The effect of ball milling on the compaction and sintering of nanocrystalline FC-0205 powder was studied in this work. As-received micron-sized FC-0205 powder was subjected to High Energy Ball Milling (HEBM) in an argon atmosphere at different milling time of 0, 8, 16, 20 and 24 hours to obtain nanocrystalline structures. Unmilled, 8 and 16 hour milled powder were compacted using uniaxial die compression at a pressure ranging from 274 MPa to 775 MPa to obtain a relative density from 74% to 95%. The steel powder compacts were sintered at temperatures ranging from 400 °C (752 °F) to 1120 °C (2048 °F) in a controlled atmosphere. Microscopy analysis using Optical Microscope (OM), Scanning Electron Microscope (SEM) and X-ray Diffraction (XRD) was performed on the milled powder, and on the green and sintered compacts to examine the grain size, morphology and agglomeration.

Three different groups of materials were chosen to investigate the uniaxial compaction of particulate solids. Dentritic and cubic sodium chloride were chosen as plastically deforming, dicalcium phosphcte and sugar as fragmentary and styrocell, homopolymer and copolyrinier as non-compactable materials. The uniaxial compaction of the materials was continuously followed by measurement of the applied force, the force transmitted radially to the die wall and the upper punch displacement. The data obtained was presented in the form of Mohr circles, stress pathways (shear-mean compaction stress planes) and a three dimensional representation in mean compaction stress, shear stress and volume change. The yield loci evaluated from Mohr circles and shear-mean compaction stress relationships of compactable and non-compactable materials were found to be similar in shape. The unloading stress profiles were however more informative. All unloading shear-mean compaction stress curves of the compactable materials cross the mean compaction stress axis to give negative values of shear stress and reach a minimum value of ^t_min' which was material and compaction pressure dependent. The unloading curves of non-compactable materials gave approximately zero shear. The parameters evaluated from the characteristic stress profiles were correlated to the tensile strength and hardness of compacts. Mathematical expressions have been proposed for the shear-mean compaction stress relationships of the materials investigated. The materials were characterised before and after compaction in terms of specific surface area, porosity and mechanical strength of compacts with compaction pressure.

La bauxite est un minerai utilisé pour l’élaboration de l’aluminium ou en tant que matière première pour les ciments techniques. Elle est employée, sous sa forme naturelle, en blocs. Ces blocs se font de nos jours de plus en plus rares et leur manutention peut entraîner des pertes sous formes de poussières non valorisées. L’objectif de ce projet est de recycler ces fines particules minérales sous forme de compactés afin d’améliorer l’usage des ressources naturelles minérales qui se raréfient. Ces compactés sont obtenus par compression directe puis avec un procédé innovant couplant vibration et compression. La poudre de bauxite est mélangée à du ciment et de l’eau, puis subit une phase de compaction. Ces compactés doivent avoir des propriétés spécifiques en termes de masse volumique, porosité et résistance mécanique. La micro-tomographie à rayons X est utilisée pour décrire le réarrangement granulaire et l’homogénéité 3D des porosités. La distribution poreuse est caractérisée par analyse d’image et comparée avec les résultats de porosimétrie mercure. Cette étude concernant l’évolution des paramètres texturaux des compactés amène une compréhension des phénomènes liés à la phase de compression. Le stockage et la maturation de ces compactés sous température et humidité contrôlées ont également été étudiés. L’optimisation des paramètres de compression et de formulation, comme la quantité d’eau ou de ciment dans le mélange et la pression de compression, a mené à l’amélioration des propriétés des compactés. Dans un second temps, la phase de compression et les propriétés des compactés ont été améliorées en utilisant une phase préliminaire de vibrations. Cette phase a été optimisée grâce à l’étude de plusieurs paramètres spécifiques comme le type, l’amplitude et la fréquence des vibrations. / The bauxite is used in aluminium elaboration or directly as a raw material for calcium aluminates in technical cements. It is used, as a raw material, as blocks. Recently bauxite blocks are rarer and rarer and their handling can lead to dust wastes that are not re-used. The objective of this project is to recycle the fine mineral particles in compacts to improve the use of natural mineral resources that are running out. These products are compacted by direct compaction and also with an innovative vibration and compaction process. The bauxite is mixed with cement and water, and then the mixture is compacted. They must have specific properties with higher density and mechanical resistance. X-Rays micro-tomography is used to describe the particle rearrangement and the 3D density homogeneity. The porous distribution is then characterized by image analysis and compared with the mercury intrusion porosimetry results. This study on textural parameters evolution of the compacts leads to improve an understanding about the phenomenon during the compaction stage. The storage with controlled temperature and humidity will also be studied. The optimization of the compression and mixture parameters, as amount of water or cement in the mixture and compression pressure, led us to get compacts with improved properties. In the final study, we improved the compression stage and the compacts properties by another stage using in-situ vibrations. The vibrations stage has been optimized studying several vibrational parameters especially the type, the duration, the amplitude and the frequency of the vibrations.

Three- different groups of materials were chosen to investigate the uniaxial compaction of particulate solids. Dentritic and cubic sodium chloride were chosen as plastically deforming, dicalcium phosphcte and sugar as fragmentary and styrocell, homopolymer and copolyrinier as non-compactable materials. The uniaxial compaction of the materials was continuously followed by measurement. of 1-.h e applied force, the force transmitted radially to the die wall and the upper punch displacement. The data obtained was presented in the form of Mohr circles, stress pathways (shear-mean compaction stress planes) and a three dimensional representation in mean compaction stress, shear stress and volume change. The yield loci evaluated from Mohr circles and shear-mean compaction stress relationships of compactable and non-compactable materials were found to be similar in shape. The unloading stress profiles were however more informative. All unloading shear-mean compaction stres's curves of the compactable materials cross the mean compaction stress axis to give negative values of shear stress and reach a minimum value of T min' which was material and compaction p.,- essure dependent. The unloading curves of non-compactable materials gaye approximately zero shear. The parameters evaluated from the characteristic stress profiles were correlated to the tensile strength and hardness of compacts. Mathematical expressions have been proposed for the shear-mean compaction stress relationships of the materials investigated. TI he materials were characterised before and after compaction in terms of specific surface aroa, porosity and mechanical strength of compacts with ccrnpaction pressure. / Sudan Government and the Institution of Chemical Engineers.

The effects of geopressuring and kerogen decomposition on mineral-fluid equilibria were calculated in order to predict the diagenetic-alteration mineralogy produced in equilibrium with kerogen-rich, geopressured sediments. These calculations indicate that several processes specific to kerogen-rich geopressured sediments contribute to the development of a characteristic alteration mineralogy. These processes are: (1) the upward flow of fluids in geopressured sediments, in contrast to the generally downward flow of fluids in normally-pressured sediments; (2) the coincidence of the depths of geopressuring (2-3 km; Fertl et al., 1976), with the geothermal temperatures necessary for CO₂ release (100°-135°C; Hunt, 1979), and CH₄ release (>90°C; Hunt, 1979); and (3) the opposing rates of sediment burial and CO₂ and CH₄ transfer into the upward-flowing fluids, which result in the geopressured pore fluids becoming enriched, and in some cases saturated, with respect to CO₂ and CH₄. Three patterns of mineral deposition during diagenesis of kerogen-rich geopressured sediments are predicted. Quartz deposition should occur at the top of the geopressured zone and decrease rapidly with increased depth as a result of the decreased flux of upward fluid flow with increased depth. Carbonate deposition should occur above the zone of CO₂ release from kerogen degradation as a result of the upward flux of CO₂ saturated fluids and subsequent decreases in fluid temperature, pressure and CO₂ solubility. Kaolinite-carbonate could deposit within and above the zone of CO₂ release from kerogen as a result of silicate dissolution by CO₂-rich acid pore fluids, followed by the potential for albite-carbonate deposition upon CO₂ depletion. In contrast, laumontite and anhydrite should not deposit during diagenesis of kerogen-rich geopressured sediments, but could deposit during diagenesis of normally-pressured or kerogen-poor geopressured sediments. An additional difference between these diagenetic environments is that quartz deposition would not be expected in normally-pressured sediments in which fluids are expected to be flowing downward. These mineralogic relationships compare favorably with observed relationships in the kerogen-rich geopressured sandstones of the Frio formation from the Texas Gulf Coast.

No description available.

No description available.

It has generally been assumed that porosity reduction during mechanical compaction of a sediment is controlled by the increase in vertical effective stress. But the theory of mechanical compaction shows that it is the mean effective stress which controls porosity reduction. According to published data, horizontal stresses increase with overpressure, as well as with depth, so mean stress and vertical stress profiles are poorly correlated in overpressured sections. In this study, a new methodology was developed whereby mudrock pore pressures were estimated principally by comparison of void ratios calculated from wireline log response with hydrostatic mean effective stress (the mean effective stress assuming the pore pressure is hydrostatic). These pressure estimates in the low permeability units were compared to the direct measurements in the aquifer units and an interpretation is made as to the origin of the excess pressure. The results of analysis of seven wells from SE Asia are presented including one study where seismic velocity analysis and basin modelling were performed to assess the pore pressure. The main conclusions of the study are: The proposed new methodology for estimating shale pore pressure from void ratio and mean effective stress analysis appears to be more consistent with the data and represents an improvement on previous methodologies using porosity and vertical effective stress or depth. Analysis of the mudrocks in this study indicates that the shales often appear to have significantly higher pressures than the adjacent aquifer units. The results of using mean (as opposed to vertical) effective stress analysis indicates that the pressure profiles in the wells studied, the profiles disequilibrium compaction can account for all or nearly all of the encountered overpressures. Evidence has been found for significant overpressure generated by fluid expansion in one of the seven wells studied.« Further work to refine the Breckels and Van Eekelen (1982) relationship between overpressure and horizontal stress is proposed to improve the accuracy of the methodology used in this study.

Abstract Tungsten carbide-cobalt powder is pressed before sintering into a compacted form using punches and a die cavity. After the powder has been pressed to a specific shape, it is sintered and shrinks a certain amount to a final size. To accommodate this shrinkage, the pressing tools are designed to a certain “shrinkage percentage” and thus the pressed component or compact is larger than the sintered component by that percentage amount. During the pressing process, there is a large amount of friction between the powder being compacted and the die cavity wall. To counter pressing friction, a lubricant is pre-mixed with the tungsten carbide powder. In the past at Powder Industries, the powder was mixed with wax and all of the tools were designed to a 20% shrinkage. In recent times, the wax in the powder has been replaced by PEG (polyethylene glycol) by most manufacturers as this increases the quality of the final product and is easier to remove in the furnaces. As a result of the new PEG lubricant, the tool wear rate at Powder Industries increased and because a higher pressure had been necessary to achieve powder pressing to the same shape and form, often the pressed components exhibited cracks or were not pressed ideally. On account of the problems introduced by PEG, correct tool design for the shrinkage was obtained by a ‘trial & error’ process. This project has been motivated by the need of establishing pressing and/or design ‘rules’ that would do away with trial and error when designing compaction tooling. The project has consisted of investigating the physical properties of 23 grades of WC-Co powder (with or without TiC and TaC) and of performing a series of pressing tests for each grade. A relationship between the apparent density of a powder and the ideal green density of the green compact pressed from the same powder has been found. Using this relationship, an equation has been derived between ideal shrinkage, powder apparent density, component sintered density and powder volatile content. Since the last three parameters are known to the tool designer, this equation can be used to calculate the ideal shrinkage when designing new compaction tooling. This method of calculating shrinkage is now in general use at Powder Industries and many successful sets of compaction tooling have already been manufactured

We focus on single punch compaction of powder metals in hollow cylindrical geometries, and pay special attention to the effects of non-uniform initial density distribution on final green densities, the effects of density-dependent powder properties and pressure dependent coefficients of friction on the evolution of the pressure and density profiles during compaction, and the time variations of the force required for ejection after the compaction pressure is removed. In studying the effects of non-uniform initial density distribution, we extend the work of Richman and Gaboriault [1999] to allow for fill densities that vary with initial location in the die. The process is modeled using equations of equilibrium in the axial and radial directions, a constitutive relation that relates the axial pressure to the radial pressure at any point in the specimen, and a plausible equation of state that relates local density to the local pressure. Coulomb friction is assumed to act at the interfaces between the specimen and both the die wall and core rod. In this manner, we determine the axial and radial variations of the final density, the axial, radial and tangential pressures, and the shear stress. Of special interest are the inverse problems, in which we find the required non-uniform initial density distribution that, in principle, will yield no variation in the final green density. For incorporating the effect of pressure and density dependent powder properties, we employ a one-dimensional model that predicts the axial variations of the pressure and density. In this model, however, we incorporate the density dependence of the radial-to-axial pressure ratio, as well as the pressure-dependence of the coefficients of friction at the die wall and core rod. The density-dependence of the pressure ratio is based on the experimental measurements of Trassoras [1998], and the pressure dependence of the friction coefficients is based on the measurements of Sinka [2000] and Solimanjad et. al [2001]. In the course of this study, we focus attention on a Distalloy AE powder, and establish the relation between its compressibility and its radial-to-axial pressure ratio. Finally, we employ linear elasticity theory to model the ejection of the green compact. In the first phase, we model relaxation of the compact after removal of the compaction pressure as a misfit of three cylinders, representing the core rod, the compact and the die wall. The known input is radial pressure distribution at the conclusion of compaction, and the output is the corresponding radial pressure distributions that prevail after the compaction pressures are removed. In the second phase, we determine the variations with punch displacement of the ejection forces required to overcome friction at the core rod and die wall. The model includes additions to the friction forces due to the radial expansion (i.e. the Poisson effect) that occurs during ejection. Predictions of the model compare well to the experimental results of Gethin et.al. [1994].