دانلود رایگان مقاله لاتین جابجایی لبه در سیلیکات دی کلسیم از سایت الزویر
عنوان فارسی مقاله:
جابجایی های لبه در سیلیکات دی کلسیم: مشاهدات تجربی و تجزیه و تحلیل مربوط به اتم
عنوان انگلیسی مقاله:
Edge dislocations in dicalcium silicates: Experimental observations and atomistic analysis
سال انتشار : 2016
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مقدمه انگلیسی مقاله:
1. Introduction
Defects such as stacking faults and dislocations, which form and propagate in crystals, significantly impact many chemical and physical properties of materials. For example, material plasticity and crack propagation are markedly influenced by dislocation core structure, dislocation-dislocation interactions, and dislocation mobilities [1]. Similarly, crystal growth can be affected by both screw [2] and edge screw dislocations [3–4]. Although dislocations have been extensively studied in metals [5–8] semiconductors [9–13] and some simple ceramics, [14–21] there have been few attempts in characterizing such defects in more complex compounds such as zeolites, forsterite (Mg2SiO4) and dicalcium silicates (Ca2SiO4) [22]. The difficulty arises due to the complicated formatting components, heterogeneous nature, and the packing arrangements of several atomic species, which often lead to low symmetry crystals. Several experimental techniques are used to study dislocations including surface and decoration methods, field ion microscopy, X-ray diffraction, high resolution transmission electron microscopy (HRTEM) and Z-contrast imaging techniques [1,23–25]. While these experiments provide means to observe and infer information about the dislocation structure, distribution and arrangement, they cannot provide precise information on dislocation energetics and mobilities, which often control the dislocations slip, slip-planes and other dislocation-mediated phenomena such as macro scale ductility and crystal growth. From a modeling standpoint, although semi-continuum Peierls-Nabarro models [26–27] are widely used to study dislocations by introducing the energies of generalized stacking faults from density functional theory to continuum model of the dislocations, the significant constraint of planar dislocations limits their applicability [28]. Alternative approaches use atomic scale simulations to calculate explicitly the dislocation core structure. In this group, fully periodic dipole approaches can simulate an infinite array of dislocations (e.g. line defects in silicon [10–11], extended defects in diamond cubic crystals [29], and impurities at edge dislocations [9]). However, this method is less straightforward for complex crystals, due to the correction for interactions between dislocation core fields [30–31], and contributions from core traction in the dislocation formation energy [32]. Recently developed cluster embedded models [33–34], based on one-dimensional periodic boundary conditions, allow to investigate systematically an isolated dislocation with atomic-scale fidelity. The cluster model, employed in this work, has been already highly successful in predicting the core energy and structure of dislocations in different material classes including ionic materials (MgO) [34], zeolites [35], wadsleyite minerals (β-Mg2SiO4) [36] and paracetamol (OH-C6H4NHCOCH3), a widely used drug known as acetaminophuse [34]. The objective of the present work is to study edge dislocations in structurally complex and low symmetry oxides, which are of both scientific and technological importance. As a model system, we focus on five reversible polymorphs of dicalcium silicates (Ca2SiO4), key ingredients of industrial cement clinkers where the defect characteristics and integrity of Ca2SiO4 crystals' structures play a key role in clinker grinding processes as well as crystal growth mechanisms [37]. The latter is of particular significance in hydration of Ca2SiO4 to precipitate semicrystalline, non-stoichiometric calcium-silicate-hydrate (C-S-H) phase, which is the chief source of strength and durability in cementitious materials [37–38]. Compared to tricalcium silicate (Ca3SiO5), the more energy-intensive and dominant ingredient of the cement clinker, Ca2SiO4 (also known as belite with shortened notation of C2S in cement chemistry) needs at least ~100 °C lower temperature to produce. However, it requires more energy for grinding it and reacts slower with water, thereby leading to delayed strength development in cement paste [39]. But given the overall economical gain due to lower manufacturing temperature of Ca2SiO4 and the augmented need to reduce greenhouse gas emissions from cement plants (currently cement manufacturing is responsible for 5–10% of the worldwide anthropogenic CO2 emissions), there is an urgent necessity to tune grinding properties and reactivity of Ca2SiO4 to make it a more sustainable cement clinker. In this perspective, understanding the defects and edge dislocations in Ca2SiO4 can provide important information on how to modulate and promote the salient properties of Ca2SiO4. Ca2SiO4 has a crystalline structure that is composed of SiO4 4− tetrahedra and Ca2+ ions with a sequence of five reversible polymorphs, namely α, αH, αL, β and γ, from high to low temperatures (Fig. 1). X-ray analysis [40] have provided the exact crystal and atomic structure of these polymorphs, which can be transformed from one to another via changing the crystal symmetry, disorder of SiO4 4− groups and slight changes in the position of the Ca2+ atoms [41–44]. The α and β polymorphs have monoclinic crystals while αH, αLand γ polymorphs have orthorhombic crystals [37] (Fig. 2).
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کلمات کلیدی:
Screw Dislocations in Complex, Low Symmetry Oxides: Core ... pubs.acs.org/doi/abs/10.1021/am5091808 by R Shahsavari - 2015 - Cited by 15 - Related articles Jan 7, 2015 - Screw Dislocations in Complex, Low Symmetry Oxides: Core .... Edge dislocations in dicalcium silicates: Experimental observations and ... Edge dislocations in dicalcium silicates: Experimental observations ... https://trid.trb.org/view.aspx?id=1428152 by R Shahsavari - 2016 - Cited by 3 - Related articles Oct 28, 2016 - Understanding defects and influence of dislocations on dicalcium silicates (Ca₂SiO₄) is a challenge in cement science. The authors report a ... Glide dislocations in diamond: first-principles calculations of ... iopscience.iop.org/article/10.1088/0953-8984/14/48/304/meta by MI Heggie - 2002 - Cited by 19 - Related articles We review first-principles calculations of dislocation core structure in diamond, and .... Edge dislocations in dicalcium silicates: Experimental observations and ... Structure, Energetics, and Impact of Screw Dislocations in Tricalcium ... onlinelibrary.wiley.com/doi/10.1111/jace.14255/abstract by R Shahsavari - 2016 - Cited by 5 - Related articles Apr 8, 2016 - This study focuses on atomistic analysis of screw dislocation in three thermodynamically reversible polymorphs of tricalcium silicate (Ca3SiO3), ... Cement gets its close-up: Team explores cement's crystalline nature to ... https://phys.org › Chemistry › Materials Science Oct 3, 2016 - A close-up view of an edge dislocation defect in a cement crystal ... Edge dislocations in dicalcium silicates: Experimental observations and ...
