where rust doth corrupt, an inaugural lecture no. 3 of futo [1990] by prof v.o. nwoko as adapted by...

8/3/2019 Where Rust Doth Corrupt, An Inaugural Lecture No. 3 of FUTO [1990] by Prof v.O. Nwoko as Adapted by U. Mark

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Adapted to electronic edition (MS Word and PDF) by Engr. Udochukwu Mark on 11/11/2011

FEDERAL UNIVERSITY OF TECHNOLOGY, OWERRI

WHERE RUST DOTH CORRUPTINAUGURAL LECTURE SERIES 3

by

V. O. NWOKOB.Sc.Tech. (Manch.); M.Sc. (Lond.); S.M. (MIT); Ph.D. (Lond.); C.Eng

Delivered on Wednesday, 14 th

November, 1990



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WHERE RUST DOTH CORRUPT

INAUGURAL LECTURE SERIES 3

Delivered at

FEDERAL UNIVERSITY OF TECHNOLOGY, OWERRI

ON

WEDNESDAY, 14TH NOVEMBER, 1990

BY

VINCENT OKENWA NWOKOB.Sc.Tech. (Manch.); M.Sc. (Lond.); S.M. (MIT); Ph.D. (Lond.); C.Eng

PROFESSOR OF CORROSION SCIENCE AND TECHNOLOGY DEPARTMENT OF MATERIALS AND METALLURGICAL ENGINEERING



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1.0 INTRODUCTION

An inaugural lecture is, in my opinion, a personal profession of faith, an integration

of one's own experiences, contributions, suggestions and belief. It is an occasion when

the lecturer publicly defends his Chair. In the choice of a subject, too complex a topicwill satisfy very few members of the audience. With this in mind, the dish to be served

in this lecture will be a limited mixed grill, limited by the confines of the areas of

specialization and interest, which in this case, happens to be in metals and materials.

Within the field of metals and materials, lies an area of concern and interest to many

people: the area of their stability when exposed to different environments. We shall

come back to this topic later.

Man's skillful use of metals and materials through the ages has undoubtedly, been

the most significant factor in the attainment of his present standard of living.1 Indeed,

the history of man is often stated in terms of the materials he learned to utilize: the

Stone Age (about 8000 BC), the Bronze Age (about 3000 BC), the Iron Age (about

1000 BC), the Plastics Age (1950 AD) and arguably, our present age can be christened

the Silicon Age.

The men of Stone Age, few Find scattered, developed little to enable them

conquer their environment.2 However, they were able to improvise their own shelters

and were able to make use of fire. The Bronze Age was another step in the

development of man's material culture. The age started with the use of pure copper

even though bronze, an alloy of copper and tin, was used subsequently and only

rarely at first. Iron began to be used first as an ornament and then slowly became the

material for swords and daggers. But for the discovery and exploitation of iron, the

Industrial Revolution which started in 1750, would trot have taken place.

The earlier division of materials was into two groups: metals and nonmetals. The

division arises because the properties of metals and non-metals are clearly quite

different.3 The traditional division of materials has been into three groups: metals,

ceramics and polymers. Later on, composites became recognized as forming distinct

group. In view of the wider approach to the structural properties and applications of



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materials, a division into four families: crystalline, amorphous, composite and cellular

has recently been suggested.4 Each of these families includes metals, polymers and

ceramics in various forms.

We are often reminded of the fact that our oil-reserves are limited andconsequently, great care must be exercised in its rate of depletion. Currently, Nigeria's

proven oil reserves are put at a little over two billion barrels. Over 60% of the world’s

recoverable proven oil reserves lie in the Middle East with nearly 20% located in

Saudi Arabia (257 m. tonnes). The massive deployment of forces in the Gulf Area by

America and other countries may not, after all be unconnected with oil.

Apart from oil, another material of strategic importance is steel. Total world steel

production has hovered between 700 and740 million tonnes per year. The world's

principal iron ore reserves are estimated at a little over 140,000 million metric tonnes. 5

It is also estimated that the iron ore reserves are sufficient to meet the world's

requirements for about 120 years.

It is obvious from the above considerations that the reserves of strategic materials;

oil, steel, alumina, antimony, bauxite, cobalt, chromium, manganese, nickel, niobium,

platinum, silicon, tin, titanium, tungsten, uranium, vanadium, zinc and a host of others

are limited and it is of vital imoortance that their conservation be taken seriously.

In this lecture, we will look at some aspects of the destruction of metals and

metallic structures through corrosion, the havoc corrosion can cause followed by

academic consideration of selected areas and after dwelling a bit on the pervasiveness

of corrosion, we-will finally end up with challenges of the future.

2.0 CORROSION

One of the greatest dangers posed to conservation of metals is the attack by

corrosion. Corrosion is the destruction of a metal by chemical or electrochemical

reaction with its environment.6 It has also been defined as the chemical reaction of a

metal with a non-metal in the surrounding environment.7 Yet another definition has

corrosion as the destruction or deterioration, of a material because of reaction with its



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environment.8 The last definition, although by a well-known authority in the field, is

somewhat imprecise in the sense that words should not be stretched beyond their

limits. Thus, we speak of iron rusting and no other metal except iron rusts. In the same

vein, metals corrode and materials deteriorate when exposed to certain environments.It is thus not right to say that zinc rusts or that materials corrode. Just as Humpty

Dumpty said to Alice in Lewis Carroll’s book 9, "When I use a word, it means just what

I choose it to mean – neither more nor less." It is better to speak of the deterioration of

materials or the environmental degradation of materials rather than the corrosion of

materials.

Based primarily on appearance; there are eight forms in which corrosion

manifests itself. The eight forms are:

1) uniform or general attack

2) localized corrosion which includes pitting and crevice corrosion

3) galvanic or dissimilar metal or two-metal corrosion

4) cracking corrosion (stress corrosion cracking and corrosion fatigue)

5) erosion corrosion

6) inter-granular corrosion

7) de-alloying or selective leaching corrosion, and

8) high temperature corrosion.

Apart from the need for conservation as indicated earlier, a prime motive for

education in corrosion and corrosion control stems from costs to the economy.

Economic losses include costs of replacing corroded structures such as condenser

tubes, vehicle exhaust pipes, metal roofing, etc. and of course, the labour involved.

Studies carried out in Australia, United Kingdom, Japan and other industrialized

countries put the cost of corrosion at 3 - 4% of the gross national product (GNP).6 A

study at the request of the US Congress found that the cost of corrosion ,approaches

4.2% GNP or roughly $180 billion in 1985.10 Unfortunately, an attempt made in 1983

at determining a figure for this country was not considered of sufficient priority. In

view of our level of industrialization, it is estimated that the cost of corrosion to



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Nigeria will be around 2% of the GNP which works out at N2, 581 million in 1988

assuming a GNP figure of N129, 080 million.

Indirect losses due to corrosion are more difficult to evaluate. The replacement of

a corroded section or a component in an oil refinery may cost a few thousand nairabut the shutdown of the plant while repairs are effected may cost millions of naira per

day. Loss of efficiency in a pipe may occur as a result of clogging of the pipe with

corrosion products necessitating increased pumping capacity. While indirect losses

are difficult to evaluate financially, the loss of precious lives is not only tragic,

stunning but also inestimable in terms of money. The accident which occured at the

Nypro Factory in Flixborough, is still fresh in the minds of corrosion specialists. In

the subsequent report11 on the incident, the investigating panel stated, "At about

4.53 p.m. on 1st June 1974 [i.e. on a Saturday], the Flixborough Works of Nypro

(UK) Limited, (Nypro) were virtually demolished by an explosion of warlike

dimensions. Of those working on the site at the time, 28 were killed and 36 others

suffered injuries. If the explosion had occurred on an ordinary working day, many

more people would have been on site and the number of casualties would have been

much greater. Outside the Works, injuries and damage were widespread but no one

was killed. Fifty-three people were recorded as casualties by the casualty bureau

which was set up by the police; hundreds more suffered relatively minor injuries

which were not recorded. Property damage extended over a wide area, and a

preliminary survey showed that 1,821 houses and 167 shops and factories had

suffered to a greater or lesser degree."

The Flixborough plant was completed in 1967 for the production of caprolactam,

which is a basic raw material in making Nylon 6, by a process the first step of which

was the production of Cyclohexanone via the hydrogenation of phenol. The

introduction of an additional plant in 1972 enabled the company to produce

cyclohexanone by the oxidation of cyclohexane instead of via the hydrogenation of

phenol. In March 1975, cyclohexane was discovered to be leaking from Reactor No. 5

in a battery of six reactors. The material of construction of the reactors was 12mm



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mild steel plate with 3 mm stainless steel bonded to it. On investigation, a vertical

crack was found in the mild steel outer layer of the reactor shell and cyclohexane was

escaping over a small part of this crack thus indicating that the inner stainless steel

layer was also defective. At a management meeting, it was decided that No.5 Reactorbe removed and that a by-pass assembly be constructed to connect Reactor No. 4 with

Reactor No. 6 after which the plant could be restarted. The report concluded that the

immediate cause of the disaster was the introduction of a modification into a well

designed and constructed plant which destroyed its integrity. What about the cracked

No. 5 Reactor? It was ascertained during the investigation that nitrate treated cooling

water had been used in the past to dilute small leakages of cyclohexane from the plant.

Examination of the crack by metallurgists showed that the crack had been caused by

nitrate stress corrosion. It is quite obvious from the sequence of events that the crack

on Reactor No. 5, that is stress corrosion cracking, was what triggered off the disaster.

A number of useful lessons are to be learnt from the Flixborough disaster.

1. Modification of a well designed and constructed plant which will destroy

structural integrity should not be allowed.

2. A replacement of Reactor No. 5 with the same material of construction should

have been done.

3. All pressure systems containing hazardous materials should be subject to

inspection and testing by competent persons after any significant modification has

been carried out and before the system is brought into use.

4. Where materials are used and in particular where corrosion is likely to occur, it is

advisable to have a metallurgical or materials engineer, If the Nypro Works in

Flixborough had one of these in their Factory, the disaster could well have been

avoided.

The Flixborough disaster is one of many such incidents caused by corrosion.

Large ships have been reported to have snapped into two and have sunk with the

loss of all hands. The crashes of the Comet type of aircraft have been attributed to

corrosion. Similar incidents which occurred much earlier have given rise to interest



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and research in corrosion and a significant reduction in the ravages due to corrosion

has been achieved by the application of currently available technology.

2.1 Corrosion at Elevated TemperaturesMetals are quite often employed for service at elevated temperatures for example in

gas turbine engines. When exposed to air or oxidizing gases (oxygen, sulphur or

halogens) corrosion may occur. This is sometimes referred to as ‘dry’ corrosion in

contrast to 'wet ' corrosion, which occurs when a metal is exposed to a moist or an

aqueous environment. Corrosion of metals at elevated temperatures or their oxidation

has always attracted interest. Oxidation has in most cases been found to obey three

main laws: the parabolic law, the linear law and the logarithmic law.

The parabolic law is represented by the equation:

where y is the thickness of scale or film on the metal, t is the time and and c

constants. The parabolic law generally holds at the higher temperatures. The oxidation

rate here is controlled by the diffusion of ions or lattice vacancies and by migration of

electrons (or positive holes) through the oxide film.

In the linear law, the rate of oxidation is constant and the equation

applies. The equation holds when the environment reaches the metal surface

through cracks or pores in the film or scale.

The logarithmic law is given by the relation:

( )

where and a are constants. The law is encountered mostly in the lower

temperature ranges or when thin films are formed.

2.2 Basis for a Two-Stage Logarithmic Oxidation Behaviour

Several attempts have been made to describe a mechanism of diffusion through



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oxides resulting in the logarithmic equation. One such attempt by Evans12 assumed

specialized flaw-paths or zones of loose structure in oxides. Another attempt13 made

use of diffusion blocks and leakage paths in the oxide. Mott14 employed the tunnel

effect of quantum mechanics to express electron flow-rate from metal to oxide, whichhe assumed controlled the oxidation process. Mott's model however accounted for

oxide films of the order of 40 angstroms whereas the general logarithmic equation in

practice holds for films as thick as 10,000 angstroms.

In the model by Uhlig15, the logarithmic oxidation equation is derived assuming

control of the rate by electron flow from metal to oxide. Electron flow during

oxidation is a function of a changing more negative (or less positive) space charge in

the oxide extending up to several thousand angstroms from the metal surface. The

increasing numbers of trapped electrons at lattice defect sites account for the changing

space charge. The space charge is composed of two parts: (1) a uniform-charge

density layer next to the metal and (2) a diffuse charge density layer beyond the

uniform layer. The situation is similar to the electrical double layer at metal surfaces in

contact with electrolyte as described by Gouy16, Chapman17 and Stern.18

Oxidation follows the logarithmic equation during the formation of both space-

charge layers with a higher oxidation rate accompanying the formation of the

diffuse layer. The Rideal-Jones19 equation

where is the activation energy for oxidation and the metal work function in

electron volts applies and the equation was derived theoretically from the same

fundamental assumptions used in deriving the logarithmic oxidation equation.

Reports on the thin-film oxidation rate of copper20 and nickel21, 22 have shown a

two-stage logarithmic behaviour. Copper oxide (Cu2O) and nickel oxide (NiO) are

both p-type semi-conductors in which cation vacancies characterize the important

imperfection sites. It was of interest to ascertain the behaviour of zinc since it forms an

n-type semi-conductor oxide, the characteristic lattice imperfections being excess

interstitial zinc ions.



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Evidence that zinc obeys the two-stage logarithmic behaviour was obtained by

Uhlig and Nwoko23 in their studies on the oxidation of the metal at 0.2 to 0.8 mm

oxygen pressure in the temperature range 125 to 206. Values of the activation

energies for the first- and second-stage oxidation were 0.34 and 0.35 electron voltsrespectively. The high density of trapped charge in zinc oxide which we calculated as

explains in part the low initial oxidation rate of zinc compared

with copper and nickel. Our work on zinc showed that although it forms an n-type

oxide, it follows a similar two-stage logarithmic behaviour with copper and nickel,

whose oxides are p-type.

For oxide films thicker than the diffuse barrier layer, the space charge disappears

and the oxide becomes electrically neutral. Thereafter, other processes such as

diffusion of ions as described by Wagner24 and confirmed in many cases25,26,27, take

place.

2.3 A Guide in the Use of Metals Where Corrosion Rate is Uniform

Where contamination of product is not critical and whenever attack is uniform,

metals can be classified into three groups according to their corrosion rates and

intended applications.6

In the first group are metals whose corrosion rate is less than 0.15 mm/y. Such metals

have good corrosion resistance and are suitable for critical parts such as valve seats,

pump shafts and impellers. The second group, are metals whose corrosion rate falls

between 0.15 and 1.5 mm/y. These have satisfactory corrosion resistance and can be

used for tanks and bolt heads. Corrosion of bolts used at battery heads sometimes

disappoint car owners. Metals whose corrosion rates are above 1.5 mm/y, belong to

the third group, are unsatisfactory and are therefore not recommended. Luckily, the

corrosion resistances of thousands of metals in different corrosive environments

have been studied and all the design engineer has to do is to consult a Corrosion

Handbook to select the most appropriate metal.



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2.4 Pitting Corrosion

Pitting and crevice corrosion come under localized corrosion, with pitting being

more common.28 It is one of the most destructive and insidious forms of corrosion. 8

It is vicious and failures resulting from pitting often occur suddenly.

Pitting often occurs on metals that are covered with a thin surface film. The film

may be produced during fabrication or by reaction with the environment the metal is

exposed to. It can occur on magnesium, aluminium, titanium, stainless steel,

chromium and copper. It may also occur on iron, steel and other metals.29

Two basic conditions must be fulfilled for the initiation and propagation of pitting

corrosion.30 First, the major part of the metal surface should be covered with an

electronically conducting, passivating or inhibiting film on which the cathodic reaction

takes place. Secondly, the medium should contain a pitting corrosion agent and the

chloride ion is a notorious one. The following areas have attracted research in pitting

corrosion31, 32:

1. Investigations aimed at precisely determining the critical potential by

different electrochemical methods

2. Effects of electrolyte composition, electrolyte flow, temperature, cold-

working, heat-treatment and alloying elements

3. Microscopic examination of sites most susceptible to pitting

4. Investigation into the structure, thickness and conductivity of oxide film

5. Study of the geometry of pits

6. Kinetics of pit growth under potentiostatic and galvanostatic

conditions

7. Measurement of pit initiation and propagation.

Most corrosion processes are electrochemical in nature. The concept of a critical

pitting potential below which pitting does not occur has been established.

Electrochemical techniques are widely used to determine critical-pitting potentials

generally in chloride environments and most of these studies have provided a means of

arranging metals n their order of resistance to pitting.



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Recently, we investigated the effect of a chelating agent, ethylene-diamine-tetra-

acetic acid (EDTA), on the pitting of type 304 stainless steel in 3% sodium chloride

using a potentiodynamic technique in conjunction with potentiostatic stepping

method

33

. At room temperature, the critical pitting potential is shifted 80 mVtowards the active end by the addition of a chelating agent. Apart from its use in

hardness determination of water, EDTA is employed in metal cleaners, rust and

scale removers. Our studies show that its use as rust and scale remover could induce

pitting in 304 stainless steel. Such findings are usually of little or no consequence

until something serious in connection with the use of such cleaning agents occurs.

At a constant potential 30 to 150 mV above the critical potential, the current

i, rises with time t according to the relation:

The value of b, the coefficient, depends on the type of attack; being 2 for pitting,

1 for crevice attack and between 1 and 2 for mixed pitting and crevice attack. It

will be fair to add here that various values have been found for the coefficient b as

well as the interpretations attached to the values.31, 34, 35

2.5 Pervasiveness of Corrosion

Wherever metals are used, corrosion is bound to rear its ugly head. Starting from

the home, an aluminium cooking pot will eventually be put out of use most probably

due to pitting corrosion at the bottom. As pointed out earlier, it can happen quite

suddenly and at-the most inconvenient time. What about the burners of the gas cooker

or the heaters including the water heater? In the office look carefully at your metal

filing cabinet particularly at the bottom drawer. Watch out for the tell-tale signs of

incipient corrosion. In our laboratories, many items of equipment have been put out of

use because of defects in components caused by corrosion. In the car or other

vehicles, watch out for signs at the bottom of the doors, at the floor of the vehicle, at

the exhaust system, at joints between metallic and non-metallic materials etc. In

electronic systems, it has been reported36 that 20% of failed devices (printed circuit



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boards, disc recorder heads, etc.) are caused by corrosion.

In industry, corrosion constitutes one of the major problems. It is particularly

severe in the chemical and oil industries leading often to a plant being shut down as

has happened to our Warri and Kaduna refineries. At one time, naphthenic acidcorrosion was a serious problem in Warri refinery. In deep, hot oil and gas wells,

equipment is often subjected to extremely corrosive conditions. High temperatures and

pressures combine with constituents such as hydrogen sulphide, chlorides and salts to

form an environment in which many low alloy and stainless steels perform

unsatisfactorily.

In power generation, failure of turbine blades due to pitting and cracking is

frequent.37 In nuclear reactors, a major problem that had to be solved was that of

finding a suitable cladding material for the nuclear fuel. A cladding material has to

have good corrosion resistance and a relatively low thermal neutron absorption.

Suitable materials in this category include aluminium, beryllium, magnesium, niobium

and zirconium. All these materials exhibited some type of corrosion problems in the

300 to 330

water of the primary coolant. Only zirconium based alloys satisfied the

need and are generally used as cladding materials for nuclear fuels.38

A wide spectrum of corrosion problems is encountered in naval environments due to

the unique combination of materials, environment and service conditions. Items of

equipment are prone to general corrosion, pitting, stress corrosion cracking, corrosion

fatigue etc. The saline atmosphere along the coast does not help matters as can readily

be attested to by those who live near the coast.

Atmospheric corrosion has always been with us. Because of the effects of pollution, it

has become common to classify atmospheric corrosion into rural, marine and

industrial. The corrosivity of the atmosphere is related to the levels of ionizable

substances present in the environment. A study on Aladja mild steel carried out here

in Owerri by Umoru and Nwoko gives a corrosion rate of about 0.15mm/y while at the

Otamiri River, the rate is 0.33mm/y.39

Underground structures (storage tanks, pipes, etc.) are not spared from corrosion



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attack. Except in swampy or high conductivity soils, the problem here is not usually

serious. Underground utilities can be affected by stray currents from DC operated

mass transit and high voltage DC power transmission systems. Corrosion of the

structure will occur by stray earth currents provided there is a net flow onto thestructure and a net flow out of the structure to earth in some other area.40

Corrosion problems occur in the pulp and paper industry, in water treatment plants,

water distribution system41 and in reinforced concrete structures including bridges.

For more than one hundred years, foreign materials have been implanted in the

mouth for dental treatment. The list of materials contains silver amalgams, gold,

cement, porcelain and more recently stainless steels and plastics. With the progress

made in medical science, the applications of implants have increased. These days,

metal screws, metal plates and rods are used to repair severe fractures. Reliable

contraception has been achieved by the implantation of objects in the uterus.

Metallic components are generally used for orthopaedic applications because of their

mechanical properties. Even in the human body, corrosion of implants occur.

Compatibility, or the absence of body reaction, is one of the major problems

associated with metal implantation. Ideally, an implant should react very slowly with

body fluids, and the products of this reaction should be non-toxic and non-

irritating.42 It is estimated that the rate of corrosion should be less than 0.03 mm/y to

avoid the possibility of tissue reactions.8

In space, because of the rarefied atmosphere, there are hardly any corrosion

problems. However, severe corrosion problems occur due to liquids such as oxidizer

and fuels and also the high temperature encountered in the blast nozzles and during re-

entry.

In short, corrosion is a pervasive problem in engineering systems.

2.6 Corrosion Control

With the exception of gold, platinum and possibly one or two others, all metals

are susceptible to attack by corrosion when exposed to the environment. Methods of



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controlling or combating corrosion fall into the following headings:

1. Design

2. Materials selection

3. Modification of the environment4. Modification of the properties of the metal

5. Use of protective coatings

6. Anodic or cathodic protection

The method adopted depends on the circumstances and in some cases a combination

of methods, (coatings plus cathodic protection can be applied).

The design stage is the first place of tackling corrosion control. At this stage,

consideration is given to the mechanical and strength requirements together with an

allowance for corrosion. If the design is carried out properly, the other methods of

corrosion control will present fewer problems. The means of protection against

corrosion must be incorporated into the technical details of a project. As part of any

measure for corrosion control, it will be necessary to provide maintenance.

In corrosion research, studies of behaviour of materials, comparisons of behaviour

of materials, analyses of case histories and programmes of tests are conducted. One of

the purposes of research is to assess service life. Table 1 gives the average range of

service lives of various items.

Table 1: Range of service lives for various items

Equipment Average service life (years)

Nuclear power plants 40

Offshore platforms 20

Bridges 50

Office buildings 30 – 40

Commercial ships 20

Cars 6 – 8

A correct assessment of the life expectancy of a component or system requires a

wide spectrum of knowledge.43 The composition and structure of materials, the type of



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environment, the design of the equipment, service conditions, inspection and

maintenance programmes all influence the effective service life. Corrosion engineers

know of many cases where an apparently harmless minor change in conditions led to

serious damages. For example, damage to concrete has occurred because reinforcingbars were too close to the surface.

Corrosion specialists have helped in increasing the service life of cars from

approximately 6 to 10 years and that of offshore structures from 20 to 25 years. They

have also developed new coating systems and have succeeded in doubling or tripling

the life of plant equipment through the development of new alloys. It has been stated

that the proper application of what is already known would permit a reduction of 15%

or more in the costs arising from corrosion. For new technologies, problems often

arise because of lack of previous experience.

The amount of available data on conditions and rates of corrosion of various metals

is very large. It is the responsibility of those requiring this information, particularly

designers and other specialists in the field of materials to find it. It may be said that

corrosion problems arise from ignorance of the corrosion risks. Where the risks are

recognized, problems arise from ignorance of the information available to allow the

risks to be assessed and protective measures adopted.

3.0 CHALLENGES OF THE FUTURE

On a personal level, it would be gratifying to have a strong and if possible the

leading corrosion research centre of this country here at the Federal University of

Technology, Owerri for reasons of economy, conservation of our materials, safety,

demands for better materials and the progress of the nation. Of the few places that

offer courses in materials and metallurgical engineering in the country this university

is indeed lucky in these days of brain drain, to have academic staff strength of ten in

the department. The staffs are of high calibre, with adequate training and experience

and some of them have been involved in corrosion one way or the other. We should

be concerned because if the proper steps are not taken, our materials resources,



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particularly metals, will be seriously depleted sooner than later.

Apart from controlling or preventing corrosion, another satisfactory way of

conserving materials and minimizing environmental damage is to recycle them

whenever feasible.

44

Metallic materials offer the greatest opportunities forrecycling45 and the use of scrap iron for steel production is an accepted practice

while aluminium scrap is frequently used.

In non-metals, Nwoko and Hammond have shown46 that bauxite waste can be

utilized for the production of pozzolana. With a suitable heat-treatment followed by

ball-milling to cement fineness, a material with pozzolanic activity, referred to as

bauxite pozzolana, can be produced.47 Pozzolanas are solid materials, either natural or

artificial, processed or unprocessed which, although not cementitious, will in finely

divided form and in the presence of water, react chemically with lime at ordinary

temperatures to form insoluble compounds possessing cementitious properties.

Without sacrificing acceptable compressive strengths, up to 40% replacement of

Portland cement by bauxite pozzolana seems possible in the preparation of concrete

and with it, a significant saving in cost. A higher compressive strength has been

achieved by a 20% replacement in a 1:2:4 concrete. A wall has been put up using this

material and studies on the durability of pozzolana cement concrete are still in

progress.48 Utilization or exploitation of waste materials will become increasingly

important and although recycling of metals appears to be in the lead that of plastics is

in its infancy.49

One of the first unattractive impressions of Nigeria to a visitor or passenger

arriving by air just before touch-down at the Murtala Mohammed International Airport

is the sight presented by the awful colours of galvanized iron roofing sheets due to

corrosion. It is a loathsome sight and this type of roofing material should be phased

out. There are now better materials in the market and happily, a few small scale

industries producing roofing materials have sprung up. The roofing tiles are of

acceptable quality, competitive in cost and do not have the disadvantage of developing

unpleasant colours. The Materials and Metallurgical Engineering Department of



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FUTO is contributing to the development of suitable roofing tiles.

With the progress in technology, there will be demands for engineering materials

capable of performing under increasingly more demanding or hostile circumstances,

for example deep oil wells, magnetohydrodynamic (MHD) channels, fusion reactorsetc. Their development depends on the availability of chemically stable materials.

New advanced materials such as high-performance ceramics, composite materials

optical fibres,, photoelectrodes, biomaterials; synthetic polymers and metastable solids

produced by rapid solidification are cropping up. With the development of these

materials, goes the need for new methods or approaches to the study of their corrosion

problems. All too often, the corrosion resistance of materials is considered only after a

failure has occurred. Unless materials are stable in the environments to which they are

exposed while in service their otherwise useful properties (strength, toughness,

electrical and thermal conductivity, magnetic and optical characteristics etc.) may be

lost.

Corrosion specialists are usually familiar with problems associated with steam

generators, condensers, reaction vessels, bridges, motor vehicles etc. These systems

will continue to demand their attention.

Corrosion is a multidisciplinary field of science and engineering. Knowledge of

the chemistry of the environment, the microstructure of the metal and the distribution

of stresses on or in the metal will be essential in the kinds of problems that concern

corrosion specialists. Such a problem as stress corrosion cracking will clearly be too

complex for any one discipline to handle.

It is clear that we can only build engineering systems with materials that are

chemically stable in service environments. Furthermore, progress in tect'i1ology

continues to demand materials that are capable of performing under increasingly

aggressive circumstances. In the 1990s and beyond, new or advanced material of

which not much is known about their corrosion characteristics will be used. Materials

and metallurgical engineers, particularly corrosion specialists will find the problems

posed by the new materials challenging.



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All engineers should be aware of corrosion and its potential for damage to

structures and equipment. Although the effort involved in increasing the, awareness of

engineers is considerable it is invariably well repaid.

Corrosion is indeed a pervasive problem. In practice, all engineering materials aresusceptible to environmental degradation. As a Christian, one is reminded of a verse in

the New Testament of the Holy Bible50 which states:

" Lay not up for yourselves treasures upon earth, where moth and

rust doth corrupt, and where thieves break through and steal "

[ Matt. 6:19, KJV ]

A newer version51 has it as:

"Do not store up for yourselves treasures on earth, where moth

and rust destroy, and where thieves break in and steal."

[ Matt. 6:19, NIV ]

In our sojourn on this planet, we have to lay up treasures to help take care of

ourselves. However, because we live here on earth, it follows that whatever material

treasure we store up, will be subject to corruption, to decay, to destruction, to

deterioration and to corrosion. Using our limited knowledge, what we in the field of

corrosion and corrosion control are doing, is to try and reduce the rate of corruption or

destruction of our metals and materials treasures, in order to extend their service life.



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ACKNOWLEDGEMENTS

I would like to acknowledge the love, encouragement and devotion of my late

mother, Mrs. Nwabure U. Nwoko who gave me so much and received so little from

me in the form of a reward having passed on, as is often euphemistically stated, to thegreat beyond before I entered a university. My sincere thanks to my wife and family,

relations, friends and colleagues for their help. To Dr. L. L. Shreir and Professor H. H.

Uhlig, my supervisors during graduate studies,I owe a debt of gratitude. I am much

obliged to Dr. A. L. Hammond (Deputy Director, Building and Road Research

Institute, Ghana) and Professor D. A. Jones (Chemical and Metallurgical Engineering

Department, University of Nevada-Reno, Nevada) for useful materials sent. I am

grateful to Prof. A. Nduka,Vice-Chancellor, Federal University of Technology, Owerri

for making it possible for me to give this lecture. My special thanks to Professor C. O.

G. Obah [the University Orator ] and members of his Committee for being so

accommodating. Finally, I sincerely thank you all, members of the audience for

coming because without you, I would have had to address a brick wall.



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New Jersey (1984)

4. K. Easterling; "Tomorrow's Materials", The Institute-of Metals, London (1988)

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(1970)

6. H. H. Uhlig and R. W. Revie; "Corrosion and Corrosion Control ", John Wiley &

Sons, New York (1985)

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U. K. Department of Industry Publication (1982)

8. M. G. Fontana and N D. Greene; "Corrosion Engineering", McGraw-Hill Book

Company (1978)

9. L. Carroll; "Through the looking Glass", -McMillan, London (1988)

10. R. M. Latanison; Materials Performance 26 (No.10) 26 9 (1987)

11. Report of the Court of Inquiry "The Flixborough Disaster" HMSO (1975)

12. U. R. Evans; Trans Electrochem Soc. 83 335 (1943)

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14. N. Mott; Trans. Faraday Soc. 35, 1175 (1939)

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22. H. H. Uhlig, J. Pickett and J.MacNairn; Acta Met. 7 111 (1959)



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23, V. O. Nwoko and H. H. Uhlig; J. Electrochem. Soc. 112`1181 (1965)

24. C. Wagner ; J. Phys. Chem. 40B 455 (1938)

25. S. K. Rhee and A. R. Spencer; Met. Trans. 2 2285 (1971)

26. E.A. Gulbransen and W.S. Wysong; J. Phys. Chem. 51 1087(1947)27. V. O. Nwoko and L. L. Shreir ; Corrosion 31 (No.7),252 (1975)

28. H. C. Man and D. R. Gabe; Corrosion Science 21 713 (1981)

29. Corrosion Basics; National Association of Corrosion Engineers, Houston (1984)

30. F. M. Abd El Wahab and A. M. Shams El Din; Brit.Corrosion Journal 13

39(1978)

31. Z. Szklarska - Smialowska; Corrosion 27 223 (1971)

32. H. P. Leckie and H. H. Uhlig; J. Electrochem. Soc. 1131262 (1966)

33. V. O. Nwoko and Z. Szklarska - Smialowska; J. Nig. Sec. Chem. Eng. 7 225

(1988)

34. Z. Szklarska-Smialowska and M. Janik-Czachor; Brit. Corr. Journal 4 138 (1969)

35. R. Gressmann; Corrosion Science 8 325 (1968)

36. Bill Dobbs and G. Slenski; Materials Performance 23 (No.3) 35 (1984)

37. O, Jones; Materials Performance 24 (No.2) 9 (1985)

38. W. E. Berry; Materials Performance 23 (No. 6) 3 (1984)

39. V. O. Nwoko and L. E. Umoru; Unpublished work (1986)

40. P. Pignatelli; Materials Performance 24 (No.2) 30 (1985)

41. V. O. Nwoko; The Nigerian Engineer 11 3 (1976)

42. N. D. Greene and D. A. Jones; Journal of Materials 1 (No. 2) 345 (1966)

43. C. C. Cabrillac, J. S. L. Leach, P. Marcus and A. Pourbaix; Metals and

Materials 3 533 (1987)

44. J. Nutting; Metals and Materials 6 83 (1990)

45. M. E. Henstock; " Design for Recyclability"The Institute of Metals, London

(1988)

46. V.O. Nwoko and A. A. Hammond; J. Construction Division, Amer. Soc. Civ.

Engrs. 104 99 (1978)



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47. V. O. Nwoko and A.A. Hammond; Conservation and Recycling 2 43(1978)

48. A.A. Hammond; Private Communication, August 1990

49. T.W. Moffit; Metals and Materials 6 559 (1990)

50. The Holy Bible, Authorized King James Version, © 1972 by Thomas Nelson Inc.,Camden, New Jersey, 08103.

51. The Holy Bible, New International Version®, Copyright © 1973, 1978, 1984 by

International Bible Society, Colorado Springs, Colorado

where rust doth corrupt, an inaugural lecture no. 3 of futo [1990] by prof v.o. nwoko as adapted by...

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