Thermal stability of advanced carbon bottom blocks for aluminum electrolysis cells

Abstract

Results of a study of the thermal stability of advanced bottom blocks simulated for operating under critical conditions are reported. The thermal stability of domestic N-3-grade bottom blocks made up of composite carbon materials subjected to radial temperature gradients generated by local current heating is shown to be not inferior to that of foreign analogs. The thermal stability is shown to correlate with electric resistivity and rupture strength of the material Thermal stability of structural elements exposed to high-temperature heavy-duty conditions has been and continues to be a major concern for researchers and practical engineers in many sectors of industry. In full measure this concern is shared by technologists who have to do with carbon materials, in particular, those used in aluminum electrolysis cells.Currently, the advanced technologies that are under development for high-capacity aluminum electrolysis cells require the use of refractories for bottom blocks high in carbon materials pretreated at high temperatures. The major components for bottom blocks used by domestic manufacturers are heat-treated thermoanthracite and artificial graphite [1,2].As shown by the engineering practice, the physicomechanical properties of bottom blocks are mainly controlled by the aggregates (or fillers) used and by the thermoanthracite:graphite ratio, mostly obeying the additivity rule [1,2]. Along with the normative specifications of quality and operational stability, the bottom blocks are recommended to be tested for thermal stability. An important characteristic of thermal stability of a material is its rupture strength, and the study of its behavior is an issue of special interest for technologists.Thermal stability, in particular, that of the bottom lining of electrolysis cells, is at present a hotly debated topic in the literature [3 -5] 2 .Thermal stability can be defined as the strength of a material subjected to thermal stresses (mechanical stresses that arise in a solid because of the nonuniform temperature distribution throughout its extent or because of the constraints to its free thermal expansion. Thermal stability as a physical attribute was shown to be related to a range of fundamental properties of matter. Thermal stability is a major property of structural materials, not infrequently the pivotal factor determining their service life. In practice, thermal stability is an important design consideration for materials exposed to high temperatures.Experimental study of the thermal stability remains a challenging problem, and researchers in the field are divided in both the choice of a unique criterion and universal methodology of its determination.A literature survey in [3] has shown that It was shown in a literature survey [3] that at present the following criteria for the thermal stability of materials in a plain stress state have gained acceptance:where s is the strength (rupture strength under normal conditions); n is Poisson's ratio; E is the elasticity modulus; a is the coefficient of linear thermal ...

Promising grades of OAO Énergorpom – ChÉZ carbon refractories for lining blast furnaces

“…by a factor of two to three. Differences in thermal shock resistance for the test grades is due to the different graphite content within their composition, that is typical for carbon-graphite material, for example hearth blocks for aluminum electrolyzers [6]. An increase in graphite content is accompanied by an increase in thermal conductivity, and a reduction in elasticity modulus.…”