Gaseous corrosion

Pollutant (if gaseous) Corrosiveness Inflammability Toxicity Reactivity... 

Gaseous corrosion is a general form of corrosion whereby a metal is exposed to a gas (usually at elevated temperatures). Direct oxidation of a metal in air is the most common cause. Cast iron growth is a specific form of gaseous corrosion in which corrosion products accumulate onto the metal surface (and particularly at grain boundaries) to the extent that they cause visible thickening of the metal. The entire metal thickness may succumb to this before loss of strength causes failure. 

There are many types of corrosion, as would be expected from its general definition. It has been traditional (4) to divide the study of corrosion into two areas the study of low temperature corrosion by aqueous or other solutions, controlled by electrochemical processes (wet) and the study of gaseous corrosion at high temperatures, controlled by thermodynamics and diffusion processes (dry). In addition to the obvious differences, the two areas have many phenomena in common. 

Gaseous corrosion in combustion applications involving condensed phased deposits is important and sodium sulfate and vanadate deposits are most corrosive. These deposits are particularly injurious to non-oxide ceramic materials. The data on corrosion resistance of ceramic materials to hot gaseous environments are presented in Table 4.94. It is clear from the data that non-oxide ceramics show lesser corrosion resistance than oxide-based ceramics. 

SF4 and diethylaminosulfur trifluoride (DAST) give alkyl fluorides not only from tertiary and secondary, as with HF, but also from primary alcohols (equation 36). Reactions with gaseous, corrosive SF4 (b.p. -38 °C) usually require temperatures of 20-100 C. The special equipment needed for reactions with toxic gases under pressure make the use of SF4 inconvenient. The introduction of DAST has removed the handling problems. DAST is a liquid reagent made from SF4 and trimethylsilyldiethyl-... 

CORROSION, GASEOUS - Corrosion with gas as the only corrosive agent and without any aqueous phase on the surface of the metal. Also called dry corrosion. 

D. A. ShiflCT, High temperature gaseous corrosion testing , ASM Handbook, Materials Park, OH, ASM International, 2003, vol. 13A, p. 650. 

F. A. Costa Oliveira, High Temperature Gaseous Corrosion of Silicon Nitride Ceramics, Dissertation, TU Delft, JRC Petten, 1992, pp. 271. 

Corrosion can also be classified based on environments. For example, we can mention the following corrosion phenomena - atmospheric corrosion, fresh water corrosion, sea water corrosion, soil corrosion, high temperature corrosion, and gaseous corrosion. 

Gaseous corrosion is the general term for the corrosion occurring in gases without liquids. It belongs to the dry corrosion category. 

When an electrolytic product is required of very high purity, a refining cell may be employed instead of a winning cell, i.e. a soluble anode is fabricated of the required metal, in a less pure condition, which may have been produced by a method other than electrolysis, or which may be scrap from later metallurgical processing, In this case chlorine is not liberated in the cell, and gaseous corrosion may be eased. It is of course necessary to reject some or all of the inert salts after each electrolysis batch, in order to obtain the full benefit of the electrolytic purification, since the impurities are of such a nature that they remain undeposited on the cathode. 

Corrosion is the attack of a gaseous or liquid phase upon a metal or other solid with a resultant destruction of the structure. The fundamental aspects of the problem of gaseous corrosion were discussed in the previous section. Since we are concerned here with solid state reactions, we shall discuss only those corrosion processes in liquid media (i. e. particularly in aqueous... 

Shifler, D. A., "High Temperature Gaseous Corrosion Testing, ASM Handbook, Vol. 13A, in press. 

Tras CHAPTER HIGHLIGHTS the coiTOsion resistance of nickel and its alloys and identifies relevant ASTM standards associated with their evaluation. The test technique selected ultimately will depend upon the specific alloy involved, the type of corrosion in question, or the end application, or a combination thereof. The following discussions will deal primarily with aqueous corrosion and the nickel-base (greater than about 30 % nickel) alloys designed for aqueous corrosion resistance. High-temperature gaseous corrosion will be addressed in other sections. 

Corrosion inhibition can thus be evaluated conveniently by sequential pulse experiments with surfaces in contact with or in the absence of corrosion inhibitors. Similar work can be carried out with gaseous corrosive agents and metal surfaces treated with corrosion inhibitor vapours such as butylamine. 

Some of the nickel-based alloys were designed to withstand high temperature and dry or gaseous corrosion whereas others are mainly designed to resist low-temperature (aqueous) corrosion. Nickel-based alloys used for low temperature aqueous or condensed systems are generally known as corrosion-resistant alloys (CRA). Only the corrosion performance of commercially available CRA will be addressed in this chapter. 

Cast iron, ductile iron, or steel pipe may be coated at the mill by a process during which the pipe is spun on the center of its longitudinal axis while a mortar mixture is sprayed onto the inside surface in a uniform, dense layer. After proper curing, provided the pipe is handled carefully, this coating can protect the pipe interior against attack by water and many other liquid and gaseous corrosive environments. 

With the increasing concern about acidifying pollutants and their influence on atmospheric corrosion rates, scientists interest has been focused on NO2 as an additional gaseous corrosion stimulant. Whereas the SO2 concentration has shown a significant decline over the past decades in many urban and industrial areas, estimated emission of NO2 has shown a continuous increase in the same type of environment [91]. Studies in laboratories using synthetic air have provided unambiguous evidence of increased corrosion rates when NO2 is added to air containing SO2 (Fig. 11). 

High-Temperature Gaseous Corrosion of Zircaloy 2 -A. H. Roebuck... 

Atmospheric or gaseous corrosion in confined environments, during transport, storage, or any other confined operation... 

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