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Topic 5 - Why Do Metals Corrode? > Part 3 - Corrosion Of Metals > Flashcards

Part 3 - Corrosion Of Metals Flashcards

(74 cards)

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1
Q

What is a mineral?

A

Natural metals that are combined with other metals

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2
Q

What is an ore?

A

A metal bearing mineral or rock, or native metal

Mineral containing a sufficiently high proportion of an economically important element to justify its extraction and processing to a pure metallic state - copper mineral

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3
Q

What is corrosion?

A

It is the deterioration of metals by chemical interaction with their environment.
Natural process that converts metals in to their oxides.

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4
Q

What is an oxide?

A

A chemical compound that contains one oxygen and one other element. Eg. Ferric oxide (one of thenposisbke oxides of iron)

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5
Q

What is oxidation?

A

The gain of oxygen by a substance.

When one substance loses an electron

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6
Q

What type of reaction is corrosion?

A

Oxidation reaction

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7
Q

What type of metal does that happen to?

A

Only to iron and it’s alloys

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8
Q

What does iron need to form rust?

A

It needs oxygen but it also needs water

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9
Q

What is responsible for the further oxidation of Fe2+ to Fe3+?

A

The oxygen dissolved in the drop of water is responsible for the oxidation of Fe2+ in Fe(OH)2 to the Fe3+ in Fe2O3.H2O (rust)

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10
Q

Why does rust split and crack?

A

Rust takes up a greater volume that the iron from which it is formed and consequently splits and cracks. The rust is also porous to water and oxygen so that more rust can be formed from underlying metal

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11
Q

Where is iron naturally found and in what form?

A

Iron is widespread in the earths crust and in sedimentary rocks iron commonly exists as an oxide.

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12
Q

What are banded iron formations?

A

They are repeated thin layers of iron oxides found in sedimentary rocks.

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13
Q

How were iron band formations produced?

A

Previously in the earths evolution, there wasn’t much oxygen in the oceans or atmosphere.

As a result the ocean was capable of dissolving large quantities of iron in the form fe+2

At that time Cyanobacteria/blue- green algae (now as a fossil stromatolites) liberated shallow waters and released lots of oxygen in the oceans and atmosphere (as a by product of photosynthesis)

This caused the iron to be changed in to ferric oxide to form banded iron stones

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14
Q

What are stromatolites?

A

They are the oldest fossils (3 billion years ago) which are the remains of cyanobacteria

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15
Q

Why did banded iron formations stop forming?

A

As oxygen abundance increases in the oceans and in the atmosphere, iron was deposited where it was produced.

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16
Q

What is an important by product of photosynthesis?

A

Oxygen

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17
Q

What are the 3 C’s for writing in science?

A

Be clear - use terminology, keep sentences fairly short and uncomplicated

Be concise

Be coherent - make sure the writing has logical flow. Coherence is related to organisation

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18
Q

If aluminium is just as reactive to oxygen as iron, then why is it used to make aircraft?

A

According to the reactivity series aluminium reacts more with oxygen than iron does. The difference is that the aluminium oxide that is produced as a result actually protects the underlying metal from further corrosion.

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19
Q

Can you think of other metals that corrode in a similar way to aluminium?

A

When copper is exposed to air it develops adherent protective coatings, initially of oxide, and subsequently thickening to form a green deposit that you can see on copper roofs. This green deposit is called ‘verdigris’ and can be composed of a variety of different copper compounds eg copper carbonate, or near the coast it may be copper chloride

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20
Q

Why is zinc used as a coating in some metals?

A

Zinc is resistant to atmospheric corrosion after the initial formation of a thin layer of zinc oxide. It is a good method for controlling metal corrosion

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21
Q

What factors other than water and oxygen can speed up corrosion?

A

Salt
Temperature
PH

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22
Q

Can you fake corrosion?

A

Yes you can but archeologists can determine if the corrosion has been artificially made or not

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23
Q

How does salt (sodium chloride) speed up corrosion?

A

NaCl generates ions when dissolved in water and these ions facilitate the transfer of electrons from one substance to another, speeding up the oxidation and reduction reactions that occur during corrosion.

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24
Q

Which ions appear in a solution when table salt dissolves in water?

A

Solid NaCl dissolves in water to produce sodium ions, Na+ and chloride ions Cl-

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25
How does chloride ions affect corrosion?
Chloride ions prevent the formation of protective oxide films on metal surfaces and subsequently increase corrosion
26
Which environment would potentially be more corrosive, inland or at the coast?
Metals will be corroded more quickly in coastal environments due to high salt levels
27
What is the formula for calculation the PH of a substance?
PH = -log10 (hydrogen ion concentration in mol dm-3 / mol dm-3)
28
What is hydrogen ion concentration measured in?
Units of mol dm-3
29
What is the PH of water?
7.0 it is considered neutral
30
How many hydrogen ions are in pure water?
0.0000001 mol dm -3 is the hydrogen ion concentration which means there is only 1 hydrogen ion for every 10 000 000 water molecules
31
Is rainwater neutral? Why?
No it is not because of carbon dioxide in the atmosphere
32
What is the PH of natural acid rain? What is natural acid rain?
5.6 Natural acid rain is rainwater with dissolved carbon dioxide from the atmosphere but it is not polluted
33
Which ion is responsible for making water acidic?
The hydrogen ion H+ is responsible for making water acidic.
34
What is acid rain?
Acid rain is rain that has dissolved sulfur dioxide (SO2) and nitrogen oxides (NOx) that comes from human pollution and reduced the PH of the rain to less than 5 Emissions such as sulfur dioxide and nitrogen oxide are oxidised in the atmosphere
35
What can acid precipitation damage?
Trees Buildings Kill aquatic life
36
Do you think acid rain is a problem in rural areas?
Yes acid rain can be a problem in rural areas dues to winds blowing polluted gases from industrial areas and large cities
37
Does high or low temperature speed up corrosion? Why?
High temperature are associated with high rates of corrosion This is because the reactants move quicker and collide more frequently resulting in faster formation of the products
38
Which of the following can hold more dissolved oxygen - warm water or cold water?
The solubility of gases in water decreases with increasing temperatures. Cold water can hold more oxygen than warm water
39
How does the temperature counteract the affect of corrosion?
High temperature will increase the rate of corrosion but this effect is counteracted by lower solubility of oxygen in warmer water
40
Are soils corrosive?
Soils can be corrosive Different components of soils can have a huge impact on the corrosion of buried metal structures
41
What are soils mainly composed of?
Water 25% Air 25% Organic matter 10% Mineral solids - 40%
42
In the context of soils what is organic matter?
It means that it is or was living
43
What is a big component of peaty soil?
It has a high proportion of organic matter
44
How would you describe soils in mountainous regions?
Contains a high proportion of inorganic matter and tend to be stony and dry
45
What 3 different categories of texture can soil be put in depending on their dominant particulate ?
Sand Silt Clay
46
What the size ranges in mm of particulate in sand?
2.0- 0.02 mm
47
What the size ranges in mm of particulate in silt?
0.02-0.002 mm
48
What the size ranges in mm of particulate in clay?
<0.002
49
How would you describe a soil with a predominant particle size of 0.015 mm?
A soil with predominant particle size of 0.015 mm is silt
50
How does sand feel?
Gritty
51
How does silt feel?
Smooth, silky or soapy
52
How does clay feel?
It sticks and can form balls or tubes
53
What are the key factors in soil that contribute to metal corrosion?
The amount of air trapped in the soil Water retention Salt content Acidity of soil
54
What type of pores dominate sandy soils?
Macropores | Pores larger than 0.08 mm
55
What type of pores dominate fine textured soils I.e. Clay?
Micropores Pores smaller than 0.08 mm
56
What are the spaces between solid materials in soils called?
Pores
57
Do smaller or larger pores usually contain water?
Smaller pores
58
Do smaller or larger pores usually contain air?
Larger pores
59
Which type of soil has a greater water holding capacity - clay or sandy soil?
Clay has a greater water-holding capacity than sandy soil due to its micropores
60
Which type of soil has greater corrosion potential - clay or sandy soil?
Clays have greater corrosion potential due to the accumulation of water and ions
61
What can soil contain from the atmosphere that can speed up metal corrosion in soils?
Rainfall picks up numerous ions from the atmosphere such as sulfur dioxide and nitrogen oxides. As the solutions move through the soil ions are exchanged with Ca, Mg, K Chloride ions can also be found in marine environments. The presence of these dissolved species together with moisture content increases the ability of a soil to corrode metals
62
What is soil acidity produced by?
Natural breakdown of rocks Decomposition of plants Industrial waste Acid rain Microbiological activity
63
What does the decomposition of organic matter in soil by microbes release?
Carbon dioxide
64
What are rusticles?
They are a formation of rust similar to icicles
65
What is the composition of rusticles?
35% ion compounds The rest is a complex community of microbes and fungi which uses iron as a source of nutrients
66
What do metals need to corrode?
Oxygen and water
67
What do shipwrecks at great depths corrode?
They deteriorate due to microbial corrosion
68
What are the most common methods used to prevent metal corroding?
Coating metal surfaces with paint or another metal Using sacrificial metal Modifying metals by blending with other elements Grease/oil provide temporary means to protect metal surfaces The resistance to corrosion of a metal can be changed by blending it with one or more metals
69
What is the disadvantage of using paint to protect metal surfaces?
If there is any rust before painting then further rusting will occur underneath. When the paint starts to peel of then rust is often at an advanced stage. Oil based sprays can displace water from the surface and provide temporary protection to rust.
70
What is galvanising?
When a metal surface is coated in zinc
71
If zinc is more reactive than iron why is it used to coat it?
Zinc oxide provides a protective layer just like aluminium
72
If there is a crack in the galvanised coating, does this affect iron underneath?
Because zinc is more easily oxidised than iron, zinc is oxidised in preference and iron remains in its metallic form
73
What is electroplating?
It is a method of coating another metal but not by dipping it in molten metal. It involves a chemical process in which ionic substances are broken down in to simpler substances when electricity is passed through them A battery is attached to both objects The negative end is attached to the object to be electroplated The positive end is attached to the object that is being used to coat the other object It will provide a thin coating
74
What is a sacrificial metal and how is it used to protect other metals from corrosion?
It is a metal that is more easily oxidised and it provide protection when it is attached to it. It does this by providing the metal with a small negative charge. This makes the metal more difficult to oxidise and form positively charged ions as this would add even more electrons to an already charged structure. The sacrificial metal corrodes away and needs to be replaced. I.e. A magnesium blocked attached to a steel cable The sacrificial metals sacrifices itself for the other metal

Topic 5 - Why Do Metals Corrode? (4 decks)

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