Surface hardening of titanium alloys by oxygen-diffusion-permeation

The surface oxygen-diffusion-permeation behaviors of T based alloys were investigated.MEF4A optical microscopy and HMV-2000 micro-hardness tester were employed to characterize the microstructure and micro-hardness of the oxygen-permeated alloys.The results show that the micro-hardness of Ti based alloys are sharply enhanced by the permeation of oxygen.The microstructure and micro-hardness of oxygen-permeated layer are strongly related to the oxygen-diffusion-permeation techniques.The solid solution of oxygen in α phase can improve the transformation temperature from αphase to βphase and enlarge the region of α phase so as to improve the microhardness of surface layer.Therefore,surface oxygen-diffusion-permeation would be a feasile method to reinforce Ti based alloys based on the solid solution of oxygen in α-Ti.At last,a diffusion-solution model was put forward.     

Mesmoproc – implementation of a maskless electrochemical surface modification process

Abstract

Conventional approaches to the fabrication of fine features in the printed circuit board and metal finishing industries typically employ a multistage photolithography stage to process each individual substrate, which is both inefficient and wasteful of valuable materials. By developing and implementing a maskless electrochemical process that decreases the use of lithography, the Mesmoproc project aims to assist European industry in these sectors.     

Preparation and magnetic properties of nickel nanorods by thermal decomposition reducing methods

The single-crystalline nickel nanorods with narrow size distribution and better magnetic properties were synthesized by thermal decomposition of nickel hydroxide nanorods precursor powders, which were produced by soft template method using nickel oxalic acid as raw material. The influences of hydrothermal reaction temperature and time on morphology of the products were investigated. The structure, morphology and magnetic properties of the products were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), thermogravimetric differential scanning calorimetry (TGA-DSC) and vibrating sample magnetometer (VSM). The as-prepared nickel nanorods are uniform with a diameter of 10–15 nm and length 70–120 nm. The results of magnetic measurements show that the specific saturation magnetization(σ_s) and coercivity values(H_c) of the nickel nanorods are 50.649 A·m²/kg and 190.0×(10³/4 π)A/m, respectively. Finally, a possible mechanism for the formation of nickel nanorods was discussed briefly.     

Exfoliation corrosion susceptibility of 8090 Al-Li alloy examined by electrochemical impedance spectroscopy

The exfoliation corrosion susceptibility and electrochemical impedance spectroscopy(EIS) of rolled and peak-aged 8090 AI-Li alloys in EXCO solution were studied, and the EIS after exfoliation was simulated. Once exfoliation occurs, two capacitive arcs appear in the EIS at high-mediate frequency and mediate-low frequency respectively. The exfoliation-attacked alloy surface consists of two parts, an original flat alloy surface and a new interface exposed to EXCO solution due to the exfoliation. The capacitance corresponding to the new exfoliation inter-face increases approximately linearly with time at early exfoliation stage, due to the enlargement of the new inter-face.Then it maintains stable, due to the corrosion product covering on the new inter-face. The exfoliation susceptibility can be judged through the average slope of the capacitance vs time curve of the early exfoliation stage. This average slope of the rolled 8090 alloy is much higher than that of the peak-aged 8090 alloy, accordingly the rolled 8090 alloy is more susceptible to exfoliation than the peak-aged 8090 alloy.     

Surface modification of Al-Pb alloy by high current pulsed electron beam

Al-Pb alloy was modified by high current pulsed electron beam and the microstructure, hardness and tribological characteristics were characterized by scanning electron microscopy, electronic microanalysis probe microanalysis, Knoop hardness indentation and pin-on-disc type wear testing machine. The results show that the microstructure and hardness can be greatly improved, and the modification layer consists of a molten zone, an overlapped zone of heat-affected and quasistatic thermal stress-affected zone and a transition zone followed by the substrate. The tribological properties of high current pulsed electron beam irradiated Al-Pb alloy are correspondingly improved largely. Optical observation and scanning electron microscopy analysis reveal that the low wear rate and lowest level in coefficient of friction at high load level for irradiated Al-Pb alloy are due to the formation of a lubricious tribolayer covering the worn surface, which is a mixture of Al2O3, Pb3O4 and silicate. The wear mode varies from oxidative wear at low load to film spalling at high load and, finally, adhesive wear.     

Surface modification of titanium implants with micro–nanotopography and NIR photothermal property for treating bacterial infection and promoting osseointegration

A double acid corrosion and subsequent hydrothermal treatment were used to fabricate a micro–nano-structured Ti substrates(Ti–M–N).Afterward,the mesoporous polydopamine(MPDA)nanoparticles as photothermal agent were prepared and immobilized on the surface of Ti–M–N samples,in order to obtain Ti–M–NMPDA sample.Unique micro–nanostructure properties and the photothermal effect of the modified Ti implant caused physical stress on the bacteria and the bacterial membrane damage,and eventually led to bacteria death.More importantly,based on excellent bioactivity and cytocompatibility of mussel-inspired materials,MPDA promoted adhesion,proliferation and osteogenic differentiation of mesenchymal stem cells in vitro.Furthermore,animal experiments in vivo further confirmed that the modified Ti implants could enhance osseointegration.     

Intergranular corrosion of 8090 Al–Li: interpretation by electrochemical impedance spectroscopy

Abstract

Aluminium–lithium alloys are widely used in the aircraft industry because of their low density and high elastic modulus. The Al–Li alloy 8090 has been well characterised from a mechanical viewpoint, but its corrosion mechanism has not been studied so completely. Recent work has focused on the use of electrochemical techniques to detect the early stages of localised corrosion and to assess the rate of corrosion taking place at specific locations in aircraft. Electrochemical impedance spectroscopy (EIS) has been used to measure and monitor the localised corrosion susceptibility of this Al–Li alloy, which is currently being used in aerospace applications, in solutions of 1M NaCl ++ 10 mL H₂O₂ (30 wt-%) at neutral pH. During the corrosion process, there is an increase in surface inhomogeneity which causes deviations from the ideal behaviour proposed by Randles. A tendency to behave as a porous electrode is evidenced in the Nyquist plot by the presence of a straight segment in the high frequency range. This response is the result of preferential dissolution at grain boundaries, which leads to the development of deep intergranular attack and promotes a non-homogenous signal distribution. At low frequencies a capacitive arc appears that may be related to the chloride adsorption involved in alloy dissolution.     

Furan- and pyrrole-containing analogs of α-quinquethiophene: spectroscopic and electrochemical properties

A series of pentacyclic analogs of α-quinquethiophene containing one or two furan or pyrrole units has been synthesized. The synthesis is based on the cyanide-catalyzed Stetter reaction, providing the ketonic precursors to the pentacycles. Spectral and electrochemical investigations show that the redox-stable mixed pentacycles display hypsochromic shifts in their absorption maxima, as well as a greater ease of oxidation, in comparison to α-quinquethiophene.     

Surface modification of an up-conversion luminescence material by overcoating with SiO2 and its characterization

The surface of an up-conversion luminescence material was modified by overcoating with SiO2, which was syn- thesized from a hydrolysis progress of tetraethoxysilane (TEOS) in alkalescent condition. By analyzing the hydrolyzed mechanism of TEOS, it was found that there was not only physical adsorption but also chemical bonding between the up-conversion material and SiO2. At the same time, some adsorption bands at 1100, 475, 950, and 3500 cm?1 were found by FI-IR, which were the characteristic bands of Si?OH and Si?O?Si. By analyzing the surface elements of the coated material by XPS, it was found that its surface only included Si, O, and C elements, and not F and Y. In the picture of XRD, there was no additional peak after surface modification, suggesting that the silica shell was amorphous. The small peak at 2θ = 23° in the X-ray diffraction pattern of the coated material was caused by the amorphous SiO2 shell, and the TEM image also proved that the surface of the material was successfully modified by overcoating with SiO2. The amount of hydroxyls was then increased on the surface of the material, which made it easy to connect with other active groups.     

Surface and electrochemical characterization of Ni–Zr intermetallic compounds

In this paper the Ni–Zr system has been considered with the aim of investigating the role of composition and structure of an early–late transition metals system on the electrocatalytic activity, for the hydrogen evolution reaction. As a matter of fact, pure Ni and Zr show low activity, while their intermetallic compounds generate a higher catalytic efficiency. Five alloys, with increasing Ni content starting from Ni₃₃Zr₆₇ up to Ni₇₅Zr₂₅, have been prepared and characterized. The alloy of composition (Ni_0.55Mn_0.30V_0.10Co_0.05)_2.1Zr has also been considered, in order to investigate the catalytic efficiency related to a Laves structure. The thickness and composition of the surface oxides have been investigated and their effect on reducing the catalytic efficiency of the as-prepared alloys has been discussed. The activity of the samples submitted to a surface activation treatment with hydrofluoric acid, that removes the oxide layer and allows to evidence the properties of the compounds, has been observed to increase significantly. The trend of the electrocatalytic efficiency with the composition of the alloys is discussed considering a synergetic effect between Ni and Zr. The Laves phase appears slightly more active than the binary intermetallic compound.     

TbRhSn and DyRhSn – Detailed magnetic and 119Sn Mössbauer spectroscopic studies

The results of magnetic studies and Mössbauer spectroscopic investigations are reported for the stannides TbRhSn and DyRhSn crystallizing in the hexagonal ZrNiAl-type structure. The polycrystalline samples of these ternary intermetallics were synthesized by arc melting from metallic precursors. Detailed ¹¹⁹Sn Mössbauer spectroscopic studies are used to investigate the hyperfine interactions and their temperature evolutions at places occupied by the diamagnetic tin nuclei. Magnetic properties of DyRhSn and TbRhSn were studied by AC/DC magnetometry in a wide temperature range. The results show that both compounds are magnetically ordered at low temperatures. DyRhSn is a non-collinear antiferromagnet with the Néel temperature T_N = 7.5 K, whereas TbRhSn undergoes a transition from a paramagnetic to an antiferromagnetic state at T_N = 20.2 K. An additional transition at T_SR = 10.3 K is detected for TbRhSn which corresponds to some changes in the magnetic moments ordering. The role of the magnetostriction effect in the evolution of the hyperfine parameters and its influence on the observed TbRhSn Mössbauer spectra is discussed. Triangular-like antiferromagnetic arrangements with rare-earth magnetic moments lying in the hexagonal plane are proposed for both compounds at very low temperatures.     

Growth of straight carbon nanotubes by simple thermal chemical vapor deposition

Straight carbon nanotubes （CNTs） were achieved by simple thermal chemical vapor deposition（STCVD） catalyzed by Mo-Fe alloy catalyst on silica supporting substrate at 700 ℃. High-resolution transmission electron microscopy images show that the straight CNTs are well graphitized with no attached amorphous carbon. Mo-Fe alloy catalyst particles play a very crucial role in the growth of straight CNTs. The straight carbon nanotubes contain much less defects than the curved nanotubes and might have potential applications for nanoelectrical devices in the future. The simple synthesis of straight CNTs may have benefit for large-scale productions.     

Surface protection of titanium and titanium–aluminum alloys against environmental degradation at elevated temperatures

Experiments have been undertaken to explore the possibility of creating an oxygen barrier coating, which is effective in preventing oxidation and oxygen embrittlement of Ti and several low-Al content Ti-base alloys during exposure to oxidizing environments at elevated temperatures. The fabrication process has involved three steps, namely co-deposition of Ti and Al by magnetron sputtering onto a substrate material to be protected, followed by vacuum annealing and plasma immersion ion implantation of fluorine. The first two steps produce an overlay of γ-TiAl while the last step provides the necessary conditions for bringing about the halogen effect upon subsequent high-temperature oxidation. Analysis techniques such as cross-sectional transmission electron microscopy (XTEM) in conjunction with electron energy loss spectroscopy (EELS), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and elastic recoil detection (ERD) have been used to study the microstructure, phase formation and depth distribution of the elements in the coating material. Following oxidation in air at 600 °C for 100 h, specimens have been prepared for metallographic analysis, and their cross sections have been characterized by scanning electron microscopy (SEM) in combination with EDX, and electron probe microanalysis (EPMA). The results obtained show that during oxidation exposure the coating is capable of forming a protective alumina-containing scale which serves as an oxygen barrier, thereby preventing oxygen embrittlement. In addition, since the only constituents of the coating are Ti and Al, it exhibits excellent chemical substrate compatibility.     

In situ UV–vis and Raman spectroscopic studies of the electrochemical behavior of N,N′-diphenyl-1,4-phenylenediamine

The electrochemical behavior of the N,N′-diphenyl-1,4-phenylenediamine (B3) in acid solution has been investigated by in situ UV–vis and Raman spectroscopies. The electrogenerated species semiquinone form (B3⁺) and monoprotonated structure of B3 (B3⁺) have been characterized as the main products of B3 oxidation. The N,N′-diphenyl-1,4-benzoquinonediimine (B2Q1) species has also been characterized in B3 neutral solution and the B3⁺ proton loss was attributed to proton absence in solution. Finally, a mechanism has been proposed concerning the electron and proton transfer that occurs during the oxidation process.     

Surface self-nanocrystallization of α+β titanium alloy by surface mechanical grinding treatment

In this work, the heavy deformation was performed on Ti6Al4V alloy by using surface mechanical grinding treatment (SMGT) in order to obtain surface nanocrystalline layer. The phase structure and microstructures in the deformation zones were characterized by XRD, SEM and TEM. The nanocrystallization mechanisms of α and α phase were clarified. The results show that a gradient structure including nano grain, quasi nanograin and micro-grains was achieved within the depth of 500 μm below the surface. The depth of nanocrystallines layer was at least 20 μm. From the non deformation zone in the center to the heavy deformation zone close to treated surface, dislocation densities gradually increased. The original coarse grains gradually evolved into dislocation cell structures and subgrains through dislocation movement. In the depth of about 20 μm below the treated surface, the subgrains began to split into nano-scale grains with high angle grain boundaries by lattice rotation and tilting mechanisms. During SMGT, β phase deformed and refined prior to α phase, and inhibited the generation of twinning in α grain. The coordinated deformation between a and β phase promoted the formation of nanocrystallines.     

Thermodynamic assessment of chemical and electrochemical stability of nickel–silicon system alloys

Phase and chemical equilibria in Ni–Si system at 298 K are considered. The possible maximum solid solubility of Si in fcc-Ni at 298 K is estimated.The Ni–Si–O state diagram at 298 K is plotted. The Ni–Si–O system invariant conditions are calculated. The potential–pH diagram of the Ni–Si–H₂O system at 298 K, air pressure of 1 bar and activities of ions in solution, equal to 1 mol/l is plotted. Basic chemical and electrochemical equilibria in Ni–Si–H₂O system are considered.     

Preliminary examination of electrochemical and spectroscopic features of trithiocarbonate collectors for sulfide mineral flotation

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Role of anions to influence inductive behavior for poly(2-amino diphenylamine-co-aniline)—an electrochemical impedance spectroscopic analysis

Electrodeposited films of polyaniline (PANI) and poly(2-amino diphenylamine-co-aniline) were generated by cyclic voltammetry. PANI and copolymer films were subjected to electrochemical impedance spectroscopy (EIS) at different applied potentials. An inductive behavior was noticed at 0.50 V. The presence of hydrolysis product has definite role in generating the inductive behavior. Inductive behavior was adequately explained through the equivalent circuit consisting of an inductor element (L). PANI and copolymer films were also subjected to impedance analysis in HCl and H₂SO₄ media to investigate the influence of anion on the inductive behavior. The inductive behavior was found to be predominant for PANI than for copolymer. For both polymers, sulphate ion influences L significantly than chloride ion.     

Photoelectron spectroscopic studies of poly(9,9-dioctylfluorene)–potassium interface,and its influence by oxygen

The electronic structure of poly(9,9-dioctylfluorene) (PFO) coated with potassium has been studied by X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS). The low work function of K led to low or no injection barrier at the K/PFO interface and induced bipolaron gap states. With increasing K coverage, the bipolaron states and the highest-occupied molecular orbitals gradually broadened, and the two shake-up peaks of C 1s XPS peaks associated with the lowest-unoccupied molecular orbitals of PFO also broadened, diminished and eventually vanished. Upon slight oxygen exposure, the two bipolaron states disappeared and the deformed features in the UPS and XPS spectra were partially recovered.