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Purpose The purpose of this study is to develop the existence and mechanism of stress corrosion cracking (SCC) for A517 steel in marine environments. Design/methodology/approach Slow strain rate test (SSRT) and constant load tests were used to investigate the SCC susceptibility of A517 steel. In addition, the additive stresses caused by the corrosion film and hydrogen entering into steel were applied to reveal the fundamental mechanism of the SCC. Findings The SCC susceptibility increased due to anodic dissolution and additive stress caused by the corrosion-produced film under anode polarization. Furthermore, the SCC susceptibility increased with increasing cathodic polarization, which is due to the increased additional stress caused by hydrogen entering into the steel. However, when the cathode polarization further increased, the additional stress remained due to the constant hydrogen content, thus the SCC susceptibility did not vary. Moreover, the SCC susceptibility of A517 steel under an alternate immersion environment (AIE) was lower than that under a full immersion environment and the steel under the AIE with 0.5 W/D had the lowest SCC susceptibility. Originality/value The stress corrosion behaviors of A517 in marine environments under various conditions were systematically analyzed.

Piezocatalysis, converting mechanical vibration into chemical energy, is an emerging technology to address environmental issues. In this work, we propose an efficient method to significantly improve the piezocatalytic activity by morphology engineering rather than composition design. The catalytic property in BaTiO3 nanocrystallites with diverse morphologies is investigated by dye degradation and hydrogen production under ultrasonic vibration. The BaTiO3 nanosheets exhibit an excellent piezocatalytic activity with a degradation rate of 0.1279 min−1 for Rhodamine B, far beyond those in previous piezocatalytic literature and even comparable to excellent photocatalysts, and also a high hydrogen production rate of 92 μmol g−1 h−1. Compared with nanowires and nanoparticles, the 2D morphology greatly enhances the piezocatalytic activity in nanosheets owing to much larger piezoelectric potential. This proves that the piezocatalytic property is dominated by the morphology-dependent piezoelectricity, rather than specific surface area as other catalysis. Dominated by bending vibrating mode, the piezocatalytic activity reaches a maximum at the piezoelectric resonating frequency, and it increases with the ultrasonic power. Moreover, it has good reusability and wide versatility for catalytic degradation. This work gives an in-depth understanding of piezocatalytic mechanism and provides a way to develop high performance and eco-friendly piezocatalysts.

Alloying elements can pronouncedly change the mechanical properties of intermetallic compounds. However, the effect mechanism of this in Mg2Si alloys is not clear yet. In this paper, systematic first-principles calculations were performed to investigate the effect of alloying elements on the ductility of Mg-Si alloys. It was found that some alloying elements such as In, Cu, Pd, etc. could improve the ductility of Mg2Si alloys. Moreover, the interatomic bonding mechanisms were analyzed through the electron localization functional. Simultaneously, the machine-learning method was employed to help identify the most important features associated with the toughening mechanisms. It shows that the ground state atomic volume (VGS) is strongly related to the stacking fault energy (γus) of Mg2Si alloys. Interestingly, the alloying elements with appropriate VGS and higher Allred-Rochow electronegativity (En) would reduce the γus in the Mg-Si-X system and yield a better ductility. This work demonstrates how a fundamental theoretical understanding at the atomic and electronic levels can rationalize the mechanical properties of Mg2Si alloys at a macroscopic scale.

Density functional theory (DFT) calculations have been carried out to investigate the hydrogen trap characteristics of a serial of nano-precipitates (VC, VN, TiN, NbN, NbC, and NiAl) in α-Fe. The H atom solution energies calculations in bulk nano-precipitates indicate that ideal nano-precipitates could not trap H atoms, while the vacancies in nano-precipitates could reduce the H atom solution energies. With respect to the coherent interfaces between α-Fe and nano-precipitates, tetrahedral sites are possible hydrogen traps. Volume evolutions and Bader charge analyses have been performed and it was found the strain at the coherent interface benefits to the hydrogen trap. In addition, the vacancies near the coherent interfaces could be fine hydrogen traps, which is attributed to the combined effect of strain and vacancy. This study could provide guidance to design nano-precipitates in steel to suppress the hydrogen embrittlement.

Medium manganese (Mn) steel has excellent strength and ductility and is widely used in the automobile industry and elsewhere; however, hydrogen embrittlement (HE) is considered as one of the most serious issues of its application. In this paper, in situ transmission electron microscopy was used to study the microstructural evolution and fracture micromechanisms of medium Mn steel under the influence of hydrogen and annealing. The results indicated that two specimens with different annealing processes showed transformation-induced plasticity and twinning-induced plasticity, albeit to a varying degree due to different microstructures with distinct mechanical properties. It was shown that hydrogen affected the fracture micromechanisms, which promoted the initiation of microcracks at the boundaries of martensite transformed from austenite. Moreover, the main cracks propagate in a zigzag fashion, following hydrogen charging, due to the hardness of the martensite. These findings provide directions for improving HE resistance through microstructural regulation of medium Mn steel.

Medium Mn steels are a class of the new-generation ultra-high-strength materials used in automotives. However, despite excellent ductility, they may suffer from delayed cracking and thus cause serious concerns. In this study, several medium Mn steels were tested with different prestrain and hydrogen charging conditions. The interaction and synergistic effects of prestrain and hydrogen content on hydrogen-induced delayed cracking behavior are investigated. The threshold stress of hydrogen-induced cracking (HIC) decreased during dynamic hydrogen charging under a constant load. In the process of dynamic hydrogen charging, for M7B and M10B steels, the normalized stress intensity factor σ/σb and the corresponding threshold stress σHIC decreased sharply as prestrain increased. This is because the volume fraction of retained austenite decreased with an increase in prestrain. Similarly, σHIC was reduced and the critical hydrogen content dropped drastically with increasing prestrain. For M7C, the influence of prestrain on threshold stress and hydrogen concentration was less than that of M7B. This is because the different treatment processes leads to a different stability of the retained austenite. By observing the SEM fractographs, the fracture surface of medium Mn steels showed different fracture characteristics, such as dimple fractures and intergranular and transgranular modes.

Purpose The purpose of this study is to develop a model extending Oriani’s formula by introducing a normalised concentration to simulate hydrogen diffusion in a multi-material system such as coated steels, under the presence of traps. Design/methodology/approach Implemented through the finite element method based on the analogy between mass diffusion and heat transfer, the governing equation was applied to investigate the combined effects of hydrogen traps and surface oxide films on hydrogen permeation in ferritic steels. Findings This study shows that the effective diffusivity varies over several orders of magnitude depending on the traps and films. This explains the divergence of measured hydrogen diffusivities in steels. It is revealed that hydrogen permeation in steels with Pd or Ni film is a trapping-dominant transport process, while hydrogen permeation in steel with oxide film is a process controlled by both trapping effect and retarding effect of oxide film. The oxide film enhances total hydrogen concentration within the steel substrate and is therefore detrimental. The Pd or Ni film has a little influence on total hydrogen concentration distribution depending on trapping energy. Originality/value Hydrogen flux curves and transient hydrogen concentration distributions can be directly obtained through the developed model. The proposed approach can also be extended to investigate other interstitial (i.e. carbon, oxygen and nitrogen) diffusion with traps revisited in complex systems.

2D MXene materials have the advantages of versatile chemical composition, tunable layer thickness, and facile functionalization nature, and can be used as catalysts for the hydrogen evolution reaction (HER). However, tuning the thermal stability and activation of in-plane activity remain a challenge. We apply high-throughput density functional theory (DFT) calculations, together with a machine learning framework, to identify 2D MXene ordered binary alloy (OBA) activity trends and guide HER catalyst design. 2D MXenes of Mn+1XnO2 (n = 1, 2, 3; X = C, N) and OBA HER catalysts of M2M′X2O2 and M2M′2X3O2 with 3d, 4d and 5d transition metal electrons were enumerated by screening, followed by catalytic activity, thermal stability, and conductivity computations. Our results indicate that 110 kinds of experimentally unexplored 2D MXene OBAs with thermostability and outstanding HER activity surpassing that of noble metal platinum were selected. Especially, the titanium element is mainly contained in the ideal catalysts of 2D MXene OBAs, which is consistent with the MXenes synthesized by experiments. Further, we show that descriptors developed using the AdaBoost ensemble learning model could accurately predict and uncover the essential geometric and chemical origin of HER activity, which is very consistent with the electronic insights. The advanced research strategy, which combines high-throughput computing with machine learning, shows robust ability for evaluating the activity trends and designing new complicated catalysts.

The effects of grain boundaries (GBs) on the initiation of hydrogen-induced blisters in pure iron were investigated using synchrotron polychromatic X-ray Laue nano-diffraction. It was found that the random GBs were more susceptible to blistering than the coincidence site lattice grain boundaries. High strain levels and severe plastic deformation were observed around the random GBs after hydrogen charging, but not on the coincidence site lattice grain boundaries.

Perovskite oxides with ionic and electronic conductivity are the key cathode materials of solid oxide fuel cells. Most of these materials, however, exhibit large cathodic polarization resistance which is mainly determined by their tardy oxygen transport kinetics. Herein, Pr 0.5 Ba 0.25-x Ca 0.25 CoO 3-δ is studied to understand the roles of Ba-deficiency in tuning oxygen transport and electrochemical behaviors in the system. Our findings indicate that Ba-deficiency can significantly accelerate oxygen surface exchange process and bring ∼77% reduction of polarization resistance in this process. It is interesting to note that Ba-deficiency can slightly slow oxygen ion bulk diffusion rate and induce a minor increase of polarization resistance in the corresponding process, which associates with the inhibited oxygen vacancy mobility caused by the interactions between negatively charged Ba vacancy and positively charged oxygen vacancy. These new findings pave a new path for solid oxide fuel cell design and chemical sensor developments.

The well-known anti-corrosive property of stainless steels is largely attributed to the addition of Cr, which can assist in forming an inert film on the corroding surface. To maximize the corrosion-resistant ability of Cr, a thorough study dealing with the passivation behaviors of this metal, including the structure and composition of the passive film as well as related reaction mechanisms, is required. Here, continuous electrochemical adsorptions of OH-groups of water molecules onto Cr terraces in acid solutions are investigated using DFT methods. Different models with various surface conditions are applied. Passivation is found to begin in the active region, and a fully coated surface mainly with oxide is likely to be the starting point of the passive region. The calculated limiting potentials are in reasonable agreement with passivation potentials observed via experiment.

The effect of hydrogen on the twinning evolution in a twinning-induced plasticity (TWIP) austenitic steel was investigated at different strain levels. The presence of hydrogen decreased the twin thickness and increased the twin density in individual twin bundles, in comparison with the hydrogen-free condition. This mechanism, reported for the first time, was termed hydrogen-enhanced densified twinning (HEDT). Based on these experimental observations, the effect of hydrogen on twinning was analyzed from the three stages of nucleation, growth and stability. HEDT may elevate the local stress, and thus significantly affect the hydrogen embrittlement (HE) of TWIP steels.

Exploring advanced cathode materials that have high electrochemical activity and superior thermal compatibility with other components is of great importance for the application of intermediate-temperature solid oxide fuel cells. In the present study, influences of Ca doping on electrochemical and physicochemical properties of NdBa 1-x Ca x CoCuO 5+δ were studied systematically. A relatively low thermal expansion coefficient (16.8 × 10 −6 °C −1 ) was obtained for the Ca-doped sample over the temperature range of 25–800 °C. Moreover, Ca doping significantly enhanced the electrochemical performance of NdBa 1-x Ca x CoCuO 5+δ . The highest densities of power for NdBa 1-x Ca x CoCuO 5+δ -based single cells at the temperatures of 800 °C increased from 1.42 W cm −2 for x = 0.0 to 1.84 W cm −2 for x = 0.3. This increase in electrochemical performance of NdBa 1-x Ca x CoCuO 5+δ cathode with Ca doping can be ascribed to enhanced concentrations of oxygen vacancies and higher electrical conductivity.

The investigations of interactions between hydrogen and transition metal surfaces are of vital importance to the comprehension of principals involved in many chemical processes. In this work, the influences of coverage on H adsorption and absorption on and in a series of transition metals have been studied. High enough hydrogen coverage is needed to make H absorption much more feasibly. The pre-adsorbed H adatoms can modify H binding energies as well as H absorption energetics and can be felt very deeply in the 2nd-subsurface. As a result, surface penetration of atomic H and further diffusion into the bulk can be facilitated, and in turn the resurfacing process of absorbed H is blocked.

Whether hydrogen diffusion can be accelerated by grain boundaries (GBs) still remains controversial. In this study, the impact of different types of GBs within the directionally solidified polycrystalline nickel specimens on hydrogen diffusion was directly observed at room temperature by combining Electron Back Scattered Diffraction (EBSD) and scanning Kelvin probe force microscopy (SKPFM). The results suggest that the coherent Σ3 twin GB provides a fast path for hydrogen diffusion, while the random GB cannot significantly accelerate the transport of hydrogen atoms. In addition, this study confirms that SKPFM is a reliable technique to allow the detection of the local diffusion and distribution of hydrogen in metals with high lateral resolution down to the GBs. Keywords: Grain boundary, Hydrogen diffusion, Scanning Kelvin probe force microscopy

Cyclic microbridge tests were applied to investigate the mechanical properties of the 100-to-400-nm-thick graphene oxide membranes. The effective Young’s moduli of different thickness graphene oxide membranes were derived and proved to be size dependent. The self-reinforcing behavior of graphene oxide membranes, which exhibits as an increase in Young’s modulus after cyclic loading, was observed and turned out to be in a relationship with thickness. A theoretical analysis is presented to explain the size dependence of the self-reinforcing Young’s moduli. This work is meaningful for the applications of graphene oxide membranes and the development of basic elements of the micro/nano-electro-mechanical systems.

The twinning behavior and hydrogen embrittlement (HE) of a twinning-induced plasticity (TWIP) steel were investigated for different pre-strains at different strain rates. The lower pre-strain rate led to thinner twins and higher twin volume fraction. The influence of the twin characteristics on HE sensitivity was analyzed from statistical data on the evolution of surface crack characteristics during secondary straining period after cathodic hydrogen charging. Based on the ratio of crack initiation sites caused by the intersection of twins and grain boundaries, it was found that thinner twins in twin bundles of similar thickness promoted the generation of hydrogen-induced cracks (HICs).

The hydrogen segregation at different individual grain boundaries (GBs) in pure nickel has been visually revealed by the contrast of the Volta potential measured by scanning Kelvin probe force microscopy (SKPFM) before and after hydrogen charging. By combining the Electron Back Scattered Diffraction (EBSD) analyses, both several typical low-Σ special GBs and the general GBs with different misorientation have been studied. The results show that the segregation degree of hydrogen atoms at GBs strongly depends on the GB structure. The hydrogen trapping capacity of the low-Σ special GBs is sequenced. For the general GBs with different misorientation, the evolution of the hydrogen segregation degree with the GB misorientation coincides with the prediction of the GB structure model.

Ammonia synthesis is one of the most studied reactions in heterogeneous catalysis. To date, however, electrochemical N2 reduction in aqueous systems has proven to be extremely difficult, mainly due to the competing hydrogen evolution reaction (HER). Recently, it has been shown that transition metal complexes based on molybdenum can reduce N2 to ammonia at room temperature and ambient pressure in a non-aqueous system, with a relatively small amount of hydrogen output. We demonstrate that the non-aqueous proton donor they have chosen, 2,6-lutidinium (LutH+), is a viable substitute for hydronium in the electrochemical process at a solid surface, since this donor can suppress the HER rate. We also show that the presence of LutH+ can selectively stabilize the *NNH intermediate relative to *NH or *NH2via the formation of hydrogen bonds, indicating that the use of non-aqueous solvents can break the scaling relationship between limiting potential and binding energies.

The technology of photocatalytic hydrogen production that converts abundant yet intermittent solar energy into an environmentally friendly alternative energy source is an attractive strategy to mitigate the energy crisis and environmental pollution. Graphitic carbon nitride (g-C3N4), as a promising photocatalyst, has gradually received focus in the field of artificial photosynthesis due to its appealing optical property, high chemical stability and easy synthesis. However, the limited light absorption and massive recombination of photoinduced carriers have hindered the photocatalytic activity of bare g-C3N4. Therefore, from the perspective of theoretical calculations and experiments, many valid approaches have been applied to rationally design the photocatalyst and ameliorate the hydrogen production performance, such as element doping, defect engineering, morphology tuning, and semiconductor coupling. This review summarized the latest progress of g-C3N4-based photocatalysts from two perspectives, modification of pristine g-C3N4 and interfacial engineering design. It is expected to offer feasible suggestions for the fabrication of low-cost and high-efficiency photocatalysts and the photocatalytic mechanism analyses assisted by calculation in the near future. Finally, the prospects and challenges of this exciting research field are discussed.

Li-rich layered oxides are promising cathode materials for advanced Li-ion batteries because of their high specific capacity and operating potential. In this work, the Li-rich layered oxide Li 1·2 Mn 0·54 Ni 0·13 Co 0·13 O 2 (LMNC), is modified via a carbonization-reduction process (yielding the corresponding reduced compound denoted LMNC-R). Compared to the pristine oxide, LMNC-R delivers significantly enhanced initial discharge capacity/columbic efficiency, remarkably improved rate performance with an accelerated Li + diffusion rate, and significantly increased capacity/voltage retention. The specific energy density and energy retention after 100 cycles increase from 378.2 Wh kg −1 and 47.7% for LMNC to 572.0 Wh kg −1 and 71.3%, respectively, for LMNC-R. The enhancement in the electrochemical performance of LMNC-R can be attributed to the synchronous formation of the oxygen non-stoichiometric Li 2 MnO 3-δ component and to the carbon/spinel double coating layer in the material that resulted from the post-treatment process. Thus, the carbonization-reduction modification process can be used to tailor the structural evolution procedure and to suppress the metal ion dissolution of the Li-rich layered oxide during cycling.

The subsurface microstructures of metallic implants play a key role in bio-tribocorrosion. Due to wear or change of local environment, the implant surface can have inhomogeneous electrochemical corrosion properties. In this work, the effect of electrochemical corrosion conditions on the subsurface microstructure evolution of CoCrMo alloys for artificial joints was investigated. Transmission electron microscope (TEM) was employed to observe the subsurface microstructures of worn areas at different applied potentials in a simulated physiological solution. The results showed that applied potentials could affect the severity of the subsurface deformation not only by changing the surface passivation but also affecting the adsorption of protein on the alloy surface.

Edge effects on mechanical properties of armchair molybdenum disulfide nanoribbons were investigated using first principles calculations. The edge eigen-stress model was applied to explain the relaxation process of forming molybdenum disulfide nanoribbon. Edge effects on surface atoms fluctuation degree were obtained from each fully relaxed nanoribbon with different width. Changes of the relaxed armchair molybdenum disulfide nanoribbons structure can be expressed using hexagonal perimeters pattern. Based on the thickness change, relaxed armchair molybdenum disulfide nanoribbons tensile/compression tests were simulated, providing intrinsic edge elastic parameters, such as eigen-stress, Young's modulus and Poisson's ratio.

Theoretical formula to determine flexible membrane deformation of microbridge test was derived based on the assumption that the membrane deformation is dominated by stretching, opposite to bending. Microbridge samples were fabricated from 0.17 μm thick free-standing graphene oxide membrane placed on patterned silicon substrates and tested with a nanoindentation system. The effective Young’s modulus was determined from the microbridge test during both loading and unloading. Combining the flexible membrane theoretical formula with deformable tension-shear model, a multiscale model was proposed to determine the shear modulus of graphene oxide membrane. The effect of temperature on Young’s modulus in different loading sequence was investigated. Polarized Raman spectroscopy and X-ray diffraction were utilized to characterize the self-stiffening behavior of graphene oxide membranes.

The effect of calcium on the properties of SmBa 1–x Ca x CoCuO 5+δ (x = 0.0–0.3) as a cathode material for intermediate-temperature solid oxide fuel cells (IT-SOFCs) is evaluated systematically. Samples exhibit a highly crystalline double perovskite phase, and their cell volumes decrease as x is changed from 0.0 to 0.3. The oxygen content and average thermal expansion coefficient (TEC) of SmBa 1–x Ca x CoCuO 5+δ decreases as the calcium content increased. An average TEC of as low as 15.3 × 10 −6 °C −1 is obtained for SmBa 0.7 Ca 0.3 CoCuO 5+δ . The area specific resistances at 700 °C decrease by approximately 50% when the calcium content is increased from x = 0.0 (0.173 Ω cm 2 ) to x = 0.3 (0.086 Ω cm 2 ). The maximum power densities of SmBa 1−x Ca x CoCuO 5+δ -based single cells at 800 °C increase from 635 mW cm −2 (x = 0.0) to 939 mW cm −2 (x = 0.3).

The small tapered specimen was used to measure the crack initiation stress of hydrogen-induced cracking with a combination of tensile test and finite element method. Based on the regression analysis of measured crack location and depth on the specimen, the crack initiation location was predicted and then the corresponding crack initiation stress could be directly calculated. A critical relative distance of stress interference between adjacent cracks was found, and the stress on the predicted crack initiation location was proved not influenced by its adjacent cracks. Accuracy and reliability of the small tapered specimen method were successfully demonstrated through comparison with traditional parallel-sided cylindrical specimen method.

In this work, we develop a two-step sintering technology special for porous ceramics to resolve the contradiction between porosity and mechanical strength. It contains a first long-time sintering at the relatively low temperature (T1) and a second fast sintering at higher temperature (T2). Porous ceramics of aluminum titanate-strontium feldspar-mullite (ASM) ternary composite were prepared by this method, and exhibit both high porosity and high mechanical strength. The effects of T1 and T2 on the phase composition, microstructure, porosity, pore size distribution, mechanical strength and thermal expansion coefficient (TEC) of ASM porous ceramics are systematically studied. The sample sintered at T1 = 1400 °C & T2 = 1500 °C shows optimum performance: the porosity, bulk density, and mean pore diameter (D50) are 63.48%, 1.20 g/cm3 and 15.94 μm, respectively; while the flexural strength reaches 9.22 MPa and the TEC is 2.9 × 10−6/K. The two-step sintering technology provides a powerful tool to develop porous ceramics with excellent comprehensive properties.

Zn is considered as a promising degradable biomaterial. However, concerns exist for its application as the degradation mechanism of pure Zn in physiological solutions is still not clear. Results indicated that the corrosion product film showed a laminated structure with complex layers, which were ZnO/Zn(OH)2, a Ca/P phase, zinc compounds, and a Ca/P phase from the inside out, respectively. The localized corrosion initiated at grain boundaries and expanded towards the interior of grains with higher corrosion susceptibility, or advanced towards the depth. Additionally, the nature of the corrosion product film and localized corrosion synergistically determined the degradation rate.

The quantitative relationship between the Volta potential measured by scanning Kelvin probe force microscope (SKPFM) and hydrogen concentration values on the pure nickel surface has been calibrated. With continuous SKPFM scanning on the back of hydrogen charged side of a foil specimen, the changing Volta potential was achieved. On the other hand, the evolution of hydrogen concentration values on the SKPFM measured surface was obtained by combining the diffusion equation and electrochemical hydrogen permeation tests, which could estimate the constant hydrogen concentration on charging surface C0 and the hydrogen diffusion coefficient inside the nickel foil D simultaneously. The results suggest that the Volta potential involving SKPFM sharply decreases with the increase of hydrogen concentration in the low hydrogen concentration range. However, the change of the Volta potential is less considerable with the increase of hydrogen concentration at a high hydrogen amount level. The relationship between the SKPFM derived Volta potential and hydrogen concentration is quantitatively described by a modified Nernst equation model. The study shows that SKPFM is a powerful tool to quantify the hydrogen distribution, but may only prevail in low hydrogen concentration range. In addition, it is reasonable to consider the Volta potential to be linearly proportional to hydrogen concentration over a wide range of potential change.

This work presents a comprehensive study of the hydrogen embrittlement (HE) behavior of a 13Cr-5Ni-2Mo supermartensitic stainless steel through two aspects: hydrogen diffusion and hydrogen concentration. Precipitated austenite reduced the effective hydrogen diffusion coefficient and hydrogen permeation flux, and thus increased the HE resistance. Further increasing the austenite content could not provide additional HE resistance as a martensitic transformation is prone to occur when a high hydrogen concentration and stress are coupled, leading to hydrogen induced crack initiation. The HE susceptibility of 13Cr-5Ni-2Mo steel is much higher than that of 960QC steel because of the higher adsorbing hydrogen concentration.

The double perovskite oxides are intriguing catalysts for energy conversion/storage and chemical sensor systems. The cation surface segregation is a stubborn issue that restricts their application. Herein, A-site cation size mismatch (MA) was proposed for the first time as a critical intrinsic parameter for controlling the surface chemistry and electrochemical performance of the double perovskite catalyst. The studies in PrBa1-xCaxCoCuO5+δ revealed that lowering MA can relieve lattice distortion, enlarge PrOδ layer space, maintain surface chemistry, and significantly improve catalytic activity and durability of the double perovskite. Specifically, as MA decrease from 26.1–18.1 %, the output peak power density of PrBa1-xCaxCoCuO5+δ-based single-cells increase from 1.47 to 2.04 W cm−2 (800 °C) while the output current density retentions rise from 82.2 to 94.7 % after 100 h (700 °C and 0.7 V). This guides the design of robust double perovskite catalysts in solid oxide cells, metal-air batteries, photocatalysis, and oxygen sensors.

A 13Cr austenitic stainless steel with a good combination of high yield strength, ductility and hydrogen embrittlement resistance was designed by combining hetero-deformation induced strengthening and martensitic transformation induced plasticity effects. Room temperature metastable austenite is promoted by adding 8 wt% Mn to a 13Cr–5Ni–2Mo supermartensitic stainless steel. A heterostructure consisting of remaining martensite grains located between lath austenite grains and micrometer-sized austenite grains embedded inside ultrafine grains, was fabricated by cold rolling (44% reduction) and annealing at 973 K through a shear reversion process. The novel 13Cr austenitic stainless steel exhibits a yield strength of 923 MPa, tensile strength of 1085 MPa and total elongation of 33.2%. The hydrogen embrittlement resistance of the novel steel was determined by incremental step loading technique testing and was increased 40% compared with that of the 13Cr–5Ni–2Mo supermartensitic stainless steel. This study provides an approach for the design and industrial fabrication of high strength (125 ksi grade level), high ductility and hydrogen embrittlement resistant stainless steels that can be used in harsh service environments containing hydrogen.

The effect of deep sea hydrostatic pressure on double layer capacity still remains unknown. In this study, a novel method to characterize the double layer capacity was put forward. Combining with the potentiodynamic polarization tests and electrochemical impedance spectroscopy (EIS) experiments under different hydrostatic pressures, it was found that pressure increased the capacity both in diffuse layer and Stern layer, which induced the increase of the current density of both oxidation and reduction reaction near the equilibrium potential.

Electrochemical experiments and first-principle calculations were conducted in this study to investigate the impact of carbon doping on the adsorption and absorption on Fe-C alloy surfaces. The generalized Iyer-Pickering-Zawenzaden model was adopted to determine the kinetics related to hydrogen adsorption/absorption. Discharge rate constant k1 was found increased with the presence of carbon, suggesting the promotion of the H2O ionization process and more hydrogen atoms were generated on the surface. Meanwhile, the recombination rate constant k2 decreased on carbon doping surface, indicating recombination process of hydrogen atoms were inhibited. Results also showed the hydrogen surface coverage dropped with increasing carbon content. Additionally, EIS results indicate that the distance between the adsorbed hydrogen atoms and the sample surfaces is reduced by carbon doping. All experimental results are in accordance with the first-principle calculation results which demonstrate that the presence of carbon elevated the binding energy for hydrogen adsorption while lowering the energy barrier for diffusion. Thus, carbon solutes reduce the stability for hydrogen atoms to adsorb on the surface and facilitate their diffusion into the bulk.

This study investigated the effects of dislocation patterns introduced by cold rolling deformation on the hydrogen absorption properties, hydrogen trap behaviors and hydrogen embrittlement (HE) resistance for Armco iron under electrochemical charging. The surface hydrogen coverage first increases and then decreases with increasing deformation, and reaches a maximum at 50% deformation. Dislocation cell walls appear when the deformation is greater than 50%. Furthermore, the HE resistance is improved when the deformation reaches 80%. Because the dislocation cell walls can be used as effective hydrogen traps when the dislocation density reaches a sufficiently high value.

To balance good strength and ductility, Medium Mn steels have been considered as the new generation materials used in automotives. However, they show delayed fracture, which is thought to relate to hydrogen. Therefore, in order to understand their mechanical properties with various hydrogen contents, it is very important to assess their safety. In this study, the effect of hydrogen on the mechanical properties of several medium Mn steels (MMSs) with different Mn content and treatments were investigated. For medium Mn steels, the stability of the retained austenite (RA) was examined and the hydrogen permeation test was performed. Austenite, as a barrier to hydrogen diffusion, leads to a tortuous diffusion path, which reduces the diffusion rate of hydrogen in MMSs. Increasing the Mn content increases the volume fraction of RA in the specimen. The stress-strain curves of MMSs were divided into three parts, determined by the stability and content of RA. Slow strain rate tensile tests with hydrogen charging were performed to investigate the behaviour of hydrogen diffusion and the mechanism of hydrogen embrittlement (HE). After the tests, the hydrogen content was measured and the fracture surface was observed and analysed. The phenomenon of HE in steels has been mainly explained based on the mechanisms of hydrogen-enhanced localised plasticity (HELP), hydrogen-enhanced decohesion (HEDE), and hydrogen assisted micro ovoid coalescence (HDMC). Due to the existence of hydrogen, fracture morphology changes from ductile mode to brittle mode. It was also found that under the same strain rate, tensile strength and elongation decrease gradually as hydrogen concentration increases, resulting in final failure.

Silicon is an important material and many empirical interatomic potentials have been developed for atomistic simulations of it. Among them, the Tersoff potential and its variants are the most popular ones. However, all the existing Tersoff-like potentials fail to reproduce the experimentally measured thermal conductivity of diamond silicon. Here we propose a modified Tersoff potential and develop an efficient open source code called GPUGA (graphics processing units genetic algorithm) based on the genetic algorithm and use it to fit the potential parameters against energy, virial and force data from quantum density functional theory calculations. This potential, which is implemented in the efficient open source GPUMD (graphics processing units molecular dynamics) code, gives significantly improved descriptions of the thermal conductivity and phonon dispersion of diamond silicon as compared to previous Tersoff potentials and at the same time well reproduces the elastic constants. Furthermore, we find that quantum effects on the thermal conductivity of diamond silicon at room temperature are non-negligible but small: using classical statistics underestimates the thermal conductivity by about 10\% as compared to using quantum statistics., Comment: 9 pages, 6 figures

The threshold stress intensity of hydrogen-induced cracking KIH, the crack propagation rate da/dt and the hydrogen diffusion coefficient D have been studied for 30CrMnSiNi2 steel. The results show a combined effect of the hydrogen concentration CH and the yield strength σys on KIH. KIH and da/dt are independent of D when σys ⩾ 1360 MPa, but KIH increases and da/dt decreases with increasing D when σys

Rice straw is an important roughage resource for ruminants in many rice-producing countries. In this study, a rice brittle mutant (BM, mutation in OsCesA4, encoding cellulose synthase) and its wild type (WT) were employed to investigate the effects of a cellulose synthase gene mutation on rice straw morphological fractions, chemical composition, stem histological structure and in situ digestibility. The morphological fractions investigation showed that BM had a higher leaf sheath proportion (43.70% vs 38.21%, p0.05) was detected in neutral detergent fiber (NDFom) and ADL contents for both strains. Histological structure observation indicated that BM stems had fewer sclerenchyma cells and a thinner sclerenchyma cell wall than WT. The results of in situ digestion showed that BM had higher DM, NDFom, cellulose and hemicellulose disappearance at 24 or 48 h of incubation (p

The effects of hydrogen on the optical properties of lead zirconate titanate (PZT) ceramics and BaTiO3 single crystals have been investigated. The experimental results showed that the color of BaTiO3 single crystals changed from light to dark after charging of hydrogen in NaOH solution at room temperature and in H2 gas at high temperature, and then, restored to light color after outgassing in the air, which were the same as PZT-5H ceramics reported earlier. Measurement of the absorbance indicated that hydrogen increased the absorbance within the visible spectrum for both PZT ceramics and BaTiO3 single crystals. The first principles calculations for Pb(Zr0.5Ti0.5)O3 and BaTiO3 showed that hydrogen increased the absorbance within the infrared and visible spectral region and the absorbance increased with the rise of hydrogen concentration. Density of states (DOS) researches indicated that hydrogen changed the DOS of the outer shell electrons, which caused the change of absorbance spectrum.

The relationship between the second phase and inclusion particles and the hydrogen-induced blisters of an industrial iron has been investigated through direct observation of opened blisters by scanning electron microscopy (SEM) with an energy dispersive spectroscopy (EDS) system and statistical analysis. The results show that every blister has a nucleation site and can propagate discontinuously or continuously under the pressure of hydrogen. Most of the nucleation sites (88%) are inclusion or second phase particles. The compositions of the inclusion or second phase particles are mainly Ti, Al, Si, Mn and S. The formation of blister is analyzed and a new mechanism for the initiating, growing and cracking of hydrogen blister is proposed.