morphology evolution process, samples subjected to different reaction durations were prepared and characterized. The pivotal influence factors on boehmite morphology, such as reaction temperature, dosage of urea and microwave power range were discussed based on the experiment facts.     

Lithium storage in amorphous TiNi hydride: Electrode for rechargeable lithium-ion batteries

In this study, amorphous TiNi phase was successfully prepared using mechanically milling for a very short time of 8 h. HRTEM confirms the formation of amorphous phase with the presence of nanocrystalline Fe particles. After hydrogenation (30 bars of H₂ for a duration of 2 h), the electrochemical reaction shows that TiNi hydride/Li cell discharges at a current of one Li for 10 h between 3 V and 0.005 V. The discharge of TiNiH electrode around x = 1 Li corresponds to a capacity of 251 mAh g⁻¹ and a hydride composition of TiNiH_1.0 at an average voltage of 0.4 V. Ex-situ X-ray diffraction pattern collected at the end of the discharge shows a mixture of amorphous TiNi compound and LiH. A general mechanism for the electrochemical reaction is then proposed: α-TiNiH + Li⁺ + e⁻ → α-TiNi + LiH. The results from DFT calculations yield an average cell voltage of 0.396 V, which is in good agreement with the experimental pseudo-plateau occurring at 0.4 V.     

Influence of microstructural inhomogeneity of individual sides of Fe81Si4B13C2 amorphous alloy ribbon on thermally induced structural transformations

As a result of the preparation process of Fe₈₁Si₄B₁₃C₂ amorphous alloy ribbon, a difference has been observed between the opposite sides of the ribbon in microstructure and surface morphology. Influence of these differences on thermally induced structural transformations was studied. Thermal treatment below 600 °C had a significant influence on the evolution of the microstructure, as well as phase composition of individual sides of the ribbon. Treatment at higher temperatures caused the microstructural differences between two sides to decrease significantly. Phase composition of the alloy samples showed the opposite trend: the differences observed were the greatest in the fully crystallized alloy, after treatment at 700 °C. These differences are the result of different numbers of nucleation sites for Fe₂B phase on respective sides of the ribbon, leading to 30% difference in its content on different sides in the fully crystallized alloy.     

The core-shell structured Fe-based amorphous magnetic powder cores with excellent magnetic properties

The Fe-based soft magnetic amorphous powder cores (AMPCs) with excellent comprehensive magnetic properties were successfully designed and fabricated using the core-shell structured FeSiBCCr/TiO₂ composite powders. The influence of the concentration of water (H₂O) for the magnetic performance of the AMPCs has been systematically studied based on careful analysis of the process of nucleation and growth of TiO₂ under different H₂O concentration in the reaction system. The growth process for the TiO₂ coating layer with the H₂O concentration in the range of 0.01–0.02 ml/g corresponds to the heterogeneous nucleation phase, while the mixing phase of heterogeneous and homogeneous nucleation occurs when the concentration of H₂O increases to 0.03 ml/g. Optimized soft magnetic properties have been achieved for the AMPCs with H₂O concentration of 0.02 ml/g, including high permeability of 81.5 with a high frequency stability up to 10 MHz, high quality factor of 102 at 530 kHz, low core loss of 42 mW/cm³ at 500 kHz for B_m = 0.01 T, and better DC-bias property of 52% at a bias field of 100 Oe due to the uniform and proper thickness insulation coating layer, which can be used to produce miniature magnetic components for applications in medium and high-frequency fields.     

A new route to mass production of metal hydroxide/oxide hydroxide nanoparticles

Aluminum hydroxide/oxide hydroxide nanofibers were self-assembled by hydration of highly activated aluminum powder using no surfactants or templates. The activation was performed by milling aluminum powder with sodium chloride as nano-miller. Transmission electron microscopy images and X-ray diffraction patterns confirm that this method leads to smaller size of aluminum particles (less than 50 nm) and increases the lattice strain. These factors provide conditions under which hydration procedure proceeds until it reaches the core of aluminum particles. The synthesized powder consists of nanofibers with thickness less then 10 nm and average length of 120 nm and specific surface area of 309 m² g⁻¹. The process is convenient, highly efficient and capable to be implemented in mass production. It may be extended to produce hydroxide/oxide hydroxide nanopowders of other metals, as well.     

Synthesis, characterization and magnetic properties of CoFe2O4 nanorods

In this work, we demonstrated a new precursor route to synthesize CoFe₂O₄ one-dimensional (1D) nanorods. CoFe₂O₄ nanorods were prepared via the thermal decomposition of CoFe₂(C₂O₄)₃ nanorod precursor, which was prepared by solvothermal method without the assistance of template or surfactant. The microstructure and magnetic property of the obtained products were characterized by x-ray powder diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), thermogravimetric (TG) and differential thermal analysis (DTA) and vibrating sample magnetometer (VSM). The results showed that the as-prepared CoFe₂O₄ nanorods were built by magnetic nanoparticles after calcining the precursor nanorods at different temperatures, and the size variation of magnetic nanoparticles with calcination temperatures leaded to variable magnetic properties.     

Agglomerates of amorphous carbon nanoparticles synthesized by a solution-phase method

A novel solution-phase method is developed for preparation of agglomerates of amorphous carbon nanoparticles under ambient atmosphere by the reaction of ferrocene and ammonium chloride in diglycol at 200 °C. Samples are characterized by X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy and N₂ adsorption-desorption isotherms. It is found that the nanoparticles are complete amorphous and agglomerate together due to the strong surface tension. The agglomerates of amorphous carbon nanoparticles with a diameter of 20-50 nm have a wide size distribution of mesopores with a Brunauer-Emmett-Teller surface area of 75.2 m² g^− 1. It is proposed that the dissolved reactants uniformly dispersing in the solutions could react at a molecular level to form uniform carbon nanoparticles.     

Facile synthesis of SiBCN powders by a carbonitriding route

SiBCN ceramic powders were facilely synthesized from the compacts of silicon, B₄C and cornstarch by a carbonitriding route. Effects of silicon content in raw materials on phase composition, chemical bond, microstructure and oxidation resistance of as-received products after heated at 1550 °C were investigated. The featured chemical bonds such as CN and BCN in as-received products were detected by X-ray photoelectron spectroscopy (XPS). The microstructure of BN(C) distributed around nano-sized α/β -SiC/SiCN grains was revealed by transmission electron microscopy (TEM). The synthesized products with the Si/B/C ratio of 1:1:1 presented better oxidation resistance than SiC because of the strengthened chemical bonds and BN(C) formation.     

A novel route for preparing binary Sm–Co bulk amorphous alloys

A novel route for preparing binary amorphous alloy was proposed using Sm–Co system as an example. The alloy ingots with given compositions were used as the parent material. The amorphous intermetallic powder obtained by ball milling the parent alloy was consolidated by the high-pressure spark plasma sintering. The bulk amorphous alloy was detected and confirmed by X-ray diffraction, differential scanning calorimetry and transmission electron microscopy. The present route is potentially applicable to prepare a variety of binary and multicomponent bulk amorphous alloys with adjustable compositions.     

Synthesis of Ultrafine Fe3O4 Powder via a Novel Ageing Process

Ultrafine Fe3O4 powder was successfully synthesized via a novel ageing process from a precursor FeO(OH), which was the hydrolysate of FeCl3 in the urea solution. The structure of as-synthesized powder was characterized by X-ray diffraction (XRD), and the morphology of these nanoparticles was investigated using a transmission electron microscope (TEM). Pure phase Fe3O4 was obtained and the mean diameter of these nanoparticles was about 21 nm. Furthermore, the study indicated that the precursor FeO(OH) played an important role in the formation of Fe3O4 nanoparticles. The mechanism was also discussed.     

Preparation of nanostructured Cu/Zr metal mixed oxides via self-sustained oxidation of a CuZr binary amorphous alloy

We propose and demonstrate for the first time an approach to synthesize nanostructured photocatalysts through combustion of metal alloys in amorphous state. This approach takes advantage of metastable state and composition homogeneity of amorphous alloys and produce photocatalysts with uniformly dispersed oxides at nanoscale by self-propagating reactions. Using CuZr amorphous ribbons as an example, we demonstrate a photocatalyst containing copper oxides and ZrO2 in the form of 10 nm-thick nanosheet with 2 nm nanopores. The new catalyst substantially outperforms those previously reported copper oxide catalysts in experiments of photocatalytic degradation of methylene blue and direct methanol fuel cells. This study opens up an avenue to fabricate nanostructured functional oxides in an environment friendly approach not only for photocatalyst but also for oxide based nanoelectronic and nanoionic applications.     

Oxidation of amorphous alloys

Owing to their unique short- or medium-range ordered microstructures and excellent mechanical, physical, and chemical properties, amorphous alloys have attracted significant interest in recent years. For the application of amorphous alloys, clarifying their oxidation processes and mechanisms is necessary since many of the surface-related properties of amorphous alloys largely depend on the surface oxide layer. The aim of this paper is to review the recent research on the thermal oxidation behaviors of amorphous alloys under pure oxygen or air condition. The contents are divided into three categories according to the number of components the research considers, i.e., the oxidation of binary, ternary, and multi-component (>3) amorphous alloys. Each section discusses the thermal stability of the amorphous matrix, oxidation kinetics, and the oxide layer and amorphous substrate, which are strongly affected by internal factors (i.e., alloy elements and microstructure) and external factors (i.e., oxidation temperature, duration, and oxygen partial pressure, etc.). The general features of the oxidation of amorphous alloys – from simple binary to complex multi-component amorphous alloys – will be summarized. This overview of the current scientific understanding on the fundamentals of these materials may provide guidelines for the development of strongly corrosion-resistant amorphous alloys.     

Structure and properties of laser-cladded Ni-based amorphous composite coatings

A (N_i0.6Fe_0.4)₆₅B₁₈Si₁₀Nb₄C₃ amorphous composite coating has been fabricated on a mild steel substrate by a laser cladding process under different heat inputs. Observation of the structure and phase showed that the thickness of the coating decreased and the amorphous fraction increased when the laser cladding heat input was lower. The cooling rate increases when the heat input decreases, which favours the formation of amorphous phase. Microhardness and wear resistance test results indicated that a lower heat input led to higher microhardness and better wear resistance of the coating. An average microhardness of 1187.0 HV0.2 was obtained with a heat input of 69?J?mm^–1.     

Structural and microstructural phase evolution during mechano-synthesis of nanocrystalline/amorphous CuAlMn alloy powders

The formation mechanism of Cu–11.5Al–4Mn alloys by mechanical alloying (MA) of pure elemental powders was investigated. During milling, the powder sampling was conducted at predetermined intervals from 1 h to 96 h. The quantitative phase analyses were done by X-ray diffraction and the particles size and morphology were studied by scanning electron microscopy. Furthermore, the microstructure investigation and phase identification were done by transmission electron microscopy. Concerning the results, the nanocrystalline Cu solid solution were formed at short milling times and, by milling evolution, the austenite-to-martensite (2H) phase transformation occurred. Moreover, the formation of considerable amount of amorphous phase and its partial transformation to crystalline phases during the milling process were revealed. It was also found that, by milling development, the powder morphology changes from lamellar to semi-spherical and their size initially increases, then reduces and afterward re-increases.