Geoelectrical measurements in Wadi Allaqi area, Eastern Desert of Egypt, and their groundwater significance.

Platinum single crystals were irradiated with fast electrons along various crystallographic directions to determine the ani-sotropy of the damage rate by resistivity measurements. The temperature dependence of the anisotropy was obtained by varying the irradiation temperature from 4.5 K to 40 K and 400 K. The results were interpreted in terms of an anisotropy of the threshold energy for atomic displacement. The evaluation was done by a computer program which fitted a threshold energy profile to the measured damage rates. The effect of details of the threshold energy profile and the effect of electron beam spreading on the anisotropy of the damage rate was studied. Two models, which may explain qualita- tively the effect of temperature on the defect production pro- cess, are discussed. The important results of this work are:

The anisotropy of the damage rate in platinum increases with increasing temperature.

Fitting of the damage rate data by a threshold energy pro-file gives:

a) Zones of minimum threshold energy are around the <ll0> and <100> direction, while the maximum threshold energy is found around the direction < 111 >.

b) with increasing temperature the area of the zones with small threshold energy around the close-packed directions

<ll0> and <100> decrease.

3.)The increasing anisotropy of the threshold energy with temperature is explained by two mechanisms:

a) The change in the defect pattern between 4.5 K and 40 K due to the instability of close pairs.

b) The defocusing of replacement sequences by thermal lattice vibration.

4.) No safe statements about the temperature dependence of the minimum and the average displacement energy are possible.

The effect of Al, Ag and Cr metal electrodes on the electrical properties of Ce---Se---Te films was studied. The relative ease of the diffusion of metallic atoms and the accompanied tendency to nucleation leads to irreversible changes of the film resistivity while annealing. The recrystallization temperature of the chalcogenide film depends strongly on the type of the metal electrode. The observed increase in the values of resistivity after annealing, was interpreted on the basis of charged dangling bond theory

The effect of Al, Ag and Cr metal electrodes on the electrical properties of Ce---Se---Te films was studied. The relative ease of the diffusion of metallic atoms and the accompanied tendency to nucleation leads to irreversible changes of the film resistivity while annealing. The recrystallization temperature of the chalcogenide film depends strongly on the type of the metal electrode. The observed increase in the values of resistivity after annealing, was interpreted on the basis of charged dangling bond theory

The thermal decomposition behaviour of UO3 gel microspheres has been studied. Thermal analysis involved DTA, TG, DTG and X-ray examination. The effects of washing the UO3 gel microspheres with hot water and with ammonia solution were investigated, as were the effects of soaking the microspheres in ammonia solution before or after washing on the crystallite size. The results indicate that the thermal decomposition of UO3 gel microspheres includes five steps: the first two for dehydration, the third for ammonia removal, the fourth for ammonia oxidation and the last step for UO3 recrystallization.

The effects of the drying conditions on the thermal behaviour of UO3 gel microspheres were studied by TG, DTA and X-ray examination. The effects of drying with air, steam or alcohol on the crystal structure and crystallite size were also studied. The results indicate that the thermal decomposition of UO3 gel microspheres involves five steps: the first two for dehydration, the third for ammonia release, the fourth for ammonia oxidation, and the last one for UO3 recrystallization. It was also found that the crystal growth varied from 110 Å after air drying to 512 Å and 496 Å after steam and alcohol treatment respectively.

Foil specimens of DIN 1.4914 martensitic stainless steel were irradiated with 6.2 MeV protons at temperatures from 673 to 810 K and tensile stresses up to 480 MPa. During the test, strain rates were determined alternately with and without irradiation. Irradiation at dose rates up to 4x10-6 dpa/s did not alter the creep rates compared to thermal creep. Stress changes caused transient strains which were of similar magnitude under irradiation and under thermal creep. The creep rates can be described by an exponential stress dependence with a temperature dependent exponential factor and by an exponential temperature dependence vith an activation energy of about 3.0 eV. The creep rates are compared to literature data for materials of similar composition. This comparison shows a strong dependence of creep strength of this material on small compositional variations. It further indicates a lower stress dependence of the creep rate under varying stresses compared to results of constant stress experiments.

This work describes the thermal decomposition behaviour of cerium oxy-carbonate. DTA, TG, DTG and X-ray examinations were performed. The results indicate that the thermal decomposition of cerium oxy-carbonate in static air at a heating rate of 10 deg min-1 involves three steps: dehydration at 58 °C, removal of crystal water at 200 oC and CO2 release at 235 oC. The activation energies of removal of crystal water and carbon dioxide release were found to be 59.48 and 82.33 kJ mol-1, respectively. Ceria-based oxygen ion conductors have high ionic conductivity, which makes them interesting materials for application as solid electrolytes at moderate temperature ( < 600°), oxygen sensors and fuel cells [1]. The powder preparation is an important step in the fabrication of homogeneous materials. Chemical coprecipitation has been used. The properties of the final product (the sintered material or a mixed oxide powder) are largely dependent on the precipitation conditions. Precipitation as oxalate followed by calcination has been used to prepare doped oxide powders. This work describes a study of the thermal analysis and X-ray diffraction of cerium oxy-carbonate, which was prepared by precipitation from cerium nitrate solution with ammonium carbonate in the presence of ammonium hydroxide [2].

The conduction behaviour of different compositions of the Bi1-xTex system with 30£ x£ 60 at. % is ohmic. Transition from metallic to semiconducting behaviour could be observed as the ambient temperature exceeds a certain value dependent on both x and the conditions of annealing. The activation energy of conduction (d Es ) calculated in the semiconducting region varied with x in an unsequential manner emphasizing the role of the existing different phases. However, the change in electrical conductivity could be attributed to a corresponding change in d Es