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1.
Satoshi Yoshida 《Journal of Non》2003,316(1):28-34
Sub-critical crack growth in binary sodium germanate glass was investigated over a wide range of the crack velocities, 10−7-10−2 m s−1, by using small-size specimens with double cleavage drilled compression configuration. For evaluating the intrinsic sub-critical crack growth, crack initiation and subsequent propagation of the crack were performed in heptane. With increasing Na2O content in sodium germanate glass, sub-critical crack growth curve shifted toward higher stress intensity factors first up to 10 mol% Na2O, but more addition of Na2O caused the curve to shift to lower stress intensity factor regions. In other words, fracture toughness shows a maximum at the composition of 10Na2O·90GeO2, whose value is 1.07 MPa m1/2. This compositional dependence of fracture toughness originates from the so-called germanate anomaly. On the other hand, the slope of sub-critical crack growth curve for the glass containing >10 mol% Na2O was much shallower than that for soda-lime glass. These glasses are very fatigable even in inert condition. It is considered that this fatigue behavior can be caused by the microscopic structural variation, which is the presence of GeO6 units in GeO2 glass network, and that these units can be the fatigue crack path. 相似文献
2.
《Journal of Non》2007,353(16-17):1582-1591
This paper presents a study on the roughness of glass fracture surfaces formed as a consequence of sub-critical crack growth. Double-cantilever-beam specimens were used in these studies to form fracture surfaces with areas under well-defined crack velocities and stress intensity factors. Roughness depends on crack velocity: the slower the velocity, the rougher the surface. Ranging from approximately 1 × 10−10 m/s to approximately 10 m/s, the velocities were typical of those responsible for the formation of fracture mirrors in glass. Roughness measurements were made using atomic force microscopy on two glass compositions: silica glass and soda lime silica glass. For silica glass, the RMS roughness, Rq, decreased from about 0.5 nm at a velocity of 1 × 10−10 m/s to about 0.35 nm at a velocity of 10 m/s. For soda lime silica glass, the roughness decreased from about 2 nm to about 0.7 nm in a highly non-linear fashion over the same velocity range. We attributed the roughness and the change in roughness to microscopic stresses associated with nanometer scale compositional and structural variations within the glass microstructure. A theory developed to explain these results is in agreement with the data collected in the current paper. The RMS roughness of glass also depends on the area used to measure the roughness. As noted in other studies, fracture surfaces in glass exhibit a self-affine behavior. Over the velocities studied, the roughness exponent, ζ, was approximately 0.3 for silica glass and varied from 0.18 to 0.28 for soda lime silica glass. The area used for these measurements ranged from (0.5 μm)2 to (5.0 μm)2. These values of the roughness exponent are consistent with values obtained when the scale of the measurement tool exceeds a critical size, as reported earlier in the literature. 相似文献
3.
Roughness analysis of fracture in precursor-derived amorphous and phase segregated Si–C–N ceramics using fractal methods is reported, towards examining the possible correlations between fractal scaling of roughness and fracture properties as well as fracture damage mechanisms. Topography of the fracture surfaces created at a crack velocity of ~10?4 m/s was recorded using atomic force microscopy, and analyzed using RMS roughness and second order height–height correlation functions. The evolution of roughness was well correlated with the evolution of structural and compositional inhomogeneities in the amorphous materials, and the formation of second phases in the phase segregated materials. All the investigated fracture surfaces displayed self-affine scaling with a correlation length of ~50–100 nm and a roughness exponent of 0.8 ± 0.1, commensurate with the universal exponent conjectured by Bouchaud et al. corresponding to dynamic damage regime. No correlation was observed between the roughness exponents and the fracture toughness of the corresponding materials. Examination of the crack opening near the tip region revealed no persistent damage cavities assignable to ‘plastic deformation’ preceding fracture, suggesting that the fracture in the Si–C–N ceramics proceeds in a brittle manner at the employed crack velocities. 相似文献
4.
The local coordination environments of Te atoms have been investigated in crystalline and glassy binary and ternary tellurides in the system Ge-As-Sb-Te using 125Te solid-state wideline nuclear magnetic resonance (NMR) spectroscopy. The average 125Te NMR chemical shifts in these materials range from 300 to 1050, 90 to 700 and − 2000 to − 4100 ppm for 2, 3 and 6-coordinated environments, respectively. Te atoms are predominantly 2-coordinated in binary Ge-Te, As-Te and ternary Ge-As-Te glasses. The 125Te NMR spectrum of the cubic Ge1Sb2Te4 phase with rock salt structure is consistent with a random distribution of Ge/Sb vacancies in the lattice. Besides the coordination number, the 125Te chemical shifts in these materials are also found to be sensitive to the chemical identity of the nearest neighbors. 125Te NMR spectroscopy shows significant future promise in its application as a technique complementary to diffraction and EXAFS in understanding the short-range structure of amorphous Ge-As-Sb tellurides. 相似文献
5.
No biocompatible Ti-based glassy alloys without a harmful element have been reported. We have examined the mechanical and chemical properties of Ti-Pd-Zr-Si glassy alloy in comparison with pure Ti metal and Ti-6Al-4V alloy which have been used so far for biomaterials. The present Ti-Pd base glassy alloys do not contain Al and Ni elements which are considered to be rather toxic. Melt-spun Ti45Zr50−xPdxSi5 glassy alloy ribbons (x = 35, 40, 45) exhibited good bend ductility and had higher Vickers’s hardness and lower Young’s modulus as compared to pure titanium and Ti-6Al-4V alloy. In addition, the Ti45Zr50−xPdxSi5 glassy alloys had higher corrosion resistance and were passivated over a wide range and at the lower passive current density of approximately 10−2 Am−2 than at of pure titanium and Ti-6Al-4V alloy in 1 mass% lactic acid and PBS(−) solutions at 310 K. 相似文献
6.
Molecular dynamics simulations have been performed for a fluorozirconate glass and its model crystals in order to investigate the mechanism of the peculiar high-pressure densification phenomenon of the glass. All the polymorphs and the pressure-induced phase-transition of the model crystals were satisfactorily reproduced. The changes in the density, the F− coordination number and the connectivity of ZrFn polyhedra during the compression-decompression process are investigated under the glassy state. The density increases under high pressure, accompanying the increases in the coordination number and the connectivity. The effect of annealing treatment near Tg is also investigated. The effect was significant around 20 GPa, around which a maximum was found in the treatment-pressure dependence of density after decompression, only for the samples with the annealing treatment before decompression. 相似文献
7.
LixFePO4 glasses have been prepared by fast-quenching method in the whole range of composition 0 ? x ? 1. The amorphous state of glassy materials is confirmed by X-ray diffraction. Information concerning the local environment of Li and Fe cations and the configuration of (PO4)3− oxo-anions is obtained by Fourier transform infrared (FTIR) spectroscopy. While the LiFePO4 crystalline materials undergo a transition from the paramagnetic to the antiferromagnetic ordering at 52 K, no magnetic ordering is observed in the vitreous samples that realize random field systems, so that a spin glass-like freezing is observed at low temperature. The paramagnetic Curie temperature of LixFePO4 is independent of x and shifted to θ = −60 K in the glassy state, due to a significant distortion of the FeO6 octahedra that alters the superexchange path inside the atomic FeO4 layers of the crystallized structure. On another hand, the PO4 tetrahedra are not significantly distorted in the glassy phase. The results are compared with highly disordered, but nanocrystallized LiFePO4 recently obtained at the early stage of synthesis by solid state reaction at 300 °C. In this latter case, the lack of long-range antiferromagnetic ordering is due to substitutional disorder among the cationic sublattice. 相似文献
8.
《Journal of Non》2007,353(32-40):3254-3259
The speed of longitudinal sound waves at 7 and 22 MHz has been measured in liquid, supercooled, and amorphous selenium, including the region around the glass transition temperature, Tg, near 35 °C. In amorphous selenium the speed of shear waves at 7 MHz was also measured. The experiments were performed with high purity Se (99.9999%) hermetically sealed in an evacuated silica ampoule. Four temperature regions with strongly different relaxation times can be distinguished between room temperature and the melting point: (1) a glassy state below Tg, which is stable on the time scale of the experiments, (2) a glassy state above Tg, which is metastable on the time scale of the experiments, (3) a region where homogeneous crystal nucleation occurs, and (4) a supercooled liquid, which is stable on the time scale of the experiments. Each region is marked by a change in the slope of the temperature dependence of the sound velocity. Near the glass transition temperature the velocities of longitudinal and transverse sound exhibit hysteresis with a step-like drop on heating and a more continuous rise on cooling. The step-like anomaly in sound velocity may be a general property of the glass transition. 相似文献
9.
The internal friction Q?1 and Young’s modulus E of Zr–Ti–Cu–Ni–Be bulk metallic glass specimens were measured using a dynamical mechanical spectrometer. Temperature dependence measurements were carried out for differently heat-treated specimens from room temperature up to a temperature above the crystallization temperature using several vibration frequencies (0.2–25 Hz). Two types of Q?1 peaks appeared: a high-temperature peak in the supercooled region, and a medium-temperature peak in the glassy state region. Both of them were shown to be Arrhenius-type anelastic peaks. From the obtained results, the kinetics of movable atoms in the material were discussed. The amplitude dependence of the internal friction was measured at a given frequency at various temperatures. Fluctuations and rapid changes were observed in Q?1 when the amplitude was gradually increased. The fluctuations were especially large near the glass transition temperature. The results were considered on the basis of the dynamics of the atoms in glass-forming materials near the glass transition. 相似文献
10.
A uniform shiny black-coloured glass was obtained using bottom ash produced by a Portuguese municipal solid waste incinerator (MSWI). The bottom ash was the single batch material used in the formation of the glass, which was obtained by vitrification of the solid waste at 1400 °C for 2 h. Under these conditions, a homogeneous melt with an appropriate viscosity to be shaped was obtained, indicating the suitability of this waste material to be employed in the development of vitreous products. The characterization of the resulting glass was performed in order to assess its structural, physical, mechanical, thermal and chemical features. The glass had a density of 2.69 g cm−3, a hardness of 5.5 GPa, a fracture strength of 75 MPa, a thermal expansion coefficient of 9.5 × 10−6 °C−1 and it exhibited a very good chemical stability. In summary, the MSWI bottom ash glass has good mechanical and chemical properties and may, therefore, be used in several applications, particularly as a construction material. 相似文献
11.
We report on a Raman scattering study of oxy-fluoride glass-ceramics with a typical composition 32SiO2:9AlO1.5:31.5CdF2:18.5PbF2:5.5ZnF2:3.5ErF3 (in mol%), which indicates a narrow size distribution of β-PbF2 fluoride nano-crystals, typically of 13 ± 1 nm, in the silica-based glass network and gives insight on how then nano-crystals are incorporated into the glassy network. The Raman spectra indicate the presence of Q0, Q1 and Q2-like units, which are SiOxF4−x tetrahedra with zero, one and two bridging oxygens, respectively. The frequency, width and depolarization ratio of Raman bands corresponding to these Qn-like units (n=0, 1, 2) indicate that Q0 units are mostly symmetric SiO4 tetrahedra, Q1 are SiO4 tetrahedra where one F may substitute for O and Q2 are SiO4 tetrahedra where one or two F may substitute for O. We argue that the non-bridging O atoms belonging to Qn tetrahedra, mostly to Q0 tetrahedra, are located near the interface between the nano-crystalline and glassy phases, allowing an easy accommodation of fluoride nano-crystals with a spherical shape, in the oxide glass network. This was in agreement with the very low-frequency Raman features found between ∼4 and 8 cm−1, due to acoustic vibrations of the nano-crystals embedded in the glassy matrix. 相似文献
12.
Difficulties in the fabrication of representative test specimens and in the application of suitable test procedures e.g., in the measurement of the test parameters viz., load, crack length etc., have so far limited the intrinsic fracture mechanical characterization of the precursor-derived ceramics (PDC). The present work reports the evaluation of the crack tip toughness (KI0) of Si–C–N ceramics, using the novel crack opening displacement (COD) approach. The fully dense PDC test specimens synthesized from a poly(ureamethylvinyl)silazane precursor covered material structures ranging from partly organic amorphous to inorganic nano-crystalline states. Critically loaded cracks were achieved using either a special loading fixture or with Vickers indentation. Crack tip CODs were measured with the atomic force microscopy (AFM). Fractography of the fracture surfaces were performed using topographic, frictional and phase contrast AFM. The measured KI0 values ranged from 0.6 to 1.2 MPa m1/2. The net change in crack resistance was affected by the stripping of OFC-hydrogen atoms in the amorphous materials and by the segregated turbostratic graphite phase in the phase-separated materials. Nano-scale crack deflection observed even in the amorphous materials indicated the presence of structural and compositional inhomogeneities within the amorphous network. 相似文献
13.
Water molecules play a fundamental role in the physics of slow crack propagation in glasses. It is commonly understood that, during stress-corrosion, water molecules that move in the crack cavity effectively reduce the bond strength at the strained crack tip and, thus, support crack propagation. Yet the details of the environmental condition at the crack tip in moist air are not well determined. In a previous work, we reported direct evidence of the presence of a 100 nm long liquid condensate at the crack tip in fused silica glass during very slow crack propagation (10?9–10?10 m/s). These observations are based on in situ AFM phase imaging techniques applied on DCDC glass specimens in controlled atmosphere. Here, we discuss the physical origin of the AFM phase contrast between the liquid condensate and the glass surface in relation to tip-sample adhesion induced by capillary bridges. We then report new experimental data on the water condensation length increase with relative humidity in the atmosphere. The measured condensation lengths were much larger than what predicted using the Kelvin equation and expected geometry of the crack tip. 相似文献
14.
We report on viscosity of a Ge17As18Se65 glass over the temperature range of 280-420 °C and the successful co-extrusion and fiber-drawing of two chalcogenide glass boules to form a core/clad. pair. The co-extrusion produces a preform with optimum diameter stability and core/clad. glass ratio, and minimum defects at the core/clad. interface in the middle 120-200 mm region of a 270 mm long preform. Core/clad. fiber is drawn successfully from the extruded preform. An optical loss of 1.7 dB m−1 at 1666 cm−1 (6.0 μm) and 6.7 dB m−1 at 6649 cm−1 (1.55 μm) is reported. 相似文献
15.
M. Abu El-Oyoun 《Journal of Non》2011,357(7):1729-13419
Differential scanning calorimetry (DSC) technique was used to study the kinetics of amorphous to crystalline transformation in Ge12.5Te87.5 chalcogenide glass. The kinetic parameters of glassy Ge12.5Te87.5 under non-isothermal conditions are analyzed by the model-free and model-fitting approaches from a series of experiments at different constant heating rates (5-50 K/min). The effective activation energy of crystallization was determined by analyzing the data using the isoconversional methods of Kissinger-Akahira-Sunose (KAS), Tang, Starink, Flynn-Wall-Ozawa (FWO) and Vyazovkin. The analysis of the present data shows that the effective activation energy of crystallization is constant throughout the entire interval of conversions and hence with temperature. The transformation mechanism examined using the local Avrami exponents indicates that one mechanism (three-dimensional growth) is responsible for the transformation process for all heating rates used. The reaction model that may describe the transformation process of the Ge12.5Te87.5 chalcogenide glass is the Avrami-Erofeev model (g(α) = [− ln(1 − α)]1/n) with n = 3 for all heating range at the whole range of crystallized fraction (α = 0.05-0.95). A good agreement between the experimental and the reconstructed (α-T) curves has been achieved. The transformation from amorphous to crystalline phase in Ge12.5Te87.5 chalcogenide glass demonstrates a single-step mechanism. 相似文献
16.
Fourier transform infrared (FTIR) reflectance spectroscopy was used to monitor corrosion mechanisms on the surface of lithium disilicate (Li2O-2SiO2) glass samples exposed to an aqueous solution for short times. The traditional mechanisms of glass corrosion were observed but a spectral feature was resolved that was previously unreported. This feature consisted of a peak suspected to result partially from a silanol (Si-OH) vibration in the region 800-1050 cm−1 that shifted and reappeared in a cyclic fashion throughout the corrosion process. The behavior of this peak tends to suggest that the creation and condensation of Si-OH groups is the reaction responsible for causing the shift of the main Si-O-Si and Si-O− peaks, a phenomenon which has previously lacked a detailed explanation. 相似文献
17.
In previous years there has been great interest in new materials for photonic devices operating at infrared (IR) and visible (VIS) regions. We report here near infrared and blue cooperative luminescence properties for Yb3+-doped GeO2-PbO glasses. Luminescence and lifetime measurements in the VIS and near-IR regions were performed to investigate the spectroscopic characteristics of the glasses. Intense emissions around 507 and 1010 nm were observed using 980 and 808 nm excitation, respectively. The VIS lifetimes (∼0.4 ms) are about half of their respective near infrared ones (∼0.8 ms), as expected for materials in which the VIS emission is caused by the cooperative effect. Regarding the IR emission, the glasses exhibited a high absorption cross-section (1.2 × 10−20 cm2) at 978 nm and an emission cross-section of 0.6 × 10−20 cm2, at 1010 nm, with a minimum pump intensity of 2.8 kW/cm2. These results suggest this glass composition as a potential material to be used in devices operating in the VIS and IR spectral range, such as 3-D displays and infrared lasers. 相似文献
18.
Highly lithium ion conducting glasses and glass–ceramics were prepared by a mechanical milling technique in the Li2S-based sulfide and oxysulfide systems. The Li2S–P2S5 glass–ceramics showed ionic conductivity as high as 3.2 × 10?3 S cm?1 at room temperature. All-solid-state batteries using these sulfide-based materials as a solid electrolyte showed excellent charge–discharge performance with high capacity and high cycleability. The cells with the combination of the SnS–P2S5 glassy electrode and the Li2S–P2S5 glass–ceramic electrolyte worked as a secondary battery, which was a first step of glassy monolithic cells with a common glass network. 相似文献
19.
The existence of special covalently bonded short-range ordering structures in a Mg65Cu25Tb10 bulk metallic glass (BMG) is confirmed by thermal expansion and compression behavior. Under ambient conditions the linear thermal expansion coefficient obtained is almost constant in the glassy state with a value of 4.0 × 10−5 K−1. By fitting the static equation of state at room temperature under ambient conditions we find the value for bulk modulus B of 48.7 GPa, which is in excellent agreement with the experimental study by pulse-echo techniques of 44.7 GPa. Unlike many bulk metallic glasses, such as Zr- and Pd-based, which bulk modulus is much larger than 100 GPa, the value B of Mg65Cu25Tb10 BMG falls into the range of SiO2 and fluorozirconate glass ZBLAN. Moreover, the elastic constant of the Mg65Cu25Tb10 BMG is almost the same as those of ZBLAN. No evidence for the high-pressure phase transitions of the Mg65Cu25Tb10 BMG has been found up to 31.19 GPa at room temperature. 相似文献
20.
Abstract The heat capacities of the title compound (C3H11,O—C6H4,- CH=N—C6H4,—C4H9, abbreviation 5O ? 4) with a purity of 99.92 mole percent have been measured with an adiabatic-type calorimeter between 11 and 393 K. The transition temperature and the enthalpy and entropy of phase transition for stable crystal → SG, SG → N and N → isotropic liquid were T c = 299.69 K/ΔH = 22.68 kJ mol?1/ΔS = 75.70 JK?1 mol?1, 325.72/7.11/21.79 and 342.48/1.78/5.22, respectively. The crystal which melts at 285.5 K is a metastable modification. The SA phase hitherto reported in between SG and N does not exist. The glassy So state was realized by rapid cooling of the specimen from the So phase. The molar enthalpy of the glassy SG state at 0 K was by (10.1±0.1) kJ mol?1 higher than that of the stable crystalline state and the residual entropy of the glassy state was (9.40±0.83) JK?1 mol?1. The relaxational heat-capacity anomaly was observed from as low as 100 K and double glass transition phenomenon occurred around 200 K; a quite unusual phenomenon which has never been observed for the glassy states of nematic and cholesteric liquid crystals. The present results give a fair evidence that the unusual glass transition phenomenon previously found for the SG state of 6O?4 (a homologous compound) is not exceptional at all but common to the smectic glasses; at least common to the glassy SG states. Two possible origins responsible for the double glass transitions have been discussed. 相似文献