2 research outputs found
Molecular Dynamics Investigation on Coke Ash Behavior in the High-Temperature Zones of a Blast Furnace: Influence of Alkalis
With
specific focus on local structural order, bonding networks,
transport properties, and viscosity of the molten ash oxides, we report
molecular dynamics simulations on the influence of alkalis (Na<sub>2</sub>O and K<sub>2</sub>O) on coke behavior within a blast furnace.
Atomistic simulations were carried out on the Al<sub>2</sub>O<sub>3</sub>–SiO<sub>2</sub>–CaO–K<sub>2</sub>O–Na<sub>2</sub>O system at 2223 K for a range and relative proportions of
Na<sub>2</sub>O and K<sub>2</sub>O. Alkalis were seen to have a strong
effect on the oxygen bonding networks; the relative proportions of
bridging and nonbridging oxygen showed a sharp increase, while significant
reductions were observed for tricluster oxygens. Total diffusion coefficients
and viscosity showed a highly nonlinear dependence on the relative
proportions of two alkalis with large changes observed in the simultaneous
presence of alkalis as compared to their individual presence. Our
studies have shown that the combined influence of alkalis on the viscosity
of molten ash, and associated coke degradation within a blast furnace,
is likely to be much smaller than previously perceived and could even
be negligible for some alkali concentrations
ReaxFF Molecular Dynamics Simulation for the Graphitization of Amorphous Carbon: A Parametric Study
A parametric study
of ReaxFF for molecular dynamics simulation
of graphitization of amorphous carbon was conducted. The responses
to different initial amorphous carbon configurations, simulation time
steps, simulated temperatures, and ReaxFF parameter sets were investigated.
The results showed that a time step shorter than 0.2 fs is sufficient
for the ReaxFF simulation of carbon using both Chenoweth 2008 and
Srinivasan 2015 parameter sets. The amorphous carbon networks produced
using both parameter sets at 300 K are similar to each other, with
the first peak positions of pair distribution function curves located
between the graphite sp<sup>2</sup> bond peak position and the diamond
sp<sup>3</sup> bond peak position. In the graphitization process,
the graphene fragment size increases and the orientation of graphene
layers transforms to be parallel with each other with the increase
of temperature and annealing time. This parallel graphene structure
is close to the crystalline graphite. Associated with this graphitization
is the presence of small voids and pores which arise because of the
more efficient atomic packing relative to a disordered structure.
For all initial densities, both potential parameter sets exhibit the
expected behavior in which the sp<sup>2</sup> fraction increases significantly
over time. The sp<sup>2</sup> fraction increases with increasing temperature.
The differences of sp<sup>2</sup> fraction at different temperatures
are more obvious in lower density at 1.4 g/cm<sup>3</sup>. When density
is increased, the gap caused by different temperatures becomes small.
This study indicates that both Chenoweth 2008 and Srinivasan 2015
potential sets are appropriate for molecular dynamics simulations
in which the growth of graphitic structures is investigated