The structural transformation of anatase TiO 2 by high-energy vibrational ball milling
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The structural transformation of anatase TiO2 by high-energy vibrational ball milling Suchitra Sen,a) M. L. Ram, S. Roy, and B. K. Sarkarb) Central Glass & Ceramic Research Institute, Calcutta 700032, India (Received 13 August 1997; accepted 30 June 1998)
The structural transformation of anatase TiO2 by high-energy vibrational ball milling was studied in detail by different analytical methods of x-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). This structural transformation involves both phase transition and nanoparticle formation, and no amorphization was observed. The crystallite size was found to decrease with milling time down to nanometer size ,13 nm and approaching saturation, accompanied by phase transformation to metastable phases, i.e., TiO2 (II), which is a high-pressure phase and TiO2 (B), which was identified in ball-milled powder reported for the first time in this paper. These phases eventually started transforming to rutile by further milling.
I. INTRODUCTION
It is well known that several phenomena occur in powder materials, metals or oxides, during mechanical comminution process1 such as (i) amorphization,2 (ii) increase of surface reactivity by formation of nanoparticles,3 (iii) mechanical alloying,4 and (iv) phase transformation.5 A phase transformation in anatase TiO2 has already been observed by high-energy ball milling by the present authors6 and Begin-Colin et al.7 also. The transformation of anatase TiO2 to a new polymorphic phase TiO2 (II) with orthorhombic structure has previously been formed by other authors from rutile8 and anatase9 only at very high pressure in the range of 150–1000 kbar by the shock wave technique. This form of TiO2 is of higher density compared to anatase having 8 : 4 coordination and is only possible if TiyO radius ratio is smaller as it is usually. This suggests that a change in atomic spacing occurs in this kind of milling process, resulting in atomic disordering in the normal structure of anatase TiO2 . Though the recent interest in nanostructured materials has been stimulated by the work of Gleiter10 in 1990 on materials produced by the gas-condensation method, the method of ball milling has received significant attention in recent times for nanoparticle formation. In the present paper, we report the experimental results of anatase TiO2 milled in a high-energy vibrational ball mill and characterized in detail with the help of x-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM), and we try to understand the mechanism of phase transition and
a)
Address all correspondence to this author. Emeritus Scientist of CSIR, I.A.C.S, Calcutta 32, India.
b)
J. Mater. Res., Vol. 14, No. 3, Mar 1999
http://journals.cambridge.org
Downloaded: 17 Mar 2015
nanoparticle formation with their interrelation, if there is any at all. II. EXPERIMENTAL
High-purity anatase TiO2 powder (99.99%) from Aldrich, Milwaukee, WI was used a
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