Vol.5 No.4 2013
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Research paper : Development of switchable mirror glass (K. Yoshimura et al.)−266−Synthesiology - English edition Vol.5 No.4 (2013) there are cases that can be relatively easily commercialized and those that are quite difficult. While we are ultimately aiming to achieve practical use of the switchable mirror for windows of buildings and vehicles, our strategy is to create commercial products starting from those that are possible, in the process of reaching our final goal.For example, the switchable mirror thin film undergoes optical change when it comes into contact with an atmosphere containing hydrogen, and therefore, hydrogen can be detected by observing this optical change.[22] The conventional hydrogen sensors must be heated, and the sensor may become an ignition source in cases where the hydrogen leaks. The hydrogen sensor that uses the switchable mirror thin film reacts with hydrogen at room temperature so there is no need of heating. Also, the switchable mirror thin film deposited on the tip of the optical fiber can be used as the sensor, and the reflectivity variation can be used for monitoring using the fiber end. This allows the hydrogen sensor to be of no danger of becoming an ignition source, as there will be no electrical circuit on the detector part. Also, as a unique usage of this material, it can be used as a “hydrogen visualizing sheet” where the presence of hydrogen can be checked visually as with the litmus paper. Since this could be relatively easily put to practice, it was commercialized by our joint researcher Atsumitec Co., Ltd., and the product has become available on the market from 2010. From the last fiscal year, joint research has been started for use in relatively small-scale applications in specific products. 4 Demonstration of energy-saving performanceAmong the applications of the switchable mirror thin film, the use for which there is greatest expectation is for the energy-saving windowpane. However, the degree to which energy-saving performance could be obtained when the switchable mirror glass is used was unknown. Therefore, we fabricated a large switchable mirror glass that can actually be installed in a building, and conducted the measurements of energy-saving performance.[23]For the windowpane that can be installed in a building, we fabricated the switchable mirror glass with the structure shown in Fig. 7(a). Pair glass consisting of two panes of transparent glass of 5 mm thickness with 8 mm gap in between was prepared, and the switchable mirror thin film was deposited using Mg4Ni thin film as the switchable layer on the inner side of the glass on the outside of the room or building. The size when mounted on the aluminum sash was 1.2 m in height and 0.8 m in width. Figures 7(b) and (c) are photographs of the mirror and transparent states of the fabricated switchable mirror windowpane. This is the view of the switchable mirror window from outside the building. It was almost a perfect mirror in the mirror state, and the interior of the room could not be seen. When it was switched to the transparent state, the window on the opposite side could be seen through the room, and it was like a transparent glass. Another characteristic of the switchable mirror glass is that, in the mirror state, the view outside can be seen when the person inside the room gazes outside from the window.The fabricated full-size switchable mirror windowpane was installed in the Testing Facility of Energy Performance seen in Fig. 5, and the measurements of the cooling load were taken. Figure 8 shows the measurements taken at the end of August. Before the measurement, the same transparent double glasses were installed in two rooms, and the temperature was set to 28 °C to check that the cooling loads were the same. Next, the window of one room was changed to the switchable mirror glass, switched to the mirror state, and the cooling load power was measured. On that day, the cooling load of the room with the transparent glass window was 1,065 Wh, while the cooling load of the room with the switchable mirror window in the mirror state was 720 Wh, and about 34 % energy savings was accomplished. It was demonstrated that when the switchable mirror windowpane in the mirror state was used, there was a significant reduction of the cooling load particularly on days with high solar radiation.Fig. 7 Switchable mirror windowpane of actual size(a) Structure, (b) mirror state, and (c) transparent stateFig. 8 Comparison of the cooling load using windows fit with transparent double glass and switchable mirror glass(a) (b) (c) 1.2 m 0.8 m 8 mm OutletInlet4 %H2 in Aror4 %O2 in ArSealSealPdMg4NiGlass(5 mm)Glass (5 mm)Inside the roomOutside the roomSwitchable mirror glass (mirror state)Transparent double glassCooling load(Wh)Time181614121086020040060080010001200

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