thermal equilibrium diagrams
DESCRIPTION
Thermal Equilibrium Diagrams. Thermal Equilibrium Diagrams. Thermal Equilibrium Diagrams show the temperatures at which phase changes take place in alloys of different percentage composition . Phase . - PowerPoint PPT PresentationTRANSCRIPT
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Thermal Equilibrium Diagrams
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Thermal Equilibrium Diagrams show the temperatures at which phase changes take place in alloys of different percentage composition.
Thermal Equilibrium Diagrams
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Phase
A Phase is a portion of a system that has uniform physical and
chemical characteristics.
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Thermal Equilibrium Diagrams are made for information gained
form Cooling Curves.
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When the temperature of a cooling molten metal alloy is plotted against time, a cooling curve is formed.
Cooling Curve
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When cooling a solid pure metal, change from a solid to a liquid at constant temperature.
This is called the Melting Point Temperature.
The heat that is released in the transition from a solid to a liquid is called hidden or Latent Heat.
Solidification Starts
Solidification Ends
LIQUID
SOLID
The Cooling Curve of 100% Copper
Remember this only happens for pure metals.
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Latent heat is the quantity of heat energy absorbed or released when a substance changes its physical phase at constant temperature.
Latent Heat
The energy that goes in breaks the bond of the atoms.
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LIQUID
SOLID
Pure Metal change
directly from Liquid to Solid
at1
temperature.
The Cooling Curve of Pure Metal
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If a metal is 100% pure and contains no traces of other elements then some under cooling may occur before solidification begins. Under cooling is when the temperature drops below the liquid to solid temperature for a short period.
Undercooling
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pera
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0 C
Time
Undercooling
Fall in temperature stops temporarily at the freezing point because of Latent heat
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The Cooling Curve of an Alloy
Solidification Starts
Solidification Ends
LIQUID
SOLID
“PASTY” STATE
Alloys change from Liquid to
Solid through a pasty state
over a temperature
range.
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Over a Temperature Range
1Temperature
Pure Metal Alloy
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Solid Solition Alloys
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Solid Solution:
When viewed under a microscope, a solid solution appears like a pure metal.
A Solid Solution is when two metals are completely soluble in each other in both the liquid and solid states.
100% LeadIron Carbon
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TASK
Using the graph paper supplied:(i) Draw the equilibrium diagram according to the given data.(ii) Label the diagram and describe the main features.(iii) For the alloy with 50% Nickel determine, from the diagram, the ratio of the phases at 1250°C.
The given table shows the solidification temperatures for various alloys of Copper and Nickel. The melting point of Copper is 1083°C and Nickel is 1453°C.
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Axis of Diagram
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TEM
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PRECENTAGE COMPOSITION
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NICKELCOPPER
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Copper/Nickel Equilibrium Diagram
NICKELCOPPER
TEM
PERA
TURE
(°
C)
PRECENTAGE COMPOSITION
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Equilibrium diagrams are made from taking information for cooling of different
percentage of an alloy and putting it on one graph.
How Equilibrium Diagrams Are Made
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The Cooling Curve of Copper/ Nickel and alloys
This is know as a TERMAL ANALYSIS
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How A Thermal Equilibrium Diagram Is Made
100% Copper
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How A Thermal Equilibrium Diagram Is Made
100% NICKLE
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How A Thermal Equilibrium Diagram Is Made
60% Copper 40% Nickel
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How A Thermal Equilibrium Diagram Is Made
40% Copper 60% Nickel
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How A Thermal Equilibrium Diagram Is Made
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Copper/Nickel Equilibrium Diagram
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Liquidus Line
Solid Phase
Liquid Phase
Liquid Phase and Solid
PhaseSolidus Line
Phases are defined as regions that differ from one another on an equilibrium diagram.
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NICKELCOPPER
Phases defined by composition (not by state – solid, liquid, gas)
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Liquid: the two metals are soluble in each other in the liquid state.
Liquidus Line: the change from fully liquid to pasty state. Above the liquidus line, the alloy is liquid. This is the beginning of solidification.
Liquid and Solid: the alloy is in a pasty form, there are two phases one Liquid and one Solid.
Solidus Line: the change from pasty to solid. Below the solidus line, the alloy is cooling and solid. This is the end of solidification.
Solid: alloy is in solid form.
Main Features of Equilibrium Diagram
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27
Introduction To Equilibrium Diagrams Equilibrium may be defined as a state of
balance or stability.
Diagrams indicates the phases the alloy is at different temperatures.
Phases are defined as regions that differ from one another on an equilibrium diagram. Phases defined by composition.
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Equilibrium refers to Balance existing in a system
In Metallurgy, Equilibrium means, that the cooling of a metal or an alloy is so slow that all the changes that might take place get the chance to do so.
The Meaning of the Term Equilibrium
Metallurgy is the study of metals and their properties
To achieve equilibrium to take place enough time for complete
diffusion is required.
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Diffusion
Diffusion is the processes by which a substance spread out through another
substance. Atoms move in a solid metal in this
manner.HIGH CONSTANTRATION
LOW CONSTANTRATION
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Diffusion in a vacuum
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Diffusion in a Solid
Atom move form high concentration to low
concentration
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Water And Sugar
A SINGLE PHASE
TWO-PHASES
How Many Phases Are There? PHOTOS
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Phase
A Phase is a portion of a system that has uniform physical and
chemical characteristics.
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Phases
Phases are defined as regions that differ from one another on an
equilibrium diagram. Phases defined by composition. NOT BY STATE (solid, liquid , gas)
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Substitution Solid Solution Alloys
Nickel Copper
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Copper/Nickel Equilibrium Diagram
Copper
Nickel
Copper
Nickel
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0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%0
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NICKELCOPPER
TEM
PERA
TURE
(°C)
PRECENTAGE COMPOSITION
1250°C
Ratio of Phases
Tie Line
iii)For the alloy with 50% Nickel determine, from the diagram, the ratio of the phases at 1250°C.
26%
66%
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Ratio of Phases
Ratio of phases at 1250℃ for 50% Nickel
26%
66%
The ratio of Solid to Liquid is:
A CB
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NICKELCOPPER
TEM
PERA
TURE
(°C)
PRECENTAGE COMPOSITION
1250°C
26% 66%
Ratio of phases at 1250°C for 35% Nickel
35%
Ratio of Phases
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NICKELCOPPER
TEM
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(°C)
PRECENTAGE COMPOSITION
1250°C
26% 66%
Ratio of phases at 1250ºC for 60% Nickel
Ratio of Phases
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Eutectic Alloys
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Eutectic Alloys
In a eutectic alloy the two metals are
completely soluble in the liquid phase but are
insoluble in the solid phase.
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TASK
Using the graph paper supplied:i. Draw the equilibrium diagram according to the given
data.ii. Label the diagram and describe the main features.
The given table shows the solidification temperatures for various alloys of Cadmium and Nickel.
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Axis of Diagram
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PRECENTAGE COMPOSITION
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BISMUTHCABMIUM
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PRECENTAGE COMPOSITION
TEM
PERA
TURE
(°
C)
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0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%0
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BISMUTHCADMIUM
TEM
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(°
C)
PRECENTAGE COMPOSITION
Cadmium / Bismuth Equilibrium Diagram
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Cadmium / Bismuth Equilibrium Diagram
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TEM
PERA
TURE
(°
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Liquid Phase
Liquidus Line
Solid PhasesSolidus Line
BISMUTHCADMIMUM
Liquid Phaseand Solid Phase
EutecticPoint
Liquid Phaseand Solid Phase
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Cadmium / Bismuth Equilibrium Diagram
TEM
PERA
TURE
(°C
)
Liquid Phase
Solid Cadmium and Eutectic
BISMUTHCADMIUM
Liquid and Solid Cadmium
Liquid and Solid Bismuth
EutecticPoint
Solid Bismuth and Eutectic
Green Line
Eutectic Alloy
Eutectic
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Solid Bismuth Solid Cadmium
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Cadmium / Bismuth∘ Cadmium Atoms∙ Bismuth Atoms
X 1 000
X 10 000 000
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Eutectic Point
The point where the liquid alloy changes to solid
without going through a liquid/solid state is called the
eutectic point.
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Partial Solubility Alloy
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The equilibrium diagram for this type of alloy is called a Partial Solubility thermal equilibrium diagram.
It is a combination of the solid solution and eutectic diagrams and is a little more complex.
Partial Solubility AlloySome metals in an alloy only
partially dissolve in each other. Lead/Tin Alloy (Solder) is an
example of this.
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Make up of Partial Solubility Alloy Equilibrium Diagram
Eutectic Alloys
Partial Solubility Alloy
Solid Solution Alloys Solid Solution Alloys
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Lead / Tin Equilibrium Diagram BASIC
Liquid Phase
Liquidus Line
Solid Phases
Solidus Line
Liquidand Solid
EutecticPoint
Liquidand Solid
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TINLEAD
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TEM
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Lead / Tin Equilibrium Diagram LINES
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TEM
PERA
TURE
(°
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Liquid Phases
Liquidus Line
SolidTINLEAD
Liquidand Solid
Liquidand Solid
Solid Solution Solid
Solution
SOLVUS LINES
Solidus Line
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Lead / Tin Equilibrium Diagram COMPLETE
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TEM
PERA
TURE
(°
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Liquid Phases
TINLEAD
β Solidand Liquid
α Solid and Liquidα Solid Solution β Solid
Solution
α and βSolid Solution
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Interstitial Solid Solution Alloys
Lead
Tin
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Task 3 (Q6 2006)Copy the given lead-tin diagram into your answer book and answer all of the following:
(i) Identify the lines labelled A, B and C; (ii) Explain what each line represents; (iii) For the alloy with 30% tin determine, from the diagram, the composition of the phases at 250°C; (iv) Indicate clearly on your diagram the eutectic point.
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(i) Labelled lines A, B and C
Liquidus line
Solidus lineSolvus line
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A – Liquidus line. For the alloy system this line represents the boundary between the fully liquid state and the beginning of solidification.
B – Solvus line. The transition line from one solid form to another solid form of an alloy is called the solvus line. This line indicates the maximum amount of tin
which can be dissolved in the lead.
C – Solidus line. The boundary line that determines the end of solidification. Below this line the alloy is completely solid.
(ii) Explain what each line represents?
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For the alloy with 30% tin determine, from the diagram, the composition of the phases at 250°C?
A – Solid composition consisting of 8% tin and 92% lead.B – Liquid composition consisting of 43% tin and 57% lead.
A B
To determine composition
of the phases
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(iv) Indicate the eutectic point
Eutectic Point
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Recap
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Copper/Nickel Equilibrium Diagram
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Liquidus Line
Solid Phase
Liquid Phase
Liquid Phase and Solid
PhaseSolidus Line
Phases are defined as regions that differ from one another on an equilibrium diagram.
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NICKELCOPPER
Phases defined by composition (not by state – solid, liquid, gas)
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Cadmium / Bismuth Equilibrium Diagram
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TEM
PERA
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Liquid Phase
Liquidus Line
Solid PhasesSolidus Line
BISMUTHCADMIMUM
Liquid Phaseand Solid Phase
EutecticPoint
Liquid Phaseand Solid Phase
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Lead / Tin Equilibrium Diagram COMPLETE
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TEM
PERA
TURE
(°
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Liquid Phases
TINLEAD
β Solidand Liquid
α Solid and Liquidα Solid Solution β Solid
Solution
α and βSolid Solution
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You should know that a pure metal has one clearly defined melting point.
Mixtures tend to solidify over a temperature range, that is they start to solidify at one temperature and do not complete the process until they reach a lower point.
A mix of 80% A with 20% B will solidify over a different range than a mix of 20% A with 80% B.
A phase diagram allows us to present all this information in a single (sometime simple) diagram.
What is a Equilibrium Diagrams
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Introduction To Equilibrium Diagrams Equilibrium may be defined as a state of
balance or stability.
Diagrams indicates the phases the alloy is at different temperatures.
Phases are defined as regions that differ from one another on an equilibrium diagram. Phases defined by composition.