Objective 01: Metallurgy and Metal Structure Flashcards
Metallurgy
The study of metals
3 Groups of Metallurgy
- Extractive
- Mechanical
- Physical
Extractive Metallurgy
The study of the extraction and purification of metals from their ores through several steps that increasingly purify the metal by removing unwanted metals
What are 3 routes that Extractive Metallurgy may be carried out?
- Pyrometallurgy
- Hydrometallurgy
- Electrometallurgy
Pyrometallurgy
Melting the ore in a furnace to release the metal
Hydrometallurgy
Dissolving the metal from the ore and recovering it as a powder
Electrometallurgy
Dissolving the metal from the ore with the use of electricity
Mechanical Metallurgy
The study of the techniques and mechanical forces that shape and make the finished forms of metal, including the effects of stress, time, and temperature
Physical Metallurgy
The study of the structure of metals
What are the properties of metals initmately related to?
Their structures
How can the properties of a metal be manipulated?
Modification of the structure, e.g. modifying chemical composition, alloys, and heat treatment
Describe Metals
- Good conductors of heat and electricity
- Generally malleable and ductile
- Occur naturally in ores in the form of chemical compounds, e.g. sulphides and oxides
- Tend to corrode, i.e. tend to react chemically with the environment and revert to compound forms, with the exception of noble metals
Are the majority of power plant components iron-based?
Yes
What occurs on the atomic level when a solid metal is heated?
- The atoms of the material increasingly vibrate as the temperature increases
- At a certain temperature, the substance melts and the cohesive bonds holding the individual atoms together breaks, allowing them to travel freely throughout the liquid
- At the melting point, heat energy is absorbed without further increase in temperature until all the metal is in liquid state
Does every metal and alloy have a fixed melting point?
Yes
Unit Cells
Fixed configuration of individual metallic atoms
What are the 3 basic structures of Unit Cells?
- Face-Centered Cubic (FCC)
- Body-Centered Cubic (BCC)
- Close Packed Hexagonal (CPH)
How many atoms make up the Face-Centered Cubic structure?
14
What are the properties of Face-Centered Cubic?
- High Ductility
- Low Shear Strength
- Low Tensile Strength
- Good Thermal and Electrical Conductivity
What are some metals that have the FCC structure in solid state?
- Gold
- Aluminum
- Silver
- Lead
- Nickel
- Gamma Iron (910-1390ºC)
How many atoms make up the BCC structure?
9
What are the properties of BCC?
- High Strength
- Low Ductility
- Very Resistant to Shear Deformities
What are some metals that have the BCC structure in solid state?
- Chromium
- Tungsten
- Molybdenum
- Vanadium
- Alpha Iron (below 910ºC)
- Delta Iron (above 1390ºC)
How many atoms make up the CPH structure?
17
What are the properties of CPH?
- Intermediate Strength
- Intermediate Ductility
What are some metals that have the CPH structure in solid state?
- Zinc
- Magnesium
- Cadmium
- Titanium
What happens to unit cells as molten metal cools and solidifies?
They become packed together to form 3D crystals that occupy a space lattice
What happens as unit cells continue to pack together as crystals?
Further growth of these crystals forms dendrites, which look like the branches of an evergreen tree, that extend through the molten matric until they contact neighbouring dendrites. These contact surfaces become the crystal or grain boundaries.
What happens to insoluble solids present in solidifying molten metal?
They are pushed ahead of the growing crystals and become trapped at the grain boundaries and between the limbs of the dendrites.
What effect does grain size have on the properties of metals?
- Smaller grain size increases tensile strength and ductility
- Larger grain size tends to resist creep and deformation under constant loading but may be prone to cracking
What primarily determines the shear strength of metals?
The type of unit cell structure exhibited
Polymorphism
The ability of a metal to change to a different unit cell structure depending on its temperature
Do most metals and alloys exhibit polymorphism?
Yes
Allotropy of Iron
The ability of iron to exist in different physical forms in the same substance
Why is allotropy consequential?
- It affects melting point, hardness, metal solubility, and alloying chemistry
- Very important in determining the way iron reacts with carbon to form steel and cast iron
What Unit Cell structure is this:
FCC
What Unit Cell Structure is this:
BCC
What Unit Cell Structure is this:
CPH
