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We investigated the synergistic effects of H2O2 concentration and pH on corrosion behavior of biomolecular, type I collagen, coatings on 3D-printed porous low elastic modulus Ti–24Nb–4Zr–8Sn (Ti2448) alloy scaffolds under equilibrium conditions in simulated inflammatory environment (i.e., acidic environment containing H2O2). Corrosion behavior in pH 7.4 or 5.2 simulated body fluid (SBF) containing 0, 30, or 150 mM H2O2 was assessed using potentiodynamic polarization curve near corrosion potential, electrochemical impedance spectroscopy at open-circuit potential (OCP), and ion release at OCP. For biomolecular-coated scaffolds, decreasing pH concurrent with the presence of H2O2 led to increase corrosion potential. In SBF with 30 mM H2O2, decreasing pH had no effect on corrosion rate or polarization resistance of biomolecular-coated scaffolds. However, in SBF with 150 mM H2O2, decreasing pH led to decrease corrosion rate and increase polarization resistance. The impedance of biomolecular-coated scaffolds decreased with increasing H2O2 concentration and decreasing pH. Regardless of H2O2 concentration and pH, the electrochemical equivalent circuit corresponding to the surface-untreated scaffolds under equilibrium conditions was a resistor-capacitor (RC) circuit, whereas the biomolecular-coated scaffolds presented two RC circuits corresponding to a dense inner protective film and a non-dense outer film. In acidic SBF containing 150 mM H2O2, the metal ions release from the biomolecular-coated scaffolds under equilibrium conditions was roughly half that from the untreated scaffolds. These findings confirmed under equilibrium conditions in simulated inflammatory environment, the type I collagen coatings on Ti2448 alloy scaffolds improved corrosion resistance by minimizing susceptibility to H2O2 concentration and acidic environment.

Trust and reputation systems play a pivotal role in modern decentralized environments, fostering cooperation and mitigating risks in various online interactions. This paper introduces a variational formulation approach to model and analyze trust and reputation systems. By formulating trust and reputation as variational problems, this approach offers a novel perspective on understanding the underlying mechanisms governing trust establishment. The variational formulation provides a mathematical framework to determine the equilibrium weighted trust values, taking into account that each trustee tries to maximize its gain, namely the benefit minus the costs. The paper illustrates the applicability of this variational formulation through a pletora of simulations, demonstrating its effectiveness in modeling trust and reputation systems. Insights gained from this approach offer valuable guidance for the design and implementation of more reliable and efficient trust and reputation mechanisms in decentralized environments [ABSTRACT FROM AUTHOR]

The cryogenic carbon capture (CCC) process is a promising post-combustion CO2 removal method. This method is very novel compared with conventional and well-developed methods. However, cryogenic carbon capture is not yet commercially available despite its techno-economic benefits. Thus, a model-based design approach for this process can provide valuable information. This paper will first introduce the cryogenic carbon capture process. Then, a comprehensive literature overview that focuses on different methods for modeling the process at the component level will be given. The modelling methods which are deemed most effective are presented more in depth for each of the key system components. These methods are compared with each other in terms of complexity and accuracy and the simplest methods with an acceptable level of precision for modelling a specific component in the CCC process are recommended. Furthermore, potential research areas in modeling and simulation of the CCC process are also highlighted. [ABSTRACT FROM AUTHOR]

[Display omitted] Empirical correlations were obtained to calculate the equilibrium pressure of the methane and natural gas (the Srednevilyui gas and condensate field) hydrates formation in sodium bicarbonate solutions, the hydration numbers and dissociation heats of these hydrates were determined. The values of the hydration numbers assume that methane forms hydrates with the CS-I structure and natural gas – CS-II. The dissociation heat of the natural gas hydrates is higher than that of the methane hydrates. [ABSTRACT FROM AUTHOR]

In this paper, we consider a supply chain network model that consists of three layers of decision-makers, namely, suppliers, manufacturers and retailers, with prices and shipments that evolve in time. We focus on the vertical integration of the levels of the supply chain and consider the retailer as the dominant player of the coalition. We give a novel reformulation of the evolutionary variational inequality related to the equilibrium conditions underlying the model. This approach, based on complementarity conditions, allows us to analyze the Lagrange multipliers associated with production capacities to understand better market's trend. We study the behavior of marginal profits and provide some results for the efficiency and the stability of the coalitions. We apply our theoretical achievements to a duopolistic model. [ABSTRACT FROM AUTHOR]

Clathrate hydrates (gas hydrates) are solid crystalline compounds formed from water molecules as host molecules and gas molecules as guest molecules. Due to the hydrogen bonds, water constructs a framework that entraps some small nonpolar molecules (typically gases) and in suitable conditions (i. e. low temperature and high pressure) gas hydrate forms. The objective of this research is to estimate the gas and refrigerant hydrate dissociation conditions with and without alcohols and sodium chloride aqueous solutions using simple empirical correlations. Generally, the empirical suggested correlations to estimate the equilibrium clathrate hydrate pressure of CH4, C2H6, C3H8, CO2, N2, H2S, R22, R23, R134a, R116, R125a, R152a, R141b, R410a, R407c, R507c, CH4 + methanol, CH4 + ethylene glycol, CH4 + triethylene glycol, CH4 + ethanol, CH4 + sodium chloride, CO2 + methanol, CO2 + glycerol, CO2 + sodium chloride, R134a + sodium chloride, R507c + sodium chloride and R410a + sodium chloride systems are a function of equilibrium hydrate temperature and concentration. A genetic algorithm was employed as an optimization method to determine correlation coefficients, and the mean squared error was selected as its fitness function. Due to the low values of the calculated absolute average deviations (between 0.00 and 7.65), except for H2S + pure water with the highest amount of the absolute average deviation percent (AAD% equal to 11.51), these correlations are capable of predicting the studied hydrate dissociation conditions.

Direct flaring of industrial waste flows specifically in the combustion chambers of heat generating plants makes it possible to significantly reduce the loss of thermal energy, as well as the capital costs of equipping thermal units without using of preliminary furnaces. However, given the increasingly strict environmental standards for the burning of various fuels, it seems important to determine the optimal combustion conditions depending on the composition of the waste products. The article shows that only a complex solution can be a successful solution to the problem of organizing high-quality combustion of industrial waste flows. On the one hand, it is necessary to obtain extremely environmentally friendly combustion products, and, on the other hand, the waste disposal process should be energy efficient. The article discusses the stages of the implementation of the projects of energy-efficient utilization of industrial waste in compliance with the established environmental standards for emissions of pollutants. The analysis of initial combustible chemical substances that are part of solid, liquid and gaseous wastes of industrial technologies is given. The main classes of fuels that determine combustion reactions are identified. Global chemical reactions and oxidation mechanisms are considered. The combustible properties, chemical composition, and degree of impact of the products of combustion of industrial waste on the environment are determined, depending on the content of various starting substances. The most difficult aspect of the flaming disposal of industrial waste flows is the presence of harmful substances of various hazard classes. The conditions for achieving complete fuel combustion, stoichiometry, and equilibrium conditions for different air/fuel ratios (depending on fuel composition) with incomplete combustion are determined. The analysis of products of incomplete combustion is given as well as of and hazard classes of the corresponding pollutants. The maximum value of the coefficient φ was determined beyond which solid carbon should be formed in a homogeneous mixture.

The cryogenic carbon capture (CCC) process is a promising post-combustion CO2 removal method. This method is very novel compared with conventional and well-developed methods. However, cryogenic carbon capture is not yet commercially available despite its techno-economic benefits. Thus, a model-based design approach for this process can provide valuable information. This paper will first introduce the cryogenic carbon capture process. Then, a comprehensive literature overview that focuses on different methods for modeling the process at the component level will be given. The modelling methods which are deemed most effective are presented more in depth for each of the key system components. These methods are compared with each other in terms of complexity and accuracy and the simplest methods with an acceptable level of precision for modelling a specific component in the CCC process are recommended. Furthermore, potential research areas in modeling and simulation of the CCC process are also highlighted.

Controlled deployment of a foldable tensegrity‐membrane system is investigated in this article. A membrane folding technique referred to as the spiral folding pattern is applied to the attached membrane to achieve compact folded shapes for the system. The foldable tensegrity‐membrane system experiences transitions between two system configurations (i.e., the tensegrity configuration and the tensegrity‐membrane configuration) due to the variation of membrane loading states during system deployment. A closed‐loop control strategy consisting of two linear parameter‐varying (LPV) controllers is designed based on control‐oriented models to regulate system dynamics. A nonlinear finite element model is used to examine the control performance. Senor noise is considered in another nonlinear finite element simulation to examine the robustness of the designed controllers. [ABSTRACT FROM AUTHOR]

The catenary is one of the most common curves; it is, in fact, the shape assumed by a homogeneous and inextensible chain, fixed to the extremities, which is subject only to its own weight. The catenary has always fascinated not only mathematicians but also architects and engineers, who have often used it in their works due to its remarkable properties. In this note, the catenary is introduced by determining its equation and considering its history from Galileo Galilei to the present day, pointing out a historical mistake. Then, some of its applications to architecture and engineering are shown and the catenary is compared to the parabola, a curve that at first sight can look similar to catenary but must not be confused with it. Finally, some variants of the catenary are considered: the weighted catenary and the catenary of equal resistance, highlighting their properties and their practical applications.

A theory of the mechanism that consists of two reversible electrode reactions coupled by kinetically controlled reversible chemical reaction is developed for square wave voltammetry on stationary planar electrode. The influences of frequency and the concentration of electro-inactive chemical reactant on the responses are investigated for thermodynamically stable intermediate. The limits of three types of responses are calculated and the formula for the estimation of the forward rate constant of chemical reaction is proposed.

Abstract Hydrate formation can cause serious problems in hydrocarbon exploration, production, and transportation, especially in deepwater environments. Hydrate‐related problems affects the integrity of the deepwater platforms, leads to equipment blockages, and also increases operational costs. In order to solve these problems, salts are used as thermodynamic inhibitors and also mixed with the drilling fluids in most drilling processes. A comprehensive understanding of hydrate formation in aqueous salt solutions is vital to overcome these problems. Statistical thermodynamic models are commonly used to predict hydrate formation conditions in different aqueous solutions. However, these models involve rigorous computations and are restricted to certain conditions. They give inaccurate predictions of hydrate equilibrium conditions for high‐temperature, high‐pressure, and high‐salinity systems. Therefore, it is paramount to develop a simple‐to‐use and reliable prediction tool. In this work, an empirical correlation is developed and successfully used to predict the equilibrium conditions of ethane, propane, and isobutane hydrates in pure water and aqueous solutions of sodium chloride, potassium chloride, calcium chloride, and magnesium chloride. Experimental data on hydrate formation conditions for these components are regressed and a generalized correlation is obtained. The predictions in this work show excellent agreement with all the experimental data in the literature.

CCWater is a computer program developed for the application of extensively being used triangular diagrams for chemical classification and for identification of equilibrium conditions of waters. The program for these diagrams were developed as a Microsoft Excel™ spreadsheet application and compiled using Visual Basic™ 6.0, which has enabled to execute an Excel™ file from a program created by Visual Basic™ 6.0. The performances of all the four diagrams were validated by applying for the same chemical concentration data of the waters that was used by the original authors of these diagrams. The results obtained from this program were consistent with those of the original authors of these diagrams. As an example, CCWater is applied for chemical characterization of thermal waters from springs and geothermal wells of five geothermal fields of Mexico, in which four are electricity producing fields (Cerro Prieto, CPGF; Las Tres Vírgenes, LTVGF; Los Azufres, LAGF, and Los Humeros, LHGF) and the fifth geothermal field (La Primavera, LPGF) is in exploration stage. Majority of the reservoir temperatures estimated by Na/K geothermometers from geothermal well waters of CPGF, LAGF, LTVGF, and LPGF are within the limits of accepted differences (within ±20%) comparing to the average BHTs of the respective geothermal well. The good performances of the geothermometers in predicting the reservoir temperatures from well waters is expected because the well waters are fully equilibrated and are of Cl type, thus fulfilling the basic requirements. In contrary, though the spring waters of LHGF and LAGF are of HCO3 type (immature) and exhibited no equilibrium conditions, they also predicted reliable reservoir temperatures. This unusual but important observation in the behavior of the spring waters of LHGF and LAGF was made possible to known by chemical classification of these waters in to different groups and estimation of the reservoir temperatures by considering each water type of a geothermal field as a separate group. This application has shown the importance of chemical type of water and the existing chemical equilibrium conditions in successful using these waters in estimation of the reservoir temperatures, and hence the necessity of the computer program like CCWater. The software CCWater is easy to use, reliable, freely available and will be useful in the application of ternary diagrams for chemical characterization and to evaluate the equilibrium conditions of geothermal waters, particularly during the initial stage of geothermal exploration. [ABSTRACT FROM AUTHOR]

In the research aimed at determining tectonic stresses from fault-slip data (the seismological data on the focal mechanisms of earthquakes, geological data on slickensides, etc.), in the past few decades, it has become a predominant practice to use the approach that we refer to as the method of the local kinematic reconstruction (MLKR) of stresses and paleostresses. In the MLKR, ignoring the equilibrium conditions, the authors assign a studied block (macrovolume x) a certain symmetric tensor T which they call without explanation a stress tensor and which is, in their opinion, the only cause of the observed slips. In the MLKR, the principal axes and the ratio of the differences of the principal values of tensor T (the so-called reduced tensor TR) are reconstructed locally, without taking into account the interaction of x with the contacting blocks, i.e., in such a manner as if macrovolume x were isolated. Tensor TR is determined based on the analysis of N events (N ≥ 4) that occurred in x over the time span Δt using only the data on the slip directions and on the orientation of the slickensided planes. This approach ignores the rate of change of the stresses, previous deformation history, and mechanical properties of the block, as well as the ratio of Δt to the stress relaxation time in the block. In this review, the key ideas of MLKR are discussed and it is shown that the underlying concept of this method is fundamentally fallacious and can lead to results that are arbitrarily inconsistent with reality since under a change in the ignored factors, tensor TR can become almost arbitrary with the same set of slips. According to the mechanics of deformable solids (MDS), uniform stresses in a quasi-statically deformed macrovolume x are genetically related to the self-equilibrated surface forces acting on x and are completely independent of deformations. In contrast, the "stresses" in MLKR are genetically caused by strains and not related to surface forces. As a result, MLKR misses the possibility to balance x, i.e., to satisfy the inviolable conservation laws of momentum and angular momentum. Besides, the TR object that is reconstructed in the MLKR is not objective: it is not frame indifferent. In the attempts to achieve the desired objective, followers of the MLKR have to implicitly return to the representations that have been rejected as early as in Cauchy's works: they do not separate the universal laws of dynamics from the mechanical properties of a particular medium. Specifically, they postulate some a priori subjective interrelations between the elements of the sought tensor TR and the slip directions, thus formulating the constitutive relations of the medium which differ from author-to-author but are attributed a meaning of the universal laws. The information about TR in the MLKR is derived from these relations rather than from the laws of mechanics. Due to this, the notions of stresses and constitutive laws in the MLKR fundamentally differ from the respective notions in the MDS. The followers of the MLKR constantly neglect the fact that the observed slip pattern not only reflects the sought stresses but also the other factors—at least, the mechanical properties of a particular medium, which should also be reconstructed from the observations rather than postulated speculatively. In the Appendix to the review, by the example of a perfectly plastic medium, we recapitulate our previously suggested scheme in which the problem of reconstructing the field of equilibrium stresses and the problem of reconstructing the constitutive relations (in this case, it is the form of the plastic potential of the medium) are separated and solved sequentially. In media that are not perfectly dissipative, separating these problems is problematic. Together, these problems constitute an absolutely new problem that has no analogs in the MDS and waits for its solution from ambitious and competent researchers. [ABSTRACT FROM AUTHOR]

Abstract Deployment of foldable tensegrity-membrane systems is investigated in this article. The major objective of deploying such systems is to extend and tension the attached membrane, which is folded initially, by changing system shapes. During this process, the system operates at two system configuration types, namely, the tensegrity configuration (where the attached membrane is slack) and the tensegrity-membrane configuration (where the attached membrane is tensioned). An energy-based approach is introduced to determine system equilibriums, and the explicit equilibrium conditions for both system configurations are derived. A nonlinear finite element model is used to study system dynamics in the process of deploying two foldable tensegrity-membrane systems. Observations related to system behaviors during deployment are discussed in detail. [ABSTRACT FROM AUTHOR]

In this paper, two new quadrilateral elements are formulated to solve plane problems. Low sensitivity to geometric distortion, no parasitic shear error, rotational invariance, and satisfying the Felippa pure bending test are characteristics of these suggested elements. One proposed element is formulated by establishing equilibrium equations for the second-order strain field. The other suggested element is obtained by establishing equilibrium equations only for the linear part of the strain field. The number of the strain states decreases when the conditions among strain states are satisfied. Several numerical tests are used to demonstrate the performance of the proposed elements. Famous elements, which were suggested by other researchers, are used as a means of comparison. It is shown that these novel elements pass the strong patch tests, even for extremely poor meshes, and one of them has an excellent accuracy and fast convergence in other complicated problems.

This work criticizes the entrenched views according to which the orientation of the principal tectonic stress axes can be determined from local (in time and space) observations of the kinematic indicators which jointly allow estimating the strain rate of a crustal block under study. The criticized approach ignores or replaces by subjective assumptions the following factors: (1) The block’s interaction with a hosting medium expressed in terms of the equilibrium conditions of the block; (2) The stress rate which (in addition to stresses) can affect the strain rate; (3)The specific macroscopic mechanical properties of the block’s material under the unknown sought stresses, including the ratio of the stress relaxation time to the period of observations. This approach, which is developed in some Solid Earth sciences and mainly in tectonophysics, is referred to in our paper as the method of local kinematic reconstruction (MLKR) of stresses. After briefly surveying the concept of forces and stresses and discussing the importance of studying the tectonic stresses, this paper refutes the MLKR notions based on general arguments and by the example of certain thought experiments. It is shown that the use of the MLKR for the conditions of the Earth’s interior does not guarantee against obtaining the results that fundamentally and drastically differ from the true tectonic stresses. In the studied rock block, depending on the factors ignored in the MLKR, the principal axes of the strain rate tensor, on one hand, and the principal stress axes, on the other hand, can be oriented discordantly in any arbitrary given fashion. In particular, in the processes accompanied by the release of elastic energy, the maximal rate of elongation can be oriented along the axis of maximal compression, whereas the maximal rate of shortening can be aligned with the axis of the maximal tension. In this paper, the deformation processes that are most detrimental to the results of stress reconstruction by the MLKR are revealed. We introduce the notion of the inherited stress-state regime in which the orientation of the axes of principal stresses during the observation period does not depend on the deformation process and, hence, cannot be in principle determined by the MLKR. An attempt to directly locally recover the stress axes from the kinematic data is a false objective because neither the physical meaning of the stress tensor nor the way it is introduced has anything to do with strains. It is concluded that the MLKR is physically inadequate and that the tectonophysical concept of locality should be abandoned in favor of returning to the notions of classical physics, namely, to using the conservation laws. By the example of several guides on tectonophysics, this paper exposes typical errors in understanding the stress reconstruction problem. [ABSTRACT FROM AUTHOR]

Analysis was performed of the effect on the bearing capacity of the ground base supporting a vertical load from a massive structure, and of the segmentation of a prism uplift into sections. Alimit equilibrium method is used for the analysis. [ABSTRACT FROM AUTHOR]

The influence of hypotheses on the shape of the slip surface and the distribution of the normal stress over it under inclined load acting on the structure is analyzed. [ABSTRACT FROM AUTHOR]

This paper reports on a wave flume experimental campaign carried out to investigate the appearance, the growth and the migration of small scale bedforms on a sloping sandy bed due to both regular and random waves. A Vectrino Profiler along with a structured light approach were used for velocity and morphodynamic measurements at two positions, one located above the horizontal bed, and the other one above the sloping beach. The velocity was computed by phase averaging the velocity measurements. Several velocity profiles were analyzed, identifying an offshore-directed steady current that extends from few centimeters above the bottom for all the analyzed water column. Ripple geometry was measured by a structured light approach and compared with that predicted by several models to shed light on the effects induced by the sloping beach on the shape and asymmetry. Along the sloping beach, the ripples appeared strongly asymmetric with the onshore half wavelengths smaller than the offshore ones. Finally, ripple geometry and migration triggered by regular waves were compared with those generated by random waves with comparable flow orbital amplitude showing a good agreement. [ABSTRACT FROM AUTHOR]

A large part of the European natural gas imports originates from unstable regions exposed to the risk of supply failure due to economical and political reasons. This has increased the concerns on the security of supply in the European natural gas market. In this paper, we analyze the security of external supply of the Italian gas market that mainly relies on natural gas imports to cover its internal demand. To this aim, we develop an optimization problem that describes the equilibrium state of a gas supply chain where producers, mid-streamers, and final consumers exchange natural gas and liquefied natural gas. Both long-term contracts (LTCs) and spot pricing systems are considered. Mid-streamers are assumed to be exposed to the external supply risk, which is estimated with indicators that we develop starting from those already existing in the literature. In addition, we investigate different degrees of mid-streamers’ flexibility by comparing a situation where mid-streamers fully satisfy the LTC volume clause (“No FLEX” assumption) to a case where the fulfillment of this volume clause is not compulsory (“FLEX” assumption). Our analysis shows that, in the “No FLEX” case, mid-streamers do not significantly change their supplying choices even when the external supply risk is considered. Under this assumption, they face significant profit losses that, instead, disappear in the “FLEX” case when mid-streamers are more flexible and can modify their supply mix. However, the “FLEX” strategy limits the gas availability in the supply chain leading to a curtailment of the social welfare. [ABSTRACT FROM AUTHOR]

Three fast and reversible electrode reactions that are connected by two reversible chemical reactions that are permanently in the equilibrium are analysed theoretically for square wave voltammetry. The dependence of peak potentials on the dimensionless equilibrium constants of chemical reactions is calculated. The influence of the basic thermodynamic parameters on the square wave voltammetric responses is analysed.

One of the main issues in designing earth structures is to ensure their slope stability. To analyze the stability of soil mass affected by seepage forces a new method has been proposed where all equilibrium conditions and boundary conditions at the ends of the surface profile are satisfied by strain and orientation of areas of shear. To find the most hazardous hypothetical failure surface a variational method was used, which involves solving Euler-Lagrange differential equation as a necessary condition for the existence of functional extremum. Since the problem can be solved in the framework of the scheme of limit equilibrium of soil masses with the use of the Mohr-Coulomb strength criterion, one of the parameters of soil strength acts as a functional for the given values of another parameter. Sufficiency of the existing functional extremum is verified numerically.

We formulate the network equilibrium problem with mixed demand which generalizes the problems of network equilibrium with fixed and elastic demand. We prove the equilibrium conditions for this problem and propose some conditions of existence of a solution that are based on the coercivity property.We establish a connection between the problem of network equilibrium with mixed demand and the problem of auction equilibrium. The results of test calculations are presented for a model example. [ABSTRACT FROM AUTHOR]

Hydrate dissociation equilibrium conditions for carbon dioxide + methane with water, nitrogen + methane with water and carbon dioxide + nitrogen with water were measured using cryogenic sapphire cell. Measurements were performed in the temperature range of 275.75 K–293.95 K and for pressures ranging from 5 MPa to 25 MPa. The resulting data indicate that as the carbon dioxide concentration is increased in the gas mixture, the gas hydrate equilibrium temperature increases. In contrast, by increasing the nitrogen concentration in the gas mixtures containing methane or carbon dioxide decreased the gas hydrate equilibrium temperatures. Furthermore, the cage occupancies for the carbon dioxide + methane system were evaluated using the Van der Waals and Platteeuw thermodynamic theory with the Langmuir adsorption model and Peng-Robinson equation of state. The data demonstrated the increasing promoting effect of carbon dioxide with its concentration. In addition, the motor current changes during the hydrate formation and dissociation processes were measured by keeping the rotation speed of the magnetic stirrer that was connected to a DC motor constant. The motor current measurements were reported and it showed that the hydrate plug formation and dissociation could be predicted by the changes in the motor current. [ABSTRACT FROM AUTHOR]

Estimation of stability of the soil body is the main objective in the design of structures and foundations. But the laws of mechanics, such as the equilibrium conditions and the boundary conditions are not observed in most methods used for estimating the stability of the soil body. To correct the noted disadvantages, the special method, in which all laws of mechanics are observed, is stated. Search for the most dangerous surface of failure is based on the variation principle. The proposed method is used to identify the impact of such factors like boundary conditions, the shape of the surface of failure, the law of normal stress distribution over the surface of failure on the estimating the slope stability. It is established that all these factors significantly effect on the estimating the stability of the soil body.

Mg2FeH6 is regarded as potential hydrogen and thermochemical storage medium due to its high volumetric hydrogen (150 kg/m3) and energy (0.49 kWh/L) densities. In this work, the mechanism of formation of Mg2FeH6 under equilibrium conditions is thoroughly investigated applying volumetric measurements, X-ray diffraction (XRD), X-ray absorption near edge structure (XANES), and the combination of scanning transmission electron microscopy (STEM) with energy-dispersive X-ray spectroscopy (EDS) and high-resolution transmission electron microscopy (HR-TEM). Starting from a 2Mg:Fe stoichiometric powder ratio, thorough characterizations of samples taken at different states upon hydrogenation under equilibrium conditions confirm that the formation mechanism of Mg2FeH6 occurs from elemental Mg and Fe by columnar nucleation of the complex hydride at boundaries of the Fe seeds. The formation of MgH2 is enhanced by the presence of Fe. However, MgH2 does not take part as intermediate for the formation of Mg2FeH6 and acts as solid-solid diffusion barrier which hinders the complete formation of Mg2FeH6. This work provides novel insight about the formation mechanism of Mg2FeH6.