The effect of frequency and environment on the fatigue crack growth behaviour of SA508 Cl. III RPV steel

This paper describes the effect of frequency and environment on the fatigue crack growth behaviour of SA508 Cl. III RPV steel. The study has shown that the effect of the Pressurised Water Reactor (PWR) environment is directly related to the frequency and the level of applied stress intensity of the test; these results further showed that the lower the frequency the greater the environmental effect, especially at low ΔK levels. No such frequency effect was observed in either the laboratory air or ultra-high purity argon environments. At a frequency of 0·1 Hz the PWR water test exhibited characteristic EAC growth, i.e. plateau growth behaviour. Fractographical examination of the fracture surface revealed that the fracture mode during plateau growth was intergranular failure. The experimental results are described and discussed in terms of the hydrogen assisted cracking mechanism.     

The fracture mechanical significance of cracks formed during stress-relief annealing of a submerged arc weldment in pressure vessel steel of type A508 Class 2

In large weldments of type A508 Cl2 cracks can form in the heat-affected zone during stress-relief annealing. The significance of such cracks with respect to catastrophic fracture is of interest from the point of view of safety, in particular for nuclear pressure vessels. In this investigation the size of reheat cracks, as formed and after fatigue growth, has been compared with the critical size for fast fracture. The latter was assessed by determination of the fracture toughness of the heat-affected zones. The fracture toughness of the heat-affected zones did not differ much from that of the parent material. The presence of microcracks reduced the fracture toughness (of a special type of simulated specimen) at 20°C by about 20%. The fracture mechanical evaluation indicates that the cracks formed during stress-relief annealing should not impair the safety of the vessel under normal conditions, except for particular geometries and when the cracks may rapidly link together during fatigue.     

Optical, electrical and structural properties of indium-doped cadmium oxide films obtained by the sol-gel technique

Indium-doped cadmium oxide films were obtained by mixing cadmium oxide and indium oxide precursor solutions by the sol-gel technique. The indium atomic concentrations in solution (x) studied were 0, 2, 5 and 10 at%. The films were sintered at two different sintering temperatures (T_s) 350 and 450 °C, and after that annealed in a 96:4 N₂/H₂ gas mixture atmosphere at 350 °C. X-ray diffraction patterns showed that all films sintered at T_s=350 °C only consisted of cadmium oxide crystals. The films sintered at T_s=450 °C consisted of cadmium oxide crystals also; however, for the highest indium atomic concentration (10 at%) the formation of cadmium indate oxide crystals was evident. All films show high optical transmission (>85%) and an increase of the direct band gap value from 2.4 to 3.1 eV, as the indium atomic concentration in solution increases. The minimum resistivity value obtained was 6.3×10⁻⁴ Ω cm for the films with x=5 at%, T_s=450 °C and annealed at 350 °C.     

Improvement of electrochemical and structural properties of LiMn2O4 spinel based electrode materials for Li-ion batteries

Spinel LiMn₂O₄ and LiM_0.02Mn_1.98O₄ (where M is Zn, Co, Ni and In) were produced via facile sol–gel method and Cu/LiMn₂O₄, Cu/LiM_0.02Mn_1.98O₄, Ag/LiMn₂O₄ and Ag/LiM_0.02Mn_1.98O₄ binary composite electrode materials were produced via electroless coating techniques as a positive electrode material for Li-ion batteries. The phase composition, morphology and electrochemical properties of the synthesized materials were investigated by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), cyclic voltammometry (CV), galvanostatic charge–discharge tests and electrochemical impedance spectroscopy (EIS). The synthesized cathode active materials are characterized as single phase spinel LiMn₂O₄ with degree of crystallization and uniform particle size distribution. Best results were obtained with electrodes substituted with In and an initial discharge capacity of 134 mAhg⁻¹ after 50 cycles. The improvement in the cycling performance may be attributed to stabilization of spinel structure by smaller lattice constant when manganese ion was partially substituted with In³⁺ ions. EIS analysis also confirms that the obvious improvement in Ag coating is mainly attributed to the accelerated phase transformation from layered phase to spinel phase and highly stable electrolyte/electrode interface due to the suppression of electrolyte decomposition.     

Effects of aluminum on the structural and electrochemical properties of LiNiO2

LiNi_1−yAl_yO₂ (0.10≤y≤0.50) compounds have been synthesized by a coprecipitation method. The characterization of the samples by X-ray and neutron diffraction, associated with Rietveld refinement analysis, has shown that for all materials, about 5% extra-nickel ions are present in the interslab space. Charge−discharge cycling of LiNi_1−yAl_yO₂ as positive electrode material in lithium cells has shown that aluminum substitution suppresses all the phase transitions observed for the LiNiO₂ system. Good cycling stability was observed, but the capacity decreases from 125 to 100 mAh/g by increasing the aluminum amount from 10 to 25% (3–4.15 V range; C/20 rate).     

The effect of capillary-trapped CO2 on oil recovery and CO2 sequestration during the WAG process

This study investigated capillary-trapped CO₂ depending on the consideration of hysteresis effect in relative permeability for various water-alternation-gas (WAG) operating conditions to ascertain the oil production process. From the simulation results of CO₂ WAG flooding method, the trapped CO₂ led to prevent water-flow, in which CO₂ acts as a gas blocker near the well. It caused the injection pressure increase during water injection period. As the trapped CO₂ in pores increased, the reservoir pressure was also increased and maintained above minimum miscibility pressure (MMP). Ultimately, it was concluded that the reservoir was kept under miscible conditions throughout WAG process, reducing residual oil and increasing oil recovery.     

Application of optimization techniques and the enthalpy method to solve a 3D-inverse problem during a TIG welding process

Tungsten inert Gas (TIG) welding takes place in an atmosphere of inert gas and uses a tungsten electrode. In this process heat input identification is a complex task and represents an important role in the optimization of the welding process. The technique used to estimate the heat flux is based on solution of an inverse three-dimensional transient heat conduction model with moving heat sources. The thermal fields at any region of the plate or at any instant are determined from the estimation of the heat rate delivered to the workpiece. The direct problem is solved by an implicit finite difference method. The system of linear algebraic equations is solved by Successive Over Relaxation method (SOR) and the inverse problem is solved using the Golden Section technique. The golden section technique minimizes an error square function based on the difference of theoretical and experimental temperature. The temperature measurements are obtained using thermocouples at accessible regions of the workpiece surface while the theoretical temperatures are calculated from the 3D transient thermal model.     

Estimation of kinetic parameters of composite materials during the cure process by using wavelet transform and mollification method

In some inverse problem, the convergence of the inverse algorithm is impossible due to the correlation of the involving parameters. Several different approaches have been used to address this problem. This paper proposes a procedure to smooth the temperature data by wavelet transform and mollification method prior to utilizing the Levenberg–Marquart method. Comparison of the two filtering methods shows that a comparable improvement in performance can be achieved specially using the mollification method. In order to examine this technique, a highly ill-posed problem was considered as a test case; that is the estimation of the composite kinetic parameters during the cure process.     

Study on the microstructures and thermal properties of SiO2@NaNO3 microcapsule thermal storage materials

In this paper a novel SiO₂@NaNO₃ microcapsule thermal storage material is successfully fabricated via water-limited sol-gel method. The effects of SiO₂ nanoparticles on the microstructures, thermal conductivity, specific heat capacity, latent heat and thermal stability are investigated. SEM and TEM investigation indicates that the spherical SiO₂ nanoparticles with an average diameters of 30 nm are coated on the surface of NaNO₃ evenly to form a homogeneous and stable core-shell structure. Microencapsulated composites are characterized by XRD and FTIR to determine the chemical compositions and structures. The thermal conductivity of SiO₂@NaNO₃ microcapsules is significantly enhanced by 62.9% (0.756 W m⁻¹ K⁻¹) compared with 0.464 W m⁻¹ K⁻¹ of that of NaNO₃. In addition, the latent heat, phase change temperature, specific heat capacity and thickness of shell of the microencapsulated NaNO₃ with 18.1 wt% SiO₂ were 310.1°C, 144.7 J g⁻¹, 1.831 J/(g·K), and 80-150 nm, respectively. Furthermore, microencapsulated NaNO₃ have excellent shape and thermal stability at working temperature range. SiO₂ nanoparticles are uniformly attached to the modified NaNO₃ by electrostatic interaction to create a physical protective SiO₂ barrier, which can effectively inhibit the leakage and cauterization of melting NaNO₃.     

The influence of small hydrogen addition on the structural and magnetocaloric properties of high-purity nanocrystalline terbium

Hydrogen absorption often induces changes of various properties of rare-earth metals. In this paper, we study the influence of hydrogenation on the structural, magnetic and magnetocaloric properties of high-purity nanocrystalline terbium. Strong (00l) texture present in the parent Tb sample is practically destroyed after the hydrogenation procedure. We observe formation of agglomerates of different sizes and shapes depending on the hydrogen content in the samples. We find traces of β-hydride (TbH₂) in the main α-hydride TbH_x phase. For TbH_x with x = 0.25 and 0.5 at.H/f.u. The effect of hydrogenation on the magnetocaloric properties is studied in magnetic fields up to 9 T. The magnetocaloric effect decreases after hydrogenation. The -ΔS_M(T) curves feature a table-like effect in the vicinity of the magnetic phase transitions in magnetic fields exceeding 1 T.     

The significance of anti-fluorite Cs2NbI6 via its structural,electronic, magnetic,optical and thermoelectric properties

The structural, electronic, magnetic, optical and thermoelectric properties of anti-fluorite Cs₂NbI₆ were investigated using full potential augmented plane wave method of density functional theory. Structurally, Cs₂NbI₆ was found to be cubic in ground state from values of tolerance factor (1.04) and formation energy (−22.3 eV). While, it's ferromagnetic nature was predicted from volume optimization process. In spin down channel, the compound was explored as indirect band gap (E_g(Γ-X) = 1.97 eV) semiconductor, while it changes to metallic in upper spin channel. Nb-d and I-p states were exposed as the main cause of spin dependent electronic nature (half-metallicity). The origin of magnetism in Cs₂NbI₆ was explained on basis of crystal field theory. The calculated magnetic moment (1.001 μ_B) was found in reasonable agreement with experimental value. The optimum absorption and optical conductivity spectra in semiconductor state explored Cs₂NbI₆ as suitable for optoelectronic devices. Furthermore, the transport properties were calculated using BoltzTrap code. The nature of carriers was predicted as n type from negative values of Seebeck coefficients. Where, the figure of merit (ZT) was found to increase up to 0.85 at 900 K. The present work not only explores Cs₂NbI₆ as potential optoelectronic and thermoelectric material, but can also inspire more experimental research on this important compound.     

Phase transition and hydrogenation properties of Ce2Ni7-type Pr2Co7 during the hydrogen absorption process

The crystal structure and hydrogenation properties of Pr₂Co₇ with a Ce₂Ni₇-type structure were investigated by X-ray diffraction (XRD) and observation of the pressure–composition (PC) isotherms. The reversible hydrogen capacity reached 0.8 H/M, and two plateaus were observed in the absorption–desorption process. The two observed hydride phases, Pr₂Co₇H_2.7 and Pr₂Co₇H_7.2, were determined to have hexagonal (space group: P6₃/mmc) and orthorhombic (space group: Pbcn) crystal structures, respectively. The crystal structure transformed in the order of hexagonal with a Ce₂Ni₇-type structure (original alloy) → same Ce₂Ni₇-type structure (Pr₂Co₇H_2.7) → orthorhombic (Pr₂Co₇H_7.2). The crystal lattice of the Pr₂Co₇H_2.7 underwent anisotropic expansion along the c-axis of the original alloy, whereas that of Pr₂Co₇H_7.2 exhibited isotropic expansion. The full width at half maximum (FWHM) values for the original alloy and hydride phases during the hydrogen absorption–desorption process were evaluated based on the XRD data. The FWHM values for the main peaks decreased as the hydrogen content increased during the absorption process, indicating that the number of lattice defects did not increase upon hydrogenation. The plateau pressures during the absorption process of the second cycle were the same as those of the first cycle, which also suggests that there were no lattice defects.     

Investigation on the possibility of using the microshear test as a surveillance method to estimate the mechanical properties and fracture toughness of nuclear pressure vessel steel,A508CL3, and its joints welded by narrow-gap submerged-arc welding

The present paper has investigated the mechanical properties of nuclear pressure vessel steel, A508CL3, and its welded joints by using the microshear test method, and the fracture toughness of A508CL3 steel and its welds has also been estimated. Moreover, a comparison has been carried out between the conventional test, microshear test and fracture mechanics test. In addition, the possibility of using the microshear test on the surveillance program of nuclear pressure vessel embrittlement due to neutron irradiation has also been considered in detail, and the results indicate that the microshear test can be used successfully to estimate the degradation of mechanical properties both for A508CL3 steel and its welded joints. It has been found that the lower the microshear toughness, the smaller the Charpy V-notch (CVN) impact toughness and fracture toughness, as well as the tearing modulus. Finally, the results show that the microshear test method may be developed as a supplemental test method or standard of ASTM E185 and E636.     

Effect of Mg-doping on the structural and electronic properties of LiCoO2: A first-principles investigation

The electronic structures of Mg-doped LiCoO₂ have been investigated by the first-principle pseudopotential method. The effect of Mg-doping content on the band structure and structural stability of LiCoO₂ is presented. The results obtained via a full relaxation of the crystalline structure show that a rational amount of Mg-doping in LiCoO₂ is helpful to enhance its electronic conductivity. However, the doping magnitude should be controlled within 15 mol% of LiCoO₂ in order to keep its crystalline structure unchanged. By combining total energy calculations with basic thermodynamics, the average intercalation voltages of this doped system have been predicted.     

The effect of annealing temperature,reaction time,and cobalt precursor on the structural properties and catalytic performance of CoS2 for hydrogen evolution reaction

In this study, cobalt disulfide (CoS₂) nanostructures are synthesized using a simple hydrothermal method. The effects of experimental parameters including cobalt precursor, reaction times, and reaction temperatures are investigated on the structure, morphology and electrocatalytic properties of CoS₂ for hydrogen evolution reaction (HER). The characterization of as-prepared catalysts is performed using X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), scanning electron microscopy (SEM), Fourier transform infrared (FT-IR), and X-ray photoelectron spectroscopy (XPS). The HER efficiency of the catalysts is examined using linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) methods in 0.5 M H₂SO₄ solution. Furthermore, chronoamperometry (CA) is used for stability evaluation. The catalyst obtained from cobalt acetate precursor, within 24 h at 200 °C exhibits superior electrocatalytic activity with a low onset potential (139.3 mV), low overpotential (197.3 mV) at 10 mA. cm^?2 and a small Tafel slope of 29.9 mV dec^?1. This study is a step toward understanding the effect of experimental parameters of the hydrothermal method on HER performance and developing optimal design approaches for the synthesis of CoS₂ as a common electrocatalyst.     

The effect of complex thermal treatment on the electrophysical and morphological properties of CdTe films obtained by chemical molecular beam deposition

The effect of chloride thermal treatment on the electrophysical and morphological properties of CdTe films of different compositions grown by the method of chemical molecular beam deposition was studied. The measurements conducted by Hall’s method and using the scanning electron microscope demonstrated that after thermal treatment in a CdCl₂ solution, the specific resistance of the CdTe film decreased from 10⁹ to 10⁶Ω cm; however, the grain size of the film remained intact and the uniform covering of the surface was observed.     

Characterization of the physicochemical and structural evolution of biomass particles during combined pyrolysis and CO2 gasification

The combination of pyrolysis and CO₂ gasification was studied to synergistically improve the syngas yield and biochar quality. The subsequent 60-min CO₂ gasification at 800 °C after pyrolysis increased the syngas yield from 23.4% to 40.7% while decreasing the yields of biochar and bio-oil from 27.3% to 17.1% and from 49.3% to 42.2%, respectively. The BET area of the biochar obtained by the subsequent 60-min CO₂ gasification at 800 °C was 384.5 m²/g, compared to 6.8 m²/g for the biochar obtained by the 60-min pyrolysis at 800 °C, and 1.4 m²/g for the raw biomass. The biochar obtained above 500 °C was virtually amorphous.     

The structural,electrical and optical properties of ZnO/Al2O3 multilayer deposited on PET substrates by RF sputtering

In this work ZnO/Al₂O₃ multilayer is deposited on PET(polyethylene terephthalate) substrate by RF sputtering in argon atmosphere and the effect of Al₂O₃ layer on optical, electrical and structural properties of ZnO is investigated. It is observed that the presence of Al₂O₃ layer between ZnO and PET reduce the transmission of light from ZnO/Al₂O₃/PET structure 11% but if a thin layer of SiO₂ ∼100 nm is applied between Al₂O₃ and PET it can be compensated. The XRD results show that the ZnO film had hexagonal wurtzite structure with (002) preferred orientation and the application of Al₂O₃ and SiO₂ layers do not have any effect on its structure. The effect of Al₂O₃ and SiO₂ layers on optical band gap of ZnO has been investigated, also the surface morphology of ZnO film is studied by scanning electron microscopy.     

Synthesis and effect of forming Fe2P phase on the physics and electrochemical properties of LiFePO4/C materials

Series LiFePO₄/C materials have been prepared by a so-called reformative solid-coordination method, which uses citric acid as the coordination agent and carbon source. A monodenate coordination band of –COO-M was proved to form gradually and that would help to disperse Li⁺ or Fe²⁺ among the homogeneous gel during the grinding process. Impure phase Fe₂P was detected out among the LiFePO₄/C composites with increasing annealed temperature. The remnant coating carbon was considered to be the reductive under the pure nitrogen gas. The amounts of carbon, particle size and morphology were investigated in detail and all the results showed to be related to the formation of Fe₂P. The electro-conductive Fe₂P phase among LiFePO₄/C composites acts as important role in increasing electronic conductivity and evidently improves the electrochemical performance of LiFePO₄/C including the less polarization phenomenon, comparatively high reversible capability, stable cycling performance and slight trend of less loss of rate capability.