Resuming notes of the course

Page 1

RESUMING BASIC PRINCIPLES OF METALLURGY Introduction Some of the important properties of solid materials depend on: • Atomic geometrical atomic arrangement → atomic structure • The interactions that exist among constituent atoms or molecules → interatomic bonding Thus, in order to study the properties of solid materials we have to study first these two elements. Atomic structure According to Bohr atomic model an atom is made of electrons that revolves around the atomic nucleus in discrete orbitals. The electrons that occupy the outermost shell are called valance electrons; these electrons are extremely important for establishing the bonding between atoms. Of course, boding between atoms are necessary to form atomic and molecular aggregate. For this reason, many of the physical and chemical properties of solids are based on these valence electrons. Interatomic bonding After studding the atomic structure, we can now focus our attention on the interatomic bonding. At large distance the mutual attraction between the negative electrons of one atom and the p ositive nucleus of the other are negligible; this because the two atoms are t oo far apart to have influence on each other . On the other hand, at small distance each atom can actually influence the others and attract the other, but when the distance decreases too much the two-positive nucleus of the atoms rejects each other and so we have a repulsive force and not an accretive force as we have had before. Of course, we can plot a graph in which we represent how the force between two atoms changes with respects to the distance between the two atoms themselves. The slope of the plot represents is proportional to the modulus of elasticity . The modulus of elasticity can also be determined by looking at the slope of the…