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Abstract: Thermal stability and reaction properties of Al–CuO system, a mixture of 50–200nm aluminum nanoparticles passivated by nitrocellulose and 12nm copper (II) oxide, were investigated with microstructure characterization, differential thermal analysis (DTA), and thermogravimetric analysis (TGA). Transmission electron microscopy observation confirmed that the passivation coating successfully hinders the oxidization. TGA revealed that the passivation shell does not influence the ignition temperature of the thermite reaction. Reaction chemistry of the nano-thermite was elucidated by heating the composite both in inert ambient and vacuum. It was found that the thermite reaction composes of three continuing steps: At 570°C, Al is oxidized into Al2O3 by reacting with CuO, which forms Cu2O and produces a significant amount of heat. Subsequently two endothermic reactions occur. Starting at 800°C, alumina reacts with Cu2O and forms CuAlO2. Above this temperature CuAlO2 will decompose and eventually produce alumina, Cu, and O2 at 1000°C. Since the nano-thermite reaction pathway differs greatly from bulk thermite reactions, these results are important to develop a nano-thermite platform that can be used for a novel low cost, low temperature, and copper based microjoining and advance IC packaging. [Copyright &y& Elsevier]

Abstract: Highly entangled TiO2 nanowires were directly synthesized by hydrothermal growth on Ti substrates at 180°C utilizing various organic solvents to oxidize Ti. The growth mechanism, microstructure and phase transition of TiO2 nanowire membranes were investigated in detail. TiO2 nanowires, with diameters of 10–20nm and lengths up to 100μm, show a phase transition from Type-B to anatase by annealing at 700°C. Robust, free standing TiO2 nanowire membranes with millimeter level thickness can be cleaved from Ti substrates or directly prepared from thin Ti foils. These porous TiO2 membranes, while effective for mechanical microfiltration, can also photocatalytically degrade pharmaceuticals such as trimethoprim under UV irradiation. [Copyright &y& Elsevier]

Abstract: Diamond-like amorphous carbon films have been deposited on silicon and quartz substrates by ablation of graphite using 120 fs pulses from an amplified Ti:sapphire laser operating at 800 nm. The results clearly show that fs-DLC films are composed of sp, in addition to sp2 and sp3 bonded species. We find that the sp concentration can be somewhat increased by deposition in vacuum at liquid nitrogen temperature. Vibrational modes involving sp, sp2 and sp3 bonds in putative molecular species in these materials have also been studied using surface enhanced Raman spectroscopy (SERS) and these results are compared to DFT simulations of Raman spectra of several linear carbon chains. It is found that the chain length of sp-bonded carbon species increases when deposition occurs in a He buffer gas indicating that sp-bonded chains present in the gas phase also become incorporated in the film during condensation. SERS spectra together with spectral simulations using DFT show that fs-DLC contains a limited number of well-defined structural components formed as the result of mixed sp, sp2 and sp3 bonding. [Copyright &y& Elsevier]

Abstract: By using top seeding melt-textured growth process, single domain bulk superconductor GdBa2Cu3O7−δ (Gd-123) was prepared in air with variable additions of nanosized SnO2 and ZrO2 powders. The inhomogeneous distribution of Gd2BaCuO5 particles was observed by scanning electron microscope study for each bulk with nanoparticles addition. A band structure composed by second phase free band, narrow second phase rich band and second phase diluted band was observed along both a–b plane and c growth sectors in the vicinity of seed site. At 77K high critical current (J c) was increased up to 99,300Acm−2 under self-field in H∥c-axis configuration in Gd-123 bulk with 0.004 ZrO2 addition, molar ratio to Gd-123. J c has a remarkable spacial distribution inside the samples while keeping T c almost stable for all addition quantities. [Copyright &y& Elsevier]

Abstract: Superconducting properties of the melt-growth bulk GdBa2Cu3O7−δ (Gd123) were studied with the addition of BaO2, fine Gd2BaCuO5 (Gd211) and Gd2Ba4MoCuO z (Gd2411) from the viewpoint of improvement of the critical current density (J c) by growth process in air. The addition of BaO2 with 0.1 in a molar ratio to Gd123 effectively enhanced J c. This is coming from the suppression of the solid solution growth in Gd123 with Ba-rich phase. The addition of the ball-milled fine Gd211 particles enhanced J c to 90,000A/cm2 at 77K under self-field. Single phase Gd2411 was successfully synthesized in air and added into Gd123 system with substitution in part by Gd211 as the second phase. The J c of the samples mixed with Gd2411 reached 84,500A/cm2 at 77K under self-field. We conclude that the present additive materials with a proper amount are very effective to improve the J c value of Gd123 bulk superconducting magnets. [Copyright &y& Elsevier]

Abstract: The RE/Ba substitution has a significant effect on the growth, microstructure and flux pinning properties of melt-processed Gd1+xBa2−xCu3O7−δ superconductors. We prepared a series of Gd1+xBa2−xCu3O7−δ, (Gd123 solid solutions) with x=−0.1,0,0.05,0.1,0.15 and 0.2. The single phase of Gd123 solid solutions was confirmed with both X-ray diffraction and DTA analysis for x=0 to 0.1 as-grown samples, quenched in air. DTA/TG analysis in air showed that the thermal stability decreases with increasing x. After the post-annealing in flowing argon gas at 940°C for 10h (ArPA), the Gd123 solid solutions with x=0.1,0.15 and 0.2 were decomposed into Gd2BaCuO5 and Gd123 solid solutions with low substitution levels and minor liquid phases. The critical transition temperatures (Tc’s) of Gd123 solid solutions with the ArPA show dramatical increase compared to the samples without ArPA. The Gd123 solid solutions annealed in O2 at 400°C show a narrower superconducting transition width than those treated at 350°C. These results contribute to improve the properties of the melt-processed bulk superconductors. [Copyright &y& Elsevier]

Abstract: Nano-sized centers for magnetic flux pinning were successfully introduced into a bulk superconductor GdBa2Cu3O7−δ (Gd123) by mixing ZrO2 nanoparticles with precursor prior the melt growth in air. Superconducting properties and structure of doped Gd123 were studied by magnetization and transmission electron microscopy, respectively. The critical current density (J c) and critical temperature indicate that the optimum addition amount is 0.2–0.8% ZrO2 in molar ratio to Gd123 as composition. With 0.4mol % ZrO2 addition, J c was increased to 100,000A/cm2 at 77K under self-field. The normalized pinning force deduced from the magnetization as a function of applied magnetic field shows single peak. Thus, the nano-sized ZrO2 addition enhanced the normal core pinning under low magnetic field, B/B irr <0.2. Particles with <50nm in diameter were observed and assigned as BaZrO3 particles locating inside single domain Gd123. The present result may assess that BaZrO3 nanoparticles or associated defects plays a role of pinning centers within a comparable range with the coherence length ξ. [Copyright &y& Elsevier]

The presence of dyes, pharmaceuticals and many other pollutants in wastewaters is critical due to severe effects on the human beings and on the environment. Here, solutions of graphene oxide (GO) and reduced graphene oxide (rGO) were tested as adsorbents for the removal of methylene blue (MB), a cationic dye, from aqueous media. The reduced forms of graphene oxide were obtained after laser irradiation of colloidal suspensions of graphene oxide, obtained by the Hummers and Offeman's method. We observed that both graphene oxide and its reduced forms are excellent adsorbents towards methylene blue. In particular, rGO showed a higher adsorption capacity than GO, suggesting that a strict control of laser irradiation time permits to obtain rGO with different degrees of reduction and therefore the residual oxygenated functional groups may influence the adsorption behaviour more or less. Characterization of the samples by atomic force microscopy (AFM) showed that produced rGO sheets via laser irradiation exhibited a discontinuous surface where some holes could be detected contributing to an enhancement of the rGO surface area that is a higher adsorption capacity. [ABSTRACT FROM AUTHOR]

Ni nanoparticles were successfully used as a melting point depressant-free filler metal to join Inconel 718 via transient liquid phase (TLP) bonding in a vacuum environment. Ni nanoparticles of 22, 29, and 42 nm in diameters were synthesized by controlling the reducing agent injection rates and the TLP bonding was carried out at up to 1050 °C with heating rates of 2–15 °C/min. Based on the Gibbs-Thomson equation and surface melting models, bonding using Ni nanoparticles occurs due to competing solid-state sintering and surface melting processes. It was found that larger particle size, faster heating rate, and higher maximum temperature resulted in higher bonding strength due to less grain boundary contamination, smaller crystallite size, and more robust metallurgical bonding, respectively. Using a faster heating rate limits the amount of solid-state nanoparticle-nanoparticle sintering that occurs at lower temperatures. The suppression of nanoparticle-nanoparticle sintering as a function of nanoparticle diameter is also discussed. The maximum bonding strength achieved is 243 MPa. According to digital image correlation, the strain is mostly sustained in the Ni-Inconel interfacial region. The fractography of Ni nanoparticle-bonded joints is also discussed in detail. Unlabelled Image • Ni nanoparticle bonding strength up to 243 MPa in a lap shear configuration • Heating rate, temperature, and particle size identified as key factors • Ni nanoparticle hardness up to 231 HV • Dense Ni NP joint achieved over 300 °C below the particle melting point [ABSTRACT FROM AUTHOR]

Evaluation of hydrogen diffusion in structural materials is essential to predict the leakage and embrittlement of hydrogen storage applications. In this work, we investigate the atomic-scale diffusion of interstitial hydrogen (H) in α-iron (Fe) over a temperature range from 350 to 900 K with different H concentrations (0.01–5%), employing classical molecular dynamics (MD) simulations. The self-diffusivity of H atoms increases with increasing temperature and decreasing concentration. With low concentrations, the calculated diffusion properties agree well with prior experiments. However, with a higher concentration (≥1%), the H diffusivity at low temperatures deviates from a high-temperature Arrhenius behavior. Through the energetic and structural analysis, we suggest that this deviation is attributed to a reduced mobility due to increased energy barrier by other H interstitials. This work contributes to the effective design of H storage applications by identifying temperature and concentration effects on permeability and addressing possible microstructural transformation. • H diffusivities in α-Fe at different temperatures and concentrations are reported. • Self-diffusivity with high H concentrations does not follow the Arrhenius relation. • Microstructural changes occurred at high H concentration and at low temperature. • H interstitials affect migration of other H atoms, contributing to cluster formation. [ABSTRACT FROM AUTHOR]

In this work, vacuum filtered and polymer mixed e-spinning membranes (ESPMs) made from or doped with Fe-based nanomaterials were successfully fabricated to remove Cd2+ ions from a neutral aqueous solution. The used Fe-based nanomaterials including FeOOH precursor Nanowires (NWs), α-Fe 2 O 3 NWs and Fe 3 O 4 nanoparticles (NPs) were synthesized by elevating the hydrothermal reaction temperature from 250 °C to 500 °C or doing post-heating treatment. The adsorption results showed that vacuum filtered membranes (VFMs) overall performed a better Cd2+ ions removal behavior than e-spinning ones. Among them, VFM made from Fe 3 O 4 NPs has the highest adsorption capacity (qt) with the adsorption amount of Cd2+ ions reaching about 29.3 mg/g within only 2 min due to the high specific surface area of NPs. Models of pseudo-first-order, pseudo-second-order and intraparticle diffusion were used to study the kinetics of Cd2+ ions removal process, and a high correlation coefficient (R2) of 0.99 was obtained when pseudo-second-order model was used. It was calculated that the equilibrium rate constant of VFM made from Fe 3 O 4 NPs has reached about 0.28 g mg−1 min−1, much smaller than those of other membranes, which indicated a high Cd2+ ions removal efficiency. • Vacuum filtered and polymer mixed e-spinning membranes (VFMs; ESPMs) were successfully fabricated. • VFMs had a higher Cd2+ ions removal efficiency than ESPMs. • Pseudo-second-order model can best satisfy the adsorption process for VFMs and ESPS. [ABSTRACT FROM AUTHOR]

We demonstrate the fabrication of in-plane and multi-layer 3D micro-supercapacitors (MSCs) based on laser carbonization of polyimide (PI) sheets. Focused femtosecond (fs) laser pulses rapidly convert the insulating PI into an electrically conductive porous carbon structure. The specific capacitance of the single-layer supercapacitor with a thickness of 80 μm reaches 22.40 mF/cm 2 (2.8 F/cm 3 ) at 0.1 mA/cm 2 charge-discharge current density. The high performance is attributed to hierarchical porous structures and the appropriate heteroatom nitrogen/oxygen doping. The 2-layer and 3-layer stacked MSCs show an improved specific capacitance as high as 37.2 mF/cm 2 and 42.6 mF/cm 2 at a current density of 0.1 mA/cm 2 , respectively, which are attractive values among the carbon material-based MSCs reported till now. The voltage and capacitance can be scaled up by simply writing MSC arrays in serial and parallel connections. The facile fabrication and superior performance of carbon-based MSCs fabricated by laser direct writing may pave the way for promising applications of flexible, portable, and wearable electronic devices. [ABSTRACT FROM AUTHOR]

Novel 3D N-doping Ta 2 O 5 nanoflowers (NFs) photocatalysts were synthesized at different annealing temperatures ranging from 700 °C to 850 °C. The microstructure, phase composition, and chemical states of those photocatalysts were characterized in details. The adsorption kinetics as well as photocatalytic performance under visible light irradiation were also investigated. Importantly, compared to N-doping Ta 2 O 5 NFs samples obtained at other nitriding temperatures, the Ta 2 O 5 NFs nitrided at 750 °C displayed high surface adsorption and photocatalytic degradation activity of Methylene Blue (MB) due to the synergistic effect of large surface area, strong surface adsorption, light absorption and photosensitization. The experiment results confirmed that the adsorption of MB to these samples and photocatalytic degradation follow the pseudo-second order chemisorption mechanism and pseudo first order degradation kinetics, respectively. The main reactive species were identified through the scavenging reaction following the order of h + > OH > O 2− . Additionally, degradation product analysis was conducted using liquid chromatography tandem mass spectrometry (LC–MS) technique combined with the UV–vis absorption spectrum. The results showed that the degradation was initiated by demethylation of the dye molecule. The current work may contribute to additional applications of these 3D N-doping Ta 2 O 5 hierarchical nanostructures such as photoelectric chemical (PEC) water splitting, surface adsorption, supercapacitors, solar cells, etc. [ABSTRACT FROM AUTHOR]

We have developed a new method for preparing a paste containing a high concentration of Ag nanoparticles for pressureless bonding. A nanoscale layer of polyvinylpyrrolidone coated on the nanoparticles prevents the coalescence of Ag nanoparticles. After heating in air, sintering and bonding occur after the decomposition of polyvinylpyrrolidone. Joint strengths were increased significantly using this new Ag nanoparticle paste as bonding material. Robust joints with shear strength above 20MPa were formed even without additional bonding pressure. [Copyright &y& Elsevier]

Abstract: Crystallization sequences of MgO–Al2O3–SiO2–TiO2 system glass were investigated by means of DTA, XRD, SEM and EDS. The mechanical properties of samples, including density, microhardness and elastic modulus, were characterized as well. The relationship between crystalline phases, heat treatment methods and mechanical properties is discussed. The results have shown that: the glass first underwent extensive phase separation into titanium-rich droplets in a silica-rich matrix, then magnesium aluminotitanate (MAT) initially precipitated in the droplet phase. With the crystallization temperature increased, β-quartzss, sapphirine, α-quartzss, α-cordierite and cristobalite made their appearance successively. When the glass was heated at 1100°C for 2h, the maximum elastic modulus of 137GPa (accompanied by a microhardness of 8.5GPa and a density of 2.924g/cm3) was obtained. [Copyright &y& Elsevier]

• A novel approach to fabricate waterproof sensors inside flexible substrate by laser direct writing. • Silver nanoparticles conductive circuits sealed inside PDMS film form a waterproof sensor. • This process can be developed as a general fabrication method for various waterproof devices. The preparation of stable, reliable and multifunctional sensors requires constant research. This study reports a novel approach to fabricate waterproof sensors inside flexible substrate by laser direct writing. Polydimethylsiloxane (PDMS) films were prepared as flexible substrates. A silver ink composed of silver nitrate, sodium citrate, and polyvinyl pyrrolidone (PVP) were used in this work. The silver ink was first coated on the surface of PDMS film. Then a 405 nm laser was used to reduce silver nanoparticles for conductive circuits on PDMS film. After cleaning the unprocessed silver ink another layer of PDMS film was covered on the silver circuits to form a waterproof sensor. The sensor can be used for detection of bending and elongation of fingers. The response time is 0.3 s, and the recovery time is 0.4 s. The sensor can respond well with high frequency and low frequency bending. It can keep its functions normally after five hundred times of bending. Moreover, the sensor can be operated normally underwater with good waterproof performance and stability. It can be safely used to monitor movement in wet conditions, rainy weather and underwater environments. Based on these experimental results, this facile process is promising for preparation of waterproof wearable sensors. [ABSTRACT FROM AUTHOR]

In this paper, the nanostructured reactive multilayer films (RMFs) are used as the intermediate layer to assist laser welding of Ti6Al4V alloy. During the welding process, the heat of the laser ignites the RMFs, and the heat released by the RMFs reaction instantaneously reaches the liquidus temperature in the center of the joint. This new joining method is helpful in reducing the laser energy input, minimizing the increasing brittleness and reducing strength effect of heat affected zone of the titanium alloy base material, and increase the joint strength of welds. The experiment confirmed that the joint with the Ni/Al RMFs as the intermediate layer can achieve a shear strength of 396 MPa at 700 W laser power, which is 3 times as high as that of the direct laser welded joints without using Ni/Al RMFs at the same power. Moreover, the Ni/Al RMFs as an intermediate layer can reduce the laser power required for welding by 10–20% without lowering the joint strength. Unlabelled Image • Laser welding was applied for Ti6Al4V with the assistance of Ni/Al reactive nanomultilayer films (RMFs) as an interlayer. • Ni/Al RMFs can reduce the laser power required for welding by 10-20% without lowering the joint strength. • NiAl brittle phase increases in the welding seam as the RMF thickness increases, thereby reducing the joint strength. [ABSTRACT FROM AUTHOR]