Atoms, ions or molecules arranged in a certain spatial structure and composition of solid, regular shape. Such as: quartz, mica
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No. 2
Atoms or ions arranged in a certain order, regular shape and some physical properties, chemical composition of solids, such as salt, quartz, mica, such as alum.
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No. 3
Atoms, ions or molecules arranged in a certain spatial order of the solid, regular appearance. Such as salt, quartz, mica, alum, etc.. Also known as crystal or crystal.
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Overview
Crystal atoms, ions or molecules in accordance with a certain periodicity in the crystallization process, the formation of the spatial arrangement of certain rules of solid geometry. Crystal has three characteristics: (1) crystal geometry rules are neat; (2) crystal has a fixed melting point, in the melting process, the temperature remains the same; (3) crystal has anisotropic characteristics. Crystalline and amorphous solid material substances (amorphous solid) of the points, but not amorphous solid does not have these characteristics. Crystal is a three-dimensional space within the particles into periodically repeated in the arrangement of the solid, with long-range order, and arranged into periodically repeated. Non-crystalline particles in the three-dimensional space is not a house periodically repeated array of solid, has a short-range order, but do not have long-range order. Such as glass. Irregular shape for the shape of the solid. Common crystal Synthetic bismuth crystal 1, long-range order: atoms inside the crystal at least within the scope of the rules of micron order. 2, uniformity: the macro-crystal nature of the internal parts are the same. 3, the anisotropy: the crystal in the different directions have different physical properties. 4, the symmetry: the ideal crystal shape and internal structure of the crystal has a certain symmetry. 5, self-limiting: crystals spontaneously form closed geometric properties of polyhedra. 6, solutions Reason: to determine the crystal orientation with the crystal along the surface of some of the nature of splitting. 7, the minimum internal energy: internal energy of the crystal forming the smallest. 8, crystal face angle conservation: the two belong to the same kinds of crystals corresponds to the angle between the planes is constant. Crystal structure composed of particles (molecules, atoms, ions) arranged in space in a regular manner at a certain point, these points have a certain geometry group, called the lattice. Structured particle emission point is called the lattice of those nodes. Diamond, graphite, salt crystal model, in fact, their lattice model. Crystal structure according to the different particles and forces can be divided into four categories: ionic crystals, atomic crystals, molecular crystals and metallic crystals. Solids can be divided into crystal, amorphous and quasi-crystal three categories. Geometry with a neat rule, fixed melting point and anisotropic solid substances, is a basic form of material existence. Whether the crystalline solid material, generally by X-ray diffraction to be identified. The internal structure of the crystal particles (atoms, ions, molecules) are regularly repeated periodically in three-dimensional arrangement of the lattice composed of some form, shape to shape on the performance of the geometric polyhedron. A geometric composition of the plane called the crystal face polyhedra, due to the different growth conditions, crystals may be some skew in appearance, but the same angle between the crystal planes (crystal plane angle) is certain, known as the crystal plane angle is not change principle. According to the internal structure of the crystal can be divided into seven crystal systems and 14 lattice types. Crystal has a certain symmetry, there are 32 kinds of symmetry elements in series, the corresponding action group called the crystal system symmetry point group. According to the different nature of the internal force between particles, the crystal can be divided into ionic crystals, atomic crystals, molecular crystals, metallic crystals such as the four typical crystal, such as salt, diamond, dry ice, and various metals. Crystals have the same single crystal and polycrystalline (or powder) of the difference. In practice, there are still mixed crystals. Speaking of crystal, have talked about from the crystal. We all know, all matter is composed of atoms or molecules from the. As we all know, the material gathered in three forms: gas, liquid and solid. But, you know its internal structure according to the characteristics of the solid can be divided into several classes? The results show that the solid can be divided into crystal, non-crystal and quasicrystal three categories. Crystal is generally present the geometry of the rules, like someone out of the same specially processed. The very regular arrangement of atoms within strict than the phalanx of soldiers but also much more tidy. If any of the crystals in the translation of an atom in a certain direction a certain distance, will be able to find a same atom. The glass, pearls, asphalt, plastic and other non-crystal, the internal arrangement of atoms is chaotic. Quasi-crystal is a recently discovered a new class of substances, their internal arrangement is different from the crystal, but also from non-crystal. What kind of material can be counted as crystal it? First, in addition to liquid crystal, the crystal is generally solid form. Second, the composition of the material of the atoms, molecules or ions laws, periodic arrangement of such material is crystal. But only from the appearance, difficult to distinguish with the naked eye crystal, amorphous and quasi-crystals. So, how can we quickly identified them? One of the most commonly used technique is X-ray technology. X-ray structural analysis of solid, you'll soon find, the crystal and amorphous, quasi-crystals are three different solids. Since the atomic arrangement within the obvious physical differences, resulting in a crystal and the physical and chemical properties of non-crystalline huge difference. For example, the crystals have a fixed melting point, when the temperature is high enough to melt a certain temperature immediately; and glass and other non-crystalline melting point is not fixed, from softening to melting is a large temperature range. Crystal structure composed of particles (molecules, atoms, ions) in the three-dimensional space arranged in a regular manner at a certain point, these points constitute a certain periodic infinite lattice geometry, called the lattice. Crystal lattice in accordance with the modern theory of crystal structure constitute the atoms, molecules or ions can be abstracted to the point geometry. The no size, no mass, can not distinguish the point in the spatial arrangement of graphics called the matrix form, as an expression of the crystal structure of the particle arrangement in the law. Constitute a lattice point is called the matrix point matrix point represents the chemical structure of the content is called primitive. Therefore, the lattice can also be seen as points on the lattice point group consisting of a collection. For a fixed space lattice, can choose the vector that it be divided into many parallel hexahedron, each parallelepiped is called a unit, and the high symmetry, small unit with few lattice points due to its grid. Lattice is periodically by the unlimited extension of these lattice made. While only 7 of space lattice shape (corresponding to the seven crystal system), 14 kinds of patterns which are simple cubic, body-centered cubic, fcc; simple tripartite; simple hexagonal; simply the Quartet, the body-centered tetragonal; simple orthogonal, at the end centered orthorhombic, body-centered orthogonal, face-centered orthogonal; simple monocline, monoclinic end of the heart; simple triclinic lattice and so on. The strength of the lattice by the lattice energy (or point). . Class instance 1 cubic diamond lead alum Gold and Iron 2 Department of Sn rutile tetragonal Scheelite Stone 3 Orthorhombic sulfur iodine silver nitrate 4, monoclinic gypsum borax sugar 5 triclinic copper sulphate acid 6 three (diamond) of arsenic crystal ice crystal graphite 7 hexagonal beryllium cadmium zinc calcium magnesium
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The basic properties of the crystal
1, self-limiting: the spontaneous formation of crystals with polyhedron shape the nature of the geometry of this nature to become self-limiting. 2, the homogeneity and anisotropy: because the crystal lattice structure is a solid, all parts of the same crystal particle distribution is the same, so the various parts of the same nature of the crystal is the same, namely, the homogeneity of the crystal; the same crystal lattice, in a different arrangement of the general direction of the particle is not the same, with the nature of the crystal vary the direction, namely, the crystal anisotropy. 3, the minimum internal energy and stability: the crystal with the same kind of material non-crystal, liquid, gas compared with the lowest internal energy. Crystal lattice structure is a solid, for the regular arrangement of its internal particle. This regular arrangement of the particles is gravity and the repulsion between particles to achieve a balance in all parts of the crystal potential energy of the lowest results. Crystallization Crystallization two types of cooling crystallization, the other is the evaporation and crystallization. Cooling crystallization: First heat the solution, evaporation of the solvent into a saturated solution, then reduce the temperature of hot saturated solution, solubility changes with temperature was larger crystals will precipitate the solute, called the cooling crystallization. Evaporation and crystallization: the solvent evaporates, the solution becomes saturated by unsaturated continue to evaporate, the excess solute will crystallize in precipitation, called evaporative crystallization. Naphthalene crystals are common, Hyperion, ice, various metals.
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Crystal symmetry
Gallium, a very easy to form a large single crystal of the metal in the crystal shape, and other macroeconomic performance also reflects the symmetry of the crystal structure. The ideal crystal structure is symmetrical shape or image. Such images can be passed through without changing any of the distance between two points after the recovery operation. This operation is called symmetric operation, translation, rotation, reflection and inversion operations are symmetrical. Make an image full recovery operation is not equivalent to form a symmetry operation group. Space in the crystal lattice structure is represented by the translation symmetry, can also contain rotation, reflection and inversion related to and reflected in the symmetry of the macro, called the macroscopic symmetry, it crystal structure must coexist with the space lattice, and mutual restraint. The result of two constraints: ① crystal structure can only exist in the symmetry axis of 1,2,3,4 and 6, ② space lattice can only have 14 forms. n times the basic rotation axis of symmetry is rotated 360 ° / n, therefore, the macro lens can be reflected in shape and axial symmetry is also limited to the axle. Because atoms are not at rest, there is foreign atom and the lattice distortion caused by some defects, the basic structure, although still consistent with the above rules, but by no means as envisaged in the intact, there are number of different forms of crystals defects. Must also be pointed out that most of metallic materials for industrial use, not just by a large single crystal of the composition, but by a large number of small crystals, that is polycrystalline. Within the block of material, each of small crystals (or grains) throughout the three-dimensional interface, with its close neighbors separated. This interface, called grain boundaries, referred to as grain boundaries. Grain boundary thickness of about two or three atoms.
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Crystal defects
In the twentieth century, people change in order to explore the substance and nature of the cause, have the crystal from the microscopic point of view of internal structure, particularly the emergence of X-ray diffraction to reveal the regularity of arrangement of particles within the crystal that the particles in the internal was ordered three-dimensional arrangement of the infinite cycle of repetitive, so-called space lattice structure of doctrine. Crystal defects: a variety of particle deviation from the crystal structure of ordered repeat cycle factors, strictly speaking, resulting in the crystal lattice structure of all the periodic potential distortion factors. If the crystal into a number of impurities. These impurities will occupy a certain position, so that destruction of the periodic arrangement of the original particle, in the mid-twentieth century and found that the presence of crystal defects, which seriously affect the crystal properties, some are critical, such as semiconducting properties, almost completely by the presence of foreign impurity atoms and defects in the decision, the color of many ionic crystals, light and so on. In addition, the strength of solids, ceramics, refractories, and solid-state reaction sintering, etc. are related to the defects of crystal defects was nearly four years, a great attention to domestic and foreign scientific content. According to defects in the true scope of crystal defects four categories: Point defects: three-dimensional size are very small, occurring only in some locations, only a few of neighboring atoms. Line defects: two-dimensional small size, large size in another dimension, electron microscopy to be. Surface defects: small size in one dimension, on the other two-dimensional large size, can be observed in the optical microscope. Bulk defects: a larger size in three dimensions, such as mosaic pieces, precipitates, voids, bubbles and so on.
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Point defects
Different reasons by the formation of three types: 1 thermal defects (defects in the lattice position) In the crystal lattice grid point appeared normal space, the location should not have appeared in particle particle (particle gap). 2 component defects Foreign particles (impurities) to replace the normal particle position or into the normal position of the gap junction. 3 charged defects Some individual crystal particles in the excited electronic state, and some leave the original particle, the formation of free electrons, electron orbit in the original electron hole left. 1. Defects and defect reaction equation symbol Defects Case symbol to binary compound MX 1) lattice space: normal end point is no particle, VM, VX 2) ion gap: In addition to the normal position of node location appears outside the particle, Mi, Xx 3) dislocation-ion: M arranged in the X position, or position of X arranged in M, if the node is in normal position, the MM, XX 4) to replace the ions: foreign matter into the crystal L, if the replacement M, then the LM, if replaced by X, the LX, if occupy interstitial sites, the Li. 5) The free electrons e '(on behalf of the existence of a negative charge), that the effective charge. 6) electron hole h • (on behalf of the existence of a positive charge), • that the effective positive charge Such as: Removed from the NaCl crystal in a Na +, leaving a vacancy caused by price imbalances, a more negative value. Removal of Na atom is equivalent to adding a negative effective negative charge, e lost → free electrons, and the remaining location for the electron hole h • 7) complex defects Simultaneous positive and negative space, the formation of complex defects, divacancies. VM + VX → (VM-VX) Defect reaction equation Must abide by three principles 1) equilibrium position - the same number of responses before and after the position (relative position in terms of material) 2) The particle balance - the same quality before and after reaction (as opposed to adding material concerned) 3) The price equilibrium - before and after reaction was neutral Example: the introduction of KCl in CaCl2: The introduction of ZrO2 in the CaO Note: only from the defect reaction equation to see that they meet the three balance is right, but in fact often only one is right, this can only be determined to know the other conditions which defect reaction is correct. OK (1) density, according to the specific experiments and calculations. 2. Thermal defects (defects in the lattice position) Heat defect of two basic forms: a-Ephron Kerr defects, b-Schottky defect (1) Kerr defects Ephron Have enough energy atoms (ions) from equilibrium position, squeeze into the gap in the lattice, the formation of interstitial ions), leaving space in the original position. Features: Vacancy and interstitial particles in pairs, equal, the crystal size does not change. Kerr Ephron in the crystal defects of the number of a great relationship with the crystal structure, lattice point particles to enter the interstitial sites, the gap must be large enough, such as fluorite (CaF2) structure of the material gap larger, easy to form , while difficult to form NaCl-type structure. In general, ionic crystals, covalent crystals the defect difficult. (2) Schottky defects Larger energy of the surface layer atoms, leaving the original surface grid points to go outside the new grid point, the original location of the formation of such vacancy on the order of the atomic lattice depths of fill, the results of the surface gradually shifted to the internal space to go. Features: The volume increase of ionic crystals, cation and anion vacancy pairs, equal amount. Compact structure, easy to form a Schottky defect. Crystal thermal properties of crystal defects and a range of physical and chemical processes, electrical conductivity, diffusion, solid state reaction, sintering, etc. have a major impact, appropriately increasing the temperature, can increase the defect concentration is conducive to diffusion, sintering effects, plus a small amount of fill additives can also improve the thermal defect concentration, some process needs to avoid possible defects, such as single crystal production, to very fast cooling. 3. Composed of defects Impurity is primarily a defect in the original crystal structure into the impurity atoms, which atoms are different in nature and the inherent, destroyed the periodic arrangement of atoms, impurity atoms occupy two positions in the crystal (1) interstitial spaces (2) grid point 4. Charge defects (Charge defect) From the physics point of view the solid band theory, non-metallic solid with price band, band gap and conduction band, when the OR, the conduction band all perfect, all is electronically filled valence band, due to thermal effects or other energy transfer process, the valence band electrons have an energy Eg, which is excited into the conduction band, when present in an electronic conduction band, leaving a hole in the valence band, hole can also be conductive, although such damage to the end of the periodic arrangement of atoms, in the hole and electron with positive and negative charge, respectively, in the formation of an additional electric field around them, causing periodic potential distortion caused by crystal imperfections, said the charge defects. Point defects are important in practice: burning sintering, solid state reaction, diffusion, semiconductor, ceramic electrical insulation is important, so that the crystal coloring.
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Line defect
When the real crystal in the crystal by impurities, temperature changes or vibration stress generated due to combat or crystal, cutting and other mechanical stress, deformation of the crystal arrangement of the internal particle, atom ranks mutual slip, there is no longer conform to the ideal crystal sequence alignment, the formation of linear defects. Intuitive definition of dislocation: the crystal is not sliding surface sliding surface and the boundary line. The line defects called dislocations, note: not a geometric dislocation line, but a certain width of the pipe, the dislocation region arranged in a serious distortion of the particle, sometimes resulting in dislocation of the crystal surface mesh occurred. Strength has a great influence on the crystal. There are two kinds of dislocations: edge dislocations and screw dislocations. 1. Edge dislocation The form can be conceived of as: in a perfect crystal, cross-section along the crystal face BCEF knife, from the BC → AD, half of the ABCD plane, the role of pressure δ, thus producing slip distance (lattice constant Burgers vector or multiple) slip plane BCEF, slip area ABCD, not slip regime ADEF, AD as the junction of Slip Line - the dislocation line. Positive side diagram: As graph Sliding the upper half of more atomic planes, the same as the blade (wood chopping), said edge dislocation. Features: slip direction and perpendicular to the dislocation line, the symbol ⊥, there is extra half a slice of atomic planes. 2. Screw dislocation Its formation can be envisaged as follows: in a perfect crystal, crystal face along the transverse knife ABCD, ABCD plane in some direction along the X Yili Shi δ, to the production of slip, slip sliding zone area ABCD is not ADEF, boundary line AD ( dislocation line) Features: slip direction and the dislocation line parallel to the dislocation line and perpendicular to the surface is not flat, were spiral-like facilities, said the screw dislocation. Edge dislocation and screw dislocation differences: a-normal surface network, b-edge dislocation, c-screw dislocation The main difference from the respective characteristics: Edge: slip direction and the dislocation line perpendicular to the surface of most atoms, the dislocation line for the curve. Screw: slip direction parallel to the dislocation line, spiral, straight dislocation line. Because the presence of dislocation crystal growth, impurity diffusion in the crystal, the crystal formation and crystal mosaic structure of a series of high-temperature creep properties and processes have a significant impact. Crystal dislocation method of study: usually with an optical microscope, X-ray diffraction electron diffraction and electron microscopy techniques such as direct observation and indirect determination. Dislocation has the following basic properties: (1) dislocation is a line of crystal defects in the atomic arrangement, not the geometric significance of the line, there is a certain scale of the pipeline. (2) slip deformation is the result of dislocation movement, not to say that dislocations generated by deformation, because a piece of crystal growth is bin in itself there are many dislocation. (3) dislocation lines can be terminated at the surface of the crystal (or polycrystalline grain boundaries), but can not terminate inside the crystal in a bin. (4) is very close to the dislocation line of the stress concentration near the high energy of the atom, easy movement.
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Surface defects
Involving a wider range (two-dimensional direction), grain boundaries, crystal face, stacking fault. 1. Crystal surface: the crystal surface at the ions or atoms with unsaturated bonds, a significant reactivity, surface structure is asymmetric, the lattice deformation by large and thus higher energy than the internal energy is a defects. 2. Grain boundary: the interface between the grains, grain orientation between the different grain boundary occurs in the arrangement on the grain boundary is a transition state and the two grains are not the same. 1) small-angle grain boundaries (mosaic blocks) Size 10-6-10-8m of the small crystal blocks, each other to a few seconds to the tiny () tilt angle of the intersection, the formation of mosaic structure, it was considered to be edge dislocations and small angle to the intersection because the grain can be considered combined together, formed at the grain interface is a series of edge dislocation. 2) high angle grain boundary, the crystal orientation different from each other, the larger angle, in the polycrystals, the crystal may appear high angle grain boundaries. In such a grain boundary, the vertices arranged close to the disordered state, the grain boundary is the defect location, so higher energy, can be adsorbed foreign particles. Grain boundary diffusion of atoms or ions fast track, but also to eliminate the local Kongwei, this special role of the solid phase reaction, may play an important role in the sintering of ceramics, refractories, and other properties such as creep of polycrystalline materials, mechanical properties and strength polarization, dielectric loss, and other great influence. 3. Stacking Ion levels occurs during stacking dislocations, stacking faults occur, such as the face-centered cubic packing in the form of ABCABCA ... ... → ABCACBABC the middle of the B layer and C layer had levels of dislocation, a defect (general knowledge) Nonstoichiometric compounds Definition: compound number of atoms of each element is not a simple integer ratio of the emergence of a fraction, such as Fe1-xO, Cu2-xO, Co1-xO and so on.
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Deviation of the fit of the compounds can be
Learned in the basic chemical formula of compounds are in line with the law of definite proportions, the ratio of the number of atoms is a simple integer ratio, such as FeO, Fe / O = 1 / 1, TiO2, Ti / O = 1 / 2, etc. Now that the formation of such a strictly stoichiometric compound is a special case, and the prevalence of so-called non-stoichiometric compounds. Non-stoichiometric compounds, there are four types of defects: (1) cation excess, the formation of anion vacancy O can also be seen as part of the escape from the lattice into a gas: Visible: The formation of non-stoichiometric compounds are mostly constituted by the variation of the oxide cations, from high into low, the formation of anion vacancies, as well as ThO2, CeO2, etc., and atmosphere related. (2) cation excess, the formation of interstitial cations Such as ZnO, CdO → Zn1 + xo, Cd1 + xO, the excess metal ions into interstitial sites, in order to maintain a neutral, equivalent electrons are bound in the gap around bits of metal ions. Example: ZnO heated in zinc vapor, the color changes gradually deepened. (3) negative electron excess, anion gap formation. Current smoking were found UO2 + X, can be seen as UO2 U3O8 in the solid solution, when the excess of negative ions into the gap position, the structure must be two electrons and holes, in order to balance the overall charge neutrality, the corresponding price increase in the positive ion electronic hole in the electric field in motion, this material is called P-type semiconductor. (4) the excess of negative ions to form positive ion vacancy Because of the positive ion vacancy, in order to maintain neutral in the positive ion vacancy around the captured electronic space, so its also a P-type semiconductor, such as Cu2O, FeO that is. Example: FeO formed by this defect in oxygen, in fact, in the FeO Fe2O3 solid solution formed in (expensive to replace cheap), that is, two Fe3 + replaces three Fe2 +, while in the crystal lattice to form a positive ion vacancy, the oxygen conditions, the oxygen into the FeO lattice structure, into oxygen ions, iron ions must be obtained from the two electrons, the Fe2 + → Fe3 +, and the formation of VFe. Visible defects in nonstoichiometric compounds formed mainly by sentiment, but also with temperature, strictly speaking, all the world are non-stoichiometric compound, but of degree.
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Comparison of the crystal melting boiling point
1. Different crystal types of low boiling point of law of melting Generally: atomic crystal> ion crystal> molecular crystals. Some of the molten metal crystal high boiling point (such as tungsten), and some very low (such as mercury). 2. The same type of high and low boiling point of law of crystal melting See their entries about (1) belong to the metal crystal (2) belong to the same atomic crystal (3) belong to the same ionic crystals (4) belong to the same molecular crystals
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Encyclopedia
jing ti Crystal crystal Crystal atoms (ions or molecules) in the three-dimensional space as a periodic repetition of the ordered arrangement of the pan with the space lattice structure of solids. Amorphous body, such as glass, do not have the space lattice structure. Atoms long-range ordered arrangement of orientation, but not for repeated cyclical shift, compatible with the symmetry and spatial grid (such as five symmetry axis) said the subject of solid crystals. The basic properties of the crystal the fundamental nature of the crystal lattice by the space (Figure 1 space lattice) structure determined law, these basic properties are as follows. Homogeneity refers to the various parts of the same crystal have the same characteristics in nature. Amorphous body also has a uniformity, but that is homogeneous statistics, the crystallization of the crystal homogeneity different. Anisotropy refers to the transistor characteristics (such as crystal, electrical conductivity, magnetic susceptibility, etc.) in different directions are different in nature. Amorphous body is isotropic. Symmetry refers to the same part of the crystal occurs through the operation of certain laws of nature repeat. Crystal symmetry is not arbitrary, it is subject to the internal structure of the grid to the laws of space, determine the crystal structure of the symmetry properties of crystal morphology and symmetry. Crystal symmetry is the basis of classification. Self-limited refers to the spontaneous formation of crystals the nature of the geometric shape of polyhedra. Crystal face, crystal edges and corners, respectively, with the top face of the outer space grid network and node ranks correspond. Was complete the actual crystal rare form of geometric polyhedron, which is due to crystal growth caused by the impact of external conditions. Refers to the minimum internal energy of the crystal and the gas, liquid and amorphous body compared with the lowest internal energy in nature. This can be from gas, liquid or amorphous body into a crystal, the release of some energy to be proved. So, relative to the crystal, amorphous body is unstable, spontaneously transformed into the tendency of the crystal. Crystal formation Crystal formation process, in essence, a material particle in accordance with the laws of spatial arrangement of the process of lattice construction. Way crystals form crystals in the phase transition. Material directly to the formation of gas condensate solid crystals. Jet condensate such as volcanic sulfur or sodium chloride crystals formed directly. Formed by the liquid crystal, first, over-cooling the melt, such as the cooling molten metal to form metal crystals; the second is supersaturation, such as the crystallization of salt in the salt minerals. From the solid to solid phase transition, including the crystallization of amorphous (such as crystallization of volcanic glass), more like a homogeneous transformation, solid solution from the solution (see isomorphism) and so on. Including the occurrence of crystal growth (the formation of nucleation) and growth (based on the continued growth of the nuclei) in two stages. Too cool or too saturated in the media, the particles can be combined to form fine crystalline particles. However, this micro-grains need to absorb some energy (called as nuclear energy, since the system can be obtained within the energy fluctuation) to grow until it reaches a certain critical size. Exceed the critical grain size of the micro-called nucleation. It can form spontaneously (homogeneous nucleation), or by means of solid-phase induced the formation of foreign matter (heterogeneous nucleation). Based on the nucleation and crystal growth can continue while the energy release. Crystal layer growth and spiral growth mechanism of the growth of two: ① layer growth, also known as two-dimensional nucleation growth. Individual particles _set_tle to the formation of crystal grain surface, due to the incremental volume and surface area of a small relatively large increments, from the energy in terms of this state is unstable, then turn off the grain particles. First, if the particles combined into a single atom or molecule thick layer of particles (called two-dimensional nucleation), and then _set_tle to the crystal surface up, will be conducive to lower total system free energy and can be stable, and the formation of the crystal surface an uplift of the platform, the platform appears concave side of the edge (Figure 2, the growth of two-dimensional nucleation icon (arrows indicate concave angular position on three sides)). When the particle surface of the concave corner of the three precipitation, the entire grain surface area only increases the volume does not change, which allows systems to maximize the total free energy drop. Therefore, the particle will have three sides concave in angular position on a priority heap, until covered with his party. Then both sides of the concave corner of particles in the accumulation and thus form a new entrant on three sides. So constantly repeated, until the whole floor covered. There can be two-dimensional nucleation and precipitation to the grain surface, repeat the above process. Therefore, the growth in the ideal case, the crystals grow layer by layer, goes out in parallel planes. ② spiral growth. There is often a real crystal in the screw dislocation (see crystal defects). Because of their presence inevitable lattice concave angle, so that priority in particle accumulation in the concave corner. However, in a screw dislocation
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English Expression
: crystalline solid
n.: crystal, crystalloid, lens, transistorisation, crystal (in radio)