Rectangular Pits Research Articles

Etch pit shapes on {110} surfaces of CaF2 crystals

{110} surfaces of CaF2 crystals are etched with different concentrations of HCl. It is found that concentrated HCl produces characteristic rectangular pyramidal etch pits and 2 volume percent HCl produces boat shaped etch pits. Such variations in the etch pit shapes on {110} surfaces of CaF2 crystals with different concentrations of HCl have been explained. Concentrated H2SO4 is found to be a suitable chemical polisher for these surfaces, the polishing rate is about 0·1μ/min.

Experimental investigation of etch pit formation on quartz sand grains

SummaryAn experimental investigation into the formation of crystallographically orientated etch pits on quartz sand grains was undertaken. The methods and materials used in the experiments differ considerably from those of other workers in this field. Using natural as opposed to artificial solutions, V-shaped or triangular etch pits as well as rectangular pits have been produced on the quartz grains after time periods of 4 hours and 20 hours. Features of intense surface disintegration have also been recorded. The etch pits are compared to those of natural occurrence on grains from the Millstone Grit (Namurian) sediments and the differences discussed.

Change in morphology and dislocation Etch Pits on the (010) Surface of Magnesium Orthosilicate Crystals

AbstractInvestigations made on the etching behaviour of magnesium orthosilicate crystals in hydrochloric acid and melts of potassium and sodium hydroxides are described. It is shown that the morphology and orientation of the etch pits depend upon the concentration, composition and temperature of the etchant used. At low concentrations of HCl acid solution, the boat shaped pits produced are oriented along [100] direction while in concentrated acid, the hexagonal pits produced are oriented along [001] direction. At intermediate concentrations of about 5 N HCl acid the pits are square. KOH melt at 400 °C is found to produce rectangular pits with their longer sides parallel to [100] direction. The effect of a mixture of KOH and NaOH in different proportions in the melt is investigated. It is observed that square pits are obtained in melt of the mixture of KOH and NaOH in the proportion of 6:4 respectively. The mechanism responsible for the change in orientation of etch pits have been explained. The implications are discussed.

Dislocations in ammonium perchlorate

The formation of etch pits on the cleavage surfaces of ammonium perchlorate single crystals has been studied by optical and electron microscopy. Ethyl and butyl alcohols and their mixtures were the most satisfactory etchants. Well defined etch pits could not be detected on the c face which dissolves very rapidly, going through three separate stages: numerous round etch pits appear, followed by elongated roughly parallel curved channels, which finally become connected, leaving nearly circular flat-topped ‘hills’ with clearly delineated terraced sides. However, when the crystals are etched in butyl alcohol, well defined rectangular pits are formed on the m face having either a 3:1 or 4:1 length-to-width ratio; they resemble elongated stepped or terraced pyramids, and are always orientated with their long sides parallel to the [001] direction.Some of the etch pits on the cleavage surfaces were found to be distributed randomly while others are clearly aligned in specific crystal directions. Strained crystals exhibit slip bands and the various possible systems were deduced by computing, from the crystal structure, the most likely low-index slip planes and slip directions which are consistent with the observed etch pit alignments and slip bands.

Phase relations and substructure in single-crystal MoSi 2

Single-crystal specimens of MoSi 2 were found to have a second phase present, identified as Mo 5Si 3 by X-ray diffraction and electron microprobe analyses. Isothermal annealing runs on bulk samples in vacuum at temperatures ranging from 1200 ° to 1600 °C for 24 h showed an increase in Mo 5Si 3 content with increasing annealing temperature. High-temperature X-ray diffraction on thin layers in vacuum showed an increase of Mo 5Si 3 content with a concomitant decrease of MoSi 2 up to 1550 °C, using Mo heaters. From 1550 ° to 1720 °C, a decrease in Mo 5Si 3 content was noted. Mass spectrometry up to 1700 °C in a vacuum of 10 −6 mm Hg did not reveal Mo-Si molecular species. Samples etched with 4 H 2 O: 1 HF: 2 HNO 3 showed the presence of individual and polygonized, chain-like, elliptical etch pits on the (001) plane. Rectangular, triangular, spiral, and hexahedral etch pits were found primarily on the (100) plane, the lattice indicating the pseudo-hexagonal character of MoSi 2 by analogy with WSi 2. Primary slip produced by hardness indentations at room temperature was found to be of the {100} < 001 > type, and secondary slip of the {110} < 001 > type was also determined for MoSi 2. The Knoop microhardness values at 100 g loads ranged from 870 to 1300 kg/mm 2 for MoSi 2. Mo 5Si 3 was found to have a microhardness value ranging from 1190 to 1330 kg/mm 2.

Surface features observed during thermal etching of Ice

Polycrystalline- and single-crystal ice specimens were etched in a saturated air atmosphere. Observations were made at about 50x magnification after etching times of a few minutes to several weeks. High-angle boundaries became visible as grooves within the first few minutes. Straight low-angle boundaries, which formed during solidification or in the course of plastic deformation, were also observed. Sharply defined short straight lines, raised above the surface of the specimen, were frequently observed and have been investigated in detail. These features developed within a few minutes and were very stable, retaining their initial appearance for as long as several hours of etching time. The lines formed either a triangular or a rectangular pattern that was related to the crystallographic orientation of the exposed surface. It was established that one family of these lines was parallel and a second was perpendicular to the C axis. Occasionally small round hillocks with a small central feature that appeared to be a crater formed during etching. The concentration of hillocks appeared to be greatest along subboundaries. A honeycomb-like network of hillocks was sometimes observed. Triangular hillocks were observed to form on the surface of some grains. The bisector of the acute angle associated with the raised part of the triangle was perpendicular to the basal plane. After extensive thermal etching, rectangular pits with well-developed facets appeared. The etching technique was used to study structural changes that occurred in ice during creep and fracture experiments.