Quantitative plane-resolved crystal growth and dissolution kinetics by coupling in situ optical microscopy and diffusion models : the case of salicylic acid in aqueous solution

The growth and dissolution kinetics of salicylic acid crystals are investigated in situ by focusing on individual microscale crystals. From a combination of optical microscopy and finite element method (FEM) modeling, it was possible to obtain a detailed quantitative picture of dissolution and growth dynamics for individual crystal faces. The approach uses real-time in situ growth and dissolution data (crystal size and shape as a function of time) to parametrize a FEM model incorporating surface kinetics and bulk to surface diffusion, from which concentration distributions and fluxes are obtained directly. It was found that the (001) face showed strong mass transport (diffusion) controlled behavior with an average surface concentration close to the solubility value during growth and dissolution over a wide range of bulk saturation levels. The (1̅10) and (110) faces exhibited mixed mass transport/surface controlled behavior, but with a strong diffusive component. As crystals became relatively large, they tended to exhibit peculiar hollow structures in the end (001) face, observed by interferometry and optical microscopy. Such features have been reported in a number of crystals, but there has not been a satisfactory explanation for their origin. The mass transport simulations indicate that there is a large difference in flux across the crystal surface, with high values at the edge of the (001) face compared to the center, and this flux has to be redistributed across the (001) surface. As the crystal grows, the redistribution process evidently can not be maintained so that the edges grow at the expense of the center, ultimately creating high index internal structures. At later times, we postulate that these high energy faces, starved of material from solution, dissolve and the extra flux of salicylic acid causes the voids to close

In Situ SR-XPS Observation of Ni-Assisted Low-Temperature Formation of Epitaxial Graphene on 3C-SiC/Si

Low-temperature (~1073 K) formation of graphene was performed on Si substrates by using an ultrathin (2 nm) Ni layer deposited on a 3C-SiC thin film heteroepitaxially grown on a Si substrate. Angle-resolved, synchrotron-radiation X-ray photoemission spectroscopy (SR-XPS) results show that the stacking order is, from the surface to the bulk, Ni carbides(Ni(3)C/NiC(x))/graphene/Ni/Ni silicides (Ni(2)Si/NiSi)/3C-SiC/Si. In situ SR-XPS during the graphitization annealing clarified that graphene is formed during the cooling stage. We conclude that Ni silicide and Ni carbide formation play an essential role in the formation of graphene

Interpretation of field-ion images from ordered Ni<SUB>4</SUB>Mo

A computer simulation procedure with which it is possible to simulate field-ion images from all the thirty domain orientations of ordered Ni4Mo has been devised. It is shown that the shell thickness to be used in the computer simulation of ordered alloys is more than that for pure metal specimens of equal radius. The interaction between prominent planes across domain boundaries in field-ion images of Ni4Mo has been worked out. Exidence for this is presented in the fom of simulated patterns

Contrast from twin boundaries in field-ion micrographs

Computer simulation and geometrical construction have been used to study the contrast from twin boundaries in field-ion micrographs. For specific orientations of the twin boundary, m rings of (hkl) planes in the matrix are expected to match with n rings of (h'k'l) planes in the twin, where m and n are integers and (hkl) and (h'k'l) are prominent planes in the matrix and the twin, respectively

The structure and growth of hollow conical single crystals of cadmium sulphide

Single crystals of CdS were grown from the vapour phase under varied conditions to detect the presence of growth faults and polytypic structures analogous to those exhibited by ZnS. No polytypism was found as all crystals displayed only the 2H structure. The addition of a little Cdl2 as impurity during crystal growth resulted in the formation of hollow conical single crystals with no change in the structure. The possible mechanism for growth of these crystals is discussed

An Atom-Probe Study of Retained Austenite in Ferritic Weld Metal High-resolution analytic techniques are used to quantitatively prove the distribution of boron and carbon in weld metal

ABSTRACT. The addition of titanium and boron to welding consumables results in an acicular ferrite microstructure that imparts excellent toughness to the weldment. An atom-probe field-ion microscopic study was carried out to study the influence of carbon and boron on the ya transformation in a ferritic weld metal and on the formation of acicular ferrite. It was observed that carbon diffuses into the remaining austenite when acicular ferrite is formed. The retained austenite can be enriched up to 7 at.-% with carbon, and it showed to be stable at a temperature of 90 K after removing some of the surrounding acicular ferrite grains. The atom-probe analysis did not indicate the presence of boron either at the y-oc interface or in the retained austenite grain

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Not AvailableA large portion of unused crop residues is burnt in the fields primarily to clear the left-over straw and stub bles after the combine harvest. Studies have reported several ill effects of crop-residue burning on soil orga nic carbon and fertility, including reduction in produc tivity in the long term, environmental pollution and human health. It also produces greenhouse gases causing global warming. Rice and wheat produce large amounts of residue in India. Non-availability of labour, the high cost of residue removal from the field and the increasing use of combines in harvesting the crops are the main reasons for burning crop residues in the fields. Rice straw is unsuitable animal feed due to its high silica con tent and wheat straw for due to its hard stem and diffi culty chewing in unchopped form. Using supplements like urea and is feeding straw sprayed with urea impro ves its nutritive value and intake. We have developed a mechanized baler equipped with a urea spraying system for spraying urea during baling operations on crop resi dues (paddy or wheat straw) to enhance their nutritional value. The developed system was evaluated in combine a harvested wheat residue field and nutritional analysis was performed. The crude protein in untreated wheat straw increased from 3.68% to 10.10% after urea treatment. The metabolizable energy was also found to improve by 3% compared to untreated straw. Thus, urea-treated bales have potential use in dairy farming.Not Availabl