Salts corrosion from

Hot Corrosion. Hot corrosion is an accelerated form of oxidation that arises from the presence not only of an oxidizing gas, but also of a molten salt on the component surface. The molten salt interacts with the protective oxide so as to render the oxide nonprotective. Most commonly, hot corrosion is associated with the condensation of a thin molten film of sodium sulfate [7757-82-6], Na2S04, on superaHoys commonly used in components for gas turbines, particularly first-stage turbine blades and vanes. Other examples of hot corrosion have been identified in energy conversion systems, particularly coal gasifiers and direct coal combustors. In these cases the salt originates from alkali impurities in the coal which condense on the internal... 

Miscellaneous Derivatives. Fimehc acid is used as an intermediate in some pharmaceuticals and in aroma chemicals ethylene brassylate is a synthetic musk (114). Salts of the diacids have shown utUity as surfactants and as corrosion inhibitors. The alkaline, ammonium, or organoamine salts of glutaric acid (115) or C-5—C-16 diacids (116) are useflil as noncorrosive components for antifreeze formulations, as are methylene azelaic acid and its alkah metal salt (117). Salts derived from C-21 diacids are used primarily as surfactants and find apphcation in detergents, fabric softeners, metal working fluids, and lubricants (118). The salts of the unsaturated C-20 diacid also exhibit anticorrosion properties, and the sodium salts of the branched C-20 diacids have the abUity to complex heavy metals from dilute aqueous solutions (88). 

Evaluate potential for external corrosion from environmental factors such as chloride bearing insulation, chemical spills, sea mist, road salt, etc. 

Water from towns main supplies is usually suitable for the preparation of water-based cutting fluids. That from factory bore holes is also generally suitable, although occasionally it contains excessive amounts of corrosive salts. Water from rivers, canals and ponds usually contains undesirable contaminants, and should be tested before use. A good first test is to mix a small quantity of emulsion and allow it to stand for 24 hours in this time, no more than a trace of the oil should separate. If serious separation occurs, the water should be analyzed to indicate the sort of remedial treatment required. 

The salts content of soils may be markedly altered by man s activities. The effect of cathodic protection will be discussed later in this section. Fertiliser use, particularly the heavy doses used in lawn care, introduces many chemicals into the soil. Industrial wastes, salt brines from petroleum production, thawing salts on walks and roads, weed-killing salts at the base of metal structures, and many other situations could be cited as examples of alteration of the soil solution. In tidal areas or in soils near extensive salt deposits, depletion of fresh ground-water supplies has resulted in a flow of brackish or salty sea water into these soils, causing increased corrosion. 

Many details in building construction may permit rain water to enter and this may be retained in crevices in metal surfaces, or between a metallic and some other surface. Water may drip on to metal surfaces. These conditions, which can involve a greater risk of corrosion than exists where a metal is exposed to the normal action of the weather, are more severe when the water contains dissolved acids, alkalis or salts derived from the atmosphere or from materials with which the water comes into contact. Normal supply waters can also cause corrosion. 

A recent application of this type of fluid is assistance in the removal of ingested salt spray from jet aircraft compressors and the neutralisation of corrosive effects. Other types of water-displacing fluids are claimed to have fingerprint neutralising properties or to be suitable for use on electrical equipment. Some oil-type materials serve temporarily as engine lubricants and contain suitable inhibitors to combat the corrosive products of combustion encountered in gasoline engines. 

Where corrosion takes place, the origins of the metal oxides and salts formed from corroded boiler system metals should be traced in a systematic fashion to establish cause and effect and avoid misclassify-ing the fundamental waterside problem. Occasionally however, it is difficult to positively confirm the starting point of a corrosion problem because it is common for corrosion products to be transported from their point of origin and deposited elsewhere in the steam-water circuit, or alternatively to act as binders and contribute to fouling and contamination of the overall boiler plant system. 

The lower tube outlet temperature promotes higher rates of salt sublimation from vapor to a corrosive fouling solid. 

Pacification is a technique for removing organics and buffers from HPLC metal and Teflon surfaces and protecting them from salt corrosion with 6 N nitric acid (see Chapter 4). First, remove the HPLC column and replace it with a column bridge. Do not flush this wash into the mass spectrometer. Wash the system with water. Remove the column and replace it with a column blank. Flush with 6 N nitric acid for at least 30min, then overnight with water. Ensure the effluent pH is back to that of lab water. Replace the column and flush with mobile phase. This should be done at least once a month to clean check valves, line, and injectors. Under no circumstances should this wash be done with an HPLC column in place or into the mass spectrometer ... 

Due to its ability to withstand high pressure, its relative low cost, and inertness, stainless steel has become the standard material of columns and other chromatographic components. However, under certain circumstances, stainless steel has been shown to interact with the sample and the mobile phase [39]. The best known example is chloride salt corrosion of stainless steel. Data indicate that nearly all common eluents dissolve iron from stainless steel [39]. It appears that proteins also adsorb to stainless steel [39], The adsorption process is fast, whereas desorption is slow, a result which leads to variable protein recoveries. A number of manufacturers are offering alternatives to stainless components with Teflon -lined columns and Teflon frits. Titanium is being explored as an alternative to stainless steel. A cheaper and simpler procedure is to oxidize the surface of the stainless steel with 6N nitric acid. This procedure should be repeated about every 6 months. 

Metals are good conductors of electricity and if the environment with which they are in contact is also conductive, then corrosion will occur via an electrochemical process. Notice that, in every case, the corrosion of the metal occurs due to interaction with its environment. Therefore, for metallic corrosion to occur, the metal or alloy must be unstable in that particular environment. Thus, changing the environment of a metal can greatly affect its rate of corrosion in either direction. For example, wrought iron gates will last indefinitely in a clean urban environment however, those same gates placed near the coastline would rapidly corrode due to the effects of salt spray from the ocean. 

Use and exposure Tin is a soft, pliable, silvery-white metal. Tin is not easily oxidized and resists corrosion because it is protected by an oxide film. Tin resists corrosion from distilled sea and soft tap water and can be attacked by strong acids, alkalis, and acid salts. Tin foil was once a common wrapping material for foods and drugs, now replaced by the use of aluminum foil. Tin is used to coat cans of fruits and vegetables, processed foods, and industrial waste. - ... 

The results of the concurrent EIS measurement are consistent with what were found with Prohesion test results shown in Figure 28.23. The earlier failure of the coating system due to partial delamination at the interface resulted in severe corrosion on the U-shaped scribed panels. The concurrent EIS measurement reveals the importance of the lateral diffusion of salts initiating from the damaged interface. This situation could be explained by Figure 28.26, which schematically depicts the pathways of electrolyte to the sampling site of EIS measurement. 

There are several types of nebulisers, for example the concentric quartz system (Fig. 3.9) or cross-flow system (Fig. 3.10) the tips of which are made from synthetic material or precious stones. The first system can be subject to blockage with solutions containing as little as 0.1% of dissolved salts due to its small capillary inlet. The second system is less fragile and is resistant to corrosion from solutions containing hydrofluoric acid. 

Amino-4-trifluorocumarin and its amino acid and peptide salts are used for fluorescent labeling of amino acids and peptides in biological studies (80JOC2283). Fluorine-containing triazoles are used to protect metals and alloys from atmospheric and salt corrosion (Scheme 1). 

Another source of aggressive species is sodium chloride. The cars used to transport rock salt suffer from advanced corrosion attack and last for approximately only 3 years (Coating Industry Expert, Private Communication, June 2000). The high cost of rehabilitation of salt carrying cars created a trend toward using unlined, covered hopper cars previously utilized to transport grain for rock salt service. When corrosion becomes considerable, the cars are scrapped. As such a process cannot continue indefinitely, more and more rock salt is expected to be hauled by trucks and barges, as the revenue seems to be insufficient to justify the corrosion-related replacement/rehabilitation costs. 

In the transportation industries, external corrosion of tanker trucks and railcar-mounted tanks is a common problem. Both general and pitting corrosion from the atmosphere and splash water from the roadway or rail bed can affect the tank s structured integrity and tightness. This problem is particularly severe in areas of the country with chloride sources such as road salt or airborne marine atmosphere and severe airborne industrial pollution. 

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