Tendency To Coalesce Research Articles

High yield and wide lateral size growth of α-Mo2C: exploring the boundaries of CVD growth of bare MXene analogues

Synthesis of Mo2C bare MXenes, without surface terminations groups, via chemical vapor deposition (CVD) on metal foils is scientifically a very intriguing crystal growth process, and there are still challenges and limited fundamental understanding to overcome to obtain high yield and wide crystal size lateral growth. Achieving large area coverage via direct growth is scientifically vital to utilize the full potential of their unique properties in different applications. In this study, we sought to expand the boundaries of the current CVD growth approach for Mo2C MXenes and gain insights into the possibilities and limitations of large area growth, with a particular focus on controlling Mo concentration. We report a facile modification of their typical CVD growth protocol and show its influence on the Mo2C synthesis, with growth times spanning up to 3 h. Specifically, prior to initiating the CVD growth process, we introduced a holding step in temperature at 1095 °C. This proved to be beneficial in increasing the Mo concentration on the liquid Cu growth surface. We achieved an average Mo2C crystals coverage of approximately 50% of the growth substrate area, increased tendency of coalescence and merging of individual flakes, and lateral flake sizes up to 170 μm wide. To gain deeper understanding into their CVD growth behavior, we conducted a systematic investigation of the effect of several factors, including (i) a holding step time on Mo diffusion rate through molten Cu, (ii) the Cu foil thickness over the Mo foil, and (iii) the CVD growth time. Phase, chemical and microstructural characterization by x-ray diffraction, x-ray photon spectroscopy, SEM and scanning/transmission electron microscopy revealed that the grown crystals are single phase α-Mo2C. Furthermore, insights gained from this study sheds light on crucial factors and inherent limitations that are essential to consider and may help guide future research progress in CVD growth of bare MXenes.

Experimental Investigation and Modelling of the Droplet Size in a DN300 Stirred Vessel at High Disperse Phase Content Using a Telecentric Shadowgraphic Probe

In this work, steady-state droplet size distributions in a DN300 stirred batch vessel with a Rushton turbine impeller are investigated using an insertion probe based on the telecentric transmitted light principle. High-resolution droplet size distributions are extracted from the images using a convolutional neural network for image-analysis in order to investigate the influence of impeller speed and phase fraction (up to 50 vol.-%). In addition, Sauter mean diameters were calculated and correlated with two semi-empirical approaches, while the standard approach only accomplished 5.7% accuracy, and the correlation of Laso et al. provided a relative mean error of 4.0%. In addition, the correlated exponent in the Weber number was fitted to the experimental data of this work yielding a slightly different value than the theoretical (−0.6), which allows a better representation of the low coalescence tendency of the system, which is usually neglected in standard procedures.

Effects of Defect on Work Function and Energy Alignment of PbI2: Implications for Solar Cell Applications

Two-dimensional (2D) layered lead iodide (PbI2) is an important precursor and common residual species during the synthesis of lead-halide perovskites. There currently exist some debates and uncertainties about the effect of excess PbI2 on the efficiency and stability of the solar cell with respect to its energy alignment and energetics of defects. Herein, by applying the first-principles calculations, we investigate the energetics, changes of work function and the defective levels associated with the iodine vacancy (VI) and interstitial iodine (II) defects of monolayer PbI2 (ML-PbI2). We find that the PbI2 has a very low formation energy of VI of 0.77 and 0.19 eV for dilute and high concentration, respectively, reflecting coalescence tendency of isolated VI, much lower than that of vacancies in other 2D materials like phosphorene. Similar to VI, a low formation energy of II of 0.65 eV is found, implying a high population of such defects. Both defects generate in-gap defective levels which are mainly due to the unsaturated chemical bonds of p-orbitals of exposed Pb or inserted I. Such rich defective levels allow the VI and II as the reservoir or sinks of electron/hole carriers in PbI2. Our results suggest that the remnant PbI2 in perovskite MAPbI3 (or FAPbI3) would play dual opposite roles in affecting the efficiency of the perovskite: (1) Forming Schottky-type interface with MAPbI3 (or FAPbI3) in which the built-in potential would facilitate the electron-hole separation and prolong the carrier lifetime; (2) Acting as the recombination centers due to the deep defective levels. To promote the efficiency by the Schottky effect, our work reveals that the II defect is favored, and to reduce the recombination centers the VI defect should be suppressed. Our results shall be beneficial in improving strategies for the related optoelectronics applications.

Investigation of silica fume as foam cell stabilizer for foamed concrete

Foamed concrete, classified as lightweight concrete, has been commonly used in construction applications for saving energy and reducing production transportation and labor costs during construction. However, due to the tendency of coalescence and disproportionation of foam cells during the preparation process, the maintenance of the fine cellular structure has become difficult. The use of a particle-stabilized foam (PSF) is an effective way to pertain or even improve its fine cellular structure and related performance. In the paper, silica fume particles with the ability to stabilize foam were used in foamed concrete. Effect of silica fume on volumetric stability of the foam sample was investigated by the relative height of foam volume change. Effect of addition of silica fume in different stages on properties of foamed concrete was explored by viscosity, density, water desorption, compressive strength, strength/weight ratio, scanning electron microscope (SEM) and pore size distribution analysis. The result showed that the volume with a whole and fine cell pores within the foam was more stable due to addition of silica fume in the liquid foaming stage. Silica fume is beneficial for stabilizing foam, but the stabilization effect varies when it is added in different stages of the paste. Sample that was prepared with addition of silica fume in the liquid foaming stage (F1) was verified to have best strength/weight ratio against the control sample without silica fume (F0) and the sample with addition of silica fume in the preparing paste stage (F2). Mechanistic model of the various cell stabilization effect on the foamed concrete that occurred by addition of silica fume at different stages was proposed and analyzed to explain the advantages of silica fume stabilized foam concrete.

Influence of rheology and surface properties on morphology of nanofibers derived from islands-in-the-sea meltblown nonwovens

Melt blowing is the most common technique to directly produce nonwovens from polymeric resins without any demand for extra bonding steps. The relatively low diameter of meltblown fibers, 1–2 μm, makes them superior in separations performance to the competing melt processing technique, spun-bonding. To further decrease meltblown fiber diameter, the islands-in-the-sea approach was investigated in this study. Immiscible blends of a water-soluble polymer, sulfonated poly(ethylene terephthalate) (SP), and hydrophilic polybutylene terephthalate (PBT) and hydrophobic polyvinylidene fluoride (PVDF) were meltblown and the SP washed away to produce nanofibers of less than 200 nm diameter. Despite a significant increase in blend drop size upon increasing the minor phase fraction, ϕ, the nanofiber diameter increased only slightly. Thus, we conjecture that nanofiber diameter is mainly controlled by fiber pinch-off, induced by quick stretching during the melt blowing process, rather than being affected by initial drop size. At a high shear viscosity ratio, ηminor/ηmatrix > 3, nanofibers showed a higher level of irregularities, particularly when the polymer flow rate decreased. At ϕ ≥ 0.2 fiber bundling was observed but with nanofibers from PVDF, due to its lower surface energy, compared with PBT, bundling decreased. Our work shows that using polymers with relatively low surface energy, and thus low tendency for coalescence, coupled with low viscosity can result in nonwoven mats of fibers with very low average diameter, low bundling, and an acceptable fiber regularity. With PVDF we achieved a record low average diameter of 36 nm. By using a water-soluble polymer matrix, such as sulfonated poly(ethylene terephthalate), concerns about cost and environmental problems related to chemical solvents are alleviated.

Online bubble size analysis in micro flotation

Measuring the size of bubbles is of fundamental interest in process engineering, especially in flotation. The size of a bubble influences its rising velocity, coalescence tendency and interaction with particles and surrounding liquid. This paper presents an online Bubble Size Analyzer (BSA) with automated image analysis software. The importance of isokinetic sampling with short residence time in the sampling system is shown. Key parameters of the image analysis software are pointed out. The BSA was used to characterize a laboratory dissolved air flotation setup. In accordance with literature, bubble size reduction with increasing saturation pressure and recycle flow was measured. It was discovered that bubble generation in the flotation setup happened by classical dissolved air flotation only when it was operated with pure water. With sodium chloride saline and complex protein solution a mixed dispersed/dissolved air flotation was observed. Maximum bubble sizes were found in water, reduced sizes in saline and minimum size in protein solution. Due to its flexible online installation, the BSA is recommended as a suitable tool for bubble size measurements in laboratory and real processes, where inline analysis is not possible.

Topography of thin films containing Ni-Ga intermetallic compounds formed on GaN(0001)

Studies, carried out in situ by scanning tunneling microscope (STM), on the topography of thin films containing Ni-Ga intermetallic compounds are presented in this report. It is shown that conditions of the film preparation influence size and shape of 3-D formations constituted of the compounds. The films are formed in two ways. The first one in which pre-deposited at room temperature Ni film is annealed at 650 oC, and the second one where Ni is evaporated directly onto the substrate kept at 650 oC. Films obtained by using the second procedure should be more suitable for catalytic applications. Grains of the compounds formed in these films do not show tendency for coalescence and are more strongly dispersed in contrary to the grains formed in the films obtained by using first procedure.

Defects in silicene: vacancy clusters, extended line defects, and Di-adatoms.

Defects are almost inevitable during the fabrication process, and their existence strongly affects thermodynamic and (opto)electronic properties of two-dimensional materials. Very recent experiments have provided clear evidence for the presence of larger multi-vacancies in silicene, but their structure, stability, and formation mechanism remain largely unexplored. Here, we present a detailed theoretical study of silicene monolayer containing three types of defects: vacancy clusters, extended line defects (ELDs), and di-adatoms. First-principles calculations, along with ab initio molecular dynamics simulations, revealed the coalescence tendency of small defects and formation of highly stable vacancy clusters. The 5|8|5 ELD – the most favorable extended defect in both graphene and silicene sheets – is found to be easier to form in the latter case due to the mixed sp2/sp3 hybridization of silicon. In addition, hybrid functional calculations that contain part of the Hatree-Fock exchange energy demonstrated that the introduction of single and double silicon adatoms significantly enhances the stability of the system, and provides an effective approach on tuning the magnetic moment and band gap of silicene.

Rapid solidification of Cu60Co30Cr10 alloy under different conditions

Metastable liquid phase separation and rapid solidification in a metastable miscibility gap were investigated on the Cu60Co30Cr10 alloy by using the electromagnetic levitation and splat-quenching. It is found that the alloy generally has a microstructure consisting of a (Co,Cr)-rich phase embedded in a Cu-rich matrix, and the morphology and size of the (Co,Cr)-rich phase vary drastically with cooling rate. During the electromagnetic levitation solidification processing the cooling rate is lower, resulting in an obvious coalescence tendency of the (Co,Cr)-rich spheroids. The (Co,Cr)-rich phase shows dendrites and coarse spheroids at lower cooling rates. In the splat quenched samples the (Co,Cr)-rich phase spheres were refined significantly and no dendrites were observed. This is probably due to the higher cooling rate, undercooling and interface tension.

Reactive Compatibilization of Poly(Butylene Terephthalate)/Acrylonitrile-Styrene-Acrylate Blends by Epoxy Resin: Morphology and Mechanical Properties

The effect on the notched Izod impact strength of poly(butylene terephthalate) (PBT) by blending it with acrylonitrile-styrene-acrylate (ASA) was examined. Epoxy resin (ER) was demonstrated to be an efficient compatibilizer for the partially compatible blends of PBT/ASA. It requires only a very small amount of ER to improve the toughness of the PBT/ASA blends drastically. Furthermore, there exists an optimum proportion of ER added to achieve maximum notched Izod impact strength. Transmission electron microscopy (TEM) observation suggests that the ER in the PBT/ASA/ER blends suppressing the tendency of coalescence of ASA, leading to better dispersion of the ASA particles. Field emission scanning electron microscopy (FESEM) shows that ER enhances the phase dispersion and the interfacial adhesion between the PBT and ASA phases, it improves the compatibility between PBT and ASA. The compositions in the interphase was continuous, which results in multiphase composites with a graded interphase. It is suggested that enhanced interphase adhesion was necessary to obtain improved dispersion, fine phase morphology, and better toughness.

Volumetric Gas−Liquid Mass Transfer Coefficient in Aerated Stirred Tank Reactors with Dense Floating Solid Particles

The effect of floating solid particles on volumetric gas−liquid mass transfer coefficients was investigated using a stirred tank of 0.2 m inside diameter (i.d.) with dual four-flat blade disk turbines for solid concentrations up to 50 vol %. Two kinds of floating solids, synthetic adsorbent particles (particle size of 375 μm and wet density of 793 kg m−3) and polypropylene particles (particle size of 480 μm and wet density of 854 kg m−3) were used. At very low impeller speeds the floating particles formed a stagnant layer on the liquid surface, and none of the solids were dispersed. As the impeller speed was increased, particles were partially dispersed, and the stagnant layer volume was reduced. With further increasing impeller speed, all solids were ultimately dispersed throughout the tank. The gas hold-up and volumetric gas−liquid mass transfer coefficient in a baffled or unbaffled stirred tank with dense floating solids particles are measured. The power consumption and gas hold-up decreased with an increase in floating solids concentration. It was found that the presence of floating solid particles significantly reduced the mass transfer coefficient at a given impeller speed. The presence of floating solids increased the apparent viscosity of the slurry and hence probably resulted in increased bubble coalescence tendency enhancing the formation of larger bubbles. They might lead to a decrease in gas hold-up or specific surface area and subsequently induce a significant decrease in the volumetric gas−liquid mass transfer coefficient. The experimental data for gas hold-up and volumetric gas−liquid mass transfer coefficient are satisfactorily correlated to power consumption, superficial gas velocity, and solid volume fraction.

Experimental investigation on bubble coalescence under nonuniform temperature distribution in reduced gravity

Results on bubble coalescences from the space experiment of thermocapillary bubble migration conducted on board the Chinese 22nd recoverable satellite are presented in this paper. Some coalescences of large spherical bubbles under microgravity are observed through bubbles staying at the upper side of the test cell. The data of bubble coalescence time are recorded and compared with theoretical predictions, which is based on a theory to describe the tendency of coalescence connected to chemical potential difference. It is implied that the theory is applicable for the experimental data of bubble coalescence. Moreover, the angle between the line of two bubble centers and temperature gradient falled mostly in the range 20°–40°.

Effect of starting material particle size on its agglomeration behavior in high shear wet granulation

The effect of anhydrous lactose particle size distribution on its performance in the wet granulation process was evaluated. Three grades of anhydrous lactose were used in the study: "as is" manufacturer grade and 2 particle size fractions obtained by screening of the 60M lactose. Particle growth behavior of the 3 lactose grades was evaluated in a high shear mixer. Compactibility and porosity of the resulting granules were also evaluated. A uniaxial compression test on moist agglomerates of the 3 lactose grades was performed in an attempt to explain the mechanism of particle size effect observed in the high shear mixer. Particle growth of anhydrous lactose in the high shear mixer was inversely related to the particle size of the starting material. In addition, granulation manufactured using the grade with the smallest particle size was more porous and demonstrated enhanced compactibility compared with the other grades. Compacts with similar porosity and low liquid saturation demonstrated brittle behavior and their breakage strength was inversely related to lactose particle size in the uniaxial compression test, suggesting that material with smaller particle size may exhibit more pronounced nucleation behavior during wet granulation. On the other hand, compacts prepared at higher liquid saturation and similar compression force exhibited more plastic behavior and showed lower yield stress for the grade with smallest particle size. The lower yield stress of compacts prepared with this grade may indicate a higher coalescence tendency for its granules during wet granulation.

Studies on the Binary Coalescence Model: II. Effects of Drops Size and Interfacial Tension on Binary Coalescence Time

A binary coalescence model of a two-component system of mixed oil drops in water is established. The original coalescence driving force directly connected to the chemical potential difference of the coalesced oil drops has been investigated under a mimetic “weightlessness” condition. Gravitation is minimized nearly to zero to overcome drop deformation by mixing hydrocarbon compounds and carbon tetrachloride. Any external force out of the drops is reduced nearly to zero, when one liquid drop goes near enough to be tangential to another. The coalescence time, defined as the binary coalescence time (tbi-coal), can be expressed as lnkdσ(1r1−1r2)=kbtbi-coal+b′ (1). The coalescence phenomenon was first proposed as initiated by chemical potential differences between liquid drops (B. Y. Yu, Ph.D. dissertation, Swiss Fed. Inst. Technol., Zurich, 1995). The greater the chemical potential difference between two liquid drops, the larger the factor σ(1/r1−1/r2); as a result, the coalescence tendency will increase (i.e., tbi-coal decreases). Equation [1], including interfacial tension, drop size difference, and thin-film coefficient supported by the experimental data, is quantitatively established.

M-integral analysis for two-dimensional solids with strongly interacting microcracks. Part II: in the brittle phase of an infinite metal/ceramic bimaterial

In order to extend the investigation addressed in Part I of this series to treat the multi-cracks problem in a finite brittle solid, this paper deals with the M-integral analysis for microcrack damage in the brittle phase of a metal/ceramic bimaterial. The basic idea is based on such a concept that the outside boundaries of the finite solid could be considered as a special kind of interface between air and the solid or between a rigid body and the solid. Following the work did by Zhao and Chen (Archive of Applied Mechanics 67, 393–406), who have found the contribution induced from the interface of the bimaterial to the J 2-integral, the first task of this paper is to reexamine the conservation laws of the J k -vector in the interaction problem among the interface and multi-subinterface microcracks. Unlike the conclusion given in Part I, the vanishing nature of both components of the J k -integral vector at infinity should include the contribution arising from the interface (as another kind of discontinuity). Only after clarifying this contribution, could new formulations of the conservation laws of the vector be deduced. This will lead to a correct way, from which the extension of the present investigation to treat a finite solid could be performed. Furthermore, the second task of this paper is aimed at providing a fundamental understanding of the interaction effect and the coalescence tendency for the microcracks based on the M-integral analysis as influenced by the existence of the ductile phase. Numerical results are given for the Cu/Al 2O 3 and the Ni/MgO bimaterial solids. It is concluded that the M-integral actually plays an important role for microcrack damage in the brittle phase of the bimaterial solids, which could be considered as a measure of the damage level and the coalescence tendency among the microcracks. It is concluded also that for a certain microcrack array the value of the M-integral in metal/ceramic bimaterial solids is always larger than that in homogeneous brittle solids. This means that the same microcrack array in the former cases shows lower stability and larger coalescence tendency than that in the later cases due to the existence of the ductile phase or due to the interaction of the microcrack array with the interface. Of great interest is that the divergencies of the M-integral values in bimaterials from those for the same microcrack array in homogeneous brittle solids are dominated by the first Dundurs parameter with no regards to the second Dundurs parameter. Finally, an extension of this investigation to treat microcrack damage in a half plane brittle solid is discussed briefly to show the potential applications of the M-integral analysis.

The oxidation of a directionally solidified Ni-Al-Cr3C2 alloy at 1100 and 1200°C in oxygen

The oxidation behavior of a directionallysolidified Ni-Al-Cr3C2 alloy ofover all composition Ni-12.3Cr-6.9Al-1.8C (wt.%) hasbeen investigated at 1100 and 1200°C under 1 atmoxygen. Experiments have also been carried out on specimens having the samecomposition but with a nonaligned structure. At1100°C, in both cases and unlike conventionalnickel-base superalloys with the same chromium andaluminum contents, aluminium was found to oxidize internallybeneath an external Cr2O3 scale.Although the volume fraction of the internalprecipitates was significant, they showed no tendency tocoalesce into a compact subsurface layer, but formed randomly distributed clustersin the alloy matrix. The kinetics of oxidation andmorphologies of the oxide scales were not substantiallyaffected either by thermal cycling or by the alloy microstructure. At the higher temperature,continuous Al2O3 scales formedbeneath thick layers of transient nickel andnickel-chromium-rich oxides; no internal precipitationof aluminum-rich oxides was observed. However, internal degradation of thedirectionally solidified specimens at 1200°C wasquite significant, due to in situ oxidation of primarycarbides. The multilayered scales formed at 1200°C spalled extensively on cooling as a consequenceof loss of contact, starting preferentially at theintersections of the Cr2C3 fiberswith the alloy-scale interface. The observed behaviorcan be attributed to a reduction in the availability of chromiumbecause of the multiphase structure of the alloy; this,in turn, resulted in an increase in the flux of oxygeninward, leading to internal oxidation of aluminum at 1100°C. The almost exclusive externaloxidation of aluminum becomes possible at 1200°C,probably because of an increase in the diffusivity ofaluminum in the alloy matrix.

Double emulsions — scope, limitations and new achievements

Multiple emulsions are complex systems, termed “emulsions of emulsions”, i.e. the droplets of the dispersed phase contain even smaller dispersed droplets themselves. Each dispersed globule in the double emulsion is separated from the aqueous phase by a layer of oil-phase compartments. Double emulsions have significant potential in many applications since, at least in theory, they can serve as an entrapping reservoir for active ingredients that can be released from the inner phase to the outer phase by a controlled and a sustained mechanism. Many of the potential applications are in pharmaceuticals. In practice, double emulsions are thermodynamically unstable systems with a strong tendency for coalescence, flocculation and creaming. Most double emulsions consist of relatively large droplets, cannot withstand storage regimes and have a strong tendency to release the entrapped matter in an uncontrolled manner. Much work has been devoted in the last decade in order to the improve the stability of the multiple emulsions and the control of the release rates of the addenda. The most recent achievements are: Use of polymeric emulsifiers to improve interface coverage and to better anchor into the dispersed phases; Reduce droplets size by improving methods of formation: improved understanding of the release mechanisms and use of various additives to control the release via the reverse micellar mechanism.

Advantages of High Magnetic Field for Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

It is well-known that mass resolving power in Fourier transform ion cyclotron resonance mass spectrometry (FTICR MS) can increase linearly with increasing applied magnetic field induction, B. Here, we show that eight other FTICR primary performance parameters theoretically also increase linearly (quadrupolar axialization efficiency, data acquisition speed), quadratically (upper mass limit, maximum ion kinetic energy, maximum number of trapped ions, maximum ion trapping duration, two-dimensional FTICR mass resolving power), or inverse-quadratically (peak coalescence tendency) with increasing B. The origin of (and conditions for) the magnetic field dependence of each of these parameters are presented and discussed. These fundamental advantages lead to corollary improvement in other FTICR performance parameters: e.g. signal-to-noise ratio, dynamic range, mass accuracy, ion remeasurement efficiency and mass selectivity for MS/MS. Finally, we note that these various advantages may be exploited in combination, so as to produce even higher enhancement in a particular parameter: e.g. signal-to-noise ratio can improve by more than a factor of B2 if mass resolving power is fixed at the same value as at lower magnetic field.

London-vdW and EDL Effects in the Coalescence of Oil Drops

Visual observations of coalescence of n-hexadecane oil drops (70-140 μm in diameter) suspended inside an aqueous phase of varying pH are reported. The oil drops are produced in situ and confined inside the aqueous-phase-filled fine capillary (100-160 μm i.d.). Rapid, spontaneous coalescence was observed at low pH (⩽2.5) as soon as two drops were very carefully brought into apparent contact. At very high pH (⩾13.0), coalescence was observed some time after the drops made contact. No coalescence was observed at intermediate pH 5.2, 7.1, and 10.9. The "coalescence times" at pH 2.2 and 2.4 were less than 0.033 s. At pH 3.2, 12, and 13.1 the coalescence times were 8, 20, and 1.8 s, respectively. The coalescence time in the acidic solution of a certain pH was distinctly lower than that in the basic solution of equivalent pOH. The coalescence tendency increased with an increase in the acidity or basicity of the aqueous phase. Also, in strongly basic or acidic media, freshly formed drops were more susceptible to coalescence. Visual observations of collision interactions are qualitatively described. When two drops were made to collide, coalescence was rapid at all pH at which coalescence was previously observed for the stationary drops. Almost no coalescence was observed at the intermediate pH's 5.2, 7.1, and 10.9, even after repeated collisions between the drops. The relative velocity of the collision interactions ranged from 100 to 2100 μm/s. The observed phenomena are explained on the basis of the London-van der Waals and electrical double layer forces, which are important either in stabilizing the thin liquid film formed between the approaching drops or in drawing the two interfaces close enough to thin the liquid film to the "critical rupture thickness range." In this range, it is believed that thin liquid film properties control the rupture process.

Kinetics of mesophase formation in a stirred tank reactor and properties of the products—V. Catalysis by ferrocene

The study is concerned with ferrocene as a catalyst precursor of an iron-catalyzed pyrolysis of pitch. Pyrolysis studies using a petroleum pitch showed the accelerating effect of iron, the limited lifetime of the catalyst iron due to poisoning by sulfur, and a strong influence of iron in the nucleation and the growth of mesophase spherulites. As compared to the pure pitch, the spherulites are nearly equal in size, and their surface is disturbed by segregated material containing iron and iron sulfide. The tendency for coalescence of these spherulites is strongly diminished.