Design,fabrication and energy-saving evaluation of five-layer structure based transparent heat mirror coatings for windows application

Transparent heat mirror which allows the transmission of visible sunlight while reflects the infrared thermal energy is an effective building energy efficiency technology for hot climatic regions.In this work,a five-layer dielectric/metal/dielectric/metal/dielectric(DMDMD)coating of Si_(3)N_(4)/Ag/Si_(3)N_(4)/Ag/Si_(3)N_(4)structure is proposed.The radiative properties of the five-layer coatings are theoretically investigated by transfer matrix method.The thicknesses of the layers are optimized by using particle swarm optimization method.The sample of the designed Si_(3)N_(4)/Ag/Si_(3)N_(4)/Ag/Si_(3)N_(4)coating is prepared and the building energy performance when applying the DMDMD coating in a simple office room is also investigated,taking the hot weather condition of Guangzhou,China as an example.The simulated results show that the Tave+Rave value of the five-layer coating is 8%higher than that of the three-layer coating,and the long-wave emittance of the five-layer coating is 24.8%lower than that of the three-layer coating.And the application of the five-layer coatings on the glazed window could provide the highest energy saving rate of 8.9%when compared with the traditional low-e coatings.

Investigation on Phase Evolution of the ZnO-B2O3-SiO2 Glass Ceramics

ZnO-B2O3-SiO2-Al2O3-Na2O glass doped with nucleating agent TiO2 was prepared with melting-quenching method and the effect of nucleating agent on the crystallization behavior and phase evolution of this glass was investigated by differential thermal analysis（DTA）,X-ray diffraction（XRD）,and scanning electron microscopy（SEM）.The experimental results show that the glass transition temperature and the first crystallization temperature decrease from 630 ℃ and 765 ℃ to 595 ℃ and 740 ℃,respectively,with introduction of TiO2 into glass.There is no diffraction peaks in the XRD pattern but it is no longer transparent for the base glass without nucleating agent after heat treatment,which suggests the serious phase separation occurred,and the observation by SEM indicates that the phase separation is developed by nucleation and growth mechanism.However,there are two different crystals ZnAl2O4 and NaAlSiO4 present in the glass containing TiO2 after heat treating at 575 ℃ for 2 h and 740 ℃ for 6 h,respectively.What is interesting is that NaAlSiO4 disappears as the crystallization time at 740 ℃ increases from 6 h to 12 h,and more ZnAl2O4 crystal is formed,namely,the further formation of ZnAl2O4 is at cost of NaAlSiO4 with increasing crystallization time.And observation of the morphology of glass ceramics shows great difference with increasing crystallization time.Moreover,the ability of ZnO-B2O3-SiO2-Al2O3-Na2O glass ceramics against attacking of 1M HCl solution is increased by the crystals precipitated in heat treatment process.

Fast and uniform growth of graphene glass using confined-flow chemical vapor deposition and its unique applications

Fast and uniform growth of high-quality graphene on conventional glass is of great importance for practical applications of graphene glass. We report herein a confined-flow chemical vapor deposition （CVD） approach for the high- efficiency fabrication of graphene glass. The key feature of our approach is the fabrication of a 2-4 μm wide gap above the glass substrate, with plenty of stumbling blocks; this gap was found to significantly increase the collision probability of the carbon precursors and reactive fragments between one another and with the glass surface. As a result, the growth rate of graphene glass increased remarkably, together with an improvement in the growth quality and uniformity as compared to those in the conventional gas flow CVD technique. These high-quality graphene glasses exhibited an excellent defogging performance with much higher defogging speed and higher stability compared to those previously reported. The graphene sapphire glass was found to be an ideal substrate for growing uniform and ultra-smooth aluminum nitride thin films without the tedious pre-deposition of a buffer layer. The presented confined- flow CVD approach offers a simple and low-cost route for the mass production of graphene glass, which is believed to promote the practical applications of various graphene glasses.

Structural characterization and temperature-dependent luminescence of CaF2：Tb^(3＋)/Eu^(3＋) glass ceramics

Tb^3＋/Eu^3＋ co-doped transparent glass ceramics containing CaF2 nanocrystals were successfully synthesized by high temperature melt-quenching method and subsequent heating. The structure and morphology of the samples were investigated by X-ray diffraction（XRD）, transmittance electron microscopy（TEM）, high resolution TEM（HRTEM） and selected area electron diffraction（SAED）. The photoluminescence properties and energy transfer process from Tb^3＋ to Eu^3＋ of CaF2：Tb^3＋,Eu^3＋ phosphors were also investigated through excitation spectra and decay curves. In addition, the emission spectra of the glass ceramics in a wide temperature range from 21 to 320 K were recorded under the excitation of 485 nm. It was found that the fluorescence intensity ratios of Tb^3＋ at 545 nm（^5D4→^7F5） to Eu^3＋ at 615 nm（^5D0→^7F2） was highly temperature-dependent with an approximate linear relationship, and the temperature sensitivity was about 0.4%/K. It is expected that the investigated Tb^3＋/Eu^3＋ co-doped CaF2 glass ceramics may have prospective application in optical thermometry.