[en] The powder characteristics are rather like the finger prints of a person so, to obtain reproducible results in any process of powder processing the characteristics of the powder should be the same . It is clear that powder characteristics are very important since any change in the impurity level or the size distribution or any other property may lead to drastic changes in the green density of the compact, the final density of the product and consequently other physical and chemical properties of the final product. These fluctuations in the properties may lead to a product which may not be proper to perform as it should be expected by the user. Finally , it may be rejected and this will lead to a loss of money and time. the characteristics which have been determined in the course of this investigation are the chemical analysis and the specific surface area

[en] In this investigation the fission and the activated products in the fuel free zone of some HGTR fuel irradiated in the AVR reactor were measured using the gamma spectrometric technique. The values in atoms per gram are plotted against the distance from the surface. It was found generally that the concentrations are higher outside and decrease from the surface to the center of the fuel element. The fission and the activated products were measured also for four fuel free spheres (moderator elements) and the same trend was found as for the other spherical fuel elements

[en] The development of a process for coating alumina crucibles with MgO protective coat in a two-step slip casting operation is described. The best milling conditions for the alumina used were wet ball milling for 24 hr. MgO had to be calcined at 1200⁰C to minimize hydration. Optimum slip casting conditions for alumina and magnesia were found to be L/S I and pH 3-6 or 9-II for the former, and L/S 3 (alcohol) and pH 8.5-10 for the latter. Sintering of Al₂O₃ and MgO in the temperature range 1150-500⁰C was investigated. Additions of NiO and MgO lowered the sintered densities at lower temperatures but improved the densification at 1500⁰C. Near theoretical density Al₂O₃ and MgO crucibles were obtained. A two-step slip casting technique was developed to coat Al₂O₃ with MgO. Certain slow firing schedules could eliminate the otherwise observed coat-crucible separation and cracks. (author)

[en] The internal release of fission products from the kernel into the coating from a disintegrated compact (capsule-3) was measured. The distribution of the fission products between the coatings and the kernels was calculated. It was found that Cs-134, Cs-137 and Ag-110 m have the highest internal release values. The internal release of all other fission products except Ru-106 and Ce-144 was mostly below the limit of detection. The results were discussed in the light of the relative migration rates of the fission products and their half life times

[en] In this report some characteristics of nickel ferrite powder prepared through the aerosolization technique by atomization were investigated. It was found that both concentration of the solution and temperature affect the powder characteristics. The increase of the pyrolysis temperature increases both the degree of crystallinity and particle size but decreases the specific surface area. Lowering the concentration of the solution. raises the decomposition efficiency and produces lower yield with smaller particle size. 9 figs., 1 tab

[en] This paper deals with application of Taguchi methodology for the preparation of an important ceramic (mullite) material by hydrolysis method at low temperature. The study aims at production of the greatest yield quantity from the reaction between aluminum nitrate nona-hydrate and silicon ethoxide to obtain mullite precursor (3Al_2O_3 .2SiO_2 ). Three factors were considered to estimate their effects on the quantity of the product yield. These factors are the reactants concentration (factor A), reacting medium temperature (factor B) and ph (factor C). Three levels for each factor were considered (A:1, 2 and 3 wt.% mullite solids), (B: 50, 60 and 70 °C) and (ph: 4, 6 and 8). Three way analysis of variance (ANOVA) and signal to noise ratio (S/N) based on a higher value is a better formula, with an orthogonal array L9 for the design of experiments (DOE) were considered. (S/N) HB, explains that the conditions that maximize the production are; concentration of 3%, reaction temperature 70 °C and ph 6. ANOVA shows that both concentration and ph are significant factors for all confidence levels 90, 95 and 99% while temperature is significant only at 90 and 95% confidence levels