Residual Gas Composition Research Articles

The origin and control of interstitial impurities in refractory complex concentrated alloys

Interstitial impurities, primarily O and N, inadvertently introduced during the processing of refractory complex concentrated alloys (RCCAs) significantly limit the mechanical properties of the alloys at room temperature. Plasma arc melting (PAM) has facilitated the quest for RCCAs, showcasing remarkable combinations of strength and ductility. In this work, the composition and chemistry of residual gases in the PAM chamber environment during arc melting and the interstitial impurities in elemental feedstocks were analyzed to quantify the origin of O and N during synthesis. Moreover, the thermodynamic mechanisms governing the origin of interstitial impurities in arc-melted MoNbTaW RCCAs were discussed. With an understanding of the mechanisms governing the content of interstitial impurities in RCCAs during PAM, arc-melted MoNbTaW RCCAs with fewer than 100 ppm O were synthesized. The arc-melted MoNbTaW RCCAs were then characterized using electron microscopy and atom probe tomography to establish the compositional architecture of grain boundaries and thereby elucidate the thermodynamic drive for segregation and oxide formation in MoNbTaW. Additionally, density functional theory calculations of a MoNbTaW grain boundary were employed to analyze the effect of local chemical fluctuations on the O segregation and oxide formation at the grain boundary. This detailed understanding of the thermodynamic mechanisms governing the origin of interstitial impurities and their grain boundary segregation in MoNbTaW RCCAs provides greater context surrounding O interactions in RCCAs, which is key for the successful development of refractory alloys with unique combinations of strength and ductility.

Time-dependent variations in desorbed gas composition: methodological analysis of asphaltite vein investigation results

In this study, a phenomenon that can have significant technical and economic impacts in the mining and unconventional gas production of hydrocarbon resources is discussed, change of gas composition during desorption period. The change is analyzed, related findings are obtained and engineering tools are forged. In this scope, a member of the Southeastern Turkey asphaltite’s gas content and composition character was examined. 12+1 samples were collected at equal intervals from an inclined drillhole that cut through the asphaltite vein. The United States Bureau of Mines (USBM) direct method was employed to determine the gas content. Gas composition analysis was performed on gas samples, which were collected four times throughout the desorption period. Residual gas composition is determined as well. During desorption period, methane and hydrogen ratios exhibited decreasing trends, while others have increasing trends. In evaluating of the collected data, the desorption order between gas compounds are revealed. Logarithmic trend functions are generated to estimate the concentrations of gas compounds at specific time points. With these functions and gas content measurement data, weighted average concentrations for gas compounds are determined. These concentration functions and the weighted average results are used to create engineering tools showing unit energy content of desorbed gas through desorption period both instantaneous and cumulative. Similarly, change in lower explosive limit and auto-ignition temperature during desoption period is shown. The weighted average gas concentrations obtained are used to interpret geological insights as they are the actual gas composition of the samples. In the study, gas content characteristic properties of Üçkardeşler asphaltite vein is comprehensively presented. Accordingly, the mean gas content, excluding one sample with a value of 2.78 m3/t at a location near a fault intersection, was found to be 1.66 m3/t. The average volumetric concentrations of methane, ethane, propane, and acetylene in the desorbed gas were determined as 61.6%, 24.5%, 10.7%, and 2.3%, respectively. The remaining part primarily consisted of heavier hydrocarbons, with low amounts of carbon dioxide and hydrogen.

In situ monitoring of industrial-scale chemical vapor deposition using residual gas analysis

The maintenance of industrial-scale equipment demands more effort and incurs higher costs compared to that of laboratory-scale equipment, necessitating the use of predictive maintenance techniques to mitigate unforeseen outcomes. This paper presents a demonstration of the in situ monitoring of industrial-scale low-pressure chemical vapor deposition equipment by using a residual gas analyzer (RGA). The RGA provides reactions of precursor gases by tracing the concentration and composition of residual gases within vacuum reactors. Furthermore, RGA analysis enables the prediction of the growth rate of the thin-film, providing insights into thin-film growth dynamics during the process. In situ monitoring using an RGA can be applied to diverse semiconductor fabrication processes, including thin-film growth, oxidation, reactive ion etching, and ion implantation, owing to its compatibility with vacuum processes. This study addresses the existing difficulties in the exploration of RGA monitoring techniques for industrial-scale equipment and bridges the disparity between laboratory-scale and industrial-scale processes.

Estimation of Absorbed Dose due to Gas Bremsstrahlung Based on Residual Gas in Electron Storage Rings

Gas bremsstrahlung, generated by the interaction between stored electrons and residual gas in electron storage rings, is an important radiation source for the shielding of synchrotron radiation (SR) facilities. In recent SR facilities, hydrogen was found dominant in the residual gas of the vacuum chambers of the electron storage rings, although air has been conventionally assumed as the bremsstrahlung target for the shielding designs of SR beamlines extended from the electron storage ring. To study the effect of residual gas composition on the dose rate outside shields, we calculated the intensity of gas bremsstrahlung based on the gas composition for both the air and the residual gas expected in the recent electron storage rings using an analytical formula and general-purpose Monte Carlo codes for particle transport calculations. The analytical shielding calculation with a realistic gas composition was found to well reproduce the energy spectra of gas bremsstrahlung simulated by the Monte Carlo codes. The correction factors between the air and the realistic gas compositions are applied to the conventional analytical formulas for dose estimation of secondary radiations generated by the interaction between the bremsstrahlung from air and beamline components.

Influence of gasoline fuel formulation on lean autoignition in a mixed-mode-combustion (deflagration/autoignition) engine

Stoichiometric spark-ignition engines suffer efficiency penalties due to throttling losses at low loads, a low specific-heat ratio of the stoichiometric working fluid, and limits on compression ratio due to end-gas autoignition leading to undesirable knocking. Mixed-Mode Combustion (MMC) mitigates these shortcomings by using a lean working fluid where a spark-initiated pilot-stabilized deflagrative flame front is followed by controlled end-gas autoignition. This MMC study investigates the effects of initial conditions (intake air temperature, intake pressure, equivalence ratio, and intake oxygen fraction) on autoignition tendency of four gasoline-range fuels with varying properties and composition. The use of fuels with varying octane sensitivity (S) allowed exploring the importance of low-temperature heat release in triggering autoignition. Fuels with high S were less reactive for conditions that promote low-temperature chemistry (operation at high intake air pressure or without N2 dilution). Conversely, an Alkylate fuel with low S showed a greater autoignition resistance at operating conditions that were unfavorable for low-temperature chemistry. Next, the effect of residual gas composition on autoignition tendency of fuels was examined with a chemical-kinetics model. Among the various molecules in the residual gas, nitric oxide (NO) enhanced the low-temperature chemistry and increased the autoignition tendency most significantly. The fuels’ autoignition response to increasing NO amount corroborates the experimental observations. Next, the sequential autoignition of the end-gas was assessed to be less impacted by thermal stratification because of lean mixtures showing relatively less low-temperature chemistry, when compared to stoichiometric mixtures. Next, the effect of changing equivalence ratio on the autoignition was found to be similar for all fuels, regardless of their S. With changing intake air temperature, the response of fuels’ autoignition tendency depended on the dilution level used. At high dilution (i.e. low intake [O2]), fuels’ reactivity increased with increasing intake air temperature. In contrast, for operation without dilution, the autoignition tendency of the low-S Alkylate fuel decreased with increasing intake air temperature, while that of high-S High Cycloalkane fuel still increased with increasing intake air temperature. In conclusion, conventional octane metrics (RON and MON) have utility in assessing the autoignition tendency under lean MMC operation. Moreover, the fuel requirements for MMC align with that of stoichiometric operation: i.e., high RON and high S fuels are desirable for stable non-knocking operation.

The 13C-depleted methane in terrigenous shale gas: A case study in the Triassic Yanchang Formation, Ordos Basin

The methane carbon isotopic composition (δ13C1) of some shale gas, and of some conventional gas in shale gas regions, is more depleted in 13CH4 than can be predicted from vitrinite reflectance (Ro) using the δ13C1-Ro equation. This is also often the case for coal bed methane. There is currently no convincing explanation for this phenomenon primarily because wellhead gas or core desorption cannot represent the original, in-situ state of the shale gas, owing to problems of desorption fractionation, lost gas, and residual gas. In this paper, we focus on shale gas in the Yanchang Formation of the Ordos Basin. To avoid the above-mentioned problems and obtain the shale gas in-situ, two shale samples, obtained from pressure coring, were used for parallel experiments. The gas desorption experiment was carried out under normal temperature and heating conditions, the core residual gas was obtained by crushing, and the components and carbon isotopic composition of desorption gas and residual gas were analyzed. The δ13C1 values for the two shale (Ro = 1.2%) desorption gas samples were −50.7‰ and −50.8‰, about 10‰ lighter than the value of −40.6‰ predicted by the empirical δ13C1-Ro formula. The δ13C1 values for the small amount of core residual gas in the two samples were −47.0‰ and −47.6‰, indicating that δ13C1 of Yanchang Formation in-situ shale gas is about 10‰ lighter than the δ13C1-Ro empirical formula predicts. This difference may be related to gas adsorption onto organic matter and clay minerals in shale. The negative δ13C1 is due to the retention of pre-biogas and early thermogenic gas. Dynamic adsorption experiments with activated carbon and a 5 Å molecular sieve show that early methane molecules preferentially occupy adsorption sites with relatively low pore radii and are likely to be replaced by late methane molecules, due to the high adsorption energy. The pore size distribution characteristics of shale in the Yanchang Formation are generally consistent with this pattern. In general, the δ13C1 of shale gas is related to adsorption, and the degree to which it is negative is related to the adsorption intensity and pore structure of the source rock.

High Vacuum Packaging of MEMS Devices Containing Heterogeneous Discrete Components

Vacuum packaging of Micro-electro-mechanical system (MEMS) devices is a hot topic for its advantages of improving performance and reducing power consumption. In this paper, the physics package of a chip scale atomic clock (CSAC), as a typical kind of MEMS device, is performed by vacuum packaging based on a systematic method proposed by us. The whole process, including low outgassing and thermal stable materials selection, prebaking for desorption, getter firing for absorption and solder reflow for vacuum sealing is introduced thoroughly. The thermogravimetric analysis or thermal gravimetric analysis (TGA) is used to analyze the thermal stability and desorption of materials. The leak rate of physics packages is measured to be less than 4 × 10−10 Pa·m3/s by helium leak detection. The residual gas pressure and composition in physics packages are analyzed after vacuum packaging. The results show a high vacuum ~0.1 Pa in the physics package. The frequency stability is improved from 4.68 × 10−11 to 1.07 × 10−11 @40,000 s. The presented method for high vacuum packaging is also applicable to other MEMS devices.

Factors influencing surface carbon contamination in ambient-pressure x-ray photoelectron spectroscopy experiments

Carbon contamination is a notorious issue that has an enormous influence on surface science experiments, especially in near-atmospheric conditions. While it is often mentioned in publications when affecting an experiment’s results, it is more rarely analyzed in detail. We performed ambient-pressure x-ray photoelectron spectroscopy experiments toward examining the build-up of adventitious carbon species (both inorganic and hydrocarbons) on a clean and well-prepared surface using large-scale (50 × 10 mm2) rutile TiO2(110) single crystals exposed to water vapor and liquid water. Our results highlight how various factors and environmental conditions, such as beam illumination, residual gas pressure and composition, and interaction with liquid water, could play roles in the build-up of carbon on the surface. It became evident that beam-induced effects locally increase the amount of carbon in the irradiated area. Starting conditions that are independent of light irradiation determine the initial overall contamination level. Surprisingly, the rate of beam-induced carbon build-up does not vary significantly for different starting experimental conditions. The introduction of molecular oxygen in the order of 10 mbar allows for fast surface cleaning during x-ray illumination. The surface carbon contamination can be completely removed when the oxygen partial pressure is comparable to the partial pressure of water vapor in the millibar pressure range, as was tested by exposing the TiO2(110) surface to 15 mbar of water vapor and 15 mbar of molecular O2 simultaneously. Furthermore, our data support the hypothesis that the progressive removal of carbon species from the chamber walls by competitive adsorption of water molecules takes place following repeated exposure to water vapor. We believe that our findings will be useful for future studies of liquid-solid interfaces using tender x rays, where carbon contamination plays a significant role.

Evidence Against Carbonization of the Thin-Film Filters of the Extreme Ultraviolet Variability Experiment onboard the Solar Dynamics Observatory.

In spite of strict limits on outgassing from organic materials, some spacecraft instruments making long-term measurements of solar extreme ultraviolet (EUV) radiation still suffer significant degradation. While such measures have reduced the rate of degradation, they have not completely eliminated it in some cases. For example, in five years, the aluminum filters used in the Extreme Ultraviolet Variability Experiment (EVE) instruments onboard the Solar Dynamics Observatory (SDO) suffered losses exceeding 40% at 30.4 nm. Comparing those losses with the negligible losses of nearby zirconium filters on the same instruments indicated that the problem was not due to carbonization on the Sun-facing side of the filter. To investigate whether the loss was due to carbon deposition on the downstream face of the Al filter, we exposed the backsides of Al and Zr filters to EUV in the presence of a volatile organic solvent in the laboratory and concluded that this could not be the cause. Given that the residual gas composition in the SDO spacecraft likely has water vapor as well as organics, these findings suggest that the transmission loss in the Al filter originated with oxidation caused by UV-activated adsorbed water.

Improvement of vacuum characteristics of cryostats for HPGe gamma-radiation detectors

Using mass spectrometry methods, the composition of residual gases and its temporal dynamics in experimental cryostats for HPGe detectors of gamma radiation, have been investigated. The studies were carried out for a vertical dipstick cryostat with vacuum chamber of small volume (1200 cm3) and an U-type cryostat having its vacuum chamber combined with vacuum cavity of a Dewar vessel (total volume 36500 cm3). Results of residual gas analysis are presented, showing the effect of Combogetter on a composition of residual gases of warm cryostats. Its use as an auxiliary getter for cryostats with HPGe detectors, maintaining a vacuum during storage or transportation, is considered.

Residual gas analysis in vacuum insulation panel (VIP) with glass fiber core and investigation of getter for VIP

Vacuum insulation panel (VIP) based on glass fiber core material has attracted considerable attention in building insulation due to lower core material cost than fumed silica. The insulation performance and service life of VIP are significantly dependent on the residual gas pressure and gas composition in VIP. Residual gas composition is measured using a newly-developed test apparatus that contains quadrupole mass spectrometer (QMS) and gas inlet system (GIS) in this paper. The results indicate that the main residual gases are nitrogen (N2), oxygen (O2) and water vapor (H2O) in the initial stage of VIP with thermal conductivity 1.52 mW m−1 K−1, while nitrogen (N2), oxygen (O2) hydrogen (H2) and water vapor (H2O) become the main residual gases after two years with thermal conductivity 6.80 mW m−1 K−1. Correspondingly, a composite getter for VIP is investigated, sorption capacities of which for hydrogen (H2), oxygen (O2) and water vapor (H2O) are measured in this paper. It is predicted that the central thermal conductivity of VIP with getter increases to 15 mW m−1 K−1 after 25 years, which is one step towards a future recommendation for building sectors.

СОСТАВ ОСТАТОЧНЫХ ГАЗОВ ИСКОПАЕМЫХ УГЛЕЙ И ОЦЕНКА ИХ РОЛИ В СОЗДАНИИ ПОЖАРОВЗРЫВООПАСНЫХ СИТУАЦИЙ В УГОЛЬНЫХ ШАХТАХ

СОСТАВ ОСТАТОЧНЫХ ГАЗОВ ИСКОПАЕМЫХ УГЛЕЙ И ОЦЕНКА ИХ РОЛИ В СОЗДАНИИ ПОЖАРОВЗРЫВООПАСНЫХ СИТУАЦИЙ В УГОЛЬНЫХ ШАХТАХ

Evaluation of the Gas Content in Archived Shale Samples: A Carbon Isotope Study

We examined 14 archived samples of shale for the chemical and 13C isotopic composition of residual gases produced as part of rock-crushing operations at a hammer mill. Results were compared with data on maturity from Rock-Eval pyrolysis and vitrinite reflectance measurements. The samples originated from three different formations (Mikulov Marls, Ostrava Formation, and Liteň Formation) located in the Czech Republic. For comparison, we examined a gas-prone shale sample from the Polish Silurian. We used changes in the chemical and isotopic composition of released gases to evaluate the isotope fractionation during gas loss and retroactively calculated the initial content of gas in the shale samples. The gas content estimates (in L of gas per ton of rock) correspond with the maturity parameters of the shales. Calculated isotope fractionation for the gas release was −3‰ for both methane and ethane. The archived samples primarily lost methane (up to 90%), with subsequent changes in the content of ethane and higher hydrocarbon levels.

Repeated impulse aging of oil-polypropylene insulation

Repeated impulse voltage has long been considered to affect the insulation property of power equipment, which is called accumulative effect. This phenomenon is widely studied on oil paper insulation but rarely on oil polypropylene film insulation, which is widely used in power capacitors and other equipment. Therefore, the accumulative effect of repeated impulse on oil polypropylene insulation is studied in this work. First, a repeated impulse accumulating test platform was set up and the accumulation characteristics of oil polypropylene insulation with repeated impulses were tested and analyzed. Next, the residual breakdown voltage, surface morphology and gas composition dissolved in the oil in different aging levels were tested. The results indicated that the OPF insulation residual breakdown voltage decreased and the film surface roughness increased when subjected to the repeated impulses. The dissolved gas contents changed along with the impulse accumulation aging. Lastly, the possible mechanisms of the accumulative effect in oil polypropylene insulation are discussed based on the test results.

A Study of the Residual Gas Composition in the Vacuum System of the Cyclotron of the Ioffe Physical Technical Institute

A Study of the Residual Gas Composition in the Vacuum System of the Cyclotron of the Ioffe Physical Technical Institute

Commissioning of vacuum system for SuperKEKB positron damping ring

The first stage commissioning of the new positron damping ring, which was constructed in the upgraded injector system of the SuperKEKB, was carried out from February to July 2018. Vacuum scrubbing in the arc sections, which occupy most of the ring, progressed smoothly, and a beam lifetime of 1000 s was obtained with a stored beam current of 10 mA and a beam dose of 0.7 A h. However, the beam lifetime did not increase with subsequent vacuum scrubbing because the beam lifetime was primarily determined by the Touschek effect. The residual gas composition during beam operation was typical of what would be expected for a vacuum system pumped by nonevaporable getter pumps. Rough Molflow+-based estimates of the photon-stimulated desorption yields of the beam pipe at the arc sections revealed that they decreased to 1.4 × 10−4 molec. photon−1 for H2 and to 2.3 × 10−5 molec. photon−1 for CO at a beam dose of 2 A h, which corresponds to a photon dose of 1 × 1023 photons m−1.

Исследование состава остаточного газа в вакуумной системе циклотрона ФТИ им. А.Ф. Иоффе

4. Using the FT-200 compact-size time-of-flight mass spectrometer developed at the Ioffe Institute, the mass spectra of the residual gas molecules in the vacuum system of the Ioffe Institute cyclotron have been obtained under various experimental conditions. The measurements were carried out in the cyclotron vacuum chamber and the end part of the ion guide near the sample irradiation chamber. It was found that the main contribution to the residual gas composition in the cyclotron chamber is made by the molecules of pump oil used (up to 82%) and water molecules (up to 15-17%), and in the ion guide near the irradiation chamber with a polymer film - water molecules (up to 63%). The data obtained are the basis for the modernization of the Ioffe cyclotron complex.

Interaction of electrons with residual gas molecules and its effect on gas bremsstrahlung radiation in electron storage rings

High energy electrons on interaction with residual gas molecules present in the vacuum chamber of electron storage rings produce gas bremsstrahlung radiation. Extensive studies have been carried out in past to evaluate dose rate from gas bremsstrahlung using various simulation techniques with air as target gas. From these studies, empirical relations were deduced to evaluate gas bremsstrahlung dose rate. However storage rings at ultra high vacuum level contains primarily hydrogen and hydrocarbon gases as residue. In this work, effect of residual gas composition in vacuum chamber on gas bremsstrahlung dose rate in electron storage rings of energy range 1–3 GeV has been studied using FLUKA Monte Carlo code. Simulation study was performed to investigate effects on energy distribution, angular distribution and absorbed dose rate of gas bremsstrahlung due to various composition of residual gas normally encountered in vacuum chambers of storage rings. The gas bremsstrahlung dose rate was found to depend on effective atomic number and molecular mass of the residual gas molecules. From the study, a new empirical formula for the estimation of gas bremsstrahlung dose rate is proposed.

Исследование влияния состава остаточных газов на твердость, адгезионные свойства и элементный состав покрытий SiC-AlN, нанесенных методом магнетронного распыления

Исследование влияния состава остаточных газов на твердость, адгезионные свойства и элементный состав покрытий SiC-AlN, нанесенных методом магнетронного распыления

Thermal conductivity of aerogel blanket insulation under cryogenic-vacuum conditions in different gas environments

Thermal conductivity of low-density materials in thermal insulation systems varies dramatically with the environment: cold vacuum pressure, residual gas composition, and boundary temperatures. Using a reference material of aerogel composite blanket (reinforcement fibers surrounded by silica aerogel), an experimental basis for the physical heat transmission model of aerogel composites and other low-density, porous materials is suggested. Cryogenic-vacuum testing between the boundary temperatures of 78 K and 293 K is performed using a one meter cylindrical, absolute heat flow calorimeter with an aerogel blanket specimen exposed to different gas environments of nitrogen, helium, argon, or CO2. Cold vacuum pressures include the full range from 1×10-5 torr to 760 torr. The soft vacuum region, from about 0.1 torr to 10 torr, is complex and difficult to model because all modes of heat transfer – solid conduction, radiation, gas conduction, and convection – are significant contributors to the total heat flow. Therefore, the soft vacuum tests are emphasized for both heat transfer analysis and practical thermal data. Results for the aerogel composite blanket are analyzed and compared to data for its component materials. With the new thermal conductivity data, future applications of aerogel-based insulation systems are also surveyed. These include Mars exploration and surface systems in the 5 torr CO2 environment, field joints for vacuum-jacketed cryogenic piping systems, common bulkhead panels for cryogenic tanks on space launch vehicles, and liquid hydrogen cryofuel systems with helium purged conduits or enclosures.