TY - JOUR
T1 - Experimental verification of the formal nucleation and growth rate equations - Initial UH3 development on uranium surface
AU - Brill, M.
AU - Bloch, J.
AU - Mintz, M. H.
N1 - Funding Information:
This study was supported by a grant from the Israel Atomic Energy Commission and the Israel Council for Higher Education. We would like to thank Mr. R. Arkush for conducting the HSM experiment and letting us use the results.
PY - 1998/2/20
Y1 - 1998/2/20
N2 - A Hot Stage Microscopy (HSM) technique was utilized for continuous observations of UH3 nucleation and growth on hydrogen exposed uranium (U-0.1 wt% Cr) surface. Such observations enabled the quantitative evaluation of both, nucleation rate function, N(t), and the average lateral growth velocity, u, of the individually growing nuclei. Knowing these kinetic parameters, the validity of the different assumptions made in the derivation of the formal nucleation and growth rate equations (i.e. the Avrami-Erofeev or Johnson-Mehl equations) can be checked. It was found that the basic assumption underlying the Avrami's approach, namely, the relation between the extended and the experimental reacted fractions, is very accurate over a wide range of surface coverages. However, the time dependence of the nucleation rate function was not monotonous, as commonly applied in the conventional treatments. Instead, the nucleation rate first accelerated, passed through a maximum and finally decayed again. At about 7-10% of the reaction, the nucleation rate decayed to zero, and saturation in the number of growing nuclei was attained. This nucleation behavior leads to overall kinetics which do not fit the simplified power law time dependence that is usually applied in the kinetic analysis of nucleation and growth processes.
AB - A Hot Stage Microscopy (HSM) technique was utilized for continuous observations of UH3 nucleation and growth on hydrogen exposed uranium (U-0.1 wt% Cr) surface. Such observations enabled the quantitative evaluation of both, nucleation rate function, N(t), and the average lateral growth velocity, u, of the individually growing nuclei. Knowing these kinetic parameters, the validity of the different assumptions made in the derivation of the formal nucleation and growth rate equations (i.e. the Avrami-Erofeev or Johnson-Mehl equations) can be checked. It was found that the basic assumption underlying the Avrami's approach, namely, the relation between the extended and the experimental reacted fractions, is very accurate over a wide range of surface coverages. However, the time dependence of the nucleation rate function was not monotonous, as commonly applied in the conventional treatments. Instead, the nucleation rate first accelerated, passed through a maximum and finally decayed again. At about 7-10% of the reaction, the nucleation rate decayed to zero, and saturation in the number of growing nuclei was attained. This nucleation behavior leads to overall kinetics which do not fit the simplified power law time dependence that is usually applied in the kinetic analysis of nucleation and growth processes.
KW - Growth
KW - Hydrogen absorption
KW - Nucleation
KW - Rate equations
KW - Uranium
UR - http://www.scopus.com/inward/record.url?scp=0032002680&partnerID=8YFLogxK
U2 - 10.1016/S0925-8388(97)00411-8
DO - 10.1016/S0925-8388(97)00411-8
M3 - Article
AN - SCOPUS:0032002680
SN - 0925-8388
VL - 266
SP - 180
EP - 185
JO - Journal of Alloys and Compounds
JF - Journal of Alloys and Compounds
IS - 1-2
ER -