Nickel coatings corrosion

Kutznelnigg, Pitting, the Typical Corrosion of Nickel Coatings , Korrosion, 13, 64 (1960) Schmeken, H., Electrochemical Measurements on Corrosion of Zinc with Regard to Pitting Possibilities , Korrosion, 13, 65 (I960)... 

The application of the tin-nickel coating for out of doors service has been restricted by fear of pore corrosion and of physical damage, and by... 

The case is different again under micro-discontinuous (i.e. micro-cracked or micro-porous) chromium, on which a definite improvement in corrosion resistance can be achieved when copper is present under the nickel coating . 

A major advantage of the electroless nickel process is that deposition takes place at an almost uniform rate over surfaces of complex shape. Thus, electroless nickel can readily be applied to internal plating of tubes, valves, containers and other parts having deeply undercut surfaces where nickel coating by electrodeposition would be very difficult and costly. The resistance to corrosion of the coatings and their special mechanical properties also offer advantages in many instances where electrodeposited nickel could be applied without difficulty. 

Phillips and Timms [599] described a less general method. They converted germanium and silicon in alloys into hydrides and further into chlorides by contact with gold trichloride. They performed GC on a column packed with 13% of silicone 702 on Celite with the use of a gas-density balance for detection. Juvet and Fischer [600] developed a special reactor coupled directly to the chromatographic column, in which they fluorinated metals in alloys, carbides, oxides, sulphides and salts. In these samples, they determined quantitatively uranium, sulphur, selenium, technetium, tungsten, molybdenum, rhenium, silicon, boron, osmium, vanadium, iridium and platinum as fluorides. They performed the analysis on a PTFE column packed with 15% of Kel-F oil No. 10 on Chromosorb T. Prior to analysis the column was conditioned with fluorine and chlorine trifluoride in order to remove moisture and reactive organic compounds. The thermal conductivity detector was equipped with nickel-coated filaments resistant to corrosion with metal fluorides. Fig. 5.34 illustrates the analysis of tungsten, rhenium and osmium fluorides by this method. 

Corrosion properties of electroless nickel coatings with codeposited PTFE or silicon carbide (SiC) particles in H2SO4 and NaCl... 

The operating conditions are also more severe. As a rule, the temperature and pressure are higher (230 to 300°C, 03 to 13.10 Pa absolute). This results in greater corrosion problems, requiring the use of high-alloy or Inconel steel tubes, and nickel-coated distribution boxes, while the shell continues to be built of carbon steeL... 

As in other molding methods, these molds must be constructed from corrosion-resistant metals. Rusting and pitting can be avoided by plating the mold with nickel to athickness of 10-50 pm.1 1 The plate must be devoid of pinholes to enhance the durability of the nickel coating and produce high quality surface parts. 

Conventional potassium hydroxide electrolytic cells are made from carbon steel. Areas with high corrosion potential are frequently clad with nickel, plastic, or ceramic material. The cathode is constructed of steel coated with a catalyst. The anodes and cathodes of bipolar cells are usually made from nickel or nickel-coated steel. Diaphragms were originally made from asbestos reinforced with nickel nets. Because of the health hazards associated with the use of asbestos, ceramics and polymers are being considered as substitute materials. 

Nickel In not too corrosive environments (electronic devices, houseware, etc.), nickel coatings are often used on metals and alloys to prevent tarnishing or corrosion. The lifetime of the layer is proportional to its thickness. The main base metals protected by nickel are iron, zinc, aluminum (and its alloys), and copper. In combination with iron, zinc, and aluminum, nickel usually is cathodic. Therefore, to provide corrosion protection on these metals, the nickel layer must be dense and free of pores. 

For industrial use, nickel coatings are applied without chromium on top, and the coatings are most often thicker, usually 25-250 pm, and up to 500 pm for some applications. Such coatings are most suitable for environments that tend to cause general corrosion with reaction products of low solubility (environments without chlorides). However, it is also stated that nickel performs well in seawater provided that the flow rate is high. Furthermore, the experience with nickel in various alkalis, neutral and alkaline salts and organic chemicals is good. 

---