Electroplating solution resistance

Turbine blades of jet engines are coated with a protective layer of platinum aluminide to impart high temperature corrosion resistance. Platinum is electroplated onto the blade using P-salt or Q-salt electroplating solutions (28,29). The platinum is then diffusion-treated with aluminum vapor to form platinum aluminide. Standards for the inspection and maintenance of turbine blades have become more stringent. Blades are therefore being recoated several times during their lifetime. 

Electroplated CoPt [96, 97] and CoSnP [98] have also been suggested for thin-film media. Both alloys are reported to have good corrosion resistance. A plated 2.25" diameter disk uses Zn in the plating solution to control coercivity [24] details of the process are not given. 

Cadmium oxide is used in storage battery electrodes. Its solution, mixed with sodium cyanide, is used in electroplating baths. Other uses are in PVC heat stabilizers as an additive to nitrile rubbers and plastics to improve heat resistance and in ceramic glazes and phosphors. 

Metal Coatings. Tellurium chlorides, as well as tellurium dioxide in hydrochloric acid solution, impart permanent and attractive black antique finish to silverware, aluminum, and brass. Anodized aluminum is colored dark gold by tellurium electro deposition. A solution containing sodium tellurate and copper ions forms a black or blue-black coating on ferrous and nonferrous metals and alloys. Addition of sodium tellurite improves the corrosion resistance of electroplated nickel. Tellurium diethyldithiocarbamate is an additive in bright copper electroplating (see Electroplating). 

Extensive work has been devoted to aluminum electroplating in nonaqueous systems. Choosing appropriate bath compositions enables aluminum to be deposited at high efficiency and purity from nonaqueous electrolyte solutions. Comprehensive reviews on this matter have appeared recently in the literature [123,455], This work has led to the development of a number of commercial processes for nonaqueous electroplating of aluminum. The quality of the electroplated aluminum is very similar to that of cast metal. For instance, electrodeposited aluminum can be further anodized in order to obtain hard, corrosion resistive, electrically insulating surfaces. It is also possible to electroplate A1 on a wide variety of metal surfaces, including active metals (e.g., Mg, Al), nonactive metals, and steel. 

Fluoroboric acid is produced commercially by the reaction of 70% hydrofluoric acid with boric acid. Fluoroborate solutions must be treated like hydrofluoric acid and handled in corrosion resistant equipment consisting of polyethylene, polypropylene, or neoprene-type rubber. The major use of fluoroboric acid is as an intermediate in the preparation of fluoroborate salts. It is also used in electroplating aluminum and in metal cleaning operations. 

Cells that use electricity can be used to deposit metals onto surfaces in a process known as electroplating. Electroplating can be used to make jewelry, mirrors, and shiny surfaces resistant to abrasion, tarnishing and corrosion. Metal salts in a solution called the plating bath are reduced to metal at the cathode of the electrochemical cell. 

This raises some important possibilities, which have not escaped the attention of the electroplating community. For example, while metal deposition is conducted in fairly concentrated solutions of the metal being plated, and at current densities well below the mass-transport limit, additives acting as inhibitors for metal deposition are often introduced at concentrations that are several orders of magnitude lower, to ensure that their supply to the surface will be mass-transport limited. In this way, the tendency for increased rate of metal deposition on certain features on the surface, such as protrusions, will be moderated by the faster diffusion of the inhibitor to the very same areas. Furthermore, if deposition occurs in the region of mixed control, which is usually the case, it must be remembered that the relevant roughness factor is quite different for the charge-transfer and the mass-transport processes, and this may well be a function of current density, since the Faradaic resistance is inherently potential dependent. 

---