J Mater sci(2007)42:4115-4119 DOI10.1007/s10853-007-1656-0 Effect of heat treatment in air on the thermal properties of sic fibre reinforced composite: Part 2 A magnesium aluminium silicate MAS) matrix glass ceramic composite R. Yilmaz·R. Taylor Abstract The thermal properties of a magnesium alu- reinforced glass ceramic composites. This carbon rich layer minium silicate (MAS)glass ceramic matrix composite has also been observed in MAs glass ceramic composites reinforced by SiC(Nicalon) fibres have been investigated This layer and its effect on the composite behaviour can be before and after heat treatment in the temperature range affected by the temperature to which the composites have 600-1, 200C. Within this temperature range, during the been exposed [2, 6, 9, 10 heat treatment at lower temperatures such as 600 and A systematic study the effect of heat treatment on the 700C, the oxidation of the carbon layer occurred and microstructure and thermal properties of a barium osumi mixture of silicon and carbon was formed in the interface. lite matrix, SiC fibre (Tyronno) reinforced glass cerar This results in a decrease in thermal diffusivity values. matrix composite has been reported in part 1 of this study After heat treatment at the temperatures higher than [11]. The changes that can occur during heat treatment are ,000C, the carbon layer was thickened and resulted in influenced by the nature of the interface formed between the higher thermal diffusivity values fibre and matrix during the processing. This in turn will be affected by the fibre and matrix chosen. In this study,a similar investigation has been carried out to monitor the effects of heat treatment on the microstructure and thermal Introduction diffusivity of a different system. In this case the system chosen was a magnesium alumina silicate (MAS) matrix SiC fibre reinforced glass ceramic matrix composites have composite reinforced with SiC(Nicalon) fibres been developing over last three decades as possible high performance materials for high temperature applications [1]. Magnesium aluminium silicate (MAS) matrix glass Experimental ceramic composites are candidate materials for high tem perature applications that have been investigated [2-6] Materials During the manufacturing stage, due to fibre and matrix reaction, a carbon rich layer is formed [7, 8] in SiC fibre The 0/90/45 degree laminated SiC/MAS cordierite com- posite was supplied by the National Physical Laboratory. This composite was manufactured by Corning using the glass slurry infiltration route followed by hot pressing. The R. Yilmaz(区) Technical Education Faculty, Metal Education Division, composite reinforcement was Nicalon fibres of approxi- Sakarya University, Esentepe Campus, 54187 Sakarya, Turkey mately 15 um in diameter. A fibre yarn was desized in a mail: ryilmaz@ sakarya. edu.tr tube furnace, drawn through a glass slurry and then wound onto a drum. The fibres were then dried to form a tape R. Taylor Manchester Materials Science Centre, University of Manchester before it was cut and stacked in a hot press. Hot pressing Institute of Science and Technology, Grosvenor Street, was carried out at a temperature above the softening point Manchester MI 7HS. England of glass but below the onset of crystallisation. After hot
Effect of heat treatment in air on the thermal properties of SiC fibre reinforced composite: Part 2 A magnesium aluminium silicate (MAS) matrix glass ceramic composite R. Yilmaz Æ R. Taylor Received: 1 January 2006 / Accepted: 13 April 2006 / Published online: 14 April 2007 Springer Science+Business Media, LLC 2007 Abstract The thermal properties of a magnesium aluminium silicate (MAS) glass ceramic matrix composite reinforced by SiC (Nicalon) fibres have been investigated before and after heat treatment in the temperature range 600–1,200 C. Within this temperature range, during the heat treatment at lower temperatures such as 600 and 700 C, the oxidation of the carbon layer occurred and mixture of silicon and carbon was formed in the interface. This results in a decrease in thermal diffusivity values. After heat treatment at the temperatures higher than 1,000 C, the carbon layer was thickened and resulted in the higher thermal diffusivity values. Introduction SiC fibre reinforced glass ceramic matrix composites have been developing over last three decades as possible high performance materials for high temperature applications [1]. Magnesium aluminium silicate (MAS) matrix glass ceramic composites are candidate materials for high temperature applications that have been investigated [2–6]. During the manufacturing stage, due to fibre and matrix reaction, a carbon rich layer is formed [7, 8] in SiC fibre reinforced glass ceramic composites. This carbon rich layer has also been observed in MAS glass ceramic composites. This layer and its effect on the composite behaviour can be affected by the temperature to which the composites have been exposed [2, 6, 9, 10]. A systematic study the effect of heat treatment on the microstructure and thermal properties of a barium osumilite matrix, SiC fibre (Tyronno) reinforced glass ceramic matrix composite has been reported in part 1 of this study [11]. The changes that can occur during heat treatment are influenced by the nature of the interface formed between fibre and matrix during the processing. This in turn will be affected by the fibre and matrix chosen. In this study, a similar investigation has been carried out to monitor the effects of heat treatment on the microstructure and thermal diffusivity of a different system. In this case the system chosen was a magnesium alumina silicate (MAS) matrix composite reinforced with SiC (Nicalon) fibres. Experimental Materials The 0/90/45 degree laminated SiC/MAS cordierite composite was supplied by the National Physical Laboratory. This composite was manufactured by Corning using the glass slurry infiltration route followed by hot pressing. The composite reinforcement was Nicalon fibres of approximately 15 lm in diameter. A fibre yarn was desized in a tube furnace, drawn through a glass slurry and then wound onto a drum. The fibres were then dried to form a tape before it was cut and stacked in a hot press. Hot pressing was carried out at a temperature above the softening point of glass but below the onset of crystallisation. After hot R. Yilmaz (&) Technical Education Faculty, Metal Education Division, Sakarya University, Esentepe Campus, 54187 Sakarya, Turkey e-mail: ryilmaz@sakarya.edu.tr R. Taylor Manchester Materials Science Centre, University of Manchester Institute of Science and Technology, Grosvenor Street, Manchester M1 7HS, England 123 J Mater Sci (2007) 42:4115–4119 DOI 10.1007/s10853-007-1656-0
4l16 J Mater Sci(2007)42:4115-4119 pressing, the glass matrix composite was given a two-stage Results and discussions nucleation and growth heat treatment to convert the glass matrix into a glass ceramic matrix X ray diffraction analysis X-ray diffraction analysis An Xrd trace of the as fabricated material from 10< 0<70 is shown in Fig. 1. Two phases can be detected o X-ray diffraction studies were carried out to identify all the cordierite (Mg2Al4SisO18) and surprisingly celsian phases present in the composite. These were performed (BaAl2Si2Og). This provides clear evidence that the base using a PhILIPS EXPERT diffractometer PW3710 X-ray frit from which this glass ceramic composite was fabricated analyses were carried out on both as fabricated and heat- contains some BaO. The presence of a peak at 20= 34.5 treated samples using plates 10 mm and 2 mm thick. shows that some crystalline Sic was present in the fibre. Scans at a step width of 0.005 for 20 values from 10 to Examination of the mound between 30 and 40 shows a 700 were used. The diffraction traces were compared significant glassy phase content was present. The formation against standard XRD patterns of a range of possible ma- of a-cordierite from mullite liquid is time and tempera trix constituents ture dependent and favoured by a slow cooling rate [4 Microstructural examination Thermal properties Polished sections of the composite for analysis were pre- Based on experience learned from studies of the BMAS pared by the following procedure. The samples were first composite [ll] only heat treatment times and temperatures cut from the plate. They were prepared by the method which are thought to be informative were selected. These mentioned in the first part 1 of this investigation [11]. were 600, 700, 1,000 and 1, 200C for 30 h. All heat Mounted samples were ground using by 400 grit Sic treatments were carried out in air. abrasive paper followed by successively finer grades of Figure 2 shows thermal diffusivity results obtained after silicon carbide papers from a 400 to 1200 grit. The samples heat treatment for 30 h at each of the four selected tem were then lightly polished using 6 and 1 um diamond peratures. After the heat treatment at 1,000C, the thermal paste. Final polishing was carried out with colloidal silica diffusivity results were consistently higher than that of the and samples were then washed, cleaned and dried. as-received material whereas the material heat treated at The samples were placed on to an aluminium stub and 1, 200C shows very similar values. The results, obtained coated with carbon or gold in order to prevent charging in for 600 and 700C, show lower thermal diffusivities than the microscope. A conducting silver paste was used with the as-received material and moreover show negligible the carbon-coated samples painted on the edge of the difference between the two heat treatment temperatures sample connecting it with the stub to improve electrical The thermal diffusivity for all heat treatment temperature contact. The surface of the heat-treated samples were converges on the as received results at surement examined using Philips 505 and 525 scanning electron temperatures for 1,000 and 1, 200C. This is in marked microscopes(SEM) operating at 20 kV. contrast to the results for SiC/BMAS composite where after Specimens were prepared for transmission electron all heat treatment temperatures the diffusivity maintains the microscopes(TEM) by a combination of mechanical same consistent difference over the whole temperature ishing and ion beam thinning techniques previously de scribed [ll]. The electron microscopy studies were carried out using Philips EM 400 and CM 20 microscopes operated at 120 and 200 kv both were equipped with an energy dispersive spectroscopy(EDS)analysis system 5100 Thermal properties Thermal diffusivity measurements were carried out using 8 the laser flash method originally described by Parker et al [12]. The thermal diffusivity equipment used at UMIST has been previously described in detail in a paper by Taylor [13]. Sample sizes and preparation were as detailed in part 1 and measurements again were arne d out over tempe Fig. 1 X-ray spectrum of as-received material of MAS/SiC ature range 100-1,000C [11]
pressing, the glass matrix composite was given a two-stage nucleation and growth heat treatment to convert the glass matrix into a glass ceramic matrix. X-ray diffraction analysis X-ray diffraction studies were carried out to identify all the phases present in the composite. These were performed using a PHILIPS E’XPERT diffractometer PW 3710. X-ray analyses were carried out on both as fabricated and heattreated samples using plates 10 mm2 and 2 mm thick. Scans at a step width of 0.005 for 2h values from 10 to 70 were used. The diffraction traces were compared against standard XRD patterns of a range of possible matrix constituents. Microstructural examination Polished sections of the composite for analysis were prepared by the following procedure. The samples were first cut from the plate. They were prepared by the method mentioned in the first part 1 of this investigation [11]. Mounted samples were ground using by 400 grit SiC abrasive paper followed by successively finer grades of silicon carbide papers from a 400 to 1200 grit. The samples were then lightly polished using 6 and 1 lm diamond paste. Final polishing was carried out with colloidal silica and samples were then washed, cleaned and dried. The samples were placed on to an aluminium stub and coated with carbon or gold in order to prevent charging in the microscope. A conducting silver paste was used with the carbon-coated samples painted on the edge of the sample connecting it with the stub to improve electrical contact. The surface of the heat-treated samples were examined using Philips 505 and 525 scanning electron microscopes (SEM) operating at 20 kV. Specimens were prepared for transmission electron microscopes (TEM) by a combination of mechanical polishing and ion beam thinning techniques previously described [11]. The electron microscopy studies were carried out using Philips EM 400 and CM 20 microscopes operated at 120 and 200 kV both were equipped with an energy dispersive spectroscopy (EDS) analysis system. Thermal properties Thermal diffusivity measurements were carried out using the laser flash method originally described by Parker et al. [12]. The thermal diffusivity equipment used at UMIST has been previously described in detail in a paper by Taylor [13]. Sample sizes and preparation were as detailed in part 1 and measurements again were carried out over temperature range 100–1,000 C [11]. Results and discussions X ray diffraction analysis An XRD trace of the as fabricated material from 10 < 2h < 70 is shown in Fig. 1. Two phases can be detected acordierite (Mg2Al4Si5O18) and surprisingly celsian (BaAl2Si2O8). This provides clear evidence that the base frit from which this glass ceramic composite was fabricated contains some BaO. The presence of a peak at 2h = 34.5 shows that some crystalline SiC was present in the fibre. Examination of the mound between 30 and 40 shows a significant glassy phase content was present. The formation of a-cordierite from mullite + liquid is time and temperature dependent and favoured by a slow cooling rate [4]. Thermal properties Based on experience learned from studies of the BMAS composite [11] only heat treatment times and temperatures which are thought to be informative were selected. These were 600, 700, 1,000 and 1,200 C for 30 h. All heat treatments were carried out in air. Figure 2 shows thermal diffusivity results obtained after heat treatment for 30 h at each of the four selected temperatures. After the heat treatment at 1,000 C, the thermal diffusivity results were consistently higher than that of the as-received material whereas the material heat treated at 1,200 C shows very similar values. The results, obtained for 600 and 700 C, show lower thermal diffusivities than the as-received material and moreover show negligible difference between the two heat treatment temperatures. The thermal diffusivity for all heat treatment temperature converges on the as received results at a measurement temperatures for 1,000 and 1,200 C. This is in marked contrast to the results for SiC/BMAS composite where after all heat treatment temperatures the diffusivity maintains the same consistent difference over the whole temperature Fig. 1 X-ray spectrum of as-received material of MAS/SiC composites 4116 J Mater Sci (2007) 42:4115–4119 123
J Mater Sci(2007)42:4115-4119 composite does not contain as much residual glassy phase the Sic/BMAS composite does [11] 0.009 TEM studies were only carried out on the samples of SiC/MAS. which were heat treated at 700 and 1.200 oC. gure 6 shows th gether with EDS data and a selected area diffraction pattern 0.007 700C. At the interface there is a clear peak for silicon with traces of oxygen and carbon. The selected area dif- fraction pattern shows that region is amorphous A TEM micrograph from the fibre/matrix interface of a 0 100 200 300 400 500 600 700 800 900 1000 1100 region heated to l,200C is shown in Fig. 7 together with a SAD pattern, which shows the region to be amorphous and two EDS analyses, one from near the fibre the other Fig. 2 Measurement of thermal di y of MAS/SiC CMC after from the centre of the interfacial region. Near to the fibre ent in air for 30 h interface can be seen a large Si peak and smaller peaks due to Mg, Al, O and C. The interface is also much thicker range [11]. To illustrate these points we compare, in Table 1(150 nm) than that observed after the lower temperature the results for two composites that heat treated in air for 30 h heat treatment and also much thicker than that observed in for three selected temperatures 100, 500, 900C he bmas material after a similar heat treatment [11] Microstructural studies SEM studies were carried out on the heat-treated samples As can be seen in Fig. 3, the sample heated at the lower In spite of the limited experimental data generated fror temperature(600C) showed significant amount of glassy this study it is clear that there are significant differences phase on the surface of the sample. Some glassy phase was thermal diffusivity values after at higher and lower tem present around the fibre was also evident. The same situ- perature heat treatments. After heat treatment at low ation seems to be occurring here. After removal of the peratures(600 and 700C), thermal diffusivity ahm carbon around the fibre gaps and voids occurred and these decrease significantly. After heat treatment at these were filled by the residual glassy phases present as in the peratures, as noted in the TEM micrographs, there is matrix. Here also cracks in the interface and debonding in the interface. This is a result of the oxidation of the between the fibre and matrix were observed(Fig 4). carbon to leave a silicon rich region noted in previous Similar observations were obtained in other studies [3, 9]. studies [10, 11 After the higher temperature heat treatment at 1,000 and The reduction in oxygen content of the interfacial layer 1, 200C the gaps around the fibre appeared to have dis- suggests that this mechanism may be a contributory factor appeared(Fig 5a, b)and also fine grain phases were ob- although not the only one to account for the dramatic de served. The higher temperature heat treatment seems to crease in thermal diffusivity values after heat treatment at provide improved bonding at the interface, which results in 700C. The rate of oxidation of C increases with the higher values of the thermal diffusivity. These SEM results temperature and the degradation is sl were in good agreement with the previous findings except kinetics of oxidation. Residual glassy phases in the matrix that recrystalisation was not as obvious as for the sem begin to soften with the temp erature results of SiC/BMAS composites. This may be because this At lower temperature, this flow was limited therefore,at Table 1 nary of the thermal diffusivity results measured at 100, 500 and 900C after heat treatment in air for 30 h erature(°C) Heat treatment temperature (C) l200 Thermal diffusivity(cm/s)x 10 l00 6.9 6 7.1
range [11]. To illustrate these points we compare, in Table 1 the results for two composites that heat treated in air for 30 h for three selected temperatures 100, 500, 900 C. Microstructural studies SEM studies were carried out on the heat-treated samples. As can be seen in Fig. 3, the sample heated at the lower temperature (600 C) showed significant amount of glassy phase on the surface of the sample. Some glassy phase was present around the fibre was also evident. The same situation seems to be occurring here. After removal of the carbon around the fibre gaps and voids occurred and these were filled by the residual glassy phases present as in the matrix. Here also cracks in the interface and debonding between the fibre and matrix were observed (Fig. 4). Similar observations were obtained in other studies [3, 9]. After the higher temperature heat treatment at 1,000 and 1,200 C the gaps around the fibre appeared to have disappeared (Fig. 5a, b) and also fine grain phases were observed. The higher temperature heat treatment seems to provide improved bonding at the interface, which results in higher values of the thermal diffusivity. These SEM results were in good agreement with the previous findings except that recrystalisation was not as obvious as for the SEM results of SiC/BMAS composites. This may be because this composite does not contain as much residual glassy phase as the SiC/BMAS composite does [11]. TEM studies were only carried out on the samples of SiC/MAS, which were heat treated at 700 and 1,200 C. Figure 6 shows the interface between fibre and matrix together with EDS data and a selected area diffraction pattern from a region near to the matrix for the sample heated to 700 C. At the interface there is a clear peak for silicon with traces of oxygen and carbon. The selected area diffraction pattern shows that region is amorphous. A TEM micrograph from the fibre/matrix interface of a region heated to 1,200 C is shown in Fig. 7 together with a SAD pattern, which shows the region to be amorphous and two EDS analyses, one from near the fibre the other from the centre of the interfacial region. Near to the fibre interface can be seen a large Si peak and smaller peaks due to Mg, Al, O and C. The interface is also much thicker (150 nm) than that observed after the lower temperature heat treatment and also much thicker than that observed in the BMAS material after a similar heat treatment [11]. Discussion In spite of the limited experimental data generated from this study it is clear that there are significant differences in thermal diffusivity values after at higher and lower temperature heat treatments. After heat treatment at low temperatures (600 and 700 C), thermal diffusivity values decrease significantly. After heat treatment at these temperatures, as noted in the TEM micrographs, there is a gap in the interface. This is a result of the oxidation of the carbon to leave a silicon rich region noted in previous studies [10, 11]. The reduction in oxygen content of the interfacial layer suggests that this mechanism may be a contributory factor although not the only one to account for the dramatic decrease in thermal diffusivity values after heat treatment at 700 C. The rate of oxidation of C increases with the temperature and the degradation is slower due to the kinetics of oxidation. Residual glassy phases in the matrix begin to soften with the temperature and flow into the gaps. At lower temperature, this flow was limited therefore, at Fig. 2 Measurement of thermal diffusivity of MAS/SiC CMC after heat treatment in air for 30 h Table 1 The summary of the thermal diffusivity results measured at 100, 500 and 900 C after heat treatment in air for 30 h Measurement temperature (C) Heat treatment temperature (C) As received 600 700 1000 1200 Thermal diffusivity (cm2 /s) · 103 100 8.5 7.4 7.4 9.2 8.7 500 6.9 6.3 6.5 7.4 6.9 900 7.1 7.1 – 7.1 7.1 J Mater Sci (2007) 42:4115–4119 4117 123
4l18 J Mater Sci(2007)42:4115-4119 ≈ (a) (b) Fig. 3 Back-scattered electron SEM images of the MAs matrix composite heated at 600C general microstructure showing glassy phase distribution in the matrix and around fibres lower heat treatment temperature such as 600 or 700C, the residual glassy phases attempt to flow to fill the voids at the interface or concentrate at local regions in the matrix. After heat treatment to higher temperatures such as 1. 000 and 1.200 oC. the microstructure of the interface hanges and the thickness increases to 150 nm. This is much higher then that noted 30 nm for SiC(Nicalon)/MAS composite [14] and 20 nm noted for SiC (Tyranno)/BMAS composite Plucknett et al. [10], Yilmaz et al. [11]. The Fig. 5 Back-scattered electron SEM images of the MAS matrix thermal diffusivity increases for the composite annealed at composite heated at (a)1,000C and(b) 1, 000C but is largely unchanged for the composite an nealed at1,200°C. nis is much larger than e chan e. The changes occurring after heat treatment and differ- BMAS [11]. The EDS data are particularly revealing and ences with the results for BMAS are of particular interest show with special emphasis on the changes occurring at the fibre/ matrix interface. The first noteworthy feature is that after (a) For the 700oCheat treatment, the carbon content of the heat treatments with all samples, the microstructure of the interface has decreased significantly. However, the interface changes. In particular at high temperatures(above carbon content increased after the 1200 C annealing 1,000C)the thickness of the interface increases mark- ( b) The Si content of the annealed samples has similar (c) Heat treatment of the sample at 1200C resulted in Mg, Al and Si exist in the interfacial layer, which suggested a concentration gradient inward from the Conclusions The following conclusion can be drawn from this study: 1. Thermal properties were determined after heat treat in the It has been found that heat treatment at lower tem- peratures(600 and 700C)causes a degradation in the ermal diffusivity. 2. Higher heat treatment temperatures (>1, 000C)re Fig. 4 Back-scattered electron SEM images of SiC/MAS composite sulted in a retention in the thermal property values and showing crack in the matrix and gap around the fibre heat treatment at sometimes even higher thermal diffusivity values were 700°C
lower heat treatment temperature such as 600 or 700 C, the residual glassy phases attempt to flow to fill the voids at the interface or concentrate at local regions in the matrix. After heat treatment to higher temperatures such as 1,000 and 1,200 C, the microstructure of the interface changes and the thickness increases to ~150 nm. This is much higher then that noted 30 nm for SiC (Nicalon)/MAS composite [14] and 20 nm noted for SiC (Tyranno)/BMAS composite Plucknett et al. [10], Yilmaz et al. [11]. The thermal diffusivity increases for the composite annealed at 1,000 C but is largely unchanged for the composite annealed at 1,200 C. The changes occurring after heat treatment and differences with the results for BMAS are of particular interest with special emphasis on the changes occurring at the fibre/ matrix interface. The first noteworthy feature is that after heat treatments with all samples, the microstructure of the interface changes. In particular at high temperatures (above 1,000 C) the thickness of the interface increases markedly, this is much larger than the change observed for BMAS [11]. The EDS data are particularly revealing and show: (a) For the 700 C heat treatment, the carbon content of the interface has decreased significantly. However, the carbon content increased after the 1200 C annealing. (b) The Si content of the annealed samples has similar. (c) Heat treatment of the sample at 1200 C resulted in Mg, Al and Si exist in the interfacial layer, which suggested a concentration gradient inward from the matrix. Conclusions The following conclusion can be drawn from this study: 1. Thermal properties were determined after heat treatment of composites at various temperatures in the air. It has been found that heat treatment at lower temperatures (600 and 700 C) causes a degradation in the thermal diffusivity. 2. Higher heat treatment temperatures (>1,000 C) resulted in a retention in the thermal property values and sometimes even higher thermal diffusivity values were obtained. Fig. 3 Back-scattered electron SEM images of the MAS matrix composite heated at 600 C general microstructure showing glassy phase distribution in the matrix and around fibres Fig. 4 Back-scattered electron SEM images of SiC/MAS composite showing crack in the matrix and gap around the fibre heat treatment at 700 C Fig. 5 Back-scattered electron SEM images of the MAS matrix composite heated at (a) 1,000 C and (b) 1,200 C 4118 J Mater Sci (2007) 42:4115–4119 123
J Mater Sci(2007)42:4115-4119 4119 m Fibre Interface Interface Matrix 200un 一200mun Fig 6 TEM bright field image, energy dispersive spectrometry spectra and SAD pattern from interfaces of the sample heated at Fig. 7 TEM bright field image, SAD pattern and energy dispersive 700 pectrometry spectra from interfaces of the sample heated at 1, 200C 3. TEM analysis after higher heat treatment temperatures References such as 1.200 oC showed that the interfacial reaction layer was much thicker which sometimes resulted in I. Prewo PM, Brennan JJ, Layden GK(1986)Am Ceram Soc Bul higher values in the thermal diffusivity 2. Kumar A, Knowles KM(1996)J Am Ceram Soc 79: 2369 4. Thermal diffusivity values of the composites exposed 3. Kumar A, Knowles KM(1996) Acta Met 44: 2923 heat treatments at lower temperatures between 600 and 4. Kumar A, Knowles KM(1996)Acta 700oC. resulted in significant decrease in the values of 5. Reich C, Bruckner R(1997)Com Sci 6. Labrugere C, Guillaumat L, Guette R(1999) thermal diffusivit 5. SeM studies show that at lower heat treatment tem Chyung K(1987)J Mater Sci 22: 3 148 peratures(600-700C)residual glass in the matrix 8 PM, Spear KE, Pontano CG(1988)Ceram Eng migrated to voids in particular to interfaces after degradation of carbon layer at interfaces 10. Plucknett KP, Sutherland S, Daniel AM, Cain RL, Taplin Acknowledgements The authors would like to thank to NPL (Na Yilmaz R tional Physical Laboratory) provision of samples of composites and 12. Parker WJ, CP, Abbot GL (1960)J Appl Phys 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 13. Taylor R(980)J Phy Instrum 13: 1193 its financial support. 14. Yilmaz r(1998)PhD thesis UMIST-UK 9 Spring
3. TEM analysis after higher heat treatment temperatures such as 1,200 C showed that the interfacial reaction layer was much thicker which sometimes resulted in higher values in the thermal diffusivity. 4. Thermal diffusivity values of the composites exposed heat treatments at lower temperatures between 600 and 700C, resulted in significant decrease in the values of thermal diffusivity. 5. SEM studies show that at lower heat treatment temperatures (600–700 C) residual glass in the matrix migrated to voids in particular to interfaces after degradation of carbon layer at interfaces. 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 its financial support. References 1. Prewo PM, Brennan JJ, Layden GK (1986) Am Ceram Soc Bull 65:305 2. Kumar A, Knowles KM (1996) J Am Ceram Soc 79:2369 3. Kumar A, Knowles KM (1996) Acta Met 44:2923 4. Kumar A, Knowles KM (1996) Acta Met 44:2901 5. Reich C, Bru¨ckner R (1997) Com Sci Tech. 57:533 6. Labrugere C, Guillaumat L, Guette A, Naslain R (1999) J Eur Ceram Soc 19:17 7. Cooper RF, Chyung K (1987) J Mater Sci 22:3148 8. Bemson PM, Spear KE, Pontano CG (1988) Ceram Eng Sci Pro 9:663 9. Bleay SM, Scott VD (1992) J Mater Sci 27:825 10. Plucknett KP, Sutherland S, Daniel AM, Cain RL, Taplin DMR, Lewis MH (1995) J Microscopy 177:251 11. Yilmaz R, Taylor R (2007) J Mater Sci 42:763 12. Parker WJ, Jenkins RJ, Butler CP, Abbot GL (1960) J Appl Phys 32:926 13. Taylor R (1980) J Phys E: Sci Instrum 13:1193 14. Yilmaz R (1998) PhD thesis UMIST-UK Fig. 6 TEM bright field image, energy dispersive spectrometry spectra and SAD pattern from interfaces of the sample heated at 700 C Fig. 7 TEM bright field image, SAD pattern and energy dispersive spectrometry spectra from interfaces of the sample heated at 1,200 C J Mater Sci (2007) 42:4115–4119 4119 123
Copyright of Journal of Materials Science is the property of Springer Science Business Media B.V. and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holders express written permission. However, users may print, download or email articles for individual use