The influence of low amounts of Sb2O3 , from 3,3x10-5 to 1,7x10-2mol.%, added to ZnO, on nucleation of inversion boundaries (IBs) in ZnO grains, grain growth and growth kinetics under the influence of IBs growth mechanism was studied. Only for additions of Sb less than the amounts required for the equilibrium thickness of Sb layer at the grain boundaries, a reduced number of ZnO grains is infected by IBs, depending on the amount of added Sb, which results in smaller or larger grains. For larger additions of Sb, IBs nucleate in most of the grains and fine grained microstructure is obtained.
COBISS.SI-ID: 20935463
Based on the microstructure characterisation, quali- and quantitative analysis of Al2O3 distribution and grain boundary analysis the influence of very low amounts of Al2O3, from 0,008 to 0,8 mol.%, on the grain growth, microstructure development and current-voltage characteristics of ZnO-based varistor ceramics was explained. The optimal addition of Al2O3 to enhance energy performance of varsitor ceramics was determined. We proposed a mechanism of grain growth inhibition induced in the complex system of ZnO-based varistor ceramics by very low amounts of Al2O3.
COBISS.SI-ID: 20661287
We report on synthesis of varistor ceramics from pre-reacted varistor phases, namely ZnO phase, Bi2O3-phase and Zn7Sb2O12 spinel phase, by high energy milling of starting mixture and sintering. Analysis of microstructural and dopants distribution showed redistribution of dopants Co, Mn and Ni from ZnO phase to spinel phase after sintering, which has negative effect on characteristics of ceramics. Intensive milling enhances nucleation of inversion boundaries which effects more uniform grain-growth, microstructure homogeneity and current-voltage characteristics of varistor ceramics.
COBISS.SI-ID: 20935719
The influence of very low additions of Bi2O3 and Bi2O3+Sb2O3 at various Sb-to-Bi ratios on the grain growth and microstructure development in ZnO ceramics is discussed. While the additions of only Bi2O3 up to 0.02 mol.% result in exaggerated growth of some grains, the addition of also Sb2O3 result, via the IBs-induced grain-growth mechanism, in uniform grain growth. Due to the formation of the pyrochlore phase,which bounds Bi2O3 and Sb2O3, the influence of IBs induced grain growth mechanism on microstructure development is evident when Sb-to-Bi ratio is either smaller or larger than 1.
COBISS.SI-ID: 20759847
The fundamentals of the IB-induced grain-growth mechanism were given. On the examples of ZnO ceramics doped with low amounts of Bi2O3 and Sb2O3 the dominant influence of IBs induced grain growth mechanism, which enabled us to prepare either fine or or coarse grained ceramics, was shown. Finally, microstructural and current voltage characteristics of low doped varistor ceramics with different break-down voltages, prepared by the use of IBs induced grain growth mechanism, were presented.
COBISS.SI-ID: 21950759