Amounts Of Gaseous Impurities Research Articles

The Influence of High-Temperature Helium and the Amount of Revert Material on the Material Properties of Inconel 738

Nickel-based alloys are considered promising materials for primary circuits of high-temperature gas reactors (HTGRs), specifically for gas turbines. The primary helium (He) coolant in the gas-turbine-based HTGRs is expected to reach temperatures of up to 900 °C; therefore, the selected materials should adequately perform over a long service life at such an environment. A promising manufacturing method in the production of reactor components is precision casting, where the content of revert (recyclate) material in the alloy differs and can influence the material behavior. In our study, Inconel alloy 738 was manufactured by casting 50% and 100% of revert material and tested in HTGR conditions to examine the influence of helium coolant on the material’s properties. Tensile specimens were exposed at 900 °C for 1000 h in helium containing a specified amount of gaseous impurities. Scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS), in combination with X-ray diffraction (XRD) and nano-, microhardness methods, were used for material characterization after performing the tensile tests at room temperature. The presence of three types of layers was observed: a thin layer formed by aluminum and chromium oxides on the surface; non-uniform surface oxides Ti3O5 with inner (Al,Cr)2O3; and the inner fine-grained Inconel Cr-enriched phase (approx. 10–20 µm below the surface), which can act as a protective surface layer. Mechanical properties of both revert materials decreased after exposure to HTGR conditions but did not show a significant difference as a result of the content of the revert material. The increase of nano-hardness in line profiles throughout the specimen’s cross-section was observed locally at the surface oxides and in the precipitates and grain boundaries. After exposure, Rp0.2 values decreased by 20% and 17.7%, and Rm values by 12.3% and 20.8% in samples with 50 and 100% revert content, respectively. Furthermore, a decrease in microhardness values (HV0.1) was detected by 4.98% in longitude and 5.80% in cross-section for samples with 50% revert material and by 3.85% in longitude and 7.86% in cross-section for samples with 100% revert material. It can be concluded that both revert materials have similar corrosion resistance in HTGR conditions. The presented results complement the knowledge about the degradation of alloys in the coolant environment of advanced gas-cooled reactors.

Trace analysis of small gas samples in sealed containers with mass spectrometry using static dilution

A sampling method for the analysis of small amounts of gases from sealed containers is described. Liquefied pressurised gas samples were expanded into a vacuum box and statically diluted with ultrapure nitrogen. The equations for the sample dilution were established, relating the measured impurity amount fractions in the sample mixture to their partial pressures in the sealed container and, in the case of oxygen, to the air pressure. Ion–molecule reaction mass spectrometry allowed identification and measurement of trace impurities corresponding to partial pressures in the range of 1 hPa in the container. The method was applied for determining the identity and amount of gaseous impurities in n-butane used in implantable gas pressure–operated drug infusion pumps. Impurities from the n-butane supply cylinder or from decomposition products, for example due to the laser welding of the Ti plugs of the containers, could be excluded by the results of saturation vapour pressure measurements, FID gas chromatograms and IMR mass spectra. The variability in pressure versus volume among tested infusion pump samples was associated with excess oxygen, attributable to an excessive residual air pressure in the gas containers before they were filled with n-butane. The sample preparation method is principally applicable to measure the composition of small amounts of gas mixtures and gaseous impurities with identified IMR mass spectra down to trace levels—even for ubiquitous substances like oxygen. The volume of the produced gas mixtures allows characterisation of the gas by standard gas analytical methods and for impurities by trace gas analytical methods.

High-Temperature Mechanical Properties of High-Purity 70 mass% Cr-Fe Alloy

An ingot of high-purity 70 mass% Cr-Fe alloy was prepared by high-frequency induction melting in a high-purity argon atmosphere using a cold copper crucible. Its tensile properties such as hot-ductility and tensile strength were measured, and compared with the results for a high-purity 50 mass% Cr-Fe alloy, a high-purity 60 mass% Cr-Fe alloy and a Ni-based super-alloy. The formation of σ-phase was also examined. The purity of a 70Cr-Fe alloy (70 mass% Cr-Fe alloy) ingot is more than 99.98 mass% and the total amount of gaseous impurities (C, N, O, S, H) in the 70Cr-Fe alloy is 69.9 mass ppm. The strength of the 70Cr-Fe alloy is higher than those of the 60Cr-Fe alloy and the 50Cr-Fe alloy at the temperatures between 293 and 1573 K, without decrease in ductility with increasing Cr content. The 70Cr-Fe alloy also possesses excellent high-temperature ductility. The σ-phase was not observed after aging of 3.6 Ms at 873 K. Consequently, the 70Cr-Fe alloy is an excellent alloy as the base of super heat-resistant alloys.

Operational experience with the JET Impurity Processing system during and after DTE1

The hydrogen-containing gases generated during operation and maintenance of a fusion machine need to be detritiated prior their discharge to the environment. The amounts of gaseous impurities with their chemical and isotopic compositions which were decontaminated in the JET impurity processing system during and after Deuterium–Tritium Experiment, DTE1, are presented. Two different techniques for impurities detritiation were tested. The first technique is based on catalytic oxidation of hydrogen-containing species followed by water decomposition in reaction with uranium at elevated temperature. The second technique is based on direct decomposition of impurities with molecular hydrogen liberation in reactions with uranium at elevated temperatures. The results of the impurity detritiation using both techniques are given.

Preparation of 10 kg Ingot of Ultra-Pure Iron

A new induction melting furnace with a cold-copper crucible has been designed and constructed using ultra-high vacuum technology. The main chamber can be evacuated to 6.7 × 10—8 Pa as the base pressure. The furnace can melt high-purity iron of 10 kg, at most, within 300 s. The total pressure becomes less than 4 × 10—6 Pa during melting of iron under the best condition. As starting materials for melting, high-purity electrolytic iron containing impurities of 25.2 massppm which is determined after the analysis of 18 elements was prepared. The content of gaseous impurities such as carbon, nitrogen, oxygen, sulfur and hydrogen is 19.6 massppm in total. It is concluded that ultra-high vacuum melting of iron is quite useful to increase the purity of iron. The total content of impurities in iron is reduced from 25.2 to 12.6 massppm by melting under the atmosphere of 7.5 × 10—6 Pa. The amount of gaseous impurities can be reduced from 19.6 to 10.1 massppm in total. Especially, the amount of oxygen is reduced from 14.1 to 7.5 massppm. These amounts of gaseous impurities are almost the limit of detection by conventional methods of analysis.

Damping effects due to small amounts of gaseous impurities in copper

Damping effects in the temperature range (80÷300) K, which are caused by gaseous contamination (O2, H2), are investigated. Especially the effects due to oxygen annealing cannot be attributed to surface oxidation. Dislocation interaction processes with dissolved oxygen must account for it. This assumption was confirmed by additional damping results, obtained on hydrogenated samples.

Effects of the nature of the atmosphere upon the amounts of gaseous impurities in powder

Effects of the nature of the atmosphere upon the amounts of gaseous impurities in powder