F.-U.-Z. Chowdhury

Effect of Zirconia Substitution on Structural and Mechanical Properties of ZTA Composites

Zirconia Toughened Alumina (ZTA) composites are attractive structural materials, which combine the high hardness and elastics modulus of the alumina matrix with additional toughening effects, due to the zirconia dispersion. In the present study, ZTA composites containing different amounts of zirconia (in the range 0-16 wt %) were prepared by slurry method and sintered at 1450oC and 1550oC for two hour. Microstructure of the composites was observed using scanning electron microscopy and phase content was detected by means of X- ray diffraction. Mechanical properties such as hardness, elastic modulus and flexural strength were measured. Density was increased with the increase of zirconia content for both sintering temperature, while grain size and elastic modulus was decreased with the same change of zirconia content. Hardness and flexural strength were carried out using the Vickers indentation and were discussed as a function of the ZrO2 content and sintering temperature. The toughening effect is attributed mainly to the zirconia t→m phase transformation. About 61% more flexural strength was found for 16 wt % ZTA composites when compared to the pure alumina.

Complex impedance and electric modulus studies of Al substituted Co0.4Cu0.2Zn0.4AlxFe2-xO4 ferrites prepared by auto combustion technique

ABSTRACT Al substituted Co0.4Cu0.2Zn0.4AlxFe2-xO4 (x = 0.0, 0.1, 0.2, 0.3, 0.4 and 0.5) ferrites have been prepared using auto combustion route. X-ray diffraction studies revealed the formation of single phase spinel type cubical structure. The dielectric properties of the samples at room temperature have been studied over the frequency range of 20 Hz to 15 MHz. The dielectric constant and loss tangent is found to decrease with increasing Al content. Dielectric spectra analysis and modulus show the non-Debye type behavior in the material. Complex impedance spectra of the samples have been analyzed and explained using the Cole-Cole expression. The complex impedance data are indicative of the dominance of grain boundary resistance. AC conductivity has a trend to decrease with Al content and a shift of hopping frequency towards lower frequency is also observed.