Jose Humberto de Araujo

Thermal decomposition of illite

The effect of heat treatment on illite in air at temperatures ranging from 750 to 1150 °C was studied using the Mossbauer effect in 57Fe. The dependence of the Mossbauer parameters and relative percentage of the radiation absorption area was measured as a function of the firing temperature. The onset of thermal structural decomposition occurred at 800 °C. With rising temperature, the formation of hematite (Fe2O3) increased at the expense of the silicate mineral.

Simulated and measured results for a S-shaped monopole patch antenna on a BiNbO 4 layer

This work presents a numerical and experimental investigation of the resonant properties of a microstrip-fed S-shaped monopole patch antenna on a high permittivity BiNbO4 ceramic substrate. The high electrical permittivity of the ceramic substrate provided a reduction in the resonator dimensions. A good agreement was observed between simulated and measured resonant frequency of the considered antenna.

Magnetic properties of the granular alloy Fe10Ag90 as a function of annealing temperature

Fe10Ag90 granular alloys have been prepared using a sol-gel process, sintered at 300 °C and annealed at temperatures between 400 °C and 700 °C. The mean size of the iron particles, obtained from X-ray diffraction, is 30.0 ± 0.7 nm. Due to the existence of a distribution of particle sizes in these samples, both blocked (BL) and superparamagnetic (SPM) particles are present simultaneously, as confirmed by magnetization measurements at room temperature. AC susceptibility measurements as a function of temperature reveal a magnetic phase transition at about 770 °C, indicating the presence of particles exhibiting bulk behavior, in the samples annealed above 550 °C. The presence of these particles has been attributed to an atomic diffusion process between the grains, forming bulk-like multiple-domain Fe particles having Curie temperatures near that of bulk a-Fe phase (TC = 770 °C).

Experimental and simulation analysis of microstrip patch antennas on BiNbO 4 ceramic substrates

An experimental investigation of the properties of microstrip rectangular patch antenna on ceramic bismuth niobato (BiNbO4) doped with vanadium (V2O5) substrates was performed. The resonant properties of the microstrip patch antenna were optimized using the Ansoft Designer and a network analyzer HP 8714C was used in the measurement setup.

Magnetic Properties and Hardness of Nanostructured WC-Co Cemented Carbide

Nacrystalline WC-10wt.%Co powders were prepared by high energy milling and liquid phase sintered. The powders with different milling time were characterized by X-ray diffraction and SEM. After sintered the WC-10wt.%Co cemented carbides exhibits ultra fine grain sizes. Coercitive field and Vickers hardness measurements on the consolided samples detected a significant increase and decrease Vickers hardness with the milling time increase in sintered samples.