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Optical Crystals
Published in Marvin J. Weber, and TECHNOLOGY, 2020
Cleavage is the tendency of a crystal to break in a certain direction yielding a relatively smooth surface. It depends on the internal structure of a crystal and can be problematic in material fabrication. The ease of cleavaging varies greatly depending on the crystal quality and the nature and direction of stress applied. In many crystals there can be more than one set of cleavage planes. However, in almost all cases only the weakest cleavage plane dominates. We use Miller indices to denote the cleavage planes. One should also note that the actual number of cleavage planes depends on the plane orientation relative to the symmetry of the crystal. For example, in the cubic system, the (100) cleavage plane has three orientations and the (111) cleavage plane has four. In the hexagonal system, there is only one (0001) cleavage plane, but three (1011) ones. In the monoclinic system, there is only one (010) cleavage plane but two (110) ones. We list only the easiest cleavage plane for each crystal. We rank them qualitatively as perfect (p) or imperfect (i). This definition is very loose. A crystal listed with a perfect cleavage plane can crack along that direction with a smooth surface if a stress is applied. The imperfect cleavage plane means that the crack does not easily move along the plane. However, a small area of oriented flat surfaces can form along the cracking surface when the crystal is fractured.
Minerals
Published in Dexter Perkins, Kevin R. Henke, Adam C. Simon, Lance D. Yarbrough, Earth Materials, 2019
Dexter Perkins, Kevin R. Henke, Adam C. Simon, Lance D. Yarbrough
If a mineral fractures to produce multiple planar and smooth surfaces, the mineral has good cleavage. If a mineral cleaves along one particular plane, a nearly infinite number of parallel planes are equally prone to cleavage. This is due to the repetitive arrangement of atoms in atomic structures. The spacing between planes is the repeat distance of the atomic structure, on the order of angstroms (Å). The whole set of parallel planes, collectively referred to as a cleavage, represents planes of weak bonding in the crystal structure. Micas are the best examples of minerals with one excellent cleavage—they break easily into sheets of very small thickness. Minerals that have more than one direction of weakness will have more than one cleavage direction. The direction and angular relationships between cleavages, therefore, give valuable hints about atomic structure.
Rock Forming Minerals
Published in Aurèle Parriaux, Geology, 2018
Cleavages are particular fracture planes along which a crystal breaks preferentially when subjected to a mechanical stress. It can be compared to a brick wall damaged by an earthquake: cracks appear at places where the bricks are joined but few bricks are broken.
Physico-chemical characterization of detrital sillimanite and garnet: Insights into REE elements, crystal structure and morphology
Published in Marine Georesources & Geotechnology, 2022
Rajan Girija Rejith, Mayappan Sundararajan, Sreekantaiyer Ramaswamy, Abdul Azeez Peer Mohamed, Manavalan Satyanarayanan
The SEM images of sillimanite are given in Figure 6. Sillimanite grains are seen as prismatic with rounded edges (Figure 6(a–e)). Conchoidal fractures with moderate relief can be seen. Removal of blocks and cleavage controlled step-like features besides the fracture plates are found next to crystal cleavage (Figure 6(g)). Irregular pits, grooves, impact V's, and solution channels are formed by the mechanical impact due to chemical action. Smoothening of the surface shows rolling topography. Some precipitation features are also noticed on the surface (Figure 6(h)) (Mallik 1986).The SEM-EDS results are shown in Figure 7(a) and Table 9. The EDS shows the concentration of Al and Si, and thereby it confirms that the mineral is sillimanite (Yugeswaran et al. 2011).The SEM images of the garnet are shown in Figure 8. Garnet grains are usually seen as highly angular with moderately high relief and show conchoidal fractures (Figure 8(a–f)). Undulatory planes and embayments are formed due to the solution effect. Large depressions with precipitation are seen on the surface due to etching. Removal of inclusions forms irregularly rounded pits (Figure 8(b)). Impact “V” modified by etching forms grooves and pits (Mallik 1986). Figure 7(b1–b2) and Table 10 show the SEM-EDS results of garnet. The EDS shows a high content of Fe K ranges 23.72–27.46% confirming the garnet belongs to the almandine group.
Application of the Optimized Pre-ozonation Treatment for Potential Resource Recovery from Industrial Textile Effluent
Published in Ozone: Science & Engineering, 2022
From the 126.2% increase in the SOUR and 81.8% increase in the biodegradability index, it can be observed that the biodegradability of real textile effluent was significantly improved after pre-ozonation treatment. The biodegradability of hydrolyzed dye compounds is limited due to the polyaromatic structure and presence of complex auxo chrome groups like -SO3Na. The bioavailability of complex compounds increases with the reduced molecular weight, higher solubility, and presence of simpler functional groups such as -OH and -COOH (Vikrant et al. 2018). The ozone molecules first react with the carbon atom from an aromatic ring attached to the azo group leading to the formation of diazonium ion and cleavage of the azo group. Due to the reaction of the ozone molecule with C = C in dye molecules, two C = O groups are produced, leading to aromatic ring cleavage. This leads to the formation of simpler organic compounds like oxalate, formate, and benzenesulfonate (Paździor, Bilińska, and Ledakowicz 2019), which are readily biodegradable. Even though the direct nucleophilic attack by ozone molecule leads to the azo group and aromatic ring cleavage, the triazine group was found to remain unaffected during ozonation treatment, highlighting the need for following biological treatment.
Sintering behavior and mechanical properties of machinable zirconia/mica composites
Published in Journal of Asian Ceramic Societies, 2019
Seiichi Taruta, Issei Yamaguchi, Tomohiko Yamakami, Tomohiro Yamaguchi
On the other hand, mica glass-ceramics are well-known machinable ceramics [37] that are applied as dental materials [37,38]. Also, machinable cordierite/mica [39], spinel/mica [40] and alumina/mica [41] composites have been successfully fabricated utilizing the excellent cleavage of mica. While machinable composites containing the h-BN [28–34] and MAX phases [35,36] are fabricated using special sintering methods with expensive apparatuses (e.g. hot pressing and SPS), machinable composites containing mica [39–41] can be fabricated without such expensive sintering apparatuses. Compared with machinable composites containing rare-earth phosphates [20–27], machinable composites containing mica [39–41] can be produced with low-temperature sintering because of sintering through a liquid phase formed by melting raw mica materials.