Ⅳ. RESULTS AND DISCUSSION
4.2. The micro-pore surface morphology of
29
-Fig. 7. XRD patterns of Ti-35Ta-10Nb alloys with variation of applied voltages in 0.15 M calcium acetate monohydrate + 0.02 M calcium glycerophospate from 240 V to 320 V for 3 min.
Fig. 8. FE-SEM images of micro-pore formed on Ti-35Ta-10Nb alloys in 0.15 M calcium acetate monohydrate + 0.02 M calcium glycerophospate ; (a) 240 V, (b) 280 V, (c) 320 V.
31
-Fig. 9 shows the FE-SEM images of micro-pore formed on Ti-35Ta-xNb alloys by anodization in 0.15 M Calcium acetate monohydrate + 0.02 M Calcium glycerophospate at 280V for 3 min. The Fig. 9(a) and Fig. 9(c) show bare micro-pore surfaces of Ti-35Ta-xNb alloys at 280 V for 3 min, the Fig. 9(b) and Fig. 9(d) show NaOH treated micro-pore surfaces of Ti-35Ta-xNb alloys at 280 V for 3 min. The process of NaOH treatment is performed in 5 M NaOH solution at for 10 min. It is conformed that more rough micro-pore surface showed in the case of NaOH treated Ti-35Ta-xNb alloys. From the investigate the micro-pore structure, it has been observed in micro-pore inside of pore in the case of NaOH treatment as shown in Fig. 10. it is confirmed that nano-sized network structure was formed. The surface of nano-sized network structure was known as Na5Ti5O11 and Na2Ti6O13 [64]. In case of similar coating, calcium phosphate film was immersed in SBF solution after alkali treatment [65]. In case of biomaterial, the sizes of network structure and micro-pore can be used for good biological materials, that is, this structure has advantage with cell culture due to provide a good cell environment and to increased surface area[66].
Fig. 9. FE-SEM images of micro-pore formed on Ti-35Ta-xNb alloys in 0.15 M calcium acetate monohydrate + 0.02 M calcium glycerophospate; (a) Ti-35Ta (b) NaOH treated Ti-35Ta (c) Ti-35Ta-10Nb (d) NaOH treated Ti-35Ta-10Nb.
33
-Fig. 10. FE-SEM images of NaOH treated micro-pore formed on Ti-35Ta alloy in 0.15 M calcium acetate monohydrate + 0.02 M Calcium glycerophospate.
The micro-pore size has influence on alloy production as shown in Fig. 9.
Fig. 11 shows the corelation between micro-pore formation time and applied voltages on Ti-35Ta-xNb alloys. The experiment is carried out for 3 min at the time of maintenance to 280V. The voltage increased proportionally up to 170V with high slope according to time, and then, variation of voltage with low slope is observed from 170V to 280V. It is thought that occurrences of spark discharge at 170 V is mainly appeared on surface due to insulation breakdown of the surface [60,61].
Fig. 12 shows The corelation between micro-pore formation time and current density on Ti-35Ta-xNb alloys. The first current density was kept continuously at 12 mA/cm2, and then, current density was suddenly changed to 0 mA/cm2 at 280 V due to the formation of barrier layer [62]. Especially, current density is changed irregularly at 0 mA/cm2. It is confirmed that electrical unstability is appeared on the surface due to fornmation of micropores. The analysis of Fig. 11 and Fig. 12 is summarized as shown in Table 7. From the Table 7, in the process of forming micro-pore structured, the rate of forming barrier layer has been slow down with addition of Nb content. In previous paper, the dissolution rate of barrier layer is influenced by metallic phase [63]. As a result, the element of Nb has influence on alloy resistance and morphology of barrier layer.
35
-Fig. 11. The corelation between micro-pore formation time and voltage on Ti-35Ta-xNb alloys.
Fig. 12. The corelation between micro-pore formation time and current density on Ti-35Ta-xNb alloys.
37 -Table 7 Voltage and current density value of Ti-35Ta-xNb alloys
Inflection point 280 V Pre stabilized 0 mA t (second) Voltage t (second) t (second) mA t (second)
Ti-35Ta 11 170 V 78 78 12.4 mA 84
Ti-35Ta-10Nb 17 172 V 132 128 13.1 mA 138
4.3. Morphology of electrochemical deposition on Ti-35Ta-xNb alloys
Fig. 13 shows FE-SEM images of NaOH treated Ti-35Ta alloy in 2.5 mM Ca(NO3)2∙4 H2O + 1.5 mM NH4H2PO4. The Fig. 13(a) and Fig. 13(b) shows FE-SEM images of HA coatings on NaOH treated Ti-35Ta-xNb alloy. Fig. 13(c) and Fig.
13(d) shows FE-SEM images of high magnifications of HA coatings on NaOH treated Ti-35Ta-xNb alloy. Both HA coatings on Ti-35Ta and Ti-35Ta-10Nb alloy were formed on surface with general forms, especially, the HA shape of Ti-35Ta alloy is larger than that of Ti-35Ta-10Nb alloy. According to previous paper, the shape of HA is important role to decide the final shape and size[67]. And it is confirmed that the shape of HA has is affected by Nb content as shown in Fig 11 and Fig 12.
39
-Fig. 13. FE-SEM images of NaOH treated Ti-35Ta alloy in 2.5 mM Ca(NO3)2∙4 H2O + 1.5 mM NH4H2PO4; (a) Ti-35Ta, (b) Ti-35Ta-10Nb, (c) high magnification of Ti-35Ta, (d) high magnification of Ti-35Ta-10Nb.
Fig. 14 shows the shapes of initial HA on Ti-35Ta-10Nb alloy in 2.5 mM Ca(NO3)2∙4 H2O + 1.5 mM NH4H2PO4. As shown in Fig. 14, the initial HA precipitation was formed in pore inside and outside. The formation of nucleation is leading to surface potential and temperature, which is evaluate to previous paper [68, 69].
Fig. 15 shows FE-SEM images of HA coating on NaOH treated micro-pore structured Ti-35Ta-xNb alloy in 2.5 mM Ca(NO3)2∙4 H2O + 1.5 mM NH4H2PO4. Fig.
15(a) shows flower-like HA shape, Fig. 15(c) shows flower-like HA shape of bi-phase. Also, the HA sizes of Ti-35Ta-10Nb alloy is bigger than that of Ti-35Ta alloy. It is confirmed that morphology of micro-pore depended on Nb content.
Fig. 16 shows FE-SEM images of HA coated and NaOH treated micro-pore structured Ti-35Ta-xNb alloy in 2.5 mM Ca(NO3)2∙4 H2O + 1.5 mM NH4H2PO4. The HA coating is formed on the whole surface, the HA size of Ti-35Ta-10Nb alloy shows the bigger than that of Ti-35Ta alloy. The deposition cycles increased, the size of precipitates increased [70]. The porous and HA doped surface of Ti-35Ta-xNb alloys has advantage of cell growth on the surface.
Especially, HA coated layer can be applicated to dental implant [71].
41
-Fig. 14. FE-SEM images of initial step of HA crystal nucleation on NaOH treated Ti-35Ta-10Nb alloy in 2.5 mM
Ca(NO3)2∙4 H2O + 1.5 mM NH4H2PO4 with 5 deposition cycles. (a) X 2,000, (b) 20,000 high magnification of (a), (c) 100,000 high magnification of (a)
Fig. 15. FE-SEM images of HA coatings on NaOH treated micro-pore structured Ti-35Ta-xNb alloy in 2.5 mM Ca(NO3)2∙4 H2O + 1.5 mM NH4H2PO4 with 30 deposition cycles; (a) Ti-35Ta, (b) high magnification of Ti-35Ta, (c) Ti-35Ta-10Nb, (d) high magnification of Ti-35Ta-10Nb.
43
-Fig. 16. FE-SEM images of HA coatings on NaOH treated micro-pore structured Ti-35Ta-xNb alloy in 2.5 mM Ca(NO3)2∙4 H2O + 1.5 mM NH4H2PO4 with 50 deposition cycles; (a) Ti-35Ta, (b) high magnification of Ti-35Ta, (c) Ti-35Ta-10Nb, (d) high magnification of Ti-35Ta-10Nb.
2 H2PO42- + 2 e- → 2 HPO42- + H2 [1]
2 H2PO4
+ 2 e- → 2PO4
+ H2 [2]
2 H+ + 2 e- → H2 [3]
2 H2O + 2 e- → H2 + 2 OH- [4]
Ca2+ + HPO42- → CaHPO4 [5]
In order to detail discussion, Fig 17 and Fig 18 show corelation between voltage and current densities for Ti-35Ta-xNb alloys. From the figures show that the current density value of non treated Ti-35Ta-xNb alloys is lower than that of micro-pore structured Ti-35Ta-xNb alloys. Also, current density is changed with Nb content. The following equation shows the reduction and oxidation of cathode reaction [64].
It is result that chemical reaction take place in electrolyte solution and surface. The anodic oxide film to containing calcium and phosphorus is ionized to calcium ion(Ca2+) and phosphorus ion(PO4
3-) as initial cathode reaction. It's ions are reaction with electrolyte solution, calcium phosphate film is formed in surface. The ionized Ca2+ and PO43-
ions in oxide film is reduced CaHPO4 and H2PO42-
and the reaction is repeated by 3 and 4.
This reaction is carried out in anodized surface, HA is coated on anodized surface by additions 5 and 6.
45
-density. Therefore, the precipitation properties of surface treated alloy is depended on surface morphology and current density.
47
-Fig. 18. The corelation between voltage and current densities on Ti-35Ta-xNb alloys.(a) HA coated Ti-35Ta, (b) HA coated Ti-35Ta-10Nb.
Table 8 Voltage value of bulk and anodize surface on Ti-35Ta-xNb alloy
0.3 V -1.5 V
start end l start - end l start end l start - end l
Bulk
Ti-35Ta -3.66 X 10-4 -7.60 X 10-4 3.94 X 10-4 2.78 X 10-3 1.61 X 10-3 1.17 X 10-3
Ti-35Ta-10Nb -3.05 X 10-4 -5.36 X 10-4 2.31 X 10-4 2.23 X 10-3 1.34 X 10-3 8.9 X 10-4
Anodized
Ti-35Ta -3.44 X 10-4 -1.45 X 10-4 1.99 X 10-4 1.44 X 10-3 1.01 X 10-3 4.3 X 10-4
Ti-35Ta-10Nb -3.05 X 10-4 -1.98 X 10-4 1.07 X 10-4 4.36 X 10-4 2.64 X 10-4 1.72 X 10-4
49 -4.5. Corrosion test
Fig. 19 shows the bulk surface and micro-pore structured Ti-35Ta-xNb alloys polarization curves after potentiodynamic test in 0.9 % NaCl solution at 36.5 ± 1 ℃. The results for Ecorr (corrosion potential), Icorr (corrosion current density) and I300 (corrosion current density of oral environment at 300 mV)is shown in Table 9. These values were obtained from the polarization curves and Tafel plots using both the cathodic and anodic branches of the curves, respectively. From non treated and micro-pore treated Ti-35Ta-xNb alloys surface, the Ecorr value of Ti-35Ta alloy is higher than that of Ti-35Ta-10Nb alloy. Also, the Icorr value of Ti-35Ta alloy is lower than that of Ti-35Ta-10Nb alloy. The polarization curves were shifted to left side with increasing Nb content and micro-pore structured Ti-35Ta-xNb alloys. It is confirmed that barrier layer and Nb2O5 film increased the corrosion resistance and it can be improved osseointegration [72].
Fig. 19. Anodic polarization curves of Ti-35Ta-xNb alloys with surface treatment.
51 Table 9 Ecorr, Icorr and I300mV value of Ti-35Ta-xNb alloy
Alloy E
corrI
corrI
300mVBulk
Ti-35Ta - 380 mV
8.63 X 10-7 A/cm2 1.84 X 10-5 A/cm2Ti-35Ta-10Nb - 393 mV
8.47 X 10-7 A/cm2 4.65 X 10-6 A/cm2Anodized
Ti-35Ta - 479 mV
8.22 X 10-7 A/cm2 3.69 X 10-6 A/cm2Ti-35Ta-10Nb - 429 mV
1.00 X 10-6 A/cm2 3.45 X 10-6 A/cm2Ⅴ.CONCLUSI ONS
In this study, the surface characteristics of hydroxyapatite film on the micro-pore structured Ti-35Ta-xNb alloys by electrochemical deposition method were investigated by using various experimental instruments.
The results were as follows;
1. Microstructure of alloys were transformed form α" phase to β phase, and a needle-like to an equiaxed structure as Nb content increased.
2. The Ti-35Ta and Ti-35Ta-10Nb alloy showed only α"+ β phase and crystal structure from XRD analysis.
3. The number of micro-pore increased as Nb content increased and the micro-pore size increased as voltage increased.
4. Nano network structure was formed on NaOH treated Ti-35Ta-xNb alloys.
5. HA size of Ti-35Ta-10Nb alloy is bigger than that of Ti-35Ta alloy.
6. Flower-like HA shape showed on the Ti-35Ta alloy surface, whereas, the bi-phase flower-like HA shape showed on the Ti-35Ta-10Nb alloy. HA size on the Ti-35Ta-10Nb alloy is bigger than that of Ti-35Ta alloy.
7. Corrosion resistance of Ti-35Ta-xNb alloys increased as Nb content increased.
53
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감사의 글
학교공지사항의 글을 보면서 찾아온 게 엊그제 같은데 벌써 석사과정의 마지막 을 앞두고 본 논문을 작성하는 시기가 찾아오게 되었습니다. 그동안 치과재료학 교실에서 많은 것을 배우고 경험하였고 이러한 바탕이 앞으로 살아가는데 도움 이 될 것이라고 믿어 의심치 않습니다. 짧다면 짧고 길다면 긴 석사과정을 무사 히 마칠 수 있게 도움을 주신 분들에게 이 글에서나마 감사의 글을 전하고 싶습 니다.
우선 지금도 많이 부족하지만 항상 많은 것을 가르쳐주셨고 경험할 수 있게 도 와주시고 지원해주신 지도교수 최한철 교수님의 은혜를 잊지 않겠습니다. 특히 교수님께서 강조하신 행실의 중요성과 예의의 중요성을 항상 기억하고 실천하는 제자가 되도록 하겠습니다. 또한 그동안 실험분석을 할 때 기꺼이 도움을 주셨 고 이번 논문심사에도 애정 어린 조언을 주시고 특히 저의 처음 해외로 나간 한 회에서 무사히 임무를 완수할 수 있도록 도움을 주신 김병훈 교수님과 저희 실 험실의 분석에 많은 도움을 주시고 이번 논문에 관심을 가져주신 안상건 교수님 께 감사의 글을 남기고 싶습니다.
이번 논문을 작성하는데 많은 조언과 관심을 가진 이강 박사님께 감사드리며 그동안 박사님께서 가르쳐주신 지식과 늦게 퇴근할 때마다 저에게 해주신 말씀 은 지금도 좋은 기억으로 저에게 남아있습니다. 맨 처음 아무것도 모를 때 들어 왔는데 상냥하게 저를 대해주신 병학이형과 은주누나, 감사합니다. 그리고 먼저 졸업하여 자리를 잡아 모르는 사항이 있어 연락을 할 때마다 친절하게 답변을
59
-조언을 해주시는 모습에 많이 배웠습니다. 그리고 이번에 들어온 지 몇 개월이 안됬지만 항상 밝고 긍정적이고 밝은 실험실 분위기를 만드는 선영이, 일을 배 울 때도 열의있게 배우는 그 모습을 보고 많이 배웠고 앞으로도 잘할것이라 믿 어 의심치 않는다. 그리고 서로 안지는 오래되었지만 치과재료학교실에 자주 오 면서 최근에 많이 친해진 정인이, 1년 동안 손미경 교수님이 없는 기간에 우리 교수님에게 많은 것을 배우게 될 것이고 분명히 많은 도움이 될거야.
끝으로 항상 묵묵히 저를 지켜봐주시고 항상 제 편인 부모님, 효도다운 효도도 제대로 못해드려도 괜찮다며 말씀해주시는 부모님, 제가 이 석사를 방황하지 않 고 끝낼 수 있게 해준 이유이자 원동력이었습니다. 그리고 자신의 꿈을 위해 오 늘도 즐겁고 열심히 생활하고 있는 내 하나뿐인 동생아, 보기 좋다. 그리고 가 진거라고는 몸밖에 없는 나의 옆에 있어주고 힘들 때마다 나에게 힘을 준 여자 친구, 내옆에 있어서 항상 고맙고 고맙다. 그 외에 석사과정에서 만난 소중한 모든 인연들에게 감사하다는 말을 남기고 글을 마치겠습니다.
2014.02.
조채익 올림