Interaction between molten aluminum and potassium fluorophlogopite

Abstract

In recent years, fused-cast materials having potassium fluorophlogopite and its analogs as the main mineralogical phase are finding ever increasing applications in various fields of industry. The minimum wettability of the fused-cast products based on potassium fluorophlogopite by the majority of molten nonferrous metals, their high thermal shock resistance up to 1000~and their satisfactory strength characteristics make it possible to use them as the elements of the linings and as the individual components and the structural elements of the melting and the dispensing (distributing) furnaces, the casting machines, and the units used for batching aluminum alloys [1][2][3].The available information concerning the corrosion resistance of the fused-cast fluorophlogopite materials under the conditions involving static action of molten aluminum does not permit one to predict the efficiency of the products under the actual service conditions. For example, the conducted experiments show that at 700-800~ the test specimens do not virtually interact (react) with molten aluminum [3]. However, the service life of the products exposed to the flowing metal (in particular, in magnetodynamic batching units) varies over a wide range (from 1.5 up to 8 months) [4]. The existing problems made it necessary to carry out dynamic tests on the fluorophlogopite materials in order to establish the reasons and the nature of their destruction.Certain systems based on synthetic fluoromicas were chosen for the present studies. With respect to phase composition, fluorophlogopite forms the main structural (mineralogical) constituent.Platelike crystals form intergrown aggregates of different sizes and f.shapes. The secondary mlnerals are present in the form of inclusions on the crystals of the main phase or fill up the intergranular spaces. As a rule, the glass phase is located at the grain (crystal) boundaries in the intergranular or intragranular pores.We studied several materials. The FT and FB-6 materials are represented by potassium fluorophlogopite and the crystals of a solid solution of the phlogopite series of the potassium-barium composition, respectively; the FK materials are obtained using 1-7 wt. % silicon carbide additive and FTB-6 contains zirconium dioxide [5,6].S~ecimens measuring 20 mm in diameter were machined from the cast preforms and were weighed on an analytical balance after degreasing. At a time, three specimens were fixed on a rotator and were heated up to the experimental temperature maintaining a heating rate of 20~After attaining the desired temperature, the specimens were immersed in molten aluminum and the rotary drive was switched on. Testing was carried out in the melt of A-99 at 710~ maintaining a linear velocity of I.i m/sec.The test duration amounted to 10-15 h.After removing from molten aluminum, the specimens were Cleaned so as to take out the residual metal and were air cooled. Thereafter, they were treated with a 20% sodium hydroxide solution containing 20% sodium phosphate and were washed with hot (80~ disti...