Purge Cycle Research Articles

Fluid retention in endoscopes: A real-world study on drying effectiveness

Outbreaks linked to inadequate endoscope drying have infected numerous patients, and current standards and guidelines recommend at least 10minutes of forced air for drying channels. This study evaluated a new forced-air drying system (FADS) for endoscopes. Drying was assessed using droplet detection cards; visual inspection of air/water connectors, suction connectors, and distal ends; and borescope examinations of endoscope interiors. Assessments were performed after automated endoscope reprocessor (AER) alcohol flush and air purge cycles and after 10-minute FADS cycles. Researchers evaluated drying during encounters with 22 gastroscopes and 20 colonoscopes. After default AER alcohol and air purge cycles, 100% (42/42) of endoscopes were still wet. Substantial fluid emerged from distal ends during the first 15seconds of the FADS cycle, and droplets also emerged from air/water and suction connectors. Following FADS cycle completion, 100% (42/42) were dry, with no retained fluid detected by any of the assessment methods. Multiple endoscope ports and channels remained wet after AER cycles intended to aid in drying but were dry after the FADS cycle. This study reinforced the need to evaluate the effectiveness of current drying practices and illustrated the use of practical tools in a real-world setting.

Features of the process of water filling the barrel of a periodic-pulse fire extinguishing installation

In the work, research was carried out, which made it possible to reveal the peculiarities of the process of filling the barrel of the periodic-impulse fire extinguishing installation with water. At the same time, a mathematical model for simulating the processes of water injection into a pipe with subsequent crushing of water by a shock wave was substantiated and proposed. To simulate the processes of water injection and water crushing in the shaft of the installation, a VOF model (volume of liquid model) is used, according to which there is no penetration of one medium into another, and which is based on the surface tracking method applied to a fixed Euler grid. On the basis of the developed mathematical model in the ANSYS software environment, numerical studies of the process of filling the barrel of a periodic-impulse fire extinguishing installation with water were carried out. According to the results of a numerical study of the process of filling the barrel of the periodic-impulse fire extinguishing installation with water, a relatively high inertia in the time of the water injection processes in relation to the gas detonation processes occurring in the periodic-impulse fire extinguishing installation was revealed. In particular, the time interval between detonation cycles in the installation operating at a frequency of 23 Hz is about 43,5 ms. If we discard the purge cycle, then we have a time interval of 21 ms, during which it is necessary to inject water into the barrel of the intermittent-impulse fire extinguishing installation. According to the results of the above studies, we have that only the time for the spread of the stream of water from one side to the other side of the barrel of the periodic-impulse fire extinguishing installation is 8 ms. The conducted research makes it possible to investigate the influence of the parameters of the fire extinguishing installation on the formation of a finely sprayed water jet, and the obtained results will significantly increase the level of operational readiness of the personnel of fire and rescue units during operational actions to extinguish internal fires.

A Europium-Based Optical Sensor for the Detection of Carbon Dioxide and Its Application for a Fermentation Reaction

A new europium-based complex, K[Eu(hfa)4] with hfa = hexafluoroacetylacetonate is synthesized and its structure confirmed via X-ray crystallography. The structure unravels an anionic octa-coordinate complex, K[Eu(hfa)4], as opposed to the neutral hexacoordinate complex Eu(hfa)3 routinely/ubiquitously presumed to be the case in the literature. The complex displayed pH-dependent, “on–off” emission changes in solution and exhibited a pKa of 6.13 ± 0.06 in ethylene glycol. In solution, the sensor complex exhibited drastic variation in emission intensity corresponding to changes in the concentration of CO2 gas purged. Based on multiple purge cycles of N2 and CO2, the emission intensity changes can be correlated to the concentration of CO2 in the solution. The sensor’s ability to quantify the CO2 presence is based on emission variations of the 5D0 → 7F2 line in the Eu(III) complex at 618 nm. The sensor exhibits a linear response to CO2 concentrations in the range of 0–25% (0–8.50 mM or 0–189.95 mmHg). Based on calibration data, the limit of detection (LOD) is determined to be 0.57% (0.19 mM or 4.33 mmHg) in solution. The I100/I0 ratio is determined to be 80.29 ± 3.79. The percent change in intensity from purging N2 to 100% CO2 is 7911.16%. Over the course of seven cycles of purging different concentrations of CO2, there is essentially no deviation in the emission intensity of the sensor in solution, indicating stability and reversibility. In addition to the analytical characterization of the sensor, the mechanism of CO2 sensing is investigated using cyclic voltammetry, IR, and Raman spectroscopy. These data indicate the reduction of europium(III) to europium(II) in an alkaline medium and suggest changes in the hfa ligand chemistry (association/dissociation and protonation) due to CO2 purging. The potential use of the sensor complex for real-life applications is herein evaluated via a well-known fermentation reaction. The CO2 generated during yeast’s anaerobic respiration in sucrose media is quantified using the sensor complex and a calibrated, commercial CO2 probe; both exhibit similar CO2 concentration values, validating the calibration curve and the viability of the complex as a bona fide sensor. Based on the data collected, a highly stable, brightly red-emissive Eu(III) complex with the ability to differentiate concentrations of CO2 in solution is hereby developed and characterized with benefits for various CO2 sensing applications.

1.1‐Millimeter Tall Vertically Aligned‐Carbon Nanotubes Grown by Cold Wall CVD Using a Novel Multiple‐Purge Method

AbstractThis paper reports a multi‐phase deposition for the growth of carbon nanotubes, intercalating phases of effective growth with purges of the reactor, based on the method recently proposed by the author to grow tall vertically aligned carbon nanotubes (VA‐CNT) in a cold‐wall system at low pressure. The test performed consists on running several growths varying the number of cycles during the deposition step and their duration, avoiding a massive study of number of cycles in function of the time and vice versa. The goal here is to verify if the chamber reconditioning and the purge cycles contribute to increase the height and the uniformity of the VA‐CNT forests. The maximum height achieved is 1.1 mm for 11 cycles, in a total time of 110.5 min, with a non‐uniformity of 6.0% under 6.8 Torr. The analysis of the saturation of the deposition is registered around 127 min.

In situ monitoring atomic layer doping processes for Al-doped ZnO layers: Competitive nature of surface reactions between metal precursors

In this work, surface reactions during the atomic layer doping (ALDp) process of aluminum-doped zinc oxide (AZO) films have been studied. Conventional supercycle and alternative quasi-simultaneous codosing methods are analyzed within the 100–200 °C substrate temperature range. Two quasi-simultaneous codosing cases are investigated: (1) diethylzinc (DEZ) followed by trimethylaluminum (TMA) and (ii) TMA followed by DEZ. Quasi-simultaneous codosing experiments featured back-to-back DEZ/TMA or TMA/DEZ precursor and H2O pulses separated by nitrogen (N2) purge cycles. The grown films were characterized via (i) real-time in situ ellipsometry to monitor the individual surface ligand exchange reactions via variations in the film thickness in each half-cycle; (ii) ex situ ellipsometry to determine the film optical constants; (iii) x-ray photoelectron spectroscopy to measure the elemental composition and chemical bonding structure, and (iv) x-ray diffraction to evaluate the crystal properties. The most significant finding of the study is the dominance of TMA over DEZ: for all of the quasi-simultaneous codosing samples, no matter which precursor is pulsed first and whether there is a time delay between TMA and DEZ pulses or not, zinc (Zn) incorporation within the AZO films is substantially lower than aluminum (Al). This result demonstrates the competitive nature of surface reactions between TMA and DEZ, where the winning side is TMA. Al is effectively incorporating into the film while severely limiting Zn-incorporation and even replacing chemisorbed Zn-groups via conversion surface reactions. As a result, the quasi-simultaneous codosing approach for AZO films using DEZ and TMA precursors leads to minimally (less than 2%) Zn-doped Al2O3 films (ZAO), depicting the advantages of controlled ALDp process via the conventional supercycle method.

Performance and water transport behaviour in Polymer Electrolyte Membrane fuel cells

Water management in fuel cells is important for avoiding the phenomenon of flooding or dehydration in the stack and for maintaining good fuel cell performance and durability. This study focuses on the evaluation of the dynamic performance and behaviour (purge cycle) of the commercial Polymer Electrolyte Membrane (PEM) fuel cell stack towards water transport (water balance) at different operating conditions. The stack was operated at different current loads (0–10 A) and operating temperature (ambient to 50 °C). The results indicated that the measured water accumulation in the stack increased with the increase in current load. The optimal current load was 4 A, with calculated efficiency of 62.8%. The optimal operating temperature was 40 °C, resulting in calculated efficiency of 52.3%. At higher temperature, the fuel cell performance decreased, and the measured water balance was not properly distributed, which could be due to the dehydration and low conductivity of the electrolyte membrane. It can be concluded that the behaviour and performance of the stack, as well as the water balance in the stack, were influenced by the operating conditions. Moreover, this study improves the understanding of fuel cell performance and behaviour based on evaluation of the water balance.

Liquid Transport in Superhydrophobic Walled Minichannels for Polymer-Electrolyte Fuel Cell Flow-Fields

Liquid water byproduct management continues to be a challenge as polymer-electrolyte fuel cell (PEFC) designs reach higher power densities. At length scales where surface tension is dominant, the wettability of flow-field channels can significantly impact the distribution of water on gas diffusion media. This work explores the impact of a super-hydrophobic coating on liquid build up and pressure drop in PEFC minichannels which are of interest because prior work has shown improved electrochemical performance at hydraulic diameters approaching 0.4 mm. Using ex-situ experimental methods and optical imaging, time series liquid water distributions were captured along with the two-phase pressure drop in a specially designed transparent test channel. The sidewalls of the minichannel were coated to achieve a contact angle of >150⁰. The liquid was injected into the channel through the back of the gas-diffusion layer (GDL) through a small pore to simulate actual PEFC conditions where liquid forms in the catalyst layer and percolates through a microporous layer. Two minichannel geometries with hydraulic diameters of 0.46 mm and 0.30 mm were tested with flow velocities ranging from ~3.0 m/s to ~15 m/s and liquid injection rates ranging from 150 µL/hr to 300 µL/hr. A digital camera collected images of the liquid water distribution at 5 Hz which was synchronized with the pressure drop data collection. Images were post processed to capture the projected area of liquid coverage on the GDL surface. For each test, periodic purge cycles were included to understand the impact these coatings may have on startup and drying scenarios. Overall, data shows that super-hydrophobic coatings lead to mixed results in reducing pressure drop for steady flow conditions compared to untreated channels. Super-hydrophobic coatings did, however, lead to consistently lower channel saturations during purge/dry cycles. A discussion of the normalized data in terms of channel saturation, two-phase pressure amplification, and Weber number is made for each case.

Numerical simulation on purge strategy of proton exchange membrane fuel cell with dead-ended anode

Proton exchange membrane fuel cells with dead-ended anode simplify fuel cell system and effectively reduce its volume, weight and cost. In this study, a three-dimensional numerical model of a dead-ended anode PEMFC with single straight channel is developed. The effect of operating conditions, including operating temperature, anode inlet pressure, and cathode relative humidity on operating characteristics of dead-ended anode PEMFC was studied in detail. What's more, the purge cycle, hydrogen utilization and energy efficiency are analyzed and the reasonable purge strategy was optimized. The results indicates that the decrease of anode partial pressure caused by the accumulation of nitrogen and liquid water is the main reason for the voltage decline during dead-ended anode operation. The purge cycle is effectively prolonged by increasing anode pressure and reducing the relative humidity of cathode. The purge cycle is extended from 437s to 562.5s as the anode pressure increased from 50 kPa to 150 kPa. The purpose of optimizing the purge strategy is to fully remove the accumulated water and nitrogen, so as to prolong the purge cycle and improve hydrogen utilization and energy efficiency. From the result, the hydrogen utilization and energy efficiency of the base case are 95.77% and 40.05%.

Atomic Layer Deposition of aTiO2 Layer on Nitinol and Its Corrosion Resistance in a Simulated Body Fluid

Nitinol is a group of nearly equiatomic alloys composed of nickel and titanium, which was developed in the 1970s. Its properties, such as superelasticity and Shape Memory Effect, have enabled its use, especially for biomedical purposes. Due to the fact that Nitinol exhibits good corrosion resistance in a chloride environment, an unusual combination of strength and ductility, a high tendency for self-passivation, high fatigue strength, low Young’s modulus and excellent biocompatibility, its use is still increasing. In this research, Atomic Layer Deposition (ALD) experiments were performed on a continuous vertical cast (CVC) NiTi rod (made in-house) and on commercial Nitinol as the control material, which was already in the rolled state. The ALD deposition of the TiO2 layer was accomplished in a Beneq TFS 200 system at 250 °C. The pulsing times for TiCl4 and H2O were 250 ms and 180 ms, followed by appropriate purge cycles with nitrogen (3 s after the TiCl4 and 2 s after the H2O pulses). After 1100 repeated cycles of ALD depositing, the average thickness of the TiO2 layer for the CVC NiTi rod was 52.2 nm and for the commercial Nitinol, it was 51.7 nm, which was confirmed by X-ray Photoelectron Spectroscopy (XPS) and Scanning Electron Microscope (SEM) using Energy-dispersive X-ray (EDX) spectroscopy. The behaviour of the CVC NiTi and commercial Nitinol with and without the TiO2 layer was investigated in a simulated body fluid at body temperature (37 °C) to explain their corrosion resistance. Potentiodynamic polarisation measurements showed that the lowest corrosion current density (0.16 μA/cm2) and the wider passive region were achieved by the commercial NiTi with TiO2. Electrochemical Impedance Spectroscopy measurements revealed that the CVC NiTi rod and the commercial Nitinol have, for the first 48 h of immersion, only resistance through the oxide layer, as a consequence of the thin and compact layer. On the other hand, the TiO2/CVC NiTi rod and TiO2/commercial Nitinol had resistances through the oxide and porous layers the entire immersion time since the TiO2 layer was formatted on the surfaces.

Dynamic Reliability Assessment of PEM Fuel Cell Systems

In this paper, a novel model for the dynamic reliability analysis of a polymer electrolyte membrane fuel cell system is developed to account for multi-state dynamics and ageing. The modelling approach involves the combination of physical and stochastic sub-models with shared variables. The physical model consists of deterministic calculations of the system state described by variables such as temperature, pressure, mass flow rates and voltage output. Additionally, estimated component degradation rates are also taken into account. The non-deterministic model is implemented with stochastic Petri nets which model the failures of the balance of plant components within the fuel cell system. Using this approach, the effects of the operating conditions on the reliability of the system were investigated. Monte Carlo simulations of the process highlighted a clear influence of both purging and load cycles on the longevity of the fuel cell system.

Sub-10\u2009nm nanogap fabrication on suspended glassy carbon nanofibers

Glassy carbon nanofibers (GCNFs) are considered promising candidates for the fabrication of nanosensors for biosensing applications. Importantly, in part due to their great stability, carbon electrodes with sub-10 nm nanogaps represent an attractive platform for probing the electrical characteristics of molecules. The fabrication of sub-10 nm nanogap electrodes in these GCNFs, which is achieved by electrically stimulating the fibers until they break, was previously found to require fibers shorter than 2 µm; however, this process is generally hampered by the limitations inherent to photolithographic methods. In this work, to obtain nanogaps on the order of 10 nm without the need for sub-2 µm GCNFs, we employed a fabrication strategy in which the fibers were gradually thinned down by continuously monitoring the changes in the electrical resistance of the fiber and adjusting the applied voltage accordingly. To further reduce the nanogap size, we studied the mechanism behind the thinning and eventual breakdown of the suspended GCNFs by controlling the environmental conditions and pressure during the experiment. Following this approach, which includes performing the experiments in a high-vacuum chamber after a series of carbon dioxide (CO2) purging cycles, nanogaps on the order of 10 nm were produced in suspended GCNFs 52 µm in length, much longer than the ~2 µm GCNFs needed to produce such small gaps without the procedure employed in this work. Furthermore, the electrodes showed no apparent change in their shape or nanogap width after being stored at room temperature for approximately 6 months.

Atomic Layer Deposition on Dispersed Materials in Liquid Phase by Stoichiometrically Limited Injections.

Atomic layer deposition (ALD) is a well-established vapor-phase technique for depositing thin films with high conformality and atomically precise control over thickness. Its industrial development has been largely confined to wafers and low-surface-area materials because deposition on high-surface-area materials and powders remains extremely challenging. Challenges with such materials include long deposition times, extensive purging cycles, and requirements for large excesses of precursors and expensive low-pressure equipment. Here, a simple solution-phase deposition process based on subsequent injections of stoichiometric quantities of precursor is performed using common laboratory synthesis equipment. Precisely measured precursor stoichiometries avoid any unwanted reactions in solution and ensure layer-by-layer growth with the same precision as gas-phase ALD, without any excess precursor or purging required. Identical coating qualities are achieved when comparing this technique to Al2 O3 deposition by fluidized-bed reactor ALD (FBR-ALD). The process is easily scaled up to coat >150 g of material using the same inexpensive laboratory glassware without any loss in coating quality. This technique is extended to sulfides and phosphates and can achieve coatings that are not possible using classic gas-phase ALD, including the deposition of phosphates with inexpensive but nonvolatile phosphoric acid.

Effects of load variation and purge cycles on the efficiency of Polymer Electrolyte Membrane Fuel Cells for stationary applications

Polymer Electrolyte Membrane Fuel Cells have become rather popular for power generation; Dead-Ended Anode design is currently adopted to limit hydrogen consumption. However, gas and water accumulation at the anode outlet decrease stack performance, and so, purges are carried out to remove them. This work focuses on a Polymer Electrolyte Membrane Fuel Cell system featuring a voltage-drop-based purging strategy; 4 electric-load conditions (0.6–1.8 kW) were imposed to evaluate how purges impact the system performance as the applied load varies. Long-duration experimental tests were conducted at a constant load to reproduce cycles typical of stationary applications; various electric, thermal, and transport parameters were measured, and efficiency was ultimately determined. An analogy between increasing the applied load and increasing the cathode-air humidity level was found in terms of purge-related hydrogen losses and purge time. Stack current intensity is not affected remarkably by purging, whereas stack voltage exhibits higher oscillations at the higher loads and is less stable at the lowest one. A relationship is suggested between voltage, anode stoichiometry, and stack temperature, especially over the initial transient trend prior to reaching an approximately steady condition. Overall stack efficiency decreases as polarization losses increase along with the applied load; fuel efficiency is almost constant, even though slightly bigger at the higher loads, which implies that lower fractions of hydrogen are lost during purges. Net efficiency is relatively flat over the operative range, so this purging strategy tends to counterbalance the effects of polarization losses. However, power used to sustain auxiliaries shows a bigger impact than purge-related energy losses.

Performance degradation of a proton exchange membrane fuel cell with dead-ended cathode and anode

Proton exchange membrane fuel cells with dead-ended cathodes and anodes can simplify the fuel cell system and reduce costs. An experiment was performed to determine the performance degradation characteristics of Proton exchange membrane fuel cells with dead-ended cathodes and anodes. The effects of operating temperature and pressure differences between the cathode and the anode on the purging period were investigated in detail. The performance and cyclic voltammetry before and after the dead-ended operation were analyzed and compared. After the experiment, the membrane electrode assembly was cut to analyze the catalytic layer cross-section membrane morphology by scanning electron microscopy. The results showed that during operation, the fuel cell performance gradually decreases until the setting value, and then quickly recovers when the cathode outlet solenoid valve is triggered during a purging cycle. The dead-ended operating period decreases with an increase in operating temperature but increases with an increase in the pressure difference between the cathode and the anode. Flooding occurs easily in a Proton exchange membrane fuel cell with a dead-ended cathode and anode, causing performance degradation. Moreover, it may cause a decrease in the electrochemical surface area of the catalyst layer. The scanning electron microscopy images showed that both the upper and middle regions of the catalyst layers remained unchanged, whereas the downstream region corroded and become thinner in the dead-ended mode after 60 h.

Gas purging effect on the degradation characteristic of a proton exchange membrane fuel cell with dead-ended mode operation I. With different electrolytes

The effect of gas purging at the cathode on the degradation characteristics of dead-ended proton exchange membrane fuel cells (PEMFCs) is investigated herein using different electrolytes. Electrochemical techniques, including the measurement of polarization curves, cyclic voltammetry (CV) and surface and cross-sectional scanning electron microscopy (SEM) of tested the membrane electrode assemblies (MEAs), are applied to characterize the performance degradation of the fuel cells. The results show that mechanical failure of the membrane induced by the repeated gas purging in the fuel cell during dead-ended operation is the main cause of performance degradation. The performance degradation and the MEA failure mechanisms are not the same among the PEMFCs with different electrolytes. The Nafion® 211 (N211) undergoes much less degradation than Nafion® XL and Nafion® 115 (N115) after 1000 purge cycles under dead-ended operation of the fuel cell, as shown through the variation of the polarization curves, the electrochemical surface area (ECSA), and the membrane thickness. However, the mechanical properties of N211 were less favorable: after only 1000 purging cycles, the single cell with N211 experienced a dramatic voltage drop caused by pinholes on the membrane. In comparison, Nafion® XL and N115 can be subjected to 1600 cycles and 1800 cycles, respectively.

Gas purging effect on the degradation characteristic of a proton exchange membrane fuel cell with dead-ended mode operation II. Under different operation pressures

Gas purging is an effective method to remove the accumulated nitrogen and liquid water during the dead-end operation of polymer electrode membrane fuel cell (PEMFC). The effect of the operation pressure on the degradation characteristic of single cell is investigated under continuous gas purging cycles. Various diagnostic techniques including electrochemical characterization, physicochemical properties, and microstructure of the membrane electrode assembly (MEA) are applied to characterize the performance of the assembled single cells. After 1000 purging cycles, the single cell exhibits an obvious performance degradation, which can be proven from the change of the electrochemical surface area (ECSA), contact angle, cracks on the membrane and membrane thickness. The single cell with a relatively low oxygen pressure of 50 kPa has serious performance degradation. Comparatively, the assembled PEMFC has an enhanced durability with a high oxygen pressure of 200 kPa during the purging cycles under dead-ended operation mode.

Thermodynamic models of the adsorption and desorption of molecular oxygen at the UV and blue emitting centers in mesoporous silica under variable oxygen pressure

The UV excited emission properties of mesoporous silica in the blue and UV range are modified by the adsorption and desorption of oxygen molecules at the two defect sites. To interpret the experimental purging cycles we model the oxygen-silica interaction at thermodynamic level, succeeding in explaining the interaction mechanism and the trend of UV centre to undergo photo-bleaching when excited under vacuum conditions. The analysis called for the presence of two different set of defects for both the centres, pinpointed as defects liable to interact with O2 and non-interacting isolated defects. To support the thermodynamic analysis, we simulated the O2 adsorption and desorption processes within the first principles DFT cluster framework. The calculated atomic configurations and the potential energy curves along selected probable reaction paths allow suggesting the kinetics of molecular oxygen interaction on examined surface silica defects and pointing at an oxygen vacancy E’-like defect as the possible result of the UV centre photo-bleaching.

The role of basal hydrology in the surging of the Laurentide Ice Sheet

Abstract. We use the Glimmer ice sheet model to simulate periodic surges over the Laurentide Ice Sheet during the Last Glacial Maximum. In contrast to previous studies we use the depth of water at the base of the ice sheet as the switch for these surges. We find that the surges are supported within the model and are quite robust across a very wide range of parameter choices, in contrast to many previous studies where surges only occur for rather specific cases. The robustness of the surges is likely due to the use of water as the switch mechanism for sliding. The statistics of the binge–purge cycles resemble observed Heinrich events. The events have a period of between 10 and 15 thousand years and can produce fluxes of ice from the mouth of Hudson Strait of 0.05 Sv – a maximum flux of 0.06 Sv is possible. The events produce an ice volume of 2.50 × 106 km3, with a range of 4.30 × 106–1.90 × 106 km3 possible. We undertake a suite of sensitivity tests varying the sliding parameter, the water drainage scheme, the sliding versus water depth parameterisation and the resolution, all of which support the ice sheet surges. This suggests that internally triggered ice sheet surges were a robust feature of the Laurentide Ice Sheet and are a possible explanation for the observed Heinrich events.

Carbon corrosion and performance degradation mechanism in a proton exchange membrane fuel cell with dead-ended anode and cathode

This paper presents the work on a PEMFC (proton exchange membrane fuel cell) with DEAC (dead-ended anode and cathode) to achieve high hydrogen and oxygen utilization. Gas purging is an effective way to remove the excess water and maintain normal operation of fuel cell while the voltage drops to the set value chosen arbitrarily due to accumulation of generated water. However, serious carbon corrosion has been observed in MEA (membrane electrode assembly) under this purging model. Voltage degradation process during one purging cycle can be divided into three stages: dehydration of membrane induced ohmic loss, quasi-equilibrium state, and flooding induced concentration polarization. To improve the lifespan of PEMFC, gas purging should be conducted before water flooding. The operation time till the quasi-equilibrium state is suggested as the purging duration in the subsequent research. The results show that with the introduction of time regulator purging strategy, the decay rate of the carbon corrosion is greatly reduced. Moreover, it has also been found that the cell performance and purge cycle duration increase with increasing operating pressure, whereas they decrease with the increase in current density.

Growth per cycle of alumina atomic layer deposition on nano- and micro-powders

Core–shell powders consisting of a tungsten particle core and thin alumina shell have been synthesized using atomic layer deposition in a rotary reactor. Standard atomic layer deposition of trimethylaluminum/water at 150 °C utilizing a microdosing technique was performed on four different batches of powder with different average particle sizes. The particle size of the powders studied ranges from ∼25 to 1500 nm. The high mass-thickness contrast between alumina and tungsten in transmission electron microscopy images demonstrates that the particle core/shell interface is abrupt. This allows for the uncomplicated measurement of alumina thickness and therefore the accurate determination of growth per cycle. In agreement with prior works, the highest growth per cycle of ∼2 Å/cycle occurred on the batch of powder with the smallest average particle size and the growth per cycle decreased with increasing average particle size of a powder batch. However, the growth per cycle of the alumina film on an individual particle in a batch is shown to be independent of the size of an individual particle, and therefore, a powder batch which consists of particles size spanning orders of magnitude has constant shell thickness on all particles. This uniformity of thickness on different particle sizes in a particular batch is determined to be due to the difficulty of removing residual water molecules from the powder during the purging cycle of the atomic layer deposition (ALD) process. Therefore, rotary ALD on a single batch of powder with wide particle size distribution provides the same shell thickness regardless of individual particle size, which may have positive implications for particle ALD applications where the shell thickness determines critical parameters, such as particle passivation and manipulation of optical properties.