Crystal Segregation Research Articles

Ａｌ‐Ｃｕ合金鋳塊の重力偏析

Cast samples having different copper concentrations were remelted and then were kept at fixed temperatures varying from 10 to 200K above the liquidus temperature of Al-Cu alloys phase diagram. The primary α aluminum dendrites appeared both just below the net, and at the top of ingot, when hypoeutectic alloys containing 31 to 33mass% Cu were solidified in a graphite mold in which a stainless steel net was set horizontally. On the other hand, the primary CuAl2 in the hypereutectic alloys containing 34 and 35mass%Cu appeared on the net and at the bottom of ingot. The primary α aluminum dendrites were less dense than eutectic liquid and floated in the melt after crystallization, and primary CuAl2 crystals sedimented in the liquid because they were denser than the eutectic liquid. The variation of holding temperatures and the duration of time in the molten state had no effect on the gravity segregation of those ingots, since no temperature gradient existed in the liquid and no thermal diffusion occurred under those conditions. Gravity segregation in Al-Cu alloys containing various copper concentrations was caused by floatation or segregation of primary crystals in the melt during solidification.

Nature and cause of compositional variation among the alkalic cap lavas of Mauna Kea Volcano, Hawaii

Most Hawaiian basaltic shield volcanoes are capped by moderately to strongly evolved alkalic lavas (MgO<4.5 wt.%). On Mauna Kea Volcano the cap is dominantly composed of hawaiite with minor mugearite. Although these lavas contain dunite and gabbroic xenoliths, they are nearly aphyric with rare olivine and plagioclase phenocrysts and xenocrysts. The hawaiites are nearly homogeneous in radiogenic isotope ratios (Sr, Nd, Pb) and they define coherent major and trace element abundance trends. These compositional trends are consistent with segregation of a plagioclase-rich cumulate containing significant clinopyroxene and Fe-Ti oxides plus minor olivine. Elements which are usually highly incompatible, e.g., Rb, Ba, Nb, are only moderately incompatible within the hawaiite suite because these elements are incorporated into feldspar (Rb, Ba) and oxides (Nb). However, in the most evolved lavas abundances of the most incompatible elements (P, La, Ce, Th) exceed (by ∼5–10%) the maximum enrichments expected from models based on major elements. Apparently, the crystal fractionation process was more complex than simple, closed system fractionation. The large amounts of clinopyroxene in the fractionating assemblage and the presence of dense dunite xenoliths with CO2 inclusions formed at minimum pressures of 2 kb are consistent with fractionation occurring at moderate depths. Crystal segregation along conduit or magma chamber walls is a possible mechanism for explaining compositional variations within these alkalic cap lavas.

Segregation and Trapping of Gold During Ion-Induced Crystallization of Amorphous Si

ABSTRACTA novel regime of crystal growth and segregation has been observed. Amorphous Si layers were uniformly doped with Au and epitaxial crystallization was induced in the temperature range 250–420°C using 2.5 MeV Ar ion irradiation. The Au segregation at the amorphous/crystal interface is analogous to behavior at liquid/solid interfaces except that the interfacial segregation coefficient of 0.007 at 320°C is independent of velocity between 0.6 and 6A/sec. This process results in the trapping of Au in crystalline Si at concentrations some ten orders of magnitude in excess of equilibrium concentration.

Co-Cr Perpendicular Anisotropy Film Deposited by Evaporation with Ion Bombardment

Changes in CoCr films induced by argon ion bombardment during film deposition by evaporation were studied. The film magnetic properties and X-ray rocking curve widths indicated that ion bombardment during deposition results in greater film uniformity, with larger crystal grains, better crystal orientation and less Cr segregation. This is probably because ion bombardment promotes atomic diffusion in films, thereby reducing grain boundaries and other lattice defects.

Petrogenesis of layered pyroxenites from the Lherz, Freychinéde and Prades ultramafic bodies (Ariége, French Pyrénées)

The pyroxenite bands in spinel Iherzolites from three high-temperature peridotite massifs (Lherz, Freychinéde and Prades) in Ariège (French Pyrénées) have geochemical features including distributions of Mg, Ca, K, Ti, Zr and REE typical of cumulates derived by high P− T crystal segregation. However, these features of the whole-rocks are not reflected in the element distribution among the minerals which was partially modified during subsequent recrystallization. In addition, samples from the margins of the pyroxenite bands were affected by secondary processes such as metasomatism or subsolidus re-equilibration. Unlike pyroxenite xenoliths from basalts which are usually assumed to be derived from alkalic basaltic magmas, the pyroxenite layers are related to tholeiitic magmas similar to the parental liquids of the Triassic dolentes encountered throughout the Pyrénées. The data show that high P− T fractionation significantly affected the ascending tholeiitic magma and suggest that the continental tholeiites could have been derived from an upper mantle source with a chondrite shaped REE pattern.

On the morphology of blends of linear and branched polyethylene

A blend of linear and branched polyethylene was examined in view of establishing conditions of cocrystallization and/or segregation. Two members of the SCLAIR series were used in 1∶1 proportions. Conditions of segregation on crystallization were first explored by DSC, which was followed by morphological examination of selected samples. This involved optical and electron microscopy, the latter using the permanganate etching technique of Bassett and Hodge. Dependent upon crystallization temperature and time, crystal segregation on different scales was observed revealing that the final product can be regarded as a morphological composite where the ratio and nature of the constituents are determined by the conditions of solidification. The particulars should be relevant to the presently evolving practice of blending different polyethylenes. Examples of the different morphologies will be demonstrated. The individuality of the lamellae of the more readily crystallizable species can become strikingly apparent which incidentally reveals details in the edge on view, such as have not been seen before, and may have relevance to the fundamentals of the structure of lamellar crystals in general.

Crystal-structure changes during tempering of hardened high-strength cast irons with nodular graphite

1. The martensite of high-strength cast iron is decomposed by a two-phase mechanism in the first stage of tempering (up to 100°C); the second stage of martensite decomposition occurs at 100–300°C and has the same character as that of high-carbon steel. 2. The decomposition of residual austenite occurs in two stages: The austenite is decomposed with the segregation of α-phase crystals and the carbon enrichment of intact austenite segments in the first stage (100–400°C); the decomposition is completed in the second stage (400–550°C) with the segregation of carbide from the carbon-enriched residual austenite. 3. Decomposition of residual austenite during tempering begins at 100°C in silicon cast iron, and at 200°C in manganese cast iron.

A Tale of Two Plutons: Petrographic and Mineralogic Constraints on the Petrogenesis of the Red Lake and Eagle Peak Plutons, Central Sierra Nevada, California

The Red Lake and Eagle Peak plutons are similar in age (K-Ar: 87-89 m.y.) and range in composition from granodiorite to granite. The Red Lake pluton is equigranular, has a locally greisened marginal zone, and shows only minor mineralogical and chemical zoning, whereas the Eagle Peak pluton is mineralogically, compositionally, and texturally zoned, with an equigranular margin and a porphyritic core. Modal and normative trends within each pluton are consistent with separation of plagioclase and mafic minerals leading to a residual liquid enriched in quartz and alkali feldspar. The formation of the prominent alkali feldspar megacrysts in the Eagle Peak core was promoted by plagioclase separation, $$H_{2}O$$ undersaturation, and a slower cooling rate relative to the Red Lake magma. Early loss of volatiles and a resulting increase in magma (melt + crystals) viscosity inhibited crystal segregation within the Red Lake pluton and prevented the development of zoning. Late stage aplites associated with both plutons formed from residual liquids created by crystal fractionation. Biotite and amphibole equilibria suggest internally buffered oxygen fugac-ity through most of the crystallization of the plutons. Comparison of mineralogic and whole rock compositional data with experimental studies on natural and synthetic sytems suggests a minimum intrusive temperature of 750°C and a load pressure of $$1.0 \pm 0.5 kb$$. Late stage hydrothermal alteration within each pluton reequilibrated feldspar compositions at subsolidus conditions. The presence of homogeneous cores in the plagioclase, early titanite crystallization in the Red Lake magma, and irregular hornblende compositions suggest refractory material was present when the magmas were intruded. Inferred source regions for the two plutons are amphibolite for the Red Lake magma and a more biotite-rich amphibolite for the Eagle Peak magma.

Metavolcanic rocks and their origin, Southern Adirondack mountains, New York

One of the problems associated with massif-type anorthosite in high grade metamorphic terranes is the absence of anorthositic extrusives. However, if anorthosite formed by crystal segregation, volcanic equivalents of the final fluid differentiate might occur. Massive, stratiform hornblende-garnet granitic gneisses occur between two metasedimentary sequences in asynclinorium south of the main Adirondack anorthosite massif and north of the Thirteenth Lake anorthosite dome. The granitic gneisses are divided into three stratigraphic units on the basis of mineralogy. The entire stratigraphic configuration has been traced 70 kilometers laterally, and the interpretation of the literature indicates that it may extend for over 100 kilometers.

High-frequency transistors by the diffused-meltback process employing three impurities

The diffused-meltback process for making transistor structures involves growing a crystal containing a donor and an acceptor impurity, cutting the crystal into pellets, melting and refreezing part of a pellet, and then diffusing. The meltback process produces through segregation a spatial discontinuity in concentrations of both impurities, with the same impurity predominating throughout the entire pellet. The diffusion process then results in the appearance of a (base) region of opposite conductivity type very close to the meltback interface. If a single donor and acceptor are used, independent control of excess impurity concentrations in emitter, base, and collector regions is not normally practicable. However, if three impurities are used (i.e., two acceptors and one donor for a germanium p-n-p transistor), they may be so chosen that a different one is predominant in each region. Some limitations on the impurity concentrations that may be obtained are inherent in the crystal growing and segregation processes, but these are not important in the fabrication of a high-frequency signal transistor.

錫青銅の鋳造偏析について

The crystal-and ingot-segregation of tin bronze has been obviously observed, and owing to some cooling rate of casting, the ingot segregation occurs inversely, i.e. the outside part of the ingot contains richer tin composition in comparison with its central part. But in the case of slow cooling (for example in the case of dry sand cast) the ingot shows normal composition distribution, —normal segregation,— and as there must be a critical point of cooling rate at which the ingot-segregation almost deminishes.In any case the crystal segregation always occurs and there must be in existence the relation between the crystal -and ingot- segregation.From the results of chemical analysis, microscopic observation, microscopic hardness test and distribution of specific gravity, our experiments (10%Sn bronze sample) have been carried out to investigate the relationship of the crystal -and ingot- segregation.

Alに對するFe及びSiの擧動に就て (I) 共晶過冷現象と偏析

Adding 1_??_6% of Fe to the purest Al (99.999%), the effect of cooling velocities on the microstructure of cast Al-Fe alloys has been studied. As the result of retardation of the crystallization of FeAl3, the eutectic point is supercooled if the alloys are cooled rapidly, and the apparent eutectic point shifts to the Fe-side. On the contrary, if the alloys are cooled slowly, the primary crystals of FeAl3 segregate in the mother-liquor and sink to the bottom of the ingot. Utilising the phenomena of segregation of the primary crystals, the composition for the eutectic point of the Al-Fe system has been studied and assigned to be 1.7% Fe. Mechanical properties of the Al-Fe alloys, cooled at various rates, have also been measured. Adding 1_??_10% Si to Al-Fe alloys, containing 5% of Fe, the molten alloys are cooled very slowly (10°/1 hr.) from the liquid in a Tammann-tube. Then structure of the ingot is examined as to the state of segregation of the primary crystals, the sorts of the ternary compounds and also the change of the phases during cooling. Further the composition of the mono-variant eutectic line, existing in the Al-Fe-Si system, has been determined by analysing the segregated portion of the ingots.