Precipitates transition

Figure 1 Selection of typical organic precipitating agents (commonly precipitated transition metal ions given in parentheses) (a) dimethylglyoxime (Ni +, Pd ), (b) 1-nitroso-2-naphthol (Fe +, Co +, Zr +, Pd +), (c) a-benzoin oxime ( cupron ) (Cu, Mo02, W02 ), (d) ammonium V-nitroso-V-phenyUiydroxylamine ( cup-ferron ) (Ti +, V02", Fe +, Zr +, 06 +, U +), (e) 8-hydroxyquino-line ( oxine ) (TiO"+, Fe +, 01 +, Zr +, Mo02 +, W02 +, Th +, U02 ), (f) 4-hydroxyphenylarsonic acid (Ti +, Zidfi...

Figure 7. A log-log plot of a sorption isotherm, with an inflection indicating the transition from adsorption to surface precipitation processes. On the right, illustrative Fourier transformed EXAFS spectra for the adsorbate (solid curve) are compared with that for a precipitate (dotted curve) to show the adsorption — precipitation transition. Data are from Charlet and Manceau (48) for Cr(III) sorbed on hydrous ferric oxide.

Another illustration of competition is during laboratory measurements of Ca2+ and Mg2+ in soil extracts. To ensure that all Ca2+, Mg2+, and EDTA, but only these ions, are present as complex ions, the solution is made alkaline to about pH 10 to precipitate transition metal ions. Then CN- (which complexes strongly with the transition metals but weakly with Ca2+ or Mg2+) is added to complex any remaining tmnsition metal cations. 

C. W. Curtis, D.R. Cahela. Hydrodenitrogenation of Quinoline and Coal using Precipitated Transition Metal Sulfides. Energy Fuels 3 168-174,1989. 

If tlie level(s) associated witli tlie defect are deep, tliey become electron-hole recombination centres. The result is a (sometimes dramatic) reduction in carrier lifetimes. Such an effect is often associated witli tlie presence of transition metal impurities or certain extended defects in tlie material. For example, substitutional Au is used to make fast switches in Si. Many point defects have deep levels in tlie gap, such as vacancies or transition metals. In addition, complexes, precipitates and extended defects are often associated witli recombination centres. The presence of grain boundaries, dislocation tangles and metallic precipitates in poly-Si photovoltaic devices are major factors which reduce tlieir efficiency. 

Gettering is a black art. It consists in forcing selected impurities (typically, transition metals) to diffuse toward unimportant regions of tlie device. This is often done by creating precipitation sites and perfoniiing heat treatments. The precipitation sites range from small oxygen complexes to layers such as an A1 silicide. The foniiation of such a... 

The actinide elements exhibit uniformity in ionic types. In acidic aqueous solution, there are four types of cations, and these and their colors are hsted in Table 5 (12—14,17). The open spaces indicate that the corresponding oxidation states do not exist in aqueous solution. The wide variety of colors exhibited by actinide ions is characteristic of transition series of elements. In general, protactinium(V) polymerizes and precipitates readily in aqueous solution and it seems unlikely that ionic forms ate present in such solutions. 

Potassium removal is required because the presence of potassium during electrolysis reportedly promotes the formation of the a-Mn02 phase which is nonbattery active. Neutralization is continued to a pH of approximately 4.5, which results in the precipitation of additional trace elements and, along with the ore gangue, can be removed by filtration. Pinal purification of the electrolyte Hquor by the addition of sulfide salts results in the precipitation of all nonmanganese transition metals. 

In another process for the synthesis of PPS, as well as other poly(arylene sulfide)s and poly(arylene oxide)s, a pentamethylcyclopentadienylmthenium(I) TT-complex is used to activate -dichlorobenzene toward displacement by a variety of nucleophilic comonomers (92). Important facets of this approach, which allow the polymerization to proceed under mild conditions, are the tremendous activation afforded by the TT-coordinated transition-metal group and the improved solubiUty of the resultant organometaUic derivative of PPS. Decomplexation of the organometaUic derivative polymers may, however, be compHcated by precipitation of the polymer after partial decomplexation. 

Bayerite (P-Aluminum Trihydroxide). Bayerite is rarely found in nature. It has been synthesized by several methods A pure product is prepared by the Schm b method (3) in wliich amalgamated aluminum reacts with water at room temperature. Other methods include rapid precipitation from sodium alurninate solution by CO2 gassing, aging of gels produced by neutrali2ation of aluminum salts with NH OH, and rehydration of transition rlio alumina. 

Silver Sulfide. Silver sulfide, Ag2S, forms as a finely divided black precipitate when solutions or suspensions of most silver salts are treated with an alkaline sulfide solution or hydrogen sulfide. Silver sulfide has a dimorphic crystal stmcture. Transition from the rhombic (acanthite) to the cubic (argentite) form occurs at 175°C. Both crystal stmctures are found in nature. 

Thiocyanates are rather stable to air, oxidation, and dilute nitric acid. Of considerable practical importance are the reactions of thiocyanate with metal cations. Silver, mercury, lead, and cuprous thiocyanates precipitate. Many metals form complexes. The deep red complex of ferric iron with thiocyanate, [Fe(SCN)g] , is an effective iadicator for either ion. Various metal thiocyanate complexes with transition metals can be extracted iato organic solvents. 

Both arsonic and arsinic acids give precipitates with many metal ions, a property which has found considerable use in analytical chemistry. Of particular importance are certain a2o dyes (qv) containing both arsonic and sulfonic acid groups which give specific color reactions with a wide variety of transition, lanthanide, and actinide metal ions. One of the best known of these dyes is... 

In solving problems of this type, it is convenient to list the material balance and the solubility ratios. The various points on the material balance are calculated by multiplying the quantity of the component which does not precipitate from solution during the transition from one point to another (normally the... 

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