Text Version
Matter
Molecule
Atoms
Charge
Electrochemical Cell
Home
Reset Electrochemical Movie
Matter
Click to Continue to menu
Glossary
Pourbaix Diagram
CorrSci
Electrochemical Cell
Partners
Electrical energy is the energy stemming from the flow of electric charge through conduction materials such as metals and electrolytes.
Chemical Energy
The standard reduction potential is the likelihood for a chemical species to be reduced, and is measured in volts at standard conditions (25°C, a 1 M ion concentration,1 atm partial pressure)
An electrolytic solution is a solution made up of ions that have dissociated due to the thermodynamic interactions between solvent and solute molecules and is electrically conductive.
a Salt Bridge is a physical connection of the oxidation and reduction reactions of the galvanic electrochemical cell that maintains the ion balance by allowing ion to migrate.
Chemical energy is the energy contained in the structure of an atom or molecule. Chemical energy is the energy stored in the bonds of atoms and molecules and released in a chemical reaction.
Salt Bridge
Electrical Energy
Solution
Electrolytic Solution
Standard Reduction Potential
A substance dissolved in another substance in which particles of one or more substances (the solute) are distributed even within the other substance (the solvent).
Kinetics is the branch of chemistry or biochemistry described by measuring and studying the rates of chemical reactions. Kinetics is unlike thermodynamics which incorporates the study of heat and temperature with the study of work and energy.
Gibbs free energy is a thermodynamic state function relating enthalpy, temperature, and entropy.
Electrical equilibrium is when oxidation-reduction reactions will occur until the system has reached a point where no net flow of the chemical and electrical species.
Thermodynamics is area of physics which incorporates the study of heat and temperature with the study of work and energy.
Kinetics
pH is a numerical representation of the measure of the acidity or basicity of an aqueous solution based on the H+ ion concentration
Thermodynamics
Electrical Equilibrium
pH
Faraday constant relates the relationship between a standard free energy of reaction and electric potential. The amplitude of the charge carried by a single mol of electrons.
An aqueous solution is any solution in which water is the dissolving solvent. Solvents may include liquids and gases.
Electron Distribution
Electron distribution is a function which gives the number of electrons per unit volume of phase space.
Faraday’s Constant
Aqueous Solution
Gibbs Free Energy
Solid is one of the four core states of matter (the others being liquid, gas, and plasma). It is the only state consisting of a definite volume and fixed shape.
Solid
Corrosion is the deterioration of material and its properties.
Electrons
An ion is an atom or group of atoms that has lost or gained one or more electrons. When it does this is no longer considered electrically neutral, it carries a charge.
Reset Pourbaix Movie
ions
Pourbaix Diagram
An electron is a negatively charged particle of an atom.
Corrodes
Electrochemical Equilibrium
Gibbs free energy is a thermodynamic state function relating enthalpy, temperature, and entropy.
Kinetics is a branch of science that studies the rate of chemical phenomena.
Gibbs Free Energy
Text
Movie
Select your information level (You can change your level choice at any time)
Click to Return Home
About Us
CorrSci incorporates everyday, real science examples into the explanation of the chemical phenomena of corrosion.  CorrSci is a research tool prototype designed to present corrosion science fundamentals to a wide audience of information seekers.  CorrSci is tailored to include everyday science examples into the explanation of the occurrence of corrosion.  CorrSci addresses the needs of its users with scientific examples that are written to match their varying levels of understanding of foundational scientific principles.Corrosion education is important because corrosion affects almost all aspects of public life. The costs associated with corrosion are borne by every producer and consumer. However, the impacts of corrosion extend beyond economic costs. Corrosion also has a significant effect on military readiness. It is essential that the U.S. works to mitigate these problems by maintaining a strong corrosion workforce.  Explanation of LevelsCorrSci is a three-part multimedia information platform that will serve as a host to the scientific fundamentals of corrosion and degradation, the tools of corrosion in regard to detection techniques and risk assessments, and the applications of corrosion in terms of rules and regulation.  The CorrSci prototype is web-based multimedia example of the accurate and easily understood communication of corrosion science to audiences made up of persons with different understandings of scientific principles.  The introduction material presented is written to address users with a sixth grade understanding of scientific principles, the intermediate material is written to address users with a secondary or post secondary education understanding of scientific principles, and the specialized material is written to address users with a concentrated understanding of scientific principles.  Although written to present information to three discrete audiences, the material is created with the intent to seamlessly transition between these levels. 
Button
A charge describes what is flowing in an electric current.
matter.
The different fields of science try to explain how different types of matter behave. Just like there are rules for how to play a game like basketball or how to play a song on an instrument, there are rules for how molecules are allowed to behave. The behavior of molecules has a lot to do with the atoms the molecules are made from. Each atom is made up of something called a nucleus, which is like a very tiny ball, orbited by an electron, which is like an even smaller ball. The electron orbits the nucleus because they have an opposite charge, and opposite charges attract. The electron is said to have a negative charge, while the nucleus has a positive charge. A charge  is a type of property we typically associate with very small types of matter, such as atoms of molecules. A charge is associated with atoms, the same way being tall or short is associated with people.
In a battery, a similar process occurs.  One side of the battery plays the role of the vendor, and the other plays the role of the buyer.  The only thing missing with just a battery is the people sitting between the vendor and buyer.  This is the reason why a battery can sit in a drawer for months without losing its ability to power things like your TV remote.  Without a clear path for the electrons to travel, they are forced to remain with the atom that doesn’t really want them.  In our popcorn vendor setup, this is the job of the wire.  The wire allows the electrons in a battery to move to where they are wanted.   [if gte mso 9]> 0 0 1 174 992 Potomac Institute for Policy Studies 8 2 1164 14.0 Normal 0 false false false EN-US JA X-NONE
Matter is a term for any type of material or thing.
If you think about the wire in a lamp, it contains more than one type of solid. It’s made up of both metal and plastic.
No matter what shape or form matter is in, we typically describe it as being in one of three states: a solid, a liquid, or a gas. Each of these states allows matter to behave in different ways. As liquids and gases, matter is relatively free to move around and change it’s special orientation. However, in solids, like in our battery set-up, this is not the case. In solids, molecules are stuck together and not allowed to move about, much like in a human pyramid.
The easiest way to accomplish this is for the vendor to hand the popcorn to the guy closest to him, then have him pass it to the next guy, and so on, until it reaches our buddy in the middle. This is illustrative of how electrons can be passed in solids, with the vendor being an atom that doesn’t want the electrons; the box of popcorn being the electrons, and the guy in the middle being our atom that wants electrons.
molecules.
The nuclei of atoms enjoy the company of electrons because they make the nucleus feel more stable. You could even say that electrons are friends of the nucleus. There are many different types of atoms, and each one has a preference for the number of electron friends they have hanging around them. Most atoms behavior is determined by their desire to obtain or lose an extra electron friend. When atoms, or combinations of atoms, change the number of electron friends they have around them it causes their behavior to change.
Molecules are a group of atoms that are connected.
Let’s think about how electrons move in a lamp.  To imagine how this would work, let’s set up a scenario where a vendor at a baseball game is trying to pass a box of popcorn down an aisle of people, so that the guy in the middle of the section doesn’t have to get up to get the box of popcorn.   [if gte mso 9]> 0 0 1 168 959 Potomac Institute for Policy Studies 7 2 1125 14.0 Normal 0 false false false EN-US JA X-NONE
However, this doesn’t explain how a battery makes a light bulb glow. Let’s address that next by imagining that in between the buyer and vendor is a guy who is in love with popcorn. The mere sight of popcorn makes him radiate with joy. Furthermore, he always has to take at least one delicious, buttery kernel every time he sees one. So now our wire, the line of people, contains one person who is almost certainly going to tax the popcorn as it moves past him. In our example with the battery, it is this tax that powers the light bulb.
          Have you ever wondered how a battery makes things work? How exactly does a battery make a light bulb shine? All things, like batteries, light bulbs, or even you are made of something called matter. Matter is a term for anything that has mass to it, such as the fly on the wall, or the mountain outside your window. All matter is made up of tiny forms known as molecules. There are many different types of molecules, which is why there are many different types of things. Molecules are themselves made up of even tinier forms called atoms. There are less than a hundred different types of atoms that occur naturally in our world, but there are an almost infinite number of ways to put them together.
When we connect the ends in our light bulb setup with a wire, the electrons are passed from the side of the battery that wants to give away electrons to the wire. The atoms then pass these electrons on, until they reach the bulb. The light bulb loves electrons and as they pass through it, the light bulb takes a few of these electrons before passing the majority of them through to the other end of the battery. When it takes these electrons, it radiates its excitement as the light we see. This will keep happening until the one side has no more electrons to give away. At that point the light bulb can’t tax the electrons to radiate light and our bulb goes out, because our battery has died.
Atoms make up every solid liquid or gas, as the smallest part.
This is similar to how a person’s money spending habits change, depending on how much money they have in their pockets. People are more willing to spend money when they have extra, and more likely to seek out money when they don’t have enough. Much like people, certain atoms have a tendency to ‘spend electrons’ and others have a tendency to ‘collect electrons.’
atoms.
charge
Despite the fact that, in solids, atoms are frozen in place, in some types of solids, the electrons are allowed to move while the nucleus remains stationary. Metals are a type of solid that allows electrons to move. Plastics are a type of solid that do not allow electrons to move.
Video Only
An ion is an atom or group of atoms that has lost or gained one or more electrons. When this occurs, the atom is no longer considered electrically neutral, it carries a charge and becomes an ion.
molecule
[if gte mso 9]> Normal.dotm 0 0 1 87 498 Full Sail 4 1 611 12.0 0 false 18 pt 18 pt 0 0 false false false
salt-bridge.
electrical energy,
ions.
An electrolytic solution is an electrically conductive solution made up of ions that have dissociated due to the thermodynamic interactions between solvent and solute molecules.
Atoms are the smallest part of an element.
                     The battery is a type of device that is referred to as an electrochemical cell.  Electrochemical cells are either man-made or naturally occurring environments, where a               that contains a unique type of molecule or atom separates two different metals.  The solution provides a path for the metals to exchange electrons through charged substances known as           An ion is an           or                  that has more or less electrons than it normally should and thus has a charge.  If we have a solution made up of ions, we would call it an If an ion has too many electrons, we would say that it has a negative charge and call it an anion.  If the opposite is true, and it does not have enough electrons, then we would say it has a positive charge and call it a cation. 
electrolytic solution.
A physical connection of the oxidation and reduction reactions of the galvanic electrochemical cell that maintains the ion balance by allowing ions to migrate.
As ions build up at both ends, the salt-bridge works to ensure that there is not too much of one type built up at either the anode or the cathode.  When too many ions begin to build up at the anode, the salt bridge allows them to move towards the cathode that has anions, as opposite charges attract.  The process also works the other way so that anions in the cathode can move to the anode side.  This is why the cathode and anode are named as such, because the cathode attracts cations and the anode attracts anions. The electrochemical cell makes electrical energy from a chemical reaction.  It turns                           the energy released as heat into the environment when an atom loses electrons, into                         which is the energy used to do work like pushing the electrons through a material, like wire. [if gte mso 9]> Normal.dotm 0 0 1 237 1351 Full Sail 11 2 1659 12.0 0 false 18 pt 18 pt 0 0 false false false
standard reduction potential,
atom,
When an atom in the anode gives up it’s electrons, they leave and move about, as  cations.  This also means that the metal begins, essentially,  to dissolve.  The process of a metal losing its electrons is called oxidation, and when oxidation leads to a substance falling apart or changing it’s structure, we refer to that as corrosion. As oxidation happens at the anode, the cathode begins to build up excess electrons.  The electrons do the exact opposite of what happens to the anode.  At the cathode the excess electrons pair up with ions that are missing electrons, most of the time causing them to change into a gas or form with a solid.  When a metal cation gains electrons we actually call this reduction, because it’s positive charge has been reduced.  [if gte mso 9]> Normal.dotm 0 0 1 171 978 Full Sail 8 1 1201 12.0 0 false 18 pt 18 pt 0 0 false false false Normal.dotm 0 0 1 114 651 Full Sail 5 1 799 12.0 0 false 18 pt 18 pt 0 0 false false false
The standard reduction potential is the likelihood for a chemical species to be reduced, and is measured in volts at standard conditions (25°C, a 1M ion concentration,1 atm partial pressure)
chemical energy,
solution
In the electrochemical cell, the metal that wants electrons more, because it does not have enough, is called the cathode, and the metal that would rather give away electrons, because it has too many, is called the anode.  When a wire connects the two metals, the anode starts to pass it’s electrons through the connecting wire to the cathode.  In order to do this, the atoms in the anode must lose electrons.
electrical equilibrium.
                    If calculations with the Nernst equation give a positive potential, it means that the change in Gibbs free energy for reaction is negative, and that electron transfer from the anodic substance to the cathodic substance will be spontaneous until equilibrium is reached.  We should remember that these thermodynamic equilibriums do not tell us anything about the                or rate at which the system will reach equilibrium. [if gte mso 9]> Normal.dotm 0 0 1 217 1241 Full Sail 10 2 1524 12.0 0 false 18 pt 18 pt 0 0 false false false
Gibbs free energy (G) is a thermodynamic state function relating enthalpy, temperature, and entropy.
thermodynamics.
So, where Gibbs free energy tells you how much energy is released in a reaction when 1 mol of reactants is converted to products, the electric potential tells you the amount of energy released when 1 mol of electrons is transferred from one substance to another.  The Nernst equation, seen here, allows us to calculate the likelihood that two substances will spontaneously exchange electrons.  We can use it to calculate the electric potential of a system when the reactants and products are at a specific concentration and temperature.
So, if a metal finds itself in an                                there are many different types of reactions that can occur, depending on: the concentrations of dissolved substances in the solution, the      , and            the                        Before anyone builds a system, they can use these equations to predict how much their design is going to lead to corrosion of parts of their system.  This is a very powerful tool, but calculating the energies for all equilibriums that can occur in a system isn’t always simple, as there can be many reactions to account for. By changing the properties of the system and calculating the electric potential, it is possible to design a system that truly limits undesired reactions.  This is the goal of material sustainment. The LED light is a great example of a situation where undesired reaction is limited by design.  In LED lights, the connection is well insulated from air, dirt, and water, protecting this part of the light from unwanted oxidation.  As a result of less energy lost to undesired oxidation, the LED light becomes more energy efficient than the traditional incandescent bulb.  [if gte mso 9]> Normal.dotm 0 0 1 108 616 Full Sail 5 1 756 12.0 0 false 18 pt 18 pt 0 0 false false false
Gibb’s free energy.
kinetics,
temperature.
electron distribution
aqueous solution
                  Corrosion takes place when two materials with different electric potentials come into contact either directly or indirectly through an electrolytic solution.  The electric potential of an electrochemical cell, like a battery, is a measure of the amount of energy that will be released when one mol of electrons is released from the Anode and driven to the cathode.  Factors such as Acidity or pH, ionic strength, and temperature influence the likelihood that a metal will corrode in a solution.  As a result, the electric potential of a system with fluctuate as these variables change. In order for any chemical reaction to occur without putting energy into the system, the reaction must lead the system to a state that is more energetically stable.  This is just basic                                The electric potential is essentially a measure of the stability of the                                     in a system.  If there is a more stable way to distribute the electrons, then oxidation-reduction will occur until the system has reached                                       The spontaneous transition of a system from one state to another, results in the release of an amount of energy, which in thermodynamics is known                  as [if gte mso 9]> Normal.dotm 0 0 1 206 1178 Full Sail 9 2 1446 12.0 0 false 18 pt 18 pt 0 0 false false false
Temperature describes the direction of energy flow or transfer between systems in contact with one another.
Each place on the graph represents a unique combination of the presence of Al’s friends. In some place he may have few proton friends, and in other places there may be many. In some places there may be few electron friends, while in other places there may be many of them.
Meet “Al the Screw.”  He is an aluminum screw.  Aluminum is a metal that many of us are familiar with because we use aluminum foil in our kitchens for cooking.
Now back to Al. Environments that allow the aluminum atoms of Al to stay together keep Al happy. Environments that cause his atoms to fall apart make him sad. This is because those environments make him fall apart or corrode. What is happy about that?
electrons
We can make a graph that helps us understand the combinations that make Al happy or sad, and it may look something like this:
What determines if a metal rusts or                    Do all metals rust? Do some metals corrode more easily than others? There are many factors that lead to the corrosion of materials, however, some factors are more important than others, and knowing how these factors change, can help us understand how likely a material is to corrode.
So, solid Al is made up of many atoms of aluminum that stick together so that Al the screw can exist. If the atoms that make up Al stopped sticking together, Al the screw would fall apart. This is why being a solid makes Al happy, because as long as his atoms stay together, he exists!
Al the Screw is like most people, in that his mood depends on his environment and who is around him.  In Al’s world, there are two types of friends, the proton and the electron friend.  Al may be happy or sad depending on the combinations of proton and electron friends he has around him.  In general, Al prefers the company of his electron friends to proton friends.  The exact combination that makes Al happy is unique to Al, and that combination may not make Fe the nail happy.      EndFragment
Certain environments that have particular combinations of protons and electrons will force the atoms that make up Al to ionize, and these ions will leave Al to go someplace else. This happens often when metals like Al find themselves in water because ions like floating around in water. These environments make Al sad, because the ions leave him and that causes him to corrode.
The next question we ask is: Why do certain combinations of proton and electron friends make Al happy or sad? To answer this, let’s look at Al when he is happy and when he is sad and see if we notice anything special.
What happens in these environments to make the atoms no longer stay together?
solid.
When we think about how a battery works, we see that one ends of the battery wants to reduce the number of electrons  it has around it, and the other end wants to increase the number of around it. What is it about the different ends of the battery that make this so? To answer this, let’s focus on a single metal.
We can relate to Al’s desire to be solid because, as humans, we are made up of lots of cells stuck together. If our cells stopped sticking together that would be bad news. I can tell you right now that if MY cells stopped sticking together I would not be happy.
corrodes?
When Al is happy we notice that he is solid.  So environments with combinations of electron and proton friends that allow him to remain solid make him happy. Why does remaining a solid make Al happy? Remember what a solid is: a solid what we call a substance that ‘stays together’.
In our discussion of the electrochemical cell, we learned that atoms can pick up or lose electrons and become special atoms we call ions.  Ions are special because they have a special property called a charge. Positive ions, which are atoms that have lost electrons, do not like other positive ions and will move away from each other. The same is true for negative ions: they too will move away from each other.
Electrical equilibrium is achieved when a system of oxidation-reduction reactions has reached a point where there is no net flow of the chemical and electrical species.
In the case of aluminum placed in water, everything is relative to our bar of aluminum.  If, in a given aqueous solution, the only object with electrons to spare is the aluminum bar, then the bar is going to lose electrons to it’s environment until                                                  is achieved.
Money doesn’t just lie around.  People have money and they exchange it.  If you have money to give away, we might describe this as free money.  The more substances you have in an aqueous solution that have free money, electrons, the more potential you have for other substances to be ‘given’ or ‘accept’ electrons.  When there aren’t substances that have ‘free money’ in a solution, we say that there is little ‘potential’ for other substances to gain electrons. [if gte mso 9]> Normal.dotm 0 0 1 109 622 Full Sail 5 1 763 12.0 0 false 18 pt 18 pt 0 0 false false false
In the Basic example, we used Al the Screw to demonstrate how the environment could effect corrosion, and make Al the Screw “Happy” or “Sad.”  Although such simplifications can help us understand the basics, let’s look at a more realistic environment that aluminum might find itself in. Let’s consider a large bar of aluminum. [if gte mso 9]> Normal.dotm 0 0 1 85 487 Full Sail 4 1 598 12.0 0 false 18 pt 18 pt 0 0 false false false
In the Basic section, this graph was labeled happy or sad, to illustrate whether Al the screw managed to hold together.When the conditions are such that the aluminum atoms can remain as a solid, we showed the aluminum as happy, and when the atoms are put into a state where they are away from each other, we show them as “sad”. As the graph shows, the amount of protons and electrons in a solution determine what amounts of aluminum in our chunk will be happy or sad, ionized, or solid. The nice part of this, is that other metals follow the same rules, not just aluminum. By making graphs, like this, for different metals, we can see how changing the number of electrons and protons in a solution will affect the tendency to become ions or solid.  This is powerful because it allows us to know, simply by looking at a graph, if a certain environment, defined by electric potential and pH, will cause a metal to corrode, ionize, or not to corrode, and remain a solid.   Now let’s show the different areas of the graph as “ion” or solid.
There is one important technicality that we need to discuss.  In aqueous solutions, we don’t have free electrons running around in the same way that protons do.  Instead, we find the number of free electrons by describing the potential for a substance in the solution to gain or lose electrons.  In this sense, free electrons are kind of like money.
Knowing this we can use a graph to represent what is happening.  The left axis represents the number of “free electrons” available to aluminum, and the bottom axis the number of protons.  Depending on the nature of the environment, the chunk of aluminum will either remains as a solid chunk, or will corrode by giving up its electrons and allowing them to form a type of charged ion.
electrochemical equilibrium
Describing an aqueous solution in terms of a number of protons hanging around isn’t a complete description.  This is because each substance in the aqueous environment also has a desire for electrons.  The two ways substances interact in an aqueous environment are that they either exchange protons, or electrons.  When they exchange protons, we say that this is acid-base chemistry, and when they exchange electrons we say that this is oxidation-reduction chemistry, or electrochemistry. [if gte mso 9]> Normal.dotm 0 0 1 121 693 Full Sail 5 1 851 12.0 0 false 18 pt 18 pt 0 0 false false false
The terms acid and base are adjectives, like the words hungry or full, and describe a molecules desire to keep or lose protons.  When we say something is an acid, we are saying that the substance is more likely to lose a proton to its environment.  When we say something is a base, we are saying that it is more likely to steal a proton from its environment.  Just as oxidation and reduction describe a process where an atom or molecule loses an electron, acidity and basicity describe a process where an atom or molecule loses protons.  [if gte mso 9]> Normal.dotm 0 0 1 154 879 Full Sail 7 1 1079 12.0 0 false 18 pt 18 pt 0 0 false false false
When we put aluminum into an aqueous solution we get various types of changes in the aluminum as it exchanges electrons and protons with the solution.  While this is happening, the aluminum is oxidized and leaves a chunk of metal to float around in the solution.  When this happens we say that the environment is corrosive because it promotes this oxidation.  Aluminum can also be oxidized to an anion, if it partners with the substance that stole its electrons to form a molecular anion.   And sometimes a substance will steal the electrons from aluminum but rather than leaving it them to float, will cause it to form another solid called an oxidized solid, or product. EndFragment
Traditional chemical equilibrium involves reactions that result from: the exchange of matter, or the dissolution of matter, into a solution.  Electrochemical equilibrium involves reactions involves oxidation-reduction reactions where free electrical charges are exchanged. [if gte mso 9]> Normal.dotm 0 0 1 117 670 Full Sail 5 1 822 12.0 0 false 18 pt 18 pt 0 0 false false false Normal.dotm 0 0 1 38 220 Full Sail 1 1 270 12.0 0 false 18 pt 18 pt 0 0 false false false
Since the Pourbaix diagram describes thermodynamic equilibria, we can use the Van’t Hoff equation, to describe chemical equilibria, and the Nernst equation for electrochemical equilibria.
One: if a reaction involves a solid, a dissolved substance, and a proton, in water, but the reaction involves no exchange of electrons…then the equation will give a straight, vertical line, because the electric potential is independent of the Standard electric potential. Two: If a reaction involves a solid, a dissolved substance, and an exchange of electrons, but no proton, the equation will give a straight, horizontal line because the electric potential is independent of pH. [if gte mso 9]> Normal.dotm 0 0 1 144 824 Full Sail 6 1 1011 12.0 0 false 18 pt 18 pt 0 0 false false false
Gibbs free energy
In addition, we must assume that all possible reaction products, chemical and electrochemical, between the metal and the aqueous solution, are known, as well as the                                 for each solid or ionic species for the temperature and pressure being considered.
Because the concentration of water is constant and Negative log of H plus can be written as pH, we can rewrite the Nernst equation again.
We can further take the complicated Pourbaix diagram and simplify it into regions that predict the susceptibility of our metal to undergo further corrosion.  In areas where the stable equilibrium between the metal and the solution is an oxidized, ionized product, we will expect the metal to corrode.  In areas where the metal remains in its reduced form, we consider this to be an area that the metal is immune from corrosion.  In areas where it forms a stable, oxidized product, we will expect the metal to be rather passive to corrosion. Passive doesn’t mean immune; it simply implies that corrosion may take place at a slower rate because layers of the metal underneath the oxidized layer will have a harder time being oxidized.  It is important to remember that while it may suggest this, it certainly does not implicitly say this because a Pourbaix diagram is a thermodynamic equilibrium plot, and cannot tell us any factual information regarding kinetics. [if gte mso 9]> Normal.dotm 0 0 1 200 1144 Full Sail 9 2 1404 12.0 0 false 18 pt 18 pt 0 0 false false false
The lines that are drawn on a Pourbaix diagram represent chemical and/or electrochemical equilibrium.  The line on the graph separates the reactants and products of the particular equilibrium represented by the line.  [if gte mso 9]> Normal.dotm 0 0 1 154 883 Full Sail 7 1 1084 12.0 0 false 18 pt 18 pt 0 0 false false false
[if gte mso 9]> Normal.dotm 0 0 1 85 487 Full Sail 4 1 598 12.0 0 false 18 pt 18 pt 0 0 false false false
Corrosion is just a context that scientists use to describe a thermodynamic reaction that leads to a substance degrading.  Understanding the fundamental forced and behaviors of the molecular components of a system allows us to better anticipate corrosion within that system.  This knowledge helps us design systems that are much better suited to withstand what would normally be corrosive environments.  Creating designs that are resistant, or can even prevent undesired corrosion, is the goal of materials sustainment.  One very useful tool in this process is the Pourbaix diagram. [if gte mso 9]> Normal.dotm 0 0 1 198 1129 Full Sail 9 2 1386 12.0 0 false 18 pt 18 pt 0 0 false false false
For each chemical equilibrium that emerges as a result of placing a solid metal into an aqueous environment, the equation can be used to generate a straight line that is either independent of the electric potential or pH, or is dependent on both.  In fact, there are only three lines are used in constructing a Pourbaix diagram.
Then further simply it. EndFragment
Click to visit pourbaix software sites
kinetics
However, we will need to slightly modify the Nernst equation to reflect the general reaction to account for the interaction of our material with the solvent, water.  In doing so, we can rewrite the Nernst equation.
You might expect that as we construct every line on the Pourbaix diagram we will have some intersecting lines that may appear as mass confusion.  However, the confusion is easily resolved by considering the equilibria involved in the intersecting lines.  For each horizontal or slanted line that is drawn, the side above the line indicated the oxidized product is stable and below the line, the reduced product is stable.  Vertical lines indicate whether or not the acid or conjugate base is stable for an acid-base pair. The most stable product is the area that remains below the lines and when it appears there is a region where multiple products should be present.  [if gte mso 9]> Normal.dotm 0 0 1 138 790 Full Sail 6 1 970 12.0 0 false 18 pt 18 pt 0 0 false false false
Academic Links (Scroll)
Watch the Pervasive Menace Music Video!
Glossary
Charge:   A charge may describe what is flowing in an electrical current.  Electrons have a charge of -1.  Protons have a charge of +1.
System:   Subsection of a defined universe being studied for its relationship with matter and energy. It may be open (exchanges matter and energy) or closed (exchanges energy).
Kinetics:   Kinetics is the branch of chemistry or biochemistry described by measuring and studying the rates of chemical reactions. Kinetics is unlike thermodynamics which incorporates the study of heat and temperature with the study of work and energy.
Electron:   An electron is a negatively charged subatomic particle found in the space about the nucleus. The electron orbits the nucleus.
Oxidation:   TReduction is a half-reaction in which a chemical species increases its oxidation number, usually by losing electrons. 
Chemical Energy:   Chemical energy is the energy contained in the structure of an atom or molecule. Chemical energy is the energy stored in the bonds of atoms and molecules and released in a chemical reaction.
Anion:   An anion is a negatively charged ion.  It possesses more electrons than protons. 
Liquid:   Liquid is composed of molecules that may move freely amongst each other; however the molecules themselves do not separate from one another.
Temperature:   Temperature is a physical property that determines the direction of heat flow or transfer between objects in contact with another object based on the kinetic energy between them.
Electron Distribution:   Electron distribution describes an electrons location based off a certain volume related to the type of atom.
Corrosion:   Corrosion is the deterioration of metals (materials) by oxidation-reduction reactions.
Anode:   An anode is where oxidaiton occurs.  In a voltaic/galvanic cell, the electrons flow from the anode to the cathode.
pH:   pH is a numerical representation of the measure of the acidity or basicity of an aqueous solution. Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline.
Matter:   Matter is something that has mass and occupies space. Matter is defined by five known phases, or states: solid, liquid, gas, plasma and Bose-Einstein condensates. The structures of each state dependent densities of the particles.
Thermodynamics:   Area of physics which incorporates the study of heat and temperature with the study of work and energy.
Faraday’s Constant:   Faraday constant is the magnitude of electric charge per one mole of electrons.
Electrical Energy:   Electrical energy is the energy stemming from the flow of electric charge through conduction materials such as metals and electrolytes.
Aqueous Solution:   An aqueous solution is a solution in which the substance responsible for dissolving the solute is water.
Reduction:   Reduction is a half-reaction in which a chemical species decreases its oxidation number, usually by gaining electrons. 
Molecule:   A molecule is the smallest physical unit of an element. It is consisting of one or more like atoms in an element or two or more different atoms from different elements.
Salt-Bridge:   Physical connection of the oxidation and reduction reactions of the galvanic electrochemical cell that maintains the ion balance by allowing ion to migrate.
Gas:   Gas is a fluid substance that is sometimes related to being air like. A expands freely in order to fill any space available to it, regardless of its quantity.
Electrochemical Equilibrium:   Electrical equilibrium is when oxidation-reduction reactions will occur until the system has reached a point where no net flow of the chemical and electrical species.
Work:   Work is the energy required to move an object against a force. Work is equal to the force times the distance the object moves.
Atom:   The smallest part of an element that retains all of that elements characteristics.  
Solid:   Solid is composed of molecules that do not move freely amongst each other. The molecules themselves do not separate from one another.
Electrochemical Cell:   The electrochemical cell is a device that facilitates chemical reactions in order to generate electrical energy.
Cathode:   A cathode is where reduction occurs.  In a voltaic/galvanic cell, the electrons flow from the anode to the cathode. 
Gibbs Free Energy:   Gibbs free energy represents the change in free energy of a reaction. I represent the difference in energy between the reactants and the products. It allows you to predict if a reaction will occur spontaneously.
Heat:   Energy transfer from one system or body to another by thermal interaction.
Electrode:   In an electrochemical cell the electrode is used to move electrons into and out of the solution. An electrode could be a metal plate or wire.
Solution:   A substance dissolved in another substance in which particles of one or more substances (the solute) are distributed even within the other substance (the solvent).
Nernst Equation:   The Nernst Equation is an mathematical expression relating the voltage of a chemical cell to its standard cell potential and to the concentrations of the reactants and product. 
Cation:   A cation is a positively charged ion.  It possesses fewer electrons than protons.
Ion:   An ion is an atom or group of atoms that has lost or gained one or more electrons. When it does this is no longer considered electrically neutral, it carries a charge.
Electrolytic Solution:   An electrolytic solution is a solution made up of ions that have dissociated due to the thermodynamic interactions between solvent and solute molecules and is electrically conductive.
Standard Reduction Potential:   The standard reduction potential is the likelihood for a chemical species to be reduced, and is measured in volts at standard conditions (25°C, a 1 M ion concentration,1 atm partial pressure)
Nucleus:   The nucleus is the central region of an atom which retains the bulk of the atom's mass, composed of  negatively charged electrons, positively charged protons.
gfgfgfgfgfgfgf
Books (scroll)
Alternative Futures for Corrosion and Degradation Research
Corrosion E-book available on iTunes!