1. Most materials tend to degrade because of various reasons. In many instances,
ID: 2073751 • Letter: 1
Question
1. Most materials tend to degrade because of various reasons. In many instances, water accelerates or stimulates the degradation process. Within this context, answer the following: a) Most metals are thermodynamically unstable in the metallic state and would spontaneously diffuse out of the solid metal to become ions in a different form What drives this behaviour and what is the effect of water in this process? (10 Marks) b) Often ceramic materials display a much lower toughness in humid conditions. Also some ceramic aggregates and natural stones would pulverise gradually with time. What drives this behaviour and what is the effect of water in this process? (5 Marks) Wood and many organic substances degrade rapidly if exposed to damp conditions for a prolonged time. What drives this behaviour and what is the effect of water in this process? c)Explanation / Answer
(a) Most metals except inert gas elements are thermodynamically unstabe and diffuse out of solid metal into ionic forms. This can be due to concentration gradient, thermal effects, mechanical damage on the surface of metal or any other microstructural defects in the form of impurities etc which aggravate or drives the behaviour of unstability. For most metals, the relationship between the atmospheric oxygen and moisture is not stable, and therefore water severly aids to the oxidation of metals leading to either a film layer formation or corrosion of the surfaces. Also, all the processes in the universe drives from higher potential to lower potential( can be energy, concentration or pressure). The property of metals to transform from metallic state to different forms is characterized by decrease in the free energy which is the driving factor for the process to take place.
(b) Again, humidity brings water vapor and the presence of moisture in the surrounding environment of ceramics starts creating a corrosive environment which leads to pitting and erosion degradation of ceramic materials. Water promotes this mechanism by bringing more moisture and oxygen content to the ceramic surrounding. The pitting phenomenon is defined as slow localized corrosion of materials. That's why natural stones and some ceramic aggravates pulverize gradually with time.
(c) Organic substances are biodegraded by small microorganisms as for them they act as nutrients. Since, biodegradation can be aerobic (in presence of oxygen) as well as anaerobic (without presence of oxygen) the degradation is rapid as mentioned in the question.principally to the effects of light and water. Water plays an important role in weathering since cyclic changes in moisture content generate stresses leading to checking and splitting. Water may also accelerate surface degradation by leaching.
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