氟濃度及應變量對鈦金屬耐蝕性質之影響

Effect of Fluoride Concentration and Strain on the Corrosion Resistance of Titanium

本研究利用電化學交流阻抗頻譜（electrochemical impedance spectroscopy, EIS）量測技術探討氟濃度及抗張應變量對鈦腐蝕行為的影響。選用的材料為ASTM F67 grade 2的商業級純鈦。利用抗張試驗機來控制鈦試片所受到的各種抗張應變量（分別為0、1、2、4、5及10%），並選用含不同NaF濃度（0.001～1%）的1% NaCl混合水溶液為試驗環境（pH=6）。利用EIS測得材料的極化電阻（polarization resistance, Rp），Rp值越大表示材料抗腐蝕能力愈佳。利用X光光電子能譜、歐傑電子能譜及能量散佈光譜進行材料表面的化學分析，並以掃瞄式電子顯微鏡觀察材料表面腐蝕形態。實驗結果顯示，Rp值受到應變量及NaF濃度明顯的影響（p<0.001），且隨著抗張應變量及NaF濃度的增加而漸減。不論抗張應變量的大小，當NaF濃度低於0.01%時，鈦表面的氧化膜（主要為TiO2）仍具有良好的保護性；當NaF濃度超過0.1%時，鈦表面氧化膜已遭氟離子破壞而生成Ti-F的化合物（Na2TiF6）。從避免鈦補綴物在口腔中遭氟離子侵蝕的角度而言，本研究結果在臨床上可提供牙科用預防藥劑（prophylaxis agents）中含氟量多寡的選用參考，並幫助瞭解應變量對鈦腐蝕性質的影響。

Titanium, which has marked corrosion resistance, can corrode in some fluoride-containing environments. In this study, the corrosion behavior of titanium in 1 % NaCl + 0~1% NaF solution (pH=6) under different tensile strains was investigated with the electrochemical impedance spectroscopy (EIS) measurement technique. The polarization resistance (Rp), which is inversely proportional to the corrosion rate, of titanium in the test solution was obtained from the EIS data. Different tensile strains, namely 1, 2, 4, 5 and 10 %, were applied to the test specimens with a tensile testing machine during the corrosion tests. Surface chemical analyses were performed with X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), and energy dispersive spectroscopy (EDS). Corrosion morphology was characterized with scanning electron microscope (SEM). The results show that the NaF concentration and tensile strain exerted a statistically significant influence on the Rp (p<0.001). The Rp decreased with increasing NaF concentration and increasing tensile strain. When the NaF concentration was lower than 0.01 %, the high Rp value was mainly ascribed to the formation of protective titanium dioxide (TiO2) on the metal surface. However, when the NaF concentration was higher than 0.1 %, the protectiveness of TiO2 was overcome by fluoride ions, leading to significant corrosion of the titanium. In view of the protection against fluoride ion attack in oral environments, the study recommends the use of optimal fluoride-containing prophylaxis agents. The effect of tensile strain on the corrosion resistance of titanium is also discussed.