Introduction To High Temperature Oxidation And Corrosion Pdf


By Michael M.
In and pdf
09.12.2020 at 02:29
6 min read
introduction to high temperature oxidation and corrosion pdf

File Name: introduction to high temperature oxidation and corrosion .zip
Size: 17143Kb
Published: 09.12.2020

Simultaneously, the effect of grain size of these metals and grain boundary displacement during oxidation process are described very clearly. The combined effect of crystal structure and grain size on the formation of oxide scale is studied in depth understanding with support from the literature search. High Temperature Corrosion.

Oh, M. High temperature oxidation of Fe Mn Si alloys results in the formation of a transformed surface layer that contains a lower concentration of manganese and a higher concentration of silicon than the underlying metal. Because the corrosion resistance of iron-silicon alloys is very sensitive to the concentration of silicon in the metal, the transformed layer is often more corrosion-resistant than the original alloy. Anodic polarization tests were used to demonstrate that a transformed layer with characteristics similar to those of a Fe Sign In or Create an Account.

Influence of Temperature on Corrosion Behavior of 2A02 Al Alloy in Marine Atmospheric Environments

Simultaneously, the effect of grain size of these metals and grain boundary displacement during oxidation process are described very clearly. The combined effect of crystal structure and grain size on the formation of oxide scale is studied in depth understanding with support from the literature search. High Temperature Corrosion. Generally, most of the metals used in common application technologies undergo deterioration on exposure to weather condition with time.

The rate of corrosion varies widely from slower to faster degree depending on the type of material. The examples of such type are iron rusts at room temperature and deteriorate faster than nickel and chromium that are attacked slowly with time. The surface layer that results due to oxidation determines nature of corrosion rate on the metal and has a strong effect on the material [ 6 ]. This area covers both theoretical predication and satisfactory subject of investigation based on the various combined areas such as metallurgical, chemical and physical discipline with thermodynamic predication [ 7 ].

Recently, a set of mechanics data available on mass transport through oxide scales during oxidation, evaporation of oxide species, the role of mechanical stress on oxide scales and the important relationships between metal elements, microstructure and oxidation. Accordingly, such information is obtained virtually prior to oxidation to obtain the physical and chemical reaction of metal species at high temperature [ 8 ]. The understanding of the oxidation phenomena and the mechanism behind the reaction species for the formation of oxide scales and its role for the formation of various layers of oxide scale on the metal were discussed.

The role of crystal structure of pure metals plays the viable role in the formation of oxide scale [ 9 ]. The main purpose of the chapter is an introduction to fundamental as well as experimental investigation of interaction of reactive species such as oxygen as the component usually metals such as high temperature.

The rate of corrosion depends on the nature of reaction products. The rate of reaction is controlled by reactants through the solid layers. The rate of formation of oxide layers on metals is accordingly [ 11 ]. The extent of reaction determines the amount of metal consumed, the amount of oxygen used and the amount of product formed during oxidation process.

There are several rate laws that apply to determine the oxidation rates such as linear, parabolic and logarithmic rates. The linear law is based on the surface reaction step towards the reactive gases of the environment. It is independent of the time of the reaction. However, the parabolic law depends on inversely proportional to square root of time and is obeyed when diffusion through scale is rate determining steps [ 12 ].

The logarithmic law is applicable to the very thin oxide films in the range of 2—4 nm [ 13 ]. Discontinuous method is the way to measure the weight of the sample within an interval of the time on exposure to high temperature. Assessment of the extent of reaction is carried out in a simple way either by observing the mass gain of the oxidized samples that is the mass of oxygen taken into scale or by observing the mass loss of the base sample which is equivalent to the mass gain by the oxide scale.

The disadvantage of this method is the many specimens are needed to study the reaction kinetics and progress of the reaction is not continuous [ 12 ]. On the other hand, this method was very simple and the apparatus required is very simple. Also at each individual point, metallographic examination of each data point is evaluated.

There are various ways to examine and analyze the surface of oxidized samples from the scale towards the base of the material. The methods are classified into two broad categories: i from the basic sample mounting to preparation and ii then examination using various techniques towards the final stage. As the epoxy method is very easy, simple and convenient way to examine the scale and the base of the sample. The polished specimens may be examined using conventional optical microscopy for the microstructures, and the elements analyzed can be carried out using scanning electron microscope.

Etching is followed on samples after metallographic preparations. Optical microscope is the simplest technique available to look the optical images of the metals before and after oxidation. The specific band energy and band states also can be determined on oxidized scales and base of the materials. The sample like pure metal is the beginning stage and simplest way of understanding the reaction kinetics and nature of reaction during high temperature in gaseous phase.

The role of temperature and duration of oxidation play the crucial role in formation of oxide layers on the surface of pure metals. Transport mechanism of ions and electrons during the oxidation of pure metals is well explained by Wagner's theory of oxidation [ 15 ]. According to Wagner's theory, oxidation rate is controlled by partial ionic and electronic conductivities of oxides and their dependence on the chemical potential of the metal or oxygen in the oxide.

According to Kofstad [ 16 ], the defect structure of oxides plays the important role in oxidation rate of metal. The consideration of the reaction is. It is obvious that the solid reaction product MO will separate the two reactants as shown in Scheme 1. In order to proceed the further reaction, one of the reactants either metal or gas O 2 must penetrate through the oxide scale interface to reach either site of the reactant species.

Since all metal oxides are ionic in nature, the possibility of transport of neutral metal through the interface is not feasible. Transport of ions through ionic solid is well explained by several mechanisms that belong to the stoichiometric crystal structure or nonstoichiometric crystal one.

There are two types of defects that predominate the mobility of ions such as Schottky and Frenkel defects concept [ 17 ]. In Schottky defects, ionic vacancies are transported by both the concentration of anionic and cationic sublattices.

However, in Frenkel defects, ionic vacancies are transported mainly by cation vacancies. The ions are free movement of oxygen on lattice sites.

However, both of the reactions could not able to explain the transport mechanism during oxidation state because neither any of the defect structure provides the mechanism for transport of electrons through the interface. Nonstoichiometric ionic compounds are classified as semiconductors that may show some positive or negative behaviour. Zinc oxide is the best example of this type of structure.

The electric charge is carried out by negative carriers either by metal deficit or metal excess [ 19 ]. The formation of defect in the ZnO crystal is represented as below [ 21 ]. The final equilibrium constant can be determined as follows. More recently, it has been reviewed that significant interstitial solution of zinc occurs in ZnO.

So still there is ambiguity about the mechanism and interpretation of ZnO [ 22 ]. Inconsistencies in different mechanisms may arise due to defect structures that are resulted from impurities of the samples especially. The process is represented as follows [ 23 ]. The vacant oxygen site is surrounded by the positive ions represent a site for high positive charge to which free electrons can be attracted. So there is possibility the following reaction takes place as follows.

This is quiet deviation from the general category. Rate of oxidation depends on how the oxidation process proceeds under those conditions where two reactants such as metal and oxygen are separated by an oxidized product. Ionic and electronic transport processes through oxide scale are accompanied by phase boundary reactions, and formation of new oxide species depends on whether cations or anions are transported through oxide layer.

Thus the transport mechanisms of oxidation process are varied with oxygen pressure and temperature. Highest oxidation rate is observed in the metal sample where highest defect concentration is possible. Point defect model refers to the movement of point defects in an associated electric field. Expansion behaviour of a passive film on a metal surface and breakdown of passive films in terms of mass and charge flux via purpose defects across the semiconductive and defective barrier layers of the passive film.

Point defect model has allowed to formulae a set of principles for designing new alloys and has led to the development of a determine for predicting localized corrosion damage functions [ 24 ].

Passive film is the defective compound layer that results ion vacancies and chemical element vacancies that were generated and exterminated at the metal—film and film—solution interfaces. However, the bilayer structure of the film compromising a defective or binary compound barrier layer adjacent to the metal and an outer layer that forms by precipitation from reaction of cation species with surroundings introduced metal interstities to the defects in the barrier layer dissolution with passive current reside within the barrier.

Metals that have useful properties including strength, ductility, thermal and electrical conductivity are used in structural and electrical application. Understanding the structure of the metals can help us understand their properties.

Metals are composed of atoms, and atoms are held by strong and delocalized bonds. These bonds are formed by a cloud of valence electrons that are shared by positive metal ions cations in a crystal lattice. An actual piece of metal consists of many tiny crystals called grains that join at the grain boundaries.

The properties of the metals are influenced by the crystal structures, e. Exposure of metals to high temperatures in air leads to oxidation of metals and to the formation of oxide scales. Oxidation of pure Fe having bcc is well documented and has led to the classical three layer scale characterization. However the oxide scales formed in the case of copper fcc consist of an outer copper oxide layer and inner porous layer. At the lower part of the temperature range the oxidation kinetics and oxide morphology depend strongly upon the formation of CuO.

The formation of CuO changes the oxidation behavior from being approximately parabolic growth to having a break way like oxidation behavior. Also with addition to crystal structure, grain shape, size, and grain boundary diffusion on high temperature play the influential role on oxidation of pure metals.

In this section we consider pure Cu, Fe and Zn at the subject of interest from the range of pure metals because of different crystal structures and the general application in industrial point of interest. Three commercially pure metals such as iron, copper and zinc having different crystal structures were taken into consideration [ 27 ].

The prepared specimens were examined using optical microscope for the microstructures of the preoxidized specimen. The specimens are further ground, polished and subsequently cleaned in acetone for oxidation species. The polished and cleaned specimens are placed in the central zone of the furnace for oxidation at dry air.

The external scales of oxidized specimens were characterized by scanning electron microscope and energy dispersive spectroscopy. The microstructure of zinc consists of coarse grains along with mechanical twins, whereas the microstructure of copper shows polyhedral grains with annealing twins.

The microstructure of pure iron shows polyhedral grains of ferrite with very distinct and sharp boundaries. The oxidation rate of pure iron having bcc crystal structure is found to be However, the oxidation rates of copper and zinc are found to be 0.

The change in oxidation rate from bcc metal to fcc and hcp metals can be attributed to the increase in atomic packing fraction of different crystal structures and also the progressive decrease in the free energy of formation of iron, copper and zinc oxidation, respectively.

The trend of oxidation rate from zinc towards iron may be both a combination of cations as well as anionic mobility. A marginal difference in thickness and structural changes in grain size and shape has been observed in the Cu 2 O inner layer compared with CuO outer layer Figures 8 and 9. Scale of the oxidation layer of Fe and Cu layers under The top oxide scale on cooling to room temperature is found to be ballooned and separated from the metal substrate without any appearance of cracks.

The observed ballooning of the scale can be attributed to the compressive stress generated within the scale as a result of higher volume of iron oxide compared to that of iron. The lower scale of the pure iron after unbounding from the base metal shows the creation of the holes and elongated cracks on the surface with irregular thickness of the surface morphology.

AN INTRODUCTION TO CORROSION AND PROTECTION OF METALS

This book is concerned with providing a fundamental basis for understanding the alloy-gas oxidation and corrosion reactions observed in practice and in the laboratory. Starting with a review of the enabling thermodynamic and kinetic theory, it analyzes reacting systems of increasing complexity. It considers in turn corrosion of a pure metal by a single oxidant and by multi-oxidant gases, followed by corrosion of alloys producing a single oxide then multiple reaction products. Upper-level undergraduate and graduate students, professionals, researchers and consultants in the field of high temperature corrosion resistance. Although written and structured as a text book, High Temperature Corrosion and Oxidation of Metals develops its analysis to the level of a research monograph.

The significant role of alloying elements with respect to the exposed medium is studied in detail. The surface morphology has expressed the in situ nature of the alloy and its affinity toward the environment. The EDS and XRD analysis has evidently proved the presence of protective oxides formation on prolonged exposure at elevated temperature. The predominant oxide formed during the exposure at high temperature has a major contribution toward the protection of the samples. The nickel—iron-based superalloy is less prone to oxidation and hot corrosion when compared to the existing alloy in gas turbine engine simulating marine environment. The corrosion issues are similar for all the applications [ 1 ].

Influence of Temperature on Corrosion Behavior of 2A02 Al Alloy in Marine Atmospheric Environments

Atmospheric corrosion results from chemical or physical reactions between a material and the surrounding atmosphere, and is one of the most widely studied topics in the field of corrosion. The corrosion of the Al alloy has been investigated in several studies. However, most of these studies were conducted in a laboratory environment [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 ] due to the rapid results and economic efficiency provided by accelerated tests. It was found that serious marine atmospheric corrosion was caused by the combined action of multifactor conditions such as sunshine, temperature, and rain on the metal surface [ 14 ]. The marine atmospheric environment is characterized by permanently high temperatures from sunshine and relatively high humidity with considerable NaCl precipitation.

Looking for other ways to read this?

ASM Milestones. Strategic Plan.

Professor Wranglen's book is based on his experience in giving an introductory corrosion science and engineering course to engineering students for over 10 years. This book is relatively short and claims only to be an introduction to the subject. This, however, does not do justice to the book. Wranglen, G. Report bugs here.

0 Comments

Leave a Reply