Wear-resistant refractories in aluminum pyrometallurgy

Abstract

Service conditions for refractories and physicochemical processes at their contact with molten aluminum are provided. Thermodynamic calculations establish the relative wear resistance of a number of oxides, silicates, and oxygen-free compounds towards aluminum in the range 700 -1200°C (937 -1473 K). The role is revealed of contact physicochemical processes at the boundary of a refractory with molten aluminum. The high resistance towards aluminum is demonstrated for high-alumina calcium aluminates, particularly bonite CaO · 6Al 2 O 3 and spinel MgO · Al 2 O 3 . The most practicable wear-resistant fuzed materials for preparing lining of melting furnaces are lime-aluminate slags of OAO Klyuchevsk Ferroalloy Plant.The practice of lining metallurgical units for preparing primary, secondary aluminum and alloys based on them has established the increased corrosiveness of the metal towards the majority of traditional refractories [1 -4]. In spite of the relatively low temperature level in the pyrometallurgy of these metals (800 -1200°C), there is intense wear of even some highly refractory materials with a melting temperature (or refractoriness) exceeding by a factor of two to three the operating temperatures in melting and other units. Use of highly refractory materials and components that exhibit resistance at service temperatures of 1550 -1700°C in ferrous metallurgy units in furnaces for the production and processing of nonferrous metals is often economically and technically undesirable since here sufficient lining durability is not achieved, and the refractory resource is not entirely used.It is generally assumed that the main reason for the intense wear of the lining of aluminum thermal units and different devices is chemical reaction of the metal with minerals of the refractory components. At the boundary of oxide compounds with molten aluminum there is an oxidation-reduction reaction causing transformation of refractory minerals into a metal phase and oxidation of aluminum to oxide (corundum or g-Al 2 O 3 ). The general scheme for chemical reaction of oxide materials with aluminum is:where Me m O n is refractory oxide compound; Me is reducing metal (element).The resistance of refractories to corrosive slag and molten metal is determined by a collection of thermodynamic and kinetic factors that specify correspondingly the fundamental possibility of chemical reactions in a refractory compound-melt system and the rate of its occurrence. The probability of reaction of aluminum with refractory compounds may be calculated by classical chemical thermodynamic methods. Given in Table 1 as an example are calculations of isobaric-isothermal potential G T 0 (Gibbs energy) for the interaction of some oxygen-containing compounds with aluminum in the range 800 -1000°C (1073 -1273 K). It is established that the thermodynamically stable oxides CaO, MgO and ZrO 2 do not react with aluminum under these conditions. All of the rest of the compounds, including mullite and silicon minerals, are subject to aluminothermaic reduction whos...

Non-traditional domestic refractory materials for aluminum metallurgy

“…In contrast to all other metallurgical and fuel slags aluminothermal materials do not have a silicate but an alumina (aluminate) substance composition that predetermines their specific thermochemical properties; one of them is a capacity not to be wetted by molten aluminum and not to react with it. This property of refractories and heat-resistant materials is called by us aluminophobicity [2].…”