Iranian Journal of Materials Science and Engineering

The main problem of cobalt oxide as a thermochemical heat storage material is its slow re-oxidation kinetics. In addition, redox (reduction and oxidation) behavior of as-received Co₃O₄ is degraded with increasing the number of redox cycles. To overcome this drawback, Al₂O₃ and Y₂O₃ were added to Co₃O₄ and  effect of mechanical activation time (2, 4, 8, and 16 h) on the redox behavior (weight change value/rate, redox reversibility, reduction and re-oxidation values, and particle morphologies) of Co₃O₄-5 wt.% Al₂O₃ and Co₃O₄-5 wt. % Y₂O₃ composites was investigated using thermogravimetry method. The composites were studied by SEM, EDS, and X-ray map analyses before and after redox reactions. Results showed that increasing the mechanical activation time improves the redox kinetics of Co₃O₄-5wt. % Al₂O₃ in comparison with as-received Co₃O₄. Although, the alumina-containing samples, activated in short time showed the better redox kinetics than samples activated in long time. It was found that increasing the activation time to more than 8 h for alumina-containing samples reduces the redox kinetics due to decreasing the positive effect of Al₂O₃ in controlling the particle size growth and sintering. In the case of Co₃O₄-5wt. % Y₂O₃, an increase in activation time generally reduced the redox kinetics. As a result, redox reactions in a 16 h-activated Co₃O₄-5wt.% Y₂O₃ composite was completely stopped. In addition, results showed that weak performance of Co₃O₄-5 wt. % Y₂O₃ is related to intensive sintering and growth of cobalt oxide particles during redox reactions

In the present work, monolithic gels were prepared through different drying procedures including
super critical, infrared wavelengths and traditional drying methods. Dense and transparent glasses
were obtained after controlled heat treatment of the dried porous xerogels in air atmosphere.
The chemical bonding as well as different properties of the prepared gels and the relevant glasses
were examined by means of Fourier transform infrared spectroscopy (FTIR), Brunauer-Emmitt-
Teller (BET) and UV-Vis spectrometer. Based on the obtained results, different drying conditions
affect the average pore size and the total pore volume of the studied gels. The mean pore size was
found to be 8.7 nm, 2.4 nm and 3.2 nm for super critical, IR radiation and slow drying in air
atmosphere, respectively. The glass network structure was significantly changed by heat treatment  temperature so that the B-O-Si bonds were formed only after 450 °C. It was found that the gel dried under super critical condition was unable to reach to its full density all over the selected sintering temperature interval.
 

The aim of the present research work is to evaluate the feasibility of processing and utilizing steel slag

in binary and ternary cement blends with limestone. The physical and microstructural properties of binary and

ternary composite cements produced by inter-grinding mixtures of ordinary Portland cement clinker, processed

steel slag and limestone in a laboratory ball mill with replacement levels varying from 0 wt.% to 30 wt.% were

studied. The effects of processed steel slag and limestone incorporation on density of dry cement mixes and water

consistency, setting time and volume stability of fresh and hardened cement pastes were investigated. Also,

density, water absorption, total open pore volume (%) and compressive strength of cement mortars were measured.

The mix with 15 wt.% limestone and 15 wt.% processed steel slag was selected as a typical ternary cement mix

for complementary studies including X-ray diffractometry, thermal gravimetry, Fourier-transform infrared

spectroscopy, and scanning electron microscopy analyses. The results show that removal of relatively high

metallic content of steel slag increases its grindability for mechanical activation and improves its hydraulic

properties effectively and makes it suitable for being recycled in cement industry. The results show that

mechanical activation of the cement mixes enhances the poor hydraulic activity of the processed steel slag and

compensates the strength loss to some extent. The physical and chemical properties of all studied composite

cement mixes comply with ASTM standard specifications, except the compressive strength of the cement mixes

at 28-days containing 20 wt.% or higher amounts of limestone ground to the relatively low Blaine specific surface

area of about 3000 cm2/g.

Phosphate glass with different Al₂O₃ and Na₂CO₃ compositions [80NaH₂PO₄-(20-x) Na₂CO₃-xAl₂O₃ with a step from 0 to 4] were prepared through melt quenching technique furnace at 900 °C. In order to determine the structure and microstructure modification of the samples after heat treatment the IR and Raman spectroscopy were performed. The X-ray diffraction (XRD) result shows an amorphous character of the prepared glass. The result obtained by differential scanning calorimetry (DSC) reveals a good thermal stability in the temperature range of 25 to 400 °C. The impedance Nyquist diagrams were investigated and modeled by resistors and constant phase elements (CPE) equivalent circuits. These measurements show a non-Debye type dielectric relaxation. Both AC and DC conductivity, dielectric constant, and loss factors were determined. Thermal activation energies were also calculated. A changes in the electrical conductivity and activation energy depend upon the chemical composition were observed. Also, a transition in the conduction mechanism from ionic to mixed ionic polaronic was noted. In the same line, electrical modulus and dielectric loss parameters are also deduced. Their frequency and temperature dependency exhibited relaxation behavior. Likewise, activation energies value obtained from the analysis of M’’ and those obtained from the conductivity are closes, which proves the optimal character of the preparation conditions.