Konsep Fasa dan DiagramKesetimbangan Fasa casting.Introduction The understanding of phase diagrams for alloy system is extremely important because there is strong correlation between microstructure and mechanical properties. and the development of microstructure of an alloy is related to the characteristics of its phase diagram In addition. phase diagram provide valuable information about melting. crystallization and other phenomena . Definition and basic concepts . Dapat dibedakan fasa padat (es) dan fasa cair (air). Komponen yang ada hanya 1 yaitu air (H2O) .Konsep Fasa Fasa berkaitan dengan keadaan materi yang terpisah dan dapat diidentifikasi dari bagian lainnya secara fisik dan dapat dipisahkan secara mekanis. Contoh: Dalam suatu sistem : air dan es dalam gelas. Dapat diidentifikasi fasa cair (bahan bakar) dan fasa gas (udara). Fasa yang ada adalah padat (gula pasir) dan fasa cair (air tebu) . Suatu sistem campuran bahan bakar (fuel) dengan udara dalam silinder. Meskipun udara terdiri dari beberapa unsur dan senyawa seperti O2 dan N2 namun keduanya satu fasa yaitu gas Terdapat sistem gula pasir dan air tebu dalam tanki putaran. . Komponennya 2 yaitu Fe dan Fe3C. Fasa yang ada adalah ferrite (α) dan cementite (Fe3C). Tinjau sistem poros baja. Gas. definable structure. More precisely: form of material with identifiable composition (chemistry).Sehingga dapat didefinisikan bahwa Phase is a form of material having characteristic structure and properties. Pure substance or solution (uniform structure throughout). liquid or solid. and distinctive boundaries (interfaces) which separate it from other phases. Phases: Phase can be continuous (air in the room) or discontinuous (salt grains in the shaker). . . chemically homogeneous and mechanically separable portion of a substance Can be continuous or discontinuous Can be solid.Phase Any physically distinct. liquid or gas Can be a pure substance or a solution . Deff : Component : frequently used in discussion.g . Solute is used to denote an element or compound present in minor concentration . components represent pure metals and/or compound of which an alloy is composed e. the component are Cu and Zn Solute and solvent. copper-zinc brass. solvent represent the element or compound that is present in the greatest amount (also called. host atoms). g. but without regard t alloy composition (e. which has two meanings: system may refer to specific body of material under consideration (e..Deff : System. a ladle of molten steel) relate to the series of possible alloys consisting of the same component.g.. the iron-carbon system) . . Components and Phases • Components: The elements or compounds that are mixed initially (Al and Cu). physically distinct and mechanically separable portion of the material with a given chemical composition and structure ( and ). • Phases: A phase is a homogenous. AluminumCopper Alloy (lighter phase) (darker phase) 15 . gas) • Example – two phases shown to the right. liquid.Multiple Solid Phases • Multiple solid phases are common in metals • Phases defined by composition (not by state – solid. dark phase and then the lighter phase . . Multiple Phases .Single Phase vs. Phase diagram are also used to make predictions about processes that involve chemical reactions among phases. ceramist. metallurgist and other scientists to organize and summarize experiment and observational data. Similar principles or rules apply to interpretations using phase diarams for igneous processes. typically as a function of one or more intensive variables such as chemical composition.*) Konsep Diagram Fasa •A phase diagram is graphical representation of the equilibrium relations among phases. temperature. pressure and the activity of a chemical component Phase diagram are used by geologist. chemist. metamorphics . Phase diagrams can be grouped according to the number of independent chemical component needed to represent chemical composition: .two component systems .One component (PT diagram) .three component system . Mengapa perlu diagram kesetimbangan? Interpretation of Phase Diagrams For a given temperature and composition we can use phase diagram to determine: 1)The phases that are present 2) Compositions of the phases 3) The relative fractions of the phases . Kesetimbangan dan Transformasi Fasa Pengertian dan Konsep Keseimbangan Kesetimbangan menyebabkan komposisi, temperatur, tekanan dan kondisi lain yang mempengaruhi suatu sistem berada pada energi terendah Sistem bahan tidak murni, terdapat impuritas atau bahan tambahan yang hasilnya merupakan larutan padat, multi kristalin, campuran kristalin atau campuran kristalin-nonkristalin Energy States Unstable: falling or rolling Stable: at rest in lowest energy state Metastable: in low-energy perch Figure . Stability states. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall. equilibrium It is useful to begin by defining a few of the terms that will be frequently used. - system - phase - component The study of phase transformations, as the name suggest, is concerned with how one or more phases in an alloy (the system) change into a new phase or mixture phases. For transformation that occur at constant temperature and pressure the relative stability of a system is determined by its Gibbs free energy (G) G = H – TS H : enthalpy, T : absolute temperature, S : entropy H = E + PV Where E : internal energy of system P : pressure V : volume The internal energy arises from the total kinetic and potensial energy Kinetic energy can arise from atomic vibration in solid or liquid and from translational and rotational energies for the atoms or molecules within a liquid or gas Potential energy arises from the interaction. or bond between the atoms within the system . 3GB The side of the reaction with lower G will be more stable .Thermodynamics G for a reaction of the type: 2A + 3B =C +4D G = (n G)products .2GA .(n G)reactants = GC + 4GD . GT1 P1 = V(P2 .Thermodynamics For other temperatures and pressures we can use the equation: dG = VdP .T1) .S (T2 .SdT (ignoring X for now) where V = volume and S = entropy (both molar) We can use this equation to calculate G for any phase at any T and P by integrating G T2 P 2 G T 1 P1 z P2 P1 VdP z T2 SdT T1 If V and S are constants. our equation reduces to: GT2 P2 .P1) . Now consider a reaction. we can then use the equation: dG = VdP .SdT G for any reaction = 0 at equilibrium (again ignoring X) . that is H ≈ E The other function that appears in the expression for G is entropy (S) which is a measure of the randomness of the system A system is said to be in equilibrium when it is in the most stable state An important consequence of the law of classical thermodynamics is that at constant T and P a closed system will be in stable equilibrium if it has the lowest G or dG = 0 . If a transformation or reaction occurs the heat that is absorbed or envolved will depend on the change in the internal energy of the system. When dealing with condensed phases (solids and liquids) the PV term is ussualy very small in comparison to E. equilibrium and chemical potential. (particle numbers will change) . This is particularly important in alloy or binary systems.Gibbs free energy.g. Gibbs phase rule Equilibrium : the most stable state defined by lowest possible G dG = 0 Solid : Low atomic kinetic energy or E low T and small S Liquid : Large E high T and large S metastable E. equilibrium Metastable : Diamond Equilibrium : Graphite Chemical potential or partial molar free energy governs how the free energy changes with respect to the addition/subtraction of atoms. . G = energi bebas Gibbs. T = temperatur mutlak. P = tekanan sistem.Hukum-hukum termodinamika Pengertian keseimbangan diberikan oleh hukumhukum termodinamika yang dinyatakan dalam energi bebas Gibbs suatu sistem n G PV TS i X i i 1 Dimana. I = potensial kimia komponen ke-i dan Xi = fraksi mol ke-i Keadaan seimbang dicapai bila harga energi bebas Gibbs G mencapai minimum . V = volume sistem. S = entropi. Bila keseimbangan dicapai. temperatur dan tekanan harus uniform dalam sistem dan potensial kimia untuk setiap komponen harus sama dalam setiap fasa yang berada dalam kesetimbangan . . How many phases do we get? What is the composition of each phase? How much of each phase do we get? Phase B Phase A Nickel atom Copper atom ..With these definitions in mind: ISSUES TO ADDRESS. and --a temperature (T ) and/or a Pressure (P) then..g. --a composition (e..... wt% Cu .. if we specify. • When we combine two elements.wt% Ni).. what “equilibrium state” would we expect to get? • In particular. . . temperatur dan komposisi) yang dapat dipertukarkan dengan bebas tanpa menimbulkan fasa baru atau mengurangi fasa yang ada Komponen adalah bilangan terkecil variabel yang independen dimana konstituen kimia membentuk komposisi fasa yang ada .Beberapa definisi Fasa merupakan bagian dari sistem yang secara fisis homogen dan dibatasi oleh permukaan yang dapat dipisahkan dengan bagian lain dari sistem Jumlah derajat kebebasan atau variasi adalah jumlah dari variabelvariabel intensif (tekanan. Bersamaan dengan itu diamati perubahan mikro dan properties material. Analisis yang bisa dilakukan : XRD dan mikroskopi . Analisis yang bisa dilakukan : DTA/TGA dan XRD Metode statik : sampel dipanaskan hingga temperatur tertentu yang diinginkan kemudian didinginkan cepat (quench).Membangun diagram fasa Metode dinamik : temperatur sampel dinaikkan atau duturunkan dari fasa cair. Sampel yang diperoleh dipandang sebagai fasa metastabil yang menggambarkan keadaan pada temperatur tinggi. . Diagram fasa komponen Fasa yang akan terjadi adalah polimorfisme nya sistem uap. cair dan satu padat beserta Variabel bebas yang dapat menghilangkan dan menimbulkan fasa adalah temperatur dan tekanan . equilibrium and chemical potential. C. T is dependent on P (or vice-versa) If 3 phases in equilibrium (e.2. number of phases in equilibrium . Gibbs free energy. 3 phases exist only at one fixed T and P. solid) 2 degrees of freedom i. can change T and P without changing the phase If 2 phases in equilibrium (e.g. number of components K.e. liquid and ) 0 degrees of freedom.g. solid.e. solid and liquid) 1 degree of freedom i.g. Gibbs phase rule Gibbs phase rule for equilibrium phase : Number of degrees of freedom F = C – K +2 Examples : Single component system C=1 and F = 3 K If 1 phases in equilibrium (e. Single component systems Assumption: Closed system ignore d For purposes of most discussions : fix pressure (unless otherwise stated) G From thermodynamics: Sliquid > Ssolid Phase transition occurs when: Gsolid Gsolid=Gliquid For pressure dependence: Gliquid TM T (K) Similar arguments apply : Vliquid > Vsolid so increasing P implies liquid to solid transition .3. Clausius Clapeyron Equation more dense (intermediate) more dense Less dense Less dense . . . . P = 2 dan C = 1 sehingga V = 1. hal ini berarti bahwa baik tekanan atau temperatur tetapi tidak keduanya dapat berubah secara bebas tanpa kehilangan fasa. P = 1 dan C = 1 sehingga V = 2. Jumlah fasa maksimal dicapai bila variansinya sama dengan nol Pada titik B. setiap perubahan temperatur dan tekanan menyebabkan hilangnya satu fasa. artinya tekanan dan temperatur keduanya dapat berubah tanpa menghilangkan fasa . terletak pada garis diagram. ketiga fasa dalam keseimbangan. menyatakan keadaan dimana dua fasa berada dalam kesetimbangan. Pada titik C. Pada titik A. . Pada 573°C terjadi transformasi -quartz ke quartz secara cepat dan reversibel sedangkan transformasi fasa yang lain terjadi sangat lambat sehingga membutuhkan waktu yang panjang untuk mencapai kesetimbangan . Pada tekanan rendah terdapat 5 fasa yaitu. -quartz. quartz. 2tridymite. -cristobalite dan silika cair. 794. Geophys. Res. The system SiO2 Fig.1 . 6.6.. AGU . 11. After Swamy and Saxena (1994). J. 99.C Systems 1.787-11. Phase Rule in OneComponent Systems Notice that in one-component systems. 51 . the number of degrees of freedom seems to be related to the number of phases. Phase Rule in One-Component Systems The phase rule should be applicable for any single- component systems in general. 52 . Number of Components (c) f=c–p+2 The number of components (c) is the minimum number of independent chemical components needed to form the system or. the number of components will also be reduced by one. If you have equal amounts (concentrations) of products formed. to define all the phases. "Independent" means: If you have equilibrium balance between reactants and products. the number of components will be reduced by one. 53 . in other words. + – Available chemical constituents are: Na . Is it correct to say c = 4 ? + – Because Na and Cl have the same amount “equal neutrality” as NaCl.Number of Components (c) f=c–p+2 Examples (Chemical reactions): If you have equilibrium balance between reactants and products. NaCl and H2O. the number of components will be reduced by one. Example 1: NaCl(s) dissolved in H2O. then c = 2 and not 4. the number of components will also be reduced by one. If you have equal amounts (concentrations) of products formed. Cl . 54 . Is it correct to say c = 3 ? Because of the equilibrium condition the number of independent components is reduced by one. Thus. the number of components will be reduced by one. If you have equal amounts (concentrations) of products formed. Example 2: CaCO3(s) CaO(s) + CO2(g) Available chemical constituents are three.Number of Components (c) f=c–p+2 Examples (Chemical reactions): If you have equilibrium balance between reactants and products. the number of components will also be reduced by one. c = 2 instead of 3. 55 . If you have equal amounts (concentrations) of products formed. the number of components will also be reduced by one. Example 2: CaCO3(s) CaO(s) + CO2(g) Can you specify the number of phases for the reaction? We have here three homogeneous. the number of components will be reduced by one. distinct parts of the system separated by definite boundaries.Number of Components (c) f=c–p+2 Examples (Chemical reactions): If you have equilibrium balance between reactants and products. p=3 56 . 57 . Example 2: CaCO3(s) CaO(s) + CO2(g) So.Number of Components (c) f=c–p+2 Examples (Chemical reactions): If you have equilibrium balance between reactants and products. the number of components will be reduced by one. what’s the number of degrees of freedom the system would have? f=c–p+2 = 2 – 3 + 2 = 1 degree of freedom. the number of components will also be reduced by one. If you have equal amounts (concentrations) of products formed. Phase Diagram of Hydrogen 58 . . Acad. 3.. .1 . Chem. 5. 597-605. Phys.C Systems 2. 5. Arts and Sci. (1936) J. Phys. Chem..7. 6. (1937) J. Amer. 964-966. 441-513. The system H2O Fig. After Bridgman (1911) Proc. Orthorhombic. S8 or S(rh) Monoclinic. S4 or S(mo) Yellow sulfur of the orthorhombic (or rhombic) crystalline form. 60 . It is the form that commonly exists under normal conditions.Phase Diagram of Sulfur Sulfur solid exists in two crystalline forms. Phase Diagram of Sulfur 61 . A More Comprehensive Phase Diagram of Sulfur 62 .