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SummaryOptical and microprobe investigations have been made on the metal and silicate portions of four particles > 1 mm extracted from the magnetic fraction of lunar soil bulk sanaple 14162,80. Three of the particles have structures and compositions similar to those encountered in the < 1-mm fraction of this bulk sample. One of the particles shows a complex arrangement of melted metal, unmelted metal, micronorite, and vitroclastic silicate material. The structure of this particle is reported in detail and its structure is explained in terms of preferential melting of metal-phosphide interfaces under the influence of shock events operating on material at a temperature of about 650°C.

SummaryThe Verkhne Dnieprovsk material (BM 51183) in the collection of the British Museum (Nat. Hist.) is chemically group IIE and therefore distinct from Augustinovka. Structurally it is a finest octahedrite, with a kamacite band-width (0.05 mm) and bulk Ni content (Scott and Wasson, 1976) appropriate to a cooling rate of 830 K Myr-1. Subsequent pre-terrestrial shock has produced localized deformation and shock-heating effects, which include mm-size globules of metal-phosphide melt product with a dendritic texture indicating resolidification at c.10 000 K sec-1. It is suggested that the phosphides were already fissured at the time of shockmelting. The structure of Verkhne Dnieprovsk, although lacking silicates, is analogous to that of Kodaikanal.

SummaryA metallographic investigation of macro- and micro-structures, supported by microprobe examination, has been made on similarly sized (< ca. 200 g) individual Cañon Diablo meteorites of rim or plains type. Plains type specimens show heat alteration zones of the ablation type. They are extensively cracked in a brittle manner and in some instances the cracks are penetrated by ablation melt product. In all cases the cracks are now penetrated by terrestrial corrosion. Cohenite and schreibersite are cracked in a brittle manner. By contrast the rim type specimens are remarkably free of internal cracking or corrosion penetration. Instead the cohenite, schreibersite, taenite, and kamacite are transected by slip faults or shear displacements along the line of which all phases appear to have slipped in a non-brittle manner. These specimens have all been subject to shock loading and particular attention is paid to the effects of shock on sphalerite, on cloudy taenite, and on martensitic plessite.Plains specimens have broken from the original projectile in a brittle manner well above the earth's surface. Rim specimens have been scabbed from the rear of the projectile as it penetrated the earth's surface. Some of the rim specimens show signs of being heated by the blast of the crater-forming explosion.

SummaryA metallographic investigation of macro- and microstructure, supported in some instances by microprobe examination, has been made on a number of nickel-rich iron meteorites from the British Museum Collection. Monahans, Wiley, Cowra, and Deep Springs are considered together as plessitic irons rather than ataxites, whilst Morradal shows an unusual and coarse plessitic structure that has been altered by pre-terrestrial shock and reheating. Cape of Good Hope, Hoba, Tlacotepec, and Chinga show chemical and structural similarities and are discussed together, as are Weaver Mountains, Klondike, and Warburton Range. Meteorites considered separately include Kokomo, Piñon, Shingle Springs, South Byron, San Cristobal, Lime Creek, and Santa Catharina. Particular attention is paid to the presence of sulphides and of phosphorus-containing phases and their influence on the formation of the macro- and microstructure of these meteorites. Patches of oriented sheen form a macroscopic feature of the Cape of Good Hope group of irons and this effect is considered in relation to details of the microstructure. Attention is drawn to the fact that in Cowra, Piñon, Weaver Mountains, South Byron, and Morradal the troilite appears to have been remelted and dispersed by a shock event that operated at a temperature sufficiently high to allow obvious shock damage to anneal out of the metal phases.

SummaryLarge samples of the hexahedrites Scottsville, Indian Valley, Okano, Puripica, and Hex River Mountains from the British Museum Collection and a sample of Lombard have been prepared for metallographic examination and details of their structures have been mapped with the aid of a specially constructed X-Yplotting device that is geared to the stage of a metallurgical microscope. The following elements of structure have been studied and an attempt has been made to discuss the circumstances under which they were formed: clear etching and frosty etching kamacite, decorated Neumann lines, giant rhabdites, plate rhabdites, rhabdite clusters, microrhabdites, cohenite or decomposed cohenite, and troilite (which in some instances is recrystallized or remelted). In general the range of structural effects is similar to that previously reported for the Angra dos Reis hexahedrite (Min. Mag. 1971, 38, 94–101). The variations of structure are discussed in relation to nickel content and trace element chemistry of the meteorites.

SummaryThe macroscopic features of a number of Gibeon meteorites have been reviewed and selected specimens have been examined in more detail by metallographic, microprobe, and X-ray diffraction techniques.A number of specimens appear to have been reheated by man and in these cases reheating temperatures are indicated. Specimens that show no signs of artificial reheating are discussed in relation to the form, distribution, and structure of the kamacite, daubréelite, and troilite. X-ray examination of the kamacite reveals partly annealed shock damage. Small monomineralic inclusions of daubréelite appear to be concentrated in the non-octahedral kamacite and show no signs of alteration By contrast all the troilite has been remelted and has dissolved contiguous plessite and daubréelite. The remelting of troilite appears to have been induced by shock at temperatures below about 450°C.

SummaryThe distribution of kamacite, taenite, and plessite suggests that kamacite nucleated at the sulphides, which appear to have been plentifully dispersed in the parent taenite. Such a process could take place without the undercooling that is usually assumed in normal octahedrites. The plessite fields show internal boundaries that are probably relics of grain boundaries in the parent taenitesulphide aggregate. Microprobe investigations have been made of nickel distributions in and between kamacite, taenite, plessite, and schreibersite, and particular attention has been paid to the nickel distribution at the internal grain boundaries in the plessite. Evidence is presented for the diffusion of nickel along these boundaries and for their migration during the later stages of formation of the microstructure.

SummaryThe kamacite contains a general precipitation of micrometre-sized particles of exsolved taenite. Larger particles are found decorating Neumann lines and at kamacite grain boundaries. The coexisting kamacite and taenite appear to have nickel contents of 6·4 % and about 53%, which are consistent with a temperature of about 330–60 °C on the binary iron-nickel equilibrium diagram.

1. The factors producing electrolytic corrosion of stainless steels are reviewed, and it is shown how several factors operating together can accentuate corrosion in certain positions in the plated fracture.2. These factors can be minimised by good metallurgy and good engineering on the part of the manufacturers.3. When and if materials become metallurgically satisfactory, or a truly inert substitute for metal is discovered, it will be possible to assess the true contribution of infection, faulty operative technique and mechanical factors to the failures of internal fixation. Such a critical assessment of these probably more important factors is at present bedevilled by uncertainty as to the purely physical condition of the materials as supplied to the surgeon.

SummaryThe Angra dos Reis (iron) has been studied metallographically and an attempt has been made to discuss the circumstances under which the following elements of structure formed: clear etching and frosty etching kamacite, decorated Neumann lines, giant rhabdites, plate rbabdites, rhabdite clusters, microrhabdites, cohenite, and remelted troilite. The remelted troilite is taken to indicate a shock event. However, since there are no metallographically visible indications of shock in the kamacite and since the back reflection X-ray diffraction pattern shows only very faint Debye-Scherrer arcs superimposed on a pattern of sharp spots, it is concluded that the shock event took place at a temperature that allowed shock effects to anneal out of the kamacite almost completely. A submicroscopic precipitate in the metallic matrix is observable with the electron microscope and may represent the final precipitation of phosphide from shocked kamacite.

SummaryA metallographic study has been made of the macroscopic and microscopic features of the Brenham pallasite. The microprobe has been used to investigate the condition of kamacite inter-faces with second kamacite grains, olivine, schreibersite, troilite, and taenite and of taenite interfaces with olivine. The results indicate that grain-boundary migration of nickel may be important in these structures.