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The paper examines the mechanochemical activation of starting minerals (kaolin, pyrophyllite, and talcum) and their effect on the solid-phase synthesis and properties of cordierite. Binary oxide compounds (spinel, mullite, enstatite, forsterite) are synthesized. It is established that binary compounds and crystalline silica should be minimized to decrease the synthesis temperature of cordierite. Processes for synthesis and production of cordierite ceramics with lower thermal expansion coefficient ((1.0-1.2) ⋅ 10 -6 °C -1 ) are developed.

Physicochemical research is conducted to examine the phase formation under dynamic and static annealing of MgO-Al 2 O 3 -SiO 2 tempered glass (composition range adjacent to stoichiometric cordierite). Thirty glass compositions are examined in this system and the range is determined over which single-phase ceramic materials with the lowest possible thermal expansion coefficient are synthesized under specific crystallization conditions.Melt crystallization provides materials based on alumina compounds, including mullite (3Al 2 O 3 ⋅ 2SiO 2 ), forsterite (2MgO ⋅ SiO 2 ), and cordierite (2MgO ⋅ 2Al 2 O 3 ⋅ 4SiO 2 ) with uniform chemical and phase compositions and controlled content of impurity phases. Two processing options may be used: (i) forming of parts from molten glass and their subsequent annealing (T ≥ 1000°C) for crystallization and (ii) production of granulated glass, its grinding, forming, and annealing using conventional ceramic processing.Single-phase α-cordierite with low thermal linear expansion coefficient (TLEC) and high thermal resistance was produced by cooling a cordierite melt at a rate of 1.5 °C/sec to 900-1100°C with subsequent annealing at these temperatures for four to five days [1]. To promote the crystallization of cordierite and decrease the volume content of the glass phase, oxide additions are used to form crystallization nuclei in glass: 3-5 wt.% ZrO 2 [2], 0.1-15 wt.% Nb 2 O 5 , Ta 2 O 5 [3], ≤10 wt.% TiO 2 [4]. This leads to a 25% decrease in annealing time, and the content of crystalline cordierite reaches 98-99 vol.%.The thermal linear expansion coefficients of samples representing stoichiometric cordierite ceramics and cordierite-based solid solutions are 2.0 ⋅ 10 -6 °C -1 over a range between 25 and 1000°C [5]. A substantial amount of the glass phase that had no admixtures of alkaline or alkaline-earth metals (ratios 1 : 1 : 4, 1 : 1 : 5, and 1 : 1 : 6 containing to 81% Si 2 ) increased the thermal expansion coefficient from 2.0 to 3 ⋅ 10 -6 °C -1 . The high content of crystalline cordierite (95-97%) resulted from arc melting of a cordierite charge consisting of serpentinite, quartz sand, and alumina [6]. When glass was heated at a rate of 10 °C/min, differential thermal analysis (DTA) revealed an exothermic effect of cordierite crystallization with a peak at 1000°C. There are no data on the thermal expansion of crystallized cordierite samples. In contrast to conventional negative attitude to alkaline oxide admixtures, it was established in [7] that about 7.56 wt.% K 2 O introduced into cordierite glass in accordance with the formula 4MgO ×