Добірка наукової літератури з теми "Pseudo-binary diffusion"

Interdiffusion coefficients of Al replacing elements in Ni-Al-X (X=Ti, V and Nb) were estimated by a series of experiments using diffusion couples of Al rich pseudo-binary systems at three different temperatures of 1423, 1473 and 1523K. In order to obtain interdiffusion coefficients of the pseudo-binary systems, the experimental data was analyzed by the Sauer and Freise method, and also impurity diffusion coefficients of Ti, V and Nb in Ni3Al were estimated by applying the Darken-Manning equation. The magnitude of interdiffusion coefficient decreased in order of V, Ti and Nb at all three temperatures. Impurity diffusion coefficients were described by the expressions: , , . The activation enthalpies obtained from the experimental data confirmed the retardation of Ti, V and Nb diffusion in Ni3Al by the anti-site diffusion mechanism. These results are consistent with our previous work on diffusion of Re and Ru in Ni3Al .

Transmission of images on the network is considered insecure which has security-related issues. In this paper, to provide security to digital images, an encryption system that uses four chaotic maps for binary key sequence generation is proposed. The system consists of stages namely, confusion, generation of random binary chaotic key sequence, pseudo-random number generation (RN), and diffusion. Keys for encryption are chosen randomly based on a pseudo random generator from the selected chaotic maps by the linear feedback shift register (LFSR). The algorithm achieves good results in terms of NPCR, UACI, and entropy values. The developed cryptosystem resists differential attacks, is sensitive to minor alterations in the keys, and has a large key space.

The performance of nonviableP. mutilusfor removal of Crystal Violet (CV) and Basic Red 46 (BR46) was investigated in single and binary systems. Batch kinetic studies were carried out as a function of pH, temperature, biomass amount, and dye concentration to determine the decolorization efficiency of biosorbent. In single system, the biosorption capacities ofP. M.reached 166 and 76.92 mg/g for CV and BR46, respectively. A comparison of kinetic models applied to the adsorption of basic dyes ontoP. Mutiluswas evaluated for the pseudo-second-order and intraparticle diffusion kinetics models. The experimental data fitted very well the pseudo-second-order kinetic model, whereas diffusion is not only the rate-controlling step. The thermodynamic study indicates that the adsorption of dyes is spontaneous and endothermic process. In binary system, the biosorption capacities ofP. Mutilusfor both dyes decreased significantly compared to that in single system. Competitive coefficients calculated on a concentration basis using Sheindorf-Rebhun-Sheintuch (SRS) equation were useful for describing the degree of competitive interaction inP. M.

A general method for the determination of multicomponent diffusion coefficients is developed using the algebraic technique of matrix diagonalization. When linear combinations of measurements from several multicomponent diffusion experiments performed with different initial concentration gradients (but with the same final composition) are analyzed as simple binary data, particular combinations may be found that transform the multicomponent diffusion coefficient matrix D to diagonal form and thus yield time-invariant, pseudo-binary diffusion coefficients: the eigenvalues of D. Since the matrix that diagonalizes D is given by the coefficients used to form the linear combinations, D is easily recovered by the inverse transformation. The advantages of the eigenvalue method are briefly discussed. For testing purposes, ternary diffusion coefficients are determined from conductance measurements for dilute aqueous NaOH + NaCl mixtures. Diffusion of NaOH in aqueous NaCl is significantly more rapid than in pure water, and large coupled flows of NaCl are observed. The results are in close agreement with behavior predicted by Onsager–Fuoss theory.

This paper proposes a novel image encryption algorithm based on an integer form of chaotic mapping and 2-order bit compass diffusion technique. Chaotic mapping has been widely used in image encryption. If the floating-point number generated by chaotic mapping is applied to image encryption algorithm, it will slow encryption and increase the difficulty of hardware implementation. An innovative pseudo-random integer sequence generator is proposed. In chaotic system, the result of one-iteration is used as the shift value of two binary sequences, the original symmetry relationship is changed, and then XOR operation is performed to generate a new binary sequence. Multiple iterations can generate pseudo-random integer sequences. Here integer sequences have been used in scrambling of pixel positions. Meanwhile, this paper demonstrates that there is an inverse operation in the XOR operation of two binary sequences. A new pixel diffusion technique based on bit compass coding is proposed. The key vector of the algorithm comes from the original image and is hidden by image encryption. The efficiency of our proposed method in encrypting a large number of images is evaluated using security analysis and time complexity. The performance evaluation of algorithm includes key space, histogram differential attacks, gray value distribution(GDV),correlation coefficient, PSNR, entropy, and sensitivity. The comparison between the results of coefficient, entropy, PSNR, GDV, and time complexity further proves the effectiveness of the algorithm.

In this paper, the modified attapulgite-reduced graphene oxide composite aerogel (ATP-RGO CA) was prepared by sol-gel method using modified attapulgite as silica source. The removal of the cationic dye malachite green (MG) and azo dye methyl orange (MO) onto ATP-RGO CA from unitary and binary systems was investigated. Morphology and microstructure studies of ATP-RGO CA were investigated by Fourier transform infrared (FTIR), scanning electron microscopy (SEM), X-ray diffraction (XRD), and specific surface area and porosity analysis. Experiments were carried out as a function of pH, contact time, initial dye concentration, and temperature in unitary and binary systems. The adsorption kinetics, isotherms, thermodynamics, and dye desorption were studied in unitary and binary dye systems. The adsorption kinetics was modeled using the pseudo-first-order, pseudo-second-order, and intraparticle diffusion kinetics equations. The equilibrium adsorption data of MG and MO dyes on ATP-RGO CA were analyzed. Thermodynamic parameters of dye adsorption were obtained. In addition, the regeneration of ATP-RGO CA was studied using dye desorption in unitary and binary dye systems. The adsorption kinetics of the dyes followed pseudo-second-order kinetics. The results indicate that the Langmuir model provides the best correlation of the experimental data. The thermodynamic studies showed that the dye adsorption onto ATP-RGO CA was a spontaneous and endothermic reaction. High desorption of MG and MO showed the regeneration of ATP-RGO CA. It can be concluded that ATP-RGO CA is suitable as an adsorbent material to remove MG and MO dyes from unitary and binary systems.

Ni-based superalloys are widely used in jet engine applications. Bond coats are applied to these alloys for protection during service in a very harsh environment at high operating temperature. The addition of Pt to the -NiAl bond coat increases the cyclic oxidation resistance and the service life by reducing sulphur segregation between the bond coat and thermally grown oxide (TGO). However, it also increases the rate of interdiffusion of Ni and Al, leading to an increase in the thickness of the interdiffusion zone (IDZ) developed between the bond coat and superalloy. This results in an unwanted loss of Al from the bond coat, leading to a decrease in the service life of the turbine blade. Hence, it is important to understand the diffusion-controlled growth and microstructural evolution of IDZ at elevated temperature based on quantitative diffusion analysis. The composition-dependent interdiffusion coefficients (not the average over a composition range) could not be estimated experimentally following the conventional diffusion couple technique in multicomponent systems. The equations for the estimation of the interdiffusion coefficients in multicomponent systems are established based on the Onsager formalism. However, the number of independent equations required for the estimation of these data could not be achieved experimentally in a system with more than three components. Therefore, all the quantitative diffusion analyses are conducted in binary and ternary systems. In a binary system, both interdiffusion and intrinsic diffusion coefficients can be estimated. However, we can estimate only the interdiffusion coefficients in a ternary system. The intrinsic diffusion coefficients cannot be estimated following the Kirkendall marker experiments because of stringent requirements, which cannot be fulfiled experimentally. Since most of the inhomogeneous bulk materials in applications are multicomponent in nature, the lack of an experimental method for estimation of these diffusion coefficients in systems with more than three components makes it impossible to understand many physicomechanical properties based on quantitative analysis. To circumvent this problem, the pseudo-binary diffusion couple in the multicomponent system is explored. In a pseudo-binary diffusion couple, only two components develop the diffusion profiles while maintaining the compositions of other components as constant making it possible to estimate the diffusion coefficients in a multicomponent system by removing various complications. However, this method is still at the nascent stage and we cannot estimate the cross interdiffusion coefficients, which are essential for understanding the influence of thermodynamic parameters on diffusional interactions between the components. Therefore, we have developed the concept of the pseudo-ternary diffusion couple method in which only three components develop the diffusion profiles keeping other components as the constant facilitating the estimation of both main and cross interdiffusion coefficients. The benefits of using both pseudo-binary and pseudo-ternary diffusion couple methods in inhomogeneous multicomponent systems are demonstrated in this study by estimating different types of composition-dependent diffusion coefficients. The steps and analyses for utilizing the pseudo-binary and pseudo-ternary methods are first described in the Ni-Co-Fe-Mo system by producing ideal diffusion profiles fulfiling the concepts behind these methods. Subsequently, the discussion is extended to the Ni-Co-Cr system for the estimation of the tracer diffusion coefficients. Steps are also suggested to avoid the complications of developing non-ideal pseudo-binary diffusion profiles. These methods are easy to adopt for research engineers. Most importantly, these allow validating the data calculated following newly proposed numerical methods by different groups, which otherwise would not be possible earlier. The tracer diffusion coefficients estimated following the radiotracer method could compare the data estimated indirectly following the newly proposed method. However, these are available now only in very few multicomponent systems. Therefore, this study is extended to the Ni-Co-Fe-Cr system for the sake of comparison of the data estimated following the pseudo-binary method with tracer diffusion coefficients measured by the radiotracer method. Along with the interdiffusion coefficients, the intrinsic diffusion coefficients are also estimated for all the components by designing the pseudo-binary couples such that Ni and Co develop the diffusion profiles keeping Fe and Cr constant in one couple, and Fe and Cr develop the diffusion profiles keeping Ni and Co constant in another couple. We have proposed the relations for calculating the tracer diffusion coefficients considering the vacancy wind effect by utilizing the thermodynamic details. A very good match was found with the data estimated directly following the radiotracer method at the equiatomic composition. Since the PB method cannot explain the diffusional interactions between the components, which plays an important role in the evolution of diffusion profiles, the concept of the pseudo-ternary diffusion couple is demonstrated in the Ni-Co-Fe-Mo system. The pseudo-ternary diffusion profiles can be intersected since the diffusion paths are restricted in two dimensions compared to the situation in which all the components develop the diffusion profiles and difficult to intersect even two diffusion paths in a multicomponent space. The modifications of the equations for estimating the diffusion coefficients in this type of diffusion couple is proposed for estimating the main and cross interdiffusion coefficients, which was otherwise impossible during the last many decades. As a next step, we have utilized these methods to estimate the composition-dependent diffusion coefficients in the B2-Ni(CoPt)Al system to understand the diffusion process based on quantitative analysis, which was not possible earlier. We found that the PB-interdiffusion coefficients of Ni and Al decrease in Co's presence but an increase in the presence of Pt. The thermodynamic driving forces show an opposite trend with respect to the composition as compared to the changes in the interdiffusion coefficients. The PT-methods indicate that the main interdiffusion coefficients increase significantly in the presence of Pt. On the other hand, the cross interdiffusion coefficients change marginally, causing a minor change in these components' diffusional interactions. These indicate a dominating role of the Pt(Co)-induced modifications of point defect concentrations. The estimated diffusion coefficients are utilized to explain the increase in the thickness of the IDZ between the B2-Ni(Pt)Al bond coat and the single crystal superalloy René N5. Further, to understand the nature of the precipitates formed in IDZ, The electron probe micro analyser (EPMA) and transmission electron microscopy (TEM) analyses are carried out. It reveals that the precipitates are rich in refractory elements. The partial or complete replacement of Pt with Pd in B2-NiAl is examined by studying the interdiffusion zone's growth rate and the spallation of the oxide layer during thermal cycling. The quantitative diffusion analysis following the PB method indicates that the PB interdiffusion coefficient of Ni and Al decreases in the presence of Pd. This reflects the decreased growth rate of the interdiffusion zone and, therefore, can be considered beneficial compared to the Pt modified bond coat. On the other hand, the spallation of the oxide layer is high in the presence of Pd. However, a partial replacement of Pt with Pd leads to superior spallation resistance against thermal cycling along with the absence of deleterious PtAl2 phase during pack cementation. The combination of Pt and Pd reduces the Al loss caused by the growth of IDZ and forms a stable oxide layer. So, this combination of Pt+Pd modified bond coat is beneficial for gas turbine applications.

Quantitative diffusion analysis in multicomponent metallic systems has been a formidable task historically and despite decades of research, most of the diffusivity estimations were limited to interdiffusion and some intrinsic diffusion coefficients in binary systems and interdiffusion coefficients in a few ternary systems until recently. The experimental complications associated with the need to intersect (n-1) serpentine diffusion paths in the n dimensional space for determining the 〖(n-1)〗^2 interdiffusion coefficients lead to various approaches like average diffusivity, square root diffusivity estimations that approximate a representative value of the diffusivity across a composition range from a single experiment. However, these values are not material constants and do not provide any information about the atomic interactions. This lack of diffusivity data in multicomponent systems has hampered the development of mobility databases essential for various simulations and physico-chemical studies of materials. This work resolves the issues with quantitative multicomponent diffusion analysis via several newly proposed methods that solves the issue of intersecting diffusion paths through the application of special constrained diffusion paths. The equations necessary to apply these methods are derived and their application is discussed mathematically and applied experimentally to the model alloy system, the NiCoFeCr equiatomic multiprincipal element alloy to compare with available radiotracer data measured for this system. The work first employs the pseudo-binary diffusion couple approach that develops a rectilinear diffusion path in the multicomponent space to the NiCoFeCr system to estimate the tracer coefficients from the intrinsic coefficients at the marker plane. The mathematical formulations derived for the same justify its namesake and the obtained tracer coefficients can be used to back calculate the intrinsic and interdiffusion coefficients. The pseudo-ternary method improves on the shortcomings of the pseudo-binary diffusion couple method and enables the estimation of tracer coefficients of three components by crossing two constrained diffusion paths in a 2d plane in addition to the main and cross interdiffusion coefficients. The body diagonal method originally proposed for determination of interdiffusion coefficients is modified here to determine the tracer coefficients of all components using only two diffusion profiles thus reducing the errors associated with crossing (n-1).paths per the original approach. This work then explores the possibilities of crossing dissimilar constrained diffusion paths by crossing pseudo ternaries of different types. Strategically crossing a rectilinear pseudo-binary diffusion path with a serpentine conventional (body diagonal) diffusion path overcomes all the previous drawbacks of pseudo binary, pseudo ternary and body diagonal methods to determine the full set of diffusivities at any desired composition and generalizes the constrained diffusion path approach to any order multicomponent system. The obtained tracer coefficients show a good match with the diffusivities measured in radio tracer experiments. Finally, based on the ideas from the constrained diffusion path experiments in the NiCoFeCr system, a constrained path approach is devised to measure the diffusivities in an Al based NiCoFeCr multiprincipal element alloy system which was not possible earlier due to unavailability of radio isotopes and the complexities of interdiffusion experiments in higher order systems. The obtained tracer diffusivities, show an excellent match with the trends extrapolated from lower order systems. Calculated intrinsic and interdiffusion coefficients demonstrate the importance of vacancy wind effect as well as the issues with using diffusivities having different dependent components to make predictions on diffusion trends among different elements.

Prothrombinase is the multi -component enzyme composed of factor Xa and the cofactor, factor Va, that assemble on a phospholipid surface in the presence of calcium ion. Fluoresence stopped-flow kinetic studies of prothrombinase assembly in the absence of the substrate, prothrombin were undertaken at saturating concentrations of calcium ion, using phospholipid vesicles (PCPS), factor Va and factor Xa modified at the active-site with the fluorophore dansyl-glutamylglycinylarginylchloro methylketone (DEGR-Xa). The substantial fluorescence enhancement of DEGR-Xa in the presence of factor Va, PCPS and calcium ion was used as a continuous measure of prothrombinase complex formation. The rate of complex formation studied under pseudo-first order conditions was most rapid when factor Va was reacted with the DEGR-Xa-PCPS binary complex. Under these conditions, the rate increased linearly with increasing PCPS concentrations and was independent of the concentration of factor Va. The reaction between Va and PCPS assessed by stopped-flow light scattering produced identical rates. The data indicate that the rate-limiting step in the reaction between Va and PCPS-bound DEGR-Xa is the initial formation of a Va-PCPS binary complex (8.4×107M−1s−1) followed by the very rapid reaction (>3×109M−1s−1) between PCPS-bound DEGR-Xa and Va. When complex formation was initiated by mixing DEGR-Xa and Va with PCPS or by mixing DEGR-Xa with Va-PCPS, the pseudo-first order rates were substantially lower. Under these conditions, increasing concentrations of factor Va inhibited the rate of prothrombinase complex formation which could be overcome by increasing PCPS concentrations. The data are consistent with the interpretation that the initial formation of the DEGR-Xa-PCPS complex is a prerequisite for prothrombinase assembly. The second order rate constant for the reaction between DEGR-Xa and PCPS (9.5×109M−1s−1 ) was independently determined by stopped-flow light scattering. Collectively, the data indicate that prothrombinase assembly proceeds via the initial formation of DEGR-Xa-PCPS and Va-PCPS binary complexes. The lipid-bound constituents then rapidly react via diffusion over the vesicle surface to form prothrombinase.(Supported by NIH grants HL-35058 and HL-34575)