A. S. Vanetsev

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 .

Microwave synthesis of lithium, copper, cobalt, and nickel ferrites

One of the most important problems of modernmaterials science is the development of new methodsfor preparing functional materials, which allow one todecrease power inputs and synthesis time [1]. Micro-wave treatment is a promising method that satisfiesthese demands.Microwave heating has some advantages over com-mon methods for heating solids and liquids. Amongthese advantages, noteworthy is the high rate and lowthermal lag, the absence of the contact between aheated material and a heater, the uniformity of bulkheating, the possibility to selectively heat componentsin mixtures, and the high efficiency [2].The absorption of microwave radiation by sub-stances occurs through two basic mechanisms associ-ated with rotation of dipoles and ionic currents. There-fore, the substances with a high permittivity or ionicconductivity absorb microwaves most efficiently. Mate-rials with a low dielectric loss factor and insulators canbe heated after adding compounds that absorb micro-waves, for example, magnetite, silicon carbide, orgraphite [2]. In salt systems, water of crystallizationmay act as such an “additive.”Over the past few years, microwave treatment hasbeen used for preparing complex oxides ( CuFe

Effect of hydrothermal and ultrasonic/hydrothermal treatment on the phase composition and micromorphology of yttrium hydroxocarbonate

The effect of hydrothermal and ultrasonic/hydrothermal treatment on the phase composition and micromorphology of yttrium hydroxocarbonates has been studied. The hydrothermal treatment of a suspension of amorphous yttrium hydroxocarbonate hydrate, Y(OH)CO3 · 1.25H2O, does not significantly alter the composition of the powder, while ultrasonication directly in the course of hydrothermal treatment under the same conditions yields crystalline yttrium hydroxocarbonate Y(OH)CO3. The thermolysis of yttrium hydroxocarbonates Y(OH)CO3 · xH2O and Y(OH)CO3 has been studied.

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

Microwave Synthesis of γ-Fe2O3

Fine-particle Fe2O3 is prepared via microwave processing of Fe(NO3)3 · nH2O, followed by low-temperature annealing. The particle size of the resulting γ-Fe2O3 is 5–6 nm after microwave processing and 80–110 nm after subsequent low-temperature heat treatment.

Kinetics of ZnFe 2 O 4 Formation in a Microwave Field

34 The development of new methods for synthesis of compounds and materials and the improvement of existing ones with the goal of decreasing time and energy consumption are among the priorities of modern inorganic chemistry. One way to achieve these goals is to use microwave heating [1, 2]. Microwave heating makes it possible to carry out very important physicochemical processes, such as dehydration, destruction of salt and hydroxide precursors, synthesis of multicomponent compounds, and sintering of ceramics, considerably enhancing the rates of these processes compared to conventional heating [1]. The amount of literature regarding the chemical applications of microwave heating has grown by several times during the last ten to fifteen years. Among others, it includes numerous works on the microwave-assisted synthesis of individual and multicomponent oxide compounds [3]. Experimental studies of the kinetics and mechanisms of solid-phase reactions in powdered reagent mixtures combined with formal kinetic analysis for suggesting the reaction mechanism (at least the rate-controlling stage) are of considerable interest. In this context, this work studies the mechanism of microwave-enhanced solid-phase reactions in the system

Synthesis of Nd0.7Ba0.3MnO3 via Microwave Processing

Nd0.7Ba0.3MnO3 is synthesized via microwave processing of neodymium, barium, and manganese nitrates in solution. It is shown that microwave processing allows the temperature and duration of Nd0.7Ba0.3MnO3 synthesis to be reduced as compared to the conventional ceramic route. The physicochemical properties of the resultant material compare well with those of samples prepared by ceramic processing techniques.

Kinetics of microwave-enhanced solid-phase reaction of NiFe2O4 formation

Microwave-enhanced solid-phase reaction between iron(III) oxide and nickel(II) oxide has been studied at 850–900°C. The formal-kinetic approach to data processing showed that microwave treatment considerably increases the rate of the solid-phase reactions and changes its rate-controlling stage.