Chemical embrittlement

Both physical aging and chemical side reactions result in a pronounced embrittlement of thermally treated polymers. Young moduli of these polymers usually become a little higher, ay passes through a maximum (in air much sooner than in vacuum or dry Ar atmosphere) and elongation at break becomes lower. Chemical embrittlement is more pronounced in polymers with an initial excess of the epoxy component. 

A cause of sudden and catastrophic failure is chemical embrittlement. This occurs when the wrong chemical enters the vessel or pipe, and causes it to fail in a very short period of time. Examples of embrittlement include the effect of caustic on stainless steels and hydrogen on various types of steel. Chemical embrittlement is particularly serious because it can happen to new equipment as easily as old, and because it may give little or no warning that it is about to occur. 

In addition to fiber and fabric influences on abrasion resistance, chemical finishes must also be considered. Many thermosetting resins used to impart durable press characteristics to ceUulosic fabrics reduce their resistance to abrasion as a result of fiber embrittlement. 

MSTMF519, Std. Methodfor Mechanical Hydrogen Embrittlement Testing of Plating Processes and Mircraft Maintenance Chemicals, American Society for Testing and Materials, Philadelphia, Pa., 1977. 

Tantalum. Above 300°C (570°F), the possibihty of reactivity of tantalum with all gases except the inert gases. Below 300°C (570°F), the possibility of embrittlement of tantalum by nascent (monatomic) hydrogen (but not molecular hydrogen). Nascent hydrogen is produced by galvanic action or as a product of corrosion by certain chemicals. 

Embrittlement is. . the reduction in the normal ductility of a metal due to a physical or chemical change. ... 

Rockwell C 22 is the commonly selected limit above which sulfide embrittlement and resultant sulfide stress cracking become problems. The change, however, is not that abrupt but the critical "gray band" is about C 20 to 25, with the point of change affected by mechanical, physical and chemical environmental factors. 

The polymers also have excellent resistance to oxidative degradation, most chemicals other than strong bases and high-energy radiation. Exposure for 1500 hours to a radiation of about 10 rads at 175°C led to embrittlement but the sample retained form stability. 

In many applications tantalum can be substituted for platinum and gold, and there are some environments in which tantalum is more corrosion resistant than platinum. Table 3.37 lists the main chemicals for which tantalum is not a suitable substitute for platinum and, conversely, those for wliich tantalum is better than platinum. Tantalum is rapidly embrittled by nascent hydrogen even at room temperature. Therefore, it is very important to avoid the formation of galvanic couples between tantalum and other metals. 

In calculating the system and barrier failures, consideration should be given to radiation embrittlement, chemical reactions, thermal shock, and metal fatigue. 

There are also occasions, particularly in hydrogen-containing atmospheres, when surface contamination of the titanium with iron can result in localised corrosion and embrittlement. This effect can be countered by avoidance of undue contamination with iron during fabrication, by postfabrication cleaning and by post-fabrication anodisingIt should be emphasized, however, that in general use in the marine and chemical industries discussed below, iron levels up to 0-2% do not adversely affect corrosion resistance. 

There are several classes of test for hydrogen embrittlement, according to the application. Three general types of mechanical test can be identified, together with chemical and electrochemical tests intended to determine the hydrogen content of steels or the rate of entry of hydrogen from an environment. 

Ion Vapour Deposition A variant of the process is ion vapour deposition, in which a high negative potential is applied to the workpiece during chemical vapour deposition. The process has been employed on a commercial scale chiefly for depositing aluminium on to steel and titanium in the aerospace industry as an alternative to cadmium plating, which is liable to cause hydrogen embrittlement, especially of high tensile steel components. The aluminium is evaporated from a wire-fed resistance-heated boat . 

Nail sickness Nail sickness is chemical decay associated with corroded metals in marine situations. Chemical degradation of wood by the products of metal corrosion is brought about by bad workmanship or maintenance, or unsuitable (permeable) timber species, all of which permit electrolyte and oxygen access which promotes corrosion. Chemical decay of wood by alkali occurs in cathodic areas (metal exposed oxygen present). Softening and embrittlement of wood occurs in anodic areas (metal embedded oxygen absent) caused by mineral acid from hydrolysis of soluble iron corrosion products. 

Chemical reaction This involves the formation of distinct compounds by reaction between the solid metal and the fused metal or salt. If such compounds form an adherent, continuous layer at the interface they tend to inhibit continuation of the reaction. If, however, they are non-adherent or soluble in the molten phase, no protection will be offered. In some instances, the compounds form in the matrix of the alloy, for example as grain-boundary intermetallic compound, and result in harmful liquid metal embrittlement (LME) although no corrosion loss can be observed. 

For any specific boiler plant, good control also may necessitate the use of certain other conjunctional treatments to support the primary chemical treatments such as sodium nitrate for protection against embrittlement. 

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