Materials structure

PART I. STRUCTURE, PROPERTIES AND GENERAL TECHNOLOGICAL PROCESSES OF CONSTRUCTION MATERIALS

1. Materials structure

The structure of materials determines the mutual location, form and sizes of structural elements. Atoms, ions, molecules, solid particles, aggregates of particles, pores(i.e. voids between particles, filled with liquid or gaseous phase) can be structural elements. Particles are minute parts of a substance, which can be obtained by mechanical means (dispersion) or physical and chemical means. The aggregates of particles form as a result of their agglomeration, in particular, when dispersion grows and the surface energy increases, and also as a result of intergrowth, as in the process of crystallization.

T he general signs and feature of structural materials, can be considered at different levels depending on the sizes of the structural elements (l). The four main structural levels which may be defined for construction materials: i.e., atom-molecule (l<10^-9 m); submicroscopic (l =10^-9...10^-7 m); microscopic (l =10^-7...10^-4 m); macroscopic (l >10^-4 m) are explained below.

1.1. Atom-molecule structure

Considering materials structure at atom-molecule level, it is possible to distinguish: crystalline materials – characterised by unit cells structure and amorphous ones; and those characterised by molecular, atomic or ionic aggregates, which does not form well-organized lattice.

A large group of natural or artificial materials and various minerals among them are crystalline in nature. Materials like cements, polymers, and slags contains both crystalline and amorphous components. The most persistent state is the crystalline one, as the energy of material here is minimal. Energy of ionic crystalline lattice is equal to the sum of the energies of separate constituent ions. Energy performance or ionic constant (IC) is determined by a formula:

, (1.1)

where is ion valence; is distance between the ions centers.

The unit cells of crystals are divided into primitive and complicated (Fig. 1.1). There are eight ions or atoms located on tops in primitive cells. In complicated elementary cells additional ions (atoms) are located on the middle of ribs or edges.

Primitive elementary cells can be divided into seven types (Table 1.1), depending on length of crystallography axes and the size of angles between them.

Table 1.1

Types of primitive elementary cells

Type of lattice	An angle between axes	Correlation of axes sizes	Designation Fig. 1.1
Triclinic			1
Monoclinic			2,3
Rhombic			4...7
Rhombohedral			9
Hexagonal			8
Tetragonal			10, 11
Cubic			12...14

Theory of crystal space lattice structuring was founded by E.S.Fedorov in 1890. He established the existence of 230 variants of space combinations of symmetrical elements with space lattices or space groups.

Minerals found in construction materials and in metals form different types of crystalline lattices. Thus establishment of their parameters constitute one of the main methods of their authentication. An example of the types of crystalline lattices of cement clinker minerals are shown in Table 1.2 below:

Most metals form highly-symmetric lattices with dense atomic package. These could be in form of a: cubic, body-centered cubic, face-centered cubic or hexagonal cell (Fig.1.2).

Table 1.2