Vacuum Fusion Research Articles

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.

真空抽出法によるアルミニウム中の分子状水素の挙動と抽出過程

The vacuum hot extraction (VHE) and the vacuum fusion extraction (VFE) methods were tried. Molecular hydrogen in aluminum having gas pores is extractive by the VHE method. The extraction proceeds through the dissociation, dissolution, diffusion and evolution processes. The molecular hydrogen requires time for extraction so longer than the diffusive hydrogen as 4hrs or more. In the VFE method, molecular hydrogen is completely extracted within 1hr. Hydrogen in aluminum having gas pores is extracted by the VHE method in the following three steps in accordance with elevated temperatures: (i) When the pores 10-2cm or more in radius in the surface layer up to 13μ in depth attain the internal gas pressure 16.5 atm or more at 250°to 480°C, they grow as blisters and evolves molecular hydrogen. Hydrogen extracted from the blisters is less than 0.04cc/100g. (ii) Hydrogen 0.61cc/100g in solution diffused in aluminum cast in a green sand mold is extracted at 480°to 660°C, Hydrogen over this value forms pores and remains in molecular state. And (iii) The residual molecular hydrogen is extracted at above 660°C.

真空抽出法によるアルミニウム中のガスの抽出過程とガス抽出曲線の観察

Most of blank and surface gases from a boat and a specimen in the vacuum gas extrcttion method is attributed to adsorption of gases in air. The value of blank or surface gas occupies 50% of the total extraction gas content when the specimen contains a small amount of gas. When the specimen is heated on the boat in the vacuum hot extracting apparatus (VHE), diffusive hydrogen starts to be extracted from about 15min. and completes after 45min. When the specimen is directly heated without the boat, extraction of hydrogen is so accelerated that the extraction time is shortened by 15 to 20min. Although the vacuum fusion extraction method (VFE) appreciably shortens the extraction time as compared with the VHE method, the advantage of time saving is counterbalanced when extracting only the diffusive hydrogen, because the blank gas of the vessel shall be considered.

Bestimmung von stickstoff in refraktärmetallen—II Titan

This is a report on round-robin tests concerning the determination of nitrogen in titanium, which were carried out by the refractory-metals group of the chemical board of the Gesellschaft Deutscher Metallhütten- und Bergleute. The following methods were used: classical and modified Kjeldahl methods, inert gas fusion and vacuum fusion extraction. With the platinum (or palladium) flux technique (noble metal to sample ratio ∼ 20 : 1, temperature ⩾ 2000°) the reductive fusion methods are capable of determining nitrogen contents ⩾ 20 ppm. Under special conditions, contents higher than 10–40 ppm can be determined by the Kjeldahl method (the lower limit varies from laboratory to laboratory). With a micro circulating distillation and determination apparatus, and dissolution of the sample within the pressure vessel, the detection limit can be lowered to 1 ppm. Because of possible interferences by reducible nitrogen compounds from the laboratory air, blanks must be determined with high-purity aluminium. The results from 7 laboratories (Kjeldahl 4; reductive fusion 3) for a titanium sample containing 138 ppm nitrogen were in good agreement (standard deviation 5 ppm).

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.

The determination of oxygen in brass and zinc by a vacuum carbon-reduction techniques

A vacuum carbon-reduction technique for the determination of oxygen in brass and zinc has been studied. As a preliminary, zinc is removed from the samples, sealed in predegassed graphite capsules, in a silica furnace maintained at ca. 850°C under vacuum in a vacuum fusion instrument. The residual contents of the capsules are then analysed in sequence at 1450°C in the main furnace of the apparatus, to which they are transferred without breaking the vacuum. The procedure developed affords a detection limit of 0.5–1 ppm of oxygen for samples weighing ca. 1.5 g.

Quantitative Analysis of Hydrogen in Titanium with an Ion Microanalyzer

Abstract Quantitative analysis of hydrogen in titanium was investigated with an ion microanalyzer. Argon ions as primaries were accelerated at a voltage of 10 kV. The diameter and the current of the beam were 1 mm and 2 μA, respectively. A mass spectrum was measured at 2×10−7 Torr. It was found that the intensity ratio of m⁄e=49(48TiH+) and 46(46Ti+) can be used for the determination of hydrogen in titanium. A linear relation was obtained between the intensity ratio and hydrogen concentration determined by the standard vacuum fusion method. The present method was applied to determine the hydrogen concentration in the surface layer of a sample treated by cathodic polarization. It was observed that hydrogen concentrations in the surface layer were much higher than those in the bulk of the sample.

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.

Determination of micro oxygen in pure nickel and cobalt by vacuum fusion with carbon chips

Determination of micro oxygen in pure nickel and cobalt by vacuum fusion with carbon chips

真空融解法による金属マンガン，アルミニウム中の酸素定量

The determination of oxygen in metallic manganese and high-purity aluminium has been made by the vacuum fusion method with a carbon chip-tin-nickel foil bath, the method being effective for the determination of oxygen in metals which involve violent evaporation and are difficult to react with carbon.In manganese, samples polished chemically and wrapped with a nickel foil (Mn:Ni foil=1∼2:2) was dropped in the crucible at 900°C and then the temperature was raised to 1550°C at the rate of 100°C/min and gases were extracted for 2 min. The oxygen extraction rate by this method was higher than those by the cupper bath and nickel-tin bath methods. The recovery of oxygen by this method was 97∼100 (%) in the known amount of manganese oxide and the deviation coefficient was within 6.6 (%) for electrolytic manganese.In aluminium, comparison of various bath methods indicated that the above-mentioned method and the iron-tin, copper and nickel-tin bath methods gave inaccurate results with incomplete extraction. By the addition of silicon to the carbon chip-tin-nickel foil bath, the oxygen extraction was increased and the results of determination were in good agreement with those by the fast neutron activation method. Samples electropolished and wrapped with a nickel foil was plunged in the crucible at 1400°C after the addition of 0.1 g of slicon and then the temperature was raised to 1800°C at the rate of 100°C/min and gases were extracted for 3 min.

Vacuum fusion-aluminium bath method for the determination of hydrogen in copper

Conventional methods (hot extraction, tin fusion, vacuum fusion, inert gas fusion) for the determination of the hydrogen content of copper and of metals or alloys bearing easily reducible oxides, are often rather inaccurate. At the relatively low temperature which is essential to minimize total blanks (and therefore errors), not only hydrogen but also water vapour is evolved; the latter is not measured when gas chromatography is used to determine hydrogen, and is lost by adsorption in other techniques. These problems are overcome by the use of a vacuum fusion procedure with an aluminium bath. The affinity of aluminium for oxygen is so high that any water formed after sample dissolution is converted to measurable hydrogen. The method allows detection of 0.05 p.p.m. hydrogen on 1-g samples.

Study on the gas distribution of the unidirectionally solidified Al-4%Cu alloy

Diffusion rate and distribution coefficient of gases during solidification in the ingot of an Al-4%Cu alloy were studied by the unidirectional solidification technique. Gas content in the ingot was measured by a vacuum fusion technique. Results obtained are as follows:(1) Diffusion rates of gases in the solid state, the coexistent state of the solid-liquid and the liquid state were 2.9×10-5, 3.8×10-5 and 6.3×10-5cm2/sec, respectively.(2) Gas distribution coefficient tended to reach unity as the solidification rate increased.(3) Gas content in the ingot became nearly in equilibrium with the atmosphere as the solidification proceeded. Thus, gas distribution in the ingot had the same pattern in nearly every sample except some cases.(4) It was found that degassing by vacuum melting and solidification was due to the diffusion rather than the bubble discharge.

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.

Test results of vacuum fusion using the durarc nonconsumable electrode: A R Vaia et al,Vide (161), Sept/Oct 1972, 204–209 ( in French)

For drug-dependent individuals, drugs of abuse that are delayed in time are discounted more steeply than money delayed in time in a hypothetical choice task. The reasons for this finding are not clear. This study examined whether steep discounting of drugs relative to money might be related to the function of drugs as primary/consumable reinforcers and money as a conditioned/non-consumable reinforcer. Twenty adults with no self-reported problems with money, alcohol, or food participated. They indicated their preferences for three hypothetical outcome types: delayed versus immediate money, delayed versus immediate food, and delayed versus immediate alcohol. Both the hyperbolic decay model and area under the curve analysis showed that money was discounted less steeply than alcohol or food, but that alcohol and food were discounted similarly. This finding replicates previous results showing that people without drug abuse problems show steep discounting of alcohol. Furthermore, this finding suggests that alcohol may be steeply discounted as part of a general process involving primary/consumable reinforcers, not necessarily because it is a drug.

Bestimmung von parts per billion sauerstoff in silizium durch eichung der IR-absorption bei 77°K

For the i.r.-absorption of oxygen in silicon new calibration curves at room temperature and 77°K are determined by means of the vacuum fusion method. The experimental techniques are reported and their sources of error are discussed. The new values for the calculation of the oxygen concentration from the absorption coefficient measured are: 4·9 ± 0·2 ppm A/cm −1 and 1·9 ± 0·1 ppm A/cm −1 at room temperature and 77°K, respectively. These values are lower by a maximum factor of 2·5 than those published in the literature. Thus the minimum detection level for the IR-absorption method at 77°K is lowered to 20 ppb A, so most of the oxygen concentration observed in silicon crystals can be determined.

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.

Effect of high speed pumps on the determination of gases in metals by the vacuum fusion method

Effect of high speed pumps on the determination of gases in metals by the vacuum fusion method

14MeV速中性子放射化分析法による酸素の定量

A method for the determination of oxygen in steel and other metals by the 16O (n, p) 16N reaction with 14MeV neutrons has been investigated. Parameters such as instrumental conditions, sample size, and interferences from other elements can be recognized and their effects are evaluated and experimentally controlled.The sample size is important to obtain a good precision and accuracy. For the industrial routine analysis a preference is given to cylindrical samples of diameter 12·5mm and thickness 10mm. In order to ensure a reliable pneumatic transport and minimize the error in counting, tolerances on the size must be kept within ± 0·2mm as strictly as possible.Interferences by B and F on the oxygen analysis are experimentally investigated. B and F of 0·1% correspond to oxygen of 70 and 420ppm, respectively.The long-term coefficient of variation for analysis of a given sample over a period of 10 days is 4 to 10%.The accuracy of this method is checked by comparison of the results with those of the vacuum fusion method. The agreement of the results obtained by the two methods is satisfactory.The determination of oxygen in various powder samples such as acid insoluble residue in steel and iron powder is also demonstrated with satisfactory results.

Solubility of water in lime-alumina-silica melts

The water solubility in fused silicates of the CaO-SiO2 and CaO-SiO2-Al2O3 systems has been measured using a vacuum fusion technique. The melts were equilibrated with nitrogen as “carrier gas” containing an accurately known water content. The solubility of water increased on the addition of lime to the melts of both systems. The effect of alumina is initially, to decrease the solubility. Additions above about 20 wt pct at a constant basicity of 0.6 however raised the water solubility of lime-silica melts. From the plot of oxygen density against the hydrogen concentration of the silicate melts of the system lime-silica-alumina studied in this investigation, it may be concluded that free hydroxyls take up interstitial positions in the silicate network. Wustite additions to lime-silica melts of basicity equal to 1 do not appear to influence the water solubility, although the rate of gas absorption from the furnace atmosphere is accelerated significantly.