The quality as well as the quantity of papers published by a journal is the primary concern of an editor. With that in mind, an editor tries to anticipate the directions in which submissions should move in the future. At present the Journal is publishing a healthy mix of papers from studies concerning phase equilibria and/or diffusion, some of which are basic in nature and others report data for specific applications. Quality is maintained by having every manuscript reviewed by two or more reviewers.
Technology today is moving into miniaturization both in electronic and nano-particle applications. This means that intergranular surface energies will become more important in the calculation of phase equilibria and at very small grain sizes might become dominant. During the last half of the twentieth century, a great deal of work was done on the nature of structural imperfections, and the imperfections included intergranular boundaries. The efforts of Fred Rhines and his students in this area stand out. Simple geometric arguments were utilized in their approach to grain geometries. Examples are ‘two points determine a line’ and ‘a point is determined by the intersection of three lines,’ etc. The polyhedral nature of grains was determined by fragmenting hot short alloys into their individual grains. The number of faces on the various polyhedra tended to be small with my memory for the average value being between five and six.
Much more information was obtained from metallographs wherein the view is a two-dimensional cut through a test specimen and a grain boundary is projected as a line and the junction of three grains is a point. After determination of the relative orientations of three adjacent grains and measurements of the angles between three grains in the micrograph, the intergranular angles in an orthogonal cut can be determined. The relative surface energies can then be determined from the tension balance at the junction point, remembering that surface energy per area is equivalent to force per length. The results showed that from coherency at zero angle the relative surface energies rose steeply with small angles of mismatch (whether tilt, twist, or mixtures thereof) to plateau at all angles other than the very limited region of the small angles. It would seem therefore that the assumption of a constant value per unit area of interface would not be in serious error.
The total interface area can be reasonably estimated from the average grain size and the average number of interfacial contacts from the grain shapes. The remaining problem is an evaluation of the absolute value of the interfacial contacts for a material of interest. Calorimetry seems to be a possibility but successful measurement would require the precision of measurement to be quite high. A simple experiment I did as a graduate student illustrates the point. The procedure was to cast a small sample of pure copper and measure the density. The value that was obtained was the sample to reduce value. The same specimen was then cold rolled with a 50% reduction in thickness in one pass and came out very hot. I then again measured the density and found the x-ray value indicating that the specimen was a single crystal or very nearly so. The density difference indicated that the as cast state contained about 0.3% void space attributable to crystalline imperfections.
The purpose of this editorial is to solicit submissions of more comprehensive reviews of the earlier work on interfacial energies and work that has been done on high precision calorimetry. I would also welcome submissions of any other ideas that are pertinent to the topics in question.