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Basic Principles in Crystallization
Published in Gerard F. Arkenbout, Melt Crystallization Technology, 2021
As follows from the preceding, crystals, e.g., in suspension, grow by the advance of the individual faces being present on the crystal. Usually, each face will grow at a different rate, and the relative growth rates of different faces determine the crystal habit or shape. Faster growing faces tend to grow out of the crystal, and by this, the slower growing ones make up the major part of the crystal surface.
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Published in Chad A. Mirkin, Spherical Nucleic Acids, 2020
Christine R. Laramy, Matthew N. O’Brien, Chad A. Mirkin
One approach to overcoming these experimental limitations and realizing lower-symmetry single crystals with spherical building blocks relies on three design principles: first, crystallization into a non-cubic unit cell; second, strong preference for a single structure (to minimize defect formation); and third, sufficient differences in facet growth rates to result in a well-defined habit [130]. Non-cubic unit cells can possess families of planes in which the constituent planes are not energetically equivalent. Because planes of the same family have symmetry with respect to each other, differences in growth rates may manifest and produce a kinetically favored crystal habit. Recent efforts that satisfy these principles show that a two-component nanoparticle system (DNA design 1) with AB2 symmetry yields an anisotropic crystal habit owing to a barrier to nucleation on one facet within a family of planes [130]. Despite the equilibrium preference for crystals bound by the lowest-surface-energy planes, this system produces a hexagonal prism-shaped crystal habit. The rectangular faces of this habit are bound by the highest surface energy facet (1010), due to a large barrier to nucleation onto this surface, which favors growth along a single direction.
Minerals and rocks
Published in A.C. McLean, C. D. Gribble, Geology for Civil Engineers, 2017
The development of an individual crystal, or an aggregate of crystals, to produce a particular external shape depends on the temperature and pressure during their formation. One such environment may give long needle-like crystals and another may give short platy crystals, both with the same symmetry. Since the mode of formation of a mineral is sometimes a clue to what it is, this shape or crystal habit is of use in the identification of some minerals. The terms used to describe crystal habit are given in Table 2.3.
Synthesis and size control of monodisperse magnesium hydroxide nanoparticles by microemulsion method
Published in Journal of Dispersion Science and Technology, 2020
Haihong Wu, Bijun Luo, Chunjuan Gao, Licong Wang, Yuqi Wang, Qi Zhang
The particle size of magnesium hydroxide synthesized by microemulsion method is mainly determined by two factors: one is the water droplet size in the microemulsion system itself, the “water droplet” is the place where the magnesium hydroxide crystallizes and grows, as the reactants start to nucleate and grow inside such water droplet, they will be restricted by the size and rigidity of the interface layer and hence produce homogenous particles with controlled size. The effect of R value and the isopropanol dosage on particle size are determined by adjusting the water droplet size and the interface layer rigidity. Another factor is the crystal habit of magnesium hydroxide in solution. When the supersaturation is low, the crystal grows faster than the nucleation, resulting in a larger particle size. When the supersaturation is higher, crystal nucleation takes precedence over crystal growth, and the number of nucleation is large, which eventually causes the particle size to become smaller. The effect of Mg2+ concentration and the molar ratio of Mg2+ to OH− on particle size are achieved by affecting the solution supersaturation.
Interpreting geology from geophysics in poly-deformed and mineralised terranes; the Otago Schist and the Hyde-Macraes Shear Zone
Published in New Zealand Journal of Geology and Geophysics, 2019
Casey C. Blundell, Robin Armit, Laurent Ailleres, Steven Micklethwaite, Adam Martin, Peter Betts
Conductivity (mS/m) and resistivity (Ωm) are the reciprocal properties estimated using FDEM methods, and refer to the apparent physical property of rocks and other materials to either conduct or resist the passage of an electric current through their mass. Three main processes contribute to the bulk electrical properties of rocks: mineral conductivity (also electronic or ‘ohmic’ conductivity), electrolytic conduction within pore-space fluid, and at the mineral-fluid interface (i.e. cation exchange capacity, ‘CEC’) (Telford et al. 1990; Schepers 2012). These processes, and therefore resistivity, are further controlled by rock type, metallic content, porosity, effective permeability and salinity, and crystal habit of minerals (Palacky 1987; Schepers 2012; Airo 2015). Processes that lead to hydrothermal alteration, metamorphism, and contribute to metallic mineral precipitation, may significantly affect electrical properties by altering the shape, distribution, connectivity and composition of minerals within a rock mass. Minerals which have appreciable conductive properties include all metallic sulphides (except sphalerite) such as pyrite, graphite, magnetite, and native metals (Airo 2015). Graphite is the only mineral which substantially overlaps the resistivity range of massive sulphides (<1 Ω·m), which were the traditional targets for FDEM exploration (Palacky 1987). Only small amounts of a conductive mineral phase are required to significantly decrease resistivity by several orders of magnitude (Palacky 1987; Telford et al. 1990).
Synthesis, crystal structure and Hirshfeld surface analysis of a new 0D nanostructured [{Ar-Cl)tetra-azo-S}2Hg] coordination supramolecular compound derived from phenyl isothiocyanate ligand
Published in Journal of Coordination Chemistry, 2019
Mohammad Kazem Mohammadi, Roushan Khoshnavazi, Samira Geravand, Mehdi Karimi, Pascal Retailleau, Ardavan Masoudiasl, Payam Hayati, Ghodrat Mahmoudi
The prediction of the growth morphology is comparable to the prediction of growth rates in various crystallographic orientations. The Bravais-Friedel law shows the a priori relationship between the morphological importance (MI) of a crystal face and its interplanar distance dhkl. The MI of a crystal face is generally understood as its relative size in a given crystal habit. Based on the Bravais-Friedel law, the observed crystal faces are those with the largest interplanar distances. The greater the interplanar distance the more important the corresponding crystal face. This law is violated occasionally; therefore, Donnay and Harker extended it by considering the screw axis and the glide planes. In this way, the Bravais-Friedel-Donnay-Harker law (BFDH law) was introduced. This law often gives a satisfactory explanation of crystal morphologies [40(c–f)]. Predicted crystal morphologies of 1 are shown in online supplementary Figure S3. The relevant parameters are reported in online supplementary Table S1. In almost all cases there is a good match between the predicted and observed morphology. It should be noted that in the case of 1, the growth of the coordination material takes place along the [001] directions. Also, nanocrystals of 1 were formed in aqueous solution by ultrasonic irradiation (Table 3).