Non-metallic Phases Research Articles

CuSe2, a Marcasite Type Superconductor

CuSe2 occurs in a room temperature form of the marcasite type1 and a high-pressure high-temperature modification of the pyrite type2. In both the marcasite and pyrite structures the cations are coordinated by six anions forming a distorted octahedron while the anions are bonded to three cations and another anion. In the pyrite structure the anion octahedra are connected by shared corners and in the marcasite structure the octahedra form chains by sharing edges. In the pyrites and the normal marcasites the deformation of the anion octahedra is not very marked. The marcasite family, however, has another branch, the loellingites, in which the deformation of the anion octahedra is much more pronounced and of opposite sign. The ratio of the octahedron edge parallel and perpendicular to the cation chains is roughly 1.1 in the normal marcasites and about 0.75 in the loellingites3,4. Different electronic structures of the cations account for the different distortions. Loellingites are found only in non-metallic phases containing d2 and d4 cations and distortions then result from the Jahn–Teller effect. Pyrites with dn cations occur for n≧5, while normal marcasites are known only for n≧6. In both the pyrite and the normal marcasite phases non-metallic properties are possible only if the cations have completely occupied d subbands, such as de3dγ2, de6, de6dγ2 and d10. Examples of these configurations are MnS2, RuS2, NiS2 and ZnS2(p) respectively. (The symbols (r), (h), (p) indicate room temperature, high temperature and high pressure modifications, respectively.) Because large distortions would be required to separate the energies of the degenerate dγ states, all d7 and d9 phases are metallic and adopt either the pyrite or the normal marcasite structure.

A study of four pallasites using metallographic, microhardness and microprobe techniques

The proportions by volume of kamacite, taenite and non-metallic phases have been determined by quantitative metallography in four pallasites: Admire, Krasnoyarsk, Brenham and Mount Vernon. Using the ratio of the kamacite/taenite phases and the Fe-Ni phase diagram, the lowest temperature ( T O ) at which these phases existed in equilibrium has been estimated. For the four pallasites these temperatures are substantially higher, and they show a wider scatter, than was observed in a previous study of five octahedrites. Metallographic and microhardness studies have shown “zoning structures” in the taenite phase near the kamacite/ taenite border. Microprobe studies of a zoned portion of the Brenham pallasite have shown these features to be dependent upon composition. The composition profiles of nickel and iron obtained by microprobe analysis of pallasites are strikingly similar to those obtained for octahedrites and may be interpreted with the use of the Fe-Ni binary phase diagram without the necessity for considering large pressures. The composition profiles of cobalt and phosphorous are also reported. It is concluded that pallasites have cooled more rapidly than octahedrites.

X-Ray Diffraction of Nonmetallic Phases Chemically Extracted from Columbium Alloys

AbstractThe identification of non-metallic phases occurring in a metallic matrix cannot always be accomplished by standard methods of X-ray diffraction analysis. Separation of the nonmetallic phases from the matrix by chemical extraction, with subsequent X-ray diffraction analysis allows identification of the nonmetallic phases without the problems associated with X-ray analysis of bulk samples.In one study of alloy carbide dispersions in columbium, X-ray diffraction of the bulk samples could adequately identify the carbides present, but it was only by studying the chemically extracted residues that an important oxygen gettering effect of one of the alloy additions was discovered. In another study, X-ray diffraction work on extraction residues of Cb-Zr alloys showed evidence of a double oxygen gettering effect producing two distinct oxides. In the built sample, some of the diffraction lines produced by one of these oxides were masked by the tines of the columbiurn matrix. Therefore, only by use of an extraction technique were these two oxides identifiable by X-ray diffraction. In a Cb–10Ti–10Mo alloy, X-ray diffraction was used to study the nature of the sub scale formed during oxidation of the alloy. At least two nonmetallic phases were found. By using chemical extraction techniques, the phase responsible for the formation of the subscale was identified as TiO.These studies demonstrate some of the advantages of the chemical extraction techniques for obtaining samples of nonmetallic phases for study by X-ray diffraction.

THE PREPARATION, STRUCTURE, AND PROPERTIES OF ALLOYS CONTAINING DISPERSED NON-METALLIC PHASES

Methods for the preparation of alloys containing dispersed non-metallic phases, particularly oxides, are reviewed and work on their structures and properties discussed. Although many difficulties are encountered in manufacture, the materials offer considerable promise for future development in respect of high-temperature strength and stability.

A quantitative metallographic study of five octahedrite meteorites

The proportions by volume of kamacite, taenite, and nonmetallic phases have been determined by quantitative metallography in five octahedrite meteorites: Grant, Bristol, Toluca, Odessa, and Canyon Diablo. Using the ratio of the kamacite/taenite phases and the Fe-Ni phase diagram, the lowest temperature (T0) at which these phases existed in equilibrium has been estimated, and its value employed in a calculation of the possible time intervals necessary for the formation of the Widmanstätten pattern in asteroidal bodies 100–200 km in radius and consisting either of an Fe-Ni alloy or of olivine with an iron core. It is concluded that the time intervals available for the formation of the Widmanstätten pattern need not have exceeded 108 years but could be longer if segregation occurred under pressure. The estimated T0 temperatures fall into two groups with mean values of approximately 460° and 525°C. The difference between these two values may be due to the different origin of the meteorites or to the different content of the nonmetallic phases.