Initial Crystal Phase Research Articles

Nanocrystals with metastable high-pressure phases under ambient conditions.

The ambient metastability of the rock-salt phase in well-defined model systems comprising nanospheres or nanorods of cadmium selenide, cadmium sulfide, or both was investigated as a function of composition, initial crystal phase, particle structure, shape, surface functionalization, and ordering level of their assemblies. Our experiments show that these nanocrystal systems exhibit ligand-tailorable reversibility in the rock salt-to-zinc blende solid-phase transformation. Interparticle sintering was used to engineer kinetic barriers in the phase transformation to produce ambient-pressure metastable rock-salt structures in a controllable manner. Interconnected nanocrystal networks were identified as an essential structure that hosted metastable high-energy phases at ambient conditions. These findings suggest general rules for transformation-barrier engineering that are useful in the rational design of next-generation materials.

Effect of the annealing temperature of multi-elemental oxides (FeCoNiCuZn)yOx on the electrocatalytic hydrogenation of nitrobenzene at room temperature

Nitrobenzene (NB) in effluent waters is a serious and complicated environmental problem due to its environmental toxicity and health hazard. In this study, the selective electrocatalytic hydrogenation of NB to aniline (AN) was studied using multi-elemental oxides (Fe0.3Co0.05Ni0.05Cu0.3Zn0.2)O, synthesized via urea hydrolysis method and heat-treated at different temperatures (300–1000 °C). The synthetic route chosen allowed the obtention of multi-phase materials and high entropy oxide (HEO) conditions, to be used as electrocatalysts, and to evaluate the effect of the crystal structure on the catalytic performance. The catalysts were characterized using physical methods scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and X-ray diffraction. The electrochemical properties were evaluated using cyclic voltammetry, linear sweep voltammetry, electrochemical impedance spectroscopy, and chronoamperometry. The polycrystalline structure obtained at 500 °C (HEO500) showed the highest selectivity (above 45%), while the more crystalline catalyst (HEO800) exhibited the highest conversion (30%) and kinetic constant (k = 9.4 × 10−3 s−1). The catalytic performance of the materials demonstrated a strong correlation with the microstructure and surface properties, like crystallite size, initial crystal phase, oxygen vacancies concentration, and redox properties. All the HEO materials exhibited a better catalytic performance than the commercial benchmark, Pt/C 5% wt catalyst, which showed no selectivity towards aniline and low conversion in 1.0 M KOH solution at -1.4 V vs Ag/AgCl. This improvement was attributed to the increase in the surface concentration of hydrogen found on the HEOs. These results highlight the importance of the surface defects on the activity and selectivity of multi-step surface-dependent catalytic hydrogenation reactions; and provide fundamental information on the importance of carefully choosing the synthesis and calcination conditions.

Image-based dissolution analysis for tracking the surface stability of amorphous powders.

Poor solubility of crystalline drugs can be overcome by amorphization – the production of high-energy disordered solid with improved solubility. However, the improved solubility comes at a cost of reduced stability; amorphous drugs are prone to recrystallization. Because of recrystallization, the initial solubility enhancement is eventually lost. Therefore, it is important to understand the recrystallization process during storage of amorphous materials and its impact on dissolution/solubility. Here, we demonstrate the use of image-based single-particle analysis (SPA) to consistently monitor the solubility of an amorphous indomethacin sample over time. The results are compared to the XRPD signal of the same sample. For the sample stored at 22 °C/23% relative humidity (RH), full crystallinity as indicated by XRPD was reached around day 40, whereas a solubility corresponding to that of the γ crystalline form was measured with SPA at day 25. For the sample stored at 22 °C/75% RH, the XRPD signal indicated a rapid initial phase of crystallization. However, the sample failed to fully crystallize in 80 days. With SPA, solubility slightly above that of the crystalline γ form was measured already on the second day. To conclude, the solubility measured with SPA directly reflects the solid-state changes occurring on the particle surface. Therefore, it can provide vital information – in a straightforward manner while requiring only minuscule sample amounts – for understanding the effect of storage conditions on the dissolution/solubility of amorphous materials, especially important in pharmaceutical science.

Effects of initial crystal structure of Fe2O3 and Mn promoter on effective active phase for syngas to light olefins

Although it is generally acknowledged that iron carbides are the active phase in Fischer-Tropsch synthesis (FTS), adjusting the formation of active phase and catalytic performance via the initial crystal structure of iron oxides has never been studied. Herein, we take one-dimensional pure phase α-Fe2O3 and γ-Fe2O3 nonporous nanorods to explore the effects of initial crystal phase of Fe2O3 on both formation of active phase and corresponding catalytic performance, in which the influence of diffusion limitation on selectivity can be ignored. In situ characterizations uncovered that the formation of iron carbides with high selectivity of light olefins strongly depends on the initial crystal phase of iron oxide and its induced metal-promoter interaction. Responding to the morphology effect and crystallographic phase effect, Mn located on surface of γ-Fe2O3 nanorods exhibit a low oxidation state due to a strong Fe-Mn interaction. This interaction was beneficial to the formation of C-poor iron carbide species at the metal-promoter interface during carburization. Hence, outstanding selectivity for light olefins (61.2%) was achieved on 0.5 Mn/γ-Fe2O3 nanorods catalyst at a CO conversion of 55.1% under industrially relevant conditions (320 °C, 1 MPa, H2/CO ratio of 1, and W/F = 5 gcat h mol−1). This finding enriches the fundamental understanding of active phase evolution and promoter effect in STO process and may guide the design of a catalyst with high selectivity.

The Notion of Hierarchy Under the Light of the Founding Fathers' Magna Opera: The Ideological Structure of the Early Jus Gentium and its Implications on the Current Debate About the Order of Values and Normative Hierarchy

As Carl Schmitt has aptly observed all great political concepts possess a certain theological attribute, connotation or origin. By applying the latter doctrine of political theology on international normativity, the author in the present paper attempts to investigate, re-discover and highlight the interdependence between the early theological values and pre-data of the doctrina christiana, and the initial phase of crystallization of international legal rules via the works of the Great Founders of the scientific discipline in question. Based on this evident interplay between theological concepts of the past and the consolidation of International Law's early doctrines, an attempt is made to discern certain fundamental principles, common to the works of all the Founders, acting as constituent pillars of the international system, establishing a definite hierarchical relation between rules, principles and ultimately rights of International Law's subjects. Furthermore, after reassessing concepts such as the vitorian “totus orbis” and the ideal of the “civitas gentium maxima”, the paper proceeds to reinterpret the function of the early visions‟ enforcement mechanisms aiming at the protection of the fundamental pillars of the international juridical cosmos, a point of paramount importance utilized to confirm the existence of a well-ordered hierarchy between the norms, principles, and rights within the Founders‟ system. Upon establishing that normative hierarchy in the original visions was based on the higher ontological importance of certain values, necessary for the perpetuation of the system, this proposition is scrutinized so as to attest whether it remains pertinent up to our days of multilevel interdependence and variable international normativity. After drawing some conclusions on the influence of the theological concepts and the doctrinal methods of theology involved in the formation of International Law, the current problematic of normative hierarchy is addressed. Finally, the essay concludes with remarks concerning the future of International Law's orientation regarding the need for a solid (or else) hierarchy, the prospect of further verticalization and a kelsenian exegesis of international adjudication vis-a-vis international community's fundamental norms.

Geochemistry and Petrography of Alkaline rocks from Monte Santo Alkaline Intrusive Suite, Western Araguaia Belt, Tocantins State, Brazil

The Monte Santo Alkaline Intrusive Suite (MSAIS) is an association syenite foid, nepheline syenite and syenite. The MSAIS rocks are intruded in metapelites of the Rio do Coco meta-volcanic-sedi- mentary Sequence and are abundant pegmathoid veins cutting all of them. The mineral paragenesis is represented by aegirina, arfvedsonite, albite and nepheline, crystallized during the initial phase of crystallization. A late magmatic phase show nepheline, perthite, calcite and biotite, and a hydrothermal phase allowed for the formation of cancrinite, sodalite, analcime and natrolita associated with altered nepheline. The geochemical analyses showed metaluminous and medium to high potassium characteristics, being classified as miaskitic rocks, according to agpaicity and the Na + K > 1/6Si indexes. However, the mineralogical assemblage suggests a low to medium agpaitic composition, which can be related to a transition from miaskitic to agpaitic crystallization regime. The rare earth elements showed depletion in heavy rare earth and a strong negative Eu anomaly and enrichments in the some lithophile elements, suggesting a differentiated pattern later, which can be associated to metasomatic alterations.

The pre-eruption conditions for explosive eruptions at Merapi volcano as revealed by crystal texture and mineralogy

We analyze the textures and mineralogy of Merapi tephra generated during explosive VEI 3–4 eruptions over the past 2000years, and compare these data with those observed for Merapi dome and flow lavas. We find that the Merapi pumiceous tephra and lava textures differ significantly with respect to small-size crystal populations, but that phenocryst textures are generally similar. A similar initial phase of crystallization is indicated for tephras and lavas in mid-crustal (>10km depth) reservoirs. Subsequent textural differences are mainly affected by ascent rate and degassing during ascent, and, for dome lavas, with temporary storage in shallower reservoirs. These differences also correspond to different eruptive styles. Our analyses include study of pumices, lava, and breadcrust-bomb samples, including samples from some of the most recent explosive episodes prior to the 2010 eruption. Textural analyses of youthful breadcrust bomb samples yield insights on one type of transition between effusive and explosive eruptive styles, involving pressure build-up under a degassed crystalline shallow-conduit plug. In general, comparison of the crystal size distributions and calculated residence times among the effusive and explosive eruptive styles suggests that the two main magma-product types resided for similar lengths of time in a mid-crustal reservoir, before ascending toward the surface and either erupting explosively (tephra), or stagnating in a shallow magma chamber prior to extrusion (lava). The interpretation is supported by the occurrences of amphibole in pristine condition in tephra and in altered state in lava. Finally the 1872 and 2010 explosive eruptions are examined and compared with others over the past three millennia. The 2010 bulk-rock compositions overlap with products of other major explosive Merapi eruptions, such as the Ngrangkah, Tegalsruni, Temusari, and Kepuharjo tephras. The 2010 products show a gradational late-stage mafic enrichment, dissimilar to 1872 which showed little (<1%) compositional variation, but similar to the Ngrangkah, Tegalsruni, and Temusari tephras. Such variation implies conventional withdrawal from a zoned magma chamber, with the more-evolved products being erupted first.

New concept of solute distribution around a diffusive crystal-solution interface of a binary Lennard-Jones mixture from the viewpoint of molecular dynamics

Directional crystallization from a binary mixture was performed by pseudo-NpT ensemble molecular dynamics. The initial crystal phase having a face-centered-cubic (fcc) structure grew toward the whole cell according to the temperature gradient in the universal cell. The growing crystal phase was not planar even though the solute molecules grew in two-dimensional coordinates because the solvent molecules disturbed the crystallization of the solute molecules at the diffusive crystal-solution interface. This represented the essential phenomenon of solute distribution during crystallization. Consequently, the growing crystal phase still contained solvent molecules having a liquid structure. The time change of the solute composition in the early phase of crystal growth showed an increase in solute composition as the time step proceeded. The resulting solute composition in this early phase was considered at different temperature gradients in the universal cell and it increased as the temperature of the initial crystal-solution interface increased. A new distribution coefficient model was proposed as a function of the difference between the local solute composition and bulk solute composition in the solution around the crystal-solution interface. The impurity-solvent distribution coefficient could be represented by the new model for faster growth of the lower temperature's initial interface. As regards a better distribution coefficient, there was found to be a very dilute solution phase over the crystal phase. The new variable "distribution rate" instead of the ambiguous variable "growth rate" was considered as a function of temperature gradient in the universal cell.

Using in situ synchrotron radiation wide angle X-ray scattering (WAXS) to study CaCO3 scale formation at ambient and elevated temperature

The formation of calcium carbonate mineral scale is a persistent and expensive problem in oil and gas production, water piping systems, power generator, and batch precipitation. The aim of this paper is to further the understanding of scale formation and inhibition by in situ probing of crystal growth by synchrotron radiation wide angle X-ray scattering (WAXS) at ambient and elevated temperature. This novel technique enables in situ study of mineral scale formation and inhibition and as such, information on the nucleation and growth processes are accessible. This technique studies bulk precipitation and surface deposition in the same system and will be of great benefit to the understanding of an industrial scaling system. It offers an exciting prospect for the study of scaling. It has been shown that the nucleation and growth of various calcareous polymorphs and their individual crystal planes can be followed in real-time and from this the following conclusions are reached. The process of scale deposition on the surface can be divided into an unstable phase and a stable phase. The initial phase of crystallization of calcium carbonate is characterized by instability with individual planes from various vaterite and aragonite polymorphs emerging and subsequently disappearing under the hydrodynamic conditions. After the initial unstable phase, various calcium carbonate crystal planes adhere on the surface and then grow on the surface. At 25 degrees C, the main plane of surface deposit is calcite and a strong (104) peak is detected. The other calcite planes (102), (006), (110) (113) and (202) are hardly detectable under this condition. At 80 degrees C, the main planes in the surface deposit are the (104), (113) and (110) planes of calcite. Stable planes of vaterite and aragonite are also observed. This paper will discuss how surface scale evolves--exploring the power of the synchrotron in situ methodology.

Isothermal Crystallization of Nylon-6/Montmorillonite Nanocomposites

The isothermal crystallization of in-situ-polymerized and melt-processed nylon-6/montmorillonite nanocomposites was studied by simultaneous small- and wide-angle X-ray scattering using synchrotron radiation. The isothermal crystallization rates, in the nucleation-controlled regime, for the nanocomposites are significantly faster than that for the pristine nylon-6 and suggest that the layered silicates act as nucleating centers. Within the experimental resolution, the initial crystal phase formed between 185 and 205 °C in the presence of the layered silicate is the metastable γ-phase, whereas the α-phase develops in the pristine nylon-6 at comparable temperatures. Additionally, the strong silicate−polymer interactions present in the in-situ-polymerized nanocomposites alter the crystallization process, creating a much weaker temperature dependence for the crystallization kinetics. Finally, the presence of well-dispersed layered silicates significantly disrupts the development of lamellar structure but does not alter the overall amounts of crystallinity.

Calcium oxalate crystallization kinetics studied by oxalate-induced turbidity in fresh human urine and artificial urine

We have studied the kinetics of oxalate-induced turbidity in fresh human urine and artificial urine. Assays are performed in 96-well plates, which allows many oxalate concentrations to be studied, repeatedly, in a short time. The metastable limit is defined in terms of the lowest oxalate concentration that gives a rate of change of attenuance significantly greater than the control. Interpretation of rates above this limit is based on ln/ln plots of initial rates against added oxalate concentration. This approach has a good theoretical basis, is well supported by our results and gives a turbidity rate index that is related to the product of the growth rate constant and a factor relating to the number and characteristics of the heteronuclei responsible for initiation of crystallization. This interpretation is posited upon the assumptions that second-order crystallization kinetics occur in unseeded urine when supersaturation exceeds the metastable limit and that aggregation during the initial phase of crystallization does not significantly contribute to changes in turbidity. Metastable limits of urine from healthy volunteers corresponded to a calcium oxalate supersaturation ratio of approx. 10. The turbidity rate index was higher in human urine than in artificial urine. The metastable limit, based on either oxalate concentration or supersaturation, for induction of calcium oxalate crystallization in normal human urine is higher than is likely to be found in normal subjects in vivo. The shape of the relationship between the metastable limit (based on oxalate concentration) and calcium concentration emphasizes the benefit of achieving a low urine calcium concentration. Comparison of the turbidity rate indices for human and artificial urine suggests that the role of nucleation promoters is more dominant than that of growth inhibitors.

Structure of nylon 6-iodine complexes and their drawability by solid-state coextrusion

The structure and drawability of nylon 6-iodine complexes, prepared from selected concentrations of I2/KI aqueous solution, have been investigated. Four steps of complex formation have been deduced on systematically increasing the concentration of I2/KI solutions in contact with films of nylon 6. Inferences from the results of x-ray diffraction and thermal analyses are the following: (1) At the lowest concentration, the initial crystal phase of nylon 6 is maintained, with the chains merely being displaced by I− 3 ions, probably lying perpendicular to the nylon 6 chain axis. (2) At intermediate concentration, the crystal consists of two different phases; one is the crystal complex with the longer intermolecular distance caused by I − 3 the other is the original nylon 6 crystal. The complexed crystal phase develops into two subphases. These are surmised to be complexed with the I − 3 ions and I − 5 ions lying parallel to the chain axis. (3) At still higher KI3 concentration, the crystal may be complexed with the 1− 5 ions. The ultimate plasticized crystal is of only one structural phase, likely complexed with the I − 5 ions. The drawability of complexed nylon 6 is affected sensitively by its structure. The drawing was done by solid-state coextrusion with a high-density polyethylene billet at a temperature close to the highest melting point of the complex. Nylon 6 film which had contained the two subphases resulted in a structure with the highest drawability, providing an uniaxial draw ratio of 48.

Glass microstructure and initial crystallization of Pb 0.32Bi 1.68Sr 1.75Ca 2Cu 3O x

Microstructure and phase development of as-quenched and annealed samples of the glass of composition Pb 0.32Bi 1.68Sr 1.75Ca 2Cu 3O x have been studied. Evidence for liquid-liquid phase separation during quenching was found The microstructure of this glass during the early stage of crystallization is similar to that found for Bi 2Sr 2CaCu 2O x (2212) glass. The first phase that crystallizes on annealing at low temperatures appears to be Cu 2O. In further heat treatments the sequential crystallization of the R-phase of (Pb yBi 2− y )Sr 2CuO x (‘2201’) composition and the Pb yBi 2−ySr 2CaCu 2O x (‘2212’) phase was found, in agreement with other studies. Phase separation determines the initial crystal phase and the development of the superconducting phases. Phase separation observed in this glass points to the possibility that immiscibility may be a common feature of a wide range of Bi(or PbBi)SrCaCuO compositions.

Mechanism of Crystallization of Hydrocortisone by Ultrasonic Irradiation

Reproducible, reduced crystal size distributions resulted from insonating a supersaturated solution, whose background particle count is controlled, at a fixed temperature. The crystallization temperature of the insonated and uninsonated samples was dependent on the number of heterogeneous nuclei present. The ultrasonic energy used in this study was in excess of the amount required to reduce the particle size. Ultrasound acted in the initial phase of crystallization. Ultrasound is believed to act by eroding, shattering, or in some way disrupting nuclei that form in a normal manner.