Properties Of Hot-pressed Composites Research Articles

The Influence of Activation Preprocessing of the B4C and SiC Powder Mixture with Al on the Phase Composition, Structure, and Properties of Hot-Pressed Composites

The paper examines how the conditions of activation preprocessing (dry and wet grinding) of B4C–Al and SiC–Al powder mixtures in a planetary-ball mill influence the formation of phases in the mixtures and the phase composition, structure, and mechanical properties of the associated hot-pressed materials. It is shown that dry grinding, unlike the conventional powder charge preparation method, induces the mechanochemical synthesis of new phases in the B4C–Al powder mixture along with its mechanical activation. The formation of new phases in the SiC–Al powder mixture does not depend on the conditions of activation preprocessing. Secondary phases form in the hot pressing of the B4C–Al and SiC–Al powder mixtures. The structure and micromechanical characteristics of the materials indicate that dry grinding of the B4C–Al and SiC–Al powder mixtures has a greater activation effect on the hot pressing process, structural uniformity, phase composition, and mechanical properties compared to the conventional powder charge preparation method.

Hydrogen Reduction and Sintering Behavior of Al<sub>2</sub>O<sub>3</sub>/CuO Powder Mixtures Prepared from Different Raw Powders

The reduction behavior of Al2O3/CuO powder mixtures, prepared from Al2O3/CuO or Al2O3/Cu-nitrate, was investigated by using thermogravimetry and hygrometry. Also, the influence of powder characteristics on the microstructure and properties of hot-pressed composites is analyzed. It was found that the hydrogen reduction process of nano-sized oxide particles and properties of sintered composites strongly depends on their distribution and size in composite powder. The formation mechanisms of nano-sized Cu dispersions are discussed based on the powder characteristics and reduction kinetics. In addition, the dependence of the microstructure and mechanical properties of hot-pressed composites on powder characteristics is discussed in terms of the initial size and distribution of Cu particles.

Dielectric properties of cyanoethylated bagasse composites

Bagasse was converted into a thermo-moldable material by cyanoethylation. The effect of reaction conditions employed during the preparation of cyanoethylated bagasse (CE-B) fibers on dielectric properties of hot-pressed composites was studied. Increase in the nitrogen content of the cyanoethylated fiber, i.e., the nitrile groups resulted in an increase in the dielectric constant and a decrease in the dissipation factor (tan δ) peak of the composites. Increase in the reaction temperature and the alkali concentration resulted in a decrease in the dielectric constant and tan δof the composites. Thickness swelling (TS) and equilibrium moisture content of composites conditioned at different relative humidities (RHs) were studied and the extent of the effect of the absorbed moisture on the dielectric properties was also studied. Increase in the nitrogen content, the alkali concentration, and the reaction temperature during the preparation of cyanoethylated fibers resulted in a decrease in TS and moisture absorption of the composites formed. The dielectric properties of the composites conditioned at 60 or 90% RH deteriorated severely. The effect of temperature on the dielectric constant and tan δof a selected CE-B composite was studied. The dielectric constant and tan δincreased as the temperature increased.