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The preparation of silicon nitride was performed by
carbothermal reduction and nitridation of pure silicon
dioxide and graphite, and its relative weight change is
measured by a thermal gravimetric analysis (TGA) reaction
system. The purpose of this thesis is to understand the
effect of different operating variables on the degree
of conversion of silicon dioxide. Finally, we can get the
optimal condition. In this thesis, the following operating
variables have been discussed: nitrogen flow rate, silica/
graphite molar ratio, grain sizes of silicon dioxide and
graphite, and reaction temperature. The analysis of this
experiment is conducted by powder X-ray diffraction(XRD),
optical microscopy scanning electron microscopy (SEM), BET
surface area and gas chromato- graph (GC). From the experiment
data, we can make the following conclusions. The first, the
nitridation extent is increased by increasing the nitrogen
flow rate. If the nitrogen flow rate exceeds 400 ml/min, the
effect is not appreciable. The second, an excess of graphite
is required to promote the degree of conversion of silicon
dioxide, however, the effect is not appreci- able when the
molar ratio is above 4. The third, reducing the grain sizes
of silicon dioxide and gra- phite may increase the degree of
conversion of sili- con dioxide. The final, the higher
the reaction temperature the faster the reaction rate, and
the effect is quite sensitive.
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