- Email: [email protected]
C composites by hydrothermal treatment in two types of solution
Materials Science and Engineering C 29 (2009) 2019–2023
Contents lists available at ScienceDirect
Materials Science and Engineering C j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / m s e c
Transformation of induction heating deposited monetite coating to hydroxyapatite coating on HT-C/C composites by hydrothermal treatment in two types of solution Xiong Xin Bo a,⁎, Zou Chun Li a, Zeng Xie Rong a, Li Ping b, Fa Yu Bo b,⁎, Tang Han Lin a, Xie Sheng Hui a a b
Shen Zhen Key Laboratory of Special Functional Materials, Department of Materials, Science and Engineering, Shen Zhen University, Shen Zhen, 518060, PR China Bioengineering Department, Beihang University, Beijing, 100191, PR China
a r t i c l e
i n f o
Article history: Received 17 January 2009 Received in revised form 24 February 2009 Accepted 20 March 2009 Available online 5 April 2009 Keywords: Coating Carbon Hydroxyapatite Scratch test Induction heating deposition
a b s t r a c t Monetite coatings on H2O2-treated carbon/carbon composites were prepared by induction heating deposition method and then converted to HA coatings by hydrothermal treatment in an autoclave with two different types of solutions, respectively NaOH aqueous solution and ammonia solution. The structure, morphology and chemical composition of the as-achieved HA coatings were characterized by XRD, FTIR SEM and EDS. The adhesion of HA coatings to the HT-C/C substrates was evaluated by a scratch test. The results showed that there are no obvious changes in the structure and morphology for the as-achieved HA coatings except to their compositions. The average critical load of the ammonia hydrothermally treated HA coatings is 10.9 N, while the NaOH hydrothermally treated HA coatings show the average one of 51 N, and the reason for it was suggested. © 2009 Elsevier B.V. All rights reserved.
1. Introduction Carbon fiber reinforced carbon (C/C) composites have been considered as one alternative material to metallic implants for applications in loaded artificial bones [1,2]. They inherit the intrinsic biocompatibility of carbon materials, and have many unique properties, such as high toughness, high strength, fatigue-proof, and corrosion resistance, especially the similar elastic modular to that of the human bone, and thus are not subjected to “stress shielding” and sequential bone absorption caused by implant materials with high modulus. Besides these, their micro-pores can be beneficial to the growth of bone tissues [3]. However, they have no bioactivity and fail to form a chemical bond with the host bone. Also, they may release carbon particles due to friction damage during surgical operations, which deposit in the neighborhood of the implant and the lymphatic node, causing “black skin effect” [4]. These drawbacks of C/C composites have limited their application. Hydroxyapatite (HA) has a chemical composition similar to that of the inorganic part of human bones and has an excellent biocompatibility in comparison with other implant materials [5]. However, HA's fracture toughness and strength are not high enough for application in human bones. In this context, C/C substrate was chosen as a framework for load-bearing and the HA
⁎ Corresponding authors. X.X. Bo is to be contacted at Tel./fax: +86 755 26536239. F.Y. Bo Tel./fax: +86 10 82339428. E-mail addresses: [email protected] (X.X. Bo), [email protected] (F.Y. Bo). 0928-4931/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.msec.2009.03.018
was used as an outer coating layer to enhance the biocompatibility and osteoconductivity. HA coatings have been coated on C/C substrate by plasmaspraying technique [6,7], but this method suffers from formation of other phases like tricalcium phosphate, characterized with lack of crystallinity. Moreover, the shear strength between HA and C/C by this method is on average 7.15 MPa [6]. This value is still poor and thus needs to be further enhanced. Additionally, the plasma spray technique is a line-to-sight process. It produces a non-uniform coating when applied to porous surfaces or complex shape substrates. Several calcium phosphate coating techniques have been used. As a result, wet chemical methods have been proposed including electrodeposition (or sono-electrodeposition) processes [8], sol–gel [9] and biomimetic techniques [10]. The main problem of these wet methods is the weak adhesion strength between the HA coating and C/C substrate, which is difficult to improve. Recently, in the authors' research group, a novel technique by the combination of induction heating deposition [11] with hydrothermal treatment was developed to coat adherent HA coating on C/C substrate [12]. By this method, an adherent HA on C/C composites with the critical load of 13.12 N could be achieved. Also, the technique was found to have the following advantages: thicker films, better control over the deposited solid phase, the ability to deposit porous or complex shapes, and lower processing temperature. Therefore it is worth a further investigation for application in implants. Generally, HA in bone is a multi-substituted − 2+ calcium phosphate, including traces of K+, Mg2+, Na+, CO2− 3 , F , Sr etc. Although the content is low in the mineral phase of bone, these ionic substitutions play an important role in bone formation and normal
2020
X.X. Bo et al. / Materials Science and Engineering C 29 (2009) 2019–2023
functions of bone tissues [13]. Thus, many efforts have been made to research the effects of these various substitutions on the physical and chemical properties. In the calcified tissues, a considerable extent of ions in HA lattice is CO2− and Na+ [14]. So, in this study, the Na-doped 3 carbonate HA coatings on H2O2-treated carbon/carbon (HT-C/C) composites were prepared using induction heating deposition/hydrothermal treatment methods, and the phase, composition and bonding strength of the coatings were tested. The reasons for the highly adhesive strength of the Na-doped carbonate HA coatings were discussed by comparison with metal ion-free carbonate HA coatings on HT-C/C composites. 2. Experimental procedure 2.1. Experimental setup and mother solution Induction heating deposition was performed by using SP-15 high frequency induction power made in Shenzhen SuanPin Power Co. Lit. The experimental setup for the induction heat deposition process was described elsewhere [12]. Briefly, this setup is composed of an induction current power consisting of a copper coil with appropriate water cooling, a glass tube of 20 mm diameter inside the coil, a peristaltic pump, a feeding tank and tubes connecting the feeding tank to the bottom of the glass tube and the top of the glass tube to the tank for the residual solution. Inside the glass tube there are two glass tubes of 16 mm diameter to support the C/C samples in a vertical position. The mother solution used in this study was prepared by dissolving the given amounts of reagent-grade chemicals of 0.1 M Ca(NO3)2 and 0.06 M NH4H2PO4 into distilled water. 2.2. C/C substrates and pretreatments C/C composites were prepared by chemical vapor infiltration (CVI) processing in Northwest Polytechnology University in China. Their density and Shore scleroscope hardness are on average 1.72 g/cm3 and 36.1 g/cm3, respectively. Cylindrical C/C samples with a diameter of 10 mm and a length of 10 mm were cut from the block. Prior to the coating runs, each sample was polished with No. 600 and No. 1000 abrasive paper, rinsed with distilled water, then cleaned ultrasonically in acetone, and dried in a desiccator. After that, samples were pretreated in high pressure steam in a 50 mL autoclave with 40 ml 2 M H2O2 solution at 433 K. After removal from H2O2 solution, these cylinders were rinsed ultrasonically with deionized water and dried in air. 2.3. Coating experiments and post-treatments
Spectrometer and KBr pellet technology. The adhesion strength of the HA coatings deposited on C/C substrates was determined by the scratch test method using an s-3400N scratch tester fitted with a Rochwell C 0.2 mm-diamond stylus with a preload of 1 N. The load speed, maximum load and scratch speed were 10 N/min, 2.5mm/min and 20 N for the ammonia solution, and 35 N/min, 2.5mm/min and 70 N for the NaOH aqueous solution respectively. The scratch trance of the HA coating was observed by a stereomicroscope (STM). 3. Results and discussion Fig. 1 shows the XRD spectra of the as-deposited and hydrothermal post-treated coatings on HT-C/C. The coating deposited by induction heating method consists of calcium hydrogen orthophosphate (CaHPO4, monetite). After hydrothermal post-treatment in the NaOH aqueous/ammonia solution, monetite phases of the two coatings were transformed to hydroxyapatite with three most intensive peaks ((211), (300) and (112)) between 2θ = 30–35° [15] which are in a good agreement with the reference data from JCSPDS 9432. XRD spectra show no significant difference for the two different HA coatings. These results indicate that both of the hydrothermal post-treatment modes help to convert monetite phase to a wellcrystallized hydroxyapatite at 373 K. As-prepared monetite coatings on HT-C/C substrate with the thickness of 200 μm or so consist of sheet-like crystals with a smooth surface. These crystals agglomerate together to form a dense morphology and their morphologies are the same as that of HA coatings after the hydrothermal post-treatment at lower than 400 times magnification. Thus, the figure of monetite coatings is not given here. After hydrothermal post-treatment, the thickness of the HA coatings shows no change and the morphologies of the two different HA coatings are presented in Fig. 2(a)–(d). It can be observed that no significant difference of surface morphology is found for the two HA coatings at lower than 400 times magnification, and both of the coatings are composed of plate-like crystals. However, when the magnification is 15,000 times, some nanometer sized grains occur on these crystals, and the size of the grains on NT-HA crystals is larger than that on AT-HA crystals. The formation of these grains is attributed to a continuous process of dissolution and a reprecipitation reported by Da silva et al. [16] during the transformation of monetite to HA. Fig. 3 shows the EDS spectra of the NT-HA and AT-HA coatings, both of which contained Ca, P and O from coatings, and Pd and Au from the sputtering targets for SEM analysis. The exact Ca/P atomic ratio is found to be 1.45 for the AT-HA coating, while the Ca/P and (Ca+Na)/P atomic ratios are found to be 1.57 and 1.68 for the NT-HA coating. These results
All the deposition experiments were carried out at the applied current of 500 A at room temperature for 1 h. At the end of each run, the coated cylinders were rinsed with distilled water and then hydrothermally treated at 373 K for 4 h in an autoclave. The two different types of solutions, 40 ml 0.1 M NaOH aqueous solution and ammonia solution respectively were used and the resultant phases were designated as NT-HA and AT-HA respectively. After hydrothermal treatment, all the coated samples were annealed in a vacuum to remove the water in the coatings at 473 K for 1 h. 2.4. Characterization The crystalline structure, morphologies and compositions of the coated samples were characterized by X-ray diffraction (XRD) using a D8 Advance X-ray diffractometer (Cu-Ka radiation), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) analysis with an s-3400N (Japan) microscope. The functional groups of HA coatings were quantitatively identified by Fourier transform infrared (FTIR). The FTIR spectra were recorded in the 400–4000 cm) 1 range, resolution 4 cm) 1, using Perkin Elmer instruments Spectrum One
Fig. 1. XRD spectra of (a) HT-C/C, (b) monetite coating on HT-C/C by induction heating deposition, and as-achieved hydroxyapatite coating by hydrothermal post-treatment in (c) the ammonia solution and (d) the NaOH aqueous solution respectively.
X.X. Bo et al. / Materials Science and Engineering C 29 (2009) 2019–2023
2021
Fig. 2. Morphologies of the coatings on HT-C/C obtained in (a, b) the ammonia solution and (c, d) the NaOH aqueous solution respectively.
indicate that the composition of the AT-HA coating is calcium-absent apatite, while for the NT-HA coating, the (Ca+Na)/P atomic ratio is very close to the theoretical Ca/P ratio of hydroxyapatite.
Fig. 4 gives the FTIR spectra of the two different HA coatings. The IR spectrum in Fig. 4(a) indicates that the AT-HA coating contains − −1 3− HPO2− are 4 , H2O, OH , and PO4 . The peaks at 3570 and 633 cm attributed to the stretching and libration modes respectively of the OH− vibration in hydroxyapatite [17,18]. The 879 cm− 1 peak is apparently caused by HPO2− ions [17]. The broad bands in the 3600 4 to 2500 cm− 1 range are assigned to water [17]. The peaks at 1094 and 1031 cm− 1 are assigned to υ3 stretching modes of PO3− 4 , and the peaks at 961 and 473 cm− 1 are assigned to υ1 stretching and υ2 bending mode of PO3− 4 respectively. Two well-separated peaks at 603 and 564 cm− 1 are both attributed to the υ4 mode of PO3− [16]. The 4 large separation of both two peaks is another indicator of a highly
Fig. 3. EDS spectra of the coatings on HT-C/C obtained in (a) the ammonia solution and (b) the NaOH aqueous solution respectively.
Fig. 4. FTIR spectra of the coatings on HT-C/C obtained in (a) the ammonia solution and (b) the NaOH aqueous solution respectively.
2022
X.X. Bo et al. / Materials Science and Engineering C 29 (2009) 2019–2023
Fig. 5. The histogram of the average critical load of the HA coatings obtained in the ammonia solution and the NaOH aqueous solution respectively.
scratch, and the coating materials are squashed along the track. After the Na-T coating is broken, it detaches from the HT-C/C substrate, resulting in the exposure of black substrate. According to the above analyses, it can be known that there are no obvious changes in the structure and morphology of the two different HA coatings except for the compositions. In addition, no Na elements are found in the exposed C/C substrate after the Na-T coating detaches are subjected to scratch test. So, it can be deduced that the higher bonding strength for the NT-HA coating, transformed from induction heating deposited monetite coating, is attributed to the incorporation of Na ions into apatite lattice. Doped elements have been suggested to have the apparent effect of crystal and grain boundary of apatite. Song et al. reported that the substitution of CO2− for PO3− lowers the 3 4 stability of Ca and thus results in a deficiency of Ca in the apatite lattice, which is the reason for forming a Ca-absent apatite in the ATHA coatings. The more the amount of CO2− 3 ions in the HA lattice is, the less the amount of calcium ions is. This is the reason that Ca/P atom ratio and crystalline for the AT-HA coating are less than those for the
crystallized apatite phase [14], well agreeing with analysis results from the X-ray diffraction data. Additionally, the IR absorption peak in the regions at 1410 cm− 1 can be assigned to the υ3a mode of the CO2− 3 ions in the apatite lattice which are typical of B-type CO2− 3 -containing apatite, while the peak at 1574 cm− 1 is assigned to the υ3b mode of Aions [17]. From the FTIR analyses, it can be confirmed that type CO2− 3 ions have resided in both OH− and PO3− sites in the asthe CO2− 3 4 prepared AT-HA coating. Compared with the AT-HA coating, except for the two peaks at 879 and 633 cm− 1, all the other peaks mentioned above can be found in the NT-HA coating. Besides these, it can also be peaks for AT-HA observed that the relative intensity of the CO2− 3 coatings is higher than that for the NT-HA coating. On the basis of the XRD, EDS and FTIR results, therefore, it can be determined that the formulae for the AT-HA coating and NT-HA coating can be expressed as Ca10 − x(PO4)6 − a − b(HPO4) b(CO3) a(OH)2 − c(CO3) c and Ca10 − xNax (PO4)6 − a(CO3)a(OH)2 − b(CO3)b respectively with 0 b x, a, b and c b 1. Fig. 5 shows the average critical load for the two different HA coatings on HT-C/C composites. As can be seen, the average critical load of the AT-HA coating is 10.9 N, while surprisingly, the NT-HA coating shows the highest critical load of 55.4 N and the average one of 51 N, which is more than five times as high as that for the AT-HA coating. The corresponding shear stresses were calculated to be about 55.8 MPa for the AT-HA coating and 125.7 MPa for the NT-HA coating respectively using the following expression [19]: 1=2
τc = ðHS Lc=π Þ
=R
ð1Þ
where τc is the shear stress, R is the radius of diamond stylus, Lc is the critical load, HS is the Shore scleroscope hardness of the C/C substrate. The stress strength of HA coatings on HT-C/C is greater than that of HA coatings deposited on C/C composites by plasma spray (7.15 MPa) [6] and the loading stress on the hip joint during gait (b35 MPa) [20]. It is also higher than that of C/C composites-bone which is 2.44 MPa, 20 weeks after implantation in mouse [21], which is high enough for handling before implant and strong enough to survive in the living body. Fig. 6(b) shows the two curves for the NT-HA coating of friction vs. load and scratch distance vs. penetration depth respectively. From the figures, it can be seen that there occurs the abrupt point (a) in the two curves at the load of 51.1 N or the scratch distance of 3.8 mm or so respectively. In combination with the stereomicroscope observation of the corresponding scratch trace on the HA coating, as shown in Fig. 6(a), this point is found to correspond to the damage site of the NT-HA coating. This means that failure appears within the coating, which can also be proved in Fig. 6(c). From Fig. 6(a), it can be seen that until the coating fails, no fracture or chip is observed at the border or inside the
Fig. 6. (a) and (c) Optical images of the scratch test performed on the hydrothermally NaOH-treated coating, and (b) plot of friction force vs. load and penetration depth vs. scratch distance.
X.X. Bo et al. / Materials Science and Engineering C 29 (2009) 2019–2023
NT-HA coating. Moreover, Na ions have a less ionic radius than Ca ions and therefore are very easy to be incorporated into the apatite crystals and occupy the vacancies on the regular apatite lattice sites occupied by Ca. Thus, the (Ca+Na)/P atomic ratio of the NT-HA coating is very close to the theoretical Ca/P ratio of hydroxyapatite, and the crystalline of the as-achieved coatings is further improved. In general, a well-developed structure is cohesively strong and helps to resist shear stress during scratching, which results in the higher adhesion strength for the NT-HA coatings than that for the AT-HA coatings. This is one reason of the enhanced adhesion for the NT-HA coatings. Additionally, Na ions are apt to segregate to the grain boundary and stabilize the grain boundary by lowering the grain boundary energy [22]. This phenomenon of doped elements, such as Na, K, Mg, Sr, Ba etc, were also found to be in human enamel [22]. After Na ions are incorporated into the lattice, the decrease in the grain boundary energy will strengthen the grain boundary cohesion, which can be explained by the Rice–Wang thermodynamic model that is expressed as follows [23]: 2γ int = 2γ int 0 − ΔEgb − ΔEs C
ð2Þ
Here 2γint and 2γint 0 are ideal cleavage work with or without doped atom, respectively. Γ is the doped atom coverage of grain boundary. ΔEgb and ΔEs are the segregation energy at grain boundary and free surface, respectively. If ΔEgb ) ΔEs b 0, doped atom enhances the grain boundary cohesion. This is the other reason of enhanced adhesion for the NT-HA coatings. 4. Conclusion Monetite coatings on H2O2-modified C/C (HT-C/C) composites were prepared by induction heating deposition method and then converted to HA coatings by hydrothermal treatment in an autoclave with two different types of solutions, respectively NaOH aqueous solution and ammonia solution. There are no obvious changes in the structure and morphology for the two different HA coatings except that in composition. The average critical load of the ammonia hydrothermally treated HA coatings is 10.9 N, while the NaOH hydrothermally treated HA coatings show the highest critical load of 55.4 N and the average one
2023
of 51 N, which is nearly five times as high as those of the HA coating in ammonia solution. The value of the adhesion between C/C composites and hydroxyapatite is high enough for handling before implant and strong enough to survive in the living body. Acknowledgement This work was supported by the National Natural Science Foundation of China with Grant No.50702034 and the ShenZhen Science and Technology Research Grant No:PT200805200295A. References [1] P. Christel, A. Meunier, S. Leclercq, P. Bouquet, B. Buttazzoni, J. Biomed. Mater. Res. 21 (1987) 191. [2] N. Cao, Q.S. Ma, J.L. Sui, Q.X. Wan, Y.P. Lu, Y.M. Chen, M.S. Li, Sur. Rev. Lett. 13 (2006) 423. [3] L. Bacáková, V. Starý, O. Kofronová, V.J. Lisá, Biomed. Mater. Res. 54 (2000) 567. [4] N. Cao, Y. Bai, Q.S. Ma, J.L. Sui, M.S. Li, Carbon 46 (2008) 3. [5] T. Kokubo, H.M. Kim, M. Kawashita, T.J. Nakamura, Mater. Sci: Mater. Med. 15 (2004) 99. [6] J.L. Sui, M.S. Li, Y.P. Lu, L.W. Yin, Y.J. Song, Surf. Coat. Technol. 176 (2004) 188. [7] J.L. Sui, M.S. Li, Y.P. Lu, Y.Q. Bai, Surf. Coat. Technol. 190 (2005) 287. [8] Y.Q. Zhai, K.Z. Li, H.J. Li, C. Wang, H. Liu, Mater. Chem. Phys. 106 (2007) 22. [9] T. Fu, L.P. He, Y. Han, K.W. Xu, Y.W. Mai, Mater. Lett. 4371 (2003) 1. [10] T. Fu, Y. Han, K.W. Xu, J.Y. Li, Z.X. Song, Mater. Lett. 57 (2002) 77. [11] J. Gómez Morales, R. Rodríguez Clemente, B. Armas, C. Combescure, R. Berjoan, J. Cubo, E. Martínez, J. García Carmona, S. Garelik, J. Murtra, D.N. Muraviev, Langmuir 20 (2004) 5174. [12] X.B. Xiong, X.R. Zeng, C.L. Zhou, Mater. Chem. Phys. 114 (2009) 434. [13] W.C. Xue, H.L. Hosick, A. Bandyopadhya, S. Bose, C.X. Ding, K.D.K. Luk, K.M.C. Cheung, W.W. Lu, Surf. Coat. Technol. 201 (2007) 4685. [14] E.A.P. De Maeter, R.M.H. Verbeeck, D.E. Naessens, Inorg. Chem. 32 (1993) 5709. [15] I. Bogdanoviciene, A. Beganskiene, K. Tõnsuaadu, J. Glaser, H. Jürgen Meyer, A. Kareiv, Mater. Res. Bull. 41 (2006) 1754. [16] M.G. Ma, Y.J. Zhu, C. Jiang, J. Phys. Chem. B. 110 (2006) 14226. [17] G.F. Xu, I.A. Aksay, J.T. Groves, J. Am. Chem. Soc. 123 (2001) 2196. [18] E.A. De Maeyer, R.M. Verbeeck, I.Y. Pieters, Inorg. Chem. 35 (1996) 857. [19] X. Cai, J.F. Gu, P.N. Zhou, X.Y. Yang, Trans. Met. Heat Treat. 18 (1997) 30 (In Chinese). [20] M.C. Kuo, S.K. Yen, Mater. Sci. Eng. C. 20 (2002) 153. [21] O. Chikara, K. Masanobu, M. Toshiki, J. Tiss. Eng. Regen. Med. 1 (2007) 33. [22] Q.M. Song, C.Y. Wang, S.L. Wen, Mater. Sci. Eng. A. 297 (2000) 272. [23] E. Wachowicz, A. Kiejna, Comput. Mater. Sci. 43 (2008) 736.
Contents lists available at ScienceDirect
Materials Science and Engineering C j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / m s e c
Transformation of induction heating deposited monetite coating to hydroxyapatite coating on HT-C/C composites by hydrothermal treatment in two types of solution Xiong Xin Bo a,⁎, Zou Chun Li a, Zeng Xie Rong a, Li Ping b, Fa Yu Bo b,⁎, Tang Han Lin a, Xie Sheng Hui a a b
Shen Zhen Key Laboratory of Special Functional Materials, Department of Materials, Science and Engineering, Shen Zhen University, Shen Zhen, 518060, PR China Bioengineering Department, Beihang University, Beijing, 100191, PR China
a r t i c l e
i n f o
Article history: Received 17 January 2009 Received in revised form 24 February 2009 Accepted 20 March 2009 Available online 5 April 2009 Keywords: Coating Carbon Hydroxyapatite Scratch test Induction heating deposition
a b s t r a c t Monetite coatings on H2O2-treated carbon/carbon composites were prepared by induction heating deposition method and then converted to HA coatings by hydrothermal treatment in an autoclave with two different types of solutions, respectively NaOH aqueous solution and ammonia solution. The structure, morphology and chemical composition of the as-achieved HA coatings were characterized by XRD, FTIR SEM and EDS. The adhesion of HA coatings to the HT-C/C substrates was evaluated by a scratch test. The results showed that there are no obvious changes in the structure and morphology for the as-achieved HA coatings except to their compositions. The average critical load of the ammonia hydrothermally treated HA coatings is 10.9 N, while the NaOH hydrothermally treated HA coatings show the average one of 51 N, and the reason for it was suggested. © 2009 Elsevier B.V. All rights reserved.
1. Introduction Carbon fiber reinforced carbon (C/C) composites have been considered as one alternative material to metallic implants for applications in loaded artificial bones [1,2]. They inherit the intrinsic biocompatibility of carbon materials, and have many unique properties, such as high toughness, high strength, fatigue-proof, and corrosion resistance, especially the similar elastic modular to that of the human bone, and thus are not subjected to “stress shielding” and sequential bone absorption caused by implant materials with high modulus. Besides these, their micro-pores can be beneficial to the growth of bone tissues [3]. However, they have no bioactivity and fail to form a chemical bond with the host bone. Also, they may release carbon particles due to friction damage during surgical operations, which deposit in the neighborhood of the implant and the lymphatic node, causing “black skin effect” [4]. These drawbacks of C/C composites have limited their application. Hydroxyapatite (HA) has a chemical composition similar to that of the inorganic part of human bones and has an excellent biocompatibility in comparison with other implant materials [5]. However, HA's fracture toughness and strength are not high enough for application in human bones. In this context, C/C substrate was chosen as a framework for load-bearing and the HA
⁎ Corresponding authors. X.X. Bo is to be contacted at Tel./fax: +86 755 26536239. F.Y. Bo Tel./fax: +86 10 82339428. E-mail addresses: [email protected] (X.X. Bo), [email protected] (F.Y. Bo). 0928-4931/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.msec.2009.03.018
was used as an outer coating layer to enhance the biocompatibility and osteoconductivity. HA coatings have been coated on C/C substrate by plasmaspraying technique [6,7], but this method suffers from formation of other phases like tricalcium phosphate, characterized with lack of crystallinity. Moreover, the shear strength between HA and C/C by this method is on average 7.15 MPa [6]. This value is still poor and thus needs to be further enhanced. Additionally, the plasma spray technique is a line-to-sight process. It produces a non-uniform coating when applied to porous surfaces or complex shape substrates. Several calcium phosphate coating techniques have been used. As a result, wet chemical methods have been proposed including electrodeposition (or sono-electrodeposition) processes [8], sol–gel [9] and biomimetic techniques [10]. The main problem of these wet methods is the weak adhesion strength between the HA coating and C/C substrate, which is difficult to improve. Recently, in the authors' research group, a novel technique by the combination of induction heating deposition [11] with hydrothermal treatment was developed to coat adherent HA coating on C/C substrate [12]. By this method, an adherent HA on C/C composites with the critical load of 13.12 N could be achieved. Also, the technique was found to have the following advantages: thicker films, better control over the deposited solid phase, the ability to deposit porous or complex shapes, and lower processing temperature. Therefore it is worth a further investigation for application in implants. Generally, HA in bone is a multi-substituted − 2+ calcium phosphate, including traces of K+, Mg2+, Na+, CO2− 3 , F , Sr etc. Although the content is low in the mineral phase of bone, these ionic substitutions play an important role in bone formation and normal
2020
X.X. Bo et al. / Materials Science and Engineering C 29 (2009) 2019–2023
functions of bone tissues [13]. Thus, many efforts have been made to research the effects of these various substitutions on the physical and chemical properties. In the calcified tissues, a considerable extent of ions in HA lattice is CO2− and Na+ [14]. So, in this study, the Na-doped 3 carbonate HA coatings on H2O2-treated carbon/carbon (HT-C/C) composites were prepared using induction heating deposition/hydrothermal treatment methods, and the phase, composition and bonding strength of the coatings were tested. The reasons for the highly adhesive strength of the Na-doped carbonate HA coatings were discussed by comparison with metal ion-free carbonate HA coatings on HT-C/C composites. 2. Experimental procedure 2.1. Experimental setup and mother solution Induction heating deposition was performed by using SP-15 high frequency induction power made in Shenzhen SuanPin Power Co. Lit. The experimental setup for the induction heat deposition process was described elsewhere [12]. Briefly, this setup is composed of an induction current power consisting of a copper coil with appropriate water cooling, a glass tube of 20 mm diameter inside the coil, a peristaltic pump, a feeding tank and tubes connecting the feeding tank to the bottom of the glass tube and the top of the glass tube to the tank for the residual solution. Inside the glass tube there are two glass tubes of 16 mm diameter to support the C/C samples in a vertical position. The mother solution used in this study was prepared by dissolving the given amounts of reagent-grade chemicals of 0.1 M Ca(NO3)2 and 0.06 M NH4H2PO4 into distilled water. 2.2. C/C substrates and pretreatments C/C composites were prepared by chemical vapor infiltration (CVI) processing in Northwest Polytechnology University in China. Their density and Shore scleroscope hardness are on average 1.72 g/cm3 and 36.1 g/cm3, respectively. Cylindrical C/C samples with a diameter of 10 mm and a length of 10 mm were cut from the block. Prior to the coating runs, each sample was polished with No. 600 and No. 1000 abrasive paper, rinsed with distilled water, then cleaned ultrasonically in acetone, and dried in a desiccator. After that, samples were pretreated in high pressure steam in a 50 mL autoclave with 40 ml 2 M H2O2 solution at 433 K. After removal from H2O2 solution, these cylinders were rinsed ultrasonically with deionized water and dried in air. 2.3. Coating experiments and post-treatments
Spectrometer and KBr pellet technology. The adhesion strength of the HA coatings deposited on C/C substrates was determined by the scratch test method using an s-3400N scratch tester fitted with a Rochwell C 0.2 mm-diamond stylus with a preload of 1 N. The load speed, maximum load and scratch speed were 10 N/min, 2.5mm/min and 20 N for the ammonia solution, and 35 N/min, 2.5mm/min and 70 N for the NaOH aqueous solution respectively. The scratch trance of the HA coating was observed by a stereomicroscope (STM). 3. Results and discussion Fig. 1 shows the XRD spectra of the as-deposited and hydrothermal post-treated coatings on HT-C/C. The coating deposited by induction heating method consists of calcium hydrogen orthophosphate (CaHPO4, monetite). After hydrothermal post-treatment in the NaOH aqueous/ammonia solution, monetite phases of the two coatings were transformed to hydroxyapatite with three most intensive peaks ((211), (300) and (112)) between 2θ = 30–35° [15] which are in a good agreement with the reference data from JCSPDS 9432. XRD spectra show no significant difference for the two different HA coatings. These results indicate that both of the hydrothermal post-treatment modes help to convert monetite phase to a wellcrystallized hydroxyapatite at 373 K. As-prepared monetite coatings on HT-C/C substrate with the thickness of 200 μm or so consist of sheet-like crystals with a smooth surface. These crystals agglomerate together to form a dense morphology and their morphologies are the same as that of HA coatings after the hydrothermal post-treatment at lower than 400 times magnification. Thus, the figure of monetite coatings is not given here. After hydrothermal post-treatment, the thickness of the HA coatings shows no change and the morphologies of the two different HA coatings are presented in Fig. 2(a)–(d). It can be observed that no significant difference of surface morphology is found for the two HA coatings at lower than 400 times magnification, and both of the coatings are composed of plate-like crystals. However, when the magnification is 15,000 times, some nanometer sized grains occur on these crystals, and the size of the grains on NT-HA crystals is larger than that on AT-HA crystals. The formation of these grains is attributed to a continuous process of dissolution and a reprecipitation reported by Da silva et al. [16] during the transformation of monetite to HA. Fig. 3 shows the EDS spectra of the NT-HA and AT-HA coatings, both of which contained Ca, P and O from coatings, and Pd and Au from the sputtering targets for SEM analysis. The exact Ca/P atomic ratio is found to be 1.45 for the AT-HA coating, while the Ca/P and (Ca+Na)/P atomic ratios are found to be 1.57 and 1.68 for the NT-HA coating. These results
All the deposition experiments were carried out at the applied current of 500 A at room temperature for 1 h. At the end of each run, the coated cylinders were rinsed with distilled water and then hydrothermally treated at 373 K for 4 h in an autoclave. The two different types of solutions, 40 ml 0.1 M NaOH aqueous solution and ammonia solution respectively were used and the resultant phases were designated as NT-HA and AT-HA respectively. After hydrothermal treatment, all the coated samples were annealed in a vacuum to remove the water in the coatings at 473 K for 1 h. 2.4. Characterization The crystalline structure, morphologies and compositions of the coated samples were characterized by X-ray diffraction (XRD) using a D8 Advance X-ray diffractometer (Cu-Ka radiation), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) analysis with an s-3400N (Japan) microscope. The functional groups of HA coatings were quantitatively identified by Fourier transform infrared (FTIR). The FTIR spectra were recorded in the 400–4000 cm) 1 range, resolution 4 cm) 1, using Perkin Elmer instruments Spectrum One
Fig. 1. XRD spectra of (a) HT-C/C, (b) monetite coating on HT-C/C by induction heating deposition, and as-achieved hydroxyapatite coating by hydrothermal post-treatment in (c) the ammonia solution and (d) the NaOH aqueous solution respectively.
X.X. Bo et al. / Materials Science and Engineering C 29 (2009) 2019–2023
2021
Fig. 2. Morphologies of the coatings on HT-C/C obtained in (a, b) the ammonia solution and (c, d) the NaOH aqueous solution respectively.
indicate that the composition of the AT-HA coating is calcium-absent apatite, while for the NT-HA coating, the (Ca+Na)/P atomic ratio is very close to the theoretical Ca/P ratio of hydroxyapatite.
Fig. 4 gives the FTIR spectra of the two different HA coatings. The IR spectrum in Fig. 4(a) indicates that the AT-HA coating contains − −1 3− HPO2− are 4 , H2O, OH , and PO4 . The peaks at 3570 and 633 cm attributed to the stretching and libration modes respectively of the OH− vibration in hydroxyapatite [17,18]. The 879 cm− 1 peak is apparently caused by HPO2− ions [17]. The broad bands in the 3600 4 to 2500 cm− 1 range are assigned to water [17]. The peaks at 1094 and 1031 cm− 1 are assigned to υ3 stretching modes of PO3− 4 , and the peaks at 961 and 473 cm− 1 are assigned to υ1 stretching and υ2 bending mode of PO3− 4 respectively. Two well-separated peaks at 603 and 564 cm− 1 are both attributed to the υ4 mode of PO3− [16]. The 4 large separation of both two peaks is another indicator of a highly
Fig. 3. EDS spectra of the coatings on HT-C/C obtained in (a) the ammonia solution and (b) the NaOH aqueous solution respectively.
Fig. 4. FTIR spectra of the coatings on HT-C/C obtained in (a) the ammonia solution and (b) the NaOH aqueous solution respectively.
2022
X.X. Bo et al. / Materials Science and Engineering C 29 (2009) 2019–2023
Fig. 5. The histogram of the average critical load of the HA coatings obtained in the ammonia solution and the NaOH aqueous solution respectively.
scratch, and the coating materials are squashed along the track. After the Na-T coating is broken, it detaches from the HT-C/C substrate, resulting in the exposure of black substrate. According to the above analyses, it can be known that there are no obvious changes in the structure and morphology of the two different HA coatings except for the compositions. In addition, no Na elements are found in the exposed C/C substrate after the Na-T coating detaches are subjected to scratch test. So, it can be deduced that the higher bonding strength for the NT-HA coating, transformed from induction heating deposited monetite coating, is attributed to the incorporation of Na ions into apatite lattice. Doped elements have been suggested to have the apparent effect of crystal and grain boundary of apatite. Song et al. reported that the substitution of CO2− for PO3− lowers the 3 4 stability of Ca and thus results in a deficiency of Ca in the apatite lattice, which is the reason for forming a Ca-absent apatite in the ATHA coatings. The more the amount of CO2− 3 ions in the HA lattice is, the less the amount of calcium ions is. This is the reason that Ca/P atom ratio and crystalline for the AT-HA coating are less than those for the
crystallized apatite phase [14], well agreeing with analysis results from the X-ray diffraction data. Additionally, the IR absorption peak in the regions at 1410 cm− 1 can be assigned to the υ3a mode of the CO2− 3 ions in the apatite lattice which are typical of B-type CO2− 3 -containing apatite, while the peak at 1574 cm− 1 is assigned to the υ3b mode of Aions [17]. From the FTIR analyses, it can be confirmed that type CO2− 3 ions have resided in both OH− and PO3− sites in the asthe CO2− 3 4 prepared AT-HA coating. Compared with the AT-HA coating, except for the two peaks at 879 and 633 cm− 1, all the other peaks mentioned above can be found in the NT-HA coating. Besides these, it can also be peaks for AT-HA observed that the relative intensity of the CO2− 3 coatings is higher than that for the NT-HA coating. On the basis of the XRD, EDS and FTIR results, therefore, it can be determined that the formulae for the AT-HA coating and NT-HA coating can be expressed as Ca10 − x(PO4)6 − a − b(HPO4) b(CO3) a(OH)2 − c(CO3) c and Ca10 − xNax (PO4)6 − a(CO3)a(OH)2 − b(CO3)b respectively with 0 b x, a, b and c b 1. Fig. 5 shows the average critical load for the two different HA coatings on HT-C/C composites. As can be seen, the average critical load of the AT-HA coating is 10.9 N, while surprisingly, the NT-HA coating shows the highest critical load of 55.4 N and the average one of 51 N, which is more than five times as high as that for the AT-HA coating. The corresponding shear stresses were calculated to be about 55.8 MPa for the AT-HA coating and 125.7 MPa for the NT-HA coating respectively using the following expression [19]: 1=2
τc = ðHS Lc=π Þ
=R
ð1Þ
where τc is the shear stress, R is the radius of diamond stylus, Lc is the critical load, HS is the Shore scleroscope hardness of the C/C substrate. The stress strength of HA coatings on HT-C/C is greater than that of HA coatings deposited on C/C composites by plasma spray (7.15 MPa) [6] and the loading stress on the hip joint during gait (b35 MPa) [20]. It is also higher than that of C/C composites-bone which is 2.44 MPa, 20 weeks after implantation in mouse [21], which is high enough for handling before implant and strong enough to survive in the living body. Fig. 6(b) shows the two curves for the NT-HA coating of friction vs. load and scratch distance vs. penetration depth respectively. From the figures, it can be seen that there occurs the abrupt point (a) in the two curves at the load of 51.1 N or the scratch distance of 3.8 mm or so respectively. In combination with the stereomicroscope observation of the corresponding scratch trace on the HA coating, as shown in Fig. 6(a), this point is found to correspond to the damage site of the NT-HA coating. This means that failure appears within the coating, which can also be proved in Fig. 6(c). From Fig. 6(a), it can be seen that until the coating fails, no fracture or chip is observed at the border or inside the
Fig. 6. (a) and (c) Optical images of the scratch test performed on the hydrothermally NaOH-treated coating, and (b) plot of friction force vs. load and penetration depth vs. scratch distance.
X.X. Bo et al. / Materials Science and Engineering C 29 (2009) 2019–2023
NT-HA coating. Moreover, Na ions have a less ionic radius than Ca ions and therefore are very easy to be incorporated into the apatite crystals and occupy the vacancies on the regular apatite lattice sites occupied by Ca. Thus, the (Ca+Na)/P atomic ratio of the NT-HA coating is very close to the theoretical Ca/P ratio of hydroxyapatite, and the crystalline of the as-achieved coatings is further improved. In general, a well-developed structure is cohesively strong and helps to resist shear stress during scratching, which results in the higher adhesion strength for the NT-HA coatings than that for the AT-HA coatings. This is one reason of the enhanced adhesion for the NT-HA coatings. Additionally, Na ions are apt to segregate to the grain boundary and stabilize the grain boundary by lowering the grain boundary energy [22]. This phenomenon of doped elements, such as Na, K, Mg, Sr, Ba etc, were also found to be in human enamel [22]. After Na ions are incorporated into the lattice, the decrease in the grain boundary energy will strengthen the grain boundary cohesion, which can be explained by the Rice–Wang thermodynamic model that is expressed as follows [23]: 2γ int = 2γ int 0 − ΔEgb − ΔEs C
ð2Þ
Here 2γint and 2γint 0 are ideal cleavage work with or without doped atom, respectively. Γ is the doped atom coverage of grain boundary. ΔEgb and ΔEs are the segregation energy at grain boundary and free surface, respectively. If ΔEgb ) ΔEs b 0, doped atom enhances the grain boundary cohesion. This is the other reason of enhanced adhesion for the NT-HA coatings. 4. Conclusion Monetite coatings on H2O2-modified C/C (HT-C/C) composites were prepared by induction heating deposition method and then converted to HA coatings by hydrothermal treatment in an autoclave with two different types of solutions, respectively NaOH aqueous solution and ammonia solution. There are no obvious changes in the structure and morphology for the two different HA coatings except that in composition. The average critical load of the ammonia hydrothermally treated HA coatings is 10.9 N, while the NaOH hydrothermally treated HA coatings show the highest critical load of 55.4 N and the average one
2023
of 51 N, which is nearly five times as high as those of the HA coating in ammonia solution. The value of the adhesion between C/C composites and hydroxyapatite is high enough for handling before implant and strong enough to survive in the living body. Acknowledgement This work was supported by the National Natural Science Foundation of China with Grant No.50702034 and the ShenZhen Science and Technology Research Grant No:PT200805200295A. References [1] P. Christel, A. Meunier, S. Leclercq, P. Bouquet, B. Buttazzoni, J. Biomed. Mater. Res. 21 (1987) 191. [2] N. Cao, Q.S. Ma, J.L. Sui, Q.X. Wan, Y.P. Lu, Y.M. Chen, M.S. Li, Sur. Rev. Lett. 13 (2006) 423. [3] L. Bacáková, V. Starý, O. Kofronová, V.J. Lisá, Biomed. Mater. Res. 54 (2000) 567. [4] N. Cao, Y. Bai, Q.S. Ma, J.L. Sui, M.S. Li, Carbon 46 (2008) 3. [5] T. Kokubo, H.M. Kim, M. Kawashita, T.J. Nakamura, Mater. Sci: Mater. Med. 15 (2004) 99. [6] J.L. Sui, M.S. Li, Y.P. Lu, L.W. Yin, Y.J. Song, Surf. Coat. Technol. 176 (2004) 188. [7] J.L. Sui, M.S. Li, Y.P. Lu, Y.Q. Bai, Surf. Coat. Technol. 190 (2005) 287. [8] Y.Q. Zhai, K.Z. Li, H.J. Li, C. Wang, H. Liu, Mater. Chem. Phys. 106 (2007) 22. [9] T. Fu, L.P. He, Y. Han, K.W. Xu, Y.W. Mai, Mater. Lett. 4371 (2003) 1. [10] T. Fu, Y. Han, K.W. Xu, J.Y. Li, Z.X. Song, Mater. Lett. 57 (2002) 77. [11] J. Gómez Morales, R. Rodríguez Clemente, B. Armas, C. Combescure, R. Berjoan, J. Cubo, E. Martínez, J. García Carmona, S. Garelik, J. Murtra, D.N. Muraviev, Langmuir 20 (2004) 5174. [12] X.B. Xiong, X.R. Zeng, C.L. Zhou, Mater. Chem. Phys. 114 (2009) 434. [13] W.C. Xue, H.L. Hosick, A. Bandyopadhya, S. Bose, C.X. Ding, K.D.K. Luk, K.M.C. Cheung, W.W. Lu, Surf. Coat. Technol. 201 (2007) 4685. [14] E.A.P. De Maeter, R.M.H. Verbeeck, D.E. Naessens, Inorg. Chem. 32 (1993) 5709. [15] I. Bogdanoviciene, A. Beganskiene, K. Tõnsuaadu, J. Glaser, H. Jürgen Meyer, A. Kareiv, Mater. Res. Bull. 41 (2006) 1754. [16] M.G. Ma, Y.J. Zhu, C. Jiang, J. Phys. Chem. B. 110 (2006) 14226. [17] G.F. Xu, I.A. Aksay, J.T. Groves, J. Am. Chem. Soc. 123 (2001) 2196. [18] E.A. De Maeyer, R.M. Verbeeck, I.Y. Pieters, Inorg. Chem. 35 (1996) 857. [19] X. Cai, J.F. Gu, P.N. Zhou, X.Y. Yang, Trans. Met. Heat Treat. 18 (1997) 30 (In Chinese). [20] M.C. Kuo, S.K. Yen, Mater. Sci. Eng. C. 20 (2002) 153. [21] O. Chikara, K. Masanobu, M. Toshiki, J. Tiss. Eng. Regen. Med. 1 (2007) 33. [22] Q.M. Song, C.Y. Wang, S.L. Wen, Mater. Sci. Eng. A. 297 (2000) 272. [23] E. Wachowicz, A. Kiejna, Comput. Mater. Sci. 43 (2008) 736.