Number Of Intermetallic Compounds Research Articles

Electron irradiation induced crystalline to amorphous transition in boron carbide

Boron carbide is one of the current candidate materials for neutron absorbers in the control systems of various nuclear reactors because of its high neutron absorption cross-section over a broad spectrum of neutron energies. It is also one of the prime candidate materials for the first wall coating in fusion reactors because its low Z constituent atoms would lead to minimum plasma contamination. On the basis of this premise, a number of irradiation experiments have been carried out on boron carbide. Transmission electron microscope (TEM) observations of neutron irradiated boron carbide have revealed small disk-shaped cavities on /111/ and sometimes on /110/ and /100/ rhombohedral planes. These cavities have been identified as high-pressure He bubbles, since they are accompanied by surrounding strain fields. With increasing irradiation temperature, the size of these bubbles increases, while their density decreases. He bubbles induced by 100 keV He ion irradiation, on the other hand, were reported to have a spherical shape. Recently, it was established by the authors' group that a number of intermetallic compounds could be rendered amorphous by high energy electron irradiation as they could be by ion irradiation. This phenomenon is of interest not only from an engineering point of viewmore » but also from a scientific perspective to clarify the mechanism of the crystalline to amorphous (C-A) transition. As an extension of the work on the intermetallics, a systematic study of the electron irradiation induced C-A transition in ceramic materials was undertaken by the authors with some preliminary results showing the presence of an electron irradiation induced C-A transition in SiC. In the present paper, it is reported that boron carbide undergoes a C-A transition by electron irradiation at 2 MV, whereas BETA-rhombohedral boron remains crystalline during the irradiation.« less

Empirical interrelations and the possibility of prediction of high-T c superconductors

It is shown that intermetallic compounds with transition metal components from the second long period and/or a nontransition element component from the first long period have a higher superconductivity temperature than analogous compounds having corresponding components from other periods of the periodic table. A possibility of high- T c superconductivity has been predicted in a number of intermetallic compounds.

Magnetic correlation in itinerant magnetic materials above T C (invited)

Although the properties of magnetic insulators are relatively well understood, the same cannot be said of materials in which the unpaired electrons participate in the Fermi surface. A number of conflicting theories exist which all give a more or less satisfactory account of the ground state properties of magnetic metals but give widely different descriptions of magnetic fluctuations above the ordering temperature (TC). The paramagnetic state of a material can be characterized by the spin-density spin-density correlation function (SDSDCF) which is accessible to measurement through the magnetic scattering cross section. We have made measurements of the paramagnetic scattering from the transition metals Cr, Mn, Fe, Ni, and a number of intermetallic compounds over a wide range of temperature. Polarization analysis was used to separate the magnetic part of the scattering cleanly. In all cases where atoms with open d shells are in contact we have found significant structure in the SDSDCF over a range of several interatomic distances. This has loosely been called ‘‘short range order above TC.’’ The resolution of the spectrometer for the majority of the measurements was some 12 THz FWHM, so that although the true equal time SDSDCF is not obtained, essentially all contributions with a lifetime greater than 5×10−10 s are included and in particular most of the thermal fluctuations up to kTC. The paramagnetic scattering results are coherent with inelastic neutron scattering data both above and below the transition temperature. It has been found difficult to give a consistent account of all these results using theories based on extensions of the Heisenberg model. The fluctuating band models, in which correlations in the paramagnetic phase appear naturally, seem more appropriate.

A model for Kondo type intermetallic compounds with small effective moments

A model, based on the analogy of fluctuations between different spin configurations and of the Kondo effect, is proposed to account for the Curie-Weiss behaviour with small effective moments observed in a number of intermetallic compounds.

Carbides in Nuclear Energy

"Carbides in Nuclear Energy." Nuclear Science and Engineering, 22(4), pp. 500–501 Additional informationNotes on contributorsWaiston ChubbAbout the Reviewer: Walston Chubb joined the Battelle staff in 1951 and is now a Fellow in the Materials Technology Division. For the past seven years he has been technical manager and consultant for a comprehensive research program to develop uranium carbide, its modifications, and associated structural materials as components for high-temperature nuclear reactors. In addition, he has been engaged in research on various other reactor materials including the alloys of zirconium, uranium, thorium, niobium, chromium and iron-chromium-aluminum, and a number of intermetallic compounds, including beryllides and nitrides, as well as carbides. Mr. Chubb is registered as a Professional Engineer in the State of Missouri and is a member of the American Society of Metals, the American Institute of Mining and Metallurgical Engineers and the American Ceramic Society. He received his technical training at Harvard and at the University of Missouri at Rolla.

Low-temperature Alloy Synthesis

THE low temperature reduction of metal ions to the finely divided free metal by sodium borohydride reduction has been reported recently1. In addition, the preparation of a number of inter-metallic compounds from mixed salt solutions using boiling hydrazine and hypophosphorous acid solutions as reducing agents has been accomplished2. It was of interest to examine the sodium borohydride reduction of solutions of two metal ions as a possible method of low-temperature synthesis of finely divided solid solution alloys. Such materials would be of particular interest in catalyst investigations, where high-surface area alloys are often difficult to obtain. Work on such reactions have, therefore, been carried out, using metals where alloy formation might reasonably be expected with suitable preparative conditions. Those chosen for initial investigation were combinations of platinum–gold, platinum–iridium, and palladium–gold. All three metals form face-centred cubic lattices, have atomic radius ratios well within the Hume–Rothery limit, and form solid solutions with each other over the entire composition range.

Diffusion in superimposed films of normal metals and superconductors

Interactions between a superconducting and normal film for the systems Sn/Al and In/Al in which the solid solubilities are very restricted and no intermetallic compounds are known to exist so that diffusion is very unlikely were investigated. The In/Mg system with large solubilities and a number of intermetallic compounds, in which diffusion is likely, was also studied. In the former case no change in the transition temperature of the superconductor and no superconducting energy gap in the normal metal could be detected. In the latter case a marked increase in the transition temperature of the superconductor was found. (C.E.S.)

The Magnetic Properties and Phase Diagram of Iron Tellurium System

In the present paper, studies on the phase diagram and magnetic properties of Fe – Te system are reported. It was found by X-ray and thermal analysis that a number of intermetallic compounds are formed from melt through peritectic reactions, and an eutectoid reaction was seen to occur between two compounds α (ca FeTe ) and β (ca FeTe 2 ) at 520°C, the reactions product having NiAs structure. The α phase shows an antiferromagnetic behavior with asymptotic Curie temperature θ=130°K, Curie-Weiss constant C =0.57, but the crystal lattice type of this compound is obscure at present. The β phase has a crystal lattice of the markasite type and is antiferromagnetic, with θ=67°K and C =1.31. The γ phase which has a crystal lattice of the NiAs type shows an antiferromagnetic behavior, with θ=800°K and C =1.15. A short discussion on the antiferromagnetism of these compounds is given.