Phase Diffusion Research Articles

Li diffusion in plagioclase crystals and glasses – implications for timescales of geological processes

Abstract. The growing interest in Li diffusion as a tool to determine timescales of short-time magmatic events, such as magma ascent during eruption, increases the necessity to better understand Li diffusion in common mineral phases. In this context, well-constrained diffusion coefficients and understanding of kinetic processes specific to mineral phases are of crucial importance. To gain further insight especially into the kinetic processes in plagioclase, we investigated the diffusion of Li between natural An61 plagioclase crystals and synthetic glasses of An80 plagioclase composition. Experiments were conducted at 200 MPa in rapid-heat/rapid-quench cold-seal pressure vessels (RH/RQ CSPVs) and internally heated pressure vessels (IHPVs) at temperatures between 606 and 1114 °C. Concentration and isotope profiles of Li were measured using femtosecond laser ablation multicollector inductively coupled plasma mass spectrometry (fs-LA-MC-ICP-MS). We adopted a multispecies diffusion model and specified boundary conditions for plagioclase of labradoritic composition. Using this model, we were able to distinguish between an interstitial (DLii) and a vacancy process (DLiA), with the interstitial process being 0.2–1 orders of magnitude faster than the vacancy process, depending on temperature. DLii=10-3.76±0.58exp⁡-180.0±12.0kJmol-1RTm2s-1DLiA=10-5.53±0.16exp⁡-151.7±3.2kJmol-1RTm2s-1 Our data indicate charge compensation of Li by Na in both the crystal and the glass. Chemical Li diffusion coefficients in An80 glass are up to 3 orders of magnitude slower compared to Li tracer diffusion in silicate and aluminosilicate glasses and melts, which is attributed to slow Na diffusion at high An content. Our results for chemical diffusion of Li in plagioclase crystals are 1.5–2 orders of magnitude slower than Li tracer diffusion in An- and Ab-rich plagioclase determined in previous studies. This indicates that earlier studies on natural intermediate plagioclase compositions have underestimated timescales by up to 2 orders of magnitude. For accurate determination of timescales from Li diffusion in plagioclase we suggest further exploring the role of Na and a possible dependence on An content.

Oxidation Behavior of Aluminide Coatings on Cobalt-Based Superalloys by a Vapor Phase Aluminizing Process

In this work, the oxidation behavior of an aluminide coating at 900, 1000, and 1100 °C was investigated. The aluminide coating was prepared on a cobalt-based superalloy using a vapor phase aluminizing process, which is composed of a β-(Co,Ni)Al phase outer layer and a Cr-rich phase diffusion layer. The experimental results showed that the oxidation of the coating at 900–1100 °C all obey the parabolic law. The oxidation rate constants of the coating were between 2.19 × 10−7 and 47.56 × 10−7 mg2·cm−4·s−1. The coating produced metastable θ-Al2O3 at 900 °C and stable α-Al2O3 at 1000 and 1100 °C. As the oxidation temperature increases, the formation of Al2O3 is promoted, consuming large amount of Al in the coating, resulting in the transformation from β-(Co,Ni)Al phase to α-(Co,Ni,Cr) phase. And the decrease in the β phase in the coating led to the dissolution of the diffusion layer.

Pressureless synthesis and consolidation of the entropy-stabilized (Hf0.25Zr0.25Ti0.25V0.25)B2-B4C composite by ultra-fast high-temperature sintering (UHS)

Entropy-stabilized Ultra High-Temperature Ceramics (UHTC) offer a groundbreaking solution to the challenges of extreme environments, showcasing enhanced mechanical properties, thermal stability, and resistance to oxidation at high temperatures. The consolidation of UHTC by ultra-fast high-temperature sintering (UHS) significantly reduces processing times and temperature and can produce dense high-performance ceramics with superior mechanical properties. This study reports the pressureless synthesis and consolidation of the entropy-stabilized (Hf0.25Zr0.25Ti0.25V0.25)B2-B4C composite through UHS within 1minute, starting from transition metal diboride powders. B4C acts as an effective sintering aid, promoting the densification of the system and the formation of a nearly single-phase hexagonal diboride with a diboride-eutectic phase. Furthermore, a secondary minor hexagonal phase rich in V and Zr is formed close to the eutectic regions. Sintering currents of 40A were necessary to reach densities higher than 90% under pressureless conditions, achieving nano hardness higher than 27.3GPa, comparable with high-entropy diborides produced by Spark Plasma Sintering. The study highlights the entropy-stabilized phase formation, diffusion, densification, and grain mechanisms involved during UHS. The work contributes to understanding entropy-stabilized ceramics produced by UHS as a faster and less energy-consuming process than more conventional sintering methods.

Phase and thermal diffusivity variation of saline water diagnosed by visual and temperature method during freezing process

Freezing step is a fundamental physical phenomenon of cooling a liquid formulation for guaranteeing product quality. In this study, freezing process of saline water under various concentrations was monitored through the visual and temperature methods. The formation of the ice crystal nuclei at the supercooling stage, and the increase of ice and ice/water layers were observed. The formation of the ice crystal nuclei and ice layer was affected by the location of vials placed on a shelf and the concentration of saline water. A saline water solution at a higher concentration had a lower ice layer height under the same freezing settings. The location of vial on the shelf affects the stability and efficiency of thermal transmission. Moreover, the concentration of saline water has the relationship with the thermal diffusivity, and ice layer is an indicator of variation of temperature and thermal diffusivity for saline water during freezing process. This study was able to replicate and observe the physical phenomena of the formation of ice crystal nuclei and the ice layer during the freezing process under laboratory conditions; as well as show how the specific concentration of the saline water solution affected the developmental speed of the ice layer.

Fast mass transfer processes of interfering trapped CO2-clusters at reservoir conditions: Experiment and theory

The gas-to-oil ratio (GOR) of a reservoir fluid plays a critical role in optimizing oil recovery and oil production strategies, improving oil recovery efficiency, and predicting reservoir behavior. Understanding the complicated kinetics of multicomponent mass transfer at the pore scale after gas injection into petroleum reservoirs is of great importance for estimating GOR and enhanced oil recovery (EOR). However, to date, there is a significant gap in the fundamental process understanding of the complex mass transfer process at reservoir conditions. Using micro-CT technology, we investigate the time dependence of CO2 mass transfer and cluster growth after high pressure CO2 injection into sedimented porous media (sintered 0.2 mm glass beads).Surprisingly, the CO2 partitioning equilibrium is already reached after 2 h. To the best of our knowledge, such a fast CO2 transport through water-saturated porous media, which cannot be explained by linear diffusion models (time scale 100 days for a diffusion length of 10 cm), has not been reported in the literature before. We proposed a conceptual model that assumes CO2 inflation of interfering gas clusters drives cascading CO2 transport. We verified this conceptual model through a time series of experiments at different initial gas saturation, analyzing in each case the spatial cluster distribution, cluster size distribution, and pore occupancy frequency.Whether CO2 inflation of the gas clusters occurs depends on the critical initial gas saturation, which is about 10%. Our main conclusion is that CO2 migration should be considered as gas phase diffusion cascading along a quasi-percolating cluster, since CO2 inflation leads to a high gas saturation of about 26%, which is close to the percolation threshold. Our experimental results support this physical hypothesis. We show for the first time that CO2 clusters can expand over large pore spaces and thus are close to the critical percolation threshold (mobility threshold). The cluster size distribution can be described by a power distribution with the critical exponent 2.19, i.e., it shows universal scaling.We model the interfering mass transfer processes of neighboring gas clusters with a multi-sphere model. Exploring different scenarios for the dissolution kinetics of an ensemble of interfering gas clusters allow a deeper understanding of the complicated mass transfer kinetics and agree well with experimental cluster analyses at specific times.

Typology of Business Incubators in Spain According to the Stages of Startups Incubation

The aim of this work was to classify the business incubators in Spain according to the four phases of the startup’s incubation process. Considering that the graduation rate implies greater survival and business success of the incubated companies, they have been identified at each stage of the incubation (spread of entrepreneurship, pre-incubation, advanced incubation, and graduation). The activities that present higher impacts on the success of the incubated companies and the activities carried out by the business incubator that have a greater relevance on the graduation of the companies have concretely been considered. Principal component (PC) cluster analysis has been applied. All the incubation variables were used simultaneously, reducing their number and grouping them into factors. Finally, the cases were grouped according to these latent variables. Principal component analysis reduced dimensionality to eight factors with a 74% explained variance. Factor 1 was positively related to pre-incubation variables; factor 2 was linked to training and collaboration variables within the entrepreneurship diffusion phase. Factor 3, named activity monitoring and control, was related to phase 3, or basic incubation variables. Cluster analysis facilitates the grouping of business incubators into three clusters: Group 1 (16% of the total), incubators with strong deficits in incubation phases 1, 2, and 3. They are small-sized business incubators, often located in rural areas or cities, with a low graduation rate. Group 2 (30%), business incubators with a very high graduation rate and strongly positive values in factors 1 and 2. Factor 3, although positive, is susceptible to improvement. They are the largest group of business incubators and usually located in industrial and technological parks. Group 3 (54%) is the majority, with values close to clusters 2 and 3.

Influence of Electrolyte Saturation on the Performance of Li-O2 Batteries.

Electrolyte saturation can strongly affect the Li-O2 battery performance. However, it is unclear to what extent saturation reduction will impact the battery capacity. In this study, we investigated the influence of electrolyte saturation and distribution within a porous positive electrode on the deep discharge-charge capacities and cycling stability. The study used both models and experiments to investigate the change of electrolyte distribution, double-layer capacitance, ohmic resistance, and O2 concentration in the positive electrode at different electrolyte saturations. Results revealed that electrodes with 60% electrolyte saturation achieved almost the same maximum discharge (6.38 vs 6.76 mAh/cm2) and charge (5.52 vs 5.65 mAh/cm2) capacities with fully saturated electrodes. The partially wet positive electrode (40% saturation) obtained more cycles than the electrode with 100% saturation before the discharge capacity dropped below the cutoff point. However, the electrode with 40% saturation had a low average charging efficiency of 88.76%, whereas the fully saturated electrode obtained 98.96% charging efficiency. Moreover, the fully wet positive electrode had the lowest overpotential during cycling (1.26-1.39 V). The measured electrochemically active surface areas showed that even 40% saturation could sufficiently wet the positive electrode surface and obtain a double-layer capacitance (18.12 mF) similar to that with 100% saturation (20.4 mF). Furthermore, a considerable increase in O2 concentration at wetted surface areas was observed for the electrolyte saturation of less than 60% due to the significantly higher O2 diffusivity in the gas phase.

Adsorption of phenolic compounds by sodium alginate-modified starch nanoparticles in a multiphase system: kinetic, thermodynamic and release characteristics studies

Starch nanoparticles (SNPs) have been recognized as potentially efficient adsorbents for polyphenols. However, their actual adsorption in complex systems such as fruit pomace extract is significantly lower than theoretical predictions and their adsorption capacity is inferior to traditional materials such as macroporous adsorbent resins, which limits their industrial application. Aiming to enhance the adsorption of apple pomace polyphenols, this study used sodium alginate (SA) modifies SNPs to create a cornstarch-based composite system (SA-SNPs). The optimal modified addition of sodium alginate was 0.3 g (g starch)-1, under this condition, the nanoparticles obtained exhibited the smallest particle size (154.60 nm) and the best adsorption performance (33.97 mg g-1 in 90 min). The SA-SNPs reached the adsorption equilibrium at 180 min, which significantly enhanced the equilibrium adsorption amount of the polyphenols (from 2.68 to 37.02 mg g-1). The adsorption process was found to follow the pseudo-second- order kinetic model and the Langmuir isotherm model, which included membrane diffusion, intra-particle diffusion, and equilibrium phases. The adsorption amount initially increased and then continued to decrease with the increase in temperature, and the whole process was exothermic and spontaneous (ΔH° = -52.394 kJ mol-1, ΔG° < 0 kJ mol-1). Additionally, SA-SNPs loaded with polyphenols demonstrated better protection of polyphenol DPPH radical-scavenging activity during storage, enhanced stability, and optimal colon-targeted sustained-release properties in complex physiological environments. This work presents a new approach to improving the adsorption capacity of SNPs and developing high-performance natural edible separation materials.

Microscopic mechanism of water-assisted diffusional phase transitions in inorganic metal halide perovskites.

The stability of perovskite materials is profoundly influenced by the presence of moisture in the surrounding environment. While it is well-established that water triggers and accelerates the black-yellow phase transition, leading to the degradation of the photovoltaic properties of perovskites, the underlying microscopic mechanism remains elusive. In this study, we employ classical molecular dynamics simulations to examine the role of water molecules in the yellow-black phase transition in a typical inorganic metal halide perovskite, CsPbI3. We have demonstrated, through interfacial energy calculations and classical nucleation theory, that the phase transition necessitates a crystal-amorphous-crystal two-step pathway rather than the conventional crystal-crystal mechanism. Simulations for CsPbI3 nanowires show that water molecules in the air can enter the amorphous interface between the black and yellow regions. The phase transition rate markedly increases with the influx of interfacial water molecules, which enhance ion diffusivity by reducing the diffusion barrier, thereby expediting the yellow-black phase transition in CsPbI3. We propose a general mechanism through which solvent molecules can greatly facilitate phase transitions that otherwise have prohibitively high transition energies.

Desulfurization Behavior of Magnetite Pellets Reduced by Isothermal Pure Hydrogen

The desulfurization behavior of magnetite pellets reduced by pure hydrogen at isothermal temperature is studied, the mechanism of self‐oxidation desulfurization is put forward, and the thermodynamic theoretical calculation and experimental verification of this mechanism are carried out. The feasibility of the reaction between iron sulfide and Fe3O4 is analyzed by HSC Chemistry 6.0 software. Additionally, a thermal gravimetric analyzer is used to further study the thermal behavior of pellet material under Ar atmosphere from 400 to 1400 K. The results show that the removal of sulfur in the isothermal reduction process of pure hydrogen does not depend on hydrogen phase diffusion and reduction temperature. During the heating process, self‐oxidation desulfurization occurs in the system, and the self‐desulfurization reaction is more inclined to Fe3O4 + FexSy → FeS + SO2. Under the experimental conditions, the temperature range of self‐oxidation desulfurization under conventional thermal field and microwave field is 700–1100 and 370–1140 K, respectively, and the desulfurization rate is 92.9% and 95.8%, respectively. The key to improving desulfurization by microwave radiation is that iron sulfide has good wave‐absorbing characteristics.

A Multilayer Nonlinear Permutation Framework and Its Demonstration in Lightweight Image Encryption

As information systems become more widespread, data security becomes increasingly important. While traditional encryption methods provide effective protection against unauthorized access, they often struggle with multimedia data like images and videos. This necessitates specialized image encryption approaches. With the rise of mobile and Internet of Things (IoT) devices, lightweight image encryption algorithms are crucial for resource-constrained environments. These algorithms have applications in various domains, including medical imaging and surveillance systems. However, the biggest challenge of lightweight algorithms is balancing strong security with limited hardware resources. This work introduces a novel nonlinear matrix permutation approach applicable to both confusion and diffusion phases in lightweight image encryption. The proposed method utilizes three different chaotic maps in harmony, namely a 2D Zaslavsky map, 1D Chebyshev map, and 1D logistic map, to generate number sequences for permutation and diffusion. Evaluation using various metrics confirms the method’s efficiency and its potential as a robust encryption framework. The proposed scheme was tested with 14 color images in the SIPI dataset. This approach achieves high performance by processing each image in just one iteration. The developed scheme offers a significant advantage over its alternatives, with an average NPCR of 99.6122, UACI of 33.4690, and information entropy of 7.9993 for 14 test images, with an average correlation value as low as 0.0006 and a vast key space of 2800. The evaluation results demonstrated that the proposed approach is a viable and effective alternative for lightweight image encryption.

Thermally-induced diffusion and structural phase transitions in Pt/Mn and Pt/Mn/Pt thin films

We demonstrate the possibility of diffusion formation of the chemically ordered L1 0-MnPt phase through the vacuum annealing of Pt(24 nm)/Mn(20 nm) and Pt(12 nm)/Mn(20 nm)/Pt(12 nm) layered stacks at 400 °C for 30 min. For the bi-layered stack annealed at 400 °C, the effect of Pt atoms segregation at the film/substrate interface was detected, which remained after annealing even at higher temperatures (500 °C and 600 °C) and prevented the whole homogenization of the chemical composition through the film depth. By contrast, for the tri-layered stack annealed at 400 °C, the presence of the additional Pt bottom layer enabled to change the rate and mechanism of reactive diffusion, leading to homogeneous distribution of components and enhanced crystallinity of the ordered L1 0-MnPt phase compared to the bi-layered sample. An explanation of the obtained experimental data is provided based on the fundamentals of mass transfer theory and its quantitative parameters (e.g. activation energy and diffusion coefficients).

Ultrahigh thermal stability and piezoelectricity of lead-free KNN-based texture piezoceramics

The contradiction between high piezoelectricity and uniquely poor temperature stability generated by polymorphic phase boundary is a huge obstacle to high-performance (K, Na)NbO3 -based ceramics entering the application market as Pb-based substitutes. We possess the phase boundary by mimicking Pb(Zr, Ti)O3’s morphotropic phase boundary structure via the synergistic optimization of diffusion phase boundary and crystal orientation in 0.94(Na0.56K0.44)NbO3−0.03Bi0.5Na0.5ZrO3−0.03(Bi0.5K0.5)HfO3 textured ceramics. As a result, a prominent comprehensive performance is obtained, including giant d33 of 550 ± 30 pC/N and ultrahigh temperature stability (d33 change rate less than 1.2% within 25-150 °C), representing a significant breakthrough in lead-free piezoceramics, even surpassing the Pb-based piezoelectric ceramics. Within the same temperature range, the d33 change rate of the commercial Pb(Zr, Ti)O3−5 ceramics is only about 10%, and more importantly, its d33 (~ 350 pC/N) is much lower than that of the (K, Na)NbO3-based ceramics in this work. This study demonstrates a strategy for constructing the phase boundary with MPB feature, settling the problem of temperature instability in (K, Na)NbO3-based ceramics.

Non-nematicity of the filamentary phase in systems of hard minor circular arcs.

This work further investigates an aspect of the phase behavior of hard circular arcs whose phase diagram has been recently calculated by Monte Carlo numerical simulations: the non-nematicity of the filamentary phase that hard minor circular arcs form. Both second-virial density-functional theory and further Monte Carlo numerical simulations find that the positional one-particle density function undulates in the direction transverse to the axes of the filaments while further Monte Carlo numerical simulations find that the mobility of the hard minor circular arcs across the filaments occurs via a mechanism reminiscent of the mechanism of diffusion in a smectic phase: the filamentary phase is not a {"modulated" ["splay(-bend)"]} nematic phase.

Modeling phase separation in solids beyond the classical nucleation theory: Application to FeCr.

Despite a large amount of work being devoted to study the phase separation in solids, the underlying physical mechanism responsible for such diffusive first-order phase transitions remains difficult to model outside the spinodal regime, i.e., in the nucleation and growth regime. This work presents an alternative of the classical nucleation theory for modeling phase separation in this regime, even for systems far from the solubility limit, i.e., for high degree of meta-stability where the classical nucleation theory does not hold. This method then allows a direct comparison between simulations and experiments always performed in solids with a high degree of meta-stability.

Effects of different gas energy shares on combustion and emission characteristics of compression ignition engine fueled with dual-fossil fuel and dual-biofuel

This study systematically investigates the energetic and environmental performance of a four-cylinder compression ignition (CI) engine fueled by gaseous and liquid dual-fuel (D-F), utilising various combinations of fossil fuels and biofuels. Fossil diesel or pure hydrotreated vegetable oil (HVO) – new generation biodiesel was used as the pilot fuel to initiate ignition of the gaseous fuel. The gaseous fuels used were natural gas (NG) and simulated biogas (BG) composed of 60 % NG and 40 % CO2 by volume, injected into the intake manifold at varying gas energy shares (GES) of 40 %, 60 %, and 80 %. Reference values were provided from conventional combustion of diesel fuel and HVO. This study used numerical simulations to examine indicators of combustion, such as ignition delay, premixed combustion phase, diffusion combustion phase, and subsequent combustion phases, across diverse fuel combinations. Within lean dual-fuel mixtures, when the gaseous fuel remained below the flammability threshold, the peak pressure was diminished, the rate of pressure rise was lowered, and the combustion process decelerated, facilitating a faster transition to the diffusion phase. As the engine load and GES increased, the excess air ratio decreased, bringing the air-fuel mixture closer to the flammability limit, which in turn altered the combustion characteristics and engine performance trends. Combustion with increasing BG content showed partial similarities to that of NG, though the high CO2 content in biogas was found to suppress combustion, functioning similarly to an exhaust gas recirculation. The study also compared brake thermal efficiency (BTE), as well as specific emissions of CO, HC, NOX, CO2, and smoke for the D-F engine operation against pure diesel and HVO at different loads and GES levels. Additionally, an overlimit function was used to assess the emission levels of D-F engines with reference to emission limits.

Effect of T’-YSZ@Al2O3 core-shell structure on fracture toughness of YSH24 ceramics

To meet the demands of higher operating temperatures in aero-engines, yttrium oxide fully stabilized cubic (C) phase hafnium oxide (YFSH) has emerged as a promising candidate for thermal barrier coatings due to its ultra-high melting and phase transition temperatures. However, its application is constrained by its inherently low fracture toughness. To enhance the fracture toughness of C-HfO2 phase ceramic, the metastable non-equilibrium tetragonal (T’) phase of Y0.08Zr0.92O1.96 (YSZ8) was synthesized using the sol-gel method. An Al2O3 layer was then coated on YSZ, forming a T’-YSZ@Al2O3 core-shell structure (with Al2O3 comprising 20 % of the YSZ volume). The phase organization stability and diffusion resistance of this T’-YSZ@Al2O3 core-shell structure were investigated. Composite ceramic bulks, with compositions x T’-YSZ@Al2O3/(1-x) YSH24 (where x is the volume fraction, x = 0, 0.1, 0.2, 0.3, 0.4), were prepared using spark plasma sintering (SPS). The impact of the T’-YSZ@Al2O3 addition on the fracture toughness of the YSH24 matrix and the toughening mechanisms were analyzed. The results indicate that the introduction of the T’-YSZ@Al2O3 core-shell structure with good structural integrity into YSH24 ceramics prevents phase transitions. As the volume fraction of the core-shell structure increases from x = 0–0.4, the fracture toughness initially rises and then decreases, reaching a maximum of 2.36 MPa·m1/2 at x = 0.3. This value represents a 38.8 % improvement compared to that of the single C-HfO2 phase YSH24 bulks. The primary toughening mechanism is attributed to the ferroelastic domain switching of T’-YSZ within the T’-YSZ@Al2O3 core-shell structure.

A numerical framework for modeling evaporation and combustion of isolated, spherically-symmetric, multi-component fuel droplets

This paper presents a comprehensive numerical framework for simulating the evaporation and combustion of isolated, spherically-symmetric, multi-component fuel droplets. The framework incorporates a detailed description of chemical reactions in the gaseous phase and is capable of modeling pure evaporation, autoignition, and hot-wire ignition scenarios.The transport equations for mass, species, and energy are solved in both the liquid (droplet) and gaseous (surrounding atmosphere) phases. Diffusion in the liquid phase is described using the Stefan–Maxwell theory, while in the gaseous phase, both molecular and thermal diffusion are considered. The model also includes the thermophoretic effect for carbonaceous particles and accounts for gas radiation through various models, ranging from optically-thin approximations to more complex methods like the P1 and discrete ordinate methods. Non-gray radiative effects are handled using the Weighted-Sum-of-Gray-Gases Model (WSGGM). Liquid/gas interface conditions are evaluated by imposing flux continuity of mass and energy, along with thermodynamic equilibrium for species. Deviations from ideal thermodynamic behavior in the liquid droplet are managed by incorporating a suitable activity coefficient or by using a proper cubic equation of state. Additionally, the presence of supporting fibers is modeled using a simplified one-dimensional approach. The transport equations are solved using the method of lines, with spatial discretization performed via the finite difference method on a body-fitted grid. The resulting system of Differential–Algebraic Equations (DAEs) is then solved using a fully-coupled approach.Thanks to its generality in terms of kinetic and thermodynamic descriptions and the reduced computational time, the proposed framework offers significant potential for advancing our understanding of the complex combustion processes of multi-component liquid fuels and for enhancing the planning and execution of experiments involving isolated fuel droplets.

Frequency stabilization of self-sustained oscillations in a sideband-driven electromechanical resonator

We present a method to stabilize the frequency of self-sustained vibrations in micromechanical and nanomechanical resonators. The method refers to a two-mode system with the vibrations at significantly different frequencies. The signal from one mode is used to control the other mode. In the experiment, self-sustained oscillations of micromechanical modes are excited by pumping at the blue-detuned sideband of the higher-frequency mode. Phase fluctuations of the two modes show near-perfect anticorrelation. They can be compensated in either of the modes by a stepwise change of the pump phase. The phase change of the controlled mode is proportional to the pump phase change, with the proportionality constant independent of the pump amplitude and frequency. This finding allows us to stabilize the phase of one mode against phase diffusion using the measured phase of the other mode. We demonstrate that phase fluctuations of either the high-frequency mode or the low-frequency mode can be significantly reduced. The results open new opportunities in generating stable vibrations in a broad frequency range via parametric down-conversion in nonlinear resonators. Published by the American Physical Society 2024

Unraveling the adsorption-limited hydrogen oxidation reaction at palladium surface via in situ electron microscopy

Palladium (Pd) catalysts have been extensively studied for the direct synthesis of H2O through the hydrogen oxidation reaction at ambient conditions. This heterogeneous catalytic reaction not only holds considerable practical significance but also serves as a classical model for investigating fundamental mechanisms, including adsorption and reactions between adsorbates. Nonetheless, the governing mechanisms and kinetics of its intermediate reaction stages under varying gas conditions remain elusive. This is attributed to the intricate interplay between adsorption, atomic diffusion, and concurrent phase transformation of catalyst. Herein, the Pd-catalyzed, water-forming hydrogen oxidation is studied in situ, to investigate intermediate reaction stages via gas cell transmission electron microscopy. The dynamic behaviors of water generation, associated with reversible palladium hydride formation, are captured in real time with a nanoscale spatial resolution. Our findings suggest that the hydrogen oxidation rate catalyzed by Pd is significantly affected by the sequence in which gases are introduced. Through direct evidence of electron diffraction and density functional theory calculation, we demonstrate that the hydrogen oxidation rate is limited by precursors' adsorption. These nanoscale insights help identify the optimal reaction conditions for Pd-catalyzed hydrogen oxidation, which has substantial implications for water production technologies. The developed understanding also advocates a broader exploration of analogous mechanisms in other metal-catalyzed reactions.