Atomic Structure:
The Basic structure of all materials that are seen or used every day conforms with a set pattern known as the atomic structure of matter. When a building is under construction, there are definite steps that are followed by the builders from its beginning to its completion. the materials used in the construction(steel girders, bricks,cement,etc.) when placed in their proper order and number, form a building. This concept of definite parts in a proper order can be related to the basic structure of all matter.
Matter:
Matter is anything that has mass and occupies space. Matter may take many forms. it may be a liquid, such as water , a gas, such as oxygen, or a solid, such as stone. Matter, as we know it, normally has weight because anything that has mass and is on or near the earth is influenced (pulled) by the force of earth's gravity. Matter may be made up of a single element, or it may be a combination of two or more elements.
Elements:
An element is a substance that cannot be changed by chemical means.
Atom:
The smallest particle to which an element can be reduced and still retain its original characteristics is the atom
One typical atom is lithium which is shown below. Composed very much like our solar system, the atom consists of a relatively large central body with small bodies revolving in orbits in orbits about it.
The simplest atom is hydrogen which is shown on the next page. This atom consists of a central body with one small body revolving around the center in an orbit. the central body is called the nucleus, and the revolving or planetary body is called electron. The nucleus contains a positive unit particle and the proton. The electron is a negative unit particle and the proton is a positive unit particle. We can replace the term "unit particle"with "charge". The word "charge" implies a potential force. For instance a gun is said to be charged if it is ready to fire.
When a particular atom such as copper is neutral, or balanced, the negative charges balance the positive charges, and the net charge on the atom is zero.
Electron charge + Proton Charge=Atom Charge
(-28) (+29) +0
If through some outside force, an electron is broken away from the outer orbit, the atom is no longer neutral. Assume that one electron is removed from a copper atom. When this action takes place, the copper atom becomes a positive body with a net charge to +1 due to the absence of one electron which would make it neutral.
Electron Charge + Proton Charge = Atom Charge
(-30) (+29) -1
In making the copper atom a positive body, the question arises: what happened to the electron? whenever an electron is removed from its orbit through the action of some outside force, it becomes a free electron. Free electrons are electrons which have been removed from their orbits and are free to move about among the atoms of the material. The external force which causes the electron to be released gives the free electron motion and thus velocity.
The movement of free electrons is shown below, where a momentary outside force removes one electron from Atom A, causing the atom to be a positively charged body.
The electrons from Atom A, Having velocity, strikes an electron in the outer ring of Atom B. In the collision, the electron from Atom A sticks in Atom B's outer orbit but, knocks out one electron from this orbit.
Because of the equal exchange of the electron in its outer orbit, Atom B still maintains its state of balance. The same process of travel and collision of the free electron occurs with Atom C and D. The velocity of the free electron leaving Atom D is now quite low because of the three collisions. Upon entering the orbit of Atom A, this free electron returns the state of balancing to the ring.
The above figure and the related discussion bring to light a very important principle: When the application of a force to a material causes the electrons of that material to move from one atom to another, the result is flow of negative electric charges; or stated in different words, an electric current is the flow or movement of electrons from one atom to another.
Conductor
Some atoms form free electrons and some do not. Consequently, some substances conduct an electric current readily and are know as conductors, while others do not conduct electric current and are know as insulators. A good conductor of electric current is a material that has a large number of electrons that easily become free when acted upon by some external force.
Insulator
An insulator is a material that has few electrons available to become free electrons.
Laws of Electrostatic Charges
There are only two laws which we must concern ourselves with:
Current
An electric current is a flow of electrons, through some material, from a point of negative potential to a point of positive potential. The rate of flow of electrons is expressed in terms of the ampere. A current flow of one ampere is said to flow at a point when one coulomb (6.24 billion billion electrons = 6.24 * 10^18 electrons) passes through a given point in one second. Expressed in a formula:
I = Q/T
Where:
I = Current in amperes
Q = Quantity of electrical charge in coulombs
T = Time in seconds
Electromotive Force (EMF)
Electromotive force is the force that pushes the electrons along a conductor that causes current flow. The strength of this electromotive force is measured with a voltmeter.
Resistance
Resistance to electric current flow is a fundamental characteristics of any material. The resistance of any conductor is directly proportional to the conductor's length and is inversely proportional to its cross-sectional area.
Practical Units
Thus far we have learned that an electromotive force (EMF) is capable of setting up a flow of current in a conductor. The next important step is to learn how much EMF is needed to set up a certain amount of current in a conductor of a given resistance. to do this, we should have definite units of measurements for electric currents, EMF and resistance.
Units of Electric Current - Ampere
Electricity makes itself known by its effects. One of its effects is chemical, and this effect is used to establish the basic unit electric current, which is the ampere.
The ampere is the unvarying electric current which, when passed through a solution of silver nitrate in water, will deposit silver at the rate of 0.001118 grain per second. The weight of the silver deposit is found by a very accurate measurement of the element before and after the run.
In practice, it is neither convenient or practical to measure electric current by this electrochemical technique. An instrument known as an ammeter is based on the magnetic effect of electric current, but its reading are based on the result of the fundamental electrochemical action.
Unit of Electromotive Force - Volt
The electromotive force or difference of potential needed to establish a flow of current in a conductor is measured in volts. The ordinary dry cell, when new, has an electromotive force of 1.5(one and one-half) volts. The unit of electromotive force is responsible for the term voltage being used to express electromotive force and difference of potential. The instrument generally used to measure electromotive force, or voltage, is the voltmeter.
Unit of Resistance - Ohm
Any substance, the atoms of which have a number of free electrons, is a conductor of electricity. Copper is a good conductor. Iron, aluminum, silver, gold, and many other metals, are all conductors of electricity. Wire made of these metals, of the same diameter and length as the copper wire, will conduct electricity, but the amount of current measured with an ammeter will be different for every metal used, other conditions, such as voltage of the battery and the dimensions of the wire, remaining the same. The quality of a conductor which limits or opposes the flow of electron, or current, is called resistance. Resistance is expressed in ohms.
The resistance of a conductor is 1 ohm when an EMF of 1 volt causes a current flow of 1 ampere to occur. In practice, the resistance of a conductor or of a circuit may be calculated when the values of the applied voltage and the resultant current are known. It may also be measured with an instrument know as an ohmmeter.
Ohms Law
There is definite relation between the voltage, the current, and the resistance of a circuit. This relation is given by Ohms law which may be expressed in the form of rules or equations. The rules are as follows:
Rule 1: The current, in amperes, is equal to the applied voltage, in volts, divided by the resistance, in ohms.
Amperes = Volts/Ohms
I = V/R
Rule 2: The resistance, in ohms, is equal to the voltage, in volts, divided by the current, in amperes
Ohms = Volts/Amperes
R = V/I
Rule 3: The voltage, in volts, is equal to the current. in amperes, multiplied by the resistance, ohms.
Volts = Amperes * Ohms
V = I*R
Ohms law is often expressed in the forms above, but with generally adopted symbols: I for current, or amperes; E for Voltage, or volts; and R for Resistance, or ohms. When expressed in this manner, Ohms Law becomes:
I = E/R or R =E/I or E = I*R
An easy way to remember Ohms Law is with a triangle relation. By covering the parameter you are looking for, the remaining characters tell you what to do. Thus, if you want to know the voltage, place your thumb over the E and that leaves you with I*R. Another example would be current. Cover the I with your thumb and that leaves you E/R.
The foregoing rules and equations show that in a direct circuit three different quantities are involved, namely, volts, amperes, and ohms. When any of these quantities are known, the third may be determined by Ohms Law.
THE TWO GENERAL TYPES OF ELECTRICITY
There are two general types of electric current flow which will be involved with corrosion and corrosion control work. These are alternating current (AC) and direct current (DC).
Alternating Current
Alternating current (AC) electricity is that which flows in one direction and then in the opposite direction in accord with an established pattern. As an example, the usual alternating current power sources used in the united states have a frequency of 60 cycles per second. This is referred to as 60 Hertz(or 60 Hz).
As can be seen from the next illustration, the current flow at the beginning of the cycle ( left side of the illustration) is zero. The current builds up to a peak in the forward direction and then drops back to zero at the end of the first half cycle. It then reverses its direction of flow and builds up to a maximum in the reverse direction. Following this, it again drops back to zero at the end of the second half cycle (which is the end of one full cycle). At this point, it again reverses direction to start the next cycle.
From this, it can be seen that there are, in effect, two net current reversals for one full cycle. This means for a normal 60 Hz alternating current power source, the current flow changes direction 120 times per second.
The shape of the normal current flow plot from the usual alternating current commercial power source is known as sine wave.
Significance of Alternating Current
Alternating current electricity is a relatively insignificant factor as a cause of corrosion except in very special cases.
In control of corrosion, however, commercial AC power sources are used as an energy source to power corrosion control equipment such as rectifiers ( which convert AC power to DC power) are widely used in impressed current cathodic protection systems.
Direct Current
Direct Current (DC) electricity is that which normally flows in one direction only rather that changing direction in accord with an established pattern as was discussed for alternating current.
An example of direct current is that from a battery powering a common flashlight.
Significance of Direct Current
DC electricity is of prime importance in the consideration of the corrosion process. It is directly involved in various types of corrosion cells. It is also directly involved in corrosion control by the use of various types of cathodic protection.
The Basic structure of all materials that are seen or used every day conforms with a set pattern known as the atomic structure of matter. When a building is under construction, there are definite steps that are followed by the builders from its beginning to its completion. the materials used in the construction(steel girders, bricks,cement,etc.) when placed in their proper order and number, form a building. This concept of definite parts in a proper order can be related to the basic structure of all matter.
Matter:
Matter is anything that has mass and occupies space. Matter may take many forms. it may be a liquid, such as water , a gas, such as oxygen, or a solid, such as stone. Matter, as we know it, normally has weight because anything that has mass and is on or near the earth is influenced (pulled) by the force of earth's gravity. Matter may be made up of a single element, or it may be a combination of two or more elements.
Elements:
An element is a substance that cannot be changed by chemical means.
Atom:
The smallest particle to which an element can be reduced and still retain its original characteristics is the atom
One typical atom is lithium which is shown below. Composed very much like our solar system, the atom consists of a relatively large central body with small bodies revolving in orbits in orbits about it.
When a particular atom such as copper is neutral, or balanced, the negative charges balance the positive charges, and the net charge on the atom is zero.
Electron charge + Proton Charge=Atom Charge
(-28) (+29) +0
If through some outside force, an electron is broken away from the outer orbit, the atom is no longer neutral. Assume that one electron is removed from a copper atom. When this action takes place, the copper atom becomes a positive body with a net charge to +1 due to the absence of one electron which would make it neutral.
Electron Charge + Proton Charge = Atom Charge
(-30) (+29) -1
In making the copper atom a positive body, the question arises: what happened to the electron? whenever an electron is removed from its orbit through the action of some outside force, it becomes a free electron. Free electrons are electrons which have been removed from their orbits and are free to move about among the atoms of the material. The external force which causes the electron to be released gives the free electron motion and thus velocity.
The movement of free electrons is shown below, where a momentary outside force removes one electron from Atom A, causing the atom to be a positively charged body.
The electrons from Atom A, Having velocity, strikes an electron in the outer ring of Atom B. In the collision, the electron from Atom A sticks in Atom B's outer orbit but, knocks out one electron from this orbit.
Because of the equal exchange of the electron in its outer orbit, Atom B still maintains its state of balance. The same process of travel and collision of the free electron occurs with Atom C and D. The velocity of the free electron leaving Atom D is now quite low because of the three collisions. Upon entering the orbit of Atom A, this free electron returns the state of balancing to the ring.
The above figure and the related discussion bring to light a very important principle: When the application of a force to a material causes the electrons of that material to move from one atom to another, the result is flow of negative electric charges; or stated in different words, an electric current is the flow or movement of electrons from one atom to another.
Conductor
Some atoms form free electrons and some do not. Consequently, some substances conduct an electric current readily and are know as conductors, while others do not conduct electric current and are know as insulators. A good conductor of electric current is a material that has a large number of electrons that easily become free when acted upon by some external force.
Insulator
An insulator is a material that has few electrons available to become free electrons.
Laws of Electrostatic Charges
There are only two laws which we must concern ourselves with:
- Like Charges repel
- Unlike charges attract
Current
An electric current is a flow of electrons, through some material, from a point of negative potential to a point of positive potential. The rate of flow of electrons is expressed in terms of the ampere. A current flow of one ampere is said to flow at a point when one coulomb (6.24 billion billion electrons = 6.24 * 10^18 electrons) passes through a given point in one second. Expressed in a formula:
I = Q/T
Where:
I = Current in amperes
Q = Quantity of electrical charge in coulombs
T = Time in seconds
Electromotive Force (EMF)
Electromotive force is the force that pushes the electrons along a conductor that causes current flow. The strength of this electromotive force is measured with a voltmeter.
Resistance
Resistance to electric current flow is a fundamental characteristics of any material. The resistance of any conductor is directly proportional to the conductor's length and is inversely proportional to its cross-sectional area.
Practical Units
Thus far we have learned that an electromotive force (EMF) is capable of setting up a flow of current in a conductor. The next important step is to learn how much EMF is needed to set up a certain amount of current in a conductor of a given resistance. to do this, we should have definite units of measurements for electric currents, EMF and resistance.
Units of Electric Current - Ampere
Electricity makes itself known by its effects. One of its effects is chemical, and this effect is used to establish the basic unit electric current, which is the ampere.
The ampere is the unvarying electric current which, when passed through a solution of silver nitrate in water, will deposit silver at the rate of 0.001118 grain per second. The weight of the silver deposit is found by a very accurate measurement of the element before and after the run.
In practice, it is neither convenient or practical to measure electric current by this electrochemical technique. An instrument known as an ammeter is based on the magnetic effect of electric current, but its reading are based on the result of the fundamental electrochemical action.
Unit of Electromotive Force - Volt
The electromotive force or difference of potential needed to establish a flow of current in a conductor is measured in volts. The ordinary dry cell, when new, has an electromotive force of 1.5(one and one-half) volts. The unit of electromotive force is responsible for the term voltage being used to express electromotive force and difference of potential. The instrument generally used to measure electromotive force, or voltage, is the voltmeter.
Unit of Resistance - Ohm
Any substance, the atoms of which have a number of free electrons, is a conductor of electricity. Copper is a good conductor. Iron, aluminum, silver, gold, and many other metals, are all conductors of electricity. Wire made of these metals, of the same diameter and length as the copper wire, will conduct electricity, but the amount of current measured with an ammeter will be different for every metal used, other conditions, such as voltage of the battery and the dimensions of the wire, remaining the same. The quality of a conductor which limits or opposes the flow of electron, or current, is called resistance. Resistance is expressed in ohms.
The resistance of a conductor is 1 ohm when an EMF of 1 volt causes a current flow of 1 ampere to occur. In practice, the resistance of a conductor or of a circuit may be calculated when the values of the applied voltage and the resultant current are known. It may also be measured with an instrument know as an ohmmeter.
Ohms Law
There is definite relation between the voltage, the current, and the resistance of a circuit. This relation is given by Ohms law which may be expressed in the form of rules or equations. The rules are as follows:
Rule 1: The current, in amperes, is equal to the applied voltage, in volts, divided by the resistance, in ohms.
Amperes = Volts/Ohms
I = V/R
Rule 2: The resistance, in ohms, is equal to the voltage, in volts, divided by the current, in amperes
Ohms = Volts/Amperes
R = V/I
Rule 3: The voltage, in volts, is equal to the current. in amperes, multiplied by the resistance, ohms.
Volts = Amperes * Ohms
V = I*R
Ohms law is often expressed in the forms above, but with generally adopted symbols: I for current, or amperes; E for Voltage, or volts; and R for Resistance, or ohms. When expressed in this manner, Ohms Law becomes:
I = E/R or R =E/I or E = I*R
An easy way to remember Ohms Law is with a triangle relation. By covering the parameter you are looking for, the remaining characters tell you what to do. Thus, if you want to know the voltage, place your thumb over the E and that leaves you with I*R. Another example would be current. Cover the I with your thumb and that leaves you E/R.
The foregoing rules and equations show that in a direct circuit three different quantities are involved, namely, volts, amperes, and ohms. When any of these quantities are known, the third may be determined by Ohms Law.
THE TWO GENERAL TYPES OF ELECTRICITY
There are two general types of electric current flow which will be involved with corrosion and corrosion control work. These are alternating current (AC) and direct current (DC).
Alternating Current
Alternating current (AC) electricity is that which flows in one direction and then in the opposite direction in accord with an established pattern. As an example, the usual alternating current power sources used in the united states have a frequency of 60 cycles per second. This is referred to as 60 Hertz(or 60 Hz).
As can be seen from the next illustration, the current flow at the beginning of the cycle ( left side of the illustration) is zero. The current builds up to a peak in the forward direction and then drops back to zero at the end of the first half cycle. It then reverses its direction of flow and builds up to a maximum in the reverse direction. Following this, it again drops back to zero at the end of the second half cycle (which is the end of one full cycle). At this point, it again reverses direction to start the next cycle.
From this, it can be seen that there are, in effect, two net current reversals for one full cycle. This means for a normal 60 Hz alternating current power source, the current flow changes direction 120 times per second.
The shape of the normal current flow plot from the usual alternating current commercial power source is known as sine wave.
Significance of Alternating Current
Alternating current electricity is a relatively insignificant factor as a cause of corrosion except in very special cases.
In control of corrosion, however, commercial AC power sources are used as an energy source to power corrosion control equipment such as rectifiers ( which convert AC power to DC power) are widely used in impressed current cathodic protection systems.
Direct Current
Direct Current (DC) electricity is that which normally flows in one direction only rather that changing direction in accord with an established pattern as was discussed for alternating current.
An example of direct current is that from a battery powering a common flashlight.
Significance of Direct Current
DC electricity is of prime importance in the consideration of the corrosion process. It is directly involved in various types of corrosion cells. It is also directly involved in corrosion control by the use of various types of cathodic protection.
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