Gases

With the adsorption g. they interact only with the surface of metal and are formed on it films by thickness, equal to diameter of one or it is several molecules. Adsorption decreases with increase in the temperature and lowering in the pressure g. above the metal. G., adsorbed on the metallic parts of the vacuum-tube instruments (those used in it will measure, to equipment), radio transmitting equipment, the converters of elektrich. energies, in the process of operation are desorbed and they disrupt the steady work of equipment (for example, they change electrical conductivity). Removal adsorbed g. by the production of this equipment is achieved by deep evacuation, application of absorbers G. (getters) it is one of the most important tasks of vacuum technology.

Majority g., except inert, forms with the solid and liquid metals true solutions. G., the molecules of which consist of several atoms (for example, sulfur dioxide, carbon dioxide, hydrogen, nitrogen), with the dissolution in the metals they are decomposed into the atoms. This facilitates introduction g. into the metal, since it decreases the energy, necessary in order to move apart the strongly interacting with each other atoms of metal. Furthermore, the part of the spent energy is compensated by its gain with chem. interaction of atoms g. and metal. Therefore the dissolution of polyatomic gases is accompanied by their dissociation. For example, diatomic gases hydrogen and nitrogen are dissolved in iron according to the reactions

Solubility g. in molten metals is considerably higher than in the solid. This frequently leads to worsening in the quality of metallic ingots because of the formation in them of the gas pockets, internal shells and porosity. Such defects appear as a result of the fact that with the gradual hardening of ingot (crystallization) in the casting mold the concentration g. in the remaining liquid so rises that g. are separated in its volume, but bubbles resultant in this case do not manage to float and to be removed to the complete hardening of ingot.

G. frequently form with the metals of the chem. connection: oxides, sulfides, nitrides. These connections are not dissolved in the metals and are separated in the form of independent phases - Vol. n. of nemetallich. of the starts, whose the presence strongly worsens mechanical. and the anticorrosive properties of metals and alloys. Therefore in the industry the different methods of removal g. from the metals adapt. One of effective - use of evacuation. In this case because of lowering in the pressure g. occurs their isolation from the metals, which takes place especially intensively, when metal is in the molten state.

They are widespread the smelting of metals and alloys, especially they became, in the vacuum ovens, the evacuation of liquid metal with the pouring and in the ladles (see vacuum melting, degassing steel). With the same purpose the scavenging of liquid metal by the inert gases uses (for example, by argon). In a number of cases the melting or heating metal in the shielding gas atmosphere, which does not contain the components, harmful for the metal, are achieved.

Lit.: Smitells k., gases n metals, translated from English. M. - L., 1940; Vacuum metallurgy, M., 1962; Zhukhovitskiy A. A., Shwartzman L. A., Physical Chemistry, M., 1963; Dushman s., the scientific bases of vacuum technology, translated from English, M., 1964. L.A.Shvartsman,

L. V. vanhkova.