Yu. V. Kolen'ko

On the Possibility of Preparing Fine-Particle Barium Zirconate by Hydrothermal Synthesis

The possibility of preparing fine-particle BaZrO3 by hydrothermal synthesis was examined. The samples prepared using three different starting mixtures were characterized by x-ray diffraction, thermogravimetry, and scanning and transmission electron microscopy techniques. By dissolving solid Ba(NO3)2 in a 0.25 M ZrO(NO3)2 solution (pH 1.5), nanocrystalline powder of the stable polymorph M-ZrO2 was obtained (particle size d = 8–10 nm), independent of the Ba(NO3)2 : ZrO(NO3)2 ratio. Hydrothermal treatment of a ZrO(OH)2 gel in neutral (pH 7.0) and ammonia (pH 11.0) media in the presence of Ba(NO3)2 yielded only the metastable phase T-ZrO2 (d = 10–12 nm), whereas treatment under similar conditions with no Ba(NO3)2 in solution resulted in a mixture of M- and T-ZrO2 . The formation of microcrystalline BaZrO3 (d = 2–5 μm) from a ZrO(OH)2 gel was observed only in a high-pH Ba(OH)2 solution (pH 13.0). Attempts to obtain BaZrO3 by boiling an amorphous ZrO(OH)2 gel at 378 K at atmospheric pressure in a high-pH Ba(OH)2 solution (pH 13.0) for 45 min with the use of microwave heating were unsuccessful: the solid phase consisted of x-ray amorphous ZrO(OH)2 .

Synthesis of Spherical Oxide Particles in Microwave Hydrolysis of Zr(IV), Ce(IV), and Ni(II) Salt Solutions

Elaboration of the methods used to synthesizespherical oxide particles is important in designing newceramic and catalytic materials [1]. Among the numer-ous methods suggested for preparing spherical parti-cles, the sol–gel method is currently the most promis-ing. In particular, Ogihara et al. [2] synthesized a mon-odisperse ZrO

Synthesis of Nanostructured Iron Oxide(III) Powders by Rapid Expansion of Supercritical Fluid Solutions

Nanostructured a-Fe 2 O 3 powders were generated by rapid expansion of supercritical fluid solutions (RESS, T=773 K, P=100 MPa) and by rapid thermal decomposition of precursors in solution ( RTDS, T=623 K, P=100 MPa) on lab RESS-setup from 0,040 M and 0,10 M aqueous solutions of Fe(NO 3 ) 3 . The size of subcrystallites is about 22-29 nm. Comparison of reactivity of α-Fe 2 O 3 powders in a model solid state reaction between a-Fe 2 O 3 powders (generated by RESS from 0,040 M solution) and Li 2 CO 3 (mole ratio 1:1) with literature data on a-Fe 2 O 3 powders produced by other methods shows that its reactivity is markedly higher. A basic essence possibility of zinc ferrite ZnFe 2 O 4 formation immediately at the stage of the rapid expansion (T=773K; P=100 MPa) of a supercritical aqueous solution of zinc and iron nitrates (molar ratio Zn:Fe=1:2; C=0. 1 M) was shown.

Mesoporous Aluminosilicates as a Host and Reactor for Preparation of Ordered Metal Nanowires

The creation of functional nanomaterials with the controlled properties is emerging as a new area of great technological and scientific interest, in particular, it is a key technology for developing novel high-density data storage devices. Today, no other technology can compete with magnetic carriers in information storage density and access rate. However, usually very small (10–1000 nm3) magnetic nanoparticles shows para- or superparamagnetic properties, with very low blocking temperatures and no coercitivity at normal conditions. One possible solution of this problem is preparation of highly anisotropic nanostructures. From the other hand, the use of purely nanocrystalline systems is limited because of their low stability and tendency to form aggregates. These problems could be solved by encapsulation of nanoparticles to a chemically inert matrix. One of the promising matrices for preparation of highly anisotropic magnetic nanoparticles is mesoporous silica or mesoporous aluminosilicates. Mesoporous silica is an amorphous SiO2 with a highly ordered uniform pore structure (the pore diameter can be controllably varied from 2 to 50 nm). This pore system is a perfect reactor for synthesis of nanocomposites due to the limitation of reaction zone by the pore walls. One could expect that size and shape of nanoparticles incorporated into mesoporous silica to be consistent with the dimensions of the porous framework.

IV International Seminar on Nonlinear Processes and Questions of Self-organization in Modern Materials Science

The major goal of the IV International Seminar on Nonlinear Processes and Questions of Self-organization in Modern Materials Science, held in Astrakhan, October 3‐5, 2002, was to highlight the general principles common in the diverse approaches to materials synthesis and characterization and to outline the critical issues in different areas of modern materials science. In most instances, materials research is concentrated on systems which evolve under highly nonequilibrium conditions and are open to energy and mass exchange with the environment. For this reason, the study of selforganization processes in physicochemical systems is of immense importance.