Prepare for your exams
Get points
Guidelines and tips
Sell on Docsity
Docsity AI

Prepare for your exams

Study with the several resources on Docsity

Earn points to download

Earn points by helping other students or get them with a premium plan

Guidelines and tips

Sell on Docsity

Docsity AI

Prepare for your exams

Study with the several resources on Docsity

Find documents

Prepare for your exams with the study notes shared by other students like you on Docsity

Search for your university

Find the specific documents for your university's exams

Docsity AINEW

Summarize your documents, ask them questions, convert them into quizzes and concept maps

Explore questions

Clear up your doubts by reading the answers to questions asked by your fellow students

Earn points to download

Earn points by helping other students or get them with a premium plan

Share documents

20 Points

For each uploaded document

Answer questions

5 Points

For each given answer (max 1 per day)

All the ways to get free points

Get points immediately

Choose a premium plan with all the points you need

Study Opportunities

Choose your next study program

Get in touch with the best universities in the world. Search through thousands of universities and official partners

Community

Ask the community

Ask the community for help and clear up your study doubts

Free resources

Our save-the-student-ebooks!

Download our free guides on studying techniques, anxiety management strategies, and thesis advice from Docsity tutors

Corrosion - Lecture 2 - Material Engineering, Lecture notes of Material Engineering

Bangalore University Material Engineering

In this document description about Material Engineering, Driving force, Galvanic Series, Solution Concentration and Temperature,Kinetics, Polarization, Corrosion Rates, Anodic Polarization Curve .

Typology: Lecture notes

2010/2011

Uploaded on 09/14/2011

xyzxyz 🇮🇳

4.8

(24)

309 documents

1 / 19

This page cannot be seen from the preview

Don't miss anything!

Driving force

•A driving force is necessary for electrons

to flow between the anodes and the

cathodes.

•The driving force is the difference in

potential between the anodic and

cathodic sites.

•This difference exists because each

oxidation or reduction reaction has

associated with it a potential determined

by the tendency for the reaction to take

place spontaneously. The potential is a

measure of this tendency.

Discover Lecture notes of Material Engineering Bangalore University

Partial preview of the text

Download Corrosion - Lecture 2 - Material Engineering and more Lecture notes Material Engineering in PDF only on Docsity!

Driving force

A driving force is necessary for electrons

to flow between the anodes and the

cathodes.

The driving force is the difference in

potential between the anodic and

cathodic sites.

This difference exists because each

oxidation or reduction reaction has

associated with it a potential determined

by the tendency for the reaction to take

place spontaneously. The potential is a

measure of this tendency.

Galvanic Series

Ranking the reactivity of metals/alloys in seawater

Platinum

Gold

Graphite

Titanium

Silver

316 Stainless Steel (passive)

Nickel (passive)

Copper

Nickel (active)

Tin

Lead

316 Stainless Steel (active)

Iron/Steel

Aluminum Alloys

Cadmium

Zinc

Magnesium

more anodic

(active)

more cathodic

(inert)

Solution Concentration and

Temperature

Ex: Cd-Ni cell with

standard 1 M solutions

V

 V

 0. 153 V

Ni

1.0 M

solution

1.0 M

2 +

solution

Cd 25°C

Ex: Cd-Ni cell with

non-standard solutions

Y

X

ln

nF

RT

V  V  V  V 

Ni Cd Ni

n = #e

per unit

oxid/red

reaction

(= 2 here)

F =

Faraday's

constant

C/mol.

Ni

Y M

solution

X M

2 +

solution

Cd

T

Kinetics, Polarization, Corrosion Rates

While it is necessary to determine corrosion tendencies by

measuring potentials, it will not be sufficient to determine

whether a given metal or alloy will suffer corrosion under a

given set of environmental conditions.

Even though the tendency for corrosion may be high, the

rate of corrosion may be very low, so corrosion may not be a

problem.

Corrosion rates are determined by applying a current to

produce a polarization curve (the degree of potential change

as a function of the amount of current applied) for the metal

surface whose corrosion rate is being determined.

The variation of potential as a function of current (a

polarization curve) enables the study of concentration and

activation processes on the rate at which anodic or cathodic

reactions can transfer electrons.

Polarization measurements can thereby determine the rate

of the reactions that are involved in the corrosion process

(the corrosion rate).



The degree of polarization is a measure of how the rates for

anodic and cathodic reactions are slowed by various

environmental factors (concentration of metal ions, dissolved

oxygen in solution, diffusion limitations; referred to as

concentration polarization) and/or surface process (activation

polarization).



All electrochemical reactions consist of a sequence of steps

that occur in series at the interface between the metal

electrode and the solution.



Activation polarization is where the reaction is limited

(controlled) by the slowest rate reaction of the steps

(adsorption H

, film formation, ease of release of electrons,

called the activation polarization).

Types of Corrosion

Uniform Attack – General

Corrosion

Galvanic Corrosion

Crevice Corrosion

Pitting

Intergranular Corrosion

Selective Leaching

Erosion Corrosion

Stress Corrosion

Dissimilar metals are physically

joined in the presence of an

electrolyte.

The more anodic metal corrodes.

Galvanic

Bilge pump -

Magnesium shell cast

around a steel core.

Aluminum Alloys

Traditionally, structural aluminum alloys in

aircraft have been 2024-T3 in damage

critical areas and 7075-T6 in strength critical

areas.

As aircraft structures became more complex,

skin materials became an integral part of the

structure and SCC became more prevalent.

The high performance aircraft designed

since 1945 have made extensive use of skin

structures machined from thick plates and

extrusions. The residual stresses induced by

heat treatment in conjunction with those

from machining made these materials

sensitive to SCC.

Narrow and confined spaces.

Crevice Corrosion

Pitting

Pitting is a localized form of corrosive

attack. Pitting corrosion is typified by

the formation of holes or pits on the

metal surface. Pitting can cause failure,

yet the total corrosion, as measured by

weight loss, may be minimal.

5th Century sword

Boiler tube

304

stainless

steel /

acid

chloride

solution

Combined chemical attack and

mechanical wear (e.g., pipe

elbows).

Erosion-corrosion

Brass water pump

Selective Leaching

Preferred corrosion of

one element/constituent

[e.g., Zn from brass (Cu-Zn)].

Dezincification.

Corrosion - Lecture 2 - Material Engineering, Lecture notes of Material Engineering

Related documents

Partial preview of the text

Download Corrosion - Lecture 2 - Material Engineering and more Lecture notes Material Engineering in PDF only on Docsity!

Driving force

A driving force is necessary for electrons

to flow between the anodes and the

cathodes.

The driving force is the difference in

potential between the anodic and

cathodic sites.

This difference exists because each

oxidation or reduction reaction has

associated with it a potential determined

by the tendency for the reaction to take

place spontaneously. The potential is a

measure of this tendency.

Galvanic Series

Solution Concentration and

Temperature

V

 V

 0. 153 V

Ni

Cd 25°C

Y

X

ln

nF

RT

V  V  V  V 

F =

Ni

Cd

T

While it is necessary to determine corrosion tendencies by

measuring potentials, it will not be sufficient to determine

whether a given metal or alloy will suffer corrosion under a

given set of environmental conditions.

Even though the tendency for corrosion may be high, the

rate of corrosion may be very low, so corrosion may not be a

problem.

Corrosion rates are determined by applying a current to

produce a polarization curve (the degree of potential change

as a function of the amount of current applied) for the metal

surface whose corrosion rate is being determined.

The variation of potential as a function of current (a

polarization curve) enables the study of concentration and

activation processes on the rate at which anodic or cathodic

reactions can transfer electrons.

Polarization measurements can thereby determine the rate

of the reactions that are involved in the corrosion process

(the corrosion rate).

Types of Corrosion

Uniform Attack – General

Corrosion

Galvanic Corrosion

Crevice Corrosion

Pitting

Intergranular Corrosion

Selective Leaching

Erosion Corrosion

Stress Corrosion

Aluminum Alloys

Traditionally, structural aluminum alloys in

aircraft have been 2024-T3 in damage

critical areas and 7075-T6 in strength critical

areas.

As aircraft structures became more complex,

skin materials became an integral part of the

structure and SCC became more prevalent.

The high performance aircraft designed

since 1945 have made extensive use of skin

structures machined from thick plates and

extrusions. The residual stresses induced by

heat treatment in conjunction with those

from machining made these materials

sensitive to SCC.

Pitting