The determination of boron in aluminium

In the literature only few information is available on absolute methods for the determination of boron in aluminium. To a large extent emission spectrochemical procedures with excitation by arc or spark are used. 

These are not considered here as sufficiently reliable calibration samples are needed, which at this time are not available. The boron concentrations to be expected in unalloyed aluminium are in the 0.5 to 10 ig/g range. 

Ichiryul and Hashimoto (1) propose the reaction with l,r-dianthrimide, whereby aluminium is first separated by ion exchange in weak acid solution (1 - 1.2 N). Xhe eluate is boiled down until the sulfuric acid starts fuming, an excess of l,l -dianthrimide is added and the solution is heated at 90°C for 90 min. After cooling, the absorbance of the resulting blue solution is measured at 630 nm. The reaction is not interfered by other elements present in the aluminium. 

Kerin (2) proposes a simple separation of the aluminium the sample (Ig) is dissolved in 10 ml sodium hydroxide (25 %), the solution is concentrated to 8 to 10 ml and acidified with 40 ml concentrated sulfuric acid. The resulting crystal sludge is taken up with water under heating and the precipitate produced during boiling filtered off. Then 13 ml concentrated sulfuric acid and 5 ml reagent (0.1 g l,l -dianthrimide in 200 ml concentrated sulfuric acid) are added to 2 ml (of 100) of the filtrate and allowed to stand for 6 hours at 70°C. The absorbance is measured at 

615 nni in comparison to concentrated sulfuric acid. 4.3 Mg/g of boron are determined with a maximum deviation from the mean value of 0.7 Mg/g (n=10). The sensitivity limit is of the order of 1 Mg/g. The most reliable procedure described thus far is the one of Analyse der Metalle (3). It works without boron separation and is suitable for the determination of boron concentrations between 10 and 100 iug/g. A boron concentration of 50 A g/g may be determined to + 15 %. The analytical procedure is as follows  

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The use of curcumine as photometric reagent for the determination of boron in aluminium and its alloys at concentrations above 1 j g/g is recommended... 

Meier et al. (20) studied this method very thoroughly zirconium is dissolved without warming up in a mixture of sulphuric and hydrofluoric acid under addition of a small amount of mannite to avoid losses of boron. The solution is then oxidized with some hydrogen peroxide and allowed to stand for 12 hours to decompose the excess of hydrogen peroxide. The further procedure is the one described in detail for the determination of boron in aluminium, except that here a pH value of 1.2 has to be used and the extraction is carried out in the presence of some hexamethylenetetramine. 

THE DETERMINATION OF BORON IN ALUMINIUM AND ALUMINIUM-MAGNESIUM ALLOYS... 

The procedure of Mortier et al. (32) for the determination of boron in aluminium and aluminium-magnesium alloy is as follows The sample is irradiated for 20 min with a 2 uA beam of 7 MeV deuterons, which are degraded to 5.3-5.7 MeV, and a surface layer is removed by chemical etching (2.3.1). To separate the sample is dissolved in an oxidizing mixture of phosphoric acid, sulphuric acid and potassium dichromate. The C02 released is absorbed in 0.5 M sodium hydroxide and the activity measured with a t-t coincidence set-up. A pure decay is obtained. The chemical yield was checked by comparing, in a separate experiment, the activity of an aluminium sample, doped with 5000 tig/g of boron, measured instrumentally and after chemical separation. The yield was 100 %. 

Politzer P, Lane P, Concha MC (2005) Computtional determination of the energetics of boron and aluminium combustion reaction. In Manaa RM (ed) Chemistry at extreme conditions. Elsevier, Amsterdam, p 473 Rice BM, Sahu S, Owens FJ (2002) J Mol Struct (Theochem) 583 69... 

Interest in the metal borides is due mostly to the presence of boron in certain steels and its interaction with other alloying elements. An example of other industrial use of borides is the use of titanium borides for the grain refining of aluminium. Thermochemical data for metal borides are, however, virtually non-existent. The reason, again, is the difficulty of finding suitable experimental methods for enthalpy and Gibbs energy determinations. 

Spectrophotometric methods have been described for the determination of copper, iron, cobalt and manganese in trichlorosilanes and in silicon tetrachloride186 boron in silicon tetrachloride and in hexachlorosilane187 and iron and aluminium in silicone polymers189. 

By far the most serious interference effects in the determination of calcium are due to anions such as phosphate, sulphate, arsenate and oxalate, and to elements such as aluminium, beryllium, boron, chromium, iron and molybdenum which can exist as anions in the flame. These all give rise to reductions in line intensities, probably due to the formation of compounds which are either of low volatility or are not dissociated. 

Discussion. This method is based upon the precipitation of lead chlorofluoride, in which the chlorine is determined by Volhard s method, and from this result the fluorine content can be calculated. The advantages of the method are, the precipitate is granular, settles readily, and is easily filtered the factor for conversion to fluorine is low the procedure is carried out at pH 3.6-5.6, so that substances which might be co-predpitated, such as phosphates, sulphates, chromates, and carbonates, do not interfere. Aluminium must be entirely absent, since even very small quantities cause low results a similar effect is produced by boron ( >0.05 g), ammonium (>0.5 g), and sodium or potassium ( > 10g) in the presence of about 0.1 g of fluoride. Iron must be removed, but zinc is without effect. Silica does not vitiate the method, but causes difficulties in filtration. 

By the middle of the nineteenth century more than 60 elements were known with new ones continuing to be discovered. For each of these elements, chemists attempted to determine its atomic weight, density, specific heat, and other properties. The result was a collection of facts, which lacked rational order, Mendeleev noticed that if the elements were arranged by their atomic weights, then valencies and other properties tended to recur periodically. However, there were gaps in the pattern and in a paper of 1871 Mendeleev asserted that these corresponded to elements that existed but had not yet been discovered. He named three of these elements eka-aluminium, eka-boron and eka-silicon and gave detailed descriptions of their properties. The reaction of the scientific world was sceptical. But then in 1874 Lecoq de Boisbaudran found an... 

Often Lewis acids are added to the system as a cocatalyst. It could be envisaged that Lewis acids enhance the cationic nature of the nickel species and increase the rate of reductive elimination. Indeed, the Lewis acidity mainly determines the activity of the catalyst. It may influence the regioselectivity of the catalyst in such a way as to give more linear product, but this seems not to be the case. Lewis acids are particularly important in the addition of the second molecule of HCN to molecules 2 and 4. Stoichiometrically, Lewis acids (boron compounds, triethyl aluminium) accelerate reductive elimination of RCN (R=CH2Si(CH3)3) from palladium complexes P2Pd(R)(CN) (P2= e g. dppp) [7], This may involve complexation of the Lewis acid to the cyanide anion, thus decreasing the electron density at the metal and accelerating the reductive elimination. 

Cyclization of enone (9) in hexane with boron trifluorideetherate in presence of 1,2-ethanedithiol, followed by hydrolysis with mercury (II) chloride in acetonitrile, yielded the cis-isomer (10) (16%) and transisomer (11) (28%). Reduction of (10) with lithium aluminium hydride in tetrahydrofuran followed by acetylation with acetic anhydride and pyridine gave two epimeric acetates (12) (32%) and (13) (52%) whose configuration was determined by NMR spectroscopy. Oxidation of (12) with Jones reagent afforded ketone (14) which was converted to the a, 3-unsaturated ketone (15) by bromination with pyridinium tribromide in dichloromethane followed by dehydrobromination with lithium carbonate and lithium bromide in dimethylformamide. Ketone (15), on catalytic hydrogenation with Pd-C in the presence of perchloric acid, produced compound (16) (72%) and (14) (17%). The compound (16) was converted to alcohol (17) by reduction with lithium aluminium hydride. 

Reductions of carbonyl groups with lithium aluminium hydride or sodium borohydride occur by hydride transfer to carbon from aluminium or boron, respectively. The course of reaction is subject to steric approach control and product development control [43-45]. Enzymic reactions may or may not form the epimer favoured in the chemical reduction. This has been discussed elsewhere [46]. It is quite clear that the steric course of a dehydrogenase reaction is determined by the structure of the enzyme. 

A Lewis acid e.g. aluminium tert-butoxide, boron trifluoride, neutral alumina) is considered to coordinate with both the 17-OH and 20-keto functions, bringing them into a cfs-relationship and effectively locking the side chain in one conformation. Product formation is then determined by the relative ease of migration of the Cps)--C(i ) and C(i6>-C(i7) bonds towards the electron-deficient C<20). The structures of the resulting ketones show that the C i3)-C(i ) bond migrates in the i7j -hydroxy compound (i), and the C(i6)-"C(i7) bond in the i7a-hydroxy isomer (2). The reason for this difference has been the subject of much speculation, and is still not clear. The factors which have been considered [202] as affecting the stability of respective transition states include ... 

The ionisation energies of the electronically active impurities have been determined primarily by photoluminescence techniques and Hall measurements. Ionisation energy levels of such impurities as nitrogen and some of the group III elements (aluminium, gallium, boron) in 3C-, 4H-, 6H- and 15R-SiC polytypes are compiled in TABLE 2. Nitrogen gives relatively shallow donor levels. In contrast, other p-type dopants have deep-level acceptor states. 

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