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Authors: ul-Ain, Barkat
Keywords: Natural Sciences
Chemistry & allied sciences
Physical chemistry
Issue Date: 2014
Abstract: The document presents innovative findings of the newly synthesized Y-type barium hexaferrites in the fields of catalysis and electronics. The barium hexaferrite, Ba2Mg2Fe12O22 and its four doped analogues (Ba2Mg2Fe12−xAlxO22, Ba2Mg2- xCoxFe12O22, Ba2Co2Fe12-2x(Zr,Ni)xO22 and Ba2Co2Fe12-2x(Ti,Mn)xO22) were synthesized by sol-gel, solid state and microwave assisted solution methods. The high concentration decomposition of nitrous oxide (N2O) was targeted first time, for the hexaferrite catalysts, as the reaction of interest due to its usage as multi- purpose propellant for aerospace technology. Separate doping of Al and Co increased the catalytic efficiency and stability for the materials prepared by conventional sol-gel method. However, in case of Al substituted samples the catalytic activity was adversely affected on exposure to microwaves. The Zr–Ni co-doped Ba2Co2Fe12-2x(Zr,Ni)xO22 (x = 0.2–1.0) series was synthesized by conventional sol–gel and microwave heating methods. Complete decomposition of N2O was achieved at temperatures of 873 K and 973 K for microwave and sol–gel prepared catalysts, respectively. In conventional sol- gel synthesis the co-doping of Ti-Mn in Ba2Co2Fe12-2x(Ti, Mn)xO22 (x= 0.2-1.0) was found best among all the studied catalysts and N2O was decomposed completely at 873K without using microwave radiations. However, the use of microwave further decreased this temperature to 583K in Co substituted series. In general it was established that the microwave irradiation improved the catalytic activity significantly of the prepared hexaferrites. Additionally, Ti-Mn doped series was also investigated for electrical, dielectric and thermoelectric properties. DC and AC resistivities increased with the dopant content while the dielectric constant decreased due to valence alteration of Fe3+ ions from the octahedral site by the dopants. Thermoelectric studies along with DC resistivity results established the electron hopping conduction mechanism in the doped ferrites. Another interesting part of this work was the synthesis of Zr and Ni co-doped Ba2Co2Fe12O22 compounds with the solid state method. AC conductivity and electrochemical impedance spectroscopic (EIS) studies of the prepared materials were conducted for the first time in a range of temperatures (123K to 473K) and frequencies (0.1Hz to 1MHz). The activation energies were calculated for high and low temperature regions and on this basis the polaron hopping and variable range hopping mechanisms were proposed, respectively, for the two temperature regions. In a nut shell the synthesized hexaferrites served as efficient catalysts for N2O decomposition with good efficiency and remarkable stability at the high reaction temperature. Furthermore, the samples owed high resistivity, low dielectric constant and low dielectric loss, the qualities which make them attractive for electronic and microwave devices. One of the achievements was introducing the microwave technology with significant improvement in the desired properties.
Appears in Collections:PhD Thesis of All Public / Private Sector Universities / DAIs.

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