The effect of the hydrothermal method of synthesis of the initial powders using chemical reagents and illite clay as the initial components on the phase composition and structure as well as some properties of mullite-zirconium ceramic was studied. It is shown that mullite and the tetragonal modification of ZrO 2 predominate in the sintered ceramic material but closed pores are also present. As the firing temperature increases and especially with the addition of illite clay the degree of sintering and therefore the compression strength increase. The elastic modulus increases with temperature difference increasing to 1000/20°C, just as with the addition of illite clay, to 35 and 95 GPa, respectively, while with 500/20 it increases to 20 and 22 GPa.Mullite and mullite-zirconium ceramic, characterized by elevated high-temperature properties, is capable of operating right up to 1400°C while retaining high mechanical properties [1]. At the present time it is used conventionally as an internal lining in glass-and steel-melting furnaces, in furnaces for firing ceramic materials, in steel-pouring ladles, and so on. This form of ceramic [2, 3] is finding increasingly wider applications in new and simultaneously unconventional technological fields, as an example, as blades, turbines, and nozzles as well as internal coatings of fuel combustion chambers of jet aircraft, where too corrosive a medium (gases from fuel combustion, such as SO 2 , SO 3 , and so on), which can cause chemical corrosion and, in consequence, degrade the mechanical properties of ceramic material right to destruction, often predominates. Since there is a need to ensure the operation of mullite and mullite-zirconium materials under relatively extreme conditions, the requirements for the mechanical indicators as well as the chemical properties of this ceramic are increasing. Factors such as the form of the initial ceramic powders, the dispersity, activation of ceramic powders, all possible additives, as well as the method of synthesis of the powders, the initial chemical reagents, and other factors can all improve these properties [2 -4].There exist many methods [5 -12] for obtaining and synthesizing mullite and mullite-zirconium ceramic, starting from the conventional techniques for production [5] from the corresponding oxides (or hydroxides) without preliminary activation of the powders followed by firing of the ceramic material. A number of investigations [6 -10] present data on the preliminary activation of powders subjected to grinding and simultaneous homogenization for different times -from 4 -5 h [6 -8] to 20 -24 h [9, 10], in some cases even to 30 -36 h [11], right up to modern methods of synthesis, such as the combustion method [12], the hydrothermal method [2, 3], and so on.As indicated in [3] the hydrothermal method of synthesizing ceramic powder (at temperatures 270 -300°C) largely results in the formation of pseudocrystalline forms of aluminosilicate (in all probability, a cluster) with molar ratio of aluminum and silicon oxides 1 : 1. Direct...
Results are provided for a study of the development of high-temperature mullite-zirconium ceramic with use of activated ceramic powders prepared by grinding for different times with addition of illite clay, and from pure oxide powders. It is shown that increased activity and amorphicity of ground particles considerably promotes formation of mullite phase at 1200°C, and also transition of the monoclinic modification of ZrO 2 to tetragonal, particularly with an increase in firing temperature. It is proposed that as a result of rapid "freezing" the structure retains the high-temperature modification of ZrO 2 , having a tendency with slow ceramic cooling to transform into the monoclinic modification.
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