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How is ultrpure Si for computer chips produced?Slide3: Melting point of an alloy Cu Ni Wt% Ni 1085ºC 1453ºC Liquid, L Solid solution, Liquidus solidus L + Slide4: A diagram in the space of relevant thermodynamic variables (e.g., T and x) indicating phases in equilibrium is called a phase diagram. Equilibrium phase diagram or Equilibrium diagram or Phase diagramSlide5: The independent chemical species (element or compound) in terms of which the composition of the system is described are called components. H2O Water +ice liquid solution + Fe3C components Water liquid H2O Liquid+solid nimbu, chini and pani shikanji Fe + C Mild steel phases System ComponentsSlide6: A single component phase diagram: Unary diagram A two-component phase diagram: Binary diagram A three-component phase diagram: Ternary diagramSlide7: Cu-Ni binary phase diagram Callister, Fig. 9.2 Any given point (x,T) on the phase diagram represents an alloy of composition x held at equilibrium at temperature T Point A: 60 wt% Ni at 1100ºC Point B: 35 wt% Ni at 1250ºCSlide8: Phase Diagrams For any given point (x,T) the phase diagram can answer the following: What phases are present? What are the phase compositions? What are the relative amounts of the phases (phase proportions or phase fractions)?Slide9: Point A: 60 wt% Ni at 1100ºC Q: Phase present? Ans: Q: Phase composition ? Ans: 60 wt%Ni Q: Phase amount ? Ans: 100%Slide10: Point B: 35 wt% Ni at 1250ºC Q: Phases present? Ans: + L Q: Phase compositions ? Tie Line Rule Q: Phase amounts ? Lever RuleSlide11: Composition of phases in the two-phase region Tie Line CL= 31.5 wt% Ni C= 42.5 wt% Ni Tie Line Rule Slide12: Amount of phases in the two-phase region Tie Lever Rule Tie-Line: A lever Alloy composition C0: Fulcrum fL: weight at liquidus point f: weight at solidus point The lever is balancedSlide13: The Lever Rule: A Mass balance Proof Prob. 7.6 f + fL = 1 Wt of Ni in alloy = W C0/100 Wt of Ni in = fWC/100 Wt of Ni in L = fL WCL/100 C f + CL fL = C0 Wt of alloy = W Wt of in alloy = fW Wt of L in alloy = fLW Wt of Ni in alloy = Wt of Ni in + Wt of Ni in L Slide14: Development of Microstructure during solidificationSlide15: Solder alloy? An alloy of Pb and Sn What is best composition of the solder alloy? Requirements: 1. should melt easily 2. should give a strong jointSlide16: L Pb Sn Solder alloy Wt % Sn 327 232 183 L L 1-2-1 rule Eutectic horizontal Eutectic diagram Liquidus Liquidus solidus solidus solvus solvusSlide17: : Pb rich substitutional solid solution of Pb and Sn crystal structure: monatomic FCC : Sn rich substitutional solid solution of Pb and Sn crystal structure: monatomic BCT Pb: monatomic fcc Sn: monatomic bctSlide18: Woods metal tea party Bi 50.0 wt% Pb 25.0 wt% Cd 12.5 wt% Sn 12.5 wt% An eutectic alloy with m.p. of 70ºC 100 g US$ 181 Anti-Fire SprinklersSlide19: Eutectic reaction Invariant reaction Callister Figs. 9.11, 12Slide20: Microstructure of hypoeutectic alloy Slide21: Amount of total and total at a temperature just below 183ºC Tie line just below 183ºC (red) Eutectc mixture Proeutectic or Primary Slide22: Amount of proeutectic at a temperature just below 183ºC Tie line just above 183ºC (green) Eutectc mixture Proeutectic or Primary = Amount of at a temperature just above 183ºCSlide23: Let the fraction of proeutectic in micrograph fpro = 0.25 Tie line just above 183ºC (green) Eutectc mixture Proeutectic or Primary Let the composition (wt% Sn) of the alloy be C0 EXPERIMENT 5Slide24: Optimum composition for solders For electronic application Eutectic solder 62 wt% Sn For general application Minimum heating Hypoeutectic solder Cheaper Allows adjustment of joint during solidification in the L rangeSlide25: Modern Trend Lead-free solders Phase diagrams can help in identification of such solders Sn-Ag-CuSlide26: Please collect your Minor I answer books from Lab in the afternoon Those who can, do. Those who can’t teach G.B. ShawSlide27: Gibbs Phase Rule Thermodynamic variables: P, T, Phase Compositions (overall composition is not considered) If there are C components then C-1 compositions have to be specified for each phase Therefore total number of composition variables: P (C-1) With Pressure and Temperature, total number of variables = P (C-1) + 2Slide28: Degrees of Freedom F: No. of thermodynamic variables that can be specified independently Gibbs phase rule states that one cannot specify all of the above P (C-1) + 2 variables independently in a system at equilibriumSlide29: Gibbs Phase Rule F = C – P + 2 F = Degrees of freedom C = No. of components in the system P = No. of phases in equlibrium If pressure and temp both are variables F = C – P + 1 If pressure is held constantSlide30: F = C – P + 1 F =2 F =1 C=2 F=3-P At eutectic reaction P=3 (L, , ) F=0 Invariant reactionSlide31: steel Cast iron The Iron-carbon system Mild steel 0-0.3 wt% C Bicycle frame Ship hull Car body Medium C steel 0.4-0.7 wt% C Rail wheel rail axle rails High C steel 0.8-1.4 wt% C Razor blades scissors, knivesSlide32: Phases in Fe-C system Phase Symbol Description Liquid L Liquid solution of Fe and C -Ferrite Interstitial solid solution of C in -Fe (high temperature bcc phase) Austenite Interstitial solid solution of C in -Fe (FCC phase of Fe) Ferrite Interstitial solid solution of C in -Fe (room temperature bcc phase) Soft and Ductile Cementite Fe3C Intermetallic compound of Fe and C (orthorhombic system) Hard and BrittleSlide33: Ferrite AusteniteSlide34: Invariant Reactions in Fe-C system Peritectic Reaction A horizontal line always indicates an invariant reaction in binary phase diagrams Eutectic Reaction Eutectoid Reaction Slide35: Eutectoid Reaction PearliteSlide36: Ammount of Fe3C in Pearlite Red Tie Line below eutectoid tempSlide37: Development of Microstructure in a hypoeutectoid steelSlide38: Proeutectoid Ferrite Pearlite Microsructure of a hypoeutectoid steel, 0.38 wt% C EXPERIMENT 5Slide39: fpearlite below TE = faustenite above TE Tie-Line above the eutectoid temperature TESlide40: Development of Microstructure in a hypereutectoid steelSlide41: Microsructure of a hypereutectoid steel, 1.4 wt% C Proeutectoid cementite on prior austenite grain boundaries PearliteSlide42: Fproeutectoid cementite=fcementite above TESlide43: Phase vs. microconstituents A phase or a mixture of phases which has a distinct identity in a microstructure is called a microconstituent Pearlite is not a phase. It is microconstituent which is a mixture of two phases and Fe3C.Slide44: Eutectoid steel +Fe3C Pearlite Hypoutectoid steel +Fe3C Pearlite + proeutectoid ferrite Hypereutectoid steel +Fe3C Pearlite + proeutectoid cementiteSlide45: A Wt % B C0 T TmA L +L C CL C < CL Principle of Zone Refining TSlide46: SemiconductorTransistor was invented by Bardeen, Brattain and Shockley At AT&T Bell Labs One needs ultrapure Si (impurity level few ppm) Zone Refining was invented by Pfann at Bell Labs as a process to obtain ultrapure Si Basis for modern Si technology You do not have the permission to view this presentation. In order to view it, please contact the author of the presentation.