Phase Phase • Any physically Any physically distinct, chemically distinct, chemically homogeneous and homogeneous and mechanically separable mechanically separable portion of a substance portion of a substance • Can be continuous or Can be continuous or discontinuous discontinuous • Can be solid, liquid Can be solid, liquid or gas or gas • Can be a pure Can be a pure substance or a substance or a solution solution
30
Embed
Phase Any physically distinct, chemically homogeneous and mechanically separable portion of a substanceAny physically distinct, chemically homogeneous.
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
PhasePhase• Any physically distinct, Any physically distinct,
chemically homogeneous chemically homogeneous and mechanically separable and mechanically separable portion of a substanceportion of a substance
• Can be continuous or Can be continuous or discontinuousdiscontinuous
• Can be solid, liquid or gasCan be solid, liquid or gas• Can be a pure substance or Can be a pure substance or
a solutiona solution
Multiple Solid Phases
• Multiple solid phases are Multiple solid phases are common in metalscommon in metals
• Phases defined by Phases defined by composition (not by composition (not by state – solid, liquid, gas)state – solid, liquid, gas)
• Example – two phases Example – two phases shown to the right, dark shown to the right, dark phase and then the phase and then the lighter phaselighter phase
Single Phase vs. Multiple PhasesSingle Phase vs. Multiple Phases
Conditions Conditions • Similar SizeSimilar Size• Same Crystal StructureSame Crystal Structure• Same ValanceSame Valance• Similar ElectronegativitySimilar Electronegativity
Equilibrium Phase DiagramEquilibrium Phase Diagram• Equilibrium: state of a system remains constant over an indefinite period of Equilibrium: state of a system remains constant over an indefinite period of
timetime
• Binary phase diagram: diagram for alloy composed of two elementsBinary phase diagram: diagram for alloy composed of two elements
• Shows relationship in a metal among Shows relationship in a metal among – temperaturetemperature
– pressurepressure
– compositioncomposition
• Gibb’s Phase RuleGibb’s Phase Rule
Types of Phase diagramsNumber of Constituents
• Unary (like the water one shown at the beginning) – one constituent
• Binary - two constituents , like an alloy (we will focus on these)
• Ternary - three constituents; requires 3-D diagram
Number of phases
• Isomorphous – one solid phase
• Polymorphous – multiple solid phases
Utilization of Phase DiagramsUtilization of Phase Diagrams• For each point of temperature and composition, three pieces of For each point of temperature and composition, three pieces of
information can be obtainedinformation can be obtained– Phase present Phase present
– The amount of each phase present ( how many ice cubes are in the glass)The amount of each phase present ( how many ice cubes are in the glass)• lever lawlever law
– Composition of each phase (chem make-up of phases)Composition of each phase (chem make-up of phases)• tie linetie line
Liquidus and Solidus Temperature
• Liquidus – The temperature at which the first solid forms during solidification
• Solidus – The temperature below which the liquid has completely solidified.
liquidus
solid
us
Wt % MgO
Tie Line –Composition of Phases
• Draw a vertical line at the composition of the “alloy” of interest ex – 40 wt % MgO see purple line
• For a given temperature draw an isotherm (horizontal line) ex at 2400 C red line
• Where line crosses “phase boundary” (in this case the liquidus line or solidus line), draw a vertical line– Ex – composition of liquid
phase is ~32% MgO; Composition of solid phase is ~ 60 % MgO
liquidus
solid
us
Wt % MgO
Lever Law – Amount of each phaseUsing the compositions of the phases determined from the tie line, calculate the amount of each phase as this:
Opposite lever arm/total length of lever * 100%
LiquidC = 32 %MgO
SolidC = 60 %MgO
AlloyC = 40 %MgO
Therefore:Amt L = (60-40)/(60-32) * 100 = 71%Amt S = (40-32)/(60-32)*100 = 29%
**Notice the compositionof the phases does not have to add up to
100% but the amount does!!*****
What’s the difference between Amount and Composition????
• Composition is the chemical make-up of the phase (if we had a glass of coke with ice in it, our liquid phase would have one chemical make-up – won’t begin to think what it might be, the liquid phase would have a chemical make-up of ~ H2O. The composition of the “alloy” would be the total chemical make-up of the ice and coke combined (which would be watery coke?)
What’s the difference between Amount and Composition????
• Amount is the quantity of the phase (if we had a glass of coke with ice in it, we could take the ice cubes out and weigh them and then weigh the coke to figure out the amount of the solid and liquid phase or use the lever law)