J Mater Sci(2007)42:763-771 Barium osumilite and celsian both start to crystallise at Acknowledgements The authors would like to thank to NPI around 970C, whereas the cordierite start to crystal (National Physical Laboratory) lise at about 1,020C and the highest percentage of with SEM and TEm studies. r yilmaz would also like to thank to crystallisation occurs at 1, 100C. Sakarya University for financial support. Conclusions References The following conclusions can be drawn from this 1. Prewo PM, Brennan JJ, Layden GK(1986)Am Ceram Soc 2. Brennan JJ, Chyung K, Taylor MP(1986) USA Patent Ne 1. The interface is one of the key factors which affect 4589900,May20 thermal properties such as diffusivity of the 3. Johnson LF, Hasselman DPH, Chung KJ(1987)JAm Ceram Soc 70: C135 Doper RF, Chy yung K(1987)J Mater Sci 22: 3148 2. Thermal properties were determined before and 5. Bemson PM, Spear KE, Pontano CG(1988)Ceram Eng Sci after heat treatment at various temperatures and Proc 9: 63 6. Chaim R, Heuer AH (1991)J Am Ceram Soc 74: 1663 mes in air. It has been found that heat treatment 7 Murty VSR, Li J, Lewis MH (1989)Ceram Er at the lower temperatures causes a considerable 10:938 degradation in the thermal diffusivity and the 8. Bonney LA, Cooper RF(1990)JAm Ceram Soc 73: 2916 thermal expansion with the greatest affect being 9. Murthy VSR, Phoraoh MW, Lewis MH (1990) Inst Phys shown after 700 oC heat treatment. However Conf Ser No 111. New Mater Appl 185 10. Lewis MH, Murthy VSR(1991)Compos Sci Technol 42: 221 temperatures higher than 900C heat treatments 11. Lewis MH, Daniel AM, Chamberlian A, Pharaoh MV,Cain resulted in retention in the thermal property values MG(1993)J Microsc 169: 109 and sometimes even higher thermal diffusivity 12. Yilmaz R(1998)PhD thesis. UMIST-UK values were obtained 13. Bleay SM, Scott VD(1992)J Mater Sci 27: 825 14. Plucknett KP, Sutherland S, Daniel AM, Cain RL, Taplin 3. TEM analysis showed interfacial structure degra DMR, Lewis MH (1995)J Microsc 177: 251 lation after heat treatments that were carried out at 15. Kumar A, Knowles KM (1996)J Am Ceram Soc 79: 2369 lower temperature(700oC)on glass ceramic matrix 16. Pharaoh MW, Daniel AM, Lewis MH(1993)J Mater Sci composites caused by the removal of carbon and the 17. Hasselman DPT(1988)Therm Conduct 19:383 occurrence of gaps between fibre and matrix and 18. Bhatt H, Donaldson KY, Hasselman DPH, Bhatt RT (1992) isolated silicon rich bridges linking the two J Mater Sci 27: 6653 4.TEM analysis after higher heat treatment temper- 19. Bhatt H, Donaldson KY, Hasselman DPH, Bhatt RT(1990) atures such as 1, 200C showed that the interfacial 20. Hasselman DPH. Venkatesawaron A, Yu M(1991)J Mater reaction layer was much thicker which sometimes Sci lett 17: 1037 resulted in higher values in the thermal diffusivity. 21. Hasselman DPH. Venkatesawaron A, Tawil H(1991)JAm 5. seM studies show that at lower heat treatment temperature(700C)residual glass in the matrix 22. Tawil H, Bersen LD, Baskaran J, Hasselman DPH (1985)J Mater Sci 20: 3201 migrated to the voids in particular to interfaces 23. Bhatt H Donaldson KY, Hasselman DPH, Bhatt RT(1992) after degradation of carbon layer at interfaces. J Am Ceram Soc 75: 334 6. SEM studies indicated that crystallisation in the 24 Hasselmann DPH, Johnson T(1987)J Compos Mater 21:508 residual glass, which resulted in an increase in 25. Parker WJ, Jenkins RJ, Butler CP, Abbot GL (1960)J Appl Phys32:926 thermal properties of the composites, occurred 26. Taylor R(1980)J Phys E: Sci Instrum 13: 1193 fter heat treatment at temperature(>1, 100C) 27. Le Strat E, Lancin M, Fourches-Coulon M, Marhic c(1998) Philos Mag A 78: 189 7. As a general conclusion it may be said that the 28. Brennan J. Prewo KM(1982)J Mater Sci 17: 2371 thermal diffusivity can be used as a qualitative non- 29. Qui G, Spear KE, Pontano CG(1993)Mater Sci Eng A destructive technique to determine the integrity of 16245 te fibre/matrix interface and to monitor micro- 30. Winter W, bogdonaw C, Muller G, Panshorst W(199 structural changes occurring in the fibres, matrix Glass Technol Ber 66: 109 and interface during manufacturing or serviceBarium osumilite and celsian both start to crystallise at around 970 C, whereas the cordierite start to crystal￾lise at about 1,020 C and the highest percentage of crystallisation occurs at 1,100 C. Conclusions The following conclusions can be drawn from this study: 1. The interface is one of the key factors which affect thermal properties such as diffusivity of the composites. 2. Thermal properties were determined before and after heat treatment at various temperatures and times in air. It has been found that heat treatment at the lower temperatures causes a considerable degradation in the thermal diffusivity and the thermal expansion with the greatest affect being shown after 700 C heat treatment. However temperatures higher than 900 C heat treatments resulted in retention in the thermal property values and sometimes even higher thermal diffusivity values were obtained. 3. TEM analysis showed interfacial structure degra￾dation after heat treatments that were carried out at lower temperature (700 C) on glass ceramic matrix composites caused by the removal of carbon and the occurrence of gaps between fibre and matrix and isolated silicon rich bridges linking the two. 4. TEM analysis after higher heat treatment temper￾atures such as 1,200 C showed that the interfacial reaction layer was much thicker which sometimes resulted in higher values in the thermal diffusivity. 5. SEM studies show that at lower heat treatment temperature (700 C) residual glass in the matrix migrated to the voids in particular to interfaces after degradation of carbon layer at interfaces. 6. SEM studies indicated that crystallisation in the residual glass, which resulted in an increase in thermal properties of the composites, occurred after heat treatment at temperature (>1,100 C) 7. As a general conclusion it may be said that the thermal diffusivity can be used as a qualitative non￾destructive technique to determine the integrity of the fibre/matrix interface and to monitor micro￾structural changes occurring in the fibres, matrix and interface during manufacturing or service. Acknowledgements The authors would like to thank to NPL (National Physical Laboratory) provision of samples of composites and Mr. I. Brough and Mr. P. Kenway for assistance with SEM and TEM studies. R. Yilmaz would also like to thank to Sakarya University for financial support. References 1. Prewo PM, Brennan JJ, Layden GK (1986) Am Ceram Soc Bull 65:305 2. Brennan JJ, Chyung K, Taylor MP (1986) USA Patent No 4589900, May 20 3. Johnson LF, Hasselman DPH, Chung KJ (1987) J Am Ceram Soc 70:C135 4. Cooper RF, Chyung K (1987) J Mater Sci 22:3148 5. Bemson PM, Spear KE, Pontano CG (1988) Ceram Eng Sci Proc 9:63 6. Chaim R, Heuer AH (1991) J Am Ceram Soc 74:1663 7. Murty VSR, Li J, Lewis MH (1989) Ceram Eng Sci Proc 10:938 8. Bonney LA, Cooper RF (1990) J Am Ceram Soc 73:2916 9. Murthy VSR, Phoraoh MW, Lewis MH (1990) Inst Phys Conf Ser No 111. New Mater Appl 185 10. Lewis MH, Murthy VSR (1991) Compos Sci Technol 42:221 11. Lewis MH, Daniel AM, Chamberlian A, Pharaoh MV, Cain MG (1993) J Microsc 169:109 12. Yilmaz R (1998) PhD thesis. UMIST-UK 13. Bleay SM, Scott VD (1992) J Mater Sci 27:825 14. Plucknett KP, Sutherland S, Daniel AM, Cain RL, Taplin DMR, Lewis MH (1995) J Microsc 177:251 15. Kumar A, Knowles KM (1996) J Am Ceram Soc 79:2369 16. Pharaoh MW, Daniel AM, Lewis MH (1993) J Mater Sci Lett 12:998 17. Hasselman DPT (1988) Therm Conduct 19:383 18. Bhatt H, Donaldson KY, Hasselman DPH, Bhatt RT (1992) J Mater Sci 27:6653 19. Bhatt H, Donaldson KY, Hasselman DPH, Bhatt RT (1990) J Am Ceram Soc 73:312 20. Hasselman DPH, Venkatesawaron A, Yu M (1991) J Mater Sci Lett 17:1037 21. Hasselman DPH, Venkatesawaron A, Tawil H (1991) J Am Ceram Soc 74:1631 22. Tawil H, Bersen LD, Baskaran J, Hasselman DPH (1985) J Mater Sci 20:3201 23. Bhatt H, Donaldson KY, Hasselman DPH, Bhatt RT (1992) J Am Ceram Soc 75:334 24. Hasselmann DPH, Johnson T (1987) J Compos Mater 21:508 25. Parker WJ, Jenkins RJ, Butler CP, Abbot GL (1960) J Appl Phys 32:926 26. Taylor R (1980) J Phys E: Sci Instrum 13:1193 27. Le Strat E, Lancin M, Fourches-Coulon M, Marhic C (1998) Philos Mag A 78:189 28. Brennan JJ, Prewo KM (1982) J Mater Sci 17:2371 29. Qui G, Spear KE, Pontano CG (1993) Mater Sci Eng A 162:45 30. Winter W, Bogdonaw C, Muller G, Panshorst W (1993) Glass Technol Ber 66:109 123 J Mater Sci (2007) 42:763–771 771