The properties of aluminum and its alloys 

Chemical reactions of aluminum

Chemical properties of aluminum

Chemical aluminum properties determined by its position in the periodic system of chemical elements.

The principal chemical reaction of aluminum with other chemical elements. These reactions are determined basic chemical properties of aluminum.

What reacts aluminum

Simple substances:

  • halogens (fluorine, chlorine, bromine and iodine)
  • sulfur
  • phosphorus
  • nitrogen
  • carbon
  • oxygen (combustion)

Complex substances:

  • water
  • mineral acids (hydrochloric, phosphoric)
  • sulfuric acid
  • Nitric acid
  • alkalis
  • oxidizers
  • oxides of less active metals (alumothermy)

What did not respond aluminum

Aluminum does not react:

  • with hydrogen
  • under normal conditions – with concentrated sulfuric acid (due to passivation – formation of a dense oxide film)
  • under normal conditions – with concentrated nitric acid (also due to passivation)

See. more on aluminum chemistry

Aluminum and air

Typically, the aluminum surface is always covered with a thin layer of aluminum oxide, which protects it from exposure to air, more precisely, oxygen. It is therefore considered, that aluminum does not react with air. If this oxide layer is damaged or removed, the fresh surface of aluminum reacts with oxygen in the air. Aluminum can burn in oxygen dazzling white flame to form aluminum oxide Al2O3.

Reaction of aluminum with oxygen:

  • 4Al + 3O2 —> 2Al2O3

Aluminum and water

Aluminum reacts with water according to the following reactions [2]:

  • 2Al + 6H2O = 2Al(OH)3 + 3H2 (1)
  • 2Al + 4H2O = 2AlO (OH) + 3H2 (2)
  • 2Al + 3H2O = Al2O3 + 3H2 (3)

As a result of these reactions are formed, respectively, following aluminum compounds:

  • modification of aluminum hydroxide bayerite and hydrogen (1)
  • modification of aluminum hydroxide bohemite and hydrogen (2)
  • aluminum oxide and hydrogen (3)

these reactions, by the way, are of great interest in the development of compact hydrogen generation systems for vehicles, which run on hydrogen [2].

All these reactions are thermodynamically possible at a temperature of from room temperature to the melting point of aluminum 660 oC. All of them are also exothermic, that is, they occur with the release of heat [2]:

  • At a temperature from room temperature to 280 ºС the most stable reaction product is Al (OH)3.
  • At a temperature of 280 to 480 ºС the most stable reaction product is AlO (OH).
  • At temperatures above 480 ºC most stable reaction product is Al2O3.

Thus, alumina Al2O3 It becomes thermodynamically more stable, than Al (OH)3 at an elevated temperature. The product of the reaction of aluminum with water at room temperature is aluminum hydroxide Al (OH)3.

Reaction (1) shows, that aluminum should spontaneously react with water at room temperature. However, in practice, a piece of aluminum, dropped into the water, It does not react with water at room temperature and even in boiling water. The thing is, that aluminum on the surface has a thin coherent layer of aluminum oxide Al2O3. This oxide film is held firmly on the aluminum surface and prevents its reaction with water. therefore, to start and maintain the reaction of aluminum with water at room temperature, it is necessary to constantly remove or destroy this oxide layer [2].

Aluminum and halogens

Aluminum reacts violently with all halogens - these are:

  • fluorine F
  • chloro Cl
  • bromine Br and
  • iodine (iodine) I,

with education, respectively:

  • ftorida AlF3
  • chloride AlCl3
  • Al bromide2Br6 and
  • Al iodide2Br6.

Reaction with hydrogen fluoride, chlorine, bromine and iodine:

  • 2Al + 3F2 → 2AlF3
  • 2Al + 3Cl2 → 2AlCl3
  • 2Al + 3Br2 → Al2Br6
  • 2Al + 3l2 → Al2I6

Aluminum and acid

Aluminum actively reacts with dilute acids: sulfuric, hydrochloric and nitric, with the formation of the corresponding salts: aluminum sulfate Al2SO4, aluminum chloride AlCl3 and aluminum nitrate Al (NO3)3.

Reactions of aluminum with dilute acids:

  • 2Al + 3H2SO4 —> Al2(SO4)3 + 3H2
  • 2Al + 6HCl —> 2AlCl3 + 3H2
  • 2Al + 6HNO3 —> 2By not3)3 + 3H2

C. Concentrated sulfuric and hydrochloric acids at room temperature does not interact, reacts when heated to form a salt, oxides and water.

Aluminum and alkalis

Aluminum in an aqueous alkali solution – sodium hydroxide – reacted to form sodium aluminate.

The reaction of aluminum with sodium hydroxide is:

  • 2Al + 2NaOH + 10H2O -> 2Na [Al (H2THE)2(OH)4] + 3H2

All critical reactions with aluminum

For completeness, we present a list of the main reactions involving aluminum from the fundamental book on aluminum [3]:

The most important reactions involving aluminum [3]

Sources:

1. Chemical Elements. The first 118 elements, ordered alphabetically / ed. Wikipedians – 2018

2. Reaction of Aluminum with Water to Produce Hydrogen /John Petrovic and George Thomas, U.S. Department of Energy, 2008

3. Thirteenth Element: Encyclopedia / A. Drozdov – RUSAL library, 2007.