Term
What is corrosion?
• ______ of materials due to reactions with
their ______.
• Materials: metals, polymers & ceramics
• Environment: liquids & gases, sometimes solids
• Ambient or elevated temperatures |
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Definition
What is corrosion?
• DETERIORATION of materials due to reactions with
their ENVIRONMENT.
• Materials: metals, polymers & ceramics
• Environment: liquids & gases, sometimes solids
• Ambient or elevated temperatures |
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Term
- Economics and ______!
• >$275 billion problem in the U.S.
• Mitigate life-threatening failures
• Prevent costly repairs in manufacturing plants.
• ____ extension – health monitoring of structures |
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Definition
- Economics and SAFETY!
• >$275 billion problem in the U.S.
• Mitigate life-threatening failures
• Prevent costly repairs in manufacturing plants.
• LIFE extension – health monitoring of structures |
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Term
ELECTROCHEMICAL CORROSION
Two reactions are necessary:
-- oxidation reaction, occurs at the ____, also called the _____ reaction
-- reduction reaction, occurs at the ____, also called the _____ reaction |
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Definition
ELECTROCHEMICAL CORROSION
Two reactions are necessary:
-- oxidation reaction, occurs at the ANODE, also called the ANODIC reaction
-- reduction reaction, occurs at the CATHODE, also called the CATHODIC reaction |
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Term
• Other reduction reactions in solutions with dissolved _____:
-- acidic solution -- neutral or basic solution |
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Definition
• Other REDUCTION reactions in solutions with dissolved OXYGEN:
-- acidic solution, O2, H+, and e- join to make water
-- neutral or basic solution, O2, water, and e- join to make OH
Basically, there would be two reduction reactions supporting the oxidation reaction
**The reaction we are most concerned with, from a metallic corrosion standpoint, is the anodic reaction** |
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Term
Cathodic reaction is when you ____ the electrons
Anodic reaction is when you ____ the electrons |
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Definition
Cathodic (reduction) reaction is when you USE the electrons
Anodic (oxidation) reaction is when you GIVE UP the electrons |
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Term
In reality, there are _____ areas of the metal surface that
serve as cathodes and others that serve as anodes.
• For mild steel in HCl, H2 is evolved at the cathodes, but over
time it may appear that _____ corrosion is occurring because anodic and cathodic areas change with ____. |
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Definition
In reality, there are LOCALIZED areas of the metal surface that
serve as cathodes and others that serve as anodes.
• For mild steel in HCl, H2 is evolved at the cathodes, but over
time it may appear that UNIFORM corrosion is occurring because anodic and cathodic areas change with TIME. |
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Term
Electrode potentials can be combined ______ to give cell
potential:
Ecell = Ecathode – Eanode
• Not all metals oxidize to form ____ with the same degree of ease
which leads to different potentials for different metal reactions |
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Definition
Electrode potentials can be combined ALGEBRAICALLY to give cell potential:
Ecell = Ecathode – Eanode
• Not all metals oxidize to form IONS with the same degree of ease which leads to different potentials for different metal reactions |
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Term
We can easily measure the potential difference across
an electrochemical cell using a ______. |
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Definition
We can easily measure the potential difference across
an electrochemical cell using a VOLTMETER. |
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Term
In the external circuit...
electrons flow from the ____ to the ____
current flows from the ____ to the ____ . |
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Definition
In the external circuit...
ELECTRONS flow from the ANODE to the CATHODE
CURRENT flows from the CATHODE to the ANODE. |
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Term
Anodes have the [more/less] positive electrode potential
Cathodes have the [more/less] positive electrode potential |
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Definition
Anodes have the LESS positive electrode potential
Cathodes have the MORE positive electrode potential |
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Term
In order to assess standard electrode potentials across a variety of electrode combinations, it is convenient to assign part of the cell potential to each electrode.
This is called a _____ potential
These _____ potentials need to be relative to a
standard which is traditionally the _____. |
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Definition
In order to assess standard electrode potentials across a variety of electrode combinations, it is convenient to assign part of the cell potential to each electrode.
This is called a HALF-CELL potential
These HALF potentials need to be relative to a
standard which is traditionally the STANDARD HYDROGEN POTENTIAL (SHE). |
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Term
The ____ is an ancient half-cell where hydrogen gas is bubbled over a platinum electrode:
2H+ + 2 e- ↔ H2
• This electrode isn’t very practical to use in
experiments.
• However, this is the standard and in a reversible cell, the potential between it an any electrode is called the reversible potential of that electrode, E.
• If operated under standard conditions, then it is the
_____ _____ _____, Eo |
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Definition
The SHE is an ancient half-cell where hydrogen gas is bubbled over a platinum electrode:
2H+ + 2 e- ↔ H2
• This electrode isn’t very practical to use in experiments.
• However, this is the standard and in a reversible cell, the potential between it an any electrode is called the reversible potential of that electrode, E.
• If operated under standard conditions, then it is the STANDARD ELECTRODE POTENTIAL, Eo |
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Term
| Since any reaction can be written as an oxidation or reduction reaction, the standard is to write it in _____ |
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Definition
| Since any reaction can be written as an oxidation or reduction reaction, the standard is to write it in REDUCTION |
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Term
Standard Hydrogen Potential:
Two outcomes:
--_______ of metal, metal is the anode
-- _______ of metal is the cathode |
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Definition
Standard Hydrogen Potential:
Two outcomes:
--CORROSION of metal, metal is the anode (giving up electrons and ions) Vmetal < 0 (relative to Pt)
-- ELECTRODISPOSITION, metal is the cathode (gaining electrons and ions) Vmetal > 0 (relative to Pt)
Vmetal = standard electrode potential |
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Term
| Metal with [smaller/greater] Vmetal corrodes |
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Definition
| Metal with SMALLER Vmetal corrodes |
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Term
Reduce Vcathod - Vanode by...
increasing molarity of anode
decreasing molarity of cathode
increasing TEMPERATURE |
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Definition
Reduce Vcathod - Vanode by...
increasing molarity of anode
decreasing molarity of cathode
increasing TEMPERATURE |
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Term
• So far, we have mainly assumed that:
• Electrochemical corrosion is the only deterioration
mechanism.
• Anodic and cathodic reactions take place all over
the electrode surface with the locations of these
reactions changing places on the surface.
• There are no significant macroscopic concentration
differences in the electrolyte along the metal
surface and the metal is fairly homogeneous.
• These assumptions lead to one type of corrosion,
______ or ______ corrosion. |
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Definition
• So far, we have mainly assumed that:
• Electrochemical corrosion is the only deterioration
mechanism.
• Anodic and cathodic reactions take place all over
the electrode surface with the locations of these
reactions changing places on the surface.
• There are no significant macroscopic concentration
differences in the electrolyte along the metal
surface and the metal is fairly homogeneous.
• These assumptions lead to one type of corrosion,
GENERAL or UNIFORM corrosion. |
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Term
The other forms of corrosion depend on deviations from the assumptions made for general / uniform corrosion which may be due to:
• The design (the macro-geometry of the metal surface)
• The combination of metal and the environment
• The state of the surface (particularly cleanliness and roughness)
• Other deterioration mechanisms |
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Definition
No Q, just think this might be important
The other forms of corrosion depend on deviations from the assumptions made for general / uniform corrosion which may be due to:
• The design (the macro-geometry of the metal surface)
• The combination of metal and the environment
• The state of the surface (particularly cleanliness and roughness)
• Other deterioration mechanisms |
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Term
General or Uniform Corrosion
• By definition, this type of attack is even over a surface leading to a relatively uniform thickness reduction.
• results in the [least/most] material mass loss.
• From an inspection point of view it is easily distinguishable as long as ___________.
• Its effects can be predictable by taking observations over time.
• Internal corrosion of pipelines or buried metallic components
can make observation more difficult.
- Corrosion proceeds relatively even across the surface with
different regions acting as ____ and ____.
• The metallic component could be submerged (e.g. in water) or exposed to moist air (e.g. near a body of water or humid air)
providing the necessary electrolyte for ionic conduction of cathodic reactants.
• Aqueous and atmospheric corrosion conditions can lead to uniform corrosion.
• Homogeneous materials without a significant passivation
tendency in the actual environment are liable to this form of
corrosion. |
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Definition
General or Uniform Corrosion
• By definition, this type of attack is even over a surface leading to a relatively uniform thickness reduction.
• results in the MOST material mass loss.
• From an inspection point of view it is easily distinguishable as long as IT CAN EASILY BE SEEN.
• Its effects can be predictable by taking observations over time.
• Internal corrosion of pipelines or buried metallic components
can make observation more difficult.
- Corrosion proceeds relatively even across the surface with
different regions acting as CATHODES and ANODES.
• The metallic component could be submerged (e.g. in water) or exposed to moist air (e.g. near a body of water or humid air)
providing the necessary electrolyte for ionic conduction of cathodic reactants.
• Aqueous and atmospheric corrosion conditions can lead to uniform corrosion.
• Homogeneous materials without a significant passivation
tendency in the actual environment are liable to this form of
corrosion. |
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Term
Uniform corrosion is assumed to be the most ____ form of
corrosion.
• However, it is not recognized as a _____ form of corrosion due to:
• Prediction of thickness reduction rate can be done by
means of simple tests. Corresponding corrosion allowance
can be added, taking into account strength requirements
and lifetime.
• Available protection methods are usually so efficient that
the corrosion rate is reduced to an acceptable level. (e.g.
Coatings, cathodic protection, change of environment) |
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Definition
Uniform corrosion is assumed to be the MOST COMMON form of corrosion.
• However, it is NOT recognized as a DANGEROUS form of corrosion due to:
• Prediction of thickness reduction rate can be done by
means of simple tests. Corresponding corrosion allowance
can be added, taking into account strength requirements
and lifetime.
• Available protection methods are usually so efficient that
the corrosion rate is reduced to an acceptable level. (e.g.
Coatings, cathodic protection, change of environment) |
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Term
FORMS OF CORROSION:
• Stress corrosion:
Corrosion at crack tips when a tensile stress is present.
• Erosion-corrosion
Combined chemical attack and mechanical wear (e.g., pipe elbows).
• Pitting
Downward propagation of small pits and holes.
• Crevice
Narrow and confined spaces.
• Galvanic
Dissimilar metals are physically joined in the presence of an electrolyte. The more anodic metal corrodes.
• Intergranular
Corrosion along grain boundaries, often where precip. particles form.
• Selective Leaching
Preferred corrosion of one element/constituent [e.g., Zn from brass (Cu-Zn)].
• Uniform Attack
Oxidation & reduction reactions occur uniformly over surfaces. |
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Definition
FORMS OF CORROSION:
• Stress corrosion:
Corrosion at crack tips when a tensile stress is present.
• Erosion-corrosion
Combined chemical attack and mechanical wear (e.g., pipe elbows).
• Pitting
Downward propagation of small pits and holes.
• Crevice
Narrow and confined spaces.
• Galvanic
Dissimilar metals are physically joined in the presence of an electrolyte. The more anodic metal corrodes.
• Intergranular
Corrosion along grain boundaries, often where precip. particles form.
• Selective Leaching
Preferred corrosion of one element/constituent [e.g., Zn from brass (Cu-Zn)].
• Uniform Attack
Oxidation & reduction reactions occur uniformly over surfaces. |
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Term
Corrosion prevention:
• Materials Selection
‒ Use metals that are relatively unreactive in the corrosion environment -- e.g., Ni in basic solutions
‒ Use metals that passivate:
‒ These metals form a thin, adhering oxide layer that
slows corrosion.
• _____ the temperature (reduces rates of oxidation and
reduction)
• Apply _____ _____ -- e.g., films and coatings
• Add _______ (substances added to solution that decrease its reactivity)
• Slow oxidation/reduction reactions by removing reactants (e.g., remove O2 gas by reacting it w/an inhibitor).
• ______ (or sacrificial) protection
‒ Attach a more anodic material to the one to be protected. |
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Definition
Corrosion prevention:
• Materials Selection
‒ Use metals that are relatively unreactive in the corrosion environment -- e.g., Ni in basic solutions
‒ Use metals that passivate:
‒ These metals form a thin, adhering oxide layer that slows corrosion.
• LOWER the temperature (reduces rates of oxidation and
reduction)
• Apply PHYSICAL BARRIERS -- e.g., films and coatings
• Add INHIBITORS (substances added to solution that decrease its reactivity)
• Slow oxidation/reduction reactions by removing reactants (e.g., remove O2 gas by reacting it w/an inhibitor).
• CATHODIC (or sacrificial) protection
‒ Attach a more anodic material to the one to be protected. |
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Term
| Two types of semiconductors: ____ and _____ |
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Definition
| Two types of semiconductors: INTRINSIC and EXTRINSIC |
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Term
Two types of electronic charge carriers:
1. ________
– negative charge
– in conduction band
2. _____
– positive charge
– vacant electron state in
the valence band |
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Definition
Two types of electronic charge carriers:
1. FREE ELECTRON
– negative charge
– in conduction band
2. HOLE
– positive charge
– vacant electron state in
the valence band |
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Term
_________ Semiconductors
• Pure material semiconductors: e.g., silicon & germanium
– Group IVA materials
• Compound semiconductors
– III-V compounds
• Ex: GaAs & InSb
– II-VI compounds
• Ex: CdS & ZnTe
– The wider the electronegativity difference between the elements the wider the energy gap. |
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Definition
INTRINSIC Semiconductors
• Pure material semiconductors: e.g., silicon & germanium
– Group IVA materials
• Compound semiconductors
– III-V compounds
• Ex: GaAs & InSb
– II-VI compounds
• Ex: CdS & ZnTe
– The wider the electronegativity difference between the elements the wider the energy gap. |
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Term
Intrinsic Semiconductors: Conductivity vs T
-- conductivity _____ with T
-- opposite to metals |
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Definition
Intrinsic Semiconductors: Conductivity vs T
• Data for Pure Silicon:
-- conductivity INCREASES with T
-- opposite to metals |
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Term
Intrinsic Semiconduction in Terms of Electron and Hole Migration:
1. If the temp is high enough, and there is an electric field (creating the + and - sides)...
2. an electron can be excited into conduction band, making it a free electron, moving towards the positive side
3. it leaves a hole, which migrates to the negative/electron side
p (#holes) = e (#free electrons) |
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Definition
No questions, just wanted to understand this plain and simple.
INTRINSIC Semiconduction in Terms of Electron and Hole Migration:
1. If the TEMP is HIGH enough, and there is an ELECTRIC FIELD (creating the + and - sides)...
2. an electron can be excited into conduction band, making it a free electron, moving towards the positive side
3. it leaves a hole, which migrates to the negative/electron side
p (#holes) = e (#free electrons) |
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Term
Band Gaps:
It is well established that conductivity of an instrinsic semiconductor starts at 0 at 0 K and increases _____ with temperature |
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Definition
Band Gaps:
It is well established that conductivity of an instrinsic semiconductor starts at 0 at 0 K and increases exponentially with temperature |
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Term
Why an exponential dependence on T?
• _____ has to jump across band gap to conduct
• This requires _____ which can be supplied thermally (heat)
• It is in the family of thermally activated processes:
In other words, _____ increases exponentially with temperature because the number of charge carriers, n, increases exponentially with temperature. |
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Definition
Why an exponential dependence on T?
• ELECTRON has to jump across band gap to conduct
• This requires ENERGY which can be supplied thermally (heat)
• It is in the family of thermally activated processes:
In other words, CONDUCTIVITY increases exponentially with temperature because the number of charge carriers, n, increases exponentially with temperature. |
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Term
• Intrinsic:
-- case for pure Si
-- # electrons = # holes (n = p)
• Extrinsic (All commercial semiconductors):
-- electrical behavior is determined by presence of _____
that introduce excess electrons or holes
-- n ≠ p |
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Definition
• Intrinsic:
-- case for pure Si
-- # electrons = # holes (n = p)
• Extrinsic (All commercial semiconductors):
-- electrical behavior is determined by presence of IMPURITIES
that introduce excess electrons or holes
-- n ≠ p |
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Term
n-type Semiconductor
- loosely bound e- occupies energy state within forbidden band gap
- excitation supplies or "donates" e- to conduction band
- because e' excited from impurity level, no hole left in valence band
n >> p |
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Definition
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Term
p-type Semiconductor
- weakly bound hole liberatoed from impurity atom via thermally excited transfer of e- from adjacent bond
- excited holes participate in conduction
- impurity atoms introduce "acceptor" energy state within band gap, just above valence band... no free e- in impurity level or conduction band |
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Definition
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Term
Temp Dependence of Carrier Concentration
- For both Ge and Si, carrier concentration ____ with temperature.
• Carrier concentration is always ____ in Ge compared with Si because Ge has smaller band gap (0.67 eV) as compared to Si (1.11 eV) |
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Definition
Temp Dependence of Carrier Concentration
- For both Ge and Si, carrier concentration INCREASES with temperature.
• Carrier concentration is always HIGHER in Ge compared with Si because Ge has smaller band gap (0.67 eV) as compared to Si (1.11 eV) |
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Term
Data for Doped Silicon:
-- conductivity increases with doping
-- reason: ____ ____ lower the activation energy to produce mobile electrons.
• Comparison: intrinsic vs extrinsic conduction...
(graph on slides needed for this to make sense, but p much, doping causes freeze out and larger temp range for extrinsic)
-- extrinsic doping level: 1021/m3 of a n-type donor impurity (such as P).
-- for T < 100 K: "freeze-out“, thermal energy insufficient to excite electrons.
-- for 150 K < T < 450 K: "extrinsic"
-- for T >> 450 K: "intrinsic" |
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Definition
Data for Doped Silicon:
-- conductivity increases with doping
-- reason: IMPERFECTION SITES lower the activation energy to produce mobile electrons.
• Comparison: intrinsic vs extrinsic conduction...
(graph on slides needed for this to make sense, but p much, doping causes freeze out and larger temp range for extrinsic)
-- extrinsic doping level: 1021/m3 of a n-type donor impurity (such as P).
-- for T < 100 K: "freeze-out“, thermal energy insufficient to excite electrons.
-- for 150 K < T < 450 K: "extrinsic"
-- for T >> 450 K: "intrinsic" |
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Term
Conduction also a function of carrier mobility (μ)
•μ ____ by thermal vibrations and impurities (dopant
concentration) in lattice
Carrier mobility and temp...
• For dopant conc. <10^24 m-3, electron and hole mobility decrease with increasing temperature
• For dopant conc. <10^20 m-3, electron and hole mobility independent of acceptor/donor concentration
• For dopant conc. >10^20 m-3, mobility decreases with increasing dopant level |
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Definition
Conduction also a function of carrier mobility (μ)
•μ REDUCED by thermal vibrations and impurities (dopant
concentration) in lattice
Carrier mobility and temp...
(good graphs on slides)
• For dopant conc. <10^24 m-3, electron and hole mobility decrease with increasing temperature
• For dopant conc. <10^20 m-3, electron and hole mobility independent of acceptor/donor concentration
• For dopant conc. >10^20 m-3, mobility decreases with increasing dopant level |
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Term
p-n Rectifying Junction
• Allows flow of electrons in ____ direction only (e.g., useful to convert alternating current to direct current).
• Processing: ____ P into one side of a B-doped crystal.
-- No applied potential: no net current flow.
-- Forward bias: carriers flow through p-type and n-type regions; holes and electrons recombine at p-n junction; current flows.
-- Reverse bias: carriers flow away from p-n junction; junction region depleted of carriers; little current flow |
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Definition
p-n Rectifying Junction
• Allows flow of electrons in ONE direction only (e.g., useful to convert alternating current to direct current).
• Processing: DIFFUSE P into one side of a B-doped crystal.
-- No applied potential: no net current flow.
-- Forward bias: carriers flow through p-type and n-type regions; holes and electrons recombine at p-n junction; current flows.
-- Reverse bias: carriers flow away from p-n junction; junction region depleted of carriers; little current flow |
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Term
CH. 17&18 Summary
• Electrical conductivity and resistivity are:
-- _____ parameters
-- geometry _____
• Conductors, semiconductors, and insulators...
-- differ in range of conductivity values
-- differ in availability of electron excitation states
• For metals, resistivity is increased by
-- ____ temperature
-- addition of ____
-- ____ deformation
• For pure semiconductors, conductivity is increased by
-- ____ temperature
-- ____ [e.g., adding B to Si (p-type) or P to Si (n-type)] |
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Definition
CH. 17&18 Summary
• Electrical conductivity and resistivity are:
-- MATERIAL parameters
-- geometry INDEPENDENT
• Conductors, semiconductors, and insulators...
-- differ in range of conductivity values
-- differ in availability of electron excitation states
• For metals, RESISTIVITY is increased by
-- INCRESING temperature
-- addition of IMPERFECTIONS
-- PLASTIC deformation
• For pure semiconductors, conductivity is increased by
-- INCREASING temperature
-- DOPING [e.g., adding B to Si (p-type) or P to Si (n-type)] |
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Term
△V = I R
what is that law called, what are the variables? |
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Definition
OHM'S LAW:
△V = I R
voltage drop (C) = Current (Amps = C/s) * resistance (Ohms) |
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Term
Resistivity, ⍴(ohm-m):
-- a MATERIAL property that is INDEPENDENT of sample size and geometry
⍴ = RA/l
⍴ = (resistance*surface area of current flow) / (current flow path length) |
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Definition
Resistivity, ⍴(ohm-m):
-- a MATERIAL property that is INDEPENDENT of sample size and geometry
⍴ = RA/l
⍴ = (resistance*surface area of current flow) / (current flow path length) |
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Term
| Resistance is _______ on sample geometry and size. |
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Definition
Resistance is DEPENDENT on sample geometry and size.
Analogous to flow of water in a pipe |
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Term
| Compare the conductivity of metals, semi conductors, ceramics, and polymers |
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Definition
| metals >> semi conductors > ceramics > polymers |
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Term
Electron Mobility:
• Under an electric field a _____ acts on free electrons which leads to ______ in a direction opposite the field due to their ____ charge.
• According to quantum mechanics, electrons do not interact with the rest of the atoms in a ____ _____.
— This should lead to current increasing with time.
• However, current reaches a _____ value the instant the field is applied due to “frictional forces” which counter the acceleration.
• These result from scattering of electrons by ____ such as impurity atoms, vacancies, interstitials, dislocations and the thermal vibration of the atoms.
• Scattering leads to electron “______.” |
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Definition
Electron Mobility:
• Under an electric field a FORCE acts on free electrons which leads to ACCELERATION in a direction opposite the field due to their NEGATIVE charge.
• According to quantum mechanics, electrons do not interact with the rest of the atoms in a PERFECT LATTICE.
— This should lead to current increasing with time.
• However, current reaches a CONSTANT value the instant the field is applied due to “FRICTIONAL forces” which counter the acceleration.
• These result from scattering of electrons by IMPERFECTIONS such as impurity atoms, vacancies, interstitials, dislocations and the thermal vibration of the atoms.
• Scattering leads to electron “DEFLECTIONS.” |
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Term
____ ____ represents the average electron velocity in the direction of applied force (electrical field)
vd = meE
where me is electron mobility (m²/V-s) |
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Definition
DRIFT VELOCITY represents the average electron velocity in the direction of applied force (electrical field)
vd = μe*E
where μe is electron mobility (m²/V-s) |
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Term
Metals: Influence of Temperature and Impurities on Resistivity
Presence of imperfections increases resistivity:
-- ____
-- ____
-- ____
-- ____
These act to scatter electrons so that they take a less direct path.
Resistivity ____ with increased:
--Temp
--wt% impurity
--%CW |
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Definition
Metals: Influence of Temperature and Impurities on Resistivity
Presence of imperfections increases resistivity:
-- GRAIN BOUNDARIES
-- DISLOCATIONS
-- IMPURITY ATOMS
-- VACANCIES
These act to scatter electrons so that they take a less direct path.
Resistivity INCREASED with increased:
--Temp
--wt% impurity
--%CW |
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Term
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Definition
| ⍴ = ⍴thermal + ⍴impurity + ⍴deformation |
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Term
In all conductors, many semiconductors and many insulting material,
only _____ conduction exists and therefore conductivity depends on the availability of electrons to participate in conduction. |
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Definition
In all conductors, many semiconductors and many insulting material,
only ELECTRONIC conduction exists and therefore conductivity depends on the availability of electrons to participate in conduction. |
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Term
Electrons availability is dependent on the arrangement of electron states (quantum states) with respect to ____ and the manner in which the states are occupied by electrons.
• There are shells (integers) and subshells (s, p, d, f with 1, 3, 5, 7 states)
• Electrons only fill the states with the lowest energies with two electrons of opposite spin per state. |
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Definition
Electrons availability is dependent on the arrangement of electron states (quantum states) with respect to ENERGY and the manner in which the states are occupied by electrons.
• There are shells (integers) and subshells (s, p, d, f with 1, 3, 5, 7 states)
• Electrons only fill the states with the lowest energies with two electrons of opposite spin per state. |
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Term
- In a solid with a large number of atoms, N, which are
bonded in a crystalline arrangement, atoms are in close
proximity and therefore electrons interact with each
other and neighboring nuclei.
• This leads to a _____ of each atomic state into a
series of closely spaced electron states in the solid.
• This begins with the _____ shell which is affected
the most. |
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Definition
- In a solid with a large number of atoms, N, which are
bonded in a crystalline arrangement, atoms are in close
proximity and therefore electrons interact with each
other and neighboring nuclei.
• This leads to a SPLITTING of each atomic state into a
series of closely spaced electron states in the solid.
• This begins with the OUTERMOST shell which is affected
the most. |
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Term
| The number of states within each band will equal the total of all states contributed by N atoms (N for s, 3N for p, etc.) |
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Definition
uhhh....
The number of states within each band will equal the total of all states contributed by N atoms (N for s, 3N for p, etc.) |
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Term
- The electrical properties are a consequence of the ____ ____ ____.
• In particular it depends on the _____ of outermost electron bands and if electrons occupy the energy states. |
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Definition
- The electrical properties are a consequence of the ELECTRON BAND STRUCTURE.
• In particular it depends on the ARRANGEMENT of outermost electron bands and if electrons occupy the energy states. |
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Term
| Four different types of band structures are possible at 0 K. |
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Definition
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Term
The energy corresponding to the highest filled state at 0 K is called the ____ Energy, Ff
• Only electrons with energies ___ than the ____ energy may be acted on and accelerated in an electric field. |
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Definition
The energy corresponding to the highest filled state at 0 K is called the FERMI Energy, Ff
• Only electrons with energies GREATER than the FERMI energy may be acted on and accelerated in an electric field. |
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Term
• Metals (Conductors):
-- For metals: empty energy states are adjacent to filled states.
-- Two types of band structures for metals
-- Thermal energy excites electrons into empty higher energy states.
1 partially filled band
2 empty band that overlaps filled band |
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Definition
• Metals (Conductors):
-- For metals: empty energy states are adjacent to filled states.
-- Two types of band structures for metals
-- Thermal energy excites electrons into empty higher energy states.
1 partially filled band
2 empty band that overlaps filled band |
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|
Term
• ________:
-- wide band gap (> 2 eV)
-- few electrons excited
across band gap
• _________:
-- narrow band gap (< 2 eV)
-- more electrons excited
across band gap |
|
Definition
• INSULATORS:
-- wide band gap (> 2 eV)
-- few electrons excited
across band gap
• SEMICONDUCTORS:
-- narrow band gap (< 2 eV)
-- more electrons excited
across band gap |
|
|
Term
| magnetism: Phenomenon by which materials assert an _____ or _____ force or influence on other materials. |
|
Definition
| magnetism: Phenomenon by which materials assert an ATTRACTIVE or REPULSIVE force or influence on other materials. |
|
|
Term
- Iron, some steels and natural mineral (lodestone) exhibit magnetic properties.
• However, all substances are influenced to some degree by the presence of a ___ ____. |
|
Definition
- Iron, some steels and natural mineral (lodestone) exhibit magnetic properties.
• However, all substances are influenced to some degree by the presence of a MAGNETIC FIELD. |
|
|
Term
- Magnetic forces are generated by moving electrically ____ particles and are often thought of in terms of fields.
• Magnetic ____ are found to exist in magnetic materials. |
|
Definition
- Magnetic forces are generated by moving electrically CHARGED particles and are often thought of in terms of fields.
• Magnetic DIPOLES are found to exist in magnetic materials. |
|
|
Term
|
Definition
H = applied magnetic field (ampere-turns/m)
B = magnetic flux density (tesla) |
|
|
Term
Flux density or induction, B:
• Magnitude of internal field strength within a _____ subjected to a ____
• Units: Tesla (webers/m²)
• B = μH
• μ = permeability which is property of medium through which H-field passes and B-field is measured
• In vacuum: Bo = moH |
|
Definition
Flux density or induction, B:
• Magnitude of internal field strength within a MATERIAL subjected to a H-FIELD
• Units: Tesla (webers/m²)
• B = μH
• μ = permeability which is property of medium through which H-field passes and B-field is measured
• In vacuum: Bo = μoH |
|
|
Term
________, μr
is a measure of degree to which a material can be
magnetized, or ease that B-field can be induced in
presence of external H-field |
|
Definition
RELATIVE PERMIABILITY, μr
is a measure of degree to which a material can be
magnetized, or ease that B-field can be induced in
presence of external H-field |
|
|
Term
______ - χm, is a measure of a material’s magnetic response relative to a vacuum
Magnetization = χm * H |
|
Definition
MAGNETIC SUSEPTABILITY - χm, is a measure of a material’s magnetic response relative to a vacuum
Magnetization = χm * H |
|
|
Term
| B is the sum of what you get in a _____ (1st term) + what the _____ contributes (2nd term) |
|
Definition
| B is the sum of what you get in a VACUUM (1st term) + what the MATERIAL contributes (2nd term) |
|
|
Term
Macroscopic magnetic properties are a consequence of magnetic moments associated with _____ _____.
• Magnetic moments arise from electron ____ and the ____ on electrons.
• Net atomic magnetic moment:
-- sum of moments from all electrons. |
|
Definition
Macroscopic magnetic properties are a consequence of magnetic moments associated with INDIVIDUAL ELECTRONS.
• Magnetic moments arise from electron MOTIONS and the
SPINS on electrons.
• Net atomic magnetic moment:
-- sum of moments from all electrons. |
|
|
Term
Origins of Magnetic Moments:
1. ____ ____ of electron around nucleus:
— Electron = moving charge
— Considered as a small current loop
— Current loop generates magnetic field
— Magnetic moment along axis of rotation
2. ____ ____:
— Spin up or down (±½) around an axis
• Each electron is small magnet with orbital and spin
magnetic moments
• Fundamental magnetic moment:
— ____ _____ (what e- is to electricity)
— mB = 9.27 x 10-24 A-m²
— Spin magnetic moment = ±mB
— Orbital magnetic moment = ml mB
where ml = magnetic quantum # |
|
Definition
Origins of Magnetic Moments:
1. ORBITAL MOTION of electron around nucleus:
— Electron = moving charge
— Considered as a small current loop
— Current loop generates magnetic field
— Magnetic moment along axis of rotation
2. ELECTRON SPIN:
— Spin up or down (±½) around an axis
• Each electron is small magnet with orbital and spin
magnetic moments
• Fundamental magnetic moment:
— BOHR MAGNETRON
— mB = 9.27 x 10-24 A-m²
— Spin magnetic moment = ±mB
— Orbital magnetic moment = ml mB
where ml = magnetic quantum # |
|
|
Term
Magnetic Moments
Indicates response of ____ to a magnetic field
_______ _____ _____ :
• Sum of magnetic moments from all electrons
• Orbital moments of some e- pairs will cancel each other
• Same true for spin moments:
--- • e.g. e- with spin up will cancel e- with spin down
• Net magnetic moment = sum of magnetic moments of all e- (both orbital and spin), taking cancellation into account
• For atom with completely filled electron shells/subshells:
--- • total cancellation of both orbital and spin moments
--- • such materials cannot be permanently magnetized!
--- • e.g. He, Ne, Ar, etc. |
|
Definition
Indicates response of ELECTRONS to a magnetic field
NET MAGNETIC MOMENT :
• Sum of magnetic moments from all electrons
• Orbital moments of some e- pairs will cancel each other
• Same true for spin moments:
--- • e.g. e- with spin up will cancel e- with spin down
• Net magnetic moment = sum of magnetic moments of all e- (both orbital and spin), taking cancellation into account
• For atom with completely filled electron shells/subshells:
--- • total cancellation of both orbital and spin moments
--- • such materials cannot be permanently magnetized!
--- • e.g. He, Ne, Ar, etc. |
|
|
Term
| 3 types of magnetism on graph |
|
Definition
|
|
Term
| no unpaired electrons = no _____ magnetism |
|
Definition
| no unpaired electrons = no PERMANENT magnetism |
|
|
Term
DIAMAGNETISM
Very ____, non-permanent; persists only when _____ ____ ____
• Induced by change in ____ motion of electron due to applied field
• Induced magnetic moment very small, in direction _____ to applied field
• μr <1
• ______ = negative, i.e. B-field induced is less than in vacuum
• Found in all materials, but only observable when other types of magnetism absent
• Essentially of no practical importance! |
|
Definition
DIAMAGNETISM
Very WEAK, non-permanent; persists only when EXTERNAL H-FIELD APPLIED
• Induced by change in ORBITAL motion of electron due to applied field
• Induced magnetic moment very small, in direction OPPOSITE to applied field
• μr <1
• SUSEPTABILITY = negative, i.e. B-field induced is less than in vacuum
• Found in all materials, but only observable when other types of magnetism absent
• Essentially of no practical importance! |
|
|
Term
PARAMAGNETISM
• Permanent dipole moment in some solids due to incomplete cancellation of electron spin or orbital magnetic moments
• _____ orientation of magnetic moments in absence of applied field
• ____ net magnetism
• Dipoles free to rotate and ______ with external field, but no mutual interaction between adjacent dipoles
• μr >1
• Susceptibility = small, positive, i.e. B-field is greater than in vacuum
• Magnetization exists only when ext. ______ applied |
|
Definition
PARAMAGNETISM
• Permanent dipole moment in some solids due to incomplete
cancellation of electron spin or orbital magnetic moments
• RANDOM orientation of magnetic moments in absence of applied field
• ZERO net magnetism
• Dipoles free to rotate and PERFECTLY ALIGN with external field, but no mutual interaction between adjacent dipoles
• μr >1
• Susceptibility = small, positive, i.e. B-field is greater than in vacuum
• Magnetization exists only when ext. H-FIELD applied |
|
|
Term
FERROMAGNETISM
Some metallic materials
- ____ magnetic moment
- large & ____ magnetizations
• e.g. transition metals Fe, Co, Ni & rare earth Gd
• _____ magnetic moments due to uncanceled e- spins
• Coupling interactions (not fully understood) cause ___ ____
magnetic moments of adjacent atoms to align, even in absence of ext. H-field
• Susceptibility as high as 106, positive, i.e. B-field much greater
than in vacuum
• Mutual electron spin alignment exists over large vol. regions - ____ |
|
Definition
FERROMAGNETISM
Some metallic materials
- PERMANENT magnetic moment
- large & PERMANENT magnetizations
• e.g. transition metals Fe, Co, Ni & rare earth Gd
• PERMANENT magnetic moments due to uncanceled e- spins
• Coupling interactions (not fully understood) cause NET SPIN
magnetic moments of adjacent atoms to align, even in absence of ext. H-field
• Susceptibility as high as 106, positive, i.e. B-field much greater
than in vacuum
• Mutual electron spin alignment exists over large vol. regions - DOMAIN |
|
|
Term
Ferromagnetism
• When all magnetic dipoles mutually aligned with external field:
‒ _____ _____ (___)
‒ Maximum possible magnetization |
|
Definition
Ferromagnetism
• When all magnetic dipoles mutually aligned with external field:
‒ SATURATION MAGNETIZATION (Ms)
‒ Maximum possible magnetization |
|
|
Term
Ferrimagnetism
• Some _____ exhibit permanent magnetization - ferrimagnetism
• Similar macroscopically to ferromagnetism, but different origin of net magnetic moment
‒-- In metals it was unpaired electron
• Ferrites, e.g. Fe3O4, ____ structure → ____ ____ structure
• Consider Fe3O4 as:
‒ Fe2+O2- + (Fe3+)2(O2-)3 i(e. containing +2 and +3 valence state Fe ions:
‒ Fe2+ → 4 Bohr magnetons/ion
‒ Fe3+ → 5 Bohr magnetons/ion
‒ O2- ions magnetically neutral
‒ Fe2+ ions in octahedral positions
‒ Half the Fe3+ ions in octahedral positions,
‒ but half also in tetrahedral positions
‒ Spin moments of all Fe3+ cancel out
‒ Magnetic moments of all Fe2+ aligned in same direction, thus
these are responsible for the net magnetization |
|
Definition
Ferrimagnetism
• Some CERAMICS exhibit permanent magnetization - ferrimagnetism
• Similar macroscopically to ferromagnetism, but different origin of net magnetic moment
‒ In metals it was unpaired electron
• Ferrites, e.g. Fe3O4, CUBIC structure → INVERSE SPINEL structure
• Consider Fe3O4 as:
‒ Fe2+O2- + (Fe3+)2 (O2-)3 i.e. containing +2 and +3 valence state Feions:
‒ Fe2+ → 4 Bohr magnetons/ion
‒ Fe3+ → 5 Bohr magnetons/ion
‒ O2- ions magnetically neutral
‒ Fe2+ Ions in octahedral positions
‒ Half the Fe3+ ions in octahedral positions,
‒ but half also in tetrahedral positions
‒ Spin moments of all Fe3+ cancel out
‒ Magnetic moments of all Fe2+ aligned in same direction, thus
these are responsible for the net magnetization |
|
|
Term
Temperature and Magnetic Behavior
• Temperature can influence magnetic characteristics due to
_____.
• Atomic thermal motions counteract coupling forces between
adjacent dipole moments leading to misalignment.
• This results in _____ saturation magnetization.
• At the _____ temperature, magnetization abruptly drops to
zero. |
|
Definition
Temperature and Magnetic Behavior
• Temperature can influence magnetic characteristics due to
PHONONS.
• Atomic thermal motions counteract coupling forces between
adjacent dipole moments that lead to misalignment.
• This results in DECREASED saturation magnetization.
• At the CURIE temperature, magnetization abruptly drops to
zero. |
|
|
Term
Ferro- and ferri-magnetic materials have small volume regions with mutual alignment of magnetic dipole moments – ______.
• Adjacent domains are separated by domain boundaries or walls.
• Normally domains are microscopic and there can be multiple in one grain of a polycrystal. |
|
Definition
Ferro- and ferri-magnetic materials have small volume regions with mutual alignment of magnetic dipole moments – DOMAIN.
• Adjacent domains are separated by domain boundaries or walls.
• Normally domains are microscopic and there can be multiple in one grain of a polycrystal. |
|
|
Term
Domains in Ferromagnetic & Ferrimagnetic Materials:
• As the applied ____ increases the magnetic domains change shape and size by movement of domain boundaries.
• “Domains” with aligned magnetic moment grow at expense of poorly aligned ones! |
|
Definition
Domains in Ferromagnetic & Ferrimagnetic Materials:
• As the applied H-FIELD increases the magnetic domains change shape and size by movement of domain boundaries.
• “Domains” with aligned magnetic moment grow at expense of poorly aligned ones! |
|
|
Term
| The magnetic hysteresis phenomenon |
|
Definition
|
|
Term
Hard magnetic materials:
-- ____ coercivities
-- used for permanent magnets
-- add particles/voids to inhibit domain wall motion
-- example: tungsten steel --
Hc = 5900 amp-turn/m)
Soft magnetic materials:
-- ____ coercivities
-- used for electric motors
-- example: commercial iron 99.95 Fe |
|
Definition
Hard magnetic materials:
-- LARGE coercivities
-- used for permanent magnets
-- add particles/voids to inhibit domain wall motion
-- example: tungsten steel --
Hc = 5900 amp-turn/m)
Soft magnetic materials:
-- SMALL coercivities
-- used for electric motors
-- example: commercial iron 99.95 Fe |
|
|
Term
|
Definition
| COERCIVITY, HC, Negative H needed to demagnitize! |
|
|
Term
MAGNETIC STORAGE (just gunna throw it all in here)
• Digitized data in the form of electrical signals are transferred to and recorded digitally on a magnetic medium (tape or disk)
• This transference is accomplished by a recording system that consists of a read/write head
-- “write” or record data by applying a magnetic field that aligns domains in small regions of the recording medium
-- “read” or retrieve data from medium by sensing changes in magnetization
• Hard disk drives (granular/perpendicular media):
-- CoCr alloy grains (darker regions) separated by oxide grain boundary segregant layer (lighter regions)
-- Magnetization direction of each grain is perpendicular to plane of disk
-- One bit on ~100 grains |
|
Definition
MAGNETIC STORAGE (just gunna throw it all in here)
• Digitized data in the form of electrical signals are transferred to and recorded digitally on a magnetic medium (tape or disk)
• This transference is accomplished by a recording system that consists of a read/write head
-- “write” or record data by applying a magnetic field that aligns domains in small regions of the recording medium
-- “read” or retrieve data from medium by sensing changes in magnetization
• Hard disk drives (granular/perpendicular media):
-- CoCr alloy grains (darker regions) separated by oxide grain boundary segregant layer (lighter regions)
-- Magnetization direction of each grain is perpendicular to plane of disk
-- One bit on ~100 grains |
|
|
Term
___________:
• Mainly and electrical phenomenon but there are magnetic
implications and these materials are primarily used in magnets generative very high fields.
• Most high-purity metals have very low, yet finite electrical
resistivity as temperature approaches 0 K.
• For a few materials where the resistivity at very low
temperatures decreases to virtually zero. |
|
Definition
SUPERCONDUCTIVITY
• Mainly and electrical phenomenon but there are magnetic
implications and these materials are primarily used in
magnets generative very high fields.
• Most high-purity metals have very low, yet finite electrical
resistivity as temperature approaches 0 K.
• For a few materials where the resistivity at very low
temperatures decreases to virtually zero. |
|
|
Term
TC = critical ____ - if T > TC not superconducting
JC = critical ______ - if J > JC not superconducting
HC = critical _____ - if H > HC not superconducting |
|
Definition
TC = critical TEMPERATURE - if T > TC not superconducting
JC = critical DENSITY - if J > JC not superconducting
HC = critical MAGNETIC FIELD - if H > HC not superconducting |
|
|
Term
_______ - Superconductors expel magnetic fields
This is why a superconductor will float above a magnet.:
• This results from attractive interactions between pairs of conducting electrons whose motions become coordinated.
• Scattering by thermal vibrations and impurity atoms is ineffiecient. |
|
Definition
MEISSNER Effect - Superconductors expel magnetic fields
This is why a superconductor will float above a magnet.:
• This results from attractive interactions between pairs of conducting electrons whose motions become coordinated.
• Scattering by thermal vibrations and impurity atoms is ineffiecient. |
|
|
Term
Advances in Superconductivity:
• Research in superconductive materials was stagnant for
many years.
– Everyone assumed TC,max was about 23 K
– Many theories said it was impossible to increase TC beyond this value
• 1987- new materials were discovered with TC > 30 K
– ceramics of form Ba1-x Kx BiO3-y
– Started enormous race
• Y Ba2Cu3O7-x TC = 90 K
• Tl2Ba2Ca2Cu3Ox TC = 122 K
• difficult to make since oxidation state is very important
• The major problem is that these ceramic materials are
_________. |
|
Definition
Advances in Superconductivity:
• Research in superconductive materials was stagnant for
many years.
– Everyone assumed TC,max was about 23 K
– Many theories said it was impossible to increase TC beyond this value
• 1987- new materials were discovered with TC > 30 K
– ceramics of form Ba1-x Kx BiO3-y
– Started enormous race
• Y Ba2Cu3O7-x TC = 90 K
• Tl2Ba2Ca2Cu3Ox TC = 122 K
• difficult to make since oxidation state is very important
• The major problem is that these ceramic materials are
INHERENTLY BRITTLE. |
|
|
Term
CH 20 Summary
• A magnetic field is produced when a ____ flows through a wire coil.
• Magnetic induction (B):
-- an internal magnetic field is induced in a material that is situated within an external magnetic field (H).
-- magnetic moments result from electron interactions with the applied magnetic field
• Types of material responses to magnetic fields are:
-- ferrimagnetic and ferromagnetic (large magnetic susceptibilities)
-- paramagnetic (small and positive magnetic susceptibilities)
-- diamagnetic (small and negative magnetic susceptibilities)
• Types of ferrimagnetic and ferromagnetic materials:
-- Hard: large coercivities
-- Soft: small coercivities
• Magnetic storage media:
-- particulate barium-ferrite in polymeric film (tape)
-- thin film Co-Cr alloy (hard drive) |
|
Definition
CH 20 Summary
• A magnetic field is produced when a CURRENT flows through a wire coil.
• Magnetic induction (B):
-- an internal magnetic field is induced in a material that is situated within an external magnetic field (H).
-- magnetic moments result from electron interactions with the applied magnetic field
• Types of material responses to magnetic fields are:
-- ferrimagnetic and ferromagnetic (large magnetic susceptibilities)
-- paramagnetic (small and positive magnetic susceptibilities)
-- diamagnetic (small and negative magnetic susceptibilities)
• Types of ferrimagnetic and ferromagnetic materials:
-- Hard: large coercivities
-- Soft: small coercivities
• Magnetic storage media:
-- particulate barium-ferrite in polymeric film (tape)
-- thin film Co-Cr alloy (hard drive) |
|
|
Term
| If two metal are electrically connected and are submersed in an electrolyte, the metal with the higher standard electrode potential with generally support the _______ reaction under standard conditions. |
|
Definition
If two metal are electrically connected and are submersed in an electrolyte, the metal with the higher standard electrode potential with generally support the REDUCTION reaction under standard conditions.
higher potential -- more cathodic --- redcat |
|
|
Term
| During electrochemical corrosion, the oxidation reaction in which electrons are given up usually takes place at the _____. |
|
Definition
| During electrochemical corrosion, the oxidation reaction in which electrons are given up usually takes place at the ANODE. |
|
|
Term
| A p-n rectifying junction makes use of what type of semiconductors? |
|
Definition
A p-n rectifying junction makes use of what type of semiconductors?
EXTRINSIC |
|
|
Term
| N-type extrinsic semiconductors attribute their conductive to properties mainly due to which charge carriers? |
|
Definition
N-type extrinsic semiconductors attribute their conductive to properties mainly due to which charge carriers?
ELECTRONS |
|
|
Term
| Insulating materials will have a wide band gap between the filled valence band and __________. |
|
Definition
| Insulating materials will have a wide band gap between the filled valence band and EMPTY CONDUCTION BAND. |
|
|
Term
The following will have a large impact on resistivity?
Dislocations
Temperature
Grain boundaries |
|
Definition
The following will have a large impact on resistivity?
Dislocations
Temperature
Grain boundaries |
|
|
Term
| Which type of magnetism can exist in all materials? |
|
Definition
Which type of magnetism can exist in all materials?
Diamagnetism |
|
|
Term
| In the presence of an applied magnetic field, a material’s magnetic response is designated using which variable? |
|
Definition
In the presence of an applied magnetic field, a material’s magnetic response is designated using which variable?
B |
|
|
Term
| Magnetization disappears in materials at the ___________ temperature. |
|
Definition
| Magnetization disappears in materials at the CURIE temperature. |
|
|
Term
| The observed relationship between an applied magnetic field and magnetic induction in a material in which a cyclic magnetic field is applied can be described as __________ ? |
|
Definition
| The observed relationship between an applied magnetic field and magnetic induction in a material in which a cyclic magnetic field is applied can be described as HYSTERIC |
|
|
Term
| Magnetic moments result from which two phenomena? |
|
Definition
Magnetic moments result from which two phenomena?
ELECTRON SPIN, ELECTRON ORBIAL MOTION |
|
|
Term
| A permanent magnet’s hysteretic relationship between an applied magnetic field and magnetic induction in the material would ideally be described as hard when it has ____ coercivity. |
|
Definition
| A permanent magnet’s hysteretic relationship between an applied magnetic field and magnetic induction in the material would ideally be described as hard when it has LARGE coercivity. |
|
|
Term
| What is the material phenomenon where resistivity decreases to nearly zero at low temperatures? |
|
Definition
What is the material phenomenon where resistivity decreases to nearly zero at low temperatures?
SUPERCONDUCTIVIY |
|
|
Term
Optical Properties
• Optical property refers to a material’s response to exposure to ____ ____ and, in particular, to ____ ____.
• Electromagnetic radiation is considered to be ___-like from a classical perspective.
• It consists of _____ and ______ fields which are perpendicular to each other and the ________. |
|
Definition
Optical Properties
• Optical property refers to a material’s response to exposure to ELECTROMAGNETIC RADIATION and, in particular, to VISIBLE LIGHT.
• Electromagnetic radiation is considered to be WAVE-like from a classical perspective.
• It consists of ELECTRIC (E) and MAGNETIC fields (H) which are perpendicular to each other and the DIRECTION of PROPAGATION. |
|
|
Term
The electromagnetic spectrum spans a wide range.
• Visible light is a narrow range: λ = 0.4-0.7 mm (400-700 nm)
• Perceived color is determined by _______
• “White” light is a mix of all colors |
|
Definition
The electromagnetic spectrum spans a wide range.
• Visible light is a narrow range: λ = 0.4-0.7 mm (400-700 nm)
• Perceived color is determined by WAVELENGTH
• “White” light is a mix of all colors |
|
|
Term
| Incident light is _____, _____, _____, and/or _____: |
|
Definition
| Incident light is REFLECTED, ABSORBED, TRANSMITTED, and/or SCATTERED: |
|
|
Term
optical classification of materials:
transparent - single crystal
translucent - polycrystalline ____
opaque - polycrystalline ____ |
|
Definition
optical classification of materials:
transparent - single crystal
translucent - polycrystalline DENSE
opaque - polycrystalline POROUS |
|
|
Term
Two Key Optical Phenomena…
• Electronic ______:
‒ EM wave includes fluctuating E-field
‒ E-field interacts with e- cloud around each atom
‒ perturbs or shifts e- cloud relative to nucleus:
‒ some radiation energy may be absorbed
‒ light waves velocity slows in medium…refraction
• Electron ______:
‒ Excitation of electron from one
occupied state to vacant higher energy state
‒ Only specific values of ΔE allowed
‒ All _____ energy absorbed
‒ Electrons cannot remain in excited
state forever…decays back to ground
state re-emits photon(s) |
|
Definition
Two Key Optical Phenomena…
• Electronic POLARIZATION:
‒ EM wave includes fluctuating E-field
‒ E-field interacts with e- cloud around each atom
‒ perturbs or shifts e- cloud relative to nucleus:
‒ some radiation energy may be absorbed
‒ light waves velocity slows in medium…refraction
• Electron TRANSITIONS:
‒ Excitation of electron from one
occupied state to vacant higher energy state
‒ Only specific values of ΔE allowed
‒ All PHOTON energy ABSORBED
‒ Electrons cannot remain in excited
state forever…decays back to ground
state re-emits photon(s) |
|
|
Term
Absorption of photons by _____ _____:
• Unfilled electron states are adjacent to filled states
• Near-surface electrons absorb visible light. |
|
Definition
Absorption of photons by ELECTRON TRANSITIONS:
• Unfilled electron states are adjacent to filled states
• Near-surface electrons absorb visible light. |
|
|
Term
Reflection of Light for Metals:
Metals are opaque because the incident radiation in the visible
range excites electrons into energy states above ____ energy.
• Absorption within a thin layer (<0.1 E-6 m)
Reflectivity = IR/I0 is between 0.90 and 0.95.
• Metal surfaces appear shiny
• Most of absorbed light is ____ at the same _____
• Small fraction of light may be absorbed
• Color of reflected light depends on wavelength distribution |
|
Definition
Reflection of Light for Metals:
Metals are opaque because the incident radiation in the visible
range excites electrons into energy states above FERMI energy.
• Absorption within a thin layer (<0.1 E-6 m)
Reflectivity = IR/I0 is between 0.90 and 0.95.
• Metal surfaces appear shiny
• Most of absorbed light is REFLECTED at the same WAVELENGTH
• Small fraction of light may be absorbed
• Color of reflected light depends on wavelength distribution |
|
|
Term
| The amount of light absorbed by a material is calculated using ______ Law |
|
Definition
The amount of light absorbed by a material is calculated using BEER'S Law
(remember: think abt how much BEER i am gunna ABSORB after this exam) |
|
|
Term
________:
• Intensity of transmitted (non-absorbed) light:
• decreases with distance x light traverses in material/medium |
|
Definition
TRANSMISSION:
• Intensity of transmitted (non-absorbed) light:
• decreases with distance x light traverses in material/medium |
|
|
Term
Reflectivity of Nonmetals
• For normal incidence and light passing into a solid
having an index of refraction n:
Refraction
• Transmitted light distorts electron clouds.
• The velocity of light in a material is lower than in a vacuum.
• n = c/v |
|
Definition
|
|
Term
Refraction of Light for Nonmetals
• Due to their electron energy band structures, nonmetallic materials can be transparent to visible light.
• Therefore, ____ and ____ should be considered.
• Light that is ____ into the interior of transparent materials experiences a decrease in velocity and is therefore bent at interfaces – ______.
• For crystalline ceramics with cubic structures and for glasses, n is isotropic.
• For non-cubic crystals, n is anisotropic. |
|
Definition
Refraction of Light for Nonmetals
• Due to their electron energy band structures, nonmetallic materials can be transparent to visible light.
• Therefore, REFRACTION and TRANSMISSION should be considered.
• Light that is TRANSMITTED into the interior of transparent materials experiences a decrease in velocity and is therefore bent at interfaces – REFRACTION.
• For crystalline ceramics with cubic structures and for glasses, n is isotropic.
• For non-cubic crystals, n is anisotropic. |
|
|
Term
Scattering of Light in Polymers
• For highly amorphous and pore-free polymers
– Little or no scattering
– These materials are _____
• Semicrystalline polymers
– Different indices of refraction for amorphous and crystalline regions
– Scattering of light at ____
– Highly crystalline polymers may be ____
• Examples:
– Polystyrene (amorphous) – clear and transparent
– Low-density polyethylene milk cartons – opaque |
|
Definition
Scattering of Light in Polymers
• For highly amorphous and pore-free polymers
– Little or no scattering
– These materials are TRANSPARENT
• Semicrystalline polymers
– Different indices of refraction for amorphous and crystalline regions
– Scattering of light at BOUNDARIES
– Highly crystalline polymers may be OPAQUE
• Examples:
– Polystyrene (amorphous) – clear and transparent
– Low-density polyethylene milk cartons – opaque |
|
|
Term
Color of Nonmetals
• Color determined by the distribution of wavelengths:
-- _____ light
-- _____ light from electron transitions |
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Definition
Color of Nonmetals
• Color determined by the distribution of wavelengths:
-- TRANSMITTED light
-- RE-EMITTED light from electron transitions |
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Term
Photoluminescence
- The light we experience everyday in buildings
- fluorescence
Arc between electrodes excites electrons in mercury atoms in the lamp to higher energy levels.
• As electron falls back into their ground states, UV light is emitted (e.g., suntan lamp).
• Inside surface of tube lined with material that absorbs UV and reemits visible light
- For example, Ca10F2P6O24 with 20% of F - replaced by Cl
• Adjust color by doping with metal cations |
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Definition
Photoluminescence
- The light we experience everyday in buildings
- fluorescence
Arc between electrodes excites electrons in mercury atoms in the lamp to higher energy levels.
• As electron falls back into their ground states, UV light is emitted (e.g., suntan lamp).
• Inside surface of tube lined with material that absorbs UV and reemits visible light
- For example, Ca10F2P6O24 with 20% of F - replaced by Cl
• Adjust color by doping with metal cations |
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Term
| The color of semiconductor materials is determined by what? |
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Definition
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Term
| Fiber optic cables are enabled by which material property? |
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Definition
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Term
| Glow-in-the dark object contain materials that can experience ________. |
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Definition
| Glow-in-the dark object contain materials that can experience PHOSPHORESENCE. |
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Term
| A light source behind an opaque object will not be visible through the object due to which interactions? |
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Definition
A light source behind an opaque object will not be visible through the object due to which interactions?
- scattering
- absorption
- reflection |
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Term
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Definition
| Ferrofluid is a unique material that acts like a magnetic solid and like a liquid. |
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