Corrosion in Ships. Experiment.

Corrosion in Ships. Experiment.

Report Abuse

Report an abuse for product Corrosion in Ships. Experiment.

Categories: , Tag:
Compare

Description

Corrosion in Ships. Experiment.

Download beautifully done presentation via purchasing for free $0

Shipwreck and Salvage
Abstract
Corrosion is a leading cause of marine vessel and equipment failure. A 2002 report by NACE International and the
U.S. Federal Highway Administration found that corrosion can cause up to US $276 billion per year in damages
(NACE International; 2002). This investigation was undertaken to investigate the affect corrosion has on different
metals. These findings can be used to better construct ships and other marine equipment. It was predicted that due to
the nature of rates of reaction that metals in more saline, more acidic, higher temperature environments would corrode
faster. It was also predicted that those metals with paint or zinc coatings would corrode at a slower pace. Five metals’



corrosive rates were investigated: bronze, steel, aluminium, copper and iron. Each metal, with the exception of iron
was given a paint and zinc coating. All were then tested under different salinities, pHs, temperatures and stress for
seven days. The results showed that salinity and temperature had little effect on corrosion within seven days, lower pH
solutions tended to corrode metal faster, while stress had little effect or mixed results. From the investigation, bronze
seemed to be the least affected by different conditions, followed by aluminium, steel, copper and iron, in that order.
Table of Contents
Abstract………………………………………………………………………..0
Introduction…………………………………………………………………0
Aim………………………………………………………………………….3
Research Questions: ……………………………………………….3
Hypotheses: …………………………………………………………….3
Variables………………………………………………………………….3
Materials………………………………………………………………………3
Salinity Method…………………………………………………………..4
pH Method………………………………………………………………….4
Water Temperature Method………………………………………4
Stress Method ……………………………………………………………..4
Data Collection……………………………………………………………5
Salinity Test Results ………………………………………………5
pH Test Results……………………………………………………..6
Stress Test Results………………………………………………….9
Water Temperature Test Results………………………. 10
Dissolved Oxygen Test Results………………………….. 16
Data Processing ……………………………………………………….. 17
Analysis…………………………………………………………………….. 23
Discussion ………………………………………………………………… 24
Appendix ………………………………………………………………….. 26



1
Introduction
“Two large ships sink every week on average
worldwide,” according to Dr Wolfgang
Rosenthal (Lang, J; 2014). An estimated 30% of
disasters involving ships are caused by corrosion,
amounting to around 4% of the Gross National
Product (Marine Corrosion Forum; 2014).
Corrosion is the culprit behind 1600 tonne cargo
ships becoming nothing more than rusted hulls in
the space of a few decades (Simth et al; 2006; pg
130).
General Corrosion
Smith et al. (2006) defined corrosion as the
“degradation of metal so that it loses strength and
becomes unable to fulfil its intended purpose,” (pg
371). Almost all types of corrosion occur due to
electrochemical cell action. This includes an anode,
where oxidation occurs (electrons are lost), a cathode,
where reduction occurs (electrons are gained), a path
bridging the two and a potential difference. There are
10 main types of corrosion, two common ones being
uniform corrosion and crevice corrosion. Uniform
corrosion is identifiable by a surface that has
roughened all over. It is caused by electrochemical cell
action, where parts of the metal with different
compositions become the anode or the cathode.
(Jacobson, A; NACE International). Iron and rust is a
common example of corrosion. Since corrosion is the
oxidation of the metal (ie the metal loses electrons),
the half reaction for iron is:
??(?) → ??2+
(??) + 2?
− … eqn 1
These ??2+ ions move through the iron to another
point where they attach to oxygen that’s dissolved in
moisture on the iron’s surface. The half equation for
the oxygen dissolved in moisture is:
?2(?) + 2?2?(?) + 4?
− → 4??−
(??) … eqn 2
The cell structure can work because the ions move
through the moisture layer (the bridging path). The
point where the iron and oxygen combine becomes
the cathode, and forms insoluble iron (II) hydroxide.
??2+
(??) + 2??−
(??) → ??(??)2(?) … eqn 3
The iron (II) hydroxide then oxidizes by oxygen (lose
electrons to oxygen), which makes rust.
… eqn 4
Generally, the more easily a metal oxidizes, the more
easily it corrodes (Smith et al; 2006; pg 371–374).
Reactivity Series and Redox Reactions
The reactivity series is an organisation of metals
according to their standard electrode potentials.
Electrode potentials (or voltages) are assigned to
metals relative to the standard hydrogen electrode.
‘Standard’ refers to an electrode in an electrolyte
concentration of 1.000mol/L and gas pressure of
100.0kPa. These values are also used in reduction half
reactions to calculate the voltage of a cell (Smith et al;
2006; pg 362 – 363).
The table can be used to predict the products of
single displacement reactions. A metal can replace one
below, but not one above (see figure 1)
Figure 1: Standard electrode potentials at 25°C
Source: Smith et al; 2006; pg 365
2
For example, zinc can replace copper, but copper
cannot replace zinc.
??(?) + ??2+
(??) → ??2+
(??) + ??(?)
… eqn 5
To calculate electromotive force (EMF), firstly write
the half reactions for the cell then substitute into:
???⊝
????? = ???⊝
???????? +???⊝
?????????
For copper with silver ions:
??(?) + 2??+
(??) → ??2+
(??) + 2??(?) … eqn6
The half reactions are:
2??+
(??) + 2?
− → 2??(?) … eqn 6.1
??(?) → ??2+
(??) + 2?
− … eqn 6.2
So, using the values from table 1:
???⊝
????? = ???⊝
???????? +???⊝
?????????
???⊝
????? = ?

?? + (−?

??)
= 0.80 − 0.34
= 0.46 ?
The reactivity series contains only metals, therefore
when they react, they form positive ions. Their
different reactivity is due to the stability of their
electron configurations. Those with more electrons are
more reactive due to their outermost electrons being
further from the nucleus and hence having a weaker
bonding force (Jarman, R; College of DuPage).
Ionic Solutions (Salinity)
Ionic solutions are formed by dissolving an ionic
substance in water (BBC Bitesize; 2014). Salinity is a
measure of the amount of salts dissolved in water. The
average level in marine environments is 35 ppt. In
oceans, salinity can be affected by temperatures,
evaporation, and the dissolved rock and soil material
from rivers entering the ocean. Salinity levels vary
around the globe – with different topography and
weather conditions – and with the depth of water –
more saline water is denser, so sinks. (University of
Waikato; 2010).
Dr. Hasan of Nahrain University-Baghdad-Iraq
investigated the effect of salt on corrosion. It was
concluded that “increased salt content led to a higher
corrosion rate and higher electrical conductivity.”
Higher electrical conductivity allows for the transfer
of ions from the metal to occur at a quicker pace.
Since water can act as a salt bridge for the metal, water
Figure 2: Salts in Seawater
NaCl accounts for 85.7% of salt in seawater,
making it the main component in saline water.
Source: University of Rhode Island; 2001
Figure 3: Effect of Salinity on corrosion rates
It can be seen that at 30°C, sea water (3.5% salt
content) has the highest corrosion rate compared
to lower salinity and distilled water.
Source: Hasan, B; 2010
2
with more salt containing more free ions provides a
faster passage for the metal.
Oxidation-Reduction Reactions
Oxidation-reduction or redox reactions refer to the
simultaneous loss and gain of electrons in a reaction.
??(?) + ??2(?) → ????2(?) … eqn 7
In equation 1, magnesium is oxidised; it loses
electrons to chlorine, effectively making it positively
charged. Chlorine gains electrons, so it is therefore
reducing.
?? → ??2+ + 2?
−… eqn 7.1
??2 + 2?
− → 2??− … eqn 7.2
Equations 2 and 3, called half equations, show the
oxidation of each element separately.
An oxidation number – the charge an element would
have it were completely ionic – is assigned to each
element. An increase in oxidation number is a sign
that oxidation has occurred, whereas a decrease
indicates reduction (Smith et.al; 2006; pg 310–319).
Cathodic Protection and Passivation
Cathodic protection is a way of preventing corrosion
where a metal is covered in a more reactive metal,
making it the cathode of a galvanic cell (Smith et.al;
2006; pg 377–380). Oftentimes, a precious metal is
added to a less expensive one. The precious metal
(such as gold or silver) will become the anode and the
less precious will be the cathode, like a silver coated
spoon. The anode dissolves and the precious metal’s
ions transfer to the cathode, where they form a
coating (Vorderman, C; 2012; pg 149).
For instance, steel is often covered in zinc. Zinc is a
common choice for cathodic protection as it is
reactive but forms an unreactive surface coating when
in contact with oxygen and water, which prevents it
from corroding; it has moderate passivating
properties. Other metals like barium, calcium and
sodium react too quickly to be efficient in ship
building (Smith et.al; 2006; pg 377–380).
Passivation involves adding a coating, such as paint or
zinc, to a metal to protect it from damage caused by
corrosion (CorrosionPedia; 2016). Self-passivation is
the formation of an unreactive layer of substances
such as oxygen on a reactive metal. For example,
aluminium forms a dull oxide layer which prevents it
from corrosion. However, not all metals are reactive
and passivate. Iron for example will continue to
corrode until the entire piece becomes the oxide
(Smith et al; 2006; pg 135).
pH and corrosion
All metals are covered with an oxide layer, which
dissolves in aqueous solutions (Thomas, J; National
Physical Laboratory). N. Al-Meer of the Foundation
of Technical Education conducted an experiment on
the effect pH and temperature have on corrosion rate
in 2011. The experiment concluded that the corrosion
rate was stable at pH8 – pH6, but accelerated at a pH
of 3. Seawater has a pH of around 8 (Smith et.al;
2006; pg 376), meaning that the corrosion of marine
vessels should not be worsened due to acidic
environments. According to Smith et al. normal
galvanic corrosion (corrosion caused by the transfer of
electrons and ions from metal to solution) occurs
more rapidly in acidic solutions than alkaline ones.
The half reactions for the corrosion of iron in water
are:
Fe(?) → ??2+
(??) + 2?
− … eqn 8 (anodic
process)
?2(?) + 2?2?(?) + 4?
− → 4??−
(??) … eqn 9
(cathodic process)
Temperature
The experiment undertaken by Dr. Hasan, also
concluded that increases in temperature increased the
Figure 4: The silver dissolves and its ions are
transferred to the object being plated, thus coating it
silver. This process is also known as electroplating.
Source: GCSE Bitesize; 2012
2
corrosion rate by changing the amount of oxygen able
to be dissolved in the water. Increased temperature
also led to a higher electrical conductivity (Hasan, B;
2010). Since oxygen features in the cathodic process
of corrosion (see eqn 2 and 3), an increase in
temperature, and therefore oxygen content, would
affect the balance of the equation. Not only that, but
also temperature is factor that when increased,
increases the rate of reaction. So therefore, the rate of
corrosion would be expected to increase with
temperature.
In a 2014 investigation into the effect of temperature
on carbon steel by Yameng Qi et al, it was concluded
that “temperature played a significant role in the
corrosion rate of steel in hydrogen sulphide
environment. The corrosion rate reached maximum
value at 40 °C, then gradually decreased obviously
with temperature.”

 

 

 

Aim
The aim of this experiment is to determine which
metals and corrosion-prevention measures are best
suited to a marine environment.
Research Questions:
Which metal is the best to use in ship building based
on its resistance to changes in pH, salinity,
temperature and stress so that corrosion is minimal?
To what extent do protective measures, such as
painting and zinc spraying, prevent corrosion?
Hypotheses:
Due to the nature of rates of reaction (where higher
concentrations, more surface area, higher temperature
ad catalysts speed up reactions) and electrochemistry
involved in corrosion, it is predicted that metals in
more acidic, more saline and higher temperature
situations will corrode at a faster rate.
It is also predicted that metals covered in either paint
of zinc spray will corrode slower as the extra layer
isolates the metal and prevents it from forming a
galvanic cell.
Variables
Independent Dependent
Salinity Mass
pH Dissolved oxygen
Temperature
Stress points
To make this a fair test, all metals being compared
will need to be added to their solution at the same
time and removed at the same time.
Materials
– 325ml 1.5% saline solution
– 1.9L 3.5% saline solution
– 325ml 10% saline solution
– 11x steel
– 11x painted steel
– 11x zinc sprayed steel
– 9x iron
Table 1: Independent and dependent variables for
experiments
Figure 5: Effect of varying temperatures on distilled water.
It is clear that at higher temperatures, the corrosion rate is
higher.
Source: Hasan, B; 2010
2
– 11x bronze
– 11x painted bronze
– 11x zinc sprayed bronze
– 11x aluminium
– 11x painted aluminium
– 11x zinc sprayed aluminium
– 11x copper
– 11x painted copper
– 11x zinc sprayed copper
– 141 test tubes
– 325ml vinegar
– 325ml distilled water
– 325ml ammonia
– Incubator
– Fridge
– Probe to record DO levels
– Laptop or iPad to connect probe to
– 50ml measuring cylinder
– Scales
Salinity Method
1. Weigh 3 of each metal and record its mass
2. Fill 13 test tubes with 1.5% saline solution,
13 with 3.5% solution and 13 with 10%
solution (25 ml in each)
3. Place one of each meal in a test tube of each
salinity (eg. 1 painted copper in each of
1.5%, 3.5% and 10%)
4. Cover all test tubes with glad wrap to avoid
evaporation
5. Every few days record any observable
changes and take photos
6. After 7 days empty the test tubes of solution
using a funnel over a waste container and
weigh the metal (for iron filings, filter paper
will need to be used)
pH Method
1. Weigh 3 of each metal and record its mass
2. Fill 13 test tubes with 25ml each of vinegar
3. Fill 13 test tubes with 25ml each of distilled
water
4. Fill 13 test tubes with 25ml each of
ammonia
5. Place one of each metal in a test tube of each
solution of a different pH
6. Cover all test tubes with glad wrap to avoid
evaporation
7. Record any observations every few days
8. After 7 days, drain test tubes using a funnel
and waste container (use filter paper for iron
filings)
Water Temperature
Method
1. Weigh mass of 3 of each metal and record
2. Fill 39 test tubes with 25ml 3.5% salinity
solution each
3. Place one of each metal in a test tube
4. Place 13 test tubes in fridge at 10°C
5. Place 13 test tubes in incubator at 35°C
6. Leave the remaining 13 at room temperature
7. Cover all test tubes with glad wrap to avoid
evaporation
8. Every few days record dissolved oxygen
levels
9. Record any observations during the
experiment
10. After 7 days empty test tubes of solution
and weigh final mass of metals
Stress Method
1. Weigh and record the mass of 3 of each
metal
2. Fill 24 test tubes each with 25ml 3.5%
salinity solution
3. Place one metal in each test tube
4. Cover all test tubes with glad wrap to avoid
evaporation
5. Record any observations during the
experiment
6. After 7 days empty tubes of solution and
record final mass
Metal
Solution: different salinities,
pHs or 3.5% saline solution
Test tube
Glad wrap secured with
elastic band
2
Data Collection
Salinity Test Results
1.5% 3.5% 10%
Initial
Mass
(g)
Final
Mass
(g)
Difference Initial
Mass
(g)
Final
Mass
(g)
Difference Initial
Mass
(g)
Final
Mass
(g)
Difference
Bronze
1.47 1.46 -0.01 1.43 1.43 0 1.44 1.43 -0.01
Iron
2.00 1.82 -0.18 2.01 1.96 -0.05 2.01 2.03 +0.02
Copper
0.46 0.46 0 0.67 0.67 0 0.32 0.31 -0.01
Aluminium
0.32 0.32 0 0.30 0.31 +0.01 0.64 0.66 +0.02
Steel
2.41 2.41 0 2.41 2.41 0 2.40 2.40 0
P Bronze
1.59 1.57 -0.02 1.66 1.64 -0.02 1.58 1.58 0
P Copper
0.58 0.56 -0.02 1.07 1.07 0 1.09 1.09 0
P
Aluminium 0.37 0.36 -0.01 0.43 0.43 0 0.37 0.37 0
P Steel
2.51 2.50 -0.01 2.58 2.57 -0.01 2.22 2.54 +0.32
G Steel
2.31 2.31 0 1.90 1.89 -0.01 2.55 2.22 -0.33
Z Bronze
1.42 1.42 0 1.46 1.47 +0.01 1.42 1.43 +0.01
Z Copper
0.86 0.86 0 0.81 0.81 0 0.47 0.47 0
Z
Aluminium 1.10 1.10 0 0.36 0.36 0 1.52 1.53 +0.01
Table 2: Results of Salinity Test
Figure 6: Setup of all test tubes will be like this.
2
Observations:
13.05.16
Steel: Much the same as before and across all salinities
Aluminium: Much the same as before and across all salinities
Iron: Lots of orange precipitate (rust), silver parts on bottom, 10% salinity has slightly more rust
Bronze: Orange precipitate (rust), same across all salinities
Copper: Blue/green dots (discoloration), water has turned a bluish colour, more so in 10%]
G. Steel: Much the same as before and across all salinities
Zn Aluminium: Much the same as before and across all salinities
Zn Bronze: 3.5% and 1% have yellow precipitate (gaps in coating?), 10% same as before
Zn Copper: Much the same as before and across all salinities
P Steel: Much the same as before and across all salinities
P Aluminium: Much the same as before and across all salinities
P Bronze: Much the same as before and across all salinities (3.5% may have had gaps in paint)
P Copper: Much the same as before and across all salinities
pH Test Results
Vinegar Distilled Water Ammonia
Initial
Mass
(g)
Final
mass
(g)
Difference Initial
Mass (g)
Final
Mass
(g)
Difference Initial
Mass
(g)
Final
Mass
(g)
Difference
Aluminium
0.35 0.35 0 0.92 0.91 -0.01 1.88 1.87 -0.01
Steel
2.41 2.41 0 2.43 2.42 -0.01 2.41 2.40 -0.01
Copper
0.33 0.31 -0.02 2.03 1.07 -0.96 0.42 0.18 -0.24
Bronze
1.42 1.23 -0.19 1.53 1.53 0 1.49 1.49 0
Iron
(filings) 2.00 1.72 -0.28 2.02 2.18 +0.16 2.03 2.09 +0.06
P
Aluminium 0.45 0.46 +0.01 0.37 0.38 +0.01 0.26 0.32 +0.06
P Steel
2.51 2.50 -0.01 2.53 2.53 0 2.54 2.54 0
P Copper
0.39 0.38 -0.01 1.11 1.09 -0.02 0.70 0.63 -0.07
P Bronze
1.55 1.54 -0.01 1.59 1.56 -0.03 1.62 1.62 0
Z
Aluminium 0.82 0.87 +0.05 0.67 0.69 +0.02 0.82 0.85 +0.03
Galvanised
Steel 2.27 2.00 -0.27 2.59 2.60 +0.01 1.85 1.84 -0.01
Z Copper
2
0.96 1.02 +0.06 0.63 0.65 +0.02 0.47 0.39 -0.08
Z Bronze
1.47 1.38 -0.09 1.40 1.41 +0.01 1.44 1.45 +0.01
Observations
Day 2 Recordings – 13/05/16
Vinegar
Steel – Discoloured water and starting to tarnish. Zinc coating (galvanisation) starting to deteriorate.
Painted Aluminium – No visible signs of corrosion
Painted Bronze – No visible signs of corrosion
Zinc Sprayed Copper – Green precipitate forming (copper forming)
Copper – Tarnish on tip of metal (metal above vinegar level so possibly vinegar dried on surface and tarnished slightly)
Bronze – Slightly discoloured water and tarnish starting to occur
Steel – No visible signs of corrosion
Painted Steel – No visible signs of corrosion
Zinc Sprayed Aluminium – Bubbling of the zinc coating
Aluminium – No visible signs of corrosion except for possible signs on rust on edges of metal
Iron – Discoloured water and oily, silver precipitate forming on the surface
Zinc Sprayed Bronze – No visible signs of corrosion
Painted Copper – Precipitate forming of metal
Distilled Water
Painted Aluminium – No visible signs of corrosion
Steel – No visible signs of corrosion
Copper – No visible signs of corrosion
Aluminium – No visible signs of corrosion
G. Steel – Cloudy water with a white precipitate forming on bottom of test tube
Painted Bronze – No visible signs of corrosion
Painted Copper – No visible signs of corrosion
Iron – Discoloured water and a group of iron filing on the surface of the distilled water. Iron filings also clumped
together at the bottom of the test tube
Zinc Sprayed Copper – No visible signs of corrosion
Zinc Sprayed Bronze – Rust occurring on the tip of the nail (possible the zinc coating was not properly applied)
Zinc Sprayed Aluminium – No visible signs of corrosion
Bronze – Particles in the distilled water and rust on the bottom of the test tube
Painted Steel – No visible signs of corrosion
Ammonia
Iron – Discoloured solution. Iron on surface of the solution and also grouped together at the bottom
Painted Steel – No visible signs of corrosion
Bronze – Solution has turned blue and particles in the solution
Aluminium – No visible signs of corrosion
Steel – No visible signs of corrosion
Copper – Blue discoloured water with a blue precipitate on the top of the metal (copper forming)
G. Steel – No visible signs of corrosion
Copper – Dark blue/violet solution
Zinc Sprayed Copper – Solution has turned slightly blue and bubbling has occurred on the metal
Zinc Sprayed Bronze – No visible signs of corrosion
Zinc Sprayed Aluminium – Bubbling precipitate on the metal
Painted Aluminium – Bubbling on paint that was applied to the metal
Painted Bronze – Solution has slightly turned blue. No signs of corrosion though
Table 3: Results of pH Test
2
Day 5 Recordings – 16/05/16

Vinegar
Painted Steel – No visible signs of corrosion
Aluminium – No visible signs of corrosion
Zinc Sprayed Aluminium – Bubbles formed on the metal
Iron – Dark coloured solution
Zinc Sprayed Bronze – Discoloured water
Painted Aluminium – No visible signs of corrosion
Steel – No visible signs of corrosion
Painted Bronze – No visible signs of corrosion
Painted Copper – Precipitate on metal however no signs of corrosion
Copper – Discoloured solution (slightly blue)
Zinc Sprayed Copper – Green precipitate on the exposed metal (exposed to air). Zinc coating starting to lift/crack
G. Steel – Discoloured solution to a reddish brown. Metal is starting to rust
Bronze – Discoloured solution to a reddish brown.
Distilled Water
Aluminium – No visible signs of corrosion
Zinc Sprayed Copper – No visible signs of corrosion
Steel – No visible signs of corrosion
Iron – Group of iron on surface and on the bottom of the test tube
Zinc Sprayed Bronze – Rusting on the tip of the nail
Painted Copper – No visible signs of corrosion
Painted Bronze – No visible signs of corrosion
Painted Aluminium – No visible signs of corrosion
Zinc Sprayed Aluminium – No visible signs of corrosion
Painted Steel – No visible signs of corrosion
Bronze – Rust forming on the bottom of the test tube
G. Steel – Cloudy substance/precipitate on the bottom of the solution (covers metal)
Copper – Green spot on the exposed metal. No other visible changes.
Ammonia
Painted Aluminium – Paint layer starting to bubble
Copper – Dark blue solution. Metal is no longer visible
Zinc Sprayed Copper – Zinc layer is no longer visible. Blue solution
Painted Bronze – Slightly blue solution
G. Steel – Tarnish layer forming
Zinc Sprayed Bronze – Rusting starting to occur
Zinc Sprayed Aluminium – Cloudy substance at the bottom of the solution. Large cloudy bubbles formed on the metal.
Iron – Discoloured water with iron formation on the surface and at the bottom of the test tube
Aluminium – No visible signs of corrosion
Painted Copper – Dark blue solution. Green precipitate forming on the exposed metal
Steel – No visible signs of corrosion
Bronze – Blue coloured solution
Painted Steel – No visible signs of corrosion
2
Stress Test Results
Unstressed Stressed
Initial Mass
(g)
Final Mass (g) Difference Initial Mass
(g)
Final Mass (g) Difference
Steel
2.41 2.41 0 2.41 2.41 0
Copper
0.75 0.75 0 0.69 0.70 +0.01
Bronze
1.45 1.45 0 1.43 1.42 -0.01
Aluminium
0.82 0.83 +0.01 1.29 1.28 -0.01
P Steel
2.48 2.47 -0.01 2.55 2.54 -0.01
P Copper
1.12 1.10 -0.02 0.69 0.69 0
P Bronze
1.62 1.62 0 1.64 1.65 +0.01
P Aluminium
0.29 0.30 +0.01 1.22 1.22 0
Z Steel
2.45 2.45 0 2.27 2.26 -0.01
Z Copper
0.48 0.48 0 0.55 0.56 +0.01
Z Bronze
1.47 1.48 +0.01 1.41 1.42 +0.01
Z Aluminium
0.35 0.36 +0.01 1.26 1.27 +0.01
Table 4: Results of Stress Test
2
Day 2 – 13.5.16 Day 3 – 16.5.16 Day 4 – 17.5.16 Day 5 – 18.5.16
Steel No visible changes No visible changes No visible changes No visible changes
Steel P No visible changes No visible changes No visible changes No visible changes
Steel G White precipitate
forming in the
bottom of the test
tube.
White precipitate
forming in the
bottom of the test
tube.
White precipitate
forming in the
bottom of the test
tube and metal is
rusting in a mottled
colour.
White precipitate
forming in the
bottom of the test
tube and metal is
rusting in a mottled
colour.
Copper Water turning a pale
blue
Water turning a
greeny blue colour
Water is a light
greeny blue
Water is a light
greeny blue
Copper P No visible changes No visible changes No visible changes No visible changes
Copper Z No visible changes Rust bubbles
forming on the metal
Rust bubbles
forming on the metal
Rust bubbles
forming on the metal
Bronze Rust accumulating in
the bottom of the
test tube
Rust accumulating in
the bottom of the
test tube
Rust accumulating in
the bottom of the
test tube and screw is
showing visible signs
of rust
Rust accumulating in
the bottom of the
test tube and screw is
showing visible signs
of rust
Bronze P FIRST DAY Rust accumulating in
the bottom of the
test tube
Rust accumulating in
the bottom of the
test tube and end of
the screws are rusting
Rust accumulating in
the bottom of the
test tube and end of
the screws are rusting
Bronze Z FIRST DAY Rust accumulating in
the bottom of the
test tube
Rust accumulating in
the bottom of the
test tube and end of
the screws are rusting
Rust accumulating in
the bottom of the
test tube and end of
the screws are rusting
Aluminium No visible changes White precipitate
forming on the metal
and white precipitate
on the bottom of the
test tube
White precipitate
forming on the metal
and white precipitate
on the bottom of the
test tube
White precipitate
forming on the metal
and white precipitate
on the bottom of the
test tube
Aluminium P No visible changes No visible changes No visible changes No visible changes
Aluminium Z No visible changes No visible changes No visible changes No visible changes
Water Temperature Test Results
35°C Room Temperature 10°C
Initial
Mass (g)
Final
Mass (g)
Difference Initial
Mass (g)
Final Mass
(g)
Difference Initial
Mass (g)
Final
Mass (g)
Difference
Copper
0.51 0.49 -0.02 0.51 0.49 -0.02 0.50 0.49 -0.01
Bronze
Table 5: Observations of Stress Test
2
1.43 1.45 0.02 1.44 1.44 0.00 1.43 1.43 0.00
Aluminium
0.28 0.28 0.00 0.52 0.50 -0.02 0.35 0.34 -0.01
Steel
2.42 2.41 -0.01 2.42 2.41 -0.01 2.42 2.41 -0.01
Iron
2.01 2.17 0.16 2.01 2.15 0.14 2.01 2.12 0.11
P Copper
1.10 1.10 0.00 1.61 1.60 -0.01 0.52 0.52 0.00
P Bronze
1.65 1.69 0.04 1.52 1.55 0.03 1.64 1.65 0.01
P Aluminium
0.29 0.27 -0.02 0.25 0.25 0.00 0.50 0.50 0.00
P Steel
2.50 2.48 -0.02 2.56 2.55 -0.01 2.56 2.55 -0.01
Z Copper
0.23 0.27 0.04 0.34 0.34 0.00 0.26 0.26 0.00
Z Bronze
1.51 1.51 0.00 1.41 1.42 0.01 1.52 1.52 0.00
Z
Aluminium 0.31 0.31 0.00 0.21 0.21 0.00 0.31 0.31 0.00
Z Steel
2.43 2.43 0.00 2.52 2.51 -0.01 2.30 2.30 0.00
Table 6: Results of Water Temperature Test
2
MATERIALS INITIAL HALFWAY FINAL
Copper Shiny copper in clear
water. No visible signs
of corrosion.
Slight blue/green tarnish on
metal. Water has a blue/green
tinge.
Very blue/green
water. Very visible
tarnish all over copper.
Painted Copper Paint intact, clear
water. No visible signs
of corrosion.
Some flecks of paint have fallen
off. Tarnish is visible in these
small areas.
Small tarnish in areas
with gaps in paint
coat. No other visible
signs of corrosion.
Zinc Sprayed Copper Zinc coating fully
intact, water clear. No
visible signs of
corrosion.
No visible signs of corrosion.
Zinc coating fully intact.
No visible signs of
corrosion. Zinc
coating full intact.
Bronze Bronze coating fully
intact, water clear. No
visible signs of
corrosion.
Most bronze has fallen off screw
(now on bottom of test tube as
an orange substance). Slight
visible signs of corrosion on nail
(now without bronze coating).
All bronze coating
fallen off, now orange
precipitate at bottom.
Screw beginning to
turn red (rust).
Painted Bronze Paint coating fully
intact, water clear. No
visible signs of
corrosion.
Visible signs of rusting (reddish
blemish and slight precipitateprobably
bronze coating
beginning to fall off) in one
particular area.
Area had grooves (due to metal
sample being a screw). Therefore,
these observations were probably
as a result of a gap/hole/missed
area in paint coating.
Very large area
tarnished (red
blemish) in same area
as previous
observation (has
grown). Bronze
coating has fallen off
within this area.
Orange substance at
bottom of test tube,
probably bronze
coating which has
come off
Zinc Sprayed Bronze Zinc coating fully
intact, water clear. No
visible signs of
corrosion.
Coating seems mostly intact,
slight reddish blemishes in small
areas in which zinc coating has
gaps/flaking/cracks/bubbles.
Water has very slight orange
tinge.
Water tinged orange,
slight tarnish in areas
where there is a gap in
zinc coating.
Aluminium Slightly shiny metal in
good condition. No
tarnish, clear water. No
visible signs of
corrosion.
White precipitate beginning to
form. Slight orange tinge on
metal in small areas. Water clear
with some floating white
precipitate.
Lots of white
precipitate. Slight
orange tinge on metal.
Painted Aluminium Paint coating fully
intact, water clear. No
visible signs of
corrosion.
No visible signs of corrosion No visible signs of
corrosion
Zinc Sprayed Aluminium Zinc coating fully
intact. Water clear. No
visible signs of
corrosion.
No visible signs of corrosion Very small amounts of
red/orange tinge on
small parts of the
metal
Steel Shiny metal in good
condition, clear water.
No visible signs of
corrosion.
Slight greenish precipitate
Small amount of orange tinge in
areas
Hardly any signs of corrosion
Slight increase in areas
with orange tinge. No
other changes.
Painted Steel Paint coating fully
intact, clear water. No
No visible signs of corrosion No visible signs of
corrosion
2
visible signs of
corrosion.
Galvanised Steel Shiny metal, clear
water. No visible signs
of corrosion.
Very small amount of dark
precipitate on metal.
Slightly more dark
tarnish/precipitate
than previous
Iron (filings) Filings sitting at
bottom of test tube,
clear water. No visible
signs of corrosion.
Filings in clusters; orange/red
precipitate (some floating
particles); some slight silver
colour; filings visibly packed
more tightly
Filings still in clusters
Very dark
More orange/red
particles
Table 6: Observations of Water Room Temperature Test
2
MATERIALS INITIAL HALFWAY FINAL
Copper Shiny metal in good
condition. Water clear.
Tiny flecks of bluish tarnish,
otherwise no other visible signs
of corrosion. Water very slightly
tinges blue/green.
Small amounts of
bluish detail. Water
slightly blue/green.
Painted Copper Paint coating fully
intact. Water clear.
No visible signs of corrosion.
Water clear.
No visible signs of
corrosion. Water clear.
Zinc Sprayed Copper Zinc coating fully
intact. Water clear.
No visible signs of corrosion.
Water clear.
No visible signs of
corrosion. Water clear.
Bronze Bronze coating fully
intact. Water clear.
All bronze coating off, water
mostly clear. Substance at bottom
of test tube, probably bronze
coating.
Bronze coating now
lying on bottom of
test tube, screw turned
a slight red colour (not
bronze). Water clear
except for bronze
particles.
Painted Bronze Paint coating fully
intact. Water clear.
Clear water. Small area of screw
has slight reddish tinge. No other
visible signs of corrosion. This
area may not have been fully
coated, explaining why this area
has slight signs of corrosion.
Slight areas of tarnish
(red/orange colour),
larger than that in
previous observations.
Water clear.
Zinc Sprayed Bronze Zinc coating fully
intact. Water clear.
Clear water. Very tip of screw
has slight reddish tinge. No other
visible signs of corrosion. Tip of
screw may not have been fully
coated, explaining why this area
has slight signs of corrosion.
Signs of tarnish
(reddish tinge) on tip,
larger area than
previous observation.
Clear water.
Aluminium Slightly shiny metal in
good condition. Water
clear.
Very small amount of white
precipitate, tiny amount of
orange tinge in small areas.
Water clear except for a few
particles of precipitate.
Slight growth in
orange area. No other
changes since last
observations.
Painted Aluminium Paint coating fully
intact. Water clear.
No visible signs of corrosion.
Water clear.
No visible signs of
corrosion. Water clear.
Zinc Sprayed Aluminium Zinc coating fully
intact. Water clear.
Slight bubbling of zinc coating
(possibly was not fully dry). No
visible signs of corrosion. Water
clear.
No changes since last
observations.
Water clear.
Steel Shiny metal in good
condition. Water clear.
No visible signs of corrosion.
Water clear.
No visible signs of
corrosion. Water clear.
Painted Steel Paint coating fully
intact. Water clear.
Tiny amounts of white
precipitate. Paint slightly bubbled
(may not have been fully dry).
No other visible signs of
corrosion, water clear except for
small amounts of precipitate.
No changes since
previous observations.
Water clear except for
small amounts of
precipitate.
Galvanised Steel Shiny metal in good
condition. Water clear.
Very small areas with dark
tarnish. Water clear.
Small areas with dark
tarnish. Water clear.
Iron (filings) Filings settled at
bottom of test tube.
Water clear.
Some clustering and slight red
precipitate.
Clustering with red
precipitate at edges.
Table 7: Observations of Water Temperature (Fridge)Test
2
MATERIALS INITIAL HALFWAY FINAL
Copper Shiny metal in good
condition. Water clear.
Blue/green tarnish in all grooves.
Water has bluish tinge.
Blue-green cloudy
water. Cloudy
precipitate on glass on
test tube. Blue/green
tarnish on metal.
Painted Copper Paint coating fully
intact. Water clear.
No visible signs of corrosion.
Water clear.
No visible signs of
corrosion. Water clear.
Zinc Sprayed Copper Zinc coating fully
intact. Water clear.
No visible signs of corrosion.
Water clear.
Bubbling of zinc
coating. Water clear.
No other signs of
corrosion.
Bronze Bronze coating fully
intact and screw in
good condition. Water
clear.
All bronze coating fallen off,
lying as orange precipitate on
bottom. Water clear.
Screw (without bronze
coating) slight reddish
colour. Water clear
Painted Bronze Paint coating fully
intact. Water clear.
Paint beginning to fall off. Small
areas reddish/orange. Water
clear.
Large areas of
reddish/orange colour.
Water clear.
Zinc Sprayed Bronze Zinc coating fully
intact. Water clear.
Most zinc coating intact. Some
orange precipitate (from the
bronze coating falling off). Zinc
may not have fully covered screw.
No major changes
since last observations.
Slightly more orange
precipitate.
Aluminium Slightly shiny metal in
good condition. Water
clear.
Slight amount of white
precipitate. Small flecks
orange/red. Water clear.
No changes since last
observations.
Painted Aluminium Paint coating fully
intact. Water clear.
Slight bubbling of paint. No
other visible signs of corrosion.
Water clear.
No changes since last
observations.
Zinc Sprayed Aluminium Zinc coating fully
intact. Water clear.
No visible signs of corrosion.
Water clear.
No visible signs of
corrosion. Water clear.
Steel Shiny metal in good
condition. Water clear.
No visible signs of corrosion.
Water clear.
No visible signs of
corrosion. Water clear.
Painted Steel Paint coating fully
intact. Water clear.
Slight bubbling of paint. Water
clear. No visible signs of
corrosion.
No changes since last
observations.
Galvanised Steel Zinc coating fully
intact. Water clear.
Dark tarnish and slight
precipitate on metal. Water clear.
Very small amounts of
white precipitate. Dark
tarnish and precipitate.
Water clear.
Iron (filings) Filings settled at
bottom of tube. Water
clear.
Clusters with some reddish
particles. Water clear.
More reddish areas.
Water clear.
Table 8: Observations of Water Temperature (Incubator)Test
2
Dissolved Oxygen Test Results
35°C Room Temperature 10°C
Initial
DO (%)
Final
DO(%)
Difference Initial
DO (%)
Final
DO(%)
Difference Initial
DO (%)
Final
DO(%)
Difference
Copper
40 41 +1 41 36 -5 37 35 -2
Bronze
41 39 -2 40 34 -6 41 40 -1
Aluminium
43 40 -3 43 34 -9 41 39 -2
Steel
44 37 -7 43 40 -3 41 39 -2
Iron
40 40 0 41 25 -16 34 33 -1
P Copper
44 41

3 41 36 -5 35 33 -2
P Bronze
42 39 -3 42 37 -5 44 41 -3
P Aluminium
44 38 -6 42 40 -2 37 36 -1
P Steel
45 34 -11 43 39 -4 40 35 -5
Z Copper
40 40 0 37 34 -3 38 37 -1
Z Bronze
41 33 -8 43 39 -4 39 33 -6
Z
Aluminium 41 41 0 43 39 -4 41 42 +1
Z Steel
36 35 -1 35 37 +2 42 42 0
Table 9: Results of Dissolved Oxygen Test
2
Data Processing
-0.2 -0.18 -0.16 -0.14 -0.12 -0.1 -0.08 -0.06 -0.04 -0.02 0 0.02 0.04
Bronze
Iron
Copper
Aluminium
Steel
Change in mass (g)
Salinity’s Effect on Unprotected Metal
10% 3.50% 1.50%
-0.35 -0.3 -0.25 -0.2 -0.15 -0.1 -0.05 0 0.05
Bronze
Copper
Aluminium
Steel
Change in Mass (g)
Salinity’s Effect on Zinc Sprayed Metal
10% 3.50% 1.50%
-0.05 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35
Bronze
Copper
Aluminium
Steel
Change in Mass (g)
Salinity’s Effect on Painted Metal
10% 3.50% 1.50%
Figure 7: The Effect of Salinity on Unprotected Metal
Figure 8: The Effect of Salinity on Zinc Sprayed Metal
Figure 9: The Effect of Salinity on Painted Metal
2
-0.04 -0.02 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18
Copper
Bronze
Aluminium
Steel
Iron (filings)
Change in Mass (g)
Temperature’s Effect on Unprotected Metal
10°C Room Temperature 35°C
-0.02 -0.01 0 0.01 0.02 0.03 0.04 0.05
Zinc Sprayed Copper
Zinc Sprayed Bronze
Zinc Sprayed Aluminium
Galvanised Steel
Change in Mass (g)
Temperature’s Effect on Zinc Sprayed Metal
10°C Room Temperature 35°C
-0.03 -0.02 -0.01 0 0.01 0.02 0.03 0.04 0.05
Painted Copper
Painted Bronze
Painted Aluminium
Painted Steel
Change in Mass (g)
Temperature’s Effect on Painted Metal
10°C Room Temperature 35°C
Figure 10: The Effect of Temperature on Unprotected Metal
Figure 11: The Effect of Temperature on Zinc Sprayed Metal
Figure 12: The Effect of Temperature on Painted Metal
2
-0.015 -0.01 -0.005 0 0.005 0.01 0.015
Copper
Bronze
Aluminium
Steel
Change in Mass (g)
Effect of Stress on Unprotected Metal
Not Stressed Stressed
-0.015 -0.01 -0.005 0 0.005 0.01 0.015
Copper
Bronze
Aluminium
Steel
Change in Mass (g)
Effect of Stress on Zinc Sprayed Metal
Not Stressed Stressed
-0.025 -0.02 -0.015 -0.01 -0.005 0 0.005 0.01 0.015
Copper
Bronze
Aluminium
Steel
Change in Mass (g)
Effect of Stress on Painted Metal
Not Stressed Stressed
Figure 12: The Effect of Stress on Unprotected Metal
Figure 13: The Effect of Stress on Zinc Sprayed Metal
Figure 14: The Effect of Stress on Painted Metal
2
-1.2 -1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4
aluminium
steel
copper
bronze
iron
Change in Mass (g)
Effect of pH on Unprotected Metal
ammonia water vinegar
-0.3 -0.25 -0.2 -0.15 -0.1 -0.05 0 0.05 0.1
aluminium
steel
copper
bronze
Change in Mass (g)
Figure: Effect of pH on Zinc Sprayed Metal
ammonia water vinegar
-0.08 -0.06 -0.04 -0.02 0 0.02 0.04 0.06 0.08
aluminium
steel
copper
bronze
Change in mass (g)
Effect of pH on Painted Metal
ammonia water vinegar
Figure 15: The Effect of pH on Unprotected Metal
Figure 16: The Effect of pH on Zinc Sprayed Metal
Figure 17: The Effect of pH on Painted Metal
2
-18 -16 -14 -12 -10 -8 -6 -4 -2 0 2
Copper
Bronze
Aluminium
Steel
Iron
Change in DO (%)
Dissolved Oxygen Levels of Unprotected Metals
10°C Room Temperature 35°C
-10 -8 -6 -4 -2 0 2 4
Copper
Bronze
Aluminium
Steel
Change in DO (%)
DO Levels of Zinc Sprayed Metals
10°C Room Temperature 35°C
-12 -10 -8 -6 -4 -2 0
Copper
Bronze
Aluminium
Steel
Change in DO (%)
DO Levels of Painted Metals
10°C Room Temperature 35°C
Figure 18: Dissolved Oxygen Levels of Unprotected Metals
Figure 20: Dissolved Oxygen Levels of Painted Metals
Figure 19: Dissolved Oxygen Levels of Zinc Sprayed Metals
2
Average changes for metals
Iron in different salinities:
??????? =
−0.18+0.02−0.05
3
… eqn 10
= −0.07
Uncertainty in mean:
0.02−0.18
2
… eqn 11
−0.08
The average change in mass for iron in salinity = −0.07 ± 0.08
Metals with stressed points
Metal Average Change (g)
Steel 0
Bronze -0.005
Copper +0.005
Aluminium 0
P Steel -0.01
P Bronze +0.005
P Copper -0.01
P Aluminium +0.005
Z Steel -0.005
Z Bronze +0.005
Z Copper 0
Z Aluminium +0.01
Metals in different salinities
Metal Average Change (g)
Steel 0
Bronze -0.00667
Iron -0.07
Copper -0.00333
Aluminium +0.01
P Steel +0.1
P Bronze -0.01333
P Copper -0.00667
P Aluminium -0.00333
Z Steel -0.11333
Z Bronze +0.006667
Z Copper 0
Z Aluminium +0.003333
Metals in different pHs
Metal Average Change (g)
Steel -0.01
Bronze 0
Iron +0.11
Copper -0.6
Aluminium -0.00667
P Steel 0
P Bronze -0.015
P Copper -0.045
P Aluminium +0.035
Z Steel 0
Z Bronze 0.01
Z Copper 0
Z Aluminium +0.025
Metals in different Temperatures
Metal Average Change (g)
Steel -0.01
Bronze +0.006667
Iron +0.136667
Copper -0.01667
Aluminium -0.01
P Steel -0.01333
P Bronze +0.026667
P Copper -0.00333
P Aluminium -0.00667
Z Steel -0.00333
Z Bronze +0.003333
Z Copper +0.013333
Z Aluminium 0
Table 10: Averages of metals with stress points
Table 11: Averages of metals in different temperatures
Table 12: Averages of metals in different salinities
Table 13: Averages of metals in different pHs
2
Change in mass across all experiments
Metal Average Change (g)
Aluminium -0.0016675
Bronze -0.004585
Steel -0.005
Copper -0.15375
Iron +0.058889
P Bronze -0.00083425
P Steel -0.0033325
P Copper -0.01625
P Aluminium +0.0075
Z Steel -0.0379075
Z Aluminium +0.00958325
Z Bronze +0.00625
Z Copper +0.00333325
Analysis
Salinity
Unprotected Aluminium (10% and 3.5%) and iron (10%) had gains
No difference in steel for any salinity
Bronze had losses in 10% and 1.5%
Iron lost 0.18 g in 1.5% salinity (ERROR)
Zinc Sprayed Copper showed no change for any salinity
Bronze and aluminium had minor gains or showed no difference
Steel lost 0.33g in 10% (ERROR)
Painted Minor losses or no difference for aluminium, copper, bronze across all salinities
Steel gained 0.32g in 10% salinity (ERROR)
Temperature
Unprotected Steel, aluminium, copper and bronze showed minor changes (up to 0.02 either side) or no
difference
Iron had greatest gains (+0.16g in 35°C, +0.14g at room temperature and +0.11 in 10°C)
(Possible ERROR)
Zinc Sprayed Relatively minor changes or none at all
Greatest was copper at 35°C, which was +0.04g
Painted Steel has minor losses across all temperatures
Bronze showed most gain (+0.04 at 35°C)
Minor or no changes at all otherwise
Stress
Unprotected Minor or no changes in mass
Zinc Sprayed Minor or no changes, most changes were +0.01
Painted Minor or no changes
Stressed copper had most change (-0.02g)
pH
Unprotected Copper in water had most loss in mass (-0.96g) (ERROR)
Minor gains or no change for rest (up to 0.03 change either way)
Steel and aluminium showed least change
Table 15: Analysis of test results for unprotected, zinc sprayed and painted metals in different salinities
Table 16: Analysis of test results for unprotected, zinc sprayed and painted metals in different temperatures
Table 17: Analysis of test results for unprotected, zinc sprayed and painted metals with stressed points
Table 14: Averages of changes in mass across all
tests for each metal
2
Zinc Sprayed Steel in vinegar lost most mass (0.27g) (ERROR)
Bronze in vinegar lost 0.09g
Copper in ammonia lost 0.08g, but copper in vinegar gained 0.06g
Others showed minor or no change
Painted Copper in water showed most loss (-0.07g)
Aluminium in water had most gain (+0.06g)
Others had minor or no changes
Steel had no change at all in any pH
Dissolved Oxygen
Unprotected Iron at room temperature dropped most (-16%)
Most decline occurs at room temperature (ranges from -3% to -16%)
Only increase was copper at 35°C (+1%)
No metal at 10°C dropped more than 2%
Zinc Sprayed Bronze dropped the most of all metals across all temperatures (Most was -8% at 35°C)
Steel was the only metal with gains (1% at 10C, 2% at room temperature)
Painted All metals showed a drop in DO levels
Change ranges from -1% to -11%
Greatest drop was steel at 35°C
Generally, 10°C metals showed less drop than metals at room temperature, but metals at 35°C
could show higher or lower decline than room temperature.
The overall averages show that aluminium changed the least in mass for unprotected metals, bronze changed the least
for painted metals and aluminium changed the least for zinc sprayed metals.
1 Bronze
2 Aluminium
3 Steel
4 Copper
5 Iron
Table 20: Ranking of metals
based on least change in mass
Discussion
The results generally show for salinity that corrosion is a gradual process. Over the seven days, there were not many
changes in mass. Unprotected metal did not tend to change more than 0.02g. As this category of metal was expected
to have the most changes in mass, it is reasonable that the painted and zinc sprayed metals showed changes closer to 0
overall. However, there did appear to be some errors.
The first error is in iron’s mass change. It seems from the results that iron changed a lot in mass over the seven days,
especially compared to the other metals. This could be a result of corrosion, whereby the smaller surface area meant
that the rate of reaction was faster. However, there were also quite significant gains in mass. This may have been
because during the measuring process rust was also measured along with the iron filings. Losses were most likely
caused by iron being washed out with the rust. In order to prevent this error in future experiments, it is recommended
that larger pieces be used. This would also reflect a marine situation better as ship metal has larger surface area.
Both painted and zinc sprayed steel showed changes much larger than expected. Painted steel in 10% salinity gained
0.32g, while zinc sprayed steel lost 0.33g in 10% salinity. Since corrosion is defined as a deterioration of metal, the
mass gains of some metals such as painted steel appear to be errors. However, due to passivation, when metal corrodes,
an oxide forms on the surface of the metal that is in contact with water. The experiment may have been stopped
before corrosion could take effect, but after the oxide layer formed, thus resulting in a slight gain in weight.
Table 19: Analysis of dissolved oxygen test results for unprotected, zinc sprayed and painted metals
Table 18: Analysis of test results for unprotected, zinc sprayed and painted metals different pHs
2
It would be expected that in lower pH environments, corrosion would occur faster and therefore the metals’ masses
would be lower. While the vinegar did appear to cause the most losses in mass, both water and ammonia also had
some significant effects. Iron, galvanised steel and zinc sprayed bronze loss 0.28g, 0.27g and 0.09g respectively in
vinegar. However, the greatest loss of all was from unprotected copper in water (-0.96g). Iron also had a substantial
gain of 0.16g in water. As for ammonia, copper lost 0.24g.
According to the Marine Corrosion Forum (2014), galvanic corrosion can be caused by poor manufacturing, thereby
causing the metal to form its own galvanic cell. This could be the case for losses such as copper in water, however
systematic error of scales or human error in recording seems more likely.
Higher temperature environments were expected to corrode metal faster as atoms are more mobile. The results
showed that higher temperatures did indeed affect the mass of metals the most, whether through gain or loss. The
largest changes were in iron; however, they were most likely errors. The other metals showed very minor changes of
±0.02g at most.
Stress points appeared to have insignificant changes in mass over the seven days.
Painting and zinc spraying showed no better resistance to corrosion than unprotected metals. For some, this was
possibly because there were gaps in the coating, allowing water to attack the surface of the metal. But mostly it seems
that corrosion could not take hold over seven days; it caused only minor changes in mass.
Conclusion
In conclusion, lower pH and higher temperatures had the most effect on corrosion rates. This was also found in N.
Al-Meer’s 2011 investigation. Salinity overall had an effect, however it was not clear form the data collected that
higher salinity had affected corrosion more. Stress points also did not tend to affect corrosion rates. Passivating metal
did not have a huge effect on the amount a metal corroded over seven days. Overall, bronze was seen to have the least
change in mass, followed by aluminium, steel, copper and iron.
2
Appendix
General Setup
Materials:
– Zinc spray
– Spray paint
– Funnel
– Tweezers
– Filter paper
– 2x pliers
– Scales
– Paper towel
– Measuring cylinder
Zinc Spray Method:
1. Lay out 4 each of aluminium, copper, steel, bronze and galvanised steel on paper towel in an open and well
ventilated space
2. Spray all metals with zinc spray, ensuring full coverage
3. Allow to dry
Pain Method:
1. Lay out 4 each of aluminium, copper, steel, bronze and galvanised steel on paper towel in an open and well
ventilated space
2. Spray all metals with spray paint, ensuring full coverage
3. Allow to dry
Stress Method:
1. Use pliers to bend one each of aluminium, steel, bronze, copper and their painted and zinc sprayed
equivalents

Reviews

There are no reviews yet.

Only logged in customers who have purchased this product may leave a review.