Nanothermodynamic analysis of the low-threshold-pressure-synthesized cubic boron nitride in supercritical-fluid systems

Abstract

A thermodynamic model in nanoscale was developed to elucidate the nucleation of the cubic boron nitrides (c-BN) synthesized in the high-pressure and high-temperature (HPHT) supercritical-fluid systems under the conditions of the low-threshold-pressure (from 2.0±0.1 to 3.0 GPa) and low-temperature (1300–1500 K). Notably, taking the nanosize-induced interior pressure into account, the nucleation of c-BN could be driven to the new stable region from the metastable region in the general accepted equilibrium phase (P,T) diagram of BN proposed by Corrigan and Bundy, upon HPHT supercritical-fluid systems. The threshold pressure of the formation of c-BN was calculated based on our model, and these results are in excellent agreement with the experiment.

Laser ablation in liquids: Applications in the synthesis of nanocrystals

“…More recently, taking the surface tension induced by nanosized curvature of crystalline nuclei into account, we have developed a thermodynamic approach at the nanometer scale to elucidate the nucleation, phase transition, and growth [181]. Up to date, this thermodynamic method has been widely used to address the nucleation, phase transition, and growth of stable and metastable phases at the nanometer scale [182][183][184][185][186][187][188][189][190][191][192][193][194][195]. Accordingly, to gain a better understanding of the phase formation upon laser ablation of solids in liquids from the pointview of thermodynamics.…”

Prediction of Formation of Cubic Boron Nitride Nanowires inside Silicon Nanotubes

“…According to experimental data, E a ) 207 kJ/mol, 18 using eqs 2 and 8, we calculated the probability curves of the phase transformation inside the Si nanotubes when r ) 5 nm and R ) 10 nm as shown in Figure 4a. Clearly, the probability of the phase transformation increases as the supersaturation and temperature increase.…”

“…12,19 Many studies show that the formation of nanosized cBN is attributed to nanosize-induced interior pressure. [18][19][20]22 Generally, in the case of the nucleation of a cluster from gases, the phase stability is quite different from that of the phase diagram that is determined at atmospheric pressure, i.e., the nuclei are under high pressure arising from so-called "capillarity" that is expressed by the Laplace-Young equation. 20 Many researchers have studied the nucleation stability of both nanodiamond and nanographite, the formation of quantum dots, and the other topics by employing the Laplace-Young equation.…”

“…It is well-known that cBN, which is the simplest and purely artificial III−V compound, can be synthesized under high pressure and high temperature similar to that for the synthesis of diamonds . However, it has been observed recently that cBN in nanoscale is also obtained at low temperature and pressure. , Many studies show that the formation of nanosized cBN is attributed to nanosize-induced interior pressure. − , Generally, in the case of the nucleation of a cluster from gases, the phase stability is quite different from that of the phase diagram that is determined at atmospheric pressure, i.e., the nuclei are under high pressure arising from so-called “capillarity” that is expressed by the Laplace−Young equation . Many researchers have studied the nucleation stability of both nanodiamond and nanographite, the formation of quantum dots, and the other topics by employing the Laplace−Young equation. − Especially, Yang et al have successfully developed a new nanothermodynamics model to analyze the metastable phase nucleation on nanoscale .…”

“…The probability of the phase transformation from the metastable phase to the stable phase is related not only to the Gibbs free energy difference Δ g but also to an activation energy ( E a − Δ g ) that is necessary for the phase transformation. The general expression of the probability f of the phase transformation from the initial states to final states is: f = exp true[ − E normala − normalΔ g R T true] − exp true[ − E normala R T true] …”