Gas fusion methods

Kashima, J., Yamazaki, T. Trace analysis for oxygen in metals by the inert gas fusion method with silicon carbide-graphite crucible. Bunseki Kagaku 15, 9 (1966). — Gas chromatog. Abstr. 1969, 701. 

In order to characterize SiC powders and sintered ceramics the total oxygen and nitrogen content as well as the contents of metallic impurities are analyzed. Total oxygen and nitrogen contents are usually determined by an inert gas fusion method (Leco TC 436) using powdered samples, whereas metallic impurities (Na, K, Ca, Mg, V, Fe, Ti, Al, Cr and Ni) and boron content are determined in acidic solutions by inductive plasma emission (ICP) spectroscopy [240-242],... 

Both oxygen and carbon were determined by the inert gas fusion method which is quite useful in measuring small amounts of these elements. Tie data show no difference in the average oxygen content of the riffled vs. the unriffled samples. Tlie carbon content is typical of the silicon nitride powders prepared by the vendor s method. 

As in the case of many metal—ahoy systems, weld ductihty is not as good as that of the base metal. Satisfactory welds can be made in vanadium ahoys provided the fusion zone and the heat-affected zone (HAZ) are protected from contamination during welding. Satisfactory welds can be made by a variety of weld methods, including electron-beam and tungsten-inert-gas (TIG) methods. It is also likely that satisfactory welds can be made by advanced methods, eg, laser and plasma techniques (see Lasers Plasma technology). 

The methods of choice for beryUium oxide in beryUium metal are inert gas fusion and fast neutron activation. In the inert gas fusion technique, the sample is fused with nickel metal in a graphite cmcible under a stream of helium or argon. BeryUium oxide is reduced, and the evolved carbon monoxide is measured by infrared absorption spectrometry. BeryUium nitride decomposes under the same fusion conditions and may be determined by measurement of the evolved nitrogen. Oxygen may also be determined by activation with 14 MeV neutrons (20). The only significant interferents in the neutron activation technique are fluorine and boron, which are seldom encountered in beryUium metal samples. 

Wood, D. F., Wolfenden, G. Determination of oxygen and hydrogen in tungsten and other metals by a vacuum-fusion gas-chromatographic method. Anal. Chim. Acta 38, 385 (1967). 

The highest melting material that can be grown by the flame fusion method is determined by the maximum temperature of the flame. A plasma torch may be used as an alternative heat source for materials that decompose in a hydrogen-oxygen or coal gas-oxygen flame. 

After fusion and cooling, the iron crucibles are opened by sawing off the top and bottom, and the alloy is then punched out of the open cylinder. In another method, the crucible is placed on a lathe, clamped at the stopper end, and its wall turned down to 0.1-0.3 mm. This thin wall can then be stripped off with a pair of pliers in the same manner as the top of a can of sardines. Since this can be done very rapidly, even those alloys which are very sensitive to air can be isolated without too much damage and can be rapidly transferred to a storage vessel filled with a protective gas. The method is also useful in cases where the alloy the crucible walls because of local... 

Nitrogen was initially determined by the inert gas fusion technique but the results were poor. The measurement was therefore repeated by the classical Kjeldahl method which provided data not only far more consistent with the silicon nitride composition but also more precise. The former technique does not seem appropriate for high nitrogen concentration. 

Surface area by nitrogen absorption method Total gas in reactor-grade uranium dioxide pellets Thorium and rare earth elements by spectroscopy Hydrogen by inert gas fusion... 

The solid resins in powder paints are produced in two different ways. In the conventional method, the resin is produced in isobutyl methyl ketone. In the fusion method, bisphenol-A is condensed catalytically without solvents to give a liquid epoxy resin. In this study, the powders were cured in a device permitting precise control of temperature, type of atmosphere, rate of gas flow, and the collection of the volatile compounds. The compounds were studied with a high-resolution GC and a GC-MS. The mass loss of the powders during curing was studied by thermogravimetry. 

Oxygen. Analyses are ordinarily made by vacuum fusion with Fe or Pt [22,23,27] or by inert gas fusion [28]. The sample is dissolved in the molten metal saturated with carbon in a graphite crucible at 1900°C and the evolved CO converted to CO2 in a CuO column and measured gas-volumetrically. More reproducible results are said to be obtained by neutron activation analysis for oxygen. With this method the sample is exposed a few minutes to 14 MeV neutrons to activate the oxygen by the nuclear reaction 0(n,Y) 0 and the amount of oxygen is obtained from the 0 activity having the half life of ty = 29.1 s [29] by comparison with that of a standard. The technique of isotopic dilution which has been used to analyze for oxygen in Ti should be applicable too [30]. 

In this process, the oil is firstly hydrolyzed to give free fatty acids which are then heated at 200-240°C with a mixture of polyol and dibasic acid. Simultaneous condensation of the polyol, dibasic acid and fatty acids thereby occurs and the latter become incorporated into the polymer structure. The process may be conducted in two ways. In the first procedure, which is known as the fusion or solventless method, the reactants are heated in a simple kettle under an inert atmosphere. At the end of the heating period, inert gas is blown into the resin to remove water and unreacted materials. In the second procedure, which is known as the solvent or solution method, a small amount (generally about 5%) of a solvent, usually xylene, is added to the reactants. The mixture is heated in a reactor fitted with equipment which condenses volatile vapours, separates water and returns the organic distillate to the reactor. The solvent facilitates removal of water by azeotropic distillation and, compared to the fusion method, allows much better temperature control. In addition, the solvent reduces the viscosity of the reactants this permits more effective agitation which contributes to easier water removal and faster reaction. The solvent also continually cleans resin from the sides of the reactor and enables a more uniform product to be prepared that is free from gel particles. However, despite these advantages of the solvent method over the fusion method, the latter is widely used since it requires simpler equipment. 

This alkali fusion gas chromatographic method determines down to 0.02% of amino groups in aromatic polyamides, polyimides and poly(amides-imides). 

Literature contains a variety of denominations for this technique or for more specific variants of it heat (or hot) extraction, reducing (or reductive) fusion, inert gas fusion or vacuum fusion, etc. It was preferred to use the term "reducing fusion" - in bppos44ioq to "oxidizing fusion" (Chapter II, section 3.8.2) - as the main characteristics of the method are that the sample is fused under reducing condi-tions (carbon crucible). 

From the radioactive decay constants and measurement of the amount of argon in a rock sample, the length of time since formation of the rock can be estimated. Essentially, the dating method requires fusion of a rock sample under high vacuum to release the argon gas that has collected through radioactive decay of potassium. The amount of argon is determined mass spectrometrically,... 

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