Explanation of Bubble Nucleation Mechanisms: A Gradient Theory Approach

Kurian J Vachaparambil,Kristian Etienne Einarsrud

doi:10.1149/2.1031810jes

Kurian J Vachaparambil, Kristian Etienne Einarsrud

Open Access

https://doi.org/10.1149/2.1031810jes

Copy DOI

Abstract

A Helmholtz free energy description of the four nucleation mechanisms used to explain the bubble nucleation in electrochemical systems is presented. The mechanisms are compared based on the nucleation energy barrier and critical nuclei radius. The theoretical analysis sheds light on the effect of parameters like contact angle on the electrode surface and pre-existing gas bubbles on nucleation energy barrier. A free energy based description of surface tension (planar interface) is also obtained from the thermodynamic framework.

Highlights

The phenomenon of nucleation is a thermodynamic process that governs phase separation in both natural and technological processes, like bubble formation in electrochemical systems
Four mechanisms proposed by Jones et al.,[3] are used to describe the experimental observations for gas bubble nucleation in supersaturated systems: r Type 1 or homogeneous nucleation occurs in the liquid bulk at highr leTvyeples of supersaturation; 2 or heterogeneous nucleation happens at surface imperfections like pits and cavities at lower levels of supersaturation comparerd to Type 1; Type 3 or pseudo-classical nucleation utilizes pre-existing gas cavities that have radii smaller than the critical radius predicted by the classical theory to lower the nucleation energy barrier
The critical radius is independent of the nucleation mechanism the nucleated bubble volume is different in each mechanism, with the bubble produced during homogeneous nucleation being largest compared to heterogeneous and pseudo-classical nucleation while non-classical nucleation does not require formation of one

Summary

Introduction

The phenomenon of nucleation is a thermodynamic process that governs phase separation in both natural and technological processes, like bubble formation in electrochemical systems. R Type 1 or homogeneous nucleation occurs in the liquid bulk at highr leTvyeples of supersaturation; 2 or heterogeneous nucleation happens at surface imperfections like pits and cavities at lower levels of supersaturation comparerd to Type 1; Type 3 or pseudo-classical nucleation utilizes pre-existing gas cavities that have radii smaller than the critical radius predicted by the classical theory to lower the nucleation energy barrier TypersT1yapned42)o;r non-classical nucleation occurs at pre-existing gas cavities whose radii is larger than the critical radius, effectively reducing the energy barrier to zero. The pre-existing gas cavities, relevant in Type 3 and 4 mechanisms, can occur from previous nucleation,[4] entrainment of gas from liquid jet[5] and solid surface trapping gases.[6] Nanobubbles, whose radii is smaller than the critical radius,[7] adhering to the solid surface could facilitate nucleation

Objectives

Discussion

Conclusion