Macroscopic and structural effects of hydrogen-bond transformations

A brief account of transformations of internal structure of hydrogen bonds, and transformations involving the breaking and formation of hydrogen bonds is highlighted for a selected group of crystals. The main stress is laid on the short bistable –OH…O= hydrogen bonds, illustrating several general properties, often blurred for weaker hydrogen bonds. A set of parameters relating the electronic structure of the oxygen atoms and geometry of hydrogen bonds is described. This allows one to combine the hydrogen bond dimensions with changes in the electronic structure of the oxygen atoms, accompanying any transformations of hydrogen bonds. Several resultant effects are described: coupling of displacements of molecules or ions with the H-atom transfer, the isotope effect of deuteration on T _c in ferroelectric crystals, a skew trajectory of a disordered H-atom with respect to the O···O direction, or shortening of the O···O distance when the H-atom becomes disordered. It is shown that hydrogen-bond patterns, molecular arrangements and thermodynamic properties of crystals are interdependent. Several examples and possible applications of the presented model are given.     

The effects of stoichiometry on the dry sliding wear of FeAl

The effects of alloy stoichiometry on the dry sliding wear behavior of B2-structured FeAl were investigated using four different FeAl alloys containing 40, 43, 48, and 50 at.% Al. Room temperature pin-on-disk tribotests were performed against an yttria-stabilized zirconia counterface in four different environments: air, oxygen, 4% hydrogen in nitrogen, and argon. It was found that the alloys had lower wear rates in both oxygen-free and water vapor-free environments, where the wear loss was roughly inversely related to the hardness. Interestingly, the wear rates were little affected by the presence of molecular hydrogen. In oxygen- or water vapor-containing environments, the effects of the environment predominated over any effects from the mechanical properties of the alloys. The tips of the worn pins were examined using both scanning electron microscopy and transmission electron microscopy, the latter using specimens produced by focused ion beam milling. Zirconia particles were found to be embedded in a tribolayer on the worn tips of the pins. The results indicate that both two-body and three-body abrasive wear, as well as plastic deformation and delamination were the main wear mechanisms. The abrasive particles largely consisted of the counterface material.     

薄规格A588 Gr.A低合金耐候结构钢的试制开发

介绍了鞍山钢铁股份有限公司2 150 mm ASP生产线薄规格A588 Gr.A低合金耐候结构钢的试制情况。通过合理的化学成分设计,结合2 150 mm ASP生产线的工艺路线,成功试制出薄规格A588 Gr.A钢板,钢板组织为准多边形铁素体和珠光体,晶粒度达到10.5级,综合力学性能优异。     

Strain effects on electronic structure and superconductivity in the iron telluride

The influence of tensile strain in the ab-plane on crystal and electronic structure of FeTe has been studied ab initio. In superconducting FeSe the Fermi surface nesting with a vector q ∼ (0.5,0.5) × (2π/a) is believed to be crucial for rising superconductivity mediated by spin-fluctuations. The results presented here indicate that tensile-strained FeTe also exhibits such conditions. Furthermore, the Fermi surface changes, related to the increase of the lattice parameter a of this telluride, are opposite to analogous effects reported for FeSe. Since a recently transition from the double-stripe to the single-stripe magnetic order in FeTe under tensile strain in the ab-plane is associated with an occurrence of superconductivity in corresponding thin films, these findings allow for drawing a consistent picture of superconductivity in FeSe_1−xTe_x systems, in general.     

Impact strength and structural refinement of A380 aluminum alloy produced through gas-induced semi-solid process and Sr addition

Semi-solid processing of A380 aluminum alloy was performed by gas induced semi-solid (GISS) process. The effects of argon inert gas flow rate, starting temperature and duration of gas purging as key GISS parameters and also modification with Sr on the structural refinements, hardness and impact strength of GISS alloys were investigated. Microstructural evolution shows that there is an important effect of the pouring temperature and Sr addition on the morphology and size of primary α(A1) in the alloy to change from coarse dendritic to fine globular structure. The best sample which has fine grains of 51.18 μm in average size and a high level of globularity of 0.89 is achieved from a GISS processing of Sr modified alloy in which the gas purging started at 610 °C. The impact strength of the GISS optimized samples ((4.67±0.18) J/cm²) shows an increase of about 40% with respect to the as-cast sample due to the globular structure and fibrous Si morphology. Moreover, the hardness of the optimized GISS sample ((89.34±2.85) HB) increases to (93.84±3.14) HB by modification with the Sr and GISS process. The fracture surface of Sr modified alloy is also dominated by complex topography showing typical ductile fracture features.     

Corrosion of steel reinforcement in structural concrete with carbon material addition

Different types of carbonaceous materials have been added to concrete mixes and their effect on the corrosion of embedded steel has been studied. Using a constant water/cement ratio of 0.42 and different amounts of carbonaceous materials and different curing periods the evolution of the corrosion process in the embedded reinforced bars has been determined. The addition of small quantities of carbonaceous materials to the mixture produces a reduction of the concrete permeability. Tests demonstrate that a decrease of the corrosion level occurs when the content ratio of carbon material addition is increased.     

Structural evolution of non-dendritic AlSi7Mg alloy during reheating

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Ground state structural stability of ordered fcc- and bcc-based LiAl compounds under first and second nearest-neighbour pair approximation

Self-consistent local density electronic structure calculations have been performed on a series of ground state ordered superstructures of lithium-aluminium alloys spanning the entire concentration range. These structures are based on both fcc and bcc lattices under the first and second nearest neighbour pair approximation which is adequate to stabilize all the stable and metastable phases of the Li---Al system. Using the efficient tight-binding linear muffin-tin orbital (TB-LMTO) method, we have calculated the volume dependent total ground state energies and the systematic trends in various cohesive and electronic properties at zero temperature, as a function of Li concentration. The predicted heats of formation for all the different ground state superstructures result in a representative stability profile, which shows that the L1₂, B32 and DO₃ structures are the most stable amongst various phases having Al₃Li, AlLi and AlLi₃ compositions, respectively. Moreover, we have parameterized the cohesive energies using the Connolly-Williams cluster expansion method and estimated the effective many-body interactions for the fcc lattice in an octahedron-tetrahedron cluster approximation, and for the bcc lattice in an irregular tetrahedron cluster approximation. These volume dependent but configuration (as well as concentration) independent interactions coming out of the TB-LMTO-CWM approach are not only important for first principles calculation of phase diagram but are also useful for predicting the evolutionary path of ordering processes.     

Modelling immersion corrosion of structural steels in natural fresh and brackish waters

The multi-phase mean-value model previously proposed for modelling the marine immersion corrosion of low carbon and low alloy structural steels is examined for application to fresh and brackish waters. Use is made of field data for brackish and fresh waters available in the literature, supplemented with data or estimates for water temperature, pH, hardness and nutrient levels. It is shown that the data exhibits consistency with the model and that it is a function of average water temperature. Corrosion in brackish and fresh waters corrosion depends on water hardness, pH and nutrient levels, with higher pH levels and lower water hardness associated with higher aerobic levels of corrosion but these are not significant for anaerobic corrosion. In the anaerobic phases 3 and 4 of the model, the available data and associated trends are interpreted as showing that elevated levels of nutrients produce higher rates of corrosion. Conversely, these phases showed very low rates of corrosion for fresh waters with very low nutrient levels. Consistent with basic corrosion theory and with laboratory observations, salinity by itself is not a clear distinguishing characteristic. The model provides a new approach to interpreting the available data for corrosion in fresh and brackish waters. It permits plausible explanations for previous apparently inconsistent observations for corrosion in brackish waters. Finally, it reinforces the need for full and detailed reporting of corrosion testing programs, including details of precise timing, location, orientation and environmental conditions including means and variations in water temperatures, DO, salinity, pH, water hardness, carbonates and various nutrients.     

A first principles study of structural and mechanical properties of Ti2AlZr intermetallic

The present work describes the structural and mechanical behaviour of three phases namely B2, D0₁₉ and O phases of Ti₂AlZr intermetallic using first principles density functional theory (DFT) within generalized gradient approximation (GGA). The equilibrium lattice constant values of B2, D0₁₉ and O phases are in good agreement with the experimental and theoretical data, respectively. Formation energy of O phase is minimum followed by D0₁₉ and B2. Bonding characteristics of these phases have been explained based on electronic density of states and charge density. All the three phases satisfy the Born stability criteria in terms of elastic constants and are associated with ductile behaviour based on G/B ratios. The B2 phase exhibits very high anisotropy in comparison to those of the D0₁₉ and O.     

Markov chain modelling of pitting corrosion in underground pipelines

A continuous-time, non-homogenous linear growth (pure birth) Markov process has been used to model external pitting corrosion in underground pipelines. The closed form solution of Kolmogorov’s forward equations for this type of Markov process is used to describe the transition probability function in a discrete pit depth space. The identification of the transition probability function can be achieved by correlating the stochastic pit depth mean with the deterministic mean obtained experimentally. Monte-Carlo simulations previously reported have been used to predict the time evolution of the mean value of the pit depth distribution for different soil textural classes. The simulated distributions have been used to create an empirical Markov chain-based stochastic model for predicting the evolution of pitting corrosion depth and rate distributions from the observed properties of the soil. The proposed model has also been applied to pitting corrosion data from pipeline repeated in-line inspections and laboratory immersion experiments.     

IR thermographic detection and characterization of hidden corrosion in metals: General analysis

Principles of infrared thermographic non-destructive testing for determining hidden corrosion in metals are summarized and discussed. 1D, 2D and 3D heat conduction models are introduced to simulate thermal processes in corroded areas. In thick metals, the lateral heat dissipation is mainly responsible for significantly smoothing the temperature contrast curves. Modelling small-size corroded sites requires 3D numerical models. Numerous defects have been simulated and the inversion formulas for determining material loss have been modelled for both flash and square-pulse heating. It has been shown that corrosion characterization inaccuracy is lower than 20% in cases representing a practical interest.     

Ion-irradiation-induced structural transitions in orthorhombic Ln2TiO5

The response of a material to a high radiation field is important when selecting materials for nuclear applications, such as structural materials, nuclear waste forms and inert matrix fuels. In the present study, the radiation response of orthorhombic, rare-earth titanates, Ln₂TiO₅ (Ln = La, Nd, Sm, Gd, Dy and Y), was investigated by 1 MeV Kr²⁺ ion bombardment at temperatures ranging from 50 to 1073 K. In situ transmission electron microscopy revealed that the radiation tolerance and irradiation-induced structural transitions vary largely with composition. Y₂TiO₅ exhibits the lowest critical amorphization temperature (T_c = 623 K), above which crystals cannot be amorphized, which is consistent with its use in the form of nanoclusters in radiation-resistant oxide-dispersion-strengthened steels. The disordered fluorite structure type of Ln₂TiO₅, with smaller Ln cations, formed as an intermediate phase prior to becoming fully amorphous. The fluorite structure type of Ln₂TiO₅, containing more vacancies as compared with that of Ln₂Ti₂O₇, may exhibit enhanced ionic conductivity, which highlights an effective way of using ion beams to modify the properties of materials.     

The role of combustion synthesis in the formation of slurry aluminization

Slurry processes have been investigated for several years as an alternative technique to conventional CVD-derived aluminizing to achieve similar diffusion coatings. This study investigates the coating formation mechanisms during heat treatment processes on pure nickel using slurries, which contain high amounts of micro-sized aluminium particles. At temperatures in the range of 550 °C–1000 °C, aluminium diffuses into the nickel substrate, promoting the formation of intermetallic nickel–aluminide layers. In order to control this process, it is important to understand the mechanisms that occur in the initial stages, when the metallic aluminium powder melts and reacts in contact with nickel. While a conversion of closely pressed nickel–aluminium into aluminide by combustion synthesis is well known, DTA measurements were undertaken to investigate if and when such processes occur in loosely packed powders. Two compositions of nickel with aluminium or eutectic aluminium–silicon alloyed particles were used in order to reveal a potential influence of the melting point of the aluminium alloy particles. The influence of the atmosphere was studied by comparing results during exposure in argon and air. Subsequently, for comparison with the more complex mechanism of slurry aluminizing, both powders were applied to pure nickel substrate and the coating formation during heat treatment at 600 °C, 650 °C, and 700 °C was investigated. The results clearly show the importance of combustion synthesis on the formation of slurry coatings on nickel. Based on the observations, four steps were identified, which lead to the formation of aluminides and the subsequent growth of the aluminide layer: After melting of the aluminium powder, a network of molten aluminium forms within and between the particles, followed by dissolution of nickel in the aluminium melt. If enough Al is available, combustion synthesis between Ni and Al takes place. After this highly exothermic reaction, solid state diffusion controls the further formation of slurry coatings on nickel. Finally, the mechanism was verified by coating industrially used superalloys with the Al-based slurry in air and argon.     

Discovering key meteorological variables in atmospheric corrosion through an artificial neural network model

This paper presents a deterministic model for the damage function of carbon steel, expressed in μm of corrosion penetration as a function of cumulated values of environmental variables. Instead of the traditional linear model, we designed an Artificial Neural Network (ANN) to fit the data. The ANN numerical model shows good results regarding goodness of fit and residual distributions. It achieves a RMSE value of 0.8 μm and a R² of 0.9988 while the classical linear regression model produces 2.6 μm and 0.9805 respectively. Besides, F_LOF for the ANN model were next to the critical value.The improved accuracy provides a chance to identify the most relevant variables of the problem. The procedure was to add/remove one after the other the variables and perform from scratch the corresponding training of the ANN. After some trial and error as well as phenomenological arguments, we were able to show that some popular meteorological variables like mean relative humidity and mean temperature shown no relevance while the results were clearly improved by including the hours with RH < 40%. The results as such might be valid for a limited geographical region, but the procedure is completely general and applicable to other regions.     

Quantitative determination of corrosion products and adsorbed water on copper in humid air containing SO2 by IR-RAS measurements

The time dependency of the amounts of corrosion products and co-existing adsorbed water on copper in humid air containing SO₂ was estimated from a series of in situ time-resolved IR-RAS spectra on the basis of the relations between the band intensities and the mass changes of the corrosion products, which were determined by simultaneous measurement of IR-RAS and QCM. The amounts of both corrosion products increased slowly at the initial stage and later increased rapidly. Although the relative humidity was kept constant, the amount of adsorbed water increased nearly the same behavior as that of corrosion products in the stage of relatively small amounts of corrosion products and later increased rapidly when the amounts of corrosion products increased. In humid air without SO₂, sulfite gradually decomposed and some of it changed into sulfate.     

Electrochemical and quantum chemical assessment of two organic compounds from pyridine derivatives as corrosion inhibitors for mild steel in HCl solution under stagnant condition and hydrodynamic flow

In this study, the inhibitive performance of two pyridine derivatives as corrosion inhibitors for mild steel was examined under stagnant condition and hydrodynamic flow in HCl solution at 25 °C. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques were employed. To explore the inhibitors adsorption mechanism, Langmuir isotherm and quantum chemical studies were used. The results of electrochemical measurements show that the inhibitor concentration has a positive effect on its efficiency while for hydrodynamic condition, it is vice versa. Corrosion attack morphologies were observed at stagnant and hydrodynamic conditions to verify qualitatively the results obtained by electrochemical methods.     

The oxidation of two ternary Ni-Cu-10 at.% Al alloys in 1 atm of pure O2 at 800-900 °C

The oxidation of the ternary alloys Ni-45Cu-10Al and Ni-30Cu-10Al has been studied at 800-900 °C under 1 atm O₂. The presence of 10 at.% Al reduces significantly the oxidation rate of the corresponding Cu-Ni alloys during the initial oxidation stages, even before the establishment of a complete Al₂O₃ layer. The weight of individual sample of the two ternary Ni-Cu-10Al alloys at 800 °C increases more rapidly than at 900 °C during the initial oxidation stage. As oxidation proceeds, the weight gain at 800 °C slows down to a degree that the total weight gain after 24 h oxidation at 800 °C is less than that at 900 °C. Due to a faster formation of the Al₂O₃ layer, which suppresses earlier the further oxidation of Cu and Ni, the external region of the scales grown on Ni-45Cu-10Al contain much less Cu and Ni oxides than those grown on Ni-30Cu-10Al. The transition from the internal oxidation to the selective external oxidation of the most reactive component Al in Ni-Cu-Al alloys is favored by higher values of the Al content, of temperature and of the Cu/Ni ratio.     

Chemical characterization and anticorrosion properties of corrosion products formed on pure copper in synthetic rainwater of Rio de Janeiro and São Paulo

This work aims to characterize corrosion products formed on copper samples exposed to synthetic rainwater of Rio de Janeiro and São Paulo. XRD and XPS were employed to determine their composition, while electrochemical techniques were used to evaluate their protective properties. XRD and XPS indicated the thickening of the corrosion layer with time. Electrochemical results showed that the protectiveness of the corrosion layer depends on the solution composition. Based on our findings a corrosion mechanism for copper in simulated rainwater is proposed where the role of NH₄⁺ ions in the cuprite layer partial regeneration is taken into account.     

Pressure effect on the structural relaxation and glass transition in metallic glasses

Two different enthalpy recovery methods were applied to investigate the effects of pressure on structural relaxation and glass transition temperature (T_g) in two metallic glasses (Pd₄₀Ni₁₀Cu₃₀P₂₀ and Zr₆₅Al_7.5Cu_27.5). The pressure-induced enhancement of T_g (dT_g/dP) was derived to be 6 K/GPa in Pd₄₀Ni₁₀Cu₃₀P₂₀ glass, while an increment of 50 K/5 GPa was observed in Zr₆₅Al_7.5Cu_27.5 glass. Activation (formation and migration) volumes of the flow defect were used to interpret the pressure dependence of the structural relaxation and T_g in terms of the free volume model. According to the measured results, the activation volume of relaxation was derived to be 16.7 ų for Pd₄₀Ni₁₀Cu₃₀P₂₀, which is much smaller than that of the polymers.