The preparation and physical properties of a series of nanocomposites based on dispersions of Montmorillonite clays in thermoset epoxy resins are reported. The effects of the variation of the concentration of the clay and the influence of a change of the functionality of the epoxy compounds and the amine curing agent are reported. The effects of the method of dispersion of the clay are studied, and it was found that ultrasound provides an effective aid to dispersion of the clay platelets. In general, the addition of clay platelets leads to an increase in the glass-rubber transition, but in the case of a highly cross-linked system, the reverse effect was observed. The effects observed are discussed in the context of the way in which the chemical structure of the monomers influence the dispersion process and the structure of the final resin system.

No abstract

In the last decades, low-density steels for forging have increasing interest in the automotive industry, and good mechanical properties are required for their real application. This paper describes the results obtained for a 0.66C11.4Mn9.9Al duplex austenitic low-density steel after applying a set of isothermal treatments at different combinations of time and temperature, aimed to promote kappa carbide precipitation, and improve the mechanical properties obtained with a water quenching treatment. The effects of the different isothermal treatments on the microstructure and on the mechanical properties have been analyzed and compared to those obtained from a quenching heat treatment. We found that isothermal treatments in the range temperature between 550–750 °C promoted the profuse precipitation of coarse kappa carbides at grain boundaries, which dramatically reduced the ductility of the alloy, whereas a traditional quenching treatment resulted in a better combination of ductility and mechanical strength.

Abstract. Concentrating Solar Power (CSP) is one of the key electricity production renewable energy technologies with a clear distinguishing advantage: the possibility to store the heat generated during the sunny periods, turning it into a dispatchable technology. Current CSP Plants use an intermediate Heat Transfer Fluid (HTF), thermal oil or inorganic salt, to transfer heat from the Solar Field (SF) either to the heat exchanger (HX) unit to produce high pressure steam that can be leaded to a turbine for electricity production, or to the Thermal Energy Storage (TES) system. In recent years, a novel CSP technology is attracting great interest: Direct Steam Generation (DSG). The direct use of water/steam as HTF would lead to lower investment costs for CSP Plants by the suppression of the HX unit. Moreover, water is more environmentally friendly than thermal oils or salts, not flammable and compatible with container materials (pipes, tanks). However, this technology also has some important challenges, being one of the major the need for optimized TES systems. In DSG, from the exergy point of view, optimized TES systems based on two sensible heat TES systems (for preheating of water and superheating vapour) and a latent heat TES system for the evaporation of water (around the 70% of energy) is the preferred solution. This concept has been extensively tested [1, 2, 3] using mainly NaNO 3 as latent heat storage medium. Its interesting melting temperature (T m ) of 306ºC, considering a driving temperature difference of 10ºC, means TES charging steam conditions of 107 bar at 316ºC and discharging conditions of 81bar at 296ºC. The average value for the heat of fusion (ΔH f ) of NaNO 3 from literature data is 178 J/g [4]. The main disadvantage of inorganic salts is their very low thermal conductivity (0.5 W/m.K) requiring sophisticated heat exchanging designs. The use of high thermal conductivity eutectic metal alloys has been recently proposed [5,6,7] as a feasible alternative. T m s of these proposed eutectic alloys are too high for currently available DSG solar fields, for instance the Mg 49 -Zn 51 alloy melts at 342ºC requiring saturated steam pressures above 160 bar to charge the TES unit. Being aware of this, novel eutectic metallic alloys have been designed reducing the T m s to the range between 285ºC and 330ºC (79bar and 145bar of charging steam pressure respectively) with ΔH f s between 150 and 170 J/g, and thus achieving metallic Phase Change Materials (PCM) suitable for the available DSG technologies.