Microwave-Assisted Hydrothermal Synthesis of Zinc-Aluminum Spinel ZnAl2O4

The drawback of the hydrothermal technique is driven by the fact that it is a time-consuming operation, which greatly impedes its commercial application. To overcome this issue, conventional hydrothermal synthesis can be improved by the implementation of microwaves, which should result in enhanced process kinetics and, at the same time, pure-phase and homogeneous products. In this study, nanometric zinc aluminate (ZnAl2O4) with a spinel structure was obtained by a hydrothermal method using microwave reactor. The average ZnAl2O4 crystallite grain size was calculated from the broadening of XRD lines. In addition, BET analysis was performed to further characterize the as-synthesized particles. The synthesized materials were also subjected to microscopic SEM and TEM observations. Based on the obtained results, we concluded that the grain sizes were in the range of 6–8 nm. The surface areas measured for the samples from the microwave reactor were 215 and 278 m2g−1.

A new class of reinforcing additives for polymer composite materials

The work is devoted to the development of a method for obtaining new environmentally friendly reinforcing additives for polymer composite materials - xerogels of mixed oxides of transition metals. A method for obtaining nanosized particles of iron and manganese xerogels from true solutions by particle coarsening as a result of a redox reaction has been investigated. The use of sol-gel technology made it possible to obtain xerogels containing particles with a spinel structure. Cationic, anionic, and neutral water-soluble polymers were used to stabilize particle sizes during synthesis. The fractional composition of xerogel nanoparticles has been investigated. It is shown that when using cationic polymers, spinels are formed with the smallest particle sizes and a narrow dispersion of the size distribution. The obtained nanosized transition metal oxides with a spinel structure are planned to be used for reinforcing composite polymer materials in order to improve the mechanical and tribotechnical properties of the composites. Modification of phenylone with ultradispersed spinel particles makes it possible to increase the tribological characteristics of composites due to the formation of a friction film on the tribocontact as a result of the specific interaction of reinforcing additives with friction surfaces. The proposed method for the synthesis of reinforcing additives is characterized by simplicity of implementation, availability of reagents, high productivity and good repeatability of results.

Effect of Al3+ Substitution on Structural and Magnetic Properties of NiZnCo Nano Ferrites

Sol-gel method incorporating auto combustion is used to prepare Al3+ substituted Ni0.4Zn0.35Co0.25Fe2-xAlxO4 with concentration (x = 0.0, 0.10, 0.20) samples. XRD shows their Cubic spinel structure with lattice constant increasing and crystallite sizes decreasing from 32.15 nm to 22.89 nm with Al3+. The spinel structure is confirmed with the help of FT-IR. They have isotropic nature with the single ferrimagnetic domain as given by VSM. The product is widely used.

Compositional modulation in ZnGa2O4 via Zn2+/Ge4+ co-doping to simultaneously lower sintering temperature and improve microwave dielectric properties

AB2O4-type spinels with low relative permittivity (εr) and high quality factor (Q × f) are crucial to high-speed signal propagation systems. In this work, Zn2+/Ge4+ co-doping to substitute Ga3+ in ZnGa2O4 was designed to lower the sintering temperature and adjust the thermal stability of resonance frequency simultaneously. Zn1+xGa2−2xGexO4 (0.1 ⩽ x ⩽ 0.5) ceramics were synthesised by the conventional solid-state method. Zn2+/Ge4+ co-substitution induced minimal variation in the macroscopical spinel structure, which effectively lowered the sintering temperature from 1385 to 1250 °C. All compositions crystallized in a normal spinel structure and exhibited dense microstructures and excellent microwave dielectric properties. The compositional dependent quality factor was related to the microstructural variation, being confirmed by Raman features. A composition with x = 0.3 shows the best dielectric properties with εr ≈ 10.09, Q × f ≈ 112,700 THz, and τf ≈ −75.6 ppm/°C. The negative τf value was further adjusted to be near-zero through the formation of composite ceramics with TiO2.

Properties of multicomponent (Mn-Ni-Co-Al-Si-Ti) oxide spinel hierarchically organized nanostructures deposited by magnetron sputtering in two temperatures.

Multicomponent spinel films were deposited on Ag/Si substrates by magnetron sputtering. Two substrate temperatures were used. XRD diffraction measurements show that the layers are composed of three metals oxides (Mn2O3, NiO, CoO). The presence of spinel phase is poorly visible. However, electron diffraction measurements (RHEED) clearly confirmed the presence of nanostructured spinel structure on top of the samples. Moreover, AFM measurements show that nanostructured spinel islands are present on the sample surface. The measurements validated that indeed, hierarchically organized spinel-oxides nanostructures were obtained. A possible model growth of the spinel nanostructures at different temperatures is discussed.