Processing of Polymer-Derived Porous SiC Ceramics

Transcription

1 Processing of Polymer-Derived Porous SiC Ceramics Porous Ceramics for CSP Applications June 26, 2013 Young-Wook Kim, Department of Materials Science & Engineering,, Seoul , Korea

2 Outline Motivation Processing Strategies Direct Foaming Extrusion Steam Chest Molding Injection Molding Powder Processing Critical Issues

3 Motivation Porosity Morphology Properties = f (microstructure, porosity) Microstructure and porosity are strongly dependent on the processing method. Property New Processing Techniques Possibility of Porosity and Microstructure Control Better understanding on the processing methods is essential.

4 Why PS-Derived SiC? 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 CO 2 solubility Energy Level Polysiloxane Appreciable preceramic polymer solubility in solvents Sintering Powder Amorphous state Nano crystalline state Reaction State Ceramic Direct foaming of polysiloxane /polyurethane solutions Self-blowing of a polysiloxane melt Direct foaming of preceramic polymers using CO 2

5 Outline Motivation Processing Strategies Direct Foaming Extrusion Steam Chest Molding Injection Molding Powder processing Critical Issues

6 Direct Foaming Method CO 2 + Preceramic polymer blends Cell growth Gas injection Nucleation Diffusion Parameters Blends Composition Nucleation Agent Cross-linking Degree Temperature Pressure Pressure Drop Rate Blowing Agent Type 1. Saturating preceramic polymers using gaseous, liquid, or supercritical CO Nucleating and growing a large number of bubbles using a thermodynamic instability. 3. Transforming the microcellular preceramics into microcellular ceramics by pyrolysis. Kim et al., J. Am. Ceram. Soc. (2003) U.S. Patent 7,008,576(2006)

7 Typical Microstructure Closed Cell Open Cell 50 µ m 100 µ m Cell size 50 m Cell density 10 7 cells/cm 3 Cell size 20 m Cell density cells/cm 3 Manoj and Kim, Sci. Tech. Adv. Mater. (2010) US Patent (2006)

8 Outline Potential Applications/Motivation Processing Strategies Direct Foaming Extrusion Steam Chest Molding Injection Molding Powder processing Critical Issues

9 Expandable Microspheres Liquid hydrocarbon Copolymer of vinylidene chloride, acrylonitrile and methylmethacrylate 10 m Heat ºC Gaseous isobutane or isopentane 40 m 7/24

10 Extrusion Processing Extrusion & in situ foaming Cross-linking Pyrolysis Carbothermal Reduction & Sintering 130 o C Compounded polysiloxane/carbon/ additives/microsphere blends Motor Hopper First Extruder Foamed Compact 200 o C Cross-linked Compact 1200 o C Reaction Macroporous SiOC + C 1450 o C 1950 o C Macroporous SiC Polysiloxane + C(Filler) SiOC + C SiOC + C SiC + CO Motor Second Extruder Die Kim et al., J. Am. Ceram. Soc. (2008)

11 Intensity Batch Composition Sample As-extruded Polysiloxane Carbon Black Batch Composition (wt%) SiC Expandable Microsphere PS PS PS PS10F PS10F SiC Sintering Additive 1.9% Al 2 O % Y 2 O Polysiloxane + C(Filler) SiOC + C SiOC + C SiC + CO

12 Complex Viscosity * (Pa.s) LDPE Template Motor Hopper First Extruder Cross Section 50LDPE/50PS Processing Motor Compounding: 115 o C Extrusion: 130 o C/40 rpm Pyrolysis: 1200 o C/1 h 10 3 Second Extruder LDPE LDPE LC0520, Nova Chemical, Canada Die Flow Direction Porosity:78% 10 2 YR Time (s) 130 o C

13 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.

15 Steam Chest Molding Principle Depressurization Steam Condition Double peak is required for good sintering (EPP/EPE) Closed Cell Permeable to Steam Pressurization Steam Filled Cell SCM Temperature Low-melting-crystals melt and contribute to good adhesion Cooling T Expanded Cell Closed cell Steam-permeable shell Bonding mechanism High Tm crystals maintain overall foam structure

16 Merits of SCM Homogeneous temperature distribution Easy to scale-up Near-net shaping of the 3D morphology

17 Experimental Carbon Source Sintering Additives Hollow Microsphere Polysiloxane Blending Steam Chest Molding 4.7 bar (149.7 o C) 45 seconds Batch Composition (wt%) 74.6% Polysiloxane % Carbon + 10% Microspheres + 3% Y 2 O 3 + 2% AlN Sample Packing Density (g/cm 3 ) SiC1 24/54 = SiC2 32/54= SiC3 40/54=0.7407

18 Experimental Pyrolysis Cross-linking at 200 for 2h Carbothermal Reduction Sintering SiC Foams Polysiloxane + C(Filler) SiOC + C SiOC + C SiC + CO Process Conditions Pyrolysis 1100 o C / 1 h / N 2 Carbothermal Reduction 1450 o C / 1 h / N 2 Sintering 1750 o C / 2 h / N 2 Kim et al., J. Am. Ceram. Soc. (2011)

19 Microstructure 62% 60% 59% Cell size and Porosity decreased with increasing the initial loading because of constrained expansion o C/2 h/n 2 Kim et al., J. Am. Ceram. Soc. (2011)

20 Density (g/cm 3 ) Porosity (%) Density/Porosity 1.40 Density Porosity % 1.34 g/cm % 1.25 g/cm Packing Density (g/cm 3 ) Kim et al., J. Am. Ceram. Soc. (2011)

21 Window Density (windows/cm 3 ) Cell Opening 1.0x m 8.0x x x m 2.0x Packing Density (g/cm 3 ) 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.

22 Microstructure g/cm 3 / 62% g/cm 3 / 59% 1750 o C/2 h/n 2 More porous struts were obtained at a lower packing density because of the greater expansion of the specimen.

23 Compressive Strength (MPa) SCM: Compressive Strength o C / 2 h 77 MPa Packing Density g/cm g/cm g/cm Porosity (%) Kim et al., J. Am. Ceram. Soc. (2011)

24 Expansion Method Ceramic precursor + Expandable Microspheres Forming Green Compact Pyrolysis Closed-Cell Ceramic Foam Foaming Preceramic Foam Crosslinking Crosslinked Preceramic Foam Parameters Content of Expandable Microspheres Foaming temperature Foaming time Cross-linking conditions Pyrolysis Temperature Extrusion speed Extrusion pressure Heating rate 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. Kim et al. U.S. Patent 7,033,527(2006)

25 Cellular SiOC Ceamics T70 T40 Closed Cell

26 Steam Chest Molding vs Expansion 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

27 Merits of SCM for Porous SiC Homogeneous temperature distribution Easy to scale-up Controllable openness of cells Near-net shaping of the 3D morphology

28 SCM: Conclusions Open-cell SiC foams with a homogeneous microstructure were fabricated from a mixture of polysiloxane, carbon black, sintering additives (Y 2 O 3 -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.

30 Injection Molding Batch composition (wt%) 74.8% PS % C + 10% Microsphere + 1.9% Al 2 O % Y 2 O 3 As-injection molded Reaction Polysiloxane + C(Filler) SiOC + C SiOC + C SiC + CO Processing Injection: 120 o C/70 ml/s Pyrolysis: 1200 o C/1 h Carbothermal Reduction: 1450 o C/1 h Sintering: 1650 o C~1750 o C/1 h Injection molded samples

31 Compressive Strength (MPa) Porous SiC by Injection Molding 1650 o C/78% Compression Molding Injection Molding Extrusion Steam Chest Molding o C/65% 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)

32 Flexural Strength (MPa) Compression Molding: Flexural Strength % hollow microspheres 10 % hollow microspheres 15 % hollow microspheres 8.3 MPa Jin & Kim (2010) Mouazer (2004) Colombo (2008) Mouazer (2005) Porosity (%) 1750 o C / 2 h Superior strength The homogeneous microstructure The lack of continuous pore channel inside of the strut Processing Flexural strength / Porosity Reference Replica 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)

33 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).

35 Experimental Sample designation Composition (wt%) -SiC -SiC Al 2 O 3 Y 2 O 3 Microsphere 0A5AY A5AY A5AY A5AY A5AY A5AY A7AY A7AY Raw Materials Mixing Template Removal 1000 o C/ 1h Sintering 1950 o C/4h /Ar

36 Flexural Strength (MPa) Fracture Toughness (MPa m 1/2 ) Specific Flow Rate (Liters/min/cm 2 ) Microstructure 100β 99β/1α 100α Flexural Strength Fracture Toughness A5AY 1A5AY 100A5AY 0A7AY 1A7AY Content of -SiC (%) Pressure (PSI)

37 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 1950 o C 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/cm 2 and 1.9 X m 2, respectively.

38 Cost-effectiveness Scale-up Improved Properties - Mechanical Properties - Permeability - Thermal Conductivity Critical Issues Polymer Processing Techniques - Steam Chest Molding - Compression Molding - Extrusion

39 Flexural Strength (MPa) Flexural Strength and Porosity Chae et al. J. Eur. Ceram. Soc. (2009) Sacrificial Template Direct Foaming Reaction Technique Powder-Processing 100 Eom et al. Mater. Sci. Engg. A (2007) She et al. J. Eur. Ceram. Soc. (2003) Ding et al. Mater. Charac. (2008) Chi et al. Ceram. Int. (2004) Jin and Kim J. Mater. Sci. (2010) Colombo et al. J. Am. Ceram. Soc. (2001) Porosity (%) Manoj & Kim, Sci. Tech. Adv. Mater. (2010)

40 Acknowledgement Jung-Hye Eom, Sue-Ho Chae, and Shin-Han Kim, 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).

41 Many Thanks for your kind attention!