"Metal Corrosion and Protection" Metal and Metal Materials PPT Courseware

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"Metal Corrosion and Protection" Metal and Metal Materials PPT Courseware

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Iron reacts with acid and the iron corrodes. Corrosion rate is slow.

Iron as the negative electrode (anode) is corroded at a faster rate.

Comparison of chemical corrosion and electrochemical corrosion of metals

The essence of metal corrosion

The process in which metal atoms lose electrons and are oxidized and consumed: M-ne-=Mn+

metal corrosion

Chemical corrosion

Corrosion caused by oxidation-reduction reactions in direct contact between metals and other substances

redox reaction occurs directly

No current is generated during the corrosion process

Metal is corroded directly

Electrochemical corrosion

Corrosion caused by the galvanic reaction of impure metals or alloys, causing the more active metal to lose electrons and be oxidized.

galvanic cell reaction occurs

There is current generated

More reactive metals are corroded

corrosion rate

Electrochemical corrosion>Chemical corrosion

connect

Often occur at the same time, but electrochemical corrosion is more common and more harmful

(1) Corrosion of steel

1. Hydrogen evolution corrosion (acidic aqueous solution)

Negative electrode: Fe - 2e -= Fe2+

Positive electrode: 2H+ +2e－= H2↑

Total reaction: Fe + 2H+ = Fe2+ + H2↑

2. Oxygen absorption corrosion (neutral aqueous solution)

Negative electrode: 2Fe - 4e =2Fe2+

Positive electrode: O2 + 2H2O + 4e = 4OH－

Total reaction: 2Fe+2H2O+O2= 2 Fe(OH)2

Subsequent reaction: 4Fe(OH)2+2H2O+O2=4Fe(OH)3

[Exchange and discussion]:

In addition to the participation of air and water, iron rusting is also affected by other factors. Please explain the following reasons for iron rusting.

1. Compared with ships traveling on inland rivers, seagoing ships are more susceptible to corrosion.

Sea-going vessels are more susceptible to corrosion because seawater contains more salts such as sodium chloride and has stronger electrical conductivity than inland water. In electrolyte solutions, electrochemical corrosion is more likely to occur.

2. There is very little rust on the surface of the food cans left in Antarctica in 1910.

Since the temperature in Antarctica is below 0°C all year round, corrosion is more likely to occur at higher temperatures.

3. The iron screws used to connect copper plates are easy to rust.

Since iron, copper and water vapor in the air form a primary battery, and iron serves as the negative electrode of the battery, it is more likely to corrode and rust.

4. When the exhaust gas sent out by the chemical plant is acidic gas, the iron products near the factory are prone to rust.

Because iron products are more susceptible to corrosion under acidic conditions than under neutral conditions.

2. Electrochemical protection of metals

Read and think:

1. What substances are related to the corrosion of iron? what is the essence

2. How to prevent iron from rusting? What's the easiest way?

Common methods in daily life to prevent iron from rusting by covering it with a protective layer:

1. Spray anti-corrosion paint on the surface of iron (such as bridges, cars, ships)

2. Oil and grease can be used to protect rotating parts made of metal in machines, such as gears.

3. Spray or wrap the metal surface with plastic (such as polyethylene, polyvinyl chloride, etc.).

4. Cover the surface of iron with a layer of enamel, such as face plates and other metal vessels.

5. Cover the surface of the iron with a layer of other metal (such as tin plating, galvanizing)

summary:

1. Two factors affecting metal corrosion.

Metal nature—whether the metal is active and pure

Medium – What substances do metals coexist with?

2. The nature of metal corrosion:

The process by which metal atoms lose electrons and become cations.

The simplest way to prevent metal from losing electrons is to isolate it from air and water and cover it with a protective layer.

3. Common protection methods for metal.

(1). Cover the metal surface with a protective layer.

a. Apply mineral grease, paint or cover with enameled plastic.

b. Plating anti-corrosion metal - electroplating, hot plating, spray plating.

c. Use chemical methods to form a dense oxide film on the surface, such as baking blue.

(2). Change the internal composition and structure of metal to enhance corrosion resistance, such as making it into stainless steel.

(3).Electrochemical protection method.

a. Cathodic protection method of sacrificial anode.

b. Cathodic protection method with impressed current.

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Update Time: 2024-10-17

This template belongs to Chemistry courseware Hunan Education Edition Ninth Grade Chemistry Volume 2 industry PPT template

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