Effect Of Lattice Defects Research Articles

Tribologically-driven steady-state hydrogen evolution from mild steel by electrochemical extraction technique

tlydrogen in material can give rise to many detrimental effects such as hydrogen embrittlement in service, tq Therefore, the study of reducing hydrogen content in material to less than a safe limit is of great importance in technology. Recently, accelerated hydrogen evolution from bearing steel during the wear process and tribologically-driven hydrogen uptake were reported by using a mass spectrometric method, t21 Baek et al. [31 have also shown wear-enhanced hydrogen evolution by an electrochemical extraction technique using a potentiostat and proposed a model for wear-enhanced hydrogen evolution. However, the proposed model t31 is still in the dark to be fully applicable to hydrogen evolution after the initial period of wear process. Considering this aspect, there is a need for additional work on a more reliable analysis. Therefore, it seems appropriate in the present work (1) to investigate the effects of lattice defects generated due to wear process on tribologically-driven hydrogen evolution from the transient analysis of the hydrogen permeation; (2) to distinguish the model governing the tribologically-driven hydrogen evolution in the later stage of wear process from that in the early stage. The chemical composition and the hardness value of pin and disc specimens used in the wear experiments are given in Table I. The pin specimens in the wear test were cylindrical rods of 3 cm length, 0.8 cm diameter with flat ends of 0.50 cm 2 area. The disc specimens for both hydrogen extraction and permeation were cylindricalshaped of 0.08 cm thickness and 2.4 cm diameter. Before the wear tests, the surface of both specimens was polished using 1000 grit emery paper and then ultrasonically cleaned in acetone for 10 minutes. Hydrogen was introduced into the disc specimens for extraction runs by cathodic charging at a current density of 5 m A / c m z in a 4 vol pet H z S O 4 aqueous solution containing 100 mg mszO3/1 as a hydrogen recombination son [41 ,,-,_ poi. . ~ ne hydrogen charging time was 4 hours, which yielded an initial hydrogen concentration, Co, of 2.49 • 10 -.5 m o l / c m 3 Fe in the specimen. The wear experiments were conducted at room temperature (298 K) in dry air using a pin-on-disc wear machine. The sliding time was taken as a wear test variable under an applied load of 9.8 N and a sliding velocity of 0.193 m/s . The increase of surface temperature due to the wear process was measured with a chromel-alumel

Effective-Hamiltonian theory for electrons in deformed crystals. III. Wavepacket dynamics in externally applied magnetic fields

For pt.II see J. Phys. C: Solid State Phys., vol.21, p.4437 (1988). A formalism for an effective-Hamiltonian description of electron dynamics in inhomogeneously distorted crystal lattices which was recently developed by Brown in 1983 and Brown and Oldfield in 1988 is extended to include the effects of an externally applied magnetic field with slow spatial variation. Spatially averaged distortion-modified operators for velocity and acceleration are derived for wavepackets constructed from suitably defined Wannier functions and simplified expressions appropriate to the small-wavevector approximation are presented for these operators. The formalism is well suited to applications concerning the effects of lattice defects on magnetic orbits and magnetotransport properties.

Effect of lattice defects in the collector region of npn Si transistors on the degradation ofhFE

The degradation of npn Si transistors by electron irradiation is investigated through the study of the annealing behavior of a common emitter current gain (hFE) and electron capture levels induced in the collector region. The hFE is degraded by electron irradiation. The electron capture levels E14a (Ec–0.20eV) and E15a (Ec–0.19 eV) are generated by exposures to an electron fluence of 1014 and 1015 electrons/cm2. From their annealing behavior, it is pointed out that electron capture levels E14a and E15a are responsible for the degradation of hFE by about 61 and 70%, respectively. Es wird die Degradation von npn-Si-Transistoren infolge einer Elektronenbestrahlung durch das Ausheilverhalten der Emitterstromausbeute (hFE) und der im Kollektorgebiet erzeugten Elektroneneinfangniveaus untersucht. hFE degradierte infolge der Elektronenbestrahlung. Die Elektroneneinfangniveaus E14a (Ec–0,20 eV) und E15a (Ec–0,19 eV) werden durch Elektronenflusse von 1014 bzw. 1015Elektronen/cm2 erzeugt. Aus dem Ausheilverhalten wird geschlossen, das die Elektroneneinfangniveaus E14a und E15a zu 61% bzw. 70% fur die Degradation von hFE verantwortlich sind.

Effect of crystal defects on the kinetic of annealing of chemical radiation damage in Fe2O3

Effect of lattice defects induced by doping elements of Ti, Sn and Nb on the thermal annealing of γ-irradiation damage in Fe2O3 was investigated. The results showed that the initial damage concentration and the susceptibility to thermal annealing depend on the type of doping elements. For the same doiping concentration they increasein the order Ti>Sn>Nb. The rate of the thermal annealing was also increased in the same order Ti>Sn>Nb. This can be interpreted as the difference in the rate of diffusion of these elements in Fe2O3.

Preparation, structural characterization, and properties of atomically clean surfaces

My first research on secondary electron emission showed that some secondary electrons from the surface of a solid had energies comparable to that of the incident electrons, i.e., they were elastically scattered incident electrons, in disagreement with results of several previous workers in this field. Several maxima in the secondary emision versus incident energy curves were related to growth of the individual crystals, caused by heat‐treatment. Subsequent to the discovery of low energy electron diffraction (LEED) by Davisson and Germer, I began a series of LEED investigations from single crystals of several elemental metals, and found many complicated features, such as fine structure of diffraction beams, which were sensitive to small changes in angles of incidence. Because Ti and Ge crystals could not be cleaned in UHV by heating alone, we were led to a method of producing atomically clean surfaces by argon ion bombardment and subsequent anneal to remove surface damage. This technique led to the discovery that atomically clean semiconductors, having a diamond‐type lattice structure such as Ge and Si, have an altered surface structure different from that of the bulk lattice, and that this structure is removed by adsorption of a monolayer of oxygen. Investigations were made of adsorption and surface reactions by the combined use of LEED, work function and mass spectrometer measurements in a single unit. Discovery was made of place exchange of oxygen and nickel atoms at Ni(100) to form metallic Ni3O as a precursor of NiO, a semiconductor. Other investigations followed on epitaxy, work functions of different faces of single crystals, effect of mechanical strain and defect density on work function, inelastic diffraction, crystals cleaved in UHV, bombardment damage, reflection of very low energy electrons, the (00) LEED beam intensity at normal incidence, alloy catalysts, surface recombination velocity, adsorption by radioactive tracer, H2–D2 exchange, and effect of lattice defects on chemisorption, oxidation and catalysis.

Influence of the plastic deformation of metals during mixed friction on their chemical reaction rate

Mechanical effects such as friction may activate chemical reactions between solids and their surrounding media. Several factors can contribute to this effect: heat of friction, the removal of protective surface layers, an increase in the effective surface area, faster transport of reacting particles and production of lattice defects by plastic deformation. The effect of lattice defects on the rate of different chemical reactions was measured. It was shown that this effect can act to increase the reaction rate by one to two orders of magnitude. The mechanical effect depends not only on the metal and the tribological stress but also on the reaction partner and the experimental conditions.

Effect of lattice defects on the luminescence spectra of anthracene crystals

Effect of lattice defects on the luminescence spectra of anthracene crystals

The effect of lattice defects on hydrogen solubility

It is shown that the model used by Flanagan and Lynch to explain the enhancement of hydrogen solubility by interaction with dislocation strain fields predicts, when some mathematical errors are corrected, enhancements that are significantly smaller than those previously estimated. Moreover, the model is incapable of explaining the observed temperature dependence of solubility enhancement. This is considered to be due to the difficulty of treating the enhancement in the vicinity of the dislocation core where the stress field of the dislocation is poorly approximated by the solution obtained using linear elasticity. A simplified model is proposed in which the interaction energy is assumed to be constant over an extended core region and the concentration enhancement is treated using Fermi-Dirac statistics; it is shown that this model gives good agreement with experimental results for hydrogen in palladium.

Effect of doping and thermal vacancies on positron annihilation in semiconductors

The effect of lattice defects on positron annihilation in semiconductors was studied. In silicon, any detectable doping effect could not be found. In germanium, the thermal equilibrium measurements of annihilation lineshapes showed no vacancy effect. From these experimental facts, the interaction of positrons with lattice defects was discussed.

The effect of lattice defects on hydrogen solubility in palladium: I. Experimentally observed solubility enhancements and thermodynamics of absorption

Measurable, and reproducible solubility enhancements have been observed for hydrogen in cold-worked palladium in the low content α-phase (273–363 K). It is shown that the solubility of hydrogen is unaffected in palladium samples which had been quenched from near their melting points. It is concluded that the stress field about the dislocation array is the principal cause of the solubility enhancement. Absorption of hydrogen at the cores of dislocations is believed to be insignificant. From absorption isotherms measured at various temperatures, the relative partial molar enthalpies and entropies of solution of hydrogen into deformed palladium have been determined. The heat of solution of hydrogen by 78% deformed palladium is approximately 880 J/H more exothermic than for well-annealed palladium in the low hydrogen content α-phase.

The effect of lattice defects on Hydrogen solubility in palladium: II. Interpretation of solubility enhancements

It is proposed that the stress-field of the dislocation array is the principal cause of the solubility enhancement observed in the low hydrogen content, α-phase of cold-worked palladium. With an assumed uniform dislocation density of 9 × 1011cm−2, the observed solubility enhancement of 1.65 (298 K) for heavily cold-worked palladium can be reproduced if the core radius is assumed to be 2 × Burgers vector. The temperature dependence of the solubility enhancement is also reasonably well predicted. The significance of measured relative partial molar enthalpies and entropies of absorption of hydrogen into cold-worked palladium is examined.

The effect of lattice defects on the low-temperature heat capacity of copper

Abstract Low-temperature specific heats of a heavily cold-worked and annealed high-purity copper were measured in the temperature range 1·5–4·2°K. The results are compared with similar measurements reported previously (Ahlers 1966). The enhancement of the electronic specific heat coefficient γ is in excellent quantitative agreement with the calculated increase of the specific heat due to vibrations of mobile dislocations (Granato 1958). In the temperature range of the measurement, this increase is proportional to the dislocation density and the temperature. A phenomenological approach to the study of the properties of a liquid via a heavily deformed solid state is discussed in terms of the stored energy and entropy of cold work.

Mössbauer Effect of Lattice Defects and Related Problems

Mössbauer Effect of Lattice Defects and Related Problems

Defects in Cadmium Selenide Single Crystals

Effects of lattice defects produced by electron irradiations and firing in Cd vapor on the photoelectric properties of CdSe have been investigated. The magnitude of persistent photoconductivity, that is, the increment of conductivity which is persistent in dark for many hours following photoexcitation at low temperature, increases by firing in Cd vapor and decreases by firing in Se 2 vapor. The persistent photoconductivity decays, as the temperature is increased, with the activation energy of 0.26 eV. Persistent photoconductivity is also produced by electron irradiation. It is considered that the persistent photoconductivity is induced by a lattice defect produced either by firing in Cd atmosphere and by electron irradiation. The threshold energy for production of the defects by electron irradiation is obtained and shown to be 270±30 keV. These defects are annealed out at 350°K. The activation energy of annealing is about 1.25 eV and frequency factor is 4×10 13 sec -1 . It is concluded that the defects re...

Effects of lattice defects on thermoluminfscence in lithium fluoride crystals

Abstract The thermoluminescent output of ‘pure’ LiF single crystals is studied as a function of annealing temperature and cooling rate. The lattice defect structure is characterized using ionic conductivity measurements. The results show that the sensitivity of such crystals to irradiation is highly dependent on prior history; specifically, the intensity of the observed 105°C thermoluminescence peak depends directly on the concentration of impurity vacany pairs present. The results also show the importance of background impurities in effecting thermoluminescent sensitivity.

Effects of lattice defects on the pressing and sintering of copper powder

Effects of lattice defects on the pressing and sintering of copper powder

On the Angular Dependence of Sputtering and Kinetic Electron Emission of Single Crystals

AbstractThe dependence of the sputtering yield K on the angle of incidence ϕ is calculated for single crystals by taking into account multiple collisions of the ions with atoms of the crystal. The secondary collisions increase the maxima of the curve K(ϕ) but do not alter the form of the minima. The effect of lattice defects on the function K(ϕ) is also considered. These defects mainly alter the minima in K(ϕ) and on the whole decrease the anisotropy of the sputtering yield. Electron emission from single crystals due to ion bombardment is treated in a similar way assuming a kinetic emission mechanism.

Nbの超電導特性と格子欠陥の関係

Nbの超電導特性と格子欠陥の関係

Diffusion of uranium in molybdenum, niobium, zirconium, and titanium

The diffusion of uranium was studied in molybdenum, niobium, zirconium, and titanium. The diffusion coefficients were determined by measuring the over-all activity of the residue of the sample, using the a-radiation of uranium enriched with the U235 isotope to 90% at temperatures 1500 to 2000° C (molybdenum, niobium) and 915 to 1200° C (zirconium, titanium). The temperature dependence of the diffusion coefficients was given by the equationsD Mo U=7.60.103 exp (−76 400/RT) cm2/sec;D Nb U=8.90.10−2 exp (−76 800/RT) cm2/sec;D Zr U=7.77,10−5 exp (−25 800/RT) cm2/sec;D Ti U=4.90. t0−4 exp (−29 300/RT) cm2/sec. The considerable differences between the diffusion mobilities and activation energies of molybdenum and niobium on the one hand and zirconium and titanium on the other were probably due to the effects of lattice defects, for example, excess vacancies arising in zirconium and titanium during polymorphic transformations.

Effect of Lattice Defects on the Magnetization Curve of Ferromagnets

This paper presents a theoretical treatment of the action of internal stresses on domain walls and on uniformly magnetized Weiss domains. The theory is based on micromagnetics, dislocation theory, and probability theory. Experimental results on the domain structure, the temperature dependence of the reversible susceptibility, and the coercive field of plastically deformed nickel, cobalt, and silicon-iron single crystals and neutron-irradiated nickel single crystals are discussed on the basis of the theory. The experiments are interpreted in terms of the magneto-elastic interaction between dislocations and magnetization and agree satisfactorily with the theoretical predictions. The observed variations of the domain structure during the magnetization process can be accounted for in terms of the theory of phases (Néel, Lawton, and Stewart) and the mobility of the domain walls.