Surface Phase Change Research Articles

Attaining high-rate hydrogen evolution via SILAR deposited bimetallic nickel cobalt boride electrode: Exploring the influence of Ni to Co ratio

For the first time, a bimetallic Nickel Cobalt Boride (NCB) film with varying Ni to Co ratios was synthesized on stainless steel via the SILAR method. The NCB2 film (1:1 ratio) exhibited a mixed phase of metal boride and oxy-hydroxide with a highly porous, flaky-type morphology, while NCB1 (1:3 ratio) and NCB3 (3:1 ratio) showed only oxidized metal phases and agglomerated clusters. EDX confirmed the purity of the samples, and XPS indicated higher oxidation in NCB1 and NCB3 compared to NCB2. For HER, NCB2 showed the lowest overpotential (80 mV) compared to NCB1 (96 mV) and NCB3 (101 mV), and the smallest Tafel slope value (71 mV/dec). HER kinetics followed a Volmer-Heyrovsky mixed reaction path. NCB2 exhibited the highest Cdl value (16.55 mF/cm2) and the largest electrochemical active surface area (413.7 cm2), outperforming NCB1 (333.125 cm2) and NCB3 (205 cm2). At an overpotential of 100 mV, NCB2's TOF value was 8.23 s⁻1, higher than NCB1 (1.4 s⁻1) and NCB3 (1 s⁻1). For OER, NCB2 showed the highest Cdl value (106 mF/cm2) and ECSA value (2650 cm2). The Faradic efficiency of NCB2 was ∼98% after 190 h. Hydrogen evolution rates for NCB1, NCB2, and NCB3 as cathodes were 952 mL/h, 1022 mL/h, and 800.8 mL/h, respectively. In a prototype electrolyzer, NCB2 enhanced the hydrogen evolution rate by 30% in bifunctional mode to 1334.6 mL/h. After 100 h, performance declined by only 2.7% due to surface oxidation and phase changes. This achievement marks a milestone towards low-cost green hydrogen production, achieving the highest rate of hydrogen evolution as ever reported.

Experimental study of dual nano-network, high-temperature resistant aerogel material as an integration of thermal management functions

Thermal management system is highly desirable to guarantee the performance and thermal safety of lithium-ion batteries, but it reduces the energy density of battery modules and even is unable to provide highly effective protection. Here, a thermal management function integrated material is presented based on high-temperature resistant aerogel and phase change material and is applied at both charge–discharge process and thermal runaway condition. In this sandwich structure Paraffin@SiC nanowire/Aerogel sheet (denoted as PA@SAS) system, SiC nanowires endow the middle aerogel sheet (SAS) a dual nano-network structure. The enhanced mechanical properties of SAS were studied by compressive tests and dynamic mechanical analysis. Besides, the thermal conductivity of SAS at 600 °C is only 0.042 W/(m K). The surface phase change material layers facilitate temperature uniformity of batteries (surface temperature difference less than 1.82 °C) through latent heat. Moreover, a large-format battery module with four 58 Ah LiNi0.5Co0.2Mn0.3O2 LIBs was assembled. PA@SAS successfully prevents thermal runaway propagation, yielding a temperature gap of 602 °C through the 2 mm-thick cross section. PA@SAS also exhibits excellent performance in other safety issues such as temperature rise rate, flame heat flux, etc. The lightweight property and effective insulation performance achieves significant safety enhancement with mass and volume energy density reduction of only 0.79% and 5.4%, respectively. The originality of the present research stems from the micro and macro structure design of the proposed thermal management material and the combination of intrinsic advantages of every component. This work provides a reliable design of achieving the integration of thermal management functions into an aerogel composite and improves the thermal safety of lithium-ion batteries.

Surface Treatment Strategies and Their Impact on the Material Behavior and Interfacial Adhesion Strength of Shape Memory Alloy NiTi Wire Integrated in Glass Fiber-Reinforced Polymer Laminate Structures.

Over the past few decades, there has been a growing trend in designing multifunctional materials and integrating various functions into a single component structure without defects. This research addresses the contemporary demand for integrating multiple functions seamlessly into thermoplastic laminate structures. Focusing on NiTi-based shape memory alloys (SMAs), renowned for their potential in introducing functionalities like strain measurement and shape change, this study explores diverse surface treatments for SMA wires. Techniques such as thermal oxidation, plasma treatment, chemical activation, silanization, and adhesion promoter coatings are investigated. The integration of NiTi SMA into Glass Fiber-Reinforced Polymer (GFRP) laminates is pursued to enable multifunctional properties. The primary objective is to evaluate the influence of these surface treatments on surface characteristics, including roughness, phase changes, and mechanical properties. Microstructural, analytical, and in situ mechanical characterizations are conducted on both raw and treated SMA wires. The subsequent incorporation of SMA wires after characterization into GFRP laminates, utilizing hot-press technology, allows for the determination of interfacial adhesion strength through pull-out tensile tests.

Development of Fe-13.8Cr-8.9Mn alloy for steel biomaterials

Traumatic, osteoarthritic, tumoral, and congenital bone issues impact human lives and health. The next generation of bone implants is made from biodegradable materials, including Fe-based materials with superior mechanical properties and high biocompatibility. However, efforts to inhibit the risk of inflammation and bacterial infection due to the biological response and corrosion properties of metals are a significant challenge. This study aims to develop biomaterials based on Fe-Cr-Mn alloys to obtain superior physical and mechanical properties through plasma nitriding. Each sample was plasma-nitridated in a vacuum chamber at various temperatures of 250–450 °C for 3 hours at a pressure of 1.8 kPa. Several main tests were performed to investigate the effects of plasma nitriding, such as the chemical compositions of raw material, surface nitrogen contents, phase changes, thickness, hardness, and corrosion. Those parameters were then used to evaluate plasma nitriding's effectiveness, including observing the change in phenomena at each temperature treatment. The results indicated that forming the S phase on the surface of Fe-13.8Cr-8.9Mn alloy is a saturated solution of nitrogen in ɣ-Fe, where the nitrogen content on the surface increases with increasing nitriding temperature. The layer's surface hardness is uniform across its whole thickness, which reduces as the grade of raw material passes through the nitride layer. The highest hardness at a nitriding temperature of 450 °C reached 625.3 VHN. The findings showed that the corrosion rate decreased significantly, reaching the lowest value, 0.0018 mm/year, at a plasma nitriding temperature of 450 °C. Plasma nitriding could enhance the physical and mechanical properties of Fe-Cr-Mn alloy

Ni-Rich Cathode Active Materials Surface Degradation in Ambient Air with Stabilisation Treatment Proposal

Ni-rich cathode active materials, such as NMC811 (Li[Ni0.8Mn0.1Co0.1]O2), are promising cathode materials due to their higher theoretical capacity of 200mAh/g, lower cobalt ratio, and overall decreased material expenses. However, the material undergoes a phase transition from layered ( ) through spinel ( ) to rock salt ( ) at high state of charge with oxygen release, and formation of rock salt structures on the surface with lithium carbonates and lithium hydroxides (Residual Lithium Compound (RLC)) while material is exposed to ambient air, all of which is followed by an increase in surface impedance and a decrease in final battery performance.Here, we explore the chemical and electrochemical evaluation of the Ni-rich cathode active material surfaces when exposed to ambient air for fourteen days (RH~40%). The combination of Fourier-transform infrared spectroscopy (FT-IR) and electrochemical impedance spectroscopy (EIS) will be investigated. These complementary non-destructive approaches will be utilised to characterise the decomposition of the original layered surface and formation of RLC. In addition, the research will be evaluated using STA, XRD, formation, diffusion coefficient, and cycle life in a half-cell using lithium-ion discs as counter electrodes. Furthermore, we show a technique for stabilising the material in air using Experimental ElectroRite®1 Additive provided by Lubrizol Ltd. which reduces the formation of the RLC and the corresponding surface phase changes, often attributed to the presence of Ni2+ ions. This work contributes to a greater understanding of the surface stabilisation through chemical treatment required and suggests routes to create stable water-based Ni-rich cathode inks.

Numerical modeling of drying from saturated to unsaturated conditions with two-phase partitioning boundaries at the medium surface and interface-dependent phase change

To accurately predict the drying of a porous medium from saturated to unsaturated conditions over time, this paper proposes two-phase partitioning boundaries for liquid water evaporation and water vapor transport at the medium surface. A non-isothermal two-phase (liquid water and gas mixtures), two-component (dry air and water vapor) transport model with nonequilibrium and interface-dependent phase change is then developed. The governing equations are then numerical solved using COMSOL Multiphysics software and applied to describe a series of laboratory soil drying tests as examples. The performance of the proposed boundaries at the surface is illustrated by comparison with other three common used boundaries. The results show that a specific flux of vapor at the surface with a zero flux of liquid water cannot be adopted to describe the drying process of initially saturated media due to the lack of interconnected gas-filled pores. The merged liquid-vapor boundary applied in the Darcy–Richards model significantly prolongs the constant rate stage when the liquid water evaporation is dominant. Then, the effects of air/gas–water interfacial area and water retention parameters on the drying process are investigated. A faster reduction in the air–water relative interfacial area at the medium surface will shorten the drying process with earlier dominance of the vapor transport. An increased entry capillary pressure and a decreased pore size distribution index for the water retention curve will result in slower drying, more loss by vapor transport and a more homogeneous distribution of pore water respect to depth. The current study can promote the understanding of the evolution of drying mechanisms of a porous medium from saturated to unsaturated conditions.

Simulation and modeling of the vaporization of a freely moving and deforming drop at low to moderate Weber numbers

The vaporization of a freely moving drop in a uniform, high-temperature gas stream is investigated through direct numerical simulation. The incompressible Navier-Stokes equations with surface tension and phase change are solved in conjunction with the energy equations of each phase. The sharp liquid-gas interface is tracked using the geometric Volume-of-Fluid (VOF) method and an immersed Dirichlet boundary condition for temperature is imposed at the interface. The simulation approach is validated by simulating water and acetone drops at nearly zero Weber numbers, and the simulation results agree very well with the empirical relation for spherical drops. Parametric simulations were conducted to investigate the aerodynamic breakup of vaporizing drops at low to moderate Weber and Reynolds numbers. The range of Weber numbers considered has covered the vibrational and bag breakup regimes. Through the simulation results, we have characterized the impact of drop deformation and breakup on the drop vaporization rate. When the drop Weber number increases, the windward surface area increases more rapidly over time. As a result, the rate of drop volume reduction also increases. The correlation between the vaporization rate and the windward surface area is examined for different Weber and Reynolds numbers. Using the approximate correlation between the drop vaporization rate and the windward surface area and the TAB model for drop deformation, a new time-dependent drop vaporization model is proposed. The present model agrees well with the simulation results and shows a significant improvement over the conventional model for spherical drops.

Wetting tuning of Al/B4C interface via femtosecond laser irradiation

The Al/B4C composites are widely used in aerospace, automotive, military and energy industries, which combine the mechanical properties of Al metal and B4C ceramics. To achieve the best composite performance, it is crucial to overcome the poor wetting between the two materials. It is well known that surface micro-nano structures can affect wetting. However, the high brittleness and hardness of B4C make it challenging to process. In this paper, we proposed a novel approach to create hierarchical micro-nano surface structures on B4C by femtosecond laser irradiation. Surface morphology, phase change, and valence bond structure before and after irradiation were characterized respectively. The wetting of B4C was characterized in terms of high-temperature metal melt wetting. Under high photon energy impact, carbon elements were precipitated, leading to forming a boron-rich phase. This new phase possesses higher chemical reactivity and is capable of promoting reactions with Al. Compared with the contact angle of the untreated sample, the contact angle decreased by 24°. This work demonstrates that femtosecond laser irradiation is a sustainable and concise technology to improve high-temperature wetting, providing a new idea for enhancing the wetting of metal/ceramic systems.

Investigation of 500 keV Si ion induced surface structuring of Ni and Ti for enhancement of field emission properties

The present paper reports the investigation of surface morphology, elemental composition, phase changes and field emission properties of Si ion irradiated nickel (Ni) and titanium (Ti). The Ni and Ti targets have been irradiated with 500 keV Si ions generated by Pelletron accelerator at various fluences ranging from 6.9 × 1013 to 77.1 × 1013 ions/cm2. Stopping range of ions in matter analysis revealed higher values of electronic stopping and sputtering yield for Ni as compared with Ti. For both irradiated metals, electronic energy loss dominant over the nuclear stopping. The growth of induced surface structures have been analysed by using field emission scanning electron microscopy (FESEM) analysis. In case of Ni, as the ion fluence increases from 6.9 × 1013 to 65.8 × 1013 ions/cm2, the formation of spherical particulates, agglomers and sputtering is observed. Although in the case of Ti, with the increase of Si ion fluence from 11.6 × 1013 to 77.1 × 1013 ions/cm2, the formation of irregular‐shaped particulates along with crater and sputtered channels is observed. X‐ray diffraction (XRD) analysis shows that no new phase is identified. However, a significant increase in peak intensity is observed with increasing ion fluence. The variation in crystallite size and dislocation line density is also observed as a function of Si ion fluence. Fourier transform infrared spectroscopy analysis shows that no bands are formed after the Si ion irradiation. Field emission properties of ion‐structured Ni and Ti are well correlated with the growth of surface structures observed by SEM and dislocation line density evaluated by XRD analysis.

Numerical Assessment of Gravity for Sloshing in Tank Using OpenFOAM

We numerically study gravity’s effect on sloshing in a two-dimensional tank which is highly filled by water (95% water and 5% air). Both fluids are considered to be incompressible and inviscid. The surface tension and phase change are neglected. OpenFOAM software is used for the simulation. A standing wave of water impacting the lid of the tank at its center and a symmetric wetted region starts to advance along the lid. The simulation carried out (only on the right-half side of the tank due to symmetric geometry of the impact) with and without gravity to investigate the influence of gravity on this impact. The numerical results are validated by comparing to published data. The effect of gravity on the size of the wetted region, free-surface elevation and on the pressure distribution has been analyzed. It is shown that gravity is affecting the free-surface elevation and consequently the size of the wetted region. These effects growth as time goes. Pressure distribution along the wetted region of the lid is also influenced by gravity.

Nanoscale Compositional Mapping of Commercial LiNi0.8Co0.15Al0.05O2 Cathodes Using Atom Probe Tomography

Nickel-rich cathodes provide improved specific capacity, which leads to higher gravimetric energy density, which, in turn, is critical for electric vehicles. However, poor long-term capacity retention at elevated temperatures/high C rates (the rate of charge and discharge on a battery) stems from material issues: surface phase changes, corrosive side reactions with the electrolyte, ion dissolution, and propagation of cracks. Introducing dopants, developing nanoscale surface coatings, and graded core–shell structures all improved the electrochemical performance of nickel-rich cathodes. However, material-level understanding of the effect of Li composition and distribution in Ni-rich cathodes is limited due to a lack of characterization methods available that can directly image Li at the nanoscale. Hence, it is critical to establish methods such as atom probe tomography (APT) that have both nanometer-scale spatial resolution and high compositional sensitivity to quantitatively analyze battery cathodes. To fully realize its potential as a method for quantitative compositional analysis of commercial Li-ion batteries, we provide a comprehensive description of the challenges in sample preparation and analyze the dependency of the analysis parameters, specifically laser pulse energy on the measured stoichiometry of elements in a high-Ni-content cathode material LiNi0.8Co0.15Al0.05O2 (NCA). Our findings show that the stoichiometry variations cannot be explained by charge–state ratios or Ga implantation damage alone during FIB preparation, indicating that additional factors such as crystallographic orientation may need to be considered to achieve quantitative nanoscale compositional analysis of such battery cathodes using APT.

Simulation of the Marangoni Effect and Phase Change Using the Particle Finite Element Method

A simulation method is developed herein based on the particle finite element method (PFEM) to simulate processes with surface tension and phase change. These effects are important in the simulation of industrial applications, such as welding and additive manufacturing, where concentrated heat sources melt a portion of the material in a localized fashion. The aim of the study is to use this method to simulate such processes at the meso-scale and thereby gain a better understanding of the physics involved. The advantage of PFEM lies in its Lagrangian description, allowing for automatic tracking of interfaces and free boundaries, as well as its robustness and flexibility in dealing with multiphysics problems. A series of test cases is presented to validate the simulation method for these two effects in combination with temperature-driven convective flows in 2D. The PFEM-based method is shown to handle both purely convective flows and those with the Marangoni effect or melting well. Following exhaustive validation using solutions reported in the literature, the obtained results show that an overall satisfactory simulation of the complex physics is achieved. Further steps to improve the results and move towards the simulation of actual welding and additive manufacturing examples are pointed out.

Oxidation Stabilization of ZrFe Alloys in Nitrogen Gas Atmosphere

A porous ZrFe alloy specimen was prepared as a 6 × 3 mm (diameter × thickness) disk. The reaction of the ZrFe alloy was confirmed while the whole system was maintained at a target temperature, which was increased from 150 oC to 950 oC in a 99.999% low purity nitrogen atmosphere, consisting of 10 ppm of impurity gas. Surface color, pore size, stabilized layer, and phase change were confirmed with optical microscopy, scanning electron microscopy-energy dispersive X-ray spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and Micro-Raman, according to temperature. The surface color of the ZrFe alloy changed from metallic silver to dark gray as the temperature increased. In the EDS and XPS results, nitrogen component was not observed, and oxygen content increased on each surface at the elevated temperatures. In this way, the ZrFe alloy was stabilized in a low purity nitrogen atmosphere, preventing rapid nitride reactions.

Oxidation Stabilization of ZrFe Alloys in Nitrogen Gas Atmosphere

A porous ZrFe alloy specimen was prepared as a 6 × 3 mm (diameter × thickness) disk. The reaction of the ZrFe alloy was confirmed while the whole system was maintained at a target temperature, which was increased from 150 oC to 950 oC in a 99.999% low purity nitrogen atmosphere, consisting of 10 ppm of impurity gas. Surface color, pore size, stabilized layer, and phase change were confirmed with optical microscopy, scanning electron microscopy-energy dispersive X-ray spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and Micro-Raman, according to temperature. The surface color of the ZrFe alloy changed from metallic silver to dark gray as the temperature increased. In the EDS and XPS results, nitrogen component was not observed, and oxygen content increased on each surface at the elevated temperatures. In this way, the ZrFe alloy was stabilized in a low purity nitrogen atmosphere, preventing rapid nitride reactions.

Engineering a Robust Interface on Ni-Rich Cathodes via a Novel Dry Doping Process toward Advanced High-Voltage Performance.

Ni-rich layered oxides have become the main force of cathode materials for EV cells with high energy density owing to their satisfactory theoretical capacity, cost-effectiveness, and low toxicity. However, the high-voltage stability of Ni-rich cathode materials still has not fulfilled the demand of power batteries due to their intrinsic structural and electrochemical instability. The commonly used modification procedures are achieved via a wet process, which may lead to surface lithium-ion deficiency, phase change, and high costs during manufacturing. Herein, we construct a multifunctional Ti-based interfacial architecture on the surface of LiNi0.6Co0.2Mn0.2O2 (NCM) cathode materials via a novel dry interface modifying process in which no solvent is employed. The Ti-based interfacial architecture accelerates the transportation of lithium ions and consequently stabilizes the interfacial structure. This approach significantly improves the cycling stability in half cells, with a 15% increase in capacity retention over 100 cycles at 1 C under a high voltage of 4.5 V. Impressively, few internal cracks are observed in a modified sample after 500 times of charge and discharge between 2.75 and 4.35 V at 1 C rate, and the capacity retention can reach 93%.

Preparation and characterization of microencapsulated organic phase change material for cool thermal energy storage applications

In this study, an ester-based phase change material (PCM) was microencapsulated into a melamine formaldehyde shell using in-situ polymerization. The Surface morphology, thermal stability, and phase change properties of the microcapsules were characterized using field-emission scanning electron microscope (FESEM), thermo-gravimetric analysis (TGA) and differential scanning calorimetry (DSC) techniques, respectively. The observed surface morphology reveals that prepared microcapsules shown near-spherical structures with smooth surfaces. The TGA results indicate that the microencapsulated phase change material (MPCM) has on-set and end set degradation temperatures as 110.3 °C and 142 °C, respectively, ensuring good thermal stability of MPCM. The enthalpy of latent heat measured using the DSC technique was around 65 kJ/kg, with onset peak melting at 8.57 °C.

IMPROVING THE SURFACE STRUCTURE OF MASSIVE PARTS BY THE PLASMA METHOD

An increase in the reliability of the operation of large-sized and massive parts by plasma hardening of their surfaces is substantiated. It has been established that the formation of several structural zones of different microhardness is observed in detail along the depth of hardening, indicating the formation of a gradient-layered structure. It has been proved that at ultrafast heating rates, which occur during surface plasma hardening, phase and structural changes move to the high temperature region, changing the kinetics of the appearance and growth of new phase nuclei. In this case, fine-grained austenite is formed, which is transformed into a highly dispersed martensitic structure, which increases the strength and reliability of the surfaces of the parts.

Unprecedented hardness of polycrystalline diamond via laser surface engineering

The use of polycrystalline diamond (PCD) as a tool material for machining intractable alloys has increased due to their excellent abrasive and wear properties. In this study, for the first time, a novel low-energy/high-frequency laser shock peening technique (LE/HF-LSP) is proposed to control the mechanical and surface properties of PCD. This technique utilises laser energies below the ablation threshold (10–100 mJ), high frequencies (35–70 kHz) and short pulse durations (in the region of ns) and is applied to the target material with/without sacrificial coatings. The results of the samples processed using this novel technique without coatings revealed a 14% increase of micro-hardness in comparison to the commercially available PCDs. In addition, this technique showed a reduction in cobalt volume by 18.42% compared to the case using coatings increasing in the range of 16.4 to 66.3%. It was also observed that using vinyl & quartz as sacrificial coatings, improved the hardness from 150 GPa to 230 GPa. On the other hand, fluence above 102.29 J/cm2 processed with vinyl and soda-lime glass as ablative and transparent overlays showed softening of the material. A transition between tensile to compressive stress has been observed when processed with vinyl and quartz. Graphitisation and deformation of cobalt have been observed from the results obtained from XRD and Raman spectroscopy. The results showed a correlation between the surface modification, micro-hardness and phase changes for PCDs revealing a relationship between the phase transition and hardness to the laser fluence. It is believed that a suitable range of coatings with a variety of acoustic impedances can be effective in controlling the mechanical properties of PCD.

Pre-Stabilization of Zr Getters for 5-Nine Purity Nitrogen Gas Purification

We confirm whether Zr powders can restrain a rapid nitrification reaction and offer a stable oxidation reaction according to temperatures in nitrogen gas purification. A pellet-type, porous Zr getter is prepared (diameter: 10 and thickness: 3 mm) using Zr powder with an average particle size of 45 μm. While maintaining the whole system, the Zr getter reaction is confirmed with an increase in temperature from 150 to 550 oC at increments of 100 oC under 99.999 % purity nitrogen atmosphere comprising of 10 ppm of impurity. Surface color, pore size, stabilized layer, and phase change are confirmed with optical microscopy, SEM-EDS, Micro-Raman, and X-ray diffraction (XRD) according to the Zr getter temperature. The surface color of the Zr getter changes from metallic silver to dark gray as temperature increases. In the EDS results, the nitrogen component is not observed, and oxygen content increases from each surface at elevated temperatures. The Raman and XRD results show the oxidation layer as a result of 350 oC annealing. Therefore, the Zr getter can be applied as a nitrogen getter under 5-nine purity nitrogen atmosphere after appropriate oxidized pre-stabilization process to prevent rapid nitrification reaction.

Synergetic effect of high Ni ratio and low oxygen defect interface zone of single crystals on the capacity retention of lithium rich layered oxides

Li-rich layered oxides (LLOs) are promising cathode materials for Li-ion batteries owing to their high capacities (>250 mAh g−1), however, they suffered from severe capacity and voltage fading caused by irreversible oxygen loss and phase changes. Herein, the structural stability of single crystalline and polycrystalline Li1.14Ni0.32Mn0.44Co0.04O2 was compared in detail. It was found that the stability of oxidized oxygen ions on the near surface was improved in single crystals, which retarded oxygen loss from surface and surficial phase changes, possibly owing to the facet regulating and low surface curvature. In addition, the formation-migration of Mn3+, one of the crucial factors that caused capacity fading of LLOs, can be mitigated by increasing Ni3+ ratio. Under the synergistic effect of low oxygen defects on the near surface and high Ni3+ ratio, stable cycling performances and higher thermal stability were obtained.