discussion of rusting


Upload: shamil-azha-ibrahim

Post on 03-Apr-2018




0 download


Page 1: Discussion of Rusting

7/28/2019 Discussion of Rusting

http://slidepdf.com/reader/full/discussion-of-rusting 1/15



CPE 435


MATRIC NO : 2011195429



Page 2: Discussion of Rusting

7/28/2019 Discussion of Rusting

http://slidepdf.com/reader/full/discussion-of-rusting 2/15


Rust is a general term for describing iron oxides. Rusting of iron takes place in the

 presence of water and oxygen when every trace of carbonic acid has been removed. Also, we can

say that the usually accepted view has been said that iron will not rust unless carbonic acid is

 present. In addition, Rusting of Iron also can be viewed as formation by the reaction of iron and

oxygen in the presence of water or air moisture. Ultimately, provided iron, oxygen, and liquid

water are brought together, chemical change takes place with the production of rust, even when

every precaution has been taken to exclude even traces of carbonic acid. Then it suddenly can

cause of corrosion of metal or iron. Corrosion is the gradual destruction of material, usually

metals, by chemical reaction with its environment. Corrosion degrades the useful properties of 

materials and structures including strength, appearance and ability to contain a vessel's contents.

Corrosion may even be brought about by carbonic acid occluded in the iron. Moreover some

corrosion mechanisms are less visible and less predictable. So, the prevention of corrosion are

concerned to avoid the rusting of metal or iron occur. Many ways of prevention of corrosion was

introduced to improve the way how to avoid the rusting of iron will lead corrosion happen.

Page 3: Discussion of Rusting

7/28/2019 Discussion of Rusting

http://slidepdf.com/reader/full/discussion-of-rusting 3/15





Redox (reduction-oxidation) reactions include chemical reaction in which atoms have

the oxidation changed. This can be either a simple redox process, such as the oxidation

of carbon to yield carbon dioxide (CO2) or the reduction of carbon by hydrogen to

yield methane (CH4), or a complex process such as the oxidation of glucose (C6H12O6) in the

human body through a series of complex electron processes.

On the other hand, Reduction-oxidation (redox) reactions are chemical reactions in which

reactants experience a change in oxidation number (which means these reactants either gain or 

lose electrons).

If an atom in a reactant gained electrons (its oxidation decreased) it was reduced.

If an atom in a reactant lost electrons (its oxidation increased) it was oxidized.

Since chemical reactions don't make or destroy electrons, oxidation and reduction must occur at

the same time. As one reactant is oxidized, the electrons it loses are accepted by another reactant

which is reduced.

Page 4: Discussion of Rusting

7/28/2019 Discussion of Rusting

http://slidepdf.com/reader/full/discussion-of-rusting 4/15

Ex :



+ Zn --> Cu + Zn



The Cu2+

is reduced (oxidation decreased).

The Zn is oxidized (oxidation increased).

In redox processes, the reductant transfers electrons to the oxidant. Thus, in the reaction,

the reductant or reducing agent loses electrons and is oxidized, and the oxidant or oxidizing 

agent gains electrons and is reduced. The pair of an oxidizing and reducing agent that are

involved in a particular reaction is called a redox pair.

Page 5: Discussion of Rusting

7/28/2019 Discussion of Rusting

http://slidepdf.com/reader/full/discussion-of-rusting 5/15



Iron is one of the widely distributed elements in the nature. One of its striking

characteristics is that it undergoes rusting on combining with water, air & carbon-dioxide due to

which its surface gets covered with a red brown flake coating called Rust. Rust is affected by

moisture, oxygen & carbon - dioxide. rust is soft and porous and it gradually falls off from the

surface of iron material. It is a continuous process and it gradually eats up iron due to which an

iron object loses its strength. It is very wasteful process and should be prevented. It is very-very

slow process (spontaneous reaction).

Also, Rusting is the corrosion of iron and readily occurs in the alloy steel. Steel is an

alloy made of iron and carbon. The carbon atoms in steel greatly increase the strength of the

metal. They prevent the iron atoms in the crystal lattice from slipping over one another.


Diagram 1.1

Page 6: Discussion of Rusting

7/28/2019 Discussion of Rusting

http://slidepdf.com/reader/full/discussion-of-rusting 6/15

Steel is widely used in the manufacture of cars, white goods and the construction industry

 because it is much stronger than iron. The carbon atoms in steel however, greatly decrease the

ability of iron to resist corrosion

Diagram 1.2

In the presence of oxygen and water a series of internal galvanic cells or batteries are created.

The carbon impurities become the site of reduction.

 Reduction half equation: 4e-+ 2H2O(l) + O2(g) ==> 4OH


The nail is most easily oxidised at points of stress. ie the tip or the head. At these points the

crystal lattice is distorted and the iron atoms are easily oxidised.

Oxidation half equation: 2Fe(s) 2Fe2+

(aq) + 4e- 

Page 7: Discussion of Rusting

7/28/2019 Discussion of Rusting

http://slidepdf.com/reader/full/discussion-of-rusting 7/15

The overall or net equation is :

2Fe(s) + 2H2O(l) + O2(g) 2Fe2+

(aq) + 4OH-(aq)


(aq) and OH-(aq) ions migrate through the water by diffusion. Refer to the above

diagram. When they meet they combine to produce the preciptate, iron(II) hydroxide,

Fe(OH)2, which is further oxidised to iron (III) hydroxide, Fe(OH)3, and finally dehydrated to

 produce rust.

The chemistry of the reaction resulting in the formation of rust can be summarized as follows.

The chemical equations for rust formation 

1.  2Fe(s) + 2H2O(l) + O2(g) 2Fe2+

(aq) + 4OH-(aq)

2.  Fe2+

(aq) + 2OH-(aq) Fe(OH)2(s)

3.  Fe(OH)2(s) =O2=> Fe(OH)3(s)

4.  Fe(OH)3(s) =dehydrates=> Fe2O3.nH2O(s) or rust

The chemical formula for rust is Fe2O3.nH2O

The overall chemical equation for the formation of rust is

Iron + water + oxygen rust

4 Fe(s) + 6 H2O(l) + 3 O2(g) 4 Fe(OH)3(s)

Iron(III) hydroxide,Fe(OH)3 then dehydrates to produce Fe2O3.nH2O(s) or rust

Page 8: Discussion of Rusting

7/28/2019 Discussion of Rusting

http://slidepdf.com/reader/full/discussion-of-rusting 8/15



Corrosion of metals can be prevented if the contact between metal and air is cut off. This is done

in a number of ways. Some of the methods are given below:

1.  Corrosion can be prevented if the metal is coated with something which does not allow

moisture and oxygen to react with it.

2.  Coating of metals with paint, oil, grease or varnish prevents the corrosion of metals.

3.  Coating of corrosive metals with non-corrosive metals also prevents corrosion. Some of the

methods by which metals can be coated with non-corrosive metals are:

4.  Galvanizing: It is process of giving a thin coating of zinc on iron or steel to protect them

from corrosion. Iron is galvanized by dipping it in molten zinc. It is then taken out and

allowed to cool. Galvanizing is an effective methods of protecting steel because even if thesurface is scratched, the zinc still protects the underlying layer.

Page 9: Discussion of Rusting

7/28/2019 Discussion of Rusting

http://slidepdf.com/reader/full/discussion-of-rusting 9/15

5.  Tinning: It is the process of giving a coating of tin, i.e., molten tin. Cooking vessels, made

of copper and brass get a greenish coating due to corrosion. This greenish coating is

 poisonous. Therefore they are given a coating of tin to prevent corrosion. This is also arewidely used in industry to prevent corrosion.

6.  Electroplating: In this method of a metal is covered with another metal using electrolysis.Silver-plated spoons, gold-plated jewelry, etc, are electroplated. But electroplating are costly

 process and not a very suitable used in industry

7.  Anodizing: In this method metals like copper and aluminum are electrically coated with a

thin strong film of their oxides. This film protects the metals from corrosion. But is only for 

the metal like copper and aluminum can occurred for anodizing

8.  Alloying: Corrosion can be also prevented by alloying some metals with other metals. The

resultant metals called alloys do not corrode easily, e.g. stainless steel.

Page 10: Discussion of Rusting

7/28/2019 Discussion of Rusting

http://slidepdf.com/reader/full/discussion-of-rusting 10/15


Chemical Inhibitor.

1.1 Background

Methods of combating corrosion which are widely used in New Zealand are chemical

inhibitors. This methods depend on controlling the charge on the metal surface, and this can be

monitored by measuring the potential of the metal. The conditions needed to stop corrosion can

then be predicted from an electrochemical phase diagram.There is a class of chemical inhibitors

which work by removing electrons from the metal, thereby pushing the potential into a positive

region where an oxide film spontaneously forms. This results in a stable, passive surface with a

very low corrosion rate. Industries apply this technology in processes where the inhibitor can be

conveniently added without causing environmental or health problems.

1.2 Literature

It is well known in surface chemistry that surface reactions are strongly affected by

thepresence of foreign molecules. Corrosion processes, being surface reactions, can be controlled

 by compounds known as inhibitors which adsorb on the reacting metal surface. The term

adsorption refers to molecules attached directly to the surface, normally only one molecular layer 

thick, and not penetrating into the bulk of the metal itself. The technique of adding inhibitors to

the environment of a metal is a well known method of controlling corrosion in many branches of 

technology. A corrosion inhibitor may act in a number of ways: it may restrict the rate of the

anodic process or the cathodic process by simply blocking active sites on the metal surface.

Alternatively it may act by increasing the potential of the metal surface so that the metal entersthe passivation region where a natural oxide film forms. A further mode of action of some

inhibitors is that the inhibiting compound contributes to the formation of a thin layer on the

surface which stifles the corrosion process.

Page 11: Discussion of Rusting

7/28/2019 Discussion of Rusting

http://slidepdf.com/reader/full/discussion-of-rusting 11/15

1.3 Finding

The class of inhibitors are those which cause the potential of the metals to rise intothe

 passivation region. They are all oxidising agents, containing elements in their higher oxidation

states. For example nitrite, which is used as an additive in cooling fluid circuits for the control of 

corrosion of steel, is a mild oxidising agent which can raise the potential of steel into the

 passivation region. A traditional pigment used in paints is red lead, Pb3O4, containing lead in the

tetravalent stale, and the formula can be written as plumbous

 plumbate Pb(II)2Pb(IV)O4. The plumbate ion is an active oxidising agent and serves to

 promote passivation of the underlying metal. The modern pigment calcium plumbate, oftenused

in paint formulations, contains the same plumbate ion PbO4

4- in a different compound.Likewise zinc chromate ZnCrO4 is also widely used in corrosion

control as a passivating inhibitor. The passivating inhibitors all share the common property of 

conferring protection on a metal by using its own natural oxide film


Corrosion can be controlled effectively by cathodic protection or inhibitors, provided the

chemical and electrical conditions are monitored in a scientific manner. The costs of stopping

corrosion can be quite high, but these costs must be faced by many industries if they wish to

achieve a high level of performance. The key factor is the scientific knowledge on whichthe

technologies are based.

Page 12: Discussion of Rusting

7/28/2019 Discussion of Rusting

http://slidepdf.com/reader/full/discussion-of-rusting 12/15

Prevention of Corrosion Case Study


The Low Level Bridge Northbound in Edmonton, Canada, was originally designed for 

trains of the Grand Trunk Pacific Railway and was the first railway bridge to cross the North

Saskatchewan River at Edmonton.Constructed between 1898 and 1900, the structure is a riveted

steel through-truss with four equal spans of 53 metres, When originally constructed, it carried a

Grand Trunk track centered between the trusses along with a second track for the Edmonton

Radial Railway streetcar offset from the centreline. The specified railway loading was CN55%-

2-8-0, which is approximately equivalent to the current Cooper E50 loading. The trusses are built

up from structural steel angles, cover plates,2 gusset plates, and lattice members. Abutments at

the banks and three concrete piersfounded on timberpiles in the river support the trusses .

The goal is to establish the structural reliability of a bridge, including evaluation of 

strength, stability, serviceability, and fatigue. Over the course of a bridge’s life, its performance

depends primarily on two variables that change with time: the loads applied and the residual

resistance of deteriorating structural members. In 2004 the City of Edmonton undertook a

condition assessment of the Low Level Bridge Northbound along with preliminary design of the

recommended rehabilitation measures. The scope of work included a detailed review of existing

file information and the original design drawings, along with field inspection of the bridge. The

Page 13: Discussion of Rusting

7/28/2019 Discussion of Rusting

http://slidepdf.com/reader/full/discussion-of-rusting 13/15

inspection work included deck and sidewalk concrete sampling and testing, a deck delamination

survey, paint testing, a truss member condition survey, and an evaluation of the previous deck 

and support structure repairs. The objective was to develop and compare rehabilitation options to

extend the life of the bridge for 50 years.

It has been shown that the material properties of steel, such as elastic moduli and yield

strength, are not influenced by the corrosion of adjacent material . However, as a result of the

formation of corrosion products over time, the thickness of structural steel members are

continually reduced. Along with a reduction in thickness, a number of other geometric properties

that govern structural behaviour are reduced, including area, moment of inertia, radius of 

gyration, and the elastic and plastic section moduli. Some of these properties do not change

linearly with a change in member thickness, but are related to its square or cube. Significant

eccentricities may be introduced with a change in the location of a member’s centroid. Both

ultimate resistance and serviceability are negatively impacted by these changes. The failure

mode that governs an individual member may change as a result of corrosion section loss. The

 build-up of corrosion products can cause a prying force between members or restrict moving

 parts from functioning properly. Stress concentrations introduced by local corrosion can degrade

the fatigue life of a member (Fisher et al. 1998). All of these issues became evident during the

condition assessment of the Low Level Bridge Northbound. The determination of the residual

capacity of corroded members requires an accurate indication of the extent and types of 

corrosion present. The measurement of remaining member thickness is a crucial part of the

assessment process. All locations of severe deterioration characterized by significant section loss

must be identified and quantified.

One of the way to prevent corrosion is localized corrosion reduces the net area of a member at a

 particular section, but does not generally reduce the gross area over an appreciable length. Stress

concentrations introduced in a tension member by localized depressions have little effect on the

ultimate strength of a member . Conceptually, penetrations caused by pitting corrosion are

similar to bolt or rivet holes, reducing the net section over a short portion of the member.

Yielding of these areas would result in an insignificant amount of member elongation, thus it is

acceptable to consider rupture of the net section at pitting locations as the governing failure

mode. If pitting corrosion is extensive, that is, present along a

Page 14: Discussion of Rusting

7/28/2019 Discussion of Rusting

http://slidepdf.com/reader/full/discussion-of-rusting 14/15

significant length of the cross section, yielding of the net section becomes a relevant issue and

must be considered. However, this is not typically the case for bridge truss members. 

The rehabilitation of the Low Level Bridge Northbound involved the replacement of about 40%

of the main truss members, repainting the bridge, rebuilding a wider sidewalk, and resurfacing

the concrete deck. Over 17,000 rivets were removed, 221 tonnes of new steel replacing existing

members, and over 34,000 new bolts were installed. There is a need for accuracy and consistency

when evaluating the performance reliability of deterioratingsteel bridge structures. Section loss

 by corrosion is usually highly variable and difficult to predict, and practical recommendations for 

the calculation of residual strength are vague and inconsistent in existing literature and governing

 bridge design standards. Based upon the information available currently, it appears that the

strength of corroded tension members should be calculated using the lower of the factored yield

strength on the corrosion-reduced effective gross area or the factored rupture strength on the

corrosion-reduced effective net area. Research is required to provide practical guidance for 

design engineers in the assessment of corrosion on remaining member strength.The technically

sound and cost-effective rehabilitation of the Low Level Bridge Northbound was completed in

2006 on time and on budget. A great example of sustainability, the bridge has adapted for over 

100 years to the changing needs of the City of Edmonton, and it is now a totally rehabilitated

structure able to serve for decades to come

Page 15: Discussion of Rusting

7/28/2019 Discussion of Rusting

http://slidepdf.com/reader/full/discussion-of-rusting 15/15


1. John O'M. Bockris and Amulya K. N. Reddy (1970). Modern Electrochemistry . Plenum Press.

2 Phillips, John; Strozak, Victor; Wistrom, Cheryl (2000). Chemistry: Concepts and Applications. Glencoe McGraw-


3 Zumdahl, Steven; Zumdahl, Susan (2009). Chemistry . Houghton Mifflin

4 Schüring, J., Schulz, H. D., Fischer, W. R., Böttcher, J., Duijnisveld, W. H. (editors)(1999). Redox:

Fundamentals, Processes and Applications, Springer-Verlag, Heidelberg,

5 http://www.corrosionclinic.com/types_of_corrosion/galvanic_corrosion.htm 

6 http://www.pipingtech.com/technical/bulletins/corrosion_protection.htm 

7. Akgul, F., and Frangopol, D.M. 2004. “Lifetime Performance Analysis of Existing Steel Girder Bridge  

Superstructures,” Journal of Structural Engineering ,

8 http://www.berkeleychurchill.com/software/chembal.php 

9 www.pnas.org