Properties of Soda Aluminosilicate Glasses: II, Internal Friction

Internal friction measurements of soda aluminosilicate glasses, the physical properties of which were reported in Part I of this series, are discussed. The low- and intermediate-temperature internal friction peaks were studied in detail and are shown to be due to the stress-controlled movement of the sodium and nonbridging oxygen ions, respectively. A close correlation was found between the temperature shift of the low-temperature peak and the activation energy for electrical conduction in the soda aluminosilicate glasses. The magnitude of the low-temperature peak was found to depend more on the structural environment of the sodium ions than on the actual soda content. Changes in the intermediate-temperature peak are explained on the basis of the structural model proposed for these glasses.     

Properties of Soda Aluminosilicate Glasses: V,Low-Temperature Viscosities*

The low-temperature viscosities of two series of sodium aluminosilicate glasses were measured by the fiber elongation method. The results suggested that a modification of the Day and Rindone structural model for sodium aluminosilicate glasses was necessary. The modified model suggests that additional (AlO_½)⁻ groups form at Al/Na ratios >1.     

Properties of Soda Aluminosilicate Glasses: Coordination of Aluminum Ions

An X-ray fluorescence technique has been used to study the coordination number of the aluminum ions in soda aluminosilicate glasses. The fact that the emission wavelength of the K α line of aluminum is slightly different for aluminum ions in different coordination states is utilized in this technique. Using this small difference in wavelength, it is shown that, depending on the Al/Na ratio, the soda aluminosilicate glasses contain aluminum ions in either fourfold and/or sixfold coordination. The X-ray fluorescence measurements are shown to support the structural model which has been proposed for the soda aluminosilicate glasses to explain the behavior of some of their physical properties.     

Properties of Soda Aluminosilicate Glasses: I, Refractive Index, Density, Molar Refractivity, and Infrared Absorption Spectra

The density, refractive index, molar refractivity, and infrared absorption spectra of soda aluminosilicate glasses containing up to 34.8 wt% alumina have been determined. Changes in these properties with composition can be explained by existing theories which assume that the aluminum ions form only A10₄ tetrahedra when the Al/Na ratio of the glass is equal to or less than 1. The aluminum ions in glasses having an Al/Na ratio larger than 1 are in both fourfold and sixfold coordination.     

Formation and Properties of Calcium Aluminosilicate Glasses

The glass-forming region for calcium aluminosilicate glasses has been determined. A number of properties of these glasses (thermal expansion coefficient, glass transformation and dilatometric softening temperature, and refractive index) have been studied. The results of these measurements suggeq that the structures of these glasses may not as closely resemble those of alkali aluminosilicate glasses as is commonly assumed. Evidence is presented which suggests that the binary calcium aluminate glasses may be phase separated.     

Elastic Properties and Molar Volume of Rare-Earth Aluminosilicate Glasses

The elastic properties, molar volume, and glass transition temperature ( T _g) of rare-earth-containing aluminosilicate glasses were investigated in the compositions of SiO₂–LnAlO₃ and SiO₂–Ln_3/4Al_5/4O₃, where Ln is Y, La, Nd, Eu, or Yb. The molar volume decreased with decreased ionic size of the Ln³⁺ ion, and T _g and elastic moduli increased in the same order. The Yb-containing glasses showed the highest Young's modulus among all the oxide glasses, even higher than the highest value ever known for glass containing Y₂O₃, as expected from the smaller ionic radius of Yb³⁺ than that of Y³⁺. The bulk modulus was found to be almost proportional to the inverse four-thirds power of the molar volume of glasses in each composition, indicating that Ln³⁺ ions can substitute for each other without changing the glass structure except for the size of the local structure around themselves. From the comparison of these properties, the structural role of rare-earth ions in these glasses is discussed.     

Effect of Composition on the Mechanical Properties of Aluminosilicate and Borosilicate Glasses

Elastic moduli and fracture toughness were determined for several glasses in the systems soda-alumina-silica, calcia-alumina-silica, and soda-boric oxide-silica. Results for the aluminosilicates are analyzed in terms of Al³⁺:Na⁺ ratios. The mechanical properties do not show maxima or minima at the Al³⁺:Na⁺ ratio of 1, in contrast to conductivity, helium permeability, and refractive index. The moduli and toughness increase with Al³⁺:Na⁺ ratio, which is consistent with increased coherency of the glass network. Glasses which contain B₂O₃ instead of Al₂O₃ have slightly higher moduli but are considerably tougher. The moduli of calcium aluminosilicate glasses are ∼25% greater than sodium aluminosilicates, whereas the fracture toughnesses are similar.     

Structure of Sodium Aluminosilicate Glasses

A series of sodium aluminosilicate glasses composed of varying ratios ( R ) of Al₂O₃/Na₂O (0.25 R 2.0) has been simulated with the molecular dynamics technique using a tetrahedral form of a three-body interaction potential. Extrema in the activation energies for sodium diffusion and in the diffusion constants for all of the atomic species were observed for glasses with equal concentrations of Al₂O₃ and Na₂O ( R = 1.0). These changes corresponded to the minimum observed experimentally in the activation energy for electrical conductivity and to the maximum observed in the viscosity for glasses with compositions of R = 1.0. The coordination of aluminum remained 4 over the entire compositional range, negating the need to invoke a coordination change of aluminum to explain the changes in the physical properties. The changes to the simulated physical properties as R passed through the equivalence point were attributed to the elimination of nonbridging oxygen, to the introduction of oxygen triclusters, and to changes in the distribution of ring structures within the glass networks.     

Effects of Water Content on the Properties of Sodium Aluminosilicate Glasses

Sodium aluminosilicate glasses of the general formula 25Na₂O. x Al₂O₃.(75 – x )SiO₂ were prepared with a range of hydroxyl contents. Both the glass transformation and isokom temperatures decrease as the hydroxyl content increases. The magnitude of the decrease in each property is a function of the alumina content of the glass, with the largest effects occurring for the glass containing 25 mol% Al₂O₃. The magnitude of the effect of water as a function of alumina content reflects the decrease in the concentration of nonbridging oxygens in the glass with increasing Al₂O₃ content, since the effect of the terminal hydroxyl species on the connectivity of the glass is enhanced by the elimination of nonbridging oxygens. The results indicate that the large effect of water content on the properties of these glasses must be considered when discussing the role of alumina in glasses.     

氧化锆对锂铝硅酸盐玻璃化学强化性能的影响

采用熔融淬冷法制备了含不同摩尔分数Zr O₂的锂铝硅酸盐玻璃,通过两步化学强化法对玻璃样片进行了化学强化,研究了Zr O₂对玻璃的稳定性、硬度和化学强化效果的影响。结果表明:随着Zr O₂的摩尔分数从0增加至5%,玻璃化转变温度随之升高,玻璃稳定无析晶现象。引入适量的Zr O₂会促进Li⁺-Na⁺离子交换,提高应力层深度,表面压应力随着Zr O₂浓度的增加而增加,并在摩尔分数为4%时达到最大值,为1 055.6 MPa。中心张应力随着Zr O₂浓度的增加先增加后缓慢减小,表明该系列样品具有较好的抗冲击能力。Zr O₂的浓度变化对强化后玻璃的硬度影响较小,在引入Zr O₂后其抗裂性有所降低,但仍具有较好的抗裂能力。     

超薄铝硅玻璃离子交换工艺研究

高强度超薄盖板玻璃是电子信息产品的重要组成部分,化学强化(离子交换)是提升超薄盖板玻璃力学性能的主要技术途径。在离子交换过程中,玻璃易产生应力弛豫等现象,导致化学强化玻璃难以具备较高的表面压应力、较大的应力层深度与较高的维氏硬度。本文采用两步法离子交换工艺,研究了熔盐、离子交换温度与时间等因素对强化后超薄铝硅玻璃应力层分布及维氏硬度等性能的影响。结果表明,本文所研发的两步法离子交换工艺,可以使玻璃兼具较高的表面压应力、较大的应力层深度与较高的表面维氏硬度。离子交换后,铝硅玻璃的表面压应力可达900 MPa以上,应力层深度可达70 μm以上,同时表面维氏硬度达7.2 GPa以上。     

Molecular Dynamics Simulations of the Structure and Properties of Low Silica Yttrium Aluminosilicate Glasses

Yttrium aluminosilicate glasses are of technological importance in photonics, nuclear waste disposal, and as a delivery vehicle for radiation therapy. Their structures are also of great interest in glass science to elucidate the principles of glass formation and structures. We provide classical molecular dynamics simulation results of a series of yttrium aluminosilicate glasses with low silica concentration. Detailed structure analyses including coordination number, pair and bond angle distributions, Si–O and Al–O network structures, and primitive ring statistics are reported. It is found that the average aluminum coordination number decreases from 4.7 to 4.2 with increasing silica content from 5 to 20 mol%, while maintaining alumina at 55 mol%. Four-coordinated aluminum ions increase from 40% to 84% in the series and the fraction of edge-sharing alumino-oxygen polyhedra decreases, indicating an increased network former role of aluminum ions with increasing silica content. Physical properties such as elastic constant, bulk modulus, Young's modulus, and Possion's ratio were calculated. The results show a decrease of bulk, Young's, and shear moduli with increasing silica and decreasing yttria contents that is in good agreement with experimental data.     

Degree of Polymerization of Aluminosilicate Glasses and Melts

This paper presents the results of analyzing the data available in the literature on the structure and properties of silicate glasses and melts that contain Ti⁴⁺, Al³⁺, and Fe³⁺ cations in addition to alkali and alkaline-earth cations. It is established that the aforementioned multivalent cations in glasses and melts have a coordination number of four and play the role of network-formers. Aluminosilicate glasses and melts with the mole fraction ratio Al₂O₃/M ₂(M)O = 1 are of special interest. For these glasses, the structure is considered to be completely polymerized and, contrary to traditional concepts, their properties depend on the concentration ratio Al₂O₃/SiO₂. Taking into account that the structure of aluminosilicate glasses involves unusual structural units (such as triclusters) and a certain number of nonbridging oxygen atoms, a formula is proposed for calculating the degree of polymerization. The proposed formula is used to calculate the degree of polymerization for a number of Na₂O · Al₂O₃ · mSiO₂ glasses and the CaO · Al₂O₃ · 2SiO₂ glass. It is demonstrated that the calculated degrees of polymerization correlate with the experimentally measured viscosities of the relevant melts.     

Infrared Spectroscopy of Lead and Alkaline-Earth Aluminosilicate Glasses

Infrared spectroscopic studies of lead and alkaline-earth aluminosilicate glasses in the series x MO- x Al₂O₃ (1 - 2 x )SiO₂ M = Mg, Ca, Sr, Ba, and Pb; 0.05 x 0.275] were carried out in the range 2000 to 200 cm⁻¹. Three major absorption bands were observed in the 1100-, 800-, and 500-cm⁻¹ regions. The frequency and the intensity of the 1100-cm⁻¹ band varied linearly with composition. For a specific value of x , the changes in the frequency, intensity, and bandwidth of this band decreased in the order Mg > Ca > Sr > Pb > Ba and the apparent disorder in the glass structure, effected by the substitution of aluminum, increased in the direction Mg < Ca < Sr < Ba, with Pb in between Mg and Ca. The force constants and the bond orders of the Si-O and Al-O stretching vibrations in each of the glasses increased monotonically as Al/(Al + Si) decreased.     

Formation of Aluminosilicate Glasses Containing Rare-Earth Oxides

Formation of aluminosilicate glasses containing oxides of rare-earth elements, e.g. Sc, Ce, Pr, Nd, Eu, Gd, Tb, Dy, Ho, Er, and Yb, was studied by melting at 1550°C and air quenching. The upper limit of the amount of rare-earth oxide which can be incorporated into the aluminosilicate glasses decreases according to the lanthanide contraction.     

Thermal Expansion of Substituted Copper Aluminosilicate Glasses

The effects of various components on the thermal expansion coefficient of low-expansion Cu₂O-Al₂O₃-SiO₂ glasses were examined. When a component of glass was substituted by another oxide, the expansion coefficient always increased, except for substitution of Al₂O₃ by B₂O₃. This result indicates that the essential components to maintain the low expansivity are Cu₂O, such trivalent oxides as Al₂O₃ and B₂O₃, and tetravalent oxide SiO₂. Glasses of the systems Cu₂O-Al₂O₃-B₂O₃, Cu₂O-Al₂O₃-GeO₂, and Cu₂O-Al₂O₃-P₂O₅, which were derived by replacing SiO₂ by other network-forming oxides, showed fairly low expansion coefficients compared with other conventional borate, germanate, and phosphate glasses. It was also found that the valence state of copper ions is important for the thermal expansion characteristics of these glasses; Cu⁺ ions contribute to the low expansion coefficient.     

Optical and Physical Properties of Some Calcium Aluminate Glasses

Calcium aluminate glasses containing alkali oxides and iron oxide will transmit infrared radiation to about 6 μ and still have satisfactory working properties. Their refractive index, density, expansion, Young's modulus, modulus of rupture, fracture velocity, Knoop hardness, and some electrical and chemical properties are evaluated.     

Some Structural and Electrical Properties of Lithium Silicate Glasses

Dielectric measurements, analyzed in terms of the Maxwell-Wagner-Sillars theories of inhomogeneous dielectrics, have been used to investigate the phase-separation characteristics of various lithium silicate glasses. Such measurements are shown to provide evidence of the continuous or discontinuous nature of separated phases and to allow estimates of their shape factors and concentrations. The results indicate that dielectric measurements are particularly useful in following phase-separation processes in glasses from the initial to the final stages.     

Bridging and Nonbridging Oxygen Atoms in Alkali Aluminosilicate Glasses

Thallium-probe ion luminescence spectroscopy and X-ray photoelectron spectroscopy were used to study the structure of sodium aluminosilicate glasses. It was demonstrated that the O1s spectral envelope for these glasses is comprised of three energetically distinct peaks, two attributed to bridging oxygen atoms (Si-O-Si and Al-O-Si) and one to nonbridging oxygen atoms (Si-O-Na). Both techniques indicate that nonbridging oxygen atoms are present in all sodium aluminosilicate glasses, for which A1 /Na is < 1.     

Elastic Properties of Some Glasses After Neutron Irradiation

The changes in Young's modulus brought about in various glasses by exposure to irradiation in a nuclear reactor are reported. These changes are a function of glass composition and particularly of the alkali content. The proposed interpretation of the changes observed at low doses is based on comparisons with the temperature ratio of Young's modulus and consideration is given to both a "hot" structural configuration and a rearrangement in cation sites. The changes observed at higher doses are explained by an increase in the specific gravity due to compaction and those at very high doses by tempering.