Metals and Steels Flashcards
What are the two main types of metals
Ferrous-has iron
and Non ferrous-doesn’t have iron
What is an alloy and why are alloys used
An alloy is a mixture of two or more materials
where the main component is a metal
Pure metals are often too soft, brittle or chemically reactive to be used on their own
Give five examples of alloys
Steel
Brass
Bronze
Solder
Pewter
Duralumin
Describe the production of iron and steel
A blast furnace is charged with iron ore, coke and limestone
flow of air is introduced from the bottom
reactions take place such as reduction of iron oxide
Molten iron is mixed with other materials for alloys such as steel
What is the relationship between carbon content in steel and the properties of the steel
Higher carbon content means stronger and harder steel
but lower ductility
Lower carbon content means more ductility but not as strong or hard
What are the requirements specified in Eurocode EN 10,025
Mechanical properties
Ductility
Toughness
Through-thickness properties
What are the types of steel in construction
Structural steel
Reinforcing steel
Miscellaneous shapes (for particle applications)
What is weathering steel
Weathering steel is a type of structural steel
that contains more phosphorous and some chromium and copper.
It forms a rust like appearance when exposed to the weather
What is stainless steel
Stainless steel is a steel alloy that has at least 10% chromium
chromium oxide protective layer forms on the surface
which can be enhanced by the addition of nickel
What is aluminium
Aluminium is a light weight, medium strength metal
that is popular in construction for facades and fittings
but is not suitable for main load bearing supports
Why is aluminium high cost?
Aluminium is not found in pure form but rather in an ore called bauxite
The extraction process is very energy intensive which adds cost
and the working process also adds the majority of the cost too
What is copper used for in construction
Heating and domestic water piping
What is corrosion in metals
Corrosion is the process by which metals become weakened,
this happens when the metal is exposed to oxygen or water and forms an oxide
at the surface due to surface atoms being in an incomplete lattice.
This then flakes off causing the metal to be weakened
What are a few ways to protect metals from corrosion
Barrier methods such as paint
Good detailing in drawings to prevent water runoff or cracks where air can get in
Passive layer meaning a thin oxide which prevents the oxidation from spreading
How can the passive layer be destroyed
The passive layer is destroyed when the alkalinity of the concrete is reduced
or when the chloride content is increased to a certain level
How does the alkalinity of concrete get decreased causing the destruction of the passive layer
Carbon dioxide from the air reacts with the hydroxides in the steel such as calcium hydroxide to for, carbonates,
this reaction reduces the pH of the solution which in turn destabilises the passive layer film
How does chloride content increase and how does this cause the destruction of the passive layer
Chloride ions usually from sea water or de icing salts
are dissolved in water and permeate through the material,
if oxygen and moisture are also present this will then cause steel corrosion
What are other ways the pH of concrete can be increased
Leaching-water finds its way in through cracks and dissolves minerals in the matrix,
this then causes minerals the leach and form deposits in the cracks
Acid attack-when acid comes into contact with the cement paste causing hydrated and un hydrated compounds to be dissolved
What are some of the key considerations for the sustainability of steel
Embodied energy i.e. the energy required to create it
Transport energy
Steel can keep its properties after being recycled-called ‘multicycling’
90% of steel waste in demolition sites is re used or recycled
Little to no site waste
