Fine Lamellae Research Articles

Thermoremanent Magnetization in Bi2O3 · Fe2O3 System

AbstractAll samples of Bi2O3 · Fe2O3 or BiFeO3, prepared by different methods, exhibit when recooled from 700 K in presence of a residual magnetic field (≈ 20 Oe) an unusual increase in susceptibility or magnetization near their Néel temperatures (≈ 540 to 600 K), and this behaviour is characterized as thermoremanent magnetization (TRM). Salient characteristics of TRM as documented by Néel are observed. Different possible mechanisms on the origin of TRM in these samples including the formation of fine lamellae of α‐Fe2O3 in Bi2O3 · Fe2O3 are discussed.

Problems inherent in the application of calcite-dolomite geothermometry to carbonatites

Calcite-dolomite geothermometry has been used extensively to determine the temperature attained during regional metamorphism of limestones. Several attempts have been made to apply the technique to carbonatites. Although doubts have been expressed recently about the realiability of the method for limestones, the difficulties inherent in using it to estimate carbonatite magma temperatures are so profound that it is of very little value, and published carbonatite magma temperatures based on the method are dubious. These studies have tended to overlook the fact that the highest temperature that can be obtained by the method is still below the liquidus temperature. They have further tended to overlook the fact that Mg diffusion from calcite into coexisting dolomite continues during sub-solvus cooling and that in carbonatites this diffusion is likely to be far more extensive than in metamorphic marbles because of the ubiquitous presence of an alkali-H2O-CO2-halogen fluid. This diffusion is very variable within single “perthitic” carbonate grains and from grain to grain. The technique of dissolution of carbonatites in cold dilute HCl leads to difficulties and should be avoided. Electron microprobe analysis can be used only on unexsolved calcite or on calcite that has exsolved only very fine dolomite lamellae. The closest approach to magmatic temperatures is obtained by wet chemical analysis of coarse calcite-dolomite “perthites”. Published carbonatite magma temperatures based on calcite-dolomite geothermometry are misleadingly low and tend to overemphasize the 300–500 ° C temperature range, whereas evidence is presented for temperatures of about 900 ° C in one Ontario carbonatite. Except in rare cases, calcite-dolomite geothermometry cannot usefully be applied to carbonatites.

Microanalysis and cell boundary velocity measurements for the cellular reaction in a Mg-9% Al alloy

Mg-Al alloys decompose on ageing via a cellular reaction that produces large cells (ca.5-50 μm in diameter) consisting of alternating fine lamellae of Mg-Al solid solution and Mg17Al12intermetallic compound. This paper reports direct, high resolution microanalysis of individual points in cells formed by ageing over a range of temperatures. The results are combined for the first time with measurements, by a novel technique, of cell boundary velocity made in the same regions that were microanalysed. It is shown directly that solute redistribution occurs primarily in the cell boundary. Furthermore the relation between profiles varies for different cell boundaries, probably because of differences in the boundary diffusion coefficient or the interaction energy between aluminium and the grain boundary.

Discontinuous coarsening reaction in the unidirectionally decomposed β-CuIn eutectoid

The morphology and kinetics of the discontinuous coarsening reaction in the unidirectionally decomposed β-CuIn eutectoid is investigated. Two types of coarsening cells can be distinguished. Type I has coarse lamellae nearly parallel to growth direction, Type II has coarse lamellae nearly normal to growth direction. In both cases, that eutectoid grain shrinks whose fine lamellae are more normal to the initial position of the eutectoid grain boundary. If fine lamellae are nearly parallel at a eutectoid grain boundary the ends of the lamellae enlarge and an overall layer of α or δ phase is formed. The growth of discontinuous cells is linear until continuous coarsening reduces the driving force. Growth rates depend on annealing temperature and initial spacings of the fine lamellae and are widely spread for individual coarsening cells. Mobilities of eutectoid grain boundaries are computed and found to be considerably lower than that of α-CuIn boundaries. Boundary diffusion coefficients are evaluated using the formula of Livingston and Cahn. The activation enthalpy of these diffusion coefficients agrees well with that of boundary mobility and growth rate. A comparison of activation enthalpies of discontinuous precipitation reaction and diffusion in α-CuIn solid solutions, as well as of volume diffusion in the β-phase, shows boundary diffusion in the α-δ and/or δ-δ sections of the eutectoid grain boundary to be possible rate-controlling factors. The coarsening ratios are between 8.3 and 4, thus differing widely from the theoretical values predicted by the maximum growth rate or maximum entropy production criterion.

Aufbau and Feinstruktur von Periderm and Lenticellen der Fichtenrinde

The histochemical and fine structural investigation of the walls of the different cell types in the periderm and lenticel tissues in the bark of spruce (Picea abies) showed that the phellem consists of an outer layer of sclerotic elements with layered secondary walls; these contain only cellulose and lignin, and no suberin. Accordingly the present designation -stone cork should be substituted by a new term «sclerotic phelloid». The spongy cork cells and phlobaphenous cork cells exhibited fine lamellae in the suberized layer after special treatments. In the central region of the lenticel of spruce bark special cells with non-suberized walls are present. They resemble the sclerotic phelloids and are designated as «loosening cells» they correspond to the complementary tissue cells of angiosperm lenticels and contribute to the increase in intercellular area for gas exchange.

Morphology of spinal electromotor neurons and presynaptic coupling in the gymnotid Sternarchus albifrons.

Spinal electromotor neurons in the gymnotid Sternarchus albitrons were studied by light and electron microscopy. In this species, the electric organ discharge, which is of high and relatively constant frequency, is generated by specialized axons which arise from the spinal electromotor neurons. The cell bodies are located in medial regions of the spinal cord. They are round to ellipsoid in outline and dendrites are not peresent. The initial myelin segment often extends partially over the cell body. Fine glial lamellae are interposed between closely adjacent cells, and somato-somatic gap junctions are not observed. The large majority of axosomatic synapses are characterized by gap junctions. Single axons are commonly found to establish gap junctions with two adjacent neurons. Only a few synapses have the chracteristics associated with chemically mediated transmission. The morphological data provide evidence for electrotonic soupling between electromotor neurons by way of presynaptic fibres. The absence of dendrites in these neurons may provide a morphological correlate for their simple relay function.

Cu-5.0 at%Si合金単結晶の圧縮試験における双晶変形

Cu-5.0 at%Si alloy single crystals having various orientations were tested at −196°C in compression. In this work, the characteristics of deformation twinning were investigated and compared with those of the previous works in the tensile test. The results are summarized as follows.(1) The onset of twinning in the compressive test is characterized by a bent in the stress-strain curve and a formation of twin bands observed by optical microscopy. Also, it has been observed by transmission electron microscopy that the twin band contains many individual fine twin lamellae and the width of these lamellae are about 0.1μ.(2) The twinning systems in the compressive test are (111)[11\bar2] and (\bar111)[\bar11\bar2], but these systems are different from that in the tensile test, namely (111)[\bar211] and (\bar1\bar11)[\bar121]; this behavior is explained by the concept of polarization of shear, i.e., unidirectionality of twinning.(3) In the compressive test by 10% strain, the region showing twinning in the stereographic triangle is limited to the orientations near [001].(4) The orientation dependence of the twinning in the compressive test cannot be explained in terms of the dislocation reaction proposed by Venables and Cohen et al.

Analbite ? monalbite transition in a heat treated twinned amelia albite

Amelia albite annealed at > 1080 °C for 3200 hrs by Duba and Piwinskii (1974) shows very fine twin lamellae (∼1 μm) after the albite law, suggesting that it once underwent transformation into monalbite. A fragment of this specimen was investigated at 27 °C, 300 °C, 550 °C, 800 °C and 930 °C using the high-temperature precession technique. As the temperature increases, the splitting angle of c*-axes (likewise c*-axes) of two twin individuals continues to decrease. The photographs taken at 930 °C show that these two splitting angles have converged to 0o, indicating completion of the transformation into monalbite. The transition point we observe supports the results of MacKenzie (1952) (920±20 °C) and Grundy et al. (1967) (930 °C) rather than those of Sueno et al. (1973) and Prewitt et al. (1974) (> 1080 °C); the discrepancy is most likely due to the differences in the degree of Al-Si disorder of the samples used in the experiments.

Studies on the tine structure of Copepoda Observations on Calanus finmarchicus (Gunnerus)

Electron micrograph studies have been carried out on several body systems of the copepod, Calanus finmarchicus . The mid-gut epithelium possesses a layer of densely packed microvilli; there are two well-developed muscle layers, an inner strongly folded layer and an outer thinner layer, both of smooth fibres. The body musculature shows the striation typical of skeletal muscle with clear ‘a’ and ‘i’ bands, the latter with a 'z' line. Microtubules run longitudinally through the muscle fibres. The cuticle is divided into an inner zone of nine and an outer zone of seven layers; each is composed of fine lamellae and exhibits a wave-like pattern. A seta has a cuticular wall structure which is essentially similar; the setules are composed of cuticular layers only and lack protoplasmic extensions. The attachment of body muscle to cuticle is by a specialized area analogous to a tendon. Fine tubules from the plasma membrane of the ‘tendon’ become grouped into dense bundles of fibres which are inserted on the cuticle as tono-filaments. The nerve fibres exhibit great variation in diameter and in thickness of the myelin sheath. The developing ovum has a large nucleus, the boundary layer of which shows prominent nuclear pores. The nucleolus is very large. The male germinal epithelium also shows a particularly large ratio of nucleus to cytoplasm. The spermatophore sac wall is intensely secretory, producing droplets which appear to form a thick laminated spermatophore wall. It is suggested that secreted materials of two types in the core substance of the spermatophore arise from the vas deferens. The same materials are present in relatively small amounts in earlier stages of spermatophore development when the sperms are tightly packed together and the spermatophore wall is very thin.

Distribution of Fe and Mg in actinolite, hornblende and biotite in some precambrian metagreywackes from Guyana, South America

Actinolite, hornblende and biotite coexisting in greenschist mafic metagreywackes have been analysed with the electron microprobe to obtain information on their chemical relationship during metamorphism. As in some other parts of the world, the two calcic amphiboles coexist in the greenschist facies because of a miscibility gap between them which is observed under conditions of low-pressure regional metamorphism; it is thought that the two amphiboles are in equilibrium, or at least that the actinolite participated in hornblendeforming reactions. Contact metamorphism by granitic intrusives of these metagreywackes has converted them to hornblende hornfelses with the assemblage hornblende, andesine, quartz, biotite±cummingtonite; the hornblendes of the hornfelses are found to have compositions between actinolite and hornblende of the greenschists, and frequently show fine exsolution lamellae of cummingtonite as a result of oversaturation in this component. The distribution of Fe-Mg between hornblende and biotite changes from the greenschist to the hornblende hornfels facies, and the KD is probably dependent on AlVI in the hornblende.

Massive phase transformation in splat-quenched β AgAl alloys

The transformation of the high temperature β phase to massive phases has been investigated in splat-quenched AgAl alloys by utilizing electron microscopy and diffraction. Very limited optical microscopic observations were also made on bulk samples. It has been found that the β phase transforms to three different massive phases, i.e., α m, μ m and ζ m. The μ m phase is observed as domains of spherical to ellipsoid shape and posseses a complex cubic β- Mn type structure. The α m and ζ m phases are observed as fine lamellae and striated structures respectively having respectively f.c.c. and h.c.p. structures. These two massive phases were also found as a duplex structure where the trace of the (001) plane of the h.c.p. structure was lying parallel to the close packed (111) plane of the f.c.c. α m phase. The massive phase transformation in the AgAl system is very similar to those observed for CuGa alloys. The microscopic details associated with the transformation, i.e., twinning, stacking faults, etc., and the stability range of these phases are discussed.

Luna 20 pyroxenes: exsolution and phase transformation as indicators of petrologic history

Pyroxenes from our sample of Luna 20 soil are predominantly orthopyroxene with subordinate pigeonite. The orthopyroxenes are chromium-rich bronzites and contain submicroscopic lamellae of augite in a twinned orientation exsolved on (100). These lamellae have a composition close to the diopside-hedenbergite join. Asymmetric diffuse streaks parallel to a ∗ indicate stacking faults parallel to (100) and possibly very thin (10–20 Å) lamellae of clinobronzite parallel to (100). Pigeonite crystals are very complex crystallographically and chemically, with optically visible (001) augite exsolution lamellae and two sets of chromite exsolution lamellae. In addition, there are submicroscopic (100) augite lamellae and a second generation of clinohypersthene lamellae which appear to have exsolved from the (001) augite lamellae. The clinohypersthene host, which has a large number of stacking faults parallel to (100), has partially inverted to hypersthene of the same composition. The hypersthene occurs as very fine lamellae (less than 1000 Å) parallel to the (100) plane of the clinohypersthene. X D Fe-Mg values for five host-lamellae pairs in pigeonite K-4 indicate a significant amount of subsolidus readjustment. We tentatively conclude that many of the bronzite and pigeonite crystals were derived from rocks crystallized from a high level magma chamber in the lunar highland crust.

Exsolution Products in Heated Chalcopyrite

Chalcopyrite, chalcopyrite-rich ore, talnakhite concentrates, and synthetic Cu–Fe–S compositions were heated, in separate experiments, and quenched. Those heated above 550 °C produced well-formed lenticular lamellae of chalcopyrite arranged in three directions at right angles to one another and set in a darker matrix with distinctly different optical and X-ray properties and different composition. The composition and structure of the matrix depends upon the bulk composition of the starting materials.When heated, chalcopyrite exsolves 10 to 15% pyrite; the remaining phase on quenching yields a grid of near-stoichiometric chalcopyrite in a matrix of talnakhite of variable composition. The presence of pyrite in the starting material does not change the result. Heated mixtures of chalcopyrite, pyrrhotite, and pyrite yield a similar grid of chalcopyrite in a matrix of high-temperature cubanite solid solution.These exsolutions form on quenching, probably at the cubic/tetragonal inversion and are not equilibrium assemblages. Twinning was not observed in samples cooled through the inversion temperature, and, therefore, the fine twin lamellae sometimes observed in natural chalcopyrite may not necessarily have been formed at the cubic/tetragonal inversion.

加工したNb-40Zr-10Ti超電導合金の不連続析出について

Discontinuous precipitation of a cold-worked Nb-40Zr-10Ti alloy was investigated by means of transmission electron microscopy, and the other properties related to the discontinuous precipitation were also examined.The results are as follows:(1) Discontinuous precipitation occurs in the cold-worked specimen. The 〈1\bar10〉 direction of the β′ phase is nearly parallel to the 〈1\bar10〉 direction of the β″ phase.(2) The β′+β″ interlamellar spacing in the cold-worked specimen is about 1/10 (0.1 to 0.2 μ, ageing at 700°C) of the solution-treated one.(3) Discontinuous precipitation occurs initially at dislocation sites.(4) The β′+β″ fine lamella in the cold-worked specimen spheroidizes and then coarses to a stable size.(5) The relationship between the crystal orientations of the β phase and the coarsed β′+β″ phase is the same as in the case of the lamellar structure.(6) On the critical current vs ageing time curve, two peaks were observed. On the hardness vs ageing time curve, however only one peak was observed, and this peak corresponds to the first peak of the critical current.

Electron microscopic investigation of lamellar mixtures of two close‐packed phases

AbstractMartensitic and massive phases containing fine lamellae of two different close‐packed structures have been studied by transmission electron microscopy. The stacking sequences involved in the lamellar mixtures are ABCBCACAB and ABC, or AB and ABC, or ABC and CBA. The fine lamellae produce fringe patterns which are similar to fringe patterns due to single stacking faults. However, by tilting the foil images can be obtained that are incompatible with single stacking faults.

The Highest Fossils in the World

In his splendid volume Geology of the Himalayas (1964; reviewed in this Number, p. 86), Professor Augusto Gansser refers (p. 164) to the rock specimens brought back from the summit of Mount Everest by the successful Swiss climbers in 1956, and also by the American team in 1963. All the various summit specimens, Professor Gansser states, are lithologically quite identical. They consist of fine-grained, thin-bedded grey calc-schists or platy limestones. The calcites are elongated conformably with the schistosity, which seems to parallel the bedding. The detrital grains are mostly quartz, acid plagioclases and some microline, together with fine sericite lamellae, paralleling the calcites. Gansser continues: “Of special interest is the fact that both samples contain crinoidal fragments. Their large uniform calcite crystals contrast with the otherwise much finer crystalline matrix. In one elongated stem-fragment the segmentation is visible (Photo. 46), while one small plate still shows the well-preserved perforation (Photo. 47).” Moreover, he observes: “These remnants, representing the highest fossils in the world, are unfortunately not sufficiently well-preserved to allow an age-determination of the top Everest limestone. They do, however, support rather than contradict the Carboniferous (to Lower Permian) age generally assigned to the Everest limestones, on the grounds that they are overlain by the (Upper) Permian Lachi Series (Odell, 1943; Wager, 1939).”

Lamellar boundary slip in polyethylene

Mechanical relaxation in polyethylene specimens prepared in various ways has been studied at 0*67 c/s and by creep experiments of 35 min duration in order to elucidate the mechanisms of the α' and α' relaxations. Internal friction measurements were made from 20 to 120 °C and creep measurements from 14 to 85 °C. The α' relaxation has five significant properties. (1) The magnitude of the α' relaxation is highly sensitive to anisotropy in the orientation of lamellae. (2) The α' retardation time can be increased by irradiation which cross links the molecules in between lamellae. (3) The α' retardation time is greater in a slowly crystallized specimen with coarse lamellae than in a quickly crystallized specimen with fine lamellae. (4) The α' creep is entirely recoverable. (5) The superposed creep curves form not one master curve but two. These properties are predicted by a model in which the cl' relaxation is due to slip at lamellar boundaries while the a relaxation occurs within the lamellae. The model predicts full recoverability of the relaxation and the retardation time of the α' relaxation to be a function of the compliance of the lamellae, the viscosity of the inter-lamellar material and the geometry of the lamellae. The experiments also proved that large variations in the spherulitic structure of polyethylene have no measurable effect on any of the properties of the cl relaxation. The α relaxation cannot therefore be due to slip at the spherulite boundary.

The Influence of Environment on the Shell Structure of Starch Granules

It is well known from light microscope studies of potato starch that the granules formed in a constant environment (of light and temperature) have a ring formation indistinguishable from that of granules formed under field conditions. Electron microscope studies have confirmed that normal potato starch granules have a fine shell structure not usually resolved by the light microscope, and also that shells do not develop in barley granules grown in a constant environment. The paper presented here reports a further study of the dependence of shell formation on environment. Potatoes were grown in a constant environment and starch granules from the newly formed tubers were examined in the light microscope, and in the electron microscope after corrosion by acid. No difference between these granules and normal granules was observed; both wide (light microscope) rings and fine lamellae developed in both granules. Parallel studies were made on wheat starch granules. In this case, shells were not differentiated in granules that developed in a constant environment, but they could be produced at will by imposing a dark period. Thus, shell formation in potato granules must be controlled by an endogenous rhythm, whereas in wheat granules it must be controlled by external environment.

Zum Feinbau der Suberinschichten im Flaschenkork

The suberinic layer of the cell wall in bottle cork was investigated by means of ultrathin sections in the electron microscope. The layer was found to consist of fine lamellae, as was expected and depicted, in cork of other plants, by Falk and El-Hadidi. Certain difficulties involved in the investigation of this lamellated structure are discussed briefly.

The influence of environment on the shell structure of starch granules.

It is well known from light microscope studies of potato starch that the granules formed in a constant environment (of light and temperature) have a ring formation indistinguishable from that of granules formed under field conditions. Electron microscope studies have confirmed that normal potato starch granules have a fine shell structure not usually resolved by the light microscope, and also that shells do not develop in barley granules grown in a constant environment. The paper presented here reports a further study of the dependence of shell formation on environment. Potatoes were grown in a constant environment and starch granules from the newly formed tubers were examined in the light microscope, and in the electron microscope after corrosion by acid. No difference between these granules and normal granules was observed; both wide (light microscope) rings and fine lamellae developed in both granules. Parallel studies were made on wheat starch granules. In this case, shells were not differentiated in granules that developed in a constant environment, but they could be produced at will by imposing a dark period. Thus, shell formation in potato granules must be controlled by an endogenous rhythm, whereas in wheat granules it must be controlled by external environment.