اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدOstwald Ripening on Nanoscale
115
0
0.0
(
0
)
تأليف
V. M. Burlakov
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
Applicability of classical Lifshitz-Slyozov theory of Ostwald ripening is analyzed and found limited by relatively large cluster sizes due to restrictions imposed by theoretical assumptions. An assumption about the steady state ripening regime poses an upper limit, while another, implicit assumption of continuous description poses a cluster size-dependent lower limit on the supersaturation level. These two limits mismatch for the clusters under certain size in the nanometer scale making the theory inapplicable. We present a more generic, molecular theory of Ostwald ripening, which reproduces classical Lifshitz-Slyozov and Wagner theories in appropriate extreme cases. This theory has a wider applicability than classical theories, especially at lower supersaturation levels, and is more suitable for nanoscale systems.
قيم البحث
اقرأ أيضاً
The phenomenon of Ostwald Ripening is generally considered a limiting factor in the monodisperse production of nanoparticles. However, by analysing the free energy of a binary AB solution with precipitated A particles we show that there is a region i
n the parameter space of component concentrations and interaction energies where smaller particles are more stable than bigger ones. The strong binding of B species to surfaces of A particles significantly decreases the particle effective surface energy, making it negative. The global minimum of free energy in such a system is thus reached when mass is transferred from bigger particles to the smaller ones, such that all particles become identical in size. The process of mass transfer is opposite to Ostwald ripening, and can be used for generating monodisperse arrays of nanoparticles.
We study Ostwald ripening of two-dimensional adatom and advacancy islands on a crystal surface by means of kinetic Monte Carlo simulations. At large bond energies the islands are square-shaped, which qualitatively changes the coarsening kinetics. The
Gibbs--Thomson chemical potential is violated: the coarsening proceeds through a sequence of `magic sizes corresponding to square or rectangular islands. The coarsening becomes attachment-limited, but Wagners asymptotic law is reached after a very long transient time. The unusual coarsening kinetics obtained in Monte Carlo simulations are well described by the Becker--Doring equations of nucleation kinetics. These equations can be applied to a wide range of coarsening problems.
The Ostwald ripening phenomenon for gas bubbles in a liquid consists mainly in gas transfer from smaller bubbles to larger bubbles. An experiment was carried out in which the Ostwald ripening for air bubbles, in a liquid fluid with some rheological p
arameters of the human blood, is reproduced. There it has been measured time evolution of bubbles mean radius, number of bubbles and radius size distribution, where the initial bubbles radii normalized distribution behaves like a Tsallis ($q$-Weibull) distribution. One of the main results shows that, while the number of bubbles decreases in time the bubbles mean radius increases, therefore smaller bubbles disappear whereas the, potentially dangerous for the diver, larger bubbles grow up. Consequently, it is presumed that such a bubble broadening effect could contribute, even minimally, to decompression illness: decompression sickness and arterial gas embolism. This conjecture is reinforced by the preliminary results of Ostwald broadening to RGBM (Reduced Gradient Bubble Model) decompression schedules for a closed circuit rebreather (CCR) dive to 420fsw (128m) with 21/79 Heliox gas mixture.
Na2C60 is believed to be an electron-hole counterpart of the Mott-Jahn--Teller insulator A4C60 salts. We present a study of infrared, ESR, NMR spectroscopy, X-ray diffraction, chemical composition and neutron scattering on this compound. Our spectros
copic results at room temperature can be reconciled in a picture of segregated, separate regions of the size 3--10 nm. We observe a significant insulating C60 phase and at least two more phases, one of which we assign to metallic Na3C60. The separation disappears on heating by jump diffusion of the sodium ions, which we followed by neutron scattering. Above ~460 K we see infrared spectroscopic evidence of a Jahn--Teller distorted (C60)2- anion.
Modern polarization theory yields surface bound charge associated with spontaneous polarization of bulk. However, understanding polarization in nano systems also requires a proper treatment of charge transfer between surface dangling bonds. Here, we
develop a real-space approach for total polarization and apply it to wurtzite semiconductors and BaTiO3 perovskite. First-principles calculations utilizing this approach not only yield spontaneous bulk polarization in agreement with Berry phase calculations, but also uncover phenomena specific to nano systems. As an example, we show surface passivation leads to a complete quenching of the piezoelectric effect, which reemerges only at larger length scale and/or spontaneous polarization.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
