Results 1 - 10 of 2098
Results 1 - 10 of 2098. Search took: 0.028 seconds
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[en] Falling-ball rheometry is used to study a suspension (volume fraction solids = 0.05) of large, neutrally buoyant rods (length = 3.175 cm, diameter = 0.154 cm) in a viscous Newtonian liquid. We find that all sizes of balls studied (0.65 cm ≤ diameter ≤ 1.90 cm) experience the same continuum that is characterized by a single viscosity which we have measured to be 2.41 times greater than that of the pure suspending liquid. The viscosity increase due to the presence of the rods is over 12 times greater than that observed for a suspension of uniform spheres having the same volume fraction. The results are free of any flow induced clustering and orientation effects and are in reasonable agreement with theoretical predictions for randomly oriented rods
[en] During the exploitation of a nuclear plant, or all other installation which uses radioactive materials, maintenance tasks or decommissioning operations are mandatory in order to preserve people health and environment. Among existing processes, decontaminating gels have been development by CEA in order to overcome the drawbacks of the traditionally used methods. These colloidal gels were originally formulated in an empirical way; however, the knowledge of their structures is important as it rules all the rheological behaviors of the material. The way these gels flow is an important parameter to the process and our laboratory measurements can be transposed to the industrial world. Moreover, other composition refinements have been developed in order to extend their field of use and efficiency. (author)
[fr]Au cours de la vie d'une installation dans laquelle est utilisee de la matiere radioactive, des etapes de maintenance, ou bien a terme de demantelement, sont necessaires afin d'assurer une protection convenable des travailleurs et de l'environnement. Parmi les procedes existants, des gels de decontamination ont ete developpes au CEA afin de pallier aux inconvenients des methodes classiquement utilisees. Ces gels colloidaux, formules a l'origine de facon plutot empirique, ont une structure qu'il convient de connaitre, celle-ci etant la clef de voute du comportement rheologique du materiau. La facon dont ils s'ecoulent est en effet un parametre important du procede, et les mesures en laboratoire qui sont effectuees sur ces systemes permettent d'en ameliorer l'implementation. En outre, de nombreux raffinements du procede, par le biais notamment d'additifs, en etendent le champ d'utilisation, et l'efficacite
[en] Solder paste is the most important strategic bonding material for surface mounting components in electronics manufacturing field. The aim of this study was to investigate the effect of thixotropic agents on the rheology of SnAgCu lead-free solder pastes and grope for materials suitable for jet printing process. The rheological behaviors consisting of viscosity, oscillation, creep recovery and thixotropy of solder pastes added with four thixotropic agents were investigated. The jet printing test was carried out at room temperature. In this paper, it is found that thixotropic agents ST and CVS can reduce the G″/G′ ratio of solder pastes calculated by the oscillation stress curve. Besides, ST and CVS can effectively improve the area of thixotropic loop and the value of unrecovered stress, which is suitable for the jet printing. T4 samples with CVS can be jetted continuously for more than 5000 points with a minimum diameter of 372.3 μm. As the demand for solid-liquid two-phase fluid materials applied to jet printing increases, rheological methods can assist with the exploration of new high viscosity lead-free solder pastes. (paper)
[en] Low-density polyethylene/plasticized starch blends (LDPE/PLST) at various compositions were prepared by melt extrusion and molding in the form of sheets under hot press. The rheology properties during mixing were studied in terms of torque and melting temperature against mixing time. The effect of different compatibilizers and electron beam irradiation on the miscibility of these blends was investigated by IR spectroscopy, mechanical testing and scanning electron microscopy (SEM). The rheology studies showed that the polyethylene graft copolymer with maleic anhydride (PEMA) as a compatibilizing agent during mixing has a pronounced effect than ethylene-vinyl copolymer (EVA) as seen from the higher torque values and melting temperatures. The IR spectroscopy suggests that the compatibilization by EVA and PEMA compounds proceeds through the formation of hydrogen bonding during mixing and this compatibility was improved after electron beam irradiation. The stress- strain curves of pure LDPE and its blends with PLST showed the behaviour of tough polymers with yielding properties. The SEM micrographs of the fracture surfaces give supports to the effect of EVA and PEMA as compatibilizers and electron beam irradiation.
[en] Improvement of rheological parameters of drilling mud with the application of nanotechnologies provides prevention of majority of complications in the process of drilling. Thus, the decrease of friction coefficient prevents blocking of drilling pipe and drilling instrument, at the same time it increases drilling speed. The systems of drilling mud developed on the basis of metal nanoparticles increase effectiveness of drilling of layers with especially complex lithological cross-sections and abnormally high and abnormally law pressures by improving their rheological parameters.
[en] True downhole rheological properties affect equivalent circulating density, hole cleaning, barite sag, surge/swab pressures during tripping, pump pressure, and bit hydraulics. Gelation and excessive viscosity are major concerns at high temperatures. When using oil-based drilling fluids lightened by an injection of de-oxygenated air (containing small amounts of oxygen, usually around five per cent) in underbalanced drilling (UBD) operations, there is a need to be able to predict the effect of oxidation on the viscosity of the oil-based muds as a function of temperature and pressure. This paper presents the results of an experimental investigation that was aimed at establishing the effect of oxidation on the viscosity of an oil-based drilling fluid. The drilling fluid was aged for 2.5 days and for 7 days in the presence of air at temperatures ranging from 100 to 150oC and at pressures ranging from 14 to 44 MPa. The viscosity of the drilling fluid samples after aging is compared with the corresponding fresh samples (before aging). The results show that oxidation causes an increase in viscosity. The amount of the increase depends on the amount of oxygen reacted, which is a function of temperature, pressure, and time. The higher temperatures of the reactors lead to the higher increases in viscosity. Furthermore, at higher temperatures, solid (mostly coke) formation was observed. (author)
[en] A new magnetorheological elastomer (MRE) composite was developed with a resistance which is strongly sensitive both to temperature and pressure. The electrical resistance of this MRE was investigated versus pressure and temperature. The resistance of the composite was recorded versus the pressure for seven different values of the temperature. The mechanism of electrical conduction was modelled and assessed experimentally. Another type of composite, prepared with a softer elastomer, showed a giant magnetoresistance (MR) with a decrease by three orders of magnitude for a field of only 100 kA m-1 (1250 Oe). It was shown that the magnetic pressure acted like mechanical pressure for fields lower than 100 kA m-1 but beyond the MR was saturating contrary to piezoresistance.