Influence of $$\hbox {TiO}_{2}$$ particle size and conductivity of the CuCrO$$_{2}$$2 nanoparticles on the performance of solid-state dye-sensitized solar cells

Solid-state dye-sensitized solar cells have been fabricated with mesoporous \(\hbox {TiO}_{2 }\) photoanode and N719 dye as photosensitizer. First, \(\hbox {TiO}_{2}\) and non-doped, Zn- and Mg-doped CuCrO\(_{2}\) nanoparticles have been synthesized by sol–gel method. In addition, the \(\hbox {TiO}_{2}\) pastes have been prepared through Pechini-type sol–gel method. The effect of \(\hbox {TiO}_{2}\) particle size, mesoporous \(\hbox {TiO}_{2}\) photoanode thickness and solid-state electrolyte thickness on the efficiency of the fabricated devices has been investigated. Our results show that in spite of the low amount of dye loading for photoanode with large \(\hbox {TiO}_{2}\) nanoparticles (80–180 nm), the dye-sensitized solar cell made from it has higher efficiency than that constructed from the photoanode comprising of small particles about 10–15 nm in size. The higher efficiency is attributed to the longer diffusion length of electrons because of a better electron transport and penetration of a large amount of \(\hbox {CuCrO}_{2 }\) nanoparticles in the porous structure of \(\hbox {TiO}_{2}\) photoanode. By using the doped \(\hbox {CuCrO}_{2}\) nanoparticles, the efficiency has been increased from 0.027% for \(\hbox {TiO}_{2}\)/N719 dye/CuCrO\(_{2}\) to 0.033% for \(\hbox {TiO}_{2}\)/N719 dye/CuCrO\(_{2}\):Zn and further increased to 0.042% for \(\hbox {TiO}_{2}\)/N719 dye/CuCrO\(_{2}\):Mg. The efficiency enhancement by doping is ascribed to the conductivity improvement due to the presence of impurity atoms.     

Effect of specimen size and geometry on ductile crack growth resistance in a C-Mn steel

The effect of specimen size and geometry on the ductile crack growth resistance of a C-Mn steel has been investigated. The resistance, expressed in the form of J-R curves, was measured using the conventionally calculated J(J_r);(b/J×dJ/da) values. The results show that for specimens of given thickness the effect of specimen geometry was due to a change in the shear lip and not to the flat fracture contribution. This conclusion is consistent with the geometry invariance found in measurements of the crack opening displacement at the growing crack tip in the flat fracture region. In addition, it has been shown that J _m can characterise crack growth resistance over a wider range of conditions than J _r.

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Résumé On a étudié les effets de la taille et de la géométrie d'une éprouvette sur la résistance à la croissance d'une fissure ductile dans un acier au C-Mn. Exprimée sous la forme de courbes J-R, la résistance a été mesurée par des valeurs de J calculées par voie conventionnelle (J _r) et par la méthode de Ernst modifiée (J _m), pour une gamme de géométries d'éprouvettes sollicitées en flexion et en traction. La résistance globale d'éprouvette ne présentant pas d'entaille latérale a été divisée en deux contributions, qui s'experiment par les zones de ruptures plates et de lèvres de cisaillement, que l'on trouve sur les surfaces de rupture.Grâce à une telle approche, on a ramené à des grandeurs rationnelles la taille et la géométrie d'une éprouvette, et on a déterminé les limites de croissance d'une fissure régies par J _r et J _m en termes de l'extension maximale admissible d'une fissure, et des valeurs minimales de (b/j×dJ/da).Les résultats indiquent que, pour des éprouvettes d'épaisseur donnée, l'effet de la géométrie d'une éprouvette est associé à une modification de la contribution des lèvres de cisaillement, et non de la portion plate de la rupture. Cette conclusion est compatible avec la constance de la géométrie que l'on observe dans des mesures du déplacement d'ouverture de la fissure à la pointe de la fissure en progrès dans la zone de rupture plate. En outre, on a montré que J _m peut caractériser la résistance à la croissance d'une fissure, sur une gamme plus large de conditions que ne le fait J _r.

     

Milling effect on the photo-activated properties of $$\hbox {TiO}_{2}$$ nanoparticles: electronic and structural investigations

Commercial PC105 titanium dioxide nanoparticles were studied under mechanical milling process. The effect of milling time and speed on the structural and electronic properties of \(\hbox {TiO}_{2}\) powder was then investigated using X-ray powder diffraction (XRD), dynamic light scattering (DLS), transmission electronic microscopy (TEM), electron paramagnetic resonance (EPR) and UV–visible spectroscopy. The related photo-catalytic properties of the milled nanoparticles were probed following the degradation rate of methylene orange (MO) under UV-light irradiation and through EPR spin-scavenging approach. Comparison with pristine powder shows that milled nanoparticles are significantly less reactive upon illumination, despite decreased radius and hence, higher specific area. Such low yield of reactive species is attributed to the apparition of the amorphous \(\hbox {TiO}_{2}\) and brookite phase upon milling, as well as increased charge carrier recombination as pointed out by the presence of sacrificial electron donor.     

Temperature and Heat Flow Rate Calibration of a Calvet Calorimeter from $$0\,{^{\circ }}\hbox {C}$$ to $$190 \,{^{\circ }}\hbox {C}$$19

This study describes the temperature and heat flow rate calibrations of a Calvet calorimeter (SETARAM, BT2.15) in the temperature range of 0–190 \({^{\circ }}\hbox {C}\). Temperature calibration is carried out using three reference materials, namely water, gallium, and indium, as specified in the International Temperature Scale of 1990 (ITS-90). The sample temperature of the Calvet calorimeter is corrected by the obtained mean value, \(-0.489 \,{^{\circ }}\hbox {C}\), of the measured extrapolated peak onset temperature (\(T_{e})\) when the heating rate (\(\upbeta )\) is zero (\(\Delta T_\mathrm{corr }(\upbeta ~=~0\))). The heat flow rate is calibrated using a reference material with a known heat capacity, namely SRM 720 \(\alpha \)-\(\hbox {Al}_{2}\hbox {O}_{3}\) (synthetic sapphire), which is traceable to the National Institute of Standards and Technology. From the heat flow rate measurements of the blank baseline and SRM 720, the proportional calibration factor, \(\hbox {K}_{\Phi }\), in the 0–190\( \,{^{\circ }}\hbox {C}\) temperature range was determined. The specific heat capacity of copper was measured with the obtained calibration values, and the measured data show consistency with the reference value.     

Effects of grain size and specimen geometry on the transformation and R-curve behaviour of 9Ce-TZP ceramics

Transformation and R-curve behaviour have been investigated in 9 mol% Ce-TZP ceramics with different grain sizes. Both single-edge notched beam and short double-cantilever beam specimens were tested to measure the crack-resistance curves. The size and shape of the transformation zone not only depend on grain size, but are also strongly influenced by the specimen geometry. This different transformation behaviour has led to different crack-resistance curves. These experimental results are discussed in terms of the thermodynamics of transformation, the effect of autocatalytic transformation, and fracture mechanics.     

基于微观机理的梁柱节点焊接细节断裂分析

高强螺栓广泛应用于钢结构节点连接,火灾高温会影响其基本材性和断裂行为,从而影响螺栓节点抗火性能甚至整体结构抗倒塌性能。基于10.9级高强螺栓火灾全过程(升温段、降温段、火灾后)单轴拉伸试验结果,结合有限元模拟,对不同温度历程和应力三轴度对应的螺栓SMCS断裂模型进行校准,并与螺栓材性试验和T-stub节点试验结果对比验证;对T-stub节点火灾全过程断裂行为进行参数分析,研究损伤准则和温度历程对节点失效模式和变形特征的影响。结果表明：校准的SMCS模型能够有效、准确地预测螺栓和节点在火灾全过程和高应力三轴度(0.3~1.2)下的受拉断裂行为,适用预测误差在12%以内;拉伸温度和峰值温度是影响高强螺栓抗断能力的主要因素,螺栓抗断能力随温度升高而提高;不同温度历程下T-stub节点可能发生翼缘板屈服断裂、翼缘板和螺栓同时屈服断裂、螺栓屈服断裂三种失效模式,且节点的变形能力(延性系数)与失效模式有关,确定钢板母材和螺栓的断裂模型是准确预测节点失效模式的关键。

     

Electronic and Magnetic Properties of the BaTiO $$_{3}$$ 3 /LaMnO $$_{3}$$ 3 Interface: a DFT Study

Journal of Superconductivity and Novel Magnetism - The electronic and magnetic properties of the BaTiO $$_{3}$$ /LaMnO $$_{3}$$ interface were investigated by means of ab initio calculations within...     

Unraveling Thermal and Dynamical Properties of the Cubic $$\mathrm{BaVO}_3$$ Perovskite from First-Principles Calculation

Using a toolkit of theoretical techniques comprising ab initio density functional theory calculations and quasiharmonic approximation, we investigate temperature dependence of dynamical properties of \(\mathrm{BaVO}_3\) perovskite. This interest is triggered by the fact that, recently, it was possible to synthesize a \(\mathrm{BaVO}_3\) perovskite, in a cubic phase, at high pressure and temperature. First-principle calculations are achieved thanks to recent development in numerical facilities, especially phonon dispersion curves which are then fully obtained. Elastic constants of the compound are dependent on temperature due to the inevitable anharmonic effects in solids. We show that at low temperature, the full account of the thermal effects incorporating the phonon densities and Sommerfeld model is more appropriate to calculate the thermal properties of a metal.     

A model for the temperature dependence of the electronic mean free path in the radiofrequency size effect

A model is proposed which takes into account the effect of the finite skin depth in a determination of the phonon-limited electronic mean free path (EMFP) by means of the radiofrequency-size-effect amplitude. The model results in a temperature dependence of the inverse EMFP which obeys neither aT ⁿ nor anaT ³+bT⁵ law, in general. Numerical examples show the pureT ³ behavior usually expected is reasonable for small Fermi radii of curvature, but that more complicated behavior can be expected for Fermi surfaces having nearly free electron curvature. Existing data from the lens of Cd, obeying an apparentT ⁵ law, are discussed in terms of the present model.     

Synthesis and characterization of $$\hbox {BaNiO}_{3}$$ using a solid-state thermal decomposition method and the preparation of its stable aqueous suspension

In the present study, the preparation of \(\hbox {BaNiO}_{3}\) nano-oxide is reported via simple solid-state thermal decomposition of \([\hbox {Ba(en)}_{4}][\hbox {Ni(H}_{2}\hbox {O})_{2}\hbox {(NCS)}_{4}]\) precursor complex for the first time. As-prepared nano-oxide was coated by citric acid to form a stable aqueous magnetic suspension. The precursor complex was characterized by conductivity measurements, ultra violet–visible spectroscopy, elemental analysis and Fourier transform infrared spectroscopy. The composition of the perovskite was confirmed by energy-dispersive X-ray spectroscopy analysis and the hexagonal structure was supported by powder X-ray diffraction. In addition, monotonous morphology of the nano-oxide was illustrated by field-emission scanning electron microscopy. Superparamagneticity of the nanoparticles were detected using a vibrating sample magnetometer. Finally, the hydrodynamic size as well as the zeta potential of the pristine and surface-treated \(\hbox {BaNiO}_{3}\) nano-oxide were measured in deionized water via a dynamic light scattering analyzer and they were compared. Results show the excellent stability of the surface-modified magnetic oxide compared to the pristine.     

The effect of specimen size on the fracture energy and softening function of concrete

This paper examines the effect of specimen size on the fracture energy of concrete, G_F, as measured using the three-point bending test on pre-notched beams prescribed by RILEM TC-50 [1]. The concept of partial fracture energy is introduced and used to explain the observed size effect. The opening displacement at the top of the notch in the test specimen at the end of the test, ω, is affected by the size of the specimen, which in turn affects the measured value of the concrete fracture energy. In theory, when the specimen is large enough to allow the fracture process zone to develop fully,w _f will reach its critical value,w _c , and the effect of specimen size onG _F will be eliminated. The experimental results included here show that in reality the size of the specimen does affect the measurement ofG _F , even when the size is such that the fracture process zone develops fully. This may be due to local plastic deformation in the area around the loading point, which is particularly significant in larger specimens. It may also be due to differences in the influence of the boundary conditions of the test for different specimen sizes. In addition, a procedure is outlined for the determination of the softening function for concrete based on the fracture energy measured in RILEM tests, in which the specimens are small enough to ensure that the energy measured is actually due to fracture and not plastic deformation.     

Electro-optical properties,decomposition pathways and the hydrostatic pressure-dependent behaviours of a double-cation hydrogen storage material of $$\hbox {Al}_{3}\hbox {Li}_{4}(\hbox {BH}_{4})_{13}$$

Electro-optical properties, the decomposition pathways and the pressure-dependent behaviours of \(\hbox {Al}_{3}\hbox {Li}_{4}(\hbox {BH}_{4})_{13}\) have been investigated using a first-principle plane-wave pseudopotential method. \(\hbox {Al}_{3}\hbox {Li}_{4}(\hbox {BH}_{4})_{13}\) is a kind of double-cation borohydride, consisting of distorted tetrahedral anions \([\hbox {Al}(\hbox {BH}_{4})_{4}]^{-}\) and cations \([\hbox {Li}_{4}(\hbox {BH}_{4})]^{3+}\), which obeys the stability criteria of decomposition reactions. Herein, two possible decomposition reactions of the compound are proposed, which release 18 hydrogen molecules (about 12.03 wt%) in the first reaction and 24 hydrogen molecules (about 16.04 wt%) in the second reaction. On increasing the pressure on the structure, the lattice parameter, the volume of unit cell, the quasiparticle band gap and also enthalpy of the system decrease nearly monotonically; therefore, the acceptor levels gradually get filled and the Fermi level shifts upward. Results of computational investigations of the structural, electronic and thermodynamic parameters and their pressure-dependent behaviours indicate that \(\hbox {Al}_{3}\hbox {Li}_{4}(\hbox {BH}_{4})_{13}\) has intriguing properties. Therefore, it would be a very promising material for hydrogen storage technology.     

Comparative Investigation on the Heat Transfer Characteristics of Gaseous $$\hbox {CO}_{2}$$ and Gaseous Water Flowing Through a Single Granite Fracture

\(\hbox {CO}_{2}\) and water are two commonly employed heat transmission fluids in several fields. Their temperature and pressure determine their phase states, thus affecting the heat transfer performance of the water/\(\hbox {CO}_{2}\). The heat transfer characteristics of gaseous \(\hbox {CO}_{2}\) and gaseous water flowing through fractured hot dry rock still need a great deal of investigation, in order to understand and evaluate the heat extraction in enhanced geothermal systems. In this work, we develop a 2D numerical model to compare the heat transfer performance of gaseous \(\hbox {CO}_{2}\) and gaseous water flowing through a single fracture aperture of 0.2 mm in a \(\upphi 50\,\times 50\hbox { mm}\) cylindrical granite sample with a confining temperature of \(200\,^{\circ }\hbox {C}\) under different inlet mass flow rates. Our results indicate that: (1) the final outlet temperatures of the fluid are very close to the outer surface temperature under low inlet mass flow rate, regardless of the sample length. (2) Both the temperature of the fluid (gaseous \(\hbox {CO}_{2}\)/gaseous water) and inner surface temperature rise sharply at the inlet, and the inner surface temperature is always higher than the fluid temperature. However, their temperature difference becomes increasingly small. (3) Both the overall heat transfer coefficient (OHTC) and local heat transfer coefficient (LHTC) of gaseous \(\hbox {CO}_{2}\) and gaseous water increase with increasing inlet mass flow rates. (4) Both the OHTC and LHTC of gaseous \(\hbox {CO}_{2}\) are lower than those of gaseous water under the same conditions; therefore, the heat mining performance of gaseous water is superior to gaseous \(\hbox {CO}_{2}\) under high temperature and low pressure.     

Scale-up and flow behavior of cohesive granular material in a four-bladed mixer: effect of system and particle size

Flow of cohesive granular materials with different moisture contents was examined in a four-bladed mixer via the discrete element method (DEM). Firstly, the mixer diameter (D) was increased while keeping the particle diameter (d) constant. It was observed that when the mixer diameter to the particle diameter ratio (D/d) was larger than a certain critical size (D/d ≥ 75), granular flow behaviors and mixing kinetics followed simple scaling relations. For D/d ≥ 75, flow patterns and mixing kinetics were found to be independent of system size, and velocities of particles scaled linearly with the tip speed of the impeller blades and particle diffusivities scaled with the tip speed of the blades and mixer diameter. These results suggest that past a certain system size the flow and mixing of cohesive particles in large-scale units can be predicted from smaller systems. Secondly, system size was kept constant and particle diameter was changed and it was observed that by keeping the Bond number constant (by changing the level of cohesion) the flow behavior and mixing patterns did not change, showing that larger particles can be used to simulate flow of smaller cohesive particles in a bladed mixer by matching the Bond numbers.     

Simulation of dynamic fracture with the Material Point Method using a mixed J-integral and cohesive law approach

A new approach to simulating fracture, in which toughness is partitioned between the crack tip and, optionally, a process zone, is applied to dynamic fracture processes. In this approach, classical fracture mechanics determines crack tip propagation, and cohesive laws characterize process zone response and determine crack root and process zone propagation. The approach is implemented in the Material Point Method, a particle method in which the fracture path is unconstrained by a body-fitted mesh. The approach is found suitable for modeling a range of dynamic fracture processes, from brittle fracture to fracture with crack bridging. A variety of ways of partitioning toughness are explored with the aim of distinguishing model parameters via experimental measurements, particularly R curves. While no unique relationship exists, R curves, or effective R curves, on a suite of materials would provide substantial insight into model parameters. Advantages to the approach are identified, both in versatility and in regards to practical matters associated with implementing numerical fracture algorithms. It is found to perform well in dynamic fracture scenarios.     

Influence of specimen size and microstructure on the fracture toughness of a martensitic stainless steel

The fracture toughness of alloy HT-9,² a martensitic stainless steel under consideration for fast reactor and fusion reactor applications, was determined from circular compact tension specimens using the multi-specimen R-curve method. Specimens with thicknesses of 11.94, 7.62 and 2.54mm and widths of 23.88 and 11.94 mm were tested to investigate the effects of specimen size on fracture toughness. The test results obtained from all specimens are in good agreement and thickness requirements for a valid J_1c test are satisfied. The experiment indicates that small specimens of HT-9 may be used for post-irradiation fracture toughness testing.Fractographic examination of the fracture surfaces reveals that fracture in HT-9 is significantly influenced by delta ferrite stringers present in the material. The fracture surface examination and crack opening displacement measurements for specimens tested at various temperatures are consistent with the temperature dependence of the J_1c results.     

An improved model for predicting the crack size and plasticity dependence of fatigue crack propagation

The angled crack problem has been given special attention in the recent years by fracture mechanics investigators due to its close proximity to realistic conditions in engineering structures. In this paper, an investigation of fatigue crack propagation in rectangular steel plates containing an inclined surface crack is presented. The inclined angle of the crack with respect to the axis of loading varied between 0° and 90°. During the fatigue tests, the growth of the fatigue crack was monitored using the AC potential drop technique. A series of modification factors, which allow accurate sizing of such defects, is recommended. Paris power law is normalized and adopted for data analysis. Subsequently, this concept is applied to predict crack growth due to fatigue loads. The results obtained are compared with those obtained using the commonly employed fracture criterion and the experimental data.     

Angular dependence of the reflectance from an isotropic polydomain medium: effect of large domain size on total reflection

We investigate the angular dependence of the reflectance from an isotropic medium consisting of optically large and anisotropic, randomly oriented domains, assuming a highly refractive, isotropic, and homogeneous incidence medium, which is presumed to have a higher refractive index than any of the domains' principal indices of refraction. By employing average reflectance and transmittance theory, we are able to show that the onset of total reflection is considerably shifted to higher angles of incidence compared with an isotropic medium with domains that are small compared with the wavelength. The onset of total reflection for a random medium with large domains is found to be dependent only on the largest principal index of refraction of the domains, assuming that all domains have the same optical properties. Therefore the shift of the onset depends on the magnitude of the optical anisotropy of the domains. Even in the case of a small optical anisotropy, large cross-polarization terms are predicted in the vicinity of the onset of total reflection. These terms show a pronounced maximum near that onset and extend beyond it.