Microwave-Assisted Vacuum Synthesis of TiO2 Nanocrystalline Powders in One-Pot, One-Step Procedure

A new method for fast and simple synthesis of crystalline TiO2 nanoparticles with photocatalytic activity was developed by carrying out a classic sol–gel reaction directly under vacuum. The use of microwaves for fast heating of the reaction medium further reduces synthesis times. When the solvent is completely removed by vacuum, the product is obtained in the form of a powder that can be easily redispersed in water to yield a stable nanoparticle suspension, exhibiting a comparable photocatalytic activity with respect to a commercial product. The present methodology can, therefore, be considered a process intensification procedure for the production of nanotitania.

Effect of argon annealing method on structural and ferromagnetic properties in Fe-doped SnO2 powders

Nanocrystalline powders of Fe-doped SnO2 (Sn1-xFexO2) (x = 0.00, 0.01, 0.03, 0.05) were prepared by a hydrothermal method. The powders were calcined in argon atmosphere at 600 °C for 2 h, causing phase transition from diamagnetic and weak ferromagnetic behavior to a ferromagnetic state. No trace and other magnetic impurity phases was detected in the samples with Fe content up to 3%. The calcined samples of Fe-doped SnO2 revealed the room temperature ferromagnetism with highest magnetization values of 434.07 memu/g at 15 kOe for x = 0.05. The room temperature ferromagnetism of samples originated from oxygen vacancies that occurred in the argon calcination process. In particular, oxygen vacancy shows a significant role in ferromagnetic coupling corresponding to F-center interaction.

Synthesis of Nanocrystalline TiO2 by the Extraction-Pyrolytic Method and its Phase Transformation in the Presence of Gadolinium

Due to its to its optical, thermal, photocatalytic and electrophysical properties, nanocrystalline titanium oxide (TiO2) is widely used in various fields. In the present work, a series of pure and Gd-modified (0.5, 5, 50 mol%) TiO2 nanocrystalline powders were prepared by a novel synthesis approach – extraction-pyrolytic method (EPM). Metal containing extracts on the basis of valeric acid were used as precursors. Thermal behavior of produced individual and mixed precursors were investigated by thermogravimetric analysis (TGA) and high temperature differential scanning colometry (HDSC). Phase composition of pure and Gd-modified TiO2 powders were studied as a function of pyrolysis temperature (450o -850°C ) and gadolinium content by X-ray diffraction (XRD) method. Photocatalytic activity of produced powders was studied by photocatalytic degradation of methylene blue (MB) under UV/VIS light irradiation.

An Improving Densification in Spark Plasma Sintering Ultrafine-grained Y2O3 Transparent Ceramic by Particle Fracture and Rearrangement

Herein, we report a new strategy on an improving densification in spark plasma sintering (SPS) ultrafine-grained Y2O3 transparent ceramic using anisotropic-shaped nanorod powders. At the low temperature stage (<600°C), fracture and rearrangement of nanorod powders will appear which can further improve the initial density of particle compact and reduce the initial particle size. When the temperature reaches beyond 600°C, the sintering efficiency of nanorod powder compact will exceed that of the green body packed by spherical powders. The ceramic sample sintered at 1300°C from nanorods is transparent with ultra-fine grain and shows good optical and mechanical properties, while the corresponding ceramic from near-spherical nanocrystalline powders is not dense enough and opaque.

Preparation, properties and application of cerium(III) methanesulfonate

Based on the results of physicochemical analysis, IR-spectroscopy, derivatographic analysis and differential scanning calorimetry, it was established that the interaction of cerium(III) carbonate with methanesulfonic acid yields cerium(III) methanesulfonate Се(SO3CH3)34H2O. Thermolysis of complex compound Се(SO3CH3)34H2O proceeds via a complex chemical mechanism and is completed at the temperature of 540–5500C producing nanocrystalline powders of cerium(IV) oxide having cubic structure with primary particle sizes of 20–30 nm, aggregate sizes of 50–200 nm and specific surface area of 62–68 m2 g–1. A probable mechanism of thermal decomposition of cerium(III) methanesulfonate is proposed, which depends on the temperature conditions of the thermal decomposition process. At low temperatures, the thermolysis of Се(SO3CH3)34H2O proceeds by the mechanism of surface oxidation with the formation of cerium oxide. At temperatures above 4500C, thermolysis is transformed into combustion with a significant heat effect and the formation of nanosized powders of cerium(IV) oxide of the corresponding morphological structure. It was found that the solutions of cerium(III) methanesulfonate show antiviral activity in vitro.

New Nitride Nanoceramics from Synthesis-Mixed Nanopowders in the Composite System Gallium Nitride GaN–Titanium Nitride TiN

Presented is a study on the preparation, via original precursor solution chemistry, of intimately mixed composite nanocrystalline powders in the system gallium nitride GaN–titanium nitride TiN, atomic ratio Ga/Ti = 1/1, which were subjected to high-pressure (7.7 GPa) and high-temperature (650, 1000, and 1200 °C) sintering with no additives. Potential equilibration toward bimetallic compounds upon mixing of the solutions of the metal dimethylamide precursors, dimeric {Ga[N(CH3)2]3}2 and monomeric Ti[N(CH3)2]4, was studied with 1H- and 13C{H}-NMR spectroscopy in C6D6 solution. The different nitridation temperatures of 800 and 950 °C afforded a pool of in situ synthesis-mixed composite nanopowders of hexagonal h-GaN and cubic c-TiN with varying average crystallite sizes. The applied sintering temperatures were either to prevent temperature-induced recrystallization (650 °C) or promote crystal growth (1000 and 1200 °C) of the initial powders with the high sintering pressure of 7.7 GPa having a detrimental effect on crystal growth. The powders and nanoceramics, both of the composites and of the individual nitrides, were characterized if applicable by powder XRD, SEM/EDX, Raman spectroscopy, Vicker’s hardness, and helium density. No evidence was found for metastable alloying of the two crystallographically different nitrides under the applied synthesis and sintering conditions, while the nitride domain segregation on the micrometer scale was observed on sintering. The Vicker’s hardness tests for many of the composite and individual nanoceramics provided values with high hardness comparable with those of the individual h-GaN and c-TiN ceramics.

High Pressure Brillouin Spectroscopy and X-ray Diffraction of Cerium Dioxide

Simultaneous high-pressure Brillouin spectroscopy and powder X-ray diffraction of cerium dioxide powders are presented at room temperature to a pressure of 45 GPa. Micro- and nanocrystalline powders are studied and the density, acoustic velocities and elastic moduli determined. In contrast to recent reports of anomalous compressibility and strength in nanocrystalline cerium dioxide, the acoustic velocities are found to be insensitive to grain size and enhanced strength is not observed in nanocrystalline CeO2. Discrepancies in the bulk moduli derived from Brillouin and powder X-ray diffraction studies suggest that the properties of CeO2 are sensitive to the hydrostaticity of its environment. Our Brillouin data give the shear modulus, G0 = 63 (3) GPa, and adiabatic bulk modulus, KS0 = 142 (9) GPa, which is considerably lower than the isothermal bulk modulus, KT0∼ 230 GPa, determined by high-pressure X-ray diffraction experiments.

Changing the Magnetic Properties of Cobalt Ferrite Nanoparticles with Different Fabrication Conditions

In this study, crystalline nanoparticles CoFe2O4 with a spinel structure were prepared by hydrothermal methods. The magnetic properties of non-calcined cobalt ferrite formed from nanocrystalline powders. The dependence of the particle size and crystalline structure of obtained nanoparticles in the synthesis conditions was examined and characterized using field emission scanning electron microscope (FESEM), and X-ray diffraction analysis (XRD). The XRD analysis revealed a high degree of crystallinity and confirmed the spinel structure of crystalline nanoparticles CoFe2O4. The FESEM image shows the presence of spherical ferrite particles with an average diameter of about 13-18 nm. The results also show that the formation of cobalt ferrite spinel structures was affected by fabrication conditions. Magnetic hysteresis loop data confirm that the magnetic properties of nanoparticles depend on the synthesis conditions. The material prepared by the hydrothermal route and calcination at 150ºC with molar ration Co2+: Fe3+ = 1:2.2 for 2 hours has higher magnetic saturation than that of the surveyed samples.

New mixed manganites-chromites RMn1–xCrxO3 and manganites-gallates RMn 1–xCrxO3

Nanocrystalline powders of new mixed manganites-chromites RMn0.5Cr0.5O3 (R = Pr, Sm, Er) and manganites-gallates RMn1-xGaxO3 (R = Pr, Sm, Eu; x = 0.25, 0.5) with orthorhombic perovskite structure were obtained by sol-gel citrate route. Crytal structure parameters and microstructural parameters of the materials were established depending on the synthesis conditions. Based on the resuts obtained formation of conntinuos solid solutions RMn1-xCrxO3 in the RMnO3-RCrO3 systems and limited solid solitions in the RMnO3-RGaO3 systems were predicted.