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標題: Electrochemical Synthesis and Characterization of Barium Titanate Films
作者: 伍祖聰
Wu, Chu-Tsun
關鍵字: 鈦酸鋇;barium titanate;陽極氧化;開路電位;動態陽極極化;濺鍍;anodic oxidation;open-circuit potential;potentiodynamic polarization;sputtering
出版社: 材料工程學研究所
本研究以電化學陽極氧化法在混和濃度0.5 M醋酸鋇及2 M氫氧化鈉的電解液中,於寬廣的電解電壓範圍內以電壓掃描及定電流模式鍍著鈦酸鋇膜操作溫度為55℃,實驗結果顯示鍍膜的表面形貌可單獨由改變電壓所控制。當電解電壓低於30V時會形成球狀小顆粒鈦酸鋇薄膜,而電解電壓高於60V時則會形成彈坑狀大顆粒鈦酸鋇厚膜。
彈坑狀大顆粒鈦酸鋇厚膜在0.1 M NaOH的腐蝕環境中,以開路電位試驗及動態陽極極化試驗測試其耐蝕性,而以純鈦片及鈦陽極氧化TiO2膜作為對照組。鈦酸鋇厚膜和TiO2膜具有相當穩定的開路電位,約在0.02 V (vs. Ag/AgCl),此電位相當接近氧氣在陰極與水反應的平衡電位。動態陽極極化試驗結果顯示鈦酸鋇膜相較TiO2膜及純鈦具有較大的極化電阻及較低的腐蝕電流,因此具有較佳的耐蝕性。此低的陽極電流顯示OH-離子透過鈦酸鋇膜的孔洞或裂縫進行擴散,在底材進行氧氣生成的陽極反應。

Barium titanate films were synthesized by potentiodynamic and galvanostatic polarization over a wide electrolytic voltage range using 0.5 M Ba(CH3COO)2 and 2 M NaOH as the electrolyte at 55℃. The morphology of the films can be tailored by solely varying the applied electrolytic voltage in the same electrolyte. The BaTiO3 thin films possessed uniformly distributed spherical-like small particles at voltages under 30 V. At voltages above 60 V, crater-shaped and large-grained BaTiO3 thick films were formed.
The crater-shaped and large-grained cubic BaTiO3 films were used for further corrosion resistance measurements using 0.1 M NaOH as the corrosive environment. Anodized TiO2 films and pure titanium specimens were also investigated for comparison. The corrosion behavior of the films was studied by means of open-circuit potential measurements and potentiodynamic polarization methods. Open-circuit potential measurements showed that BaTiO3 and TiO2 films existed quite stable corrosion potential of about 0.02 V (vs. Ag/AgCl). This corrosion potential is very close to the open-circuit cathodic potential of oxygen reacting with water. From potentiodynamic polarization results the BaTiO3 films posses better corrosion resistance than TiO2 and pure Ti specimens. The high polarization resistance of BaTiO3 films suggests that the anodic current may be due to the O2 evolution on the exposed Ti surface by transporting OH- ions through open pores of the oxide to react on the titanium surface.
Spherical-like BaTiO3 films were also synthesized on heterogeneous substrates such as silicon wafer by combining sputtering and electrochemically anodic oxidation techniques over a wide electrolytic duration from a few seconds to 24 hours. From the J-V curves of anodization, Ti-coated substrates with much smaller grains are electrochemically more active than pure titanium substrates. The substrates have developed much large grains of BaTiO3 film as compared to the tiny grains for pure titanium substrates at the initial stage of growth. The most possible reaction route for the formation on Ti/Si substrates is that BaTiO3 particles nucleate and grow in the liquid phase before depositing onto the substrates. The liquid state reaction would enhance the growth of the particles and then result in the large grain size. For pure titanium substrate BaTiO3 particles nucleate mainly on the surface of titanium oxide precursors. The solid state reaction would then cause a fast nucleation but slow growth, therefore much smaller grain sizes are obtained.
Appears in Collections:材料科學與工程學系

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