Synthesis and Characterization of Silicon Carbide Powders Converted from Metakaolin‐Based Geopolymer

Abstract

Silicon carbide (SiC) ceramic powders were synthesized by carbothermal reduction in specific geopolymers containing carbon nanopowders. Geopolymers containing carbon and having a composition M 2 OÁAl 2 O 3 Á4.5SiO 2 Á12H 2 O+18C, where M is an alkali metal cation (Na + , K + , and Cs + ) were carbothermally reacted at 1400°C, 1500°C, and 1600°C, respectively, for 2 h under flowing argon. X-ray diffraction and microstructural investigations by SEM/EDS and TEM were made. The geopolymers were gradually crystallized into SiC on heating above 1400°C and underwent significant weight loss. SiC was seen as the major phase resulting from Na-based geopolymer heated to ≥1400°C, even though a minor amount of Al 2 O 3 was also formed. However, phase pure SiC resulted with increasing temperature. While a slight increment of the Al 2 O 3 amount was seen in potassium geopolymer, Al 2 O 3 essentially replaced cesium geopolymer on heating to 1600°C. SEM revealed that SiC formation and a compositionally variable Al 2 O 3 content depended on the alkaline composition. Sodium geopolymer produced high SiC conversion into fibrous and globular shapes ranging from~5 lm to nanosize, as seen by X-ray diffraction as well as SEM and TEM, respectively.

Sodium silicate activated slag‐fly ash binders: Part I – Processing, microstructure, and mechanical properties

“…Stoichiometric geopolymers provide excellent fire resistance, ambient temperature production, excellent strength (compressive and flexural), and a lower carbon footprint into the atmosphere during manufacturing as compared to ordinary Portland cement (OPC) . Furthermore, geopolymers are increasingly being considered as matrices for reinforced composites, a variety of refractory applications, corrosion‐resistant coatings, and as precursors to ceramic formation …”

“…12 Furthermore, geopolymers are increasingly being considered as matrices for reinforced composites, 8,[13][14][15][16] a variety of refractory applications, corrosion-resistant coatings, and as precursors to ceramic formation. 17 Fly ash is a by-product of coal-burning power plants. Pulverized coal ignites when it is burned in air inside a furnace where temperatures exceed 1200°C.…”

Mechanical and microstructural analysis of geopolymer composites based on metakaolin and recycled silica

“…Geopolymer composites have been produced with different types of particles with the aim of modifying their microstructural, mechanical, and thermal properties. Nanopowders of carbon, α‐alumina and mullite nanosilica, cordierite, zircon, quartz and illite clay mineral, refractory particles ground electrical porcelain, hollow ceramic microspheres, chamotte, river sand and vermiculite have been incorporated into geopolymers. The incorporation of α‐Al 2 O 3 in high volumes increases the compressive strength of the geopolymer and the incorporation of 10.5 wt% chamotte particles into geopolymer pastes based on metakaolin decreases the crystallization temperature of the leucite and increases the flexural strength of the composite …”

Highly porous mullite ceramics from engineered alkali activated suspensions

“…A valuable inspiration came from previous experiences concerning geopolymers embedding a reactive carbon filler, allowing for carbothermal reduction and nitridation of ion‐exchanged geopolymers, with the obtainment of SiAlONs, in the form of powders. A similar approach is known to lead to SiC nanoparticles . In our case, the introduction of the filler, consisting of γ‐phase Al 2 O 3 (already known to yield mullite by interaction with silicone resins, pyrolized in air, as silica precursors), did not compromise the shaping into highly porous foams, by frothing.…”