Sieverts' law, in
physical metallurgy {{unreferenced, date=April 2017
Physical metallurgy is one of the two main branches of the scientific approach to metallurgy, which considers in a systematic way the physical properties of metals and alloys. It is basically the fundamentals and ap ...
and in
chemistry
Chemistry is the scientific study of the properties and behavior of matter. It is a natural science that covers the elements that make up matter to the compounds made of atoms, molecules and ions: their composition, structure, proper ...
, is a rule to predict the
solubility
In chemistry, solubility is the ability of a substance, the solute, to form a solution with another substance, the solvent. Insolubility is the opposite property, the inability of the solute to form such a solution.
The extent of the solubi ...
of
gases in
metal
A metal (from ancient Greek, Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts electrical resistivity and conductivity, e ...
s. It is named after German chemist
Adolf Sieverts
Adolf Ferdinand Sieverts (7 October 1874 – 8 January 1947) was a German chemist, best known for his work on solubility of gases in metals. He originated Sieverts's law. He was a doctoral student of Otto Wallach
Otto Wallach (; 27 March 1847 ...
(1874–1947). The law states that the solubility of a
diatomic
Diatomic molecules () are molecules composed of only two atoms, of the same or different chemical elements. If a diatomic molecule consists of two atoms of the same element, such as hydrogen () or oxygen (), then it is said to be homonuclear. O ...
gas in metal is proportional to the square root of the
partial pressure
In a mixture of gases, each constituent gas has a partial pressure which is the notional pressure of that constituent gas as if it alone occupied the entire volume of the original mixture at the same temperature. The total pressure of an ideal g ...
of the gas in
thermodynamic equilibrium
Thermodynamic equilibrium is an axiomatic concept of thermodynamics. It is an internal state of a single thermodynamic system, or a relation between several thermodynamic systems connected by more or less permeable or impermeable walls. In the ...
.
[C. K. Gupta, "Chemical metallurgy: principles and practice", Wiley-VCH, 2003, p.273.] Hydrogen
Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-to ...
,
oxygen
Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements ...
and
nitrogen
Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
are examples of dissolved diatomic gases of frequent interest in metallurgy.
Justification
Sieverts' law can be readily rationalized by considering the reaction of dissolution of the gas in the metal, which involves
dissociation of the molecule of the gas. For example, for nitrogen:
: N
2 (molecular gas) 2 N (dissolved atoms)
For the above reaction, the
equilibrium constant
The equilibrium constant of a chemical reaction is the value of its reaction quotient at chemical equilibrium, a state approached by a dynamic chemical system after sufficient time has elapsed at which its composition has no measurable tendency ...
is
:
where:
: ''c''
at is the concentration of the dissolved atoms into the metal (in the case above, atomic nitrogen N),
: ''p''
mol is the partial pressure of the gas at the interface with the metal (in the case above, the molecular nitrogen N
2).
Therefore,
:
See also
*
Henry's law
In physical chemistry, Henry's law is a gas law that states that the amount of dissolved gas in a liquid is directly proportional to its partial pressure above the liquid. The proportionality factor is called Henry's law constant. It was formulate ...
*
Graham's law
Graham's law of effusion (also called Graham's law of diffusion) was formulated by Scottish physical chemist Thomas Graham in 1848.Keith J. Laidler and John M. Meiser, ''Physical Chemistry'' (Benjamin/Cummings 1982), pp. 18–19 Graham found ...
References
{{reflist
Metallurgy
Materials science