Effect of sintering temperature on Ba0-Al2o Sio, glass ceramic coating for carbon fibre o reinforced silicon carbide matrix composites X. H Zheng , Y.G. Du, ). Y. Xiao, W.J. Zhang and C. Y Liang Bao-Al2O3-SiO2(BAS)glass ceramic coatings were prepared on carbon fibre reinforced silicon carbide matrix composites(C/SiC)by in situ sintering. The effect of sintering temperature on the final phase and microstructure of the coatings were studied. The results show that higher degree of crystallisation in the Bas glass is achieved at higher sintering temperatures and more crystalloids are melted by the residual glass with low viscosity at the same time. Considering these two factors, the crystallinity of Bas glass ceramic should have a peak value at a specific sintering temperature. The sample sintered at 1473 K has an obvious transition layer of 40 um in thickness between the coating and the composite, which enhances the adhesion strength between them. The oxidation resistance of C/SiC composites with BAS protective coatings was characterised using isothermal oxidation tests at 1773 K for 15 min. The weight loss of the composites with BAS coatings is decreased with the increase of the sintering temperature Keywords: Composite materials, Glass ceramics, Coatings, Sintering Introduction phases was studied. The phase composition and micro- structure of coatings sintered at different temperatures Carbon fibre reinforced silicon carbide(C/SiC) compo- were characterised and their oxidation resistance was ites have potential use as the key engine components in tested aeronautics and space applications. Precursor infiltra tion and pyrolysis(PIP)is an efficient and low cost method to prepare C/SiC composites, but defects in the Experimental procedure composites made by PIP are inevitably. In addition, the The C/SiC composites used in the present work were thermal mismatch between the carbon fibre and silicon made by the PIP method in the National University of arbide also causes defects in composites. These defects Defense Technology in China. The samples used in the ll cause the rapid oxidation of composites in oxygen present work were 10x 4 mm in size. After being rich atmospheres above 673 K. As a result, the applica- cleaned with water and ethanol, the samples were dried tions of C/Sic composites within oxidising atmospheres at 423K The BAs glass ceramic coatings were prepared by Applying resistant coatings to the surface of carbon situ reaction method with BAS glass as starting composites is an effective way to protect the composites materials on the surface of the C/SiC composites at from oxidation. Glass ceramic is composed of crystal designated temperatures. The starting composition of phase and glass phase. At high temperatures, the high the bAs glass was: 37BaO-29SiO3-24A12O3-6B2O3- melting point crystalline phase provides strength for the 2ZrO2-2Co203(wt-%). Reagent grade powders were coating and helps to retain its shape, while the glass will weighed, mixed together and then melted in a platinum melt and flow into cracks in the coating and composite. crucible at 1823 K for 2 h. The melt was quenched in Bao-AlO3-Sio2(BAS) glass ceramic has the highest distilled water to form glass frits, which were subse melting point of 2033 K among glass ceramic materials, quently milled in distilled water for 2 h to obtain glas which makes it an attractive candidate for protective powder. The mean particle size of the fine glass powder coating materials. The main objective of the present was 2-3 um. An organic solvent was designed: 10 wt-% research is the preparation and testing of bas glass tirbutyl citrate, 79. 2 wt-% butyl carbitol, 2.8 wt-% ethyl paper,the effect of sintering temperature on the final The bas glass powder(70- o- 1.4-butyrolactone was mixed into the organic solvent(30 wt-%) to create a suspending glass paste. The glass paste was applied to all sides of the C/ Materials Engineering, National University of SiC composites with brush and then the assembly was Defense Technology, Changsha 410073, China dried in a furnace at 423 K for 20 min. The resulting corrEspondingauthoremailzheng_nudt@163.com samples covered by green glass coatings were fired at a 2008 Institute of Materials, Minerals and Mining accepted 9 May 2008 Do10.1179/174328408X323122 Materials Science and Technology 2008 VOL 24 No 11 1399
Effect of sintering temperature on BaO–Al2O3– SiO2 glass ceramic coating for carbon fibre reinforced silicon carbide matrix composites X. H. Zheng*, Y. G. Du, J. Y. Xiao, W. J. Zhang and C. Y. Liang BaO–Al2O3–SiO2 (BAS) glass ceramic coatings were prepared on carbon fibre reinforced silicon carbide matrix composites (C/SiC) by in situ sintering. The effect of sintering temperature on the final phase and microstructure of the coatings were studied. The results show that higher degree of crystallisation in the BAS glass is achieved at higher sintering temperatures and more crystalloids are melted by the residual glass with low viscosity at the same time. Considering these two factors, the crystallinity of BAS glass ceramic should have a peak value at a specific sintering temperature. The sample sintered at 1473 K has an obvious transition layer of 40 mm in thickness between the coating and the composite, which enhances the adhesion strength between them. The oxidation resistance of C/SiC composites with BAS protective coatings was characterised using isothermal oxidation tests at 1773 K for 15 min. The weight loss of the composites with BAS coatings is decreased with the increase of the sintering temperature. Keywords: Composite materials, Glass ceramics, Coatings, Sintering Introduction Carbon fibre reinforced silicon carbide (C/SiC) composites have potential use as the key engine components in aeronautics and space applications.1 Precursor infiltration and pyrolysis (PIP) is an efficient and low cost method to prepare C/SiC composites,2 but defects in the composites made by PIP are inevitably. In addition, the thermal mismatch between the carbon fibre and silicon carbide also causes defects in composites.3 These defects will cause the rapid oxidation of composites in oxygen rich atmospheres above 673 K. As a result, the applications of C/SiC composites within oxidising atmospheres are limited. Applying resistant coatings to the surface of carbon composites is an effective way to protect the composites from oxidation.4,5 Glass ceramic is composed of crystal phase and glass phase. At high temperatures, the high melting point crystalline phase provides strength for the coating and helps to retain its shape, while the glass will melt and flow into cracks in the coating and composite.6 BaO–Al2O3–SiO2 (BAS) glass ceramic has the highest melting point of 2033 K among glass ceramic materials,7 which makes it an attractive candidate for protective coating materials. The main objective of the present research is the preparation and testing of BAS glass ceramic coatings on C/SiC composites. In the present paper, the effect of sintering temperature on the final phases was studied. The phase composition and microstructure of coatings sintered at different temperatures were characterised and their oxidation resistance was tested. Experimental procedure The C/SiC composites used in the present work were made by the PIP method in the National University of Defense Technology in China.8 The samples used in the present work were 106564 mm in size. After being cleaned with water and ethanol, the samples were dried at 423 K. The BAS glass ceramic coatings were prepared by in situ reaction method with BAS glass as starting materials on the surface of the C/SiC composites at designated temperatures. The starting composition of the BAS glass was: 37BaO–29SiO2–24Al2O3–6B2O3– 2ZrO2–2Co2O3 (wt-%). Reagent grade powders were weighed, mixed together and then melted in a platinum crucible at 1823 K for 2 h. The melt was quenched in distilled water to form glass frits, which were subsequently milled in distilled water for 2 h to obtain glass powder. The mean particle size of the fine glass powder was 2–3 mm. An organic solvent was designed: 10 wt-% tirbutyl citrate, 79?2 wt-% butyl carbitol, 2?8 wt-% ethyl cellulose, 3 wt-% span-85, 5 wt-% 1,4-butyrolactone. The BAS glass powder (70 wt-%) was mixed into the organic solvent (30 wt-%) to create a suspending glass paste. The glass paste was applied to all sides of the C/ SiC composites with brush and then the assembly was dried in a furnace at 423 K for 20 min. The resulting samples covered by green glass coatings were fired at College of Aerospace & Materials Engineering, National University of Defense Technology, Changsha 410073, China *Corresponding author, email zheng_nudt@163.com 2008 Institute of Materials, Minerals and Mining Published by Maney on behalf of the Institute Received 26 February 2008; accepted 9 May 2008 DOI 10.1179/174328408X323122 Materials Science and Technology 2008 VOL 24 NO 11 1399
Zheng et aL Effect of sintering temperature on Ba0-AL03-SiO glass ceramic coating a Hexagonal-BaAl, Si, O 77-0189 the glass ceramic coating sintered at 1473 K. As the sintering temperature increases, the crystals in the Monoclinic-BaAl i10 38-1450 ceramic phase of the coating grow more rapidly, which increases the percent of crystalloids in the coating. At the same time, the viscosity of the glass phase decreases and more crystalloids dissolve into the melt, which reduces the overall quantity of crystalloids in the coating. These two factors compete during sintering to determine the final crystallinity of glass ceramic coat- 1323K ngs. The optimum conditions are achieved at 1323K as evidenced the high degree of the crystallinity of the ngs fired at that temperature the sintering temperature, all the 1473K coatings contain two crystalline phases: hexacelsian and monoclinic celsian. During the heat treatment, the first phase to crystallise from bas glass is the 60 metastable, high temperature hexacelsian phase, rather than the stable, low temperature monoclinic celsian x-ray diffraction patterns of Bao-A120-Sio 2 glass phase. The rate of hexacelsian to monoclinic celsian eramic coatings fired at different temperatures transformation in BAs glass ceramic is very slug The transformation can be accelerated by increasing the sintering temperature, prolonging the sintering time, temperatures of 1123, 1323 and 1473 K in an argon usIng isostatic pressing" or adding proper nucleation rotective atmosphere to obtain the bas glass ceramic agents. In the present study, more monoclinic celsian phase is detected at higher temperatures The phase composition of the fired coatings was Morphology of glass ceramic coatings analysed by X-ray diffraction (XRD). The morphology After the sintering process, the coatings on the and microstructure of the glass ceramic coatings was composite samples were dense and crack free. In the characterised by scanning electron microscopy (SEM) sintering, BAs glass powders are softened at 1053 K, and the element distribution of the interface between the and densification are achieved. Then at temperatures coatings and composites was studied using SEM and above 1093 K, crystallisation occurs in the dense glass energy dispersive spectroscopy (EDS). The oxidation coating.Because the onset of cry stallisation occurs resistance of the coatings was tested using isothermal after the glass has fully densified, BAS glass ceramic oxidation tests at 1773 K for 30 min. The samples were coatings are dense by sintering weighed before and after the oxidation on an electronic balance with a sensitivity of +0-1 mg The cross-sections of the samples with glass ceram coatings are shown in Fig. 2. No obvious defects are detected in the interfaces between the coatings and Results and discussion composites. The sample fired at 1123K has a very clear Crystallographic component of coatings interface, while the sample fired at 1473K has a transition layer between the coating and the composite. During the sintering process, the glass in the protective The layer is about 40 um in thickness. Based on the coatings crystallises to form glass ceramic, and a dense, location of carbon fibres in the transition layer, a crack free coating is fabricated. Figure I shows the conclusion can be drawn that the transition layer is XRD patterns of the glass ceramic coatings prepared at formed by the diffusion of the surface phase into the different temperatures. The coatings prepared at differ- composites. To test this theory, a line profile for the ent temperatures show different degrees of crystallinity. coating was taken on. The position of the line profile is The surface coating of composites fired at 1323 K shows marked in Fig. 2, and the results of the test are shown in the highest degree of crystallinity, which falls sharply in Fig 3. The content of Ba increases gradually in the transition lay 50um 50 2 Morphologies of cross-section of celsian glass ceramic coatings fired at different temperatures 1400 Materials Science and Technol 2008vou24No11
temperatures of 1123, 1323 and 1473 K in an argon protective atmosphere to obtain the BAS glass ceramic coatings. The phase composition of the fired coatings was analysed by X-ray diffraction (XRD). The morphology and microstructure of the glass ceramic coatings was characterised by scanning electron microscopy (SEM) and the element distribution of the interface between the coatings and composites was studied using SEM and energy dispersive spectroscopy (EDS). The oxidation resistance of the coatings was tested using isothermal oxidation tests at 1773 K for 30 min. The samples were weighed before and after the oxidation on an electronic balance with a sensitivity of ¡0?1 mg. Results and discussion Crystallographic component of coatings During the sintering process, the glass in the protective coatings crystallises to form glass ceramic, and a dense, crack free coating is fabricated. Figure 1 shows the XRD patterns of the glass ceramic coatings prepared at different temperatures. The coatings prepared at different temperatures show different degrees of crystallinity. The surface coating of composites fired at 1323 K shows the highest degree of crystallinity, which falls sharply in the glass ceramic coating sintered at 1473 K. As the sintering temperature increases, the crystals in the ceramic phase of the coating grow more rapidly, which increases the percent of crystalloids in the coating. At the same time, the viscosity of the glass phase decreases and more crystalloids dissolve into the melt, which reduces the overall quantity of crystalloids in the coating. These two factors compete during sintering to determine the final crystallinity of glass ceramic coatings. The optimum conditions are achieved at 1323 K as evidenced the high degree of the crystallinity of the coatings fired at that temperature. Regardless of the sintering temperature, all the coatings contain two crystalline phases: hexacelsian and monoclinic celsian. During the heat treatment, the first phase to crystallise from BAS glass is the metastable, high temperature hexacelsian phase, rather than the stable, low temperature monoclinic celsian phase.9 The rate of hexacelsian to monoclinic celsian transformation in BAS glass ceramic is very sluggish. The transformation can be accelerated by increasing the sintering temperature, prolonging the sintering time,10 using isostatic pressing11 or adding proper nucleation agents.12 In the present study, more monoclinic celsian phase is detected at higher temperatures. Morphology of glass ceramic coatings After the sintering process, the coatings on the composite samples were dense and crack free. In the sintering, BAS glass powders are softened at 1053 K, and densification are achieved. Then at temperatures above 1093 K, crystallisation occurs in the dense glass coating.13 Because the onset of crystallisation occurs after the glass has fully densified, BAS glass ceramic coatings are dense by sintering.14 The cross-sections of the samples with glass ceramic coatings are shown in Fig. 2. No obvious defects are detected in the interfaces between the coatings and composites. The sample fired at 1123 K has a very clear interface, while the sample fired at 1473 K has a transition layer between the coating and the composite. The layer is about 40 mm in thickness. Based on the location of carbon fibres in the transition layer, a conclusion can be drawn that the transition layer is formed by the diffusion of the surface phase into the composites. To test this theory, a line profile for the coating was taken on. The position of the line profile is marked in Fig. 2, and the results of the test are shown in Fig. 3. The content of Ba increases gradually in the 1 X-ray diffraction patterns of BaO–Al2O3–SiO2 glass ceramic coatings fired at different temperatures 2 Morphologies of cross-section of celsian glass ceramic coatings fired at different temperatures Zheng et al. Effect of sintering temperature on BaO–Al2O3–SiO2 glass ceramic coating 1400 Materials Science and Technology 2008 VOL 24 NO 11
Zheng et aL. Effect of sintering temperature on Ba0-AL203-SiOa glass ceramic coating transition layer 20 8留 10 1001150120 50 Distance /um 4 Thermal oxidation curves (1773 k of coated samples fired at different temperatures 3 Energy dispersive spectroscopy line profiles of Ba, AI Si,O and C from composite to coating fired at 1473 K materials were absent from the samples. However, the average weight loss of these samples is only 7-62% transition layer from the composite to the coating The transition layer is important for the protective However, other elements in the coating such as Al and Si efficiency of BAS coatings. On the one hand, it has a change minimally. The areas around the carbon fibres graded composition which reduced the thermal mis- are as bright as the coating and EDS patterns show that match between the coating and composite Lowering the this area has a high Ba content. The diffusion of Ba mismatch can result in the reduction of the susceptibility makes the coating bind tightly with the composite. The of glass ceramic coatings to cracks On the other hand, samples with coatings sintered at different temperatures the transition layer has good adhesion strength to both were hoisted and fell from 2 m high. This test was the coating and composite because it is formed by the repeated for 8 times. After that, the coating sintered at diffusion of coating materials. Both of the effects do 1323 K was broken and fell off the surface of comp improve the protective capabilit meanwhile, the coatings sintered at 1323 and 1473 K Glass with low viscosity seals the defects in the surface adhesion strength of the interface between the composite composite. However, glass with too low viscosity may and the coating is excellent after processing at higher flow easily down from the surface of the composite. If temperatures above 1323 K. oxidised for longer periods, the e surrace coating will Oxidation tests protective ability may be lost entirely. The coatings Isothermal oxidation tests were carried out at 1773 K sintered at 1473 K, which have more glass phase, are for 30 min. After oxidation, the surfaces of the samples easier to flow off the samples at high temperatures, such prepared at 1123 K were cracked, and some coatings as 1773 K. Consequently, the higher sintering tempera flaked off. Whereas, the coatings prepared at 1323 and tures at 1473 K are impeded for the stability of glass 1473 K were glassy and fat after testing. As Fig. 1 ceramic coatings at high temperatures. Considering the indicates, the coating prepared at 1123 K has more protective capability and the stability at high tempera hexacelsian phase. The hexagonal celsian phase has a tures, the optimal temperature for heat treatment is high coefficient of thermal expansion (CTE) 1323 K in the present work To improve the oxidation (8 10K ). Consequently, the CTE of this coating resistance of the glass ceramic coating, the temperature is much higher than that of the composite (2- dependant viscosity of the coating should be adjusted to 3 K). During the cooling process, thermal an optimal value. stresses cause the formation of cracks in the outer the cracks and oxidises the composite. The cte of conclusions monoclinic celsian is 3 x10-6K, which is close to that bAS glass ceramic is an appropriate candidate material of composite. As a result, samples fired at 1323 and to protect C/SiC composites from oxidation at high 1473 K can retain tightly on the C/Sic composite after temperatures. With the increase of sintering tempera- oxidation tests. Figure 4 shows the weight loss of the ture the crystallisation of bas glass ceramic has a peak samples fired at different temperatures. The weight loss value. Meanwhile, the diffusion of the elements in BAS of the samples decreases with the increase of processing glass ceramic is favourable and a transition layer is temperature. The weight loss of the samples prepared at formed between the coating and the composite. This 1123 K is the highest, 21-88%. The coating fired at transition layer improves the adhesion strength of the 1323 K retained its surface morphology after oxidation coating to the composite and reduces the thermal stress testing, with only minor microcracks and a weight loss in the coating. The oxidation resistance of bas glass of 15.25%. During the course of oxidation, the coatings ceramic coated C/SiC composites is improved by the prepared at 1473 K flowed badly and some coating increase in the sintering temperature. However, the Materials Science and Technology 2008 VOL 24 No 11 1401
transition layer from the composite to the coating. However, other elements in the coating such as Al and Si change minimally. The areas around the carbon fibres are as bright as the coating and EDS patterns show that this area has a high Ba content. The diffusion of Ba makes the coating bind tightly with the composite. The samples with coatings sintered at different temperatures were hoisted and fell from 2 m high. This test was repeated for 8 times. After that, the coating sintered at 1323 K was broken and fell off the surface of composite; meanwhile, the coatings sintered at 1323 and 1473 K kept dense and integrated. The result shows that the adhesion strength of the interface between the composite and the coating is excellent after processing at higher temperatures above 1323 K. Oxidation tests Isothermal oxidation tests were carried out at 1773 K for 30 min. After oxidation, the surfaces of the samples prepared at 1123 K were cracked, and some coatings flaked off. Whereas, the coatings prepared at 1323 and 1473 K were glassy and flat after testing. As Fig. 1 indicates, the coating prepared at 1123 K has more hexacelsian phase. The hexagonal celsian phase has a high coefficient of thermal expansion (CTE) (861026 K21 ).15 Consequently, the CTE of this coating is much higher than that of the composite (2– 361026 K21 ). During the cooling process, thermal stresses cause the formation of cracks in the outer coating and oxygen diffuses into the composite through the cracks and oxidises the composite. The CTE of monoclinic celsian is 361026 K21 , which is close to that of composite. As a result, samples fired at 1323 and 1473 K can retain tightly on the C/SiC composite after oxidation tests. Figure 4 shows the weight loss of the samples fired at different temperatures. The weight loss of the samples decreases with the increase of processing temperature. The weight loss of the samples prepared at 1123 K is the highest, 21?88%. The coating fired at 1323 K retained its surface morphology after oxidation testing, with only minor microcracks and a weight loss of 15?25%. During the course of oxidation, the coatings prepared at 1473 K flowed badly and some coating materials were absent from the samples. However, the average weight loss of these samples is only 7?62%. The transition layer is important for the protective efficiency of BAS coatings. On the one hand, it has a graded composition which reduced the thermal mismatch between the coating and composite. Lowering the mismatch can result in the reduction of the susceptibility of glass ceramic coatings to cracks. On the other hand, the transition layer has good adhesion strength to both the coating and composite, because it is formed by the diffusion of coating materials. Both of the effects do improve the protective capability. Glass with low viscosity seals the defects in the surface effectively and prevents the diffusion of oxygen into the composite. However, glass with too low viscosity may flow easily down from the surface of the composite. If oxidised for longer periods, the surface coating will become too thin to protect the composite and its protective ability may be lost entirely. The coatings sintered at 1473 K, which have more glass phase, are easier to flow off the samples at high temperatures, such as 1773 K. Consequently, the higher sintering temperatures at 1473 K are impeded for the stability of glass ceramic coatings at high temperatures. Considering the protective capability and the stability at high temperatures, the optimal temperature for heat treatment is 1323 K in the present work. To improve the oxidation resistance of the glass ceramic coating, the temperature dependant viscosity of the coating should be adjusted to an optimal value. Conclusions BAS glass ceramic is an appropriate candidate material to protect C/SiC composites from oxidation at high temperatures. With the increase of sintering temperature, the crystallisation of BAS glass ceramic has a peak value. Meanwhile, the diffusion of the elements in BAS glass ceramic is favourable and a transition layer is formed between the coating and the composite. This transition layer improves the adhesion strength of the coating to the composite and reduces the thermal stress in the coating. The oxidation resistance of BAS glass ceramic coated C/SiC composites is improved by the increase in the sintering temperature. However, the 3 Energy dispersive spectroscopy line profiles of Ba, Al, Si, O and C from composite to coating fired at 1473 K 4 Thermal oxidation curves (1773 K) of coated samples fired at different temperatures Zheng et al. Effect of sintering temperature on BaO–Al2O3–SiO2 glass ceramic coating Materials Science and Technology 2008 VOL 24 NO 11 1401
Zheng et aL Effect of sintering temperature on Ba0-AL03-SiO glass ceramic coating coa tings sintered at 1473 K flow severely off the 6.L.F. Cheng Y. D Xu, L.T. Zhang and R Gao: Carbon, 2001, 39 posite at the test temperature, and the coating cannot keep integrality. As a result, 1323 K is the 7. G. Gouadec. P. Colomban and N. P. Bansal: J. Am. Cera. Soc. 2001.84.1129-1135 ptimal sintering temperature. 8.X. B. He, X. H. Qu, C. R. Zhang and X. G. Zhou: Rare Mel. Mater. Eng. 2005. 34 9. M.J. Hyatt and N. P. Bansal: J. eferences I.R. Naslain: Compos. Sci. Technol., 2004, 64, 155-170. Zhou:J. Chn. Ceram Soc. 2008. 36. 128-131 2. w. w. Zheng, Z. H. Cheng, Q. S. Ma and F. Li: J. Mater. Se 1.N. P Bansal and C. H. drummond: Mater. Sci. Left. 1994. 13 53-55 2004,39,3521-3522. 12. C. Liu, S. Komarneni and R. Roy: J. AIm. Cera. Soc., 1995, 78 3 ng, L. F. Cheng, L. T. Zhang and Y. D. Xu: Mater. Left, 3245-3247 13. Y. F Lu,Y G. Du, J. Y. Xiao and w.J. Zhang: J Inorg. Mater. 4. Q.G. Fu, H.J. Li. x. H. Shi, K.Z. Li, J. Wei and M. huang 14. A.R. Boccaccini, w. Stumpfe, D. M.R. Taplin and C. B Ponton 5. J. Zhao, L. Liu Q. Guo, J. L. Shi and G. T. Zhai: Mater. Lett. Mater. Sci. Eng. A. 1996. A219. 26-3 200660.1964-1967 15. N. P. Bansal and M. J Hyatt: J. Mater. Res, 1989, 4, 1257-1265. 1402 Materials Science and Technol 2008voL24 011
coatings sintered at 1473 K flow severely off the composite at the test temperature, and the coating cannot keep integrality. As a result, 1323 K is the optimal sintering temperature. References 1. R. Naslain: Compos. Sci. Technol., 2004, 64, 155–170. 2. W. W. Zheng, Z. H. Cheng, Q. S. Ma and F. Li: J. Mater. Sci., 2004, 39, 3521–3522. 3. Q. Zhang, L. F. Cheng, L. T. Zhang and Y. D. Xu: Mater. Lett., 2006, 60, 3245–3247. 4. Q. G. Fu, H. J. Li, X. H. Shi, K. Z. Li, J. Wei and M. Huang: Mater. Lett, 2006, 60, 431–434. 5. J. Zhao, L. Liu, Q. Guo, J. L. Shi and G. T. Zhai: Mater. Lett., 2006, 60, 1964–1967. 6. L. F. Cheng, Y. D. Xu, L. T. Zhang and R. Gao: Carbon, 2001, 39, 1127–1133. 7. G. Gouadec, P. Colomban and N. P. Bansal: J. Am. Cera. Soc., 2001, 84, 1129–1135. 8. X. B. He, X. H. Qu, C. R. Zhang and X. G. Zhou: Rare Mel. Mater. Eng., 2005, 34, 579–580. 9. M. J. Hyatt and N. P. Bansal: J. Mater. Sci., 1996, 31, 172–184. 10. X. H. Zheng, Y. G. Du, J. Y. Xiao, Y. F. Lu, J. F. Wu and W. Y. Zhou: J. Chn. Ceram. Soc., 2008, 36, 128–131. 11. N. P. Bansal and C. H. Drummond: J. Mater. Sci. Lett., 1994, 13, 53–55. 12. C. Liu, S. Komarneni and R. Roy: J. Am. Cera. Soc., 1995, 78, 2521–2526. 13. Y. F. Lu, Y. G. Du, J. Y. Xiao and W. J. Zhang: J. Inorg. Mater., 2008, 23, 159–164. 14. A. R. Boccaccini, W. Stumpfe, D. M. R. Taplin and C. B. Ponton: Mater. Sci. Eng. A, 1996, A219, 26–31. 15. N. P. Bansal and M. J. Hyatt: J. Mater. Res., 1989, 4, 1257–1265. Zheng et al. Effect of sintering temperature on BaO–Al2O3–SiO2 glass ceramic coating 1402 Materials Science and Technology 2008 VOL 24 NO 11
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