Zeolite Trap Research Articles

14C AMS measurement of CO2 samples with the high throughput HVE gas interface system

Abstract The newly designed HVE gas interface enables the AMS measurement of carbon samples in CO2 form. The CO2, e.g. resulting from the sample combustion in an elemental analyzer, is adsorbed in a zeolite trap and subsequently transferred to a motor-driven syringe. Once diluted with He, the gas mixture is transferred into the ion source of the AMS system. A carbon ion beam is formed in the ion source and mass-analyzed by the AMS system, resulting in 13C/12C and 14C/12C isotopic ratios. The HVE gas interface features two traps and two syringes to maximize the sample throughput, which results in more than 10 samples per hour. The first performance results of CO2 gas sample AMS measurements that were performed with the HVE gas interface in combination with the HVE 210 kV AMS system are presented in this paper. The measurements show that the gas interface contribution to the 14C/12C background is in the 10–15 level and to the precision is at or below 1%.

Hydrocarbon-Water Adsorption and Simulation of Catalyzed Hydrocarbon Traps

Catalyzed hydrocarbon traps (HC traps) are being developed to provide HC control during the cold start. HC traps are made up of an adsorbent material, such as a zeolite, and a three way catalyst (precious metal based) present on the same monolith to provide trapping and oxidation functions. Traps are typically formulated with a multi-layer washcoat structure with the catalyst layer on top, and the trapping material placed under. The HC traps operate by storing (trapping) the unburned hydrocarbon molecules in the adsorbent material at a lower temperature when adsorption is favored and oxidation does not occur, and subsequently releasing these trapped HCs when the catalyst has heated sufficiently to convert the HCs to carbon dioxide and water.This paper presents the results of a modeling, laboratory and vehicle study on the performance of HC traps. First we present procedure to evaluate trap performance in the laboratory that provides the kinetic parameters for HC adsorption. A mathematical model is presented that can be used to simulate the HC trap. The feedgas to the zeolite trap on vehicle contains both HCs and water, present in the vehicle exhaust. The various HC species and water compete for adsorption on the zeolites. Lab experiments conducted on zeolites to study the competitive adsorption of various HCs and water is presented. Experiments have been conducted where different HCs and water are sequentially adsorbed on the zeolite, and TPD conducted. For modeling, Langmuir isotherm is assumed to represent the adsorption phenomena on the zeolite sites. Exothermic effects of water adsorption on acidic zeolites have been presented. Details on the experiments done to estimate the heat of adsorption of water on zeolites, and the modeling results of water adsorption on zeolites have also been provided.

Towards radiocarbon dating of single foraminifera with a gas ion source

Carbonate shells from foraminifera are often analysed for radiocarbon to determine the age of deep-sea sediments or to assess radiocarbon reservoir ages. However, a single foraminiferal test typically contains only a few micrograms of carbon, while most laboratories require more than 100μg for radiocarbon dating with an accelerator mass spectrometry (AMS) system. The collection of the required amount of foraminifera for a single analyses is therefore time consuming and not always possible. Here, we present a convenient method to measure the radiocarbon content of foraminifera using an AMS system fitted with a gas ion source. CO2 is liberated from 150 to 1150μg of carbonate in septum sealed vials by acid decomposition of the carbonate. The CO2 is collected on a zeolite trap and subsequently transferred to a syringe from where it is delivered to the ion source. A sample of 400μg (50μgC) typically gives a 12C− ion source current of 10–15μA over 20min, yielding a measurement precision of less than 7 per mil for a modern sample. Using this method, we were able to date a single 560μg Cibicides pseudoungerianus test at 14,030±160 radiocarbon years. Only a minor modification to our existing gas handling system was required and the system is fully automatable to further reduce the effort involved for sample preparation.

A novel approach to process carbonate samples for radiocarbon measurements with helium carrier gas

Most laboratories prepare carbonates samples for radiocarbon analysis by acid decomposition in evacuated glass tubes and subsequent reduction of the evolved CO2 to graphite in self-made reduction manifolds. This process is time consuming and labor intensive. In this work, we have tested a new approach for the preparation of carbonate samples, where any high-vacuum system is avoided and helium is used as a carrier gas. The liberation of CO2 from carbonates with phosphoric acid is performed in a similar way as it is often done in stable isotope ratio mass spectrometry where CO2 is released with acid in septum sealed tube under helium atmosphere. The formed CO2 is later flushed in a helium flow by means of a double-walled needle mounted from the tubes to the zeolite trap of the automated graphitization equipment (AGE). It essentially replaces the elemental analyzer normally used for the combustion of organic samples. The process can be fully automated from sampling the released CO2 in the septum-sealed tubes with a commercially available auto-sampler to the graphitization with the automated graphitization. The new method yields in low sample blanks of about 50000years. Results of processed reference materials (IAEA-C2, FIRI-C) are in agreement with their consensus values.

A versatile gas interface for routine radiocarbon analysis with a gas ion source

In 2010 more than 600 radiocarbon samples were measured with the gas ion source at the MIni CArbon DAting System (MICADAS) at ETH Zurich and the number of measurements is rising quickly. While most samples contain less than 50μg C at present, the gas ion source is attractive as well for larger samples because the time-consuming graphitization is omitted. Additionally, modern samples are now measured down to 5 per-mill counting statistics in less than 30min with the recently improved gas ion source.In the versatile gas handling system, a stepping-motor-driven syringe presses a mixture of helium and sample CO2 into the gas ion source, allowing continuous and stable measurements of different kinds of samples. CO2 can be provided in four different ways to the versatile gas interface. As a primary method, CO2 is delivered in glass or quartz ampoules. In this case, the CO2 is released in an automated ampoule cracker with 8 positions for individual samples. Secondly, OX-1 and blank gas in helium can be provided to the syringe by directly connecting gas bottles to the gas interface at the stage of the cracker. Thirdly, solid samples can be combusted in an elemental analyzer or in a thermo-optical OC/EC aerosol analyzer where the produced CO2 is transferred to the syringe via a zeolite trap for gas concentration. As a fourth method, CO2 is released from carbonates with phosphoric acid in septum-sealed vials and loaded onto the same trap used for the elemental analyzer. All four methods allow complete automation of the measurement, even though minor user input is presently still required. Details on the setup, versatility and applications of the gas handling system are given.

A revolutionary graphitisation system: Fully automated, compact and simple

Abstract A new graphitisation system, directly coupled to an elemental analyser, has been developed for convenient, fast and efficient sample preparations for radiocarbon measurement by means of accelerator mass spectrometry. We demonstrate an alternative to the cryogenic transport of CO2 into the graphitisation reactors with liquid nitrogen, which is used by others. Instead, the CO2 coming from an EA is absorbed on a single column filled with zeolite. The CO2 can then be easily released by heating the zeolite trap and transferred to the reactor by gas expansion. The system is simple and fully automated for sample combustion and graphitisation.

Sorption of 137Cs from undisturbed forest soil in a zeolite trap

A method to study the time-integrated migration of radiocaesium (137Cs) from undisturbed coniferous forest soil cores is presented, which is based on a natural zeolite trap enclosed in a semi-permeable membrane that can be mounted into soil cores. Results show that higher zeolite trapping of 137Cs occurred in a forest soil with high soil-plant transfer parameters, low pH and high organic contents. Part of the biologically bound 137Cs that was associated within the soil microflora and microfauna appears to increase the migration of 137Cs after heating of the soil cores. Therefore, migration and mobility of 137Cs in forest soil seems to depend to a major extent upon the soil's physical and chemical parameters, particularly the activity concentration of 137Cs in soil solution, soil pH, percentage of soil organic matter (OM%) and soil mineral type.

A new energy-efficient approach to high vacuum pumping

Recent experiments have shown that an efficienty trapped mechanical rotary pump operating with completely degassed oil is capable of pressures in the 10 −7 mbar range. By greatly enlarging the zeolite trap and mounting it immediately adjacent to the work chamber it can be made to funtion simultaneously as a high speed sorption pump for vapours. Outgassed vapours from the work chamber and vapours originating from the pump oil are both pumped by the zeolite. The zeolite is operated at room temperature except during bakeout and is maintained at very low surface coverages to obtain corresponding low equilibrium pressures of water and hydrocarbons. Gases which are not sorbed by the zeolite are pumped by the mechanical pump. Vapour pumping continues for periods of months even when all power to the system is shut down. High vacuum is attainable within a few minutes after reapplying power. If desired, the zeolite can be cooled to raise the pumping speeds for all gases to approximately those for vapours, and to reduce ultimate pressures to the 10 −8 mbar range. This principle can be used as the basis for practical pumping systems which provide clean high vacua with low power consumption. Two pumping stations with speeds for vapours in the 12/s −1 and 400ls −1 range, respectively, are discussed.

A sniffing attachment with improved response time and sensitivity

A sniffing attachment with improved sensitivity and response and clean up times for use with a helium leak detector has been developed. The attachment consists of a zeolite trap cooled to liquid nitrogen temperature in series with a sniffing leak which is much bigger than those normally used in the probes. Response time of the order of 12.5 s and detection limit of 50 ppb helium concentration are obtained without difficulty. It has been used over a period of nearly 1 year and has given satisfactory performance.

Some Tests on Noncooled Zeolites

Tests were performed to investigate the trapping and pumping properties of two kinds of zeolite as a function of temperature and duration of baking. Residual gas spectra were also recorded. The results showed that a vacuum system made up by a rotary pump and a noncooled zeolite trap can reach pressures down in the 10−6-Torr range without oil or water vapor contamination.

Suppression of excited species from a sputter-ion pump by a zeolite trap: A E Barrington, Rev scient Instrum, 36(4), 1965, 549

Suppression of excited species from a sputter-ion pump by a zeolite trap: A E Barrington, Rev scient Instrum, 36(4), 1965, 549

Suppression of Excited Species from Sputter-Ion Pump by a Zeolite Trap

Zeolite trap of migrating photon radiated by metastable argon atoms from sputter ion pump to ion collector

Design and Performance of Nottingham Type Ionization Gauge

A modified Nottingham gauge described in this paper has a thin gold film deposited on glass envelope as the screen electrode. Both ends of the electron collecting electrode, a cylindrical grid type, are electronically closed by a pair of wire net. The gauge sensitivity was stable and no effect of Balkhausen-Kurz oscillation was observed in the operating range while in Bayard-Alpert gauge the effect sometimes caused trouble. As this result operation of the gauge at a larger electron emission current than that for a conventional B-A gauge was proved feasible, which in turn results in practically higher sensitivity of the gauge.Electron bombarding power required for outgassing of electrode is about 40 watt d.c.. Glass wall temperature was less than 40°C for normal operation of 0.5 milliampere electron emission. The sensitivity for nitrogen is 20.4±3, the upper limit of linearity is 4μA in ion current for nitrogen. Limit of measurement caused by soft X-ray effect was estimated to be 7×10-11 Torr of nitrogen equivalent pressure. The ultimate pressure of zeolite trap and diffusion pump system used in this study was 2× 10-10 Torr. Some behaviours of the system near the ultimate vacuum are also described.