Acid zinc baths

Zinc plating in acid baths, using zinc sulphates, produces a matt zinc deposit and is primarily used for coating steel wire and strip. Zinc chloride baths produce a lighter deposit. Continuous filtration in the order of 10-15 pm is recommended in both cases. Acid zinc baths are susceptible to contamination with iron, which must be periodically precipitated as iron hydroxide by hydrogen peroxide treatment. This precipitate is difficult to filter because of its gelatinous nature. 

Examples of plating solutions having good throwing power include cyanide plating baths such as copper, zinc, cadmium, silver, and gold, and noncyanide alkaline zinc baths. Examples of poorer throwing power baths are acid baths such as copper, nickel, zinc, and hexavalent chromium. 

Epitaxial effects are not limited to single-crystalline substrates. The possibility for substrate-induced epitaxial development in the difficult case of ZnSe (cf. conventional electrodeposition) has been established also by using strongly textured, albeit polycrystalline, zinc blende (111) CdSe electrolytic films to sustain monolithic growth of ZnSe in typical acidic selenite baths [16]. Investigation of the structural relations in this all-electrodeposited ZnSe/CdSe bilayer revealed that more than 30-fold intensification of the (111) ZnSe XRD orientation can be obtained on the textured (111) CdSe films, compared to polycrystalline metal substrates (Fig. 4.2). The inherent problems of deposition from the Se(IV) bath, i.e., formation of... 

Over 22.7 million kg (50 million lb) of zinc sulfate are used annually in the U.S. for the manufacture of approximately 454 million kg (one billion lb) of viscose rayon. Zinc is used as a regeneration retardant in the acid spinning bath. Because it is not consumed in any of the viscose reactions, these 22.7 million kg (50 million lb) of zinc represent process losses, through dragout by the filaments to the subsequent wash streams, filter backwashing, splashes, leaks, and the washing of equipment.14... 

Electrodeposition on Other Electrodes Trejo et al. [224] have investigated the influence of the zinc chloride concentration on the zinc nucleation process on GC electrode in KCl solutions under conditions close to those employed in commercial acid deposition baths for zinc. The results show that the nucleation process and the density number of sites are dependent on ZnCh concentration. The deposits are homogeneous and compact, although a change in morphology is observed as a function of ZnCl2 concentration. 

Trejo etal. [225, 226] have also investigated the influence of several ethoxylated additives (ethyleneglycol and PEG polymers of different molecular weights) on the nucleation, growth mechanism, and morphology of zinc electrodeposited on GG from an acidic chloride bath. Results have shown that the presence of additives modifies the nucleation process and determines the properties of the deposits. 

Point-of-Source Recovery - in certain circumstances, it is possible to utilize reverse osmosis to effect a "zero discharge" electroplating rinse water recovery system. The rinse water from the first rinse is pumped to a reverse osmosis system that concentrates the salts and directs them back to the plating bath. The purified rinse water (permeate) is directed to the last rinse, and neither solute nor solvent is lost. in the united States there are approximately 150 reverse osmosis systems operating in this manner on nickel baths and 12 on acid copper. There are also a few installations operating on copper cyanide, hexavalant chrome, and acid zinc. 

Anodes. There are two types of anodes soluble and insoluble. Most electroplating baths use one or the other specifically however, a few baths use either or both. Chromic acid plating baths use insoluble anodes alkaline zinc cyanide baths use both noncyanide alkaline zincs may use either. Soluble anodes are designed to dissolve efficiendy with current flow and preferably, not to dissolve when the system is idle. A plating solution having the anode efficiency close to the cathode efficiency provides a balanced process that has fewer control problems and is less cosdy. If the anode efficiency is much greater than the cathode efficiency and there are only small solution losses, the dissolved metal concentration rises until at some time the bath has to be diluted back or the excess metal has to be reduced by some other means. If the anode efficiency is less than the cathode efficiency, the dissolved metal decreases, pH decreases, and eventually metal salt additions and other solution corrections are required. Based on the cost of metal, it is usually considerably more economical to plate from the anode rather than add metal salt. Copper cyanide, for example, costs about twice as much to add than to dissolve a comparable amount of copper anode. Additionally, the anion added with the metal salt may build up in the plating solution. 

Nowack and Habermehl [64] recorded a significant drop in cathodic efficiency, from 90% to 20%, as the current density in a silent system was changed from 100 to 200 Am-2 for bright nickel. Ultrasound was highly beneficial and the efficiency remained very high (70%) at the much higher current density of800 A m-2. Similar improvements were also recorded for copper from acidic sulfate baths [65], and for zinc from a zincate solution [66]. 

The objective of this research work is to develop a highly conductive copper alloy based diffusion barrier for copper metallization. The criteria for selection was that minimal increase in resistivity resulted on addition of one atomic percent of second element to copper. The copper-1 at.% zinc alloy conforms to this criteria and hence was selected as a candidate material for further study. Pure copper can easily be electroplated from simple acid copper baths, but the alloys of copper are more difficult when the deposition potential of individual elements is widely separated as in the present case. A Cu-Zn alloy can be deposited from baths containing coordinating agents. Having established that a Cu-Zn alloy can be successfully electroplated, an alloy of composition Cu-3.5%Zn was sputter deposited to develop an MOS capacitor and electrical testing was performed on as-sputtered and annealed samples. The bias temperature stability tests indicate that the alloy possesses promising diffusion barrier properties. 

To Obtain Byrogallic Add. It may be prepared by boating goUio acid (previously dried at 212 Fahr.) m a glass retort, by means of a chloride of zinc bath, to 419 , when the pure acid sublimes, and forms in crystals on the neck of the retort, and in the receiver, which should be kept well cooled. 

Diphenyl sulfide 304 Thiophenol (7 g) is added to a solution of sodium (1.2 g) in ethanol (7 ml), the alcohol is removed by heat, copper powder (Naturkupfer C) (0.2 g) and iodo-benzene (12.9 g) are added, and the whole is heated for 2.5 h in an oil-bath at 235-240° (bath-temperature). After cooling, the product is taken up in a little ethanol and acidified with dilute sulfuric acid, zinc dust is added, and the mixture is distilled in steam. Unchanged iodobenzene passes over and some diphenyl sulfide produced as by-product is reduced to thiophenol. After cooling, the residue in the distillation flask is filtered, the zinc-containing precipitate is filtered off and extracted with ether, and the extract is dried over calcium chloride and fractionated, giving diphenyl sulfide (6.1 g), b.p. 295°. 

Plating solutions for continuous strip, caHed electrogalvanizing, sheet, and wire are usuaHy simple zinc sulfate solutions, although chloride and mixed variations have found some use. A typical bath for strip may contain 350 g/L zinc sulfate heptahydrate and 30 g/L ammonium sulfate. Baths are operated at pH 3.0—4.5, 40—55°C, at currents of 1000—6000 A/m. Zinc thickness is often 0.3—4.3 am. A wide variety of additives have been used to produce some grain refinement, eg, dextrin, Hcorice, glucose, and gelatin. Wire plating, which may have 13—130 am zinc plate, has been plated in more acidic zinc sulfate... 

Vasilakopoulos D, Bouroushian M, Spyrellis N (2009) Electrocrystallisation of zinc from acidic sulphate baths A nucleation and crystal growth process. Electrochim Acta 54 2509-2514. doi 10.1016/j.electacta.2008.11.059... 

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