Phase Diffusion Research Articles

Liquid Phase Diffusion Analysis of WC–Co–Ni–Fe/HSS Composite Materials Based on DICTRA

Liquid Phase Diffusion Analysis of WC–Co–Ni–Fe/HSS Composite Materials Based on DICTRA

Novel, Fast, Strong, and Parallel: A Colored Image Cipher Based on SBTM CPRNG

Novel, Fast, Strong, and Parallel: A Colored Image Cipher Based on SBTM CPRNG

Phase formation and elemental transport in the vacuum diffusion bonding between CoCrFe0.2NiMn and CoCrFe16NiMn multicomponent alloys

To efficiently explore the influence of Fe content on the phase stability of the multicomponent CoCrFexNiMn (hereafter abbreviated as Fex) alloys. A diffusion layer with continuous, concentration gradient of Fe element is created based on diffusion couple technique. The microstructure and element distribution of the diffusion bonded layer between Fe0.2 and Fe16 alloys are analyzed. A new layer of FCC and HCP solid solution phases generates in the diffusion zone, which is consistent with the prediction of parametric approach and phase diagram calculation. As diffusion proceeds, the FCC phase is transformed from the BCC phase with the decreasing of Fe content and the HCP phase might be the transitional phase during this transition. The newly formed FCC and HCP phases are shown specific orientation relationships with the BCC phase. Elemental analysis indicated that the diffusion rate of the alloy components in the FCC phase is Cr > Mn > Co > Ni. The large concentration gradient in the diffuse interface and grain boundaries diffusion of BCC phase promoted the Fe diffusion, causing the BCC phase to transform into FCC phase.

Strategies for Achieving Ultra-Long ORR Durability-Rh Activates Interatomic Interactions in Alloys.

The stability of platinum-based alloy catalysts is crucial for the future development of proton exchange membrane fuel cells, considering the potential dissolution of transition metals under complex operating conditions. Here, we report on a Rh-doped Pt3Co alloy that exhibits strong interatomic interactions, thereby enhancing the durability of fuel cells. The Rh-Pt3Co/C catalyst demonstrates exceptional catalytic activity for oxygen reduction reactions (ORR) (1.31 A mgPt -1 at 0.9 V vs. the reversible hydrogen electrode (RHE) and maintaining 92 % of its mass activity after 170,000 potential cycles). Long-term testing has shown direct inhibition of Co dissolution in Rh-Pt3Co/C. Furthermore, tests on proton exchange membrane fuel cells (PEMFC) have shown excellent performance and long-term durability with low Pt loading. After 50,000 cycles, there was no voltage loss at 0.8 A cm-2 for Rh-Pt3Co/C, while Pt3Co/C experienced a loss of 200 mV. Theoretical calculations suggest that introducing transition metal atoms through doping creates a stronger compressive strain, which in turn leads to increased catalytic activity. Additionally, Rh doping increases the energy barrier for Co diffusion in the bulk phase, while also raising the vacancy formation energy of the surface Pt. This ensures the long-term stability of the alloy over the course of the cycle.

Strategies for Achieving Ultra‐Long ORR Durability—Rh Activates Interatomic Interactions in Alloys

AbstractThe stability of platinum‐based alloy catalysts is crucial for the future development of proton exchange membrane fuel cells, considering the potential dissolution of transition metals under complex operating conditions. Here, we report on a Rh‐doped Pt3Co alloy that exhibits strong interatomic interactions, thereby enhancing the durability of fuel cells. The Rh−Pt3Co/C catalyst demonstrates exceptional catalytic activity for oxygen reduction reactions (ORR) (1.31 A mgPt−1 at 0.9 V vs. the reversible hydrogen electrode (RHE) and maintaining 92 % of its mass activity after 170,000 potential cycles). Long‐term testing has shown direct inhibition of Co dissolution in Rh−Pt3Co/C. Furthermore, tests on proton exchange membrane fuel cells (PEMFC) have shown excellent performance and long‐term durability with low Pt loading. After 50,000 cycles, there was no voltage loss at 0.8 A cm−2 for Rh−Pt3Co/C, while Pt3Co/C experienced a loss of 200 mV. Theoretical calculations suggest that introducing transition metal atoms through doping creates a stronger compressive strain, which in turn leads to increased catalytic activity. Additionally, Rh doping increases the energy barrier for Co diffusion in the bulk phase, while also raising the vacancy formation energy of the surface Pt. This ensures the long‐term stability of the alloy over the course of the cycle.

Unraveling L12 Al3X (X=Ti, Zr, Hf) nano-precipitate evolution in aluminum alloys via multi-scale diffusion simulation

The evolution of L12 Al3X (X = Ti, Zr, Hf) nano-precipitates in Al-X alloys was studied by multi-scale diffusion simulation using a combination of first principles calculation and finite element method. The results show that the diffusion coefficient in Al-X solid-solution phase follows DAl>DZr>DHf>DTi, which are in excellent agreement with available experimental values. On the other hand, the mobility of X atoms in L12 Al3X phases is reversed, following DAlAl3X>DTiAl3Ti>DHfAl3Hf>DZrAl3Zr. The calculated Al and X diffusion coefficients in both Al-X solid-solution and L12 Al3X ordered phases were used to simulate the evolution of L12 nano-precipitate embedded in Al-X solid-solution matrix. It is found that only Zr could promote the formation of nano-precipitates at 650 K, the common heat-treatment temperature for advanced Al alloys. At lower temperature, the sluggish atomic movement hinder the nucleation of L12 phase, while at higher temperature the precipitates redissolve into the Al matrix. The multi-scale diffusion simulation underlines the indispensable role of diffusion in L12 Al3X phases on the nano-precipitate evolution, and also provides a feasible way to the rationally design of precipitate strengthening alloys.

Cosmic-ray diffusion in two local filamentary clouds

Context. Hadronic interactions between cosmic rays (CRs) and interstellar gas have been probed in γ rays across the Galaxy. A fairly uniform CR distribution is observed up to a few hundred parsecs from the Sun, except in the Eridu cloud, which shows an unexplained 30–50% deficit in GeV to TeV CR flux. Aims. To explore the origin of this deficit, we studied the Reticulum cloud, which shares notable traits with Eridu: a comparable distance in the low-density region of the Local Valley and a filamentary structure of atomic hydrogen extending along a bundle of ordered magnetic-field lines that are steeply inclined to the Galactic plane. Methods. We measured the γ-ray emissivity per gas nucleon in the Reticulum cloud in the 0.16–63 GeV energy band using 14 years of Fermi-LAT data. We also derived interstellar properties that are important for CR propagation in both the Eridu and Reticulum clouds, at the same parsec scale. Results. The γ-ray emissivity in the Reticulum cloud is fully consistent with the average spectrum measured in the solar neighbourhood, but this emissivity, and therefore the CR flux, is 1.57 ± 0.09 times larger than in Eridu across the whole energy band. The difference cannot be attributed to uncertainties in gas mass. Nevertheless, we find that the two clouds are similar in many respects: both have magnetic-field strengths of a few micro-Gauss in the plane of the sky; both are in approximate equilibrium between magnetic and thermal pressures; they have similar turbulent velocities and sonic Mach numbers; and both show magnetic-field regularity with a dispersion in orientation lower than 10°–15° over large zones. The gas in Reticulum is colder and denser than in Eridu, but we find similar parallel diffusion coefficients around a few times 1028 cm2 s−1 in both clouds if CRs above 1 GV in rigidity diffuse on resonant, self-excited Alfvén waves that are damped by ion-neutral interactions. Conclusions. The loss of CRs in Eridu remains unexplained, but these two clouds provide important test cases to further study how magnetic turbulence, line tangling, and ion-neutral damping regulate CR diffusion in the dominant gas phase of the interstellar medium.

Diffusion coefficients and atomic mobilities in the BCC phase of the Al–Nb–V system

Diffusion coefficients in the BCC phase of the Al–Nb–V ternary system are studied for the first time, including an assessment of the atomic mobilities. Ternary interdiffusion coefficients are obtained from the intersecting diffusion paths of several sets of diffusion couples that are annealed at both 1100 °C and 1200 °C. Existing experimental data from the pertinent binary systems are also employed for the assessments of atomic mobilities using the 1-parameter Z-Z-Z binary diffusion coefficient model developed by Zhong et al [1]. Interdiffusion coefficients in the BCC region of the Al–V system are also extracted through a forward-simulation analysis and incorporated into the mobility modeling. A complete description of diffusion in the BCC phase of the Al–Nb–V system is presented following the Binary and Cross-Binary Parameters Only (BCBPO) model developed by Zhong and Zhao [2]. Our data will be valuable input to diffusion-related simulation of refractory high entropy alloys containing aluminum.

Molecular simulation study on interfacial microstructural changes of CO2 flooding in tight porous environment

In this research, the interfacial microstructure dynamics during CO2 flooding in tight porous reservoirs were explored through molecular dynamics simulations. Initially, the study focuses on the structural attributes of the gas–liquid interface in a static state, noting a transition from dissolution to swelling as tightness increases. Subsequently, the research diverges into two distinct areas: the quasi-static and dynamic displacement processes. The analysis of diffusivity and dissolution in the oil phase under quasi-static conditions indicates that the interaction energy between components is influenced by the degree of tightness. In contrast, during dynamic displacement at a constant pressure, tight reservoirs exert an anchoring effect, hindering the movement of the oil phase at 3 MPa. However, at 10 MPa, CO2 is likely to achieve a gas breakthrough in less tight reservoirs, while the adsorption strength of residual oil in the reservoirs concurrently escalates. The study concludes that the stability of the interfacial region plays a dual role in determining the sustainability of liquid exchange in these processes.

Recycling multisource industrial waste residues as green binder for cemented ultrafine tailings backfill: Hydration kinetics, mechanical properties, and solidification mechanism

Incorporating mine tailings with industrial waste residues (IWRs) is progressively used to manufacture filling materials, which provides an eco-friendly disposal method for IWRs and alleviate their impact on the environment. In this study, steel slag (5, 10, 15, 20 wt%), fly ash (5, 10 wt%) and blast furnace slag (52, 57, 65, 74 wt%) as the precursor, carbide slag (16, 18, 20 wt%) and desulfurization gypsum (0, 2, 3 wt%) as the activator were reutilized to synthesize the IWRs-based binder for cemented ultrafine tailings backfill (CUFTB). Experimental tests were conducted to determine the setting time, hydration heat release, mechanical behavior, and microstructure characteristics. The hydration kinetics and solidification mechanism were expounded correspondingly. Results elucidate that the initial and final setting time of CUFTB are respectively 12.08–13.92 h and 16.92–20 h <24 h much longer than the transport time in pipeline and meets the operational requirements of mine site. Hydration process of CUFTB includes initial dissolution, induction, acceleration, deceleration, and decline stages. As the hydration proceeds, the initial stage of CUFTB is regulated by nucleation and crystal growth (NG), and gradually shifted to interactions at phase boundaries (I) or diffusion (D). The high content of carbide slag (20 wt%) promotes the hydration reaction, resulting in the increase of heat release. IWRs-based binder hydrates to form calcite, ettringite, hydroaluminite, and gehlenite. Especially, the gel products are mainly C-A-S-H, C-(Al,Na)-S-H, C-(Al,K)-S-H with Ca/Si ratio <1, demonstrating a fundamental distinction from Portland cement. Under the bonding and padding of hydration products, tailings particles are solidified well. After curing of 28 days, CUFTB exhibit high UCS values exceeding 2.0 MPa, presenting an evident improvement of 26.70% ∼ 39.20% compared to those made of Portland cement. These findings are referential for preparation of cemented paste backfill by reutilizing IWRs in mine filling field.

Medical image encryption system based on a simultaneous permutation and diffusion framework utilizing a new chaotic map

In telemedicine, diverse medical images transmitted between doctors and patients contain sensitive personal information. Thus, there is an urgent need for reliable and efficient medical image encryption to protect these medical images during transmission. In this paper, a simultaneous permutation and diffusion framework (SPDF) is introduced for medical image encryption based on a new chaotic map. Firstly, combining the Chebyshev map and the iterative chaotic map with infinite collapse (ICMIC), we propose a one-dimensional chaotic system (1D-CICMIC) which exhibits higher ergodicity and unpredictability compared to other 1D chaotic maps through comprehensive analyses. Secondly, in order to enhance permutation effect, we modify traditional Josephus traversing with a dynamic scrambling method where the scrambling scheme of the current pixel depends on the value of the previous diffused pixel. Thirdly, we develop a simultaneous permutation and diffusion framework, wherein the diffusion is embedded into the modified Josephus traversing to prevent attackers from targeting the scrambling and diffusion phases separately. Finally, based on 1D-CICMIC and SPDF, an encryption system is proposed. It adopts plaintext correlation in the diffusion operation, which strikes a balance between ciphertext sensitivity and plaintext sensitivity, offering resistance against chosen-plaintext attack (CPA), noise attack and data loss. Simulation results show that the proposed algorithm has high encryption efficiency and can withstand various common attacks.

A robust medical image cryptosystem based on hyperbolic chaotic system and circular bit-shifting-flipping techniques

Due to the hasty growth of digital technology, securing medical images for transmission and storage is a significant issue. Information on the texture of medical images is essential for diagnosis. Hence, protecting these content has become a great challenge in the e-Healthcare system. So, we propose a novel dynamic circular bit shifting and bit-flipping process in the diffusion phase of the image cryptosystem to provide high level protection for the medical image. In the developed framework, at first, the hyperbolic chaotic map is executed for generating three hyper chaotic series and these chaotic series are utilized for encryption process. In encryption process, primarily the secret image is confused by utilizing any two chaotic series, then the confused image is divided into blocks and each block is diffused by executing the proposed dynamic circular bit shifting and bit-flipping process which greatly increases the probability and complexity level of the developed cryptosystem. Evaluation using different medical images represents that the proposed model has robustness, high efficiency, key sensitivity and also has the ability to withstand different attacks. This has been represented using the results of security measures and statistical analysis, such as Shannon entropy (7.997), CC (< 0), NPCR (99.63 %), UACI (37.14 %), SSIM (< 0), FSIM (< 0.5), PSNR (6.88). These results prove that the developed medical crypt can efficiently provide better security for medical images utilized in real time medical application like e-Healthcare and telemedicine.

Phase field-volumetric lattice Boltzmann model of ion uptake in porous nuclear waste form materials under continuous flow

The flow field within the mesopores of sorbent particles plays a crucial role in radionuclide diffusion and ion uptake kinetics, thus, impacting the overall performance of porous nuclear waste form materials. To fundamentally understand the influence of microstructures and material properties on the radionuclide absorption and retention processes requires a coupled multi-physics model that considers the advection and diffusion within the flow field, the reaction at liquid-solid interfaces, and finally, the solid-state diffusion within a complex nanoporous medium. This study employs the volumetric lattice Boltzmann method (VLBM) to accurately and efficiently calculate the steady state velocity field inside the mesopores of sorbent particles. The obtained velocity field is then utilized to calculate the advection of ions in the steady flow. A phase field (PF) model of ion uptake is used to describe the reaction occurring at the solid-liquid interface and diffusion inside the porous medium. The integrated PF-VLBM model is verified in terms of the mass conservation and numerical efficiency and validated qualitatively with experimental observation data. Then, it is applied to study the influence of thermodynamic and kinetic properties, as well as flow field conditions on the ion uptake kinetics. The numerical results demonstrate that the ion uptake kinetics in porous particles has three distinct stages, which is in agreement with the observations in continuous flow experiments. In the first stage, the kinetics is predominantly controlled by the flow field and ion diffusivity in the liquid phase. The kinetics in the second stage is primarily governed by ion diffusivity in the solid phase. In the third stage the system reaches a dynamic equilibrium with a net zero uptake flux at the interface. It is also found that porous structures significantly affect the efficiency and capacity of ion uptake. The simulation results can help to understand the physics behind the observed ion uptake kinetics in experiments and to facilitate the development of constitutive equations that can account for heterogeneous microstructures in engineering performance codes.

Mapping carbon nanotube aspect ratio, concentration and spinning in FCCVD synthesis controlled by sulphur

Floating catalyst chemical vapor deposition (FCCVD) enables ultrafast synthesis of CNTs and other 1D nanoparticles and their direct assembly as macroscopic solids. The chalcogen growth promotor in FCCVD produces high aspect ratio CNTs that can aggregate in the gas phase and form an aerogel which can be continuously spun as macroscopic fibres or sheets. We study the role of sulphur in controlling CNT morphology and aggregation by synthesising CNTs under a wide range of S/C ratios (0.001 to 5 wt.%) and determining their diameter and length distributions, number concentration and form of aggregation. Increasing S/C ratio in this range increases mean number of CNT walls from 1 to 8, decreases mean length from 34 to 6 µm, but CNT number concentration remains approximately constant at 8 × 108#/cm3. Assuming growth within the first 3 cm of the reactor, longitudinal growth rate spans 1.5- 6.5 µm/s for the different CNT morphologies, but with similar mass throughput of 700 attogram/catalyst. This indicates the amount of carbon reaching the catalyst and solidifying as CNT remains constant regardless of the sulphur available in the catalyst, suggesting the rate limiting process is not at the catalyst/promoter interface but instead in the transport of carbonaceous active precursors to the catalyst, either due to their diffusion in the gas phase or decomposition kinetics. The CNTs produced range from polymer-like, which readily bundle and form aerogels, to rod-like that do not. We include aerogelation “phase diagrams” for different CNT concentrations, aspect ratios and CNT bending stiffness.

On the Lanthanide Effect on Functional Properties of 0.94Na0.5Bi0.5TiO3-0.06BaTiO3 Ceramic.

The beneficial effects of lanthanide incorporation into 0.94Na0.5Bi0.5TiO3-0.06BaTiO3 (BNT-BT) matrix on its functional properties were investigated. The conventional solid-state method was used for synthesizing samples. The structural refinement revealed that all samples crystallized in R3c rhombohedral symmetry. Raman spectroscopy study was carried out using green laser excitation and revealed that no clear perceptible variation in frequency is observed. Dielectric measurements unveiled that the introduction of rare earth obstructed the depolarization temperature promoted in BNT-BT, the diffusive phase transition decreasing with increasing lanthanide size. Only dysprosium addition showed comparable diffusion constant and dielectric behavior as the unmodified composition. Further, the comparison of the obtained ferroelectric hysteresis and strain-electric field loops revealed that only Dy-phase exhibited interesting properties comparing parent composition. In addition, the incorporation of lanthanides Ln3+ into the BNT-BT matrix led to the development of luminescence characteristics in the visible and near infrared regions, depending on the excitation wavelengths. The simultaneous occurrence of photoluminescence and ferroelectric/piezoelectric properties opens up possibilities for BNT-BT-Ln to exhibit multifunctionality in a wide range of applications.

Theoretical analysis of the effect of isotropy on the effective diffusion coefficient in the porous and agglomerated phase of the electrodes of a PEMFC

In polymer membrane fuel cells (PEMFC), the pore microstructure and the effective diffusion coefficient (Deff\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$D_{eff}$$\\end{document}) of the catalytic layer have a significant impact on the overall performance of the fuel cell. In this work, numerical methods to simulate PEMFC catalytic layers were used to study the effect of isotropy (Ixy\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$I_{xy}$$\\end{document}) on the Deff\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$D_{eff}$$\\end{document}. The proposed methodology studies reconstructed systems by Simulated Annealing imaging with different surface fractions of microstructures composed by two diffusive phases: agglomerates and pores. The Deff\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$D_{eff}$$\\end{document} is determined numerically by the Finite Volume Method solved for Fick's First Law of Diffusion. The results show that the proposed methodology can effectively quantify the effect of isotropy on the Deff\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$D_{eff}$$\\end{document} for both diffusion phases. Two trends were obtained in the magnitude of the Deff\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$D_{eff}$$\\end{document} concerning the change in isotropy: (1) an analytical equation is proposed in this article for Deff≥5%D0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$D_{eff} \\ge 5\\% D_{0}$$\\end{document} and (2) numerical solutions are determined for Deff<5%D0.\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$D_{eff} < 5\\% D_{0} .$$\\end{document} In our analytical equation are both a lineal and a logarithmic sweep. When the surface fraction is ∅=\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\emptyset =$$\\end{document} 50%, the Deff\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$D_{eff}$$\\end{document} decreases more linearly than ∅=10%\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\emptyset = 10\\%$$\\end{document} at the beginning of the isotropy change, which indicates that small changes in isotropy in the particulate material modify it drastically; under these conditions the diffusion coefficient in the pore is predominant. (3) When the surface fraction is less than 50%, the Deff\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$D_{eff}$$\\end{document} decreases more exponentially at the beginning and more linearly at the end of the isotropy change, which shows that small isotropy changes in the bar-aligned material drastically alter it. In this trend, diffusion in the agglomerate is less affected by isotropy. The proposed methodology can be used as a design tool to improve the mass transport in porous PEMFC electrodes.

Determination of phase boundaries and diffusion coefficients of copper in spinel CuCr2Se4 and delafossite CuCrSe2 by galvanostatic intermittent titration technique (GITT)

Determination of phase boundaries and diffusion coefficients of copper in spinel CuCr2Se4 and delafossite CuCrSe2 by galvanostatic intermittent titration technique (GITT)

Multi‐chaotic maps and blockchain based image encryption

SummaryThe vast technological developments make data transmission more frequent over networks. So, the data needs to be secured and for that reason, there is a requirement to develop an effective encryption model. This article proposes a novel image encryption model using multi‐chaotic maps and blockchain (MCBE). Chaotic maps have been used in encryption models as chaotic maps have the properties of randomness, and non‐periodicity that get utilized in improving the efficiency of an encryption model. Logistic and tent maps have been employed as multi‐chaotic maps to make the encryption process effective in this work. A logistic map has a simple structure and is easily implementable but has some drawbacks like small keyspace. Keyspace and randomness are enhanced by using a tent map along with a logistic map. The proposed MCBE methodology applies to grayscale or colored images having different file formats and sizes. Initially, in the confusion phase, the permutation of the original image is performed based on a random permutation that changes the original image pixel's position. The encryption model applies multi‐chaotic maps, row‐wise and column‐wise in the diffusion phase to promote the efficiency of the encryption model. Finally, blockchain has been implemented using the SHA‐256 hash function to obtain the encrypted image that enhances the security by increasing the keyspace, to resist brute force attacks. The evaluation performance of the MCBE has been analyzed against various attacks namely statistical attacks, differential attacks, NIST randomness test, noise, and cropping attacks. The evaluated keyspace is which has high key sensitivity with a correlation of encrypted images close to 0. Maximum achieved entropy value of 7.9998, SSIM value between original and encrypted images nearby 0 confirms the dissimilarity. The Number of Pixels Change Rate (NPCR) value of 99.62%, and the value of Unified Average Changed Intensity (UACI) value of 33.54% are within the specified standard range. The calculated correlation coefficient, NPCR, and UACI values have been compared with the existing algorithms, and the results show that the proposed MCBE methodology has better performance than the other state‐of‐the‐art methods. The experimental results indicate that the chaotic ranges generated by multi‐chaotic maps and the SHA‐256 hash function improve the keyspace and security of the encryption model confirming the efficacy of the proposed model MCBE.

Effects of multi-walled carbon nanotubes on microstructure transformation of water before carbon dioxide hydrate formation

There is no consensus on the micro mechanism of gas hydrate formation. The essence of water conversion into hydrates is the transformation of disorderly arranged water into the water with specific structure under a certain condition. This study used different multi-walled carbon nanotubes (MWCNTs) as solid promoters for gas hydrate formation. By comparing the effects of nanotubes modified with hydroxyl, carboxyl and amidogen on the microstructure transformation of water before CO2 hydrate formation, the micro mechanism and influence rules of gas hydrate formation were systematically study. The results indicated that the conversion of water to hydrates mainly manifested as the mutual conversion of strong/weak hydrogen bonding water. Due to the Brownian motion and dispersion of MWCNTs, the hydrogen bonds of the weak hydrogen-bonded water weakened (the corresponding peak blue shifts), and the distance between water molecules (dO−O) expanded, forming relatively loose hydrate, which was conducive to gas diffusion in the solid hydrate phase and increased the final gas consumption. Meanwhile, the strengthening of strong hydrogen bonded water increased the rate of hydrate formation.

Continuous visbreaking of heavy oil in medium and high-pressure steam environments

Continuous visbreaking of heavy oil in a tubular reactor was studied under pressurized steam environments at 10 MPa (MPS) and 18 MPa (HPS). Within the operating range considered, heavy oil and pressurized steam exhibit a liquid-vapor two-phase structure. During the transition from the MPS environment to the HPS environment, the dissolution of water into the oil phase is promoted, thereby reducing the viscosity of the oil phase. According to the lumped reaction kinetics analysis, the reaction behavior of the lumped component VR2 with a boiling point higher than 700 °C determines the visbreaking efficiency in the early visbreaking stage to a large extent. Dealkylation of VR2 and condensation of the lightest lumped component show sensitive responses to improved diffusion in the oil phase. At 400 °C and a space time of 37 min, visbreaking in HPS environment can achieve a viscosity reduction rate of 90%. Meanwhile, the asphaltene content of the product is lower than the feedstock value.