Plating bath alkaline

Pt—Q—Salt, [Pt(NH3)2(HP04)] and [Pt(OH)3] (259,260). Chloride-based baths have been superseded by P-Salt-based baths, which are more stable and relatively easily prepared. Q-Salt baths offer even greater stabiUty and produce hard, bright films of low porosity. Plating under alkaline conditions employs salts of [Pt(OH3)] . These baths are easily regenerated but have low stabiUty. Platinum films have uses in the electronics industry for circuit repair, mask repair, platinum siUcide production, and interconnection fabrication (94). Vapor deposition of volatile platinum compounds such as [Pt(hfacac)2] and... 

Concentrated waste solutions are obtained from spent metal plating baths and etchants. However, the majority of metal wastes are soflds or sludges obtained from the hydrolysis of metal-bearing solutions and industrial process effluents. Most of these water-insoluble wastes are composed of hydroxides or basic salts of the contained metals. Eor processing by hydrometallurgical routes the materials must be brought into solution usually by acid or ammoniacal or alkaline digestion. 

Electroplating. Most silver-plating baths employ alkaline solutions of silver cyanide. The silver cyanide complexes that are obtained in a very low concentration of free silver ion in solution produce a much firmer deposit of silver during electroplating than solutions that contain higher concentrations. An excess of cyanide beyond that needed to form the Ag(CN)2 complex is employed to control the concentration. The silver is added to the solution either directly as silver cyanide or by oxidation of a silver-rod electrode. Plating baths frequently contain 40—140 g/L of silver cyanide... 

The metal-plating baths used are acidic copper sulfate and alkaline silver cyanide. Acid contamination ia the alkaline silver cyanide bath will release extremely poisonous hydrogen cyanide gas. Eor this reason, the two plating setups should be isolated from each other. Both plating baths should be weU... 

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. 

Plating Bath Purification. Purification, often needed once a plating bath is made, is used periodically to maintain the plating solutions. Alkaline ziac plating solutions are sensitive to a few mg/L of heavy-metal contamination, which can be precipitated usiag sodium sulfide and filtered out. 

The use of alkaline tin plating baths continues to stimulate research into the anodic dissolution of tin into sodium hydroxide solution . It has been shown that in the prepassive region, tin (11) oxide and hydroxide exist on the surface of the metal. At the onset of passivity, these change to tin (IV) oxide and hydroxide and the extent of surface hydration changes rapidly. ... 

Fig. 13.2 Linear plats of the effect of current density an the porasity, expressed as p.p.m. Cu, for three different gald-plating baths. The numbers next ta each point show the actual average thickness Orm) for each test. Bath A was a proprietary alkaline cyanide bath using silver as a brightener. Bath D was an acid gold bath containing cobalt and an ethylenediamine tetraacetic...

A method to circumvent the problem of chalcogen excess in the solid is to employ low oxidation state precursors in solution, so that the above collateral reactions will not be in favor thermodynamically. Complexation strategies have been used for this purpose [1, 2]. The most established procedure utilizes thiosulfate or selenosulfate ions in aqueous alkaline solutions, as sulfur and selenium precursors, respectively (there is no analogue telluro-complex). The mechanism of deposition in such solutions has been demonstrated primarily from the viewpoint of chemical rather than electrochemical processes (see Sect. 3.3.1). Facts about the (electro)chemistry of thiosulfate will be addressed in following sections for sulfide compounds (mainly CdS). Well documented is the specific redox and solution chemistry involved in the formulation of selenosulfate plating baths and related deposition results [11, 12]. It is convenient to consider some elements of this chemistry in the present section. 

The major waste sources during normal nickel-chromium plating operations are alkaline cleaners, acid cleaners, plating baths, posttreatment baths, and auxiliary operation units. 

The greatest tonnage decrease in cyanide plating has occurred lor zinc plating. As of this writing, less than one-third of all zinc is plated Irom cyanide baths. The remainder is plated from alkaline noncyunidc. zinc potassium chloride, and zinc ammonium chloride balhs. 

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. 

Let us try and understand this. As stated, Ni plating baths (as well as other acidic baths such as those of Cu and Zn) show poor throwing power. This is so because their CE values are =100% at the low and high current density values, and so macroscopic irregularities on a cathode will lead to nonuniform deposits. Alkaline baths, on the other hand, have a better macro throwing power. This is the case since, in order to remain in solution in such a bath, the metal ion, to be deposited, must be present in complex ions. These ions, in turn, encounter high concentration polarization. Also, in most complex baths the deposition potentials are amenable to hydrogen evolution, which competes with metal deposition such that CE falls as current density is increased. That kind of behavior results in a more uniform deposit on... 

Use Textiles (dyeing and printing), alkaline tin-plating bath. 

---