Etch Pit Morphology Research Articles

Mineral precipitation and dissolution in aqueous solution: in-situ microscopic observations on barite (001) with atomic force microscopy

Crystal growth and dissolution mechanisms on the barite (001) surface have been observed in-situ in aqueous solution as a function of the saturation state at molecular scales using Atomic Force Microscopy (AFM). On freshly cleaved barite (001) surfaces, cleavage steps with a step height of 7 Å occur, representing the height of a unit cell in the c direction. Growth and dissolution occurs via the advance and retreat of steps with a step height of half a unit cell (3.5 Å). In supersaturated BaSO 4 solution, monolayer step growth increases linearly with the BaSO 4 concentration. Step velocities of one BaSO 4 half-unit cell layer are faster in [100] relative to [−100], whereas in the underlying BaSO 4 half-unit cell layer, step velocities are faster in [−100] than in [100]. A 2 1 screw axis parallel to [001] causes the directional growth in opposite directions in different half-unit cell layers. At low to moderate supersaturations, up to about 80 μM BaSO 4, spiral growth is the dominant growth mechanism, whereas at higher BaSO 4 concentrations, surface nucleation dominates the growth process. In the presence of a crystal growth inhibitor (NTMP, nitrilotri(methylenephosphonic) acid), the nucleation rate as well as step growth is retarded depending on the inhibitor concentration. The morphology of monolayer step edges becomes irregularly curved and jagged, thus suggesting that NTMP molecules attach preferentially to step edges. In pure water, shallow etch pits form with a morphology defined by monolayer steps parallel to [010] and [110]. All etch pits within one BaSO 4 layer point in the same direction, whereas etch pits in the underlying BaSO 4 layer point in the opposite direction, as a result of the 2 1 screw axis. Chelating agents, such as EDTA, ethylenediaminetetraacetic acid, dissolve barite effectively by the formation of Ba-EDTA surface complexes and their desorption resulting in an increased etch pit formation rate. Different types of etch pits could be distinguished: (i) shallow etch pits are defined by steps parallel to [010] and [110], (ii) whereas deep etch pits are defined by steps parallel to [100] and [010]. Step velocities of retreating monolayer steps parallel to [110] retreat faster than steps parallel to [010] resulting in an elongated etch pit morphology. With increasing EDTA concentration from 0.1 mM to 100 mM, the velocity of steps parallel to [110] is reduced by one order of magnitude. Etch pit morphology as well as monolayer step kinetics suggest that EDTA molecules attach to the barite (001) surface and detach a BaEDTA 2− complex preferentially from steps parallel to [110].

Dynamic etching of natural rhombohedral calcite cleavage planes

AbstractDynamic etching of natural rhombohedral calcite cleavage plane in low concentration of monocarboxylic acid (such as formic, acetic and propionic acids) is studied and interesting results are obtained. Eccentricity of rhombic etch pits increase indefinitely as stirring rate increase in low concentration of monocarboxylic acids, whereas peak value of eccentricity is obtained with stirring rate when there is a change in etch pit morphology. Change in etch pit morphology and change in eccentricity with stirring rate is explained with the help of lateral reaction rates along various directions. Eccentricity variation with stirring rate is compared with concentration variation with concentration of different monocarboxylic acids.

The effect of carboxylic acids on the dissolution of calcite in aqueous solution. Part 1.—Maleic and fumaric acids

The effects of maleic and fumaric acids and their mono- and di-anions on the dissolution of calcite in aqueous solution have been studied over a wide pH range (3–8.5) by (i) the channel flow cell method, (ii) etch pit morphology measurements and (iii) the determination of adsorption isotherms. It is established that the mono-anion of maleic acid reacts with CaCO3via a first order heterogeneous process of rate constant 0.014 cm s–1 indicating a significant inhibition of the dissolution reaction as compared to dissolution in HCl of comparable pH. The inhibition is attributed to adsorption of the dianion and the shapes of the etch pits are used to infer the crystallographic environment of the adsorption sites on the (100) surface. In contrast the monoanion of fumaric acid shows no such inhibition. Under conditions where both maleic mono- and di-anions are present it is demonstrated that a Langmuirian adsorption of the latter occurs at dislocations greatly reducing the rate of dissolution. Again the fumaric acid system is impotent. Around pH 8 where the dissolution reaction is controlled by a process involving H2O, rather than a proton source, strong inhibition is observed in the presence of Langmuirian adsorption of trace amounts of the maleate dianion (10–6 mol dm–3). Much higher levels (10–3 mol dm–3) of fumarate dianion are required for a comparable effect.

Etch pit morphology in CdTe

Etch pit morphology in CdTe

局部陽極溶解理論を取り入れたＡｌ陽極溶解形態のコンピューターシミュレーション ＩＩ 横方向へのピット成長とピット分布

局部陽極溶解理論を取り入れたＡｌ陽極溶解形態のコンピューターシミュレーション ＩＩ 横方向へのピット成長とピット分布

Change in the etch pit morphology of bismuth with temperature

The effect of temperature on the etch pit morphology of the (111) cleavage planes of bismuth single crystals are described. A chemical etchant which revealed the emergent ends of dislocations was used. The shape of the dislocation etch pits changes from the characteristic triangular shape at room temperature to a hexagonal shape as the etching temperature is increased to 60 °C. This change in etch pit morphology is explained in terms of the removal of atoms from steps.

Influence of impurities on the etching of NaCl crystals

The effect of CdCl2, CuCl2·2H2O, MnCl2·4H2O and FeCl3·6H2O impurities and undersaturation on the rates of macroscopic dissolution,vp, lateral etching away from a dislocation line,vt, and normal etching along the dislocation line,vn, and on the surface micromorphology of the {100} face of NaCl single crystals in water, methanol and 96% ethanol is investigated. The dependence of etch rates on impurity concentration,ci, showed that the addition of a salt to the solvent always leads to a decrease invp, which attains a minimum value after a particular value ofci. The concentration dependence ofvt andvn is relatively complex, but often both decrease or increase simultaneously. A change in etch-pit morphology is caused by increasing the concentrations of all additives in ethanol and methanol. The dependence of etch rates on the undersaturation of methanol and methanol containing 10−3 M CdCl2 showed that dislocation etch pits are formed only for undersaturations greater than 0.02 and 0.06, respectively. These results as well as the roughening of etched surfaces at low impurity concentrations, the formation of terraced etch pits and the difference between etch pits at aged and fresh dislocations are discussed.

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.

Etch pit morphology on calcite cleavages by hydrochloric acid

AbstractEtch pit morphology has been studied on calcite cleavages by different concentrations of hydrochloric acid. Magnitudes of lateral reaction rates are very high concentration while they are decreasing as concentration decreases. Due to formation of finite or infinite lateral reaction rates at some particular concentration etch pit morphology changes. It is shown that the morphology changes are systematic. The underlying chemical equations are given for different etch pit morphology.

Dissolution kinetics of MgO crystals in aqueous acidic salt solutions

The revelation and morphology of dislocation etch pits as well as the rates of macroscopic dissolution and selective etching on the {1 0 0} plane of MgO crystals in aqueous solutions of various inorganic salts are investigated in relation to the nature and concentration of salt in solution and the etching temperature. It is found that addition of a salt generally facilitates etch pit formation and that the rates of surface dissolution and selective etching increase with additive concentration, etchant temperature and character and ageing of dislocations, while the etch pit morphology depends on the concentration and chemical nature of an impurity, etching temperature and the ageing of the dislocations. It is also observed that some fast etching solutions produce very shallow etch pits at screw dislocations. The results are discussed from a consideration of solution pH, standard electrode potentials of metals and stability of complexes present in solution. The importance of the surface entropy factor in revealing etch pits at screw dislocations is pointed out.

Etch Pit Morphology on Calcite Cleavages by Glacial Acetic Acid

AbstractEtch pit morphology has been studied on calcite cleavages by different concentration of glacial acetic acid. Lateral reaction rates are very less at high concentration as well as low concentration of glacial acetic Acid. Etch pit morphology changes due to formation of finite or infinite lateral reaction rates at some particular concentration called transition concentration. The underlying chemical equations are given for different etch pit morphology.

Cu結晶の(111)面転位ピットの形態変化について

Dislocation etch pits on the (111) surface of Cu crystals have been observed to study the effects of the composition, stirring rate and temperature of etchants and the small addition of Al in Cu. The etchants are Young’s solutions containing (NH4)2S2O8, NH4OH and NH4Br. The dislocation etch pit morphology strongly depends on the composition of the etchants. It is shown that the pit size varies with the concentration of the etchant and the pit shape varies with the ratio of each components in the etchant. At a ratio (NH4)2S2O8:NH4OH:NH4Br nearly equal to 1∼1.5:6:0.3, the triangular pyramid pits surrounded with 〈110〉 sides are produced, while, off this ratio, the etch pits tend to become more or less rounded. On the other hand, the stirring of the etchant increases the pit size remaining its shape unchanged. Such a tendency is also indicated with an increase of etchant temperature from 260 to 300 K, except a slight rounding of etch pit at 300 K. Moreover, with the addition of Al, the etch pits become small and rounded, though the straight-sided pits are revealed when etched with etchant containing high concentration of (NH4)2S2O8. Some discussions about the effects of the etching condition are given in connection with the kink nucleation and motion at the surface steps.

Thermal etch pits on calcite cleavages

AbstractThermal etch pits are observed on calcite cleavages when the latter are kept at 520°C to 560°C in atmosphere for some hours. Boundaries of the above etch pits are circular, hexagonal and rhombic and they are dependent upon the temperature of etching. Different etch pit morphology is observed in chemical etching on calcite cleavages. It is conjectured that origin of thermal etch pits are different from that of chemical etch pits.

Etch pit morphology and calcium sulphate growth on {111} faces of calcium fluoride crystals etched in sulphuric acid

AbstractAn investigation of the etching behaviour of cleaved octahedral faces of calcium fluoride crystals in sulphuric acid of different concentrations and at various temperatures is carried out. It is observed that the morphology of dislocation etch pits depends on the temperature and concentration of the acid. With an increase in the acid concentration, growth of whiskers, elongated platelets, hexagonal and dice‐shaped elevations, spherulites and sheaves is observed. Temperature of the etchant also has an effect on their formation. By X‐ray diffraction techniques, the compounds forming the whiskers and elongated platelets, and hexagonal and dice‐shaped features are identified as CaSO4 · 2 H2O and CaSO4, respectively. The mechanism of the growth of CaSO4 · 2 H2O and CaSO4 and the change in the morphology of selective etch pit are discussed.

H3PO4 — etching of {001}‐faces of InP, (GaIn)P, GaP, and Ga(AsP)

AbstractThis paper shows that hot H3PO4 is a suitable etchant for the production of dislocation etch pits on {001}‐InP, (InGa)P, GaP, Ga(AsP), and {111}‐GaP. The effects upon etch pit morphology of the misorientation of samples and the type of dislocations are investigated in detail.

Selective etching studies on cesium iodide crystals

The etching behaviour of {100} faces of cesium iodide crystal in solutions composed from a number of inorganic salts (CuCl 2.2H 2O, CsCuCl 3, Cs 2CuCl 4, CuI, C 32H 16N 8Cu, FeCl 3, NiCl 2, CoCl 2, CdCl 2, NH 4OH, NH 4Cl, etc .) and water in different alcohols (methanol, rectified and absolute ethanol, isopropanol and butanol) is studied. It is shown that all the used alcohols can serve as a solvent for the selective etching and only copper salts, which are capable to dissociate and form complex compounds composed of Cu-H 2O-Cl, can be used as additives. Data on the dependence of etch pit size and morphology on CuCl 2.2H 2O content are presented. From the spectral data the etching solutions containing different amount of CuCl 2.2H 2O, the nature of different complexes present in the etching solutions is inferred. On the basis of the nature of the complexes, some features of selective etching, e.g. change in etch pit morphology, surface roughening at low CuCl 2.2H 2O concentrations, etc. are discussed.

Effect of CuCl2 · 2 H2O additive in ethanol on dissolution and selective etching behaviour of CsI crystals

Abstract{100} faces of Kyropoulos grown CsI crystals had undergone a selective etching, and CsI spheres of ∼ 10 mm in diameter were subjected to dissolution at room temperature for 10 hrs. The results are: pure ethanol does not bring about any anisotropy in dissolution, addition of CuCl2 · 2 H2O leads to an anisotropy in dissolution of CsI, change in CuCl2 · 2 H2O concentration changes etch pit morphology, whereas the dissolution form does not depend on additive concentration. With increasing CuCl2 · 2 H2O etching rates at first increase, later decrease, dissolution rates linearly increase.

Role of the distributed impurities in the etching of potassium chloride crystals

The concentration of the distributed impurity calcium in KCl crystals is varied and its influence on the etching action has been studied. As the concentration of the distributed impurity calcium is increased in KCl crystals, the etched samples show the following essential features: (a) increase in the distinctness of the etch pits; (b) a progressive increase in the degree of surface roughness; and (c) gradual variation of the etch pit morphology. These observations suggest that the distributed impurity calcium acts as an additional poison during etching.

Cu(II)を溶解抑制剤としたLiF(100)面のエッチパターンと溶液内Cu(II)錯体の構造との関連

Cu(II)を溶解抑制剤としたLiF(100)面のエッチパターンと溶液内Cu(II)錯体の構造との関連

Fe(III)を溶解抑制剤としたLiF(100)面のエッチパターンと陰イオンの役割

Fe(III)を溶解抑制剤としたLiF(100)面のエッチパターンと陰イオンの役割