Vacuum Fusion Analysis Research Articles

TiAl–Nb melt interaction with AlN refractory crucibles

The paper considers contamination of cast TiAl-based alloy, related microstructure evolution and chemical contact interaction when using refractory aluminium nitride crucibles/moulds as an alternative to the traditional Al 2O 3-, ZrO 2- and Y 2O 3-based oxide ceramics. A series of melting tests has been performed in resistive SiC electro-furnace with Ti–46Al–8Nb (at%) alloy in 99.99% purity AlN boat crucibles with fixed melt superheating times 5, 12 and 25 min at 1670 °C and consequent quenching with high-purity Ar gas flow. As-cast samples were examined by X-ray diffractometry, SEM, SIMS, EDX, EBSD and vacuum fusion analysis of O, N, C and S interstitials content with respect to the initial material. The key features of TiAl–Nb melt interaction with AlN ceramics are revealed. As a result of slow thermal dissociation AlN → Al + N, and the reaction of nascent nitrogen with the melt, a solid continuous TiN-based reaction layer is formed up to 6.4 μm in thickness, together with an enriched Al liquid film between it and the crucible wall. It causes perfect wetting of crucible with the melt and easy removal of the solidified sample. The partial suitability of AlN crucible is restricted by 12 min of the melt superheating from the point of view of invariable (α 2 + γ)-microstructure and reasonable contamination of the as-cast samples.

05/02854 The law of stable equilibrium and the entropybased boiling curve for flow boiling

The Faraday technique was employed to determine the principal magnetic susceptibilities of a scandium single crystal at room temperature, with several field strengths in the range 6–11 kOe. The field-dependence of the experimental data was quite weak, and it was deduced that only about 15% of the 60 ppm of iron, indicated by chemical analysis to be present in the starting material, was clustered to a sufficient extent to couple ferromagnetically. Bulk paramagnetic susceptibilities were obtained in the standard manner from reciprocal-field plots up to infinite-field values. The bulk susceptibilities were interpreted as indicating an oxygen content of 1.8 ± 0.3 at.% in the crystal. This interpretation used the extensive data of Spedding and Croat as a standard for the magnetic susceptibilities of pure scandium, and used their results for the effects, on the susceptibility, of various impurities. The validity of the oxygen analysis was substantiated by vacuum-fusion analysis on an equivalent piece of scandium metal.

Diffusion of oxygen in liquid copper and nickel

The diffusivities of oxygen in liquid copper and nickel were determined from 1300°C to 1560°C by a capillary gas-reservoir method. A diffusion cell designed to behave as if of semi-infinite length and consisting of liquid copper or nickel held in an alumina capillary was used. A H2O-H2 gas mixture maintained a constant oxygen potential at the metal-gas interface. A controlled furnace hot zone of 15 cm was obtained with six separate windings of Pt-10%Rh wire. To prevent convection the top of the diffusion cell was adjusted to be hotter than the bottom. The solidified diffusion columns were sectioned and analysed for oxygen by vacuum fusion analysis. Oxygen diffusivities, D, were calculated through use of a solution of Fick's second law. For copper D is 1.52 × 10-8 m2/s at 1295°C and 3.78 × 10-8 m2/s at 1560°C; for nickel D is 3.12 × 10-8 m2/s at 1450°C and 3.39 × 10-8 m2/s at 1580°C. The results for copper can be represented by the Arrhenius relationship ln D equals -19570/RT + 3.21 where E and R are in calories or -81900/RT + 3.21 where E and R are in joules (1350-1560°C) and where the numerator, E, is oxygen diffusion activation energy/mol K and R is the gas constant.

The microstructural properties of highly nitrogenated iron and iron-aluminum powders

A study has been made of highly nitrogenated pure iron and iron-aluminum alloy powder containing 2 wt.% Al (Fe-2Al) using Mossbauer spectroscopy and X-ray diffraction. The samples were prepared by high-temperature, high-pressure diffusion of nitrogen. They were prepared in a hot-isostatic-pressure (HIP) furnace at 1000 °C at nitrogen pressures up to 200 MPa. The alloy powders contained up to 8 at.% nitrogen as determined by vacuum fusion analysis. XRD analysis indicates that for the pure iron powders, the lattice spacing remained independent of nitrogen concentration, but that for the Fe-2Al powders, it decreased with increasing nitrogen concentration. Mossbauer analysis showed that for the pure iron powders, most of the nitrogen was associated with the formation of the iron nitride Fe4N. For the alloy powders containing less than 5 at.% nitrogen, all of the nitrogen was contained interstitially. The presence of nitrogen completely eliminated the conduction-electron spin-density oscillations observed in many ferromagnetic alloys.

Separate Determination of Microamounts of Bulk and Surface Oxygen in Ultra-Pure Iron by a Surface-Area-Variation Method

A microamount of bulk oxygen in ultra-pure iron was determined separately from surface-contaminated oxygen by a surface-area-variation method. In this method, the total oxygen values (μg/g) for specimens with different specific surface areas were determined by means of a vacuum fusion analysis, and were plotted against the specific surface areas (cm2/g); the quantity of oxygen in the bulk (μg/g) was determined from the intercept of the regression line and the oxygen quantity per unit area of surface (μg/cm2) from the slope. A surface treatment method capable of controlling the depth of the surface oxygen layer at an atomic level was developed in order to prevent scattered bulk oxygen values caused by an irregular surface oxygen layer. Specimens were etched in a mixed solution of hydrogen peroxide, hydrofluoric acid and de-ionized water (volume ratio 17:1:2) under an argon atmosphere. A high sensitivity vacuum fusion gas analyzer with a Pirani gauge was used in this experiment. Bulk oxygen over 0.03μg/g in ultra-pure iron could be analyzed independently from the influence of surface oxygen. Bulk oxygen in an electrolytic pure iron sample was determined as 0.08±0.004μg/g with surface oxygen of 0.31±0.001μg/cm2.

Vacuum fusion determination of oxygen in gadolinium, terbium metal and iron-terbium alloy

The extraction conditions for the accurate determination of oxygen in gadolinium, terbium and iron-terbium alloy using vacuum fusion analysis were studied. The influence of the gettering effect, the analyzing temperature and the weight ratio of the bath metal to the sample were investigated. Oxygen values of gadolinium and terbium were measured by the graphite crucible, the graphite capsule, the tin bath, the iron-tin bath and the platinum-tin bath techniques in the temperature range of 1500–2100 °C using vacuum fusion analysis. These oxygen values were compared with those obtained by inert gas fusion analysis. In inert gas fusion analysis, the samples were analyzed with iron and tin in a tin capsule, and the samples with platinum in a tin capsule were analyzed in a graphite capsule enclosing with carbon powder. Oxygen values of both metal samples in the graphite capsule at 2000 °C, with an iron-tin bath at 1850 °C and a platinum-tin bath at 2000 °C in vacuum fusion analysis, were respectively in good agreement within their errors; the oxygen values of gadolinium were also in good agreement with that from inert gas fusion analysis in the iron-tin bath, but those of terbium were not in agreement. This agreement for gadolinium guarantees the reliability of the conditions for the accurate determination, and the difference of oxygen values for terbium suggests a need for further consideration on the conditions of the inert gas fusion analysis.

Reaction Of Nitrides And Oxide With Bath Metals In Gas Analysis In Metals

Abstract Abstract Reactions of two nitrides, an oxide (α-SiaNi, A1N and α-AI2O3) and bath metals (platinum, iron and tin) in graphite capsules were investigated in vacuum fusion analysis by measuring gas extraction curves with a quadrupole mass spectrometer which can simultaneously measure nitrogen and carbon monoxide from the furnace. From the characteristic gas extraction patterns of each bath metals, gas release reaction mechanisms and their temperatures were studied. Key Words: Quadrupole mass spectrometerVacuum fusionGas extraction curvesSilicon nitrideAluminum nitrideAluminum oxide

The decomposition mechanism of nitrides and oxides in vacuum fusion analysis

The decomposition mechanism of nitrides and oxides in vacuum fusion analysis

Separation of Surface and Bulk Gases in Contact Materials of Vacuum Switches-Determination of Gases and Effect on Vacuum Breakdown

Meaningful analysis for very small quantities of gases in contacts can be obtained only by the method which permits differentiating between surface and bulk gases. The graphite capsule method and copper bath method in vacuum fusion analysis were compared, and the surface area variation method and two-stage gas extraction method were investigated for the separation of surface and bulk gases. As a result of these investigations, the surface and bulk gas content of the copper-tellurium alloy can be determined by the surface area variation method. The bulk oxygen content of the ingot, forged- and vacuum-refined copper-tellurium alloy is 3.8 parts per million (ppm), 1.7 ppm, and 0.1 ppm, respectively. The surface oxygen content, however, is conversely 1.5 µg/cm2, 2.4µg/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and 3.7µg/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , respectively. In high vacuum, gases are released from the electrodes as the voltage is applied between the electrodes. The released gases increase exponentially whether the spark breakdowns occur or not. It is suggested that the released gas at the spark breakdown corresponds to surface gas, which is considered as water vapor mostly absorbed on the electrode. After the spark breakdowns occur repeatedly, water vapor from the surface layers is depleted, namely, the surface conditioning takes place. Therefore, the released gas without spark breakdown corresponds to the bulk gas, which is mostly hydrogen.

Quantitative non-destructive magnetic analysis of oxygen in a scandium single crystal

The Faraday technique was employed to determine the principal magnetic susceptibilities of a scandium single crystal at room temperature, with several field strengths in the range 6–11 kOe. The field-dependence of the experimental data was quite weak, and it was deduced that only about 15% of the 60 ppm of iron, indicated by chemical analysis to be present in the starting material, was clustered to a sufficient extent to couple ferromagnetically. Bulk paramagnetic susceptibilities were obtained in the standard manner from reciprocal-field plots up to infinite-field values. The bulk susceptibilities were interpreted as indicating an oxygen content of 1.8 ± 0.3 at.% in the crystal. This interpretation used the extensive data of Spedding and Croat as a standard for the magnetic susceptibilities of pure scandium, and used their results for the effects, on the susceptibility, of various impurities. The validity of the oxygen analysis was substantiated by vacuum-fusion analysis on an equivalent piece of scandium metal.

A dynamic mechanism of gas absorption in the furnace of the vacuum fusion analysis

A dynamic behavior of both extracted gas and metal vapor evolved from fused steel sample (NBS#1041) in the vacuum fusion analysis was studied. Metal vapor was trapped on a moving surface of an alkalineless glass tape which passes by a 10 mm wide window at a speed of 2 mm per sec. Iron and manganese deposited on the surface of the tape were extracted in an ethanolamine-NaOH solution and determined by a polarographic method.A variation in the pressure change of the extracted gas was recorded with a Pirani gauge at an outlet of the extraction pump. And these results were compared with the analytical values of oxygen obtained by an ordinary method [See Bunseki Kagaku, 14, 540 (1965) ].The difference in the extent of gas absorption in the successive analyses was closely related to the degree of the overlap with the metal vapor which at first evolved within 4 to 20 sec after the addition of a sample in a crucible.The gas absorption in a vacuum fusion analysis was proved to be reduced by such a method using a metal bath or graphite capsules, which prevent the overlap of the evolution of gas and metal vapor.

The reaction of a titanium alloy with hydrogen gas at low temperatures

An investigation of the effect of temperature on the surface hydriding reaction of Ti-5Al-2.5Sn alloy exposed to hydrogen at 250 psig was made. The temperature range studied extended from 160 °F to −160 °F. Reaction conditions were controlled so as to expose a vacuum-cleaned, oxide-free alloy surface to an ultra-pure hydrogen atmosphere. Reaction times up to 1458 h were studied. The hydriding reaction was extremely sensitive to experimental variables and the reproducibility of reaction behavior was poor. However, it was demonstrated that the reaction proceeded quite rapidly at 160 °F; as much as 1 mil surface hydriding was observed after exposure for 162 h. The amount of hydriding was observed to decrease with decreasing temperature at 75 °F, −36 °F, and −76 °F. No surface hydriding was detected either by vacuum fusion analysis or by metallographic examination after exposure for 1458 h at −110 °F or −160 °F. Tensile properties were unaffected by surface hydriding of the severity developed in this program (up to 1 mil thick) as determined by slow strain rate testing of hydrided sheet tensile samples.

Comparison of Metal Bath Techniques in Vacuum Fusion Analysis by an Isotope Dilution Method

Comparison of Metal Bath Techniques in Vacuum Fusion Analysis by an Isotope Dilution Method

真空溶融-質量分析法による鉄鋼中の極微量ガス分析装置の試作

A mass spectrometer was applied for vacuum fusion analysis of micro-amounts of gases in iron and steel produced by vacuum melting and vacuum casting. The gases extracted from the metal specimen in a vacuum fusion furnace were collected directly in the gas reservoir through a mercury diffusion pump, and the individual constituents were determined by the mass spectrometer (Gas Detector, ATLAS-WERKE AG.). The limits of detection for this apparatus were 0.07 μg of oxygen, 0.1 μg of nitrogen and 0.005 μg of hydrogen. The analysis took approximately 30 minutes. From the extraction curve with vacuum fusion it was proved to be extracted gases from iron and steel within 2 minutes.

1537. Mechanism of the reduction of oxide inclusions by carbon in liquid iron during vacuum fusion analysis

1537. Mechanism of the reduction of oxide inclusions by carbon in liquid iron during vacuum fusion analysis

1298. Vacuum fusion analysis with a mass spectrometer: ML Aspinal, Analyst, 91, 1966, 33–41

1298. Vacuum fusion analysis with a mass spectrometer: ML Aspinal, Analyst, 91, 1966, 33–41

Vacuum fusion analysis with a mass spectrometer

The suitability of a mass spectrometer for vacuum fusion analysis is discussed; the equipment and its mode of operation and calibration are described. The objections to using an oil pump for extracting the gases liberated from the metal samples have been overcome with this apparatus.Results for oxygen determination in steels, molybdenum and zirconium have been independently checked by using a fast neutron-activation technique, and the results of two methods are shown to be in good agreement.Oxygen levels of 116 p.p.m. have a standard deviation of 6 p.p.m. and coefficient of variation of 5 per cent. Although most of the work has been carried out on oxygen determinations, nitrogen results are quoted for two standard iron samples showing that the method is also acceptable for nitrogen determinations. Nitrogen levels of 31 p.p.m. have a standard deviation of 3 p.p.m. and a coefficient of variation of 10 per cent.The limits of detection for the equipment are 0·1 µg of oxygen, 0·1 µg of nitrogen and 0·01 µg of hydrogen.

A versatile gas analysis apparatus incorporating a small mass spectrometer

A gas analysis apparatus is described consisting of a metal vacuum system which includes a mass spectrometer, connected by a capillary leak to a glass vacuum system which can be readily modified to suit any particular problem. This arrangement provides for a wide variety of experiments, examples of which are the analysis of small quantities of gas such as occur in bubbles in glass, desorption studies and vacuum fusion analysis. The minimum quantity of gas that is detectable with this apparatus is approximately 5 1. μtorr. The mass spectrometer may also be used as a leak detector with a detection limit of 0.1 1. ntorr sec-1.

Determination of oxygen in titanium by vacuum fusion analysis with platinum bath technique

Determination of oxygen in titanium by vacuum fusion analysis with platinum bath technique

Determination of Oxygen, Hydrogen, and Nitrogen in Refractory Metals

The reliability of the results obtained by vacuum extraction and the applicability of the technique to refractory metals are presented. The advantages of vacuum extraction relative to conventional iron bath vacuum fusion analysis are given. (J.E.D.)