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Deteriorative Property of Materials
Transcript of Deteriorative Property of Materials
Property Resistance Definition Environment Summary 3 Factors of Deterioration Deteriorative Property it refers to the
surroundings of the object Some metals are more intrinsically resistant to corrosion than others, either due to the fundamental nature of the electrochemical processes involved or due to the details of how reaction products form. For some examples, see galvanic series. If a more susceptible material is used, many techniques can be applied during an item's manufacture and use to protect its materials from damage. What is deterioration? Deterioration is a gradual decline,
as in quality, serviceability, or vigor. is the property of the material to stand
chemical reactivity with the environment, corrosion, and resistance. Chemical reactivity is the tendency of a substance to undergo chemical changes in a system. Corrosion is the disintegration of an engineered material into its constituent atoms due to chemical reactions with its surroundings. In the most common use of the word, this means electrochemical oxidation of metals in reaction with an oxidant such as oxygen. Environmental Factors
that influence the
deterioration of materials Meteorological and
climatic factors Moisture Temperature Solar Radiation Wind Effect Galvanic corrosion Corrosion in
passivated materials Microbial corrosion Types of Corrosion It occurs when two different metals and/or alloys have electrical contact with each other and are immersed in an electrolyte. This effect is a galvanic couple where the more active metal corrodes at an accelerated rate and the more noble metal corrodes at a retarded rate. When immersed, neither metal would normally corrode as quickly without the electrically conductive connection. What type of metal(s) to use is readily determined by following the galvanic series. For example, zinc is often used as a sacrificial anode for steel structures. Galvanic corrosion is of major interest to the marine industry and also anywhere water (via impurities such as salt) contacts pipes or metal structures. Passivation is the process of making a material "passive", usually by the deposition of a layer of oxide that adheres to the metal surface. In air, passivation affects the properties of almost all metals–notable examples being aluminium, zinc, titanium, and silicon (a metalloid). In the context of corrosion, passivation is the spontaneous formation of a hard non-reactive surface film that inhibits further corrosion. This layer is usually an oxide or nitride that is a few nanometers thick. Examples of specific passivated materials are:
Nickel Pourbaix Diagram of Iron Pitting corrosion Pitting corrosion, or pitting, is a form of extremely localized corrosion that leads to the creation of small holes in the metal. The driving power for pitting corrosion is the depassivation of a small area, which becomes anodic while an unknown but potentially vast area becomes cathodic, leading to very localized galvanic corrosion. Intergranular corrosion Intergranular corrosion (IGC), also known as intergranular attack (IGA), is a form of corrosion where the boundaries of crystallites of the material are more susceptible to corrosion than their insides. (Cf. transgranular corrosion.) Crevice corrosion Crevice corrosion is a corrosion occurring in spaces to which the access of the working fluid from the environment is limited. These spaces are generally called crevices. Examples of crevices are gaps and contact areas between parts, under gaskets or seals, inside cracks and seams, spaces filled with deposits and under sludge piles. High temperature corrosion Microbial corrosion, or bacterial corrosion, is a corrosion caused or promoted by microorganisms, usually chemoautotrophs. It can apply to both metals and non-metallic materials, in both the presence and lack of oxygen. High temperature corrosion is chemical deterioration of a material (typically a metal) under very high temperature conditions. This non-galvanic form of corrosion can occur when a metal is subject to a high temperature atmosphere containing oxygen, sulfur or other compounds capable of oxidising (or assisting the oxidation of) the material concerned. Intrinsic Chemistry Passivation The materials most resistant to corrosion are those for which corrosion is thermodynamically unfavorable. Any corrosion products of gold or platinum tend to decompose spontaneously into pure metal, which is why these elements can be found in metallic form on Earth, and is a large part of their intrinsic value. More common "base" metals can only be protected by more temporary means. Environment
Resistance Sources http://en.wikipedia.org/wiki/Corrosion http://www.witpress.com/contents/c0322.pdf