In the work, the processes of phase reconstruction and properties of ceramics
obtained from high-siliceous clay-sand, clay-cullet, and clay-sand-cullet
mixtures are considered. It is possible to perform plastic molding of blanks
from the given mixtures due to the presence of montmorillonite in clay and
sand and sintering at 800 oC for 8 h under conditions of oxygen deficiency.
Depending on the composition of the initial mixtures, specimens ranging in
color from gray to black can be obtained. It has been established by the
XRD, IR spectroscopy, and electron microscopy methods that the synthesized
material is glass ceramics consisting of quartz, feldspars, and a glass
phase. Depending on the content of the initial components in the mixtures,
it is possible to obtain glass ceramics with high strength properties or
coarse-pored glass ceramics whose properties are similar to those of foamed
ceramics.
The low-temperature synthesis of bricks prepared from high-siliceous clays by the method of plastic molding of blanks was used. For the preparation of brick blanks, binary and ternary mixtures of high-siliceous clays, black sand, and bottle glass cullet were used. Gray-black low-porosity and high-porosity ceramics was obtained by sintering under conditions of oxygen deficiency. It has been established that to initiate plastic in mixtures containing high-siliceous clay, it is necessary to add montmorillonite/bentonite additives, carry out low-temperature sintering, and introduce low-melting glass additives with a melting point ranging from 750 to 800 °C. The performed investigations have shown that the sintering of mixtures with a total content of iron oxide of about 5 wt% under reducing conditions at Tsint. = 800°C for 8 h leads to the formation of glass ceramics consisting of quartz, feldspars, and a phase. The main sources of the appearance of a dark color is the formation of [Fe3+O4]4- and [Fe3+O6]9- anions in the composition of the glass phase and feldspars. By changing the contents of clay, sand, and glass in sintering, it is possible to obtain two types of ceramic materials: (a) in the form of building bricks and (b) in the form of porous fillers.
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