Corrosion of aluminosilicate refractories by molten aluminum and melts based upon it in melting and casting units

Abstract

Corrosion mechanisms are proposed for aluminosilicate refractories by molten aluminum taking account of new ideas about physicochemical reaction of molten aluminum with refractory. With a negative volumetric effect for aluminum reactions with components of aluminosilicate refractories reaction products will not form a continuous film, and with a positive volumetric effect the reaction products will split pores and cause material cracking. A porous aluminum oxide film will not be a barrier for the reaction of aluminum with refractory. The possibility for aluminosilicate refractories of wetting by molten aluminum and the size of pores permeable for penetration of molten aluminum in relation to presence or absence of antiwetting additions are determined.Action of aluminum on refractory materials involves chemical reaction (increasing with introduction of alloying additions), erosive action, thermal shock (with metal pouring), and mechanical action (with loading of ingots). Account should also be taken of the action of fluxing additions (although considerably less than in ferrous metallurgy).Integration into the world market has required in our country both examination of ideas about the reaction of aluminosilicate refractories laid down in 1960 -80s, and introduction of new refractory materials for the aluminum industry, more resistant to the action of molten aluminum. Ideas formulated in the 1960 -80s about the physicochemical reaction of aluminum with refractories required considerable reworking. Not all possible reactions with refractory components were considered for the alloys based on aluminum and fluxing addition components, and almost no attention was devoted to wetting of refractories by molten aluminum, and the structure of refractories for producing aluminum alloys.In previous work for introduction of corundum refractories into the melting and casting units of the aluminum industry no consideration was given to the fact that magnesium is one of the main components of aluminum alloys of the 5 -6th group, and it reacts with Al 2 O 3 with formation of aluminum-magnesium spinel. A first approximation is given in Table 1 [ 1 -3] for information about the possible reaction of molten aluminum with oxides comprising refractory materials. On the basis of data about enthalpy values for oxide formation it is may be noted that all oxides placed to the right of Al 2 O 3 cannot be reduced by molten aluminum. Conversely, TiO 2 , SiO 2 , and FeO have a capacity to react with molten aluminum: 4Al + 3SiO 2 ® 2Al 2 O 3 + 3Si.(1)In the presence of magnesium spinel formation is possible:Data in Table 1 do not take account of the following situations:in molten aluminum there are always both impurities (alkali metals, gases) and additions (magnesium, strontium, zirconium, etc.) that on one hand are corrosive agents, and on the other hand in view of their activity, strengthen the corrosive action of aluminum; oxides in a bonded state (for example SiO 2 in calcium silicate, magnesium silicate and even in aluminum silicate) are l...

Effects of Different Calcium Compounds on the Corrosion Resistance of Andalusite-Based Low-Cement Castables in Contact with Molten Al-Alloy

“…[21,46] Amorphous phases undergo reactions with molten metals more easily because of the higher numbers of dislocations and boundary defects, and thus, the kinetics of the reactions between the molten metal and refractory are enhanced in this case. [44] At the same time, glassy phase formation increases the density and strength of the refractory at low temperatures.…”

“…[2][3][4] Wollastonite is resistant to molten aluminum alloy and has been shown to prevent metal penetration and corundum growth in the refractory material. [16] The use of wollastonite is based on the assumption that calcium silicates act as a barrier against the oxidation of molten aluminum. [17] Limited work has been carried out on the use of calcium oxide (CaO) as the additive for aluminum casting refractories.…”

Intéraction entre les particules d'alumines, les alliages d'aluminium et ses inclusions durant la filtration d'aluminium avant la coulée /

“…2.13. It is also mentioned by Yurkov [70] and Allaire [71] that the sodium is oxidized again via either direct oxidation (>10" 19 atm P 02 ), or reduction of other impurities such as SiO 2 . etc.…”

“…It was observed that corrosion under dynamic conditions is more severe than it is under static conditions. Other researchers [70][71][72] who studied the corrosion of aluminosilicate refractories by molten aluminum also discussed the impact of impurities such as iron oxide and sodium oxide on the corrosion resistance of refractories. It is reported in these studies that Na2O is one of the most important impurity in alumina.…”

“…Software is slightly different than the one shown in Equations 2.12 and 2.13. Yurkov [70] claims that this oxide layer exists as a thin film on the metal surface. The extent of aluminum/alumina interaction is correlated with the consistency of oxide film which may act like a barrier for magnesium diffusion through particle.…”