Influence Of Crystallization Conditions Research Articles

Influence of Crystallization Conditions on the As-Cast Structure of Fe-Mn-Si Alloy with a Shape Memory Effect

Nowadays, smart materials with special functional properties, in particular shape memory alloys, are widely used in more and more units of various equipment. Fe-based alloys of the Fe-Mn-Si-Cr-Ni-X system, due to their relatively low cost and sufficiently high manufacturability, can be widely used in various fields. It is shown that in the studied alloys, alloying elements can be divided into system-forming (10–30 wt.% Mn and 3–10 wt.% Si), and additional (Cr, Ni, V, N, Cu, etc.) elements, which add to improve the shape memory effect. It is shown that the one problem of Fe-SMAs is the evaporation of manganese in the melting. Criteria for the selection of alloys considering the temperature regime of melting with minimal evaporation of manganese and satisfactory overheating above the liquidus temperature have been developed. The Fe-35Mn-8Si alloy were produced at laboratory scale. The effect of the cooling rate during solidification on the structural heterogeneity of the test ingots poured into a cast iron chill mold and into a sand mold is studied. Using pin molds, in which conditions are created that inhibit the shrinkage of the solidifying ingot and provoke cracking, their resistance to hot cracks has been studied. The secondary dendrite arm spacings and the segregation coefficients of manganese and silicon were determined depending on the crystallization conditions. Critical parameters of the technology have been determined, the optimization of which makes it possible to produce Fe-SMAs at industrial scale.

Unexpected Structural Properties in the Saturation Region of the Odd–Even Effects in Aliphatic Polyethers: Influence of Crystallization Conditions

Unexpected Structural Properties in the Saturation Region of the Odd–Even Effects in Aliphatic Polyethers: Influence of Crystallization Conditions

Structure, physical and mechanical properties of bronze castings obtained by continuous and centrifugal casting

The influence of crystallization conditions (continuous and centrifugal casting) of small-sized BrА1Fe4Ni4 bronze castings on the structure, phase composition, and hardness was studied. It was found by metallographic and X-ray diffraction methods that the castings consist of (α + γ')-eutectoid, α phase and AlCu, Al2Cu3 intermetallic compounds. The matrix phase in the alloy, crystallized by centrifugal casting, due to its higher alloying with Al atoms, has an increased value of the crystal lattice parameter, compared with the case of continuous casting. The hardness of the casting obtained by centrifugal casting increases compared with continuous casting, which is due to the formation of a more dispersed structure, as well as a large solid solution hardening of the matrix phase of the casting.

The influence of crystallization conditions on the macromolecular structure and strength of γ-polypropylene

The influence of the crystallization temperature and the pressure on the crystallization kinetics, structure and compression strength of γ-polypropylene was investigated. Samples were produced in a custom-made high-pressure crystallization cell and characterized by differential scanning calorimetry (DSC), wide angle X-ray scattering (WAXS) and transmission electron microscopy (TEM). It could be shown that the strength is mainly affected by the mean lamellar thickness. The strength of γ-PP is at least 40% higher than α-PP at the same mean lamellar thickness. This confirms the hypothesis that the arrangement of non-parallel chains restricts the number of possible slip systems so that almost no mobile dislocations are generated. The mode of nucleation is only slightly affected by the crystallization pressure. The Avrami coefficient is n = 2.5 ± 0.1 at the beginning of crystallization and largely independent of pressure.

Covalent Assisted Supramolecular Synthesis: The Influence of Crystallization Conditions on Co-Crystals of “Masked” Isoniazid Derivatives

Eight co-crystals of covalently modified isoniazid were synthesized, using either 3- or 4-hydroxybenzoic acid as the co-former. It was demonstrated that, for the co-crystallization of “masked” isoniazid by benzophenone derivatives, a small change in reaction or crystallization conditions played a large role in the outcome of the resulting supramolecular structure, whereas the addition of either one or two methyl substituents to the benzophenone rings did not affect the supramolecular structure of the resulting co-crystals. Changing the reflux time for the supramolecular synthesis resulted in stoichiometric variation. Adding larger quantities of one of the starting supramolecular reagents as “additives” resulted in polymorphism. Using a catalyst for the covalent modification of isoniazid during one-pot supramolecular synthesis prevented the formation of a solvate.

Influence of crystallization conditions and of gaseous ammonia treatment on mesoporous TiO2 properties

After surfactant removal by ethanol extraction, amorphous mesoporous titania, synthesized through a soft templating method have been crystallized under different atmosphere: synthetic air, nitrogen followed by exposition to oxygen flow and pure nitrogen at 300, 350 or 380 °C. The photocatalysis efficiency towards methyl orange degradation of the materials crystallized under oxidizing conditions increases with the calcination temperature thanks to the enhancement of crystallinity and the growth of anatase particles. However, if samples are heated under nitrogen followed by exposition to oxygen flow the mesopores collapse during the transformation of the amorphous titania walls at 380 °C. By contrast, under pure nitrogen atmosphere the photodegradation of the dye is not governed by the anatase particles but it is related to the specific surface area of the photocatalyst. A good compromise between avoiding the collapse of the mesostucture and improving photocatalytic efficiency consists in crystallizing the amorphous TiO2 under synthetic air at 380 °C.In the synthesis procedure, to avoid the mesostucture collapse upon surfactant removal, a treatment of the hybrid mesophase under ammonia atmosphere is needed to complete the condensation of the titania precursor. Because of the possible interactions between ammonia and amorphous titania but also with surfactant, a wormhole-like structure is obtained, when the hybrid mesophase is exposed either at high NH3 pressure or for a long time. Conditions under which this step is performed also strongly affect the photocatalytic efficiency of the crystallized TiO2. Our results show that when the ammonia pressure is increased or when the treatment is prolonged, interaction of NH3 with amorphous titania through Lewis adsorption promotes the nucleation of rutile. Therefore, upon calcination less amorphous TiO2 particles can be transformed into nanosized anatase. Consequently, a decay of the photocatalytic efficiency is noted.

Expanding the Pool of Multicomponent Crystal Forms of the Antibiotic 4-Aminosalicylic Acid: The Influence of Crystallization Conditions

Finding new multicomponent crystal forms of commercially available pharmaceuticals is important, as they represent a straightforward way to drastically influence the solid-state properties of a drug. The antibiotic 4-aminosalicylic acid (ASA) is known to exist in several multicomponent crystal forms, and in this work we expand the world of ASA cocrystals and salts by reporting new crystalline forms comprising diazabicyclo[2.2.2]octane (DABCO), and caffeine. All species were characterized by X-ray single crystal, powder diffraction, and thermal behavior. This study contributes to the rationalization of preferred functional groups for the synthesis of 4-aminosalicylic acid new multicomponent crystal forms and highlights the relevance of the reaction conditions in the achievement of those forms.

Effects of heat treatment on Na-ion conductivity and conduction pathways of fluorphosphate glass-ceramics

Fluorphosphate glass-ceramics Na2O-NaF-B2O3-P2O5-TiO2-ZrO2 (NTBPZ) were prepared by the conventional melt-quenching method following with the reheat treatment. High temperature phases of NaTi2(PO4)3, Na2HPO4 and Na2HPO4(H2O)2 nanocrystals were precipitated in the glass-ceramics. The influence of crystallization conditions on structure and ionic conductivity of the glass-ceramics was studied using X-ray diffraction, scanning electron microscope, and Electrochemical impedance spectra (EIS). And the results showed that the Na-ion mobility closely depends on the type and the distribution of the nanocrystal conductors. A room-temperature conductivity as high as 5.52×10−5S/cm was achieved for the glass-ceramic crystallized at 600°C for 20h. The effects of the heat treatment on Na-ion conduction pathways were also discussed.

Influence of crystallization conditions on the structure and modifying ability of Al–Sc alloys

The influence of the modes of thermal-and-temporal treatment and cooling rate of metallic alloys on crystallization regularities of Al–Sc alloys and their structure, properties, and modifying ability are established. Castings of Al–Sc alloy, which were prepared by the electrolysis of salt melts KF–NaF–AlF3–Sc2O3 at 820–850°C, are used as the initial charge for casting. It is established that, by varying the magnitude of melt overheating and casting temperature, it is possible to vary the crystal shape, amount, and size in wide limits. The modifying action of cast and rapidly quenched master alloys, as well as the master alloy produced by electrolysis, is tested for Al–4.5% Cu alloy. The largest effect of milling the structure of the Al–4.5% Cu–0.4% Sc alloy is attained when using the rapidly quenched master alloy.

Influence of crystallization conditions on the tensile properties of radiation crosslinked, vitamin E stabilized UHMWPE

Radiation crosslinking for ultra-high molecular weight polyethylene results in improved wear resistance but a reduction in mechanical properties. Incorporation of vitamin E has been known to decrease the rate of oxidative degradation occurring through radiation crosslinking and prevents the need for post-irradiation melting with subsequent loss of crystallinity. In this study, we aimed to determine the effect of thermal treatments prior to crosslinking on the morphology and tensile properties of vitamin-E-containing polyethylene. Vitamin-E-blended polyethylene was melted and subsequently quenched in ice water in order to induce high rate crystallization. A second group was additionally annealed at 126°C following quenching and all samples were irradiated using electron beam radiation to a dose of 100kGy. The morphology of control, quenched and quench-annealed polyethylene was characterized using small angle x-ray scattering and differential scanning calorimetry. Tensile properties of these polyethylenes were measured before and after radiation crosslinking with equilibrium swelling experiments performed to assess the crosslink density of irradiated samples. This study shows how the tensile properties of polyethylene can be enhanced by varying thermal treatments prior to crosslinking; and thus how it may be possible to offset the reduction in tensile properties afforded by the crosslinking process.

Influence of Crystallization Conditions on Relaxation Properties of Polymer Near‐Surface Layers

AbstractRelaxation properties of polymer near‐surface layers were investigated with the help of thermoluminescent method using Nanoluminograph (PlasmaChem GMbH, Germany). The gel‐ and melt‐crystallized films from PE of different molecular weight were studied. The light sum of thermoluminescence in the temperature range of various relaxation transitions was compared. It is found that it is primarily controlled by the type of morphology forming during crystallization and the arrangement of the structural units on a surface. The glass transition temperature in near‐surface layers appeared to be lower that that in the bulk. Bulk glass transition temperature was determined by radiothermoluminescence, DMA and DSC techniques.

The influence of crystallization conditions on the onset of dendritic growth of calcium carbonate

AbstractUnderstanding the crystallization of calcium carbonate is relevant in numerous fields like biomineralization, geology and industrial applications where calcium carbonate forms. In order to enhance the knowledge about the formation of calcium carbonate with focus on the vaterite polymorph, in this work calcium carbonate has been crystallized in aqueous solutions at temperatures from 5 °C to 90 °C. Special attention has been directed to higher temperatures for which the effect of the initial supersaturation on the resulting crystal morphologies and the onset of dendritic growth have been studied. In analogy to snow crystal formation, it has been found that in a certain temperature range hexagonal plate‐like crystals form at low supersaturation whereas dendritic patterns start to appear at higher supersaturation. The symmetrical branches characteristic for dendritic growth get less pronounced as the temperature is decreased. The results reported here related to the interdependence between supersaturation, crystal morphology and growth mechanisms, can be used in future works to predict particle formation and to design crystal architectures. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Influence of Crystallization Conditions on the Growth of Polycrystalline Particles

AbstractThe effect of initial supersaturation and temperature on crystal morphology below and above the threshold for the onset of spherulitic growth has been compared for calcium carbonate, L‐glutamic acid, and an aromatic amine derivative in aqueous systems. For the vaterite polymorph of calcium carbonate is has also been documented how spherulites (polycrystalline particles) develop with time in a solvent mixture of water and monoethylene glycol. For the three studied substances, the temperature was found to have different effects on the compactness of the crystals. The influence of supersaturation on the onset of spherulitic growth and particle morphology, however, bears striking similarities for the investigated substances. While monocrystalline particles are found at low supersaturation, polycrystalline particles form with increasing degree of branching when supersaturation is increased.

Influence of crystallization conditions on crystal morphology and size of CaCO3 and their effect on pressure filtration

AbstractThe temperature, supersaturation, seeding procedure, stirring speed and other parameters were varied in crystallization experiments of calcium carbonate performed in aqueous solutions to control size, particle size distribution and morphology of the particles. Particle size information was obtained by focused beam reflectance measurements and the Coulter Counter Multisizer. Crystals of CaCO3 could be crystallized as spherical polycrystalline particles of the vaterite polymorph, needle‐like crystals of aragonite and both cube‐like and novel plate‐like crystals of calcite. Filtration experiments for calcium carbonate, performed at a constant pressure difference of 2 bar, show that spherical particles with a larger size show better filterability and that spheres with a wider size distribution, as a result of high supersaturation and nucleation, give higher average cake resistance values. Comparing different particle morphologies, plate‐like crystals and needle‐like crystals show worse filterability than spherical particles and cube‐like particles. © 2011 American Institute of Chemical Engineers AIChE J, 2012

The influence of crystallization conditions on the morphology of lactose intended for use as a carrier for dry powder aerosols.

Lactose has been widely used as a carrier for inhalation aerosols. The carrier morphology is believed to affect the delivery of the drug. The aim of this study was to investigate the effects of crystallization conditions on the morphology of alpha-lactose monohydrate intended for use as the carrier for dry powder aerosols. The crystallization of lactose was carried out from aqueous solutions at different supersaturations, temperatures, different stages of crystallization and in the presence of different water-miscible organic solvents. The majority of lactose crystals were found to be either tomahawk-shaped or pyramidal after crystallization at an initial lactose concentration between 33-43% w/w, but these became prismatic if the lactose concentration was increased to 50% w/w. A further increase in the lactose concentration to 60% w/w led to the preparation of elongated cuboidal crystals. Higher initial lactose concentrations tended to result in the crystallization of more elongated particles. Crystallization at 40 degrees C was shown to prepare lactose crystals with a more regular shape and a smoother surface than those crystallized at 0 degrees C. Lactose particles generated during the later stage of crystallization were found to be more regular in shape with a smoother surface than those prepared in the earlier stage. The addition of 10% (v/v) methanol or ethanol or acetone to the mother liquor increased the growth rate of lactose particles whereas addition of propanol or glycerine inhibited the rate of crystal growth. Lactose crystals prepared in the presence of glycerine were more regularly shaped with a smoother surface than those prepared in the presence of ethanol or acetone. All the resultant crystals were shown to comprise alpha-lactose monohydrate. Lactose crystals could be prepared with a precisely defined morphology by means of carefully controlling the crystallization conditions.

Influence of Crystallization Conditions on Rheology and Microstructure of Dense Suspensions of Crystals of Eflucimibe

AbstractThe crystallization process of eflucimibe, a new ACAT inhibitor, was carried out in a mixture of two solvents, ethanol and n‐heptane, by cooling. During the process, as the volume fraction of crystals was raised, the suspension went towards a very structured gel‐like network. This phenomenon acts as a brake to the extrapolation of the process. Experiments were carried out in a glass double‐jacketed 750 mL reactor in a LABMAX controlled system. At the end of the crystallization, rheological flow characteristics at constant ambient temperature were determined. The samples behave like a plastic fluid. The evolution of the elastic and viscous moduli as a function of the applied strain for a given oscillation frequency was measured. The results showed that the variation of the elastic modulus with particle concentration follows a power law. It was shown that for particle concentration higher than 2 % (volume fraction) needle‐like growing crystals form a network in which solvent is trapped.

Influence of Crystallization Conditions in Production of Citric Acid on the Properties of Forming Calcium Sulfate

The boundaries of phase equilibria involving calcium sulfate crystal hydrates in a citric acid solution were calculated. The influence exerted by an excess amount of sulfuric acid on the stability of calcium sulfate crystal hydrates in citric acid solutions was considered. The possibility of achieving a hemihydrate mode of citric acid extraction from calcium citrate was studied.

Influence of crystallization conditions on the mechanism and rate of crystal growth of potassium sulphate

AbstractGrowth rate of potassium sulfate crystals was studied in a fluidized bed crystallizer. Higher growth rates were observed at larger bed heights. Larger crystals grow faster than smaller size crystals due to the changed fluid dynamics. The growth rate was found to be very sensitive to the pH value of the solution. The growth rate increases with increasing the pH value and the increase of growth in the acidic medium is faster than in the basic medium. The presence of small amounts of Cr3+ ions reduces the growth rate of potassium sulfate dramatically. The presence of Cr3+ ions lowers the saturation temperature and increases the width of the metastable zone, i.e. shifts the metastability of the solution to be at lower level of supersaturation.

Influence of the crystallization conditions on the morphology of the contact layer of polyethylene crystallized on graphite: Atomic force microscopy studies

AbstractThe influence of crystallization conditions on the morphology of the contact layer of high‐density polyethylene crystallized on graphite has been investigated. The characteristic morphology of the polyethylene contact layer consists of striated, ribbonlike structures organized in domains in which the striations follow the same direction. The directions in different domains reflect the threefold symmetry of the graphite lattice. From the dependence of the width of ribbons on the crystallization conditions (i.e., the cooling rate and annealing), it has been concluded that the polymer chain is aligned parallel to the striation directions and that the ribbon width corresponds to the lamellar width. Therefore, the lamellar width in the contact layer (60 and 80 nm for cooling rates of 10 and 0.2°/min, respectively) is considerably bigger than in the bulk (ca. 26 nm). In addition, the chain orientation can be uniform over large areas, but the domain orientation can be disturbed by the presence of pits only one atomic layer deep (0.335 nm) if they are formed on the graphite surface. These results show the great importance of the nanostructure of the support for polymer chain alignment and epitaxial crystallization of polymers. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1329–1336, 2002

Influence of crystallization conditions on the crystalline transformation behavior of nylon 10 14

Three kinds of nylon 10 14 crystals with different perfections were prepared under various crystallization conditions. The Brill transition behavior of these nylon 10 14 crystals was investigated by variable-temperature X-ray diffraction. It was found that the crystallization conditions influence the Brill transition temperature greatly. The Brill transition temperature of the lamellar crystals grown from dilute solution is so high that no Brill transition temperature can be observed before melting. However, for crystals postannealed at 125 °C, the Brill transition temperature is as low as 130 °C. The results show that the Brill transition behavior of nylons is strongly dependent on the crystallization conditions, for example, the perfections of the crystals.