Formation of α/β-Si3N4nanoparticles by carbothermal reduction and nitridation of geopolymers

Cengiz Bagci, Qun Yang, Waltraud M. Kriven

Research output: Contribution to journalArticlepeer-review


Silicon nitride (Si3N4) particles with various α/β-Si3N4ratios were fabricated from geopolymer (GP)-carbon compositions (M2O·Al2O3·4.5SiO2·12H2O+18C), where M is an alkali ion (Na+, K+ and Cs+). They were made by carbothermal reduction and nitridation at 1400°, 1500°, and 1600°C for 2 hours under flowing nitrogen. Characterization of carbothermally reacted GP-carbon compositions was based on XRD, SEM-EDS, HRTEM, and selected area electron diffraction analyses. Depending on the alkaline composition of GP, the carbon content and the reaction temperature, a compositionally variable α/β-Si3N4 or SiAlON was achieved. Crystallization of the GPs gradually increased by heat treatment over 1400°C with corresponding weight loss. It was found that NaGP, KGP, and CsGP crystallized into a major phase of α-Si3N4, β-Si3N4, and SiAlON, respectively. Prolonged heating at 1600°C led to an increase in the α/β-Si3N4 ratio in NaGP due to the formation of aluminum nitride, while it led to a decrease in α/β-Si3N4 ratio in KGP. In the case of CsGP, SiAlON replaced the pollucite which mainly formed at lower temperatures. Transmission electron microscopy revealed that the needle-like particles were of ~0.5 µm in size and consisting of α/β-Si3N4 mixtures.

Original languageEnglish (US)
Pages (from-to)6542-6551
Number of pages10
JournalJournal of the American Ceramic Society
Issue number11
StatePublished - Nov 1 2019


  • geopolymers
  • nanoparticles
  • nitrides
  • synthesis

ASJC Scopus subject areas

  • Ceramics and Composites
  • Materials Chemistry


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