The Science and Technology of High Temperature Hf-SiCN(O) Polymer Derived Ceramics

Rishi Raj Ph.D. Students: Kalvis Terauds Ilya Lisenker

August 06, 2013

AFOSR-NASA FA9550-09-1-0477

Active Collaborators: D. B. Marshall (Teledyne): CMCs P. Kroll (UT Arlington): Molecular Modeling J. Marschall (SRI, Int.): Plasma Testing Y. Shinoda (Tokyo Institute of Technology): Oxide/non-Oxide Nanocomposites. Emerging Collaborations: *Prof. Steven George (Chemistry, CU) : MLD Prof. Chuck Winter (Chemistry, Wayne State): Synthesis

*A. Abdulagatov, K. Terauds, J. Travis, A. Cavanagh, R. Raj, S. George, "Pyrolysis of Titanicone Molecular Layer Deposition Films as Precursors for Conducting TiO2-Carbon Composite Films", J. Phys. Chem., accepted, in press.

Highlights: (i)  Oxidation and phase transformation

in materials made with HfSiCNO (polymer derived) and HfO2.

(ii)  Performance of Fiber Preforms: infiltrated with above.

(iii)  Focus on SiC/HfSiCNO Interface: interfacial energy and bubble nucleation.

Ab-Initio!

molar C 13

Polymer-Derived oxide/non-oxide Ceramics

Raman

Si1-xHfx

Polymer-Derived Matrix: Impede Oxidation

Carbon Fiber Tows

HfSiCNO Matrix (infiltration)

Processing Defects

• Active Oxidation (recession) • CO Bubbles

Nanophase HfSiCNO-HfO2

(Terauds, Marshall and Raj) (Lisenkar, Terauds, and Raj)

Hf/Si →∞0←

Overgrowth

Matrix of the

Powder Particle

(a) (b)

Hf/Si = 0.22

Oxidized for 50h at 1500oC in air

HfSiCNO Hf/Si = 0-38%

• Molecular structure • Solubility, Precipitation and Coarsening • Oxidation Behavior

Processing

Alkoxide (Hf t-butoxide)

Polymer (Ceraset)

Hf, O, C, H Si, N, C, H

Crosslink at 300°C

Pyrolysis at 1000°C

Mix precursors

Oxidize 1400°C - 1600°C

Structure of HfSiCN

Hypothesis: Hf substitutes for Si; (same valency, similar strength of Hf-N, Hf-C and Hf-O bonds)

Bond-Energy Calculations (manual)

Bond energies are relative to Si-C and Si-N

Hf N

N

C

C

��

��

��

�

���

���

Enth

alpy

(kJ.

molï�

)

MO4 MC1O3 MC2O2 MC3O1 MC4

Hf Zr

Ti

V

Al

NbTa

Oxygen containing mixed bonds

favorable

unfavorable

Hf

Hf-Si-C-N-O: S22 model Hf-coordination

Hf(1) Hf(2) Hf(4) Hf(3)

Hf(5) Hf(6) Hf(7) Peter Kroll

N C

O

Hf

29 atoms Si 7 atoms Hf

Infer that Hf substitutes for Si in the Amorphous Structure

Solubility Limit: (Hf/Si) < 0.22

Samples pyrolyzed at 1000oC in Ar

HfSiCNO Powder Oxidation (S08)

HfSiCNO Powder Oxidation (S08) 1500oC 50h Air

0

10

20

1 10 25 50

Wei

ght F

ract

ion

(%)

Oxidation Time (h)5

SiO2(cristobalite)

HfO2(M)

HfO2(T)

HfSiO4

1500°C, AirHfSiCNO

Quantitative X-ray diffraction with Nb standard

Oxidation of HfSiCNO

Key Results: • HfO2 precipitates from solution. • HfO2 reacts with silica in the oxidation scale to form HfSiO4 (hafnon). • The evolution of a unique microstructure during oxidation.

What is the coarsening rate of HfO2 precipitates?

materials science model

ab-initio experiment

A New Paradigm Goal: Predict Oswald Ripening

Unknown: transport kinetics =diffusivity* x solubility

calculate heat of solution

predictive model w/o adjustable parameters

+

*Diffusivity is related to viscosity via Stokes Einstein

valid

ate

with

on

e or

two

expe

rimen

ts

(Raj) (Kroll)

manuscript to be submitted

S Y N E R G Y PREDICT PERFORMANCE

DISCOVER NEW MATERIALS

Overgrowth

Matrix of thePowder Particle

bright spots are precipitates of hafnia

(a) (b)

(c) (d)

1 m

5 m

∆Hmix ≈ 1.2 eV

Peter Kroll

x HfO2= exp(−1.2eV

RT)

•Relate diffusivity to the viscosity through Stokes Einstein •Calculate the rate of coarsening of hafnia precipitates. •Predict oxidation protection

Nanophase HfSiCNO-HfO2

(Terauds, Marshall and Raj) (Lisenkar, Terauds, and Raj)

300 nm

10% SiCN

As-Pyrolyzed

Sintered in argon (1450°C)

Sintered in air (1450°C)

HfO2-10%SiCN

Raman Spectra confirms the presence of PDC at Grain Boundaries.

0 200 400 600 800 1000 1200

Intensity,  a.u.

Wavenumber,  cm-­‐1

Raman  Spectrum,  HfO2 -­‐ 10%PDC,  30  hours  at  temperature

♦ -­‐ HfO2♦

♦

♦♦♦ ♦♦

♦♦

♦

♦♦♦

♦♦ ∇ -­‐ HfSiO4

∇∇ ∇

∇∇

♦

As  Sintered

1,300°C

1,400°C

1,500°C

1,600°C∇

in air

RAMAN

0100200300400500600

1,300  °C 1,400  °C 1,500  °C 1,600  °C

Flexural  Stren

gth,  M

pa

Oxidation  Temperature,  °C

Hafnia  /  10%  PDC  Flexural  Strength3  point  bending

0  hrs

10  hrs

30  hrs

Jochen Marschall SRI, International

Oxidation in the Plasmatron

Atomic Oxygen

YS Samples

YS3 1200oC

Off +0.55mg

YS4 1200oC

On +2.74 mg

Dual Phase (HfO2 – SiC) Composites

Yutaka Shinoda (Tokyo Institute of Technology) & David Marshall

Oxidation at 1600oC in air: Minimal effect on Strength

Thermal Conductivity

Values are much higher than predicted by models for isolated dispersions: SiC have an interconnected structure.

KC

Km

= 1(1− f )3

Every, Tzou, Raj, 1992

X-ray patterns of as-sintered and oxidized HfO2-30vol%SiC ceramics

HfSiO4

HfO2 (monoclinic)SiO2 (crystobalite)

2 [º ]

Inte

nsity

[cps

]

5. X-ray di!raction of the oxidation scale formed at di!erent tempera-tures. Note the presence of HfSiO4, and the absence of cristobalite at the high temperatures.

5 µm

127

µm

100 µm

1600oC, 10h, air

hafium silicate hafium oxide

0

20

40

80

100

120

140

1200 1300 1400 1500 1600

Thic

kkness o

f O

xid

e S

cale

, µm

Oxidation Temperature [ºC]

60

unoxidized HfO2-SiC

HfO2 + SiC + 32O2 = HfSiO4 +CO ↑

• Oxide scale is a matrix of HfSiO4 with a dispersion of HfO2. • 13.8% volume expansion ensures a robust oxidation scale. • The scale has good mechanical properties. • CO is partly sequestered within bubbles, and partly diffuses out to the atmosphere (based upon pressure calculation).

Oxidation behavior of Infiltrated Fiber Preforms

Polymer Derived SiCN

Polymer Derived HfO2or HfO2 powder

HfO2/SiCN

SiCN vol% = 5-40%

HfSiCNO

Hf/Si = 0-40%

Unoxidized

Oxide Scale

Epoxy

1 µm 1500oC, 50h, air

Polymer Derived SiCN

Polymer Derived HfO2or HfO2 powder

HfO2/SiCN

SiCN vol% = 5-40%

HfSiCNO

Hf/Si = 0-40%

Unoxidized

Oxide Scale

Epoxy

1 µm 1500oC, 50h, air

Unoxidized material

Oxide layer (10 um)

Epoxy

Powder oxidation, 1500°C, 1000 hours

Please note the absence of CO bubbles in HfSiCNO (because they are amorphous)

Hf/Si = 0.38

Oxidation behavior of Infiltrated Fiber Preforms

Polymer Derived SiCN

Polymer Derived HfO2or HfO2 powder

HfO2/SiCN

SiCN vol% = 5-40%

HfSiCNO

Hf/Si = 0-40%

Epoxy

•Hf/Si of 0.38 is a promising matrix*. •New processing approach to counter shrinkage.

*(i) HfSiO4 will prevent recession in streaming-humid atmosphere. (ii) CO bubble nucleation is impeded.

Optical micrograph of as-infiltrated sample

HfO2/SiCN infiltration

Oxidation behavior of Infiltrated Fiber Preforms

Polymer Derived SiCN

Polymer Derived HfO2or HfO2 powder

HfO2/SiCN

SiCN vol% = 5-40%

HfSiCNO

Hf/Si = 0-40%

Epoxy

•Hf/Si of 0.38 is a promising matrix*. •New processing approach to counter shrinkage.

*(i) HfSiO4 will prevent recession in streaming-humid atmosphere. (ii) CO bubble nucleation is impeded.

Optical micrograph of as-infiltrated sample

HfO2/SiCN infiltration

Oxidation Expts and Observations

1500oC, water, 5-30h

Three Reactions: free surface of the matrix matrix-CVI (SiC) interface (c) inside CVI (SiC) free surface from C-fiber burnout

(a) (b)

(a)

(b)

CO Bubble formation (bloating) SiC + 3

2O2 → SiO2 +CO ↑

Streaming  H2O,  1400°C,  25hrs  

1600oC, 100hrs, air (dry O2)

bubble

Schiroky et al. 1986

SiC Single Crystal

HfO2 top-coat

oxidized SiCN(O)interlayer

1500 oC 100h, ambient air

Oxidation Expts and Observations

1500oC, water, 5-30h

free surface of the matrix matrix-CVI (SiC) interface

(a)

(b)

(b)

(a)

CVI SiC

Epoxy

HfO2/SiCN Infiltrated Layer

At the Free Surface

Oxidation as a function of depth from outer surface

(a)

At  outer  surface   At  300  μm  depth  

HfSiO4 and HfO2 HfSiO4, HfO2, and SiO2 SiCN and HfO2

Streaming H2O, 1500°C, 30 hours

Epoxy

SiO2 HfO2 (light)

HfSiO4 (dark)

At  100  μm  depth  

Streaming H2O, 1500°C, 30 hours

HfO2 (light) and HfSiO4 (dark)

bubble pockets are confined to within the matrix

(These results are comparable to those from HfO2-SiC Dual-Phase Nanocomposites.)

1500oC, water, 30h

(b) CVI SiC

Epoxy

HfO2/SiCN Infiltration

At the Matrix / CVI-SiC Interface

CVI SiC

w/o SiO2

SiO2 on SiC exposed by C-burnout

HfO2-SiCN matrix

Streaming H2O, 1500°C, 5 hours Flow direction

some ballooning: bubbles at surfaces of CVI-SiC exposed by C-fiber burnout

Oxidized 1500°C, 100 hours, air

Recession at the unprotected leading edge

Streaming H2O, 1500°C, 30 hours

Flow direction

recession

SiC HfSiCNO/HfO2

Steam Steam

Bubbles Bloating? within the matrix (w/o bloating)

Recession Yes No

SiC HfSiCNO/HfO2

Air Air

Bubbles Yes (bloating)

within the matrix (w/o bloating)

Recession No No

Temp :1400 − 2000oCpO2 = 10

–6 −1 atmIn steam SiC suffers active oxidation

Failure Mechanisms: 1.  Bubbles, 2.  Active Oxidation (Recession)

Bubble Nucleation and Growth

• Model (What is the “DNA” of the phenomenon?) • Focus in SiC-Silica Interface • ab-initio materials discovery chemical synthesis experiment repeat

Phenomena have their genesis in atoms and molecules!

the DNA

1600oC 100h, ambient air

The Mechanism: •SiC-oxide interfacial energy determines the nucleation barrier. •Viscosity of silica significantly affects incubation time.

The Concept: Hf doping into silica may affect interfacial energy. Viscosity?

The Steps: ab-initio for material discovery (Peter Kroll) followed by synthesis (Steve George/Chuck Winter), followed by experiment…..

Influence of water on interfacial energies and viscosity?

Bubble Nucleation and Growth: Analysis and Remediation

b-SiC a-SiO2 a-SiO2

Surface energy, g = [E(model)-E(b-SiC)+E(a-SiO2)]/Area = 1.4 ± 0.2 J/m2

“natural” cavities, due to surface bridges O on SiC

Interface structure b-SiC(100)||a-SiO2

SiC-SiO2 interfaces

• how much open void space accumulates towards the interface? • impact of HfO2 on surface structure (preferred segregation?) • pCO higher at interface – impact on transport mechanism of CO?

Tentative but Significant Observations: (i)  HfSiCNO matrix can prevent recession in streaming wet

environments.

(ii)  The HfSiCNO matrix shifts bubble formation (nucleation) from the SiC interface to within the matrix, where the bubbles can be accommodated without bloating.

The degree of recession and the change in the bubble formation behavior remain to be rigorously substantiated.

SUMMARY

Plan for the coming year: •Quantify bubble nucleation and active oxidation (recession) mechanisms. •Develop process for HfSiCNO infiltration of fiber preforms. •Ab-initio of interfaces and viscosity, materials discovery and chemical synthesis to test viability.

Publish three to five additional papers.

in press

BUILDING FOR THE FUTURE

• One-week long summer workshops in Boulder attended by young and experienced researchers, industry, universities and international institutes: www.engineceramic.org. 1st Workshop - 2012 2nd Workshop – 2014 • (unsuccessful) DMREF proposal to NSF (FY 2013) involving, Wayne State (Chuck Winters), Case Western (Frank Ernst + Jennifer Carter), Akron (Greg Morscher), Cornell (Leigh Phoenix), Dave Marshall and General Electric.