crystalmeltphasediagrams晶体熔体相图.ppt

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1、The Gibbs Phase Rule The phase rule allows one to determine the number of degrees of freedom (F) or variance of a chemical system. This is useful for interpreting phase diagrams.F = 2 + C - F FWhere F is the number of degrees of freedom, C is the number of chemical components and F is the number of

2、phases in the system. The number two is specified because this formulation assumes that both T and P can be varied.Phase Rule Significance for Phase Diagrams For two dimensional phase diagrams: Stability fields: Areas (T-P, T-X, P-X space) where a phase or phase assemblage (more than one phase) is s

3、table. Equilibrium boundary lines: These define the limits of stability fields. These represent values of intensive parameters where phases in adjacent fields coexist. Triple points: Points where equilibrium boundary lines meet. All phases in the adjacent stability fields must coexist.Silica Phase D

4、iagram and Phase RuleSingle Component System: F = 2 + C - F = 3 - FStability FieldF= 1; F = 2; divariantBoundary LineTriple PointF= 2; F = 1; univariantF= 3; F = 0; invariantFrom Swamy et al., 1994Wet and Dry Melting Relations for AlbiteFrom Burham & Davis, 1974; Boettcher et al., 1982Dry MeltingCur

5、veWater Saturated Melting CurveWater UndersaturatedMelting Curves(2, 5, & 8 kbar)Binary Phase Relations - Definitions Liquidus line: the line that represents the locus of depressed freezing points as a second component is added to the system. Solid phases are not stable at temperatures above those d

6、efined by the liquidus line or surface. CaMg2Si2O6cpxCaMg2Si2O6o RTlnaCaMg2Si2O6cpxCaMg2Si2O6cpxCaMg2Si2O6o RTln XCaMg2Si2O6cpxif XCaMg2Si2O6cpx1.0 then RT lnXCaMg2Si2O6cpx 0.0and CaMg2Si2O6cpxCaMg2Si2O6oif XCaMg2Si2O6cpx 0.9 then RT lnXCaMg2Si2O6cpx 0.0and CaMg2Si2O6cpxCaMg2Si2O6oDi-An Binary Eutec

7、tic Phase DiagramBinary Phase Diagram Definitions Eutectic point: Lowest T point on the liquidus at which a unique melt of fixed composition is in equilibrium with two or more phases. Isopleth: line of constant chemical composition. Isotherm: line of constant temperature Tie line: portion of isother

8、m that connects two stable coexisting phases, in this case L (representing the silicate liquid) and S (pure crystalline anorthite feldspar)The Lever Rule S x(x y) Follows directly from the Law of Conservation of Mass.Allows one to calculate either algebraically or graphicallythe modal abundance of e

9、ach phase at every temperature. Ly(x y)MASS OF LIQUIDMASS OF SOLIDBULK COMPOSITIONCooling History in a Binary Eutectic SystemIntersection with liquidus: F = 1 (T or X)Eutectic point: F = 0Initial State: F = 1 + C - F 1 2 - 1 2 (T & X)subsoliduscoolingF = 1dQ/dt is constantF1F1F2F2F2F2F3F3 CPl specif

10、ic heat of liquid; HmAn latent heat of xtalDi-An Binary Eutectic Free Energy RelationsMgO-SiO2 Incongruent Binary Melting RelationsPeritectic point: binary systemwith 3 phases, one of whichis liquid, are in a reaction relation.At R, the reaction point:Mg2SiO4 + SiO2 (in melt) =2MgSiO3 + latent heatE

11、nstatite melting yields liquid richer in silica.Equilibrium vs. Fractional CrystallizationEquilibrium Crystallization:crystals continuously reactand re-equilibrate with themelt at P-T-X conditionschange. Melt-xtal reactions are reversibleFractional Crystallization:Crystals are immediately isolated,

12、removed, orfractionated from the residual melt so that nofurther reactions can occur.Melt-xtal reactions areirreversible.Binary Phase Loop with Solid SolutionliquidussolidusPlagioclase Differentiation MechanismsGabbro - Plane Polarized LightPlagioclase zoningCrystal Settlingzoned plagPerthiticpyroxe

13、neHawaiian Basalt Phase Relations at 1 atmFrom Wright & Okamura, 1977Temperatures measured in borehole1170C1130C1075C1020CGeneralized Basalt Phase DiagramFrom Green, 1982进入夏天，少不了一个热字当头，电扇空调陆续登场，每逢此时，总会进入夏天，少不了一个热字当头，电扇空调陆续登场，每逢此时，总会想起那一把蒲扇。蒲扇，是记忆中的农村，夏季经常用的一件物品。记想起那一把蒲扇。蒲扇，是记忆中的农村，夏季经常用的一件物品。记忆中的故乡，

14、每逢进入夏天，集市上最常见的便是蒲扇、凉席，不论男女老忆中的故乡，每逢进入夏天，集市上最常见的便是蒲扇、凉席，不论男女老少，个个手持一把，忽闪忽闪个不停，嘴里叨叨着少，个个手持一把，忽闪忽闪个不停，嘴里叨叨着“怎么这么热怎么这么热”，于是三，于是三五成群，聚在大树下，或站着，或随即坐在石头上，手持那把扇子，边唠嗑五成群，聚在大树下，或站着，或随即坐在石头上，手持那把扇子，边唠嗑边乘凉。孩子们却在周围跑跑跳跳，热得满头大汗，不时听到边乘凉。孩子们却在周围跑跑跳跳，热得满头大汗，不时听到“强子，别跑强子，别跑了，快来我给你扇扇了，快来我给你扇扇”。孩子们才不听这一套，跑个没完，直到累气喘吁吁，。孩

15、子们才不听这一套，跑个没完，直到累气喘吁吁，这才一跑一踮地围过了，这时母亲总是，好似生气的样子，边扇边训，这才一跑一踮地围过了，这时母亲总是，好似生气的样子，边扇边训，“你你看热的，跑什么？看热的，跑什么？”此时这把蒲扇，是那么凉快，那么的温馨幸福，有母亲此时这把蒲扇，是那么凉快，那么的温馨幸福，有母亲的味道！蒲扇是中国传统工艺品，在我国已有三千年多年的历史。取材的味道！蒲扇是中国传统工艺品，在我国已有三千年多年的历史。取材于棕榈树，制作简单，方便携带，且蒲扇的表面光滑，因而，古人常会在上于棕榈树，制作简单，方便携带，且蒲扇的表面光滑，因而，古人常会在上面作画。古有棕扇、葵扇、蒲扇、蕉扇诸名，实即今日的蒲扇，江浙称之为面作画。古有棕扇、葵扇、蒲扇、蕉扇诸名，实即今日的蒲扇，江浙称之为芭蕉扇。六七十年代，人们最常用的就是这种，似圆非圆，轻巧又便宜的蒲芭蕉扇。六七十年代，人们最常用的就是这种，似圆非圆，轻巧又便宜的蒲扇。蒲扇流传至今，我的记忆中，它跨越了半个世纪，也走过了我们的扇。蒲扇流传至今，我的记忆中，它跨越了半个世纪，也走过了我们的半个人生的轨迹，携带着特有的念想，一年年，一天天，流向长长的时间隧半个人生的轨迹，携带着特有的念想，一年年，一天天，流向长长的时间隧道，袅道，袅