Sodium peroxide, fusion with

Insoluble iridium dioxide from the sodium peroxide fusion is dissolved in aqua regia, oxidized with nitric acid, and precipitated with ammonium chloride as impure ammonium hexachloroiridate(IV), To purify this salt, it is necessary to redissolve the compound and precipitate out the... 

Micro amounts of sulfur in polymer are usually determined by oxygen flask combustion, sodium peroxide fusion in a metal bomb followed by titration [30], pyroluminescence [36] or ICP-AES. An oxygen flask combustion photometric titration procedure capable of determining total sulfur in polymers in amounts down to 50 ppm was reported. The repeatability of the sulfur determination in polyolefins in the oxygen flask is 40% at 50 ppm level, improving to 2% at the 1 % level [21]. Crompton [31] has also combined Schoniger flask combustion with a colorimetric procedure for the determination of phosphorous in polymers in various concentration ranges (0.01 to 2%, 2 to 13%). 

Applications Basic methods for the determination of halogens in polymers are fusion with sodium carbonate (followed by determination of the sodium halide), oxygen flask combustion and XRF. Crompton [21] has reported fusion with sodium bicarbonate for the determination of traces of chlorine in PE (down to 5 ppm), fusion with sodium bisulfate for the analysis of titanium, iron and aluminium in low-pressure polyolefins (at 1 ppm level), and fusion with sodium peroxide for the complexometric determination using EDTA of traces of bromine in PS (down to 100ppm). Determination of halogens in plastics by ICP-MS can be achieved using a carbonate fusion procedure, but this will result in poor recoveries for a number of elements [88]. A sodium peroxide fusion-titration procedure is capable of determining total sulfur in polymers in amounts down to 500 ppm with an accuracy of 5% [89]. 

Uranium in mineral ores An approximately 10 per cent solution of the sample containing 25-50 per cent free nitric acid (by volume) is prepared by a suitable method (e.g. a potassium hydroxide or sodium peroxide fusion, followed by treatment with nitric acid). A portion of the sample (0 05 ml) is spotted upon filter paper in the usual manner and allowed to dry in the air. The solvent consists of 2-methyltetrahydroxyfuran (tetrahydrosylvan) saturated with water and to which sufficient concentrated nitric acid has been added to give a 2-5-10 per cent concentration of nitric acid. The paper strip is removed when the solvent front has moved 5-7 cm beyond the test patch, and dried in a current of warm air. The uranium moves in a narrow band near the solvent front. The paper is sprayed with 1 per cent potassium hexacyanoferrate(II) solution. A brown stain appears in the presence of uranium. The quantity of uranium may be estimated by comparison with standard stains prepared with known amounts (0-1-200 pg) of uranium. 

Lead can be recovered from mineral samples by sodium peroxide fusion (R3)(R8) followed by dissolution of the melt In nitric acid. For many roclc and soil samples, leaching with hot dilute (L 3) nitric acid (H13) or with hot concentrated sulfuric acid followed by nitric acid (P2) or with a sulfuric acid-hydrofluoric acid mixture (I2) has been found to be adequate. 

When the sodium peroxide fusion is carried out as described, only a small amount of insoluble matter should be found in the aqueous extract of the fusion product, but this material can interfere with the detection of the end-point of the titration. For the best results the extract should be set aside overnight, so that a clear portion can be withdrawn for titration. 

Sodium peroxide fusion in a metal bomb has also been used to decompose polymers prior to the determination of down to 50 ppm sulphur. In the procedure described in Method 81 sodium is removed from the fusion product by means of a cation exchange resin and the sulphate is determined by titration with standardised 0.005M barium perchlorate. Chlorine, fluorine and nitrogen in amounts up to 2 mg. in the sample are without serious effect on the determination of sulphur. The effect of larger amounts of fluorine can be suppressed by the addition of boric acid. 

The chromates of the alkali metals and of magnesium and calcium are soluble in water the other chromates are insoluble. The chromate ion is yellow, but some insoluble chromates are red (for example silver chromate, Ag2Cr04). Chromates are often isomorph-ous with sulphates, which suggests that the chromate ion, CrO has a tetrahedral structure similar to that of the sulphate ion, SO4 Chromates may be prepared by oxidising chromium(III) salts the oxidation can be carried out by fusion with sodium peroxide, or by adding sodium peroxide to a solution of the chromium(IIl) salt. The use of sodium peroxide ensures an alkaline solution otherwise, under acid conditions, the chromate ion is converted into the orange-coloured dichromate ion ... 

Acid-cataly2ed hydroxylation of naphthalene with 90% hydrogen peroxide gives either 1-naphthol or 2-naphthiol at a 98% yield, depending on the acidity of the system and the solvent used. In anhydrous hydrogen fluoride or 70% HF—30% pyridine solution at — 10 to + 20°C, 1-naphthol is the product formed in > 98% selectivity. In contrast, 2-naphthol is obtained in hydroxylation in super acid (HF—BF, HF—SbF, HF—TaF, FSO H—SbF ) solution at — 60 to — 78°C in > 98% selectivity (57). Of the three commercial methods of manufacture, the pressure hydrolysis of 1-naphthaleneamine with aqueous sulfuric acid at 180°C has been abandoned, at least in the United States. The caustic fusion of sodium 1-naphthalenesulfonate with 50 wt % aqueous sodium hydroxide at ca 290°C followed by the neutralization gives 1-naphthalenol in a ca 90% yield. 

Organic selenium compounds and siUceous materials (rock, ore, concentrates) are fused with mixtures of sodium carbonate and various oxidants, eg, sodium peroxide, potassium nitrate, or potassium persulfate. For volatile compounds, this fusion is performed in a bomb or a closed system microwave digestion vessel. An oxidizing fusion usually converts selenium into Se(VI) rather than Se(IV). 

Quantitatively, sulfur in a free or combined state is generally determined by oxidizing it to a soluble sulfate, by fusion with an alkaH carbonate if necessary, and precipitating it as insoluble barium sulfate. Oxidation can be effected with such agents as concentrated or fuming nitric acid, bromine, sodium peroxide, potassium nitrate, or potassium chlorate. Free sulfur is normally determined by solution in carbon disulfide, the latter being distilled from the extract. This method is not useful if the sample contains polymeric sulfur. 

Nickel ware. Crucibles and dishes of nickel are employed for fusions with alkalis and with sodium peroxide (CARE ). In the peroxide fusion a little nickel is introduced, but this is usually not objectionable. No metal entirely withstands the action of fused sodium peroxide. Nickel oxidises in air, hence nickel apparatus cannot be used for operations involving weighing. 

Substances which are insoluble or only partially soluble in acids are brought into solution by fusion with the appropriate reagent. The most commonly used fusion reagents, or fluxes as they are called, are anhydrous sodium carbonate, either alone or, less frequently, mixed with potassium nitrate or sodium peroxide potassium pyrosulphate, or sodium pyrosulphate sodium peroxide sodium hydroxide or potassium hydroxide. Anhydrous lithium metaborate has found favour as a flux, especially for materials containing silica 12 when the resulting fused mass is dissolved in dilute acids, no separation of silica takes place as it does when a sodium carbonate melt is similarly treated. Other advantages claimed for lithium metaborate are the following. 

Naturally, the flux employed will depend upon the nature of the insoluble substance. Thus acidic materials are attacked by basic fluxes (carbonates, hydroxides, metaborates), whilst basic materials are attacked by acidic fluxes (pyroborates, pyrosulphates, and acid fluorides). In some instances an oxidising medium is useful, in which case sodium peroxide or sodium carbonate mixed with sodium peroxide or potassium nitrate may be used. The vessel in which fusion is effected must be carefully chosen platinum crucibles are employed for... 

A. Dry Process Discussion. The oxidation is carried out by fusion with sodium peroxide, or, less efficiently, with sodium carbonate and potassium nitrate ... 

In Figure 3-6 are plotted the k values (ordinates) for various chlorinated hydrocarbon polymers, the chlorine contents as determined analytically after fusion with sodium peroxide being the abscissas. The x-ray results were obtained in about one tenth the time required for the conventional analyses. The experimental points lie close to the solid line in Figure 3-6. The deviations from the solid line may be due to any one or any combination of the following causes. 

Haslam et al. [32] reported the determination of Al in polyolefins by AAS. Typical AAS tests on rubber compounds involve several steps. The sample is combusted, and the resulting ash is dissolved in distilled de-ionised water. The solution is then used for AAS [126]. AAS or EDS can also be used for element analysis of filler particles. In order to determine the uniformity of tin compounds in polychloroprene after milling and pressing, Hornsby et al. [127] have ashed various pieces from one composition. After fusion of the residue with sodium peroxide and dissolution in HC1, the Sn content was determined by means of AAS. Typical industrial AAS measurements concern the determination of Ca in Ca stearate, Zn in Zn stearate, Ca- and Zn stearate in PE, Ca and Ti in PE film or Al and V in rubbers. 

Leidie A process for extracting the platinum metals from their ores by fusion with sodium peroxide, followed by a complex separation process. Developed by A. Quennessen, a leading French manufacturer of platinum in the 19th century, and E. Leidie. The process is still used for extracting precious metals, and in chemical analysis. 

Other elements which occur in organic compounds, such as phosphorus, arsenic, other non-metals, and metals in organic combination, are detected by destroying the organic material by oxidation (with nitric acid in a sealed tube or by fusion with potassium nitrate or sodium peroxide) and then applying the usual tests. 

The treatment of this insoluble residue may vary. In one typical process, residue is subjected to fusion with sodium peroxide. Ruthenium and osmium are converted to water-soluble sodium ruthenate and osmate, which are leached with water. The aqueous solution is treated with chlorine gas and heated. The ruthenate and the osmate are converted to their tetroxides. Ruthenium tetroxide is distilled out and collected in hydrochloric acid. The tetroxide is converted into ruthenium chloride. Traces of osmium are removed from ruthenium chloride solution by boiling with nitric acid. 

Detection.—Apart from naturally occurring ores of vanadium, vanadium steels, and ferrovanadium, the commonest compounds of vanadium are those which contain the element in the pentavalent state, viz. the pentoxide and the various vanadates. The analytical reactions usually employed are, therefore, those which apply to vanadates. Most vanadium ores can be prepared for the application of these reactions by digesting with mineral acids or by alkaline fusion with the addition of an oxidising agent. When the silica content is high, preliminary treatment with hydrofluoric acid is recommended. Vanadium steels and bronzes, and ferrovanadium, are decomposed by the methods used for other steels the drillings are, for instance, dissolved in sulphuric acid and any insoluble carbides then taken up in nitric acid, or they are filtered off and submitted to an alkaline fusion. Compounds of lower valency are readily converted into vanadates by oxidation with bromine water, sodium peroxide, or potassium permanganate. 

Palladium, like rhodium, but unlike platinum, dissolves in fused potassium hydrogen sulphate, yielding palladous sulphate. Fusion with sodium peroxide converts it into palladium monoxide. Heated with sulphur combination takes place with incandescence. 

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