Corrosion silver

Use Urea and melamine resins, polyacetal resins, phenolic resins, ethylene glycol, pentaerythritol, hexamethylenetetramine, fertilizer, disinfectant, biocide, embalming fluids, preservative, reducing agent as in recovery of gold and silver, corrosion inhibitor in oil wells, durable-press treatment of textile fabrics, industrial sterilant, treatment of grain smut, foam insulation, particle board, plywood, a versatile chemical intermediate. 

Some sulfur compounds can also have a corroding action on the various metals of the engine system, varying according to the chemical type of sulfur compound present. Fuel corrosivity is assessed by its action on copper and is controlled by the copper strip test (ASTM D-130, IP 154), which specifies that not more than a slight stain shall be observed when the polished strip is immersed in fuel heated for 2 h in a bomb at lOO C (212°F). This particular method is not always capable of reflecting fuel corrosivity toward other fuel system metals. For example, service experience with corrosion of silver components in certain engine fuel systems led to the development of a silver corrosion test (IP 227). The mercaptan sulfur content (ASTM D-1219, ASTM D-3227, IP 104, IP 342) of jet fuels is limited because of objectionable odor, adverse effect on certain fuel system elastomers, and... 

Manufacturing resins, ethylene glycol, and other chemicals. Fertilizer, disinfectant, embalming fluids, preservatives, industrial sterilants. Particle board, plywood, and foam insulation. Reducing agent in the recovery of gold and silver. Corrosion inhibitor in oil wells. Durable-press treatment for fabrics. A versatile chemical intermediate. 

By taking advantage of LTMGC s rapid temperature programming and cool down time, it is also possible to measure individual sulfur species, analogous to ASTM D 5623. Conditions have also been developed using the same analytical apparatus to detect the major elemental sulfur allotropes (Sj, S3, S, S7, and Ss) in gasoline at levels that can cause silver corrosion. 

Formation of black silver sulfide is visible on silver wool when 10 mg of silver wool was placed in about 1.5 g of the reference gasoline containing 2.6 ppm elemental sulfur and heated as described above. No visible formation of silver sulfide occurred with silver wool in the reference fuel prior to the addition of elemental sulfur. This is illustrated in Fig. 5, where A represents silver wool heated in the reference fuel versus B, which represents silver wool heated in the reference fuel that contained 2.6 ppm elemental sulfur. Even though the pictures in Fig. 5 were obtained under magnification, the silver corrosion was readily apparent to visual inspection without magnification. The surface of the silver wool became even darker when exposed to higher levels of elemental sulfur as one would expect, and it appeared that the entire surface became coated at about the 10-15 ppm level. Further experimentation was not pursued in this area, as it was demonstrated that the more qualitative silver wool test and quantitative GC analysis appear to be correlated. One could expect to find an optimum ratio between the amount of sample and silver wool to maximize the visible contrast that is observed, however. 

It is apparent that elemental sulfur species that are suspected to cause silver corrosion can be detected at the appropriate levels that contribute to the fuel gauge issue. Of course, the ability to make a rapid total sulfur measurement is extremely useful in many circumstances. For instance, in a process plant upset, speciation of sulfur may be desirable only when a total sulfur specification is exceeded. In those circumstances, it is desirable to be able to simply change operating conditions back and forth between total sulfur and speciated sulfur analysis, and this is achievable using LTMGC. 

An aging atudy has heen completed which evaluated a number of polymeric materials for potential use as 1) protective coatings for back surfaces of mirrors and 2) solar hellostat edge seals. These investigations were conducted in an artificial weathering chamber that accelerated thermal cycling. We observed the primary mirror failure mode to be silver corrosion resulting from moisture exposure. 

One of the most widely investigated effects is the atmospheric sulfidation of silver used in electronics. The mechanisms of silver corrosion in polluted dry and humid atmospheres have been studied [28]. For example, the reaction of silver and H2S in air can occur directly... 

Finally, other tests to control jet fuel corrosivity towards certain metals (copper and silver) are used in aviation. The corrosion test known as the copper strip (NF M 07-015) is conducted by immersion in a thermostatic bath at 100°C, under 7 bar pressure for two hours. The coloration should not exceed level 1 (light yellow) on a scale of reference. There is also the silver strip corrosion test (IP 227) required by British specifications (e.g., Rolls Royce) in conjunction with the use of special materials. The value obtained should be less than 1 after immersion at 50°C for four hours. 

Deteriora.tlon. Apart from physical damage that can result from carelessness, abuse, and vandaUsm, the main problem with metal objects Hes in thek vulnerabihty to corrosion (see Corrosion and corrosion control) (127,128). The degree of corrosion depends on the nature and age of the object. Corrosion can range from a light tarnish, which may be aesthetically disfiguring on a poHshed silver or brass artifact, to total mineralization, a condition not uncommon for archaeological material. 

Another ak pollutant that can have very serious effects is hydrogen sulfide, which is largely responsible for the tarnishing of silver, but also has played a destmctive role in the discoloration of the natural patinas on ancient bronzes through the formation of copper sulfide. Moreover, a special vulnerabihty is created when two metals are in contact. The electromotive force can result in an accelerated corrosion, eg, in bronzes having kon mounting pins. 

Bronze disease necessitates immediate action to halt the process and remove the cause. For a long time, stabilization was sought by removal of the cuprous chloride by immersing the object in a solution of sodium sesquicarbonate. This process was, however, extremely time-consuming, frequentiy unsuccesshil, and often the cause of unpleasant discolorations of the patina. Objects affected by bronze disease are mostiy treated by immersion in, or surface appHcation of, 1 H-henzotriazole [95-14-7] C H N, a corrosion inhibitor for copper. A localized treatment is the excavation of cuprous chloride from the affected area until bare metal is obtained, followed by appHcation of moist, freshly precipitated silver oxide which serves to stabilize the chloride by formation of silver chloride. Subsequent storage in very dry conditions is generally recommended to prevent recurrence. 

These salts are corrosive and are to be considered toxic because of the presence of Ag+ ions. The American Conference of Government Industrial Hygienists (ACGIH) (1992—1993) has adopted TWA values of 0.01 mg/m for silver metal and 0.01 mg/m for soluble silver salts. TWA for fluorides as F ions is 2.5 mg/m. The MSDS should be consulted prior to use. Skin contact and inhalation should be avoided. 

Aqueous formaldehyde is corrosive to carbon steel, but formaldehyde in the vapor phase is not. AH parts of the manufacturing equipment exposed to hot formaldehyde solutions must be a corrosion-resistant alloy such as type-316 stainless steel. Theoretically, the reactor and upstream equipment can be carbon steel, but in practice alloys are required in this part of the plant to protect the sensitive silver catalyst from metal contamination. 

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. 

Lead—silver alloys are used extensively as soft solders these contain 1—6 wt % silver. Lead—silver solders have a narrower free2ing range and higher melting point (304°C) than conventional solders. Solders containing 2.5 wt % silver or less are used either as binary alloys or combined with 0.5—2 wt % tin. Lead—silver solders have excellent corrosion resistance. The composition of lead—silver solders is Hsted in ASTM B32-93 (solder alloys) (7). 

Under severe conditions and at high temperatures, noble metal films may fail by oxidation of the substrate base metal through pores in the film. Improved life may be achieved by first imposing a harder noble metal film, eg, rhodium or platinum—iridium, on the substrate metal. For maximum adhesion, the metal of the intermediate film should ahoy both with the substrate metal and the soft noble-metal lubricating film. This sometimes requires more than one intermediate layer. For example, silver does not ahoy to steel and tends to lack adhesion. A flash of hard nickel bonds weh to the steel but the nickel tends to oxidize and should be coated with rhodium before applying shver of 1—5 p.m thickness. This triplex film then provides better adhesion and gready increased corrosion protection. 

Copper and nickel can be alloyed with zinc to form nickel silvers. Nickel silvers are ductile, easily formed and machined, have good corrosion resistance, can be worked to provide a range of mechanical properties, and have an attractive white color. These alloys are used for ornamental purposes, as sHverplated and uncoated tableware and flatware in the electrical iadustry as contacts, connections, and springs and as many formed and machined parts (see Electrical connectors). 

Zinc phosphate, Zn2(P0 2> forms the basis of a group of dental cements. Chromium and zinc phosphates are utilized in some metal-treating appHcations to provide corrosion protection and improved paint adhesion. Cobalt(II) phosphate octahydrate [10294-50-5] Co2(P0 2 8H20, is a lavender-colored substance used as a pigment in certain paints and ceramics. Copper phosphates exhibit bioactivity and are used as insecticides and fungicides. Zinc, lead, and silver phosphates are utilized in the production of specialty glasses. The phosphate salts of heavy metals such as Pb, Cr, and Cu, are extremely water insoluble. 

Copper and tin phosphides are used as deoxidants in the production of the respective metals, to increase the tensile strength and corrosion resistance in phosphor bronze [12767-50-9] and as components of brazing solders (see Solders and brazing alloys). Phosphor bronze is an alloy of copper and 1.25—11 wt % tin. As tin may be completely oxidized in a copper alloy in the form of stannic oxide, 0.03—0.35 wt % phosphoms is added to deoxidize the alloy. Phosphor copper [12643-19-5] is prepared by the addition of phosphoms to molten copper. Phosphor tin [66579-64-4] 2.5—3 wt % P, is made for the deoxidation of bronzes and German silver. 

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