Microstructure of Silica in the Presence of Iron Oxide

The microstructures that are developed when iron oxide reacts with excess silica at elevated temperatures are described. Compacts of powdered quartz and iron oxide were heated to various temperatures and under selected conditions of oxidation to determine the effect of these parameters on microstructure. The results show that temperature has a small but measurable effect on the geometry of the silica and liquid phases. The oxidation level does not have an effect on the geometry of the phases in this system other than to reduce the liquid content by introducing magnetite as a secondary phase. The strength of silica brick in the presence of high liquid contents probably arises from the interfacial-energy relations which maintain considerable solid-to-solid contact at elevated temperatures.     

Slip Behavior and Hardness Indentations in MnSe and MnSe-MnS Solid Solutions

Single crystals in the solid solution series MnSe-MnS were prepared, and selected surfaces were indented with either a Vickers or a Knoop microindenter. Information on mechanical behavior was obtained by observation of slip traces around indentations and by study of Knoop hardness anisotropy. Manganous selenide exhibits {111}     and {110}     as primary and secondary slip mechanisms, respectively, in contrast to the {110}     mechanism preferred by MnS. In the system MnSe-MnS, the primary slip mechanism changes gradually with composition. The {110}     mechanism of MnS is much more sensitive to temperature than the {111}     mechanism of MnSe, and a large solid solution hardening effect accompanies the substitution of sul-fide for selenide ions.     

Deformation and Fracture of MnTe and MnSe-MnTe Solid Solutions

Single crystals of MnTe and solid solutions in the system MnSe-MnTe were prepared; selected surfaces were indented with either a Vickers or a Knoop microindenter. Information on mechanical behavior was obtained by observation of slip traces and by study of Knoop hardness anisotropy. Hexagonal NiAs-type MnTe and MnTe-rich Mn(Te,Se) solid solutions show plastic deformation attributable to {1012} twinning, basal slip, and pencil glide in 〈1120〉. Fracture occurs as primary {0001} and secondary {1010} cleavage. Vickers and Knoop hardnesses were greater on the basal plane than on prism planes. Cubic MnSe-rich Mn(Te,Se) solid solutions show both {111}〈110〉 and {110}〈110〉 slip with {100} and {110} fracture in crushed fragments and around surface indentations. Knoop hardness anisotropy is like that in MnSe. The rate of solid solution hardening is greater than for comparable substitutions of sulfide ions in the MnSe matrix.     

Reaction Between Nitrogen and Spinel in Chromium

The reaction between nitrogen dissolved in chromium and a dispersion of magnesium aluminate particles in chromium at high temperatures is discussed. The equilibrium state for various nitrogen concentrations in a 94 chromium-6 spinel mixture was investigated between 1200° and 1400°C. Experimental techniques included electron-beam microprobe analysis and mass spectrometry. Partitioning of nitrogen between chromium and spinel was strongly in favor of the spinel. Mass spectrometry indicated coordination of nitrogen with magnesium in the spinel lattice. The spinel-nitrogen reaction is important because it can prevent the embrittling of chromium by nitrogen.     

Transformation of Quartz to Tridymite in the Presence of Binary Silicate Liquids

The isothermal transformation rates for quartz to tridymite were studied in the presence of binary silicate liquids between the eutectic temperature and 1470°C. Oxide pairs included Na₂O-SiO₂, PbO-SiO₂, FeO-SiO₂, and Cu₂O-SiO₂. Micrographic and X-ray analytical procedures were used. Transformation was most rapid at intermediate temperatures, thus providing typical TTT curves. The rates increased as the liquid contents of the binary pairs were increased. Transformation was more rapid for the pairs which had higher SiO₂ contents in their equilibrated liquids. Transformation proceeded as a solution-reprecipitation reaction. Initially, metastable cristobalite precipitated more rapidly than the tridymite; however, it redissolved and eventually disappeared, leaving only tridymite as the solid phase. An empirical equation was adapted to the transformation.     

Preferred Orientation in Microstructures of Eutectics Between Compounds

The microstructures of eutectics between compounds were studied for systems MnO-MnS, NaCl-NaF, NaBr-NaF, LiF-NaF, and FeO-FeS. With the exception of FeS, all the compounds had the NaCl-type structure. In the systems having only NaCl-type structures, the lamellas of the two eutectic phases had matching crystal orientations. There was less consistency among the eutectic systems, however, than between the phase pairs. The crystal growth directions in all five systems were different, and no more than two of the systems had the same set of inter-facial planes. One must conclude that the two phases within a eutectic of compounds do not solidify independently of one another. It is suggested that the two phases of an NaCl-type eutectic pair crystallize as a "single" ionic crystal with imperfections present to accommodate the dimensional mismatch.