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No description available.

No description available.

In case of metalworking operations, the purpose of lubrication is served by a complex mixture of two or more phases, these mixtures are known as metalworking fluids (MWFs). For many decades oil-in-water emulsions have been used as metalworking fluids. The particular advantage of using oil-in-water emulsion in metalworking operations is that it combines the cooling property of water and the lubrication property of the oil. To explain the lubrication mechanism for oil-in-water emulsions as metalworking fluids a variety of models and theories has been proposed. To understand the lubrication mechanism, the role of each ingredient in the tribological process needs to be studied. In the present study a model for lubrication which determines force and proximity regimes of droplets based on the droplet size distribution is proposed. Dynamic light scattering (DLS) is used to characterize the emulsions. The small droplets are found to be the ones which enhance lubricity. DLVO (Derjaguin-Landau-Verwey-Overbeek) theory is used to validate the results. The concentration and type of surfactant is found to be the performance controlling parameter. A further analysis of the three interfacial energetics; oil/water, oil/substrate, water/substrate, is studied in the presence and absence of surfactants with the help of a Goniometer, Fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM). Such energetics reflects the rate at which the excess surfactant molecules accumulate at the water/oil interface and desorb into the phases. The tribological response is recorded using AFM and the nanotribometer (NTR). Frictional response of the chemisorbed self-assembled monolayer of surfactant (sodium oleate) on the steel substrate reflects that a tribofilm helps in lubricating the contact under boundary lubrication by creating a low shear strength material. Water being the continuous phase in oil/water emulsion a thin water layer adjacent to steel substrate is always present. This thin layer on the solid substrate acts as a barrier to the lubricating oil droplets to reach the metal surface. The focus of the present work is also to investigate conditions which permit the disjoining of the water film to allow the oil to lubricate the metal substrate. AFM is used to study the interaction force between an oil droplet and the steel substrate through water. An oil encapsulated SiO2 colloidal probe used to simulate the oil droplet. The charge regulatory status of the substrates and interfaces are found to be critical in mapping the force characteristics when DLVO interaction is considered. The condition for activation of non-DLVO (hydration, hydrophobic, capillary) forces are also identified and found to be dependent on the physical states of surfaces. Disjoining of the thin film can be controlled by selecting surfactants based on interfacial energetics and attractive force characteristic can be achieved to facilitate lubrication.

La valorisation des minéraux calciques est un problème mondial. La flottation est une technique utilisée pour séparer ces minéraux puisqu’elle joue sur leurs propriétés superficielles. Cependant, c’est un défi scientifique important puisque les propriétés de surface des minéraux calciques sont très proches. Les difficultés de séparation de ces derniers sont donc dues, aux similitudes entre leurs propriétés chimiques de surface, mais aussi leurs propriétés électrocinétiques et leur stabilité en milieu aqueux. L’application des résultats de recherche fondamentale porte sur les minéraux purs dont 4 calcites et une apatite d’origines différentes. L’objectif principal est d’étudier les propriétés et les paramètres impliqués dans les mécanismes de séparation des minéraux calciques tels que l’importance de la solubilité, la spéciation de surface du minéral, la charge globale de la surface du minéral et la densité d’adsorption des tensio-actifs. Les propriétés électrocinétique permettent de déterminer le type de collecteur à employer pour faire flotter sélectivement les minéraux et pour choisir le pH optimal de séparation. Deux collecteurs, l’oléate et le linoléate de sodium (structure de la chaîne hydrocarbonée différente) ont été utilisés pour étudier la flottation des minéraux calciques. Une étude des mélanges de ces deux collecteurs avec différents ratios molaires a montré un contraste de séparation à pH 5 avec le ratio molaire 2 :1 à pH 5 et le ratio 1 :1 à pH 9. De plus, Les effets synergiques entre collecteur ionique (oléate ou linoléate de sodium) et non-ionique (PX type alcool) en présence ou non des déprimants tels que l’amidon et le silicate de sodium ont été étudiés pour améliorer la la sélectivité de la séparation calcite apatite. Les isothermes d’adsorption de l’oléate et du linoléate de sodium, en présence ou non d’un collecteur non-ionique, obtenus par la méthode de Gregory mettent en évidence leurs co-adsorption sur la surface de la calcite et de l’apatite. Ceci a aussi été confirmé par les déplacements des bandes de vibration symétriques et asymétriques des groupements CH2-CH3 sur les spectres infrarouges en réflexion diffuse. L’adsorption du linoléate de sodium sur la calcite orange présente différentes régions, ce qui peut être expliqué par une adsorption en multicouche résultant de la condensation bidimensionnelle du collecteur sur une surface hétérogène. Cependant, l’adsorption de l’oléate de sodium sur l’échantillon de calcite avec les impuretés de Mg est linéaire. L’apatite de Madagascar et la calcite optique présentent une saturation des sites d’adsorption à partir d’une concentration 3.10-5 M en oléate de sodium (CMC) / Valorization of calcium minerals is a global problem. Flotation is a technique used for the separation of these minerals since it plays on their surface properties. However, this is an important scientific challenge because the surface properties of calcium minerals are very similar. The difficulties of separation of these minerals are then due to the similarities between their chemical surface properties, but also their electrokinetic and their stability in aqueous solutions. The application of the basic research results will focus on 4 calcites and one apatite of different origins. The main objective is to study the properties and parameters involved in the separation mechanisms of calcium minerals such as the importance of the solubility, the surface speciation of the mineral, the overall loading of the mineral surface and the density of adsorption of surfactants. The electrokinetic properties therefore make it possible to determine the type of collector to be used to selectively float the minerals and to choose the optimum separation pH. Two collectors, sodium oleate and linoleate (different semi-developed formula), were used to study the flotation of calcium minerals. The mixture of these two collectors with different molar ratios was also studied showing a separation contrast at pH 5 with the molar ratio 2: 1 and the ratio 1: 1 at pH 9. In addition, the synergistic effects between ionic collector (oleate or sodium linoleate) and non-ionic (PX alcohol type) in the presence or absence of depressants such as starch and sodium silicate have been studied to improve recovery and selectivity. The adsorption isotherms of sodium oleate and linoleate, in the presence or absence of a non-ionic collector, obtained by the Gregory method demonstrate their co-adsorption on the surface of calcite and apatite. This was also confirmed by the displacements of the symmetric and antisymmetric vibration bands of the CH2-CH3 groups on the infrared spectra in diffuse reflectance. The adsorption of sodium linoleate on one of the calcite minerals (calcite orange) shows different regions which can be explained by multi-layer adsorption resulting from the two-dimensional condensation of the collector on a heterogeneous surface. However, the adsorption of sodium oleate on calcite orange is linear. The apatite from Madagascar and calcite optical have a saturation of the adsorption sites from a concentration of 3.10-5 M in sodium oleate (CMC)