Presence Of Spherulites Research Articles

Impact of spherulite-type crystalline defects on the mechanical and electrochemical properties of Ti40Cu36Zr10Pd14 metallic glasses

One of the limitations to the use of certain bulk metallic glasses is related to the formation of crystalline zones or defects, often called “spherulites”, during the casting process. In the case of Ti40Zr10Cu36Pd14 (at%) metallic glass, which is a candidate for biomedical applications, spherulites of diameter up to few hundreds of microns were previously reported, but their crystallographic features and their role in the mechanical behavior and the corrosion resistance remains to be determined.In this work, a detailed description of the microstructure of spherulites is provided. Tensile, compression and fatigue tests were carried out. In addition, corrosion behavior was studied by global and local electrochemical measurements. The spherulites have a deleterious effect on the tensile and fatigue strength of the alloy, even if it still retains strength properties that are far superior to conventional crystalline materials. The electrochemical studies do not show any difference in potential between the spherulite and the amorphous matrix, which indicates that the presence of spherulites is probably not the direct cause of the pitting phenomenon observed, which is unfortunately a clear drawback of this alloy when considering biomedical implants.

Influence of hydrothermal activity on the mineralogical-petrophysical properties of an atypical doleritic reservoir rock: A case study of the Gabes Gulf (north Africa, Tunisia)

The Gabes Gulf located in the South Mediterranean Sea (Southeastern part of Tunisia) is a prolific petroleum-producing area with several oil and gas fields and it's the subject of significant discoveries. The area is affected by intense tectonic events and several stages of hydrothermal activities. During drilling at the MX area in NE of the Gabes Gulf, a magmatic intrusion has been encountered within a reservoir rock (i.e., Douleb Formation). The objectives of the present study are (1) to investigate the impact of the hydrothermal activities on this magmatic intrusion and (2) to characterize the potential modifications in its mineralogy and petro-physical properties that can affect the migration/accumulation of hydrocarbons. To do so we combine optical microscopy, X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectrometry, micro-Raman spectroscopy, electron microprobe analyses, and petro-physical measurements.Our results show that the initial magmatic intrusion (dolerite) is composed mainly of plagioclase, clinopyroxene, and olivine. Based on petrographic observations, this intrusion subjected to several stages of hydrothermal fluid alterations that modified the primary texture and mineralogy. Albite, calcite, ankerite, dolomite, pyrite, quartz, anatase, kaolinite, and chlorite are the main secondary mineral products. During this alteration process, carbonates, pyrite, and quartz precipitated in vesicles, forming amygdules structure with enveloped zones indicating a fluctuation of fluid chemistry during their formation. In addition, petrographic observations indicate an interaction between feldspars exsolution and metasomatic processes in the studied area.The dissolution mechanisms, as well as the textural modifications in the dolerite induced by the hydrothermal activity, are underlined by the presence of spherulites, pores, and micropores. Such modifications significantly improved the porosity of the dolerite body. Conversely, the new mineralization that filled the fractures and micro-fractures, have reduced the inter-pore connections, and thus reduced its permeability. The present work demonstrates the important role of hydrothermal activity on the petro-physical properties of magmatic intrusions and how it could facilitate the migration/accumulation of hydrocarbons. Our results open the door for further investigations to check the potential presence of hydrocarbons within this doleritic intrusion.

Impact of Spherulite-Type Crystalline Defects on the Mechanical and Electrochemical Properties of TiCuZrPd Metallic Glasses

One of the limitations to the use of certain bulk metallic glasses is related to the formation of crystalline zones or defects, often called “spherulites”, during the casting process. In the case of Ti 40 Zr 10 Cu 36 Pd 14 (at.%) metallic glass, which is a candidate for biomedical applications, spherulites of diameter up to few hundreds of microns were previously reported, but their crystallographic features and their role in the mechanical behavior and the corrosion resistance remain to be determined.In this work, a detailed description of the microstructure of spherulites is provided. Tensile, compression and fatigue tests were carried out. In addition, corrosion behavior was studied by global and local electrochemical measurements. The spherulites have a deleterious effect on the tensile and fatigue strength of the alloy, even if it retains properties that are far superior to conventional crystalline materials. The electrochemical studies do not show any difference in potential between the spherulite and the amorphous matrix, which indicates that the presence of spherulites is probably not the direct cause of the pitting phenomenon observed, which is unfortunately a clear drawback of this alloy when considering implants.

Formation of Spherulites in Electrodeposited Alloys Fe-Ni and Fe-Cr-Ni

With the use of the methods of scanning electron microscopy and X-ray diffractometry the distinctive features of spherulites creation during electrodeposition of Fe-Ni and Fe-Cr-Ni alloys from sulfate electrolyte on low-carbon steel substrate is analyzed. The presence of spherulites is detected not only in near-substrate layers of the deposits but also on the surface of quite thick (50 mm) coatings. The increase of the coatings thickness causes the increase of sperulites size due to their selective growth. The formation of sherulites occurs at quet high current density (10 A/dm2). It is shown that spherulites formation may happen on non-indifferent substrates. The interdependence of the processes of formation of spherulite structure and crystallographic texture of the nickel containing electrodeposited alloys is discovered. The formation of sperulites is accompanied by appearance of <111> axial texture of the coatings.

Formation of spherulites and pentagonal quasicrystals in metals being electrodeposited

The aim of the work was experimental verification of validity of the phenomenon of phase formation through a stage of liquid state in metals being electrodeposited. The idea of the work was based on the known fact, that at minor undercooling of melt solidification of metal usually occurs in dendritic form, and at significant undercooling of melt dendritic form transfers to spherulite one. At that spherulites, as a rule, are being formed on the interface between metal and a melting-pot. Besides, superfast solidification of greatly undercooled melt causes formation of quasicrystals with pentagonal symmetry. Therefore, if metals being electrodeposited really pass through a stage of undercooled liquid state and rapidly solidify at the deposition temperature, than spherulite forms of crystallization and pentagonal quasicrystals should be detected in their layers adjacent to the cathode. As the result of experimental investigations accomplished by the method of scanning electron microscopy formation of spherulites and pentagonal quasicrystals in the adjacent to the cathode layers of metals (copper, lead and cobalt) being electrodeposited was discovered. It is shown, that presence of spherulites and pentagonal quasicrystals in electrodeposited metals is the result of superfast solidification of undercooled liquid metallic phase being formed during electrochemical deposition of metals. Formation of spherulites and pentagonal quasicrystals in the adjacent to the cathode layers of metals being electrodeposited proves the validity of the phenomenon of phase formation through a stage of liquid state in metals being electrodeposited.

Extinction of spherulites and improvement of polyethylene properties by the use of lithium carbonate

AbstractPolyethylene (PE) consists of nonpolar molecular chains having simple structural units. Physically, this polymer is so stable and flexible that it is widely used for insulation of electric wires and power cables, as well as for fabrication of various molded products. The crystalline texture and the presence of spherulites are major factors determining the mechanical and electrical properties of polyethylene.For the purpose of improving these properties of PE, the spherulites are eliminated completely by heat mixing of PE with Li2CO3. PE processed in this manner is free of spherulites, has a uniform structure and excellent electrical, mechanical, and thermal properties, such as short treeing length, high dielectric breakdown strength, and high tearing impact strength. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 148(2): 22–38, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10296

Spherulites in Calcrete Laminar Crusts: Biogenic CACO3 Precipitation as a Major Contributor to Crust Formation

ABSTRACT Spherulites (calcitic fibro-radial spherulitic polycrystals) are a major component of calcite layers in Quaternary calcrete laminar crusts. To explain the formation of spherulites, petrographic and chemical studies were performed on Pleistocene calcrete laminar crusts, Holocene biological crusts, and laboratory (in vitro) cultures of cyanobacterial strains. Spherulites were found to be formed of acicular and radiating crystals, either smooth and regular-edged, or twisted and irregular-edged. Spherulites were composed of low-Mg calcite, the concentration of Mg in the spherulites increasing from nucleus to periphery. The shape and chemistry of the in vitro spherulites and laminar crust spherulites were identical. The structure, elementary crystal shape, and size of spherul tes can be used to differentiate them from Microcodium, with which they are commonly confused in the literature. Spherulite genesis can be linked to cyanobacterial activity involving photosynthetic uptake of HCO-3, leading to CaCO3 precipitation, the bicarbonate causing release of equivalent amounts of OH- in the mucilaginous sheath. The main steps in cyanobacteria biomineralization producing spherulites are: (1) uptake of CO2 and/or HCO-3 from the medium as the inorganic carbon source for photosynthesis, (2) release of OH- in the sheath, (3) carbonate' ion formation resulting from the reaction of OH- and HCO-3, followed by (4) CaCO3 precipitation. This process involves two steps in desert environments: during dry spells, the cyanobacterial mat calcifies, leading to spherulite production and the fo mation of thin, clear microsparitic layers. During wet periods, a thin sedimentary deposit forms, mixing micrite, detrital particles, and inherited or new tiny spherulites with the mucilaginous mat of cyanobacteria, which traps all of this material. An organo-micritic layer forms. During the following dry spell, the process is repeated and the laminar crust is formed. In conclusion, the presence of spherulites in the laminar crust is indicative of subaerial exposure, the crust being a terrestrial stromatolite.

Effect of spherulites on the mechanical properties of nylon 66

AbstractThe presence of spherulites in nylon 66 increases the yield point and reduces the effects of variations in per cent crystallinity. Decreasing the size of the spherulites through increased nucleation results in a higher flexural modulus and yield point, a lower ultimate elongation, and a loss of ductility. These effects are markedly reduced by raising the temperature or water content. The effects of spherulite size in nylon and grain size in metals such as mild steel are compared.