الفهرس 
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Abstract
The present thesis includes five parts. The most important results abd conclusions of the various parts are 5 given below.
In the first part, a literature survey concerning the crystal defects, catalytic activity and oxide spinels properties were given, with a special emphasize on the kinetics of reactions in the solid state.
The second part consists of preparation of mixtures of various compositions of ZnO-Si02’ Ti02-Si02 and Zn0-
Al203’ by the impregnation method. These systems were calcined at three different temperatures namely 300, 600 and 1000°C. The structure of the various prepared samples were characte-rized and studied by differential thermal analysis -thermo-gravimetry (DTA-TG), Infrared spectra (IR) add X-ray diffrac-
tion techniques.
The acidity, basicity and surface area of the ure oxides and oxide mixtures were measured. The various oxide mixtures showed higher acidic and basic strengths, or Zn0-
(
Si02 and TiO2-Si02 systems the acidity and basicity increases-A
by increasing the calcination temperature from 300 to 600°C. While for ZnO-Al203 systems the reverse order was observed. But for all systems both acidity and basicity have lowest values at a calcination temperature of 1000°C. In general, the trend of acidity and basicity change for all systems is in a good agreement with the surface area measurements.
The third part included the measurement of the reac-tivity of H202 decomposition in aqueous media as a convenient Lest for measuring the catalytic properties of the various systems. Effect of calcination temperature and composition of the systems was studied. The rate of H202 decomposition was found to be dependent to a large extent on the number of acidici as well as basic sites on the surface of the solids. The surface area of the solids played also some role in this respect. In view of the above concepts two mechanisms were preposed for the H202 decomposition on basic and/or acidic sites.
The activation energies for the decomposition of H202 on the different investigated systems were calculated. The data showed that, the activation energies varied with both composition and calcination temperature in a reverse order
of the variation of acidic and basic siles number.
In the Rourth part, the electrical conductivity measu-rments were carried out for ZnO-Si02’ Ti02-Si02 and ZnO-A1203 mixture systems, calcined at 300, 600 and 1000°C. The elec-trical conductivity ( o ) was followed in the temperature range from room temperature up to 500°C. The increase or decrease of ( o ) values in case of Zn0-Si02 system was interpreted in terms of Zn0iO4 formation of low conductance, In case Ti02-Si02 system the change in (o ) values was attri-buted to the removel of OH groups from SiO2.xH20 and for
the change of the stoichiometry of Ti02. The low (a) values at certain compositions of Zn0-Al203 system was attributed to the formation of ZnAl204 having low conductance.
In the fifth’ part, the kinetic of solid-solid reaction was followed in the temperature range 750° - 1200°C for BaCO3-Ti02 system using isothermal and dynamic thermogravimetric techniques. Kinetic analysis of the reactions were discussed in view of state reaction models based on diffusion of reactants through continuous product layer, phase boundary reaction, first order reactions
and random nucleation models. Kinetic analysis of data
by linear regression analysis according to various theore-tical models showed that the formation of BaTiO3 is best described by three-dimensional phase boundary (R3) which gave the highest correlation coefficient than the other
models.
Kinetic analysis of isothermal data was carried
out for weight fraction (o<) values in the range 0.05(04 <0.85. It was found that the BaTiO3 formation was increased
with increasing the temperature. Kinetic analysis of dynamic TG curves were discussed and a critical composition was made of two integral methods: one of Coats and Redfern and the other of Ozawa. The results showed that the Ozawa method gives better correlationand the results
are in good agreement with those obtained under isothermal thermogravimetric conditions.