Tantalum Ribbon Research Articles

Investigation of interaction between lithium and tantalum under a silicon film coating by electron-stimulated desorption technique

The electron-stimulated desorption of Li+ ions from lithium layers adsorbed on the tantalum surface coated with a silicon film has been investigated. The measurements are performed using a static magnetic mass spectrometer equipped with an electric field-retarding energy analyzer. The threshold of the electron-stimulated desorption of lithium ions is close to the ionization energy of the Li 1s level. The secondary thresholds are observed at energies of about 130 and 150 eV. The threshold at an energy of 130 eV is approximately 30 eV higher than the ionization energy of the Si 2p level and can be associated with the double ionization. The threshold at 150 eV can be caused by the ionization of the Si 2s level. It is demonstrated that the yield of Li+ ions does not correlate with the silicon amount in near-the-surface region of the tantalum ribbon and drastically increases at high annealing temperatures. The dependence of the current of Li+ desorption on the lithium concentration upon annealing of the tantalum ribbon at T>1800 K exhibits two maxima. The ions desorbed by electrons with energies higher than 130 and 150 eV make the largest contribution to the current of lithium ions after the annealing. The yield of lithium ions upon ionization of the Li 1s level at an energy of 55 eV is considerably lesser, but it is observed at higher concentrations of deposited lithium. The results obtained can be interpreted in the framework of the Auger-stimulated desorption model with allowance made for relaxation of the local surface field.

Thermodesorption of silicon from textured tantalum ribbons

The interaction of silicon with tantalum is studied by the Auger spectroscopy and temperature-controlled desorption technique. It is shown that, at a monolayer coating, the adsorbed silicon atoms penetrate into the bulk of a substrate at temperature T≥1400 K. The spectral shape and the annealing curves are explained by the influence of the Si-Si lateral repulsion in an adsorbed layer on the desorption and diffusion of the Si atoms into the bulk. Some ratios between the kinetic parameters are determined from analysis of the experimental data. Their application in numerical calculations based on the model proposed earlier makes it possible to determine (from comparison of the calculated and experimental data) the kinetic parameters for all the processes of the interaction between silicon and the tantalum substrate during the temperature-controlled desorption (desorption, transfer into the bulk, diffusion, and migration of silicon onto the surface). An adequate description of the experiment is obtained only under the assumption that the diffusion at the final stages of temperature-controlled desorption after reaching a maximum occurs within a thin layer near the surface, so that the migration of the Si atoms to the surface and desorption proceed more rapidly than their diffusion into the bulk.

Kinetics of silicon interaction with textured tantalum ribbons

The kinetics of silicon interaction with textured tantalum ribbons having a predominantly (100)-oriented surface has been studied by Auger electron spectroscopy. For T 1320 K to form Ta 4Si, with only one third of the original silicon monolayer being left on the surface. The activation energy of Ta5Si3 decomposition is 4.3±0.2 eV. The activation energy of Si thermal desorption at low coverages is 5.4±0.2 eV.

Réactions solide-gaz suivies par microscopie électronique en atmosphère controlée (M.E.A.C.). - I. Réalisation d'un microréacteur fonctionnant à haute température et en M.E.A.C.

A high temperature reaction specimen chamber for an electron microscope has been realized. The specimen under electron microscope observation can be heated at about 1300 K in a gas at a pressure of about 200 Torr. The specimen is placed on a film covering the minute hole (0.5 mm) in the tantalum ribbon and heated by an electric current sent through the ribbon. The minute hole in the ribbon and molybdenum apertures on either side of the ribbon are set to enable the passage of electron beam. The displacement of the heater is controlled by an accessory operating lever. The overflow gas from the specimen chamber is pumped out separately from the evacuation system of main column. The working parameters: temperature, gas pressure and cross-sections of scattered electrons through gas layers, have been determined for the best use of the microreactor.

Beam Optics in the FXR 1.5 MeV, 4 kA Injector

The 20 MeV, 4 kA linear induction accelerator (FXR), currently under construction at LLNL, will use a cold cathode injector. The foil cathode consists of a 0.03 mm tantalum ribbon wound in a spiral with successive turns spaced 0.8 mm apart. The emitted current will be 15-20 kA but will be reduced to 4 kA by collimating immediately beyond the anode. This will minimize the beam emittance and maintain a good impedance match with the low impedance driving source. Computer simulation was used extensively to optimize the configuration of the beam forming electrodes, the emitter geometry, and the overall focusing and beam transport system in the injector region. This paper will discuss the approach used and the problems encountered in the design of the diode geometry and of the overall beam optics. Preliminary experimental results will be presented and will be compared with the computer model predictions.

The adsorption of lanthanum hexaboride on tantalum

The work function of the lanthanum hexaboride (LaB6) layer evaporated on a tantalum ribbon surface was measured as a function of the evaporation time, using thermionic diode and electron beam methods. The work function decreases rapidly, passes through a minimum and saturates. The value of φmin depends strongly on the temperature of the tantalum ribbon (2.8, 2.5 and 1.7 eV for 868, 715 and 20°C, respectively). Diffusion of some species (maybe lanthanum) from the evaporated layer to the clean part of the tantalum ribbon was observed and the activation energy for diffusion (1.7 eV/atom) was measured.

Analysis for lead in undiluted whole blood by tantalum ribbon atomic absorption spectrophotometry.

We describe a modified tantalum ribbon atomic absorption procedure for determining lead in undiluted whole blood. An instrumentation Laboratory (I.L.) Model 151 atomic absorption spectrophotometer equipped with an I.L. Model 355 Flameless Sampler was used. The Flameless Sampler was slightly modified to include three-cycle operation instead of the normal two cycles. This modified single-beam system, equipped with background correction, allows 5-microliter specimens of whole blood to be quickly and accurately analyzed. No sample preparation other than vortex mixing is involved and method reliability has been demonstrated during an extended period of successful participation in proficiency testing studies conducted by the Center for Disease Control. This tantalum ribbon methodology has further been demonstrated to be effective both as a primary screening procedure and as a confirmatory procedure, when coupled with erythrocyte protoporphyrin determinations, in screening over 300 000 clients during a three-year period of use in the Early and Periodic Screening, Diagnosis and Treatment (EPSDT) Program in Texas.

Bestimmung von spuren seltener erden in anderen seltenen erden durch atomabsorption mit elektro-thermischer atomisierung und durch emissions-spektrographie mit dem gleichstromdauerbogen

The determination of traces of rare earths in other rare earths by atomic absorption with electrothermal atomization and by d.c. arc emission spectrography The determination of traces of some rare earth elements (Yb, Eu, Tm, Sm, Dy, Ho, Er) in matrices of other rare earths by a.a.s. with electrothermal atomization (tantalum ribbon), and of traces of Tm and Dy by a.e.s. with d.c. arc excitation is described. The influence of the boiling points of the traces and matrices on the possibility and the sensitivity of the a.a.s. determinations is discussed. The results of the methods are compared. Better absolute, and in most cases also relative, detection limits can be achieved by a.a.s.

Untersuchungen zur bestimmung seltener erden durch atomabsorption mit elektrothermischer atomisierung

The determination of rare earths by atomic absorption spectrometry with electrothermal atomization The electrothermal atomization of traces of rare earths has been investigated with different atomizers (carbon rod, graphite furnace, tantalum ribbon). The best analytical results are obtained with a modified tantalum thermal atomizer, because the formation of rare earth carbides is then impossible. Mixed argon—hydrogen atmospheres improve the concentration of atoms in the plasma, because hydrogen reduces the rare earth oxide radicals. The optimal analytical conditions are described. The detection limits are: 25 pg Yb, 22 pg Eu, 62 pg Tm, 2000 pg Sm, 300 pg Ho, 300 pg Dy, 1300 pg Er.

Mass Spectrometric Determination of Zirconium from a Resin Bead

Abstract A sensitive, isotope dilution technique has been developed for the analysis of sub-microgram amounts of zirconium. The analysis is based on the increased thermal ion emission for Zr adsorbed on a single anion resin bead. Zr is isolated from a solution containing the sample and a highly enriched 94Zr (96%) spike. The determination is made possible by using a high-sensitivity pulse-counting 2-stage 30-cm radius mass spectrometer. The detection limit depends upon the amount of the isotope spike added and the desired precision. Fifty nanograms of zirconium (sample plus spike) produce sufficient ion signals for reliable isotopic analysis so that fission Zr can be measured with blank correction to a precision of 3%. By this method for fission Zr in spent reactor fuel particles, contamination from normal Zr and Mo can be corrected out by making isotopic measurements before and after spiking and scanning masses 90 and 95 during analysis. Since neither masses 90 nor 95 are stable fission products, their presence is due to sample contamination and can be used for correction based on their normal isotopic distributions. Zone-refined tantalum ribbon, essentially free of normal Zr and Mo was selected as the ionizing filament. This method can be adapted to a wide variety of samples.

Contamination of tap water by lead pipe and solder.

We report here potential sources of lead contamination from a tap water distributing system using lead service pipes and soldering alloy to join copper pil~s. In this note, we present data of lead levels in tap water of the City of Victoria, B.C., Canada and our findings on the dissolution of lead from the distributing syste[n. Lead service pipes were used in the city of Victoria about 40 years ago to convey water from the city main to about 8,000 to i0,000 older bouses. MATERIALS AND METHODS Water sanples were collected from the city reservoir and from the taps of households in areas with and without lead pipe delivery system. The lead concentrations in water were analyzed by a flameless atomic absorption technique in a lead-free clean room. AIl water samples were collected and stored in acid cleaned polyethylene bottles, acidified inm~diately to a pli of about one with quartz-distilled nitric acid and analyzed within eight hours of collection. The lead concentrations were determined by pipetting 50~i aliquots of sample onto the tantalum ribbon atomizer MTA-2 of a double-beam Jarrell-Ash 82-810 atomic absorption spectrophotc~eter and measuring the absorption at 2833 ~ using a specially-built fast response peak reader. A nonabsorbing lead-line at 2820 ~ was used for background correction.

Étude par spectrométrie de masse en vision directe des interactions sous basse pression du pentachlorure de tantale avec le tantale à haute température

We have studied the kinetics of the pyrolysis of tantalum pentachloride at low pressure and high temperature using a tantalum ribbon placed in an ultra high vacuum apparatus; all of the reaction products were detected by means of line-of-sight mass spectrometry. For low chlorine surface coverages the reaction product is atomic chlorine, along with the formation of a tantalum deposit on the surface. At higher surface coverages tantalum tetrachloride is observed corresponding to an attack of the substrate. Together, these results were interpreted in terms of a theoretical model developed previously for the interactions between transition metals and oxygen containing molecules, then chlorine, and experimentally verified in all these cases. This model can be summarized by the existence of three steps: (i) the dissociative adsorption of the incident molecule, (ii) the desorption of atomic chlorine, and (iii) the desorption of the tetrachloride formed by surface reaction favored at high surface coverages.

Adsorption of Oxygen and Nitrogen on a Gas-Free Tantalum Ribbon

Adsorption of Oxygen and Nitrogen on a Gas-Free Tantalum Ribbon

High temperature low pressure reactions of oxygen with tantalum as studied by Auger electron spectroscopy and line-of-sight mass spectrometry

The oxidation of a polycrystalline tantalum ribbon has been studied at low oxygen pressures (⩽ 10–4 Pa) from 1300 to 2300 K using Auger electron spectroscopy A.E.S. to determine the surface oxygen coverage θ, line-of-sight mass spectrometry to measure the oxide evaporation fluxes of TaO and TaO2, and electrical resistivity to measure the dissolved oxygen concentration. For a 10–4 Pa oxygen pressure, three temperature regions are observed by A.E.S.: (i) < 1500 K the precipitation of Ta2O5, (ii) from 1500 to 1750 K the formation of TaO on the surface, and (iii) > 1800 K the adsorption of oxygen on the tantalum surface above the dissolved layer. In this latter temperature region, A.E.S. provides a direct measure of the oxygen surface coverage. In this high temperature region the activation energy for TaO evaporation was found to be 710–105 θ kJ mol–1, that for TaO2 evaporation 822–209 θ kJ mol–1, and the endothermic heat of reaction passing from an adsorbed to a dissolved oxygen atom was determined to be 121–59 θ kJ mol–1.

Determination of cadmium in fish tissue by flameless atomic absorption with a tantalum ribbon.

Determination of cadmium in fish tissue by flameless atomic absorption with a tantalum ribbon.

Isotopic Analysis of Molybdenum by Surface Ionization Mass Spectrometry and a Carbonization Technique

A technique to increase and stabilize the ion production of molybdenum and some other elements has been developed in their isotopic analysis by single-filament surface ionization mass spectrometry. A mixture of the element (5-100μg, dilute sulfuric acid solution)and five to ten as much glycerol(5v/v% aqueous solution purified by ion exchange)was mounted on a ribbon filament and was charred in air to slightly wet tar, and then heated in the mass spectrometer ion source under a vacuum of-5×10-7 Torr to appropriate temperatures by slowly increasing the filament current. As the filament material, rhenium ribbon was suitable for Mo and Hf, and tantalum ribbon for Cr samples. The sample coated in the form of oxo-compounds was reduced possibly through intermediate or direct carbonization during mass spectrometry and the sample pretreatment outside or inside the instrument was shortened. Stable ion currents of 10-13; to 10-11 A for Mo+, Hf+, and Cr+ ions were obtained and found to be usable in routine isotopic analysis.

Determination of cadmium in biological materials by atomic absorption

A variety of biological samples such as blood, urine, hair, nail and kidneys has been analysed cadmium. Tantalum ribbon flameless and conventional flame-aspiration atomic-absorption techniques were employed for the analysis.

An evaluation of some atomic absorption systems for the determination of lead in blood

An evaluation was made of 8 atomic absorption systems for the determination of lead in capillary blood in order to determine their suitability for the routine analysis of 100 specimens per day. The precision of results obtained with the Delves cup or tantalum ribbon was better than that with the graphite crucible. Using the Delves cup, results with the filter paper disc technique were higher and less precise than those with liquid blood samples. Other systematic differences in accuracy between methods were found which could not be related to either instrumental configuration or sample form.

Determination of Traces of Boron in Heat-Resisting Alloy Standards by Isotope Dilution Mass Spectrometry

Traces (0.6∼130ppm) of boron in heat-resisting alloy standards of J AERI(Japan Atomic Energy Research Institute)and of NBS(National Bureau of Standards, U. S.)were determined by isotope dilution mass spectrometry which involved addition of 95% enriched boron-10 as the spike and isolation of boron from acid solution of samples by methyl borate distillation. The tantalum ribbon single filament technique was used for isotopic analysis of boron. Except for one JAERI standard, the results obtained by isotope dilution gave a relative standard deviation of less than 3%. Determination of boron in boron-added water samples, fly ash standard NBS 1633 and geochemical rock standards JG-1 and JB-1 was also carried out for comparison.

Maximization of sensitivities in tantalum ribbon flameless atomic absorption spectrometry

Maximization of sensitivities in tantalum ribbon flameless atomic absorption spectrometry