Abstract:
The continued coffee demand in Kenya has amplified the
generation of its husk wastes causing disposal problems.
This has led to serious pollution to the environment.
Therefore, developing a greener and cost-effective ways
to handle these wastes is necessary. The current study
entailed the use of extracted silica and coffee husk biochar
as novel precursor materials for the synthesis of silicon
nitride (Si3
N4
) composite in an ammonia environment.
The silica was extracted from raw sand by alkali fusion
route. The biochar was prepared by pyrolytic treatment of
raw coffee husk biomass at 300 o
C for 5 hours followed
by acid leaching. The sand, extracted silica, raw and
biochar samples and silicon nitride composites were
characterized using X-Ray Fluorescence (XRF), Fourier
Transform Infrared (FT-IR), X-Ray Diffractometer
(XRD), Scanning Electron Microscope (SEM), Energy
Dispersive X-Ray (EDX) and Thermogravimetric
Analyzer (TGA). The results showed that the raw sand
contain quartz, calcite, microcline and clinochlore. The
results for the extracted silica showed a highly amorphous
silica containing hydroxyl (-OH) and siloxane (Si-O-Si)
functional groups. The alkali fusion process increased the
silica content to > 92 % from 83 % with oxide impurities
reduced to < 1 %. The characterization of biochar samples
showed a highly amorphous, porous carbon structure
with aromatic carbon bonds (C=C) and a negligible ash
content. The characterization of Si3
N4 powder showed
thermally stable, porous and highly amorphous material
with α-Si3
N4
and - Si3
N4
phases. The FT-IR results
showed Silicon-Nitrogen-Silicon (Si-N-Si), silanol (Si-
OH), Silicon-Nitrogen (Si-N) and Silicon-Silicon (Si-
Si) as important functional groups present in silicon
nitride composite material. The results revealed a greener
approach of Si3
N4 synthesis for application in vast
industrial fields.
