ADVANCE IN THE THEORY OF CERAMICS/LIQUID METAL SYSTEMS WETTABILITY. PECULIARITY OF CONTACT PROCESSES FOR TRANSITION AND NON—TRANSITION METALS

Abstract

The review and some general comments devoted to scientific problems of high temperature wetting and adhesion in systems liquid metals—solid ceramic materials were done including the analysis of data received in a last time. The theoretical treatment of high temperature wetting processes and mechanism based on traditional thermodynamic notions and new approach on atomic and atomic-electron level were developed. As ceramics various substrates namely substrates with predominated ionic interatomic bonds (oxides for example) which usually hardly wetted by liquid metals are considered first of all. The contribution of nonequilibrium and equilibrium parts of adhesion to wetting process are considered and analysed. The ”active“ metals viz metals with high enough chemical affinity for solid phase atoms or iones were divided on transition metals (d-electron orbitals are partly occupied by electrons) and nontransition metals (dorbitals are empty or completely full by electrons).  The wettability in first case (transition metals) is much more intensive than that for nontransition metals inspite of thermodynamic factors (chemical affinity of metal for atoms of solid phase are closed). Many experimental data illustrate these regularity. The Ligand field theory is proposed to explane and to give treatment on electron level superiority of transition metals in adhesion activity. An adhesion activity of nontransition metals to solid substrates (oxides) is much low or moderate and dewetting phenomena are frequently observed in this case. This especial feature is explained by formation at the interface nonstable of intermediate valency compounds which can be subjected to reaction of disproportionation. Some practical recommendations related to regulation and governing wetting processes in various technological procedures were done.