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.     

Liquid structure as a guide for phase stability in the solid state: Discovery of a stable compound in the Au–Si alloy system

A new crystalline ground state was discovered in the Au–Si system through first-principles electronic structure calculations. The new structure was found using the experimentally and theoretically determined local atomic structure in the liquid as a guide for the solid state. Local atomic structure in the liquid was matched with that for all known crystal structures as compiled in the Pauling File structural database. The best matching crystalline structures were then explicitly calculated using first-principles methods. Most candidate crystal structures were found to be close, but above the enthalpy of a composition weighted average of the face-centered cubic Au and diamond structure Si terminal phases, but one crystal structure was more stable than the terminal phases by about 10 meV atom^–1 at T = 0 K. As first-principles simulations of local structure are feasible for most liquid alloys, the present methodology is applicable to other alloys lying near a eutectic composition.     

Analysis of Size Mismatch of the Lattices of α- and α2-phases in Model Titanium Pseudo-α-Alloys

Metal Science and Heat Treatment - Analysis of lattice mismatch of the α- and α2-phases is performed as a function of the original structure and solid solution alloying for titanium...     

90 years of thermal analysis as a control tool in the melting of cast iron

Since its first literature mention in conjunction with cast iron in 1931 by Esser and Lautenbusch,thermal analysis(TA)has journeyed a long way.Today it is an accepted and widely used tool for process control for all types of cast irons.This paper reviews the latest progress in the development of equipment and analysis methods that make TA successful in applications such as the estimation of chemical composition,graphitization potential,and the shape and number of graphite aggregates.The potential and limitations of the prediction of shrinkage defects propensity are analyzed in some details.Examples of attempts at prediction of mechanical properties and shrinkage propensity are also discussed.Several graphs showing the data scattering are presented to convey the reader a better sense of the accuracy of various predictions.     

Elasticity-based model of the variant selection observed in the β to α phase transformation of a Zircalloy-4 sample

The β→α texture inheritance of a Zircalloy-4 sample has been investigated after an α→β→α transformation cycle. The final inherited α texture has been determined from a crystal orientation map determined by electron back-scattering diffraction, whereas the texture of the high temperature β phase has been reconstructed by a method analysing the orientations and misorientations of α variants. The comparison of the α texture calculated from the parent β texture without variant selection with the experimental sharp α texture shows differences due to a strong variant selection mechanism occurring during the phase transformation at cooling.A model of a variant selection mechanism based on the elastic anisotropy of the parent β phase leads to a simulated inherited α texture with the main characteristics of the experimental texture.     

Chemical,Electrochemical and Quantum Chemical Studies for Famotidine Drug as a Safe Corrosion Inhibitor for α-Brass in HCl Solution

Protection of Metals and Physical Chemistry of Surfaces - Expired Famotidine was tested as a corrosion protection for α-brass in 1 M HCl using modified methods: weight loss (WL), Tafel...     

Computer simulation of the core structure of the <111> screw dislocation in α-iron containing copper precipitates:: I. structure in the matrix and a precipitate

Strengthening due to small coherent BCC precipitates of copper is an important component of in-service irradiation hardening of ferritic pressure-vessel steels. The dislocation effects involved are studied here by atomic-scale computer simulation. Many-body interatomic potentials for the Fe–Cu alloy system are used to investigate stacking-fault-energy surfaces and to simulate the atomic structure of the <111> screw dislocation in both pure α-iron and the metastable BCC phase of copper. In iron, the core has the well-known three-fold form of atomic disregistry. In BCC copper, however, the core becomes delocalised by transformation of the copper as the lattice parameter is reduced to mimic the strain experienced by precipitates. Simulation of the screw dislocation threading through the centre of a BCC copper precipitate in an α-iron matrix shows that the extent of core delocalisation depends on precipitate size. The dislocation energy changes indicate a significant dislocation pinning effect due to this dislocation-induced precipitate transformation process.     

Characterization of the microstructure and hardness of the HAZ in a 800MPa grade RPC steel

The microstructure and hardness of the HAZ in a 800MPa grade ultra-low-carbon microalloyed steel were studied.The results indicate that the heat affected zone(HAZ) of the RPC (Relaxation- Precipitation- Controlling) steel possesses a continuous gradient structure, and can be classified into three zones, i. e. CGHAZ (coarse-grain HAZ) , FGHAZ (fine-grain HAZ) and ICHAZ(intercritical temperature HAZ). The microstructures in the HAZ are all composed of bainite-like structure.The microstructure in the CGHAZ mainly consists of lath-like bainite and granular bainite . The influences of heat input and t8/5 on the hardness in the HAZ of RPC steel are notable. With the increase of heat input and t8/5, the softening tendency of HAZ becomes obvious. The hardening phenomenon that normally occurs in the CGHAZ does not take place with this steel in the range of experimental conditions. The softening in the ICHAZ is bound to occur. Hence appropriate welding technologies need to be selected.     

Atomic structural environment of Y in the residual glass phase of silicon nitride and α-sialon

The atomic structural environments around Y ions in the residual glass phase of Si₃N₄ and α-sialon densified with Y₂O₃ and Al₂O₃ have been investigated using extended X-ray absorption fine structure (EXAFS). In the residual glass phase, on average, the Y–O/N nearest neighbor bond length is determined to be 2.30 Å, which corresponds to the Y–O bond length in cubic Y₂O₃, indicating that O is the dominant nearest neighbor of Y. The fitted apparent Y–O/N nearest neighbor coordination number is ~4, which is apparently lower than that when Y is dissolved in a bulk glass, indicating that Y occupies substitutional Si sites. It is also further suggested that the Y–O/N polyhedron in the residual glass phase in silicon nitride and α-sialon is more distorted in comparison with that when Y is dissolved in a bulk glass phase.     

Recent progress in the determination of gallium, indium, and thallium

This mini-review covers the literatures of the determination of gallium, indium, and thallium by instrumental analysis with computer-assisted searching over the period of 1994 to 2003. Some papers appearing in the early of 2004 are also included. Because the rapid progress in the instnLment has been made, these new papers are prioritized in selection in the similar papers. The contents are considered to be separation and preconcentration, spectrophotometry, spectrofluorimetry,electroanalyses, atomic absorption spectrometry, inductively coupled plasma-atomic emission spectrometry, inductively coupled plasma-mass spectrometry and so forth.     

Hydrogen defects in α-Al2O3 and water weakening of sapphire and alumina ceramics between 600 and 1000°C—I. Infrared characterization of defects

Hydrogen impurities in materials influence their properties, including flow strength. α-Al₂O₃ single crystals and polycrystalline ceramics were annealed in supercritical water between 850 and 1025°C, under pressures in the range 1500–2000 MPa. A few specimens were further subjected to plastic deformation. Hydrogen penetration was examined using infrared absorption measurements of O–H bond vibrations, which revealed two kinds of hydrogen defects. In single crystals, defects are characterized by sharp O–H absorption bands assigned to interstitial protons. Hydrogen impurities of hydrothermally annealed ceramics and of all hydrothermally deformed specimens are characterized by broad O–H bands assigned to molecular water. The grain boundaries of hydrothermally annealed ceramics are severely damaged. The kinetics of hydrogen penetration is consistent with diffusion data.     

Characterization of the microstructure and hardness of the HAZ in a 800MPa grade RPC steel

0Introduction Intheprojectof“NewGenerationSteelMaterials”, oneoftheeffectiveapproachestoachieve800MPagrade steelsistoadoptRPCphasetransformationtechnique[1]. Atpresent,12 millimeter thickplatesteelwithyield strengthover800MPahasbeenobtainedbymeansofthis…     

Raman and FTIR studies of phase transitions in the organic superconductor κ-(BEDT-TTF)2Cu[N(CN)2]Cl

The Raman active CC stretching modes and CH₂ deformation modes and the infrared active CN mode are studied as a function of temperature in κ-(BEDT-TTF)₂Cu(N(CN)₂)Cl under pressure. Effects of the structural and superconducting transitions on these excitations are analyzed. The CH₂ and CN modes are sensitive to the thermal expansion around 80 K and to a possible superlattice transition around 160 K while the CC stretching Raman modes ν₂(A_g) are influenced by the formation of the superconducting state.     

Thermal exposure induced α2+γ→B2(ω) and α2→B2(ω) phase transformations in a high Nb fully lamellar TiAl alloy

As-HIPped Ti–44A1–8Nb–1B was exposed to 700 °C air for up to 3000 h. It has been found that the β phase removed by hot isostatic pressing (HIPping) reforms as ordered B2 with ω phase during parallel decomposition of α₂ lamellae to α₂+γ lamellae and perpendicular decomposition of single α₂ laths into α₂ short sections, causing phase transformations of α₂+γ→B2(ω) and α₂→B2(ω).     

The Effect of 10-Methylacridinium and Potassium Iodides on the Salt Passivation of Copper and α-Brass in Chloride Solution

A comparative study of potassium and 10-methylacridinium iodides as inhibitors of copper and -brass anodic dissolution depending on the potential, rotational speed of disk electrode, and concentration of additives is performed. The effect of additives on the film formation at the metal surface is determined.     

Review Recent progress in the determination of gallium, indium, and thallium

This mini-review covers the literatures of the determination of galliumindiumand thallium by instrumental analysis with computer-assisted searching over the period of 1994 to 2003. Some papers appearing in the early of 2004 are also included because the rapid progress i nthe instrument has beeen made these new papers are peioritized in selecton in the simiar papers the contents sre considered to be separation and preconcentra sepectrophotomaetry electroanalyses atomic absorption spectrometry inductively coupled plasma-atomic emission spectrometry inductively coupled plasma-mass spectrometry and so forth     

Kinetics and Mechanism of the Anodic Ionization of Nickel in a Chloride–Bromide Solution

The kinetics of the anodic ionization of nickel is studied voltammetrically on a rotating disc electrode ( of 100.5 to 235.5 rad/s) in a solution containing 1 M NiCl₂+ 1 M NH₄Br (pH 3.30 ± 0.05) at a temperature of 22, 44, 60, or 80°C. The slopes of the Tafel segments in the polarization curves are practically independent of temperature (b _a= 83.5 ± 1.5 mV), which reflects their anomalous temperature behavior. The experimental data agree with a multistage mechanism of the nickel ionization involving the successive transfer of two electrons and the sorption–desorption of intermediate products and the electrolyte anions. Temkin's isotherm is used for describing the adsorption process.     

Kinetics and thermodynamics of the α→γm massive transformation in a Ti–47.5 at.% Al alloy

Continuous cooling experiments, utilizing in situ, high-speed computer-controlled temperature and electrical resistivity measurements, were performed to study the kinetics and thermodynamics of the α→γ_m massive transformation in a Ti–47.5 at.% Al alloy. Samples of the alloy were heated by controlled direct resistance heating in vacuum to the α-phase field and cooled at various rates either in vacuum or by controlling the flow of a helium jet quench. The results have shown that the α→γ transformation is sensitive to cooling rate and is accompanied by large discontinuous changes in resistivity and thermal arrest. Lamellar, feathery and massive γ_m are observed with increasing cooling rate. Correlation of the resistivity–temperature–time data with microstructure allowed the determination of the cooling velocity range in which the massive transformation takes place, the reaction temperatures of this transformation as a function of cooling rate, and the growth rate of the massive γ_m phase as a function of undercooling below T₀. The enthalpy and driving force associated with the formation of the massive γ_m phase were determined and compared with those in other alloy systems; the experimental values of the driving force were also found to compare well with theoretically calculated values. Comparison of estimates of the activation enthalpy for boundary diffusion obtained with values for bulk diffusion established that the α→γ_m massive transformation is controlled by interfacial rather than volume diffusion. Possible growth mechanisms of the massive phase, whether by a ledge process or by continuous growth, were examined and are discussed.