6 Corrosive metals | Corrosion of steel

corrosive metal

Corrosive metal – Corrosion of metal involves the chemicals that react in the presence of water along with oxygen.

When Corrosion of steel happens rust is formed.

Theories of corrosion for Corrosive metal

corrosive metal
corrosive metal-Steel
The transformation of metals by natural agencies into various compounds of oxides is stated by the termed corrosion.
The corrosion of ferrous metals in the construction field is termed as rusting.
The development of iron oxides is also called rusting.
Given below theories of corrosion for corrosive metal –Steel
  1. Chemical action theory
  2. Electrolytic theory

1. Chemical action theory for corrosive metal-Steel

The combined action of moisture, carbon dioxide and oxygen involves the corrosion of metal 
  and steel ends in water-soluble ferrous bicarbonate Fe(HCO3)2 compound.
Ferrous bicarbonate oxidises and converts into ferric carbonate. 2Fe(OH)CO3.
Ferric carbonate later transforms into hydrated ferric oxide (Fe(OH)3 and
carbon dioxide CO2 gas liberated.
Chemical reaction :
Fe + O + 2 CO2 + H2O = Fe(HCO3)2
2Fe(HCO3)2 + O =2Fe(OH)CO3 + 2 CO2 + H2O
Fe(OH)CO3 + H2O = Fe(OH)3 + CO2

2.Electrolytic theory for corrosive metal

The metal contains cathodic and anoxidic areas as per this electrolytic theory.
When electrolytes like moisture, water etc connect to these areas, corrosion will occur.

What are 6 Corrosive metals?

Given below 6 corrosive metals which starts corrosion when they expose with water or moisture
  1. Iron
  2. Copper
  3. Zirconium
  4. Magnesium
  5. Cadmium
  6. Titanium

What causes Corrosion of steel in Concrete?

Few causes for  corrosion of steel in RCC in construction is given below:
  1. If reinforcement is used in overcrowded and small concrete regions.
  2. The higher water-cement ratio in concrete
  3. Usage of improper construction methods.
  4. Incompetent design procedures
  5. From exposed concrete surface by not implementing sufficient cover to steel.
  6. Due to the moisture content present in the concrete
  7. Due to the salts present near concrete.
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Effect of corrosion of steel in concrete

The development of cracks is the significant effect of corrosion.
 The areas where shear stress is more in that area there will be rapid progress of crack and due to loss of bond slipping occurs.

Corrosion prevention methods for corrosive metal

For preventing corrosion of steel in concrete the given below methods are used.
  1. Using proper water-cement ratio in concrete
  2. By not utilising reinforcement in more overcrowded areas like columns, slab beams joints etc.
  3. From the exposed concrete surface by implementing sufficient cover to steel.
  4. By not utilising the aggregates materials with a high content of salt.
  5. Before concrete is placed, proper cleaning of reinforcement is done for removing flakes with the help of wire brush.
  6. By applying anti-corrosive primers Steel anti-corrosion treatment is done on the steel exterior.

Anti-corrosion treatments for corrosive metals

When metals come in contact with salts, moisture, water etc, Various methods are used to retard from corrosion.
Given below are few anti-corrosion treatments methods generally practised.
  1. Treatment of surfaces
  2. Application of coatings
  3. Reactive Coatings
  4. Anodization
  5. Biofilm coating

1.Treatment of Surfaces

 To retard from corrosion Surface treatments are practised.
Metals are developed for painting in this process.
 While doing this type of treatment proper supervision needs to take.

2.Application of coatings

 The most common anti-corrosion treatments are plating, Enamel painting and painting on surfaces.
Between structural material and environment, they act as a barrier of corrosion-resistant material.
Example: Coatings of Zinc on steel surfaces.

3.Reactive Coatings

corrosion inhibitors are utilised for controlling the environment.
These chemicals overcome the electrochemical reactions by forming a chemically impermeable coating on the metal surfaces.

4.Anodization

By bringing higher active anode and  transforming an anode into cathode is termed as anodization
It is very flexible to corrosion and weathering.
For building facades.anodization is used in common.
Example: Aluminium Alloys

5.Biofilm coating

In higher corrosive environment bacteria films are practised to the exteriors of metals.
By this process, the corrosion resistance substantially increases.

 Corrosion resistance metals

The corrosion resistance metals are given below which are used in residential and industrial buildings.
  1. Stainless steel
  2. Aluminium metal
  3. Copper, bronze and brass
  4. Galvanized steel

1.Stainless steel (SS)

Non corrosive metal-stainless steel railing
Non-corrosive metal-stainless steel railing
Few types of stainless steel are SS 316, SS 304, SS 316L.
Stainless Steel alloys contain more amount of Chromium (18%) and less amount of iron and chromium is more reactive than iron.
Oxygen when reacts with Chromium when forms Chromium oxide and become shielding layer on the exterior of Stainless steel.
This layer shields  Stainless steel from Corrosion and limits from oxygen responding with an iron present inside the SS.
This SS alloys also include molybdenum, nickel which helps stainless to convert rust-resistant.
In the house construction, Stainless Steel utilised for hand railings etc works.

2.Aluminium metal

non corrosive metal -aluminium alloy wheel
non-corrosive metal -aluminium alloy wheel
For body parts in bikes, aeroplanes, cars aluminium is utilised due to its lightweight and corrosive resistant.
Rust can’t form on its Aluminum metals surface as it has less or don’t contain iron.
A thin layer of oxide is formed on the exterior of aluminium when it reacts with water and this layer makes it more corrosion resistant and protects the metal.

3.Copper, Bronze and Brass

non corrosive metal-copper pipes
non-corrosive metal-copper pipes
This Brass, Bronze, Copper contain no or Iron. So these metals don’t rust.
But oxygen reacts with Copper to form Copper oxide.
In the course of time, this copper oxide develops a green patina, which shields the metal from more corrosion.
 Along with other metals, Bronze contains tin and copper.
This bronze is a higher resistance to corrosion compared to copper.
Brass is an alloy of zinc, copper and other metals which are resistant to corrosion.

4.Galvanised Steel or Galvanic Steel

non corrosive metal-galvanised steel
non-corrosive metal-galvanised steel
For rusting the Galvanised steel will take a large time.
By coating Zinc on Carbon steel Galvanised or galvanic steel is formed.
This Zinc will act as a protecting layer and make Galvanised steel to become corrosion resistant steel.
The zinc will react with oxygen to form zinc oxide if the zinc on exterior got damaged and this zinc oxide continues to protect Galvanised steel from corrosion by forming a layer on the exterior surface.

Conclusion:

So the corrosive metal steel is protected by utilising above protection methods and anti-corrosion treatments and other non-corrosive metals used in various construction and industrial fields.

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About Ashwini Kumar

Ashwini Kumar is a graduate in civil engineering from NIT Warangal. He has 8+ years of experience in the construction field. He is the author, founder of the Easy Home Builds blog

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