Effect of crucible material on optical bandgap and activation energy of Na<Subscript>2</Subscript>O-CdO-P<Subscript>2</Subscript>O<Subscript>5</Subscript> glasses

In the sodium cadmium phosphate glasses, the effect of diffused alumina from alumina crucible has been assessed by measuring various properties such as mass density, refractive index, optical bandgap and dc conductivity. The results of measurements corresponding to glasses prepared in alumina crucible have been compared with those of glasses prepared in platinum crucible with and without adding Al₂O₃. The Optical bandgap and direct current (dc) electrical conductivity of the Na₂O-CdO-P₂O₅ glasses prepared in alumina and platinum crucibles have been determined at room temperature. These glasses have also been electrically characterised in the temperature range 293–423 K. Activation energy E_a of the samples prepared in alumina crucible lies in the range 0.60–0.96 eV whereas it stands in the range of 0.57–0.94 eV for the samples prepared in platinum crucible.     

CdS/CdSSe quantum dots in glass matrix

The compositions containing 55 and 60% of silica have been formulated for preparation of glass filters having sharp cut-off at 475 and 575 nm. To achieve cut-off at these wavelengths, the glasses have been doped with CdS/CdSSe and melted at 1200–1300°C. The glass samples were transparent and pale yellow in colour due to presence of CdS/CdSSe tiny nano crystal (Q-dots). In situ growth of CdS/CdSSe nano crystals imparts the yellow/orange/red colour to these glasses. Optical study shows that as prepared glasses have optical cut-off in the range 350–370 nm. The linear crystal growth of CdS/CdSSe in glasses exhibits red shift in optical cut-off. The optical filter having cut-off at 475 nm can be prepared by doping CdS and cut-off filter of wavelength 575 nm by CdSSe. The TEM results show that the CdS/CdSSe nano crystals (Q-dots) ranging from 2–5 nm are uniformly distributed into the glass matrix.     

Crystal growth of orthorhombic BaSi2 by the vertical Bridgman method

Melt growth of BaSi₂ by the vertical Bridgman (VB) growth method was initiated from barium metal (3 N grade) and semiconductor-grade silicon. Because Ba is highly reactive at the growth temperature (≈1500 K), the crucible materials were chosen to avoid chemical reactions and sticking between the crucibles and the molten and vapor Ba. Crucibles made of molybdenum, quartz, alumina, SiN_x-coated quartz, chemical vapor deposition (CVD) pyrolytic graphite (PG), and chemical vapor deposition SiC-coated graphite were examined, and the semiconductor orthorhombic BaSi₂ was obtained in quartz, alumina, and molybdenum crucibles. The crystalline forms of the grown crystals depend on the crucible materials and growth conditions.     

Sn对Ge-Se-Te玻璃结构与光学特性的影响

采用熔融淬冷法制备了系列Ge₃Se₅Te₂Sn_x(x=0、0.4、0.8、1.2、1.6、2.0, mol%)硫系玻璃。采用X射线衍射(XRD)图谱、差示扫描量热曲线(DSC)、可见/近红外光谱、傅里叶红外(FTIR)光谱、显微拉曼光谱等手段对玻璃的物化性能及结构进行表征, 研究发现Sn的引入导致Ge-Se-Te玻璃系统物化性能的变化: 玻璃的转变温度T_g降低、红外截止波长发生红移, 并有效地降低了杂质吸收峰对样品红外透过率的影响。利用Philips网络约束理论计算的玻璃平均配位数及拉曼光谱的变化, 讨论了引入Sn对Ge-Se-Te玻璃的影响。     

Preparation and characterization of TiO2-BaO-ZnO-B2O3 glass systems for optical devices

We study the TiO₂-BaO-ZnO-B₂O₃ glass system, where the ZnO and B₂O₃ compositions were constant and the ratio TiO₂/BaO was varied from 0.87 to 1.76. A super kanthal resistance furnace was used to melt the compounds inside an alumina crucible, at 1200 °C, for 10 min. After melting, the glasses were poured out into steel moulds and rapidly cooled by quenching. The glasses obtained were homogeneous, bubble free and transparent. They were characterized by X-ray diffractometry, Fourier transform infrared spectroscopy (FTIR), UV-VIS spectroscopy, dilatometry, density and linear refractive index. An infrared cut off caused by the composition influence was found in both IR and UV-vis spectra. From dilatometry T _d and T _g were verified as being anomalous. The linear thermal expansion coefficient presented an anomalous behaviour in relation to TiO₂ concentrations. The density and linear refractive index increased with increasing TiO₂/BaO ratio arriving at their peak value of TiO₂/BaO=1.5 and then decreasing. The dependence of softening point T _d on the ratio TiO₂/BaO exhibited the same behaviour. It is suggested that Ti⁴⁺ plays a dual part in the glass system, assuming a predominantly tetrahedral coordination in the low titania region and a predominantly octahedral coordination in the high titania region. With a heat treatment of the glass around 600 °C, we observed a rapid change of refractive index with increasing temperature.     

Refractive-index dispersion for BaF2-GdF3-ZrF4-AlF3 glasses

Refractive-index dispersion measurements were performed on bulk specimens of 2-, 4-, or 6-mol % AlF(3) doped 33BaF(2)-4GdF(3)-63ZrF(4) (mol %) glass and 4-mol % LiF, CsF, YF(3), CdF(2), SnF(2), or PbF(2) doped 31.68BaF(2)-3.84GdF(3)-60.48ZrF(4)-4AIF(3) (mol %) glass in the wavelength region from 0.4047 to 5.3036 microm. The material dispersion curve and zero material dispersion wavelength were estimated on the basis of refractive- index dispersion measurements. The slope of the material dispersion curve for these fluoride glasses was less steep than that for SiO2 glass in the wavelength range estimated. The zero material wavelength lambda(0) shifted to a shorter wavelength with increasing AlF3 concentration. The lambda(0) is 1.675 microm for 31.68BaF(2)- 3.84GdF(3)-60.48ZrF(4)-4AlF(3) (mol %) glass. When 4-mol % LiF, CsF, YF(3), CdF(2), SnF(2), or PbF(2) were doped into these glasses, each lambda(0) shifted from 1.675 to 1.670, 1.668, 1.673, 1.681, 1.683, or 1.704 microm, respectively. The temperature dependence values of the refractive-index dispersion and material dispersion for 31.68BaF(2)-3.84GdF(3) -60.48ZrF(4)-4AIF(3) (mol %) glass were also obtained. The temperature coefficients of the refractive index were negative values (dn/dT(relative) = -1.0 X 10(-5)/degrees C) and the wavelength dependence of dn/dT was small. The wavelength lambda(0) shifted from 1.675 to 1.605 microm, due to the rise in the measurement temperature from 25 degrees C to 250 degrees C.     

Investigation of the characteristics of platinum group metal modified alumina nanofibers

Alumina nanofibers containing either platinum or rhodium crystalline nanoparticles have been successfully fabricated by electrospinning a solution of polyvinylpyrrolidone mixed with platinum or rhodium chloride and subsequent calcination and hydrogen reduction. Transmission electron microscopy images indicate that the platinum and rhodium nanoparticles are well dispersed on the electrospun alumina nanofibers. X-ray diffraction results demonstrate that the platinum and rhodium nanoparticles are crystalline, while the alumina matrix is amorphous. Furthermore, X-ray photoelectron spectroscopy was used to investigate the chemical nature of these nanofibers containing noble metals before and after calcination and hydrogen processing.     

镀膜浮法玻璃的风化性能

采用人工加速风化的方法研究了镀有SiO2薄膜的浮法玻璃的风化性能,并与相同风化条件下的浮法玻璃原片的表面状态进行了比对,从风化机理上进行了分析。红外反射光谱和扫描电镜分析结果表明,镀有SiO2薄膜的浮法玻璃和未镀膜玻璃随着风化温度和风化时间的增加,均呈现风化现象逐渐加重的现象。但前者风化程度明显低于后者,尤其当风化条件(70℃,75%RH,风化15d)恶劣时,镀膜玻璃表面只出现了小块斑点和红外光谱的略微变化;而未镀膜玻璃表面则出现大面积的侵蚀斑块,在红外谱图上不仅≡Si—O—Si≡特征峰发生位移,而且出现了C?O的特征峰。说明SiO2膜层能够很好地阻挡玻璃表面Na+与空气中H+、H3O+的交换,有效地抑制玻璃表面风化的发生。     

Contact angle of E and borosilicate glasses in different atmospheres

The contact angle of E and borosilicate glasses in various atmospheres such as air, steam, glycols, etc, show that the ambient atmosphere significantly affects the wetting behaviour of these glasses with platinum 20% rhodium alloy. The change in the contact angle is attributed to the bond formation between the cations and anions in the substrate, glass and atmosphere. Steam and oxygen which increase the non-bridging oxygens in the glass as well as increase the negativity of the glass surface increase wetting. Glycols and glycerins reduce non-bridging oxygens and increase the surface positivity groups which reduce wetting. As the requirement of oxygen for complete oxidation of atmospheric combustibles increases, the wetting increases and consequently the contact angle decreases.     

nGeSe2-GeO2系氧硫玻璃的制备与性能

本文报道了由传统的熔融淬冷法制备的一系列硒基氧硫玻璃((GeSe2)100-x(GeO2)x(x=0,5,10,15,20,25)。通过显微硬度,DSC,可见/红外吸收光谱和拉曼光谱探究了氧化物的引入及引入量对硒基硫系玻璃的力学性能、热力学稳定性、光学透过性能和结构的影响。玻璃的摩尔体积随着GeO2含量的增加而降低,玻璃的显微硬度随着GeO2含量的增加而增强;DSC测试表明玻璃的抗析晶能力也随着GeO2的加入明显提高;红外透射光谱表明加入GeO2能够增大玻璃3~5μm波段处的红外透过率。试验结果表明,氧的引入在一定程度上提高了氧硫玻璃的热、力学性能以及在3~5μm中红外波段处的透过率,因而可以应用在有毒气体检测和生物探测等中红外光学领域。     

Microstructural evolution in two alkali multicomponent silicate glasses as a result of long-term exposure to solid oxide fuel cell environments

The microstructural evolution in two potential solid oxide fuel cell (SOFC) sealing glass materials exposed to air and a gas mixture of steam + H₂ + N₂ at 800 °C up to 10000 h was determined. The glass exposures were performed on common SOFC substrates like alumina and zirconia. Characterization of the crystalline phases and pore size distribution was performed for the specimens with various exposure conditions. Comparison of the microstructural and chemical stability of the two glasses was performed based on known trends related to glass chemistry. It was observed that multicomponent glasses followed few rules for chemical and microstructural stability reported in the literature for glasses with fewer components. The two glasses examined in this study displayed adequate resistance to devitrification but marginal resistance to porosity changes in the SOFC environment exposure. The implications of the results for the design and long-term performance of SOFC seals are discussed.     

Blue cooperative luminescence properties in Yb3+ doped GeO2–PbO–Bi2O3 vitreous system for the production of thin films

Germanate glasses are of interest for optoelectronic applications because they combine high mechanical strength, high chemical durability and temperature stability with a large transmission window (400 to 4500 nm) and high refractive index (2.0). GeO₂–PbO–Bi₂O₃ glasses doped with Yb³⁺ were fabricated by melting powders in a crucible and then pouring them in a brass mold. Energy Dispersive Spectroscopy showed that the glass composition has a high spatial uniformity and that the Yb concentration in the solid sample is proportional to the Yb concentration in the melt, what was confirmed by absorption measurements. Intense blue emission at 507 nm was observed, corresponding to half of the wavelength of the near infrared region (NIR) emission; besides, a decay lifetime of 0.25 ms was measured and this corresponds to half of the decay lifetime in the infrared region; these are very strong indications of the presence of blue cooperative luminescence. Larger targets have been produced to be sputtered, resulting in thin films for three dimensional (3D) display and waveguide applications.     

Evidence for a threshold in the biosolubility of aluminosilicate vitreous fibers

Two series of aluminosilicate glasses have been synthesized with the nominal composition (64 − x) SiO₂–x Al₂O₃–36 Na₂O/CaO with x varying from 9 to 19 mol%. They have been corroded in static conditions in a solution that mimics in a simplified manner the intracellular medium of the lung alveolar macrophages (37 °C, pH 4.6, citric acid). The original and corroded glasses have been studied by ²⁷Al and ²⁹Si MAS NMR. Both series display a sharp increase in the silicon dissolution rate with the alumina content. The glass network dissolves extremely slowly, whereas the release of excess sodium is very fast, for the glasses with low alumina content. On the opposite, the glasses with high alumina content dissolve much more rapidly in a nearly congruent manner. The crossover between the two behaviors occurs for x = 13, which corresponds to 33% of aluminum in the glass-former network. The sharp crossover from slow to fast network dissolution is explained in terms of connectivity of the silica sub-network. Above a certain amount of alumina, the silicon sub-network is no more percolating and the corroded glass breaks up into colloids. The sharpness of the transition and the relatively low alumina content required for fast dissolution are related to a structural feature of the aluminosilicate glasses, namely the aluminum self-avoidance that decreases the connectivity of the silica sub-lattice.     

B2O3-Al2O3-SiO2透明玻璃陶瓷研究

玻璃陶瓷属于一类多晶陶瓷材料.通过调整玻璃基质和晶相组成可以制备出具有良好的力学、热学、电学和光学性能的玻璃陶瓷材料.采用传统的熔融和退火技术制备出含B2O3-Al2O3-SiO2-Li2O-K2O组分的硼铝硅玻璃,并通过成核和长晶工艺最终制备出透明玻璃陶瓷.配合料在铂金坩埚中于1450℃下熔融2h,然后经两步热处理制度控制晶核的生成和晶粒的长大.采用差热分析技术确定成核和长晶温度.采用X射线衍射技术对不同热处理制度下的玻璃陶瓷样品进行分析,以确定最佳成核和长晶条件.采用扫描电子显微镜分析玻璃陶瓷形态,晶粒尺寸及其在残余玻璃相中的分布.采用UV-Vis-Nir分光光度计测定玻璃陶瓷样品的透过率.     

Role of the nature of support on the structure of Au-Rh bimetallic nanoparticles

Au, Rh, and Au-Rh clusters were studied on Al₂O₃, TiO₂ powders and titania nanowire by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and infrared spectroscopy (FTIR). On the XP spectra of the Au-Rh/TiO₂ and Au-Rh/Al₂O₃ powders and wires the binding energy of the Au 4f emission was practically unaffected by the presence of Rh, the position of Rh 3d remained also constant on alumina, while it shifted to lower binding energy with gold admixture on titania. New emission for Rh 3d at 309.2 eV and for Au 4f at 85.6 eV developed on titania wire case. The bands due to Rho-CO and (Rho)₂-CO were observed on IR spectra of titania supported bimetallic samples. The peak due to Rh⁺-(CO)₂ was less intense on bimetallic nanowire. All three bands however are intense on Au-Rh/Al₂O₃. The results were interpreted by electron donation from titania through gold to rhodium. “Core-shell” bimetallic structures are supposed on Au-Rh/titania wire.     

As2Se3-AsTe-CuI系统玻璃的形成和结构研究

为了探索新的透红外材料,本文研究了Ａｓ２Ｓｅ３－ＡｓＴｅ－ＣｕＩ系统玻璃的形成区,备了一系列不同ＡｓＴｅ和ＣｕＩ含量的玻璃。     

Préparation et propriétés de couches minces de titanate de baryum

Films of barium titanate were deposited by flash evaporation from tungsten and iridium crucibles in the presence of a low partial pressure of oxygen during the deposition. In a second more satisfactory method, a layer of TiO₂ was deposited by reactive cathodic sputtering followed by a layer of BaO deposited by evaporation from BaCO₃ in a platinum crucible. The thermal synthesis of BaTiO₃ was completed by heating the substrate of iridium or platinum at temperatures up to 1100°C.     

The corrosion resistance of high ZrO2 fusion-cast Al2O3-ZrO2-SiO2 glass refractories in soda lime glass

The corrosion resistance to soda lime glass of fusion-cast high zirconia Al₂O₃-ZrO₂-SiO₂ compositions is evaluated. It is concluded that these materials offer no improvement in corrosion resistance over the typical commercially available 40 wt% zirconia refractory in this glass. Furthermore, it is concluded that an optimum mixture of alumina and zirconia exists which has better corrosion resistance to soda lime glass than either end member. Finally, it is suggested that this trend in corrosion resistance is due to the interdependent solubilities of alumina and zirconia in the glass.     

Physical properties of some rare earth tellurite glasses

Mossbauer and IR spectra as well as the electrical conductivity have been measured to give an idea about the structure and the electrical properties of some rare earth tellurite glasses containing Fe₂O₃. The glasses denoted [1 – (2x + 0.05)] TeO₂ ·xFe₂O₃ · (x + 0.05) Ln₂O₃, wherex = 0.0 and 0.05 and Ln = lanthanum, neodymium, samarium, europium or gadolinium, were prepared by fusing a mixture of their respective reagent grade oxides in a platinum crucible at 800° C for one hour. The Mossbauer parameters such as isomer shift, quadruple splitting and line width were found to be a function of the polarizing power (charge/radius) of the rare earth cations. The Mossbauer parameters were not affected by the heat treatment of the glass samples. Both of the Te-O-Ln and Te-O-Fe stretching vibrations were obtained from the IR results which indicate that the rare earth oxides and iron oxide are partially covalent. The electrical resistivity was measured as a function of temperature from 293 to 520 K. Both the electrical resistivity and the activation energy were found to be a function of the atomic number (Z) of the rare earth cations. The results were interpreted on the basis of the electronic structure of the glass.     

A study of optical absorption in tellurite and tungsten-tellurite glasses

A series of glass specimens was prepared from TeO₂ glass and from the binary tungsten tellurite glasses (TeO₂-WO₃) and their densities, optical absorption edges and infrared absorption spectra were measured. It was found that the fundamental absorption edge is a function of glass composition, and absorption in this region is due to indirect electronic transitions in k-space. The main infrared absorption bands in the TeO₂-WO₃ glasses are related to those characteristics of the TeO₂ component.