Elastic Properties of Glasses

A theoretical study of the possible mechanisms involved in the elastic deformation of a silicate glass indicates that if the only work done when such a glass is deformed is in the stretching or compressing of the Si-O-Si links, Poisson's ratio should be 0.25. Values less than this can be explained when the energy of deformation of the SiO₄ tetrahedra is considered and values greater than 0.25 if one takes into account the work done in deforming large modifying ions which fill the interstices in which they are located.     

Elastic Properties of Alkali Phosphomolybdate Glasses

Ultrasonic velocities at 10 MHz have been measured in two series of lithium, sodium, and potassium phosphomolybdate glasses with two fixed P₂O₅ concentrations. Elastic moduli, Poisson's ratio, and Debye temperature have been calculated. The composition dependence of most of the properties of lithium glasses exhibits a trend opposite to that of potassium glasses. Properties of sodium glasses lie between the other two alkali systems. Alkali oxide modification is suggested to be accompanied by ring reformation in lithium and sodium glasses. Ring size effects have been shown to account for all of the composition dependence.     

Gamma Irradiation Studies of Some Borate Glasses

The gamma-ray-induced optical absorption in a series of cabal (calcium-boron-aluminum) glasses was studied and is interpreted, wherever possible, in terms of structural concepts. A resolution of the observed absorption spectra showed that three Gaussian-shaped bands were induced with their maxima at about 2.3, 3.5, and 5.0 e.v. (550, 350, and 250 m_μ). The 2.3-e.v. band decreased in intensity with increasing CaO content, reaching a minimum intensity at a composition corresponding to the four-coordination of about 20% of the boron. Further increase in CaO content was associated with an increase in the intensity of this band. The intensity of the 3.5-e.v. band decreased gradually with increased mole per cent of CaO and increased with increased Al₂O₃. The 5.0-e.v. band showed an abrupt increase in intensity which corresponded to the appearance of non-bridging oxygens in the network. Replacing Ca²⁺ by Mg²⁺, Sr²⁺, or Ba²⁺ or replacing Li⁺ by Na⁺ or K⁺ showed that glasses containing large ions of low field strength give less induced absorption than glasses containing small ions of high field strength. A potassium alumina borate glass melted under reducing conditions gave a considerably higher ultraviolet transmission, before irradiation, as compared with the same glass melted under normal conditions. The gamma-induced absorption of these two glasses showed that reducing conditions resulted in a decrease in the intensity of the 2.3- and 3.5-e.v. bands, whereas it caused an increase in the far-ultraviolet-induced absorption. The effect of additions of arsenic, thallium, titanium, germanium, and some rare-earth oxides is discussed.     

Elastic Properties and Short-to Medium-Range Order in Glasses

Very different materials are named "Glass," with Young's modulus ( E ) and Poisson's ratio (ν) extending from 5 to 180 GPa and from 0.1 to 0.4, respectively, in the case of bulk inorganic glasses. Although glasses have in common the lack of long-range order in the atomic organization, they offer a wide range of structural features at the nanoscale and we show in this analysis that beside the essential role of elastic properties for materials selection in mechanical design, the elastic characteristics ( E , ν) at the continuum scale allow to get insight into the short- and medium-range orders existing in glasses. In particular, ν, the atomic packing density ( C _g) and the glass network dimensionality appear to be strongly correlated. Maximum values for ν and C _g are observed for metallic glasses (ν∼0.4 and C _g>0.7), which are based on cluster-like structural units. Atomic networks consisting primarily of chains and layers units (chalcogenides, low Si-content silicate, and phosphate glasses) correspond to ν>0.25 and C _g>0.56. On the contrary, ν<0.25 is associated with a highly cross-linked network, such as in a-SiO₂, with a tri-dimensional organization resulting in a low packing density. Moreover, the temperature dependence of the elastic moduli brings a new light on the structural changes occurring above the glass transition temperature and on the depolymerization rate in the supercooled liquid. The softening rate depends on the level of cooperativity of atomic movements at the source of the deformation process, with an obvious correlation with the "fragility" of the liquid.     

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.     

氟化铟玻璃若干性质研究

一、引言 自70年代中期Poulain等人发现氟锆酸盐玻璃后,在最近十几年中,相继出现了氟铪、氟钍和氟铝等为基础的氟化物玻璃形成系统。许多科学工作者为改善玻璃的析晶性能、化学稳定性和光学性能,在理论上和实用上做了大量的工作,对玻璃的形成、结构、性质及相互间的关系也进行了深入的研究,取得了一定的进展。与此同时,为了获得性能更为优良的玻璃,人们也在进一步探索新的形成系统。氟化铟玻璃系统是最新一代的氟化物玻璃。国     

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.     

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.     

Properties of Soda Aluminosilicate Glasses IV, Relative Acidities and Some Thermodynamic Properties

Electrochemical cells using the oxygen electrode reactions of Förland and Tashiro were constructed from soda aluminosilicate glasses (containing up to 34.8 wt% alumina) and sodium silicate glasses. The emf developed by these cells was measured as a function of temperature. The relative acidities of the glasses, as indicated by the activities of the soda, increased with increasing alumina content, the rate of change increasing when the Al/Na ratio reached 1. The entropy change for the cell reaction went through a maximum. These properties are correlated with the measurements of, and the structural model used in, the previous three parts of this series. Measurements were made to show that the emf values obey an additive relation.     

Thermal Neutron Irradiation of Y-Ba-Cu-O Superconductor

A Y-Ba-Cu-O superconductor was irradiated at 360 K in the NRX reactor, with a well-thermalized flux of 1.82 × 10¹⁷ n/(m²·s) (E < 1 MeV). Superconducting characteristics at 90 K disappeared by a fluence of 6.6 × 10²¹ n/m² (10 h) but were recovered after a postirradiation heat treatment at 760 K in flowing oxygen. The results suggest that suitable shielding will be required for any application which exposes the superconductor to neutron irradiation.     

On the Electric and Dielectric Properties of Some Boro-Lead Sulphate Glasses

Glass Physics and Chemistry - Binary oxide glass system of the composition (100 – x)B2O3?xPbSO4 [0 ≤ x ≤ 40] is prepared by the press-quenching technique. The X-ray...     

Properties of Yttria-Aluminoborate Glasses

In the Y₂O₃–Al₂O₃–B₂O₃ system, homogeneous glasses were obtained from compositions containing from 50 to 65 mol% B₂O₃. The density, refractive index, and thermal expansion increase as Y₂O₃ replaces either B₂O₃ or Al₂O₃. These glasses have a dilatometric softening temperature above 665°, and below 300°C their dc electrical resistivity exceeds that of fused silica. The infrared absorption spectra indicate that BO₃, BO₄, and AlO₄, groups are present in these glasses.     

Elastic Moduli of Glasses by a Dynamic Method

The elastic moduli and speed of sound of twenty-three optical glasses, a series of Na₂O₃, CaO₃, SiO₃, and B₂O₃ glasses, and some specimens of fused silica were measured by a dynamic method. Each specimen, in the shape of a prismatic bar, was vibrated in four different ways: longitudinally, flexurally on the wide side, flexurally on the thin side, and torsionally. Good agreement was found on Young's modulus as determined by the first three methods. The torsional mode was used to obtain the shear modulus. Statically and dynamically determined values of Young's modulus for six sample glasses also showed good agreement.     

Analysis of Boron in Borosilicate Glasses by Neutron Transmission

A rapid method for the determination of boron in borosilicate glasses by neutron transmission has been developed. The glass sample is dissolved in 48% HF, placed in a polyethylene cell which is located near a Ra-Be neutron source. The neutron source and sample cell are embedded in a parafEn moderator. The attenuation of the neutron flux, which can be related to the boron concentration in the cell, is monitored with a BF₃ enriched B¹⁰ proportional counter. Boron determinations can be made in approximately 40 minutes with an accuracy of ±%. Owing to the low sensitivity (approximately 1 mg.) the major disadvantage of the method is the large sample size necessary. The method, however, is well suited for use as a quality control procedure.     

Titanium Centers Induced in Borate Glasses by Irradiation

The electron paramagnetic resonance of alkali borate glasses containing Ti was observed at 9.1 GHz before and after room-temperature X irradiation. The irradiation-induced spectra can be separated into (1) the well-known complex borate resonance with an average g value greater than that of the free electron (2.0028) and (2) a resonance with a lower g value. The latter resonance consists of two asymmetric ESR lines, one broad and the other narrow, whose characteristics are reported. These lines were not observed in the corresponding Ti-free base glasses; they arise from induced Ti centers. The broad asymmetric line ( T ₁) corresponds to a Ti^3.1 ion in sixfold coordination, whereas the narrow asymmetric line ( T ₂) corresponds to a Ti³⁺ ion in a different structural configuration. Lines T ₁ and T ₂ are stable at room temperature, not easily saturated with microwave power, and exhibit behavior independent of the complex borate resonance. The total relative intensity of these lines depends on the total Ti concentration in the glass, the Ti⁴⁺/Ti³⁺ ratio in the glass before irradiation, and the structure of the glass.     

Effects of Neutron Irradiation on the Mechanical Properties of Magnesium Aluminate Spinel Single Crystals and Polycrystals

The effect of fast neutron irradiation on the mechanical properties of magnesium aluminate spinel single crystals and polycrystals, such as bending strength, fracture toughness, Young's modulus, and hardness, was summarized based on the reported data. Essentially, the changes in these properties are dependent on the nature and concentration of neutron-irradiation-induced defects. Furthermore, the efficiency of damage accumulation is known to be dependent on temperature. Spinel shows superior resistance to the formation of defect aggregates, and the recombination of point defects occurs efficiently under neutron irradiation; therefore, the change in mechanical properties is not critical, up to very high neutron fluences, and the spinel maintains its structural integrity.     

Optical Properties and Effect of Gamma Irradiation on Bismuth Silicate Glasses Containing SrO, BaO or PbO

Optical and FT Infrared spectroscopic measurements have been utilized to investigate and characterize binary bismuth silicate glass together with derived samples by replacements of parts of the Bi₂O₃ by SrO, BaO, or PbO. This study aims to justify and compare the spectral and shielding behavior of the studied glasses containing heavy metal ions towards gamma irradiation. The study also aims to measure or calculate the optical energy band gap of these glasses. The replacements of parts of Bi₂O₃ by SrO, BaO or PbO caused some changes within the optical and infrared absorption spectra due to the different housing positions and physical properties of the respective divalent Sr2+, Ba2+, Pb2+ ions. The stability of both the optical and infrared spectra of the studied bismuth silicate glass and related samples towards gamma irradiation confirm some shielding behavior of the studied glasses and their suitability as radiation shielding candidates.     

Optical Properties of Diatomic Glasses

The ability of elements to form glasses, the leading part played by the elements of Group VI (O, S, Se, and Te), and the possible influence of the elements of Group VII (F, Cl, Br, and I) are discussed. New glasses suggested by previous work were melted and the refractive index ( n ) and coefficient of dispersion ( v ) of some of them were measured. Inspection of the n, v plots of oxide, sulfide, selenide, and telluride glasses shows that the area corresponding to them extends toward high values of refractive index ( n _max= 5.3) and low values of dispersion coefficient ( v _min=4).