Metal precipitation

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. 

Gold compounds are all easily reduced in alkaline solution to metallic gold which may occur in colloidal form and so be red, blue or intermediate colours. Reduction to gold, followed by weighing of ihe metal precipitated, may be used in quantiiaiive analysis. 

After epoxidation a distillation is performed to remove the propylene, propylene oxide, and a portion of the TBHP and TBA overhead. The bottoms of the distillation contains TBA, TBHP, some impurities such as formic and acetic acid, and the catalyst residue. Concentration of this catalyst residue for recycle or disposal is accompHshed by evaporation of the majority of the TBA and other organics (141,143,144), addition of various compounds to yield a metal precipitate that is filtered from the organics (145—148), or Hquid extraction with water (149). Low (<500 ppm) levels of soluble catalyst can be removed by adsorption on soHd magnesium siUcate (150). The recovered catalyst can be treated for recycle to the epoxidation reaction (151). 

Precipitation is affected by pH, solubiUty product of the precipitant, ionic strength and temperature of the aqueous stream, and the presence of metal complexes. For each metal precipitant, there is an optimum pH where its solubiUty is lowest and hence, the highest removals may be achieved. When an aqueous stream contains various metals, the precipitation process caimot be optimized for each metal, sometimes making it difficult to achieve effluent targets for each. SolubiUty products depend on the form of the metal compound and ate lowest for metal sulfides, reflecting the relative insolubiUty of these compounds. For example, the solubiUty product for lead sulfide [1314-87-0] is on the order of compared to 10 for lead carbonate. Metal... 

The function of pH adjustment is to neutralize acids and bases and to promote the formation of precipitates (especially of heavy metal precipitates) which can subsequently be removed by conventional settling techniques. These purposes are not mutually exclusive, precipitates can be formed as the result of neutralizing a waste. Conversely, neutralization of the waste stream can result when adjusting the pH to effect chemical precipitation. Typically, pH adjustment is effective in treating inorganic or... 

Zement-kalk, m. hydraulic lime, -kalkmdrtel, m. lime-and-oement mortar, -kalkstein, m. hydraulic limestone, -kohle, /. cementation carbon, -kufe, -kiipe, /. cement (or concrete) vat. -kupfer, m. cement copper, -mastiz, m. mastic cement, -metoll, n. metal precipitated by the cementation process. -miUk, /. thin cetnent mortar. 

After the end of the interaction, the melt is cooled down to room/ambient temperature, and the metal and salts are crushed and leached using mineral acids and water to separate the metal. The metal precipitates mostly in the form of dendrites, which are pressed and sintered into bars to be converted into wire, sheet and powder. 

Rh(N02)6 is of some importance in the traditional extraction of rhodium. Impure RI1CI3 is neutralized and treated with NaN02 Na3Rh(N02)6 is soluble under these conditions (though base metals precipitate), but when ammonium chloride is added, (NH4)3Rh(N02)6 precipitates. The potassium salt is similarly relatively insoluble. All these salts are believed... 

Chelating agents as metal precipitants advances, 1960-1965. F. H. Firsching, Chelates Anal. Chem., 1969, 2,117-148 (203). 

The reactivities of potassium and silver with water represent extremes in the spontaneity of electron-transfer reactions. The redox reaction between two other metals illustrates less drastic differences in reactivity. Figure 19-5 shows the reaction that occurs between zinc metal and an aqueous solution of copper(II) sulfate zinc slowly dissolves, and copper metal precipitates. This spontaneous reaction has a negative standard free energy change, as does the reaction of potassium with water ... 

When a strip of zinc metal is dipped in a solution of copper(II) sulfate, zinc is oxidized to 7n (a >5 )1 and q) is reduced to copper metal. The insoluble metal precipitates from the solution, hi the molecular views, water moiecuies and spectator anions have been omitted for clarity. 

Some electrodes are made of substances that participate in the redox reactions that transfer electrons. These are active electrodes. Other electrodes serve only to supply or accept electrons but are not part of the redox chemistry these are passive electrodes. In Figure 19-7. both metal strips are active electrodes. During the redox reaction, zinc metal dissolves from the anode while copper metal precipitates at the cathode. The reactions that take place at these active electrodes are conversions between the metals contained in the electrodes and their aqueous cations. 

Shikazono, N. (1974c) Present-day hydrothermal system associated with base metal precipitates — (I). Mining Geology, 24, 367-376 (in Japanese with English abst.). 

Chemical compositions of hydrothermal solutions are summarized in Table 2.2 and chemical compositions of precipitates are presented in Table 2.3. Cl concentration of hydrothermal solutions precipitating base metals is high compared with hydrothermal solution not associated with base metal precipitations. 

Submarine metal precipitation at back-arc basins around the Japanese islands... 

Nitta, T., Adachi, M., Takahashi, M., Inoue, K. and Abe, Y. (1991) Heavy metal precipitation from geothermal fluid of 87N-15T production well in the Okuaizu geothermal field, Tohoku District, Japan. Mining Geology, 41, 231-242 (in Japanese). 

A different situation occurs for the reductive polarography of an ion whose metal does not amalgamate then the metal precipitates on the dme surface without further diffusion, so that... 

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