Introduction Corrosion is the destructive attack of a metal by its reaction with the environment...

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Introduction Corrosion is the destructive attack of a metal by its reaction with the environment What is Corrosion? Note that the word “corrosion” refers to the degradation of a metal by its environment.

Transcript of Introduction Corrosion is the destructive attack of a metal by its reaction with the environment...

Page 1: Introduction Corrosion is the destructive attack of a metal by its reaction with the environment What is Corrosion? Note that the word “corrosion” refers.

Introduction

Corrosion is the destructive attack of a metal by its reaction with the environment

What is Corrosion?

Note that the word “corrosion” refers to the degradation of a metal by its environment.

Page 2: Introduction Corrosion is the destructive attack of a metal by its reaction with the environment What is Corrosion? Note that the word “corrosion” refers.

According to ‘ASTM' corrosion glossary, corrosion is defined as "the chemical or electrochemicalreaction between a material, usually a metal, andits environment that produces a deterioration of the material and its properties”.

What is rusting ?What is white rust ?

Other definitions include Fontana's description that corrosion is the extractive metallurgy in reverse,2 which is expected since metals thermodynamically are less stable in their elemental forms than in their compound forms as ores.

Page 3: Introduction Corrosion is the destructive attack of a metal by its reaction with the environment What is Corrosion? Note that the word “corrosion” refers.

Physical Processes of Degradation

Physical degradation processes include the following:

1. Fracture2. Fatigue3. Wear4. Erosion or cavitation erosion5. Radiation damage

Page 4: Introduction Corrosion is the destructive attack of a metal by its reaction with the environment What is Corrosion? Note that the word “corrosion” refers.

Red rust

Waterline

Page 5: Introduction Corrosion is the destructive attack of a metal by its reaction with the environment What is Corrosion? Note that the word “corrosion” refers.

Environmentally assistedprocess

Example

Fracture Stress-corrosion cracking Stress-corrosion cracking of bridgecables, of landing gear on aircraft

Fatigue Corrosion fatigue Vibrating structures, such as aircraftwings, bridges, offshore platforms

Wear Fretting corrosion Ball bearings in chloride-contaminated oil

Table 1.1 Physical degradation processes and their environmentally assisted counterparts

Environmentally Assisted Degradation Processes

Page 6: Introduction Corrosion is the destructive attack of a metal by its reaction with the environment What is Corrosion? Note that the word “corrosion” refers.

Cavitation erosion

Cavitation corrosion Ship propellers, pumps, turbine blades,fast fluid flow in pipes

Radiation damage

Radiation corrosion Increased susceptibility of stainless steelsto dissolution or to stress-corrosioncracking [1, 2]

Page 7: Introduction Corrosion is the destructive attack of a metal by its reaction with the environment What is Corrosion? Note that the word “corrosion” refers.

Electrochemical Reactions

Corrosion is an electrochemical process. That is, corrosion usually occurs not by direct chemical reaction of a metal with its environment but rather through the operation of coupled electrochemical half-cell reactions.

Half-Cell Reactions

Page 8: Introduction Corrosion is the destructive attack of a metal by its reaction with the environment What is Corrosion? Note that the word “corrosion” refers.

Anodic Reactions

The loss of metal occurs as an anodic reaction. Examples are

Fe(s) → Fe2+(aq) + 2e− (1)Al(s) → Al3+(aq) + 3e− (2)2Cu(s) + H2O(1) → Cu2O(s) + 2H+(aq) + 2e− (3)

Page 9: Introduction Corrosion is the destructive attack of a metal by its reaction with the environment What is Corrosion? Note that the word “corrosion” refers.

The following reaction is also an anodic reaction:

Page 10: Introduction Corrosion is the destructive attack of a metal by its reaction with the environment What is Corrosion? Note that the word “corrosion” refers.

Cathodic Reactions

In a cathodic reaction?

2H+(aq) + 2e− → H2(g)

Page 11: Introduction Corrosion is the destructive attack of a metal by its reaction with the environment What is Corrosion? Note that the word “corrosion” refers.

Another common cathodic reaction is the reduction of dissolved oxygen to hydroxyl ions, a reduction reaction which occurs in neutral or basic solutions.

O2(g) + 2H2O + 4e− → 4OH−(aq)

Page 12: Introduction Corrosion is the destructive attack of a metal by its reaction with the environment What is Corrosion? Note that the word “corrosion” refers.

Coupled Electrochemical Reactions

At anodic sites: Fe Fe+2 + 2e–

At cathodic sites: 2 H+ + 2e– H2

Overall reaction: Fe + 2 H+ Fe+2 + H2

Page 13: Introduction Corrosion is the destructive attack of a metal by its reaction with the environment What is Corrosion? Note that the word “corrosion” refers.

The reason that two different electrochemical half-cell reactions can occur on the same metal surface lies in the heterogeneous nature of a metal surface.

The heterogeneous nature of a metal surface showing various types of imperfections

Page 14: Introduction Corrosion is the destructive attack of a metal by its reaction with the environment What is Corrosion? Note that the word “corrosion” refers.

Kesimpulan :

1.Rx oksidasi2.Rx reduksi3.Media elektrolit4.Jalan untuk perpindahan

Page 15: Introduction Corrosion is the destructive attack of a metal by its reaction with the environment What is Corrosion? Note that the word “corrosion” refers.

A Note About Atmospheric CorrosionThe need for the presence of an electrolyte as a condition for corrosion to occur is illustrated by the phenomenon of atmospheric corrosion, i.e., the corrosion of metals in the natural outdoor atmosphere.

Page 16: Introduction Corrosion is the destructive attack of a metal by its reaction with the environment What is Corrosion? Note that the word “corrosion” refers.

Fig. 2.7 The continuation of reactions initiated in Fig. 2.6. (a) The precipitation of ferrous hydroxide on the iron surface. (b) The conversion of ferrous hydroxide to a hydrated ferric oxide

Page 17: Introduction Corrosion is the destructive attack of a metal by its reaction with the environment What is Corrosion? Note that the word “corrosion” refers.

The Faraday and Faraday’s Law

Faraday’s law states that the mass (w) of metal corroded is given by

19 19 23

2

1 1,6 10 1 1,6 10 6,0225 10 96450=96500 C/mol

Fe Fe 2

massa (g) Fe yang teroksidasi bila teramati arus sebesar 1 A selama 1 jam?

C=1 C/s 60 mnt x 60 s/mnt =

massamol

ArC

i C i tt

e C mol e C

e

Berapa

3600 C 3600 C 0,037 mol e

96500 C/mol

1Banyak besi yang teroksidasi : 0,037 mol = 0,018 mol

2

W=

e

i t eitAr unsur w

nF FAr

en