Aqua regia Table

TELLURIUM. TCAS 13494-80-91. Chemical element, symbol Te, at. no. 52. at. wL 127.60, periodic table group 6, mp 450°C, bp 690°C, density 6.24 g/cm3 (crystalline form at 25°C), 6.00 (amorphous farm at 25°C). Elemental tellurium has a hexagonal crystal structure with trigonal symmetry. Tellurium is a silver-white brittle semi-metal, stable in air, and in boiling H2O, insoluble in HC1, but dissolved by HNOj or aqua regia to form telluric acid. The element is dissolved by NaOH solution and combines with chlorine upon heating to form tellurium tetrachloride. 

While we have not yet carried out detailed kinetic measurements on the rate of photocorrosion, our impression is that the process is relatively insensitive to the specific composition of the strontium titanate. Trace element compositions, obtained by spark-source mass spectrometry, are presented in Table I for the four boules of n-SrTi03 from which electrodes have been cut. Photocorrosion has been observed in samples from all four boules. In all cases, the electrodes were cut to a thickness of 1-2 mm using a diamond saw, reduced under H2 at 800-1000 C for up to 16 hours, polished with a diamond paste cloth, and etched with either hot concentrated nitric acid or hot aqua regia. Ohmic contacts were then made with gallium-indium eutectic alloy, and a wire was attached using electrically conductive silver epoxy prior to mounting the electrode on a Pyrex support tube with either epoxy cement or heat-shrinkable Teflon tubing. 

Extraction methods based on solutions of chelating agents, such as EDTA and DTPA, or salts of weak acids, such as ammonium acetate (CH3COONH4) (Lakanen and Ervio, 1971 Lindsay and Norwell, 1969), can be used to assess plant-available trace element contents of soils and to evaluate more robustly human exposure to environmental risks in an urban context. A study carried out in the main cities of Campania region in southern Italy (Albanese, 2008) demonstrated how the bioavailable concentrations of some trace elements such as Zn, Pb and Cu in soils, determined using ammonium acetate-EDTA extraction, are much lower than the elemental concentrations determined by an aqua regia extraction on the same samples (Table 8.1). 

Table 8.1 Maximum, minimum, mean and standard deviation (expressed as milligram per kilogram) values of ammonium acetate-EDTA (AA-EDTA) and aqua regia elemental concentrations in 29 soil samples from the city of napoli (Albanese, 2008)...

Detection.—Metallic palladium is the most readily fused of the platinum metals (see Table, p. 5). When heated in air the surface becomes coated with oxides which tint it. The metal is soluble in aqua regia, sparingly soluble in nitric acid, but more readily soluble in the fuming acid, yielding palladous nitrate, from which a brown precipitate of basic salt may be obtained on dilution with water provided the add is not present in too great an excess. A mixture of concentrated hydrochloric acid with chloric add 3 is recommended as a useful... 

Examine for Pb, Bi, Cu, and Cd by Table VII.6 in Section VII.23. After separation of Cu and Cd, acidify the solution with dilute HC1, introduce a few zinc granules and after several minutes filter off any solid and wash with water. Dissolve the ppt. in 2 ml aqua regia, evaporate just to dryness, dissolve the residue in 2m HC1 and add dimethylglyoxime reagent. 

Subject to this complication, the friction properties of the group are generally similar to those of molybdenum disulphide. The actual coefficients of friction vary with load, speed, temperature and humidity, but some reported figures are shown in Table 14.6. The chemical properties are also similar to those of molybdenum disulphide. They are resistant to attack by water, alkalis and most acids, but are attacked by aqua regia and hot concentrated hydrochloric, nitric or sulphuric acids. The most significant differences are in their electrical conductivity and their oxidation resistance. 

As noted earlier, Wollaston collected the undissolved residue from each batch process, and resubmitted the combined residues to a second purification sequence. The purified platinum obtained from the residues was also worked successfully, and we checked the purity of such platinum by combining the residues from both of the procedures we repeated, and purified the crude residue by the second chemical sequence the analytical results are given in Table V. As might be expected, this second treatment with aqua regia much reduces the proportion of platinum in the undissolved residue, and increases the relative amounts of iridium and rhodium. 

Eor total metal solubilization a representative unfrozen sample of 0.5 g, dried at 110°C and finely powdered, is dissolved in a Teflon bomb by an acid mixture of 5 ml of 40% HE, 1 ml of aqua regia (HNO3-HCI 1 3 v/v) and 5 ml of MQ water, heated at 180°C for 90 min and then cooled to room temperature. 5 ml of saturated H3BO3 solution are then added to the Teflon bomb and, after dilution to 50 ml in a volumetric flask, the solution is analyzed by ICP-AES. To test the accuracy of the total solubilization method several certified reference materials in sediment matrices are always analyzed along with the unknowns, obtaining results in a good agreement with certified values, as reported in Table 8.2. 

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