采用原位变温X射线衍射技术研究不同气氛下TiO_2的相变机理

Study of the Phase Transformation of TiO_2 with In-situ XRD in Different Gas

以TiO2凝胶为模型化合物,利用原位变温X射线衍射(XRD)研究了不同气氛下TiO2的相变过程,对比研究原位和非原位情况下的相变情况。研究表明,各种气氛下,原位和非原位时不同气氛下TiO2相变过程均有不同。其中,最常见的空气气氛下非原位与原位测定的TiO2从无定型向锐钛矿转变的温度相差近200℃。在500℃以前,TiO2从无定型向锐钛矿转变主要受动力学控制,高温相变过程后在冷却过程中会发生不同程度的可逆相变。原位研究的结果表明,相对空气气氛,惰性的氮气虽会在一定程度上抑制锐钛矿相的生长,但却会加速锐钛相向金红石相转变的进程。还原性的氢气氛较之氩气处理的TiO2具有更好的结晶度,这说明外部环境中的氧可以促进TiO2晶相生长,但在无外部氧环境的情况下,还原性气氛可以一定程度地抵消缺氧环境对相变的不利影响。

TiO2 sample was prepared by sol-gel method from chloride titanium.The phase transformation of the prepared TiO2 sample was studied by in-situ XRD and normal XRD in different gas.The experimental results showed that the phase transformation temperatures of TiO2 were different under in-situ or normal XRD in different kinds of gas.The transformation of amorphous TiO2 to anatase was controlled by kinetics before 500 ℃.In-situ XRD showed that the growth of anatase was inhibited,but the transformation of anatase to rutile was accelerated under inactive nitrogen in contrast to air.Also better crystal was obtained under hydrogen than in argon.These all showed that external oxygen might accelerate the growth of TiO2,but reduced gas might partly counteract the negative influence of lack of external oxygen.The mechanism of phase transformation of TiO2 was studied by in-situ XRD in order to control the structure in situ.