La zone Segment-Piston-Chemise (SPC) d’un moteur thermique est une source importante de dissipation d’énergie liée au frottement sévère. Il est important d’optimiser les lubrifiants agissant dans cette zone car ils ont un impact essentiel sur la durée de vie des pièces mécaniques et la réduction de la consommation énergétique des véhicules. Le dépôt de revêtements sur certaines pièces soumises à des frottements sévères est également une alternative intéressante, en particulier les revêtements carbonés de type DLC et diamant nanocristallin (NCD). La formulation des nouveaux lubrifiants moteurs doit tenir compte de la présence éventuelle de ces nouveaux matériaux. Dans ce travail de doctorat, l’action tribochimique de nouveaux additifs à base de molybdène, couplés à un additif anti-usure de type ZnDTP et à d’autres additifs de type modificateur de frottement, a été étudiée. Ces derniers sont depuis longtemps connus pour leur grande capacité à réduire le frottement grâce à la formation du composé lamellaire di-sulfure de molybdène (MoS2), notamment les additifs MoDTC dimer. Cependant la quantité importante de soufre qu’ils contiennent reste problématique du fait de son impact néfaste sur l’environnement. L’effet synergique d’un additif au molybdène purement organique, appelé Mo-organique, en combinaison avec un additif ZnDTP et d’une triamine grasse, a été découvert. Ce nouveau mélange ternaire permet de réduire jusqu’à 20% la contenance en soufre d’une formulation lubrifiante globale tout en améliorant les performances tribologiques par rapport à celles du MoDTC classique. De ce fait, une réduction du coefficient de frottement atteignant 50% a été observée. Une caractérisation physico-chimique multi-échelles des tribofilms binaires et ternaires dérivés du Mo-organique a été réalisée en utilisant une approche multi-techniques (XPS, ToF-SIMS, FIB/HRTEM). Un mécanisme réactionnel hypothétique conduisant à la formation du MoS2, passant par un composé intermédiaire de type « thiomolybdate » a été proposé. / The friction in the Piston-ring area is a significant cause of the energy waste. It is important to optimize the lubricants acting in this zone because they have an essential impact on the service life of the mechanical parts and the reduction of the energy consumption of vehicles. The coating on relevant part is also an interesting alternative, such as the carbon coating of the DLC type or a nano-crystalline diamond (NCD) coating. If such coating materials are used, the composition of new lubricants has to be adapted correspondingly. This doctoral work-studies the tribo-chemical action of new additives with molybdenum, coupled with an anti-wear additive of the ZnDTP type as well as with some other friction-modifying additives. Some of these additives, especially the MoDTC dimer, are known to reduce the friction through formation of the lamellar di-sulfur composite of molybdenum (MoS2). However, due to high sulfur content these additives produce significant adverse environmental effects. A synergy effect has been proven of a purely organic molybdenum additive, called Moorganic, combined with a ZnDTP additive and from a fatty triamine. This new ternary mixture allows reducing up to 20% the sulfur content in the lubricant’s global formula and improves the tribological properties in comparison with the classical MoDTC. Consequently, the observed reduction of friction coefficient reached 50%. Using the multi-technic approach (XPS, ToF-SIMS, FIB/HRTEM) we realized a multi-scale physicochemical characterization of the binary and ternary tribo-layers that derived from the Mo-organic. A reactional mechanism that leads to the MoS2 formation has been proposed; it goes through the intermediate composite of the « thiomolybdate » type.

This project investigates the optimisation of platinum-group metals recovery at the Mimosa Mine in Zimbabwe. The first part of this research investigates how collector performance can be improved by using collector combinations (mixtures) of the standard sodium iso-butyl xanthate with a secondary collector. The synergistic effect of the sodium-iso-butyl-xanthate (SIBX) combined with trithiocarbonates (TTCs) or dithiophosphates (DTP) was investigated. The short chain and the long chain TTCs were investigated. These collector combinations were studied at various molar percent ratios. The SIBX:DTP combination was studied at a 1:1 mass ratio or molar ratio of 1:1.3. Amongst all the collector combinations, it was established that the SIBX/DTP combination improved sulphur recoveries by 10% and subsequently the PGE+Au recovery by 10% compared to when the SIBX was used on its own. The C4-TTC showed poor performance in the sulphur recovery; however an improvement in PGE + Au recovery was noticeable. There was generally no significant metallurgical improvement with respect to final grades and recoveries with C10 and C12TTC mixtures with SIBX. However, the 6.25 molar per cent substitution of SIBX by C12TTC appeared to show some improvement on sulphur but not on PGM+Au recovery and grade. It was therefore concluded that the SIBX/DTP combination at 1:1 mass ratio (total moles of 0.64) showed a potential to improve the grades and recoveries of the Mimosa Mine. The Mimosa ore is characterised by an unusually large amount of talc, which often causes problems during the flotation of the PGM minerals due to the fact that talc consumes high amount of reagents. Therefore the purpose of the second part of this thesis was to investigate the possibility of removing talc prior to the flotation process by de-sliming. Two cyclones (36.9 mm and 76.0 mm) were used for de-sliming the flotation feed. De-sliming the ore was able to reduce the depressant dosage up to 300 g/t as opposed to 500 g/t that is used at Mimosa Mine. / Dissertation (MSc)--University of Pretoria, 2008. / Materials Science and Metallurgical Engineering / unrestricted

Grâce à ses propriétés d’antioxydant, d’anti-usure et éventuellement d’extrême pression le dithiophosphate de zinc (ZDDP) fait partie des additifs les plus utilisés dans les lubrifiants pour moteurs thermiques. De nos jours, dans un souci de respect de l’environnement, de nouveaux lubrifiants possédant de bonnes performances en lubrification (frottement faible et usure limitée) sont développés en prenant compte des limitations d’utilisations actuelles du ZDDP. L’idée étant de réduire dans ceux-ci les teneurs en phosphore et soufre (Normes euros VI), éléments essentiels du ZDDP qui endommagent les pots catalytiques. L’objectif de cette thèse est l’étude du comportement tribologique du phosphate de zinc di alkyl (ZP) en comparaison avec le ZDDP. La méthodologie expérimentale étudiée pour comprendre le mécanisme d’action de ces additifs, associe des essais de frottement à descaractérisations physico-chimiques des surfaces frottantes après essais.Cette comparaison a été effectuée en fonction de la température (25°C et 100°C), la vitesse de glissement (25, 50 et 100 mm/s) et la concentration en additif (200 et 600 ppm dephosphore). Les meilleures actions anti-usure sont obtenues avec le ZDDP pour une température de 100°C et une vitesse de glissement de 100 mm/s et le ZP pour une température de 25°C et une vitesse de glissement de 25 mm/s. Les analyses de surface XPS, AES, XANES et MET-EDX ont permis de mettre en évidence la présence d’un film protecteur constitué principalement de phosphate de zinc, ceci pour les deux additifs.Une synergie de comportement tribologique a été mise en évidence avec un lubrifiantconstitué de ZP (usure faible) et d’oléate d’urée (frottement faible). Des essais complémentaires sur un tribomètre dynamique ont permis d’étudier le niveau de frottement du tribofilm formé à partir du ZDDP. Le caractère visqueux du tribofilm de ZDDP a été mis en évidence. / Thanks to its antioxidant, anti-wear and extreme pressure properties, zinc dialkyldithiophosphate (ZDDP) is nowadays the most used anti-wear additives in engine oil. Due to environmental protection concerns, new lubricants with good tribological performances (low friction and low wear) are developed. This research aims to evaluate the current limitations of ZDDP and to find alternative environmentally friendly solutions. Thus, the target is to reduce the quantity of phosphorus and sulphur in lubricants, two essential elements of ZDDP molecule that damage catalytic. The objective of this thesis is to study tribological behavior of zinc phosphate di alkyl (ZP) in comparison to ZDDP. The experimental method performed is the coupling of friction test with surface physico-chemical characterisation of rubbing surface after tests.This comparison carried out according to the temperature (25°C and 100°C), the sliding speed (25, 50, 100 mm/s) and additives concentrations (200 and 600 ppm). The best anti-wear efficiency is obtained with the ZDDP additive at 100°C - 100 mm/s and with the ZP at 25°C - 25 mm/s. For both additives and under these conditions, tribofilms are mainly made of zinc phosphate.A tribological synergy are obtained with a lubricant contained ZP (low wear) and oleyl urea (low friction). Complementary tests were made on a original dynamic tribometer for a better understanding of ZDDP tribofilm friction behavior. The viscous character of ZDDP tribofilm was obtained.

Apresenta-se a comparação de duas metodologias para pré-concentração e determinação de Cd em amostras de águas estuarinas e água de mar. As metodologias comparadas foram a extração líquido-líquido no ponto nuvem e a extração por retenção dos analitos em fase sólida. Em ambos os métodos houve necessidade de formação de complexos de Cd previamente à extração. Dois agentes complexantes foram testados o O-O dietilditiofosfato (DDTP), e 1-(2- tiazolilazo)-2-naftol (TAN). A extração no ponto nuvem foi realizada utilizando o surfactante não iônico octil fenoxipolietoxietanol (Triton X-114) que à temperatura de \'40 graus\'C forma uma fase micelar viscosa de volume reduzido. Após separação das micelas, estas foram dissolvidas em solução de ácido nítrico facilitando a análise por ICP OES. A pré-concentração em fase sólida por retenção dos íons complexados foi realizada colocando-se uma coluna de Amberlite XAD 4 em sistema em fluxo. Foram ajustadas as vazões de carregamento da coluna e eluição de forma a aumentar os fatores de pré-concentração. Os volumes das soluções finais foram de 2 mL de forma a obter resultados em triplicata na análise por ICP OES. A quantificação foi efetuada pelo método das adições de padrão. Os dois procedimentos foram comparados considerando as eficiências relativas de pré-concentração, a facilidade para efetuar os procedimentos e a percentagem de recuperação das medidas / Two methodologies for determination of Cd in estuarine and seawater samples were studied. The methodologies for pre-concentration of analytes by surfactant-mediated cloud point extraction and solid phase retention in a resin column were compared. In both cases the prior formation of Cd ions complexes with O,O-diethyldithiophosphate (DDTP) and 1-(2-thiazolylazo)-2-naphtol (TAN) was carried out. The Cloud point extraction was attained with the non ionic surfactant ctylphenoxypolyethoxyethanol (Triton X-114) at \'40 graus\'C . The reduced volume of surfactant micelles was easily separated and dissolved using the solution containing nitric acid which facilitate the analysis by ICP OES. The solid phase pre-concentration was performed by retention of the complexed ions in the Amberlite XAD 4 resin column in a flow scheme. The flow-rates for sample loading and elution were adjusted to increase the preconcentration factor. The final volumes collected of 2 mL were further analyzed in triplicate by ICP OES. Quantification was performed by the standard addition method. Both pre-concentration procedures were compared considering the relative efficiencies, the complexity of procedures and recovery percent of results

Apresenta-se a comparação de duas metodologias para pré-concentração e determinação de Cd em amostras de águas estuarinas e água de mar. As metodologias comparadas foram a extração líquido-líquido no ponto nuvem e a extração por retenção dos analitos em fase sólida. Em ambos os métodos houve necessidade de formação de complexos de Cd previamente à extração. Dois agentes complexantes foram testados o O-O dietilditiofosfato (DDTP), e 1-(2- tiazolilazo)-2-naftol (TAN). A extração no ponto nuvem foi realizada utilizando o surfactante não iônico octil fenoxipolietoxietanol (Triton X-114) que à temperatura de \'40 graus\'C forma uma fase micelar viscosa de volume reduzido. Após separação das micelas, estas foram dissolvidas em solução de ácido nítrico facilitando a análise por ICP OES. A pré-concentração em fase sólida por retenção dos íons complexados foi realizada colocando-se uma coluna de Amberlite XAD 4 em sistema em fluxo. Foram ajustadas as vazões de carregamento da coluna e eluição de forma a aumentar os fatores de pré-concentração. Os volumes das soluções finais foram de 2 mL de forma a obter resultados em triplicata na análise por ICP OES. A quantificação foi efetuada pelo método das adições de padrão. Os dois procedimentos foram comparados considerando as eficiências relativas de pré-concentração, a facilidade para efetuar os procedimentos e a percentagem de recuperação das medidas / Two methodologies for determination of Cd in estuarine and seawater samples were studied. The methodologies for pre-concentration of analytes by surfactant-mediated cloud point extraction and solid phase retention in a resin column were compared. In both cases the prior formation of Cd ions complexes with O,O-diethyldithiophosphate (DDTP) and 1-(2-thiazolylazo)-2-naphtol (TAN) was carried out. The Cloud point extraction was attained with the non ionic surfactant ctylphenoxypolyethoxyethanol (Triton X-114) at \'40 graus\'C . The reduced volume of surfactant micelles was easily separated and dissolved using the solution containing nitric acid which facilitate the analysis by ICP OES. The solid phase pre-concentration was performed by retention of the complexed ions in the Amberlite XAD 4 resin column in a flow scheme. The flow-rates for sample loading and elution were adjusted to increase the preconcentration factor. The final volumes collected of 2 mL were further analyzed in triplicate by ICP OES. Quantification was performed by the standard addition method. Both pre-concentration procedures were compared considering the relative efficiencies, the complexity of procedures and recovery percent of results