Ahmad Md Imteyaz, Bhattacharya S S, Fasel Claudia, Hahn Horst
Department of Metallurgical and Materials Engineering, Materials Testing Facility, Materials Forming Laboratory, Indian Institute of Technology Madras, Chennai 600036, India.
J Nanosci Nanotechnol. 2009 Sep;9(9):5572-7. doi: 10.1166/jnn.2009.1110.
Of the three crystallographic allotropes of nanocrystalline titania (rutile, anatase and brookite), anatase exhibits the greatest potential for a variety of applications, especially in the area of catalysis and sensors. However, with rutile being thermodynamically the most stable phase, anatase tends to transform into rutile on heating to temperatures in the range of 500 degrees C to 700 degrees C. Efforts made to stabilize the anatase phase at higher temperatures by doping with metal oxides suffer from the problems of having a large amorphous content on synthesis as well as the formation of secondary impurity phases on doping. Recent studies have suggested that the as-synthesised phase composition, crystallite size, initial surface area and processing conditions greatly influence the anatase to rutile transformation temperature. In this study nanocrystalline titania was synthesised in the anatase form bya chemical vapour synthesis (CVS) method using titanium tetra iso-propoxide (TTIP) as a precursor under varying flow rates of oxygen and helium. The anatase to rutile transformation was studied using high temperature X-ray diffraction (HTXRD) and simultaneous thermogravimetric analysis (STA), followed by transmission electron microscopy (TEM). It was demonstrated that the anatase-rutile transformation temperatures were dependent on the oxygen to helium flow rate ratio during CVS and the results are presented and discussed.
在纳米晶二氧化钛的三种晶体同素异形体（金红石、锐钛矿和板钛矿）中，锐钛矿在各种应用中展现出最大潜力，尤其是在催化和传感器领域。然而，由于金红石在热力学上是最稳定的相，锐钛矿在加热到500摄氏度至700摄氏度范围内时容易转变为金红石。通过掺杂金属氧化物在更高温度下稳定锐钛矿相的努力存在合成时非晶态含量高以及掺杂时形成二次杂质相的问题。最近的研究表明，合成后的相组成、微晶尺寸、初始表面积和加工条件对锐钛矿向金红石的转变温度有很大影响。在本研究中，以四异丙醇钛（TTIP）为前驱体，通过化学气相合成（CVS）法在不同氧气和氦气流速下合成了锐钛矿形式的纳米晶二氧化钛。使用高温X射线衍射（HTXRD）和同步热重分析（STA），随后进行透射电子显微镜（TEM）研究了锐钛矿向金红石的转变。结果表明，锐钛矿 - 金红石转变温度取决于CVS过程中的氧气与氦气流速比，并给出了结果并进行了讨论。
