Vol.5 No.4 2013

Research paper : Development of switchable mirror glass (K. Yoshimura et al.)−265−Synthesiology - English edition Vol.5 No.4 (2013) switching in the fabricated device (about 3 cm on each side) is shown in Fig. 4. When -5 V voltage is applied to the switchable mirror thin film side, the Mg-Ni layer becomes hydrogenated as the hydrogen ion inside the tungsten oxide thin film transfers, and the mirror state changes to the transparent state in about 20 seconds. When +5 V is applied, the hydrogen ion drops out of the Mg-Ni layer and transfers into the tungsten oxide thin film, and the transparent state changes to the mirror state in about 15 seconds.The switchable mirror device is characterized by the fact that any substrate can be used for film forming. Therefore, if a transparent plastic substrate is used instead of a glass substrate, a bendable switchable mirror film can be fabricated. The plastic device where switching can be done at the same level as the glass substrate has been successfully developed.[21] If the switchable mirror film can be realized, the switchable mirror property can be achieved by simply covering the existing glass with it, and the range of application will expand significantly.For the gaschromic switchable mirror, a sample with a large surface area can be fabricated easily by a large sputtering machine, and switching can be accomplished in about 20 seconds even if it is of a meter size. However, for the electrochromic switchable mirror, the switching speed declines rapidly as the size increases, and initially, a piece of glass of about 15 cm square took about one hour to switch. We worked to increase the switching speed using various methods, and currently, switching can be accomplished in about 30 seconds for the 15 cm square sample. Further breakthrough is necessary to realize an electrochromic switchable mirror of larger sizes, and this is being studied as the most important topic for the electrochromic switchable mirror.3 Research scenario for achieving practical use of the switchable mirror glassTo achieve practical use of the switchable mirror glass, joint research with glass manufacturers is mandatory. However, as mentioned in the “Introduction,” the Japanese glass manufacturers terminated the research for switchable glass at around 2000, and it was necessary to raise the awareness of the glass manufacturers that this can be done practically and it is worth restarting the R&D for switchable glass. Therefore, we thought it was important to speed up solving the unsolved problems at that moment, and to show how much energy-saving performance would increase when this glass was used.The Materials Research Institute for Sustainable Development not only studies the materials, but also has a dedicated building to measure the energy-saving performance when such materials are used. Figure 5 is the photograph of the Testing Facility of Energy Performance that is built on the compounds of the AIST Chubu in Nagoya. The third floor of this building is divided into small rooms each with a size of about 2.5 m on one side. There is a single window on the south side of each room, and two windowpanes can be installed. Each room is equipped with the same air conditioning device, and the power consumption of the air conditioning can be monitored individually. By installing various types of windowpanes in each room, the load on the air conditioning for each room when it is set at a certain temperature can be compared. As described in the following chapter, the switchable mirror glass that can be installed in a building was fabricated, the energy-saving capacity was evaluated and compared with the conventional energy-saving glass, and the major reduction on the cooling load was demonstrated. By conducting measurements in this environment, important findings were obtained that could not be obtained if the research was limited to studying materials only. For example, it was found that the orientation of the window was very important with the energy-saving glass and that it is necessary to carefully consider the entry of sunlight. By feeding back such findings to the materials research, the development of glass with higher energy-saving performance becomes possible.On the other hand, the switchable mirror thin film has various uses other than for building glass. Figure 6 shows the major applications. In achieving practical use of these materials, 2.5 m 2.3 m 2.5 m 1.2 m 1.6 m S N Fig. 5 Environment Friendly Experiment BuildingFig. 6 Application of the switchable mirror thin filmHydrogen visualizing sheetHydrogen sensorOptical partsMobile deviceGoggle, eyeglassesDecoration material (furniture, toys)Building windowpaneCar window (other than windshield)Windshield for carDifficultEasy


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