24,861 research outputs found
Effects of porosity in a model of corrosion and passive layer growth
We introduce a stochastic lattice model to investigate the effects of pore
formation in a passive layer grown with products of metal corrosion. It
considers that an anionic species diffuses across that layer and reacts at the
corrosion front (metal-oxide interface), producing a random distribution of
compact regions and large pores, respectively represented by O (oxide) and P
(pore) sites. O sites are assumed to have very small pores, so that the
fraction of P sites is an estimate of the porosity, and the ratio
between anion diffusion coefficients in those regions is .
Simulation results without the large pores () are similar to those of
a formerly studied model of corrosion and passivation and are explained by a
scaling approach. If and , significant changes are
observed in passive layer growth and corrosion front roughness. For small
, a slowdown of the growth rate is observed, which is interpreted as a
consequence of the confinement of anions in isolated pores for long times.
However, the presence of large pores near the corrosion front increases the
frequency of reactions at those regions, which leads to an increase in the
roughness of that front. This model may be a first step to represent defects in
a passive layer which favor pitting corrosion.Comment: 8 pages, 6 figure
Phase diagram of a 2D Ising model within a nonextensive approach
In this work we report Monte Carlo simulations of a 2D Ising model, in which
the statistics of the Metropolis algorithm is replaced by the nonextensive one.
We compute the magnetization and show that phase transitions are present for
. A phase diagram (critical temperature vs. the entropic
parameter ) is built and exhibits some interesting features, such as phases
which are governed by the value of the entropic index . It is shown that
such phases favors some energy levels of magnetization states. It is also
showed that the contribution of the Tsallis cutoff is essential to the
existence of phase transitions
Interface Collisions
We provide a theoretical framework to analyze the properties of frontal
collisions of two growing interfaces considering different short range
interactions between them. Due to their roughness, the collision events spread
in time and form rough domain boundaries, which defines collision interfaces in
time and space. We show that statistical properties of such interfaces depend
on the kinetics of the growing interfaces before collision, but are independent
of the details of their interaction and of their fluctuations during the
collision. Those properties exhibit dynamic scaling with exponents related to
the growth kinetics, but their distributions may be non-universal. These
results are supported by simulations of lattice models with irreversible
dynamics and local interactions. Relations to first passage processes are
discussed and a possible application to grain boundary formation in
two-dimensional materials is suggested.Comment: Paper with 12 pages and 2 figures; supplemental material with 4 pages
and 3 figure
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