Influence of spinel phase composition on ZnO varistors properties

The method of directed synthesis of the constituent phases (DSCP) was applied to investigate the influence of spinel phase composition on characteristics of ZnO varistors. Six varistor mixtures differing only in chemical composition of the spinel phase were prepared. The phase ratio as well as the compositions of ZnO and intergranular gamma-Bi2O3 phases were the same in all samples. Characterization of prepared varistors was performed by X-ray diffraction, SEM and electrical measurements. It was shown that it is possible, in certain cases, to estimate additive redistribution taking into account changes in lattice constants of ZnO, spinel phases and varistor composition. Comparison of six different raristor mixtures shows that it is possible to reduce the number of components of the system if all main constituents of the varistor microstructure are still present. Results confirmed advantages of the DSCP method in preparation of varistors of required phase composition and properties

Mechanochemical synthesis of gamma-Bi2O3

A series of gamma-Bi2O3 phases doped with Zn, Si, Pb and Fe was prepared by mechanochemical treatment of corresponding oxide mixtures with a nominal composition 6Bi(2)O(3) (.) MOx (MOx = ZnO, SiO2, PbO) and 12Bi(2)O(3) (.) Fe2O3 using high-energy ball mill. The products are characterized by X-ray powder diffraction technique. Influence of milling conditions: milling time from 5 min to 10 h, milling medium (steel or ZrO2) and injected mechanical power on unit-cell parameters and crystallinity of products, as well as on reaction kinetics are investigated and discussed

Ni-Sn coatings as cathodes for hydrogen evolution in alkaline solution. Chemical composition, phase composition and morphology effects

In this work the hydrogen evolution reaction (HER) onto Ni-Sn alloy coatings deposited at different current densities from the bath containing 0.1 M Sn2+ and 0.1 M Ni2+ ions in the pyrophosphate-glycine solution, was investigated by polarization curves and electrochemical impedance spectroscopy (EIS) measurements. Their morphology and chemical composition were investigated by scanning electron microscopy equipped with an energy-dispersive X-ray spectroscopy (SEM-EDS), while the phase composition was investigated by X-ray powder diffraction (XRPD). It was shown that their chemical composition, phase composition and morphology depend on the deposition current density. In deposited samples all detected phases, face centered cubic (fcc) Ni, close packed (hcp) hexagonal Ni3Sn, hexagonal Ni(1-i-x)Sn (0 lt x lt 0.5) which adopts NiAs structure type and monoclinic Ni3Sn4 (CoSn structure type), were of low crystallinity. The increase of the Ni-Sn alloy coatings catalytic activity for HER in 6 M KOH with increasing the deposition current density was shown to be the consequence of the change of all three parameters: chemical composition, phase composition and morphology, with the effect of morphology being the most pronounced