Outgassing Model Research Articles

Predicting CO2 Gas Layer Thickness due to Mantle Outgassing in the Exoplanet Census

The exchange of molecules between a planet’s interior and exterior is a major component of planetary development and atmospheric formation. Recently, detailed observational studies of exoplanet atmospheres have become possible, enabling robust testing of planetary outgassing models. In this Note, we apply the Dorn et al. stagnant lid model for outgassing to the observed exoplanet census to produce predictions for the atmospheric scale heights that may be observed. We also model atmospheric mass loss due to photoevaporation to determine if the predicted atmospheres would likely be retained and therefore observable.

Sintering of vesiculating pyroclasts

Hot volcanic pyroclasts can sinter, vesiculate, and outgas in concert – a combination of processes which remains poorly constrained. And yet this combination of processes can occur coincidently during deposition from pyroclastic density currents, in conduit-filling pyroclastic debris, and in tuffisites. In many of these settings, it is the sintering-driven evolution of permeability that is key to gas transport through the evolving deposit. Here, we experimentally and theoretically investigate the evolution of the permeable networks during sintering of hot fragmental volcanic systems, which are hydrous and oversaturated at the experimental conditions. Firstly, we find that vesiculation results in shutting of the inter-granular porous network as bubble growth drives expansion of the particles into one another, destroying interconnected pores. Secondly, we observe that degassing by diffusion out of the particle edge results in contraction of the vesicular particles, re-opening pore spaces between them. Therefore, we find that vesiculation, and diffusive outgassing compete to determine both the intra-fragment vesicularity and the permeability during sintering. The development of intra-fragment vesicularity directly impacts the inter-fragment pore space and its connectivity, which decreases during vesiculation and subsequently increases during diffusive outgassing, prompting complex, non-linear permeability evolution.The relative dominance of these processes is fragment size dependent; proportionally, fine fragments lose gas at a higher rate than coarser fragments during diffusive outgassing due to larger surface area to volume ratios. As the systems progress, larger fragments retain a higher proportion of gas and so attain greater vesicularities than finer ones – and therefore, the coarse fragmental pyroclasts experience a greater, yet transient, reduction in connected porosity and permeability. We suggest that where vesiculation is sufficient, it can lead to the complete loss of connected porosity and the sealing of permeable pathways much earlier than in a sintering-only system. Our results suggest that classical sintering models must be modified to account for these vesiculation and diffusive degassing processes, and that only a combined vesiculation, sintering, and diffusive outgassing model can resolve the evolution of permeability in hot clastic volcanic systems.

Seasonally varying outgassing as an explanation for dark comet accelerations

Significant nonradial, nongravitational accelerations with magnitudes incompatible with radiation-driven effects have been reported in seven photometrically inactive near-Earth objects. Two of these objects exhibit large transverse accelerations (i.e., within the orbital plane but orthogonal to the radial direction), and six exhibit significant out-of-plane accelerations. Here, we find that anisotropic outgassing resulting from differential heating on a nucleus with nonzero spin-pole obliquity, averaged over an eccentric orbit, can explain these accelerations for most of the objects. This balanced outgassing model depends on three parameters — the spin pole orientation (R.A. and Dec.) and an acceleration magnitude. For these “dark comets” (excepting 2003 RM), we obtain parameter values that reproduce the observed nongravitational accelerations. We derive formulae for the component accelerations under certain assumptions for the acceleration scaling over heliocentric distance. Although we lack estimates of these objects’ spin axes to confirm our values, this mechanism is nevertheless a plausible explanation for the observed accelerations, and produces accurate perturbations to the heliocentric motions of most of these objects. This model may also be applied to active objects outside of the dark comets group.

Fitting the Light Curve of 1I/‘Oumuamua with a Nonprincipal Axis Rotational Model and Outgassing Torques

In this paper, we investigate the nonprincipal axis (NPA) rotational state of 1I/‘Oumuamua—the first interstellar object discovered traversing the inner solar system—from its photometric light curve. Building upon Mashchenko, we develop a model which incorporates NPA rotation and Sun-induced, time-varying outgassing torques to generate synthetic light curves of the object. The model neglects tidal forces, which are negligible compared to outgassing torques over the distances at which ‘Oumuamua was observed. We implement an optimization scheme that incorporates the NPA rotation model to calculate the initial rotation state of the object. We find that an NPA rotation state with an average period of 〈P〉 ≃ 7.34 hr best reproduces the photometric data. The discrepancy between this period and previous estimates is due to continuous period modulation induced by outgassing torques in the rotational model, as well as different periods being used. The best fit to the 2017 October data does not reproduce the 2017 November data (although the later measurements are too sparse to fit). The light curve is consistent with there being no secular evolution of the angular momentum, which is somewhat in tension with the empirical correlations between nuclear spin-up and cometary outgassing. The complex rotation of ‘Oumuamua may be the result of primordial rotation about the smallest principal axis if (i) the object experienced hypervolatile outgassing and (ii) our idealized outgassing model is accurate.

Direct Detection of Free H2 Outgassing in Blisters Formed in Al2O3 Atomic Layers Deposited on Si and Methods of Its Prevention.

The phenomenon of blistering, seen in atomic layer-deposited aluminum oxide layers caused by thermal treatment, represents a serious problem in the field of device fabrication. Determining its causes and controlling them have been a major task in this field. Various groups have so far confronted the challenge, with several mechanisms having been proposed, but it is still under investigation. This paper reports how we have systematically characterized and summarized the blistering phenomenon from the viewpoints of annealing temperature and Al2O3-Si interface conditions. In this study, we have succeeded in directly detecting hydrogen gas generation from the interface between Si and Al2O3 using blister-penetrating Raman spectroscopy. The results have enabled us to propose a mechanism for blister formation using a hydrogen outgassing model. Based on our model, we also propose a method of suppressing blister formation by applying surface treatment or passivation to eliminate the Si-H bonds. These discoveries and methods will provide important insights that are applicable to a wide range of applications such as electronic devices and nanostructured solar cells.

Remote sensing of cometary bow shocks: modelled asymmetric outgassing and pickup ion observations

ABSTRACT Despite the long escort by the ESA Rosetta mission, direct observations of a fully developed bow shock around 67P/Churyumov–Gerasimenko have not been reported. Expanding on our previous work on indirect observations of a shock, we model the large-scale features in cometary pickup ions, and compare the results with the ESA Rosetta Plasma Consortium Ion Composition Analyser ion spectrometer measurements over the pre-perihelion portion of the escort phase. Using our hybrid plasma simulation, an empirical, asymmetric outgassing model for 67P, and varied interplanetary magnetic field (IMF) clock angles, we model the evolution of the large-scale plasma environment. We find that the subsolar bow shock standoff distance is enhanced by asymmetric outgassing with a factor of 2 to 3, reaching up to $18\,000\, \rm {km}$ approaching perihelion. We find that distinct spectral features in simulated pickup ion distributions are present for simulations with shock-like structures, with the details of the spectral features depending on shock standoff distance, heliocentric distance, and IMF configuration. Asymmetric outgassing along with IMF clock angle is found to have a strong effect on the location of the spectral features, while the IMF clock angle causes no significant effect on the bow shock standoff distance. These dependences further complicate the interpretation of the ion observations made by Rosetta. Our data-model comparison shows that the large-scale cometary plasma environment can be probed by remote sensing the pickup ions, at least when the comet’s activity is comparable to that of 67P, and the solar wind parameters are known.

Outgassing test methodology for contaminant emission model based on diffusion theory

Contamination is always troublesome in spacecraft development, but it has yet to be investigated because outgassing, transportation, deposition, and re-emission largely depend on spacecraft design. Designing spacecraft requires an accurate estimate of contaminant emission and deposition. Particularly for today’s sophisticated spacecraft, analytical tools would be indispensable—but current simulations need to be improved. Our study addresses the first phase in the occurrence of contamination: improving the outgassing model. We focused on diffusion-limited phenomena because the diffusion rate of outgassing molecules in materials is thought to be much slower than their desorption rate at the surface. A new outgassing test method and analytical procedure was originally devised for extracting the parameters of the diffusion model. In comparing the desorption and diffusion models, we developed a model for the emission of outgassing molecules based on the diffusion theory and updated some functions of Japan’s Spacecraft Induced Contamination Environment analysis software (J-SPICE). From this, we developed J-SPICE2 and installed the diffusion model to the software for calculating outgassing behavior.

Effect of mantle oxidation state and escape upon the evolution of Earth’s magma ocean atmosphere

Context. The magma ocean period was a critical phase determining how Earth’s atmosphere developed into habitability. However, there are major uncertainties in the role of key processes such as outgassing from the planetary interior and escape of species to space that play a major role in determining the atmosphere of early Earth. Aims. We investigate the effect of outgassing of various species and escape of H2 for different mantle redox states upon the composition and evolution of the atmosphere for the magma ocean period. Methods. We included an important new atmosphere-interior coupling mechanism: the redox evolution of the mantle, which strongly affects the outgassing of species. We simulated the volatile outgassing and chemical speciation at the surface for various redox states of the mantle by employing a C-H-O based chemical speciation model combined with an interior outgassing model. We then applied a line-by-line radiative transfer model to study the remote appearance of the planet in terms of the infrared emission and transmission. Finally, we used a parameterized diffusion-limited and XUV energy-driven atmospheric escape model to calculate the loss of H2 to space. Results. We have simulated the thermal emission and transmission spectra for reduced and oxidized atmospheres present during the magma ocean period of Earth. Reduced/thin atmospheres consisting of H2 in abundance emit more radiation to space and have a larger effective height than oxidized/thick atmospheres, which are abundant in H2O and CO2. We obtain that the outgassing rates of H2 from the mantle into the atmosphere are a factor of ten times higher than the rates of diffusion-limited escape to space. We estimate the timescale of total mass loss of outgassed H2 via escape to be few tens of million years, which is comparable to other studies. Conclusions. Our work presents useful insight into the development of the terrestrial atmosphere during the magma ocean period and provides input to guide future studies that discuss exoplanetary interior compositions and their possible links with atmospheric compositions that might be estimated from observed infrared spectra by future missions.

Outgassing Environment of Spacecraft: An Overview

With the advancements of materials science and technology, organic materials found significant applications in aerospace industry. But under the orbital thermal and vacuum environment, organic materials can outgas and the outgassed products and induced environment often degraded performances of spacecraft or its subsystem. In this article, the typical impacts of outgassing environment on spacecraft are explained briefly. Then the outgassing theory, test method, identification of compounds and control measures were reviewed in detail. The need for transient and long-term outgassing model is discussed. The standard test methods of E595 and E1559 are compared. The promising new techniques such as infrared spectrometry and/or mass-spectrometry with thermogravimetric analysis is proposed for the identification of outgassed compounds. The vacuum bakeout and molecular absorber for outgassing control are reviewed and for the last more research work is needed.

The habitability of stagnant-lid Earths around dwarf stars

Context. The habitability of a planet depends on various factors, such as the delivery of water during its formation, the co-evolution of the interior and the atmosphere, and the stellar irradiation which changes in time. Aims. Since an unknown number of rocky extrasolar planets may operate in a one-plate convective regime, i.e. without plate tectonics, our aim is to understand the conditions under which planets in such a stagnant-lid regime may support habitable surface conditions. Understanding the interaction of the planetary interior and outgassing of volatiles in combination with the evolution of the host star is crucial to determining the potential habitability. M-dwarf stars in particular possess a high-luminosity pre-main sequence phase that endangers the habitability of planets around them via water loss. We therefore explore the potential of secondary outgassing from the planetary interior to rebuild a water reservoir allowing for habitability at a later stage. Methods. We compute the boundaries of the habitable zone around M-, K-, G-, and F-dwarf stars using a 1D cloud-free radiative-convective climate model accounting for the outgassing history of CO2 and H2O from an interior evolution and outgassing model for different interior compositions and stellar luminosity evolutions. Results. The outer edge of the habitable zone strongly depends on the amount of CO2 outgassed from the interior, while the inner edge is mainly determined via the stellar irradiation, as soon as a sufficiently large water reservoir has been outgassed. A build-up of a secondary surface and atmospheric water reservoir for planets around M-dwarf stars is possible even after severe water loss during the high-luminosity pre-main sequence phase as long as some water has been retained within the mantle. For small mantle water reservoirs, between 62 and 125 ppm, a time delay in outgassing from the interior permits such a secondary water reservoir build-up especially for early and mid-M dwarfs because their pre-main sequence lifetimes are shorter than the outgassing timescale. Conclusions. We show that Earth-like stagnant-lid planets allow for habitable surface conditions within a continuous habitable zone that is dependent on interior composition. Secondary outgassing from the interior may allow for habitability of planets around M-dwarf stars after severe water loss during the high-luminosity pre-main sequence phase by rebuilding a surface water reservoir.

Volatile distributions in and on the Moon revealed by Cu and Fe isotopes in the ‘Rusty Rock’ 66095

The Apollo 16 ‘Rusty Rock’ impact melt breccia 66095 is a volatile-rich sample, with the volatiles inherited through vapor condensation from an internal lunar source formed during thermo-magmatic evolution of the Moon. We report Cu and Fe isotope data for 66095 and find that bulk-rocks, residues and acid leaches span a relatively limited range of compositions (3.0 ± 1.3 wt.% FeO [range = 2.0–4.8 wt.%], 5.4 ± 3.1 ppm Cu [range = 3–12 ppm], average δ56Fe of 0.15 ± 0.05‰ [weighted mean = 0.156‰] and δ65Cu of 0.72 ± 0.14‰ [weighted mean = 0.78‰]). In contrast to the extreme enrichment of the light isotopes of Zn and heavy isotopes of Cl in 66095, δ65Cu and δ56Fe in the sample lie within the previously reported range for lunar mare basalts (0.92 ± 0.16‰ and 0.12 ± 0.02‰, respectively). The lack of extreme isotopic fractionation for Cu and Fe isotopes reflects compositions inherent to 66095, with condensation of a cooling gas from impact-generated fumarolic activity at temperatures too low to lead to the condensation of Cu and Fe in the sample, but higher than required to condense Zn. Together with thermodynamic models, these constraints suggest that the gas condensed within 66095 between 700 and 900 °C (assuming a pressure of 10−6 and an fO2 of IW-2). That the Cu and Fe isotopic compositions of sample 66095 are within the range of mare basalts removes the need for an exotic, volatile-enriched source. The enrichment in Tl, Br, Cd, Sn, Zn, Pb, Rb, Cs, Ga, B, Cl, Li relative to Bi, Se, Te, Ge, Cu, Ag, Sb, Mn, P, Cr and Fe in the ‘Rusty Rock’ is consistent with volcanic outgassing models and indicates that 66095 likely formed distal from the original source of the gas. The volatile-rich character of 66095 is consistent with impact-generated fumarolic activity in the region of the Cayley Plains, demonstrating that volatile-rich rocks can occur on the lunar surface from outgassing of a volatile-poor lunar interior. The ‘Rusty Rock’ indicates that the lunar interior is significantly depleted in volatile elements and compounds and that volatile-rich surface rocks likely formed through vapor condensation. Remote sensing studies have detected volatiles on the lunar surface, attributing them dominantly to solar wind. Based on the ‘Rusty Rock’, some of these surface volatiles may also originate from the Moon’s interior.

Numerical Model for Molecular and Particulate Contamination Transport

A new model for simulating molecular and particulate contamination transport is described. This model is implemented in the Contamination Transport Simulation Program (CTSP). The code uses techniques found in rarefied gas and plasma dynamics codes and represents the contaminants as simulation macroparticles. This kinetic approach allows the code to consider external forces and interparticle interactions. Macroscopic properties such as contaminant plume partial pressure can also be computed. CTSP implements various contamination-specific material sources including a detailed model for molecular outgassing and a model for particulate detachment. The code is demonstrated with four examples focusing on mass transport between two parallel plates, computation of the steady-state equilibrium in a closed vessel, characterization of a test article outgassing rate from a quartz crystal microbalance measurement, and the use of purge gas to reduce the particulate fallout in atmospheric conditions. Simulation results are compared to analytical models.

Exploring the scale-dependent permeability of fractured andesite

Extension fractures in volcanic systems exist on all scales, from microscopic fractures to large fissures. They play a fundamental role in the movement of fluids and distribution of pore pressure, and therefore exert considerable influence over volcanic eruption recurrence. We present here laboratory permeability measurements for porous (porosity = 0.03–0.6) andesites before (i.e., intact) and after failure in tension (i.e., the samples host a throughgoing tensile fracture). The permeability of the intact andesites increases with increasing porosity, from 2×10−17 to 5×10−11 m2. Following fracture formation, the permeability of the samples (the equivalent permeability) falls within a narrow range, 2–6×10−11 m2, regardless of their initial porosity. However, laboratory measurements on fractured samples likely overestimate the equivalent permeability due to the inherent scale-dependence of permeability. To explore this scale-dependence, we first determined the permeability of the tensile fractures using a two-dimensional model that considers flow in parallel layers. Our calculations highlight that tensile fractures in low-porosity samples are more permeable (as high as 3.5×10−9 m2) than those in high-porosity samples (as low as 4.1×10−10 m2), a difference that can be explained by an increase in fracture tortuosity with porosity. We then use our fracture permeability data to model the equivalent permeability of fractured rock (with different host rock permeabilities, from 10−17 to 10−11 m2) with increasing lengthscale. We highlight that our modelling approach can be used to estimate the equivalent permeability of numerous scenarios at andesitic stratovolcanoes in which the fracture density and width and host rock porosity or permeability are known. The model shows that the equivalent permeability of fractured andesite depends heavily on the initial host rock permeability and the scale of interest. At a given lengthscale, the equivalent permeability of high-permeability rock (10−12 to 10−11 m2) is essentially unaffected by the presence of numerous tensile fractures. By contrast, a single tensile fracture increases the equivalent permeability of low-permeability rock (<10−15 m2) by many orders of magnitude. We also find that fractured, low-permeability rock (e.g., 10−17 m2) can have an equivalent permeability higher than that of similarly fractured rock with higher host rock permeability (e.g., 10−15 m2) due to the low-tortuosity of fractures in low-porosity andesite. Our modelling therefore outlines the importance of fractures in low-porosity, low-permeability volcanic systems. While our laboratory measurements show that, regardless of the initial porosity, the equivalent permeability of fractured rock on the laboratory scale is 2–6×10−11 m2, the equivalent permeability of low-permeability rock is significantly reduced as the scale of interest is increased. Therefore, due to the scale-dependence of permeability, laboratory measurements on pristine, low-permeability rocks significantly underestimate the equivalent permeability of fractured volcanic rock. Further, measurements on fractured rock samples can significantly overestimate the equivalent permeability. As a result, care must be taken when selecting samples in the field and when using laboratory data in volcano outgassing models. The data and modelling presented herein provide insight into the scale-dependence of the permeability of fractured volcanic rock, a prerequisite for understanding outgassing at active volcanoes.

Modelling observations of the inner gas and dust coma of comet 67P/Churyumov-Gerasimenko using ROSINA/COPS and OSIRIS data: First results

Context. This paper describes the initial modelling of gas and dust data acquired in August and September 2014 from the European Space Agency's Rosetta spacecraft when it was in close proximity to the nucleus of comet 67P/Churyumov-Gerasimenko. Aims. This work is an attempt to provide a self-consistent model of the innermost gas and dust coma of the comet, as constrained by the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) data set for the gas and by the Optical, Spectroscopic, and Infrared Remote Imaging System (OSIRIS) data set for the dust. Methods. The model uses a previously developed shape model for the nucleus, and from this the water sublimation rate and gas temperatures at the surface are computed with a simple thermal model. The gas expansion is modelled with a 3D parallel implementation of a Direct Simulation Monte Carlo algorithm. A dust drag algorithm is then used to produce dust densities in the coma, which are then converted to brightnesses using Mie theory and a line-of-sight integration. Results. We show that a purely insolation-driven model for surface outgassing does not produce a reasonable fit to ROSINA/COPS data. A stronger source in the “neck” region of the nucleus (region Hapi) is needed to match the observed modulation of the gas density in detail. This agrees with OSIRIS data, which shows that the dust emission from the “neck” was dominant in the August-September 2014 time frame. The current model matches this observation reasonably if a power index of 2-3 for the dust size distribution is used. A better match to the OSIRIS data is seen by using a single large particle size for the coma. Conclusions. We have shown possible solutions to the gas and dust distributions in the inner coma, which are consistent with ROSINA and OSIRIS data.

Unravelling textural heterogeneity in obsidian: Shear-induced outgassing in the Rocche Rosse flow

Obsidian flow emplacement is a complex and understudied aspect of silicic volcanism. Of particular importance is the question of how highly viscous magma can lose sufficient gas in order to erupt effusively as a lava flow. Using an array of methods we study the extreme textural heterogeneity of the Rocche Rosse obsidian flow in Lipari, a 2km long, 100m thick, ~800year old lava flow, with respect to outgassing and emplacement mechanisms. 2D and 3D vesicle analyses and density measurements are used to classify the lava into four textural types: ‘glassy’ obsidian (<15% vesicles), ‘pumiceous’ lava (>40% vesicles), high aspect ratio, ‘shear banded’ lava (20–40% vesicles) and low aspect ratio, ‘frothy’ obsidian with 30–60% vesicles. Textural heterogeneity is observed on all scales (m to μm) and occurs as the result of strongly localised strain. Magnetic fabric, described by oblate and prolate susceptibility ellipsoids, records high and variable degrees of shearing throughout the flow. Total water contents are derived using both thermogravimetry and infrared spectroscopy to quantify primary (magmatic) and secondary (meteoric) water. Glass water contents are between 0.08–0.25wt.%. Water analysis also reveals an increase in water content from glassy obsidian bands towards ‘frothy’ bands of 0.06–0.08wt.%, reflecting preferential vesiculation of higher water bands and an extreme sensitivity of obsidian degassing to water content. We present an outgassing model that reconciles textural, volatile and magnetic data to indicate that obsidian is generated from multiple shear-induced outgassing cycles, whereby vesicular magma outgasses and densifies through bubble collapse and fracture healing to form obsidian, which then re-vesiculates to produce ‘dry’ vesicular magma. Repetition of this cycle throughout magma ascent results in the low water contents of the Rocche Rosse lavas and the final stage in the degassing cycle determines final lava porosity. Heterogeneities in lava rheology (vesicularity, water content, microlite content, viscosity) play a vital role in the structural evolution of an obsidian flow and overprint flow-scale morphology. Post-emplacement hydration also depends heavily on local strain, whereby connectivity of vesicles as a result of shear deformation governs sample rehydration by meteoric water, a process previously correlated to lava vesicularity alone.

Coupling the nongravitational forces and modified Newton dynamics for cometary orbits

In recent work (Milgrom 2009, Blanchet & Novak 2011), the authors showed that MOdified Newton Dynamics (MOND) have a non-negligible secular perturbation effect on planets with large semi-major axes (gaseous planets) in the Solar System. Some comets also have a very eccentric orbit with a large semi-major axis (Halley family comets) going far away from the Sun (more than 15 AU) in a low acceleration regime where they would be subject to MOND perturbation. They also approach the Sun very closely (less than 3 AU) and are affected by the sublimation of ices from their nucleus, triggering so-called non-gravitational forces. The main goal of this paper is to investigate the effect of MOND perturbation on three comets with various orbital elements (2P/Encke, 1P/Halley and 153P/Ikeya-Zhang) and then compare it to the non-gravitational perturbations. It is motivated by the fact that when fitting an outgassing model for a comet, we have to take into account all of the small perturbing effects to avoid absorbing these effects into the non-gravitational parameters. Otherwise, we could derive a completely wrong estimation of the outgassing. For this work, we use six different forms of MOND functions and compute the secular variations of the orbital elements due to MOND and non-gravitational perturbations. We show that, for comets with large semi-major axis, the MONDian effects are not negligible compared to the non-gravitational perturbations.

Hydrogen traps in the outgassing model of a stainless steel vacuum chamber

This article describes a model for hydrogen outgassing into a stainless steel vacuum chamber. It accounts for the geometry of the chamber components, the hydrogen dissolved in those components, and the processes of diffusion, recombination, and trapping. Strongly bound or “trapped” hydrogen, which occurs at heterogeneities such as dislocations and grain boundaries, can hold most of the dissolved hydrogen even though those locations comprise fewer than 0.1% of all lattice sites. Four simplifications allowed practical use of the model: (1) Each component was described as a one-dimensional object. (2) The hydrogen initially dissolved in each component was described as a uniform concentration. (3) Accurate, consistent values were used to describe diffusion and recombination in stainless steel types 304 and 316 [Grant et al., J. Nucl. Mater. 149, 180 (1987); 152, 139 (1988)]. (4) Only one type of hydrogen trap was considered, and trapping was ignored in components made from vacuum remelted stainless steel. The simple model was developed and validated by comparing it to outgassing measurements. Traps were required to describe the outgassing from a component made of drawn stainless steel 304. The initial hydrogen concentration in that component was comparable to concentrations found elsewhere by thermal desorption and almost 100 times larger than in the components made of vacuum remelted 316 stainless steel. The model's usefulness was illustrated by using it to predict the outgassing of a vacuum chamber made of type 304 stainless steel.

Particle-in-cell simulation on effect of outgassing on flashover and breakdown on dielectric surface in high-power microwave environment

For investigating the mechanism of high power microwave flashover and breakdown on dielectric surface with outgassing, firstly, the theoretical modeling is put forward, including dynamic equations, particle-in-cell (PIC) method, secondary emission, Monte-Carlo collision (MCC) method and outgassing model. Secondly, based on the theoretical modeling, the 1D3V PIC-MCC code is programmed by authors. By using this code, the flashover and breakdown on dielectric surface with weak and strong outgassing course under different gas moving velocities are studied numerically. The numerical results are concluded in the following. The flashover and breakdown on dielectric surface are caused by continuous increase of deposited power. For weak outgassing, multipacting is dominant. As outgassing coefficient increases, multipacting is promoted by ionization collision. The typical phenomena are the increases of space-charge field, average energy of surface-collision electrons and the number of surface-collision electrons. Here, the surface-collision electrons are caused by multipacting mostly. With the increase of gas molecule velocity, ionization course is suppressed by gas pressure decreasing near to the dielectric surface. For strong outgassing, ionization collision is dominant. As outgassing coefficient increases, the number of ions increases exponentially with ionization frequency increasing, multipacting is suppressed by ionization collision. The typical phenomena are the negative value of space-charge field on dielectric surface, the decrease of average energy of surface-collision electrons, and the exponential increase of surface-collision electrons caused by ionization collision near to dielectric surface. Here, the surface-collision electrons are caused by ionization mostly. With the increase of gas molecule velocity, the depth of gas is enlarged, thereby promoting the ionization collision.

Effect of polyimide baking on bump resistance in flip-chip solder joints

The effect of polyimide (PI) thermal process on the bump resistance of flip-chip solder joint is investigated for 28nm technology device with aggressive extreme low-k (ELK) dielectric film scheme and lead-free solder. Kelvin structure is designed in the bump array to measure the resistance of single solder bump. An additional low-temperature pre-baking before standard PI curing increases the bump resistance from 9.3mΩ to 225mΩ. The bump resistance increment is well explained by a PI outgassing model established based on the results of Gas Chromatography–Mass Spectrophotometer (GC–MS) analysis. The PI outgassing substances re-deposit on the Al bump pad, increasing the resistance of interface between under-bump metallurgy (UBM) and underneath Al pad. The resistance of interface is twenty-times higher than pure solder bump, which dominates the measured value of bump resistance. Low-temperature plasma etching prior to UBM deposition is proposed to retard the PI outgassing, and it effectively reduces the bump resistance from 225mΩ to 10.8mΩ.

LYRIDS AND PERSEIDS METEOROIDS: RECONCILIATION AND DISCREPANCY BETWEEN COMETARY OUTGASSING THEORY AND ELECTROPHONIC SOUND DATA

We obtain the diameter of the most massive grains that might be ejected from the nuclear surface of the comets C/1861 G1 (Thatcher) and 109P/Swift-Tuttle using an outgassing model. The prevenient meteoroids of these two comets produce the known Lyrids and Perseids showers and it is thought that they produce electrophonic sounds. We compare our results with the minimum sized of such meteoroids capable of generating such sounds and we reconcile the discrepancy found by Beech in the case of the Lyrids. However, we conclude that the only outgassing mechanism is not compatible with the existence of electrophonic sounds due to Perseid meteoroids, and other mechanisms must be invoked to justify the presence of meter-sized boulders in the Perseid stream.