Journal of Non-crystalline Solids

Abstract Intermediate-range orders (IROs) have important roles on the glass transition process which is explained by their self-organization. We propose that a periodic Turing pattern, which is based on the reaction diffusion equation proposed by Turing, is constituted in a supercooled liquid and glass by IROs in a wide temperature range. The nonequilibrium structural state determines the fictive temperature and the residual entropy of a glass at the hypothetical equilibrium transition. There are two structural relaxation times in a glass with their own fictive temperatures, namely, Tf1 and Tf2, which are indicated by the configurational states of molecules inside and outside IROs, respectively (Tf1

For the purpose of developing biodegradable magnesium alloys with suitable properties for biomedical applications, Mg–Zn–Ca–Ag metallic glasses (MGs) were synthesized by copper-mold casting and melt spinning. The effects of Ag addition on the glass formation, thermal stability, microhardness, hydrogen evolution, corrosion resistance, and cytocompatibility of the Mg-based glassy alloys were studied in vitro. The corrosion resistance and the capability of suppressing the hydrogen evolution are enhanced for the Ag-containing alloys, in comparison to the Mg–Zn–Ca MG, though the incorporation of Ag decreases the glass-forming ability but influences insignificantly on microhardness. The higher cellular viability of the Ag-containing alloys than that of the Ag-free alloy was also revealed by direct cell-culture experiments. Thus, Mg–Zn–Ca–Ag MGs possess the potential to be employed as biodegradable materials.

Abstract In this study, the fabrication and magnetic characterization of amorphous/nanocrystalline Co70B20Si5Fe4Mo1 alloy by means of mechanical alloying (MA) and melt spinning (MS) process have been investigated. The produced samples were characterized using X-ray diffraction (XRD), differential scanning calorimetry (DSC), vibrating sample magnetometer (VSM) and scanning electron microscopy (SEM). The results showed that fully amorphous phase can only be formed by means of melt spinning processes, and the final product during mechanical alloying is the combination of nanocrystalline (CoHCP + CoFCC (about 10 nm)) and amorphous phases. The produced melt spun amorphous ribbons exhibit soft magnetic properties with the coercivity and saturation of magnetization in the range of 1.5–2 Oe and 90–120 emu/g, respectively.

Abstract In this work, thermally stimulated depolarization current (TSDC) and dielectric relaxation spectroscopy (DRS) techniques were performed in complementarities to characterize the dielectric relaxation processes in poly(methylmethacrylate) (PMMA) polymer. Three relaxations were highlighted. Based on correlation between TSDC and DRS data, they were attributed respectively to dipolar β and α relaxations as well as interfacial ρ relaxation. New experimental procedure of fractional polarization was used to investigate space charge trap depth distribution within the band-gap of PMMA. Then the individual peaks were fitted to Bucci–Fieschi model, to evaluate the relaxation parameters. The obtained values were discussed in correlation to those evaluated from DRS data fitted to Havriliak–Negami and Arrhenius models. The various observed peaks in the thermograms are discussed on the basis of space charge polarization. The trap energies were evaluated from the fit to the Bucci–Fuschi model. Similarly other parameters such as relaxation time and charge release are evaluated.

Off-stoichiometric glasses in the Ba–Ga–Ge–Se system with Se excess or deficiency (BGGS ± Se) are synthesized and their structure is characterized using Raman and multinuclear ( 77 Se, 71 Ga) magic-angle-spinning nuclear magnetic resonance (MAS NMR) spectroscopy. The results reveal that the structure of these off-stoichiometric BGGS ± Se glasses consists of a charge-compensated, partially covalent network of corner-sharing (Ga/Ge)Se 4 tetrahedra where [GaSe 4 ] − tetrahedra charge balance the Ba 2 + cations. Addition of excess Se to a stoichiometric BaSe–Ga 2 Se 3 –GeSe 2 glass with BaSe:Ga 2 Se 3 > 1 results in the formation of Se–Se linkages, while Se deficiency is accommodated via the formation of homopolar Ge–Ge bonds, in agreement with the continuously-alloyed structural scenario of purely covalent chalcogenide glasses. Such composition-dependent structural evolution is shown to be consistent with the corresponding variation in density and glass transition temperature. • Atomic structure of off-stoichiometric glasses in the system Ba–Ga–Ge–Se is studied. • Raman and multinuclear NMR spectra, density, and T g are reported. • Stoichiometry plays an important role in controlling the mode of Se incorporation. • Network shows characteristics of charge-compensated and continuously alloyed scenarios.

Abstract The effects of B 2 O 3 on the crystallization and properties of Li 2 O–ZnO–Al 2 O 3 –SiO 2 (LZAS) vitrified bonds were investigated for diamond grinding tool application. The results show that the [BO 3 ] in the glass structure increased with increasing B 2 O 3 content. The glass transition temperature and the first crystallization peak temperature decreased, while the second crystallization peak temperature increased with increasing B 2 O 3 content. The increase in B 2 O 3 content has a little influence on the value of Avrami exponent ( n ), keeping two-dimensional crystal growth mechanism. Realized composite with 8 mol% B 2 O 3 of LZAS vitrified bond has a higher crystal volume fraction and a uniform sphere-shaped microstructure. Moreover, vitrified bond B8 exhibits a high bending strength (198 MPa), a good chemical durability (20 days, DR = 3.1 × 10 − 9  g/cm 2  min), an appropriate TEC (4.63 × 10 − 6 /°C) and a good wettability to diamond abrasives, suggesting that it would be a promising material for diamond grinding tool.

Abstract Photoconductivity spectra in amorphous Se have been analyzed on the basis of the geminate-pair model. It predicts that around the Urbach edge the photoconductivity spectrum exhibits also an exponential variation ~ exp( hν / E U p ) with the steepness parameter given as E U p  ≈  k B T , which may be universally held in other materials. In amorphous Se films, however, the exponential variation tends to be masked by below-gap responses, the origin being speculative. We also discuss the photoconductivity spectra in super-gap regions.

Abstract Amorphous Ge 1−x S x (0.0⩽x⩽0.62) films were prepared by a laser ablation method, and their low frequency Raman scattering spectra were measured at 20 K. Two distinct vibration regimes were observed in the spectra. In the regime at higher frequencies, the power-law dependence of the reduced Raman intensity (I∝ωt) changes with an increase in x for x>0.2 in such a way that t increases from 1.4 to 1.7 as x increases from 0.2 to 0.62. By applying a fracton model, the fractal dimension is found to decrease with an increase in x over the range 0.2⩽x⩽0.62.

An assessment is given of the driving forces causing shrinkage during drying of organometallic gels. Both the elastic and viscous responses of the gel to those forces are analyzed, so that the stresses and strains resulting from drying can be calculated. The principle causes of contraction are assumed to be the large interfacial energies between the solid, liquid, and vapor phases. The extent of chemical reactions that occur during drying is assumed to be proportional to the change in interfacial area, so the corresponding change in chemical potential can be included as a contribution to interfacial energy. Three contributions to the capillary stress are identified, the largest being the redistribution pressure that drives the liquid from the wet region of the gel into the dry exterior region. This causes the contraction rate of the wet region to exceed that of the dry region. The rate of liquid flow through the pores of the gel is analyzed. The shrinkage rate is shown to be controlled by the viscosity of the solid phase of the gel. as well as the rate of transport of pore liquid.

Abstract Glass powder (GP) obtained by grinding waste bottle glass has been recently introduced in construction materials as a supplementary cementing material (SCM). The behavior of SCMs strongly depends on surface chemistry, which governs their reactivity. The freshly ground glass (FGP) was analyzed by X-ray photoelectron spectroscopy (XPS) and changes in the chemical composition of its surface were monitored over time up to one year. The carbonation level that could affect the long-term reactivity of GP was also assessed. The results indicate a higher sodium content of the surface of the early milled glass. Surficial sodium and calcium contents tend to decrease over time with a negligible level of carbonation after one year. Furthermore, in order to assess the reactivity of GP in cementitious media over time, the fresh and hardened properties of mortars made with 20% FGP and two-year-old GP (OGP) as partial replacement of cement were characterized. The FGP mortar had reactivity slightly higher than that of the OGP with early setting due to surficial alkalis. Both GPs, however, had similar pozzolanic properties, particularly with a high water-to-binder (w/b), suggesting that age does not affect GP reactivity, at least in a cementitious medium.

To investigate the effect of novel nucleating agents, this study investigates the crystallization behavior of a MgO–Al2O3–SiO2 glass with molybdenum or tungsten oxide addition. Under a reducing condition, crystals formed in the bulk of the supercooled liquids, whereas melting in air yielded only surface crystallization. The first crystalline phase precipitated inside the glass was enstatite and Mg–petalite in glasses doped with molybdenum and tungsten oxides, respectively, whereas the surface precipitate was cordierite. Molybdenum oxide yielded a finer microstructure of the glass-ceramic than tungsten oxide. Some fractions of the nucleating agents were considered to be reduced to metallic states and dispersed through the glasses, providing heterogeneous nucleating sites for enstatite and Mg–petalite.