Carbon Content of High‐Purity Alkaline Earth Oxide Single Crystals Grown by Arc Fusion

Abstract

On the fine scale revealed by TEM, the material is characterized by predominant dendritic 3C crystals. All these dendritic crystals have equivalent orientations and are not polycrystals like those found in dendritic growth of metals. The branching-off characteristic of 3C dendritic growth is thus due to symmetry of its having three equivalent close-packed directions. Since both trunks and branches have exactly the same orientation and since the direction of the spines is parallel to the < 1 1 1 > directions, S i c crystals seem to grow in one of the < 1 1 1 > directions under the present conditions. Some X crystals were also found to grow in a columnar fashion in one of the < I 11> directions, much as in S i c whiskers. These columnar crystals exhibit twin bands perpendicular to the growth direction.Both the 2H and the one-dimensionally-disordered crystals are uniaxial and grow in acolumnarfashion in thec direction. SinceSiC does not usually form regular crystalline boundaries between crystals of different orientation, as observed in common metals, presumably because of the high energy involved in dislocation formation, these crystals do not form dendritic structures with branching-off as do the 3C crystals. However, several onedimensionally-disordered crystals were found to grow together with a columnar habit, making small angles with one another. Precise details of the structure of such small-angle grain boundaries are not known .The one-dimensionally-disordered crystals are characterized by the fact that the stacking order of the crystal is almost completely random, whereas the structure is perfect in the other two dimensions. The existence of the one-dimensionally-disordered structure reflects the general characteristic of polytypism of S i c , i.e. that the energy of the structure does not depend on its stacking order and that any polytype is equally pr~bable.~.'" The situation is also reflected by the extremely low stacking-fault energy.6 The stacking order of S i c crystals thus seems to be affected by local growth conditions,'" as demonstrated by the distribution of disordered crystals in the present case. One-dimensionally-disordered crystals, however, should not be considered simply as heavily faulted 3C crystals. ,A study of such one-dimensionally-disordered crystals by highresolution electron microscopyz1 revealed that the structure con-sisted of random layers of thin a-and P-phase lamellas of various thicknesses.2t Acknowledgments: The writers are indebted for valuable discussions to J. E.

Equations of state of FeO and CaO

“…Final sample preparation was carried out in a glove box under a controlled atmosphere and no evidence was found for even partial or superficial hydration of the samples used in this study. The MRC samples are of variable colour ranging from clear to light brown (darker portions of the crystals were avoided), whereas the ORNL samples are uniformly clear; presumably the colour is due to carbon impurities (Freund, Debras & Demortier 1977;Freund & Demortier 1978). Archimedean densities of virtually all of the CaO samples were found to be slightly less than the X-ray value p o = 3.345 Mg m-3 (Table 2).…”

Aplicaciones de simulación por ordenador, reacciones nucleares y difusión elástica al análisis de superficies de materiales

“…In making the predictions for nuclear reactions induced by deuterons, we used available data of stopping power of the ions in the samples (21,22,28,29). For the reactions (d,p) in 12 C, (d,α) and (d,p) in 16 O we used available data of differential cross sections for these reactions (6,30,20). In particular, the differential cross section data for the 12 C(d,p 0 ) 13 C reaction permitted very good computed fits to spectra from a thick flat, high purity target of pyrolitic grafite for several deuteron bombarding energies of 1.12-1.86 MeV, θ R =4.5 +-1º, and θ L =165º and 135º.…”

“…The choice of the bombarding energy was made to give insignificant yields of deuteron induced reactions in 28 Si. The spectrum from the reactions (d,p) in 12 C, (d,α) and (d,p) in 16 O is shown in Fig. 5.…”

“…In both the "energy method of analysis" for nuclear reactions and in elastic scattering, an energy spectrum is acquired of ions emitted from different depths in the sample, for a single energy of an incident ion beam (3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13), as detailed in the present work. Depth profiling of light nuclei such as 16 O and 12 C, has been reported in several contexts (14,15), including applications in ceramics and glass industry (16,17). In the "energy method of analysis", which is appropriate for ion-ion reactions, the energy spectrum which is acquired, intrinsically contains information about target composition and concentration profiles.…”

High-quality fused electrotechnical periclase from chemically purified raw material

“…It should be noted that the separation of soot was observed on the surface of crystals in a hydrogen atmosphere at 800~ [8]. One of the effective methods of removing carbon is to apply a long enough heat treatment to the periclase (not less than 2 h) at 1200-1300~ in an oxidizing atmosphere.…”