processing of polymer-derived porous sic ceramics

Young-Wook Kim

Functional Ceramics Laboratory, Department of Materials Science & Engineering, The University of Seoul, Seoul 130-743, Korea

Processing of Polymer-Derived

Porous SiC Ceramics

Porous Ceramics for CSP Applications

June 26, 2013

Motivation

Processing Strategies

Direct Foaming

Extrusion

Steam Chest Molding

Injection Molding

Powder Processing

Critical Issues

Outline

Functional Ceramics Laboratory The University of Seoul

Motivation

Porosity Morphology

Property

New Processing

Techniques

→ Possibility of

Porosity and

Microstructure

Control

Properties =

f (microstructure, porosity)

Microstructure and porosity are strongly dependent on the processing method.

Better understanding on the processing methods is essential.


Low processing temperature

Additive-free densification

Low-cost polymer processes

Extrusion without organic binders

Compression molding, Injection molding

Steam chest molding

Utilization of unique polymer properties that can not be found in

ceramic powders

Appreciable plasticity

In situ gas evolution ability

Appreciable CO2 solubility

Appreciable preceramic polymer solubility in solvents

Why PS-Derived SiC?

Energy Level

Reaction State

Sintering Polysiloxane

Amorphous state

Powder

Nano

crystalline state

Ceramic

Direct foaming of polysiloxane /polyurethane solutions

Self-blowing of a polysiloxane melt

Direct foaming of preceramic polymers using CO2


Motivation


Direct Foaming

Extrusion

Steam Chest Molding

Injection Molding

Powder processing

Critical Issues

Outline


Direct Foaming Method

+

CO2

Preceramic

polymer

blends

Gas injection Diffusion

Cell growth Nucleation

1. Saturating preceramic polymers using gaseous, liquid, or supercritical CO2.

2. Nucleating and growing a large number of bubbles using a thermodynamic instability.

3. Transforming the microcellular preceramics into microcellular ceramics by pyrolysis.

Parameters

Blends Composition

Nucleation Agent

Cross-linking Degree

Temperature

Pressure

Pressure Drop Rate

Blowing Agent Type

U.S. Patent 7,008,576(2006) Kim et al., J. Am. Ceram. Soc. (2003)

Typical Microstructure

US Patent (2006)

• Cell size ∼50 m

• Cell density ∼107 cells/cm3

• Cell size ∼20 m

• Cell density ∼1010 cells/cm3

Closed Cell

50 µ m 100 µ m

Open Cell

Manoj and Kim, Sci. Tech. Adv. Mater. (2010)

Potential Applications/Motivation


Direct Foaming

Extrusion

Steam Chest Molding

Injection Molding

Powder processing

Critical Issues

Outline


Expandable Microspheres

10 m

40 m

Heat

100-180ºC

Liquid

hydrocarbon

Copolymer of

vinylidene chloride,

acrylonitrile and

methylmethacrylate

Gaseous

isobutane or

isopentane

7/24


Processing

Foamed Compact Cross-linked Compact

Macroporous

SiOC + C

Extrusion

& in situ foaming

Macroporous

SiC

Cross-linking Pyrolysis

Carbothermal Reduction & Sintering

Compounded polysiloxane/carbon/

additives/microsphere blends

130o

C 200o

C

1200o

C

1450o

C 1750-

1950oC

Polysiloxane + C(Filler) → SiOC + C

SiOC + C → SiC + CO

Extrusion

Reaction


Kim et al., J. Am. Ceram. Soc. (2008)

Motor

Motor Die Second Extruder

First Extruder

Hopper

Batch Composition

As-extruded

10 20 30 40 50 60 70 80 90

Inte

nsity

2

SiC


Sample Batch Composition (wt%)

Polysiloxane Carbon Black SiC Expandable

Microsphere Sintering Additive

PS5 79.2 11.1 0 5

1.9% Al2O3 + 2.8% Y2O3

PS10 74.8 10.5 0 10

PS15 70.4 9.9 0 15

PS10F10 66.0 9.3 10 10

PS10F20 57.3 8.0 20 10



Compounding: 115oC

Extrusion: 130oC/40 rpm

Pyrolysis: 1200oC/1 h

Processing

LDPE Template

Motor

Motor Die Second Extruder

First Extruder

Hopper Cross Section

Flow Direction


50LDPE/50PS

0 500 1000 1500 2000 2500 3000 3500 400010

1

102

103

YR3370

LDPE

Co

mp

lex V

isco

sity

* (P

a.s

)

Time (s)

130oC

Porosity:78%

LC0520,

Nova

Chemical,

Canada

LDPE

Extrusion: Conclusions

Porous SiC ceramics were fabricated from extruded blends of carbon-filled polysiloxane using expandable microspheres as sacrificial templates.

Open cells were obtained by (i) in situ foaming of expandable microspheres during extrusion, (ii) pyrolysis of polysiloxane from the extruded blends, and (iii) carbothermal reduction of polysiloxane-derived SiOC by carbon.

The porosity could be controlled from 60% to 85% by adjusting the microsphere content, the sintering temperature, and the filler content.


Motivation


Direct Foaming

Extrusion

Steam Chest Molding

Injection Molding

Powder processing

Critical Issues

Outline



• Principle

Steam Chest Molding

Steam Closed Cell

Permeable to Steam Steam Filled Cell

Pressurization

Expanded Cell

T

Low-melting-crystals melt and

contribute to good adhesion

High Tm crystals

maintain overall foam

structure

• Condition

Double peak is

required

for good sintering

(EPP/EPE)

Depressurization

Cooling

Closed cell Steam-permeable shell Bonding mechanism

SCM Temperature

Merits of SCM

Homogeneous temperature distribution

→ Easy to scale-up

Near-net shaping of the 3D morphology


http://ciamp.mie.utoronto.ca/BeadFoamingSteamChestMolding.html

http://www.google.co.kr/url?sa=i&rct=j&q=&esrc=s&frm=1&source=images&cd=&cad=rja&docid=EUAI1xwyfhN6tM&tbnid=7Li9tCTL2OisLM:&ved=0CAUQjRw&url=http://www.hiwtc.com/products/mould-with-steam-chest-1553-11178.htm&ei=Vna5UbuPH4WjiAfG_ICAAg&bvm=bv.47883778,d.aGc&psig=AFQjCNF_CLr_wqnMaNSuuqgHba52awVxuA&ust=1371195294114652

Experimental

Batch Composition (wt%) 74.6% Polysiloxane + 10.4% Carbon + 10% Microspheres + 3% Y2O3 + 2% AlN

Sample Packing Density (g/cm3)

SiC1 24/54 =0.4444

SiC2 32/54=0.5926

SiC3 40/54=0.7407

Polysiloxane

Blending Steam Chest

Molding

4.7 bar

(149.7oC)

45 seconds

Hollow Microsphere

Carbon

Source

Sintering Additives


Experimental

Cross-linking

at 200℃ for 2h

Pyrolysis

SiC Foams

Carbothermal

Reduction

Sintering

Process Conditions

Pyrolysis 1100oC / 1 h / N2

Carbothermal Reduction 1450oC / 1 h / N2

Sintering 1750oC / 2 h / N2





Microstructure

59%

62% 60%

Cell size and Porosity

decreased with increasing

the initial loading because of

constrained expansion.

1750oC/2 h/N2



0.4 0.5 0.6 0.7 0.81.20

1.25

1.30

1.35

1.40

Density

Porosity

Packing Density (g/cm3)

De

nsity (

g/c

m3)

55

60

65 P

oro

sity

(%)

Density/Porosity

62%

59%

1.34 g/cm3

1.25 g/cm3



Cell Opening

0.4 0.5 0.6 0.7 0.82.0x10

8

4.0x108

6.0x108

8.0x108

1.0x109

Packing Density (g/cm3)

Win

do

w D

en

sity (

win

do

ws/c

m3)

Cell opening increased with increasing initial packing density.

Free expansion was limited by the fixed mold volume, leading

to less expansion and more contact between the microspheres.

12 m

16 m


Microstructure

0.444 g/cm3 / 62% 0.741 g/cm3 / 59%

More porous struts were obtained at a lower packing density

because of the greater expansion of the specimen.

1750oC/2 h/N2


56 58 60 62 640

20

40

60

80

100

120

Packing Density

0.444 g/cm3

0.593 g/cm3

0.741 g/cm3

Co

mpre

ssiv

e S

treng

th (

MP

a)

Porosity (%)

SCM: Compressive Strength

1750oC / 2 h

77 MPa



Expansion Method

1. Blending of ceramic precursor and expandable microspheres 2. In situ foaming 3. Cross-linking the foamed body 4. Transforming the foamed body into ceramic foams by pyrolysis and sintering.

Parameters

Content of Expandable

Microspheres

Foaming temperature

Foaming time

Cross-linking

conditions

Pyrolysis Temperature

Extrusion speed

Extrusion pressure

Heating rate Crosslinked

Preceramic Foam

+

Ceramic

precursor

Forming

Pyrolysis

Foaming

Green Compact

Preceramic Foam

Closed-Cell Ceramic Foam

Crosslinking Expandable

Microspheres

Kim et al. U.S. Patent 7,033,527(2006)

Cellular SiOC Ceamics

Closed Cell

T70 T40


Characteristic Steam Chest Molding Expansion

Heating Medium Steam Air

Blowing Agent Steam Hydrocarbon

Temperature

Uniformity Highly Uniform Uniform (ΔT)

Maximum Size Large (~m) Small (~cm)

Mold Fixed Volume Fixed Volume

Shape Versatility 3D/Complex Shape 3D/Complex Shape

Cell Type Open/Closed Closed

Steam Chest Molding vs Expansion


Merits of SCM for Porous SiC

Homogeneous temperature distribution

→ Easy to scale-up

Controllable openness of cells

Near-net shaping of the 3D morphology


SCM: Conclusions

Open-cell SiC foams with a homogeneous microstructure

were fabricated from a mixture of polysiloxane, carbon black,

sintering additives (Y2O3-AlN), and microspheres using a

newly developed process based on a steam chest molding

and carbothermal reduction process.

The typical compressive strength of the open-cell SiC foam

was 77 MPa at 60% porosity.


Motivation


Direct Foaming

Extrusion

Steam Chest Molding

Injection Molding

Powder processing

Critical Issues

Outline


Injection Molding


Injection: 120oC/70 mL/s

Pyrolysis: 1200oC/1 h

Carbothermal Reduction: 1450oC/1 h

Sintering: 1650oC~1750oC/1 h

Processing

Batch composition (wt%)

74.8% PS + 10.5% C + 10% Microsphere

+ 1.9% Al2O3 + 2.8% Y2O3



Reaction

As-injection molded

Injection molded samples

1650oC/78%

Porous SiC by Injection Molding


1750oC/65%

55 60 65 70 75 80 85 900

20

40

60

80

100

120

Compression Molding

Injection Molding

Extrusion

Steam Chest Molding

Co

mp

ressiv

e S

tre

ng

th (

MP

a)

Porosity (%)

Injection molding process leads

to an enhanced expansion of

microspheres and results in the

formation of large pores.

Eom et al., J. Ceram. Soc. Jpn. (2012)

Compression Molding: Flexural Strength

74 76 78 80 82 84 861

2

3

4

5

6

7

8

9

10

11

12

13

Jin & Kim (2010)

Mouazer (2004)

Colombo (2008)

Mouazer (2005)

7 % hollow microspheres



Fle

xu

ral

Str

en

gth

(M

Pa)

Porosity (%)

1750oC / 2 h

8.3 MPa

Processing Flexural strength / Porosity Reference

Replica 0.5-2.0 MPa at 80% porosity Zhu et al. Mater Sci Eng A (2002)

Template 6 MPa at 80% porosity Jin & Kim, J Mater Sci (2010)

Foaming 2.9 MPa at 72-88% porosity Colombo, J Eur Ceram Soc (2008)

Gel Casting 5.1 MPa at 80% porosity Mouazer et al. Adv Eng Mater (2004)

The homogeneous

microstructure

The lack of continuous

pore channel inside of

the strut

Superior strength


IM: Conclusions

Open-cell silicon carbide foams were fabricated from a blend of carbon-filled polysiloxane using injection molding.

Injection molding process led to an enhanced expansion of microspheres and resulted in moderate compressive strength (~9 MPa at 74% porosity).


Motivation


Direct Foaming

Extrusion

Steam Chest Molding

Injection Molding

Powder processing

Critical Issues

Outline


Experimental


Sample

designation

Composition (wt%)

-SiC -SiC Al2O3 Y2O3 Microsphere

0A5AY 60 0 3 2 35

1A5AY 59.4 0.6 3 2 35

3A5AY 58.2 1.8 3 2 35

10A5AY 54 6 3 2 35

50A5AY 30 30 3 2 35

100A5AY 0 60 3 2 35

0A7AY 58 0 4.2 2.8 35

1A7AY 57.4 0.6 4.2 2.8 35

Raw Materials

Mixing

Template Removal

Sintering

1000oC/ 1h

1950oC/4h /Ar

Microstructure


100β 100α

0 20 40 60 80 1000

10

20

30

40

Flexural Strength

Fracture Toughness

Content of -SiC (%)

Fle

xu

ral S

treng

th (

MP

a)

0.2

0.3

0.4

0.5

0.6

0.7

0.8

Fra

ctu

re T

ou

gh

ne

ss (M

Pam

1/2)

0 5 10 15

0

5

10

15

20

25

Pressure (PSI)

Spe

cific

Flo

w R

ate

(Liters

/min

/cm

2)

0A5AY

1A5AY

100A5AY

0A7AY

1A7AY

99β/1α

Powder Processing: Conclusions

By adjusting the initial -SiC content in the processing of macroporous SiC

ceramics, the SiC grain morphology can be controlled from equiaxed to

large platelet grains. Large platelet -SiC grains were obtained from

powder or a mixture of / powders containing small (≤10%) amounts of

powders by sintering at 1950oC for 4 h.


The flexural strength increased with increasing -phase content and

showed a maximum strength of 26 MPa at a porosity of 56% when the

starting material contained 100% -SiC particles.

The permeability of macroporous SiC ceramics is dependent on both the

porosity and microstructural characteristics. However, the development of

large platelet SiC grains was very effective in increasing the permeability of

the macroporous SiC ceramics at an equivalent porosity. The specific flow

rate at a Δp of 15 psi and the permeability of macroporous SiC ceramics

fabricated from β-SiC ceramics (porosity ~58%) were 23.3 L/min/cm2 and

1.9 X 10-12 m2, respectively.

Critical Issues


Cost-effectiveness

Scale-up

Improved Properties

- Mechanical Properties

- Permeability

- Thermal Conductivity

Polymer Processing Techniques

- Steam Chest Molding

- Compression Molding

- Extrusion

Flexural Strength and Porosity

30 35 40 45 50 55 60 65 70 75 80 85 90

0

25

50

75

100

125

150

Chi et al.

Ceram. Int.

(2004)

Ding et al.

Mater. Charac.

(2008)

She et al.

J. Eur. Ceram. Soc.

(2003)

Eom et al.

Mater. Sci. Engg. A

(2007)

Colombo et al.

J. Am. Ceram. Soc.

(2001)

Jin and Kim

J. Mater. Sci.

(2010)

Chae et al.

J. Eur. Ceram. Soc.

(2009)

Fle

xu

ral S

tre

ng

th (

MP

a)

Porosity (%)

Sacrificial Template

Direct Foaming

Reaction Technique

Powder-Processing

Manoj & Kim, Sci. Tech. Adv. Mater. (2010)


Acknowledgement


Jung-Hye Eom, Sue-Ho Chae, and Shin-Han Kim Functional Ceramics Laboratory, Department of Materials Science &

Engineering, University of Seoul, Korea

Masaki Narisawa Osaka Prefecture University, Japan

Chul B. Park and Wentao Zhai Department of Industrial and Mechanical Engineering, University of Toronto,

Canada

Chunmin Wang

General Electric Global Research Centre, China

This study was supported by a grant from the National Research

Foundation of Korea (NRF).


Many Thanks for your kind attention!

processing of polymer-derived porous sic ceramics

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