Electric Free Energy Research Articles

Intermolecular Electrostatic Interactions in Cytochrome c Protein Monolayer on Montmorillonite Alumosilicate Surface: A Positive Cooperative Effect.

Montmorillonite (MM) crystal nanoplates acquire anticancer properties when coated with the mitochondrial protein cytochrome c (cytC) due to the cancer cells' capability to phagocytize cytC-MM colloid particles. The introduced exogenous cytC initiates apoptosis: an irreversible cascade of biochemical reactions leading to cell death. In the present research, we investigate the organization of the cytC layer on the MM surface by employing physicochemical and computer methods-microelectrophoresis, static, and electric light scattering-to study cytC adsorption on the MM surface, and protein electrostatics and docking to calculate the local electric potential and Gibbs free energy of interacting protein globules. The found protein concentration dependence of the adsorbed cytC quantity is nonlinear, manifesting a positive cooperative effect that emerges when the adsorbed cytC globules occupy more than one-third of the MM surface. Computer analysis reveals that the cooperative effect is caused by the formation of protein associates in which the cytC globules are oriented with oppositely charged surfaces. The formation of dimers and trimers is accompanied by a strong reduction in the electrostatic component of the Gibbs free energy of protein association, while the van der Waals component plays a secondary role.

Using Electropulsing to Control the Surface Quality of Casts

This paper reports on the mechanisms and provides worked examples of using pulsed electric current to improve the surface properties of conductive materials during solidification. A rough surface is formed via the freezing of thermomechanical fluctuations and external disturbances during solidification. Pulsed electric current provides an extra driving force for the fluctuations to relax in a shorter duration toward the equilibrium state before the material loses the fluidity during cooling. This additional mechanism is associated with the electric current free energy, which depends on the current density distribution at various materials geometries, including the surface profile. The mechanism has been validated by experimental characterization of the surface roughness evolution with and without electropulsing treatment.

Giant hyperferroelectricity in LiZnSb and its origin

Hyperferroelectricity (HyFE) is an intriguing phenomenon in which spontaneous polarization persists under an open-circuit boundary condition (OCBC) despite the existence of a depolarization field. However, small polarization and shallow well depth have been found so far in most hyperferroelectric materials, which severely limits their applications. Using first-principles density functional theory, we report the discovery of a giant hyperferroelectricity in LiZbSb. The HyFE spontaneous polarization is shown to be remarkably large with $\mathrm{P}=0.282\phantom{\rule{0.16em}{0ex}}\mathrm{C}/{\mathrm{m}}^{2}$ under OCBC, which is one order of magnitude greater than the HyFE polarization in ${\mathrm{LiNbO}}_{3}$. Furthermore, HyFE in LiZnSb is found to be exceptionally stable with a well depth of electric free energy $\mathrm{\ensuremath{\Delta}}F=\ensuremath{-}332\phantom{\rule{0.16em}{0ex}}\mathrm{meV}$, which makes LiZnSb a possible hyperferroelectric solid at room temperature. The origin of the giant hyperferroelectricity in LiZnSb is identified and is attributed to the large mode effective charge of the soft longitudinal-optic phonon and the large high-frequency dielectric constant.

Stimulating the inverse transformation of amorphous second-phase particles in irradiated Zr alloy to modulate the nanostructure

Amorphization of the second phase particles in irradiated zirconium alloys tends to lead to defect formation, radiation growth and corrosion resistance reduction, while conventional annealing requires higher temperature to promote amorphous crystallization transformation, which may reduce the performance of materials. Based on the difference of electrical properties between the second phase particles and the matrix, the pulsed electric current can induce the crystallization of amorphous second phase particles at a lower temperature by introducing additional electrical free energy, so as to achieve the microregion regulation of materials. The pulsed electric current effectively reduces the recrystallization activation energy of the second phase particles from 96 kJ/mol to 63.68 kJ/mol, thus lowering the recrystallization barrier to accelerate its process. The proposed pulsed electric current can rapidly reverse the crystal structure of amorphous second phase particles at lower temperatures, which provides a novel idea for adjusting the microstructure of metal materials.

Impurity iron separation from molten secondary aluminum by pulsed electric current

Secondary aluminum has received extensive attention due to its low energy consumption, low emissions, and good recyclability; however, the high impurity iron content in secondary aluminum limits its development. Traditional iron removal methods generally have the problems of high cost and low efficiency. Therefore, exploring an efficient, economical, and environmentally friendly iron removal method is of great significance for achieving sustainable development and adhering to a circular economy. The effect of pulsed electric current on the distribution of impurity element iron in secondary aluminum melt was investigated. Compared to the non-pulsed sample, iron impurity accumulates near the cathode and at the bottom in the pulsed sample, while the content in the middle region is greatly reduced, that is, the impurity iron in the secondary aluminum melt is effectively driven and separated. Based on the difference in the effective charge number between Al and Fe, the iron atoms are forced to diffuse and move directionally toward the cathode under the action of electromigration, resulting in a gradual increase in the concentration of iron atoms near the cathode. According to the Al-Fe phase diagram, the increase of iron content makes the solidification point of the alloy to the right, and the solidification temperature of the alloy increases. In other words, at the same temperature, the Fe-rich phase is preferentially precipitated near the cathode. Due to the different electrical conductivity from the matrix, the Fe-rich phase migrates to the bottom of the melt driven by electrical free energy.

Effect of pulsating solidification on the surface properties of conductive materials.

Application of pulsed electric current to solidifying conductive materials leads to a rapid and significant reduction of surface roughness. This is validated experimentally in the present work for multi-component oxides. The surface geometry of the casts without and with pulsating treatment was measured using a Leica DCM-3D Profiler. The pulsating treatment reduces the roughness of solidified materials by more than 50%. The unmeasurable points, which account for nearly 2% of total area, were interpolated using an artificial multi-layer neural network. Both the experimentally measured and neural network interpolated surface profile data were implemented to the calculation of electric current free energy. The results show that the electric current free energy can overtake surface energy and provide a significant driving force to the kinetics of surface evolution in solidification. Distortion of the electric field is noticed around the interface.

Eliminating reversible hydrogen embrittlement in high-strength martensitic steel by an electric current pulse

Hydrogen embrittlement has been a great issue in ultrahigh-strength automotive steel applications. Few studies on solving hydrogen embrittlement have been conducted in terms of removing hydrogen, and most studies focus on improving the resistance to hydrogen embrittlement through microalloying. In this study, an electric pulse was used to solve hydrogen embrittlement by removing hydrogen at 120 Hz (frequency), 180 μs (duration), and 200 A (current intensity). The temperature of the samples reached 105 °C under these parameters. Compared with the samples heat treated at the same temperature, the precharged samples processed by electric pulses had a lower hydrogen content and less ductility loss. Moreover, electric pulse processing can also reduce the approximate equilibrium concentration of hydrogen compared with heat treatment. This is due to the introduction of electrical free energy, which reduces the barrier to hydrogen diffusion, and pulsed electric current also accelerates the hydrogen diffusion.

Correlation of ferrite-phase reconfiguration and mechanical properties in thermally aged duplex stainless steel

The thermal aging behavior and subsequent recovery treatment of duplex stainless steel are investigated by mechanical properties testing and microstructure characterization. After thermal aging at 475 °C for 500 h, the ferrite phase undergoes severe spinodal decomposition and precipitation, which results in a significant increase in yield strength, and a substantial reduction in ductility. Combining the nano-indentation, geometric phase analysis, and tensile testing, it can be confirmed that spinodal decomposition is the main contributor to the hardening of the ferrite phase. The hardening of the ferrite phase is induced by the semi-coherent interface between α´-phase and α-phase and higher shear modulus of Cr-enriched domains. The increased yield stress calculated by the simplified equation is in good agreement with the experimental value. When the aged samples were treated by high-temperature annealing and pulsed electric field, the hardening is significantly eliminated, and the ductility is correspondingly restored. Further, the essence of the difference in required temperature to restore deteriorated performance is the change of system free energy caused by temperature and pulsed electric field. • The ferrite phase undergoes severe decomposition after aging at 475 °C for 500 h. • Ferrite hardening is mainly caused by spinodal decomposition. • Pulsed electric field and annealing can restore the deteriorated performance. • Electric free energy decreases the required temperature for restoring performance.

Morphological instability of the G-phase induced a different contribution to hardening of ferrite phase in a duplex stainless steel

G-phase plays an indispensable role in the hardening of ferrite during thermal aging process of the duplex stainless steel. Although there are many studies on quantifying the contribution of spinodal decomposition and G-phase precipitation to the hardening of ferrite, details regarding the influence of G-phase morphology transformation on hardening are lacking. These knowledge gaps hinder a deep understanding of the correlation between G-phase and ferrite hardening, and hence hinder the exploration of new techniques for repairing performance degradation. In this study, after aging at 400 °C and 475 °C, driven by the minimization of interfacial energy, the morphology of G-phase changes from sphere to cube, and consequently the contribution of G-phase to hardening increases significantly. After annealing at 550 °C, the G-phase does not dissolve, but coarsens, resulting in a further increase in the contribution to hardening. The difference from annealing is that after pulsed electric field treatment at 460 °C, the unstable spherical G-phase precipitates are almost completely dissolved, while the stable cubic G-phase is spheroidized. The behaviors of dissolution and spheroidization are driven by the intervention of the electric free energy, and as a result, the hardening caused by G-phase is eliminated or relieved due to the dissolution and refinement of G-phase. It is conceivable that this work is a decisive step to completely repair the deteriorated performance of duplex stainless steel after long-term operation.

Electric Current Aligning Component Units during Graphene Fiber Joule Heating

AbstractJoule heating is featured with an extremely high rising rate of temperature with hundreds of kelvin per second, which has shown superiorities of high efficiency and energy conservation in graphene fabrication. Herein, we design a dynamic joule heating system for continuous synthesis of graphene fibers with ultrashort high‐temperature (≈2000 °C), treating time (≈20 min), and low electric energy consumption (≈2000 kJ m−1). During the joule heating fabrication, the current flowing through the fibers can manipulate the configuration of graphene sheets, the basic component units of fiber, and induce their alignment. Theoretical simulations reveal that graphene sheets tend to rotate towards the current direction under the current induced electric field for the highest stability with the lowest electric free energy and zero rotation torque. Therefore, the electrical and mechanical performances of as‐fabricated graphene fibers can be further improved in comparison with thermally annealed graphene fibers without applying current.

Suppression of the surface roughness and fluctuation frequency by electric method

The descriptions of materials surface geometry by noise theory and metrological method have been compared. An equation to reproduce the roughness and fluctuation frequency is suggested to model the surface. Numerical calculation shows that the surface area is dependent not only on the roughness but also the fluctuation behaviour. Using Boltzmann distribution to describe the forming possibility of various surface geometries enables to link possibility to system free energy. Through the numerical calculation of electric free energy, it is fount that electric field possess a significant retardation effect to the amplitude and frequency of surface fluctuation. The critical value of electric potential gradient to generate an electric effect to be comparable to surface energy is typically around 1 V/cm, which is achievable in engineering practise. Further calculation shows that the critical values for various liquid iron surfaces are between 2.27 and 4.10 V/cm and that for liquid aluminium are between 0.26 and 0.47 V/cm. The reduced surface fluctuation curvature and surface area contribute to lubrication, corrosion resistance, crack initiation and wear resistance of materials.

Quantization effects in semiconductor nanostructures and singlet fission in molecular chromophores for photovoltaics and solar fuels

Hot carriers in semiconductors are electrons and/or holes that have energies greater than carriers that reside at the top and bottom of the conduction and valence bands, respectively; the latter carriers are in equilibrium with the lattice and have a temperature equal to the lattice (ambient) temperature. Hot carriers are created in semiconductors upon the absorption of photons with energies greater than the bandgap. The excess energy above the bandgap energy is in the form of kinetic energy. The hot carriers can cool to the lattice temperature via electron–phonon scattering and establish separate Boltzmann distributions for electrons and holes at the band edges. Thus, upon cooling, the excess kinetic energy of the hot carriers is transformed into heat and is unavailable to be converted into electrical or chemical free energy in a solar photon-converting cell. This hot-carrier cooling process significantly limits the maximum possible power conversion efficiency (PCE) of the free energy of solar photons into electrical free energy or chemical free energy in chemical bonds of fuels. However, if hot-carrier cooling can be slowed such that the hot carriers can be extracted before cooling to create higher photovoltages, or utilized to create additional electron-hole pairs through carrier multiplication, then beneficial use can be made of the excess energy of hot carriers and the maximum thermodynamic PCE can be dramatically increased. Quantization effects in semiconductor nanostructures, unique properties of some bulk semiconductors, and exciton multiplication in both semiconductors and molecular chromophores that undergo singlet fission have shown a path forward for potential dramatic increases in the PCEs of solar photons into electricity and solar fuels. The status, history, and future promise of the science and technology of these future approaches for different types of photovoltaic cells and cells for solar fuels will be discussed.

Breaking thermodynamic and kinetic barriers in superalloy homogenization process by electropulsing to improve mechanical properties

During the solidification of superalloy, dendrite segregation will be inevitably formed, causing uneven structure and performance. Segregation elimination and atomic diffusion in the alloy need to overcome kinetic and thermodynamic limitations. However, traditional thermal homogenization has disadvantages such as high energy consumption and low efficiency. Moreover, the coarse grains after the traditional treatment deteriorate the workability. Here it was found that the limitations of the thermal homogenization process can be broken through electropulsing. The electrical free energy can change the thermodynamic state of the system, reducing the dissolution temperature of η phases precipitated in the interdendritic space to a lower one of 1100 °C. Meanwhile, electromigration increases the atomic diffusion rate and significantly shortens the processing time. The time decrease effectively prevents the grain growth, which will further improve the workability of the ingot. Compared with the thermal homogenization process, the sample treated by pulsed electric current has better plasticity.

Effect of High Density Current Pulses on Microstructure and Mechanical Properties of Dual-Phase Wrought Superalloy

In this study, high density electric current pulse (ECP) treatment was introduced instead of the conventional solution treatment, and the γ′ phase was completely dissolved under the ECP treatment within only several milliseconds at 1148 °C. Due to the extremely short treatment time and high cooling rate, the growth of γ-phase matrix grain and γ′ phase precipitate was effectively retarded. By comparing with the conventional heat process, the grain size of ECP treated sample was controlled to about 15 μm, the size of the re-precipitated γ′ phase reduced from 65 to 35 nm, and the number density of γ′ precipitate increased from 1.46 × 108 to 3.03 × 108/mm2. The Vickers hardness, ultimate tensile strength and yield strength of the ECP treated sample were significantly improved. According to the theoretical derivation of kinetics, the ECP treatment introduces an extra electrical free energy which promoted the dissolution of γ′ phase. The ECP treatment may provide a new method for solution treatment of the Ni-based superalloy.

The Genetic Algorithm: Using Biology to Compute Liquid Crystal Director Configurations

The genetic algorithm is an optimization routine for finding the solution to a problem that requires a function to be minimized. It accomplishes this by creating a population of solutions and then producing “offspring” solutions from this population by combining two “parental” solutions in much the way that the DNA of biological parents is combined in the DNA of offspring. Strengths of the algorithm include that it is simple to implement, no trial solution is required, and the results are fairly accurate. Weaknesses include its slow computational speed and its tendency to find a local minimum that does not represent the global minimum of the function. By minimizing the elastic, surface, and electric free energies, the genetic algorithm is used to compute the liquid crystal director configuration for a wide range of situations, including one- and two-dimensional problems with various forms of boundary conditions, with and without an applied electric field. When appropriate, comparisons are made with the exact solutions. Ways to increase the performance of the algorithm as well as how to avoid various pitfalls are discussed.

Bidirectional rotation control of a carbon fiber in nematic liquid crystal using AC electric field

Colloidal particles dispersed in nematic liquid crystals are aligned along the orientation that minimizes the elastic free energy. Through applying an electric field to a nematic colloidal system, the orientation of the director can change. Consequently, colloidal particles realign to minimize the total free energy, which is the sum of the elastic and electric free energies. Herein, we demonstrate that if the preferred rotation directions given by the electric and elastic free energies are different during realignment, the rotation direction of the particle can be controlled by how we apply the electric field. When the strength of the electric field gradually increases, the particles rotate in the same direction as the rotation of the director. However, when a sufficiently high electric field is suddenly applied, the particles rotate in the opposite direction. In this study, we analyzed the effect of free energy on the bidirectional rotation behavior of the particles using a theoretical model. This study provides an effective approach to control the rotational behavior of colloidal particles over a wide-angle range between two orientational local minima.

Removing hydrogen in solid metal using electric current pulse

Hydrogen in solid metals can cause accidental fracture of engineering alloys in service, and thus has become an important issue in industrial applications, such as power generation, hydrogen storage, petroleum transport and hydrocarbon extraction. Through experiments, it was found that the elimination rate of hydrogen atoms in high strength alloy was greatly accelerated, and the equilibrium hydrogen content in the samples was decreased to a quite low level. The electric current provided an additional free energy term for the alloy system based on the current density distribution. The electrical free energy tends to reduce the electrical resistance of the system. Meanwhile, hydrogen atoms in lattice and traps caused the local electrical conductivity changes, thereby changing the current distribution and bringing the free energy of the alloy system to a new state. In this case, the diffusion activation energy and the height of energy barrier for hydrogen trapping sites were decreased. As a result, the diffusion coefficient became larger and the irreversible hydrogen were decreased, so the content of diffusible hydrogen was increased, and the hydrogen removal was accelerated. In principle, the proposed treatment helps to remove hydrogen from solid metal to a rather low level to avoid further hydrogen-induced damages, and should work for majority of alloys especially the high strength alloys.

Electric Current Field‐Assisted Inclusions Capture by Bubbles in Molten Steel

Electric current is used to assist bubbles in removing inclusions from molten steel. Generally, large‐size bubbles do not effectively remove inclusions but instead convectively agitate the molten steel. The results show that the number of inclusions in the sample is reduced by 45% after the large‐size bubbles are coupled with the pulsed current, whereas the amount of inclusions in the sample treated only with large‐size bubbles does not change much. Numerical calculation reveals that electric current induces a force acting on the inclusion as the inclusion is close to a bubble. According to the nature of the force, there are three different effects, i.e., repulsion, attraction, and driven. The electric free energy change is calculated as well when an inclusion is captured by a bubble. Electric current causes a longer contact time and a shorter induction time between inclusions and bubbles, thus improving the collision and attachment probability and decreasing the detachment probability. As a result, inclusions are more easily captured by bubbles.

Breaking the Orientation Pinning Limit Using an External Field

Recrystallized texture formed by preferential grain growth limits grain growth owing to orientation pinning. Thus, it is impossible to achieve both increased grain size and texture strength during initial recrystallization by using only heat treatment. Here we focus on the preparation of materials with coarse grains and strong texture. Orientation pinning can be broken by imparting extra electric free energy, thus accelerating diffusion in the grain boundaries.

Numerical Studies on Electrical Interaction Forces and Free Energy between Colloidal Plates of Finite Size.

By solving the nonlinear Poisson-Boltzmann (PB) equation with a finite element method (FEM), three-dimensional (3D) spatial distributions of the electric potential (ψ, scaled) in electrolyte solutions having two charged parallel finite plates (including cubes and prismatic rods) are determined for various separations (d, scaled by the Debye length, κ-1), surface potentials (ψs), and plate dimensions (length × width × thickness, each scaled by κ-1). The total interaction force between two plates, F, is the sum of the electrostatic double-layer (EDL) repulsion (the osmotic pressure, Fosm) and the Maxwell electrostatic stress (Fes). The EDL repulsion is estimated using the distribution of ψ not only between the facing surfaces of two parallel plates but also around the other extremities of the plates. The Maxwell stress (Fes) is localized near the extremities to act as a repulsive force on the midplane between the two plates. The ratio Fes/F is 0.07-0.5, depending on d, ψs, and dimensions. It is found that, with increasing dimensions, the total F values per unit area calculated for finite plates, F̃, decreasingly approach the exact ones for parallel infinite plates, F̃inf; for example, at d = 1 and ψs = 5, the ratio F̃/F̃inf is 2.83 for plates with dimensions of 1 × 1 × 1 and 1.18 for plates of 10 × 10 × 1. The repulsions arising from the extremities cannot be neglected for plates with dimensions <10 × 10 × 1. Furthermore, the total interaction forces (F) are calculated at a series of discrete d values, respectively, for parallel plates. We introduce a force fitting function, Ff(d), with parameters that can be determined so that Ff(d) fits well to the calculated serial F values. By integrating the Ff(d), we obtain the interaction free energy, G(d), for finite parallel plates that consists of two Γ functions.