Experimental studies of the vapor phase nucleation of refractory compounds. IV. The condensation of magnesium

Abstract

Magnesium nucleation was studied over the range of approximately 700 to 950 K in a gas evaporation apparatus. Measured supersaturation ratios ranged from approximately 37 to 4.2 over this temperature range, respectively. A comparison of these data and Classical Nucleation Theory shows that the two are not consistent. Although there is a good correlation between the supersaturation and the temperature data when plotted in accordance with Scaled Nucleation Theory, some of the derived parameters are slightly below the limits predicted by the theory.

Overview: Homogeneous nucleation from the vapor phase—The experimental science

“…Nucleation rates measured in the LFDC are in range of 10-10 7 cm −3 s −1 . Another LFDD is the gas evaporation condensation chamber (GECC) [82][83][84][85]147,148 used to investigate nucleation in metals. The metal is heated in a crucible, and the hot vapor diffuses into a cool inert stagnant carrier gas to induce particle formation.…”

“…We will not address heterogeneous nucleation, [44][45][46] and only address ion induced nucleation 47,48 and nucleation driven by chemical reactions in the context of atmospheric new particle formation. It is not possible to discuss all the experimental systems of interest 49 that range from simple gases [50][51][52][53][54][55][56] (Ar, N 2 , and CO 2 ) through organics of increasing complexity (alkanes and alcohols), and even metals [82][83][84][85][86] (Na, Mg, Fe). Rather, we will illustrate the progress in experimental nucleation research primarily using the results for water and aqueous systems both because of the critical role water nucleation plays in industry and in the environment, and because the data set is incredibly rich.…”

Nucleation and growth of Mg condensate during supersonic gas quenching

“…In particular, a reduction of 10% for the value of the surface tension value of water was used by Hill et al [3]. In the case of studies involving metals, the reduction in surface tension required to match the theory with experimental results was 40% for mercury [13] and $42% for magnesium [8]. The latter result is derived by the authors from scaled nucleation theory and we have used it for our calculations here.…”

“…It is interesting to note that similar issues relating to the definition of critical cluster size are encountered in molecular dynamic studies of condensation behaviour [10]. The effective surface energy, sticking coefficient and thermal accommodation coefficient are those used by Ferguson et al [8] for their calculations concerning condensation of magnesium. The critical radius and nucleation rate of particles are sensitive to the ratio of the vapour pressure to the saturation pressure.…”

“…These criticisms have focused on the poor agreement between the theory and experimental results for refractory materials [8], the inappropriateness of using bulk surface tension values to predict the behaviour of clusters [9], the validity of assuming pseudo-equilibrium and steady state at the liquid-gas interface [10] and other theoretical issues beyond the scope of this paper. These criticisms have stimulated various corrections to the theory and new theoretical treatments of the problem including density functional methods, Monte Carlo methods [9] and molecular dynamics [10].…”