Metallic Iron Grains Research Articles

Kinetic model of ammonia synthesis in the solar nebula

The synthesis of ammonia in the primitive solar nebula was probably catalyzed by metallic iron grains because the gas phase reaction is kinetically inhibited. A preliminary kinetic model predicts a maximum of 3% of the nitrogen in the form of ammonia at the time of planetary accretion. Rates of reaction were derived from industrial data on ammonia iron catalysts. Due to the low rates of reaction, molecular nitrogen remains the dominant species even at the low temperatures where chemical equilibrium favors ammonia formation. Thus planetary atmospheres formed from a reservoir composed largely of molecular nitrogen. The non-equilibrium volatile gases (CO and N 2) suggested to comprise most of the carbon and nitrogen in comets is consistent with the model.

Numerical models of the primitive solar nebula

Numerical models have been constructed to represent probable conditions in the primitive solar nebula. A two solar mass fragment of a collapsing interstellar gas cloud has been represented by a uniformly rotating sphere. Two cases have been considered: one in which the internal density of the sphere is uniform and the other in which the density falls linearly from a central value to zero at the surface (the uniform and linear models). These assumptions served to define the distribution of angular momentum per unit mass with mass fraction. The spheres were flattened into disks, and models of the disks were found in which there was a force balance in the radial and vertical directions, subject to certain approximations, and with everywhere the assigned values of angular momentum per unit mass. The radial pressure gradient of the gas was included in the force balance. The energy transport in the vertical direction involved convection and radiative equilibrium; the principal contributors to opacity at lower temperatures were metallic iron grains and ice. The models contained two convection zones, an inner one due to the dissociation of hydrogen molecules, and an outer one in which there was a high opacity due to metallic iron grains. The characteristic semithickness of the disks ranged from about 0.1 astronomical units near the center to about one astronomical unit near the exterior. Characteristic angular momentum transport times and radiation lifetimes for these models of the initial solar nebula were estimated. Both types of characteristic lifetime were as short as a few years near the inner part of the models, and became about 10 4 years or longer at distances greater than ten astronomical units.

Piezo-remanent magnetization of lunar rocks

Characteristics of the piezo-remanent magnetization (PRM) of lunar rocks are particularly interesting in comparison with the PRM of terrestrial rocks, because ferromagnetic constituents in lunar materials are metallic iron grains whose average magnetostriction coefficient\((\bar \lambda )\) is negative. Experimentally observed characteristics of the PRM of lunar rocks are substantially the same as those of the PRM of terrestrial rocks and magnetites, in which\(\bar \lambda \) is positive. These experimental results indicate that the acquisition mechanism of PRM is due to a non-linear superposition of the magnetoelastic pressure upon the magnetostatic pressure on both sides of the 90° domain walls in ferromagnetic particles, as suggested by Nagata and Carleton.

Metal grains in Apollo 12 igneous rocks

The Apollo 12 igneous rocks we have examined contain abundant disseminated grains of metallic iron with a wide range of Ni and Co contents. The compositions of these metal grains vary to a degree not found in terrestrial igneous rocks or in meteorites. Ni and Co are generally higher in metal grains enclosed by the earliest-formed minerals (olivine and chromite) and are lower in those associated with later phases. The metal grains do not indicate the former presence of an immiscible metal liquid but have formed by reduction from the silicate melt. Formation of the metal grains accompanied, and may be a direct result of, the crystallization of the major phases under low oxygen partial pressures. The crystallization of chromite, for example, from a melt containing divalent chromium, may have resulted in the reduction of ferrous iron to metal. The presence of nickel-iron grains in lunar igneous rocks indicates that metal grains in lunar soil need not be exclusively of meteoritic origin.

On grains of metallic iron in dolerites from New Hampshire

On grains of metallic iron in dolerites from New Hampshire

Scientific Serials

THE American Journal of Science and Arts, January. —Contributions to meteorology, being results derived from an examination of the observations of the United States Signal Service, and from other sources, by Elias Loomis.—On some points in connection with vegetation, by J. H. Gilbert.—Observations on a property of the retina first noticed by Tait, byOgdenN. Rood.— On grains of metallic iron in Dolerytes from New Hampshire, by George W. Hawes.—On certain phenomena of binocular vision, by Francis E. Nipher.—Notes on the Vespertine strata of Virginia and West Virginia, by William M. Fontaine.—On the production of transparent metallic films by the electrical discharge in exhausted tubes, by Arthur W. Wright.