Chương 3 cơ CHÊ ăn mòn điện hóa học KIM LOẠI

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3.1Định nghĩa !"#$%&'()*+#,-./"("'01 !"20*3 43,5
43678
3.2 Điều kiện để sự ăn mòn điện hóa học kim loại xảy ra #$7,"%&29:4;$,-4<") '=
Pin ăn mòn gồm có >"&" ,4?@A+#,-"4BC>D
.>"&"" 4,4?@A+#,-"4B7>D
">E97F"#*?; 43":478,G "&" ,4;$"&"" 4,4>D
7>EC*+#,-HI"&" ,4;$" 4,4?; 43":4784J>
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2.3 Cơ chế ăn mòn điện hóa học kim loại
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?K #$S74J7"9*T4O,UV"#-4R"&" ,4% "&"" 4,4.L43,
+#,->
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:4,2* ?2>L943L"V"!#$":4C*3 %&= !"+#,-
W#-Scơ chế ăn mòn điện hóa học các kim loại như sau:
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Chú ý: PW3,797F" 244HX"S"4T.bN9 '01?I>S;cd<e
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3.3 Đặc điểm của sự ăn mòn điện hóa học kim loại: 3
Pk0
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1,2* ;$'01+J20*3 ld464-I;F43]+(" 9k01,2* 20*3 
43L"&" ,4D'01+J20*3 43L"&"" 4,4
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Ăn mòn thép carbon trong không khí ẩm:
7,+],2*4620*3 4-"("63O") HHSV"!#$%&=+O?"3O;"O",33,%,>
W3L"&" ,4rOrO
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The principal causes of corrosion are carbon dioxide and hydrogen sulphide as most oil field systems arc or are made anaerobic. Oxygen can be a contributing
factor in open tanks and pits or if insufficient, or incorrectly applied, oxygen scavenger is used in water injection plant.
The relative corrosivity of these three gases is, approximately
O
2
; CO
2

; H
2
S
1 ppm ; 75 ppm ; 150 ppm
But due to the higher concentrations of CO
2
and H
2
S that can be present and the high system pressures very high corrosion rates can be seen in practice. In
particular a combination of CO
2
and H
2
S with other factors can lead to very high localised corrosion rates.
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s`k=
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The Corrosion Cell
Corrosion as a chemical reaction, is best illustrated by the operation of a galvanic cell such as a simple battery shown in
Fig.1.2.
Figure 1.2-Schematic diagram of a simple battery
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Here the galvanic cell comprises of an iron plate and a copper plate immersed in salt water. The reaction will not take

place if the plates are not connected. Once the plates are connected by a wire (without which there would be no
reaction) the corrosion reaction is able to get under way by dissolving the iron into positively charged particles called
"ions” and negatively charged "electrons". The electrons flow through the circuit to the copper plate where they react
with dissolved oxygen to form "hydroxyl ion”. At the same time iron ions flow through the solution to complete the
electrical circuit. The volt renter in circuit is indicating a "voltage'' or "potential difference" being generated be tween
the iron and copper. Thus the galvanic cell is a simple form of the "corrosion cell". From the above description we can
see that t here are essential constituents in a corrosion cell. these are:
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