Accession Number : AD0711932

Title :   A REVIEW STUDY OF NUCLEATION AND ITS ROLE IN SOLIDIFICATION.

Descriptive Note : Final rept. 13 Apr 66-13 Jan 69,

Corporate Author : TUFTS UNIV MEDFORD MASS DEPT OF CHEMICAL ENGINEERING

Personal Author(s) : Van Wormer,Kenneth A. , Jr

Report Date : 15 JUN 1969

Pagination or Media Count : 118

Abstract : A review study of nucleation and its role in determining grain size in solidification is presented. It is demonstrated that nucleation is an essential aspect of most phase transformation processes when the unstable phase is initially free of all fragments of the more stable phase to be formed. Occurrence of multi-nucleation events for many transformations; the required maintenance of a critical metastability for continued classical nucleation; and the feedback effect of crystal or cluster growth tending to destroy this metastability are emphasized. Limitation of grain density to the density of growth centers which can be generated by nucleation and then maintained is discussed. Secondary nucleation, which includes such processes as crystal fragmentation, is emphasized as a separate route from classical nucleation by which growth centers can be generated. A theoretical analysis of the interaction of homogeneous nucleation and crystal growth under ideal conditions is presented. Preliminary results predict grain density should vary with the 1.45 power of cooling rate. (Author)

Descriptors :   (*NUCLEATION, *CRYSTAL GROWTH), (*METAL CRYSTALS, NUCLEATION), SUPERCOOLING, COOLING, PHASE STUDIES, GRAIN SIZE

Subject Categories : Physical Chemistry
      Properties of Metals and Alloys
      Crystallography

Distribution Statement : APPROVED FOR PUBLIC RELEASE