Thermodynamics of High Temperature Thermodynamics of High Temperature Materials SystemsMaterials Systems

Hans Hans JürgenJürgen SeifertSeifert

Freiberg University of Mining and Freiberg University of Mining and Technology, GermanyTechnology, Germany

Summer SchoolSummer SchoolAdvanced Advanced ThermostructuralThermostructural MaterialsMaterialsSanta Barbara, August 9, 2006Santa Barbara, August 9, 2006

Thermodynamics of High Temperature Materials System sThermodynamics of High Temperature Materials System s

Hans Hans JürgenJürgen SeifertSeifert

1. Introduction and motivation for thermodynamic calcul ations- 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 ofSi-(B-)C-N ceramics

OutlineOutline

Thermodynamics of High Temperature Materials System sThermodynamics of High Temperature Materials System s

Hans Hans JürgenJürgen SeifertSeifert

4. Computational thermodynamics in heat shieldengineering

- The Y-Si-C-O system database- Active / passive oxidation of SiC- Phase reactions of Yttrium silicates and C/C-SiCcomposites

- High temperature stability issues in the engineering of heat shields

5. Conclusions

OutlineOutline

ComputationalThermodynamics and

Modeling+

Experiments, Analysis

Fundamental Research

Materials Engineering,Processing

Combined Approach

Computational Thermodynamics

Ab-initioCalculation

TheoryQuantum Mechanics,

StatisticalThermodynamics

ExperimentsDTA, Calorimetry,

EMF, Knudsen Effusion ,Metallography ,

X-ray Diffractometry, ...

Modelswith adjustable

Parameters

Estimates

Adjustment ofParameters

Phase Diagrams

Equilibria

Storage inDatabases

GraphicalRepresentation

Application

Thermodyn. FunctionsG, H, S, Cp

Opt

imiz

atio

nE

quili

briu

mC

alcu

latio

ns

Kinetics

CALPHAD

CALculationof PHAse Diagrams

• Development of Optimized Thermodynamic Datasetsstored in Computer Databases

• Calculation of :- Thermodynamic Functions- Liquidus Surface- Isothermal Sections- Isopleths- Potential Phase Diagrams

CALPHAD (CALculation of PHAse Diagrams)

Requires Modeling of Stoichiometric and Solution PhasesTaking into Account the (Crystal-) Structures and Site Occupancies

- Phase Fraction Diagrams- Phase Compositions- Scheil Solidification…

• LUKAS (BINGSS, BINFKT, TERGSS, TERFKT)• THERMO-CALC• FACTSAGE• PANDAT• MALT, MALT2• MTDATA• JMATPRO• GEMINI• ...

CALPHAD (CALculation of PHAse Diagrams)Software

• SGTE, Scientific Group Thermodata Europe - SSOL2, SSOL4- SSUB3- Noble Metals

• Thermo-Calc: Steels, Ni-base, slags, ...• ThermoTech: Ni-base, Al-, Mg-, ...• PML: Al-, Ceramics• ...

CALPHAD (CALculation of PHAse Diagrams)Databases

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

Phases in the Partial Ce – O System

Related Crystal Structures:

CeO2-x (ss) CaF2 - type (Strukturbericht C1)

Compound Energy Formalism:(Ce+3, Ce+4)1(O-2,Va)2

C-Ce2O3 (ss) Mn2O3 - type (Strukturbericht D53, Ordered State of C1)Unit Cell: composed of 8 CaF2-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 Mn2O3.

Ce2O3 Stoichiometric phase description (Strukturbericht D52)

Four compounds defined:

A : DA : EB : DB : E

Gibbs free energy for every compound to be determined

“Compound Energy” Formalisms –Reference Compounds

(A,B) k(D,E)lSolution phase with two sublattices and 4 species

Here:(Ce+3, Ce+4)1(O-2,Va)2

“Compound Energy” Formalism –Surface of Reference

(A,B) k(D,E)lSolution phase with two sublattices and 4 species

Stochiometric coefficient (s: sublattice)

(A,B) k(D,E)l

Modeling of solution phases; sublattice model described in the Compound Energy Formalism

Site fraction of spezies A onsublattice s

Solution phase with two sublattices and 4 species

(A,B) k(D,E)l

Compound Energy Formalism –Excess term of Gibbs free energy

Solution phase with two sublattices and 4 species

Compound Energy Formalisms –Gibbs free energy of solution phases

Mixing Gibbs Energy

Phases in the Partial Ce – O System

CeO2-x (ss) CaF2 - 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.

)1('4 yyCe −=+

yyCe =+

'3

4'' y

yVa =

41''

2

yyO

−=−

+1000 – 1330CeO2, Ce2O3Ce3O5

Partial pressures

O2

Thermo-gravimetry

Kitayama

et al.

(1985)

5.

+1353, 1296,1244

CeO2Partial pressures

O2

Micro-Calorimetry

Campserveux& Gerdanian

(1978)

4.

+900, 1000,

1100, 1227, 1300

CeO2.00Partial pressures

O2

Experiment with CO2 &

CO2 /H2 mixture

Iwasaki & Katsura

(1971)

3.

+2000 - 30001600 - 20001825 - 23201550 – 2040

CeO1.51 --CeO1.53CeO1.5 -CeO1.34

Partial pressures

CeO, CeO2,Ce(g), CeO

Mass Spectroscopy

& Mass Effusion

Ackerman & Rauh

(1971)

2.

+909 - 1442CeO1.5-CeO2

Partial pressures

O2

Experiment with CO2/CO

& H2O/H2

Bevan & Kordis(1964)

1.

RemarkTemperature(K)

CompositionMeasured Quantity

Experimental Technique

PaperNo.

+298Ce2O3.00∆H for Ce2O3Bomb calorimetry

Kuznetzov, et al. (1960)12.

-320-1200CeO1.72 –

CeO2

Specific heat,

∆H trans.

CalorimetryRicken et al. (1984)11.

+400-1000 Ce2O3Heat capacityPlane temperature

wave method

Basily & El-Sharkawy

(1979)10.

+5-350Ce2O3.02Heat capacityCryogenic Calorimetry

Justice & Westrum(1969)

9.

+5-300CeO2Heat capacity, Adiabatic

CalorimetryWestrum &

Beale Jr.(1961)

8.

-608-1172CeO2Heat capacity, CalorimetryKuznetzov& Rezukhina

(1960)7.

-1900-2150

1850-2050

CeO1.99, Ce2O2.96

Partial pressures,

CeO2, Ce2O3

Knudsen cell, Mass

spectrometry

Marushkin

et al. (2000)6.

+320-1200CeO1.79 –CeO2

Thermal expansion coefficient

DilatometryRiess, Koerner & Noelting

(1988)

17

+1023-1773CeO2-x∆W/WThermo-gravimetry

Panlener, Blementhal & Garnier(1975)

16.

+1353CeO1.5 –

CeO2

Partial molalenthalpy

∆Hsoln. (O2)

Micro

Calorimetry

Campserveux& Gerdanian

(1974)

15.

-298.15CeO2Heat of formation

CeO2, CeC1.5, CeC2

Bomb calorimetry

Baker, Huber, Holley & Krikorian

(1971)

14.

-298.15Ce2O3Heat of combustion

Ce2O3

Oxygen Bomb

Calorimetry

Baker & Holley

(1968)

13.

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

Heat capacities of Ce2O3 and CeO2. Enthalpy increment (heat contents) ofCeO2.

H.J. Seifert, P. Nerikar, H.L. Lukas, Int. J. Mater. Res. 97 [6] (2006) 744-752.

Chemical potentials of oxygen for ceria as a function of compositionand temperature.

Chemical potentials of oxygen for ceria as a function of compositionand temperature.

Chemical potentials of oxygen for ceria as a function of compositionand temperature.

Chemical potentials of oxygen for ceria as a function of compositionand temperature.

Chemical potentials of oxygen for ceria as a function of compositionand temperature.

Chemical potentials of oxygen in the two-phase areas.

Partial Enthalpies of Oxygen in CeO2

Mole fraction O

kJ/m

ol

2CeO

OH 2CeO

OH

Thermodynamics of High Temperature Materials System sThermodynamics of High Temperature Materials System s

Hans Hans JürgenJürgen SeifertSeifert

1. Introduction and motivation for thermodynamic calcul ations- 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 ofSi-(B-)C-N ceramics

OutlineOutline

• Produced by thermolysis (1323 K, Ar) of polymer precursors

• Amorphous, purely homogeneous inorganic materials

Precursor-derived Si-B-C-N Ceramics

• NCP200: 40.1Si 23C 36.9N(at.%)- Starts to crystallize at 1700 K (N2)- Thermal stability up to 1800 K (N2)

• T2-1: 29.1Si 41.7C 19.4N 9.8B(at.%) - X-ray amorphous, nanocrystalline- Thermal stability up to 2300 K

Monomer Unit

Precursor Polymer

Preceramic Network

Amorphous Ceramic

Crystalline Ceramic

Synthesis

Crosslinking (200-400°C)

Thermolysis (1000-1400°C)

Crystallization ( > 1400°C)

Process for Precursor-derived Si-(B-)C-N Ceramics

Monomer

Polymer

Amorphous Solid

Polycrystalline CeramicNovel ceramics with high temperature stability and withgood resistance to oxidationcan be obtained frommolecular units withoutsintering aid.

Si-C binary subsystem

J. Gröbner, PhD thesis, 1994

Gas

Si(l) + Gas

2114 K

Gas + Si3N4

Si3N4 + Si(l)

Si3N4 + Si(s)

1687 K

Si3N4

Si(s)

Si(l)

Si-N binary subsystem

Isopleth from Carbon to Si3N4 in the Si-C-N System

Isothermal Section of the Ternary System Si-C-N

T = 3000 K(2727 °C)

N

C SiSiC

Si3N4

N

C SiSiC

Si3N4

N

C SiSiC

Isothermal Sections of the Ternary System Si-C-N

T < 1484°C(1757 K)

1484°C< T < 1841°C T > 1841°C(2114 K)

Si1N1.6C1.33 (VT50, Polyvinysilazane, Hoechst AG, Frankfurt, Germany)

Si1N0.6C1.02 (NCP200, Polyhydridomethylsilazane, Nichimen Corp., Tokyo, Japan)

Si3N4 + 3C = 3SiC +2N2(1)

Si3N4 = 3Si + 2N2

(2)

P = 1 bar

Si1N1.6C1.33 (VT50)

Calculated Phase Fraction Diagrams of Precursor Derived Ceramics

1484

°C

Si3N4 + 3C = 3SiC +2N2

-35

-30

-25

-20

-15

-10

-5

0

5

1000 1200 1400 1600 1800 2000

Temperature (°C)

Mas

s Lo

ss (

%)

Thermogravimetrical (TG) analysis of precursor-derived Si-C-N ceramics

VT50

NCP200

Ceramics:Si1N0.6C1.02

Calculated Phase Fraction Diagram of Precursor Derived Ceramics

1484

°C

1841

°C

NCP200, Polyhydridomethylsilazane (Nichimen Corp., Tokyo, Japan)

N

C SiSiC

Si3N4

Reaction Path

Phase Fraction Diagram

-35

-30

-25

-20

-15

-10

-5

0

5

1000 1200 1400 1600 1800 2000

Temperature (°C)

Mas

s Lo

ss (

%)

Thermogravimetrical (TG) analysis of precursor-derived Si-C-N ceramics

VT50

NCP200

-40

-35

-30

-25

-20

-15

-10

-5

0

5

1200 1400 1600 1800 2000 2200

Temperature (°C)

Mas

s Lo

ss (

%) MW36

VT50

MW33

NCP200

T2-1

(Si-B-C-N)

Si3N4 + 3C = 3SiC + 2N2

Si3N4 = 3Si + 2N2

(Si-C-N)

Thermogravimetrical (TG) analysis of precursor-derived Si-B-C-N ceramics

Calculated Phase Fraction Diagram ofT2-1- Derived Ceramic Si3.0B1.0C4.3N2.0

1484

°C

Si3.0B1.0C4.3N2.0

( T2-1 precursor, PML,Max-Planck-Institut,Stuttgart, Germany )

C Si

B

N

BN

B4+ δC

SiBn

SiB6

SiB3

Si3N4

SiC

mol-%

B mol-%

Bmol

-% B

mol-% Si

mol-% Nmol-%

C

B2CN2

BC2N

BC3NBC4N “C3N4“ SiC2N4 Si2CN4

C Si

B

N

BN

B4+ δC

SiBn

SiB6

SiB3

Si3N4

SiC

mol-%

B mol-%

Bmol

-% B

mol-% Si

mol-% Nmol-%

C

B2CN2

BC2N

BC3NBC4N “C3N4“ SiC2N4 Si2CN4

Isothermal Section at 1500 K in the Ternary System Si-B-C

T = 1500 K(1227 °C)

B4+δC

C

B

N

SiC

BN

Si3N4

SiBn

SiB6

SiB3

Si

Calculated Potential Phase Diagram

1 bar

10 bar

Si3N4

Calculated Potential Phase Diagram

1 bar

10 bar

1484°C

1700°C

1841°C

2034°C

(2034°C)

(1700°C)

Carbon activity - temperature diagram

I0 bar pressure :

ac. = 1 1973 K (1700°C)

ac. = 0.17 2307 K (2034°)

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.

SiC

N

B

Isopleth from B to Si1C1.6N1.33 (VT50) in the Si-B-C-N System

SiC

N

B

Isopleth from B0.1C0.65Si0.25 to B0.1N0.65Si0.25 in the Si-B-C-N System(at 10 mol-% B and 25 mol-% Si)

B0.1C0.65Si0.25 B0.1N0.65Si0.25

X (Si)

X (N

)

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 G + B4C = L + C + BN 2597 U1

G + L = BN + SiC + C 2586 U2

L + C = SiC + B4C, BN 2568 U3L + C = B4C + SiC

u42568

2590 MG = L + SiC + BN

L + C = SiC, G 3095 d1

L, SiC, BN, B4C

G, L, SiC, BN

2311 L + B = B4C + SiBn, BN D1

2114 G + L = Si3N4 + SiC, BN D3

2123 L + SiBn=SiB6 + B4C, BN D2

2372 u5

2123 u7

L + SiBn=B4C + SiB6

2278 u6

L + B = B4C + SiBn

L + B4C = B + BN

L + C + BN + B4C

L, BN, B4C, SiB6

G, Si3N4, SiC, BN

L, Si3N4, SiC, BN

L, BN, B4C, SiBn

BN, B4C, SiB6, SiBn

G + L + C + BN

G, L, SiC, BN

SiC, C, BN, B4C

BN, B4C, SiBn, B

L, SiC, C, BN

G, SiC, C, BN

G + L = Si3N4 + SiCu8

L + B = SiBn, BN d22310

G + L = Si3N4, BN d4

L + SiBn = SiB6, BN d32123

21142114

1669

1687 D5

u10

d10

1757 D4G + SiC = C + Si3N4, BN

L = Si, Si3N4, BN, SiC

1757 u9G + SiC = C + Si3N4

1687 d5

L = Si, SiC, Si3N4

1687 d6

L = Si, Si3N4, BN

1669 D6L + SiC = B4C + Si, BN

1657 D7L = Si + SiB6,, BN, B4C

1471 D8Si + SiB6 = SiB3, B4C, BN

Si3N4, SiC, C, BN G, Si3N4, C, BN

Si3N4, SiC, BN, SiL, SiC, BN, Si

SiC, BN, Si, B4C L, BN, Si, B4C

BN, Si, B4C, SiB6

BN, Si, B4C, SiB3 BN, B4C, SiB3, SiB6

1657 d8

L = Si + SiB6, BN

L + SiC = B4C + Si

1657 d7L = Si + SiB6, B4C

1471 d9

Si + SiB6=SiB3, B4C1471

Si + SiB6 = SiB3, BN

2273 K

1873 K

1673 K

298 K

B

B4C

N

C Si

BN

SiC

SiBn

SiB6

LSi3N4

Si-B-C-N phase diagram at 1673 K with 4 of 9 4-phase equilibria

Si-B-C-N concentration tetrahedron with indicatedplane at a constant B content of 25 at.%

B

N

C SiSiC

Si3N4

B4+δC

BN

SiBn

SiB6SiB3

T = 1400°C (1673 K)

B4+δC

C

B

NT2-1

SiC

BN

Si3N4

SiBn

SiB

6 SiB3

Si

Si-B-C-N concentration tetrahedron with indicatedplane at a constant B content of 10 at.%

Si3.0B1.0C4.3N2.0

( T2-1 precursor, PML,Max-Planck-Institut,Stuttgart, Germany )

Isothermal Section at 10 mol-% B in the Si-B-C-N System

T = 1400°C(1673 K)

B4+δC

C

B

N

T2-1

SiC

BN

Si3N4

SiBn

SiB6

Si

T = 1873 K(1600 °C)

Isothermal Sections at 10 mol-% B in the Si-B-C-N System

T = 1673 K(1400°C)

B

C Si

a-BNCy

a-Si3+ xCxN4-x41

N

Si3N4

B4+δC

BN

SiBn

SiB6

SiB3

a - Si-B-C-N

a - BNCy +

t - BNCy Si3N4 SiC

41

System Si-B-C-N- Metastable phase separation -

a-Si3+ xCxN4-x

B

N

C SiSiC

Si3N4

B4+δC

BN

SiBn

SiB6

SiB3

stable

not stable

a - Si-B-C-N

a - Cy(BN) +

t - BNCy Si3N4 SiC

T2-1

a-BNCy

a-Si3+ xCxN4-x41

a-Si3+ xCxN4-x41