Liquid media corrosion

Because sodium, which is liquid between about 100°C and 881°C, has excellent properties as a heat-transfer medium, with a viscosity comparable with that of water and superior heat conductivity , much attention has been paid to liquid sodium corrosion testing of metal and alloys. Indeed, ASTM have issued a Standard Practice which can be used for determination... 

As previously indicated, many microorganisms produce EPS or slime, and several researchers have investigated the role of EPS in corrosion [86-88]. EPS consist of polysaccharides and proteins, plus significant amounts of nucleic acids, (phospho) lipids and humic substances [89-91]. The final composition of the EPS matrix results from a combination of the following active secretion, shedding of cell surface material, cell lysis, and/or adsorption of substances from the environment. EPS are usually acidic and contain functional groups, such as carboxylic and amino acids that, as mentioned earlier, readily bind metal ions. EPS can bind metal ions from the substratum or from a liquid medium and control interfacial chemistry at a metal/biofilm interface. EPS are also implicated in increased resistance of biofilm cells to biocides and other antimicrobial compounds [9]. 

With regard to the cathodic processes, it can be observed that any liquid medium, even organics, able to solvate the metal ions, may give rise to corrosion in the presence of any suitable cathodic process. The cathodic processes in inorganic environments may be numerous, not only the oxygen reduction or the hydrogen evolution, for example, the reduction of the nitrates to ammonia, that of the sulfates to sulfides, and that of the ferric to ferrous salts. 

Three phase catalytic oxydations involving molecular oxygen are not frequent in chemical industry. In this field, most gas-liquid processes use dissolved salts as homogeneous catalyst. It is very difficult indeed to find solid catalysts which can resist to corrosion by the liquid medium in which oxidations take place. 

To evaluate the effect of slurries or moving liquids on corrosion, a special test loop may build through which the solid-contairring medium or high velocity medium is circulated by means of a pump. Tubular specimens are relatively easy to obtain. They may be exposed in the velocity test loop, and have a nice response to erosion corrosion calculatiorrs. 

In the discussion of the reversibility of the Rehbinder effect, it was implied that there is a thermodynamically stable interface present between the mutually saturated solid phase and liquid medium and that the effect vanishes when the liquid medium is ranoved, for example, by evaporation. These two peculiarities make the Rehbinder effect principally different from the corrosion caused by the action of aggressive media. At the same time, one must realize that complete segregation is not possible various processes can cover a fairly broad spectrum from idealized cases involving purely mechanical failure to purely corrosive processes (or dissolution). The Rehbinder effect, which involves the adsorption-induced lowering of strength, stress-facilitated corrosion, and corrosive fatigue, often occupies intermediate positions in these series. In this type of phenomenon, the action of external forces and the action of chemically active media both contribute to the net result in certain proportions. 

Corrosion is, as already explained in Section 5.3.2, the material damage caused by chemical or electrochemical reaction with a surrounding medium. The corrosive media can be a gas or a liquid. Electrochemical corrosion is common in metal alloys and metal compounds in which liquid media play a role. Here, an electrolyte acts on a metal and usually produces a top layer. In the case of water on steel, this top layer is rust. 

This is an irreveisible reaction and, consequently, its rate is affected only by temperature and the concentrations of the species on the left side of the equation. Therefore, the rate of reaction 3-3 (and of corrosion) increases with increasing hydrogen ion concentration (i.e., decreasing pH), with increasing temperature, and, because the reaction is electrochemical, with increasing conductivity of the liquid medium. 

Galvanic corrosion has appeared ever since two different metals were put together in a liquid medium, that is to say since the Iron Age, when iron was put in contact with brass and copper. Marine archaeology shows such cases of galvanic corrosion in wrecks of ancient ships. 

A corrosion test in which the specimens are intermittently exposed to a liquid medium at definite time intervals. 

A wire element (made of the metal of interest) is mounted in a suitable casing and exposed to the corrosive medium, which can be either liquid or gas. The element decreases in thickness due to corrosion and, as most corrosion products have greater electrical resistance than the metals from which... 

Principles and Characteristics Water is an interesting alternative for an extraction fluid because of its unique properties and nontoxic characteristics. Two states of water have so far been used in the continuous extraction mode, namely subcritical (at 100 °C < T < 374 °C and sufficient pressure to maintain water in the liquid state) and supercritical (T>374°C, p>218 bar). Unfortunately, supercritical water is highly corrosive, and the high temperatures required may lead to thermal degradation of less stable organic compounds. However, water is also an excellent medium for extraction below its critical temperature [412], Subcritical water exhibits lower corrosive effects. 

Coupling Medium. Distilled water has proven to be more effective than tap water as the conducting liquid as evidenced by greater cavitation in the reaction flasks (and faster reaction rates). Moreover, distilled water leads to significantly less corrosion of the bath walls. Other low vapor pressure liquids such as ethylene glycol can be used. 

Various fluorinations, which need principally much energy for the generation of the reagent fluorine, are carried out electrochemically in liquid hydrogen fluoride, even in an industrial scale [66]. Owing to the extreme toxicity and the corrosive medium, special precautions are necessary. 

Carbonylation of methanol to form acetic acid has been performed industrially using carbonyl complexes of cobalt ( ) or rhodium (2 ) and iodide promoter in the liquid phase. Recently, it has been claimed that nickel carbonyl or other nickel compounds are effective catalysts for the reaction at pressure as low as 30 atm (2/4), For the rhodium catalyst, the conditions are fairly mild (175 C and 28 atm) and the product selectivity is excellent (99% based on methanol). However, the process has the disadvantages that the proven reserves of rhodium are quite limited in both location and quantity and that the reaction medium is highly corrosive. It is highly desirable, therefore, to develop a vapor phase process, which is free from the corrosion problem, utilizing a base metal catalyst. The authors have already reported that nickel on activated carbon exhibits excellent catalytic activity for the carbonylation of... 

Kinetics of Ceramic and Glass Corrosion by Gases. The attack of ceramics and glasses by gaseous reactants is much more prevalent than corrosion due to liquids. In addition to the chemical composition of the attacking medium, the geometry of the ceramic solid is of tantamount importance to its corrosion resistance. That is, a... 

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