Home - Education Resources - NDT Course Material - Materials and Processes
 

Materials/Processes

Selection of Materials
Specific Metals
  Metal Ores
  Iron and Steel
  Decarburization
  Aluminum/Aluminum Alloys
  Nickel and Nickel Alloys
  Titanium and Titanium Alloys


General Manufacturing Processes

Metallic Components
Ceramic and Glass Components
Polymers/Plastic Components
Composites

Manufacturing Defects
Metals
Polymers
Composites

Service Induced Damage
Metals
Polymers
Composites
Material Specifications

Component Design, Performance and NDE
Strength
Durability
Fracture Mechanics
Nondestructive Evaluation

Atomic Bonding
(Metallic, Ionic, Covalent, and van der Waals Bonds)

From elementary chemistry it is known that the atomic structure of any element is made up of a positively charged nucleus surrounded by electrons revolving around it. An element’s atomic number indicates the number of positively charged protons in the nucleus. The atomic weight of an atom indicates how many protons and neutrons in the nucleus. To determine the number of neutrons in an atom, the atomic number is simply subtracted from the atomic weight.

Atoms like to have a balanced electrical charge. Therefore, they usually have negatively charged electrons surrounding the nucleus in numbers equal to the number of protons. It is also known that electrons are present with different energies and it is convenient to consider these electrons surrounding the nucleus in energy “shells.” For example, magnesium, with an atomic number of 12, has two electrons in the inner shell, eight in the second shell and two in the outer shell.

All chemical bonds involve electrons. Atoms will stay close together if they have a shared interest in one or more electrons. Atoms are at their most stable when they have no partially-filled electron shells. If an atom has only a few electrons in a shell, it will tend to lose them to empty the shell. These elements are metals. When metal atoms bond, a metallic bond occurs. When an atom has a nearly full electron shell, it will try to find electrons from another atom so that it can fill its outer shell. These elements are usually described as nonmetals. The bond between two nonmetal atoms is usually a covalent bond. Where metal and nonmetal atom come together an ionic bond occurs. There are also other, less common, types of bond but the details are beyond the scope of this material. On the next few pages, the Metallic, Covalent and Ionic bonds will be covered in more detail.