Young's modulus sound velocity and Young's modulus of Ti-, Zr- and Hf-based amorphous alloys

The Young's modulus sound velocity (V_E) and the Young's modulus of amorphous ribbons for (Ti, Zr, Hf)_100?x (Si, Ge)_x binary and (Ti, Zr, Hf)_85?xM_x(Si, Ge)₁₅ (M = V ? VIII group transition metal) ternary systems were measured as a function of alloy composition. V_E increases with increasing silicon or germanium content and with the replacement of titanium, zirconium or hafnium by M elements except tantalum or hafnium, and tends to increase with the Debye temperature of the constituent elements themselves. E increases linearly with increasing σ_f and H_v, and ratios of σ_f/E and H_v/3E show a nearly constant value (? 0.018) for Zr_100?xSi_x and Zr_85?xM_xSi₁₅(M = Ti, V, Nb, Ta or Mo) amorphous alloys. Considering the compositional dependence of these mechanical properties (E, σ_f and H_v) and the strong correlation among them, it is suggested that (1) the short-range ordering due to the strong interaction among constituent atoms causes an increase in E, σ_f and H_v, and (2) all the early transition metal-based amorphous alloys possess a common mechanism for plastic flow.     

On the anomalies in density,Young's modulus and glass temperature of PdSi glasses

The densities, Young's moduli and glass transition temperatures have been measured for binary PdSi glassy alloys. These glassy alloys exhibit a negative deviation from Vegard's law an enhancement in Young's modulus and a tendency to lower the glass transition temperature in the region of the eutectic composition. The observed nonlinearity in these physical properties is shown to be better agreement with an alloy mixing effect rather than the structural ordering model.     

Vicker's Hardness of glass

An equation has been derived for the direct calculation of Vicker's hardness number of glasses from their chemical compositions. The method is based on a consideration of deformation during indentation, which was related to Young's modulus and the average single bond strength of a glass.Excellent agreement is obtained between calculated and measured values of Vicker's hardness number for a variety of glasses.     

Calculation of bulk modulus,shear modulus and Poisson's ratio of glass

Combining Grüneisen's equation with our Young's modulus equation of glass, new formulae were semi-empirically derived for the calculation of bulk modulus, shear modulus and Poisson's ratio of glass. Considering packing density of atoms and bond energy in unit volume the elastic moduli of glass can be calculated. The agreements between calculated and observed values of the moduli of glass are satisfactory for more than 30 glasses.     

The growth of controlled profile crystals by Stepanov's method

Single crystals in the shapes of plates, tubes and rods of various cross sections are widely used in many areas of science and technology. Of great importance is the production of such single crystal specimens directly from the melt. By Stepanov's method, the desired shape of the crystal is obtained by the proper selection of a device which shapes the melt column which rises due to the capillary effect. The capillary parameters determine the shape of the profile curve. The thermal parameters, taking into account the equilibrium crystal shape, define the position and shape of the crystallization front. The use of the shaper makes the process self-stabilizing. A negative feedback which damps out perturbations appears in the crystal-melt system and thus permits the production of controlled profile crystals with constant cross-section along their length. Thermoelastic stresses created in ribbons and rods as a result of temperature-induced misfit deformations are considered. The generation of dislocations in crystals occurs mainly due to stresses arising near the crystallization front. Various versions of the method and their applications to some materials are discussed.     

Quantitative calculation of immiscibility ranges of multi-component borate, silicate and borosilicate glass systems

Using the phase diagram data of binary systems, in this paper a great number of binary immiscibility equations have been calculated by computer. Based on those equations, the formulae for the calculation of ternary and multi-component systems have been derived. Generally, the results of the calculation agree with the experimental data.     

Ab initio calculation of vibrational frequencies of Ge0.25S0.75−yIy glass

The vibrational frequencies of Ge₄, S₄, I₄, SI₃, Ge₂I₂, S₂I₂, Ge₂S₂, Ge₂SI, GeS₃, GeI₂S, Ge₃S and GeI₃ are computed using first principles. These frequencies are compared with those found experimentally in the Raman spectra of Ge_0.25S_0.75−xI_x glass. In this way, it is found that Ge₄, GeI₂S and GeI₃ tetrahedra occur in the glass. These tetrahedra are of different sizes so they stack to form the floppy phase of the glass.     

27Al NMR structural study on aluminum coordination state in bismuth doped silica glass

The aluminum coordination state in bismuth doped silica glass, which has new broad infrared emission at 1.3 μm regions, was investigated by using ²⁷Al NMR, and it is demonstrated that 6-fold coordinated aluminum ions with corundum structure are dominant in bismuth doped silica glass until Bi₂O₃ concentrations of 1.0 mol% with Al₂O₃. The aluminum ion efficiently affects the creation of a Bi luminescent center at an intensity of Bi₂O₃ (1.0 mol%)–Al₂O₃ (2.3 mol%)–SiO₂ (96.7 mol%); the sample is three orders of magnitude larger than the Bi₂O₃ (1.0 mol%)–SiO₂ (99.0 mol%) sample. Aluminum ions with corundum structure in silica glass have a very important role for the configuration of peculiar Bi luminescent centers.     

Molecular dynamics of poly (oxybutylene)s confined in pores of Vycor glass

We have investigated the relaxation dynamics of poly (oxybutylene), POB, chains of various lengths, with different end groups (OH and CH₃) in bulk and in confinement using dielectric relaxation spectroscopy. It is known that POB chains exhibit, apart from the segmental (main) relaxation process, the dielectric normal mode process which reflects the global chain motions. The comparative study of OH- and methyl-ended POB chains in bulk reveals the marked effect of association of hydroxyl end groups and indicates that the decrease in the density of the methylated specimens results in the acceleration of both relaxation processes, main and normal mode relaxations. For the confined POB chains the data indicate that the segmental relaxation process becomes faster (the effect being more pronounced for the methylated POB chains). A decrease in T_g of about 8 K for the methyl- and 2 K for OH-ended POB chains is estimated. Regarding the average relaxation rates of the normal mode process our data indicate that global chain mobility is not affected by the confinement.     

Ab initio calculation of vibrational frequencies of GexPxS1−2x glass

The vibrational frequencies of GeS₄, GeP₄, Ge₂S₆, GeP₃, Ge₃P, Ge₂P₂, P₂S₂, P₃S, P₄S₃, α-P₄S₄, β-P₄S₄, α-P₄S₅, β-P₄S₅, P₄S₇, P₄S₉ and P₄S₁₀ are theoretically computed from the first principles. The Raman frequencies of Ge_xP_xS_1−2x glass are obtained for x varying from 0.05 to 0.019. The computed fundamental frequencies of clusters are compared with those experimentally found. In this way, we are able to identify the vibrating clusters in the real glass. The clusters identified in the real glass are found to be Ge₂P₂, P₄S₃, α-P₄S₄, β-P₄S₄, β-P₄S₅, P₄S₇, P₄S₉, β-P₄S₅, Ge₂S₆, Ge₃P.     

In situ high temperature 27Al NMR study of structure and dynamics in a calcium aluminosilicate glass and melt

The temperature dependence (25–1400 °C) of ²⁷Al NMR spectra and spin–lattice relaxation time constants T₁ have been studied for a calcium aluminosilicate (43.1CaO–12.5Al₂O₃–44.4SiO₂) glass and melt using an in situ high temperature probe, and the glass has been characterized by ambient temperature, high field MAS NMR. The peak positions and the line widths show a consistent behavior as motional averaging of the quadrupolar satellites increases with increasing temperature. The rate of decrease with temperature of T₁ drastically increases near the glass transition temperature T_g, which suggests a change in NMR relaxation process from vibrational to translational motions. Above the T₁ minimum (≈1200 °C), NMR correlation times obtained from T₁ are in good agreement with shear relaxation times estimated from viscosity, suggesting that microscopic nuclear spin relaxation is controlled by the same dynamics as macroscopic structural relaxation, and thus that atomic-scale motion is closely related to macroscopic viscous flow.     

Self-diffusivity of iron in alkali–lime–alumosilicate glass melts

Self-diffusion coefficients of iron were measured in glass melts with the basic mol% composition of 16 R₂O, 10 CaO, x Al₂O₃ and (74 − x) SiO₂ with x=0, 5, 10, 15 and R=Li, Na, K and Cs in the temperature range of 900–1300°C using square-wave voltammetry. All diffusion coefficients had an Arrhenian dependence which depended on the type of alkali present and the Al₂O₃-concentration. Larger alkali cations, e.g. Cs⁺, as well as an increase in the Al₂O₃-content led to a decrease in the diffusion coefficients and also to an increase in viscosity. Within one glass composition, the Stokes–Einstein equation is fulfilled with respect to the dependence of the diffusivity upon viscosity. At constant viscosity, however, increasing size of the alkali cation and increasing Al₂O₃-content led to larger iron diffusion coefficients.     

Static fatigue in glass — A reappraisal

The delayed failure of soda-lime glass was tested after different surface and heat treatments and at different humidities. It was found that the treatment history of the glass strongly influenced the characteristics times of failure and the effect of humidity on these times. However, the functional dependence of log failure time on relative stress was similar for most treatments. Analysis of the distributions of failure times at particular stresses showed that the log failure time was not linear with applied stress, as often assumed. The experimental data fit better inverse proportionality between log time and relative stress. Analysis of previous data on crack propagation (‘K - ν curves’) in glass also showed this proportionality. Some theoretical reasons for these results are examined.     

Reduced glass transition temperature and glass forming ability of bulk glass forming alloys

Onset temperature (solidus) T_m and offset temperature (liquidus) T_l of melting of a series of bulk glass forming alloys based on Zr, La, Mg, Pd and rare-earth elements have been measured by studying systematically the melting behaviour of these alloys using DTA or DSC. Bulk metallic glass formation has been found to be most effective at or near their eutectic points and less effective for off-eutectic alloys. Reduced glass transition temperature T_rg given by T_g/T_l is found to show a stronger correlation with critical cooling rate or critical section thickness for glass formation than T_rg given by T_g/T_m.