Prospects for using aluminosilicate refractories for aluminum electrolyzers. Part 2. Resistance of aluminosilicate refractories to the action of commercial electrolyte

Abstract

Data are provided for laboratory studies of the resistance of aluminosilicate refractories to the action of commercial electrolyte. It is established that refractory ShPD M -45, prepared using a mullite-corundum chamotte, is most resistant to electrolyte action. Results are provided for studies in the change of mineral composition and phase transformations in aluminosilicate refractories during reaction with commercial electrolyte. It is shown that long-prismatic titanium-containing mullite is more resistant to the action of the fluoride ion than short-prismatic material.The service life of an aluminum electrolyzer is mainly governed by the resistance of refractory linings of the cathode assembly to the action of an incoming corrosive medium. There is information about tests of refractory materials for cryolite resistance. Different test procedures, their characteristics and comparisons are provided in [1,2].Data from laboratory studies are provided in this article for the resistance of aluminosilicate refractories ShA-5, ShPD-43 and ShPD M -45 [3] to the action of a commercial electrolyte with a cryolite ratio (c.r.) of 2.4. Tests were performed by a petrographic method in reflected and transmitted light in MBI-6 and MIN-8 microscopes respectively. The resistance of aluminosilicate refractories in contact with molten commercial electrolyte was determined with a steady-state method by heating test articles in a Tamman furnace followed by a study of the change in mineral and phase composition of the refractories. Cylindrical holes of identical diameter and depth were made in articles, and they were filled with a uniform amount of commercial electrolyte with c.r. of 2.4 containing, apart from the main components, calcium and magnesium fluorides. The prepared samples were placed in a hermetically sealed alundum crucible and heated in a Tamman furnace to 1000°C with isothermal soaking at 1000°C for 1 h. Cooling took place in the furnace.After testing refractory specimens changed in color. At the surface of specimens from the side of the opening reaction zones were seen in the form of concentric circles of different color. The diameter of the original hole increased (Fig. 1), and its relative increase for specimens of ShA-5, ShPD-43, and ShPD M -45 was 47.5, 33.3 and 16.1% respectively.A specimen of ShA-5 after testing had a dingy lilac color. Over its surface (at the top of the hole and over the side) glassy new formations were seen in the form of circles with a diameter of 4 mm and leakages from the direction of the depression (hole), i.e. coarse pores with a diameter of 1.0 -1.5 mm. The electrolyte was converted into glass. With separation over the length of the depression two zones seen: a working zone 5 -10 mm thick of green color, and a glassy and transition zone yellow in color. The base of the specimen was the least changed zone (Fig. 2a ).A specimen of ShPD-43 after testing had a gray color. At its surface from the direction of the hole in the form of circles there was a working zone green in color and then t...

Prospects of the use of aluminosilicate refractories for aluminum electrolyzers. Part 3. The role of the glass phase formed in the operation of aluminum electrolyzers

“…With allowance for the higher resistance of the ShPDm-45 refractory to the action of industrial electrolyte as compared to the resistance of ShPD-43 and for the data of our previous study [6] (Part 2 of the present paper) we may conclude that the action of the fluoride ion is resisted not only by the prismatic titanium-bearing mullite but also by the titanium-bearing glass phase.…”

Future application of aluminosilicate refractories for aluminum electrolyzers. Part 4. Wettability of aluminosilicate refractories with molten industrial electrolyte and sodium fluoride

“…In addition, lower sub-fluoride compounds, CaF, MgF, fluorides of variable nonstoichiometric composition, fluorides of iron FeF 2 and FeF 3 , fluorides of iron of nonstoichiometric composition [13, aluminum oxyfluoride AlOF and oxyfluoride of variable composition AlOF 1 -x , oxygen suboxides Al 2 O and SiO are present. Studies of the present article and those provided in [4,7,8,14] establish that sodium vapor, lower fluoride and oxide compounds of aluminum, silicon, calcium, magnesium, diffusing in the refractory, lead to a change in its chemical and phase compositions.…”

“…Taking account of previous studies [7,8] and experimental data presented in Part 2 of the article [4] and in this communication, it is possible to conclude that as a result of the action of subsidiary corrosive gaseous products of electrolysis (and under extreme conditions when joints open with breakthrough of molten electrolyte) there is removal of silicon not only in the form of SiO 4 , Na 2 SiF 6 , but also in the form of SiO.…”

“…Previous studies by the authors of this article [4] established that aluminosilicate refractory ShPD M -45, produced with addition of mullite-corundum chamotte, is more resistant to the action of molten industrial electrolyte than refractory ShPD-43 prepared by normal technology. The aim of the present work is to study wetting of different aluminosilicate refractories by molten industrial electrolyte with a.o.…”

Study of the mineral and phase composition of aluminosilicate refractory ShPDM-45 after service in an aluminum electrolyzer of OAO Zaporozh’e aluminum combine

“…carnegieite, and also sodium silicate Na 2 Si 2 O 5 with N g = 1.497 and N p = 1.508 [11]. According to immersion analysis data on the basis of the fact that the refractive indices exhibit an additive property, it has been established that in nepheline there is fluorine in the form of a solid solution, b-phase [12] with a cryolite content of 1.711% [7]. In addition, in the working zone there are dark platelets with optical properties corresponding to iron fluoride and subfluoride FeF 2 with N g = 1.347, FeF 3 with N g = 1.408, N p = 1.141, FeF x (2 < x < 3) with N = 1.33 -1.416, that was established previously from the results of x-ray structural studies [13,14].…”