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Basic of the Chalcogenides
Published in Abhay Kumar Singh, Tien-Chien Jen, Chalcogenide, 2021
Abhay Kumar Singh, Tien-Chien Jen
As described above, non-crystalline substances do not possess long-range ordering of atoms in their periodic arrangement. To define non-cystalline solids, some necessary and sufficient parameters need to be followed [88]. To describe the simplest ideal single crystal structure, it is essential to know the structure of an elementary cell or a short-range order of the arrangement of atoms. Therefore, it is necessary to add at least one defective subsystem to define any real single crystal. In the case of describing the polycrystal structure, both short-range ordering and addition of defects are desired. Along with materials morphology such as crystal size distribution, crystal texture, formation of spherulites are also important parameters. Therefore to consider any substance as a non-crystalline solid the following four parameters should be defined: Short-range order of atomic arrangementMedium-range order of atomic arrangementMorphologyDefect subsystem
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Published in Joseph C. Salamone, Polymeric Materials Encyclopedia, 2020
Spherulite is a spheriform cluster of primary crystallites with spherical symmetry. Crystallites start from a central nucleus and uniformly grow in all spatial directions, radially, with noncrystallographic small-angle branching in between. The branching of growing crystallites provides complete space filling. A spherulite can be considered an optically uniaxial crystal. Therefore, the PLM micrograph of a spherulite shows a dark central cross (Maltese cross) with wings coincident with the respective plans of polarizer and analyzer.
Crystalline Polymers
Published in Timothy P. Lodge, Paul C. Hiemenz, Polymer Chemistry, 2020
Timothy P. Lodge, Paul C. Hiemenz
On the basis of a variety of experimental observations, including an analysis of the ubiquitous Maltese cross, a number of aspects of the structure of spherulites have been elucidated. The spherulites are aggregates of lamellar crystals radiating from a single nucleation site. The latter can be either a spontaneously formed single crystal or a foreign body. The spherical symmetry is not present at the outset, but develops with time. Fibrous or lath-like lamellar crystals grow away from the nucleus, and begin branching and fanning out. As the lamellae spread out radially and three-dimensionally, branching of the crystallites continues to sustain the spherical morphology. Figure 13.24 represents schematically the leading edge of some of these fibrils, one of which has just split.
Cylindrically symmetric rotating crystals observed in crystallization process of InSiO film
Published in Science and Technology of Advanced Materials: Methods, 2023
Bo Da, Long Cheng, Xun Liu, Kunji Shigeto, Kazuhito Tsukagoshi, Toshihide Nabatame, Zejun Ding, Yang Sun, Jin Hu, Jiangwei Liu, Daiming Tang, Han Zhang, Zhaoshun Gao, Hongxuan Guo, Hideki Yoshikawa, Shigeo Tanuma
The different colors in the EBSD-normal direction (ND) maps in Figure 2(b) indicate the different orientations inside the rotating crystal islands. Orientation changes are visible within one island, and there is only one snowflake-like crystal ‘grain’ without any significant crystal misorientation boundary in each rotational crystal island. The image analysis shows that the central area of every rotational crystal island spherulite has a homogeneous orientation rotational velocity, branching into larger features with a slightly different orientation rotational velocity upon further growth. However, it should be noted that such a rotational crystal is still a whole grain, which is entirely different from the previously reported ones [51,72] with spherulites that are spherical (or circular) structures consisting of fibers growing radially and quasi-isotopically from a single nucleation point. The orientation of the different island centers varies within a limited number of orientations, including [211], [222], [440], [400], and [622] zone axes, consistent with the observation from our XRD experiment [44].
Evidence of loss of N2/O2 adsorption selectivity of Li zeolite due to ion exchange between sodium and lithium cations
Published in Chemical Engineering Communications, 2023
Nathaphon Ardhan, Sasikarn Nuchdang, Supak Tontisirin, Chantaraporn Phalakornkule
Figure 6 shows the SEM images of the active, inactive and regenerated samples. The shapes of the zeolite beads can be observed from the SEM images at 70 times magnified with a scale of 500 µm. The beads of the active sample had round shape and smooth surface, while the beads of the inactive and regenerated samples showed some distortion. In addition, the surfaces of the beads in the inactive and regenerated samples became less smooth and some cracks appeared. The changes in the shapes and surfaces of the beads in the inactive and regenerated samples might be associated with an expansion of the zeolite framework. It has been reported in the literature that the structure of exchanged zeolite could expand due to ion exchange processes. For example, it was reported in Price et al. (2017) that the unit cell size of zeolite A increased after exchanging the Na+ ions with larger cations, e.g., K+ and Ca2+. The crystal morphology of the zeolite samples can be observed from the SEM images at 6,000 times magnified with a scale of 10 µm. The crystal morphology of the zeolites was a spherulite shape with crystallite size ca. 3-4 µm in diameter. The morphology was similar to that of LSX reported in Tontisirin (2015).
When hydrogen bond tailors molecular packing in non-anisometric molecules. The case study of N-alkyl 1,3-diphenyl-4,5-dihydro-1H-pyrazole-5-carboximidamides
Published in Liquid Crystals, 2021
Sumana Y. Kotian, Shridevi D, Srikantamurthy Ningaiah, Aloir A. Merlo, André A. Vieira, Ivan H. Bechtold, K. M. Lokanatha Rai
Upon heating, none of the target pyrazolines showed liquid crystal properties, the only transition from the crystal phase to the isotropic phase was recorded (Table 1). Upon cooling, pyrazolines with long alkyl chains (n = n-dodecyl, n-tetradecyl, n-hexadecyl, n-octadecyl) exhibited a texture under cross polarisers that can be related to a monotropic columnar mesophase (Colh). This texture upon cooling from the isotropic phase is shown in Figure 1. XRD data collected for four homologous are summarised in Table 2. Notably, compounds 4d-4g possess a weak tendency towards crystallisation upon cooling. Figure 2 displayed a collection of pictures that were taken of the 4d-4g where the spherulite-like texture is dominant with some domains are formed by the crystal phase. The texture formation quality is dependent on the size of the alkyl group and the cooling rate. For short alkyl chains such as found in 4a, 4b and 4c, the crystalisation process is faster than the formation of spherulite-like texture as observed for longer alkyl groups. The results in POM for longer alkyl groups 4d-4g showed that the samples sandwiched between a glass slide and coverslip remain stable at room temperature for days without any crystallisation.