Outgassing Of H2 Research Articles

Stable carbon isotope evolution of formaldehyde on early Mars

Organic matter in the Martian sediments may provide a key to understanding the prebiotic chemistry and habitability of early Mars. The Curiosity rover has measured highly variable and 13C-depleted carbon isotopic values in early Martian organic matter whose origin is uncertain. One hypothesis suggests the deposition of simple organic molecules generated from 13C-depleted CO derived from CO2 photochemical reduction in the atmosphere. Here, we present a coupled photochemistry-climate evolution model incorporating carbon isotope fractionation processes induced by CO2 photolysis, carbon escape, and volcanic outgassing in an early Martian atmosphere of 0.5–2 bar, composed mainly of CO2, CO, and H2 to track the evolution of the carbon isotopic composition of C-bearing species. The calculated carbon isotopic ratio in formaldehyde (H2CO) can be highly depleted in 13C due to CO2-photolysis-induced fractionation and is variable with changes in atmospheric CO/CO2 ratio, surface pressure, albedo, and H2 outgassing rate. Conversely, CO2 becomes enriched in 13C, as estimated from the carbonates preserved in ALH84001 meteorite. Complex organic matter formed by the polymerization of such H2CO could explain the strong depletion in 13C observed in the Martian organic matter. Mixing with other sources of organic matter would account for its unique variable carbon isotopic values.

Radiation Effects on Type I Fiber Bragg Gratings: Influence of Recoating and Irradiation Conditions

Fiber Bragg gratings (FBGs) present strong advantages for temperature or strain sensing in harsh radiation environments even if their properties are affected by radiations. The amplitudes and kinetics of these radiation induced changes depend on numerous parameters, intrinsic or extrinsic to the FBGs themselves. In this paper, we characterized 40 keV X-ray radiation effects on type I FBGs inscribed in prehydrogenated SMF-28 from Corning through an ultraviolet laser exposure at 244 nm (cw). We performed a systematic study of the influence of several FBG manufacturing parameters on their radiation response up to 100 kGy (SiO2) highlighting radiation-induced Bragg wavelength shifts (RI-BWS) up to 130 pm (∼13°C error for temperature measurements) but no decrease of those FBG reflectivity. Among the investigated parameters are the duration and temperature (100°C and 300°C) of the thermal treatments applied post-inscription to stabilize the FBG and to complete the H2 outgassing. For such type of FBG, the device has to be recoated after inscription; we then characterize the impact of this manufacturing step on the FBG response showing that its recoating with NOA-81 acrylate slightly degrades its radiation resistance. In addition to this study, the influence of two other parameters have also been characterized: RI-BWS increases with the dose rate in the range 1–50 Gy/s and a pre-irradiation at 1.5 MGy does not stabilize type I FBG response to a second irradiation.

Investigations of medium-temperature heat treatments to achieve low outgassing rates in stainless steel ultrahigh vacuum chambers.

The authors investigated the outgassing rates and fluxes of vacuum chambers constructed from common 304L stainless steel vacuum components and subjected to heat treatments. Our goal was to obtain H2 outgassing flux on the order of 10-11 Pa l s-1cm-2 or better from standard stainless steel vacuum components readily available from a variety of manufacturers. The authors found that a medium-temperature bake in the range of 400 to 450°C, performed with the interior of the chamber under vacuum, was sufficient to produce the desired outgassing flux. The authors also found that identical vacuum components baked in air at the same temperature for the same amount of time did not produce the same low outgassing flux. In that case, the H2 outgassing flux was lower than that of a stainless-steel chamber with no heat treatment, but was still approximately 1 order of magnitude higher than that of the medium-temperature vacuum-bake. Additionally, the authors took the chamber that was subjected to the medium-temperature vacuum heat treatment and performed a 24-h air bake at 430°C. This additional heat treatment lowered the outgassing rate by nearly a factor of two, which strongly suggests that the air-bake created an oxide layer which reduced the hydrogen recombination rate on the surface. [http://dx.doi.org/10.1116/1.4983211].

Achieving ultra high vacuum conditions in SMARTEX-C: control of instabilities and improved confinement

SMall Aspect Ratio Toroidal Experiments in a C-shaped trap (SMARTEX-C) attempts to confine electrons in a toroidal trap using static electric and magnetic field. Confinement of these electrons is largely limited by charge losses due to the presence of background neutrals and by short pulsed magnetic field. Ions formed due to electron impact ionization of background neutrals lead to instabilities that are ultimately observed to limit the confinement. Lowering the amount of neutrals in the trap is therefore of paramount importance. In SMARTEX-C, prior to electron injection, the trap is pumped down to base pressures of the order of 2 ± 1 × 10−8 mbar. However, as one turns on the electron source (tungsten filament emitting thermionically) pressure in the system increases to ∼ 1 × 10−7mbar. Partial pressure analysis of the vacuum system indicates predominant presence of H2 during filament operation. Replacing the copper current-leads for electron source with stainless steel-304 led to reduction of H2 outgassing. Additionally, viton seals have been replaced with Aluminum wire-seals that allow baking at elevated temperatures and further reduce out-gassing. All these measures have led to an improvement in the base pressure to 7±1 × 10−9 mbar even during filament operation. Confinement of electron plasmas in the trap has thus significantly improved.

Metal Foaming Studied In Situ by Energy Dispersive X‐Ray Diffraction of Synchrotron Radiation, X‐Ray Radioscopy, and Optical Expandometry

AbstractThree synchronized methods are combined for studying in situ the foaming process of AlSi11 powder precursors containing either as‐received TiH2 or pre‐oxidized TiH2−x. The phase transformations are followed by energy dispersive X‐ray diffraction (ED‐XRD) of synchrotron radiation. The internal structure of the foam is monitored by X‐ray radioscopy and a video camera records the overall foam expansion. Complementary mass spectrometry follows the H2 gas release. Phase transformations of TiH2 and TiH2−x particles inside Al–Si foams are reported in this work for the first time and they are different than the ones observed for loose powders under Ar flow because the solid metal matrix initially retards H2 outgassing, but also because after melting the liquid reacts with TiH2 forming the ternary compounds Ti(AlxSi1−x)2 in the semi‐solid state and Ti(Al1−xSix)3 in the liquid state of the alloy. Further reasons for the larger expansion obtained when using pre‐oxidized TiH2−x are revealed as well. The oxide shell of pre‐oxidized TiH2−x not only shifts the onset of H2 release towards higher temperatures, but it also hinders the reaction between blowing agent and melt, stabilizing the structure of TiH2−x thus preserving its role as a good blowing agent for foaming Al‐based alloys.

Reduction in hydrogen outgassing from stainless steels by a medium-temperature heat treatment

The authors carried out heat treatments, in-vacuum or in-air at 400 °C, to reduce the hydrogen outgassing rate from stainless steels. An outgassing rate as low as 2×10−14 Torr ℓ s−1 cm−2 was routinely achieved by a medium-temperature bakeout, but it took much longer time than reported to perform intensive thermal treatment. The result shows that the diffusion process governs degassing only at the early stage of degassing while the recombination limits outgassing at low concentrations. Air baked chambers had somewhat lower outgassing rates than in-vacuum baked chambers, suggesting that the surface oxide acts as a further barrier for H2 outgassing. However, the main effect may be attributed to the removal of mobile hydrogen through diffusion. The results showed that the ultralow outgassing rate can be reproducibly achieved for stainless steel chambers with the established heat treatment procedure. The study also showed that the ultralow outgassing property of a treated chamber can be restored by a low temperature (>150 °C) postbakeout, after exposure to ambient air.

XHV System for Surface Analysis Using a New Getter to Reduce Hydrogen.

For almost the past two decades, surface analysis instruments have maintained an UHV environment which is achieved by UHV pumps. Recently, the XHV environment has been required in surface analysis, but an instrument which has many parts in a vacuum is eventually limited in the baking temperature. To achieve an XHV environment in a surface analysis instrument, H2 is the key component. Thus we tested a nonevaporable getter pump to reduce the amount of H2 and we have measured the residual mass spectrum in a practical instrument using a low outgassing rate mass spectrometer. We obtained a low range of 10-9 Pa using the NEG pump and conventional pumps with relatively low baking temperature. The ion source of the sputter-etching gun was mainly the outgassing of H2 under operating conditions, and hence the pumping speed was not sufficient to maintain the amount of H2 from the ion gun.

Characteristics of UHV stepping motors

Characteristics of an ultrahigh vacuum (UHV) stepping motor have been examined for practical use. The temperature rise of the motor in the energized-and-rest condition was measured as a function of the coil current. The result showed that it is approximately proportional to the electric power fed to the coil. The outgassing from the motor increased significantly at temperatures above 100 °C. The components of the released gas were the usual species in vacuum such as H2, H2O, CO, CO2, and hydrocarbons. Initially a small amount of NH3 was also observed at temperatures higher than 150 °C. This gas might originate from a small amount of the epoxy resin used for bonding the rotor and the permanent magnets. It decreased rapidly during the test operation. In the running mode, the outgassing of H2, CH4, H2O, CO, and CO2 increased with the revolution rate. The amount of the H2 released from the motor with the silver-ion plated ball bearings was larger than that with the MoS2 coated ball bearings. The lifetime of the MoS2-coated ball bearings was longer than that of the Ag ion plated ones.

スループット法による大気暴露後のガス放出速度測定とその温度依存性

Outgassing rate measurements for each residual gas species from the ECB treated type 304L stainless steel chamber were carried out using through-put method. After one hour's air-exposure, H2O was found to be a dominant desorbed species. Other than H2O, H2, CO and CO2 were observed. Partial pressure of H2O decreased in proportion to t-1.26, which means that the activation energy of desorption of H2O is not a fixed value but has a certain distribution. The decreasing rate of H2 varied from ∝t-0.82 to ∝t-0.49, which can be explained by an assumption that the H2 outgassing is composed of the diffusive evolution of dissolved hydrogen and the associative desorption of H adatoms caused by the dissociative adsorption of H2O. The decreasing rate of CO and CO2 varied in proportion to t-0.49 and t-0.51, respectively. The total pressure was composed by the sum of the partial pressures of these four species.In accord with the variation of surrounding temperature, each partial pressure was found to fluctuate. This fluctuation is found to be useful for obtaining the physical parameters of the outgassing process.

Outgassing and desorption of the stainless‐steel beam tubes after different degassing treatments

Chemical cleaning, vacuum firing, glow discharge cleaning, and in situ bakeout have become standard practice for lowering the outgassing rate and removing surface contaminants in the ultrahigh vacuum systems of particle accelerators and storage rings. This paper presents the work done with the thermal outgassing of several long stainless‐steel (304LN and 316L) beam chambers with areas of more than 1×104 cm2 . They were measured between 20 and 500 °C after vacuum firing, glow discharge cleaning, or reactive gas (nitric oxide) cleaning. Outgassing rates of low 10−13 and low 10−14 Torr 1/s cm2 were achieved for H2 and CO, respectively, with vacuum firing alone. The outgassing of H2 in this temperature range is consistent with that due to bulk diffusion with an enthalpy of 9±1 kcal/mole. The photon stimulated desorption of the chamber surface after the above treatments were also studied by exposure to an intense photon beam at the National Synchrotron Light Source. The effectiveness and merits of reactive gas cleaning in removing the surface contaminants in large vacuum systems are compared to those of vacuum firing and glow discharge cleaning.

紫外線照射による表面清浄化の実験

A bakeout procedure is effective for reducing outgassing of a vacuum chamber. But it is difficult and so long times are needed for the large and complicated chambers such as the recent fusion machines to heat up and down uniformly. So if possible, it is desired not to heat the chamber and to reach our needed outgassing level as fast as possible.Recently, new surface cleaning method which simultaneously irradiates ultraviolet ray and ozone to be cleaned surface in room atmosphere is successively used, mainly in a semi-conductor processing. So we examined to turn on a low pressure mercury lamp which mainly emitted 184.9 and 253.6 nm in a vacuum chamber, and investigated these outgassing characteristics. Graphite liners were installed inside of the chamber.It was found that the total pressure increased during turning on the lamp, and simultaneously, the outgassing of H2, CO, CO2, CH4, etc also incleased, while H2O and O2 were slightly reduced. Weakly bonded gas molecures on the surface were desorbed by the energy of ultra-violet ray, and particularly, in part of adsorbed H2O molecures were dessociated.

Water dissolved in olivine: A single‐crystal infrared study

Polarized infrared spectra of the hydrogen impurities in an olivine single crystal, approximately (Mg0.9Fe0.1)2SiO4, from the Zargabad Island, Red Sea, are reported in the range 4200–3000 cm−1. In the O‐H stretching frequency region, two groups of IR absorption bands occur which show the same pleochroism and the same temperature‐induced shift between room temperature and 80 K. Each of these IR groups is composed of three equidistant bands at 3614, 3591, 3567 m−1 and at 3576, 3530, 3485 cm−1 (80 K values). These distinct multiplets are assigned to the OH−‐compensated octahedral and tetrahedral vacancy defects [OH·V″oct]′ and [OH·V′tetr]*, respectively. It is suggested that the reduced effective charge of the tetrahedral, i.e., Si‐type, vacancy is due to Si entering a nearby nonideal site for partial charge compensation. The multiplet splitting, 23 and 45 cm−1, is due to the isomorphous substitution of Mg and Fe on the adjacent M1 and M2 positions to which the proton‐bearing oxygen is bound. This leads to the combinations (Mg Mg Si), (Mg Fe Si), (Fe Fe Si) and (Mg Mg Mg), (Mg Mg Fe), (Mg Fe Fe) at the octahedral M2 and at the tetrahedral vacancy sites, respectively. An IR signal which would correspond to the fully OH−‐compensated divalent cation vacancy defect [OH·V″octHO·]* appears to be absent. Instead a weak absorption band is observed in the range of the H‐H stretching frequency of molecular H2. By analogy to molecular H2 in MgO and CaO single crystals and in fused silica it is concluded that OH− pairs, associated with this type of defects, undergo a charge transfer conversion into (H2 + O22−). The H2 are loosely bound to the peroxy entities which probably form peroxy bridges between SiO4 tetrahedra, e.g., Si‐O‐O‐Si. Outgassing of H2 would leave excess oxygen behind, shifting the stoichiometry of the olivine in a direction which has never been discussed before.

Interaction of Polyethylene and Tritium Gas as Monitored by Raman Spectroscopy

Irradiation of high-density polyethylene by ~1 atm overpressure of T2 gas at 23+- 2 degrees C has been shown to produce severe damage, about 200 MRad dose, within 6 months. Production rate of H2 gas from irradiation due to polymer incorporation of tritium increased quickly within the first 2 months, after which it slowed considerably. It is proposed that outgassing of H2 acted to inhibit diffusion of solubilized HT or T2 into the bulk, thereby limiting increases in polymer T incorporation and thus damage rate. Damage to the HDPE sample was found to be nonuniform. Laser fluorescence from the sample surface irradiated by the supply of T2 gas was ~10{sup}3-fold greater in the energy deposition layer than the fluroescence from bulk polymer after 2 months. This factor was within an order of magnitude of calculated dosages to surface and bulk. Fluorescence from the bulk, apparently caused by unsaturated polyene groups formed during irradiation, grew in time about proportionally to H2 generation and thus dose. An appreciable concentration of radical or ion-radical polyenes at room temperature could be recombined by bleaching for 15 minutes at ~150 degrees C; these species appeared to reform over night at room temperature.