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941.
942.
Abbas Farzaneh Georg Troll Wolfram Neubauer 《Fresenius' Journal of Analytical Chemistry》1979,296(5):383-385
Summary This simple method for the determination of boron takes a total time of 20 min. Samples are mixed with CaF2 suprapur in the ratio 31 and pyrohydrolized in a Leco induction furnace for 15 min under steam of H2O. The BF3 liberated is collected in a NaOH-Na2CO3 solution (10 g NaOH +1 g Na2CO3 per liter). This solution is filled up to 200 ml with twice distilled water; 2 ml of this solution is mixed with conc. sulphuric acid and carminic acid solution and filled up to 50 ml. The absorption is measured by a Zeiss Elko II photometer with filter S 59. Analyses of four internations reference samples show excellent precision with a relative standard deviation of less than 5% (e.g. for a boron content of 2.1 ppm in granite G-2).
Schnelle Spurenbestimmung von Bor in silicatischem Material
Zusammenfassung Die Borbestimmung mit dieser schnellen und einfachen Methode benötigt ca. 20 min. Die Proben werden mit CaF2 Suprapur im Verhältnis 31 vermischt und in einem Leco-Induktionsofen 15 min unter Einleitung von Wasserdampf pyrohydrolysiert. Das entstandene BF3 wird in einer NaOH-Na2CO3-Lösung(10 g NaOH+1 gNa2CO3pro Liter) aufgefangen. Diese Lösung wird mit zweifach destilliertem Wasser auf 200 ml aufgefüllt; 2 ml dieser Lösung werden mit konz. Schwefelsäure und Carminsäure-Lösung versetzt und auf 50 ml aufgefüllt, bevor ihre Absorption mit einem Zeiss — Elko II — Photometer mit Filter S 59 gemessen wird. Analysen von 4 internationalen Referenzproben zeigen eine hohe Präzision mit einer relativen Standardabweichung von weniger als 5% (z. B. für einen Gehalt von 2,1 ppm Bor im Granit G-2 des USGS).相似文献
943.
944.
Influence of dispersing agents and solution conditions on the solubility of crude kaolin 总被引:3,自引:0,他引:3
Experiments measuring the solubility of kaolin particles in terms of the concentration of aluminum and silicon ions in supernatant were carried out as a function of the pH of the slurry over a wide range of dosages of different dispersing agents varying from 0.5 to 12 mg/(g solids). The concentrations of the metal ions in supernatant were found to be strongly affected by the type and the dosage of the dispersants and pH of the solution. In this study, the mechanism of the reaction between the dispersing agents and kaolin particles was studied and the dissolution capacities of metal ions (aluminum and silicon) were identified from kaolin particles in the absence and presence of dispersing agents. The three anionic dispersing agents used were sodium polyacrylate (Na-PAA), sodium hexametaphosphate (Na-HMP), and sodium silicate (Na-silicate), based on the industrial application of these agents and their ability to produce a stable dispersion for this purpose. 相似文献
945.
Highly syndiospecific polymerization of styrene catalyzed by allyl lanthanide complexes 总被引:2,自引:0,他引:2
Kirillov E Lehmann CW Razavi A Carpentier JF 《Journal of the American Chemical Society》2004,126(39):12240-12241
Allylic complexes of lanthanides bearing a fluorenyl-based ligand are active single-component catalysts for the polymerization of styrene, giving highly syndiotactic polymers (rrrr > 99%) with low to high molecular weight (Mn = 8000-135 000) and narrow polydispersities (Mw/Mn = 1.25-2.1). 相似文献
946.
2,3-Diaminophenol 4, 3,4-diaminophenol 5, 4-methoxy-1,2-diaminobenzene 6, 3,4-diaminobenzenethiol 7, 2,3-diaminobenzoic acid 8, and 3,4-diaminobenzoic acid 9 were reacted with 2,4-pentanedione to yield the corresponding benzo[b][1,4]diazepinium salts, respectively. The hydroxy-benzo[b][1,4]diazepinium salts 17 and 18 do not form mesomeric betaines (MB) on deprotonation. Instead, they are converted into the diimines 24 and 25. By contrast, the 7-mercaptobenzo[b][1,4]diazepinium salt 20 yields the corresponding thiolate on increasing the pH of the solution. This MB, which possesses 4n pi-electrons, does not fit into the classification system of heterocyclic mesomeric betaines accepted today. Deprotonation of the betaine results in the formation of an instable anionic thiolate 31 which oxidizes immediately to the disulfide 32. The carboxy derivatives 21 and 22 readily form cross-conjugated mesomeric betaines. Whereas the diimine 34 proved to be instable, the sodium salt of the diimine 36 was unambiguously characterized. An X-ray single crystal analysis of 22 as its picrate is presented in order to gain additional insights into these 4n pi-electron systems. 相似文献
947.
In order to study the design flexibility of photonic bandgap structures, we investigate different examples of 1D traditional
Bragg layers and 2D photonic crystals. We have also considered a simple case of 3D woodpile structures. It turns out that
in systems with large gaps, the evanescent waves penetrate into the bulk only distances comparable to one lattice constant.
Therefore confinement of light can also be achieved without long range order, which leads to the introduction of novel photonic bandgap designs. Adhering to some constraints, the changes
in the photonic bandgap in disordered structures are negligible. The important quantity to characterize the presence or absence
of modes is the local photonic density of states, however bandgap phenomena in size and position disordered arrangements can
also be verified with plane wave supercell calculations as well as finite difference time domain techniques. 相似文献
948.
1-Hydroxyanthraquinone has been annelated to a tetracyclic ketoester containing the major structural features of 4-deoxyaklavinone. The cyclization of the A-ring involves the first case of an anionic alkylation of an anthraquinone at a position which is not ortho to a phenolic function. 相似文献
949.
950.
The conducting liquid interface is found to undulate in an alternating magnetic field. It was shown earlier that ifM =B
0
2/μηω, B0, ω, μ andη being the amplitude (complex) of the alternating longitudinal magnetic field imposed at the interface, the angular frequency
of the field, the magnetic permeability and the viscosity respectively, and ifM
c was the critical value ofM then the planar layer was stable or unstable according asM < M
c orM > M
c. In this paper we have determined the stability criterion when in addition to the alternating longitudinal field there acts
a uniform field in the same direction. After comparing our results with those obtained earlier, in the absence of the uniform
field, we find that the additional uniform field has a significant destabilizing effect. 相似文献