Morphology control and texture of hematite particles by dimethylformamide in forced hydrolysis reaction
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Morphology control and texture of hematite particles by dimethylformamide in forced hydrolysis reaction Kazuhiko Kandori, Naoki Ohkoshi, Akemi Yasukawa, and Tatsuo Ishikawa School of Chemistry, Osaka University of Education, Asahigaoka 4-698-1, Kashiwara-shi, Osaka 582-8582, Japan (Received 15 January 1997; accepted 20 August 1997)
The effects of dimethylformamide (DMF) on morphology and texture of hematite particles produced from a forced hydrolysis reaction of FeCl3 –HCl solution were investigated by transmission electron microscopy (TEM), x-ray diffraction (XRD), Fourier transform infrared spectrometry (FTIR), thermogravimetry and differential thermal analysis (TG-DTA), N2 and H2 O adsorption, and zeta potential measurements. The morphology of synthetic hematite particles was concentration dependent; they changed from large sphere with a diameter of ca. 600 nm to diamond-like shape with increasing DMF concentration in the aging solution accompanying a reduction of their size to 80 nm without incorporation of DMF in the particles. This fact was explained by an acceleration of phase transformation from b –FeOOH to hematite with an elevation of the solution pH owing to dimethylamine produced from a hydrolysis of DMF at an elevated temperature. TEM and XRD suggested that the diamond-like hematite particles formed above 6–10 vol % DMF possess a single-crystal nature. Gas adsorption technique revealed that the particles produced above 10 vol % DMF possess a high thermal stability. TG and FTIR indicated that the hematite particles produced with DMF contained small amounts of OH2 ions in the lattice though they provided a single-crystal nature.
I. INTRODUCTION
Uniform metal oxide particles with various morphologies are model materials to utilize for understanding aggregation, flocculation, and precipitation. The advantages of using powders consisting of uniform particles, especially spherical ones, for processing ceramic materials have been amply documented. Despite their wide applications, little is known about the structures and properties of uniform particles. Recently, the authors have focused on synthetic hematite (a –Fe2 O3 ) particles of small spherical (diameter: ca. 100 nm) and cubic shapes (edge length: ca. 1 mm),1 large spherical (diameter: ca. 820 nm), and diamond-like shapes (long axis length: ca. 60 nm)2 produced from forced hydrolysis reactions of FeCl3 –HCl solution and characterized these particles by various means. It was revealed in the previous paper that the polycrystalline uniform cubic and large spherical hematite particles produce ultramicropores by a thermal treatment in vacuo. More recently, we found that various kinds of amines influence the formation of hematite particles from forced hydrolysis reaction of acidic FeCl3 –HCl solution and attain characteristic hematite particles with various morphologies such as cubic (edge length: ca. 400 nm), double-spherical (long axis length: ca. 600 nm), small spherical (diameter: ca. 100 nm), and diamond-lik
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