Thermochemistry of Silicates · • Thermochemistry of Silicates - Stability of silicates in...

National Aeronautics and Space Administration

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Thermochemistry of Silicates

Gustavo Costa and Nathan Jacobson

NASA Glenn Research Center

Cleveland, OH

[email protected]

https://ntrs.nasa.gov/search.jsp?R=20150007887 2020-03-09T21:23:58+00:00Z


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Outline of Presentation

• Silicates in Materials Science, Mineralogy, Geology and Planetary Science

- Silicate Mineral Subclasses

• Thermochemistry of Silicates

- Stability of silicates in different environments and their acid-base chemistry

- Partial thermodynamics quantities (activity): An indicator of reactivity

- Thermodynamic activity in silicates

- Methods to measure activity

• Thermochemistry of Olivine

• Thermochemistry of Rare earth Silicates

-Results for Y2O3-SiO2 and Yb2O3-SiO2 systems

• Summary: Silicates


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Coating applications:

3

Ceramics in non-moving parts:

• Combustor liners

• Exhaust nozzles

Eventually moving parts!

Modern Solid-state Chemistry• Mesoporous based Silicates Sensors: pH, metal cation and humidity

• Rare-Earth Silicates and Vitreous Silica:

- Electronic devices: microwave, semiconductors, ferromagnetics, ferroelectrics,

lasers and phosphors

- High-Temperature Materials: refractory bricks and coatings

Silicates in Materials Science

Felsche, “The Crystal Chemistry of the Rare-Earth Silicates, Springer 1973, 99-197. Melde et al, Sensors, 2008, 8, 5202-5228.


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Ocurrence

- Over 90 % of the Earth’s crust consists of silicate minerals

Silicates in Geology, Mineralogy and Planetary Science

- Moon, Mars, Asteroids, Comets, Interplanetary dust particles and..

..Hot, rocky

exoplanets

8%

3%

5%

5%5%

11%12%

12%

39%

Plagioclase

Alkali feldspar

Quartz

Pyroxene

Amphibole

Mica

Clay

Other Silicates

Nonsilicates

G. E. Brown, Rev. Mineral. Geochem., 5, 275-381, 1980. M. T. DeAngelis etal., Am. Mineral., 97, 653-656, 2012.

D. Perkins, Mineralogy, 3, Prentice Hall, 2011.


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- (FexMg1-x)2SiO4

- Ortorrombic structure (Pbnm).

- Red – oxygen.

- Blue –A sites, silicon.

- Green – B sites, magnesium or iron.

Silicate Mineral Subclasses

D. Perkins, Mineralogy, 3, Prentice Hall, 2011.


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Thermodynamics and Acid-Base Chemistry

Enthalpy of formation of orthosilicates

vs. ionic potential (z/r) of divalent cations

z/r < 2 strongly basic

2 z/r < 4 basic

4 < z/r < 7 amphoteric

z/r > acidic

MgO + SiO2= MgSiO3 Ionic Potential (z/r)

and

Acid-Basic ScaleBase Acid Enstatite

A. Navrotsky, American Mineralogist, 79, 589-605, 1994..

Thermodynamic

Activity as Indicator

of Stability?

C a

Concentration

Activity

coefficient


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Partial Thermodynamics Quantities: Activity and Vapor

Pressure Measurement

R

S

TR

HP

C

aPRTKRTSTHG

vvM

MMpvvv

1ln

ionconcentrat C ;coeficientactivity

a

)/ln(ln

M (s) = M (g)

Activity Pressure

R

Hvslopeplot with Hofft van'a is vs1/TlnP M

kITMPerSpectromet Mass

Au(l) = Au(g)

∆v𝐻𝑜 = -R*(-41.162) = 342.20 kJ/mol

Tables = 342 kJ/mol

section cross ionizationσ

re; temperatuAbsoluteT

intenisty;ion I constant; instrumentk

M; of pressure partialPM


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Solutions: A1-B1-βC1-γ

Same Phase; Variable Stoichiometry

• Important solution parameters

• Quantify how vapor pressure is reduced due to solution formation

• Example: Olivine—can treat as solution of FeO, MgO, SiO2

• Use data to calculate thermodynamic activity of each component

• Measure thermodynamic parameters for olivine solutions

– e.g. ln a(FeO) vs 1/T slope is partial molar enthalpy

– Input to codes to model:

• Atmospheres of hot, rocky exoplanets

• Vapor over lava

1

][][K

(g)O 1/2Fe(g)FeO(s)

2/12/1

p

2

22

o

O

o

Fe

FeO

o

O

o

Fe PP

a

PP

Thermodynamic Activities

2/1

2/1

2/1

p

2

][

][

][K

(g)O 1/2Fe(g)1) a on,FeO(soluti

2

2

2

o

O

o

Fe

OFe

FeO

FeO

OFe

PP

PPa

a

PP


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Methods to measure silica activity

• Oxidation-reduction equilibrium using gas mixtures or electrochemical cells

• High temperature reaction calorimetry

• Knudsen Effusion Mass Spectrometry

vapor

sample

Effusion orifice

Mass spectrometer: Intensity Pressure Activity

Exact approach depends on the system

*A. I Zaitsev and B. M. Mogutnov, J Mater Chem 5, 1063 (1995)

RE-silicates - Reducing agent is used for to boost vaporization of SiO2 without

changing solid composition

Olivine – Single cell configuration is used to attain higher temperatures


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Knudsen Effusion Mass Spectrometry (KEMS)

• 90 magnetic sector; non-magnetic ion source ion counting detector no mass discrimination

• Cross axis electron impact ionizer

• Resistance heated cell; multiple Knudsen cell system

• Measurements to 2000C, Pressure to 1 x 10-10 bar

section cross ionization

(K) eTemperatur

constant instrument

i component of pressure

i

i

iii

S

T

k

p

STIkp

Use Multi-Cell Flange for a(SiO2)

Design of E. Copland 2002

Intensity Pressure Activity

Olivine and Rare – Earth Silicates


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Olivine - Results


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93% forsterite and 7% fayalite, Fo93Fa7 - (Fe0.7Mg0.93)2SiO4

*Uncertainties of

the analyses are

given in

parentheses.

807876747270686664626058565452504846444240383634323028262422201816141210

13,000

12,500

12,000

11,500

11,000

10,500

10,000

9,500

9,000

8,500

8,000

7,500

7,000

6,500

6,000

5,500

5,000

4,500

4,000

3,500

3,000

2,500

2,000

1,500

1,000

500

0

-500

-1,000

-1,500

-2,000

-2,500

-3,000

-3,500

-4,000

forsterite 87.68 %

enstatite 7.08 %

Silica 0.84 %

Sapphirine 0.45 %

Clinochlore 3.94 %

XRD pattern and Rietveld refinement of the as received olivine samples.

ICP-OES analysis

of the as received

olivine samples.

Forsterite – 87.7 ± 0.3%

Enstatite – 7.1 ± 0.2%

Silica – 0.84 ± 0.6%

Sapphirine – 0.5 ± 0.1%

Clinochlore – 3.9 ± 0.2%

Phase content

Olivine – Starting Material and Characterization


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10 20 30 40 50 60 70 80

Rela

tiv

e I

nte

nsit

y (

a. u

.)

2 (degree)

A

B

C*

Olivine

Protoenstatite*

XRD patterns of the olivine samples : (A) green sand from Hawaii, (B)

after KEMS up to 1850 K in a Mo Knudsen cell (C) after KEMS up 2079

K in an Ir Knudsen cell.

XRD patterns of the olivine samples : (A) as received , (B) after KEMS

up to 2084 K in a Mo Knudsen cell (C) after KEMS up to 1850 K in a

Mo Knudsen cell (D) after KEMS up 2079 K in an Ir Knudsen cell.

10 20 30 40 50 60 70 80

Protoenstatite*

*

D

Sapphirine-1A

C

B

Tugarinovite

Olivine

Quartz

Enstatite

Rela

tiv

e I

nte

nsit

y (

a. u

.)

2 (degree)

Clinochlore

A

*

Side view (cross-section) of the Mo Knudsen

cell containing the olivine sample heat treated

up to 2084 K.

Element

Wt (%)Sample as

receiveda

After KEMS in a

Mo cell

After KEMS in a Ir

cell

Al 0.0120(6) 0.016(6) 0.2(1)

Ca 0.035(2) 0.009(2) 0.04(2)

Co 0.0120(6) 0.003(2) 0.004(3)

Cr 0.052(3) 0.035(4) 0.06(1)

Fe 5.01(3) 0.006(3) 0.93(3)

Mg 30(2) 35.0(1) 34(1)

Mn 0.075(4) 0.003(1) 0.031(3)

Na 0.0080(4) - -

Ni 0.27(1) 0.005(3) 0.006(3)

Sc 0.0040(2) - -

Si 20(1) 19.3(1) 21.8(8)

Mo 0 0.04(2) 0

Ir 0 0 0.06(3)

Chemical composition of the olivine powder samples Fo93Fa7 before

and after KEMS up to 2084 K.

Olivine – Impurities and Container Issues


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Temperature dependence of ion intensity ratios of Mg+,

Fe+, SiO+, O+ and O2+ in the olivine sample.

Measurements show good agreement with the phase

diagram calculated by Bowen and Shairer.

Fegley and Osborne, “Practical Chemical Thermodynamics

For Geoscientists, Elsevier 2013, Fig. 12-11.

4.4 4.6 4.8 5.0 5.2 5.4 5.6 5.8

7

6

5

4

3

2

1

0

Fe

SiO

Mg

O

O2

104 T

-1(K

-1)1805 ºC

2300 2200 2100 2000 1900 1800 1700

-lo

gP

(kP

a)

T (K)

N. L. Bowen and J. F. Schairer, Am. J. Sci. 29, 151-171 (1935).

Complete van’t Hoff Plot

Interesting discontinuity at melting


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4.9 5.0 5.1 5.2 5.3 5.4 5.5 5.6 5.7 5.8

-1.4

-1.2

-1.0

-0.8

-0.6

-0.4

-0.2

0.0

0.2

0.4

log

(aS

iO)

10-4T

-1(K

-1)

2000 1950 1900 1850 1800 1750T (K)

2/1

2/1

2/1

p

][

][

][K

2

2

2

o

O

o

M

OM

MO

FeO

OM

PP

PPa

a

PP

Thermodynamic Activities in Olivine - (FexMg1-x)2SiO4

MO(solution, a<1) = M(g) + 1/2O2(g)

From FactSage or measured by KEMS

SiO

4.9 5.0 5.1 5.2 5.3 5.4 5.5 5.6 5.7 5.8

-2.0

-1.8

-1.6

-1.4

-1.2

-1.0

-0.8

-0.6

-0.4

-0.2

0.0

log

(aM

gO)

10-4T

-1(K

-1)

2000 1950 1900 1850 1800 1750T (K)

Fe, Mg or Si

Fe

MgO

4.9 5.0 5.1 5.2 5.3 5.4 5.5 5.6 5.7 5.8

-2.0

-1.8

-1.6

-1.4

-1.2

-1.0

-0.8

-0.6

-0.4

-0.2

0.0

log

(aF

eO)

10-4T

-1(K

-1)

2000 1950 1900 1850 1800 1750T (K)


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Rare earth Silicates


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Low Reactivity of Rare earth Silicates

17

Si(OH)4(g) , MOH(g) H2O(g)

SiO2, MO(Underline indicates in solution)SiC + 3/2 O2(g) = SiO2 + CO(g)

• SiO2 + 2 H2O(g) = Si(OH)4(g)

Meschter and Opila., Annu Rev Mater Res 43, 559 (2013)

N. S. Jacobson, J Am Ceram Soc 97, 1959 (2014)

P[Si(OH)4] = K a SiO2 [P(H2O)]2

Y and Yb silicates

Need to be measured!

Exposure Time (hrs)

0102030405060708090100

Wt. Change (mg/cm2 )

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

0.5

CVI (ACI)[1232 C]

Ml[1232 C]

CVI (ACI)[1274 C]

MI[1107 C]

SiC/SiC CMC HPBR Paralinear Weight Change

(1100 -1300C, 6 atm; Robinson/Smialek 1998)

Si(OH)4 volatility (Opila et al., 1998-2006)


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Key Parameters in Boundary Layer Limited Transport

Modeling

• SiO2(pure or in silicate soln) + 2 H2O(g) = Si(OH)4(g)

• Reduce a(SiO2) reduce recession. Recession drives need for coatings

4)(

2)(

33.0

)(

5.0

)()(

33.0

)(

5.0

Si(OH) ofy diffusivit phase gasviscosity

dimension sticcharacteridensity gas stream free velocitystream free

664.0

664.0

4

22

4

4

44

4

OHSi

OHSiO

OHSi

OHSi

OHSiOHSi

OHSi

D

L

PaKLTR

D

D

L

LTR

PD

D

LFlux

L

Combustion

Gases

Gas Boundary

Layer

Si(OH)4(g)

SiO2

ν = 0

Free Stream

Gas Velocity

ν


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Calculated Y2O3-SiO2 Phase Diagram:

Fabrichnaya-Seifert Database

19

Indirect evidence suggests that the SiO2 thermodynamic activity is

lower in the Y2O3-Y2SiO5 and Y2SiO5-Y2Si2O7 regions

But there are no direct measurements!

1600

1800

2000

2200

2400

2600

2800

TE

MP

ER

AT

UR

E_

KE

LV

IN

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

MOLE_FRACTION SIO2

THERMO-CALC (2010.08.10:09.24) : DATABASE:USER AC(O)=1, N=1, P=1.01325E5;

Y2O3 + MSY2O3 + MS

MS

+ D

S

MS

+ D

S MS

+ S

iO2


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• Vapor pressure of SiO2 too low to measure in temperature range of interest

• Need measurable signal for SiO2—use reducing agent to make excess SiO(g). Tried

several, selected Mo or Ta

– For a(SiO2) < ~0.02

• 2Ta(s) + 2SiO2(soln) = 2SiO(g) + TaO(g) + TaO2(g)

– For a(SiO2) > ~0.02

• Mo(s) + 3SiO2(soln) = 3SiO(g) + MoO3(g)

– Note reducing agent must not change solid phase composition

• Monosilicates + disilicates +Ta – leads to tantalates

• Need to account for non-equilibrium vaporization

• SiO overlaps with CO2 (m/e = 44)

– Use LN2 cold finger for improved pumping

– Shutter to distinguish vapor from cell and background

– Gettering pump for CO2

20

Issues with Measuring a(SiO2) in RE Silicates


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Approaches use two phase regions

Two cells:

• Au

• 3Ta + Y2O3 + Y2O3 SiO2

2Ta(s) + 3SiO2(soln) = 3SiO(g) + TaO(g) + TaO2(g)

- Using Peq(SiO) and FactSage (free energy minimization)

- Correction for non-equilibrium vaporization

21

1 – Monosilicate + RE2O3 2 – Monosilicate + Disilicate

33.0

3

3

3

3

2

33.0

3

3

2

32

33.0

3

3

2

32

3

2

3

3

)()(

)()()(

)()()(

33

)()(1)(

33

)(

)()(

MoOISiOI

MoOISiOISiOa

K

MoOPSiOPSiOa

MoOSiOSiOMo

K

MoOPSiOPSiOa

MoOSiOSiOMo

SiOa

MoOPSiOPK

oo

oo

Three cells:

• Au (reference)

• 3Mo + Y2O3 2SiO2 + Y2O3 SiO2

• 3Mo + SiO2

Mo(s) + 3SiO2(soln) = 3SiO(g) + MoO3(g)

- Compare cells 1 and 2

- Less data processing than with Ta

- Correction is not needed.

Cell 3

Cell 2

1 2

3

Cells are part of the system


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Monosilicate + RE2O3

1600

1800

2000

2200

2400

2600

2800

TE

MP

ER

AT

UR

E_

KE

LV

IN

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

MOLE_FRACTION SIO2


Y2O3-SiO2 Yb2O3-SiO2


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XRD after KEMS Measurements of RE Monosilicates + RE2O3 + Ta:

Sample: 4-7-12A

Position [°2Theta] (Copper (Cu))

10 20 30 40 50 60 70

Counts

0

2500

10000

22500

NJ 4-7-12A

Y2O3

Y2O3.(SiO2)

Ta

Ta3Si

41

49

4

4

wt (%)Phase

Yb2O3

Yb2O3.(SiO2)

Ta

Ta2Si

24

66

2

2

wt (%)Phase

Yttrium monosilicate + Y2O3 + Ta Ytterbium monosilicate + Yb2O3 + Ta


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Raw Data—log (IT) vs 1/T

Cell (1): Au Reference Cell (2): Ta + Y2O3 + MS

Tabulated 346.3 kJ/mol


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Y2O3 + Y2O3.(SiO2)

*Liang et al. “Enthalpy of formation of rare-earth silicates Y2SiO5 and Yb2SiO5 and N-containing silicate Y10(SiO4)6N2”, J.

Mater. Res. 14 [4], 1181-1185. **J. A. Duff, J. Phys. Chem. A 110, 13245 (2006)

Yb2O3 + Yb2O3.(SiO2)

RE2O3(s, 1600 K) + SiO2(s, 1600 K) RE2SiO5(s, 1600 K) H1 = measured in this work

RE2SiO5(s, 1600 K) RE2SiO5(s, 298 K) H2 = H1600 K – H298 K

RE2O3(s, 298 K) RE2O3(s, 1600 K) H3

SiO2(s, 298 K) SiO2(s, 1600 K) H4

2 RE(s, 298 K) + 3/2 O2(g, 298 K) RE2O3(s, 298 K) H5

Si(s, 298 K) + O2(g, 298 K) SiO2(s, 298 K) H6

2 RE(s, 298 K) + Si(s, 298 K) + 5/2 O2(g, 298 K) RE2SiO5(s, 298 K) H7 = ∆𝐻𝑓,𝑅𝐸2𝑆𝑖𝑂5,298 𝐾

H(SiO2, 1600 K) = (5200.26)·R·2.303 = 99.57 kJ/mol

Y2O3.(SiO2) -2907 ± 16 -2868.54 ± 5.34

Yb2O3.(SiO2) -2744 ± 11 -2774.75 ±16.48

KEMS Calorimetry*

Hf, RE silicate, 298 K (kJ/mol)

a(SiO2), 1650 KOptical basicity**

0.786

0.729

0.000804

6.0 6.1 6.2 6.3 6.4 6.5 6.6 6.7

-4.0

-3.5

-3.0

-2.5

-2.0

-1.5

-1.0

log

[a(S

iO2)]

T-110

-4(K

-1)

y = -1412.60(1/T)-1.67

1650 1600 1550 1500

T (K)

H(SiO2, 1600 K) = (1412.60)·R·2.303 = 27.05 kJ/mol

0.00298


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Monosilicate + Disilicate

1600

1800

2000

2200

2400

2600

2800

TE

MP

ER

AT

UR

E_

KE

LV

IN

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

MOLE_FRACTION SIO2


Y2O3-SiO2+ Y2O3-2SiO2 Yb2O3-SiO2+ Yb2O3-2SiO2


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XRD after KEMS Measurements of RE Monosilicates + Disilicates + Mo:

Y2O3.(SiO2)

Phase

Yb2O3.(SiO2)

Mo

56

36

8

wt (%)Phase

Ytterbium monosilicate + disilicate + Mo

Yb2O3.2(SiO2)

Yttrium monosilicate + disilicate +Mo

Position [°2Theta] (Copper (Cu))

10 20 30 40 50 60 70

Counts

0

400

1600

3600

6400

NJ 2-07824

Peak List

Y2 ( Si O4 ) O; Monoclinic; 04-007-4730

Mo; Cubic; 04-004-8483

Y2 Si2 O7; Monoclinic; 00-038-0440

Ln2 Si2 O7; Monoclinic; 00-021-1014

Y2 Si2 O7; Monoclinic; 00-042-0167

Y2O3.2(SiO2)

Mo


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Y2O3.(SiO2) + Y2O3.2(SiO2) Yb2O3.(SiO2) + Yb2O3.2(SiO2)

5.30 5.35 5.40 5.45 5.50 5.55 5.60 5.65

-1.2

-1.0

-0.8

-0.6

-0.4

-0.2

0.0

log

[a(S

iO2)]

T-1 10

-4 (K

-1)

1880 1860 1840 1820 1800 1780

T (K)

a(SiO2), 1650 KOptical basicity**

0.786

0.729 0.194

Y2O3.(SiO2)

Yb2O3.(SiO2)

Y2O3.2(SiO2)

0.699

0.657

Yb2O3.2(SiO2)

0.281


www.nasa.gov 29

L

Combustion

Gases

Gas Boundary

Layer

Si(OH)4(g)

SiO2

ν = 0

Free Stream

Gas Velocity

ν

Now Have the Needed Quantities for Modeling Recession

3.86E-4

0.13488

0.00143

0.09312

0.48

0.0

0.1

0.2

0.3

0.4

0.5

JS

i(O

H) 4

(mg

/cm

2-h

)

– T = 1300C; P = 10 bar; P(H2O) = 1 bar

– v = 20 m/s

– L = 10 cm

– = 5 x 10-4 g/cm-s

– = 2.2 x 10-3 g/cc

– DSi(OH)4 = 0.19 cm2/s

– log K = -2851.2/T – 3.5249 (Si(OH)4(g) transpiration measurements)

– a(SiO2) from activity measurements

2)(

33.0

)(

5.0

22

4

4

664.0 OHSiO

OHSi

OHSi

PaKLTR

D

D

LFlux


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Summary

• The reduced SiO2 activity in Rare-earth silicates should limit their reactivity with water vapor

• Solid State rare earth oxides—activity of SiO2

– Need reducing agent to obtain a measurable signal for SiO(g), which in turn relates to activity of

SiO2. Reducing agent must not change solid phase composition.

– Method and choice of reducing agent depends on particular silicate

• Thermodynamic data for gas phase hydroxides and solid candidate coating recession modeling input

data

30

• Secondary phases of the olivine sample were removed at temperatures > 1060 C.

• Mo and Re cell reacts with olivine sample. Ir must be used

• The main vapor species of the olivine sample are Mg+, O+, O2+, SiO+ and Fe+ following this order of

evaporation.

• The melting point of the olivine sample was determined by the ion intensity discontinuity to be 1805 C.

• Temperature dependence of partial pressures of the species were determined and their activities. Next

steps

• Vaporization coefficient measurements

• Fundamental understanding of thermodynamic is critical to models and structure-property relationships

– Vapor pressure techniques—Knudsen effusion mass spectrometry

• Silicates are everywhere – from minerals to electronic materials to aircraft engines

Olivine

Rare-Earth Silicates


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Acknowledgements

• Helpful discussions with B. Opila (Formerly NASA Glenn now

University of Virginia)

• Multiple cell and sampling system improvements to mass

spectrometer: E. Copland (formerly NASA Glenn now CSIRO,

Sydney, Australia)

• XRD: R. Rogers (NASA Glenn)

• NASA/ORAU Post-doctoral Fellowship Program

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