Question

reason of linear weight gain and linear weight loss during oxidation

Answer 1

One of the requirements of a high-temperature material— for example, in a turbine blade or a super-heater tube—is that it should resist attack by gases at high temperatures and, in particular, that it should resist oxidation. Turbine blades do oxidize in service and react with H2S, SO2, and other combustion products. Excessive attack of this sort is obviously undesirable in such a highly stressed component. This chapter answers various questions: Which materials best resist oxidation, and how can the resistance to gas attack be improved? The Earth's atmosphere is oxidizing. By using the earth as a laboratory and looking for materials that survive well in its atmosphere, some idea of oxidation resistance can be obtained. The Earth's crust is almost entirely made of oxides, silicates, aluminates, and other compounds of oxygen; and being oxides already, they are completely stable. Alkali halides, too, are stable: NaCl, KCl, and NaBr are widely found in nature. In contrast, metals are not stable: only gold is found in “native” form under normal circumstances; all the others in the data sheets will oxidize in contact with air. Polymers are not stable either as most of them may burn if ignited, meaning that they oxidize readily. Coal and oil are found in nature but that is only because geological accidents have sealed them off from all contact with air.