M.Tech. / The study into the effect of additives used in nickel powder precipitation by sodium hypophosphite has been carried out. Reduction experiments were conducted in a 10 L stainless steel batch reactor fitted with 3 baffles, 4-bladed axial impeller, heating element, thermocouple and thermostat. Nickel seed was used to initiate the reduction process, sodium hypophosphite was used as a reducing agent, and ammonia solution was used to adjust pH, poly(ethylene-comaleic anhydride) (EMA) was used as the first additive and poly(acrylic acid) (PA) as the second additive. Reduction experiments were conducted at a temperature between 60oC to 70oC, pH around 8 and a reaction time of 3 min. Synthetic nickel sulfate solution and sodium hypophosphite solutions at concentration of 0.5 g/L were used as nickel feed solution and reducing agent, respectively. Additives were investigated at high and low concentrations of 5 mg/L and 10 mg/L. The effect of additives on reduction behavior of nickel was investigated by studying the evolution of the volume distribution, moments, specific surface area, and rate of reduction and purity of the powder product. EMA was found to be a growth promoter and PA was found to be a growth inhibitor. The highest reduction rate was observed in the presence of EMA and the lowest in the presence of PA. The SEM micrographs of the powder obtained in the presence of EMA and PA showed that the powder was spherical shaped, open, dentritic and more porous compared with that of the seed particles. Both additives were found to increase the pore size of the powder particles. The presence of particle fragments observed in the scanning electron micrographs confirmed breakage as one of the major particulate process. The addition of additives significantly affected the volume distribution at lower concentrations of 5 mg/L. The extent of aggregation increased with increasing dosages of PA and decreased with increasing dosages of EMA. The highest specific surface area was obtained in the presence of 5 mg/L of EMA.

Thesis (Ph.D.)--McMaster University, 2005. / Supervisor: Ken Coley. Includes bibliographical references (leaves 204-211).

Os produtos feitos de ferro puro contendo Ni expandiram enormemente as aplicaÃÃes de produtos sinterizados, incluindo a fabricaÃÃo de peÃas que suportam altas cargas em automÃveis tais como transmissÃes. O diagrama de equilÃbrio de ligas Fe-Ni demonstram a presenÃa de fases α e FeNi3, porÃm as transformaÃÃes de fases necessitam de uma satisfatÃria homogeneizaÃÃo quÃmica, obtidas por processos convencionais de fabricaÃÃo de ligas por elevaÃÃo dos componentes ao estado lÃquido. Jà a sinterizaÃÃo por fase sÃlida facilita a formaÃÃo de clusters, uma vez que as partÃculas se unem sem mudanÃa de estado, o que implica em regiÃes cuja composiÃÃo quÃmica difere bastante da composiÃÃo global. Deste modo, este trabalho pretende contribuir com um estudo direcionado a identificaÃÃo de fases em ligas Fe-Ni e Fe-Ni-Mo sinterizadas a temperatura de 1100ÂC e processadas por moagem de alta energia (MAE), de forma a avaliar: a interface dissimilar formada entre os elementos, analisar os fenÃmenos encontrados na mesma e identificar caracterÃsticas metalÃrgicas apÃs a sinterizaÃÃo que contribuam para aumento da dureza, microdureza, limite de resistÃncia a traÃÃo e mÃdulo de elasticidade. O estudo apresentarà a determinaÃÃo do diagrama de equilÃbrio atravÃs do software ThermoCalc, tÃcnicas de difraÃÃo por raios X e espectrometria de raios X por energia dispersiva (EDS), alÃm de anÃlises de microscopia optica e microscopia eletrÃnica de varredura (MEV). Os resultados mostraram a presenÃa das fases estÃveis como α(CCC) e fase metaestÃveis como FeNi (CFC Austenita). As anÃlises microscÃpicas demonstram tambÃm uma heterogeneidade com diferentes percentuais de NÃquel e Ferro ao longo das amostras. / The products made of pure iron containing Ni greatly expanded the applications of sintered products , including the manufacture of parts that withstand high loads such as transmissions in cars . The equilibrium diagram of Fe-Ni alloys demonstrate the presence of α and FeNi3 phase , but the phase transformations require a satisfactory chemical homogenization obtained by conventional processes for production of alloys by elevation of the liquid components .The solid-phase sintering facilitates the formation of clusters , since the particles together without change of state, which implies regions whose chemical composition differs significantly from the overall composition . Thus , this paper aims to contribute to a study aimed at identifying phases in alloys Fe - Ni and Fe - Ni - Mo sintered at temperature of 1100  C and processed by high energy ball milling ( RBM ) in order to assess the following: interface formed between dissimilar elements , analyze the phenomena found in it and identify metallurgical characteristics after sintering contributing to increased hardness, microhardness , ultimate tensile strength and modulus of elasticity . The study shall determine the equilibrium diagram through Thermocalc software , diffraction , X-ray spectrometry and X-ray energy dispersive ( EDS ) , and the analysis of optical microscopy and scanning electron microscopy (SEM ) . The results showed the presence of stable phases as α (CCC) and metastable phase as FeNi (CFC austenite). The microscopic analysis also demonstrated heterogeneity with different percentages of Nickel and Iron along the samples.

Les techniques de frittage ultrarapide « naturel » (sans charge) comme le frittage par micro-ondes ou par induction présentent de nombreux avantages. Toutefois, le développement de ces techniques passe par une compréhension et une maitrise des mécanismes mis en jeu. A la fois similaires et complémentaires, ces procédés de chauffage-frittage ont été étudiées par une approche expérimentale afin d’approfondir les connaissances dans le domaine du Frittage Ultrarapide Naturel (FUN). Au cours de cette thèse, l’étude du frittage par micro-ondes de composites céramiques Al2O3-(Y)ZrO2 (3 à 40%vol.) a été menée parallèlement à celle du frittage par induction d’une poudre métallique micronique de nickel. La démarche expérimentale adoptée a consisté à réaliser des expériences de frittage à vitesses de chauffage imposées (de 25 à 1000°C/min) sur ces matériaux modèles et des pièces de petites dimensions, en se référant aux comportements en frittage conventionnel tant au niveau macroscopique qu’au niveau microscopique. / The techniques of ultrafast pressureless sintering as microwave or induction sintering offer manyadvantages. However, the development of these techniques requires an understanding and a control ofthe mechanisms involved. Both similar and complementary, these processes of heating-sintering havebeen studied by an experimental approach to increase knowledge in the field of Ultrafast PressurelessSintering.In this thesis, the study of microwave sintering of Al2O3-(Y)ZrO2 composites has been conductedin parallel with induction sintering of a submicronic nickel powder. The experimental approach usedconsisted in carrying out sintering experiments at imposed heating rates (from 25 to 1000°C/min) onchosen materials and small parts, referring to conventional sintering behavior at the macroscopic andmicroscopic scale.

Do metal particles (including particles of pure metals, alloys, metal oxides and compounds) pose a hazard or risk to human health? In the light of this question, this thesis summarizes results from research conducted on metal particles, and describes the elaboration and implementation of an in vitro test methodology to study metal release from particles through corrosion and dissolution processes in synthetic biological media relevant for human exposure through inhalation/ingestion and dermal contact. Bioaccessible metals are defined as the pool of released metals from particles that potentially could be made available for absorption by humans or other organisms. Studies of bioaccessible metals from different metal particles within this thesis have shown that the metal release process is influenced by material properties, particle specific properties, size distribution, surface area and morphology, as well as the chemistry of synthetic biological test media simulating various human exposure scenarios. The presence of metal particles in proximity to humans and the fact that metals can be released from particles to a varying extent is the hazard referred to in the title. The bioavailable metal fraction of the released metals (the fraction available for uptake/absorption by humans through different exposure routes) is usually significantly smaller than the bioaccessible pool of released metals, and is largely related to the chemical form and state of oxidation of the released metals. Chemical speciation measurements of released chromium for instance revealed chromium to be complexed to its non-available form in simulated lung fluids. Such measurements provide an indirect measure of the potential risk for adverse health effects, when performed at relevant experimental conditions. A more direct way to assess risks is to conduct toxicological in-vitro testing of metal particles, for instance on lung cell cultures relevant for human inhalation. Induced toxicity of metal particles on lung cells includes both the effect of the particles themselves and of the released metal fraction (including bioaccessible and bioavailable metals), the latter shown to be less predominant. The toxic response was clearly influenced by various experimental conditions such as sonication treatment of particles and the presence of serum proteins. Thorough characterization of metal particles assessing parameters including chemical surface composition, degree of agglomeration in solution, size distribution, surface area and morphology was performed and discussed in relation to generated results of bioaccessibility, bioavailability and induced toxicity. One important conclusion was that neither the surface composition nor the bulk composition can be used to assess the extent of metals released from chromium-based alloy particles. These findings emphasize that information on physical-chemical properties and surface characteristics of particles is essential for an in-depth understanding of metal release processes and for further use and interpretation of bioaccessibility data to assess hazard and reduce any risks induced by human exposure to metal particles. / QC 20100803