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Formation of α/β‐Si 3 N 4 nanoparticles by carbothermal reduction and nitridation of geopolymers
Author(s) -
Bagci Cengiz,
Yang Qun,
Kriven Waltraud M.
Publication year - 2019
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/jace.16545
Subject(s) - carbothermic reaction , materials science , crystallization , high resolution transmission electron microscopy , nitride , transmission electron microscopy , carbon fibers , sialon , silicon nitride , chemical engineering , silicon , alkali metal , analytical chemistry (journal) , mineralogy , nanotechnology , metallurgy , ceramic , composite material , composite number , chemistry , carbide , organic chemistry , layer (electronics) , chromatography , engineering
Silicon nitride (Si 3 N 4 ) particles with various α/β‐Si 3 N 4 ratios were fabricated from geopolymer (GP)‐carbon compositions (M 2 O·Al 2 O 3 ·4.5SiO 2 ·12H 2 O+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‐Si 3 N 4 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‐Si 3 N 4 , β‐Si 3 N 4 , and SiAlON, respectively. Prolonged heating at 1600°C led to an increase in the α/β‐Si 3 N 4 ratio in NaGP due to the formation of aluminum nitride, while it led to a decrease in α/β‐Si 3 N 4 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‐Si 3 N 4 mixtures.