Constitutive Law for the Densification of Fused Silica, with Applications in Polishing and Microgrinding

We discuss a constitutive model describing the permanent densification of fused silica under large applied pressures and shear stresses. The constitutive law is assumed to be rate-independent and uses a yield function coupling hydrostatic pressure and shear stress, a flow rule describing the evolution of permanent strains after initial densification, and a hardening rule describing the dependence of the incremental densification on the levels of applied stresses. Normality, or lack thereof, of the permanent strain increments to the current yield surface in stress space allows for various relative contributions of densification and shear flow in the ensuing deformation. The constitutive law accounts for multiaxial states of stress, since during polishing and grinding operations complex stress states, with large shear components due to friction and abrasion, occur in a thin surface layer due to the action of abrasive particles. We apply the constitutive law in estimating the extent of the densified layer during the mechanical interaction of an abrasive grain and a flat surface under polishing and grinding conditions. The grain is assumed to be spherical and in Hertz contact with the surface, or sharp and in point contact. The effect on the densified depth of stress relaxation due to densification is discussed.     

In Situ Cube-Corner Indentation of Soda–Lime Glass and Fused Silica

Indentation fracture with a cube-corner diamond pyramid on soda–lime silicate glass and fused silica is investigated during the entire indentation cycle in both silicone oil and ambient-air environments. Radial cracks form immediately on loading in all cases. The two-component, elastic-contact + elastic-plastic mismatch (residual) stress field model that has been used successfully to describe radial crack evolution at Vickers indentations fails to describe the fracture response with the cube-corner. The amplitudes of both elastic-contact and residual stress-intensity factors as deduced from these cube-corner experiments are up to a factor of 10 greater than have been previously observed.     

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     

熔融石英陶瓷制品在浮法玻璃热工设备上的应用

介绍了熔融石英陶瓷制品在先进的浮法玻璃企业的应用情况,参照我国企业的有关现状,对使用效果进行了分析和对比,并阐述了这类制品在国内浮法玻璃企业应用的前景和必要性。     

Water Entry into Silica Glass During Slow Crack Growth

Hydrogen concentration depth profiles on surfaces of SiO₂ glass fractured slowly in water and rapidly in oil were determined by nuclear reaction analysis. It was found that water enters SiO₂ glass during slow crack growth in water.     

石英陶瓷的应用

介绍了石英陶瓷在玻璃行业以外，冶金、化工、航空航天等领域的应用，包括应用的石英陶瓷制品、应用特点及条件。     

石英陶瓷的研究应用现状及发展前景

本文综述了石英陶瓷的应用现状,对其研究、应用进行了较为详细的探讨,然后介绍了石英陶瓷增强技术的发展情况,并对石英陶瓷的发展前景和趋势作了介绍。     

Hot Pressing of Fused Silica

The hot pressing of powdered fused silica at temperatures below the melting and devitrification regions is described. The fabrication of high-density shapes of fused silica is possible by this process. A relation expressing densification as a function of viscosity, time, applied pressure, and initial compaction is essentially substantiated.     

Metastable-Phase Formation During the Crystallization of Magnesium Metaphosphate Glass

We have observed a previously unreported metastable intermediate phase during the crystallization of magnesium metaphosphate (Mg(PO₃)₂) glasses to the equilibrium ring phase, Mg₂P₄O₁₂. Our current hypothesis is that the metastable phase contains metaphosphate chains, as in other crystalline alkaline-earth metaphosphates. This type of phase could form by low-energy rearrangement of the polyphosphate chains in the glass structure. Thus, its formation might be favored at low temperatures where there is insufficient thermal energy to break the metaphosphate chains and form tetrametaphosphate rings.     

Aqueous Gelcasting of Fused Silica Using Colloidal Silica Binder

An aqueous‐based gelcasting of fused silica ceramics by using colloidal silica binder was developed. Fused silica slurries having different volume percentage of solid loading from 63 to 74 vol% in colloidal silica were made and the rheological properties were evaluated. It was found that the slurry with 73 vol% of solid loading with viscosity 0.70 Pa.s is suitable for this gelcasting system. The influence of solid loading on physical and mechanical properties of gelcast green and sintered bodies has been studied. The fabricated green body by using colloidal silica binder exhibited a flexural strength of 9 MPa and 88% of theoretical density with 2.2% of drying shrinkage while the sintered sample exhibited flexural strength of 60 MPa and 95% of theoretical density with 4.3% of sintering shrinkage. It was observed that, the nano silica particles from the colloidal silica binder is filling the interstitial positions in the consolidated fused silica green body and enhancing physical and mechanical properties.     

Formation of a Protective Layer During the Hydration of Cement

The mechanism for the slow rate of reaction between portland cement and water during the early stage is not well understood, but it probably is controlled by either the rate that the reactants diffuse through a barrier that surrounds the unreacted cement grains or by the rate that nuclei of the stable product form and grow or by both rates. New evidence using environmental scanning electron microscopy is presented about the structure of a layer that forms around the particles of cement. Preliminary observations that relate mixing to the structure of the layer are also presented.     

浮法玻璃窑炉用熔融石英陶瓷制品的注凝成型研究

介绍了熔融石英陶瓷的注凝成工艺，并通过注凝成型工艺制作出了大规格异型的浮法玻璃窑炉用熔融石英陶瓷产品。     

熔融石英陶瓷的性能及其应用

介绍了石英陶瓷的性能特点、制备过程及应用领域     

石英玻璃坩埚和玻璃堆垛项目的引进、技改和创新的探讨

通过对两家企业分别引进石英玻璃坩埚和玻璃堆垛机项目的成败分析,以及对成功引进后进行技术改造和创新的过程分析,总结出了技术引进、技改和自主创新的协同发展是企业发展壮大的根本.     

Interpretation of the Infrared Spectra of Fused Silica

A vibrational analysis was performed for fused silica assuming short-range order in the glassy network. This order is described by an average structural unit based on the model α-quartz. The analysis uses a group theoretical method and the Wilson FG-matrix techniques to predict 16 normal mode vibrational frequencies based on a diagonal force field. The most probable values of the force constants, which were obtained from the best fit between the calculated vibrational frequencies and the measured spectral values, are:

Although the selection rules are not adhered to, 15 predicted frequencies are within the ranges of the spectra of fused silica reported in the literature.     

钠钙硅酸盐玻璃和铅玻璃的离子溅射抛光

采用20keV的离子注入机对钠钙硅酸盐玻璃和中铅玻璃进行离子溅射抛光.玻璃样品在N 离子剂量为1×1014ions/cm2、1×1017ions/cm2,束流强度150μA/cm2于室温下抛光.讨论了离子溅射抛光后玻璃表面的形貌.     

Variations in Solution Chemistry During the Low-Temperature Formation of Hydroxyapatite

Both the kinetics and the microstructure of monolithic hydroxyapatite formed by a low-temperature dissolution and precipitation reaction strongly depend on the conditions in solution during the reaction. The relationships between the molar ratio of the particulate reactants (dicalcium phosphate and tetracalcium phosphate), the solution chemistry, and the rates of formation of hydroxyapatite are examined. During reaction, steady-state solution conditions are rapidly achieved. However, the steady states attained are not those associated with the metastable invariant point involving the reactants. Rather, the steady-state condition varies depending on the molar ratio of the reactants. The ultimate product of the reactions investigated is calcium-deficient hydroxyapatite. Hydroxyapatite formation occurs in two stages: initial formation of nearly stoichiometric hydroxyapatite followed by its conversion to calcium-deficient material. Microstructural evidence indicates that the formation of hydroxyapatite occurs in association with dicalcium phosphate, eventually causing the dissolution of the hydroxyapatite reactant to become diffusionally controlled. Effects of common ions, sodium chloride and magnesium chloride, on the chemistry of the aqueous phase and on microstructural development are investigated.     

Glass Formation, Properties and Structure of Soda–Yttria–Silica Glasses

The glass-formation region of the soda–yttria–silica system was determined. The glasses within this region were measured to have a density of 2.4 to 3.1 g/cm³, a refractive index of 1.50 to 1.60, Vickers hardness values of 3.7 to 5.8 GPa, softening temperature between 500° and 780°C, and a coefficient of thermal expansion of 7 × 10^-6/oC to 19 × 10^-6/o C. Aqueous chemical durability measurements were made on select glass compositions while infrared transmission spectra were used to investigate the glass structure and its effect on glass properties. A compositional region was identified which exhibited high thermal expansion, high softening temperatures, and good chemical durability.