Metalurgia do pó é o uso de metais na forma de pó para a manufatura de produtos. Pós metálicos são combinados (misturados) e compactados em um molde. O material compactado recebe um tratamento térmico ou é sinterizado em um ambiente controlado para a união das partículas para formar um produto denso e resistente. Injeção de pós metálicos tem se destacado mundialmente na produção de componentes de pequenas dimensões e formas complexas em substituição a fundição sob pressão e a sinterização convencional. Atualmente a injeção de pós metálicos está se tornando uma opção competitiva relativamente à peças fundidas, forjadas, usinadas e estampadas. O presente trabalho revisa as técnicas de injeção de pós metálicos e aplica o processo de injeção à baixa pressão utilizando pó de aço inoxidável 316L com granulometria fina (15 &#956m). Os produtos injetados, uma vez extraídos o VO e sinterizados, foram submetidos à ensaios de tração, dureza e micrográficos. Os resultados obtidos são apresentados e discutidos. O trabalho, para a sua viabilização, incluiu a reforma de uma injetora de bancada à baixa pressão e a construção de moldes de injeção. / Powder metallurgy is the use of metals in the powder form for the manufacture of products. Metallic powders are combined (mixed) and compacted in a die. The compacted material receives a thermal treatment or it is sintered in an controlled atmosphere for the particle binding to form a dense and resistant product. lnjection of metallic powders has if globally highlighted in the production of components of small dimensions and complex forms in substitution the pressure casting and the conventional sintering. Nowadays the injection of metallic powders is becoming relatively a competitive option than casting, forging, machining and stamping. The present work revises the techniques of injection of metallic powders and it applies the injection process to the low pressure using powder of stainless steel 316L with fine granulation (15 &#956m). The injected products, once debinded and sintered, were submitted to tensile test, hardness and micrography. The results are presented and discussed. In this work, included the reform of a low pressure injection machine and construction of injection dies.

by Monica Cheung Wai, Eppie Wong Yuen Yee. / Thesis (M.B.A.)--Chinese University of Hong Kong, 1990. / Bibliography: leaf 65. / ABSTRACT --- p.ii / TABLE OF CONTENTS --- p.iii / ACKNOWLEDEGMENTS --- p.v / Chapter I. --- INTRODUCTION --- p.1 / Chapter II. --- STUDY OF THE PURCHASE OF DETERGENT POWDER / Chapter 2.1 --- Market Situation for Detergent Powderin Hong Kong --- p.3 / Chapter 2.2 --- Rationale of the Study --- p.4 / Chapter 2.3 --- Scope of the Study --- p.5 / Chapter 2 .4 --- Objectives of the Study --- p.6 / Chapter III. --- LITERATURE REVIEW / Chapter 3.1 --- Relevance of Understanding Consumer Purchase Behaviour in the Marketing Concept --- p.8 / Chapter 3.2 --- Howard Model of Consumer Behaviour --- p.8 / Chapter 3.3 --- "Engel, Kollat and Blackwell Model" --- p.9 / Chapter 3.4 --- Definition of Detergent Powder Purchase --- p.10 / Chapter 3.5 --- Research Findings : Hoyer --- p.11 / Chapter 3.6 --- Choice Tactics in Detergent Powder Purchase --- p.13 / Chapter 3.7 --- Product Information in Memory --- p.16 / Chapter 3.8 --- Applicability of Hoyer's Research Findings --- p.17 / Chapter 3.9 --- Relevance of Judgmental Models in Detergent Powder Purchase --- p.17 / Chapter IV. --- METHODOLOGY AND FRAMEWORK FOR ATTACK / Chapter 4.1 --- The Pilot Study --- p.21 / Chapter 4.2 --- The Observation Phase --- p.22 / Chapter 4.3 --- The Questionnaire Survey --- p.23 / Chapter V. --- SUMMARY OF RESEARCH FINDINGS / Chapter 5.1 --- Observation Survey --- p.27 / Chapter 5.2 --- Salience of Various Evaluative Criteria --- p.28 / Chapter 5.3 --- Propensity for Brand Switching --- p.29 / Chapter 5.4 --- Consumers' Evaluation of the Product Attributes of their Current Brand --- p.32 / Chapter 5 .5 --- Attitude --- p.34 / Chapter 5.6 --- Difference in Purchase Behaviour among Consumers across Demographic Profiles --- p.35 / Chapter 5.7 --- Demographic Profile of the Sample --- p.38 / Chapter VI. --- DISCUSSION AND IMPLICATIONS / Chapter 6.1 --- Decision Process Behaviour and Advertising Strategy --- p.43 / Chapter 6.2 --- Brand Switching Behaviour and Promotional Strategy --- p.45 / Chapter 6.3 --- Satisfaction with Current Brand and Relevance of Promotional Efforts --- p.46 / Chapter 6.4 --- Salience of Evaluative Criteria -- Pricing and Product --- p.47 / Chapter 6.5 --- Purchase Behaviour among Consumers across Demographic Profiles -- and its Marketing Implications --- p.48 / Chapter 6.6 --- Limitations of the Study and Suggestions for Further Research --- p.49 / APPENDICES / Chapter Appendix A: --- Observation Sheet --- p.51 / Chapter Appendix B: --- Schedule of Questionnaire Survey --- p.52 / Chapter Appendix C: --- The Questionnaire (English and Chinese versions) --- p.53 / Chapter Appendix D: --- Research Data --- p.58 / Chapter Appendix E: --- T-test Table- --- p.61 / Chapter Appendix F: --- F-test Table --- p.63 / BIBLIOGRAPHY --- p.65

La demande croissante de poudres d‟alliages métalliques aux propriétés spécifiques utilisées en particulier en projection thermique et fabrication rapide pousse les chercheurs à améliorer et à optimiser sans cesse les procédés de production de ces poudres. L‟objectif affiché sur ces procédés est de maîtriser à la fois morphologie/ distribution de taille des particules produites et coût de fabrication. Actuellement, la majorité de ces poudres est produite par des procédés d‟atomisation par fluide et essentiellement par le procédé d‟atomisation gazeuse. Parmi ces procédés, le procédé Nanoval utilisant une buse «De Laval» est l‟un des plus performants en termes de distribution granulométrique et de rendement.L‟objectif principal de ce travail de thèse vise à améliorer la compréhension des phénomènes physiques mis en jeu par le procédé Nanoval afin d‟en optimiser le fonctionnement. Deux approches composent ce travail :- une partie numérique de modélisation sous Fluent. Deux modèles ont été étudiés, un modèle monophasique relatif à l‟écoulement gazeux dans l‟unité d‟atomisation (passage de l‟autoclave à la chambre d‟atomisation) et un modèle diphasique relatif à la constriction du filament de métal liquide en sortie de buse de coulée. Cette étude numérique a permis de mettre en évidence l‟effet des paramètres opératoires tels que la pression d‟atomisation et le diamètre de la buse de coulée sur la dynamique du jet de gaz, sur la striction du filament de métal liquide ainsi que les zones de forte pression et de haute vitesse avant, pendant et après la désintégration du filament métallique.- une partie expérimentale pour laquelle la mise en place d‟outils de diagnostic in–situ a été nécessaire pour la caractérisation du procédé en cours de fonctionnement. Trois analyses ont été conduites. La première renseigne de la dynamique du jet d‟atomisation évaluée à partir de mesures de Vélocimétrie par Images de Particules (PIV) à proximité de la sortie de la buse De Laval. La deuxième concerne les caractéristiques à l‟écrasement des particules sur un substrat placé dans la chambre d‟atomisation. La troisième et dernière analyse porte sur les propriétés des particules produites et la comparaison avec la matière récupérée après refroidissement dans l‟autoclave. Différents paramètres opératoires ont été explorés (pression d‟atomisation, diamètre de la buse de coulée, pression dans la chambre d‟atomisation, nature du métal) et reliés à leur influence sur la vitesse et le diamètre des particules. Des relations directes entre les résultats de ces trois analyses ont pu être démontrées ainsi qu‟une bonne adéquation entre résultats expérimentaux et résultats issus de la modélisation. / The growing demand for metal alloy powders with specific properties used in thermal spray application and rapid manufacturing encourages researchers to improve and optimize their manufacturing processes. The aim of these processes is to master both morphology/particle size distribution and manufacturing cost. Today the vast majority of powders are produced by fluid atomization and mainly gas atomization process. Among them, the Nanoval process, consisting of a De Laval nozzle is one of the most outstanding process in terms of granulometric distribution and output.The main objective of this thesis is to improve the understanding of the physical phenomena occurring in the Nanoval process to optimize the way it operates. Two approaches will be developed:- A numerical study using Fluent. The two following models were studied, one monophasic concerning gas flow in the atomization unit form autoclave to atomization chamber and the other, a diphasic model concerning the finest part of the filament in the exit of the melt nozzle. This numerical study has highlighted the effect of parameters such as atomization pressure, nozzle diameter on the gas dynamics, fine filament, high-pressure and high speed areas before, during the process and after the disintegration of the metallic filament.- And an experimental study which required the implementation of the in-situ diagnosticTools to characterize the process under working conditions. Three analyses were carried out. The first concerns the dynamics of the atomization jet from Velocimetry measures by Particle Image Velocimetry (PIV) close to De Laval nozzle exit. The second deals with the characteristics obtained when particles impact the substrate in the atomization chamber. The third describes the particle properties and deals with the comparison with the matter in the autoclave after cooling process. Different operating parameters were explored (atomization pressure, melt nozzle diameter, pressure in the atomization chamber, nature of metal) and linked to their influence on the particle velocity and diameter. Narrow links between the analysis results were demonstrated as well as a good adequacy between experimental and modeling results.

Les paysans stockent entre 60 et 80% de la production des grains qui est régulièrement infestée par les insectes ravageurs. Les plantes insecticides méritent dêtre valorisées à travers notamment leur huile essentielle afin de limiter la dépendance des paysans aux insecticides chimiques, largement utilisés au Nord du Cameroun et dont les dangers sont bien connus. Lanalyse chromatographique de quelques huiles essentielles locales, révèle que Cymbopogon citratus (DC.) Stapf. (Poacée), Ocimum gratissimum L. (Lamiacée) et Ocimum suave Willd (Lamiacée) sont constituées respectivement du citral, du thymol et de leugénol à plus de 50%. Les huiles essentielles de Annona senegalensis Pers. (Annonacée), Hyptis spicigera Lam. (Lamiacée), et Xylopia aethiopica (Dunal) A. Rich. (Annonacée), contiennent majoritairement des monoterpènes hydrocarbonés dont lα-phellandrène, lα-pinène, le sabinène et le β-pinène. H. spicigera et X. aethiopica, dont la composition varie suivant lorigine de la plante, sont les plus efficaces contre Callosobruchus maculatus (F.) et Sitophilus zeamais (Motsch.), principaux ravageurs primaires des greniers au Nord du Cameroun. Lactivité insecticide de H. spicigera est marquée par sa teneur en α-pinène (39,0%) tandis que celle de X. aethiopica est due à leffet synergique de ses composés. La volatilité des huiles essentielles nécessite des supports aptes à réguler le relarguage des molécules volatiles. Avec plus de 90% de molécules volatiles libérées en 7 jours, la poudre des infrutescences de X. aethiopica, qui contiennent plus de 5% dhuile essentielle, bien que toxique contre C. maculatus, ne permet pas de réguler et de prolonger la libération des molécules volatiles. Le kaolin testé dégrade lhuile essentielle X. aethiopica tandis que lincorporation de lamidon à la gomme arabique permet de libérer en 7 jours, 40,5 à 55,9% des molécules volatiles suivant la proportion damidon. Cette combinaison est un système qui autorégule le relarguage en deux phases. La première phase a un taux de relarguage élevé qui entraîne un effet « Knock down » sur C. maculatus, et la seconde phase présente un relarguage lent et prolongé qui pourrait, par un effet répulsif, éviter linfestation des grains stockés. Cette étude est une contribution du projet « STOREPROTECT PIC-2003 » à la protection des denrées stockées par lutilisation des ressources locales au Nord du Cameroun.

A new class of materials, known as multi-functional energetic structural materials (MESMs), has been developed. These materials possess both strength and energetic functionalities, serving as candidates for many exciting applications. One of such applications is ballistic missiles, where these materials serve as part of structural casing as well as explosive payload. In this study, the dynamic compressive behavior of two types of MESMs in the intermediate strain rate regime is investigated. The first type is a thermite mixture of Al and Fe₂O₃ particles suspended in an epoxy matrix. The second type is a shock compacted mixture of Ni and Al powders. Compression experiments on a split-Hopkinson pressure bar (SHPB) apparatus are carried out at strain rates on the order of 103 s-1. In addition, a novel method for investigating the dynamic hardness of the Al + Fe₂O₃ + Epoxy materials is developed. In this method, high-speed digital photography is used to obtain time-resolved measurements of the indentation diameter throughout the indentation process. Experiments show that the shock compacted Ni-Al material exhibits a rather ductile behavior and the deformation of the Al + Fe₂O₃ + Epoxy mixtures is dominated by the polymer phase and significantly modulated by the powder phases. The pure epoxy is ductile with elastic-plastic hardening, softening, and perfectly plastic stages of deformation. The Al and Fe₂O₃ particles in Al + Fe₂O₃ + Epoxy mixtures act as reinforcements for the polymer matrix, impeding the deformation of the polymer chains, alleviating the strain softening of the glassy polymer matrix at lower levels of powder contents (21.6 - 29.2% by volume), and imparting the attributes of strain hardening to the mixtures at higher levels of powder contents (21.6 - 49.1% by volume). Both the dynamic and quasi-static hardness values of the Al + Fe₂O₃ + Epoxy mixtures increase with powder content, consistent with the trend seen in the stress-strain curves. To quantify the constitutive behavior of the 100% epoxy and the Al + Fe₂O₃ + Epoxy materials, the experimentally obtained stress-strain curves are fitted to the Hasan-Boyce model. This model uses a distribution of activation energies to characterize the energy barrier for the initiation of localized shear transformations of long chain polymeric molecules. The results show that an increase in powder content increases the activation energy, decreases the number of transformation sites, causes redistribution of applied strain energy, and enhances the storage of inelastic work. These effects lead to enhanced strength and strain hardening rate at higher levels of powder content.

Accurate statistical characterization of nanomaterials is crucial for their use in emerging technologies. This work investigates how different structural characteristics of metal nanoparticles influence the line profiles of the corresponding powder diffraction pattern. The effects of crystallite size, shape, lattice dynamics, and surface strain are all systematically studied in terms of their impact on the line profiles. The studied patterns are simulated from atomistic models of nanoparticles via the Debye function. This approach allows for the existing theories of diffraction to be tested, and extended, in an effort to improve the characterization of small crystallites. It also begins to allow for the incorporation of atomistic simulations into the field of diffraction. Molecular dynamics simulations are shown to be effective in generating realistic structural models and dynamics of an atomic system, and are then used to study the observed features in the powder diffraction pattern. Furthermore, the characterization of a sample of shape controlled Pt nanoparticles is carried out through the use of a developed Debye function analysis routine in an effort to determine the predominant particle shape. The results of this modeling are shown to be in good agreement with complementary characterization methods, like transmission electron microscopy and cyclic voltammetry.

This thesis outlines the work done on in-situ synthesis of Al2O3-ZrO2-SiCw ceramic composites and their property evaluation. The introductory chapter deals with the literature survey on ceramic matrix composites, properties desirable for structural applications and toughening mechanisms associated with these composites. The role of whisker toughening in ceramic matrix composites, the growth mechanisms involved in whisker growth and the conditions that favour or hamper the whisker growth are also discussed. The advantages and disadvantages of in-situ synthesis of composites as compared to physical mixing are also dealt with. The objective and scope of the work undertaken are outlined at the end. The second chapter describes the experimental techniques associated with carbothermal synthesis and characterisation of reaction products as well as properties of hot pressed bulk composites. The equipments used for this work are described here. The third chapter focuses on the results obtained by the carbothermal reduction of mixtures of kaolin, sillimanite and zircon taken in various proportions. The formation of the product phases with respect to variations in temperature, variations in composition and effect of catalyst is analysed with the help of XRD while their morphology is analysed using SEM. The conditions favouring the formation of tetragonal zirconia without the addition of stabilizers is also enumerated here. The fourth chapter deals with the compaction of these composite powders and the evaluation of some physical, thermal and mechanical properties. Density and porosity, coefficient of thermal expansion, modulus of rupture and fracture toughness of the composite specimens are evaluated and compared with binary and ternary composites made by other methods. Finally the thesis concludes by summarizing the work done and briefly projecting the areas for future work.

Thesis (Ph. D.)--University of Missouri-Columbia, 2003. / Typescript. Vita. Includes bibliographical references (leaves 160-167). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 2003. / Typescript. Vita. Includes bibliographical references (leaves 160-167). Also available on the Internet.

Agglomerated milk powders are produced to give improved properties such as flowability, dispersibility, reduced dustiness and decreased bulk density. A key function of these powders is to dissolve "instantly" upon addition to water and because of this they are also called "instant milk powders". They are produced by agglomerating the undersized fines that are returned to the top of the spray drier with milk concentrate droplet spray. Interaction occurs in a collision zone, often with multiple sprays and fines return lines. Agglomeration can be a difficult process to control and operators find it hard to fine tune the process to produce specific powder properties. This work aimed to understand the effects of key droplet and fines properties on the extent of agglomeration to allow a mechanistic understanding of the process. Three scales of spray drier were investigated in this study with different rates of evaporation; a small scale drier (0.5 - 7 kg water h-1), a pilot scale drier (80 kg water h-1) and a range of commercial production scale driers (4 - 15 000 kg water h-1). A survey of operators of commercial scale driers showed that control of instant milk powder production to influence bulk density is highly intuitive. Fines recycle rates were expected to be important in control of agglomeration processes and were estimated on a specific plant by using the pressure drop measured in the fines return line. A model based on pressure drop along a pneumatic pipeline under-predicted the experimental values for pressure drop due to solids, which means a calibration curve should be generated for each specific drier. Fines recycle rates were predicted to be significantly higher at 95 to 130 % of production rates compared to those expected by operators of 50%. Experimental measurements agreed with existing models for the effect of temperature on the density and viscosity of milk concentrates. Experimental results showed that the surface tensions of concentrated milks were within the same range as literature values for standard milks below 60°C, but were significantly higher for milk above 60°C. This is thought to be linked to the mechanism of skin formation due to disulphide cross linking at high temperatures and concentrations. Powder properties were also established for selected products produced on the commercial scale driers. These powders were then used in experiments on the two smaller driers. Because collision frequency depends on the velocity and droplet size of sprays; these properties were measured for the small scale drier and estimated, where possible, for the pilot and commercial driers. The small scale agglomerating spray drier was configured to alter droplet and particle properties when interacting a vertical fines particle curtain with a horizontal spray sheet. An extensive design and improvement process was carried out to ensure the system consistently delivered these streams in a controllable manner. The processes of collision and adhesion occur very quickly inside the spray drier. In order to assess the extent of agglomeration that has occurred, the feed streams must be compared to the final product stream. An ideal way to do this is to use an agglomeration index which compares the particle size distributions of the feed (fines recycle and spray streams) and the particle size distribution of the product stream (the agglomerated powder). The index described changes between these steams across the particle size distribution and is called an agglomeration efficiency, ξg. However, it was found that the presence of fines in the product of the one-pass design obscured the agglomerates formed. The agglomeration efficiency, ξg, was modified to become ξh which subtracted the fines stream from the agglomerated product distribution. In this way ξh models industrial operation where the fines are recycled, by effectively just comparing the spray and product streams entering and leaving the process. The small scale drier was used for an experimental study on natural and forced agglomeration, where the drier was operated with spray only, then with spray and fines. For natural agglomeration, SEM images of the product powder indicated that little agglomeration occurred between spray droplets. The product yield was unacceptably low (~ 40%) due to adhesion of spray droplets to the drying chamber wall opposing the horizontal spray. When the fines curtain was introduced in the forced agglomeration experiments, product yield increased above 50% because the fines acted as collectors for the spray droplets. However, the agglomeration performance of the modified spray drier was lower than expected. The equipment design was then optimised by considering three key issues; fines dispersion, droplet dispersion and stickiness, and agglomerate breakdown. Final experiments studied agglomeration at low fines to spray mass flux ratios and showed that increasing the fines size had a positive effect on agglomeration efficiency,ξh. The agglomeration study at pilot scale identified the effect of key variables, total solids, concentrate and fines flow rate, and fines size on the agglomeration efficiency. A dimensionless flux approach was used to explain the experimental results. The fines to spray mass flux ratio and the projected area flux ratio (at constant concentrate flow rate) were found to be the most suitable to represent the physical processes during agglomeration. Experimental results showed that a higher dimensionless flux resulted in more agglomeration and as well as small fines size and atomising low solids concentrate. The critical Stokes number highlighted the importance of particle size and collision velocity on the outcome of the collision as well as the importance of stickiness on adherence following the collision. A statistical analysis established a relational model for predicting the agglomeration efficiency based on fines size, total solids and the fines to spray mass flux ratio. This thesis has gained insight into agglomeration processes during spray drying and knowledge about how to define the extent of agglomeration. Practical findings from this research can have a significant impact on successful spray drying operation for instant powders. There are some practical steps to be taken industrially to promote the control of agglomerating spray driers. The first step is to measure and control the flow of fines recycled to the top of the spray drier. The next step is to validate the findings at industrial scale and link the agglomeration index to the bulk powder properties. However, there are many challenges that remain to be tackled in the area of milk powder agglomeration. Milk powder agglomeration at the top of the spray drier is a complex process involving many different variables. A more detailed study of the micro processes that occur during agglomeration will give increased understanding of the relationships between key operating variables and agglomerate properties.