Balance Helium Research Articles

Mechanical Unloading of the Respiratory System during 5km Cycling Time Trials in Hypoxia

In trained endurance athletes, the ability to defend arterial oxy-hemoglobin saturation (SaO2) during high intensity constant-workload exercise in moderate hypoxia depends in part on the ability to increase minute ventilation (V̇E). Previous data have shown, however, that despite the existence of a substantial amount of ventilatory reserve (V̇Eres) in some cyclists, V̇E surprisingly does not increase during 5km time trials (5kTT) in hypoxia, despite a significant decrease in both SaO2 and mean power output (PTT) from normoxia. PURPOSE: To determine the effect of reducing the work of breathing (Wb) on V̇E, breathlessness (RPB), and PTT during a 5kTT in hypoxia in highly trained cyclists. We hypothesized no change in RPB, while V̇E would increase with an attenuated decrement in SaO2 and PTT from normoxia. METHODS: Fourteen trained male cyclists (V̇O2max = 58.7 ± 4.7 ml·kg-1·min-1) performed a 5kTT under 3 conditions at sea level: ‘CON’ (FiO2 = 0.21), ‘HYP’ (FiO2 = 0.16), and ‘HYP+He’ (FiO2 = 0.16, with balance helium). Esophageal balloons were used to assess Wb in each condition. Inspiratory capacity maneuvers were performed at each km, and flow-volume loop analyses were used to assess the %EFL and V̇Eres. The modified Borg scale (0-10) was used to assess RPB at each km. RESULTS: Wb decreased from HYP to HYP+He by 30 ± 18% (p < 0.01). Despite a substantial V̇Eres throughout CON (52 ± 44 L·min-1), V̇E was not different between CON (117.4 ± 17.9 L·min-1) and HYP (124.8 ± 17.9 L·min-1) but increased during HYP+He (139.5 ± 22.0 L·min-1; p < 0.05). While SaO2 decreased from CON to HYP by 10 ± 1% (p < 0.01), SaO2 increased by 4 ± 1% from HYP to HYP+He (p < 0.01). PTT decreased from CON to HYP (-14.2%; p < 0.01) and increased from HYP to HYP+He (+5.5%; p < 0.01). When comparing HYP to HYP+He, a significant correlation was observed between ΔSaO2 and ΔPTT (r = 0.69; p < 0.05). RPB increased from CON (6.0 ± 2.0) to HYP (7.0 ± 2.0; p < 0.05) and was unchanged from HYP to HYP+He (6.6 ± 2.0). CONCLUSIONS: In moderate hypoxia, a low ventilatory reserve does not limit 5km time trial performance, where by design, individuals are free to adjust power output. The ability to utilize ventilatory reserve while remaining below a critical threshold of perceived breathlessness appears conducive to maintaining aerobic exercise performance in moderate hypoxia.

Issues with analyzing noble gases using gas chromatography with thermal conductivity detection.

The noble gases, namely neon, argon, krypton and xenon, have many uses including in incandescent and gas discharge lighting, in plasma televisions, shielding gas in welding, in lasers for surgery and semiconductors, and in magnetic resonance imaging (MRI) of the lungs. When incorporating these noble gases in industries, especially the medical field, it is important to know accurately the composition of the noble gas mixture. Therefore, there is a need for accurate gas standards that can be used to determine the noble gas amount-of-substance fraction in the appropriate mixture application. A recent comparison of mixtures containing four noble gases in a helium balance showed mixed results among National Metrology Institutes. Significant differences, 0.7 to 3.8% relative, were seen in the analytical amount-of-substance assignments versus the gravimetric value of the noble gases in the comparison mixture when using "binary standards", i.e. neon in helium, argon in helium and krypton in helium, as applied by the National Institute of Standards and Technology. Post-comparison studies showed that when all four noble gases were included in the standards, the agreement between analytical and gravimetric values was within 0.05% relative. Further research revealed that different carrier gases (hydrogen, helium and nitrogen) resulted in varying differences between the analytical and gravimetric values assignments. This paper will discuss the findings of these analytical comparisons. Graphical abstract ᅟ.

Online helium inventory monitoring of JLab cryogenic systems

There are five cryogenic plants at Jefferson Lab which support the LINAC, experiment hall end-stations and test facility. The majority of JLab’s helium inventory, which is around 15 tons, is allocated in the LINAC cryo-modules, with the majority of the balance of helium distributed at the cryogenic-plant level mainly as stored gas and liquid for stable operation. Due to the organic evolution of the five plants and independent actions within the experiment halls, the traditional inventory management strategy suffers from rapid identification of potential leaks. This can easily result in losses many times higher than the normally accepted (average) loss rate. A real-time program to quickly identify potential excessive leakage was developed and tested. This program was written in MATLAB© for portability, easy diagnostics and modification. It interfaces directly with EPICS to access the cryogenic system state, and with and NIST REFPROP© for real fluid properties. This program was validated against the actual helium offloaded into the system. The present paper outlines the details of the inventory monitoring program, its validation and a sample of the achieved results.

The role of the graphite divertor tiles in helium retention on the LHD wall

In this study, global particle balance of helium (He) long pulse discharge with graphite divertor in the Large Helical Device (LHD) and He retention in graphite from lab-scale experiments were compared in order to determine the role of the graphite divertor in He retention on the LHD wall. Global He particle balance analysis was conducted in long-pulse discharges in LHD with only turbo molecular pump. The analysis showed that static He retention was ∼2.9 × 1022 He and the ratio of retained He (= retention over fluence) was ∼0.45%. In the lab-scale study, He retention was measured by Thermal Desorption Spectroscopy (TDS) after ion irradiation or plasma exposure. The ratio of retained He were 0.1 ∼ 0.5% in all conditions, which was well consistent with LHD results. Therefore, it may be concluded that graphite divertor tiles have an important role in He absorption in the LHD wall at the initial phase of discharges.

In-pore synthesis of ZnCO$$_3$$ in various adsorbents for NH$$_3$$ and SO$$_2$$ adsorption

A highly porous adsorbent capable of broad spectrum filtration of toxic industrial chemicals (TICs) is necessary for many civilian and military applications. To promote the gas adsorption of TICs such as NH\(_3\) and SO\(_2\), a biphasic carbon silica composite (CSC) and other single phase carbonaceous and siliceous materials functionalized with sparingly soluble ZnCO\(_3\) are considered. The adsorption capacities of these substrates functionalized via both in-pore synthesis and a wet impregnation have been measured with very low concentrations of both TICs in a balance of helium. Along with capacity performance, the functionalized materials have been characterized using X-ray diffraction, microscopy, and porosimetry techniques. Results show successful incorporation of a well dispersed ZnCO\(_3\) phase when incorporated via in-pore synthesis. All ZnCO\(_3\) functionalized materials enhance adsorption capacities compared to impregnant-free substrates. Characterization results show reduced pore volumes and surface areas of functionalized materials while maintaining structural integrity. In order to target both adsorbates effectively, in-pore synthesis of ZnCO\(_3\) on CSC provides high adsorption performance with NH\(_3\) and SO\(_2\) capacities of 4.2 and 0.59 mol/kg, respectively.

Unraveling the mechanism of propanoic acid hydrodeoxygenation on palladium using deuterium kinetic isotope effects

A combined experimental and computational kinetic isotope effect (KIE) study was performed for the catalytic hydrodeoxygenation (HDO) of deuterium-labeled propanoic acid (PAc-2, 2-D2) over Pd catalyst. For the experimental study, the kinetics were measured in a plug flow reactor over a 5wt% Pd/C catalyst at 200°C and 1atm under differential conversion using a reactor feed consisting of 1.2% PAc and 5% or 20% H2, with balance helium. Different experimental KIE values for the high (kH/kD=1.13±0.04) and low (kH/kD=1.62±0.05) partial pressures of hydrogen were observed. Density functional theory calculations were performed to obtain the reaction parameters of the elementary steps involved in the HDO of PAc on Pd (111), and a microkinetic model was developed to estimate the KIE for the low hydrogen partial pressure case from first principles. The computed result (kH/kD=1.49) is in good agreement with the experiment. In addition, the product distribution favored C2H6 and CO, suggesting decarbonylation (DCN) is the main reaction pathway. This provides strong evidence for the proposed mechanism for the formation of C2H6 on both Pd (111) and supported Pd nanoparticles presenting primarily that exposed crystal face.

CO2 adsorption on diatomaceous earth modified with cetyltrimethylammonium bromide and functionalized with tetraethylenepentamine: Optimization and kinetics

The carbon dioxide (CO2) adsorbent diatomaceous earth (DE) was modified with cetyltrimethylammonium bromide (CTAB) and functionalized with varying levels of tetraethylenepentamine (TEPA). The CO2 absorption at atmospheric pressure was optimized by varying the TEPA-loading level (0–40% (w/w)), operating temperature (40–80 °C) and water vapor concentration (0–16% (v/v)) in a 10% (v/v) CO2 feed stream in helium balance using a full 23 factorial design. The TEPA/CTAB-DE adsorbents were characterized by X-ray diffractometry, Fourier transform infrared spectrometry and thermogravimetric analyses. The CO2 adsorption capacity increased as each of these three factors increased. The TEPA loading level-water concentration interaction had a positive influence on the CO2 adsorption while the operating temperature–water concentration interaction was antagonistic. The optimal condition for CO2 adsorption on 40%TEPA/CTAB-DE, evaluated via a factorial design response surface method (RSM), was a temperature of 58–68 °C and a water vapor concentration of 9.5–14% (v/v), with a maximum CO2 adsorption capacity of 149.4 mg g−1 at 63.5 °C and 12% (v/v) water vapor concentration in the feed. Validation and sensitivity tests revealed that the estimated CO2 adsorption capacity was within ±4% of the experimental values, suggesting that the RSM model was satisfied and acceptable. From three kinetic models (pseudo-first-order, pseudo-second-order model and Avrami's equation), assessed using an error function (Err) and the coefficient of determination (R2), Avrami's equation was the most appropriate to describe the kinetics of CO2 adsorption on the 40%TEPA/CTAB-DE adsorbent and suggested that more than one reaction pathway occurred in the CO2 adsorption.

Breathing Helium–Hyperoxia and Tolerance of Partitioned Exercise in Patients With COPD

Partitioning exercise by 1-legged cycling is more effective than conventional training in patients with chronic obstructive pulmonary disease. Similarly, inhaling helium-hyperoxia can extend conventional exercise tolerance. This study aimed to determine whether breathing helium-hyperoxia could increase the tolerance of a high-intensity exercise session achieved by 1-legged cycling. Participants completed 2 high-intensity, constant power, 1-legged cycle tests to intolerance (tlimit). In a randomized order, they inspired 40% oxygen with the balance helium via mask and 1-way valve, 1-legged helium-hyperoxia (1L-HH), or room air with supplemental oxygen via a nasal cannula, 1-legged nitrogen-hyperoxia (1L-NH). We assessed quadriceps fatigue from the change in maximal voluntary contraction (FMVC) and transcutaneously stimulated twitch force (Ftwitch). Fifteen participants (forced expiratory volume in 1 second [SD] = 36 [18]% predicted; forced expiratory volume in 1 second/forced vital capacity = 34 [14]%; peak oxygen uptake = 12.8 [2.9] mL · kg · min) completed the study. Self-reported "leg fatigue" was a reason for stopping 25 of 30 tests. There was no significant difference in tlimit (0.2 [-1.4 to 1.8] min) between 1L-HH (12.2 [5.2] min) and 1L-NH (12.0 [4.1] min), or in FMVC measured shortly after HH and NH tests (P= .09). The Ftwitch was less after exercise (P< .05) in both conditions, without a difference between conditions (P= .46). Inspiring a helium-hyperoxia mixture does not increase the endurance of what would be a typical training session, breathing supplemental oxygen, of high-intensity 1-legged constant power exercise. Leg muscle fatigue was similar after 1-legged exercise with and without breathing the helium mixture.

A method for direct, semi-quantitative analysis of gas phase samples using gas chromatography–inductively coupled plasma-mass spectrometry

A new and complete GC–ICP-MS method is described for direct analysis of trace metals in a gas phase process stream. The proposed method is derived from standard analytical procedures developed for ICP-MS, which are regularly exercised in standard ICP-MS laboratories. In order to implement the method, a series of empirical factors were generated to calibrate detector response with respect to a known concentration of an internal standard analyte. Calibrated responses are ultimately used to determine the concentration of metal analytes in a gas stream using a semi-quantitative algorithm. The method was verified using a traditional gas injection from a GC sampling valve and a standard gas mixture containing either a 1ppm Xe+Kr mix with helium balance or 100ppm Xe with helium balance. Data collected for Xe and Kr gas analytes revealed that agreement of 6–20% with the actual concentration can be expected for various experimental conditions.To demonstrate the method using a relevant “unknown” gas mixture, experiments were performed for continuous 4 and 7hour periods using a Hg-containing sample gas that was co-introduced into the GC sample loop with the xenon gas standard. System performance and detector response to the dilute concentration of the internal standard were pre-determined, which allowed semi-quantitative evaluation of the analyte. The calculated analyte concentrations varied during the course of the 4hour experiment, particularly during the first hour of the analysis where the actual Hg concentration was under predicted by up to 72%. Calculated concentration improved to within 30–60% for data collected after the first hour of the experiment. Similar results were seen during the 7hour test with the deviation from the actual concentration being 11–81% during the first hour and then decreasing for the remaining period. The method detection limit (MDL) was determined for the mercury by injecting the sample gas into the system following a period of equilibration. The MDL for Hg was calculated as 6.8μg·m−3. This work describes the first complete GC–ICP-MS method to directly analyze gas phase samples, and detailed sample calculations and comparisons to conventional ICP-MS methods are provided.

Influence of Co2 on the Catalytic Performance Of La2O3/CeO2 and CaO/CeO2 Catalysts in the Oxidative Coupling of Methane

In this work the La2O3/CeO2 (33 mol % of La) and CaO/CeO2 (33 mol % of Ca) catalysts were prepared by the impregnation method and characterized by XRD and CO2-TPD. The catalytic properties of the catalysts were tested in the OCM process at 1073 K using the methane/oxygen mixture of the mole ratio 3.7 or 2.5 additionally containing CO2 and helium balance. It was found that in the presence of both catalysts an addition of CO2 enhances the selectivity to the ethylene and ethane and it does not have any negative influence on methane conversion. In the case of the CaO/CeO2 catalyst the promoting effect of CO2 was the highest. When the partial pressure of CO2 equals to 39 kPa the increase in selectivity from 36 to 41% was noted while the conversion of methane equal to 19.4-19.7 %.

Photocatalytic Degradation of Acetaldehyde by Sol-Gel TiO&lt;sub&gt;2&lt;/sub&gt; Nanoparticles: Effect of the Physicochemical Properties on the Photocatalytic Activity

Nowadays, nanostructured semiconductor materials offer promising opportunities for a new generation of materials such as TiO2nanoparticles with improved properties for their application in the environmental catalysis field. It is well known that the phocatalytic activity of the TiO2nanoparticles is strongly dependent on the surface area, crystal size, phase composition and synthesis method. Thus, the preparation conditions clearly affect the photocatalytic activity of the TiO2nanoparticles. This work deals with the study of the structure of TiO2nanoparticles that were synthesized by the sol-gel method (using isopropanol as solvent), and calcined at 200 and 500°C. The obtained samples were characterized by the XRD-Rietveld refinement, BET and TEM techniques; and tested in the photodecomposition of acetaldehyde. The evaluations were carried out at room temperature by using CH3CHO (300 ppmv), O2(2.0 %) in helium balance in a quartz glass photoreactor (gas phase) with a 365-UV light lamp. According to the results, the sample that presented the highest activity in the photocatalytic oxidation of acetaldehyde (96.4%) was the one annealed at 200 °C. This sample showed the following proportion of phases: anatase (62.88%) with a tetragonal structure (a=0.3790926, b=0.3790926, c=0.9495732) nm; and b) brookite (37.12%) with an orthorhombic structure (a=0.9167624, b=0.5416461, c=0.5210546) nm. The surface area was 189 m2/g and the average crystal size was 7.03 nm. From the results, it can be seen that this material showed high activity in the photocatalytic degradation of acetaldehyde because of: the presence of a mixture of the anatase (higher proportion) and brookite phases, nanometric crystal size and high surface area obtained in this TiO2material. According to the aforementioned, this material can be considered as a good option for the decomposition of acetaldehyde and other volatile organic compounds (VOCs) in confined spaces.

Thermal Desorption Gas Chromatography and Positron Annihilation Spectroscopy Contribution to Alpha Decay Studies in Actinide-Doped Matrices

A thermal desorption system coupled with a gas analyzer has been adapted and nuclearized to investigate He behavior in actinide-doped samples used to simulate alpha decay aging. This technique widely used in standard laboratories allows measurements of the helium balance and reduced diffusion coefficients, and a preliminary evaluation of helium locations (related to defects and thermal annealing). In our system implemented in a hot cell, small samples are annealed at up to 1100° in controlled atmosphere. They are inserted in a 10 to 20 cm3 vessel connected to a micro gas chromatography detector. Initial system calibration allowed concentration measurements within about 10%. Comparisons with the CNRS/CRPG rare gas analysis laboratory at Nancy, France, were applied on natural uranium oxides originating from Oklo (Gabon) and Mistamisk (Canada). The latest results obtained on Mistamisk samples are in good agreement, with a maximum relative deviation of 14%. The data were used to determine the activation energy of about 1 eV·at−1. On (U,Pu)O 2 and PuO 2 samples the experiments highlight the impact of defects (up to 100 dpa) on He mobility. The defect population must now be characterized to improve our knowledge of He/defect interactions and mechanisms. In addition and synergy to the macroscopic release measurements by gas chromatography, positron annihilation spectroscopy, an effective nondestructive technique for vacancy defect investigation, was also developed and nuclearized in our hot cell laboratory as part of a project supported by the NOMADE and MATINEX research groups. Specific protocols for doped sample analysis were also developed and validated with UO 2 and (U,Pu)O 2 samples.

Effects of shielding gas compositions on arc plasma and metal transfer in gas metal arc welding

This article presents the effects of shielding gas compositions on the transient transport phenomena, including the distributions of temperature, flow velocity, current density, and electromagnetic force in the arc and the metal, and arc pressure in gas metal arc welding of mild steel at a constant current input. The shielding gas considered includes pure argon, 75% Ar, 50% Ar, and 25% Ar with the balance of helium. It is found that the shielding gas composition has significant influences on the arc characteristics; droplet formation, detachment, transfer, and impingement onto the workpiece; and weld pool dynamics and weld bead profile. As helium increases in the shielding gas, the droplet size increases but the droplet detachment frequency decreases. For helium-rich gases, the current converges at the workpiece with a “ring” shape which produces non-Gaussian-like distributions of arc pressure and temperature along the workpiece surface. Detailed explanations to the physics of the very complex but interesting transport phenomena are given.

Capture of solar wind alpha‐particles by the Martian atmosphere

Integration along He++ test‐particle trajectories in the self‐consistent electromagnetic fields generated by three‐dimensional hybrid simulations of the solar wind/Mars interaction is used to evaluate the removal of solar wind α‐particles due to charge‐exchange processes with neutral species of the Martian exosphere. The total removal rate of solar wind He++ ions, transformed into either singly ionised or neutral helium, is equal to 6.7 × 1023 s−1, which corresponds approximately to 30% of the flux of solar α‐particles through the planetary cross‐section. The deposition rate of helium neutral atoms, created by double electronic capture on exospheric oxygen, impacting the exobase, and penetrating below where it can be trapped, is about 1.5 × 1023 s−1. That means an important contribution of the solar wind source to the helium balance of the Martian atmosphere. The implantation of the solar helium into the Martian atmosphere shows an asymmetry related to the orientation of the motional electric field of the solar wind, −VSW × BIMF.

Effects of thermal treatment on physico-chemical and catalytic properties of lanthanum manganite LaMnO3+y

Abstract Lanthanum manganite oxides were prepared by citric acid gel process. The precursor gel was thermally decomposed in four steps allowing high composition homogeneity and textural stabilisation. As the calcination temperature increased, the lattice constants increased whereas the average oxidation state of manganese decreased resulting in lower cation vacancies (lower y values in LaMnO 3+ y ). The specific surface area (SSA) was found to decrease from 13 to 1.5 m 2 g −1 when the sintering temperature was raised from 600 to 1000 °C. Well characterized (XRD, ATD-ATG, chemical analysis, surface area, SEM, XPS) perovskite phase LaMnO 3+ y synthetized after calcination at 700–1000 °C was tested for total methane oxidation in a fixed bed reactor with feed containing 1% methane, 4% oxygen and the balance helium. The catalytic activity was found to decrease with increasing calcination temperature and correlates not only with the bulk structure of the perovskite phase and consequently oxygen mobility but also with the content of manganese and its surface concentration. At low temperature ( 600 °C), the redox system is assumed to occur with the oxygen ions being transported through the lattice to the reduction site for reaction. This mechanism seems to be favoured by the increase of bulk cation vacancy amount.

SAES ST 909 Pilot Scale Methane Cracking Tests

Pilot scale (0.5 kg) SAES St 909 methane cracking tests were conducted for potential tritium process applications. Up to 1400 hours tests were done at 700°C, 202.7 kPa (1520 torr) with a 0.03 sLPM feed of methane plus impurities, in a 20 vol% hydrogen, balance helium, stream. Carbon dioxide gettered by St 909 can be equated to an equivalent amount of methane gettered, but equating nitrogen to an equivalent amount of methane was nitrogen feed composition dependent. A decreased hydrogen feed increased methane getter rates while a 30°C drop in one furnace zone increased methane emissions by over a factor of 30. The impact of gettered nitrogen can be somewhat minimized if nitrogen feed to the bed has been stopped and sufficient time given to recover the methane cracking rate.

Water/hydrogen/hexane multicomponent selectivity of thin MFI membranes with different Si/Al ratios

MFI films with a thickness of about 550 nm were prepared on α-alumina substrates. The surface Si/Al ratios (XPS) were 157 and 62 for silicalite-1 and ZSM-5 films, respectively, and in accordance, XRD data indicated lower ratios for ZSM-5 films. Higher ratios were observed by ICP-AES for crystals grown in the bulk of the synthesis mixtures. Six membranes of each type were prepared. Porosimetry measurements showed that all membranes were of high and similar quality. Single gas permeances for H 2, N 2, He, CO 2 and SF 6 at 25 °C were very similar within each type of membranes. However, the average hydrogen permeance was 27% lower and the average H 2/SF 6 single gas permeance ratio was 67% higher for ZSM-5 membranes. These differences are attributed to a narrower effective pore diameter for the ZSM-5 membranes due to the sodium counter ions. Separation of mixtures of H 2O, H 2 and n-hexane (helium balance) was investigated in the temperature range 25–350 °C. The highest separation factors α-H 2O/H 2 were observed at 25 °C and were 14.3 and 19.7 for silicalite-1 and ZSM-5, respectively. The membranes were selective also at 100 °C and the separation factors were about 3.2 and 6 for silicalite-1 and ZSM-5, respectively. However, the selectivity decreased at elevated temperatures and the separation factor approached 1 at temperatures above 180 °C for both membrane types. The observed water selectivity was attributed to weak adsorption of water on polar sites. A low (1.5–3) α-H 2O/ n-C 6 separation factor was observed for both membrane types for the entire investigated temperature range.

High-Throughput Nanoparticle Catalysis: Partial Oxidation of Propylene

Partial oxidation of propylene was investigated at 1 atm pressure over Rh/TiO(2) catalysts as a function of reaction temperature, metal loading and particle size using high-throughput methods. Catalysts were prepared by ablating thin sheets of pure rhodium metal using an excimer laser and by collecting the nanoparticles created on the external surfaces of TiO(2) pellets that were placed inside the ablation plume. Rh nanoparticles before the experiments were characterized by transmission electron microscopy (TEM) by collecting them on carbon film. Catalyst evaluations were performed using a high-throughput array channel microreactor system coupled to quadrupole mass spectrometry (MS) and gas chromatography (GC). The reaction conditions were 23% C(3)H(6), 20% O(2) and the balance helium in the feed, 20,000 h(-1) GHSV and a temperature range of 250-325 degrees C. The reaction products included primarily acetone (AT) and to a lesser degree propionaldehyde (PaL) as the C(3) products, together with deep oxidation products COx.

Influence of O2 and H2O on Carbothermal Reduction of SO2 by Oil-Sand Fluid Coke

To develop a new process for removing high-concentration SO2 from industrial flue gases, the carbothermal reduction of SO2 by oil-sand fluid coke at 700 degrees C was investigated by varying the inlet concentration of either O2 or H2O. Concentrations of O2 and H2O ranged from 0 to 20% and from 0 to 30%, respectively, in a stream of SO2 (18%) with the balance helium. Addition of O2 and H2O was found to enhance SO2 reduction. The enhancement was attributed to the reducing gases, CO and H2, produced by solid-gas reactions between carbon and O2 or H2O. The effects of O2 and H2O on sulfur yield, however, were bifacial: adding O2 and/or H2O increased the sulfur yield when SO2 conversion was incomplete, otherwise, it decreased the sulfur yield through the formation of sulfides such as H2S. The results of a thermodynamic analysis were in a good agreementwith the experimental results, suggesting that gas-solid reactions were slow enough to allow gas-phase equilibrium. This study indicates that carbon, such as oil-sand fluid coke, can be utilized to remove SO2 in flue gases containing O2/H2O and to convert it to elemental sulfur.

Helium gas permeability of SiC/SiC composite used for in-vessel components of nuclear fusion reactor

Abstract SiC/SiC composite is a candidate material of blanket in fusion reactors since silicon carbide is a low activation material and the temperature of helium coolant can be taken high, 1100 K. Helium gas permeability of SiC/SiC composite, however, has been little measured so far for this purpose. For SiC/SiC composites made by several methods, the helium gas permeability was measured using a vacuum system consisting of high and low-pressure chambers, and its application for the blanket was discussed. The permeability of SiC/SiC composite made by the method called as nano-powder infiltration and transient eutectoid (NITE) process was observed to be very low, 10−11 m2/s. A change of the permeability owing to heat cycles was also measured. The increase of the permeability was observed to be not large. The leak flux of helium through the SiC/SiC coolant pipe and first wall of blanket module was analyzed based upon the density balance of helium. It is shown that the leak rate into fusion plasma can be taken lower the helium production rate due to fusion reactions if the pumping is attached to the blanket module. Then, the fuel dilution due to the helium leak may be avoided even when the SiC/SiC blanket modules are employed.