Papers by Author: Hoon Park

Abstract: TiO2 nanoparticle was synthesized by the flame method using a metal organic precursor of titanium tetraisopropoxide (TTIP, Ti(OC3H7)4), which was controlled by varying the ratio and flow rate of gas mixtures consisting of oxygen (oxidizer), methane (fuel) and nitrogen (carrier gas). The morphology and the size distribution of nanoparticles were observed with TEM and FESEM, and the phase evolution was analyzed by XRD measurement using a monochromator. The crystalline phases of TiO2 nanoparticle depended strongly on the temperature distribution in the flame, whereas the morphology was not sensitive. During the flame synthesis of TiO2 nanoparticle, anatase TiO2 nanoparticle was predominantly synthesized at the high flame temperature and rapid flame cooling condition. The low flame temperature and long flame length enabled to form almost rutile TiO2 nanoparticle (>95%). The anatase nanoparticle was formed by a homogeneous nucleation and has finally kept the anatase phase without the phase transformation any more in the flame. However, the rutile TiO2 nanoparticle was not formed directly and homogeneously in flame, and was manufactured by the phase transformation such as amorphous
anatase
rutile. It was proved that the rutile phase was nucleated heterogeneously from the amorphous or anatase particles.

Abstract: The spherical anatase TiO2 nanoparticle of 50 nm in diameter was manufactured by flame method and was subsequently heat-treated to investigate the transformation behavior from anatase to rutile using TEM observation. The anatase particle was facetted at the free surface and a neck formed between the anatase particles prior to the phase transformation. This resulted in the severe lattice distortion at the region of the interface. Unfortunately, we could not find the rutile grain nucleated in the anatase particle due to very fast grain growth. All the phase boundaries observed in HRTEM images existed in the contact between anatase and rutile particles. The nucleation of rutile phase in anatase particle was suppressed at the low heat-treated temperature but the grain growth of rutile particles after the phase transformation grew very fast by the sweeping phenomena of grain boundary. It leaded to the microstructure without the rutile phase traped in anatase particle.