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<p>The patterns of the formation of geopolymers based on naturally enriched kaolin (KR-1 brand, Eleninskoe deposit, Russia) were studied under conditions of its alkaline activation in a reaction medium (10 <i>M</i> NaOH and water glass) with different silicate modulus (SiO<sub>2</sub>/Al<sub>2</sub>O<sub>3</sub>). The prepared samples were examined by X-ray phase diffraction, scanning electron microscopy, and low-temperature nitrogen adsorption/desorption. The mechanical strength of the samples for compression and bending was determined. When the silicate modulus ranges from 2.0 to 2.5, zeolite NaY crystallizes in the studied systems accompanied by a decrease in the strength of the samples (2–3 MPa for compression and 2.7 MPa for bending) and an increase in their specific surface area (170 m<sup>2</sup> g<sup>−1</sup>). At SiO<sub>2</sub>/Al<sub>2</sub>O<sub>3</sub> ranging from 2.5 to 3.0, an X-ray amorphous phase of the geopolymer with high strength characteristics (compressive strength reaches 67 MPa, bending strength is 7.5 MPa) and a low specific surface area (30 m<sup>2</sup> g<sup>−1</sup>) is formed. At higher values of the silicate modulus (3.0 &lt; SiO<sub>2</sub>/Al<sub>2</sub>O<sub>3</sub> &lt; 3.5), an X-ray amorphous phase consisting of a geopolymer and unreacted water glass is formed, while the compressive strength of the material decreases (25–40 MPa).</p>

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Investigation of geopolymerization and recrystallization processes of metakaolin in an alkaline medium with different SiO2/Al2O3 molar ratios

  • 期刊论文

  • 发表日期：

    2025年11月1日

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  • A. A. Alekseev,
  • Yu. A. Alikina,
  • O. Yu. Golubeva

摘要

The patterns of the formation of geopolymers based on naturally enriched kaolin (KR-1 brand, Eleninskoe deposit, Russia) were studied under conditions of its alkaline activation in a reaction medium (10 M NaOH and water glass) with different silicate modulus (SiO2/Al2O3). The prepared samples were examined by X-ray phase diffraction, scanning electron microscopy, and low-temperature nitrogen adsorption/desorption. The mechanical strength of the samples for compression and bending was determined. When the silicate modulus ranges from 2.0 to 2.5, zeolite NaY crystallizes in the studied systems accompanied by a decrease in the strength of the samples (2–3 MPa for compression and 2.7 MPa for bending) and an increase in their specific surface area (170 m2 g−1). At SiO2/Al2O3 ranging from 2.5 to 3.0, an X-ray amorphous phase of the geopolymer with high strength characteristics (compressive strength reaches 67 MPa, bending strength is 7.5 MPa) and a low specific surface area (30 m2 g−1) is formed. At higher values of the silicate modulus (3.0 < SiO2/Al2O3 < 3.5), an X-ray amorphous phase consisting of a geopolymer and unreacted water glass is formed, while the compressive strength of the material decreases (25–40 MPa).