Acid copper bath

One of the most important processes in metallurgy is copper deposition. Galvanoplastic conditions imply a copper-acid bath over a pre-multilayer of copper from a copper-alkaline cyanide bath. The study of copper underpotential deposition on platinum is of special interest in electrochemistry in spite of its catalytic properties being rather poor with respect to fuel cell applications [101-104]. The mechanism of copper deposition and the presence of copper(I) ions as an intermediate have been... 

A high percentage of the ammonia can be recovered from the spin-bath effluent and by washing prior to the final acid bath. During acidification, remaining ammonia is converted to the sulfate and recovered when the acid wash Hquor is treated with carbonate to recover the copper. Ammonia residuals in the large volumes of washwater can only be removed by distillation. Overall about 75—80% of the ammonia requited to dissolve the cellulose can be recovered. 

The pH effect in chelation is utilized to Hberate metals from thein chelates that have participated in another stage of a process, so that the metal or chelant or both can be separately recovered. Hydrogen ion at low pH displaces copper, eg, which is recovered from the acid bath by electrolysis while the hydrogen form of the chelant is recycled (43). Precipitation of the displaced metal by anions such as oxalate as the pH is lowered (Fig. 4) is utilized in separations of rare earths. Metals can also be displaced as insoluble salts or hydroxides in high pH domains where the pM that can be maintained by the chelate is less than that allowed by the insoluble species (Fig. 3). 

Copper-plating bath compositions of various types have been used. A typical bath formulation consists of 200 g copper sulfate crystals, 30 mL cone, sulfuric acid, 2 mL phenylsulfonic acid, and 1000 mL distUled water. A pure copper anode may be used a copper anode containing a trace of phosphoms reduces sludge accumulation in the plating bath. 

The siHcone impression materials are very compatible with gypsum products, give casts having exceUent hard surfaces, and can be electroplated with either copper or silver. However, the acidic copper sulfate bath gives more acceptable results. 

Phthalocyanine Dyes. These days are synthesized as the metal complex on the textile fiber from, eg, phthalonittile and metal salts. A print paste typicaUy contains phthalonittile dissolved in a suitable solvent and nickel or copper salts. During a heat or steam fixation of 3—5 min, the dye is formed. The color range is restricted to blue and green shades and can be influenced to some extent by the choice of metal salt. A hot acid bath during afterscouting completes the process. 

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. 

Whenever insoluble anodes are used, the pH of the plating solution decreases along with the metal ion concentration. In some plating baths, a portion of the anodes is replaced with insoluble anodes in order to prevent metal ion buildup or to reduce metal ion concentration. Lead anodes have been used in acid copper sulfate baths, and steel anodes have been used in alkaline plating baths. 

When plating any substrate less noble than copper, only a few mg/L of dissolved copper in the acid baths can adversely affect adhesion. Coatings can be too thin to be visible, yet contribute to poor adhesion. Small additions of thiourea have been used to prevent copper immersion, but it acts as a potent inhibitor, and work should be re-electrocleaned after the acid. Work should be exposed to the mildest acid treatments possible. Over-etching should be avoided. 

Acid Copper. Bath compositions are shown in Table 8. The acid sulfate bath is by far the most widely used copper plating bath, both for plating and for electroforming and electrowinning. The fiuoborate baths have been Htde used in spite of the high current densities possible. Additional information can be found in the Hterature (98,99). 

Removal of deposits and corrosion products from internal surfaces revealed irregular metal loss. Additionally, surfaces in wasted areas showed patches of elemental copper (later confirmed by energy-dispersive spectroscopy) (Fig. 13.12). These denickelified areas were confined to regions showing metal loss. Microscopic analysis confirmed that dealloying, not just redeposition of copper onto the cupronickel from the acid bath used during deposit removal, had occurred. 

On ferrous metals immersion deposition in the copper sulphate bath produces non-adherent deposits, and a cyanide copper undercoat is therefore normally used. Where the use of a cyanide strike cannot be tolerated, an electroplated or immersion nickel deposit has been used . Additions of surface-active agents, often preceded by a sulphuric acid pickle containing the same compound, form the basis of recent methods for plating from a copper sulphate bath directly on to steel ". 

In all of the four acidic baths on the seeded ABS surfaces copper crystals were obtained. However, conductive copper layers were obtained only from the H2S04, H3PO4, and CH3COOH baths, but not from a HNO3 containing bath (99). 

The electrical surface resistance of the copper layers from different acidic baths after different depositions times is shown in Table 8.10. 

A large number of commercially important plating processes occur from complex ion baths in which the metal is a constituent of an anionic complex, e.g. copper, zinc, cadmium, silver and gold are all commonly plated from cyanide baths, and tin plates from a stannate bath in which [SnIV(OH)6]2 is present. Chromium is commonly plated from a chromate bath although in this case the background medium is acid rather than alkaline. Thus the mechanism of deposition of metals from anionic complexes is of particular interest. It will be instructive to comment on two situations, one occurring in alkaline baths, the other in acidic baths. 

Price [67] has reviewed the application of atomic absorption to a variety of plating solutions. Iron, lead and zinc are reported as the main impurities in cyanide copper-plating baths which may contain up to 200gl 1 of copper sulphate a twenty-fold dilution of the sample for trace determination is recommended. Nickel baths may contain 60 gl 1 of nickel and it may be necessary to monitor copper, zinc, iron, lead, chromium, calcium and magnesium at the ppm level. The standard addition method is probably best for such an application. Zinc has been extracted with trioctylamine-hydrochloride when present in the range 0.03—10pgml-1 in a nickel plating solution [68]. The zinc was re-extracted back into 1M nitric acid for... 

Other factors, of course, come into play in an actual plating bath. For example, plating from an acid bath takes place at around 0.3 V, NHE, whereas in a cyanide bath, copper is deposited at a much more negative potential. The former occurs at a positive rational potential, while the latter occurs at a negative rational potential. This affects the choice of additives and their adsorption characteristics. Also, the values of ( ) and d( ) /d( ) may be different in the two cases. The foregoing example is not intended to be a quantitative interpretation of the benefits of cyanide baths, but rather an illustration of how considerations of a rather fundamental nature can assist in solving applied problems. 

Consider the electroplating of copper, an established industrial process. It is well known to the expert in the field that fast plating of thick layers can be achieved in a so-called acid bath, which consists of CuSO in H SO (with some additives, which need not concern us at this point). If, on the other hand, one wishes to obtain a smooth and uniform deposit on an intricately shaped body, an alkaline cyanide bath is better. The alkaline bath consists of copper ions in an excess of KCN (kept at high pH, to prevent the formation of volatile and highly poisonous HCN). In this bath copper exists as the negatively charged complex ion [Cu(CN) ]. Now, we recall that to achieve uniform current... 

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