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Non-equilibrium materials and mechanochemistry

 

Mechanochemical treatement is a procedure of milling of the powders in various types of mills (“mechanochemical reactors”) during which ensues a number of physical and chemical changes in material. Mechanochemical treatment has been recognized as a capable technique for the synthesis of wide range of materials, among them those which are difficult to synthesize by other methods, like the compounds of mutually unsolvable elements and the compounds with high melting temperature.

During many years of working in this field at the Institute, a number of various metal and ceramic systems have been synthesized by mechanochemical treatment (table) and their structural changes during milling as well as the influence of the milling parameters on kinetics and the product of milling treatment were studied. Characteristic for the examined systems is the forming of highly disordered structure: nanocrystalline and amorphous. Several phenomena were identified as responsible for the ensuing reactions induced by milling: permanent breaking and adhesiveness of powder particles as well as the forming of atomically clean areas (“fresh areas”); forming of nanocrystalline structures and local heating (appearance of high-energy, localized and short-term places – “hot spots”).

Using mechanochemical method combined with self-propagating high-temperature combustion synthesis, it is possible to synthesize various composite systems of very contemporary contents. Finely dispersed phases of TiO 2 and ZrO 2 within the electroconducting Cu matrix were produced, as well as W submicron particles by shelite reduction (CaWO4) with magnesium and aluminium.

From the standpoint of applications, mechanochemically prepared materials may be used in electronics, electrochemistry, catalysis, biomedicine, etc.

Phenomena emerging during the course of mechanochemical treatment are numerous and complex, therefore insufficiently known. On that account, we make continuous efforts to study mechanism of mechanically induced reactions, therewith an influence of milling parameters on the kinetics and structure attained as a result of a dissipation of mechanical energy.

Materials synthesized by mechanochemical treatment

Starting material

Product

Milling medium

Atmosphere/lubricant

Cu - 50 at.%Zr powder mixture

Amorphous CuZr alloy

Hardened steel

Air/ dry milling

Ni - 50 at.%Ti powder mixture

Amorphous NiTi alloy

Hardened steel

Argon/ ethanol

Powder mixture of La, Ni, Ce, Co, Mn and Al

Amorphous alloy of nominal composition La 0.8 Ce 0.2 Ni 2.5 Co 0.2 Mn 0.4 Al 0.3

Hardened steel

Argon/ hexane

Powder mixture of Mg, Ni and Cu (or V)

Nanocrystalline Mg2Ni type alloy, i.e., Mg2Ni0.75 Cu0.25 , Mg2Ni0.6Cu0.4 and Mg2Ni0.75V0.25

Hardened steel

Argon/ ethanol

ZnO - 50 at.%Al2O3 powder mixture

ZnAl2O4 spinel

Corundum

Air/ dry milling

NiO - 50 mol.%Fe2O3 powder mixture

NiFe2O4 spinel

Hardened steel

Air / dry milling

a -Fe2O3

a -Fe2O3 - Fe3O4 - FeO

Hardened steel

Air or oxygen/ dry milling

Bi2O3 - 60 mol.%TiO2 or Bi4Ti3O12

Amorphous Bi 4 Ti3O12

Hardened steel

Air/ dry milling

Powder mixture of a -Bi2O3 and PbO (or ZnO, SiO2 and Fe2O3 )

g -Bi 2O3

Hardened steel or zirconia

Air/ dry milling

Powder mixture of La2O3 , TiO2 , MgO and Fe2O3

LaMg 0.5Ti x Fe yO3 perovskite

Hardened steel

Air/ dry milling

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