Phase Diffusion Process Research Articles

An Analysis of Capacitive Contributions of the Cell Impedance during High-Temperature CO2 and Co-Electrolysis

High-temperature electrolysis is often studied by electrochemical impedance spectroscopy (EIS). The EIS spectra are analyzed using equivalent circuit models (ECM). In many cases, these models use basic elements such as resistor, capacitances or inductances. The discussion of the modelling results is often limited to resistances [e.g. 1-4]. Only some rare papers discuss capacitances as well [e.g. 5-7]. A detailed analysis of all capacitive contributions of the overall cell impedance in electrolysis mode in dependence on temperature, current and composition is missing in literature.The present study provides this detailed analysis of the capacitive contributions, which in the models are usually represented by constant phase elements (CPEs). Impedance spectroscopy measurements of high-temperature CO2 and co-electrolysis on conventional fuel electrode supported cells were performed. The cells consisted of a Ni/YSZ fuel electrode, a YSZ electrolyte, a GDC barrier layer and a (La,Sr)CoO3 air electrode. The spectra were analyzed by an ECM consisting of an inductance, a serial resistance and four RQ elements (resistance and constant phase element in parallel). The dependences of the resistances on operating conditions were already reported elsewhere [1,8].The variation of the parameters temperature, current and composition showed different trends for the single elements. For example, the capacitive contribution of processes 1 – 3 (high to middle frequency range) increases with temperature while it decreases for process 4 (low frequency range). The low frequency process had been assigned to a gas phase diffusion process according to the dependence of the corresponding resistance [1]. The CPE element of process 4 also shows a prominent dependence on the current density. This might correlate with the changing ratio of CO2 to CO in the gas phase and thus support the assignment. Further results of the dependencies of the elements will be presented and discussed.[1] S. Foit, L. Dittrich, T. Duyster, I. Vinke, R.-A. Eichel, L.G.J. de Haart, Processes 2020, 8, 1390.[2] S.E. Wolf, L. Dittrich, M. Nohl, T. Duyster, I.C. Vinke, R.-A. Eichel, L.G.J. de Haart, J. Electrochem. Soc. 2022, 169, 034531.[3] S.D. Ebbesen, X. Sun, M. B. Mogensen, Faraday Discuss. 2015, 182, 393–422.[4] A. Leonide, V. Sonn, A. Weber, E. Ivers-Tiffée, J. Electrochem. Soc. 2008, 155, B36.[5] S. Primdahl, M. Mogensen, J. Electrochem. Soc. 1997, 144, 3409.[6] E.-C. Shin, J. Ma, P.-A. Ahn, H.-H. Seo, D. T. Nguyen, J. S. Lee, Electrochim. Acta 2016, 188, 240-253.[7] X. Ge, C. Fu, S. H. Chan, Phys. Chem. Chem. Phys. 2011, 13, 15134-15142.[8] L. Dittrich, Tailoring of the Synthesis Gas Composition during High-Temperature Co-Electrolysis (Aachen, Germany) (2021).

A self-correction single particle model of lithium-ion battery based on multi-population genetic algorithm

At present, the Single Particle (SP) model and the Extended Single Particle (ESP) model become a serious concern because they have real usage potentials for the battery management system. However, utilization of the models relies too much on accurate model parameters. Measuring accurately the parameters is a tough task, since they change with the battery condition during the actual use. In this study, Multi-Population Genetic Algorithm (MPGA), a certain kind of GA's improved algorithm, has been adopted to propose a Self-Correction Single Particle Model (SC-SPM). The SC-SPM can self-correct the measured values by sensing the terminal voltage change, which gives more accurate results for the solid phase diffusion process. To verify the proposed SC-SPM, four groups of simulations are performed, indicating that the SC-SPM is more accurate at observing the solid phase diffusion process when the battery condition changes beyond a certain range, and helping BMS better estimating other battery states. At the same time, the single step calculation time is <0.5 s which can meet the requirement of on-line application.

Volatilization kinetics and thermodynamic stability of antimony sulfide under vacuum conditions

Antimony sulfide can be produced by vacuum distillation of lead antimony sulfide ore. In this paper, the volatilization kinetics of antimony sulfide under vacuum conditions was studied for the first time using a self-made vacuum furnace, and the stability of antimony sulfide was explained through thermodynamic calculations. The results show that under a system pressure of 20 Pa and a temperature range of 873 K–1073 K, the apparent volatilization activation energy of antimony sulfide is 57.6 kJ/mol, and the volatilization control step of antimony sulfide is a gas phase diffusion process. As the temperature increases from 873 K to 1073 K, the volatilization rate of antimony sulfide increases from 0.20 g cm−2 min−1 to 0.88 g cm−2 min−1 by 4.4 times. As the system pressure increases from 20 Pa to 100 Pa, the volatilization rate of antimony sulfide decreases rapidly, decreasing by nearly 11.4 times. Antimony sulfide will not decompose within the range of system pressure above 20 Pa and temperature below 1073 K.

Engineering structure constructed CoP anode with enhanced bulk phase diffusion ability for superior potassium-ion storage

Due to its considerable theoretical capacity and high availability through conversion reaction, CoP is regarded as a promising candidate for potassium-ion batteries (PIBs). However, huge volume change and low intrinsic conductivity seriously impede the further development of CoP anode in PIBs. Generally, structural design and composition regulation can well improve potassium storage performance of CoP via increasing capacitive contribution rate, but are unfavorable for realizing a high energy density in a K-full cell. Therefore, how to optimize the bulk phase diffusion ability of CoP to enhance the diffusion-dominated potassium storage is of great importance. Herein, CoP nanoparticles (about 20–40 nm) with enormous voids embedded in carbon-cage structure encapsulated in N-doped amorphous carbon are reported (CoP/C@NC-PDA), in which CoP particles with appropriate nano-size benefit the bulk phase diffusion process. Besides, the existence of amorphous carbon coating layer and voids can provide sufficient space to buffer volume expansion, while carbon-cage architecture and its high graphitization degree accelerate fast ions/electrons transfer, respectively. As a result, CoP/C@NC-PDA achieves an excellent diffusion-controlled capacity ratio (77.5% at 0.05 A g−1, 75.0% at 1.0 A g−1), and a good cycle lifespan over 1000 cycles with nearly 100% Coulombic efficiency.

Thermal diffusion behavior of Fe/Cu/Ni multilayer coatings: a molecular dynamics study

In this paper, the thermal diffusion behavior of Fe/Cu/Ni multilayer coatings was investigated by molecular dynamics. The results show that the Fe, Cu, and Ni elements can diffuse each other at 1250 K. Meanwhile, the intrinsic diffusion coefficients and interdiffusion coefficients of the Fe, Cu, and Ni were calculated. Besides, the diffusion mechanism for high melting-point elements of Fe and Ni at 1250 K was analyzed in the paper. According to the simulation result, the Fe and Ni lattices were disturbed by the active Cu particles. Fe and Ni particles at higher energies may move out of their original positions and migrate into the Cu lattice randomly. Thus, the Fe and Ni elements were involved in the thermal diffusion. This can be confirmed by the decrease of the peak and the disappearance of the secondary peak in the radial distribution function curves. However, the position of the curve peaks did not change. Thus, the lattice structure was still maintained during the whole diffusion process. The thermal diffusion of the three elements was carried out by particle substitution at the lattice positions. It was a solid phase diffusion process. Furthermore, there was a clear particle diffusion asymmetry at the original interface of the element. It was consistent with the diffusion asymmetry of diffusion-couple experiments. The primary reason for this diffusion asymmetry was the difference in the interaction potential of the three elements. This asymmetry was ultimately reflected in the intrinsic diffusion coefficient and the interdiffusion coefficient of each element. For the Fe–Cu–Ni ternary system, the largest diffusion coefficient was copper and the smallest was iron at 1250 K.

Growth of self-aligned nonlayered TaC nanosheets on liquid copper by a solid phase diffusion strategy

Compared with layered 2D materials, nonlayered 2D materials combine atomic thickness and high-activity surface, leading to many unique properties. Herein, a solid phase diffusion strategy is raised to obtain self-aligned nonlayered TaC single crystals on liquid copper. Because of the immiscibility of Cu and Ta, a β-Ta nanolayer with a thickness of ∼7 nm would form on the surface of liquid copper by a long-time solid phase diffusion process. After introducing CH4, the β-Ta nanolayer could be converted into 10 μm TaC single crystals with a thickness of 10 nm. With the extension of the reaction time, TaC single crystals would form an ordered self-aligned state spontaneously under the action of lateral capillary force. Finally, the self-aligned TaC nanosheets are assembled into large-size TaC films with a thickness of 10 nm. This strategy paves a new way to grow large-size nonlayered 2D transition metal carbides.

Experimental investigation on a floating multi-effect solar still with rising seawater film

In this paper, a floating multi-effect solar still using parabolic concentrators to directly heat rising seawater film is investigated. The novel desalination device integrates solar still and two concentrators as a whole, which avoids the installation of a heat exchange pipeline and can float on the ocean to produce freshwater. The floating still consists of a front parabolic concentrator, a rear parabolic concentrator, and several embedded distillation cells. The distillation cell is composed of a hydrophilic wick, a condensing plate, and a narrow space in between. The parabolic concentrator greatly increases the solar heat to improve the temperature gradient and enhance the phase transition and diffusion process of water vapor. During desalination, the rising seawater film for evaporation is formed in the hydrophilic wick by capillary force. Through indoor steady-state experiments, some key parameters such as solar irradiance and incident angle on the temperature, water yield and gain output ratio (GOR) of the still were studied. Results indicate that the maximum temperature gradient in the 5-effect still can reach 48.5 °C. Under a 900 W/m2 irradiation, the water productivity and GOR are 2.7 kg/m2/h and 2.2, respectively. Additionally, outdoor experiments show that the daily freshwater reaches 4.7 kg/m2 with an average irradiation of 543 W/m2.

Tuning the distribution of Tb in Nd-Fe-B sintered magnet to overcome the magnetic properties trade-off

A trade-off between the coercivity and other magnetic properties (remanence and maximum energy product) is a dilemma in current grain boundary diffusion (GBD) Nd-Fe-B sintered magnets. Here we report a new solid-liquid phase separation diffusion method for Nd-Fe-B magnets, which substantially and comprehensively enhances permanent magnetic performance, especially demagnetization curve squareness. The results show Tb diffused preferentially into the inside of magnets through the molten Nd-rich grain boundary phase during the liquid phase diffusion process. Then, uniform core-shell structures were formed during the subsequent solid phase diffusion process. This new GBD strategy increases the diffusion depth and avoids the evident Tb gradient that cause the deterioration of the magnetic performance of current GBD magnets. The microstructure and magnetic domain evolution in the Nd-Fe-B magnets diffused with both current and newly-developed techniques were also compared and investigated.

Fabrication of porous forsterite-spinel-periclase ceramics by transient liquid phase diffusion process for high-temperature thermal isolation

Porous forsterite-spinel-periclase ceramics with low thermal conductivity were synthesized via a transient liquid phase diffusion process by using pre-synthesized pellets and fused magnesia powder. The effects of sintering temperature on the pore formation, phase composition, sintering behavior, and properties of the resulting porous ceramics were investigated. The pre-synthesized pellets had a porous structure and contained a large amount of cordierite and enstatite. During the sintering progress, the pellets were converted into a transient liquid phase, which diffused into the solid MgO matrix. The liquid phase diffusion reaction promoted forsterite and spinel formation, which resulted in the in-situ formation of large pores. At elevated temperatures, the liquid phase disappeared and a large number of well-developed grains were simultaneously precipitated from the liquid phase. Porous ceramics with thermal conductivities of 0.42–0.48 W/(m·K) and refractoriness under load values of 1588 °C and 1624 °C were obtained after sintering at 1600 °C for 3 h.

Investigation of Morphology of Aluminum Co-Doped Scandium Stabilized Zirconia (ScAlSZ) Thin Films

The morphology of aluminum co-doped scandium stabilized zirconia (ScAlSZ) thin films formed by e-beam deposition system was investigated experimentally and theoretically. The dependencies of surface roughness, and the films’ structure on deposition temperature and deposition rate were analyzed. It was shown experimentally that the dependence of the surface roughness on deposition temperature and deposition rate was not monotonic. Those dependencies were analyzed by mathematical modeling. The mathematical model includes the processes of phase separation, adsorption and diffusion process due to the film surface curvature. The impacts of substrate temperature, growth rate on surface roughness of thin films and lateral nanoparticle sizes are shown by the modeling results. Modeling showed that the roughness of the surface of grown films became higher in most cases as the substrate’s temperature rose, but the higher deposition rate resulted in lower surface roughness in most cases. The results obtained by simulations were compared to the relevant experimental data. The non-linear relationships between surface roughness of grown films and lateral size of nanoparticles were also shown by our modeling results, which suggested that the variation in the surface roughness depending on the substrate temperature and growth rate was related to the lateral size of nanoparticles.

Numerical Simulation of Leakage and Diffusion Process of LNG Storage Tanks

To investigate the evolution process of LNG (Liquefied Natural Gas) liquid pool and gas cloud diffusion, the Realizable k-ε model and Eluerian model were used to numerically simulate the liquid phase leakage and diffusion process of LNG storage tanks. The experimental results showed that some LNG flashed and vaporized rapidly to form a combustible cloud during the continuous leakage. The diffusion of the explosive cloud was divided into heavy gas accumulation, entrainment heat transfer, and light gas drift. The vapor cloud gradually separated into two parts from the whole “fan leaf shape”. One part was a heavy gas cloud; the other part was a light gas cloud that spread with the wind in the downwind direction. The change of leakage aperture had a greater impact on the whole spill and dispersion process of the storage tank. The increasing leakage aperture would lead to 10.3 times increase in liquid pool area, 78.5% increase in downwind dispersion of methane concentration at 0.5 LFL, 22.6% increase in crosswind dispersion of methane concentration at 0.5 LFL, and 249% increase in flammable vapor cloud volume. Within the variation range of the leakage aperture, the trend of the gas cloud diffusion remained consistent, but the time for the liquid pool to keep stable and the gas cloud to enter the next diffusion stage was delayed. The low-pressure cavity area within 200 m of the leeward surface of the storage tank would accumulate heavy gas for a long time, forming a local high concentration area, which should be an area of focus for alert prediction.

Mechanical oscillator thermometry in the nonlinear optomechanical regime

Optomechanical systems are promising platforms for controlled light-matter interactions. They are capable of providing several fundamental and practical novel features when the mechanical oscillator is cooled down to nearly reach its ground state. In this framework, measuring the effective temperature of the oscillator is perhaps the most relevant step in the characterization of those systems. In conventional schemes, the cavity is driven strongly, and the overall system is well-described by a linear (Gaussian preserving) Hamiltonian. Here, we depart from this regime by considering an undriven optomechanical system via non-Gaussian radiation-pressure interaction. To measure the temperature of the mechanical oscillator, initially in a thermal state, we use light as a probe to coherently interact with it and create an entangled state. We show that the optical probe gets a nonlinear phase, resulting from the non-Gaussian interaction, and undergoes an incoherent phase diffusion process. To efficiently infer the temperature from the entangled light-matter state, we propose using a nonlinear Kerr medium before a homodyne detector. Remarkably, placing the Kerr medium enhances the precision to nearly saturate the ultimate quantum bound given by the quantum Fisher information. Furthermore, it also simplifies the thermometry procedure as it makes the choice of the homodyne local phase independent of the temperature, which avoids the need for adaptive sensing protocols.

Parametric study of the phase diffusion process in a gain-switched semiconductor laser for randomness assessment in quantum random number generator

The quantum phase noise in a pulsed semiconductor laser is studied thoroughly in the context of its utilization as a quantum entropy source in a quantum random number generator (QRNG) device. We performed a numerical analysis of the phase diffusion process for a semiconductor laser in the continuous-wave operation mode and gain-switched (GS) mode. The result demonstrates the amplification of randomness in the GS mode, which is gauged physically by the variance VarΔϕ. The variance value, which is mathematically related to the temporal distance between the laser pulses used in the experimental setup, also determines the stability of the setup. Furthermore, we show how the QRNG probability distribution is influenced by several experimental factors such as the quality of the interference process and the noise in the detection system.

Physics-based fractional-order model with simplified solid phase diffusion of lithium-ion battery

Abstract Solid phase diffusion plays an important role in the long-term performances of lithium-ion batteries. Current mechanistic model for describing the solid phase diffusion has low computational efficiency and obscure physical meanings. A simple but effective physics-based solid phase diffusion model is of great significance for the impedance characterization and aging diagnosis of lithium-ion batteries. In this paper, a physics-based fractional-order model is established by simplifying the solid phase diffusion process through Pade approximation. A full-cell fractional-order model is constructed by combining the medium-high frequency dynamic model. The proposed model has a clear physical meaning and can be used to characterize full-cell performances. Furthermore, this paper provides solutions to identifying the parameters of the full-cell fractional-order model by decoupling the dynamics in frequency and spatial domain. The established full-cell fractional-order model is validated under various working loads. The results show that the proposed physics-based fractional-order model with simplified solid phase diffusion improves the computational efficiency with little loss of accuracy, indicating that the proposed model is an appropriate candidate for online applications.

Numerical Simulation of Propellant Diffusion Considering Chemical Reaction

Gas phase diffusion process of UDMH and NTO in confined space was investigated and the mechanism of the reaction between the propellants was analyzed in order to study the diffusion process considering chemical reaction between propellants based on numerical simulation. According to the results of numerical simulation, the propellant concentration distribution, resultant of reaction distribution, as well as temperature distribution was obtained. Results showed that the leakage diffusion process can be divided into three stages: heavy gas deposition stage, rapid reaction stage and equilibrium diffusion stage. In the heavy gas deposition stage, propellants are mainly affected by gravity. During the rapid reaction stage, the chemical reaction between propellants plays a certain role in the diffusion process. In the equilibrium diffusion stage, the bottom temperature of the confined space increased significantly, the highest temperature reached 306K.

A novel and green preparation of porous forsterite ceramics with excellent thermal isolation properties

This work provides a novel and green approach to preparing porous forsterite ceramics by a transient liquid phase diffusion process based on fused magnesia and quartz powders without detrimental additives. The size of quartz particles markedly affected the sintering behaviors, phase composition, microstructure and properties of the porous forsterite ceramics. Fine quartz particles (D50, 3.87 µm) accelerated the rate of the forsterite formation at elevated temperatures and promoted solid-state sintering behavior of the porous ceramics. Conversely, coarse quartz particles (D50, 25.38 µm) reduced the rate of the solid state reaction and a large amount of unreacted SiO2 and enstatite (MgSiO3) phases transformed into a transient liquid-phase during the firing process. This effect resulted in a high porosity (approximately 58.89%) and formation of many large pores (mean pore size of 42.36 µm). These features contributed to the excellent thermal isolation properties of the prepared porous forsterite ceramics. The strength of the obtained porous ceramics (about 23.6 MPa) is relatively high compared with those of conventional ceramics.

Transient liquid phase diffusion process for porous mullite ceramics with excellent mechanical properties

Porous mullite ceramics were fabricated by the transient liquid phase diffusion process, using quartz and fly-ash floating bead (FABA) particles and corundum fines as starting materials. The effects of sintering temperatures on the evolution of phase composition and microstructure, linear shrinkage, porosity and compressive strength of ceramics were investigated. It is found that a large amount of quartz and FABA particles can be transformed into SiO2-rich liquid phase during the sintering process, and the liquid phase is transient in the Al2O3-SiO2 system, which can accelerate the mullitization rate and promote the growth of mullite grains. A large number of closed pores in the mullite ceramics are formed due to the transient liquid phase diffusion at elevated temperatures. The porous mullite ceramics with high closed porosity (about 30%) and excellent compressive strength (maximum 105 MPa) have been obtained after fried at 1700 °C.

Nonlinear frequency transduction of nanomechanical Brownian motion

We report on experiments addressing the non-linear interaction between a nano-mechanical mode and position fluctuations. The Duffing non-linearity transduces the Brownian motion of the mode, and of other non-linearly coupled ones, into frequency noise. This mechanism, ubiquitous to all weakly-nonlinear resonators thermalized to a bath, results in a phase diffusion process altering the motion: two limit behaviors appear, analogous to motional narrowing and inhomogeneous broadening in NMR. Their crossover is found to depend non-trivially on the ratio of the frequency noise correlation time to its magnitude. Our measurements obtained over an unprecedented range covering the two limits match the theory of Y. Zhang and M. I. Dykman, Phys. Rev. B 92, 165419 (2015), with no free parameters. We finally discuss the fundamental bound on frequency resolution set by this mechanism, which is not marginal for bottom-up nanostructures.

Surface passivation of black silicon phosphorus emitters with atomic layer deposited SiO2/Al2O3 stacks

Black silicon (b-Si) is a promising surface structure for solar cells due to its low reflectance and excellent light trapping properties. While atomic layer deposited (ALD) Al2O3 has been shown to passivate efficiently lightly-doped b-Si surfaces and boron emitters, the negative fixed charge characteristic of Al2O3 thin films makes it unfavorable for the passivation of more commonly used n+ emitters. This work studies the potential of ALD SiO2/Al2O3 stacks for the passivation of b-Si phosphorus emitters fabricated by an industrially viable POCl3 gas phase diffusion process. The stacks have positive charge density (Qtot = 5.5·1011 cm-2) combined with high quality interface (Dit = 2.0·1011 cm-2eV-1) which is favorable for such heavily-doped n-type surfaces. Indeed, a clear improvement in emitter saturation current density, J0e, is achieved with the stacks compared to bare Al2O3 in both b-Si and planar emitters. However, although the positive charge density in the case of black silicon is even higher (Qtot = 2.0·1012 cm-2), the measured J0e is limited by the recombination in the emitter due to heavy doping of the nanostructures. The results thus imply that in order to obtain lower saturation current density on b-Si, careful optimization of the black silicon emitter profile is needed.

Estimation of phase diffusion rates in a condensate interferometer using the Gross–Pitaevskii equation

Atom interferometers using Bose–Einstein condensates are fundamentally limited by a phase diffusion process that arises from atomic interactions. Numerical solution of the Gross–Pitaevskii equation is here used to accurately calculate the diffusion rate for a Bragg interferometer. It is seen to agree with a Thomas–Fermi approximation at large atom numbers and a perturbative approximation at low atom numbers. Most experiments to date operate in the crossover region between these two regimes. Even in this case, it is found that that the diffusion time is governed in a simple way by the ratio of the healing length to the size of the condensate.