Determination of traces of carbon, nitrogen and oxygen in molybdenum and tungsten

The determination of carbon and nitrogen in molybdenum and of carbon, nitrogen and oxygen in tungsten, is described. The analytical techniques applied were charged-particle activation (carbon, nitrogen and oxygen), photon activation (carbon and oxygen), combustion (carbon) and vacuum-fusion extraction (nitrogen and oxygen). Chemical methods yielded upper limits in the 2-5 mug/g range. Activation analysis yielded 100 and 8 ng/g for carbon in molybdenum and tungsten respectively, 500 and 74 ng/g for nitrogen in molybdenum and tungsten respectively and 70 ng/g for oxygen in tungsten. The results obtained by charged-particle and photon activation agreed satisfactorily.     

Utilisation des accelerateurs en analyse par activation,notamment pour la caracterisation des materiaux purs

The principal means of activation, their potential performances and their special fields of application are reviewed briefly. The possibilities offered by charged particles and gammaphotons regarding the determination of light elements or other impurities in pure materials are surveyed. Examples relatives to the evaluation of boron, carbon, nitrogen, oxygen or fluorine contents in metals (Na, Al, Ti, Ni, Cu, Zr, Mo, Ta, W, Pb, etc.), alloys (PbCuTe, PbSnCd) and semiconductors (Si, AsGa, InP, etc.) are given. For some of these products, the results obtained by nuclear methods are compared with values supplied by other analytical techniques. Once the concentration levels of these impurities fall below 1 μg·g⁻¹, the superiority of the former methods appears clearly.      

Activation analysis with charged particles

Activation methods are important because of their sensitivity. The accuracy and precision obtainable with charged-particle activation analysis (CPAA) have been significantly improved; the accuracy has been demonstrated in inter-laboratory and inter-method comparisons. The inherent complexity of CPAA makes it unsuitable for routine work, but the method is valuable for special applications, e.g., certification of reference materials, and for the determination of certain elements. Most applications concern the determination of light elements in metals and semi-conductor materials. After removal of surface layers by chemical etching, the concentrations of carbon, nitrogen and oxygen found by CPAA in some industrial metals, (e.g., aluminium, molybdenum and tungsten) proved to be orders of magnitude lower than expected from the results of other procedures. Other applications are the determination of medium- and high-Z elements, (e.g., calcium, cadmium, thallium and lead) in metals; these elements are very difficult to determine with neutron activation. Environmental powdered materials can be analyzed accurately; because of their low thermal conductivity, they must be irradiated under helium instead of vacuum to avoid volatilization of matrix components.     

Principe,possibilites et applications de l'analyse par activation aux photons gamma

The various photonuclear reactions suitable for analytical purposes, their specificity and their performances are reviewed. The influence of the experimental irradiation conditions on the theoretical detection limits permitted and on the relative importance of competitive nuclear reactions liable to interfere is examined, with special reference to the determination of carbon, nitrogen and oxygen. It is shown that these parasitic effects of nuclear origin may be eliminated by the choice of the maximum irradiation energy. Examples are given of applications relative to trace determinations of lights elements, especially carbon, nitrogen, and oxygen, in metals or semi-conductors and to instrumental multi-element analyses of biological materials, atmospheric sampling filters and above all agricultural products.

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Conférence plénière prononcée dans le cadre du: 5th Symposium on the Recent Development in Activation Analysis, Oxford (GB), 17–21 Juillet 1978.     

Determination of light elements in metals and semiconductors by charged particle activation analysis

The determination of boron, carbon, nitrogen and oxygen in metals and semiconductors by charged particle activation analysis (CPAA) is reviewed. It is shown that CPAA is a sensitive and accurate method suitable for the analysis of reference materials.     

Depth distribution of light elements in heavy matrices with charged-particle-induced reactions

Two different methods are described for measuring the depth distribution of carbon, nitrogen and oxygen in metals: Proton activation makes use of resonances in the excitation function of the (p, γ) reactions for depth determination, and with the aid of the different half-lives for for β⁺-decay provides information on the different constituents present. The other method makes use of the shape of neutron groups in the time-of-flight spectra from deuteron-induced reactions. Depths of some tens of microns with a resolution of fractions of a micron are studied. The detection limit is of the order of 100 ppm.     

Utalisation des deutons et des tritons de faibles energies pour le dosage du carbone et de l’oxygene presents a la surface d’echantillons metalliques

The oxygen and carbon concentrations on metal surfaces were determined by two methods. The first method was based on the detection of the emitted particles in the¹²C(d,p)¹³C and¹⁶O(d, p)¹⁷O reactions, the second one on the measurement of the induced radioactivities in the¹²C(d,n)¹³N and¹⁶O(t,n)¹⁸F reactions, respectively. The results, obtained by the two different methods for high purity metals, were in agreement. A type of error which exists in the determination of trace amounts of carbon and oxygen in pure metals by combustion and reductive fusion was quantitatively demonstrated. This error exists also in the determination of oxygen by 14 MeV neutron bombardment.      

Systematic errors in vacuum and inert gas fusion analysis for oxygen in metals

Determinations of oxygen in metals by conventional vacuum or inert gas fusion are usually based on the assumption that oxygen is extracted from the melt wholly as carbon monoxyde. A qualitative thermodynamic approach is used to demonstrate that whilst this is true for most metals in the Periodic Table, a significant number of them can yield oxygen partially as gaseous species other than carbon monoxide, so that systematic errors are obtained. Practical suggestions are made to overcome this inconvenience. Vacuum fusion and neutron activation results on different metals are given.     

The determination of traces of O, N and C in the refractory metals Mo and W-an international effort

The influence of traces of O, N and C on the physical and especially the mechanical properties of the refractory metals Mo and W is discussed. The technological and economic importance of determination of O, N and C in Mo and W is elucidated. The Commission of the European Communities launched a relevant multidisciplinary Community Programme as early as 1969. The present state, within this programme, of the determination of O, N and C in Mo and W is outlined. Additional studies by the refractory metals group of the chemistry section of the Gesellschaft Deutscher Metallhütten and Bergleute (GDMB) are also reported on. Oxygen. Two round-robin tests were conducted by the "non-metals in refractory metals" group of the Community Bureau of Reference (BCR) for the determination of oxygen in molybdenum. Reducing fusion, 14-MeV neutron-, photon- and charged-particle activation analysis yielded comparable results of about 15 ppm O. Homogeneity studies were conclusive and the reference material was certified and is available from BCR. Oxygen concentrations in tungsten turned out to be even lower, certainly below 5 ppm. Only activation analytical methods will be adequate to determine the true oxygen content and work in this direction is being undertaken. Nitrogen. Relevant BCR round-robin tests for traces of N in Mo and W were not conclusive. Discrepancies were also found in a first round-robin test by the GDMB. It was possible, however, to reveal systematic errors frequently encountered in the classical Kjeldahl method, which turned out not to be applicable to the determination of nitrogen below 1O ppm. Only a newly devised micro-Kjeldahl method is capable of determining nitrogen down to 1 ppm and results for Mo are in good agreement with those of fusion methods. Nitrogen contents in W are presumably in the 100 ppM range and only determinable by ultrahigh-vacuum diffusion extraction and activation methods. Carbon. Carbon contents in Mo and W are also often presumably in the range of 1-10 ppm and thus not determinable by classical combustion methods. Additionally, discrepancies occur between results of combustion in resistance-heated furnaces with temperatures up to 1300 degrees and in high-frequency induction furnaces with temperatures up to 2000 degrees . The GDMB-group is investigating this phenomenon.     

Inter-laboratory comparison of the chemical analysis of silicon nitride

Summary The results of a round robin for the determination of nitrogen, oxygen and carbon and the common metallic impurities like Al, Ca, Fe, Mg and Na in silicon nitride are reported. The following analytical methods have been tested: nitrogen by acid decomposition under pressure followed by Kjeldahl distillation; oxygen by carrier-gas hot extraction; carbon by combustion in oxygen and infrared detection; metallic impurities after acid decomposition under pressure and evaporation of silicon fluoride by AAS or ICP-OES.     

Zur Bestimmung von Stickstoff,Sauerstoff und Kohlenstoff in Hafniumverbindungen

Methods are described for the determination of nitrogen and oxygen in hafnium compounds using a high-vacuum hot extraction equipment. HfN is analyzed in the presence of Pd as the bath metal at a temperature of about 2000° C and HfC with Ni and NiCe as the bath metal after enveloping the sample weight in a platinum foil using a temperature of about 2100° C. Hf-carbonitrides were analyzed dependent on the nitrogen content similar to the HfN or HfC. The values determined in this way are compared with results obtained using other methods. The total carbon content is determined coulometrically using WC as standard. In determining the free carbon care has to be taken of preventing a falsification by polymerisation products formed during sample dissolving.     

Isothermalisobaric molecular dynamics simulation of diatomic liquids and their mixtures

Isothermalisobaric ensemble molecular dynamics simulations have been performed for systems of two-center Lennard-Jones molecules for pure fluids as well as binary mixtures. The results obtained from various ensemble averages have been compared for pure fluid simulations of Lennard-Jones model diatomic fluids. The excess enthalpy and excess volume of three equimolar mixtures (argonnitrogen, argonoxygen, and nitrogenoxygen) have been calculated and compared with values obtained from previous NVT molecular dynamics and perturbation theory. Pair distribution functions obtained from various methods are compared for the equimolar mixture of nitrogen and oxygen and used to study the effect of attractive forces on the local structure. For four other systems (argonethane, methaneethane, carbon disulfidecarbon tetrachloride, and carbon disulfidetetrachloroethylene), excess enthalpies and excess volumes from NPT simulations are used to test the ability of perturbation theory to predict these properties and are also compared with experimental data. The comparison of simulation and experiment clearly shows the need to improve the available parameters for cross interactions in binary mixtures.     

Determination of nitrogen and carbon in refractory nitrides and carbonitrides by means of Dumas gas chromatography

The applicability of an automated Dumas-GC method for the determination of nitrogen and carbon in refractory materials was investigated. Analyses were carried out to determine nitrogen and carbon in TiN, ZrN and Ti(C,N) using CuO, V₂O₅ and Pb₃O₄ as oxidizing additives. The reproducibility of the analyses obtained with V₂O₅ was better than ± 1 rel% for major constituents. An estimation of the accuracy of the Dumas-GC method shows that this rapid and low-cost method can compete with other methods, at least for the refractory nitrides and carbonitrides of the transition metals.     

The determination of organochlorine pesticides and polychlorinated biphenyls by combustion tube decomposition and molecular emission cavity analysis

The determination of microgram quantities of chlorine in polychlorinated biphenyls and organochlorine insecticides by molecular emission cavity analysis is described. Samples either pure, in admixture or mixed with sand were decomposed at 900 ± 50°C in a quartz combustion tube in a humidified oxygen atmosphere. The products of decomposition were bubbled through water or 1% ammonia and 4-μl aliquots of the solution obtained were injected into a stainless steel indium-lined cavity and heated in a nitrogen/hydrogen flame. The chlorine was quantified by comparing the intensity of the InCl emission at 360 nm with that obtained from hydrochloric acid standards. The effect of potential interferences such as alkali and alkaline earth metals, nitrogen, phosphorus, sulphur, carbon aluminium and iron were studied. Except for the alkali and alkaline earth elements, the recoveries of the compounds burned were not affected. Where the elements interfered, methods for eliminating the interferences are described. The chlorine recovery was usually >90%.     

In Process Citation

A rapid simple method is described for the determination of carbon in organic compounds. The technique is based on a flash-combustion of the weighed sample (1-3 mg) in a hot empty combustion chamber at 950-1050 degrees and swept by a stream of oxygen at a rate of 80-100 ml min . Together with this flash and dynamic combustion in oxygen, a cupric oxide filling at 850 degrees is necessary. Halogens and sulphur oxidation products are retained by means of a silvered alumina filling at 750-800 degrees . Water and acidic oxides of nitrogen are absorbed at room temperature by means of magnesium perchlorate and manganese dioxide respectively. Carbon dioxide is absorbed in the cathodic compartment of an automatic coulometer and generates H(+) ions which are neutralized by OH(-) obtained by electrolysis. This method makes possible the determination of carbon in compounds containing halogens (including fluorine), phosphorus and metals. However, some metal compounds with polynuclear rings in their molecules give low results and require the addition of an oxidant to the sample in the boat for complete combustion. Vanadium pentoxide seems to be the best oxidant in the present working conditions. Solid samples are weighed and analysed in platinum or porcelain boats; liquid samples are weighed in Pyrex capillaries which are laid in platinum boats and covered with a small piece of platinum gauze. When normal liquid samples are analysed, one tip of the capillary is broken before its introduction into the combustion tube but in the case of volatile liquid samples the sealed capillary is introduced into the combustion chamber, where it explodes. The precision obtained is better than that of the classical methods.     

Bestimmung von stickstoff in refraktärmetallen—I molybdän und wolfram

This is a report on round-robin tests concerning the determination of nitrogen traces in molybdenum and tungsten, which were carried out by the refractory metals group of the chemistry section of the Gesellschaft Deutscher Metallhütten- und Bergleute. The following methods were used: classical and modified Kieldahl methods (in particular, a newly developed micro-Kjeldahl method), inert-gas fusion, vacuum fusion and ultrahigh-vacuum diffusion extraction. As the nitrogen values obtained by the first round-robin test exhibited considerable scatter, possible shortcomings of the various Kjeldahl methods, as well as the quantitative nitrogen recovery by the extraction methods, were carefully examined. The second round-robin test then gave the following results: the nitrogen content of the investigated molybdenum sheet was 2 ppm, the content of the tungsten sheet 0.5 ppm. Classical Kjeldahl methods are not applicable to the determination of nitrogen contents below 10 ppm. Frequently, detection limits of Kjeldahl methods range considerably above 10 ppm, mainly because of contamination by reagents and/or the laboratory atmosphere. The micro-Kjeldahl method and the hot-extraction and fusion-extraction methods are capable of determining nitrogen contents down to 1 ppm at best. The only method available for nitrogen determinations in metals at sub-ppm levels is by ultrahigh-vacuum diffusion extraction. The good agreement between the nitrogen values obtained for molybdenum by the micro-Kjeldahl method and by the various extraction methods is the most reliable proof of the quantitative nitrogen recovery by the extraction methods.     

混合稀土储氢合金中氧和氮的测定

研究了混合稀土储氢合金中氧和氮的测定方法。针对稀土金属高温易挥发、分解的特点,选择适宜的加热温度,使用镍浴,选择高温座坩埚进行试验：选择出了合适的助熔剂的预处理方法。方法已用于实际样品。对含氧0．43％、含氮0.018％的试样,分析精密度为氧4．3％,氮5.9％,加标回收率氧为93％～104％,氮为92％～110％。     

Contribution of nuclear analysis methods to the certification of BCR reference materials for non-metals in non-ferrous metals

A number of reference materials for oxygen in different non-ferrous metals have been certified by BCR in the frame of a multidisciplinary Community project. The contribution of nuclear analysis methods is illustrated by several examples concerning the optimization of sample preparation techniques, the analysis of low and high oxygen non-ferrous metals and the extension of the program to other non-metals, especially nitrogen and carbon. Communication presented at the 5th Symposium on the Recent Development in Activation Analysis, Oxford, 17–21, July 1978. Scientific Secretary of BCR-Sub Working Group “Non-metals in non-ferrous metals”.     

Contribution to the study of carbon and nitrogen determination by activation,using the nuclear reactions12C(α, n)15O and14N(d,n)15O

The carbon and nitrogen activation curves were determined for the nuclear reactions¹²C(α, n)¹⁵O and¹⁴N(d, n)¹⁵O, within the limits of the following maximum energies: 40 MeV for α-particles, and 21 MeV for deuterons. Inferences are made concerning the potential possibilities of these activation methods, from the sensitivity aspects, for the determination of carbon and nitrogen, with reference to the problem of the main interferences which have also been studied experimentally. The chemical separation process used to isolate¹⁵O after irradiation is described. Concrete examples of carbon and nitrogen determinations by these methods are given.     

Simultaneous determination of oxygen, nitrogen and hydrogen in metals by pulse heating and time of flight mass spectrometric method

The inert gas fusion and infrared absorption and thermal conductivity methods are widely used for quantitative determination of oxygen(O), nitrogen(N) and hydrogen(H) in metals. However, O, N and H cannot be determined simultaneously with this method in most cases and the sensitivity cannot meet the requirement of some new metal materials. Furthermore, there is no equipment or method reported for determination of Argon(Ar) or Helium(He) in metals till now. In this paper, a new method for simultaneous quantitative determination of O, N, H and Ar(or He) in metals has been described in detail, which combined the pulse heating inert gas fusion with time of flight mass spectrometric detection. The whole analyzing process was introduced, including sample retreatment, inert gas fusion, mass spectral line selection, signal acquisition, data processing and calibration. The detection limit, lower quantitative limit and linear range of each element were determined. The accuracy and precision of the new method have also been verified by measurements of several kinds of samples. The results were consistent with that obtained by the traditional method. It has shown that the new method is more sensitive and efficient than the existing method.