Structure of Materials Flashcards
To revise the fundamentals of materials for PhD
Why, generally speaking, are ceramics brittle while metals are ductile?
Because the covalent and ionic bonds in ceramics are much stronger than metallic bonds in metals
The two phases of composite materials?
- Reinforcing Phase 2. Matrix phase
Three categories of composite materials based on strengthening mechanism?
- Dispersion Strengthened 2. Particle Reinforced 3. Fiber Reinforced
How many types of atoms are there?
There are 109 different types of atoms, one for each element in the periodic table - periodic elements are substances that scientists found that could not be made any simpler using chemical reactions.
What are the three types of classification of material structures?
- Atomic structure
- Microstructure
- Macrostructure
What is the atomic structure of a material?
The way atoms are arranged, types of bonding between atoms, features that can’t be seen.
What is microstructure?
Features of a material that can be seen using a microscope
What is macrostructure?
Features that can be seen with the naked eye
What properties does the atomic structure have an effect on?
Chemical, physical, thermal, electrical, magnetic and optical properties
Microstructure and macrostructure have a larger effect on what type of properties?
Mechanical properties and the rate of chemical reaction
What is an atom made up of?
A positively charged nucleus (containing protons and neutrons) surrounded by electrons revolving around it
What is the atomic number of an element?
The atomic number indicates the number of protons in the nucleus
What is the atomic weight of an atom?
The atomic weight indicates how many protons and neutrons are in the nucleus
How many electrons are there usually in an atom?
Because atoms like to have balanced charge, there are usually the same number of electrons as there are protons
What is a metallic bond?
In a metallic bond, the electrons leave the outer shells of metal atoms forming a sea of delocalised electrons and positive metal ions - this is because metal atoms have only partially filled outer shells
What is a covalent bond?
Usually these are bonds between non-metals and is when atoms that have nearly a full outer shell share electrons to get a full outer shell
What are ionic bonds?
This is when metal and nonmetal atoms come together. This is when the metal atoms lose electrons to get an empty shell while nonmetal atoms take these lost electrons to gain a full shell, creating negative and positive ions
What are Van der Waal bonds?
These are particularly important in plastics and polymers. These are bonds between molecules that allow sliding and rupture to occur. In plastics the molecules are very long and so the van der Waal forces are very large.
What is an amorphous solid?
A solid substance with its atoms held apart at equilibrium spacing, but with no long-range periodicity in atom location in its structure.
Examples of amorphous solids?
Glass and some plastics.
Are amorphous solids isotropic?
Yes, they have the same physical properties in all directions.
What are crystalline solids?
Solids with regular, repeating arrangement of atoms or molecules.
Examples of crystalline solids?
Minerals, sand, clay, limestone, metals, carbon, salts (over 90% of natural and artificial solids are crystalline)
What is a unit cell?
A way of describing crystal structures, describes the arrangement within the solid of a small representative group of atoms or molecules. By multiplying identical unit cells in three directions, the location of all particles are determined.