Electroplating cathode corrosion

Electroplating passive alloys Another application of strike baths reverses the case illustrated in the previous example. The strike is used to promote a small amount of cathode corrosion. When the passivation potential of a substrate lies below the cathode potential of a plating bath, deposition occurs onto the passive oxide film, and the coating is non-adherent. Stainless steel plated with nickel in normal baths retains its passive film and the coating is easily peeled off. A special strike bath is used with a low concentration of nickel and a high current density, so that diffusion polarisation (transport overpotential) depresses the potential into the active region. The bath has a much lower pH than normal. The low pH raises the substrate passivation potential E pa, which theoretically follows a relation... 

Of related interest, Ramachandran and coworkers have reported a range of papers on the influence of mass transport [154-156], including diffusion-reaction problems [157]. Further work was reported on a variety of current distribution problems [158-161] in the early 1990s, with a comparison of the FEM and the BEM efficiency reported by Matlosz and coworkers [162]. A two-dimensional study of coplanar auxiliary electrodes was reported by Mehdizadeh and coworkers [163] and was used to assess the influence of the electrode configuration on uniform growth over the cathode electrode. Electroplating and corrosion protection in industrial cell configurations have also been addressed by Druesne and coworkers [164,165]. 

Indium chemicals and electroplated metal deposits ate replacing mercury (qv) in the manufacture of alkaline batteries (qv). Indium, like mercury, functions to reduce outgassing within the battery and promotes the uniform corrosion of the anode and cathode while the battery is under electrical load. Indium inorganic chemicals also find use as catalysts in various chemical processes. 

The metallic substrate, clean and rinsed, is immersed wet in the plating cell. The base metals which are usually plated present an essentially metallic surface to the electrolyte, and the slight corrosive action of the rinse water in preventing the formation of any substantial oxide film is important. A critical balance of corrosion processes in the initial stages is vital to successful electroplating, and for this reason there is a severe restriction on the composition of the electroplating bath which may be used for a particular substrate. This will be discussed later. The substrate is made the cathode of the cell it may be immersed without applied potential ( dead entry) or may be already part of a circuit which is completed as soon as the substrate touches the electrolyte ( live entry). Live entry reduces the tendency for the plating electrolyte to corrode the substrate in the period before the surface... 

Rating the results of corrosion tests on electroplated coatings cathodic to the substrate Guidance on stationary outdoor exposure corrosion tests... 

Electrodeposited chromium coatings. Electrolytic corrosion testing Coatings cathodic to the substrate-rating of electroplated test specimens subjected to corrosion tests... 

Closely related to electrorefining is electroplating, the coating of one metal on the surface of another using electrolysis. For example, steel automobile bumpers are plated with chromium to protect them from corrosion, and silver-plating is commonly used to make items of fine table service. The object to be plated is carefully cleaned and then set up as the cathode of an electrolytic cell that contains a solution of ions of the metal to be deposited. 

Electroplating of magnesium for purposes of surface finishing, cathodic protection against corrosion, etc. 

A similar technique is used to perform electroplating. This technique allows a thin coat of metal to be plated on the surface of another to improve appearance, resist corrosion, or, in the case of jewelry, save money on precious metals. In this technique, the metal to be plated is made a cathode in an electrolytic cell with a molten metal or metallic salts. 

Sacrificial anode — is a piece of metal used as an anode in electrochemical processes where it is intended to be dissolved during the process. In -+ corrosion protection it is a piece of a non-noble metal or metal alloy (e.g., magnesium, aluminum, zinc) attached to the metal to be protected. Because of their relative -+ electrode potentials the latter is established as the -+ cathode und thus immune to corrosion. In -+ electroplating the metal used as anode may serve as a source for replenishing the electrolyte which is consumed by cathodic deposition. The sodium-lead alloy anode used in the electrochemical production of tetraethyl lead may also be considered as a sacrificial anode. 

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. 

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