Annealing Of Glass Research Articles

Stresses in glass plate joined with other materials: Modeling and experimental validation

The previously developed relaxation model for annealing of glass seals with other materials has been applied widely. It remains unclear whether there are a specific low temperature and very long-term iso-thermal treatments at which this simple model ceases to work correctly and requires complication or even revision. With the aim to determine the minimum fictive temperature at which the relaxation model of annealing of glass seal with an elastic material is still applicable, the stresses in the sandwich S52-2 glass-molybdenum seals are measured at different stabilization temperatures. The experimental temperature-time dependences of the stresses are compared with those calculated using the relaxation model of seal annealing. The use of this relatively simple model leads to a quite satisfactory agreement (even if not identical at all the temperatures) in the range from the glass transition temperature to 380${}^\circ$C for stabilization durations as long as 81 days. This treatment duration makes it possible to reach a structural temperature of 434${}^\circ$C, which is considerably lower than the structural temperature (525${}^\circ$C) obtained upon simple cooling of glass at a rate of 3 K/mm.

Structure of an Automated System for the Calculation of Annealing Regimes for Glass Articles

The factors needed to identify an optimum energy-saving annealing regime for glass articles are considered. A structure of an automated system for the calculation of glass annealing conditions is proposed, which makes it possible to model and optimize the process of annealing of sheet, container, and household glass.

Fluorescence spectra and homogeneous line widths of Cr 3+ in glass nucleating ferroelectric Li 2Ge 7O 15

We report optical studies of the new material – Cr 3+-doped lithium–germanate glass, containing Li 2Ge 7O 15 (LGO) nanocrystalline particles. While only broadband 4T 2– 4A 2 fluorescence from the low-field octahedral Cr 3+ sites was observed from Cr 3+ ions in the glass, in LGO nanocrystals high-field Cr 3+ centers emit 2E– 4A 2 (R–lines) fluorescence. The process of crystallization in the course of isothermal annealing of glasses was monitored spectroscopically and the nucleation of LGO crystallites was observed starting from the smallest clusters. Using the 2E– 4A 2 fluorescence spectra it is possible to detect the ferroelectric phase transition in LGO:Cr 3+ nanocrystals, whose critical temperature was found to be similar to that of the bulk crystals. Long-lived spectral holes were burned in the inhomogeneously broadened R-lines of Cr 3+ in LGO nanocrystals at low temperatures. The linear temperature dependence of hole widths shows that the homogeneous broadening of 4A 2– 2E transitions of Cr 3+ in nanocrystals is due to interaction of Cr 3+ electronic levels with the two-level systems (TLS) of the surrounding glass. The range of the Cr 3+-TLS elastic dipole–dipole interaction is estimated.

Development of nanocrystals in amorphous Al-alloys

Rapidly quenched aluminum-based metallic glasses have been found to undergo a partial transformation upon heating that yields a fine-scaled dispersion of Al-nanocrystals within an amorphous matrix. The origin of the nanocrystallisation process is discussed based upon calorimetric and structural investigations of Al92Sm8 samples prepared using different processing pathways. Additionally, the early stages of the nanocrystal development was monitored by isothermal calorimetry techniques on long time scales. The results strongly indicate that the nanocrystals originate from quenched-in nuclei. Isothermal annealing of Al88Y7Fe5 glasses at 245 °C revealed that α-Al nanocrystals develop at temperatures well below the primary crystallisation onset temperature after short time periods. On annealing, an additional phase evolves, which gives an exothermic signal in DSC at about 330 °C. XRD measurements have been performed to study the phase formation sequence at high temperature. The formation of additional phases is related to a modification of the matrix composition near the nanocrystal/amorphous interface due to a pronounced concentration gradient as a result of the unequal component diffusivities.

Structural relaxation in metallic glasses

Structural relaxation in several transition metal based metallic glasses has been studied using differential scanning calorimetry (DSC), X-ray diffraction (XRD), electrical resistivity, acoustic emission and Mossbauer spectroscopy techniques. Annealing of metallic glass below the crystallization temperature gives rise to discontinuous changes in electrical resistance. These changes are accompanied by acoustic emissions. The latter process provides an indication for the viscous flow in the matrix. In diverse alloy compositions, it has been observed that changes in electrical resistivity which begin instantly with the onset on isothermal annealing do not follow diffusion kinetics. Mossbauer experiments also show that neither long range diffusion nor the formation of a new phase occurs as a result of annealing. It is concluded that viscous flow is the mechanism for structural relaxation induced by isothermal annealing and short range ordering during this process is also a consequence of the viscous flow process.

A New Quick Test to Determine the Structure of Opacified Glasses

The structure of glass opacified with phosphor is investigated as a function of its thermal prehistory using the positron annihilation method, x-ray phase, and electron microscope analysis. Structural differences are identified, which depend on the wall thickness of articles and the temperature conditions of annealing. It is proposed to use this method for a quick test of the homogeneity and the degree of annealing of opaque glasses.

Physical Ageing of Silicate Glasses at Room Temperature: The Choice of Quantitative Characteristics of the Process and the Ranking of Glasses by Their Tendency to Ageing

Practical aspects of the model proposed earlier that treats the ageing of glasses as a complex relaxation process developing through several independent channels are discussed. The experimentally obtained or estimated parameters characterizing five channels are considered. A simplified technique for calculating the index of glass ageing completeness over any period (up to 50 years) and the ageing rate at any age on the basis of the temperature corresponding to a viscosity of 1013.5P is proposed. It is revealed that the proposed model possesses the following property: the completeness of ageing of glass at any age is determined by its ageing rate at an age of about one year. Forty two optical and other glasses are ranked in order of their tendency to ageing according to the above parameters. The ranking of the known thermometric glasses corresponds to the tendency of these glasses to ageing in thermometric practice. The data on the glass ageing, which were obtained from measurements of refractive indices and scale lengths, are compared. It is shown that artificial ageing can proceed in the course of fine annealing of optical glasses. Consideration is given to a number of conditions whose fulfillment in the experiments on the glass ageing can favor successful solution of the problem. It is demonstrated that there are parallels between the model interpretation of glass ageing and the modern description of ageing processes in biological populations.

Surface tensile layer generation during thermal annealing of phosphate glass

Surface tensile layers (up to 20 MPa) are generated during thermal annealing of metaphosphate glass in ambient air. The surface tensile stress is caused by changes in properties of the phosphate glass, particularly the glass transition temperature and the coefficient of thermal expansion, due to the glass reaction with water vapor and diffusion of OH groups into the region just below the surface (<2 mm). An increase in the OH content of the glass from about 80 to 5000 ppmw causes a decrease in the glass transition temperature from 468 to 405°C and an increase in the linear thermal expansion coefficient from 12.9 to 14.2 × 10 −6 K −1. A mechanism for the generation of the tensile surface layer is proposed and simulated experimentally by fusion-bonding at 500°C two samples of the same composition but with OH contents that differ by up to 50×. The stresses in the annealed fusion-bonded samples are determined from measured stress birefringence. Peak tensile stresses calculated by finite element analysis agree with measured values to within 30%.

Cooling rates of hyaloclastites: applications of relaxation geospeedometry to undersea volcanic deposits

Glass fragments from three different hyaloclastites have been used to evaluate the range of cooling rates experienced by undersea volcanic deposits. We found that the glass fragments retain structures with a range of apparent quench rates from 25 to 0.15 K min–1. The most rapid cooling rates are interpreted to be those resulting from cooling of the lava near the water interface. Simple conductive cooling models produce a range of quench rates comparable to those of the more rapidly cooled samples. The very slow apparent quench rates are unlikely to result from simple linear cooling through the glass transition, because of the onset of crystallization; instead, they are indicators of a more complex thermal history that involves the annealing of glasses at temperatures within the glass transition interval for a dwell time sufficient to allow the relaxation of the glass to lower temperature structures. The thermal history recorded in these samples illustrates the complexity of eruptive processes and demonstrates that quench rates for natural glasses retain information relevant to more complex cooling models.

Adequacy of mathematical models of the glassware annealing process

The adequacy of the previously developed mathematical model of the glass tube annealing process is experimentally confirmed. The model is refined with respect to annealing of construction glass blocks by taking into account the effect of the barometric rarefaction inside the glass block air cavity on the process of the origin and distribution of stresses in the article, and the adequacy of the refined model is experimentally proved.

Temperature Dependence of the High‐Frequency Viscoelastic Behavior of a Soda‐Lime‐Silica Glass

The high‐frequency viscoelastic behavior of a soda‐lime‐silica glass has been investigated using the Brillouin scattering technique. The temperature dependence of instantaneous elastic constants and very short‐time relaxation mechanisms have been measured in a temperature range between 100° and 1000°C. Variations in the elastic constants in the transition region are significant, and have to be taken into account for numerical computations of tempering and annealing of glasses. A complex thermorheological behavior is observed for very fast relaxation mechanisms in the transition range, whereas intermediate and slow relaxation mechanisms exhibit a simple thermorheological behavior. The viscoelastic behavior of this glass can be adequately represented by assuming a different thermorheological behavior in the alpha‐ and β‐relaxation regimes.

Automatic control of operating conditions in the annealing lehr of a thermally polished glass line

A computerzed system was developed and integrated into a thermally polished glass line to control the temperature parameters in its annealing lehr. This served to optimize the annealing of Metelitsa glass, to cut down to 2 h the time required for the lehr to attain steady-state operation, and to raise the glass yield to 0.75. Suitable prompts were devised for operators in charge of the annealing operation, and the optimal format was found for the presentation of information about the on-going process.

Processing effects on mechanical and superconducting properties of Bi2201 and Bi2212 glass ceramics

Bi2212 and Bi2201 were prepared by annealing of glass with the composition Bi 2.18Sr 2CaCu 2O 8+ d . Using this preparation technique, structural and microstructural properties such as phase formation, grain size and oxygen content can easily be affected by different annealing conditions, i.e. by variation of time and temperature. Hence, the deformation behaviour and the critical temperature ( T c) are a function of the annealing conditions. This could be shown by creep experiments and AC susceptibility measurements. Samples with nanocrystalline microstructures exhibit substantially better plasticity under stress than samples with larger grains. Good superconducting properties could be achieved in nearly single-phase Bi2212 samples with grains extending over several hundred nanometers to a few micrometers in the direction of the c axis.

Temperature study in flash annealing of metallic glasses

A method to determine the temperature of metallic amorphous alloys when heated with a current pulse (`flash annealing`) is proposed. With some energetical considerations we calculate the temperature of the sample during the fast heat treatment. Theoretical curves calculated in that way are in good agreement with experimental results. The temperature of the sample during the pulse is experimentally determined by measuring the spontaneous magnetization during the current heating and comparing this with the magnetization-temperature curve obtained when heating in a conventional furnace. The influence of the different parameters appearing in the mathematical expressions on the heating process, such as the characteristics of the material, the geometry of the ribbon or the annealing conditions, is also studied.

Thermal strain and viscous flow of glass films

The effect of viscous flow on thermal strain in fluids is especially significant for materials such as glass. Thermally strained glass flows to accommodate the volume change caused by expansion or contraction. Viscous flow is responsible for the observed phenomenon of stress relaxation which occurs during annealing of glass. In this paper we present a mathematical solution to the problem of viscous flow in thermally strained compressible fluids. This result is used to study thermal stress in glass films undergoing heating and cooling. The effect of viscous flow on thermal stress is demonstrated numerically and is used to explain experimental observations of stress relaxation in glass films which were reported elsewhere. This paper includes a general formulation of the mechanics of slow viscous flow of compressible Newtonian fluids in the presence of a thermal strain.

Thermoviscoelastic theory of freezing of stress and strain in a symmetrically cooled infinite glass plate

Abstract The Gardon and Narayanaswami theory of annealing and tempering of glass is rederived in a unifying way using the framework of the theory of thermoviscoelasticity. It is extended by including the effect of isothermal pressure relaxation in addition to the relaxation of shear stress. In the new theory, relaxation of shear stress, isotropic stress (pressure) and thermal stress, which causes thermal expansion, are treated on the same level. The thermal expansion coefficient, a frequency-dependent quantity like bulk and shear modulus, has high- and low-frequency limits identified with the thermal expansion coefficients of glass and liquid. The results of numerical calculation of stresses and strains in a symmetrically cooled infinite plate for the extended theory illustrate the decisive importance of the dispersion of the thermal expansion coefficient.

EPR study of structural defects in ion-implanted multicomponent silicate glasses

Radiation defects induced by ion bombardment of multicomponent silicate (MCS) glasses are investigated and discussed. In MCS glasses, implanted with B +, P +, N +, Ag +, Sb +, W + ions at energies varying between 30 and 380 keV and doses ranging from 10 13 to 10 18 ions/cm 2, two types of electron paramagnetic resonance (EPR) signal, differing from those observed in γ-irradiated samples, are found. Ond of them, denoted by S, is a narrow, almost symmetric signal with g-values ranging from 2.0018 to 2.0034 which is attributed to a vacancy-type defect with one dangling silicon bond. The other signal, denoted by A, is an anisotropic line with g 1 = 2.015, g s = 2.008 and g 3 = 1.999 (±0.001) which is ascribed to interstitial oxygen species. It is shown that the appearance of the S- and A-signals and their relative intensity depend on the energy, dose and atomic mass of the incident ions. It is also found that an anisotropic EPR spectrum with g = 2.29 ± 0.01 and g = 2.04 ± 0.01 appears after γ-irradiation and subsequent annealing of MCS glasses implanted with Cu + ions at energies ranging from 150 to 250 keV and doses varying between 3 × 10 14 and 1 × 10 15 ions/cm 2. It is assumed that this spectrum belongs to Cu + ions which have trapped a positive hole produced by γ-irradiation, becoming Cu 2+. MCS glasses treated by TiB + and TiP + ion-mixing with boron doses of 6.2×10 15 and 3×10 17 ions/cm 2 and phosphorus dose 2 × 10 17 ions/cm 2 were studied. Ti 3+ was found to have no EPR signal, although titanium results are present from Rutherford backscattering and secondary ion mass spectroscopy measurements.

Electron Spin Resonance Studies of Gamma-Irradiation Damage in Simulated Nuclear Waste Glass

The effects of γ-irradiation on a simulated nuclear waste glass were studied by electron spin resonance spectroscopy (ESR), and were compared with the results on silica glass and Pyrex glass. Three kinds of glasses were γ-irradiated up to the dose of 1.22 MGy and the ESR spectra were obtained. The intensity of ESR spectra were obtained as a function of irradiation dose and annealing temperature. The spectrum of the waste glass was characteristic of two typical peaks, Peak 1 was the strong resonance at g=4.3 showing the existence of four coordinated Fe3+ and Peak 2 was the weak and broad resonance at g= 2.0 showing the existence of six coordinated Fe3+. The ESR spectra of the waste glass before and after γ-irradiation were almost overlapped and a little difference only in the intensity was observed. While in silaca glass and Pyrex glass, the peaks from E'γ center and boron-oxygen hole center (BOHC) were observed to arise after irradiation. The absolute intensity of. Peaks 1 and 2 described above changed in complicated way depending on the dose. The result suggests oxidation or reduction of iron takes place in the waste glass depending on the dose. The isochronal annealing of irradiated glasses shows most of γ-ray- induced damages in the waste glass are restored even at room temperature, although most of the damages in silica glass and Pyrex glass are disappeared at the temperature from 550 to 600 K. The results show that the waste glass with a few weight percent of iron is resistent to radiation than other commercial glasses.

Electron spin resonance studies of gamma-irradiation damage in simulated nuclear waste glass.

The effects of r-irradiation on a simulated nuclear waste glass were studied by electron spin resonance spectroscopy (ESR), and were compared with the results on silica glass and Pyrex glass. Three kinds of glasses were r-irradiated up to the dose of 1.22 MGy and the ESR spectra were obtained. The intensity of ESR spectra were obtained as a function of irradiation dose and annealing temperature.The spectrum of the waste glass was characteristic of two typical peaks, Peak 1 was the strong resonance at g=4.3 showing the existence of four coordinated Fe3+ and Peak 2 was the weak and broad resonance at g=2.0 showing the existence of six coordinated Fe3+. The ESR spectra of the waste glass before and after r-irradiation were almost overlapped and a little difference only in the intensity was observed. While in silaca glass and Pyrex glass, the peaks from E'r center and boron-oxygen hole center (BOHC) were observed to arise after irradiation. The absolute intensity of Peaks 1 and 2 described above changed in complicated way depending on the dose. The result suggests oxidation or reduction of iron takes place in the waste glass depending on the dose. The isochronal annealing of irradiated glasses shows most of r-ray-induced damages in the waste glass are restored even at room temperature, although most of the damages in silica glass and Pyrex glass are disappeared at the temperature from 550 to 600 K. The results show that the waste glass with a few weight percent of iron is resistent to radiation than other commercial glasses.

Rapid annealing of metallic glasses under tension

Pulse heat treatment using 0.4 s current pulses was applied to Fe 80B 14Si 6 amorphous ribbons above its Curie temperature in order to avoid magnetically induced anisotropy. After relaxation the pulse heat treatment was continued while applying 128 MPa mechanical stress to obtain induced anisotropy. The results of pulse annealing were monitored by coercive force and effective anisotropy measurements carried out between the pulses at room temperature. It is shown that pulse annealing enables a magnetically soft relaxed state to be achieved and if mechanical stress is applied during the process, induced anisotropy can be developed.