Anisotropy in Single-Crystal Refractory Compounds: Proceedings of an International Symposium on Anisotropy in Single-Crystal Refractory Compounds, held on June 13–15, 1967, in Dayton Ohio. Sponsored by the Ceramics and Branch of the air Force Materials La

Approximately forty invited papers were presented. An attempt was made to bring together scientists working in the area of anisotropy on single-crystal refractory compounds and in related areas in order to review the state-of-theart in this important area of research and to insure widespread dissemination of recent findings and ideas. The welcoming address, given by Alan M. Lovelace, Director of the Air Force Materials Laboratory, emphasized the role of the United States Air Force as the host at this Symposium and set the informal tone for the seven technical sessions of the Symposium. In his opening address, Harris M. Burte, Chief of the Metals and Ceramics Division, Air Force Materials Laboratory, reemphasized the need for proper characterization of materials, especially refractory compounds, and outlined the main reasons for holding this first International Symposium on Anisotropy in Single-Crystal Refractory Compounds. The purpose for holding the Symposium thus firmly crystalized, Fred W. Vahldiek, general chairman, then said a few introductory remarks, and the Symposium was in session. An attempt was made at this Symposium to cover the principal parameters on anisotropy of refractory compounds relative to their structure, bonding, non-stoichiometry, and thermal and mechanical behavior. Special emphasis was placed on the role of imperfections in crystals, including dislocations, slip, twinning, and stacking faults, and correlating these with the anisotropy in properties observed. Materials primarily discussed were refractory oxides, carbides, borides, silicides, and nitrides of the transition metals. Several contributions necessitated, on fundamental grounds, the discussion of other metallic and nonmetallic materials in order to have a homogeneous understanding of anisotropy. Although many of the papers presented stimulated heated oral discussions, no attempt was made to record v vi FOREWORD these, and thus they are not included in this Proceedings. In general, the questions asked dealt with controversial points, or were the type that required an explanation or further data from the respective speakers, and a relatively select few conferees were involved. It is presumed that many of these points of controversy and/ or explanation are being further pursued by the scientists directly concerned. The overall assessment of the Symposium could be stated as follows: It was brought out during the course of the Symposium that there is a considerable gap at the moment in relating basic concepts, such as dislocations, electronic crystal structure, etc. to the bulk physical, chemical and mechanical properties of refractory compounds. Whereas considerable progress has been made in the last decade or so on the understanding of these compounds, the state-of-the-art as to the basic properties and behavior of these materials is still lagging far behind metallic systems. The key to many of the inherent problems associated with refractory compounds such as how to make them more ductile, how to increase their high-temperature insulation and thermal shock resistance properties, and how to improve the strength and load-carrying capabilities seems to lie in the controlled changes in the stoichiometry, impurity content, and especially the electronic structure of these materials. Much can be learned about the refractory compounds by referring to the behavior and properties of the respective "host" metals. It was pointed out that in refractory inorganic nonmetallic or ceramic materials research the problems are often associated with the difficulty in obtaining suitable thin single-crystal specimens for study. Recent developments in transmission electron microscopy, electron microprobe, and microfocus x-ray techniques should allow a careful compositional and structure analysis as well as purity and homogeneity control of refractory compounds, such as are essential if single-crystal and polycrystalline refractories are to be meaningfully compared. Of course, much more work is needed on the physical, chemical, and mechanical properties of the refractory compounds. Among the principal recommendations are the following: (1) Work in single-crystal refractory compounds such as exemplified by this Symposium is essential, and should be continued at an ever increasing rate if one is ever to understand the behavior and the inherent nature of these materials and how to properly modify them so that they may fulfill a useful function in the presently existent and newly developed aerospace and other systems. In this, fundamental studies, such as for example the understanding and changing of the basic electronic structure, play an increasingly important role. (2) Specialized symposia of this type should be held periodically -perhaps every two or three years -sponsored by the United States Air Force and/or by other interested agencies, in order to insure the best advancement of the state-of-the-art relative to the anisotropy in refractory materials research. Front Matter....Pages i-xix Front Matter....Pages 1-1 Some Aspects of the Crystal Chemistry of Borides, Boro-Carbides and Silicides of the Transition Metals....Pages 3-22 Application of the Electron Microprobe to the Study of Refractory Metal Carbides, Oxides, and Silicides....Pages 23-36 Equilibrium Particle Size and Paracrystalline Distortions....Pages 37-54 Crystallographic Polarity of WC....Pages 55-66 Tabulation of Indices and Interplanar Angles for Rapid Identification of Crystallographic Planes....Pages 67-101 Front Matter....Pages 103-103 The Electronic Structure of Refractory Metals, Compounds, and Alloys....Pages 105-119 Bonding, Imperfect Structure, and Properties of the Refractory Nitrides of Titanium, Zirconium, and Hafnium....Pages 121-138 The Nature of the Electrical Conduction Transient Behavior of Rutile....Pages 139-149 Electronic Structure of Transition Carbides and Nitrides....Pages 151-159 Front Matter....Pages 161-161 Non-Stoichiometry and Bonding in Refractory Monocarbides....Pages 163-175 The Conversion of Cubic and Hexagonal Silicon Carbide as a Function of Temperature and Pressure....Pages 177-197 Phase Relationships and Defect Structure in Dimolybdenum Carbide....Pages 199-248 Influence of Octahedral Subcells on the Electrical Properties and Bonding Characteristics of Molybdenum Carbides....Pages 249-266 Front Matter....Pages 267-267 Thermodynamic Properties of Refractory Transition Metal Compounds....Pages 269-297 Some Properties of Eutectic “Crystals” of MnO-MnS....Pages 299-315 Selected Problems in the Analysis of Refractory Materials....Pages 317-339 On the Role of Diffusion in the Plastic Deformation of Transition Metal Carbides....Pages 341-356 Anisotropy in Emissivity of Single-Crystal Refractory Materials....Pages 357-381 Anisotropic Thermal Expansion Characteristics of Some Crystal Structures....Pages 383-389 Electron Paramagnetic Resonance Absorption and Other Physical Properties of Chromium Oxide and Other Crystals Containing Chromium as Impurity....Pages 391-400 Back Matter....Pages 401-405