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A two-step scheme is presented for estimating the chloride diffusivity of pure cement paste. In the scheme, gel pores are included in the solid skeleton, composed of calcium hydroxide, unhydrated cement and calcium silicate hydrate, while capillary pores and the solid skeleton constitute pure cement paste. In combination with percolation theory, the effective medium method was modified to formulate the chloride diffusivities of the solid skeleton and pure cement paste sequentially. Detailed analysis was conducted to calibrate the percolation exponent for the high-diffusivity phase and the chloride diffusivity of the pore solution. Comparisons with various test results were made to verify the proposed scheme. Unlike existing analytical methods, the physical properties, volume fractions and morphological relationships of various phase constituents and the shapes, percolation behaviour and different roles of gel and capillary pores are all taken into account simultaneously. The calibrated chloride diffusivity of the pore solution was found to be considerably close to that derived by molecular dynamics simulation, suggesting that the scheme represents a more realistic pure cement paste. The scheme can reasonably evaluate the chloride diffusivity of pure cement paste at medium and long curing ages.

Here, a strategy to overcome the stiff and brittle nature of cellulose-derived carbon nanofibrils (CCNFs) is proposed through a facile, low-cost, and scalable approach. Flexible and conformal CCNFs with a low bending rigidity below 55.4 mN and tunable conductivities of 0.14-45.5 S m

In this study, a method suitable for on-line rapid species classification of western hemlock and amabilis fir (hem-fir) green mix of timber was developed and tested with the use of near infrared spectroscopy (NIRS) and chemometrics. The spectra of 600 wood specimens obtained from each species were collected over the wavelength range of 350–2500 nm. They were thereafter pretreated by smoothing; first derivative, second derivative and standard normal variate and calibration models were developed using the wavelength range of 800–1800 nm by partial least squares-linear discriminant analysis (PLS-LDA) and least squares-support vector machines (LS-SVM). The effects of wood surface (transverse, tangential and radial), wood zone (heartwood and sapwood) and sample moving speed (0, 0.5 and 1 m/s) were also explored. LS-SVM is superior to PLS-LDA in terms of classification performance at moving conditions. The best results were obtained using the LS-SVM method when spectra were collected on the transverse surface at a speed of 1 m/s and pretreated by smoothing. The sensitivity, specificity, and accuracy for both calibration and validation sets were all 100%. Collectively, NIR spectroscopy combined with LS-SVM is capable of on-line species separation of green hem-fir mix prior to wood drying.

Visible and near-infrared (VIS–NIR) spectroscopy was used for classifying and predicting the properties of thermally modified Western hemlock wood. The specimens were treated at 170 °C, 212 °C, and 230 °C. The dimensional reduction was performed using linear discriminant analysis, and the resulted dataset was used for wood classification using the support vector machines and the linear vector quantization neural network. The VIS–NIR dataset was also used to predict the wood moisture content, swelling coefficient, water absorption, density, dynamic modulus of elasticity, and hardness. The “adaptive neuro-fuzzy inference system” (ANFIS), “Group Method of Data Handling” (GMDH), and “multilayer perceptron” (MLP) neural networks were employed for predicting the wood properties. It was shown that regardless of the type of the neural network, NIR dataset provided a robust model with 100% classification accuracy, which can be implemented in industrial scale for in-line timber quality control. The results indicated that the ANFIS and GMDH neural network showed higher performance than the MLP model for predicting the wood properties. While the VIS–NIR data resulted in a promising accuracy for predicting the wood moisture content and dimensional stability parameters, it did not seem suitable for the prediction of wood density and its mechanical properties. The performance of the VIS–NIR spectroscopy method for classification and characterization of heat-treated timber was compared with that obtained using the color measurement and the stress wave method detected by the acoustic emission sensor.

Because of their good flexibility and capacity to capture the dynamic mechanical energy by converting it into electrical signals, polymeric piezoelectric nanogenerators (PENGs) have broad application prospects in mechanical vibration detection and acquisition as sensors and self-powered systems. Here, a flexible PENG film based on hydroxypropyl cellulose (HPC) as the matrix, polyvinylidene fluoride (PVDF) as an auxiliary electrospinning reagent and BaTiO3 nanoparticles (NPs) as a piezoelectric nanofiller is constructed by electrospinning and post-treatments for macromolecule rearrangement and thus piezoelectricity enhancement. This PENG demonstrates a superior sensitivity (23.33 mV kPa−1) which is over 3.9 times those of the commercial PVDF and polyvinylidene fluoride-trifluoroethylene films. This performance enhancement is ascribed to the HPC dissolution and regeneration during post-treatments, resulting in the formation of outer wrappers around fibrils and thus an interconnected fibrous network with junction nodes between adjacent fibers for stress transfer efficiency. The partial crystal phase transformation of PVDF during film densification may also play a role in the increase of piezoelectricity. A series of practical application scenarios are established to demonstrate the highly promising potential of this fibril-based composite membrane for multifunctional force sensing and energy collection.

The intention of this paper is to estimate the steady-state chloride diffusion coefficient of mature cement paste through laboratory test and theoretical analysis. In the test, the chloride diffusion coefficient of cement paste with water/cement ratios of 0.3, 0.4, 0.5, and 0.6 is measured at curing ages from 28 to 1800 days. The test results show that, for cement paste cured for smaller than 360 days, the chloride diffusion coefficient reduces quickly with the increase of curing age. For cement paste cured for larger than 360 days, however, the chloride diffusion coefficient decreases slowly with increasing the curing age. In view of the multi-phase and multi-scale characteristics of cement paste, a three-step scheme is developed to derive the chloride diffusion coefficient analytically. In the scheme, the chloride diffusion coefficients of the inner and outer hydration products and the solid phase are formulated with a two- and three-phase composite sphere models, respectively. Finally, for the bi-continuous cement paste system composed of a solid phase and capillary pores, the effective medium method is adopted to deduce the chloride diffusion coefficient. Eight sets of experimental data, obtained in this paper and collected from the literature, are used to verify the analytical scheme. It is concluded that the developed three-step analytical scheme can evaluate the chloride diffusion coefficient of mature cement paste with reasonable accuracy.

Since the deterioration of marine reinforced concrete structures is, to a great extent, related to the movement rate of chloride ions in concrete, it is essential to determine the chloride diffusion coefficient of concrete through experiment or theoretical prediction. This paper proposes a numerical algorithm for evaluating the chloride diffusion coefficient of concrete with crushed aggregates. In the numerical algorithm, the mesostructure of three-phase concrete is reconstructed by generating polygonal aggregates of various sizes and placing them within a simulation element with periodic boundary conditions. The random walk algorithm is then applied to the simulated three-phase concrete for computing the chloride diffusion coefficient. With this algorithm, the reasonable values of the random walk radius and the number of simulations are determined. Finally, comparisons are made between the calculation results and the experimental ones obtained from the literature to verify the numerical algorithm. Based on several numerical examples, three primary factors, the aggregate content, and the thickness and chloride diffusion coefficient of interfacial transition zone, influencing the chloride diffusion coefficient of concrete, are evaluated quantitatively. This paper concludes that the proposed numerical algorithm is effective in evaluating the chloride diffusion coefficient of concrete with crushed aggregates.

Autophagy induced by titanium dioxide nanoparticles (TiO2 NPs) has been realized nowadays, but the underlying mechanisms remain largely unknown. Animal studies have confirmed that autophagy might be an important mechanism to impair placenta development, but the reversal of damage is not clear. Here, we used human HTR-8/SVneo (HTR) cells as a proper model to explore how autophagy is regulated in TiO2 NP-exposed human placenta cells. Our studies showed that TiO2 NPs could enter HTR cells and locate in cytoplasm. Although they did not affect cell viability even under 100 μg ml-1, autophagy was observed and cell migration ability was severely impaired. Further study showed that TiO2 NPs increased the expressions of both miR-96-5p and miR-101-3p and then, they targeted mTOR and decreased the expression of mTOR proteins. In addition, miR-96-5p also targeted Bcl-2 to down-regulate Bcl-2 protein level, which is also a key regulator of autophagy. We proved that when two microRNA inhibitors were added, cell autophagy was, to a greater extent, reversed compared with the result when one inhibitor was added, and the cell migration ability was also reversed to a greater degree. Our studies revealed that TiO2 NPs might impair placenta development via autophagy. Moreover, miR-96-5p as well as miR-101-3p may act as potential targets to reverse TiO2 NP-induced autophagy and placenta dysfunction.

Zinc oxide is a cost-efficient and eco-friendly material for solar-to-chemical energy conversion. However, the relatively wide band gap and poor stability restrict its practical applications. Herein, we report on the modification of ZnO nanosheets with a porous atomically thin ZnS overlayer. The as-prepared ZnS/ZnO/ZnS sandwich nanosheets exhibit a reduced band gap (2.72 eV) and yet a slightly elevated conduction band minimum, which remarkably broadens the wavelength range for light absorption and generates electrons with enough reducing capability. At the same time, the newly-prepared sandwich nanosheets possess alternatively exposed ZnS and ZnO surface patches, which attract and accommodate photo-generated holes and electrons, respectively. In addition, the ZnS overlayer catalyzes and accelerates hole-consumption reactions, thus preserving electrons for efficient water splitting. As a result, the ZnS/ZnO/ZnS sandwich nanosheets demonstrate intensive light absorption, fast charge separation, long electron lifetime, and eventually the highest hydrogen production rate reported for oxide catalysts so far. This work proves that passivation with an ultrathin layer is a potent approach for energy-band engineering, and semiconductor sandwich nanostructures are promising for highly efficient water splitting under sunlight.

Owing to its importance in the assessment of reinforced concrete structures, it is essential to determine the chloride diffusivity of fly ash concrete. This paper presents an investigation into the diffusion characteristics of chloride ions in fly ash concrete. Through experiment, the relationship between chloride diffusivity and curing age up to 1800 days is measured and the effects of curing age, water/binder ratio, aggregate volume fraction, and fly ash content (i.e., percentage of total cementitious material by mass) on chloride diffusivity are evaluated. It is found that the chloride diffusivity decreases with the increase of curing age, aggregate volume fraction, and fly ash content, but increases with the increase of water/binder ratio. In analytical modeling, an equivalent aggregate model is constructed and the equivalent interfacial transition zone (ITZ) thickness is derived analytically. With the equivalent aggregate model, three-phase fly ash concrete reduces to a two-phase composite material. By extending the Maxwell method, the chloride diffusivity of fly ash concrete is formulated. Finally, the validity of the analytical method is verified by experimental results.

It is fascinating and challenging to endow conventional materials with unprecedented properties. For instance, cadmium sulfide (CdS) is an important semiconductor with excellent light response; however, its potential in gas-sensing was underestimated owing to relatively low chemical activity and poor electrical conductivity. Herein, we demonstrate that an ideal architecture, ultrathin nanoflake arrays (NFAs), can improve significantly gas-sensing properties of CdS material. The CdS NFAs are grown directly on the interdigitated electrode to expose large surface area. Their thickness is reduced below the double Debye length of CdS, permitting to achieve a full depletion of carriers. Particularly, the prepared CdS nanoflakes are enclosed with high-energy {0001} facets exposed, which provides more active sites for gas adsorption. Moreover, the NFAs exhibit the light-trapping effect, which further enhances their gas sensitivity. As a result, the as-prepared CdS NFAs demonstrate excellent gas-sensing and light-response properties, thus being capable of dual gas and light detection.

The purpose of this paper is to present a Brownian motion simulation for the chloride diffusivity of concrete. According to stereological theory, the probability density function and cumulative distribution function for the circular aggregates in terms of the number of aggregates are derived. By coating each aggregate with an interfacial transition zone (ITZ) layer of equal thickness, concrete is then reduced to a two-phase composite material, composed of a bulk cement paste and equivalent aggregates. The equivalent ITZ thickness and the chloride diffusivity of each equivalent aggregate are formulated in an analytical manner. The Brownian motion simulation is used to compute the chloride diffusivity of concrete. Finally, the validity of the numerical simulation is verified with two sets of experimental results and the effects of the aggregate area fraction, the chloride diffusivity of ITZ, and the ITZ thickness on the chloride diffusivity of concrete are evaluated in a quantitative manner. The paper concludes that the numerical simulation can predict the chloride diffusivity of concrete with an average relative error smaller than 6% for the two selected verification examples.

We report the synthesis of CdTe nanowire arrays (NWAs) in solution by laser driven absorption and desorption of gold catalysts. The process can be conducted under ambient conditions and completes in several minutes. The obtained NWAs possess a monocrystal structure, high density and uniform distribution, showing promise for device construction.

The organic–inorganic hybrid solar cell (HSC) is regarded as a promising candidate for third-generation solar cells. Currently, their performance hovers at a low level due to the contradiction between the exciton diffusion and light absorption of the organic layer. In the present work, we provide an efficient solution by designing a hollow electrode for the HSC, which contains CdS nanoflake arrays (NFAs) coated with a thin organic active layer and a roof-like metallic electrode. The hollow electrode facilitates light absorption, charge separation, and hole transportation simultaneously, and as a result, the novel HSC outperforms traditional solid and core–shell HSCs. Our work demonstrates that the reasonable design of the electrode structure is of great importance for improving the power conversion efficiency of HSCs.

this paper introduced two parameters, step height and end face Angle by improving the structure of the prestressed combination concave die to improve mould work performance, Analyzed the step height of 0-10mm, end face Angle of 0-35o, the change of stress, with the help of MATLAB software fitting the equivalent stress and the function relation between the step height and transverse Angle. Using stepwise slanting end face combination concave die can improve the bearing capacity and reduce the fracture and deformation of the die.

Freestanding ultrathin metallic nanosheets (FUMNSs) with atomic thickness attract extensive attention because they display remarkable advantages over their bulk counterparts by virtue of their large specific area, high aspect ratio, and unsaturated surface coordination. The state of the art of research on FUMNSs is reviewed here, wherein the important progress from the aspects of material category, synthetic strategy, and practical application are introduced, and it is demonstrated that FUMNSs will play an important role in the fields of optoelectrics, catalysis, and magnetism.

Cadmium chalcogenide nanocrystals (CCNCs) are regarded as promising materials for photoelectrochemical (PEC) water splitting. However, the relatively low PEC response and poor stability restrict their practical applications. In the present work, we demonstrate that a well-designed inverse opal structure (IOS) composed of CCNCs can achieve an unprecedentedly high photocurrent and hydrogen production rate. In particular, the IOS electrode remains stable during 3 h of continuous illumination, which is even superior to those photoanodes with surface passivation and/or co-catalysts. Quantitative investigation reveals that the IOS possesses high charge-separation efficiency and light-absorption capacity, which eventually result in excellent PEC performance.

Surficial defects in semiconductor can induce high density of carriers and cause localized surface plasmon resonance which is prone to light harvesting and energy conversion, while internal defects may cause serious recombination of electrons and holes. Thus, it is significant to precisely control the distribution of defects, although there are few successful examples. Herein, an effective strategy to confine abundant defects within the surface layer of Cu1.94S nanoflake arrays (NFAs) is reported, leaving a perfect internal structure. The Cu1.94S NFAs are then applied in photoelectrochemical (PEC) water splitting. As expected, the surficial defects give rise to strong LSPR effect and quick charge separation near the surface; meanwhile, they provide active sites for catalyzing hydrogen evolution. As a result, the NFAs achieve the top PEC properties ever reported for CuxS-based photocathodes.

The working principle of turbodrill is discussed in this paper, through discussing the structural characteristics of the turbine shaft, it is pointed out that the part where minimum axis diameter of the turbine shaft is, the hollow area of the turbine shaft, and the hollow place where is the thread at the bottom of the turbine shaft are the three most dangerous parts. With the structure of the turbine shaft of 195mm turbodrill as an example, the strength calculation methods and calculation results of the three most dangerous parts are given. Through comparative analysis on various advanced international parametric design platform, the SolidWorks is chosen as a basic platform for parameterization, this paper puts forward the parametric method of 195mm turbine shaft and the series design of turbine shaft have been achieved. The strength calculation method and parametric method of the turbine shaft have been developed and used in the series design in Yangtze university of China.

Downhole motor is an instrument to drill oil wells, different from rotary drilling in working methods. While downhole motor works, the drilling stem of which remains still supplies power to bits directly so that a much higher transmission efficiency of power can be achieved. Downhole motor has been a key developing downhole tool recently. It is installed in a limited space with a certain diameter, asking for a higher power, so the design of which is rather difficult. This paper mainly studies the key components of downhole motor in structure design and its working characteristics. And parametric design employed in series design to shorten design cycle is presented in this paper. After taken Solidworks as a basic software platform and turbodrill turbine section with diameter of 245mm as an original model, parametric design of key components in downhole motor has been achieved by setting the parameters of key components, adding relations, editing program, creating a new part etc. Parametric design methods presented in this paper has already been applied in series design of downhole motor at Yangtze University.

In predicting the chloride diffusivity in concrete as a three-phase material, composed of aggregates, interfacial transition zone (ITZ), and bulk cement paste, not only the volume fractions, physical properties, and interactions of the three phase constituents but also the ITZ percolation effect should be taken into account. This paper attempts to develop an effective medium method to achieve this. Based on the stereological analysis of the aggregate size distribution and the statistical geometry of composites, the ITZ volume fraction is formulated analytically for the general aggregate gradation. By taking the ITZ-coated aggregate as an “equivalent aggregate”, the three-phase concrete is reduced to a two-phase composite material. An analytical solution is then derived for the chloride diffusivity in concrete applying the general effective medium theory. The primary advantage of the derived analytical solution is that the ITZ percolation effect and the Hashin–Shtrikman bounds are taken into account. Finally, the validity of the derived analytical solution is verified with two sets of experimental data and the effects of the ITZ thickness of and the chloride diffusivity in ITZ on the chloride diffusivity in concrete are evaluated through sensitivity analysis. The paper concludes that the presented analytical solution can predict the chloride diffusivity in concrete with an average relative error of 6%.

Through discussing the working characteristics of turbodrill and structural particularity of the coupling, the feasibility of couplings series design by parameterized design method has been presented. Through taking advantage of Proe, selecting a turbodrill with diameter of 195mm as the original model, the series design and parameterized design of coupling have been achieved. This paper puts forward four design skills through analyzing the parameterized design of the coupling. The method has been developed and used in the series design of oilfield turbodrill in Yangtze university of China.

Owing to its importance in the durability assessment and design of reinforced concrete structures exposed to chloride-ladden environments, it is essential to determine the chloride diffusivity in concrete. This paper presents a numerical method for predicting the chloride diffusivity in concrete with aggregate shape effect. To reduce the number of elements, an equivalent aggregate model is constituted by modeling the aggregate as inclusion and the interfacial transition zone (ITZ) as matrix and the chloride diffusivity in equivalent aggregate is derived analytically. Based on the simulated mesostructure of concrete, the lattice model is applied to the analysis of chloride diffusion in concrete. In this analysis, the physical properties of each phase constituent are taken into account in the formation of element matrix of bar elements. After the validity of the developed numerical method is verified with two independent sets of experimental results, the effect of aggregate shape on the chloride diffusivity in concrete is evaluated in a quantitative manner. It is found that, when the aspect ratio of elliptical aggregate particles increases from 1 to 3, the chloride diffusivity in concrete decreases by 6.48%, 8.94%, and 10.67% for a given chloride diffusivity ratio of ITZ to cement paste at 2, 6, and 10, respectively. The paper concludes that the numerical method developed in the paper can predict the chloride diffusivity in concrete with an average relative error smaller than 7% for the two selected verification examples.

An n -layered spherical inclusion model is presented in this paper for predicting the elastic moduli of concrete with inhomogeneous interfacial transition zone (ITZ). In this model, concrete is represented as a three-phase composite material, composed of the aggregate, bulk paste, and an inhomogeneous ITZ. An analytical solution for the ITZ volume fraction is derived for the general aggregate gradation. By constituting a semi-empirical initial cement gradient model, the local water/cement ratio, degree of hydration, and porosity at the ITZ are estimated. The inhomogeneous ITZ is then divided into a series of homogenous concentric shell elements of equal thickness. The elastic moduli of concrete are determined by solving the n -layered spherical inclusion problem. Finally, the validity of the model is verified with three independent sets of experimental data and the effects of the maximum aggregate diameter, aggregate gradation, and ITZ thickness on the Young’s modulus of concrete are evaluated in a quantitative manner. The paper concludes that the proposed n -layered spherical inclusion model can be used to predict the elastic moduli of concrete.

In this paper, the double-wall carbon nanotube oscillator resonant phenomena and energy dissipation are simulated by use of molecular dynamics simulation. The simulation run at different temperatures , and the double-walled carbon nanotube oscillator resonance phenomenon is verified，the vibration displacement curve which carbon tubes versus time and the changes in restoring force of carbon tubes suffered in the process of oscillation process are obtained and the friction is discussed from the point of view of energy dissipation. By statistical calculation, the double-walled carbon nanotube resonant amplitude of the process is found quickly decay with temperature increasing, and the friction per atom will enlarge with temperature increased, but the restoring force of inner tube is almost constant.

A simple method for predicting the chloride diffusivity of cement paste is presented. In this method, cement paste is modeled as a two-phase composite material, consisting of solid matrix and pore space. By incorporating the classical percolation theory into the effective medium approach, an explicit solution is formulated for the chloride diffusivity of cement paste. Two parameters involved in the solution are determined by fitting the solution to experimental data. After the validity of the simple method is verified with experimental results obtained from the literature, the effects of the water/cement ratio and the degree of hydration on the chloride diffusivity of cement paste are evaluated in a quantitative manner. The paper concludes that the proposed simple method can predict the chloride diffusivity of cement paste with reasonable accuracy.

Agarose microbeads were prepared by premix membrane emulsification with Shirasu-Porous; Glass (SPG) membrane and Polyethylene (PE) membrane. The effects of membrane parameters, including pore size, pore size distribution, contact angle between membrane surface and the water phase, shape of pore opening and membrane thickness on size and uniformity of agarose beads were investigated in this study. The results showed that pore size distribution and shape of pore opening did not affect the emulsification results apparently within a wide range in premix membrane emulsification, not as the result in general emulsification. The contact angle between the water phase and the membrane surface must be large enough to obtain uniform-sized agarose beads in both direct membrane emulsification and premix membrane emulsification. The results also showed that the membrane pore size and thickness affected the size distribution of emulsion. Thicker membrane resulted in more uniform and smaller emulsion when the number of pass through membrane is controlled. There was a linear relationship between the number average diameter of agarose beads and membranes pores size in premix membrane emulsification. Agarose beads with diameters from 3.06 to 9.02 mu m were prepared by controlling membranes pore size. The ratio of the number average diameter of agarose beads to membrane pore diameters was found to be 0.486. (C) 2008 Elsevier B.V. All rights reserved.

The ceramic thermal barrier coatings (TBCs) play an increasingly important in advanced gas turbine engines because of their ability to further increase the engine operating temperature and reduce the cooling, thus help achieve future engine low emission, high efficiency and improve the reliability goals. Currently, there are two different processes such as the plasma spraying (PS) and the electron beam-physical vapor deposition (EB-PVD) techniques. The PS coating was selected to test the elastic modulus. Using the nanoindentation and resonant frequency method, the mechanical properties of ceramic top-coat were measured in-situ. According to the theory of the resonant frequency and composite beam, the testing system was set up including the hardware and software. The results show that the accurate characterization of the elastic properties of TBCs is important for stress-strain analysis and failure prediction. The TBCs systems are multi-layer material system. It is difficult to measure the elastic modulus of top-coat by tensile method. The testing data is scatter by nanoindentation method because of the microstructure of the ceramic top-coat. The elastic modulus of the top-coat between 20–1 150 °C is obtained. The elastic modulus is from 2 to 70 GPa at room temperature. The elastic modulus changes from 62.5 GPa to 18.6 GPa when the temperature increases from 20 °C to 1 150 °C.

Uniform-sized agarose beads with diameters less than 10 μm and agarose content as high as 14 wt% were prepared by premix membrane emulsification. Agarose aqueous solution was used as the water phase. A mixture of liquid paraffin and petroleum ether containing hexaglycerin penta ester (PO-500) was used as the oil phase. The water phase was mixed with the oil phase at 60 °C and a coarse W/O emulsion was produced in a homogenizer. Then, the coarse emulsion was extruded through a hydrophobic membrane under high pressure to form an emulsion, which was slowly cooled under gentle agitation to form gel beads. The effects of preparation conditions on emulsification results were investigated and it showed that the pressure, number of passes, petroleum ether/liquid paraffin (v/v) in the oil phase, the concentration of PO-500 and concentration of agarose in the water phase, all affected the size and uniformity; coarse emulsion did not affect the emulsification results. The coefficient variation (C.V.) of agarose beads under optimal preparation conditions was 9.8%. This method realized microbeads with both uniform sizes and high agarose contents that are difficult to be prepared by conventional emulsion methods.

In order to develop an environment-friendly method of forming a chemical conversion coating on 2024 aluminium alloy surface without the toxic hexavalent chromium compounds, in this paper a process with sodium molybdate and potassium permanganate as the main compositions of the treating bath has been investigated. Solution composition and process parameters have been optimized. The chemical conversion coating has good corrosion resistance, evaluated with dropping test. Micro-structure and components of the conversion coating have been studied by various micro-analysis methods, and the growth mechanism of the chemical conversion coating has also been investigated.

A simple spline integral equation method is presented in this paper for the axisymmetrical bending of circular plates with variable thickness. Firstly, the fundamental solution of a second-order differential equation is derived. With the slope of the deflection surface taken as an unknown function, an integral equation is then established for circular plates with variable thickness. The integral equation is solved numerically by cubic spline interpolation and the deflection and bending moment at any point within the circular plate are obtained. Finally, the validity of the proposed method is verified with the analytical solution obtained from the literature.

A simple and efficient spline integral equation method is presented in this paper for the axisymmetrical bending of circular plates with large deflection. Based on two second-order differential equations in terms of the slope of the deflection surface and the radial displacement of the circular plate, two integral equations are derived. The circular plate is then equidistantly divided into a circular plate element and a series of annular plate elements along its radial direction and the slope of the deflection surface and the radial displacement are both approximated by cubic spline interpolation. The two integral equations are solved numerically and the displacements and internal forces at any point within the circular plate can be obtained. Finally, some numerical results are presented for illustrating the validity of the proposed method. It can be concluded that the proposed numerical method can be used to analyze circular plates with large deflection with reasonable accuracy.

Practical experience and observations suggest that corrosion affected reinforced concrete (RC) structures are more prone to cracking than other forms of structural deterioration. Concrete cracking incurs considerable costs of repairs and inconvenience to the public due to interruptions. This gives rise to the need for prediction of the time to surface cracking of concrete in order to achieve cost-effectiveness in maintaining the serviceability of RC structures. The intention of this paper is to develop a numerical method for predicting the time to surface cracking of corrosion affected RC structures. In this method, concrete with embedded reinforcing steel bars is modeled as a thick-wall cylinder. With an exponential curve modeling the energy dissipation process in concrete, the element transfer matrix is derived analytically. The time to surface cracking is then determined by solving the nonlinear problem numerically. Finally, the validity of this numerical method is verified by comparing with experimental results collected from the research literature.

Crack width is a significant parameter for assessing service life of reinforced concrete structures in chloride-laden environments. Corrosion-induced concrete cracking is a predominant causal factor influencing premature degradation of reinforced concrete structures, incurring considerable costs for repairs and inconvenience to the public due to interruptions. This gives rise to the need for accurate prediction of crack width in order to achieve cost-effectiveness in maintaining serviceability of concrete structures. It is in this regard that the present paper attempts to develop a quasi-brittle mechanical model to predict crack width of chloride contaminated concrete structures. Assuming that cracks be smeared uniformly in all directions and concrete be a quasi-brittle material, the displacement and stress in a concrete cover, before and after surface cracking, were derived respectively in an analytical manner. Crack width, as a function of the cover depth, steel bar diameter, corrosion rate and time, was then determined. Finally, the analysis results were verified by comparing the solution with the experimental results. The effects of the cover depth, steel bar diameter and corrosion rate on the service life were discussed in detail.

A three-phase composite circle model is presented in this paper to assess the effect of interfacial transition zone (ITZ) on the chloride diffusion coefficient of concrete. Firstly, the distribution of circular aggregate particles was simulated in a square concrete element. Based on the simulated concrete mesostructure, the Monte Carlo algorithm was adopted to numerically evaluate the ITZ area fraction for different concrete mixes. A parametric study was then conducted to quantify the effects of the largest aggregate diameter, ITZ thickness and aggregate gradation on the ITZ area fraction. Secondly, the ITZ was modeled as a thin-wall annular plate located between a circular aggregate particle and a thick-wall cement paste annular plate. With the three-phase composite circle model, an analytical solution was derived for the chloride diffusion coefficient of concrete. Finally, the derived solution was verified by experimental results obtained from the research literature and a quantitative relationship between the thickness and chloride diffusion coefficient of ITZ was established.

A differential effective medium scheme for the chloride diffusivity of concrete with spheroidal aggregate particles is presented. By taking the interfacial transition zone (ITZ)-coated aggregate particle as an "equivalent aggregate particle," the three-phase concrete is reduced to a two-phase composite material. The differential effective medium theory is then adopted to derive an analytical approximation for the chloride diffusivity of concrete. After the validity of the analytical approximation is verified with two sets of experimental results, the effects of various key factors on the chloride diffusivity of concrete are evaluated quantitatively. Numerical results indicate that the chloride diffusivity of concrete increases with an increase in chloride diffusivity and thickness of ITZ, but decreases by increasing the aggregate aspect ratio and maximum aggregate diameter. It is also found that the aggregate gradation has a significant influence on the chloride diffusivity of concrete.

The purpose of this paper is to present a lattice method for predicting the Youngs modulus of concrete with two types of elliptical aggregate. After distributing fine and coarse aggregates within a rectangular unit, the finite element method is adopted to estimate the Youngs modulus of concrete. Compared with previous studies, the method considers the aggregate shape effect and the difference in Youngs modulus between fine aggregate and coarse aggregate. After the validity of the method is verified with two sets of experimental results, the effects of various factors on the Young s modulus of concrete are quantified. It is found that the Young's modulus of concrete increases with an increase in aggregate aspect ratio, minimum aggregate diameter, or both, but decreases by increasing the interfacial transition zone thickness. It is also found that the maximum aggregate diameter and aggregate gradation have little effect on the Young's modulus of concrete.

Mg ion conductors, MgAl2O4 and MgZr4(PO4)6, were prepared by solid state reaction. Their electrical properties were measured and their application in electrochemical sensors for on-line determination of Mg in molten Al in the refining process and alloying process was examined. The activation energies for Mg ion conduction in MgAl2O4 and MgZr4(PO4)6 are 2.08 eV and 1.7 eV, respectively. The sensors have been found to respond rapidly to the change of Mg content in molten aluminium around 1000 K.

The chemical composition and solid state reaction of the nano-Ti(CN) base cermets in different sintering temperature were studied. The total carbon and oxygen content in compact were declined gradually with the increasing of sintering temperature, the nitrogen content in compact began to decline above 1100°C, the peak of de-gassing of N2 was formed before the emergence of liquid phase, the decomposition of N2 was arisen acutely above 1500°C. Mo2C and TaC diffused and took part in solid state reaction with Ti(CN) above 900°C, the solid state reaction was finished below 1200°C. WC diffused and took part in solid state reaction with Ti(CN) above 1100°C, it was dissolved below 1250°C, there were only two phases, Ti(CN) and Ni(Ni+Co), in the alloy.

The composition, microstructures and properties of the Ti(CN) based cermets have been characterized by using SEM/BSE and energy spectrometer. Results shows that the carbon content of the cermets through N2 and Ar sintering was lower by 0.5% than vacuum sintering and the nitrogen content of the cermets through N2 sintering was higher by 20~25% than the Ar and vacuum atmosphere sintering. When sintered in Ar or N2, the balance between the carbon and nitrogen in the cermets was broken to form a surface defects, which would result in poor properties. The structure of vacuum sintering is more uniform and the properties are better.

A new type of limiting current oxygen sensor which uses yttria (8%mol) stabilized zirconia (YSZ) as oxygen ion conducting solid electrolytes and dense La0.8Sr0.2FeO3 (LSF) as diffusion barrier was developed successfully. The oxygen sensor shows excellent performance at oxygen concentrations range of from 0 to 21%. The advantages of the sensor are simple construction, low cost and potential long term stability.

The effect of longitudinal spacing of transverse reinforcement on the confining stress in concrete columns is studied analytically. A linear-elastic solution is obtained for circular columns laterally confined by hoops. From this solution, an effective confining stress at any point and an average confining factor for circular transverse cross sections are defined. The relationship between the average confining factor and the longitudinal spacing of hoops is established from the numerical results of the analytical solution. The same procedure is then applied through a series of finite-element analyses to square columns transversely reinforced with welded-wire fabric. The resulting formula relating the longitudinal spacing and the average confining factor is remarkably similar to that found from the circular column analysis.

Determining the water permeability of cement paste is of great practical significance in view of cement paste water transport's importance in cement-based material design and durability assessment. The authors present an analytical cement paste water permeability prediction method. The cement paste model is an isotropic two-phase composite material, with gel and capillary pores included in two separate phases, since capillary pores have a considerably larger contribution to cement paste water permeability and a considerably larger scale than gel pores. An analytical solution is derived for cement paste water permeability through the introduction of a hypothetical homogeneous nonzero water permeability medium and application of general effective medium theory. The proposed method's primary advantage is each phase constitutent's physical properties and morphological characteristics, the Hashin-Shtrikman bounds, and the interaction of the two phases are all taken into account. Finally, there is verification of analytical solution validation with experimental results obtained from the literature. The conclusion that cement paste water permeability can be predicted with reasonable accuracy by the analytical solution is reached.

Interfacial transition zone (ITZ) constitutes the weakest link in the normal concrete matrix and significantly affects the properties of the concrete. To quantitatively evaluate the effect of ITZ on the physical and mechanical behavior of concrete, it is imperative to characterize the microstructure of ITZ. The intention of this paper is to investigate the characteristics of ITZ microstructure in a statistical manner In this paper an algorithm is developed to simulate the three-dimensional distribution of cement particles between aggregates in concrete.