Heteroepitaxial growth of Au@Pd core–shell nanocrystals with intrinsic chiral surfaces for enantiomeric recognition

Noble metal surfaces with intrinsic chirality serve as an ideal candidate for investigating enantioselective chemistry due to their superior chemical durability and high catalytic activity. Recently, significant advance has been made in synthesizing metal nanocrystals with intrinsic chirality. Nonetheless, the majority reports are limited to gold. Herein, through a heteroepitaxial growth strategy, the synthesis of metal nanocrystals with intrinsic chirality to palladium was extended for the firs...     

Controlling of silicon–insulator–metal junction by organic semiconductor polymer thin film

Electrical and photovoltaic properties of a metal–semiconductor–insulator–polymer–metal diode were investigated. The n-Si/SiO₂/MEH-PPV/Al diode shows a rectifying behavior with the rectification ratio of 2.22 × 10⁵ at ±5 V and exhibits a non-ideal behavior due to the series resistance and oxide-organic layers. The organic semiconductor makes a contribution to the I–V characteristics of the diode and the trap-charge limited space charge and space charge limited current mechanisms were observed for the diode. The current–voltage characteristics of the n-Si/SiO₂/MEH-PPV/Al diode under different illumination intensities give an open circuit voltage (V_oc) along with a short circuit current (I_sc). This suggests that the n-Si/SiO₂/MEH-PPV/Al diode is a photovoltaic device with V_oc = 0.456 V and J_sc = 7.89 × 10^?8 A/cm² values under 100 mW/cm² illumination intensity. The photoconductivity mechanism of the diode is controlled by monomolecular recombination. The interface state density D_it values with time constant τ_it of the diode under dark and illumination conditions were found to be 2.53 × 10¹⁰ eV^?1 cm^?2 with 5.09 × 10^?5 s and 2.50 × 10¹⁰ eV^?1 cm^?2 with 8.27 × 10^?5 s, respectively. The obtained results indicate that the n-Si/SiO₂/MEH-PPV/Al diode is a photo-sensitive diode.     

Electrodeposition of gold–indium alloys

The gold–indium alloy system has a number of intermetallic, differently coloured phases, of interest to the jewellery industry, and giving rise to the name blue gold. The present study is aimed at finding out the effect of electrolysis conditions on the morphology, elemental and phase composition of the Au–In alloy coatings from different electrolytes – with cyanide, acetate and glycine – as well as establishing the conditions for formation and observation of spatio-temporal structures on the surface of the electrode, similar to those observed during the electrodeposition of other indium alloys with silver, cobalt and palladium. It was established, that blue coloured matt coatings could be obtained from acetate–citrate electrolytes and the process of electrodeposition of gold–indium alloy from glycine electrolytes is a very promising one because of the possibility to obtain a variety of spatio-temporal structures on the surfaces of the electrode which could allow the comparison with other known cases of electrodeposition of similar structures in many other alloy systems.     

Nanocrystalline Fe–C alloys produced by ball milling of iron and graphite

A series of nanocrystalline Fe–C alloys with different carbon concentrations (x_tot) up to 19.4 at.% (4.90 wt.%) are prepared by ball milling. The microstructures of these alloys are characterized by transmission electron microscopy and X-ray diffraction, and partitioning of carbon between grain boundaries and grain interiors is determined by atom probe tomography. It is found that the segregation of carbon to grain boundaries of α-ferrite can significantly reduce its grain size to a few nanometers. When the grain boundaries of ferrite are saturated with carbon, a metastable thermodynamic equilibrium between the matrix and the grain boundaries is approached, inducing a decreasing grain size with increasing x_tot. Eventually the size reaches a lower limit of about 6 nm in alloys with x_tot > 6.19 at.% (1.40 wt.%); a further increase in x_tot leads to the precipitation of carbon as Fe₃C. The observed presence of an amorphous structure in 19.4 at.% C (4.90 wt.%) alloy is ascribed to a deformation-driven amorphization of Fe₃C by severe plastic deformation. By measuring the temperature dependence of the grain size for an alloy with 1.77 at.% C additional evidence is provided for a metastable equilibrium reached in the nanocrystalline alloy.     

Glycine–nitrate combustion engineering of neodymium cobaltite nanocrystals

NdCoO_3 nanocrystals formed via glycine–nitrate combustion method followed by heat treatment has been systematically studied. Formation of NdCoO_3 nanocrystals with minimal size of 7–10 nm from X-ray amorphous combustion products has been elucidated to be a very rapid process, occurring at the temperature of 550–600 ℃ for5–30 min. The comparison of the minimum sizes of NdCoO_3 crystallites obtained from the offered empirical relation d_(min)=l_(unit cell)·N(where N is 7–12 and ‘unit cellis elementary cell parameter) and the data determined on the basis of X-ray diffraction(XRD) and transmission electron microscopy(TEM) showed good correlation. The existence of special nanoporous microstructure and spatial limitations prevent NdCoO_3 particle growth. The kinetic equation based on Avrami–Erofeev nucleation model was offered to be correlated well with experimental data of fractional conversion(a) versus isothermal time(s). The apparent activation energy(Ea=(338 ± 32) kJ) of formation of NdCoO_3 nanocrystals from X-ray amorphous combustion products obtained in excess of oxidant followed by heat treatment at 550–600 ℃ was determined.     

Investigation of annealing effects on microstructure of hybrid nanocrystal–polymer solar cells by impedance spectroscopy

We have fabricated hybrid bulk heterojunction solar cells with blends of MEH-PPV (poly[2-methoxy,5-(2-ethylhexoxy)-1,4-phenylene vinylene]) and nano-CdS as electron donor and electron acceptor, respectively. The effect of thermal annealing was investigated with impedance spectroscopy (IS) and capacitance–voltage (C–V) characteristic measurements on devices. The IS and C–V characteristic manifested very different before and after thermal annealing. We performed equivalent circuit to explain the effect of thermal annealing. The thermal treatment of nanocrystal–polymer films is seen to aid in the formation of a continuous network for electron transport between nanorods, and hence improves devices performance. The method based on the IS is available to probe the microstructure of hybrid bulk heterojunction solar cells before and after thermal annealing, and therefore detect the mechanism for the annealing improvements.     

Determination of elastic properties of consolidated nanocrystalline alloys iron–copper by means of acoustic echography and interferometry

Iron and copper powders were co-milled in a planetary mill in order to obtain nanometric products. The mechanical characteristics of hot compacted nanocrystalline Fe–Cu alloys with various compositions have been determined based on the measurement of the longitudinal, transverse and Rayleigh wave velocities by acoustic echography and interferometry.     

Improving gold recovery of Pb–Zn sulfide ore by selective activation with organic acid

Free gold and gold wrapped in sulfides are considered as the object of gold floatation. However,floatation of free gold exhibits more variables in practice.In this study, improving gold recovery of a Pb–Zn sulfide ore from Yunnan Province, China, was investigated. The results show that free gold and auriferous sulfides account for 94.99 % of total gold. Without adding organic acid in floatation, only 82 % recovery of gold could be obtained.Gold recovery in Au/Pb concentrates increases by 9.29 %with oxalate added and by 7.35 % with citric acid added,respectively, while performances of lead and arsenic nearly keep a constant. A possible reason is that free gold is of wonderful selectivity against pyrite with organic activators.A new method to enhance gold recovery is proposed.     

Room-temperature synthesis of gold nanoparticles — Size-control by slow addition

We report a simple and rapid process for the roomtemperature synthesis of gold nanoparticles using tannic acid, a green reagent, as both the reducing and stabilising agent. We systematically investigated the effect of pH on the size distribution of nanoparticles synthesized. Based on induction time and σ-potential measurements, we show that particle size distribution is controlled by a fine balance between the rates of reduction (determined by the initial pH of reactants) and coalescence (determined by the pH of the reaction mixture) in the initial period of growth. This insight led to the optimal batch process for size-controlled synthesis of 2–10 nm gold nanoparticles — slow addition (within 10 minutes) of chloroauric acid into tannic acid.     

Observation of dendritic growth and fragmentation in Ga–In alloys by X-ray radioscopy

Abstract

Capabilities of the X-ray attenuation contrast radioscopy were utilised to provide a real time diagnostic technique for observations of dendritic growth and fragmentation during solidification of a Ga–30In (wt-%) alloy. The solidification process was visualised by means of a microfocus X-ray tube providing shadow radiographs at spatial resolutions of about 10 μm. Experiments have been carried out to solidify the Ga–In alloy unidirectionally either starting from the bottom or the top of the specimen. The first case is significantly affected by solutal convection, which governs a redistribution of solute concentration. A detachment of dendrite side arms, which is unambiguously caused by melt flow, was not observed. Dendritic fragmentation occurs during the solidification in the reverse top down direction. Variations of the applied cooling rate excited a transition from a columnar to an equiaxed dendritic growth (CET).     

Enhanced growth of intermetallic phases in the Ni–Ti system by current effects

The effect of direct current upon interfacial reactions in the Ni–Ti system was investigated. Isothermal diffusion couple experiments were conducted under varying current densities to de-couple Joule heating from intrinsic effects of the current flux. Current densities of up to 2546 A cm⁻² were used in the temperature range of 625–850 °C. All of the intermetallic compounds (NiTi, Ni₃Ti and NiTi₂) present in the equilibrium phase diagram were identified in the product layer. In addition, β-Ti solid solutions formed in samples annealed above the α→β temperature, 765 °C. The growth of all product layers was found to be parabolic and the applied current was found to significantly increase the growth rate of the intermetallic layers. Using Wagner’s analysis the present results were compared to published results on current-free diffusion couples. The intrinsic growth rate constant of the NiTi₂ intermetallic was found to be 43 times higher under the influence of 2546 A cm⁻² than that obtained without a current at 650 °C. The effective activation energy for the formation of all phases was found to decrease with increasing current density. The effect was strong for all phases but the decrease was most marked for Ni₃Ti. In this case, the activation energy decreased from 292 kJ mol⁻¹ under the influence of a current density of 1527 A cm⁻² to 86 kJ mol⁻¹ when the current density was 2036 A cm⁻². The results are explained in terms of current induced changes in the growth mechanism arising from changes in the concentration of point defects or their mobility.     

Orientation dependence of secondary recrystallisation in silicon–iron

Experiments and analyses have been carried out to reach a better understanding of the mechanism of Goss texture formation during the secondary recrystallisation of silicon steel processed by the single cold reduction route. A new experimental approach demonstrated the effect of misorientation on the growth rates of secondary grains and it is shown that these rates are controlled by the proportion of matrix grains having Σ9 CSL relationships to growing secondary grains. It is considered that the Σ9 boundaries have lower energy than general grain boundaries and so are less strongly inhibited by Zener drag. The relative infrequency of Σ9 boundaries around the periphery of secondary grains is seen as evidence for their sacrificial behaviour. Other experiments involving growth of randomly oriented nuclei provide independent support for the important role of Σ9 boundaries during secondary recrystallisation in this steel.     

Selective removal of nickel from iron substrate by non-cyanide strippers

A novel nickel stripper using ammonia as the key component was developed to substitute cyanide for re-moving nickel film from iron substrates. Its compositions are；ammonia 150 g/L, hydrogen peroxide 50 g/L, ammo-nium chloride 100 g/L, EDTA 7.5 g/L, copper chloride 15 g/L and glucopyrone 1.2 g/L. The optimum operating conditions are: pH9.5-11, temperature 40-50℃ and stripping time 1 h. It shows many advantages over the tradi-tional cyanide stripper including no toxicity, mild operation, lower cost, larger holding capacity, faster stripping rate and good protection for the base metal, and can meet the technical requirements in industry.     

The phase diagram of the terbium–gold alloy system

The terbium-gold phase diagram has been investigated in the 0–100 at% Au field by differential thermal analysis (DTA), X-ray diffractometry (XRD), optical microscopy (LOM), scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). Eight intermetallic phases were found, namely: Tb₂Au orthorhombic oP12–Co₂Si, peritectic decomposition at 1000°C, TbAu, L.T. form, orthorhombic oC8–CrB type and H.T. form, cubic cP2–CsCl type, congruent melting at 1590°C, Tb₃Au₄ trigonal hR42–Pu₃Pd₄ type, peritectic decomposition at 1340°C, Tb₇Au₁₀ tetragonal tI136–Gd₇Au₁₀ type, peritectic decomposition at 1210°C, TbAu₂ tetragonal tI6–MoSi₂ type, congruent melting at 1265°C, TbAu₃ orthorhombic oP8–TiCu₃ type, congruent melting at 1215°C, Tb₁₄Au₅₁ hexagonal hP65–Gd₁₄Ag₅₁ type, peritectic decomposition at 1175°C, and TbAu₆ tetragonal tP56–SmAu₆ type, peritectic decomposition at 855°C. Four eutectic reactions were found to occur at 880°C and 20.0 at% Au, at 1195°C and 62.5 at% Au, at 1160°C and 71.0 at% Au and finally at 805°C and 89.0 at% Au. A catatectic reaction occurs in the Tb-rich region. The experimental results are discussed and compared with the general behaviour of the other R–Au systems.     

Kinetics of stripping of gold loaded in DBC organic phase by sodium sulfite

The kinetics of stripping of gold loaded in dibutyl carbito (DBC) organic phase by sodium sulfite was investigated in a Lewis cell. After the stirring speed reached 400 r·min-1, the reaction of gold stripping conformed with the pseudo-first-order reaction. The stripping rate of gold was in direct proportion to interfacial area, concentration of sodium sulfite and reaction temperature. The experimental results showed that the process of stripping gold was controlled by inter-facial chemical reaction, and its activation energy was 36.06 kJ·mol-1. The kinetics equation was put forward for gold stripping by sodium sulfite.     

Bulk single crystal growth of SiGe by PMCZ method

A new type of magnetic device was used to replace the conventional electro-magnetic field for CZSi (doped with Ge) growth. The device was composed of three permanent magnetic rings and called PMCZ device. The lines of magnetic force are horizontally distributed at radial 360? Using the ring permanent magnetic field, thermal convection in melt and centrifugal pumping flows due to crystal rotation could be strongly suppressed so that the fluctuations of temperature and micro-growth rate at solid/liquid interface could be restrained effectively. In the PMCZ condition, the growing environment of SiGe bulk single crystal was similar to the crystal growth in space under the condition of micro-gravity. The motion of impurities (Ge, oxygen, etc.) had been controlled by diffusion near the solid/liquid interface. Oxygen concentration became lower and the distribution of composition became more homogeneous along longitudinal direction and across a radial section in the grown SiGe crystal. The mechanism of PMCZ sup     

Mechanism and kinetics of iron extraction from high silica boehmite–kaolinite bauxite by hydrochloric acid leaching

The chemical and mineral compositions of bauxite recovered from the Severoonezhsk Bauxite Mine (Arkhangelsk region, Russia) were studied by XRD, ICP-OES, TG/DSC, SEM, TEM, and Mössbauer spectroscopy. The iron-containing minerals of the bauxites were found to comprise alumogoethite (α-Fe_1–xAl_xOOH), alumohematite (α-(Fe_1–xAl_x)₂O₃), alumoakaganeite (β-Fe_1–xAl_xO(OH,Cl)), and chromite (FeCr₂O₄). The efficiency of Fe extraction from the bauxite by HCl leaching was 82.5% at 100 °C, HCl concentration of 10%, solid/liquid ratio of 1:10, and the process duration of 60 min, with aluminum loss from the bauxites below 4.5% of the total Al contents in the bauxite. Analysis of the kinetics of the iron leaching process proved diffusion to be the limiting stage of the process at 90–100 °C. Bauxite residue after leaching presented traces of α-Fe_1–xAl_xOOH and β-Fe_1–xAl_xO(OH,Cl), and most of the iron content was in the FeCr₂O₄. In bauxite residue after HCl leaching, in addition to iron oxide, the contents of chromium and calcium oxides significantly decreased. The iron chloride liquor after leaching contained the rare earth elements (REE) of 6.8 mg/L Sc, 4.1 mg/L Ce and 2.3 mg/L Ga.     

Bioleaching of refractory gold ore （ Ⅲ ）——Fluid leaching Jinya refractory gold concentrate by Thiobacillus ferrooxidans

A novel fluidized-bed reactor was designed and installed for bloleaching in a semi-continuous way, by which a process for biuleaching-cyanidation of Jinya refractory gold arsenical concentrate was studied. The arsenic extraction rate reaches 82.5 % after 4-day batch biooxidation of the concentrate under the optimized condition of pH 2.0, ferric ion concentration 6.Sg/L and pulp concentration 10%. And leached rate of gold in the following cyanida.tion is over 90%. The parameters of three series fluidized-bed reactors exhibit stability during the semi-continuous bioleaching of the concentrate.Armmic in the concentrate can be got rid of 91% after 6-day leaching. Even after 4 days, 82% of arsenic extraction rate was still obtained. The recovery rates of gold are 92 % and 87.5 % respectively in cyaniding the above bioleached residues.The results will provide a base for further commercial production of gold development.     

Synthesis and photocatalytic properties of InVO4 sol containing nanocrystals by mild hydrothermal processing

The precursor precipitation of InVO₄ was synthesized by co-precipitation using indium trichloride (InCl₃), ammonium metavanadate (NH₄VO₃) and ammonia (NH₃H₂O) as raw materials. The InVO₄ sols with orthorhombic phase were obtained by hydrothermal treatment (the precursor precipitation solution at 423 K, for 4 h). The precursor and sol of InVO₄ were characterized by X-ray diffraction (XRD), Fourier Transform Infra-red spectra (FT-IR), scanning electron microscopy (SEM) measurements. The XRD patterns indicate that the InVO₄ precursor is amorphous phase, InVO₄ sol contains orthorhombic InVO₄ nanocrystals. The results also reveal that the pH value of the reaction mixture and reaction temperature play important roles to the target phase. InVO₄-TiO₂.thin films on glass slides were prepared by the dip-coating method from the composite sol. The photocatalytic properties of the InVO₄-TiO₂ thin films were investigated by the photocatalytic degradation of methyl orange solution. The results indicate that it has better photocatalytic activities than pure TiO₂ thin films or pure InVO₄ thin films with UV light.