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Rio de Janeiro, Brazil

Mendoza Reales O.A.,Federal University of Rio de Janeiro | Pearl W.C.,Halliburton Brazil Technology Center | Paiva M.D.M.,Halliburton Brazil Technology Center | Miranda C.R.,Petrobras | Toledo Filho R.D.,Federal University of Rio de Janeiro
Frontiers of Structural and Civil Engineering | Year: 2015

This work studies the influence of a commercial dispersion of multi wall carbon nanotubes (MWCNT) on the hydration of a class G cement paste, at room and elevated down-hole temperatures. The MWCNT dispersion was produced with a solids concentration of 3.0 % by mass and an anionic surfactant as dispersing agent. Cement pastes with water-to-cement ratio of 0.45 and additions of solid MWCNT by mass of cement up to 0.50 % were studied. Isothermal calorimetry results showed a clear retardation of the hydration of cement caused by the surfactant contained in the MWCNT dispersion. Nevertheless, thermogravimetric evaluations showed that once the hydration reaction resumed, the retardation effect of the surfactant did not have a negative impact on the amount of hydration products precipitated. It was concluded that the commercial MWCNT dispersion presents a good potential to be applied in oil well cement pastes. © 2015 Higher Education Press and Springer-Verlag Berlin Heidelberg Source


Alicke A.A.,Pontifical Catholic University of Rio de Janeiro | Leopercio B.C.,Pontifical Catholic University of Rio de Janeiro | Marchesini F.H.,Halliburton Brazil Technology Center | De Souza Mendes P.R.,Pontifical Catholic University of Rio de Janeiro
Fuel | Year: 2014

The rheological characterization of biodiesel at low temperatures is discussed. Gelling typically occurs in this range, and consequently the mechanical behavior becomes viscoplastic. We illustrate that the rheology of the gelled biodiesel is a strong function of the shear and thermal histories, and due to this dependence the testing conditions must be determined prior to the execution of a rheological measurement. We describe in detail how to determine these conditions by means of the thermal cycle test. Finally we present flow curves for different temperatures, to further illustrate the impact of gelling on the biodiesel rheology. We also discuss an important source of specious data that seems to be often overlooked in the literature. © 2014 Elsevier Ltd. All rights reserved. Source


Marchesini F.H.,Pontifical Catholic University of Rio de Janeiro | Marchesini F.H.,Halliburton Brazil Technology Center | Naccache M.F.,Pontifical Catholic University of Rio de Janeiro | Abdu A.,Pontifical Catholic University of Rio de Janeiro | And 2 more authors.
Applied Rheology | Year: 2015

An experimental and numerical investigation of the rotational rheometry of yield-stress materials is performed, using waterbased Carbopol dispersions. The flow and fluid characterization in different rheometer geometries, namely the smooth Couette, the grooved Couette, and the vane-in-cup are analysed. The bi-dimensional flow governing equations are solved numerically, using the finite volume method and Fluent software (Ansys Inc.). The viscoplastic behavior of Carbopol dispersions is modeled using the Generalized Newtonian constitutive equation with the regularized viscoplastic viscosity function proposed by de Souza Mendes and Dutra [1], herein called SMD function. The flow pattern and the presence of apparent wall slip in rheometric measurements of yield-stress materials are investigated and discussed. © Appl. Rheol. Source

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