石墨與二氧化鈦複合材料在氧空缺影響下之晶體結構與微結構分析及其應用

The Crystal Structure, Microstructure and Application of Graphite-Titanium Dioxide Composites under the Influence of Oxygen Vacancies

張競予(Ching-Yu Chang)

指導教授 ： 謝宗霖

國立臺灣大學/工學院/材料科學與工程學研究所/碩士(2014年)

https://doi.org/10.6342/NTU.2014.10398

摘要

本文探討以石墨作為基材(matrix)之陶瓷複合材料：石墨/銳鈦礦二氧化鈦(後簡稱為銳鈦礦)及石墨/金紅石二氧化鈦(後簡稱為金紅石)，在95 % N2 + 5 % H2氣氛下高溫燒結成塊材後，其微結構與晶相的演化，並呈現此複合材料應用於導電塗料的成果，所使用的起始原料皆為粉末。
首先，本研究發現石墨的高還原能力，會增加複合系統中的氧空缺濃度，致使系統中的銳鈦礦及金紅石之晶體結構發生變化：其一，石墨/銳鈦礦複合系統中的銳鈦礦，其相轉變至金紅石之溫度低於純銳鈦礦系統，此現象源自於系統中氧空缺濃度的提高，使得鈦與氧原子重新排列的活化能降低；其二，本研究利用不同比表面積的石墨作為基材，製備石墨/金紅石複合系統，以探究石墨對於金紅石的影響為何。實驗結果顯示，此系統燒結過後皆會出現異於金紅石以及石墨的相，藉由TEM選區繞射圖形鑑定為缺乏氧離子的亞氧化鈦(TinO2n-1)，隨著選用石墨的比表面積增加，所得到成分比例之缺氧量亦會隨之提高，分別為Ti20O39、Ti8O15以及Ti7O13。本研究推論，高比表面積的石墨，能夠吸附較多的金紅石粉末，增加金紅石內之氧空缺濃度。
另一方面，從石墨/二氧化鈦複合系統的電阻量測中發現，由於複合材料中的二氧化鈦能夠吸收紫外光波段，進而產生光致激發載子，使得複合材料之電阻值在照光前後發生改變。為了將此系統中，光致調控電阻之特性應用於導電塗料，本研究仿造鉛筆成分，於複合系統中添入高嶺土，其除了具備高導電性外，同樣具有敏銳的光致調控電阻特性。最後，我們根據研究成果提出兩種導電塗料的應用方法，適用於電腦閱卷讀卡系統之判讀，期能改善現今光學判讀之準確率。

關鍵字

石墨 ； 二氧化鈦 ； 複合結構 ； 氧空缺 ； TinO2n-1 ； 導電塗料

並列摘要

In this study, we unveiled the evolution of the crystal structures and the unique application of several graphite-matrix composites: graphite/A-TiO2 (anatase TiO2) as well as graphite/R-TiO2 (rutile TiO2). All specimens were prepared through press-and-sinter process under 95 % N2 + 5 % H2 reducing atmosphere.
Initially, the crystal structures of A-TiO2 and R-TiO2 in the composites were quite abnormal. The phenomena should be attributed to large amounts of oxygen vacancies reduced by graphite. In graphite/A-TiO2 system, the phase transition temperature from A-TiO2 to R-TiO2 was lower than pure A-TiO2 system, since high concentration of oxygen vacancy would render rearrangement of Ti2+ and O2- easier. In the case of graphite/R-TiO2, some oxygen-deficient phase — TinO2n-1 was acquired. Interestingly, when graphite with higher specific surface area was used, TinO2n-1 with more oxygen deficiency would be correspondingly obtained, including Ti20O39, Ti8O15 and Ti7O13 respectively. According to this tendency, we proposed that graphite with higher surface area could absorb more R-TiO2 to induce more oxygen vacancies in the composites.
Finally, the resistance of the composites would alter sensitively after illumination of UV light due to generation of photo-induced carriers from TiO2. Considering the application of this specific property to conductive paint, we added kaolin into the composites to make them real pencils. It was found that their resistance behavior was quite similar to the original composites. Based on this essential result, two kinds of application of the conductive paint we prepared were offered. By means of the application, improving accuracy of judging answering cards could be accomplished.

並列關鍵字

graphite ； TiO2 ； composite ； oxygen vacancy ； TinO2n-1 ； conductive paint

參考文獻

1. 柯揚船．皮特斯壯, “聚合物：無機奈米複合材料” 五南: 臺北市, (2004)

2. H. O. Pierson, “Handbook of Carbon, Graphite, Diamonds and Fullerenes,” William Andrew, (1994).

3. D. D. L. Chung, “Review Graphite,” Journal of Materials Science,” 37 [8] 1475-89 (2002).

4. M. C. Sousa and J. W. Buchanan, “Observational Models of Graphite Pencil Materials,” Computer Graphics Forum, 19 [1] 27-49 (2000).

5. X. Chen and S. S. Mao, “Titanium Dioxide Nanomaterials:  Synthesis, Properties, Modifications, and Applications,” Chemical Reviews, 107 [7] 2891-959 (2007).