144 research outputs found
Inhomogeneities and iron diffusion in a Thailand tektite Semiannual report, Apr. 1969
Electron microscopic examination of Thailand tektit
Cooling-Rate Effects in Sodium Silicate Glasses: Bridging the Gap between Molecular Dynamics Simulations and Experiments
Although molecular dynamics (MD) simulations are commonly used to predict the
structure and properties of glasses, they are intrinsically limited to short
time scales, necessitating the use of fast cooling rates. It is therefore
challenging to compare results from MD simulations to experimental results for
glasses cooled on typical laboratory time scales. Based on MD simulations of a
sodium silicate glass with varying cooling rate (from 0.01 to 100 K/ps), here
we show that thermal history primarily affects the medium-range order
structure, while the short-range order is largely unaffected over the range of
cooling rates simulated. This results in a decoupling between the enthalpy and
volume relaxation functions, where the enthalpy quickly plateaus as the cooling
rate decreases, whereas density exhibits a slower relaxation. Finally, we
demonstrate that the outcomes of MD simulations can be meaningfully compared to
experimental values if properly extrapolated to slower cooling rates
Elastic properties of TeO2-B2O3-Ag2O glasses.
A series of glasses [(TeO2) x (B2O3)1−x ]1−y [Ag2O] y with x = 70 and y = 10, 15, 20, 25 and 30 mol% were synthesised by rapid quenching. Longitudinal and shear ultrasonic velocity were measured at room temperature and at 5 MHz frequency. Elastic properties, Poisson's ratio, microhardness, softening temperature and Debye temperature have been calculated from the measured density and ultrasonic velocity at room temperature. The experimental results indicate that the elastic constants depend upon the composition of the glasses and the role of the Ag2O inside the glass network is discussed. Estimated parameters based on Makishima–Mackenzie theory and bond compression model were calculated in order to analyse the experimental elastic moduli. Comparison between the experimental elastic moduli data obtained in the study and the calculated theoretically by the mentioned above models has been discussed
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