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Impact of Composition and Heat Treatment on Pore Size in Borosilicate Glass Microspheres Fabienne C. Raszewski, Erich K. Hansen, Ray F. Schumacher, David.

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Presentation on theme: "Impact of Composition and Heat Treatment on Pore Size in Borosilicate Glass Microspheres Fabienne C. Raszewski, Erich K. Hansen, Ray F. Schumacher, David."— Presentation transcript:

1 Impact of Composition and Heat Treatment on Pore Size in Borosilicate Glass Microspheres Fabienne C. Raszewski, Erich K. Hansen, Ray F. Schumacher, David K. Peeler, Scott W. Gaylord*, Nathan A. Carlie*, Laeticia Petit* and Kathleen A. Richardson* David A. Crowley, Manager Laboratory Directed Research and Development Process Science and Engineering Section February 26, 2008 Materials Innovations in an Emerging Hydrogen Economy, Cocoa Beach, FL, February 24 – 28, 2008

2 2 Background – Hollow Glass Microspheres (HGMs)  Glass bubbles with a solid shell  Typical compositions – Soda lime silica (container glass) – Borosilicate (Pyrex® - like)  Traditional applications – Low density fillers for foams, composites and concrete – Paints and coatings  Modern applications – Hydrogen storage – Gas Separation Matthew M. Hall, Alfred University (10 – 200+ μm)

3 3 Background – Phase Separation  Phase separation in bulk glass – Oil in water concept – Formation of two completely separate phases  Example – Borosilicate glasses  Structures – Droplets – Interconnected  Phases – Silica rich – B 2 O 3 /alkali rich Depends on temperature and composition B.R. Wheaton and A.G. Clare, J. Non-Cryst. Solids (2007).

4 4 Background – Porous Bulk Glasses  Formed from phase separated glasses  Interconnected structure – Dissolve non – durable B 2 O 3 /alkali rich phase – Durable SiO 2 rich phase remains Sponge – like structure “Passageways” throughout material  Example – Vycor TM (aka “Thirsty Glass”) Excellent absorbing properties Filtration 3D Representation R. Pellenq, B. Rousseau and P. E. Levitz. Phys. Chem. Chem. Phys (2001).

5 5 Porous Walled HGMs Vycor TM type composition Interconnected microstructure Fabricate HGMs Treat in acid to dissolve B 2 O 3 /alkali rich phase PWHGMs Heat Treatment

6 6 Potential Applications of PWHGMs  Hydrogen storage  Molecular sieves  Drug/bioactive delivery systems  Indicators – Environmental – Biological – Chemical

7 7 Research Objectives  Porosity could govern potential use and/or performance of material under certain environmental conditions  Determine if porosity changes with – Composition – Heat treatment conditions Temperature Time  Develop a “compositional road map” – Tailor microstructure for specific applications

8 8 Concept: Heat Treatment and Composition Effects  Surface of PWHGM – Many pores  Glass shell – Small passageways connecting exterior to interior of HGM heat treatment temperature or time composition Change these features by either heat treatment temperature or time or composition PWHGM Glass shell

9 9 Research Objectives  Porosity governs potential use and/or performance of material under certain environmental conditions  Determine if porosity changes with – Composition – Heat treatment conditions Temperature Time  Develop a “compositional road map” – Tailor microstructure for specific applications

10 10 Defining the Immiscibility Dome B Regions 1 and 3 Region 2  Unknowns – Location of baseline composition – Size and shape of immiscibility dome  Challenge to define compositional changes to base composition

11 11 Defining the Immiscibility Dome B Regions 1 and 3 Region 2  Unknowns – Location of baseline composition – Size and shape of immiscibility dome  Challenge to define compositional changes to base composition

12 12 Glass Selection  Baseline composition from previous work – Based on the Na 2 O – B 2 O 3 – SiO 2 system – Known to produce both HGMs and PWHGMs for specific application  Change two critical parameters to compositionally map this region – SiO 2 concentration (wt%) Constant B/R molar ratio – B 2 O 3 /alkali (B/R) molar ratio Constant SiO 2 +6 SiO 2 B +3 SiO 2 -3 SiO 2 -6 SiO 2 B/R +0.5 B/R -0.5

13 13 Process Melt glass Make Frit Size Frit HGMs Acid Leach PWHGMs Microscopy Porosity Microscopy Flame Process Microscopy – Clemson University Porosity Measurements - Micromeritics Heat Treat* * For comparison some HGMs were acid leached without any heat treatment

14 14 Path to a PWHGM HGM Heat Treatment 580°C 600°C Acid Treatment PWHGM

15 15 Impact of Heat Treatment Non heat treated 8 hours 600°C  Pore size is extremely small in sample with no heat treatment – At 200,000X pores are barely detectable (Pore diameter: ~100 Ǻ)  Heat treatment enhances the formation of the interconnected microstructure – Pores are clearly visible at only 50,000X (Pore diameter: ~1000 Ǻ) Baseline composition 600 nm 150 nm

16 16 Impact of Heat Treatment  Considerable increase in pore volume with heat treatment  Pore diameter increases from ~100 Ǻ to ~1000 Ǻ Baseline composition – Mercury Porosimetry Data

17 17 Impact of Heat Treatment Temperature  Microstructure is strongly influenced by temperature 20°C – Only a 20°C difference in temperature  Mercury porosimetry results are inconclusive for 8 hours at 580°C – Sample treated at 600°C for 8 hours has a pore diameter of ~1000 Ǻ 8 hours at 580°C 8 hours 600°C Baseline composition – Same Magnification 600 nm

18 18 Impact of Heat Treatment Time 8 hours at 580°C 24 hours 580°C  Variation in microstructure is minimal for heat treatment times of 8 – 24 hours  Heat treatment time is not as effective as heat treatment temperature Baseline composition Apparent “cracking” is due to sample preparation

19 19 Impact of Heat Treatment Time Baseline composition – Mercury Porosimetry Data  Very little (if any) increase in pore volume  No noticeable shift in pore diameter

20 20 Impact of Composition +3 SiO 2 B/R +0.5 B/R -0.5 Similar microstructures…. Base +6 SiO 2 -6 SiO 2 -3 SiO 2 Heat treatment for 8 hours at 600°C Images taken at same magnification

21 21 Impact of Composition  All compositions yield interconnected morphology  Possible influence of composition on microstructure – Varying degrees of porosity – Mercury porosimetry data is inconclusive

22 22 Impact of Composition +3 SiO 2 B/R +0.5 B/R -0.5 Similar microstructures…. Base +6 SiO 2 -6 SiO 2 -3 SiO 2 Heat treatment for 8 hours at 600°C Images taken at same magnification

23 23 Impact of Composition  All compositions yield interconnected morphology  Possible influence of composition on microstructure – Varying degrees of porosity – Mercury porosimetry data was inconclusive

24 24 Conclusions  Task Objectives – Determine the impact of heat treatment time and temperature and composition on porosity  TEMPERATURE – PRIMARY EFFECT No HT 580°C 8 hrs. 600°C 8 hrs. Increase in the degree of phase separation/porosity with increasing heat treatment temperature ~100 Ǻ ~1000 Ǻ

25 25 Conclusions  COMPOSITION – SECONDARY EFFECT* – Micrographs indicate variations in the degree of porosity – *Assuming no confounding effects of HGM diameter/wall thickness  HEAT TREATMENT TIME – NO EFFECT  HEAT TREATMENT TIME – NO EFFECT (8 – 24 hours) 580°C 8 hrs. 580°C 24 hrs. No change with heat treatment time

26 26 Acknowledgements  LDRD for funding this work  George Wicks and Leung K. Heung for their technical insight  Frances Williams, Irene Reamer, Phyllis Workman and Debbie Marsh for laboratory and technical assistance  Clemson team for all microscopy work (Kathleen Richardson, Laeticia Petit, Scott Gaylord and Nathan Carlie)  Micromeritics for conducting the mercury porosimetry analyses on all samples  Don Blankenship for assistance with the analysis of the mercury porosimetry data

27 27 Back-up Slides

28 28 Approximate Compositions Glass ID SiO 2 B2O3B2O3B2O3B2O3 R2OR2OR2OR2OOthers B/R ratio Base* SiO SiO SiO SiO B/R B/R R.F. Schumacher, E.K. Hansen, D.K. Peeler, G.G. Wicks, and L. Heung, SRNL-PSE Rev. 0, November 2006.

29 29 Flame Process Flame Former Sized glass frit containing blowing agent Hollow Glass Microspheres Flame Cooling water

30 30 HGMs  Typical range of average HGM diameters is 45 – 75 μ m

31 31 Glass Selection  “Zero Glasses” – Remove minor components – GOAL: Simplify composition while still maintaining desired microstructure – Eliminate one component at a time from original composition CaO ZnO P 2 O 5 Fluorine Determine if HGMs can still be fabricated and impacts on yield ONLY PWHGMs of these glasses were not made Impact of elimination on porosity is unknown

32 32 HGM Yield  Base composition is superior to all others  Fluorine can be eliminated** – Simplifies melting  Calcium is extremely important in HGM formation  Yield is unaffected by removing ZnO or P 2 O 5 Change SiO 2 Change B/R Zero Glasses ** on a yield basis ONLY

33 33 Viscosity and HGM Yield  Viscosity increases with SiO 2 and B 2 O 3 content  HGM formation and viscosity are linked, BUT – Composition clearly influences yield more strongly in these glasses than viscosity

34 34 PWHGM Yield Non heat-treated 600°C for 8 hrs.  Yield appears to be unaffected by composition  Heat treatment increases yield – Connectivity increases causing more material removal Suspect data – sample had a high moisture content

35 35 Compositional Changes (wt%) as a Function of Processing and Unit Operations  B 2 O 3 and R 2 O volatilize during flame forming  B 2 O 3 and R 2 O are leached out during acid treatment  PWHGMs are rich in SiO 2 DescriptionSiO 2 B2O3B2O3 R2OR2O Glass (Target)60227 HGMs (Actual)70165 PWHGMs (Actual)8851

36 36 Impact of Composition – Bulk Glass Plates B/R +0.5 B/R -0.5 Base +6 SiO 2 -6 SiO 2 Differences in microstructure do exist. Heat treatment for 8 hours at 600°C Images taken at same magnification

37 37 Path Forward  Optimize heat treatment time – Less than 8 hours may be sufficient – Investigate times greater than 24 hours  Simplify composition – Determine effects on microstructure and yields  Determine influence of flame former operating parameters on yield, microstructure, etc.

38 38 Conclusions Composition Temperature Yield OPERATIONAL PERSPECTIVE Adjust composition if certain physical properties are required Possible limitations: Size of pores Yield Potential to control porosity in any composition by temperature alone What factor(s) are most important to end – user? Use composition with highest yield if a PWHGM is the only requirement


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