Etch Figures Research Articles

Microstructural studies of fluidized-bed β-silicon carbide

The fluidized-bed vapour phase deposition of β-SiC on nuclear fuel granules can produce polygonal crystals. The examination of these and their etch figures by scanning electron microscopy indicates an internal structure composed of {111} planar sheets. The disposition of these sheets is discussed with the aid of three-dimensional models. It is concluded that a maximum of four sheet orientations can occur. From these, six families of sheet pairs can be made by appropriate combinations: these are labelled according to the [110] directions of the spines created by their intersections. The sheets produce traces on the external crystal faces, and the various possible juxtapositions of these traces are discussed.

Etching of GaN Using Phosphoric Acid

Hot phosphoric acid is found to be useful for etching and characterizing epitaxial crystals grown on (0001) sapphire substrates. The obtained etch rates are 0.2–1.0 μm/min and the activation energy is about 4.4 kcal/mole in the temperature region of 50°–200°C. Hydration of Ga ion is considered the rate‐determining step of the etching action. The x‐ray diffraction and the infrared spectrometric studies indicate that the ortho and meta phosphoric ions play an important role as attacking ions in etching. This phosphoric acid etching reveals crystal defects in undoped (n), Zn‐doped (i), and i‐n structure epitaxial crystals. Conical hexagonal pyramid pits and truncated hexagonal pits develop in the undoped layers, and they tend to be arranged along the slip direction and are attributed to certain dislocations. These hexagonal pits are densely generated near the interface of the epitaxial layer and the substrate. The density of the pits decreases exponentially with crystal growth. The pits are apt to increase in density and size when the carrier concentration is high (1019–1020 cm3). The rounded etch figures develop in Zn‐doped crystals and sometimes in the undoped crystals with a high carrier concentration (1019 cm−3). Etching also indicates that there is a significant difference in growth patterns between the Zn‐doped and the undoped crystals even if the Zn‐doped layer is continuously deposited on the undoped layer. This implies a difference in the crystal growth mechanism between these crystals.

Relationship between habit and etch figures of corundum crystals grown from molten cryolite flux

Single crystals of corundum were grown on a seed from a Na 3AlF 6 flux doped with Cr 2O 3 or Dy 2O 3. The perfection of these crystals was investigated by measuring the etch pit density after etching with K 2S 2O 7. Doping with Cr 2O 3, did develop the c(0001), r{10 1 1};, and n {22 4 3} planes, whereas the second-order prism a {11 2 0} planes were not observed. Doping with Dy 2O 3, caused the formation of hexagonal prismatic crystals composed of the c(0001), r{10 1 1}, and a {1120} planes. The respective average dislocation densities of crystals grown under the optimum conditions were of the order of 10 4 cm -2 on both the (0001) and the {11 2 0} planes. The shapes of etch pits on the equilibrium habit for the c(0001), n{22 4 3}, r{10 1 1} and a{1120} were of equilateral triangle, isoscele triangle, scalene triangle, and deformed-rhombic form, respectively. The geometrical symmetry of the etch pits correspond to the Laue projection symmetry on the individual plane.

Etch figures and crystal structures

AbstractThe etch figures on some of the naturally occurring faces of crystals of sodium chloride, cuprite, alpha‐quartz, tourmaline and topaz are compared with the atomic arrangements on the etched surfaces. The etch figures are influenced in their shape and orientation relative to the natural faces by a number of factors. One of these factors is the crystal structure. In every example of an etched pit bounded by straight edges, it was found that there exists in the crystal structure a continuous chain of relatively strong inter‐atomic bonds, running parallel to the straight edge. The study of tourmaline indicates the direction in which all the SiO4 tetrahedra are pointing relative to the external form.

Thermal etching of CaWO4 crystals

(011) cleavages of single crystals of calcium tungstate, grown by the flux-evaporation method in this laboratory, have been subjected to thermal etching between temperatures of 1110 and 1430 °C in a vacuum chamber at a pressure of 10−5 Torr. The etch figures thus obtained successfully reveal the emergence sites of dislocations in the crystals. An excellent correlation between thermal and chemical etch pittings has also been obtained on mirror cleavages. Quantitative measurements made on the etch rate and weight loss with temperature show that the process of the removal of ledges from the cleavage surface has an activation character. The activation energy for evaporation at dislocation sites is less than that responsible for overall evaporation from the exposed surface. The implications are discussed.

A general method of determining orientation in the cubic crystal system on the basis of geometrical evaluation of etch figures

A method is proposed for determining orientation metallographically from etch figures. The method is based on a general geometrical view, enabling an evaluation of orientation on all materials belonging to the cubic system. The great advantage of the method is the possibility of compiling tables. The authors provide the connection between the measurable etch-figure angles and the hkl indexes of the sample surface in the form of equations. The equations are ready for computerizing; however, to eliminate the need for a computer, the mentioned connection has been given in tables. The etch-figure technique is determined to give a useful completion for cases where other methods will hardly be applicable, or be too costly, or cause loss of time.

Observations of dislocations in zinc by chemical etching

A new chemical etch has been found to be effective for revealing dislocations intersecting the basal planes of zinc. The etch works for surface whose orientation is within 0.5° of the basal plane. Evidence is available that there is a one-to-one correspondence between etch figures and dislocations. Crystals with densities as high as 10 7 dislocations per cm 2 have been successfully etched.

Sur l'interprétation de la forme des figures de corrosion observées sur les faces {01.2} de l'hématite

Investigations of the external forms of etch figures observed on the faces {01.2} of hematite, have shown the influence of the speed of dissolution in the glide plane and the influence of the density of ions along directions parallel to those faces.

Growth and etching of KD 2PO 4 crystals in solutions containing acetate ions

Single crystals of KD 2PO 4 grown from supersaturated solutions containing acetate ions develop faces of the forms {100} and {011} with microscopic facets of {112} and {1 2 1} orientation. The facets in the later stage of growth vanish, but for a short periods of growth, a reduction of the scalenohedron{1 2 1} to a sphenoid of the third order can be observed. The etch figures also show disphenoidal symmetry. These results, as well as neutron diffraction observations on the planes (002), (006), (110), (330) and (222) reduce the generally accepted space group of KD 2PO 4 from I 4 2d to I 4 .

Dislocation etch pits in zinc selenide

It is shown that triangular etch pits are produced at the points of emergence of dislocation lines on the (111) zinc faces of single crystals of zinc selenide. Conical etch pits can be produced on the (¯1¯1¯1) selenium faces with a solution of one part HCl to three parts HNO3. Etch patterns produced following indentation confirm the identity of the etch pits. Triangular etch figures which are associated with stacking fault tetrahedra have also been observed.

Thermal etching figures in ceramic bodies

Thermal etching figures in ceramic bodies

The Influence of the Complexing Agent Concentration on the Etch Rate of Germanium

This paper reports the effect of the concentration of the complexing agent in an etching solution on the etch rate and surface morphology. The {100} surface of germanium was etched in a solution of the basic composition in the volume ratio 1:1:4, where was tartaric, acetic, citric, oxalic, and acids, and mannitol. There was no change in the shape or orientation of the etch figures with variation of the type or orientation of the complexants. It was found that the etch rate was a function of the concentration of the complexant when the concentration of the oxidizing agent was held constant. The variation in etch rates and activation energies with the complexing agent concentration indicated that the reactions are diffusion controlled. A model is proposed for the crystal‐solution interface which is consistent with the interdependence of the etch rates and the complexing ratio of the germanium.

純タングステンの転位ピットおよび光像の作成について

The electrolytic and chemical etching conditions for revealing dislocation pits and light figures on the principal planes of the zone-refined tungsten single crystals were as follows:(1) Clear dislocation pits on the(001) plane were easily produced by either electrolytic etching or chemical etching as already reported and dislocation pits on the(111)plane were obtained by electrolytic etching in(16%NaOH+picric acid 4 g)electrolyte. Dislocation pits on the(110)plane were not revealed even in the various etching conditions.(2) Etching figures from which clear light figures on the (001),(111) and (110) planes could be obtain were revealed by either chemical etching in {30%K3Fe(CN)6 [1 part]+3%NaOH [1 part]} solution or electrolytic etching in sodium hydroxide solution added picric acid.

Studies on hot extrudability of aluminum and 6063 alloy cast billet due to working pressure and structural flow

The macro-structural flow during deformation of metals was observed in the extrusions of commercially pure aluminum and 6063 alloy at 500°C under farious extrusion conditions. The deformation behavior concerning the extrusion pressure and the macro-structure obtained by experiments was discussed with respect to the effects of ram speed, die angle, and reduction in diameter.The following results were obtained:(1) As for a given extrusion ratio (R) an approximate linear relationship was empirically obtained between extrusion pressure (P) and logarithm of (R). As for a given extrusion velocity (V), there also existed an approximate relationship between logarithm of (P) and logarithm of (V). Each factor expressing the ratio between the values in these relationships depended upon extrusion conditions such as extrusion ratio and extrusion speed. When extrusion pressures were measured for three die angles, the value of (P) was smaller with the increase of die angle (α).(2) The flow of the macro-structure of cast billet during the extrusion process could be divided into the following zones; dead metal, inner shearing, entry to the die, neck of the die, extruded product, etc. It was found that the extrusion characteristics of cast billets could be explained with respect to the grain refining behavior of structures in these zones.(3) The microscopic examination of the structure and etching figures showed that the feathery grains having a twin plane of (111) were converted into granular grains having a plane of (110) during hot dynamic extrusion at 500°C. However, the mechanism of the rotation of these deformed crystals remained still unsolved.

Morphology of Etch Pits on Germanium Studied by Optical and Scanning Electron Microscopy

A comparison is made between optical and scanning electron microscopy techniques on germanium surfaces that have been etched in several common chemical etchants. The morphology of the etch pits due to dislocations and different types of surface preparation are discussed. The high resolution and depth of field of the scanning electron microscope allowed resolution of the fine structure of the etch figures. Due to the manner in which the image is formed on the scanning electron microscope, the limit of resolution is much higher and light interference encountered using standard metallurgical microscopes is eliminated.

Single Crystal Growth of Titanium Carbide by Chemical Vapor Deposition

Various forms of titanium carbide crystals were deposited on graphite substrates from the vapor phase consisting of hydrogen, titanium tetrachloride, and a hydrocarbon in the temperature range of 1200°–1350°C. The correlations between the crystal morphology and the growth conditions (temperature, gas flow‐rates, concentrations, impurities, etc.) were investigated. The decomposition of the hydrocarbon was found to play an important role on the growth process. By x‐ray diffraction, it was concluded that the growth direction of these crystals was mainly <111> although sometimes kinked toward . The growth mechanism of the single crystal was further studied by observation of the etching figures of the cross section which showed hexagonal growth layers. Finally the tensile strength of needle or pillar crystals was measured and a linear relation (on log‐log scale only) was confirmed between the diameter and the strength.

The Needle-Growth Mechanism of Reduced Copper

Cross sections of needle-like copper powders reduced from aqueous cupric sulphate solution by glucose were examined. They were exclusively pentagonal.From these sections and their etch figures, a multiply twinned decahedron structure was suggested.We demonstrated that the growth of the needle-crystals could be explained on the basis of twinaccelerated growth mechanism and further discussed the growing mechanism of the decahedrons larger than that might be expected from the thermodynamical speculation.Some observations in favor of these explanations were given.

Chemical etching of dislocations in GaSe

An etch-pit method has been developed for revealing non-basal dislocations in GaSe single crystal. Shallow background pits, probably nucleated at defects such as vacancies and vacancy clusters, are observed following exposure of the surface to water vapour. The morphology of the etch figures and the variation in etching rates along the primary basal directions are discussed. A tendency for cleavage steps to run in directions is probably a result of the ionic contribution to the intralayer bonding.

Acid Dissolution of Chlorites: Release of Magnesium, Iron and Aluminum and Mode of Acid Attack

AbstractThe acid dissolution of 8 chlorites in 2N Si-saturated HCl showed that there was no preferential dissolution of Al in octahedral positions and that the octahedral and tetrahedral sheets in the chlorite structure were equally attacked. An analysis of chemical data suggested a simple two-dimensional diffusion model in which the acid attack on the chlorite particles proceeded from the edges inward leaving a reacted layer which formed a diffusion barrier. Microscopic examination showed, however, that the acid attack was not simply an edge attack but started at any point where cracks, structural defects and weaknesses apparently predisposed sites to acid attack. It was also clear from the formation of etch figures and solution channels that the product layer at least partially dissolved or disintegrated during the progress of acid attack. The residue which remained after acid attack appeared to be an opaline amorphous hydrated silica as was indicated by index of refraction measurements. The orderly arrangement of etch figures on flakes of some chlorites reflected certain crystal symmetry elements. The results indicate that the acid dissolution technique to determine the ratio of Al in octahedral and tetrahedral positions can not be used as an aid in the calculation of structural formulae for chlorites.

Thermal etching of dislocations in zinc crystallites grown from the vapour

Small single crystals of zinc of 99.99% purity were grown from the vapour at a temperature slightly less than the melting point. The dislocation structure of these crystallites was studied by thermal etching, which occurs when the crystals are cooled from the growth temperature to 10 to 15°C below the melting point in a few minutes. Various types of etch figures were observed and the mechanisms of their formation are discussed. It seems, on the basis of the available evidence, that the etch figures correspond to dislocations.