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.     

ESR studies of photogenerated polarons in regioregular poly(3-alkylthiophene)–fullerene composite

Electron spin resonance (ESR) studies of photogenerated polarons in composite of regioregular poly(3-octylthiophene) (PAT8) and fullerene (C₆₀) using variable photoexcitation energy up to 4.1 eV are reported. Two transient light-induced ESR (LESR) signals of photogenerated positive and negative polarons on PAT8 (g₁=2.002) and C₆₀ (g₂=1.999), respectively, are observed below 200 K, which are caused by photoinduced electron transfer between PAT8 and C₆₀. A remarkable enhancement of the LESR signals in excitation spectrum at around 1.8 eV is observed compared with the case of pure regioregular PAT8, which is consistent with the enhancement of the photoconductivity at around 1.8 eV where optically forbidden transition of C₆₀ occurs. Spin–lattice relaxation time of the polaron spins of PAT8 is obtained considering inhomogeneous broadening of the ESR linewidth due to the hyperfine interactions, which is at least approximately 18 times longer than that of C₆₀. Prompt and persistent LESR signal components are observed by transient response of the LESR signal. The prompt contribution shows a monotonic increase with increasing excitation-light intensity, while the persistent contribution is found to be excitation intensity independent due to deep traps of the photogenerated polarons.     

Spectroscopic studies on poly(4,4′-methylenedianiline) salts and their bases

Poly (4,4′-methylenedianiline) (PMDA) salts were prepared by chemical polymerization using different protonic acids. The PMDA bases were obtained by dedoping the corresponding salts using NH₄OH. The FT-IR and UV-Vis spectroscopic results have shown the absence of the quinoid structure in PMDA systems, which could be attributed to the presence of methylene spacer in the polymer backbone. The electron paramagnetic resonance (EPR) spectra suggest the presence of polarons in PMDA salts and their bases. There is a rough correlation between the conductivity and yield of PMDA salts, which depends on the counter anion used. The results for PMDA systems are compared with those of related systems and discussed.     

Influence of microstructural characteristics on corrosion behavior of Mg–5Sn–3In alloy in Hank's solution

The microstructural observation, the mass loss test, potentiodynamic polarization measurements and corrosion morphology examinations were conducted to study the influence of microstructural characteristics on corrosion behavior of Mg–5Sn–3In alloys in Hank's solution after extrusion. The results show that the corrosion rate of the as-cast alloy is similar to that of as-extruded alloy; however, the local corrosion susceptibility is greatly weakened in the as-extruded alloy, especially in the extrusion direction. The relatively uniform corrosion morphology of the as-extruded alloy is attributed to refined Mg₂Sn particles, uniform distribution of Mg₂Sn particles and favorable crystal orientation. Meanwhile, the cytotoxicity tests confirm that the Mg–5Sn–3In alloy exhibits cytotoxicity of Grade 0–1 for NIH3T3 cells, suggesting an acceptable cytotoxicity of this alloy in the vitro assay.     

In situ observation of solidification behavior in undercooled Pd–Cu–Ni–P alloy by using a confocal scanning laser microscope

In the undercooled melt of Pd₄₀Cu₃₀Ni₁₀P₂₀ alloy, the solidification behavior including the nucleation and growth of crystals at the micrometer level has been observed in situ by use of a confocal scanning laser microscope combined with an infrared image furnace. The Pd₄₀Cu₃₀Ni₁₀P₂₀ alloy specimens were cooled from the liquid state to various undercooled states under a helium gas flow. Images of solidification progress were obtained by the charge-coupled device image sensor of the confocal scanning laser microscope. Depending on the degree of undercooling, the morphology of the solidification front changed among various types: faceted front, columnar dendritic front, cellular grain and equiaxed grain, etc. The velocities of the solid–liquid interface were measured to be 10⁻⁵–10−7 m/s, which are at least two orders of magnitude higher than the theoretical crystal growth rates. Combining the morphologies observed in the three undercooling regimes and their solidification behaviors, we conclude that phase separation takes place in the undercooled molten Pd₄₀Cu₃₀Ni₁₀P₂₀ alloy. The continuous-cooling–transformation (CCT) diagram was derived from the experimental time–temperature-transformation diagram constructed from solidification onset times under various isothermal annealing conditions. The CCT diagram suggests that the critical cooling rate for glassy solidification is about 1.8 K/s, which is in agreement with previous calorimetric findings.     

Electrochemical cleavage of a Si–Si bond in poly[(tetraethyldisilanylene)oligo(2,5-thienylene)] films

Electrochemical stability of poly[(tetraethyldisilanylene)oligo(2,5-thienylene)] (DSmT; m refers to the number of thienylene units) films is investigated by means of in situ UV–vis–NIR spectroscopy, in situ and ex situ fluorescence spectroscopy, gel-permeation chromatography, and FT-IR spectroscopy. It is found that a Si–Si bond in DSmT film with m=3 to 5 is cleaved at potentials as low as 0.5 V versus Ag/Ag⁺ in acetonitrile, resulting in dissolution of oligothiophene-like species. The decomposed products are oxidized to form another polymer film on the surface of an original DSmT film and a doping reaction observed earlier takes place on the composite polymer film.     

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.     

Strong stacking behavior and large third-order nonlinear optical susceptibility χ(3) of head-to-head-type poly(3-alkynylthiophene-2,5-diyl), HH-P3(CCR)Th

The head-to-head-type poly(3-alkynylthiophene-2,5-diyl) HH-P3(CCR)Th has been shown to exhibit a strong tendency to self-assemble. The UV–vis spectrum of HH-P3(CCDec)Th (Dec = decyl) in 1,2-dichlorobenzene at 131 °C showed a peak at λ_max = 520 nm, which shifted to λ_max = 553 nm at 25 °C, with a shoulder peak at 608 nm. However, the UV–vis spectrum of an HH-P3(CCDec)Th film showed a more pronounced shift in its UV–vis absorption peak to a longer wavelength. These phenomena are the characteristics of the self-assembly of the polymer molecule. The HH-P3(CCDec)Th film had a large third-order nonlinear optical susceptibility χ⁽³⁾ of 3.6 × 10⁻¹¹ esu.     

In situ synchrotron X-ray diffraction studies of hydrogen desorption and absorption properties of Mg and Mg–Mm–Ni after reactive ball milling in hydrogen

Reactive ball milling in hydrogen was applied to synthesize nanocrystalline Mg- and Mg8Mm20Ni-based hydrides with crystallite size below 10 nm. These hydrides were studied by in situ synchrotron X-ray diffraction performed at the Swiss–Norwegian Beam Lines of the European Synchrotron Radiation Facility, Grenoble. Characterization of the phase-structural and microstructural state of the constituents during the reversible processes of synthesis and decomposition of the hydrides upon application of hydrogen pressure or vacuum at temperatures 20–350 °C and kinetics of hydrogen uptake was performed. Details of the mechanism of the phase-structural transformations were provided by high time resolution of the synchrotron X-ray diffraction data, high sensitivity in determining formation of the phase constituents, excellent accuracy in yielding the crystallographic characteristics and in probing the microstructural evolution of the constituents formed.     

Dielectric relaxation properties of poly(ethylene-terephthalate)–polyaniline composite films

The dielectric relaxation measurements on poly(ethylene-terephthalate) (PET) containing adsorbed aniline and polyaniline (PAni), prepared by polymerization into the PET matrix, have been performed between 173 and 403 K in the frequency range 1 to 10⁷ Hz. The influence of aniline and PAni on the β-relaxation of PET and the effect of the presence of PAni on the α-relaxation of PET have been studied. For the films PET–PAni doped with HCl, two relaxation processes around 0.5–5 kHz and 0.2–1 MHz were observed.     

Electrochemical synthesis of poly(para-phenylene) on platinum electrode in glacial acetic acid–sulfuric acid solvent

In concentrated sulfuric acid–glacial acetic acid solvent benzene is oxidized to poly(para-phenylene) (PPP) if the concentration of glacial acetic acid is less than 40 vol.%. Depending on the potential applied the chains containing 11–18 monomer units are formed. PPP forms quasi-reversible redox system, which is deactivated if oxidized at potentials greater than +1.35 V (vs SCE).     

Growth behavior of Cu6Sn5 in Sn–6.5 Cu solders under DC considering trace Al: In situ observation

High resolution time-resolved X-ray imaging with synchrotron radiation has been used to in situ observe the growth behavior of Cu₆Sn₅ intermetallic compounds (IMCs) during solidification in Sn–6.5 Cu and Sn–6.5 Cu–0.2 Al (wt. %) solders under applied direct current (DC) field. The morphological evolution of Cu₆Sn₅ with I-like, X-like, Y-like and bird-like shapes is directly observed. It is shown that trace levels of Al have a marked effect on the solder microstructures and refining the size of the primary Cu₆Sn₅. The solidification pathway leading to the refinement is observed in real time using synchrotron microradiography. After adding the trace Al, I-like shapes bifurcate into X-like shapes. Furthermore, when DC field with 10 A/cm² is applied, both the growth rate and the mean size of Cu₆Sn₅ are increased but decreased when 100 A/cm² is applied. Meanwhile, the effect of thermodynamic potential barrier caused by DC field on the growth behavior of Cu₆Sn₅ is discussed.     

Kinetic and thermodynamic studies of adsorption of gallium(Ⅲ) on nano-TiO_2

Nano-TiO2 was employed for the adsorption of gallium from aqueous solution in batch equilibrium experiments to investigate its adsorption properties. It was found that the adsorption efficiency of Ga(Ⅲ) was more than 96% at pH 3.0. The adsorption capacities and rates of Ga(Ⅲ) onto nano-TiO2 were evaluated as a function of solution concentration and temperature. The results were analyzed using the Langmuir adsorption isotherms. Adsorption isothermal data could be well interpreted by the Langmuir model. The mean energy of adsorption, 15.81 kJ·mol-1, was calculated from the D-R adsorption isotherm. The kinetic experimental data properly correlate with the pseudo-second-order kinetic model. The thermodynamic parameters for the process of adsorption have been estimated. The △ H Οand △ GΟvalues of gallium(Ⅲ) adsorption on nano-TiO2 showed an endothermic and spontaneous nature of adsorption.     

In situ production of ultra-fine Ti(C,N)–TiB2–Co cermets by reactive hot processing from the Co–Ti–C–BN system

In this paper, ultra-fine Ti(C,N)–TiB₂–Co cermets were prepared by reactive hot processing from the Co–Ti–C–BN system. Microstructure observation indicated that Co and TiB₂ uniformly distributed in the ultra-fine Ti(C,N) matrix. Carbon contents in the reactants had a great influence on the porosity and properties of synthesized cermets. In the range of 11.76–13.79 at.% carbon, dense samples were obtained. With increasing carbon contents, the relative density and hardness decreased due to the existence of residual carbon. The wear resistance of dense Ti(C,N)–TiB₂–Co cermets were better than that of YT15 cemented carbide. In addition, the reaction process in the Co–Ti–C–BN system was explored by differential scanning calorimeter and X-ray diffraction. Results revealed that Ti(C,N) was synthesized through the solid solution of carbon into TiN, and the addition of Co to Ti–C–BN mixtures promoted the production of Ti(C,N) by the formation of Co–Ti liquid.     

Effect of deposition sequence of platinum and ruthenium particles into nanofibrous network of polyaniline–poly(styrene sulfonic acid) on electrocatalytic oxidation of methanol

This study reports on the preparation of Pt- and Ru-based electrocatalysts through electrodeposition of Pt and Ru particles into the nanofibrous network of polyaniline (PANI)–poly(styrene sulfonic acid) (PSS). The sequence of electrodeposition of Pt and Ru particles was changed and the electrocatalysts, PANI–PSS–Pt–Ru and PANI–PSS–Ru–Pt, were obtained. Scanning electron microscopy (SEM), X-ray photoelectron microscopy (XPS), and cyclic voltammetry (CV) were employed to investigate the morphology, structural and electrochemical properties of the electrocatalysts, PANI–PSS–Pt–Ru and PANI–PSS–Ru–Pt. The distribution of Pt and Ru particles into PANI–PSS matrix was analyzed by the Auger depth profiles. The electrochemical behavior PANI–PSS–Pt–Ru and PANI–PSS–Ru –Pt and the electrocatalytic behavior toward oxidation of methanol were evaluated by cyclic voltammetry. PANI–PSS–Ru–Pt exhibited a superior electrocatalytic performance for methanol oxidation as compared to PANI–PSS–Pt–Ru.     

Adsorption behavior and mechanism of Bi(III) ions on rutile–water interface in the presence of nonyl hydroxamic acid

The adsorption behavior and mechanism of Bi(III) ions on the rutile–water interface were investigated through micro-flotation, Zeta potential measurement, adsorption amount measurement and X-ray photoelectron spectroscopy (XPS). According to the results of micro-flotation, Bi(III) ions could largely improve the rutile flotation recovery (from 62% to 91%), and they could increase the activating sites and reduce the competitive adsorption between nonyl hydroxamic acid negative ions and OH^? ions, which determined that Bi(III) ions were capable of activating rutile flotation. The adsorption of Bi(III) ions onto the rutile surface led to the shift of Zeta potential into the positive direction, which was good for the adsorption of nonyl hydroxamic acid anions. In addition, the results of XPS indicated that the chemical environment around Ti atom had not changed before and after the adsorption of Bi(III) ions. Based on the adsorption mechanism of Bi(III) ions, it was deduced that firstly Bi(III) ions occupied the vacancies of the original Ca²⁺, Mg²⁺ and Fe²⁺ ions on the rutile surface; secondly Bi(III) ions covered on the rutile surface in the form of hydroxides.     

In situ scanning electron microscopy observation of deformation and fracture behavior of Ti-3Zr-2Sn-3Mo-25Nb alloy

The plastic deformation and fracture processes of Ti-3Zr-2Sn-3Mo-25Nb alloy for surgical implants were directly observed by in situ scanning electron microscopy(SEM).The effect of phase transformations on deformation-induced martensitic transformation accompanying the cyclic tensile fracture processes was investigated.The results reveal that the metastable alpha martensites(α")promotes deformation-induced martensitic transformation to ductile fracture,whereas the omega(ω)and alpha(α)phases drastically prevent slip dislocation and deformation-induced martensitic transformation to brittle fracture.     

In situ Study on the Growth Behavior of Primary Al_3Ni Phase in Solidifying Al–Ni Alloy by Synchrotron Radiography

The growth behavior of Al_3Ni intermetallic compounds(IMCs)during the directional solidification of Al-10 wt%Ni alloy was investigated by synchrotron radiography.Two main growth patterns of primary Al_3Ni phase,I-like and V-like,appeared during solidification,and I-like Al_3Ni phase grew faster than V-like phase,which can be explained by the minimum energy criterion.The growth of I-like phase can be divided into two stages and was mainly affected by undercooling and Ni concentration.We also found that V-like Al_3Ni phase can evolve into M-like phase during solidification.