Passivity copper

An attempt was made to correct the copper corrosion problem by different types of fuel treatments (25). JP-5 samples were subjected to clay or silica gel filtration, or treatment with activated charcoal to remove the corrosive compounds. None of these treatments was successful. Samples were also treated with barium nitrate (to precipitate out sulfonates), sodium hydroxide (to extract mercaptans), and air bubbling to oxidize the corrosive compounds. These chemical treatments also were unsuccessful. However, JP-5 fuel (which failed the copper corrosion test) passed if benzotriazole, sometimes used to passivate copper surfaces, was added to the fuel in low concentrations (2 ppm) using FSII as a solvent. This technique is effective for reducing jet fuel attack on copper-nickel pipes used aboard aircraft carriers (26). 

Fluorine [Matheson] is pretreated to remove HF and SiF4 impurities and is handled in a passivated copper vacuum line designed for fluorine use. Approximately I g of NaF and four stainless steel balls are placed in a 200-mL high-pressure stainless steel Hoke cylinder [Koch Associates] and a high-pressure stainless steel needle valve [Koch Associates] is attached to the cylinder. The cylinder is evacuated on the copper line and cooled to — 196°. A total of 50 mmol of fluorine is carefully condensed into the cylinder. The cylinder valve is closed. The cylinder is allowed to warm slowly to ambient temperature in an empty, precooled Dewar flask (- 196°). It is removed from the vacuum line, shaken to loosen and spread the NaF, placed on its side for 2 days, and shaken periodically. The cylinder is reattached to the vacuum line, and the space between the valves (interspace) is evacuated. A stainless steel infrared cell (8.0 cm) with AgCl windows is attached to the vacuum line and evacuated. A high-pressure infrared spectrum (2 atm) indicates that traces of CF4 are present, but HF and SiF4 are absent. ... 

Reactive MD Modeling of Cl Interaction with Passivated Copper Surfaces... 

FIGURE 7.10 Side view models showing the system and protocol adopted for the reactive molecular dynamics simulation of the interaction of chloride ions with passivated copper surfaces. Left Cu(l 11) slab covered by CU2O thin films with O-deficient (top) and O-enriched (bottom) terminations after thermal relaxation at 300 K. Middle filling the gap with 20 M Cl" aqueous solution (pH 7). Right complete system after relaxation for 250 ps at 300 K showing preferential interaction of the chlorides ions with the O-deficient surface. Periodic boundary conditions apply along the x-, y-, and z-directions.Adapted from Jeon et al. [135], 1229, with permission from the Ameriean Chemical Society. 

W.Th., Kok, H.B. Hanekamp, P. Bos and R.W. Frei, Amperometric detection of amino acids with a passivated copper electrode. Anal Chim. Acta, 1983, 142, 31- 5. 

Figure 19.6a shows a comparison of the calculated steady-state thickness of the barrier layer with the experimental results as a function of applied potential, while the steady-state current for passive copper in sulfide-containing sodium chloride solution calculated from... 

For example,copper has relatively good corrosion resistance under non-oxidizing conditions. It can be alloyed with zinc to yield a stronger material (brass), but with lowered corrosion resistance. Flowever, by alloying copper with a passivating metal such as nickel, both mechanical and corrosion properties are improved. Another important alloy is steel, which is an alloy between iron (>50%) and other alloying elements such as carbon. 

Fluorine can be handled using a variety of materials (100—103). Table 4 shows the corrosion rates of some of these as a function of temperature. System cleanliness and passivation ate critical to success. Materials such as nickel, Monel, aluminum, magnesium, copper, brass, stainless steel, and carbon steel ate commonly used. Mote information is available in the Hterature (20,104). 

Monel and nickel are the preferred materials of constmction for cylinders and deHvery systems however, copper, brass, steel, and stainless steel can be used at room temperature, providing that these metals are cleaned, dried, and passivated with a fluoride film prior to use. Studies have shown that fluorine passivation of stainless steel and subsequent formation of an iron fluoride layer prior to WF exposure prevents reaction between the WF and the stainless steel surface (23). 

Anodes. Lead—antimony (6—10 wt %) alloys containing 0.5—1.0 wt % arsenic have been used widely as anodes in copper, nickel, and chromium electrowinning and metal plating processes. Lead—antimony anodes have high strength and develop a corrosion-resistant protective layer of lead dioxide during use. Lead—antimony anodes are resistant to passivation when the current is frequendy intermpted. 

Copper-containing lead alloys undergo less corrosion in sulfuric acid or sulfate solutions than pure lead or other lead alloys. The uniformly dispersed copper particles give rise to local cells in which lead forms the anode and copper forms the cathode. Through this anodic corrosion of the lead, an insoluble film of lead sulfate forms on the surface of the lead, passivating it and preventing further corrosion. The film, if damaged, rapidly reforms. 

Silver reduces the oxygen evolution potential at the anode, which reduces the rate of corrosion and decreases lead contamination of the cathode. Lead—antimony—silver alloy anodes are used for the production of thin copper foil for use in electronics. Lead—silver (2 wt %), lead—silver (1 wt %)—tin (1 wt %), and lead—antimony (6 wt %)—silver (1—2 wt %) alloys ate used as anodes in cathodic protection of steel pipes and stmctures in fresh, brackish, or seawater. The lead dioxide layer is not only conductive, but also resists decomposition in chloride environments. Silver-free alloys rapidly become passivated and scale badly in seawater. Silver is also added to the positive grids of lead—acid batteries in small amounts (0.005—0.05 wt %) to reduce the rate of corrosion. 

An especially insidious type of corrosion is localized corrosion (1—3,5) which occurs at distinct sites on the surface of a metal while the remainder of the metal is either not attacked or attacked much more slowly. Localized corrosion is usually seen on metals that are passivated, ie, protected from corrosion by oxide films, and occurs as a result of the breakdown of the oxide film. Generally the oxide film breakdown requires the presence of an aggressive anion, the most common of which is chloride. Localized corrosion can cause considerable damage to a metal stmcture without the metal exhibiting any appreciable loss in weight. Localized corrosion occurs on a number of technologically important materials such as stainless steels, nickel-base alloys, aluminum, titanium, and copper (see Aluminumand ALUMINUM ALLOYS Nickel AND nickel alloys Steel and Titaniumand titanium alloys). 

Electroforrning is the production or reproduction of articles by electro deposition upon a mandrel or mold that is subsequendy separated from the deposit. The separated electro deposit becomes the manufactured article. Of all the metals, copper and nickel are most widely used in electroforming. Mandrels are of two types permanent or expendable. Permanent mandrels are treated in a variety of ways to passivate the surface so that the deposit has very Httie or no adhesion to the mandrel, and separation is easily accompHshed without damaging the mandrel. Expendable mandrels are used where the shape of the electroform would prohibit removal of the mandrel without damage. Low melting alloys, metals that can be chemically dissolved without attack on the electroform, plastics that can be dissolved in solvents, ate typical examples. 

Yellow brass Admiralty brass Aluminum bronze Red brass Copper Silicon bronze 70-30 cupronickel Nickel (passive)... 

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