Intergranular material

The decomposition kinetics of mercury fulminate [725] are significantly influenced by ageing, pre-irradiation and crushing these additional features of reaction facilitated interpretation of the observations and, in particular, the role of intergranular material in salt breakdown. Following a slow evolution of gas ( 0.1%) during the induction period, the accelerator process for the fresh salt obeyed the exponential law [eqn. (8)] when a < 0.35. The induction period for the aged salt was somewhat shorter and here the acceleratory process obeyed the cube law [eqn. (2), n = 3] and E = 113 kj mole-1. 

The disordered stmcture within dislocations may also contain other defects and be a zone of preferential concentration of impurities where the strain associated with the presence of each anomalous constituent is decreased. These also provide the paths for low-temperature ionic migration. Intergranular material, between blocks of relatively perfect material, contains relatively high dislocation densities and also impiuities. These have been recognized generally as zones of preferred onset of chemical reactions. 

Pitting corrosion often occurs in the presence of halide ions at positions where local elements can form. In alloys local elements can form between the (less noble) intergranular material and the granules and can lead to dissolution of the intergranular material starting at the surface (grain disintegration). 

Binder. A substance added to a ceramic raw material of low plasticity to facilitate its shaping and to give the shaped ware sufficient strength to be handled materials commonly used for this purpose include sulphite lye, sodium silicate, molasses, dextrin, starch, gelatine, etc. The term bond (q.v.) is also sometimes used in this sense but is better reserved to denote the intergranular material that gives strength to the fired ware. 

The intergranular material, glassy or crystalline, that gives strength to fired ceramic ware. 

With materials with high resistance to intergranular stress corrosion, f/ can be more positive in group I and more negative in group IV. Corrosion susceptibility increases with rising temperature (see Chapter 21). 

The two types of hot eorrosion eause different types of attaek. High-temperature eorrosion features intergranular attaek, sulfide partieles and a denuded zone of base metal. Metal oxidation oeeurs when oxygen atoms eombine with metal atoms to form oxide seales. The higher the temperature, the more rapidly this proeess takes plaee, ereating the potential for failure of the eomponent if too mueh of the substrate material is eon-sumed in the formation of these oxides. 

Embrittlement embrittlement and for improperly heat treated steel, both of which give intergranular cracks. (Intercrystalline penetration by molten metals is also considered SCC). Other steels in caustic nitrates and some chloride solutions. Brass in aqueous ammonia and sulfur dioxide. physical environments. bases of small corrosion pits, and cracks form with vicious circle of additional corrosion and further crack propagation until failure occurs. Stresses may be dynamic, static, or residual. stress relieve susceptible materials. Consider the new superaustenitic stainless steels. 

Some of the most obvious examples of problems with gas and materials are frequently found in refining or petrochemical applications. One is the presence of hydrogen sulfide. Austenitic stainless steel, normally a premium material, cannot be used if chlorides are present due to intergranular corrosion and subsequent cracking problems. The material choice is influenced by hardness limitations as well as operating stresses that may limit certain perfonnance parameters. 

There apparently exists a critical amount of liquid phase for the optimization of grain/interface boundary sliding during superplastic deformation. The optimum amount of liquid phase may depend upon the precise material composition and the precise nature of a grain boundary or interface, such as local chemistry (which determines the chemical interactions between atoms in the liquid phase and atoms in its neighboring grains) and misorientation. The existence of an equilibrium thickness of intergranular liquid phase in ceramics has been discussed [14]. This area of detailed study in metal alloys has not been addressed. 

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