Comparison of 80-keV D+ Ion Implantation with Thermal D2 Doping in Silica by FTIR and ESR Spectroscopy

Behavior of deuterium atoms in fused silica, which were implanted by 80-keV D⁺ (D₂⁺, D₃⁺) ions or doped thermally by D₂ (or D₂O), was studied by infrared Fourier transform spectroscopy (FTIR) and by ESR spectroscopy. When 80-keV deuteron ions are implanted into fused silica, OD bonds are formed. The OD bonds are also formed by thermal doping with D₂ or D₂O. When the deuterated silica is γ-ray irradiated at 77 K, D atoms are formed by rupture of the OD bonds. The efficiency of the OD bond rupture in the deuteron-implanted silica is much less than that in the D₂-doped silica. It is concluded from the results of thermal annealing that the low efficiency of the OD bond rupture in the deuteron-implanted silica is due to the radiation damage accompanying the implantation process. However, the decay rate and detrapping energy of deuterium atoms, once formed in the silica, are similar in both cases.     

Properties and Network Constitution of rf-Sputtered Amorphous Films in the System Silicon Dioxide–Aluminum Orthophosphate

Amorphous films in the system SiO₂–AlPO₄ were prepared by means of the rf-sputtering method, and their physical properties, such as density, refractive index, and temperature coefficient of Young's modulus, and infrared spectra were measured. Also, the K α X-ray emission spectra of silicon and aluminum were measured in order to investigate the coordination state of these cations in the amorphous films. The density and the refractive index were close to those of amorphous SiO₂ and AlPO₄ and the compositional dependence showed a small deviation from linearity. The temperature coefficients of Young's modulus were positive for all of the samples. The infrared absorption spectra of all of the samples were similar to those of SiO₂ glass and amorphous AlPO₄ film, and there was no evidence of the presence of P═O bonds. The coordination states of silicon and aluminum ions in the present amorphous films were the same as those in fused silica and AlPO₄ crystal, respectively. The results of the properties, infrared absorption spectra, and X-ray emission spectra suggest that SiO₄ tetrahedrons and AlO₄–PO₄ connecting tetrahedral dimers constitute the network of the present amorphous films. A small deviation of the physical properties from an additive rule was thought to result from the difference in the bond character between the newly formed Si–O–Al and Si–O–P bonds and the bonds in the end members, Si–O–Si and Al–O–P.     

Kinetic Behavior of H and D Atoms in γ-Irradiated SiO2 as Studied by ESR Spectroscopy

The decay of hydrogen atoms, produced by γ irradiation of fused silica and quartz, was studied by ESR spectroscopy. The decay of H atoms in silica cannot be explained by a secondorder kinetics nor by a simple first-order kinetics. Also, the decay is not composed of several first-order processes with different activation energies. The data for the decay of H atoms can be described by a first-order kinetic equation with a timedependent rate constant of the form k(t) = Bt ^α−1, where B and α are constants. The decay kinetics of D atoms in deuterated fused silica and H atoms in a single crystal of quartz are also explained by use of the time-dependent rate constant. The apparent activation energies for the decay of H and D atoms in the silica are 15 to 16 kJ/mol and 14 to 15 kJ/mol, respectively. The decay rates for D and H atoms in the silica are similar.     

Hydrothermal synthesis of giant single crystals of MFI type zeolite: Modified bulk material dissolution method

In the present study, we aimed at the development of an easy and reproducible synthesis method of giant MFI zeolite crystals. We used a new synthesis method, modified bulk material dissolution (M-BMD) method, in which a piece of quartz glass tube was inserted as a silica source in a small PTFE sleeve together with ZSM-5 powder as seed crystals. We adopted a higher HF concentration (25 mmol/25 ml) of the synthesis solution than that usually used. By using this method, only a few crystal nuclei were formed separately from each other on the surface of the quartz glass tube in the PTFE sleeve and giant zeolite crystals were reproducibly synthesized on it. Giant single crystals of MFI as large as 5.0 mm were successfully synthesized at 453 K for 90 days by using the M-BMD method.     

不同方法制备的高纯SiO2纤维的结构及其形成

用Ｒａｍａｎ光谱和Ｘ射线径向分布函数研究了高纯石英熔融法、酸沥滤法和溶胶－凝胶法三种不同方法制取的高纯ＳｉＯ２纤维的结构。结果表明，不同方法制备的ＳｉＯ２纤维中的断键数目相差很大，并且都远高于块状石英玻璃，断键上连接的原子团也与制备方法有关。径向分布函数表明，沥滤法纤维中存在一种Ｓｉ－Ｏ－Ｓｉ连接，其Ｓｉ－Ｓｉ原子间距分布于近邻Ｓｉ与次近邻Ｓｉ之间。结合不同制备方法的特点对各种纤维结构的形成机理进     

Radiation-Induced Mobility of Substitutional Hydrogen in MgO

The distribution of hydrogen between substitutional sites and Mg(OH)₂ precipitates in MgO single crystals depends on the thermal treatment of the crystal. Isochronal annealing studies of quenched and slow-cooled crystals indicate that the substitutional H, as monitored by the O–H stretching frequency at 3296 cm^-1, is not mobile at <800 K. However, under the influence of electron irradiation, H is mobile below room temperature. The net result of the irradiations is the appearance of the paramagnetic vacancy left behind by the H and an enhancement of the amplitude of the Mg(OH)₂ absorption band. The mobility of the substitutional H, which was found to be a strong function of the irradiation temperature, was greater at 290 K than at 85 K. A mechanism for the displacement of the substitutional H is proposed.     

Indentation Behavior of Soda-Lime Silica Glass, Fused Silica, and Single-Crystal Quartz at Liquid Nitrogen Temperature

In an attempt to elucidate the processes involved in the formation of indentation impressions, Vickers hardness measurements have been made on soda-lime silica glass, fused silica, and crystalline quartz indented at room temperature and 77 K. The hardness of all three materials increases by a factor of ∼2.5 on cooling to liquid nitrogen temperature. High-magnification SEM photographs revealed that the deformation and cracking patterns of the glasses changed strikingly: no shear lines were observed within the indentations, and ring cracking occurred instead of radial/median cracking. In addition, cracking occurs at much higher loads than at room temperature. The hardness results have been explained in terms of volume flow (densification) rather than shear flow (viscous or plastic) for the glasses at low temperature. The quartz crystal, on the other hand, deformed plastically at both room temperature and 77 K. Cracking differences result from changes in both flow and water activity     

Structure of Neutron-Irradiated Quartz and Vitreous Silica

The structure of quartz and vitreous silica disordered by heavy irradiation (10²⁰ neutrons per cm.²) of fast neutrons was studied by means of X-ray diffraction and infrared spectroscopy. The results indicate that the structure of the disordered amorphous form of silica resembles closely that of vitreous silica. The average Si–O distance (1.61 a.u.) remains unchanged, but the average Si–O–Si bond angle decreases from 142° to 138°; the radial distances of the more distant neighbor atoms show a wider distribution in the disordered material. It is suggested that the disordered form of silica results from thermal effects (thermal spikes) accompanying the passage of knocked-on atoms through the solid.     

Structure–Property Correlations in Y–Ca–Mg–Sialon Glasses: Physical and Mechanical Properties

The physical and mechanical properties of 12 glasses from the Y–(Mg,Ca)–Si–Al–O–N and (Mg,Ca)–Si–Al–O–N systems were investigated. The effect of the substitution of magnesium for calcium through two series of glasses, one consisting of oxides glasses and the other of glasses containing 6 at.% of nitrogen (15 e/o N), was considered. The change of the glass transition temperature through the glass series provides evidence for a mixed-alkaline-earth effect between magnesium and calcium species. The indentation hardness ( H ), Young's modulus ( E ), and indentation fracture toughness ( K _C) were found to increase significantly with either the magnesium or the nitrogen content, and nitrogen also seems to enhance the effect of magnesium on the properties. The network structure was analyzed both by ²⁹Si and ²⁷Al Magic Angle Spinning Nuclear Magnetic Resonance and by neutron scattering experiment, which allows for the estimation of some atomic bond lengths in such complex glasses. Nitrogen was found to have a significant structural effect on the magnesium environment and on the glass polymerization degree, and hence on the glass properties.     

Irradiation-induced brittle-to-ductile transition in α-quartz

Silicate materials such as quartz and silica glass are inherently brittle in nature. Here, using atomistic simulations, we demonstrate that the quartz crystal exhibits a brittle-to-ductile transition when irradiated. We show that the nanoscale plasticity observed in the irradiated structure is reminiscent of metal-like plasticity, which is neither observed in the isochemical crystalline or glassy structure. Invoking an energy landscape approach, we demonstrate that the local atomic self-organization facilitated by the shallow energy landscape is at the origin of this plastic behavior. Overall, the results suggest that the irradiation could be a methodology to induce a ductile transition in materials that are otherwise brittle.     

Crystallization of 60SiO2–20MgO–10Al2O3–10BaO Glass Ceramics

Three distinctly different microstructures of silica (as quartz and crystobalite), alumina, enstatite, and celsian, were found to develop in a 60SiO₂–20MgO–10Al₂O₃–10BaO glass ceramic. At 1010°C, growth of wormy fibrillar crystals was observed, indicating that crystal growth was diffusion controlled. At the intermediate temperature of 1080°C, a coarse cellular microstructure developed with multiple spherical particles nucleated on their surfaces and in the surrounding glass. At 1200°C, the glass crystallizes in a denderitic morphology but the dendrites were actually fragmented into multiple cube-shaped enstatite crystals, indicating a transition to interface-controlled growth. The crystals coarsen with time but maintain their order along the dendrite skeletons.     

玻璃熔窑高纯硅质热补料的生产与使用

以高纯熔融石英为主要原料研制了一种高纯硅质玻璃窑用热补料。通过加入助结合剂、助烧结剂等,提高了热补料的理化性能。同时由于熔融石英本身的低热膨胀性,使其具有优良的抗热震性。该热补料经玻璃厂实际使用,效果良好。     

Trapped Electrons in Irradiated Quartz and Silica: I, Optical Absorption

Evidence is given for the correlation between an optical absorption band at 2300 a.u. and an electron spin resonance system developed in quartz after ⁶⁰Co γ-irradiation. The results of bleaching γ-irradiated quartz and silica at 78°K. and at room temperature are presented and discussed. Also, further observations upon annealing these color centers are given.     

Studies of Chemical Bonding in Glasses by X-Ray Emission Spectroscopy

Silicon and aluminum K β band X-ray emission spectra of a series of lithia-aluminosilica (LAS) glasses were determined using the X-ray spectrometric systems of commercially available electron microprobes. Comparison with spectra of reference materials, including glassy and crystalline forms of silica, high-quartz-phase crystals of the L:A:S-1:1:2 (mol ratio) composition (high-eucryptite), and 6- and 4-coordinated aluminum oxides, led to tentative assignment of spectral peaks to specific electronic transitions. Molecular orbital theory and crystallographic structural data were used to assign bands in crystalline materials. The LAS glass spectra indicated progressive bond weakening with decreasing silica content; the K β peak shifts permitted approximate calculation of the decreases in Si–O and Al–O bond energies, which were as great as 30 kcal/mol relative to SiO₂ (for the L:A:S-1:1:2 glass).     

Water adsorption on silica and calcium-boroaluminosilicate glass surfaces—Thickness and hydrogen bonding of water layer

Adsorption isotherm of water on silica (modeled with fused quartz) and calcium-boroaluminosilicate (Ca-BAS) glass surfaces as a function of relative humidity (RH) was studied using Fourier transform infrared (FTIR) spectroscopy. The effective thickness of the adsorbed water layer and the distribution of hydrogen bonding interactions of water molecules in the adsorbed layer were determined by comparing the transmission FTIR spectra collected at the Brewster incidence angle with the theoretically calculated spectra. In the sub-monolayer regime (<30% RH), differences between the water spectra on fused quartz and Ca-BAS glass could be related to the areal density of hydroxyl groups as well as the elemental composition of the surface determined with x-ray photoelectron spectroscopy. In the transition regime (30%–60% RH), multilayers start growing and the difference between the fused quartz and Ca-BAS surfaces diminishes as the humidity increases. In the multilayer regime (>60% RH), the total amount as well as the hydrogen bonding interactions of adsorbed water layers become insensitive to the surface chemistry and are governed mostly by the phase transition (vapor condensation) behavior. Overall, this study reveals how the water layer thickness and structure on the multicomponent silicate glass surface in ambient conditions are different from those on the pure silica surface.     

The structure of sodium silicate glass from neutron diffraction and modeling of oxygen-oxygen correlations

It is shown that modeling the first oxygen-oxygen peak in the neutron correlation function of a glass enables structural information about other correlations to be obtained, and the method is illustrated by application to a sodium silicate glass. The first O–O coordination number can be calculated from network theory, and sodium silicate crystal structures show that the mean O–O distance can be calculated from the Si–O distance, despite the distortion of the SiO₄ tetrahedra. Modeling the O–O peak for a sodium silicate glass allows the Na-O bond length distribution to be determined. For a binary glass with 42.5 mol% Na₂O, it is found that the Na–O coordination number is 4.8(2) with an average bond length of 2.45 Å, and the Na–O bond lengths are more widely distributed than in sodium silicate crystal structures. Sodium ions are bonded mostly to non-bridging oxygens (NBOs), and the Na–NBO coordination number may be four as in crystals. Sodium ions are also bonded to a smaller number of bridging oxygens (BOs). Contrary to previous reports, it is not concluded that Na–NBO bonds are shorter than Na–BO bonds, but instead that the Na–BO distribution is relatively narrow, whilst the Na–NBO distribution extends to both shorter and longer distance. The broad distribution of Na–O bond lengths arises from a relatively broad distribution of Na–NBO bond valences, subject to the overall requirement of charge balance.     

Structural analysis of 5-[thiazol-2-yldiazenyl]pyrimidine-2,4,6(1H,3H,5H)-trione in both solid state and solution

The synthesis, crystal structure analysis and characterisation of 5-[thiazol-2-yldiazenyl]pyrimidine-2,4,6(1 H ,3 H ,5 H )-trione are reported. This dye was characterised by ultraviolet–visible, Fourier Transform–infrared, proton nuclear magnetic resonance spectroscopy, mass spectrometry techniques and elemental analysis. Both the effects of pH value and solvent polarity upon the absorption properties of the dye have been presented. In addition, the structure of the dye has been determined by a single crystal X-ray diffraction method. The dye was triclinic in P-1 with a  = 8.2419(2) Å, b  = 10.6225(3) Å, c  = 12.5106(3) Å, α = 90.543(1)°, β = 102.79(3)°, γ = 103.858(1)°, V  = 1035.26(5) Å³, D _calc = 1.634 g/cm³ and Z  = 2. The asymmetric unit contains two crystallographically independent C₇H₅N₅O₃S molecules, alongside one half of the solvent C₂H₆O₂ molecule. In the crystal structure, intramolecular N–H…N and intermolecular N–H…N, N–H…O, O–H…N, C–H…O and C–H…N hydrogen bonds link the molecules to form a supramolecular network in which they seem to be effective in the stabilisation of the structure.     

Fusion of Quartz and Cristobalite

The melting point of quartz is established to be below 1450°C. and possibly above 1400°C. The product of fusion is a liquid of high viscosity which undergoes slow transformation to give the commonly encountered vitreous silica. At temperatures between 1450deg; and 1700°C., both cristobalite and glass are formed when quartz is heated in air for periods in excess of 15 minutes. The quartz-cristobalite transformation is sensitive to the ambient atmosphere. After heating to temperatures above 1730°C., inhomogeneities are still present in both fused quartz and fused cristobalite in the form of unmelted microcrystals. Their presence is indicated by X-ray diffraction, metallographic, infrared, and hardness measurements.     

Crystallization Kinetics of Internally Nucleated Vitreous Silica

It has recently been observed that cristobalite can hetero-geneously nucleate and grow internally in vitreous silica. When the glass-crystal composite is cooled to room temperature, β-cristobalite is metastably retained as a result of the large tensile stresses developed during cooling. Although these crystals are not obvious, they can be readily observed with a polarizing microscope or polariscope. As long as the cristobalite does not transform when cooled to room temperature, repeated increments of crystal growth can be measured on the same growing crystal. Crystal growth was measured on electrically melted quartz glass at 1350° to 1620°C. The observed growth rates were linear with time and were the lowest that have been measured in vitreous silica. The kinetic data agreed with the general form of the crystal growth equation μ= (AΔT)/_ν. Since the growth is internal and free from surface contamination, the measured rates are considered to be very near the intrinsic rates for the material.