Journal of Materials Science and Engineering A 6 (3-4) (2016) 71-74 doi: 10.17265/2161-6213/2016.3-4.005
Multilevel Structure and Properties of Metals and Polymers within the Unified Model of Chemical
Oleg Sirotkin and Rostislav Sirotkin* Department of Materials Science and Engineering, Kazan State Power Engineering University, Kazan 420066, Russia
Abstract: The object of the work is to examine metallic and polymer materials from a single point of view in terms of their structure. As a result, a unified classification of levels of structural organization of metallic and polymer materials, based on the unified model of chemical bond, was proposed. The unity of different materials’ nature at chemical structural level is shown. The effect of the type of chemical bond on subsequent levels of materials’ structural organization, difference in properties and contribution of specific levels to some properties of materials are shown.
Key words: Metals, polymers, chemical bond, structure, property.
1. Introduction 2. Results and Discussion
Among various natural and synthetic materials, These classifications are traditionally based on materials based on metals (mostly alloys), as well as systematization of metals’ structures (with no organic and inorganic (such as glasses, ceramics) reference to structures formed by polymers – one of polymers, are of special interest for materials science. the most important class of materials), while the Due to huge practical importance, it is these groups of location of nanostructures in these classifications is materials that are best studied including their not clearly specified. Therefore the corrected universal structural characteristics [1, 2]. In metallography classification of levels of structural organization for materials structure is traditionally divided into four metallic and nonmetallic materials can be presented as levels [3]: macrostructure (~ 10-1 m), microstructure follows (Table 1) [4-6]: microstructure (including 3 (~ 10-4 m), substructure (~ 10-7 m) and fine structure sublevels: electron-nuclear, molecular (both form fine (submicrostructure) (~ 10-9 m). Contemporary structure) and nanostructure), mesostructure and achievements of structural chemistry and physics, as macrostructure. well as mechanics, have led to the need to develop a Dimensional characteristics of these levels for unified approach to structural hierarchy: metals and polymers, as well as the elements that macrostructure (fractures, dendrites and polyhedral these levels composed of, are given in Table 1. This structures, grains and their orientation, ~ 10-3 ~ 10-1 classification is also applicable to ceramic materials, m); mesostructure (structure within grains, as their microstructure (including the electron-nuclear dislocations and dislocation ensembles, disclinations, one) is similar to the one in polymers (primarily polygons, ~ 10-7 ~ 10-3 m); microstructure (X-ray covalent bonding of atomic cores) and metals structure, formed by point defects, crystal lattices, (polycrystals). Main conclusions, which can be made ~ 10-10 ~ 10-7 m), including apparently nanostructures. while analyzing Table 1, are as follows: Electron-nuclear microstructure (1а) is common for any kind of metallic and nonmetallic material, as any * Corresponding author: Rostislav Sirotkin, Ph.D., associate material is formed by chemical elements (atomic professor of materials science, research fields: materials structure, structure properties relations and chemical bond. cores) tied by chemical bonds;
72 Multilevel Structure and Properties of Metals and Polymers within the Unified model of Chemical Bond
Table 1 Classification of main levels of structural organization of metallic and polymer materials. Structural levels and their Structural elements in metals Structural elements in polymers dimensional range 1 2 3 1. Microstructure: Atomic cores and collectivized electrons, which provide chemical bonding (predominantly metallic 1а) electron-nuclear bond in metals and mainly covalent bond in polymers); Point defects: vacancies, etc. ~1 – 5 Å (1-5·10-10 m) (0,0001-0,0005 mkm) fine 1b) molecular Fragments of macromolecules (atomic Primary “aggregates” of atomic cores, in metals there ~5 – 10 Å groups) tied by van der Waals (vdW) and are no molecules (0.5-1 × 10-9 m) hydrogen bonds (0.0005-0.001 mkm) Nanoparticles (0.001-0.1 mkm) and interfaces; Macro (oligo-) molecules tied by intra- and 1c) nanostructure Fragments, blocks, polygons (0.1-1 mkm) и intermolecular vdW and hydrogen ~10 – 10 000 Å coherent-scattering region (0.001-0.01mkm); Line interactions; SMS*: nanoparticles and (10-9-10-6 m) defects: dislocations and disclinations (0.1-1 mkm) interfaces; crystallites, lamellae; Line defects 2. Mesostructure Subgrains (1-100 mkm) and subgrain boundaries; SMS: small axialites, hedrites and spherulites ~104-107 Å Grains (100-1000 mkm) and boundaries between up to several dozens of mkm; Planar and (10-6-10-3 m) them; Planar defects (dislocation assemblies) small bulk defects (voids, etc.) SMS: large supramolecular formations in the 3. Macrostructure Structures formed by grains (fibres, dendrites, etc.) form of large axialites, hedrites and ~107-109 Å (10-3-10-1 m) and interfaces; Bulk defects (cavities, cracks, etc.) spherulites (over several dozens of mkm); Large bulk defects (cracks, etc.) *SMS - Supramolecular structures in polymer materials.
Table 2 Specifics of structure and properties of substances depending on dominant chemical bond type. Metallic Compounds (nonmolecular, Covalent – Polymer Compounds Characteristic berthollides) (molecular, daltonides) 1 2 3 I. Composition Homo- and heteronuclear Homo- and heteronuclear a) DEC → 100 %, СM >> СC (СI) а) DEC → 50 %, СC >> СM and СI; b) Collectivized electrons are minimally b) Collectivized electrons are localized localized between nuclei; between nuclei; II. Specificity of chemical bond, c) Electronic density, δ, is minimal between the c) Electronic density, δ, is maximum between determined by the character of nuclei and uniformly distributed (δ’ = δ”) nuclei (normally it is shown as a dash that collectivized electrons' distribution connects nuclei) between atomic nuclei
III. Structure
( ) n n Е Ме е Е Ме 1. Electric conductivity 1. Dielectric properties 2. Ductility 2. Elasticity IV. Characteristic properties 3. High density 3. Low density 4. Metallic luster and opaqueness 4. Transparency V. Aggregate state Solid substance Solid or liquid substance (solution, melt)
The differences in structure of subsequent levels metallic or ionic) and manifest themselves starting (and, consequently, properties) are determined by from molecular- and nano-sublevels of metallic and specificity of chemical bond (primarily covalent, nonmetallic materials and then on meso- and
Multilevel Structure and Properties of Metals and Polymers within the Unified model of Chemical Bond 73 macrolevels. materials’ structure at fine and nanolevels (e.g., upon These conclusions are summarized in more detail in formation of nanomaterials), which should lead to Table 2. acquisition by the materials of new properties The DEC (Degree of electrons collectivization) is essential for practical use in modern products and determined as the number of atomic cores (n) within a structures. chemical compound’s structure localizing In addition, the materials ultimate properties are collectivized electrons, which provide chemical determined by the cumulative contribution of each of bonding [7-11]: the above levels or sub-levels of structural DEC 100 100/n (1) organization. As a result, in general, any property while covalent character (СC), metallic character (СМ) (physical, mechanical, chemical, etc.) of metallic or and ionic character (СI) of chemical bond within its nonmetallic material can be determined as a sum of unified model (Eq. (2)), which unites the three types, contributions of all structural levels [4]: are calculated according to the procedure [7, 12]. MP f ( (kii MP)) (3)
ψ с1ψCOV c 2 ψ MET c3ψ ION (2) where, MP – material’s property; MPi – material’s where, Ψ is the wave function; C1, C2 and C3 are property determined by a certain structural level coefficients, which, respectively, determine the shares according to Table 1; ki - coefficient, which takes into of covalent, metallic and ionic components of account contribution of a given structural level of chemical bond and are equal to 1 or 100%, in total . material to a certain (physical, mechanical, chemical,
As a result, difference in CC/CM/CI ratio in metals etc.) property (Table 1). and polymers leads to qualitative differences in their Despite the fact that all structural levels contribute (1b) sublevel of microstructure (nonmolecular and to properties of any material, as a rule, for many molecular ones, respectively). This, in turn, leads to properties one can point out a level of structural fundamental difference in their properties organization whose contribution to a certain property (conductor/dielectric, plasticity/elasticity, high is dominant. For example, electron-nuclear structure density/low density, etc.). It has to be pointed out that determines such characteristics of metals as plasticity in polymers, unlike metals, the presence of (corresponding to diffusion and self-diffusion macromolecules bonded by relatively weak mechanisms), stiffness (characterized by Young’s van-der-Waals physical forces sets conditions for their modulus), electrical conductivity, resistance to existence in two states: liquid (solution or melt) and corrosion; nanostructure determines crowdion and solid (Table 2). It is for this reason processing of dislocation plasticity. Magnetic properties are polymers occurs at temperatures approximately ten determined by the structural elements (magnetic times lower than processing of metals. domains), whose size corresponds to nano- and The importance of creation of a universal mesostructure, while brittleness – by the elements of classification of structural levels for different nano-, meso- (dislocations and their ensembles) and materials stems both from theoretical needs to macrostructure (cracks). Similar correlations can be concretize the main object and basic notion of drawn for polymer materials: ageing due to materials science – material and from practical macromolecules’ destruction and cross-linking is reasons. The latter, in particular, is due to the fact that determined by characteristics of electron-nuclear at the moment special emphasis is laid on structure; intermolecular bonds of molecular structure development of approaches to forming and regulating have an effect on most physical and mechanical
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