Dislocation Sites Research Articles

New electrolytic etchant for dislocation etch pits in Ni 3Al single crystals

A new etchant for developing etch pits at screw dislocation sites in Ni 3Al single crystals was tested. Using this etchant, both fresh and aged dislocations can be revealed on {001} surfaces. The usefulness of the etching technique was demonstrated further on crystals which had been plastically deformed either under an impact load or under a hardness indentation. It was shown that there is a direct correspondence between the etch-pit pattern and slip lines around the indentation. Observations were also made on the dislocation etch pits in Ni 3Al single crystals alloyed with boron and hafnium.

Microtunnelling during selective alloy dissolution and during pitting

AbstractThe kinetics and the morphology of selective dissolution of alloys containing a noble component and of pitting of passive metals are discussed emphasizing common properties of both localized dissolution processes. Dealloying of CuAu(Pd)‐alloys and pitting of aluminum and aluminum alloys are considered as typical cases. Dealloying requires the nucleation of terrace site vacancy clusters, since easily dissolvable kink sites of screw dislocations are blocked by noble metal atoms. Pitting requires the nucleation of pores in the passive oxide film, which inhibits active metal dissolution. In both cases, rapid local crystallographic attack, ranging from etch pitting to very narrow tunnelling, is involved in the nucleation process. The term tunnelling is appropriate for all these events. While the scale of tunnelling events is much larger in the case of pitting compared with the case of dealloying, the calculation of the breakthrough potential of dealloying and of pitting is basically equivalent. Gross pitting, ending in the formation of macroscopic holes, is the result of localized renucleation of tunnelling events due to localized accumulation and hydrolysis of metal halogenide salt solution.

The selective adsorption of Thiobacilli to dislocation sites on pyrite surfaces

The selective adsorption of <i>Thiobacilli</i> to dislocation sites on pyrite surfaces

冷間加工した高純度鉄中の水素トラップ効果

For the purpose of separative determination of trap parameters for some types of H-trapping sites in a 35 pct-reduced high purity iron, a study has been performed with use of a two-steps electrochemical permeation technique. Two types of trapping sites, T I and T II, have been confirmed to exist. The T I sites have a binding energy of 63.1 kJ·mol−1 and a density of 1×1023 m−3. They are mostly annihilated by recovery annealing at temperatures below about 673 K. The sites T II have a binding energy of 46.4 kJ·mol−1 and a density of 7×1023 m−3. They are also significantly reduced on annealing at temperatures below about 573 K, but a final reduction occurs at around 730 K accompanied by recrystallization. The sites T II are believed to be core sites of edge dislocations. The significant reduction of T II on annealing at low temperatures suggests that the segregation of interstitial impurity atoms to dislocation-core sites precludes their occupancy by hydrogen. Another type of trapping sites, T III, having a binding energy roughly of 30 kJ·mol−1 are also pressumed to exist. The concentration and temperature dependency of H-diffusivity in the deformed iron can be well explained in terms of the coexistence of the three types of trapping sites.

Hydrogen Trapping in Cold Worked High-Purity Iron

Hydrogen trapping in deformed iron has been studied by time lag measurements based upon a double-step electrochemical permeation technique. Two types of trapping sites, TI and TII, have been confirmed to exist in iron deformed 35% by rolling. TI sites have a binding energy of 63.1 kJ/mol and a density of 1×1023/m3. Most of them annihilate by annealing below 673 K. TII sites have a binding energy of 46.4 kJ/mol and a density of 7×1023/m3. TII sites are also significantly reduced by annealing at temperatures below 573 K, while a further reduction occurs by recrystallization around 730 K. TI and TII sites are believed to be vacancies trapped by interstitial impurity atoms and core sites of dislocations, respectively. The significant reduction of TII by annealing at low temperatures suggests that the segregation of interstitial impurity atoms to dislocation-core sites precludes their occupancy by hydrogen. An another type of traps having a binding energy of about 30 kJ/mol has also been presumed to exist.

Standardization of radon measurements

Radon escaping from soil into homes appears to present the single greatest source of radiation exposure that most people will ever face. Measurement protocols for the relatively inert gas inextricably link the method of collection with the counting of the specimen. The most commonly used methods depend on the measurement of dislocation sites on plastic α-track detectors or on the adsorption of radon onto activated charcoal for subsequent counting of the γ-rays produced by decay of the radon progeny. The uncertainties inherent to the radon-measurement methods used commercially in the United States are far greater than those for measurements of other environmental radionuclides. The results of this preliminary study raise doubts as to whether existing proficiency-testing programs can provide assurance that radon-measurement methods are representative of actual conditions in any dwelling.

Typical hillocks and spirals on flux-grown DyFeO3 crystal surfaces

Multi-sided and almost rectangular growth hillocks on (1 1 0) faces of flux-grown DyFeO3 crystals are illustrated. Some such hillocks exhibit spiral growth layers originating from the summits of hillocks. Spiral growth layers originating from more than one initiation centre interact, giving rise to closed loop, interlocked and interlaced or other complex growth formations. The origin of the multi-sided hillocks is attributed to preferential growth at the sites of screw dislocations in DyFeO3 crystals. Defects other than screw dislocations also stimulate growth on (1 1 0) faces of DyFeO3 crystals. An example of this is offered. The mechanism of independent growth on (1 1 0) faces of these crystals is discussed.

Acute sports injuries requiring hospital care.

The present investigation reports 138 consecutive patients injured in sports, who needed treatment as in-patients in a one year period. More injuries were sustained in soccer than in other sports. The lower extremity was the site of most injuries, fractures and dislocations being the most common type of injury. At follow-up 50% of the patients complained of discomfort. The average stay in hospital after a sports injury requiring hospital care was 6 days. In 52% of the patients the duration of sports incapacity was at least six months and in seven per cent the sports incapacity after the sustained injury was permanent.

Topographic study of the dissolution kinetics of sodium chloride

The effects of undersaturation, temperature and stirring on the dissolution kinetics at dislocation sites in sodium chloride crystals in the etchant ethyl alcohol + cadmium chloride (as poison) have been studied. It is seen that the results are not consistent with the theoretical predictions.

Etch patterns on borax crystals

AbstractEtch patterns obtained on habit as well as cleaved matched faces of borax crystals are described. Morphology of all the etch pits is discussed. It is found that all the pits are formed at the sites of dislocations. A report about various dislocation configurations is given. From the dislocation density measurements, it is established that the borax crystals grown are of very good quality.

Minority carrier lifetime in the region close to the interface between the anodic oxide and CdHgTe

This paper describes minority carrier lifetime in n-type CdHgTe surface layers, especially the relationship between minority carrier lifetime and dislocations. A new method has been developed to evaluate lifetime in the surface layer of semiconductors. This method measures the concentration of minority carriers remaining after injection by utilizing surface potential measurement of an MIS diode. Computer simulation reveals how dislocations affect minority carrier lifetime and confirms the validity of this method. Experimental results indicate the dislocation-induced recombination is dominant for dislocation densities over 5×10 5 cm -2 and that minority carrier lifetime is inversely proportional to dislocation density. These results are similar to the results of the R 0 A product as a function of dislocation densities that have been reported by Colombo and Syllaios. The conjugate pairs r (radius of dislocation pipe) and s (recombination velocity at the dislocation site) are 0.3 to 0.5 cm 2 s -1. The lifetimes become almost constant - scatter 3 to 4 μs - for dislocation densities less than 2×10 5 cm -2. Lifetime is not dominated by dislocations in this dislocation density range.

On the thermodynamic theory of dislocation etch‐pit formation

AbstractA logarithmic function of total dislocation energy, which includes Cabrera's and Schaarwächter's dislocation energy equations, is used to derive thermodynamic conditions for etch‐pit formation at dislocation sites. It is found that Cabrera's mechanism holds when the ratio of dislocation core radius rh to Frank's radius rF approaches zero. When 0 &lt; rh/rF &lt; 1, Cabrera‐type mechanism also holds, but the activation energy barrier is smaller than that in the original Cabrera's model and the undersaturation barrier Δμ* for spontaneous nucleation increases with an increase in rh/rF ratio. When rh/rF =1, the value of Δμ* is four‐times the value predicted by Cabrera's model. For rh/rF &gt; 1, Schaarwächtertype mechanism involving no undersaturation barrier holds. A resume of Cabrera's and Schaarwächter's theories is also given.

Friction, wear and the hardness of boron-implanted 18W4CrIV steel

The hardness, friction and wear behaviour of 18W4Cr1V steel was investigated before and after implantation with 200 keV B + ions to doses of between 10 13 and 10 18 ions cm −2. Friction and wear were measured on a pin-on-disc machine and the variations in hardness were studied with a Vickers microhardness tester. Wear resistance increased almost linearly with B + ion dose. There was negligible change in hardness at doses below 10 15 B + ions cm −2. Above this dose the hardness was observed to increase almost linearly with B + ion dose to about 80% at 10 18 ions cm −2. The magnitude of the change in hardness, however, was observed to depend on the measuring load; the lighter the load, the higher was the measured increase in the hardness of the implanted surface. B + ion implantation was found to increase significantly the friction of 18W4Cr1V steel at doses above 10 16 B + ions cm −2. Below this dose there was a slight reduction in friction. These changes are considered to be associated with solid solution hardening of the steel by the implanted B + ions. Boron is an interstitial in steel and its implantation produces negligible lattice damage. As such, most of the implanted ions occupy defect and dislocation sites and act as barriers to the propagation of dislocations during the plastic deformation of steel. The specimens were analysed by Rutherford back-scattering and the topography of the wear tracks was studied with a Talysurf machine.

Positron annihilation study of the effect of hydrogen during the plastic deformation of a steel

Positron lifetime measurements were conducted on spheroidized low carbon steel (AISI 1009) deformed without hydrogen, hydrogen charged after deformation and hydrogen charged during deformation. These were measured as a function of tensile strain at a constant value of hydrogen input fugacity (250 MN m −2). Decoration of dislocation sites with hydrogen reduced the relative intensity of the short-lifetime component. Deformation with hydrogen in the steel increased the relative intensity of the long-lifetime component, signifying an increase in concentration of vacancy agglomerates or microvoids.

Evidence of screw dislocations on (002) cleavages of lithium carbonate single crystals

Well-defined triangular etch pits are produced on etching (002) cleavages of lithium carbonate single crystals with 2% citric acid. On etching of cleavage face and matched face these pits nucleate at the intersection sites of dislocations with the cleavage face. On successive etching of a cleavage face, shallow irregular arrays of pits do not enlarge in size as compared to other isolated pits on the same face. These irregular arrays of pits have reasonable correspondence on an etched match face, suggesting they form at dislocation sites.

Dislocation activities in SnI 2 and SnI 4 single crystals

As-grown (010) and (111) surfaces of SnI 2 and SnI 4 single crystals respectively were successively chemically etched in 0.15 M hydrochloric acid solution. It was established that the pits indicate the sites of dislocations in these crystals. This was further confirmed from a comparison of the etch patterns before and after the (010) and (111) surfaces were chemically polished. The average density of the dislocations was found to be greater in SnI 2 crystals than in SnI 4 crystals. The lateral and normal velocities of the growth of pits in these crystals were then measured at various temperatures. The time dependence of the growth of the pits was found to be linear, whereas the temperature dependence of the growth was found to be exponential, i.e. V = A exp( -E kT ) . The dissolution parameters, i.e the activation energies and the pre-exponential factors for dissolution along the surface and along the dislocation lines, were computed. It was observed that the activation energies for dissolution along the various directions were different and were greater for SnI 4 than for SnI 2 crystals. The implications are discussed.

Dissolution Rates at Dislocation Sites on the (111) Surface of Cu Single Crystals Etched in Young&amp;rsquo;s Solution at 290 K

Dissolution Rates at Dislocation Sites on the (111) Surface of Cu Single Crystals Etched in Young&amp;rsquo;s Solution at 290 K

Etch pit studies in alkali halide crystals

Among several techniques which have been developed for observing dislocations in crystals, etching technique is the most convenient and simplest method. The main aim of this report is to describe the results of a survey of etch pit studies undertaken in alkali halide crystals and to extend the available data in this field. This review lays emphasis on the application of etch pit method to study dislocations in alkali halide crystals. Different aspects of the problem presented include: 1.(i) A brief survey of various etchants reported for different alkali halide crystals.2.(ii) Role of etching parameters such as poison concentration, temperature, stirring, undersaturation of the solvent etc on etch pit morphology.3.(iii) Mechanism of etch pit formation.4.(iv) Mechanism involved in the orientation and morphological changes in etch pits.5.(v) Role of impurities on etch pit formation.6.(vi) Dissolution kinetics at dislocation sites.7.(vii) Surface dissolution.8.(viii) Dislocation velocity measurements.9.(ix) The origin and mechanism of formation of 'Anomalous solution phenomena' obtained on cleavage planes of alkali halide crystals.10.(x) The origin and mechanism of thermal etch pits in alkali halide crystals.

Chemical kinetics of dissolution of BaMoO4 crystals

AbstractAn etchant capable of revealing the sites of dislocations in the flux‐grown crystals of BaMoO4 has been established. Using this etchant (HNO3), effect of etching time, acid concentration and temperature on the selective etch rate is demonstrated. It is established that the process of dissolution in unstirred HNO2 solutions is one of the diffusion rate controlled; an empirical equation governing the kinetics has been suggested.

The role of impurities on chemical etch pits in potassium-doped Li2CO3 single crystals

IAthium carbonate (Li2CO3) single crystals were grown by the zone melting technique [1] in CO2 atmosphere, doping with 1% K2CO 3 by weight. The etch pits on undoped crystal cleavages etched in 2% citric acid were triangular in shape with well defined sides, whereas the doped crystal cleavages revealed triangular pits which were anomalous in nature. When the trapped impurities were in bulk the etch pits revealed irregular contours, while in traces, pits showed grooves extending from the bottom point of the pit. On observing the etch figures in a scanning electron microscope, as well as from the etching experiments, it was conjectured that the impurities preferred dislocation sites. That the impurities become trapped in the interior of the crystal has been ascertained from the Laue X-ray transmission diffraction patterns. Much useful information can be obtained from the studies on different types of etch pits and their density regarding the nature of defects, impurity content and the history of growth of crystals. Pate1 and co-workers [2, 3] have shown that the te.rracing nature of etch pits are found due to the precipitation of impurities along the dislocation lines. It is quite probable that the fission fragment lying along the dislocation line may deviate the geometrical shape of the etch pit due to the preferential etching along the fission track giving rise to a groove or a wing shape to the etch pits. The anomalous nature of the etch pits formed due to the dissolution of the fission fragments present in the body of the crystal has been reported by Fleischer