Maria José Lourenço

Thin-film characterization for high-temperature applications

Most thin films produced by a wide variety of methods, either physical or chemical (PVD, CVD, sputtering, etc.) for temperature sensor applications, can be used only in very narrow ranges of temperatures, where their components are not subjected to differential thermal expansions, recrystallizations, and grain size modifications. This paper reports the production and characterization of thin films of platinum and titanium in ceramic substrates by one of the physical vapor deposition techniques, the e-gun evaporation. The choice of materials and the determination of film thickness, density, electrical resistivity, surface roughness, and structural characterization (X-ray, SEM, and AES) are studied. Special emphasis is given to the thermal and electrical behavior of these films between room temperature and 1000°C.

Simulation of the Transient Heating in an Unsymmetrical Coated Hot-Strip Sensor with a Self-Adaptive Finite Element Method

The transient heating in an unsymmetrical, coated, hot-strip sensor was simulated with a self-adaptive finite-element method (SAFEM). The first tests of this model show that it can be used to determine, with a small error, the thermal conductivity of liquids, from the transient temperature rise in the hot strip, which is deposited in a substrate and coated by an alumina spray.

Ionanofluids: New Heat Transfer Fluids for Green Processes Development

Ionanofluids represent a new and innovative class of heat transfer fluids that encompass multiple disciplines like nanoscience, mechanical, and chemical engineering. Apart from fascinating thermophysical properties, the most compelling feature of ionanofluids is that they are designable and fine-tunable through base ionic liquids. Besides presenting results on thermal conductivity and specific heat capacity of ionanofluids as a function of temperature and concentration of multiwall carbon nanotubes, findings from a feasibility study of using ionanofluids as replacement of current silicon-based heat transfer fluids in heat transfer devices such as heat exchangers are also reported. By comparing results on thermophysical properties and estimating heat transfer areas for both ionanofluids and ionic liquids in a model shell and tube heat exchanger, it is found that ionanofluids possess superior thermophysical properties particularly thermal conductivity and heat capacity and require considerably less heat transfer areas as compared to those of their base ionic liquids. This chapter is dedicated to introducing, analyzing, and discussing ionanofluids together with their thermophysical properties for their potential applications as heat transfer fluids. Analyzing present results and other findings from pioneering researches, it is found that ionanofluids show great promises to be used as innovative heat transfer fluids and novel media for the exploitation of green energy technologies.

Amino-silica microcapsules as effective curing agents for polyurethane foams

The present paper regards the development of functional microcapsules (MCs), containing encapsulated glycerol, to act as sustainable solid curing agents for one-component polyurethane (PU) foams. They consist of silica-based MCs with an aminosilane surface treatment, obtained through sol–gel processing technique. These MCs are intended to burst and release their content only at the spraying process, in order to promote an accelerated curing of the PU foam. The superficial amino groups react with the isocyanate groups present in the PU pre-polymer, producing polyurea moieties on the MCs’ surface, which prevents the leaching of encapsulated glycerol inside the PU aerosol can. This enables the long shelf life of the product, required for commercial application. The amino-silica MCs exhibit a perfect spherical shape, without significant leaching, in opposition to silica-based MCs and led to a significant increase in the curing rate of the PU foam. The study involved various characterization techniques, such as scanning electron microscopy, Fourier transformed infrared spectroscopy, thermogravimetric analyses, leaching and curing speed evaluation.

Amino surface functionalized microcapsules as curing agents for polyurethane foams

ABSTRACT This work regards the manufacturing process and assessment of amino surface functionalized microcapsules (MCs) containing glycerol in their core, for application in one-component polyurethane (PU) foams to act as a sustainable curing catalyst. Microemulsion techniques combined with sol–gel processing, involving the development of specific steps during the synthesis, were found to enable this type of functional active microparticles. The MCs should only burst and release their content at the spraying stage, in order to assist and promote an accelerated curing of the foam. It has been found that the surface treatment employed in the last step of inorganic silica MCs synthesis procedure, using an amino silane, led to the best curing performance for PU foams. In fact, the amino functionalized MCs exhibited a more perfect spherical format and less aggregation than the inorganic MCs, did not exhibit significant leaching, and led to a significant increase in the curing rate of the PU foam. The study involved characterization techniques, such as scanning electron microscopy, Fourier transformed infrared spectroscopy, thermal gravimetric analyses, leaching, and curing speed evaluation.