Aluminum gravimetric analysis

Although preliminary separations may be required, in other instances the precipitation step in gravimetric analysis is sufficiently selective that other separations are not required. The pH is important because it often influences both the solubility of the analytical precipitate and the possibility of interferences from other substances. For example, calcium oxalate is insoluble in basic medium, but at low pH the oxalate ion combines with the hydrogen ions to form a weak acid. 8-Hydroxy-quinoline (oxine) can be used to precipitate a large number of elements, but by controlling pH, we can precipitate elements selectively. Aluminum ion can be precipitated at pH 4, but the concentration of the anion form of oxine is too low at this pH to precipitate magnesium ion. 

PURPOSE OP EXPERIMENT Prepare KA1(S04)2 12H20, an aluminum alum, from aluminum metal. (Note Experiment 14 describes the gravimetric analysis of the sulfate content in alum.)... 

To validate tire model, an alumina gel rod (20 x 20 x 80 mm ) was dried convec-tively on an aluminum plate, sealing all surfaces except the top one (see Fig. 5.41a). Evolution of average moisture content, several local temperatures in the gel as well as moisture profiles (by gravimetric analysis of gel shces) were measured, all being in good agreement with the simulation results. Fig. 5.39 shows a comparison of experimental and simulated moisture profiles. 

Various other reagents are also useful for gravimetric analysis, for example dimethylglyoxime (a) for nickel and oxine (b) for aluminum and magnesium (Fig. 2(a) and (b)). 

Using this chemical phenomenon, heavy-metal fluoride glasses were prepared using trifluoroacetates of zirconium, barium, lanthanum, aluminum and sodium [21]. Eigure 10.2 shows thermal gravimetric analysis of the ZBLAN powder in this process. A drastic decrease in weight (47.4%) was observed in the range of 220-300 °C, which was attributed to the decomposition from the trifluoroacetate to the sohd ZBLAN fluoride. 

Thermal Analysis. The char yield, at lOOO C, as measured by thermal gravimetric analysis, of a number of aluminum imine-derived polymers, has been obtained. The values range from 15 to 85 weight % retention depending upon the starting nitrile and the polymerization conditions. Primary weight loss typically occurs between 250 and 500 C 42). 

Vol. 3 Photometric Determination of Traces of Metals. Fourth Edition Part I General Aspects. By E. B. Sandell and Hiroshi Onishi Part IIA Individual Metals, Aluminum to Lithium. By Hiroshi Onishi Part IIB Individual Metals, Magnesium to Zirconium. By Hiroshi Onishi Vol. 4 Organic Reagents Used in Gravimetric and Volumetric Analysis. By John F. Flagg (out ofprint)... 

The demands for accuracy frequently dictate the procedure chosen for an analysis. For example, if the allowable error in the determination of aluminum is only a few parts per thousand, a gravimetric procedure is probably required. If an error of 50 ppt can be tolerated, however, a spectroscopic or electroanalytical approach may be preferable. 

A standard wet chemical analysis (ASTM D-811) is available for determination of aluminum, barium, calcium, magnesium, potassium, silicon, sodium, tin, and zinc. The procedure involves a series of chemical separations with specific elemental analysis performed by using appropriate gravimetric or volumetric analyses. 

The polymerization kinetics were studied via time-conversion relationships at different dose rates (Figures 6-9). The radiation curing was carried out at room temperature in closed aluminum capsules. Percent monomer conversion was determined gravimetrically for N-vinylpyrrolidone. Evaporation was accomplished under vacuum in a ventilated oven at 50 °C until the weight was constant. For butyl methacrylate and polyester resins, the residual monomer content was determined by gas chromatographic analysis after immersion of the cured products in acetone. 

---