The electron-dislocation interaction and electronic effects at low-temperature deformation

The effect of the electronic state of crystals on the processes of their plastic flow is considered. Presented are the results of the observation and study of the effects of the electrondislocation interaction at a low-temperature deformation of metals.     

Quantum effects in low temperature plastic deformation

A quantum mechanical calculation of the transition rate of a dislocation segment across an obstacle of finite width is performed. Compared with previous theories the achievement of the new treatment is that the finite compliance of the force distance profile is taken into account in the evaluation of the oscillatory modes. As a consequence, not only the DEBYE temperature of the dislocation line but also the obstacle compliance enters the transition rate and determines the temperature regime in which quantum effects become observable. Furthermore, the results of classical thermal activation theory that is valid at high temperatures are for the first time derived from first principles.     

Indentation-induced microhardness changes in glasses: Possible fictive temperature increase caused by plastic deformation

The microhardness around a large indentation was measured for different types of glasses. In soda-lime silicate glass, a typical normal glass, the region in the immediate vicinity of the indentation was found to exhibit a lower hardness than the region far removed from the indentation. In silica glass, a typical anomalous glass, the region in the immediate vicinity of a large indentation was found to exhibit a higher hardness than the region far removed from the indentation. Asahi less brittle glass, an intermediate glass between normal and anomalous glasses, was found to exhibit little change in hardness in the vicinity of the large indentation. These findings can be explained by a deformation-induced fictive temperature increase leading to a lower hardness for soda-lime silicate glass and a higher hardness for silica glass.     

The effect of changes in relative humidity on the hydration rate of Pachuca obsidian

The effect of relative humidity on the hydration rate of obsidian and other glasses has been debated since the early work of [I. Friedman, R. Smith, Am. Antiquity 25 (1960) 476]. While more recent work has been in general agreement that a relative humidity dependence does exist, hydration profiles as a function of relative humidity have not been obtained. In this paper we present the results of a study in which samples of Pachuca obsidian were hydrated for approximately 5 days at 150 °C at relative humidities ranging from 21% to 100%, and the resultant profiles were measured by secondary ion mass spectrometry (SIMS). The results suggest that the hydration rate is, indeed, a function of relative humidity, but for the relative humidity levels commonly observed in most soils the effects on hydration dating are expected to be relatively small. In addition, analysis of the surface values as sorption isotherms and comparisons with nitrogen sorption isotherms suggests that water is relatively strongly bound to the obsidian surface. By assuming a situation in which the ‘surface’ refers to active centers within the glass we have shown that an adsorption model provides a useful approach to modeling the diffusive process.     

The low-temperature specific heat of PTFE (Teflon) at pressures to 5.2 kbar

The specific heat of PTFE (Teflon) has been measured between 0.3 and 20 K at zero pressure, and between 1 and 20 K at five other pressures ranging up to 5.2 kbar. The specific heat anomalies typical of amorphous materials were observed. The linear term is smaller than for other organic polymers and is closer in magnitude to those of high purity glassy insulators. At zero pressure the T³ term in the specific heat exceeds that calculated from the sound velocities by 24%. The evolution with pressure of the T³ term and of the maximum in C/T³ are very similar, suggesting a close relation between the vibrational modes that contribute to these features in the specific heat. This result and the relatively simple structure of Teflon rule out independent localized oscillators as the source of the maximum in C/T³.     

Thermal stresses in a cylinder: Application to optical waveguide blanks

An analysis is presented for the calculation of thermal stresses in a hollow cylinder with free ends, in which the elastic and thermal properties are all functions of radius, r. When Young's modulus and Poisson's ratio vary with r, the solution is obtained by the method of successive approximations, but the first approximation is sufficiently accurate for most purposes. For the particular case of optical waveguide blanks, it is shown that the variation in set point with radius can have a significant effect on the calculated stresses. When variations in all properties are considered, the calculated axial stress is in good agreement with a measured value.     

The strain relaxation in a lattice-mismatched heterostructure

Strain relaxation phenomena of the heteroepitaxial lattice-mismatched semiconductors have been investigated. The relationship between the residual in-plane strain and the width of the misfit cell was obtained geometrically. The residual in-plane strain was calculated for various film thicknesses by using the energy minimization theory on the misfit cell in the In_xGa_1−xAs/GaAs(1 0 0) heterostructure system. A generalized strain relaxation model is presented on the basis of the energy minimization theory.     

Deformation behaviors of a tungsten-wire/bulk metallic glass matrix composite in a wide strain rate range

Using melt infiltration casting a composite (W-BMG) of Zr_41.25Ti_13.75Ni₁₀Cu_12.5Be_22.5 bulk metallic glass reinforced with tungsten wires has been produced and its quasi-static and dynamic deformations are investigated within the strain rates ranging from 1 × 10⁻⁴ to 2 × 10³ s⁻¹. The lengthwise frozen-in stress of the composite during the fabrication process is also calculated. The quasi-static stress–strain behavior is discussed in detail in light of the observation of the appearances of the specimens. The study reveals that the strain rate sensitivity exponent of 0.022 of the W-BMG composite is half that of the monolithic tungsten, which is a result of the frozen-in stress.     

The Real Structure of Ge Ions-implanted Si Crystals Subjected to Thermal Annealing

In the experiment an (111) oriented silicon plate was subjected to implantation by 80 keV Ge ions. Then, the thermal annealing of this sample was carried out in a vacuum of 5 · 10⁻⁸ Tr. The effectiveness of the annealing has been analyzed by means of X-ray topography, double crystal X-ray spectrometry and reflection high energy electron diffraction. The rocking curves in reflection and transmission as well as changes in anomalous absorption coefficient were measured. The results have been compared with effects of pulsed-laser annealing investigated by AULEYTNER et al. an thermal annealing (PRUSSIN ).     

Variation of strain in granular GaAs:MnAs layers

Granular GaAs(MnAs) layers with different Mn concentration and various layer thickness were grown by MBE method and subjected to annealing at 500°C under ambient and enhanced hydrostatic pressure. Distinct influence of hydrostatic pressure applied during annealing on strain state of layers as well as on hexagonal MnAs inclusions was found. Pressure induced strain of inclusions is related to different bulk moduli of GaAs and of hexagonal MnAs. Formation of hexagonal inclusions depends on concentration of Mn in interstitial position in as-grown samples.     

The Thermal Response Function of Traditional Knudsen-Cells in MBE

Precise thermal control of Knudsen-type evaporation cells in MBE requires basic knowledge on the thermal behaviour of the cell on any alteration of the heating power. This paper deals with the cell's response in temperature, when the cell is subject to a jumplike change in heating power. Particular care is devoted to deviations from pure exponential behaviour, if the temperature transition function between two equilibrium states is concerned. It is shown, that the jump response function for a finite increase in heating power is equivalent to that of an infinite small one, whereby an effective temperature — amounting to 70% of the temperature jump height — has to be introduced.     

Effect of heating rate on glass foaming: Transition to bulk foam

Glass fining has an undesirable side effect: glass foaming. In a recent experimental study, the foam volume responded dramatically when the rate of temperature-increase varied from 5 to 15 °C/min. This observation indicates that an enhanced temperature-increase rate (a natural consequence of the increased processing rate experienced as a result of the transition to oxy-fuel firing) may exert a substantial influence on glass foaming in advanced glass-melting furnaces. This paper attributes this effect to the change of mode of foam formation as a response to an increased rate of heating.     

X-ray diffraction study of the effects of boron on occurrence of deformation faults in Ni3Al alloy

Ni₃Al and Ni₃Al alloys containing varying amounts of boron in L1₂ phase were prepared. All the samples were suitably annealed and then cold-worked by hand filing. X-ray diffraction data are collected on annealed and cold-worked samples. The deformation fault probabilities have been evaluated by two methods, viz. peak shift analysis of powder pattern X-ray reflections of annealed and cold-worked samples, and lattice parameter change between annealed and corresponding cold-worked samples. The values obtained by both the methods are in reasonable agreement. It has been found that the deformation fault probability of Ni₃Al and Ni₃Al containing boron alloys are very high compared to Ag and Cu base alloys. Further the deformation fault probability of Ni₃Al is more sensitive to boron addition. It has been found that at least 1.22 at. % of boron goes into the Ni₃Al lattice.     

Electro-optical effects in anisotropic crystals: I. The Pockels effect

The perturbation-theory method is proposed to calculate the induced anisotropy optical effects in crystals with different symmetries. On its basis, the influence of the Pockels effect on the light propagation in crystals with different symmetries is analyzed using Fedorov’s approach of invariant vector fields. This approach has many advantages over known methods in calculating different versions of Pockels effect application for different purposes. Calculation schemes are presented that make it possible to select longitudinal and transverse versions of electro-optical sensors and modulators, which can be used, in particular, to design optical measuring transformers and electric field sensors in high-voltage power lines.     

Thermal stresses in optical fibers: Fluid core assumption

Comparison with a viscoelastic analysis shows that, for a step-index optical waveguide, the “fluid core” assumption provides a better approximation to the thermal stresses than the “elastic core” assumption. In this paper, we present an analysis of the stresses in a graded-index fiber, based on the fluid core assumption. A more realistic estimate of the setting temperature is also provided. The influence of the calculated stresses on the refractive index profile is shown to be significant.     

The effects of argon gas flow rate and furnace pressure on oxygen concentration in Czochralski silicon single crystals grown in a transverse magnetic field

The effects of the argon gas flow rate and furnace pressure on the oxygen concentration in a transverse magnetic field applied Czochralski (TMCZ) silicon single crystals were examined through experimental crystal growth. A gas controller which had been proposed by Zulehner was used for this series of experiments. In the TMCZ gas-controlled crystals, a decrease in the oxygen concentration with a decrease in furnace pressure was found. A clear relationship between the oxygen concentration and the argon gas flow rate was not obtained due to the limited experimental conditions. The relationships between the oxygen concentration and the furnace pressure and the argon gas flow rate previously observed for Czochralski (CZ) crystals by a similar gas controller were confirmed by the present gas controller. The oxygen concentration changes in the TMCZ and the CZ crystals were analyzed in terms of the calculated flow velocity of the argon gas between the gas controller and the silicon melt surface. In contrast with the CZ gas-controlled crystals, the oxygen concentration was decreased with an increase in the flow velocity of argon gas in the TMCZ gas-controlled crystals. The surface temperature model and the melt flow pattern model which had been proposed in the previous report are discussed again in light of the present experimental results.     

Boroxol rings in SiO2–B2O3 glasses: Influence on low-temperature thermal properties

The heat capacity of a rapidly quenched B₂O₃–SiO₂ glass has been measured by adiabatic calorimetry from 10 to 350 K. The vibrational entropy derived from the measurements, S₂₉₈–S₀ = 54.16 ± 0.10 J/mol K, is close to the linear trend defined by the entropies of pure SiO₂ and B₂O₃ glasses. Owing to the strong sensitivity of S₂₉₈ − S₀ to the oxygen coordination of cations, this result is in agreement with the 3- and 4-fold coordination found for Si and B, respectively, in binary borosilicates. Because additivity of heat capacity extends below 90 K, where the low-frequency modes of boroxol rings dominate the vibrational density of states, the results indicate also that the fraction of boron atoms in these rings is proportional to the B₂O₃ content. According to recent NMR evidence, these conclusions apply to truly homogenous glasses at a microscopic scale.     

Mercury pollution and remediation: the chemist's response to a global crisis

Environmental mercury pollution is a growing global problem. Due to its unique properties, mercury has in the past been widely used by a variety of industries. This has led to the deposition of large amounts of mercury into the environment, where it is naturally redistributed but not naturally removed. In its methylated form, this mercury tends to accumulate in marine life, eventually reaching levels that can be toxic to humans. Fortunately a variety of remediation methods, including phytoremediation, filtration, and chemical precipitation, are currently in development. One precipitation leagent called MetX appears extremely promising. It binds mercury and other soft heavy metals irreversibly and produces precipitates that do not leach. This technology and many others holds the promise of a future victory over mercury pollution.