Effect of Bath Concentration on Coagulation Kinetics at the Early Stage during Wet Spinning of PAN Copolymer Nascent Fibers

A mathematical model was proposed to simulate the effect of bath concentration on coagulation kinetics at the early stage of wet spinning for the poly(acrylonitrile-co-vinyl acetate)/dimethylsulfoxide (DMSO)/water system. The dependence of critical precipitation time, components concentration distribution, and the radius of nascent fibers on the concentration of DMSO in the DMSO/water coagulation bath were estimated by solving the model equation numerically. The experimental results indicated the model was suitable to simulate the dynamic features of the early stage of the coagulation process. The critical precipitation time was found to increase with bath concentration. The mode of phase separation was changed from instantaneous demixing to delayed demixing as DMSO bath concentration increased. The simulation results showed that bath concentration influenced the phase separation path which determined the polymer concentration distribution in the spinning solution. As a result, nascent fibers with different structures would form in wet spinning and a radial homogeneous structure would be obtained when the DMSO bath concentration increased to some extent.     

Investigation of Polyvinylidene Fluoride Membranes Prepared by Using Surfactant OP-10 Alone or with a Second Component,as Additives,via the Non-Solvent-Induced Phase Separation (NIPS) Process

Polyvinylidene fluoride (PVDF) flat-sheet membranes were prepared via a non-solvent-induced phase separation (NIPS) method at 60°C using a hydrophilic surfactant OP-10 (octylphenol polyoxyethylene ether) solely (Blank) or with a second additive [H₂O or lithium chloride (LiCl)] as pore-forming agents. The influence of OP-10 concentration on the surface tension, viscosity, and precipitation rate of PVDF/(H₂O, LiCl, or Blank) systems were investigated, and the ultrafiltration and mechanical properties of the resultant membranes were measured. It was found that an increased demixing rate during the coagulation process was the reason for the change in membrane morphology and properties. An obviously improved flux and slightly decreased mechanical properties and rejection were found in membranes prepared using a high concentration of OP-10 and the second component as additives. SEM pictures revealed an increased porous structure on the resultant membrane surface. A hypothesis was proposed to explain these phenomena; the reoriented surfactant molecules at the interface facilitated the water diffusion channels, which finally became the porous structure on the membrane surface. The weakened mechanical properties were due to the macrovoid structure in its membrane cross-section, which developed from the micelle structure in the casting solution. This hypothesis was further confirmed in a PVDF/OP-10/polyethylene glycol (PEG) system. A consistent conclusion was obtained.     

Study of ion–solvent interactions and activation energy of LiBr in DMSO,H<Subscript>2</Subscript>O and DMSO–H<Subscript>2</Subscript>O mixtures at various temperatures

The Jones–Dole B coefficients of the electrolyte Lithium bromide (LiBr), reference salts tetra butyl ammonium tetra phenyl borate (BU₄NBPh₄), tetra butyl ammonium bromide (BU₄NBr), and potassium chloride (KCl) in dimethylsulfoxide (DMSO), water, and DMSO–water mixtures were obtained at different temperatures range from 25 to 45 °C For this, the relative viscosities were measured for Lithium bromide (LiBr) and reference salts in DMSO, water, and DMSO–water mixtures at above-mentioned temperatures. The B coefficients of these electrolytes were behaved as structure makers in DMSO, while in H₂O and DMSO–H₂O mixtures, the B-coefficient values were less positive showing the weak structure-making effect. Ionic viscosity B coefficients allow us to assess the behavior of ions in the solvent mixtures. In this study it was observed that all the values of ionic B coefficient of (Li⁺) were positive and small showing the weak structure-making effects. It was also observed that Br⁻ ions maintain negative B coefficient values in all DMSO–H₂O mixtures, except in 60% DMSO mole fraction. From this it can be concluded that Br⁻ ion behaved as a structure breaker in water and in all DMSO–H₂O mixtures except in 60% DMSO mole fraction mixtures. The low B _± values of alkali metal ions and Br⁻ ions in water are due to the breakdown of the tetrahedral structural of water and the formation of strongly structured solvated ion. It is also observed that the values of the energy of activation of the flow for LiBr are greater in DMSO–water mixtures and in pure water than in DMSO. This may be due the presence of a network of hydrogen bonds which cause the hindrance in the flow of the solution of LiBr in DMSO–water mixtures and in pure water than in DMSO.     

Magnetic properties of CoFeP films prepared by electroless deposition

Structure and magnetization of CoFeP films prepared by the electroless deposition were systematically investigated by varying the bath composition and deposition parameters to optimize soft magnetic properties. The cobalt content in the CoFeP films varies from 40.4 to 94.9 wt% by controlling the bath composition. Increase of the metallic ratio FeSO₄·7H₂O/(CoSO₄·7H₂O+FeSO₄·7H₂O) affects the films’ microstructure, which switches from amorphous to crystalline structure. The magnetic properties of CoFeP films reveal that the coercivity (H_c) values range from 80 up to 185 A/m and the saturation magnetization (M_s) from 82 to 580 eum/g depending on the bath composition, deposition parameters and heat-treatment conditions. Increase of M_s and remanent magnetization (M_r) as well as decrease of H_c are observed for the CoFeP films with bath pH, temperature and the metallic molar ratio increasing. It is also found that the H_c is enhanced with the increase of NaH₂PO₂·H₂O concentration. CoFeP films showing good soft magnetic properties with coercivities less than 140 A/m and M_s close to 600 emu/g can be obtained in high pH bath and thereafter heat treatment. The deposit is found to be suitable as soft magnetic materials for core materials.     

A Monte Carlo model for determination of binary diffusion coefficients in gases

A Monte Carlo method has been developed for the calculation of binary diffusion coefficients in gas mixtures. The method is based on the stochastic solution of the linear Boltzmann equation obtained for the transport of one component in a thermal bath of the second one. Anisotropic scattering is included by calculating the classical deflection angle in binary collisions under isotropic potential. Model results are compared to accurate solutions of the Chapman–Enskog equation in the first and higher orders. We have selected two different cases, H₂ in H₂ and O in O₂, assuming rigid spheres or using a model phenomenological potential. Diffusion coefficients, calculated in the proposed approach, are found in close agreement with Chapman–Enskog results in all the cases considered, the deviations being reduced using higher order approximations.     

Effect of nickel on the initial growth behavior of electroless Ni-Co-P alloy on silicon substrate

In this work the small amounts of NiSO₄ was added to a basic electroless plating bath of CoSO₄ with Na₂H₂PO₂ as reducing agent for the deposition of Co-Ni-P film on a silicon substrate. The initial growth behavior, containing plating rate, chemical composition, crystal structure, surface morphology and micro-structure, of the electroless plating film was characterized by scanning electron microscope (SEM) and transmission electron microscope (TEM). The results showed that the growth morphology variation of the Co-Ni-P films deposited in the basic CoSO₄ + small amounts of NiSO₄ bath is the same as that of Co-P film deposited in the basic CoSO₄ bath, the plating rate of the Co-Ni-P film is much more rapid than that of the Co-P film, the Ni/Co wt.% in the Co-Ni-P film is greatly larger than that in the plating bath, and the structure of as-deposited film is crystalline at first stage and later stage.     

Preparation and application of core–shell Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>/polythiophene nanoparticles

The Fe₃O₄/polythiophene nanoparticles, possessing core–shell structure, were prepared by two-step method. In the first step, the Fe₃O₄ particles were synthesized via co-precipitation of FeCl₃ and FeSO₄, using the NH₃·H₂O and N₂H₄·H₂O as precipitant system. In the second step, the thiophene adsorbed and polymerized on the surface of the Fe₃O₄ in the solvent of chloroform. Raman, FTIR, EDS, XRD, TEM, Zeta potential measurement and TG-SDTA were employed to characterize the composition and structure of the products. The results showed that the Fe₃O₄/polythiophene nanoparticles were successfully synthesized with good dispersion and stable core–shell structure, provided with average particle size of approximately 20 nm, in which the diameter of Fe₃O₄ core was approximately 14 nm and the thickness of polythiophene shell was approximately 3–4 nm. Then, the nanoparticles were added into alkyd varnish to prepare a composite coating. The neutral salt spray test, paraffin control test and mechanical test were carried out to identify the properties of the composite coating. It was found that the composite coating had good performances of anticorrosion and paraffin controlling when the mass fraction of the nanoparticles was 0.8–1 wt% in alkyd varnish. As a multifunctional material, the Fe₃O₄/polythiophene nanoparticles can be used in the internal coating of pipeline and have great potential application in crude oil pipeline transportation.     

Preparation of High-Quality Polyacrylonitrile Precursors for Carbon Fibers Through a High Drawing Ratio in the Coagulation Bath During a Dry-Jet Wet Spinning Process

Excellent poly(acrylonitrile-co-itaconic acid) (99/1) (PAI) nascent fibers, which have an important role in preparing high-quality precursors for carbon fibers, were prepared by a dry-jet wet spinning process. Their structures were determined by X-ray diffraction (XRD), scanning electron microscopy (SEM) and an ultrasound solvent etching method, as well their properties being determined by a strength and extension meter and a fineness meter, both designed specifically for fibers. When a high drawing ratio, over 300%, was applied to the fibers in the dry-jet wet spinning coagulation bath, the molecular chains were easy to orient and regularly arrange, resulting in the relative crystallinity, crystal size and amorphous orientation degree of the nascent fibers being improved. The fibrils with large diameter were formed, increasing the bulk density with the overall porosity and pore numbers decreasing. Therefore, the nascent fibers had smaller diameters, higher strength, higher rupture elongation and smaller coefficients of variation. The optimum high performance PAI precursor fibers, with 0.59dtex in titer, 7.51cN/dtex in tensile strength, 7.9% in rupture elongation and the final carbon fiber with 5.54GPa in tensile strength, were obtained through a post-spinning treatment in which they were subjected to a high coagulation bath draw ratio and carbonization.     

Synthesis and characterization of V3O7⋅H2O nanobelts

V ₃O₇?H₂O nanobelts were prepared by a hydrothermal method at 190 ^°C using V ₂O₅?nH₂O gel and H₂C₂O₄?2H₂O as starting agents. The nanobelts obtained have diameters ranging from 40 to 70 nm with lengths of up to several micrometers. Their morphology and structure have been characterized by XRD, SEM, TEM and IR spectroscopy. The effect of the annealing temperature on the morphology of the resulting product has been investigated. XRD and SEM showed that thermal annealing of the V ₃O₇?H₂O sample in air led to the collapse of the V ₃O₇?H₂O nanobelt structure and the convert into V ₂O₅ nanobelts. For the first time V ₂O₅ nanobelts with an ultrahigh aspect-ratio have been obtained in air. Furthermore, electrical conductivity and static magnetic susceptibility measurements have been carried out.     

The effect of deposition temperature on the surface coverage and morphology of iron-phosphate coatings on low carbon steel

The influence of deposition temperature and concentration of NaNO₂ in the phosphating bath on the surface morphology and coverage of iron-phosphate coatings on low carbon steel was investigated. The phosphate coatings were chemically deposited on steel from phosphate bath at different temperatures (30-70 °C) and with the addition of different amounts of accelerator, NaNO₂ (0.1, 0.5 and 1.0 g dm⁻³). The morphology of phosphate coatings was investigated using scanning electron microscopy (SEM) and atomic force microscopy (AFM). The composition of iron-phosphate coatings was determined using energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD). Surface coverage was evaluated by the voltammetric anodic dissolution (VAD) technique.It was shown that the increase in temperature of the NaNO₂-free phosphating bath up to 70 °C caused an increase in surface coverage. The addition of NaNO₂ in the phosphating bath significantly increased the surface coverage of phosphate coatings deposited at temperatures lower than 50 °C. The phosphate crystals were of laminated and needle-like structures for deposits obtained at temperatures lower than 50 °C, while at higher temperatures needle-like structure was transformed to laminated structure. The increase in NaNO₂ concentration in the phosphating bath from 0.1 to 1.0 g dm⁻³ did not significantly increase the surface coverage, but decreased the crystals size, consequently favouring the phosphate nucleation and better packing of the crystals.     

Characterization of core-shell nanoparticles by small angle neutron scattering

The Ni₃Si-type nanoparticles dispersed in a mixture of H₂O/D₂O were characterised by SANS using the contrast variation method. The existence of a core-shell structure in the nanoparticles with a Ni₃Si(Al) core and amorphous SiO_x shell is confirmed by the SANS measurements. The nanoparticles were produced by extracting precipitates from a bulk Ni-13.3Si-2Al ( at. %) alloy using electrochemical phase separation technique and were pre-characterised by X-ray diffraction and transmission electron microscopy. By comparing the precipitate morphology in the Ni-Si-Al alloy with the extracted nanoparticles in the SANS measurements, it is clearly established that the precipitates shape and size are unaffected by the extraction process and that the amorphous shell forms on top of the particle core. However, the present measurement could not confirm or exclude the presence of H atoms in the shell structure. PACS 61.12.Ex; 61.12.-q; 61.46.Df; 61.82.Rx     

Thermomagnetically Responsive γ‐Fe2O3@Wax@SiO2 Sub‐Micrometer Capsules

A three steps synthesis route is proposed to generate thermosensitive and magnetically responsive γ‐Fe₂O₃@Wax@SiO₂ sub‐micrometer capsules with a paraffinic core and a solid and brittle shell. The process integrates Pickering‐based emulsions, inorganic and sol–gel chemistries to promote monodisperse in size wax droplets, γ‐Fe₂O₃ nanoparticles and mineralization of the wax/water interfaces. Hybrid capsules are obtained with an average size around 800 nm, representing the first example of sub‐micrometer capsules generated employing Pickering emulsions as templates. Cetyltrimethylammonium bromide (CTAB) cationic surfactant added during mineralization at concentrations between 0.17 and 1.0 wt% impacts the shell density. The shell density seems to improve its mechanical strength while affording a low wax expansion volume without breaking for CTAB concentrations above 1.0 wt%. At lower CTAB concentration (0.17 wt%), the silica shell becomes less bulky and cannot resist the wax dilatation induced by the solid‐to‐liquid phase transition imposed by hyperthermia. The magnetically induced heating provided by the internal magnetic moments is sufficient to melt the wax core, expanding its volume, inducing thereby the surrounding silica shell rupture. Such γ‐Fe₂O₃@Stearic Acid@Wax@SiO₂ sub‐micrometer capsules allow a sustained wax release with time, whereby 20% of the wax is released after 50 min of alternating magnetic field treatment.     

Collision cross sections and swarm coefficients of water vapour ion clusters (H2O)nH+ with n = 1, 2 and 3 in N2, O2 and air

The ion swarm transport coefficients such as reduced mobility, diffusion coefficients and reaction rates of three water vapour ion clusters (H₂O) _n H⁺ (with n = 1, 2 and 3) in N₂ and O₂ have been determined from a Monte Carlo simulation using calculated and measured elastic and inelastic collision cross sections. The elastic momentum transfer cross sections have been determined from a semi-classical JWKB approximation based on a rigid core interaction potential model. The inelastic cross sections have been deduced from the measured ones in the case of similar ion cluster. Then, the cross sections sets are fitted using either the measured reduced mobility at low electric field in the case of (H₂O) _n H⁺ in N₂ or the zero-field mobility calculated from the Satoh's relation and the measured ones in N₂. From the sets of elastic and inelastic collision cross sections thus obtained in pure N₂ and O₂, the ion transport and reaction coefficients for (H₂O) _n H⁺ are then calculated in dry air and also extended over a wide range of reduced electric field in N₂ and O₂. These ion data are very useful for modelling and simulation of non-equilibrium electrical discharges more particularly in humid gases at atmospheric pressure.     

Facile Fabrication of Dendritic Mesoporous SiO2@CdTe@SiO2 Fluorescent Nanoparticles for Bioimaging

A seeded watermelon‐like mesoporous nanostructure (mSiO₂@CdTe@SiO₂, mSQS) composed of a novel dendritic mesoporous silica core, fluorescent CdTe quantum dots (QDs), and a protective solid silica shell is successfully fabricated by loading QDs into dendritic mesoporous silica nanoparticles through electrostatic interaction, and then coating with a solid silica shell by the modified Stöber method. The shell thickness of mSQS can be tuned from 0 to 32 nm as desired by controlling the reaction parameters, including the amount of silica precursor, tetraethyl orthosilicate, that is introduced, the solvent ratio (H₂O:ethanol), and the amount of catalyst (NH₃?H₂O). These fluorescent mSiO₂@QDs@SiO₂ nanoparticles possess excellent stability and thickness‐dependent cytotoxicity, and are successfully applied to bioimaging.     

Direct observation of low-temperature catalytic decomposition of H3BO3 shell in core/shell Ni/H3BO3 nanoparticles

Decomposition of H₃BO₃ to B₂O₃ in core/shell Ni/H₃BO₃ nanoparticles was in situ recorded by transmission electron microscope as the irradiation time. The direct observation provides compelling evidence of the synergetic effect of the Ni core and the H₃BO₃ shell, revealing the catalytic mechanisms of metal nanostructures that induce the decomposition at 124 °C, lower than the bulk counterpart at 300 °C. This phenomenon can be theoretically explained by considering the weakening of B–O bond at the Ni–H₃BO₃ interface, and has important implications in understanding the lubricant behavior of H₃BO₃ in frictional wear.     

Generating Metallic Amorphous Core–Shell Nanoparticles by a Solid‐State Amorphization Process

Metallic crystalline/amorphous core–shell nanoparticles consisting of a crystalline Pd core (c‐Pd) surrounded by an amorphous Fe₂₅Sc₇₅ shell (a‐FeSc) are prepared by inert‐gas condensation. A phase transformation of the c‐Pd by a solid‐state diffusion process resulting in an amorphous core (a‐PdSc) surrounded by an amorphous FeSc shell is observed if the core–shell structure is irradiated at ambient temperature with 300 keV electrons. The amorphization process seems to involve the diffusion of irradiation‐induced defects and is presumably driven by the large negative heat of mixing of Pd and Sc, as well as by the excess enthalpy of the interfaces between the c‐Pd regions and the surrounding a‐FeSc. The structural transformation reported here opens a new way to producing metallic amorphous core–shell nanoparticles of different chemical compositions and probably novel properties.     

Diffusion von18O in Eis-Einkristallen

The coefficient of¹⁸O diffusion in single crystals of ice was measured at various temperatures ranging from ?5°C to ?29,5°C. The¹⁸O concentration was determined by the nuclear reaction¹⁸O(p, n)¹⁸F caused by recoil protons due to fast neutron irradiation. It was found that the coefficients of¹⁸O and³H diffusion are of the same order of magnitude and that they have the same activation energy. This shows that¹⁸O and³H diffusion is caused by the migration of whole H₂O-molecules. A mechanism of migration over molecular vacancies is discussed.     

Measurements of Silica Aggregate Particle Growth Using Light Scattering and Thermophoretic Sampling in a Coflow Diffusion Flame

The evolution of silica aggregate particles in a coflow diffusion flame has been studied experimentally using light scattering and thermophoretic sampling techniques. An attempt has been made to calculate the aggregate number density and volume fraction using the measurements of scattering cross section from 90° light scattering with combination of measuring the particle size and morphology from the localized sampling and a TEM image analysis. Aggregate or particle number densities and volume fractions were calculated using Rayleigh–Debye–Gans and Mie theory for fractal aggregates and spherical particles, respectively. Using this technique, the effects of H₂ flow rates on the evolution of silica aggregate particles have been studied in a coflow diffusion flame burner. As the flow rate of H₂ increases, the primary particle diameters of silica aggregates have been first decreased, but, further increase of H₂ flow rate causes the diameter of primary particles to increase and for sufficiently larger flow rates, the fractal aggregates finally become spherical particles. For the cases of high flame temperatures, the particle sizes become larger and the number densities decrease by coagulation as the particles move up within the flame. For cases of low flame temperatures, the primary particle diameters of aggregates vary a little following the centerline of burner and for the case of the lowest flame temperature in the present experiments, the sizes of primary particles even decrease as particles move upward.     

Synthesis and characteristics of nano-size sandwich structure (Y,Gd)BO3: Eu3+ phosphors

The sandwich structure core–shell–shell nanospheres SiO₂@(Y,Gd)BO₃:Eu³⁺@SiO₂ (SiO₂@YGB@SiO₂) have been synthesized by depositing YGB nanoparticles on silica core surface through the precipitation method, followed by sol–gel processing of tetraethoxysilane (TEOS) to form smooth silica shell over the surface of YGB. The phosphors were characterized by X-ray diffraction (XRD), scanning electronic microscope (SEM), transmission electronic microscope (TEM) and photoluminescence spectra. The results showed that the phosphors with spherical morphology can be produced easily by assembling the core–shell or core–shell–shell structure, and the XRD patterns indicated that the crystallinity of YGB is weakened due to the core–shell structure, which resulting from the local site symmetry of Eu³⁺ was decreased. The photoluminescence properties of the product are compared with those of the pure YGB, the core–shell structure SiO₂@YGB and YGB@SiO₂. The emission intensity, relative luminous efficiency and Red/Orange values of phosphors are increased in the order SiO₂@YGB@SiO₂>SiO₂@YGB>YGB@SiO₂>YGB; and the chromaticity coordinates of the phosphors are shifted from orange of pure YGB to red of SiO₂@YGB@SiO₂.     

YBCO熔融织构准单晶中的进氧和脱氧扩散研究

采用热重法研究了YBCO熔融织构准单晶中氧的化学扩散过程. 与以往的实验不同，采用固定 氧偏压变化温度的方法获得氧浓度梯度. 拟合实验所得重量等温弛豫曲线可知，在375—600 ℃温区内，熔融织构准单晶的氧化学扩散系数比单晶体高出约50％，但都约为10^{-10c m2s-1，激活能为～1eV. 对YBCO熔融织构准单晶中的进氧和脱氧研 究表 明两者具有相同的速率，证实实验过程中环境氧分压的改变会导致进氧和脱氧过程不一致. 关键词： 高温超导 氧扩散 熔融织构 热重法}