Characterization of crystalline titanium dioxide synthesized at room temperature

Abstract

A process has been developed to synthesize crystalline titanium dioxide powders from aqueous solutions at low temperatures (T<100°C) and atmospheric pressure. Processing at slow reaction rates causes the formation of the thermodynamically favored rutile phase. Faster reaction rates promote the formation of anatase, the statistically favored phase. Processing at intermediate rates causes a mixture to be formed (Fig. 1). This paper reports the TEM and SEM characterization of rutile, precipitated at 40°C.Specimens for TEM were collected on holey carbon grids suspended vertically in the stirred solution. After removal, the grids were washed in isopropyl alcohol and dried under a heat lamp. For SEM analysis, a drop of the solution was placed on the specimen holder and dried. The top surface was then washed with isopropyl alcohol to remove any contamination and observed.The bright field image (Fig. 2b) of the rutile precipitates shows them to have a nominal size of 50-100 ran. The sharpness of the (002) ring in the electron diffraction pattern (Fig. 2a) indicates the needles are elongated in the [002] direction. The corresponding dark-field image (Fig. 2c) shows that individual needles are comprised up of smaller particulates (HR-TEM shows them to be ∼3 nm in size). It is important to note that in each needle, all the particulates diffract together or they all do not, indicating a common orientational relationship.