The effect of metal transfer modes and shielding gas composition on the emission of ultraafine particles in MAG steel welding

The present study aims to characterize ultrafine particles emitted during gas metal arc welding of mild steel and stainless steel, using different shielding gas mixtures, and to evaluate the effect of metal transfer modes, controlled by both processing parameters and shielding gas composition, on the quantity and morphology of the ultrafine particles. It was found that the amount of emitted ultrafine particles (measured by particle number and alveolar deposited surface area) are clearly dependent from the main welding parameters, namely the current intensity and the heat input of the Welding process. The emission of airborne ultrafine particles increases with the current intensity as fume formation rate does. When comparing the shielding gas mixtures, higher emissions were observed for more oxidizing mixtures, that is, with higher CO2 content, which means that these mixtures originate higher concentrations of ultrafine particles (as measured by number of particles. by cubic centimeter of air) and higher values of alveolar deposited surface area of particles, thus resulting in a more hazardous condition regarding welders exposure.

The effect of shielding gas feeding method in laser welding of steel

Gas shielding plays an important role in laser welding phenomena. This is because it does not only provide shielding against oxidization but it has an effect in beam absorption and thus welds penetration. The goal of this thesis is to study and compare the effects of different shielding gas feeding methods in laser welding of steel. Research method is a literature survey. It is found that the inclination angle and the arrangement of the gas feeding nozzles affect the phenomena significantly. It is suggested that by designing shielding gas feeding case specifically better welding results can be obtained.

Hitsaussuojakaasujen tehokas ja taloudellinen käyttö

Suojakaasun päätehtävänä on suojata hitsaustapahtumaa ympäröivän ilman vaikutukselta. Päätehtävän lisäksi suojakaasullavoidaan vaikuttaa suoraan tai välillisesti lähes kaikkiin hitsauksen asioihin, joista laatu, tehokkuus ja taloudellisuus muodostuvat. Suojakaasuja tarvitsevat hitsausmenetelmät ovat: kaasukaarihitsausprosessit (MIG/MAG-, TIG- ja plasmahitsaus), laserhitsaus sekä näiden yhdistelmät eli hybridihitsausmenetelmät sekä MIG-juotto. Hitsaussuojakaasujen peruskaasu tänä päivänä on argon, johon hitsausprosessista tai materiaalistariippuen sekoitetaan hiilidioksidia, heliumia, vetyä tai happea. Pääsääntöisesti hitsaussuojakaasut ovat kahden komponentin kaasuja, mutta 3-komponenttikaasut ovat yleistymässä. Sopivalla suojakaasuseostuksella saadaan erittäin merkittävä hyöty tuottavuuden lisääntyessä ja laadun parantuessa. Suojakaasujen oikealla toimitusmuodolla on merkittävä vaikutus kokonaiskustannuksiin. Uudet, kehittyneet sekoitinlaitteet mahdollistavat tarkat osakomponenttien sekoittamiset hitsauspaikalla. Seokset ovat jatkuvasti analysoitavissa ja jäljitettävissä. Suojakaasujen kierrätys on erityisesti kalliiden kaasujen, kuten helium ja argon, kohdalta tulevaisuuden haaste ja mahdollisuus. Suojakaasulla on suuri merkitys hitsauksen tuottavuuteen, taloudellisuuteen ja myös hitsausympäristöön ja työturvallisuuteen. Robottihitsauksen lisääntyminen asettaa vaatimuksia, joihinoikein valitulla suojakaasulla voidaan myönteisesti vaikuttaa. Tehokashitsaus on valmistusprosessin tärkeä osa, jossa oikein valituilla suojakaasuilla saavutetaan merkittävä tuottavuuden lisäys vaikuttamalla kaariominaisuuksiin, tunkeumaan, roiskeisiin, nopeuteen, hitsimetallurgiaan, lämmöntuontiin ja hitsausympäristöön. Diplomityössä tutkittiin casena Peikko Finland Oy:n suojakaasujärjestelmät, niiden tehokkuus, toimivuus ja sopivuus konepajan tuotantoon ja erityisesti robottihitsaukseen.

Suojakaasuseoksen koostumuksen vaikutus CO2-laser-MAG-hybridihitsauksessa

Hitsaavassa teollisuudessa kilpailukyvyn säilyttäminen edellyttää hitsauksen tehokkuuden nostoa. Niinpä metalliteollisuus etsii kuumeisesti uusia yhä tehokkaampia hitsausmenetelmiä. CO2-laserin ja MAG:in yhdistelmän muodostamalla hybridihitsauksella saadaan aikaan syvä tunkeuma kuten laserhitsauksessa, mutta sallitaan laserhitsausta väljemmät railotoleranssit. Samalla muodonmuutokset vähenevät huomattavasti verrattuna perinteiseen kaarihitsaukseen. Kaariavusteisessa laserhitsauksessa yhdistetään laserhitsaukseen perinteinen kaarihitsaus eli MIG/MAG-, TIG- tai plasmahitsaus. Menetelmää voidaan kutsua myös hybridihitsaukseksi ja sillä hyödynnetään molempien prosessien edut välttyen yksittäisten prosessien haitoilta. Prosessin haittapuolena on parametrien suuri määrä, joka on rajoittanut menetelmän käyttöönottoa. Diplomityössä tutkittiin suojakaasuseoksen koostumuksen vaikutusta rakenneteräksen CO2-laser-MAG-hybridihitsauksessa. Laserhitsauksen ja MAG-hitsauksen suojakaasuvirtaukset yhdistettiin siten, että heliumseosteinen suojakaasu tuotiin MAG-polttimen kaasukuvun kautta. Suojakaasun heliumpitoisuus nostettiin niin korkeaksi, että estettiin laserhitsauksen muodostaman plasman syntyminen. Samalla hitsauskokeissa opittiin paremmin ymmärtämään prosessia ja sen parametrien riippuvuutta toisiinsa. Tutkitut suojakaasuseokset koostuivat heliumista, argonista ja hiilidioksidista. Hitsauskokeiden perusteella havaittiin, että suojakaasuseoksen optimaalinen heliumpitoisuus on 40-50 %. Tällöin laserin tunkeumaa häiritsevää plasmapilveä ei synny ja prosessi on stabiili. Päittäisliitosten hitsauksessa suojakaasuseoksen 2 %:n CO2-pitoisuudella saadaan aikaan hyvin vähän huokosia sisältävä hitsi, jonka tunkeumaprofiilin muoto ja liittymä perusaineeseen on juoheva. Pienaliitoksilla 7 %:n CO2-pitoisuudella prosessi pysyy stabiilina ja vähäroiskeisena. Tunkeuma hieman levenee hitsin keskeltä ja hitsin liittyminen perusaineeseen on juoheva.CO2-laser-MAG-hybridihitsauksella aikaansaadaan laadukkaita hitsejä taloudellisesti, mikäli käytetyt parametrit ovat oikein valittuja. Parametrit on sovitettava jokaiseen hitsaustapaukseen erikseen, eikä niitä välttämättä voida suoraan käyttää toisessa tapauksessa.

Effect of Shielding Gases in Laser Welding of Aluminium Alloys

High reflectivity to laser light, alloying element evaporation during high power laser welding makes aluminium alloys highly susceptibility to weld defects such as porosity, cracking and undercutting. The dynamic behaviour of the keyhole, due to fluctuating plasma above the keyhole and the vaporization ofthe alloying elements with in the keyhole, is the key problem to be solved for the improvement of the weld quality and stabilization of the keyhole dynamics isperhaps the single most important development that can broaden the application of laser welding of aluminium alloys. In laser welding, the shielding gas is commonly used to stabilize the welding process, to improve the welded joint features and to protect the welded seam from oxidation. The chemicalcomposition of the shielding gas is a key factor in achieving the final qualityof the welded joints. Wide range of shielding gases varying from the pure gasesto complex mixtures based on helium, argon, nitrogen and carbon dioxide are commercially available. These gas mixtures should be considered in terms of their suitability during laser welding of aluminium alloys to produce quality welds. The main objective of the present work is to study the effect of the shielding gascomposition during laser welding of aluminium alloys. Aluminium alloy A15754 was welded using 3kW Nd-YAG laser (continuous wave mode). The alloy samples were butt welded with different shielding gases (pure and mixture of gases) so that high quality welds with high joint efficiencies could be produced. It was observed that the chemical composition of the gases influenced the final weld quality and properties. In general, the mixture gases, in correct proportions, enabled better utilisation of the properties of the mixing gases, stabilized the welding process and produced better weld quality compared to the pure shielding gases.

The mechanism of protection of molten magnesium by cover gas mixtures containing sulphur hexafluoride

Experimental studies have been undertaken, involving in situ observations of the interaction between cover gas mixtures and molten magnesium. It has been shown that, in the presence of sulphur hexafluoride (SF6), the contact angle between solid MgO and molten magnesium is reduced, resulting in the wetting of MgO by magnesium metal. In contrast, it was observed that the absence of SF6 results in a large contact angle, poor wetting of the MgO by magnesium metal and a non-adherent surface film. It is proposed that the formation of an adherent, protective surface film under a cover gas mixture containing SF6 is due to capillary forces acting within the film.

Vulvar Lichen Sclerosus: Efficacy of Photodynamic Therapy Under Conscious Sedation with Inhaled 50% Nitrous Oxide and Oxygen Mixture

Anogenital lichen sclerosus is a chronic, inflammatory, mucocutaneous disorder of significant morbidity. Common symptoms include pruritus, pain, dysuria, and dyspareunia, frequently of difficult control. Photodynamic therapy (PDT) may be an effective therapeutic option in selected cases refractory to first--‐line treatment options. However, procedure--‐related pain is a limiting factor in patient adherence to treatment. Conscious sedation and analgesia with a ready--‐to--‐use gas mixture of nitrous oxide and oxygen is useful in short--‐term procedures. It provides a rapid, effective, and short--‐lived effect, without the need for anesthesiology support. A 75--‐year--‐old woman presented with a highly symptomatic, histologically confirmed vulvar lichen sclerosus, with at least 15 years of evolution. Pain, pruritus, and dysuria were intense and disabling. Treatment with ultrapotent topical corticosteroids proved to be ineffective despite patient compliance. She was then referred for PDT. A total of 3 sessions were performed, held at a mean interval of 9 weeks, and under the analgesic and sedative effect of nitrous oxide/oxygen gas. Response to treatment was evaluated through a daily, self--‐reported pain rating scale. Dysuria remitted completely after the first PDT session. An 80% reduction in pruritus and pain was observed after the third session, and has been sustained for the past six months without further need for topical corticotherapy. Treatment sessions were well tolerated and pain-- free, with no side effects to report. PDT appears to be effective in the symptomatic treatment of vulvar lichen sclerosus. To the authors’ knowledge this is the first case reporting the use of inhaled nitrous oxide/oxygen gas mixture during PDT performed in the genital area. Its analgesic and sedative effects may increase patients’ adherence to this painful procedure. Furthermore, given its safety, it can be easily managed in outpatient clinics by trained dermatologists.

Gas tungsten arc welding of NiTi shape memory alloy

Shape memory alloys are characterized by the ability of recovering their initial shape after being deformed and by superelasticity. Since the discovery of these alloys, a new field of interest emerged not only for the scientific community but also to many industries. However, these alloys present poor machinability which constitute a constrain in the design of complex components for new applications. Thus, the demand for joining techniques able to join these alloys without compromising their properties became of great importance to enlarge the complexity of existing applications. Literature shows that these alloys are joined mainly using laser welding. In the present study, similar NiTi butt joints, were produced using TIG welding. The welds were performed in 1.5 mm thick plates across the rolling direction. A special fixture and gas assist device was designed and manufactured. Also a robot arm was adapted to accommodate the welding torch to assure the repeatability of the welding parameters. Welds were successfully achieved without macroscopic defects, such as pores and distortions. Very superficial oxidation was seen on the top surface due to insufficient shielding gas flow on the weld face. The welded joints were mechanically tested and structurally characterized. Testing methods were used to evaluate macro and microstructure, as well as the phase transformation temperatures, the mechanical single and cyclic behaviour and the shape recovery ability. Differential Scanning Calorimetry (DSC), Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), microhardness measurements were techniques also used to evaluate the welded joints. A depletion in Ni in the fusion zone was seen, as well as a shift in Ms temperature. For strain values of 4% the accumulated irrecoverable strain was of about 30% and increased with the strain imposed during cycling. Nevertheless, a complete recovery of initial shape was observed when testing the shape memory effect on a dedicated device that introduces a deformation of 6.7%. That is, the welding procedure does not remove the ability of the specimens to recover their initial shape.

Kaarihitsauksen suojakaasun tunnistus ja virtauksen mittaus ultraäänellä

Kaasukaarihitsauksessa suojakaasuna käytetään yleensä argonin ja hiilidioksidin tai argonin ja heliumin seoksia. Suojakaasu vaikuttaa useisiin hitsausominaisuuksiin, jotka puolestaan vaikuttavat hitsauksen laatuun ja tuottavuuteen. Automaattisella suojakaasun tunnistuksella ja virtausmäärän mittauksella voitaisiin tehdä hitsauksesta paitsi käyttäjän kannalta yksinkertaisempaa, myös laadukkaampaa. Työn tavoite on löytää mahdollisimman edullinen ja kuitenkin mahdollisimman tarkasti kaasuseoksia tunnistava menetelmä, jota voitaisiin hyödyntää MIG/MAG-hitsauskoneeseen sisäänrakennettuna. Selvä etu on, jos menetelmällä voidaan mitata myös kaasun virtausmäärä. Äänennopeus kaasumaisessa väliaineessa on aineen atomi- ja molekyylirakenteesta ja lämpötilasta riippuva ominaisuus, joka voidaan mitata melko edullisesti. Äänennopeuden määritys perustuu ääniaallon kulkuajan mittaamiseen tunnetun pituisella matkalla. Kaasun virtausnopeus on laskettavissa myötä- ja vastavirtaan mitattujen kulkuaikojen erotuksen avulla. Rakennettu mittauslaitteisto koostuu kahdesta ultraäänimuuntimesta, joiden halkaisija on 10 mm ja jotka toimivat sekä lähettimenä että vastaanottimena. Muuntimet ovat 140 mm:n etäisyydellä toisistaan virtauskanavassa, jossa suojakaasu virtaa yhdensuuntaisesti äänen kanssa. Virtauskanava on putki, jossa on käytetty elastisia materiaaleja, jotta ääniaaltojen eteneminen kanavan runkoa pitkin minimoituisi. Kehitetty algoritmi etsii kahden lähetetyn 40 kHz:n taajuisen kanttiaaltopulssin aiheuttaman vasteen perusteella ääniaallon saapumisajanhetken. Useiden mittausten, tulosten lajittelun ja suodatuksen jälkeen tuntemattomalle kaasulle lasketaan lämpötilakompensoitu vertailuluku. Tuntematon kaasu tunnistetaan vertailemalla lukua tunnettujen kaasuseosten mitattuihin vertailulukuihin. Laitteisto tunnistaa seokset, joissa heliumin osuus argonissa on enintään 50 %. Hiilidioksidia sisältävät argonin seokset puolestaan tunnistetaan puhtaaseen hiilidioksidiin asti jopa kahden prosenttiyksikön tarkkuudella. Kaasun tilavuusvirtausmittauksen tarkkuus on noin 1,0 l/min.

Dynamics of gas levels inside packages containing minimally processed Pera orange

The purpose of this study was to evaluate the changes in concentrations of O2 and CO2 inside packages of minimally processed Pera orange. Previously selected oranges that were washed, sanitized, and chilled were peeled using hydrothermal treatment (immersion of fruits in water at 50 °C for 8 minutes). The peeled oranges were then packed in five different plastic packages under passive and active modified atmosphere (5% O2 + 10% CO2 + 85% N2). The fruits were stored at 6 °C and 12 °C. The package headspace gas composition was evaluated for twelve days at 6 °C and nine days at 12 °C. The polypropylene film (32 µm) promoted modified atmosphere similar to that initially injected (5% O2 + 10% CO2 + 85% N2) at 6 °C and 12 °C. With regard to the atmosphere modification system, the injection of a gas mixture anticipated achieving an equilibrium atmosphere inside the packages at 12 °C. At 6 °C, the gas composition inside the packages was kept close to that of the injection, but the equilibrium was not verified.

Avaliação da influência dos parâmetros de processo de soldagem MIG no surgimento de poros em tubos de alumínio

The process of electric arc welding with shielding gas (GMAW) is being increasingly used in various industrial applications. This process occurs by which an electric arc is established between the work piece and a consumable in the form of wire, the arc melts the wire continuously as it is fed to the weld pool. The weld metal is protected from the atmosphere by flowing a gas (or gas mixture) inert or active. This paper presents a study of the welding process GMAW - MIG on aluminum tubes, alloy 6101 - T6, used in the manufacture of armored busbar, intended for driving electric power plants. 5(five) were welded specimens, changing certain welding parameters at each time was monitored welding joint as well as the interpass temperature. Tests were performed bending, tensile and macrographical analysis of body-of-evidence and through its results was possible to reach a better welding condition, which minimizes the appearance of pores, since the porosity has great influence on the mechanical strength and electrical conductivity of welded pipes

Trasporto di materia in membrane polimeriche e nanocomposite per la separazione di gas

Membrane-based separation processes are acquiring, in the last years, an increasing importance because of their intrinsic energetic and environmental sustainability: some types of polymeric materials, showing adequate perm-selectivity features, appear rather suitable for these applications, because of their relatively low cost and easy processability. In this work have been studied two different types of polymeric membranes, in view of possible applications to the gas separation processes, i.e. Mixed Matrix Membranes (MMMs) and high free volume glassy polymers. Since the early 90’s, it has been understood that the performances of polymeric materials in the field of gas separations show an upper bound in terms of permeability and selectivity: in particular, an increase of permeability is often accompanied by a decrease of selectivity and vice-versa, while several inorganic materials, like zeolites or silica derivates, can overcome this limitation. As a consequence, it has been developed the idea of dispersing inorganic particles in polymeric matrices, in order to obtain membranes with improved perm-selectivity features. In particular, dispersing fumed silica nanoparticles in high free volume glassy polymers improves in all the cases gases and vapours permeability, while the selectivity may either increase or decrease, depending upon material and gas mixture: that effect is due to the capacity of nanoparticles to disrupt the local chain packing, increasing the dimensions of excess free volume elements trapped in the polymer matrix. In this work different kinds of MMMs were fabricated using amorphous Teflon® AF or PTMSP and fumed silica: in all the cases, a considerable increase of solubility, diffusivity and permeability of gases and vapours (n-alkanes, CO2, methanol) was observed, while the selectivity shows a non-monotonous trend with filler fraction. Moreover, the classical models for composites are not able to capture the increase of transport properties due to the silica addition, so it has been necessary to develop and validate an appropriate thermodynamic model that allows to predict correctly the mass transport features of MMMs. In this work, another material, called poly-trimethylsilyl-norbornene (PTMSN) was examined: it is a new generation high free volume glassy polymer that, like PTMSP, shows unusual high permeability and selectivity levels to the more condensable vapours. These two polymer differ each other because PTMSN shows a more pronounced chemical stability, due to its structure double-bond free. For this polymer, a set of Lattice Fluid parameters was estimated, making possible a comparison between experimental and theoretical solubility isotherms for hydrocarbons and alcoholic vapours: the successfully modelling task, based on application of NELF model, offers a reliable alternative to direct sorption measurement, which is extremely time-consuming due to the relevant relaxation phenomena showed by each sorption step. For this material also dilation experiments were performed, in order to quantify its dimensional stability in presence of large size, swelling vapours.

Developments for transactinide chemistry experiments behind the gas-filled separator TASCA

Topic of this thesis is the development of experiments behind the gas-filled separator TASCA(TransActinide Separator and Chemistry Apparatus) to study the chemical properties of the transactinide elements.rnIn the first part of the thesis, the electrodepositions of short-lived isotopes of ruthenium and osmium on gold electrodes were studied as model experiments for hassium. From literature it is known that the deposition potential of single atoms differs significantly from the potential predicted by the Nernst equation. This shift of the potential depends on the adsorption enthalpy of therndeposited element on the electrode material. If the adsorption on the electrode-material is favoured over the adsorption on a surface made of the same element as the deposited atom, the electrode potential is shifted to higher potentials. This phenomenon is called underpotential deposition.rnPossibilities to automatize an electro chemistry experiment behind the gas-filled separator were explored for later studies with transactinide elements.rnThe second part of this thesis is about the in-situ synthesis of transition-metal-carbonyl complexes with nuclear reaction products. Fission products of uranium-235 and californium-249 were produced at the TRIGA Mainz reactor and thermalized in a carbon-monoxide containing atmosphere. The formed volatile metal-carbonyl complexes could be transported in a gas-stream.rnFurthermore, short-lived isotopes of tungsten, rhenium, osmium, and iridium were synthesised at the linear accelerator UNILAC at GSI Helmholtzzentrum für Schwerionenforschung, Darmstadt. The recoiling fusion products were separated from the primary beam and the transfer products in the gas-filled separator TASCA. The fusion products were stopped in the focal plane of TASCA in a recoil transfer chamber. This chamber contained a carbon-monoxide – helium gas mixture. The formed metal-carbonyl complexes could be transported in a gas stream to various experimental setups. All synthesised carbonyl complexes were identified by nuclear decay spectroscopy. Some complexes were studied with isothermal chromatography or thermochromatography methods. The chromatograms were compared with Monte Carlo Simulations to determine the adsorption enthalpyrnon silicon dioxide and on gold. These simulations based on existing codes, that were modified for the different geometries of the chromatography channels. All observed adsorption enthalpies (on silcon oxide as well as on gold) are typical for physisorption. Additionally, the thermalstability of some of the carbonyl complexes was studied. This showed that at temperatures above 200 °C therncomplexes start to decompose.rnIt was demonstrated that carbonyl-complex chemistry is a suitable method to study rutherfordium, dubnium, seaborgium, bohrium, hassium, and meitnerium. Until now, only very simple, thermally stable compounds have been synthesized in the gas-phase chemistry of the transactindes. With the synthesis of transactinide-carbonyl complexes a new compound class would be discovered. Transactinide chemistry would reach the border between inorganic and metallorganic chemistry.rnFurthermore, the in-situ synthesised carbonyl complexes would allow nuclear spectroscopy studies under low background conditions making use of chemically prepared samples.

Comparison of magnetic resonance imaging of inhaled SF6 with respiratory gas analysis

Magnetic resonance imaging of inhaled fluorinated inert gases ((19)F-MRI) such as sulfur hexafluoride (SF(6)) allows for analysis of ventilated air spaces. In this study, the possibility of using this technique to image lung function was assessed. For this, (19)F-MRI of inhaled SF(6) was compared with respiratory gas analysis, which is a global but reliable measure of alveolar gas fraction. Five anesthetized pigs underwent multiple-breath wash-in procedures with a gas mixture of 70% SF(6) and 30% oxygen. Two-dimensional (19)F-MRI and end-expiratory gas fraction analysis were performed after 4 to 24 inhaled breaths. Signal intensity of (19)F-MRI and end-expiratory SF(6) fraction were evaluated with respect to linear correlation and reproducibility. Time constants were estimated by both MRI and respiratory gas analysis data and compared for agreement. A good linear correlation between signal intensity and end-expiratory gas fraction was found (correlation coefficient 0.99+/-0.01). The data were reproducible (standard error of signal intensity 8% vs. that of gas fraction 5%) and the comparison of time constants yielded a sufficient agreement. According to the good linear correlation and the acceptable reproducibility, we suggest the (19)F-MRI to be a valuable tool for quantification of intrapulmonary SF(6) and hence lung function.

Hydrocarbon gas concentrations in sediments from ODP Leg 164 sites

Residual concentrations and distributions of hydrocarbon gases from methane to n-heptane were measured in sediments at seven sites on Ocean Drilling Program (ODP) Leg 164. Three sites were drilled at the Cape Fear Diapir of the Carolina Rise, and one site was drilled on the Blake Ridge Diapir. Methane concentrations at these sites result from microbial generation which is influenced by the amount of pore-water sulfate and possible methane oxidation. Methane hydrate was found at the Blake Ridge Diapir site. The other hydrocarbon gases at these sites are likely the product of early microbial processes. Three sites were drilled on a transect of holes across the crest of the Blake Ridge. The base of the zone of gas-hydrate occurrence was penetrated at all three sites. Trends in hydrocarbon gas distributions suggest that methane is microbial in origin and that the hydrocarbon gas mixture is affected by diagenesis, outgassing, and, near the surface, by microbial oxidation. Methane hydrate was recovered at two of these three sites, although gas hydrate is likely present at all three sites. The method used here for determining amounts of residual hydrocarbon gases has its limitations and provides poor assessment of gas distributions, particularly in the stratigraphic interval below about ~100 mbsf. One advantage of the method, however, is that it yields sufficient quantities of gas for other studies such as isotopic determinations.