The compaction behaviour of boehmite has been studied under isothermal conditions, with special emphasis devoted to hot pressing in the temperature range 300 to 600°C. The present work indicates that it is possible to produce a hard dense compact under certain conditions. However, the behaviour of the material during reactive hot pressing appears to be more complicated than can be explained by simple sintering or kinetic theories. To aid in understanding the mechanisms of compaction during a phase transformation, the behaviour of the system during reactive hot pressing was studied from a purely phenomenological point of view, a viscoelastic model. By using viscoelastic theory it is possible to relate ideal elastic and energy-absorbing or damping viscous parameters to the behaviour of boehmite during R.H.P. While the apparent compact density varied as a complex function of temperature, it was found that the overall compaction behaviour of boehmite could be adequately described by a second order linear differential equation, which in turn could be related to a combination of elastic (displacement sensitive) and viscous (strain rate sensitive) components. The viscous nature of the powder during R.H.P. reached a maximum value just before the boehmite to gamma transition (380 to 443°C), suggesting that strong particle interaction was occurring. It is anticipated that R.H.P. from 380 to 443°C will lead to the most favourable particle rearrangement for producing a hard gamma phase at 500°C. In producing the "hard phase" it was important to maintain a critical water concentration. Approximately 4% retained water was necessary for forming a hard dense compact. On the other hand in the presence of an excessive water vapor pressure, the unreacted boehmite powder appeared to transform directly to alpha alumina, resulting in a friable compact. Thus the need for maintaining the correct vapor pressure during R.H.P. is essential. Production of the "hard phase" material at 500°C appears promising as an intermediate step in producing strong translucent bodies upon subsequent sintering at 1000°C. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

(in English): This thesis aims at collecting, cataloguing and analysing bronze objects from the area of the East Aegean-West Anatolian Interface in the second millennium B.C. Based on closer typological assessment and comparanda, the question of eventual local specific production along the Interface, different from the Aegea or Eastern Mediterranean, is being investigated here. From up to 217 collected items, indeed many types of bronzes, especially swords, razors and spearheads indeed show a set of specific features. Also, the characteristic of bronze metals differs in Lower Interface with stronger minoan-mycenaen influnce from items in Upper Interface which seems to be following more anatolian features.

The aim of this study was to study the extraction of zinc from the mineral sphalerite, especially the leaching of concentrate recovered from the Rosh Pinah tailings by means of ferric chloride. To this end, the literature on zinc processing was surveyed and knowledgeable persons were consulted. The study also addressed the leaching kinetics of an upgrade Rosh Pinah tailings dam concentrate as well as those of a synthetic zinc sulphide in a ferric chloride medium. Valuable results were obtained, from the leaching of sphalerite concentrate in ferric chloride medium. An activation energy value of 45.82 kJ/mol was obtained, which compares well with what has been published in the literature. A chemical control model and a diffusion control model were applied to the data obtained. From neither of the models a straight-line relationship could be deduced over the leaching range. At t < 45 minutes it seems that the process is controlled by chemical reaction at the interface; at t > 45 minutes it seems that the process is controlled by diffusion through the product layer. If therefore seems that the rate-controlling step can be related to the process of diffusion through the product layer. The mixed control model proposed by Huang and Rowson, [1-(1-x)1/3+y/6[(1-x)1/3+1-2(1-x)2/3]=kMt, was applied to data obtained during this study. The resultant graphical fit was near perfect, indicating that sphalerite leached in ferric chloride follows a mixed control mechanism for the conditions reported in the study. An activation energy of 20.71 kJ/mol was determined for this model by using the following equation: / Dissertation (MSc)--University of Pretoria, 2006. / Chemistry / unrestricted

The mechanical treatment of solids is one of the most common and widely used operations. The volume of solids subjected to chemical treatment is very large too. Therefore, combining these two ways into one seems to be a logical solution. This method is called the mechanochemical processing of materials. Processing materials in this way has many advantages. On the one hand, this processing is economically as well as technologically feasible. Even the materials that not react together in conventional way can be prepare in this way. The mechanochemistry/mechanochemical synthesis utilizes the mechanical energy to activate chemical reactions and structural changes. The aluminothermic reduction reactions induced by the high – energy ball milling are gaining importance because of the potential applications like the synthesis of microcrystalline and nanocrystalline in – situ metal matrix composites. The mechanical activation of the chemical reactions by high energy ball milling often changes the reaction mechanism and produces metastable materials. Changes of reaction mechanisms during mechanical alloying on four different systems were studied. The system was based on this composition: Al - B2O3 - X (X = C, Ti, Nb, Cr). The possibility of another in – situ reactions during spark plasma sintering process (SPS) was also investigated. All systems were mechanically alloyed under the same conditions. After alloying, on each system scanning electron microscopy was performed and qualitative and quantitative analysis was performed using X-ray diffraction. The indentation hardness and the indentation modulus of elasticity were evaluated using nanoindentation. All analyzes were performed after mechanical alloying as well as SPS and the results were compared to each other. Based on the results, a change of reaction mechanisms was proposed for all systems. It has been found that metal matrix composites are formed and, when chromium is used, hybrid composite material reinforced with intermetallic phase and aluminum borate has been developed.

The aim of this thesis is a complex processing of obtained technical findings in the area of cutting materials, especially the evaluation and comparison of work possibilities recommended by prime world manufacturers for effective usage and application of coated and uncoated cemented carbides. Characteristics of cemented carbides in terms of production, marking method, physical and mechanical properties and application. Comparison of cemented carbides in the range of production of the most significant world tool and cutting material producers. Cutting efficiency evaluation of the tool. Recommended areas and operating conditions for effective usage of cemented carbides and their technical economic evaluation.

Topic of the diploma thesis is Mg-Zn bulk material preparation process by powder mixtures sintering at hot pressing. Structure, porosity and physically-mechanical properties of prepared bulk materials was evaluated. Obtained results and their interpretation were served as feedback for following optimization of individual processing parameters of bulk materials preparation. Thesis solving focuses on study and control of processes during bulk material preparation and description of the processes from physically-chemical point of view of the structure creation and final material properties.

stainless steel, duplex steel, vakuum metallurgy, decarburization