Reactions with Nonmetals

The halides Cl2, Br2, and I2 do not react with alumina, but fluorine (F2) does:

2Al2O3 + 6F2 = 4AlF3 + 3O2

Table 20 Gibbs Free energies of reactions of metals with 1 atm. of oxygen at 1,000°C from [28, 29, 46-48]

Solid metals

-AG (kJ mol-1)

Liquid metals

-AG

Y

1,017

Zr

849

Ca

1,013

Ti

678

CE

962

Si

644

Mg

937

V

619

Ba

879

Mn

586

Li

870

Cr

544

Al

845.6

One atm.

-AG (kJ/mol)

of metal vapor

Na

444

Zn

418

K

326

Metal + O2 = oxide

At 1,000°C the Gibbs free energy for this reaction is about -2133 kJ mol-1, showing a strong tendency to react.

Reactions of the gases H2, H2O, CO, and CO2 with alumina can be deduced from the reactions:

Al2O3 + 3H2 = 2Al + 3H2O

(16)

Al2O3 + 3CO = 2Al + 3CO2

(17)

At equilibrium at 1,000°C the ratio of H2/H2O is about 1010 and CO/CO2 about 2(10)10. It is impossible to reduce the water or carbon dioxide levels so low in any practical reaction process, so effectively H2 and CO do not reduce Al2O3. Even at 2,000°C these ratios are about 3(10)4 and 2(10)5, which are difficult levels to maintain in prac­tice. A possible reaction of alumina with carbon is

2Al2O3 + 6C = Al4C3 + 3CO2 (18)

However, the Gibbs free energy of this reaction is +1131 kJ mol-1 at 1,000°C and +504.6 kJ mol-1 at 2,000°C, so it will take place only at very low carbon dioxide concentrations.

Other chemical reactions of alumina can be examined with the thermodynamic data in [28-30, 47-48].