Zinc Deposition

The diffusion heat treatment lowers the mechanical properties. The resistance of this protection against weathering or water has not been reported. This process is not widely used, probably because anodising is easier to carry out. 

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Zinc. Zinc deposits in the United States extend from Maine through the Appalachian Mountains, and west through the Mississippi Valley into the Rocky Mountain states. U.S. reserves are estimated to be 27 x t Zn (108). World reserves and resources are 135 and 110 x 10 t, respectively. The... 

Reference 38 is a good guide to the selection of plate thickness test methods. Test methods may vary with the purity and electrochemical activity of the deposit. Metals deposited from commercial plating solutions are seldom pure. For example, zinc deposits from the three commonly used baths, ie, cyanide, chloride, and zincate, vary significantly in purity and activity (39). Standard ASTM test methods for determining plate thickness are... 

The reproducibility of test results between labs using the neutral salt spray tests has not been consistent, but the repeatability, within one lab, is better, and the test has value in comparing variations in coating systems. Correlation of hours of exposure in the salt spray test to actual performance of the plated part in service, even in marine atmospheres, is not consistent and usually avoided. A classic example is that cadmium deposits outlast zinc deposits on steel in salt spray tests and clean marine atmospheres, yet zinc outlasts cadmium when exposed to real, industrial atmospheres, because of the presence of sulfur-bearing corrodents in industrial environments. An important variable in salt spray testing is the position of the surface to be tested. Whereas the surface of test panels is specified to be 15—30° from the vertical (40), when salt spray testing chromated zinc-plated specimens, this range has appeared excessive (41). 

Protection of niobium and its alloys from oxidation in air is accomplished by coating, e.g. with zinc deposited by holding in zinc vapour at 865°C or coating with a layer of chemically stable oxide, nitride or silicide. Silicide coatings applied by pack cementation, fused slurry or by electrolytic methods have been found to be one of the most effective means of preventing oxidation of the metal. 

Both share more or less the same merits but also the same disadvantages. The beneficial properties are high OCV (2.12 and 1.85 V respectively) flexibility in design (because the active chemicals are mainly stored in tanks outside the (usually bipolar) cell stack) no problems with zinc deposition in the charging cycle because it works under nearly ideal conditions (perfect mass transport by electrolyte convection, carbon substrates [52]) self-discharge by chemical attack of the acid on the deposited zinc may be ignored because the stack runs dry in the standby mode and use of relatively cheap construction materials (polymers) and reactants. 

For the most part, iron, copper, nickel, and zinc deposits found in the boiler section are the result of corrosion processes taking place somewhere else within the overall system. Similarly, mill scale from new boilers may be released and redeposited elsewhere, plugging BD lines and boiler tubes. 

Thomas Edison was faced with the problem of measuring the electricity that each of his customers had used. His first solution was to use a zinc coulometer, an electrolytic cell in which the quantity of electricity is determined by measuring the mass of zinc deposited. Only some of the current used by the customer passed through the coulometer. (a) What mass of zinc would be deposited in 1 month (of 31 days) if... 

Monofunctional and Polyfunctional Electrodes At monofunctional electrodes, one sole electrode reaction occurs under the conditions specified when current flows. At polyfunctional electrodes, two or more reactions occur simultaneously an example is the zinc electrode in acidic zinc sulfate solution. When the current is cathodic, metallic zinc is deposited at the electrode [reaction (1.21)] and at the same time, hydrogen is evolved [reaction (1.27)]. The relative strengths of the partial currents corresponding to these two reactions depend on the conditions (e.g., the temperature, pH, solution purity). Conditions may change so that a monofunctional electrode becomes polyfunctional, and vice versa. In the case of polyfunctional electrodes secondary (or side) reactions are distinguished from the principal (for the given purpose) reaction (e.g., zinc deposition). In the electrolytic production of substances and in other practical applications, one usually tries to suppress all side reactions so that the principal (desired) reaction will occur with the highest possible efficiency. 

Fig. 7. Alloy composition versus (a) the shift in the aluminum deposition potential, AEai and (b) the shift in the copper/zinc deposition potential Ai cu,Zn, for the deposition of fee Cu-Al and hep Zn-Al alloys, calculated by using Eq. (12) and Eq. (13) and the free energy curves from Figure 6. Reproduced from Stafford et al. [104] by permission of The Electrochemical Society.

Anderson, G. M. and G. Garven, 1987, Sulfate-sulfide-carbonate associations in Mississippi Valley-type lead-zinc deposits. Economic Geology 82,482 488. 

Smith, G.J. and O.J. Rongstad. 1981. Heavy metals in mammals from two unmined copper-zinc deposits in Wisconsin. Bull. Environ. Contam. Toxicol. 27 28-33. 

Evans, T. L., Campbell, F. A., Krouse, H. R. 1968. A reconnaissance study of some western Canadian lead-zinc deposits. Economic Geology, 63, 349-359. 

Cathode deposit morphology can also be affected by the presence of trace elements in solution. An SEM micrograph of a zinc deposit from a pure or unadulterated electrolyte and time duration of two minutes at 10 mA/cm2 is shown in Figure 3. When U0 parts per billion of antimony was added to this solution, and a similar electrodeposition cycle was performed, an approximate ten-fold increase in crystallite size was obtained (see Figure U). 

A great number of measurements have been reported for articles electroplated with zinc. The various aims have been evaluation of the corrosion rate of zinc that had been plated in a number of commercial cyanide-free zinc baths," comparison of the corrosion rate of a composite material (zinc with codeposits of various oxides) and of pure zinc deposits," corrosion testing of various alloyed zinc platings (Zn-Ni, Zn-Co, Zn-Fe), with or without subsequent post-treatment. Most of the work in the last category was only recorded in internal reports. The published work consists of an examination of the corrosion behavior of a ctoomated Zn-Fe... 

The information you have just learned permits a very precise control of electrolysis. For example, suppose you modify a Daniell cell to operate as an electrolytic cell. You want to plate 0.1 mol of zinc onto the zinc electrode. The coefficients in the half-reaction for the reduction represent stoichiometric relationships. Figure 11.23 shows that two moles of electrons are needed for each mole of zinc deposited. Therefore, to deposit 0.1 mol of zinc, you need to use 0.2 mol of electrons. 

FIG. 14. Coverages of zinc and sulfur per cycle, after three ECALE cycles, as a function of the potential used to deposit sulfur. The zinc-deposition potential was held constant at —0.9 V. 

A novel method of generating finely divided zinc metal is by the use of pulsed sonoelectrochemistry using an ultrasonic horn as the cathode [85], Normal electrolysis of ZnCl2 in aqueous NH4CI affords a zinc deposit on the cathode. When the electrolysis is pulsed at 300 ms on/off and the cathode is pulsed ultrasonically at a 100 ms 200 ms on off ratio the zinc is produced as a fine powder. This powder is considerably more active than commercial zinc powder e. g. in the addition of allyl bromide to benzaldehyde (Eq. 3.9). 

Leach, D.L. et al. 2005. Sediment-hosted lead-zinc deposits a global perspective. Economic Geology 100th Anniversary Volume, 561-608. 

Rozendaal, a. Stumpfl, E.F. 1984. Mineral chemistry and genesis of Gamsberg zinc deposit. South Africa. Transactions of the Institution of Mining and Metallurgy. Section B Applied Earth Science, 93, B161-B175. 

Abbot J.G., Gordey, S.P., Templeman-Kluit, D.J. 1986. Setting of stratiform, sediment hosted lead zinc deposits in Yukon and northeastern British Columbia, In Morin, J.A. (ed.), Mineral Deposits of the Northern Cordillera. Canadian Institute of Mining and... 

Distal exhalative manganese enriched stratigraphy to carbonate-hosted zinc deposits, Adirondack Lowlands, New York State, U.S.A. 

Sangster, D.F. 2002. The role of dense brines in the formation of vent-distal sedimentary-exhalative (SEDEX) lead-zinc deposits field and laboratory evidence. Mineraiium Deposita, 37, 149-157. 

Keywords sou geochemistry, partial extraction, selective extraction, Matagami, Perseverance zinc deposit. 

Cadmium was discovered by F. Stromeyer in 1817. In nature, it is mostly found in zinc deposits. The mineral, greenocktite (CdS) is found associated with the zinc ore, sphalerite (ZnS). Similarly zinc carbonate contains otavite (CdCOs) in small amounts. Its abundance in the earth s crust is estimated to he 0.15 mg/kg and in sea water 0.11 irg/L. 

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