Purge Gas Research Articles

Experimental investigation of the corrosion behavior of Eurofer97 steel in contact with Lithium ceramic breeder pebbles under specific Helium Cooled Pebble Bed breeding zone atmosphere

For sub-sized fatigue specimens made of EUROFER97 in unconstrained contact to ceramic breeder pebbles, exposed to purge gas conditions for different durations in an oven, a chemical surface attack was observed which led to a significant reduction of fatigue lifetime [Aktaa et al., 2020]. To better reproduce the flow of the purge gas in the breeding zone of a Helium-Cooled Pebble Bed Breeding Blanket, the experiment was now repeated by placing the same kind of samples in the helium loop HELOKA HEMAT, where the gas is permanently circulated in a closed circuit, and its water content is controllable. The composition of the gas was monitored with a mass spectrometer and humidity sensors. The samples were exposed to a mixture of helium and 0.1vol% hydrogen at DEMO relevant operating conditions (550 °C, 1.2 bars abs.) for a duration of 8, 16, 32, and 64 days, respectively. New sample holders were designed which allow direct contact of the samples with the gas mixture. A special procedure for the handling of the test section was implemented to avoid contact of the hygroscopic pebbles with air humidity during the preparation phase and during the extraction of the samples from the test rig.The present contribution discusses the various considerations on which the test rig design was based, followed by a description of the experimental setup and preliminary results of the testing campaign. These are similar to the results achieved in the oven experiment. In the future, the loop will be used for tests with up to 200 Pa partial pressure of steam in helium; a mixture that is considered relevant for the DEMO purge gas composition.

Experimental Investigation on Pressure Drops of Purge Gas Helium in Packed Pebble Beds for Nuclear Fusion Blanket

The flow characteristics of purge gas helium in the pebble bed of the tritium breeding blanket are important in analyzing the tritium purging process and optimizing the design of the solid breeder blanket. Therefore, the flow characteristics of helium gas in randomly packed pebble beds are investigated experimentally with a focus on the analysis of the pressure loss distribution. The results show that gas velocity, bed dimension, and pebble diameters have an obvious influence on the helium flow characteristics in pebble beds. With the increase in the inlet helium gas velocity, the pressure drop gradient of helium in the pebble bed gradually increased. With increases in the pebble bed dimension, the pressure drop gradient of helium in the pebble bed gradually increased. With the increase in the pebble diameter, the pressure drop gradient gradually decreased. In addition, the effect of temperature on the pressure drop of helium in the pebble bed was also preliminarily investigated. The pressure drop gradient of the helium through the pebble bed obviously increased with the increase in the helium and the bed temperature. The experimentally obtained pressure loss characteristics can be used for the validation of the simulation of a blanket pebble bed and as input parameters in the thermo-hydraulic analysis of solid-tritium breeder blankets.

Investigation of Wall Effect on Packing Structures and Purge Gas Flow Characteristics in Pebble Beds for Fusion Blanket by Combining Discrete Element Method and Computational Fluid Dynamics Simulation

In a tritium-breeding blanket of a fusion reaction, helium, used as a tritium-purging gas, will purge the tritium breeder pebble beds to extract the tritium in blanket. The purge gas flow characteristics will affect the tritium extraction efficiency. The effect of the fixed wall on the pebble packing structures and purge gas flow characteristics was investigated by combining the discrete element method (DEM) and computational fluid dynamics (CFD) method. The results indicate that the fixed wall leads to a regular packing of the pebbles adjacent to the fixed wall in association with drastic fluctuations in the porosity of the pebble bed, which can affect the purge gas flow behaviors. Further analyses of helium flow behaviors show that the helium pressure in the pebble bed decreases in a linear manner along the flow direction, whereas the pressure drop gradient of helium increases gradually with an increase in the packing factor. The reduction in porosity in the pebble bed leads to a notable escalation in helium flow velocity. Concerning the direction perpendicular to the helium gas flow, the evolution of the cut-plane averaged velocity of helium is similar to that of the porosity, except in the region immediately adjacent to the wall. The pressure drop and flow characteristics obtained in this study can serve as input for the thermohydraulic analysis of the tritium blowing systems in the tritium-breeding blanket of a fusion reactor.

Gypsum-derived CaO catalytic pyrolysis of palm oil in a continuously packed bed reactor

This study employed a Gypsum-derived CaO catalyst with 10 wt% MgCO3 to convert palm oil into biofuel via pyrolysis in a continuous packed-bed reactor at atmospheric pressure without purge gas. The reaction occurred within the 500–550 °C temperature range, with varying catalyst calcination temperatures. ASTM D86 distillation to separate the pyrolytic oil into biogasoline (75–150 °C), biokerosene (150–250 °C), and biodiesel (250–330 °C) was conducted. The physical and chemical properties of products and catalysts using various techniques were determined. Notably, calcination temperature changes minimally affected the final oxygen content in the product but significantly influenced the textural properties of the catalyst. At a reaction temperature of 525 °C, the 10% MgCO3 catalyst calcined at 850 °C yielded the highest volume of distilled product distilled from pyrolytic oil, accounting for 100% of pyrolytic oil (equivalent to 66.44 vol% of palm oil). It implies that 100% of pyrolytic oil could be converted to distilled oil completely by the distillation process. The primary constituents of the pyrolytic oil were aliphatic and olefinic compounds, with a notable presence of ketones, mainly in the C5 to C33 range. C17 ketones were prominent, constituting approximately 5 wt% of the pyrolytic oil (equivalent to 2.92 wt% of palm oil). These ketones likely resulted from the decarboxylation of carboxylic acids and aldol condensation reactions facilitated by CaO or MgO catalysts. CaO decarboxylation was confirmed by the presence of CaCO3 in the spent catalyst. Additionally, the pyrolytic oil exhibited an acidity of approximately 5.72 mg KOH/g, primarily attributed to phenolic compounds, confirmed through GCxGC-FID, GCxGC-TOFMS, and 1H NMR spectroscopy.

High-temperature interaction of water vapor with lithium ceramics Li2TiO3

Selection of materials for fusion reactors and, in particular, for blanket systems is one of the most important tasks that determine the development of fusion energy. Lithium ceramics Li2TiO3 is considered as prospective candidate for solid breeders of future fusion reactors' blankets. The paper presents the results of high-temperature tests of Li2TiO3 + 5 mol% TiO2 ceramics, performed under conditions of blowing with argon containing impurities of water vapor of different isotopic compositions (H2O, HDO, D2O) in the range of temperature from 100 °C to 1400 °C. The vapor–gas mixture for the experiment was prepared in a special mixing tank. The interaction of Li2TiO3 + 5 mol% TiO2 ceramics with chemically active gases and water vapors was investigated by thermogravimetry (TG), differential scanning calorimetry (DSC) and mass spectrometry (MS) methods. As a result of experiment, the dependences of the sample mass change during heating under single purge gas composition was obtained. Mass spectra that characterize the changes in the qualitative composition of the gas mixture in the reaction chamber with the investigated sample were recorded and subsequently analyzed. An isotope effect is observed during the experiment: the release of D2 gas begins significantly earlier than the release of HD gas. The observed effect appears only in the high-temperature region (above 1050 °C), which characterizes the investigated material as almost completely chemically neutral towards water vapor.

Influence of Different Powder Conditioning Strategies on Metal Binder Jetting with Ti-6Al-4V.

Metal binder jetting shows great potential for medical technology. This potential can be exploited by integrating binder jetting into existing process routes known from metal injection molding. The biggest challenge here is the flowability and packing behavior of the powders used, due to their low size distributions. This paper investigates different powder-drying strategies to improve flowability using a statistical experimental design. Because of its relevance for medical applications, spherical Ti-6Al-4V powder with a size distribution under 25 µm is dried under various parameters using vacuum and gas purging. The investigated parameters, time and temperature, are selected in a central-composite-circumscribed test plan with eleven tests and three center points. The target parameters-water content, flowability and impurity levels (oxygen, nitrogen)-of the powder are analyzed. For validation, practical test trials are carried out on an industrial binder jetting system with unconditioned powder and conditioning with optimized parameters, comparing the manufactured parts and the powder bed. An optimized drying cycle with a duration of 6 h at 200 °C was determined for the investigated powder. Significant improvements in the dimensional accuracy (from ±1.5 to 0.3%) of the components and the visual impression of the powder bed are demonstrated.

Open-source electrochemical cell for in situ X-ray absorption spectroscopy in transmission and fluorescence modes.

X-ray spectroscopy is a valuable technique for the study of many materials systems. Characterizing reactions in situ and operando can reveal complex reaction kinetics, which is crucial to understanding active site composition and reaction mechanisms. In this project, the design, fabrication and testing of an open-source and easy-to-fabricate electrochemical cell for in situ electrochemistry compatible with X-ray absorption spectroscopy in both transmission and fluorescence modes are accomplished via windows with large opening angles on both the upstream and downstream sides of the cell. Using a hobbyist computer numerical control machine and free 3D CAD software, anyone can make a reliable electrochemical cell using this design. Onion-like carbon nanoparticles, with a 1:3 iron-to-cobalt ratio, were drop-coated onto carbon paper for testing in situ X-ray absorption spectroscopy. Cyclic voltammetry of the carbon paper showed the expected behavior, with no increased ohmic drop, even in sandwiched cells. Chronoamperometry was used to apply 0.4 V versus reversible hydrogen electrode, with and without 15 min of oxygen purging to ensure that the electrochemical cell does not provide any artefacts due to gas purging. The XANES and EXAFS spectra showed no differences with and without oxygen, as expected at 0.4 V, without any artefacts due to gas purging. The development of this open-source electrochemical cell design allows for improved collection of in situ X-ray absorption spectroscopy data and enables researchers to perform both transmission and fluorescence simultaneously. It additionally addresses key practical considerations including gas purging, reduced ionic resistance and leak prevention.

High temperature viscoelastic behaviour of sugarcane bagasse char and coal blends: Role of oxygen and porosity of char on fluidity reduction

This paper focuses on the introduction of sugarcane bagasse, an agricultural byproduct, as a renewable carbon-based additive to metallurgical coal to produce biocoke for the steel industry. Through subjecting pelletized sugarcane bagasse samples to various pyrolysis conditions, chars with varying properties were generated. With increasing final pyrolysis temperature (200, 400, 600, and 800 °C), a rise in carbon content and decline in oxygen, nitrogen and hydrogen levels in the chars were observed. The presence of an inert purge gas during pyrolysis prompted abundant micropore formation between 400 and 600 °C, yielding high specific surface area (SSA > 300 m2/g) chars at 600 °C and 800 °C. Conversely, chars produced in a fixed (unpurged) nitrogen environment exhibited minimal porosity and consequently low SSAs (<5m2/g). These various chars were then blended (at 10 % addition) with a medium-volatile bituminous coal to evaluate their impact on the viscoelastic properties of the coal. Chars pyrolyzed to lower final temperatures had the greatest detrimental effect on blend fluidity due to (1) their continued devolatilization which introduced void spaces in the blend creating pathways for the exhaust of coal volatiles, and (2) their elevated oxygen content, which scavenged essential mobile hydrogen needed to facilitate viscoelastic behaviour. Furthermore, chars with similar oxygen content but substantially different (by over two orders of magnitude) SSAs generated comparable coal-char blend viscosity profiles, indicating that the presence or absence of micropores in an additive does not significantly influence the viscoelastic behaviour of the coal. The reduction in blend fluidity for the addition of chars pyrolyzed to 800 °C was comparable to the modelled addition of inertinite macerals, implying that these high-temperature chars predominantly serve as inert solid additives. Comparison to a blend with 10 % mesoporous activated charcoal as the additive confirmed that it is mesopores that destroy fluidity, while micropores do not play a significant role. Mesopores were identified to adsorb/trap the relatively large tar-like compounds that are responsible for coal plasticity. Collectively, this research identifies three key factors contributing to fluidity reduction in coal-additive blends: void creation, oxygen content, and mesoporosity. These findings offer insights into optimizing biocoke production processes.

Comparative analysis of gas release from biphasic lithium ceramics pebble beds of various pebbles sizes and content under neutron irradiation conditions

This paper presents the results of 4 reactor campaigns on the irradiation of biphasic lithium ceramics containing different ratios of lithium orthosilicate (LOS) and lithium metatitanate (LMT) components (25 and 35 mol% LMT in LOS). The size distribution of pebbles in pebble beds was 250–1250 μm and 500–710 μm, respectively. The studies were carried out sequentially with each type of ceramics. In experiments carried out using the vacuum extraction method, the composition of gases released from lithium ceramic samples was registered in in-situ mode. The absence of purge gas during the experiments minimized the possibility of T2O and HTO formation, significantly simplifying processing of the results and providing more opportunities for results analysis. The main goal of the present paper was to identify the general patterns of the release of gases with mass numbers M2 (H2), M4 (He + HT), M6 (T2) and M18 (H2O) from ceramic samples throughout the entire irradiation experiment in 4 campaigns. Release trends of main gases with mass numbers M2, M4, M6 and M18 for all four campaigns are presented and their comparative analysis was performed. The average partial pressure of tritium release in the form of T2 and HT molecules for all campaigns was determined as 5.8 × 10-7 Torr. The dependences of formation rates of helium release peaks on the irradiation time were plotted. The nature of peak emissions does not have a monotonic relationship; upon irradiation, both an increase in the frequency of peaks and a decrease in it are observed. During irradiation, the process of peak helium release does not stop.The simulation was carried out by the finite element method, assuming that tritium release from the sample is determined by diffusion and desorption processes from the sample surface. The experimental curves are satisfactorily described by a number of sets of desorption and diffusion parameters. One way or another they lie in the range of specified values. The Arrhenius dependences of the effective diffusion coefficient and desorption coefficient obtained for lithium ceramics 35 LMT are equal to:D=5,2×10-11m2sexp-21kJmoleRT,K=1.21×10-4m2sexp-64kJmoleRT.The values of the effective diffusion coefficient and tritium desorption coefficient in 25 LMT ceramics were 15 and 20% lower than in 35 LMT ceramics.

Inert supports enhanced sulphur-resistant of iron-based oxygen carriers in chemical looping combustion of element sulphur

Sulphur chemical looping combustion (CLC) produces concentrated SO2 at low reaction temperatures. Here, the reaction mechanism of iron-based oxygen carriers (OCs) with sulphur and the cyclic reaction performance of the OCs were studied. The OCs were prepared on three inert supports (ZrO2, MgAl2O4, and Al2O3) with seven loading ratios using sol-gel method. The effects of the inert support, sulphur gasification temperature, OC reduction temperature, and N2 purge gas flow rate on the reaction between sulphur and OCs were investigated. For both Fe5Al5 and Fe5MgAl5 reductions, the FeO combined with Al2O3 to form FeAl2O4 spinel instead of being reduced further. Nevertheless, no spinel was formed in Fe2O3/ZrO2 (Fe5Zr5) reduction, but the over-reduction of FeO to Fe occurred. The reaction conditions were then optimized. The SO2 yields in the FR reached 87.68–91.61 %, and the FeS and FeS2 formed in the FR released SO2 in the AR. The three oxygen carriers (Fe5Al5, Fe5Zr5, and Fe5MgAl5) exhibited stable reactivity for ten cycles. Overall, Fe5Al5 was the optimal oxygen carrier for sulphur CLC, with respect to oxygen delivery, SO2 concentrations in the FR, and stability in redox cyclic reactions.

Thermodynamic limits of the depolymerization of poly(olefin)s using mechanochemistry.

Mechanochemistry is a promising approach for chemical recycling of commodity plastics, and in some cases depolymerization to the monomer(s) has been reported. However, while poly(olefin)s comprise the largest share of global commodity plastics, mechanochemical depolymerization of these polymers in standard laboratory-scale ball mill reactors suffers from slow rates. In this work, the observed reactivities of poly(styrene), poly(ethylene) and poly(propylene) are rationalized on the basis of thermodynamic limitations of their depolymerization by depropagation of free radical intermediates. In addition, subsequent phase partitioning equilibria for the removal of monomers from the reactor via a purge gas stream are discussed for these polymers. For poly(styrene), a typical vibratory ball mill supplies just enough energy for its depolymerization to be driven by either thermal hotspots or adiabatic compression of the impact site, but the same energy supply is far from sufficient for poly(propylene) and poly(ethylene). Meanwhile, removal of styrene from the reactor is thermodynamically hindered by its lower volatility, but this is not an issue for either propylene or ethylene. The implications of these thermodynamic limitations for mechanochemical reactor design and potential for mechanocatalytic processes are highlighted.

Low-Power Consumption IGZO Memristor-Based Gas Sensor Embedded in an Internet of Things Monitoring System for Isopropanol Alcohol Gas.

Low-power-consumption gas sensors are crucial for diverse applications, including environmental monitoring and portable Internet of Things (IoT) systems. However, the desorption and adsorption characteristics of conventional metal oxide-based gas sensors require supplementary equipment, such as heaters, which is not optimal for low-power IoT monitoring systems. Memristor-based sensors (gasistors) have been investigated as innovative gas sensors owing to their advantages, including high response, low power consumption, and room-temperature (RT) operation. Based on IGZO, the proposed isopropanol alcohol (IPA) gas sensor demonstrates a detection speed of 105 s and a high response of 55.15 for 50 ppm of IPA gas at RT. Moreover, rapid recovery to the initial state was achievable in 50 μs using pulsed voltage and without gas purging. Finally, a low-power circuit module was integrated for wireless signal transmission and processing to ensure IoT compatibility. The stability of sensing results from gasistors based on IGZO has been demonstrated, even when integrated into IoT systems. This enables energy-efficient gas analysis and real-time monitoring at ~0.34 mW, supporting recovery via pulse bias. This research offers practical insights into IoT gas detection, presenting a wireless sensing system for sensitive, low-powered sensors.

RESEARCH AND EVALUATION OF THE METHOD OF ACTIVATION OF THE GAS FLOW FOR ALLOYING WITH GASEOUS NITROGEN"

Increasing the strength of steels and improving their operational qualities is one of the main tasks contributing to solving the issue of reliability, durability of parts and structures. Alloying, including nitrogen, occupies a special place among the large number of ways to improve the properties of steels.&#x0D; Nitrogen, as an alloying element, has been known for a long time, and its sufficiently high content in the atmosphere makes nitrogen even more attractive to technologists. However, it has limited solubility in iron alloys, especially with a high content of other components.&#x0D; There are various methods of gas activation, but in order to ensure relatively low energy costs and having positive experience of works on electric high-voltage activation of oxygen, it was proposed an option of activation by creating an electric brush discharge.&#x0D; The research was carried out on a physical bench that simulates the section of the lance at the outlet for the supply of activated gas when using different types of closed-type discharge devices. The devices differed by the arrangement of one of the electrodes: with a submerged non-insulated electrode and a protruding almost completely insulated electrode. The effect of purge gas pressure and arc length (distance between electrodes) on the efficiency of the nitrogen-containing gas flow ionization process (using air as an example) was analyzed. It was established that when using a discharge device with a submerged electrode, the current strength that forms the activated gas has a quadratic function on the distance between the electrodes with a maximum at a distance of about 15 mm and a purge gas pressure of 0.25—0.3 MPa. With a further increase in pressure, the visible discharge disappears and the current decreases.&#x0D; When using a discharge device with a protruding electrode, much higher indicators of the strength of the ionized current were obtained while maintaining a visual discharge even at high pressures of the purging gas (0.6MPa). At the same time, the current strength increases with an increased discharge distance — with the highest values at low blow-by pressures. That is, the version of the discharge device with a protruding electrode is more promising from the point of view of activation of the nitrogen-containing gas stream.

(Digital Presentation) Direct Regeneration of NMC622 Cathode Material from Spent EV Li-Ion Batteries Via Hydrothermal Re-Lithiation

With the increasing demand for electric vehicles, there is a need to address the issues associated with the increasing number of waste or spent Li-ion batteries. A simpler and less expensive approach to recycle cathode materials from spent batteries, compared to hydrometallurgy and pyrometallurgy, is direct regeneration. In this study, a facile and cost-effective hydrothermal re-lithiation method, followed by post-annealing, was explored to repair the structure, morphology, and composition of spent NMC622. The effects of annealing temperature and purging gas on the physicochemical properties of the regenerated NMC622 were evaluated. The regenerated NMC622, annealed at 800°C under O2, exhibited an XRD profile that closely resembled that of the as-received spent NMC622, with peaks indexed to the planes of the α-NaFe2O4 structure and without any impurities. Additionally, it achieved the highest I(003)/I(104) ratio and the closest c/3a ratio to that of the as-received spent NMC, indicating that the original structure was successfully repaired after regeneration. It also exhibited less agglomeration, with a narrower particle size distribution than the as-received spent NMC622, indicating that the morphology was improved after regeneration. Elemental composition analyses further confirmed that the spent NMC622 was successfully regenerated using the employed method, as the Li content after regeneration increased from 6.99 to 7.20 wt%, a value close to the theoretical (7.16%). In general, this simple and inexpensive direct regeneration strategy provides a new perspective for lithium-ion battery regeneration, which can be extended to other battery systems in the future.

New Characterizations for PEFC Under Sub-Zero Temperature

The operation of fuel cells at sub-zero temperature results in direct deposition of ice or production of supercooled water that freezes upon interacting with nucleation seeds. Ice formation can lead to irreversible mechanical damages in membrane electrode assembly (MEA), particularly at interfaces, which is detrimental to the performance and safety of fuel cells. The mitigation strategies are focused on temperature elevation, including assisted heating, catalytic heating, and starvation (low potential) heating; however, these are associated with parasitic loss that reduces overall efficiency of the system. An alternative method is to develop porous media that are capable of ensuring oxygen transport pathways in the presence of ice or retaining supercooled water without phase transition until the cell reaches above 0ºC.The development of ice-resistant porous media for sub-zero operation is hindered by limitations on material characterization and performance evaluation techniques. The most common characterization technique is differential scanning calorimetry (DSC), by which water-saturated porous media is subjected to rapid temperature cycles to measure melting and freezing peaks. The DSC is a well-established and convenient technique that is suitable for statistical analysis; however, the sample size is limited to the mm-scale, and water must be injected in hydrophobic media prior to the DSC measurement where water saturation level and morphology are unpredictable. In situ testing of novel materials are performed on single cell hardware, in which the temperature is controlled by circulating a coolant through endplates or cooling channels that are placed several mm to cm away from an MEA. Such pseudo-active cooling system results in a significant difference (and delay) between the coolant and cell temperatures, influenced by heat production due to cell operation as well as freezing/melting. On the other hand, free heating operation starting from sub-zero is not desirable, since product heat is dissipated to current collectors and endplates that have much greater mass per active area in comparison to stack. As a result, most of sub-zero tests are performed on isothermal condition.Our previous works [1,2] introduced a unique single fuel cell hardware featuring temperature control and heat flux measurement (TCHM) system. Thermoelectric coolers and tangential gradient heat flux sensors enable a precise control of temperature in the MEA and detection of freezing and melting events during the cell operation. We have advanced the TCHM controlling software and integrated them on the custom fuel cell test bench. In this work, two novel techniques are introduced for sub-zero application for fuel cell porous media: (1) advanced calorimetry and (2) non-isothermal cold start.The advantages of our advanced calorimetry include testing of a large sample area up to 12cm2 and control of water quantity in a gas diffusion layer (GDL). Through neutron imaging, we validated capillary water injection method in the GDL and reduced saturation level with drying gas purging. Using techniques, we analyzed the effect of GDL structures and hydrophobicity on repeated freezing-thaw cycle to assist design of ice-resistant material. Additionally, we successfully implemented non-isothermal cold-start at -20 ºC in addition to isothermal condition, as seen in Figure 1. After the calibration of the TCHM units, the heating load was emulated to match that of the stack, corresponding to the heating rate between 10-15 K/min.The methods introduced in this study are expected to make a significant contribution towards the development of GDLs and catalyst layers that suppress ice formation and related mechanical damages. In particular, the non-isothermal cold-start provides a flexible, precise temperature control in the MEA, which can bridge the gap between the single cell and stack testing. Reference [1] J. Lee, E.R. Carreon-Ruiz, M. Siegwart, P. Boillat, Segmentation for Preventing Ice Propagation in Operating Fuel Cells, Meet. Abstr. MA2021-02 (2021) 1066. https://doi.org/10.1149/MA2021-02361066mtgabs.[2] M. Siegwart, F. Huang, M. Cochet, T.J. Schmidt, J. Zhang, P. Boillat, Spatially Resolved Analysis of Freezing during Isothermal PEFC Cold Starts with Time-of-Flight Neutron Imaging, Journal of The Electrochemical Society. 167 (2020) 064510. https://doi.org/10.1149/1945-7111/ab7d91. Figure 1

Atomic Layer Etching of GaN and AlGaN Using CH4/H2, H2 and HCl Chemistry

Modern microelectronic components for high-power and high-frequency applications require reliability and reproducibility of the production processes. Atomic layer etching (ALE) represents a key technology for achieving these requirements.An ALE sequence is characterized by a chemical modification step that affects only the top atomic layer of the surface (adhesion) and an ion assisted non-reactive inert gas etching step that removes only this chemically modified area due to creation of volatile byproducts. These two steps are separated by inert gas purge. This grants the etching of single atomic layers. The etching step can be triggered by thermal energy or kinetic energy by impinging particles (e.g. ion bombardment by a plasma). The low energy required for ALE guarantees low-damage etching.In literature ALE processes using Cl2 are often reported. In this work, the results of plasma-enhanced ALE of GaN and AlGaN using different chemistries of CH4/H2, H2 and HCl as etch gases are presented. The experiments were performed with a highly customized etch facility equipped with a capacitively coupled plasma source (CCP, 60 MHz) and a substrate bias generator (RF, 2 MHz). The investigations were carried out on epitaxially deposited GaN on sapphire with masks of protective resist and SiO2 as well as GaN-AlGaN heterostructures with patterned SiO2 maskings. For process analysis optical emission spectroscopy (OES) was carried out. The etching rate and roughness were determined by ellipsometry and atomic force microscopy (AFM) as well as scanning electron microscopy (SEM).Observations by OES indicate a successful excitation and dissociation of the etching molecules. With rising plasma powers physical sputtering effects were revealed. At the beginning of the process development continuous etching processes were examined. With CH4/H2 chemistry using GaN samples it was found that the etching behavior is strongly influenced by the type of masking material. Protective resist resulted in a low etch rate of 7.5 nm/min and significant damage of the masking material. The cause of this behavior is assumed to be redeposition of material by interaction of methane, resist, and plasma. With the change to a hard mask of SiO2 etch rates of 45 to 72 nm/min were achieved, increasing with RF-power and CH4/H2 ratio. Adding methane led to detrimental side effects such as dendrite growth and wall formation on the transient region of unmasked to former masked sample areas. In the further development of the ALE process an etch chemistry using only hydrogen as the chemical etchant was used resulting in an etch per cycle (EPC) of about 3 Å for GaN samples. Further investigations of ALE with hydrogen etch chemistry on GaN-AlGaN samples revealed that AlGaN, in contrast to pure GaN, could not be etched successfully with this chemistry.Substituting CH4/H2 or H2 to HCl enables the etch of AlGaN. The investigations carried out indicate that this etching process is also a self-limiting ALE. AFM measurements revealed an EPC of 1.2 Å for lower RF-powers (50 W). Increasing the RF power to 150 W only slightly enhance the EPC to 2.0 Å. The surface roughness tends to decrease with rising RF-power from 50 to 300 W.

Morphological and Electrical Characterization of AlGaN/GaN Heterostructures Modified By Atomic Layer Etching

Modern microelectronic components for high-power and high-frequency applications based on III-V compound semiconductors offer high break down voltage (GaN: 5 MV/cm and AlN: 15 MV/cm) at low specific on-resistance. However, it requires reliability and reproducibility of the production processes. Going to higher frequencies (5 GHz and beyond) and more integration in consumer electronics, smaller structure sizes are needed. This is going along with increasing demands on the manufacturing processes like dry etching. The main goal is to reach smaller and high controllable etching rates, going down to single atomic layers, low damage, and minimized surface roughness. Atomic layer etching (ALE) represents a key technology in order to achieve such requirements.An ALE process consists of two independent steps forming a repeatable cycle with a specific etching amount per cycle (EPC). First a surface modification is done by a chemical precursor i.e., adsorbing or oxidizing the surface. The second step is the removal of the modified layer, either physically by low energy non-reactive ion bombardment (Plasma Enhanced ALE [PEALE]) or chemically by a reactive species (Thermal ALE). The two steps are separated by an inert gas purge. This purging grants the removal of the chemistry after the first step, preventing further chemical reaction and transporting the chemical products out of the chamber after the second step.In this study, a PEALE conducted on different tools is used, for gate and contact recess study in a AlGaN/GaN heterostructure to form high electron mobility transistors (HEMT) with reduced ohmic contact resistance and threshold voltages. The results show a reduction of ohmic contact resistance at reduced forming temperatures and a linear dependence of the threshold voltage on gate recess depth. In order to determine the etching rate and roughness, atomic force microscopy (AFM) measurements were performed.The PEALE module is either integrated into a cluster tool consisting of atomic layer deposition (ALD) and chemical vapor deposition (CVD) or done in a combined ALD/ALE chamber. This opens the possibility of etching and depositing in-situ, reducing contamination and degradation of the substrate material.By this means, metal insulator semiconductor (MIS)-HEMTS with a recessed gate are studied. The monitoring of the individual processes is achieved by test structures like transfer length method structures (TLM) and metal oxide semiconductor (MOS), which showed the improved electric performance of these devices and may indicate unwanted interface issues, respectively. Additional, pre- and post-treatments could improve the interfaces further. The results will be presented and discussed in terms of ALE process development and optimization.This work was financially supported within the ALEStar project by the government of the Free-state of Saxony and the European Regional Development Fund under grant no. SAB 100402929.

Model Investigation of Argon Injection into Liquid Steel at Ladle Furnace Station with Using of Innovative Module.

High-quality steels are defined primarily by a small quantity of non-metallic inclusions and a high degree of chemical homogenisation. The ladle furnace (LF) is the most important metallurgical unit in which the quantity of non-metallic inclusions can be significantly reduced while ensuring metal chemical homogenisation. It is achieved largely due to appropriate controlling and the use of increasingly developed inert gas purging techniques. Various types of porous plugs (channel or radial type) are used in the metallurgical ladles. In aggregate units of intermediate-ladle type, various types of channel plugs and/or gas curtains are successfully used. In the research presented herein, a new and innovative module for inert gas injection into liquid steel for deep refining was tested. The presented research relates to the innovative module using to replace the standard porous plug in the steelmaking ladle on the outside-furnace (LF) processing station. Hybrid modelling methods (numerical and physical modelling) were used to carry out research. Module using causes significantly faster alloy additive dispersion in ladle volume compared with the standard solution (the standard porous plug). Furthermore, the obtained flowing structure positively affects liquid steel refining and mixing processes after alloy additive addition. A new technological solution, i.e., gas-injection module-differs from the traditional porous plugs currently used in the steel mills in terms of geometric parameters, external and internal structure, and what is most importantly, terms of the active surface area-shall be understood in as the surface area wherein slots occur.

Self-cleaning effect and secondary swirling clean gas for suppressing particle deposition on vortex finder of gas cyclones

In order to suppressing the particle deposition on vortex finder, a series of gas cyclones with the secondary swirling clean gas were developed inspired by the gas purge effect. Effects of the width and extension length of the flow channel as well as the secondary inlet velocity and running time on the particle deposition pattern, the deposited particle mass and the cyclones’ performance were experimentally investigated, respectively. The results show that the ultrafine particles (Stokes number Stk < 0.0358) are mainly loose deposited on the walls under the secondary gas. Compare to the conventional cyclone with single tangential inlet, the total deposited particle mass of the improved cyclone has a maximum reduction more than 60%, and the collecting efficiency is increased up to 97.5% under the basically same pressure drop. The corresponding no-deposition area is increased by about 13%, and remains constant in spite of extending the running time. Moreover, an interesting phenomenon named “self-cleaning effect” of the vortex finder was captured for the gas cyclones, and mechanism of the secondary clean gas on the particle deposition is preliminarily analyzed. The results can deepen the understanding of the particle deposition on the vortex finder and guide the design of the anti-coking gas cyclones.

Thermal effect of high-power laser propagation in complex channels and its mitigation

We investigate the channel thermal effect resulting from the gas thermal blooming effect and mirror thermal deformation on the beam quality, and we propose a mitigation measure for blowing purge gases. Without gas blowing, the gas thermal blooming effect opposes the influence of mirror thermal deformation on the beam phase, resulting in significant phase distortion and offset. Noticeable distortion and divergence of the laser spot was also observed. After blowing purge gases, the beam phase was primarily determined by the mirror thermal deformation. Simultaneously, the mean-squared beam width decreased uniformly, improving the symmetry and energy concentration of the laser spot. However, the laser spot tended to stabilize when the gas velocity exceeded a certain threshold.