Yoshiko Suwa

Polymorphic transformation of titanium dioxide by mechanical grinding

The effect of mechanical grinding on the structural transformation of titanium dioxide was studied by using several anatase samples prepared from different starting materials and with various particle sizes. Three anatase samples were prepared by hydrolysis of Ti(O·i-C3H7)4, TiCl4, and TiOSO4·2H2O and one is commercial reagent grade anatase. Each of the as-prepared or heat-treated samples (1.0 g) was ground in a mortar of sintered alumina for up to 96 h in air. The stability of brookite synthesized by grinding was examined by heating in air and under hydrothermal pressure. From the relative amount of the phases estimated by the measurement of the integrated intensity of X-ray line profile and of X-ray crystallite size, DTA and TG, IR spectra, and observation by electron microscope, it is concluded that: 1. the transformation proceeds by a consecutive process from anatase to rutile through brookite by grinding; 2. the smaller the initial particle size of anatase, the more stable the intermediate phase of brookite; 3. the very fine crystals of 5∼20 nm of anatase can be grown to 50∼150 nm of rutile by grinding for 96 h; 4. the rate process of the transformation depends on the initial particle size and is independent of the difference in starting materials or of surface adsorbants; 5. an appropriate lattice distortion introduced by grinding is considered to stabilize the brookite phase; and 6. the lattice constant and the density of brookite synthesized by grinding,a0=0.5447±0.005 nm,b0=0.9150±0.0005 nm,c0=0.5141±0.0005 nm, andDx=4.14 g cm−3 agree with those in natural brookite.

Preparation and properties of yttrium magnesium silicate with apatite structure

A new phase of yttrium magnesium silicate having the apatite structure was prepared at 1500°C in air. Its chemical composition can be varied from (Y4Mg)Si3O13 to (Y4∼3.3Mg1∼1.3)Si3∼3.4O13. Hexagonal unit cell dimensions ao and co of (Y4Mg)Si3O13 are 9.298 ± 0.002A and 6.635 ± 0.001A respectively and its axial ratio c/a is 0.714. It is optically uniaxial negative with ϵ = 1.810 ± 0.005, ω = 1.820 ± 0.005, ω − ϵ = 0.010. Cleavages parallel and perpendicular to the c-axis were recognized.

Synthesis of fluoride garnets {Na3}[M3+2](Li3)F12 (M = Al, Cr, and Fe) from aqueous solution and their properties

Abstract The garnet-type fluorides, Na3M2Li3F12 (M = Al, Cr, and Fe) were synthesized as the coprecipitates of ∼1 to 10 μm powders from HF solutions. The garnet structures were always obtained under acidic conditions. The incorporation of water molecules into the structure of the Cr and Fe garnets was observed. After heat treatment at 300°C, very small unknown peaks were observed in the X-ray powder pattern in addition to the garnet phase which had a slightly smaller value of the lattice constant than that of hydrous garnets. From the measurement of magnetic properties and Mossbauer effects, the Fe and Cr garnets were found to be paramagnetic with both ions in the trivalent state. Presentation of infrared spectra of the garnets is also included.