臺灣博碩士論文加值系統

鎂合金在近年在作為可降解醫材的開發上備受矚目，鎂具有無毒性、生物相容性和可降解等優點，可以改善多種醫材的性能和限制，然而鎂合金有降解過快造成組織痊癒前無法維持植入物的功能等問題，因此有許多關於鎂合金的研究是著重在控制腐蝕速率。
在過去很多研究把重點放在鎂合金腐蝕的整體變化來進行定量分析，然而只考慮總體腐蝕的變化並不足以確定植入物的機械性能。因此本研究使用微計算機斷層掃描來研究鎂合金局部和內部的腐蝕行為。μCT提供了實用的方法來研究腐蝕行為的細節，但其在可降解生物材料中的應用仍需要進一步去評估，因此本研究的目的是確認使用μCT進行腐蝕坑行為進行定性和定量分析的可行性，而結果顯示使用μCT分析腐蝕坑是可行且有用的方法。特別是在三維影像、腐蝕坑深度和表面積的探討，μCT比其他許多研究腐蝕行為之方法是更直觀且更具優勢的。
此外在本研究中也利用μCT得到的腐蝕實驗數據，開發了分析鎂合金孔隙腐蝕行為的模擬模型，而模擬中的腐蝕坑行為和趨勢與實驗結果是一致的。以此模擬模型對表面積變化作更進一步的討論，藉由模擬長時間腐蝕的結果可以看出表面積變化對質量損失速率的影響在後期是不能忽視。另外此模擬腐蝕模型還具有潛力去結合有限元素法，來探索機械性質與腐蝕之間的相互影響，以實現可降解醫材和植入物的開發。

Magnesium alloys have recently been attracting attention as a degradable biomaterial. They have advantages including non-toxicity, biocompatibility, and biodegradability. To develop magnesium alloys into biodegradable medical materials, previous research has quantitatively analyzed magnesium alloy corrosion by focusing on the overall changes in the alloy.
However, considering only the changes in overall corrosion behavior is not sufficient to determine the mechanical properties related to biomedical implants. Therefore, this study investigated local and internal corrosion patterns using micro-computed tomography. The introduction of μCT (X-ray micro-computed tomography) provides a practical approach by which to study corrosion behavior in detail, but its use in the degradable biomaterials requires further assessment. The objective for this study is to examine the feasibility of using μCT for the qualitative and quantitative analysis of corrosion pits behavior. The results showed that μCT is a feasible and helpful method for analyzing corrosion pits. Especially in the three-dimensional image, the depth of the corrosion pits and the surface area, relative to many other methods of studying corrosion behavior, μCT is more intuitive and more advantageous.
Furthermore, in this study, the simulation models used to analyze the pitting corrosion behavior of magnesium alloys were developed by using the corrosion experimental data from μCT. The trend of the pit behavior and corrosion patterns in the simulation were consistent with the experimental results. Using this simulation model to further discuss the surface area changes, and based on these validated models considering long-term applications, it was shown that the effect of changes on the surface area on mass loss rate cannot be ignored. Furthermore, there is further potential to combine this method with the FE method to explore the interaction between mechanical factors and corrosion in order to develop degradable materials and biomedical implants.

中文摘要 I
ABSTRACT II
誌謝 III
CONTENTS V
LIST OF TABLES VIII
LIST OF FIGURES IX
CHAPTER 1. INTRODUCTION 1
1.1 Research background 1
1.1.1 Advantage of magnesium alloy as medical material 1
1.1.2 Limitations of Mg alloy as a medical material 1
1.1.3 Development and improvement of Mg alloy as a medical material 1
1.2 Motivation and purposes 2
1.3 Introduction to magnesium 3
1.3.1 Physical properties of magnesium 3
1.3.2 Chemical properties of magnesium 4
a. Hydrogen Evolution Measurement 4
b. Thermodynamic tendency 4
c. Surface film 4
1.3.3 Magnesium alloys 5
1.4 Corrosion of Magnesium and Magnesium Alloys 7
1.4.1 Localized corrosion of passive films 7
1.4.2 Localized corrosion of coated Mg alloys 8
1.4.3 Factors that affect corrosion 9
1.4.4 Evaluation of corrosion 9
a. Mass loss measurements 9
b. Electrochemical measurements 11
c. The issue of changes in surface area 13
1.5 Evaluation of magnesium alloy corrosion pits using μCT 14
CHAPTER 2. MATERIALS AND METHODS 16
2.1 Experimental Procedure 16
2.1.1 Sample preparation 17
2.1.2 Microstructural characterization 17
2.1.3 Immersion Tests 17
2.1.4 Micro-computed tomography 17
2.1.5 Image and data processing 18
2.1.6 Overall corrosion rate of specimens 21
2.2 Algorithm for simulated corrosion 22
CHAPTER 3. RESULTS 26
3.1 Experimental Procedure 26
3.1.1 Feasibility of using μCT to study corrosion behavior 26
a. Comparison of μCT and SEM images 26
b. Comparison of ML with previously reported results 28
3.1.2 Using μCT to analyze corrosion pits 29
a. The issue of surface area 30
b. Mass loss per unit area 31
c. Number of pits 32
d. Maximum depths of corrosion pits 34
e. Ratio of corrosion area on the surface 35
f. Eccentricity and pit sizes 36
3.2 Simulation 38
3.2.1 Convergence and Stability Analysis of ML 40
a. Convergence analysis by different grid sizes 40
b. Stable analysis by the same grid size 41
3.2.2 ML comparison in simulation and experiment 43
3.2.3 Comparison of corrosion patterns in the simulation and experiment is sections at different depths 44
CHAPTER 4. DISCUSSION 48
4.1 EXPERIMENTAL PROCEDURE 48
4.2 SIMULATION 50
CHAPTER 5. CONCLUSION 52
APPENDIX: THE EFFECT OF SURFACE AREA INCREASE AND REMOVAL OF THE SUSPENSION ELEMENTS FOR A LONG-TERM CORROSION SIMULATION 54
REFERENCES 57

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