Isothermal Diffusion Research Articles

Experimental verification of a common assumption in the use of concentration-dependent interdiffusion coefficient

There has generally been a view that concentration-dependent interdiffusion coefficient, D(C), obtained at any diffusion temperature and time is a material constant and can be reliably used to predict diffusion effects at all other isothermal diffusion times. This notion which is implicitly predicated on the assumption that diffusion-induced stress (DIS) rapidly and completely relaxes once formed and does not influence D(C) is experimentally verified in the present work. The results of the study show that reliably computed D(C) from concentration profile obtained at long diffusion time fails to correctly predict concentration profiles at shorter diffusion periods, due to isothermal variation of the D(C) with time. Accordingly, instead of continuing to assume that D(C) is time-independent and can be reliably used to predict diffusion effects at any isothermal diffusion time, without appropriate experimental support, proper experimental verification of this crucial concept in other alloy systems, as done in the present work, is imperative.

Adsorptive membrane separation for eco-friendly decontamination of chlorpyrifos via biochar-impregnated cellulose acetate mixed matrix membrane.

In this work, the phase inversion approach is used to synthesize a blended mixed matrix membrane from cellulose acetate polymer and sugarcane bagasse biochar. The experiments were carried out to estimate the extent of chlorpyrifos (CPS) pesticide removal. The results showed that the removal rate was more than 99% in making the filtered water suitable enough for domestic use. The physical and functional characteristics of the membranes, such as permeability, and contact angle were identified. The changes in the membrane characteristics were observed using scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray diffraction both before and after the experimental trials. Experiments were conducted to assess not only the rejection characteristics of CPS, as a function feed concentration, but also the effect co-ions on the rejection used to analyze the composition both before and after filtration. The effects of initial CPS concentration, biochar loading, and co-ions on the membrane were investigated. The membranes showed contact angles between 70° and 97° and a permeability between 0.25 × 1010 m Pa-1 s-1 and 0.31 × 1010 m Pa-1 s-1. The effective removal of CPS from the contaminated aqueous stream was attributed to a combination of adsorptive uptake and membrane-based separation. CPS was found to get adsorbed onto the membrane matrix through an intraparticle diffusion mechanism along with an irreversible monolayer adsorption. The membrane-solute adsorptive interaction was represented by Langmuir isotherm and intraparticle diffusion models with a maximum adsorption capacity of 192.3 mg g-1. The findings indicated the efficacy of biochar-cellulose acetate mixed matrix membrane for sustainable and eco-friendly treatment of chlorpyrifoscontaminated water.

Adsorptive removal of oxytetracycline hydrochloride using bagasse-based biochar powder and beads

Oxytetracycline Hydrochloride (OTC), a common antibiotic used to treat specific illnesses in humans and animals, is characterized by poor absorption into cells, low volatility, and high hydrophilicity. It is a potent contaminant that poses a serious threat to the ecosystem, particularly the aquatic sources. Adsorption onto natural adsorbents is one of the most successful, economical, and ecologically friendly ways to remove antibiotics from waste water. The present work focuses on the adsorption of OTC utilizing alginate biochar beads (AlBCB) and biochar powder (BC) derived from bagasse. The influence of several factors were studies and optimized through batch studies employing BC and AlBCB. After 50 min BC displayed a removal of 97%, at an initial concentration of 10 ppm. The experimental data was discovered to follow PFO kinetics and fit with the Freundlich isotherm adsorption model. AlBCB, after a contact time of 40 min, indicated a maximum percentage removal of 86% for initial concentration of 10 ppm OTC. Al-biochar beads showed the maximum percentage removal at pH 10. 0.5 g of adsorbent was used to carry out all batch experiments at room temperature. The adsorption fitted Freundlich adsorption isotherm and intraparticle diffusion kinetics.

A systematic evaluation of physiochemical properties and solar-driven photocatalytic activity of nanosized Mn doped CdS on Methylene Blue dye

Manganese ions were incorporated into CdS nanosystem using wet chemical protocol at different pH values namely 9.0,10.0 and 11.0 and the same were used for photocatalytic degradation of Methylene blue (MB) dye via adsorption phenomena. Several standard analytical techniques were employed to analyse the synthesized nanocompounds: XRD, scanning electron microscopy with energy-dispersive X-ray spectroscopy, transmission electron microscopy, UV-Vis absorption spectroscopy, Fourier transform infrared spectroscopy, and vibrating-sample magnetometry. The structural analysis revealed the presence of primary cubic zinc blende structure with secondary phases. The morphological studies confirmed the formation of nanostructured particles for all pH values, amongst, pH 10.0 grown particles were showing less agglomeration and better particle stabilization. The TEM analysis confirmed the particle size of 23 nm. The absorption edge and its position shown by UV-Vis absorption analysis exhibited a broad envelope and strong blue shift due to an uneven size distribution and nanodimensional state formation of particles, respectively. The elevation to superparamagnetic state from native diamagnetic state of CdS due to Mn ions incorporation was confirmed by VSM studies. The dual phase composition significantly enhanced the photocatalytic efficiency by improving charge separation and extending light absorption. The MnS phase effectively trapped electrons, reduced recombination rates and facilitated the generation of reactive species. The photocatalytic degradation of methylene blue dye was more efficient (88.87 %) under direct sunlight exposure. Additionally, the enhanced surface properties and adsorption characteristics, as confirmed by the Freundlich isotherm and intraparticle diffusion model, contributed to the superior degradation performance.

Effects of chemical reactions in the presence of temperature variations and isothermal mass diffusion over an inclined plate

A detailed study of the erratic circulation around an unbounded inclined plate under fluctuating temperature and isothermal mass dispersion was carried out with a chemical reaction. This work concentrated on the harmonic inclination of the plate in its plane, and the accurate solution of the non-dimensional governing formulations was made possible by the Laplace transform technique. To evaluate their impact on different profiles, the investigation examined a variety of physical factors, including phase inclination, chemical response variable, Schmidt number, thermal Grashof number, mass Grashof number, and duration. Notably, the speed per second increased with decreasing phase angle. Furthermore, a decrease in either the thermal radiation variable or the chemical response variable induced an increase in velocity.

Diffusion properties of Gabonese tropical hardwoods and European softwoods measured with low-tech equipment and by an inverse method

This paper presents an experimental approach to studies of the sorption and diffusion properties of wood. Five timber species - three African tropical hardwoods, Padauk, Okoume and Iroko, and two temperate softwoods, Silver fir and Douglas fir - were studied in adsorption mode. Specimens with 10- and 20-mm longitudinal (L) and transverse (RT) thickness were waterproofed on their sides to force diffusion in those directions. After kiln drying the specimens were hung with nylon wires under cover in a home-made box in which salt solutions provided constant relative humidity (RH), and conditioned at 43, 55, 75, 84 and 97% RH in successive steps. Temperature was maintained between 20 and 24°C. During the equilibration steps the samples were periodically weighed without altering the environmental conditions imposed, by hanging the nylon wire to a spring gauge through a small hole in the box cover. The sorption isotherm properties and diffusion parameters were obtained using an inverse method based on optimization of a 1D finite difference model. The parameters obtained show a decreasing correlation between diffusion coefficient and density, as observed by several authors in the literature. They also illustrate the impact of extractives on the sorption isotherm parameters. These results show that tropical species with high density or many extractives behave very differently to European softwoods, which impedes the application of Eurocode 5 equilibrium standards for these species.

Phosphate adsorption on dried alum sludge: Modeling and application to treatment of dairy effluents

This study evaluates Alum sludge from drinking water treatment plants for the efficient and cost-effective removal of phosphates from aqueous solutions. Extensive characterization and batch experiments have established that optimal phosphate removal was achieved with a sludge dosage of 20 g L−1 (at an initial phosphate concentration of 100 mg L−1), a pH of 5, a temperature of 23 °C, and a stirring speed of 200 rpm. These conditions significantly reduced phosphate levels, ensuring compliance with legal discharge limits. The Langmuir isotherm, pseudo-second-order kinetic and intraparticle diffusion models best described the adsorption process, highlighting the spontaneous and endothermic nature of the phenomenon. The sludge effectively reduced phosphate concentrations to acceptable levels when applied to dairy effluents. This study underscores the potential of Alum sludge as a viable solution for phosphate management in environmental cleanup efforts.

Silicon regulation of the interface microstructure and shear strength of rheological cast-rolling aluminum/steel composite plates

This study reports the preparation of medium-thickness aluminum/steel composite plates with different diffusion layers using rheological cast-rolling technology. The thermodynamic software and first-principles were employed to determine the effects of different silicon contents on the solidification process and mechanical properties of the 6061 aluminum/steel composite plates. The research revealed that the Fe2Al5 phase on the steel side possessed a tongue-like preferential growth at a silicon content of less than 1.2 wt%. A granular Al–Fe–Si phase was formed on the aluminum side of the diffusion layer when the silicon content exceeded the saturation solubility (1.8 wt%), which completely suppressed the tongue-like preferential growth of the Fe2Al5 phase. First-principles calculations revealed that the matrixes showed superior toughness in comparison to binary intermetallic compounds (IMCs), while the toughness of binary IMCs surpassed that of ternary IMCs. The mechanical properties showed that the shear strength of the sample prepared by rheological cast-rolling was higher than that of composite casting and close to that of composite rolling, reaching a maximum value of 73.4 MPa. The shear strength initially increased and then decreased with an increase in isothermal diffusion time, and the fracture location was transferred from the loose FeAl3 to the Fe2Al5 phase. An increase in silicon content resulted in a slight increase in the microhardness of the diffusion layer, a delay of the peak value of the shear strength, and a reduction in the gradient of the shear strength. A substantial decrease in peak shear strength was observed when the silicon content reached 1.8 wt%.

A thermodynamic extremal principle incorporating the constraints from both fluxes and forces. II. Application to isothermal diffusion in multi-principal element alloys

The thermodynamic extremal principle incorporating the constraints from both fluxes and forces proposed in part I was applied to isothermal diffusion in multi-principal element alloys (MPEAs) to propose the so-called double-constraint model. The model cannot reduce physically to the previous model considering only the constraint from fluxes (i.e., the single-constraint model) but in special cases reduces to Fick’s law and Darken’s equation, showing its reliability. Similar to the previous pair-wise model and single-constraint model, the solutes and solvent do not need to be defined in advance in the double-constraint model and the model can be also applied directly to diffusion in MPEAs. Applications to isothermal diffusion in CoCrFeMnNi pseudo-binary diffusion couple and CoCrFeNi, CoCrFeMnNi body-diagonal diffusion couples showed that the present double-constraint model overall predicted better the experimental results than the previous single-constraint model, indicating again the necessity to consider the constraints from both fluxes and forces in the phenomenological theory of Onsager.

Evaluation of Sb-Nd and Te-Nd phases within the U-Zr fuel matrix and their interactions with HT9 alloy

Antimony (Sb) and tellurium (Te) were investigated as potential additives for U-10Zr (wt.%) metallic fuel to limit the fuel-cladding chemical interaction (FCCI) with HT-9 alloy. Neodymium (Nd) was utilized to simulate the formation of lanthanide-based solid fission products which are known to play a detrimental role in FCCI. Fuel alloys of U-Zr-Sb-Nd and U-Zr-Te-Nd were evaluated in their annealed condition and compared against their as-cast conditions. Isothermal diffusion couple experiments were performed between U-Zr-Nd, U-Zr-Sb-Nd, and U-Zr-Te-Nd against the cladding alloy HT9 to evaluate the effectiveness of the additives to stabilize Nd within the fuel alloys, as well as investigate the interaction regions that form between the different fuel alloys and HT9. SbNd and Sb3Nd4, and TeNd are found to be the primary neodymium-based phases formed in the U-Zr-Sb-Nd and U-Zr-Te-Nd alloys, respectively. The zirconium-based phase, Zr2Sb, is also found to form within the former alloy. All phases were found to remain stable through the diffusion experiments and exhibited no interaction with HT9 constituent elements. Preferential interaction between Nd with additivities Te and Sb compared to constituting elements in HT9 was further verified based on density functional theory (DFT) calculated enthalpy of mixing.

Prediction of the weighted-mean soil water diffusivity in supporting the falling rate stage of evaporation

Daily soil evaporation from drying soil can be described as isothermal linear diffusion process, resulting in a simple equation for estimating soil evaporation rate. However, determining soil water diffusivity and subsequently the crucial parameter of weighted-mean diffusivity, essential for estimating soil evaporation rate, is challenging and time-consuming. In this paper, the soil water diffusivity was re-evaluated by considering the effect of film flow, a phenomenon often overlooked but recently argued by Wang et al. (2019, https://doi.org/10.1029/2019WR025003) as the dominant process in the falling rate stage of evaporation. Theoretical derivation reveals a universal relationship between soil water diffusivity and matric potential, independent of soil types. Additionally, soil water diffusivity can be expressed in the form of an exponential function, a form commonly assumed empirically in the literature. Testing with various datasets suggests that the theoretically derived soil water diffusivity generally agrees closely with observations for matric potentials less than about −1 m, wherein the diffusivity accounting for capillary flow shows significant underestimation. Furthermore, a simple function is derived for estimating the weighted-mean diffusivity, enabling a direct estimation of soil evaporation rates in the falling rate stage. Testing with various data sets of different soil types and ambient conditions generally demonstrates close agreements between the estimated soil evaporation rates and observations, indicating that the developed method provides a robust estimation of the weighted-mean soil water diffusivity. When the initial matric potential of the linear diffusion process of drying is higher than about −1 m, which usually occurs under very high atmospheric demand conditions or for very coarse-textured soils, however, the effects of capillary flow were found to be important and need consideration. The effects of vapor diffusion were also discussed and found to have a negligible impact on the estimation of weighted-mean soil water diffusivity.

Modeling and optimization of engineering parameters for the treatment of textile wastewater using modified clay/TiO2/ZnO

Abstract The objective of this project was to develop a new hybrid nanocomposite that would maximize chemical oxygen demand (COD) and color removal from effluent from the actual textile industry to overcome the water crisis brought on by increasing industrialization and urbanization. This study is the first to use modified clay/TiO2/ZnO nanocomposites for adsorbing actual textile wastewater treatment. The adsorption capacity from the dye removal was evaluated to optimize the three engineering parameters (pH, adsorbent dose, and time) utilizing response surface methodology. An isotherm kinetic intra-particle diffusion model was developed to study the sorption phenomena. The best fit for sorption was provided by Langmuir isotherms, with an R2 of better than 0.99. The sorption process follows the pseudo-second-order kinetics that favors chemisorption, following kinetic theory. The sorption process is endothermic, viable, and spontaneous in nature, according to a thermodynamic study. At the optimal pH (5.5), adsorbent dose (0.55 g), and time (75 min), the maximum COD and color removal were achieved to be 94 and 91% with a maximum sorption capacity of 660 mg/g. In this optimization, the adj. R2 and R2 correlation coefficients were calculated as 0.7213 and 0.7653, respectively. The hybrid composite seems to be effective for treating real effluents.

INVESTIGATION OF THE DIFFUSION OF TWO GASES EQUALLY DILUTED WITH DIFFERENT BALLAST GASES

Both liquid and gaseous mixes have significant significance in numerous natural and artificial processes. This elucidates the comprehensive examination of such systems in a diverse array of various applications. The presence of several processes of heat and mass transfer in gas mixtures without an interfacial boundary in the system causes the emergence of thermoconcentration gravitational fluxes, resulting in density inhomogeneity of the medium. Isothermal diffusion in helium and methane gas mixtures in a stationary medium of propane and nitrous oxide ballast gases at various pressures has been experimentally studied. It is shown that in systems where the two main gases helium and methane were diluted with propane, and then helium with propane, and methane with nitrous oxide, a repetitive unstable diffusion state of varying intensity occurs with increasing pressure. The effect of the diluent gas on the transfer of two main gases in three-component and four-component systems is significant, since the ballast gas can either accelerate, slow down, or leave the diffusion mixing process unchanged. The comparison between experimental and calculated data on the Stefan-Maxwell theory shows a noticeable difference between them.Key words:convection, diffusion, ballastgas, multicomponent gas mixtures.

Water transport through mesoporous amorphous-carbon dust

The diffusion of water molecules through mesoporous dust of amorphous carbon (a-C) is a key process in the evolution of prestellar, protostellar, and protoplanetary dust, as well as in that of comets. It also plays a role in the formation of planets. Given the absence of data on this process, we experimentally studied the isothermal diffusion of water molecules desorbing from water ice buried at the bottom of a mesoporous layer of aggregated a-C nanoparticles, a material analogous to protostellar and cometary dust. We used infrared spectroscopy to monitor diffusion in low temperature (160 to 170 K) and pressure (6 × 10−5 to 8 × 10−4 Pa) conditions. Fick’s first law of diffusion allowed us to derive diffusivity values on the order of 10−2 cm2 s−1, which we linked to Knudsen diffusion. Water vapor molecular fluxes ranged from 5 × 1012 to 3 × 1014 cm−2 s−1 for thicknesses of the ice-free porous layer ranging from 60 to 1900 nm. Assimilating the layers of nanoparticles to assemblies of spheres, we attributed to this cosmic dust analog of porosity 0.80−0.90 a geometry correction factor, similar to the tortuosity factor of tubular pore systems, between 0.94 and 2.85. Applying the method to ices and refractory particles of other compositions will provides us with other useful data.

Moisture sorption isotherm and effective diffusion coefficient of porcelain stoneware spray-dried powder

Moisture sorption isotherm and effective diffusion coefficient of porcelain stoneware spray-dried powder

Hydrogen diffusion in Zr-2.5Nb pressure tubes specimens between 300°C-400°C by in-situ neutron imaging experiments

Zirconium (Zr) alloys are widely used in nuclear power plants as fuel cladding and are susceptible to hydrogen (H) degradation. For long operational service, Zr-based components can suffer a mechanism known as Delayed Hydride Cracking (DHC) associated to an increase of the crack propagation velocity by the re-orientation and precipitation of Zr hydride. In this process, the H mobility has a great influence. In the present work, the isothermal diffusion of H in Zr-2.5%Nb specimens obtained from a CANDU pressure tube were studied at consecutive temperatures of 300°C, 350°C, 375°C and 400°C. H content and mobility were quantified by in-situ neutron imaging experiments performed on ANTARES, the cold neutron imaging facility of FRM II. The time evolution of the H concentration across the specimen allowed the determination of diffusion coefficients, and an assessment of the limitations of existing models commonly used to describe H diffusion.

Precipitates evolution and fracture mechanism of the isothermally solidified TLP bonding joints between 316LN stainless steel and IN718 Ni-based alloy

In this study, the dissimilar TLP bonding joints of Inconel 718 nickel-base alloy and AISI 316LN stainless steel free of brittle athermal solidification zone (ASZ) were obtained. It was recognized that a good metallurgical bonding is achieved at the interface between the isothermal solidification zone (ISZ) and diffusion affected zone on the side of IN718 alloy (hereafter referred to as DAZ-IN718), while the interface of ISZ and DAZ-316LN is more sensitive to crack initiation. A lot of precipitates were found in DAZ on both sides near the base metal, which were identified as Cr2B, Cr5B3, Nb3B2, and BN. Moreover, two different sizes of voids form at the ISZ/DAZ-316LN interface. The bigger voids are caused by BN phases, while the smaller voids were identified as Kirkendall voids. The tensile test results indicate that the tensile strength and elongation decrease with increasing bonding time. In-situ tensile tests and digital image correlation (DIC) analysis indicate that there are two factors that cause the fracture of dissimilar TLP bonding joints at the ISZ/DAZ-316LN interface. The first factor is the brittle BN phases and Kirkendall voids at the ISZ/DAZ-316LN interface. During tensile tests, dislocations slide along the slip surface until they are blocked by precipitates in the DAZ, resulting in extremely high-stress concentrations at these locations. Moreover, the second factor is the poor ability of DAZ-316LN to resist plastic deformation. The high degree of strain concentration in DAZ-316LN also promotes the formation of microcracks at the ISZ/DAZ-316LN interface.

A novel tri-metal adsorbent used for defluoridation technique from groundwater: performance and mechanism.

In this research article, a novel adsorbent (Zn-Fe-Al) was synthesized successfully by a simple chemical route where three oxides combined to enhance affinity towards fluoride. The physicochemical properties of the adsorbent were used to characterize and assess its effectiveness in defluoridation with both synthetic and groundwater. The TEM results demonstrated the overlapping of metals, and EDX shows the metals present in the adsorbent. The maximum defluoridation efficiency (97%) of Zn-Fe-Al was obtained at an optimized initial pH 7 and adsorbent dose 0.08 g L-1. The fluoride adsorption on Zn-Fe-Al followed the D-R isotherm and intraparticle diffusion. The maximum adsorption capacity of Zn-Fe-Al was found to be 187 mg g-1. The adsorption of fluoride on Zn-Fe-Al was found to be endothermic and spontaneous. The Zn-Fe-Al adsorbent exhibited satisfactory defluoridation performance on real groundwater. The co-existing ions were also investigated. The adsorption mechanisms for fluoride were electrostatic interaction and ion exchange. These results demonstrated that Zn-Fe-Al adsorbent was considered high potential for effective defluoridation of groundwater.

Grafted polymeric organogel using low molecular weight gelator as an effective medium for expulsion and purification of cationic dyes and organic pollutants from contaminated surface water

An increase in water pollution is a major concern for the safety of living organisms. The present work revolves around synthesizing an organogel capable of absorbing contaminated pollutants like solvents and removing cationic dyes from water surfaces. The organogel prepared using a LMWG (low molecular weight gelator) was characterized using FT-IR, SEM, NMR, TGA, and XRD spectra. Water contact angle determination was also carried out to observe the hydrophobicity. Swelling kinetics, adsorption isotherm, and intra-particle diffusion model are reported after the respective absorption and adsorption study by the gel. The highest swelling was observed in Acetic acid with swelling of 10 times its original weight. Adsorption of dyes exhibited the highest removal efficiency of 99.35% within 60 min. The organogel holds the capability to reuse dye solutions for up to 10 cycles while also holding the capacity to remove from a binary mixture of dyes. The prepared organogel serves as a potential adsorbent for environmental remediation with the potential of maximum swelling and selectivity for cationic dyes.

β-cyclodextrin grafted multi-walled carbon nanotubes/chitosan (MWCNT/Cs/CD) nanocomposite for treatment of methylene blue-containing aqueous solutions

β-cyclodextrin (CD) was grafted with multi-walled carbon nanotubes/chitosan (MWCNTs/Cs) to obtain MWCNTs/Cs/CD nanocomposite (NC) for methylene blue (MB) adsorption from aqueous media. TEM, XRD, TGA, Raman spectra, and BET & BJH analyses were utilized to characterize and confirm the successful synthesis of as-prepared NC. MB capture was investigated by considering the parameters of pH (1.9–9.0), temperature (∼16–63 °C), sonication time (∼5–15 min), MB concentration (∼1.2–48 mg/L), and NC dose (0.03–0.26 mg). The obtained responses were then modelled using CCD, generalized regression neural network (GRNN), and least squares support vector machine (LS-SVM), of which the latter found to provide most reliable and accurate results (RMSE = 0.0235, MAE = 0.020, AAD = 0.0047, and R2 = 0.999). Moreover, the genetic algorithm-based optimization results showed that under the respective values of 7.05, 45.5 °C, 10 min, 23 mg/L, 0.12 g, MWCNTs/Cs/CD NC would be able to remove 96.75% of MB with an adsorption capacity of 603 mg/g, through different mechanisms mainly electrostatic interactions. Following from Dubinin-Radushkevich (D-R) isotherm (qs = 460.66 ± 8.9 and R2 > 0.99) and intraparticle diffusion kinetic (R2 = 0.75–0.90) models indicated a chemical adsorption mechanism. Besides, thermodynamic parameters (ΔH◦ = −66.9 kJ/mol, ΔG◦ = between −3.77 kJ/mol and −8.52 kJ/mol, and ΔS◦ = 237.1818 J/mol K) confirmed an endothermic and spontaneous nature for the adsorption. These findings along with appropriate recyclability (five times), turn the as prepared NC to a promising material in removing MB from aqueous solutions.