ZrC-SiC nanopowders were prepared by carbothermal reduction of ZrO2 and SiO2 with carbon black in argon gas atmosphere, using microwave energy as an alternative heating source. The samples were characterized by XRD, SEM and BET surface area analysis. The results indicate that highly crystalline ZrC-SiC composites with a mean particle size of about 80 nm can be synthesized at a relatively low temperature (~1420 °C). Microwave-assisted heating to obtain the ZrC-SiC nanopowders significantly reduces the synthesis time to only 40 min when compared with the long reaction times involved in conventional carbothermal reduction, which requires about 8 hours to obtain ZrC and 2 hours to obtain SiC.

Abstract Nanoparticles nickel-doped cobalt ferrites [NixCo1-xFe2O4 (x = 0.0, 0.25, 0.50, 0.75 and 1.0 of Ni2+)] were prepared by the microwave combustion synthesis, using a stoichiometric mixture of metal nitrates and urea as the oxidizer and fuel to drive the reaction. The effect of microwave irradiation on the phase composition was favorable to promote the formation of fluffy foams and nanoparticles sizes. The fast internal heating with microwaves leads to a reduction in synthesis time, to only 2 min. The structural, chemical and magnetic properties of the nickel-doped cobalt ferrites were analyzed by XRD, TEM, SEM and BET. The XRD results confirmed the formation of pure and single-phase spinel structure. The crystallite size of the nanoparticles was in the range of 38 - 50 nm. SEM images show nanoparticles with spherical shape and homogenous morphology. The TEM analysis shows necked near-spherical particles with an average size of ~30 - 50 nm, reflecting the highly crystalline nature of these nanoparticles. The magnetic measurements of all the samples were recorded using vibrating sample magnetometer (VSM) at room temperature in 10 kOe. Increasing the nickel content directly affects the structural characteristics of the particles, causing a reduction in the coercive field.

The influence of MgO and La2O3 on the fast sintering of mullite was evaluated in this work. High-purity mullite was doped with MgO and La2O3, conventionally sintered, fast sintered, and microwave-sintered in rapid sintering cycles. The results showed that MgO and La2O3 strongly affected the densification of fast sintered samples; and only doped bodies reached high densities when fast sintered. However, the densification behavior of doped samples was dependent on the amount of sintering aids. MgO doped samples presented better densification behavior than La2O3 doped samples. Microwave-processed samples required a balance between power, time and amount of additives to obtain highly dense and homogenous microstructures.

In the present work the effect of the microwave hybrid fast sintering of mullite-Al2O3 with non-stoichiometric mullite composition was investigated. Samples were fast sintered using a range of microwave power from 1.2 to 2.1 kW. The mullitization process of the silica-rich composition was faster than that of the alumina-rich composition. Alumina-rich mullite showed higher densities and smaller grain size than alumina-poor mullite. It was concluded that the microwave hybrid sintering of mullite was very sensitive to composition.

This work evaluated the catalytic activity of TiO2 synthesized by the Pechini method. with varying molar ratios of 2:1, 3:1 and 4:1 of citric acid/metallic cations, in the photocatalytic degradation of methyl red dye in aqueous solution. The samples were characterized by X-ray diffraction, phase quantification by Rietveld structure refinement, and textural analysis by nitrogen adsorption, and their photocatalytic performance was bench- tested. The results indicated that the 3:1 and 4:1 samples contained two phases, with 84.4 and 89% of anatase phase and 15.6 and 11% of rutile phase, respectively. The 2:1 sample contained only anatase phase. The total discoloration of methyl red dye in 24 hours confirmed the high photocatalytic efficiency of the 2:1 sample, which was ascribed to the formation of monophasic anatase.

Commercially available alumina powder with high-purity submicrometer particle size and narrow particle size distribution was fully densified by a microwave hybrid fast firing technique. The alumina compacts were surrounded by susceptor material, which helped the heating of the samples, and sintered in a microwave oven at a frequency of 2.45 GHz and a power level of 1.8 kW. The sintered samples reached densities of 99% in sintering cycles of 30 to 40 minutes, a much shorter time than conventional sintering processes. The sintered samples showed uniform microstructures with powder particle size/average grain size rations higher than 1:2.

The constant heating rate method employed in sintering studies offers several advantages over the isothermal method, particularly the fact that all the parameters that describe the sintering phenomena can be obtained from a single sample. The purpose of this work is to determine the parameters of sintering kinetics of nanosized Ni-Zn ferrite powders synthesized by combustion reaction. The nonisothermal sintering method was studied using a constant heating rate (CHR). The Ni-Zn ferrite powders, with average particle size varying from 18 nm to 29 nm, were uniaxially pressed and sintered in an horizontal dilatometer at a constant heating rate of 5.0 °C/min from 600 °C up to complete densification, which was reached at 1200 °C. The compacts were characterized by scanning electron microscopy (SEM). Experimental results revealed three different sintering stages, which were identified through the Bannister Theory. The shrinkage and the shrinkage rate analyzed showed a viscous contribution in the initial sintering stage, which was attributed to the mechanism of structural nanoparticle rearrangement.