Pyramidal Faces Research Articles

New technology of KDP crystal growth

A new technology of KDP crystal growth is proposed for crystals grown at {101} or {011} pyramidal face seed. By the Holden method using temperature reduction, large single crystals were obtained. The grown crystals were optically characterized.

Zircon inclusions in corundum megacrysts: I. Trace element geochemistry and clues to the origin of corundum megacrysts in alkali basalts

Zircons enclosed in corundum megacrysts from basalts have a short prismatic habit with the prism slightly more developed than the pyramidal faces. The {110} prism is dominant compared with {100}, indicating crystallisation from alkaline-peralkaline environments. Rare zircon decomposition reactions suggest the possible presence of a primary SiO 2 phase in the source paragenesis for corundum megacrysts. The zircon inclusions are geochemically distinctive: high Y (up to 1.2%), U (UO 2 up to 1.7 wt%), Th (ThO 2 up to more than 2 wt%), Hf (up to 3.4 wt%), and REE (ΣREE up to 5000 ppm). They form a cogenetic group that is characterised by extreme REE fractionation with preference for the HREE varying from 30–100× chondritic Sm to 5000–20000× chondritic Lu. REE partitioning between zircon and silicate liquid is evaluated. The parental melts calculated for the zircon inclusions and other corundum-related zircons, using zircon/melt partition coefficients derived in the present paper, show concave-down REE patterns with a maximum Sm concentration close to 100× chondritic Sm abundance. Such REE patterns represent highly evolved melts after extensive fractionation of low-Ca feldspar prior to and throughout the crystallisation of zircon. The characteristics of zircon inclusions provide evidence that corundum megacrysts must have crystallised from alkaline and highly evolved melts under very reducing conditions, implying that the corundum is unlikely to have formed as high pressure phenocrysts in the host mafic magmas.

Chemical etching of natural fluorapatite crystals in acid solutions studied with the scanning electron microscope

AbstractDifferent aspects of the chemical etching process for natural fluorapatite (FAP) crystals in pure phosphoric acid solutions and for those with additives of Ca2+ and H2SO4 have been studied by means of the scanning electron microscope. The resulting experimental data obtained in the etching process are very sensitive to dissolving conditions, type of crystal face, and the presence or absence of any epitaxial coatings on the surface of dissolving crystals. It was found that the pyramidal crystal faces of the FAP have the highest dissolution rate value and, as a result, are not etched at all. The prism and pinacoid faces usually are covered by hexagonal etch pits under the same conditions. Additives of Ca2+ to the phosphoric acid solution result in transition from a chemical etching to a chemical polishing process, and additives of H2SO4 result in epitaxial coatings of CaSO4· xH2O (x = 0,0.5, 2) and shapeless pits formation.

Growth kinetics and morphology of potassium dihydrogen phosphate crystal faces in solutions of varying acidity

Changes in the solution acidity do not influence the growth rate of bipyramidal faces, however, within the limits of 20% it can be changed by uncontrollable impurities existing in the solution. For steps on prismatic faces in acid and alkali solutions a decrease of the critical supersaturation σ∗, at which a sharp increase of the velocity occurs, is observed. This is indicative of the decrease of the surface concentration of the adsorbed impurity, which retards the growth. The more the solution composition deviates from the stoichiometric one, the more does the value of σ∗ diminish. It is shown that pH does not affect the free surface energy of end faces of steps and their kinetic coefficients. The values of kinetic coefficients of steps of different orientation on prismatic and pyramidal faces are determined. The features of the macrosteps formation with the supersaturation increase are described in solutions of varying acidity. The effect of pH on the crystal habit is discussed.

Three-dimensional finite element simulation of Vickers indentation on coated systems

Abstract Three-dimensional finite element simulation is applied to investigate the general behavior of coated samples subjected to an indentation test. MARC®, a commercially available finite element software package, was used to study the Vickers indentation process on the following two representative systems: copper-coated high-speed steel as an example for a soft layer on a hard substrate and titanium nitride-coated high-speed steel as the reverse situation. The calculation provides the deformation characteristics and material displacements under or after local load as well as the stress distribution inside the coating and across the interface into the substrate. The results are given in two different cross-sectional planes, i.e., along the plane through one pair of the opposite pyramidal edges and along the plane perpendicular to one pair of the opposite pyramidal side faces. Distinct differences are obtained with respect to the material deformation, extension and shape of the stress fields and the plastically deformed zone. The indenter load vs. indentation depth relationship during loading and unloading as well as the hardnesses at peak load are also calculated for both examples. The hardness determination is based either on the diagonal of the residual permanent imprint (Vickers definition) or on the contact depth when loaded (similar to the plastic depth in the depth-sensing instrument) or on the real loaded contact area as provided by the finite element simulation.

Study of Bulk and Film-Substrate Composite Materials Behaviour Under Vickers Indentation By Three-Dimensional Finite Element Simulation

ABSTRACTThree-dimensional finite element simulation is employed to investigate the general indentation behaviour of bulk materials and corresponding film-substrate systems in Vickers hardness test. MARC™, a routine finite element software package was used on the following samples: bulk aluminium, bulk steel and their respective film-substrate systems, i.e., aluminium on steel as soft film on hard substrate and steel on aluminium as reverse situation. The results are given in two different cross-sectional planes, i.e., through opposite pyramidal edges and perpendicular to pyramidal side faces. In all cases the calculation provides a general view of the deformation characteristics, but also values for material displacement and the extension and shape of the stress fields as well as the plastically deformed zone under load or after load release. The indenter load versus indentation depth relation during loading and unloading are also calculated for all the examples.

Structure-function relationships in an antifreeze polypeptide. The role of neutral, polar amino acids.

An alanine-rich, alpha-helical antifreeze polypeptide (AFP) from the winter flounder and seven analogs with variations in the arrangement of neutral, polar amino acids were synthesized. Circular dichroism studies determined that all of the peptides, except for one containing a proline residue, were essentially 100% alpha-helical. Freezing point depression data, analyzed by three methods, showed that rearrangement of polar residues resulted in moderate to complete loss of anti-freeze activity. It was observed that ice crystals grow as hexagonal bipyramids in dilute solutions, with a constant c to alpha axis ratio of about 3.3. Above a critical threshold concentration, which may depend on the AFP to ice binding constant and reflect the onset of cooperative interactions, growth ceases until the temperature is lowered to the freezing point. We conclude that a specific arrangement of both threonine and asparagine (or aspartic acid) residues is critical for maximal activity and that the AFPs probably bind to the pyramidal faces of ice with a specific orientation. These conclusions are consistent with a recent report (Knight, C. A., Cheng, C. C., and DeVries, A. L. (1991) Biophys. J. 59, 409-418) that a similar AFP adsorbs to the [2021] pyramidal planes of ice in dilute solution.

Kinetic Investigations within the Transition Region from Polyhedral to Skeletal Growth Mode (V). Growth Kinetics of the Pyramidal Face of Zinc Single Crystals under Diffusion Conditions

Kinetic Investigations within the Transition Region from Polyhedral to Skeletal Growth Mode (V). Growth Kinetics of the Pyramidal Face of Zinc Single Crystals under Diffusion Conditions

Effect of impurities on the growth of KDP crystals: Mechanism of adsorption on (101) faces

The results of the dependence of growth rate, R 001, along 〈001〉 directions of KDP crystals in aqueous solutions at 30°C on the concentration c i, up to 4.0×10 -6 mol/mol, of Fe 3+ and Cr 3+ impurities in aqueous solutions at different supersaturations are presented and discussed. It is observed that with an increase in c i, in the case of Fe 3+ impurity R 001 first increases and then decreases at 4.2% supersaturation. For Fe 3+ impurity at 6.3% supersaturation and for Cr 3+ impurity at 6.3% and 8.55% supersaturations, R 001 regularly decreases with an increase in c i. At 13% supersaturation, R 001 increases with an increase i n the concentration of both Fe 3+ and Cr 3+ impurities. The effect of impurities on growth rates at 4.2%, 6.3% and 8.5% supersaturations is discussed in terms of changes in the thermodynamic and kinetic parameters involved in the crystal growth theories. The increase in R 001 at 13% supersaturation is, however, explained by considering the formation of three-dimensional impurity nuclei on the pyramidal faces. The analysis suggests that adsorption of both Fe 3+ and Cr 3+ impurity takes place at kink sites on (100) and (101) faces.

Three-dimensional structures of natural snow crystals shown by stereo-photomicrographs

Stereo-photomicrographs of natural snow crystals are shown. They are useful to clarify the three-dimensional nature of natural snow crystals. Most of the plate-like snow crystals consist of two or more plates in different levels. Single plate crystals are rather rarely observed in natural snow crystals. Most of the columnar crystals are hollow so that the 46° halo is rarely observed, because of the lack of a refracting angle of 90°. Apparent pyramidal faces of bullet crystals are not the crystallographic faces but only mere skeleton structures. This finding can explain why the 8° halo is rarely observed in nature, even though bullet crystals are common in cirrus or cirrostratus clouds.

The influence of pH on the habit and the rate of α-LiIO 3 crystal growth

The influence of the pH on both the habit and the growth rate of α-LiIO 3 crystals grown from solution by a constant temperature evaporation method has been studied under static and rotary conditions. The results indicated that the morphology of the α-LiIO 3 crystals grown had hexagonal prismatic faces {10ovbar|10} and hexagonal double pyramidal faces {10ovbar|11} and that the crystal growth rates along the z-direction V [0001] were faster than the rates in the opposite z-direction V [000 1 ] if the pH was more than a critical amount (pH c). If however, the pH was less than pH c, then the crystal habit was bounded by the prismatic faces {10ovbar|10} and the pyramidal faces {10ovbar|11} and {12ovbar|32}, and V [0001] was slower than V [000 1 ] . The mechanism to explain the reversal of the growth rate at pH c was proposed by means of the electrical double layer theory and the molecular adsorption theory.

Zircon in charnockitic rocks from rogaland (southwest Norway): Petrogenetic implications

Zircons separated from monzonoritic rocks and quartz mangerites (igneous and metamorphic) have been studied for various mineralogical, chemical and physical properties (colour, zoning, presence of core, U distribution, morphology, lattice parameters, thermoluminescence) to determine the relationships with chemical composition of the host rocks and geological setting. The zircons grade from nearly perfectly crystalline to slightly metamict types. The crystal morphology shows prismatic habits and a striking lack of well-developed pyramidal faces, possibly indicating growth in a dry formation environment. The zircons can be divided into two groups. The first one comprises zircons from monzonoritic rocks. They are unzoned, devoid of brownish core, with a uniform U distribution, and low U content (except in Hidra). The second group comprises zircons from igneous and metamorphic quartz mangerites; they contain brownish, zoned, U-rich cores. In rocks where temperature of crystallization can be determined, Watson and Harrison's (1983) experimental data indicate strong zircon saturation. The cores are considered as inherited, a fact that can be accounted for either by dry anatexis or bulk contamination. In the Bjerkreim-Sokndal layered lopolith, previous isotopic data are confirmed, which indicate that the acidic upper part of the massif is not comagmatic with the anorthosito-noritic lower part and the monzonoritic rocks.

Enlargement of the cross section of KDP crystals by splicing techniques

Splicing techniques have been developed to speed up the enlargement of the cross section of KDP crystals. An n 2 ( n = 1, 2, 3, 4,…) array of {001} or {101} oriented seeds has been applied to grow KDP crystals of up to 72 cm 2 in cross section. X-ray topography and laser scanning tomography were used to characterize KDP crystals which were grown together by seed splicing. Clear crystals, which are free from cracks and dislocations, have been successfully grown after a second generation. The results of the present work demonstrates that the growth of large size KDP crystals with tigh perfection for, among others, laser technology would be feasible, using splicing techniques. It follows from X-ray topographs that, if two seeds are mounted together with a misorientation of about 1°, during growth a locally highly stressed area develops between the uniting seeds, which can be characterized as a quasi-large-angle boundary. The strongly disturbed boundary region proceeds in a direction normal to the growing pyramidal face (101) and grows out of this crystal at the adjacent prism face after travelling a small distance through the crystal. After this boundary has left the crystal, it continues to grow as one perfect crystal having the same quality as a “one-seed crystal”. Thanks to the splicing process, however, the diameter of the KDP crystal is enlarged.

Surface microtopographic study of KDP crystals grown at the boiling point

Abstract The surface microtopography of prism and pyramidal faces of KDP crystals grown at the boiling point is investigated. Inclusions, block structures and isolated growth hillocks are observed. The origin of these growth structures and the mechanism of growth of the crystals are discussed. From an analysis of the results it is inferred that the formation of inclusions, block structures and growth hillocks (dislocations) is determined by the behaviour (i.e. association, dissociation and rearrangement) of growth steps and that the crystal grows by the pilling up of layers originated by two-dimensional nucleation, dislocation or other defects on the surface.

The mechanism of tapering on KDP-type crystals

The anomalous wedge-like shape of KH2PO4-type single crystals, also called tapering, is reconsidered. A reformulation of the problem is given on the basis of a detailed observation of the boundary between prismatic and pyramidal growth sectors by means of transmitted light polarization microscopy. A narrowing of both pyramidal and prismatic sectors can be identified to constitute tapering. The first being due to an overall retardation of prismatic growth layers caused by impurity adsorption, whereas the narrowing of the pyramidal sectors is due to the inability of pyramidal growth layers to reach the prismatic crystal edge. The retardation of pyramidal growth layers can be explained in terms of a change in electrostatic parameters near the crystal edge or by assuming a fundamental roughness of the crystal edge. A connected net analysis shows the presence of two equally stable {022} nets parallel to the pyramidal faces. In a polar environment this equality is broken, favouring a {011} double layer growth mechanism which can also explain in principle the low segregation coefficient for three-valent positive metal ions in the pyramidal growth sector.

Microscopic investigations of morphological structures on the pyramidal faces of KDP and DKDP single crystals

AbstractStudying a number of {101} faces of KDP and DKDP single crystals in the as‐grown state we found in most cases one, rarely few, clearly stepped growth hillocks covering the whole face. The geometry of these growth hillocks was determined from photomicrographs; the step heights were measured with a profilometer. To prove our results we carried out X‐ray topographic investigations and in‐situ observations on KDP crystals. In addition we studied the as‐grown faces of ADP and LiJO3 single crystals.

Effect of recrystallization on the characters of alite in Portland cement clinker

Alite, as well as belite, undergoes recrystallization during clinkering and grows large at the expense of small crystals. The growth is more noticeable in the direction perpendicular to (0001) than in the direction parallel to it. The crystals that are initially basal tablets become massive granules with the pyramidal faces well-developed. The recrystallization causes a considerable decrease in the concentration of the foreign ions in solid solution and thus occasionally lowers the crystal symmetry of elite to triclinic. These observations give evidence that the chemical composition of alite depends on its kinetics of crystallization from the interstitial melt.

Evidence for spiral growth on the pyramidal faces of KDP and ADP single crystals

Microscopic observations of the pyramidal {101} faces of KDP (KH 2PO 4) and ADP (NH 4H 2PO 4) single crystals grown from aqueous solutions revealed that three different types of growth features are possible: growth hillocks, cooperating growth spirals with macro step heights of a few hundredsÅngströms and nucleation. From the correspondence between the locations of the growth hillocks and the etch pits formed after slightly dissolving the crystal in water, the growth hillocks could be identified as growth spirals, mostly originating from single dislocations. The growth spirals consisting of macro steps could be related to dislocation bundles. These bundles are often formed due to lattice closure errors after the formation of a liquid inclusion. Some typical phenomena as pseudo eccentricity of the growth spirals, step retardation due to strain fields and rhythmical bunching have been observed. In the case of highly perfect KDP crystals with hardly no dislocations ending on the {101} faces, crystal growth is governed by a nucleation mechanism.

福岡県田川郡香春三ノ岳産,Zn,Mgを含むマンガンジテッ鉱の鉱物学的性質

Mineralogical properties of large single crystals of Zn and Mg-bearing manganoan magnetite from Kawara-Sannotake, were described. The magnetite crystals which are 2.5 cm in maximum diameter, take the basic form of rhombic dodecahedron with frequent combination of smaller face of o(111) and unusual pyramidal face m(311). A typical example of chemical formula for the magnetite crystals, determined by electron microprobe analysis is given below.(Zn0.402+Mn2.452+Fe5.153+)8.00[Mg0.473+Fe4.652+Fe10.873+]15.99O32.00A precise determination of lattice parameter for this magnetite gave 8.4387 A, which is larger than that of foliated magnetite of ordinary composition from the same locality, 8.3940 A. Specific gravity is 5.089 measured and 5.080 calculated. In polished sections of the manganoan magnetite crystal, pyrrhotite, chalcopyrite and quartz can be observed as inclusions. Reflectivity in air for this crystal seems to be somewhat darker than that of the foliated magnetite. Its intensity of magnetization at 19°C under external magnetic field of 10 K·Oe attains 93.1 emu/g, and the theoretical value based on the cation distribution in its crystal structure at 0°K is calculated to be 106.5 emu/g, whereas the ordinary magnetite shows 96.7 emu/g. Curie temperature of the manganoan magnetite is 466°C, which is lower than that of ordinary magnetite, 580°C. DTA experiments carried out in air show two exothermic reactions. The lower temperature peak at 300°C is small but sharp, and the other exothermic plateau starts rapidly from its Curie temperature. The Zn and Mg-bearing manganoan magnetite crystals are supposed to be generated by reaction of locally pre-existing iron-manganese ore formation with hydrothermal solution, which involves Zn, Mg and (Sn ?), etc., as the later different mineralization from the skarnization widely developed in this area.

Unusual Types of Single Ice Crystals Originating from Frozen Cloud Droplets

Abstract Laboratory experiments were conducted to study the formation process of unusual types of ice crystals, using a cold chamber in the temperature range −15 to −25°C. Ice crystals of the bottle type seem to originate from frozen water droplets with spicules. Ice crystals of twin columns (or twin bullets) with plates were found. By observing the various stages of development of pyramidal faces of ice crystals with plates and ice crystals of “single bullet” type–it was concluded that these pyramidal portions of ice crystals may originate from the spicule of frozen droplets or from hemispherical frozen droplets, and that the pyramidal faces can survive further growth at temperatures colder that −25°C.