Smart Materials and Structures

Konatsu Kamimoto is a pursuing her Graduation in the Department of Environmental and Life Sciences of Toyohashi University of Technology. She entered Toyohashi University of Technology in 2016. She belongs to the Inorganic Materials Laboratory, and she is doing synthesis and physical property evaluation of phosphors. Currently, she is focusing on elucidating the relationship between the crystal structure of the phosphor and the luminescent properties and analyzing the mechanism.

In the Li2O-Nb2O5-TiO2 system, Li1+x−yNb1−x−3yTix+4yO3 (0.05 ≤ x≤0.3, 0≤y≤ 0.182) (LNT) forms with a superstructure known as the M-phase, which is formed by the periodical insertion of an intergrowth layer in a matrix with a trigonal structure. To apply this unique structure as a host material of phosphor, new phosphors have been investigated based on LNT or related structures made by a conventional electric furnace. However, the synthesis of a homogeneous M-phase required treatment at 1373 K for over 24 h. The sintering time depended on the Ti content, and annealing was repeated in an electric furnace for 24–264 h until a homogeneous structure was formed by the insertion of periodical intergrowth layers. Accordingly, a fast sintering technique that uses lower energy is required for the practical application of this material as phosphors and electro ceramics. This time, we pioneered a new rapid sintering technique, which uses a simpler furnace that only requires the control of air pressure. The LNT solid solution material, with various Ti content of 15-30 mol%, was sintered at 1273 K-1373 K for 30 min-1 h under various air pressures (0.35 MPa–0.60 MPa) using the newly developed an air-pressure control atmosphere furnace (FULL-TECH FURNACE CO., Ltd., Osaka, Japan). To clarify the mechanism of the rapid sintering, various microscales to nanoscale characterization techniques were used: X-ray diffraction, a scanning electron microscope, a transmission electron microscope (TEM), a Cs-corrected scanning TEM equipped with electron energy-loss spectroscopy and X-ray absorption fine structure spectroscopy. As a result, the biggest grain of LNT with Ti 20 mol% could be synthesized at 1373 K for 30 min under 0.35 MPa. It was confirmed that a homogeneous phase was obtained from the TEM image and selected area electron diffraction (SAED) patterns from the [010] axis. We concluded that through the control of air pressure, the interstitial oxygen enabled rapid sintering with a combination of vacancies, and that accordingly, grain growth and the distribution of Ti ions improved somewhat surprisingly.

Andrea Cacciatore is a Senior Researcher in GPI (Global Product Innovation)-Italcementi SpA, where he has been working since 2007. He has completed his MSc in Materials Engineering from Università del Salento studying hydrothermal and mechanochemical synthesis of titania-graphitic composites materials. His R&D work focuses on smart materials for building applications, taking into account in particular photocatalytic, cool, and Graphitic Related Materials. Since 2007 he has been involved in the concrete applications of dynamic and static cool materials in the freamwork of the Italian founded Project COOL IT.

This paper reports a selection of results achieved in the framework of the Italian funded project “COOL-IT”. The study evaluates thermal/optical characteristics of experimental cement-based thermochromic envelopes for buildings energy efficiency applications. In Europe, 50% of the energy consumption of the building sector, and related GHG emissions, concerns heating and cooling systems consumptions, with cooling energy demand expected to rise significatively by 2050. The design and use of selected cool concrete building envelopes for future sustainable cities can contribute to decrease buildings energy loads - mainteining indoor thermal comfort too-as well as to mitigate urban heat island phenomenon. Within this context, the use of thermochromic cementitious materials for buildings energy saving has been investigated. Experiments with cement-based coatings and mortars have been performed, incorporating microincapsulated thermochromic pigments (commercially available) of organic nature having a selected transition temperature of 31°C. At lower temperatures, the thermocromic products appear grey (Dark Phase) while, when exposed to higher temperatures, they enhance their solar reflectance becoming whiter (White Phase). Higher values of total solar reflectance result in lower surface temperatures, thus building cooling loads and urban overheating are decreased too. An accelaretd test method has been set up to evaluate aging of thermochromic coatings. The results show a good compatibility of some selected pigments with cementitious matrix and their poor stability over time (few hours), due to phtodegradation under UV and VIS radiations.