Thermodynamics of High Temperature Materials Systems

Transcription

1 Freiberg University of Mining and Technology, Germany Thermodynamics of High Temperature Materials Systems Hans Jürgen Seifert Summer School Advanced Thermostructural Materials Santa Barbara, August 9, 2006

2 Thermodynamics of High Temperature Materials Systems Outline Hans Jürgen Seifert 1. Introduction and motivation for thermodynamic calculations - Computational thermodynamics - CALPHAD approach (CALculation of PHAse Diagrams) - Thermodynamic databases and software 2. Thermodynamic optimization of the Ce-O system - Thermodynamic modeling of solution phases 3. Precursor-derived Si-(B-)C-N ceramics - High temperature reactions of silicon carbide and silicon nitride ceramics - Crystallization and high temperature stability of Si-(B-)C-N ceramics

3 Thermodynamics of High Temperature Materials Systems Outline Hans Jürgen Seifert 4. Computational thermodynamics in heat shield engineering - The Y-Si-C-O system database - Active / passive oxidation of SiC - Phase reactions of Yttrium silicates and C/C-SiC composites - High temperature stability issues in the engineering of heat shields 5. Conclusions

4 Combined Approach Computational Thermodynamics and Modeling + Experiments, Analysis Fundamental Research Materials Engineering, Processing

5 Computational Thermodynamics Theory Quantum Mechanics, Statistical Thermodynamics Estimates Experiments DTA, Calorimetry, EMF, Knudsen Effusion, Metallography, X-ray Diffractometry,... CALPHAD Optimization Ab-initio Calculation Models with adjustable Parameters Adjustment of Parameters CALculation of PHAse Diagrams Thermodyn. Functions G, H, S, C p Storage in Databases Equilibrium Calculations Application Equilibria Phase Diagrams Kinetics Graphical Representation

6 CALPHAD (CALculation of PHAse Diagrams) Development of Optimized Thermodynamic Datasets stored in Computer Databases Calculation of : - Thermodynamic Functions - Liquidus Surface - Isothermal Sections - Isopleths - Potential Phase Diagrams - Phase Fraction Diagrams - Phase Compositions - Scheil Solidification Requires Modeling of Stoichiometric and Solution Phases Taking into Account the (Crystal-) Structures and Site Occupancies

7 CALPHAD (CALculation of PHAse Diagrams) Software LUKAS (BINGSS, BINFKT, TERGSS, TERFKT) THERMO-CALC FACTSAGE PANDAT MALT, MALT2 MTDATA JMATPRO GEMINI...

8 CALPHAD (CALculation of PHAse Diagrams) Databases SGTE, Scientific Group Thermodata Europe - SSOL2, SSOL4 - SSUB3 - Noble Metals Thermo-Calc: Steels, Ni-base, slags,... ThermoTech: Ni-base, Al-, Mg-,... PML: Al-, Ceramics...

9 Calculated Ce O System in Solid State from 60 to 67 mol. % O in comparison with experimental data.

10 Phases in the Partial Ce O System Related Crystal Structures: CeO 2-x (ss) CaF 2 - type (Strukturbericht C1) Compound Energy Formalism: (Ce +3, Ce +4 ) 1 (O -2,Va) 2 C-Ce 2 O 3 (ss) Mn 2 O 3 - type (Strukturbericht D5 3, Ordered State of C1) Unit Cell: composed of 8 CaF 2 -type cells. ¼ of O-ions removed, remaining atoms re-arrange towards these vacancies. Compound Energy Formalism: (Ce +3, Ce +4 ) 2 (O -2 ) 3 (O -2,Va) 1 Contains more O atoms than the ideal formula of the Mn 2 O 3. Ce 2 O 3 Stoichiometric phase description (Strukturbericht D5 2 )

11 Compound Energy Formalisms Reference Compounds (A,B) k (D,E) l Solution phase with two sublattices and 4 species Four compounds defined: A : D A : E B : D B : E Gibbs free energy for every compound to be determined Here: (Ce +3, Ce +4 ) 1 (O -2,Va) 2

12 Compound Energy Formalism Surface of Reference (A,B) k (D,E) l Solution phase with two sublattices and 4 species

13 Modeling of solution phases; sublattice model described in the Compound Energy Formalism (A,B) k (D,E) l Solution phase with two sublattices and 4 species Stochiometric coefficient (s: sublattice) Site fraction of spezies A on sublattice s

14 Compound Energy Formalism Excess term of Gibbs free energy (A,B) k (D,E) l Solution phase with two sublattices and 4 species

15 Compound Energy Formalisms Gibbs free energy of solution phases Mixing Gibbs Energy

16 Phases in the Partial Ce O System CeO 2-x (ss) CaF 2 - type (Strukturbericht C1) Compound Energy Formalism: (Ce +3, Ce +4 ) 1 (O -2,Va) 2 Cubic close pack of Ce ions, where all the tetrahedral voids form the sublattice on which the 2-x O-ions are statistically distributed. Electroneutrality condition determines that site fractions on the two sublattices are not independent: Single variable y is equal 2 x. ' y Ce + 3 = ' y Ce + y 4 = (1 y) '' y Va = '' y O 2 y 4 1 y = 4

17 No. Paper Experimental Technique Measured Quantity Composition Temperature (K) Remark 1. Bevan & Kordis (1964) Experiment with CO 2 /CO & H 2 O/H 2 Partial pressures O 2 CeO 1.5- CeO Ackerman & Rauh (1971) Mass Spectroscopy & Mass Effusion Partial pressures CeO, CeO 2, Ce(g), CeO CeO CeO 1.53 CeO CeO Iwasaki & Katsura (1971) Experiment with CO 2 & CO 2 /H 2 mixture Partial pressures O 2 CeO , 1000, 1100, 1227, Campserveux & Gerdanian (1978) Micro- Calorimetry Partial pressures O 2 CeO , 1296, Kitayama et al. (1985) Thermogravimetry Partial pressures O 2 CeO 2, Ce 2 O 3 Ce 3 O

18 6. Marushkin et al. (2000) Knudsen cell, Mass spectrometry Partial pressures, CeO 2, Ce 2 O 3 CeO 1.99, Ce 2 O Kuznetzov& Rezukhina (1960) Calorimetry Heat capacity, CeO Westrum & Beale Jr. (1961) Adiabatic Calorimetry Heat capacity, CeO Justice & Westrum (1969) Cryogenic Calorimetry Heat capacity Ce 2 O Basily & El- Sharkawy (1979) Plane temperature wave method Heat capacity Ce 2 O Ricken et al. (1984) Calorimetry Specific heat, H trans. CeO 1.72 CeO Kuznetzov, et al. (1960) Bomb calorimetry H for Ce 2 O 3 Ce 2 O

19 13. Baker & Holley (1968) Oxygen Bomb Calorimetry Heat of combustion Ce 2 O 3 Ce 2 O Baker, Huber, Holley & Krikorian (1971) Bomb calorimetry Heat of formation CeO 2, CeC 1.5, CeC 2 CeO Campserveux & Gerdanian (1974) Micro Calorimetry Partial molal enthalpy H soln. (O 2 ) CeO 1.5 CeO Panlener, Blementhal & Garnier(1975) Thermogravimetry W/W CeO 2-x Riess, Koerner & Noelting Dilatometry Thermal expansion coefficient CeO 1.79 CeO (1988)

20 Calculated Ce O System in Solid State from 60 to 67 mol. % O in comparison with experimental data.

21 Heat capacities of Ce 2 O 3 and CeO 2. Enthalpy increment (heat contents) of CeO 2. H.J. Seifert, P. Nerikar, H.L. Lukas, Int. J. Mater. Res. 97 [6] (2006)

22 Chemical potentials of oxygen for ceria as a function of composition and temperature.

23 Chemical potentials of oxygen for ceria as a function of composition and temperature.

24 Chemical potentials of oxygen for ceria as a function of composition and temperature.

25 Chemical potentials of oxygen for ceria as a function of composition and temperature.

26 Chemical potentials of oxygen for ceria as a function of composition and temperature.

27 Chemical potentials of oxygen in the two-phase areas.

28 Partial Enthalpies of Oxygen in CeO 2 kj/mol HH CeO 2 CeO2 O O Mole fraction O

29 Thermodynamics of High Temperature Materials Systems Outline Hans Jürgen Seifert 1. Introduction and motivation for thermodynamic calculations - Computational thermodynamics - CALPHAD approach (CALculation of PHAse Diagrams) - Thermodynamic databases and software 2. Thermodynamic optimization of the Ce-O system - Thermodynamic modeling of solution phases 3. Precursor-derived Si-(B-)C-N ceramics - High temperature reactions of silicon carbide and silicon nitride ceramics - Crystallization and high temperature stability of Si-(B-)C-N ceramics

30 Precursor-derived Si-B-C-N Ceramics Produced by thermolysis (1323 K, Ar) of polymer precursors Amorphous, purely homogeneous inorganic materials NCP200: 40.1Si 23C 36.9N (at.%) - Starts to crystallize at 1700 K (N 2 ) - Thermal stability up to 1800 K (N 2 ) T2-1: 29.1Si 41.7C 19.4N 9.8B (at.%) - X-ray amorphous, nanocrystalline - Thermal stability up to 2300 K

31 Process for Precursor-derived Si-(B-)C-N Ceramics Monomer Polymer Synthesis Monomer Unit Precursor Polymer Preceramic Network Crosslinking ( C) Thermolysis ( C) Amorphous Solid Amorphous Ceramic Polycrystalline Ceramic Crystallization ( > 1400 C) Crystalline Ceramic Novel ceramics with high temperature stability and with good resistance to oxidation can be obtained from molecular units without sintering aid.

32 J. Gröbner, PhD thesis, 1994 Si-C binary subsystem

33 Si-N binary subsystem Gas Si(l) + Gas Si 3 N K Gas + Si 3 N 4 Si 3 N 4 + Si(l) 1687 K Si 3 N 4 + Si(s) Si(l) Si(s)

34

35

36 Isopleth from Carbon to Si 3 N 4 in the Si-C-N System

37 Isothermal Section of the Ternary System Si-C-N T = 3000 K (2727 C)

38 Isothermal Sections of the Ternary System Si-C-N Si 1 N 1.6 C 1.33 (VT50, Polyvinysilazane, Hoechst AG, Frankfurt, Germany) Si 1 N 0.6 C 1.02 (NCP200, Polyhydridomethylsilazane, Nichimen Corp., Tokyo, Japan) N Si 3 N 4 + 3C = 3SiC +2N 2 (1) N Si 3 N 4 = 3Si + 2N 2 (2) N Si 3 N 4 Si 3 N 4 C SiC Si C SiC Si C SiC Si T < 1484 C (1757 K) 1484 C < T < 1841 C T > 1841 C (2114 K) P = 1 bar

39 Calculated Phase Fraction Diagrams of Precursor Derived Ceramics Si 3 N 4 + 3C = 3SiC +2N 2 Si 1 N 1.6 C 1.33 (VT50) 1484 C

40 Thermogravimetrical (TG) analysis of precursor-derived Si-C-N ceramics Mass Loss (%) NCP200 VT Temperature ( C)

41 Calculated Phase Fraction Diagram of Precursor Derived Ceramics NCP200, Polyhydridomethylsilazane (Nichimen Corp., Tokyo, Japan) Ceramics: Si 1 N 0.6 C 1.02 Phase Fraction Diagram Reaction Path N 1484 C Si 3 N C C SiC Si

42 Thermogravimetrical (TG) analysis of precursor-derived Si-C-N ceramics Mass Loss (%) NCP200 VT Temperature ( C)

43 Thermogravimetrical (TG) analysis of precursor-derived Si-B-C-N ceramics 5 0 T2-1 Mass Loss (%) Si 3 N 4 + 3C = 3SiC + 2N 2 VT50 NCP200 MW36 MW33 (Si-B-C-N) Si 3 N 4 = 3Si + 2N (Si-C-N) Temperature ( C)

44 Calculated Phase Fraction Diagram of T2-1- Derived Ceramic Si 3.0 B 1.0 C 4.3 N 2.0 Si 3.0 B 1.0 C 4.3 N C ( T2-1 precursor, PML Max-Planck-Institut, Stuttgart, Germany )

45 B SiB n SiB6 B 4+ δ C BN SiB 3 B 2 CN 2 mol-% B BC 3 N BC 4 N BC 2 N mol-% C SiC mol-% B N C 3 N 4 SiC 2 N 4 Si 2 CN 4 Si 3 N 4 mol-% B mol-% N C mol-% Si Si

46 Isothermal Section at 1500 K in the Ternary System Si-B-C T = 1500 K (1227 C)

47 B SiB n B 4+δ C SiB 6 SiB 3 BN N Si 3 N 4 C SiC Si

48 Calculated Potential Phase Diagram 10 bar 1 bar Si 3 N 4

49 Calculated Potential Phase Diagram 1484 C 1700 C 1841 C 2034 C 10 bar 1 bar

50 Carbon activity - temperature diagram (2034 C) I0 bar pressure: ac. = K (1700 C) ac. = K (2034 ) (1700 C) Estimating a pressure of 10 bar and a carbon activity of 0.17, it can be concluded that the thermal stability of precursor-derived Si-B-C-N ceramics remains up to 2000 C.

51 B N C Si

52 Isopleth from B to Si 1 C 1.6 N 1.33 (VT50) in the Si-B-C-N System B N C Si

53 Isopleth from B 0.1 C 0.65 Si 0.25 to B 0.1 N 0.65 Si 0.25 in the Si-B-C-N System (at 10 mol-% B and 25 mol-% Si) X (N) X (Si) B 0.1 C 0.65 Si 0.25 B 0.1 N 0.65 Si 0.25

54 B - C - N B - C - Si B - C - N - Si C - N - Si B - N -Si 2722 u1 G + L = BN + B4C 2657 u2 G + L = C + B4C 2597 u3 G + B4C = C + BN 2372 u5 L + B4C = B + BN 2568 u4 L + C = B4C + SiC 2278 u6 L + B = B4C + SiBn L + C + BN + B4C 2597 G + B4C = L + C + BN U1 G + L + C + BN G, L, SiC, BN 2586 G + L = BN + SiC + C U2 L, SiC, G, SiC, C, BN C, BN 2568 L + C = SiC + B4C, BN U3 SiC, C, BN, B4C 2311 L + B = B4C + SiBn, BN D1 BN, B4C, SiBn, B L, BN, B4C, SiBn 2590 M G = L + SiC + BN 3095 d1 L + C = SiC, G L, SiC, BN, B4C G, L, SiC, BN 2310 d2 L + B = SiBn, BN 2273 K 2123 u7 L + SiBn=B4C + SiB L + SiBn=SiB6 + B4C, BN D d3 L + SiBn = SiB6, BN L, BN, B4C, SiB6 BN, B4C, SiB6, SiBn 2114 G + L = Si3N4 + SiC, BN D3 G, Si3N4, SiC, BN L, Si3N4, SiC, BN 2114 u8 G + L = Si3N4 + SiC 2114 d4 G + L = Si3N4, BN 1873 K 1669 u10 L + SiC = B4C + Si 1757 G + SiC = C + Si3N4, BN D4 G, Si3N4, C, BN Si3N4, SiC, C, BN 1687 L = Si, Si3N4, BN, SiC D5 Si3N4, SiC, BN, Si L, SiC, BN, Si 1669 L + SiC = B4C + Si, BN D u9 G + SiC = C + Si3N d5 L = Si, SiC, Si3N d6 L = Si, Si3N4, BN 1673 K SiC, BN, Si, B4C L, BN, Si, B4C 1657 d7 L = Si + SiB6, B4C 1657 L = Si + SiB6,, BN, B4C D d8 L = Si + SiB6, BN BN, Si, B4C, SiB d9 Si + SiB6=SiB3, B4C 1471 Si + SiB6 = SiB3, B4C, BN D d10 Si + SiB6 = SiB3, BN BN, B4C, SiB3, SiB6 BN, Si, B4C, SiB3 298 K

55 Si-B-C-N phase diagram at 1673 K with 4 of 9 4-phase equilibria B SiB n B 4 C SiB 6 BN N Si 3 N 4 L C SiC Si

56 Si-B-C-N concentration tetrahedron with indicated plane at a constant B content of 25 at.% T = 1400 C (1673 K) B 4+δ C B SiB n SiB 6 SiB 3 BN N Si 3 N 4 C SiC Si

57 Si-B-C-N concentration tetrahedron with indicated plane at a constant B content of 10 at.% Si 3.0 B 1.0 C 4.3 N 2.0 ( T2-1 precursor, PML, Max-Planck-Institut, Stuttgart, Germany ) B SiB n SiB B 4+δ C 6 SiB 3 BN N T2-1 Si 3 N 4 C SiC Si

58 Isothermal Section at 10 mol-% B in the Si-B-C-N System B 4+δ C B SiB n SiB 6 N BN T2-1 Si 3 N 4 C SiC Si T = 1400 C (1673 K)

59 Isothermal Sections at 10 mol-% B in the Si-B-C-N System T = 1673 K (1400 C) T = 1873 K (1600 C)

60 System Si-B-C-N - Metastable phase separation - B SiB n a - Si-B-C-N B 4+δ C BN SiB 6 SiB 3 a - BNC y + a-si 3+ x C x N 4-x t - BNC y Si 3 N 4 SiC 1 4 N a-bnc y Si 3 N 4 C a-si 1 3+ x C x N 4 4-x Si

61 a - Si-B-C-N B SiB n stable a - C y (BN) + a-si 1 3+ x C x N 4 4-x B 4+δ C SiB 6 SiB 3 not stable t - BNC y Si 3 N 4 SiC BN a-bnc y N Si 3 N 4 C T2-1 SiC a-si 1 3+ x C x N 4 4-x Si