Early Stages Of Crystallization Research Articles

A new crystallization pattern of nested tetrahedral lamellar structure for the face-centered cubic metals with low stacking fault energy

It's well known that the lamellar (LAM) and five-fold-twinning (FFT) structures are two primary patterns during the early crystallization stage of FCC (face-centered cubic) metals. In this letter, we add a new third one, i.e. a nested tetrahedral lamellar (NTL) structure. In common with LAM and FFT, NTL is also a mixture of FCC and HCP (hexagonal close-packed). Differently, NTL has four tetrahedral growth orientations corresponding to four cellular bulges and a central core of tetrahedral shells nested one-by-one. This NTL acts also as the precursor of FFT and it has great differences in growth morphology and kinetics with LAM.

Polymorphic homocrystallization and phase behavior of high-molecular-weight Poly(L-lactic acid)/poly(D-lactic acid) racemic mixture with intentionally enhanced stereocomplexation ability via miscible blending

Promoting stereocomplex (SC) crystallizability is prerequisite for preparing the highly stereocomplexed polymer materials with better physical property. However, the intentionally enhanced SC crystallizability can exert severe effects on the homocrystallization and thus lead to the more complicated crystallization kinetics and polymorphic structure in stereocomplexable polymers. To elucidate the unique crystallization behavior of the stereocomplexable polymers with intentionally enhanced SC crystallizability, we choose the high-molecular-molecular (HMW) racemic poly(L-lactic acid)/poly(D-lactic acid) (PLLA/PDLA) mixture blended with poly(ethylene glycol) (PEG) as the model system. Intriguingly, incorporation of small amount of PEG leads to the fractionated crystallization kinetics (multiple crystallization peaks) and the formation of unique β-form homocrystals (HCs) of PLLA/PDLA component, different from the common α/α′-HCs generated in usual HMW PLLA/PDLA blends. Formation of β-HCs is preferred in the PLLA/PDLA/PEG blends with the PEG mass fraction of 2%–5% at low crystallization temperature (80–110 °C). We propose that the β-HC formation stems from the constrained effects of precedingly-formed SCs in the early stage of crystallization; such effects become more significant in PLLA/PDLA/PEG blends due to the enhanced SC crystallizability. This study would be essential to understand the unique crystallization kinetics and polymorphic structure of HMW PLLA/PDLA mixture with intentionally enhanced SC crystallizability.

Amorphous-microcrystal combined manganese oxides for efficiently catalytic combustion of VOCs

Catalytic combustion is an efficient technology for the volatile organic compounds (VOCs) elimination. The effect of crystalline integrity on catalytic combustion activity over MnOx has been investigated, and the amorphous MnOx with partial crystallization (Crystallinity = 6 %) shown higher activity than pure amorphous and intact crystal MnOx (Crystallinity = 1 % and 100 %, respectively). Firstly, amorphous MnOx has been prepared by glucose reduction method and the crystalline integrity has been adjusted by tuning the hydrothermal temperature and time. Besides, the various characterizations illustrated that the appropriate crystalline integrity can result in enhancing catalytic combustion reactivity due to the synergistic impact of amorphous and crystalline phase. The amorphous phase has abundant structure defects and unsaturated coordination bonds, which enhances adsorption ability of catalyst. Simultaneously, the crystalline phase drives electrons migration, which favors the adsorption and activation of oxygen and speeds up the redox reaction rate. The synergy between amorphous and crystal phase gives catalyst the most of dominant adsorbed oxygen species, Mn4+ species and the strongest oxygen supply capacity. Furthermore, mesoporous structures were formed in the early stage of crystallization of amorphous MnOx which gave the manganese oxides the largest specific surface area (192 m2/g). This work shows a novel strategy to design and prepare efficient non-precious metal catalysts for VOCs catalytic combustion.

A New Crystallization Pattern of Nested Tetrahedral Lamellar Structure for the Face-Centered Cubic Metals with Low Stacking Fault Energy

It's well known that the lamellar (LAM) and five-fold-twinning (FFT) structures are two primary patterns during the early crystallization stage of FCC (face-centered cubic) metals. In this letter, we add a new third one, i.e. a nested tetrahedral lamellar(NTL) structure. In common with LAM and FFT, NTL is also a mixture of FCC and HCP (hexagonal close-packed). Differently, NTL has four tetrahedral growth orientations corresponding to four cellular bulges and a central core of tetrahedral shells nested one-by-one. This NTL acts also as the precursor of FFT and has great differences in growth morphology and kinetics with LAM.

Improving Retention Rate of LiNi0.8Co0.15Al0.05O2 Cathode Material Synthesized Using Glycerol Solvent

Abstract This paper reports an enhanced retention rate of LiNi0.8Co0.15Al0.05O2 (NCA) cathode material for Li-ion batteries synthesized with glycerol as a solvent and a reactant. Glycerol is a fuel and the heat released during synthesis could be considered as an additional free energy source for material preparation. Scanning electron microscopy (SEM) images and X-ray diffraction (XRD) results show an early stage of crystallization of the produced powder. Early crystallization in the NCA material at low temperatures was believed to hinder cationic mixing that would occur at higher temperatures during calcination. As a result, cycling of the NCA material shows a very stable capacity. The NCA material displays 97% capacity retention at 1C (1C = 200 mA/g) after 50 cycles, 87.6% at 0.3C after 100 cycles, and 93.6% at 0.1C after 70 cycles, which are better than those reported previously.

High mobility of lattice molecules and defects during the early stage of protein crystallization.

Protein crystals are expected to be useful not only for their molecular structure analysis but also as functional materials due to their unique properties. Although the generation and the propagation of defects during crystallization play critical roles in the final properties of protein crystals, the dynamics of these processes are poorly understood. By time-resolved liquid-cell transmission electron microscopy, we observed that nanosized crystal defects are surprisingly mobile during the early stages of the crystallization of a lysozyme as a model protein. This highly dynamic behavior of defects reveals that the lattice molecules are mobile throughout the crystal structure. Moreover, the disappearance of the defects indicated that intermolecular bonds can break and reform rapidly with little energetic cost, as reported in theoretical studies. All these findings are in marked contrast to the generally accepted notion that crystal lattices are rigid with very limited mobility of individual lattice molecules.

Nanohydroxyapatite and its textures as potential carriers of promising short-lived lead isotopes

The possibility of sorption and cocrystallization binding of lead(n) with nanohydroxyapatite (HAP) acting as a potential carrier of short-lived lead radionuclides 211,212Pb was studied. The peculiarities of the kinetics were revealed, and the isotherms of sorption of lead ions on hydroxyapatite with different textures were constructed. A multistage sorption mechanism accompanied by a change in the structure and morphology of the sorbent was studied. The possibility of the formation of a new phase (hydroxypyromorphite) of lead during the sorption and cocrystallization interaction was shown. The introduction of lead into the synthesis of HAP at the early stages of crystallization exerts the highest effect on its morphology and structure. The optimization of the formation of the HAP-Pb composite over the course of the process will make it possible to use the short-lived 211Pb radionuclide in subsequent experiments.

BaTiO3 nanotubes by co-axial electrospinning: Rheological and microstructural investigations

BaTiO3 (BT) nanotubes (NTs) were synthesized using a co-axial electrospinning process. BT precursor/PVP-ethanol and heavy mineral oil were used as the shell solution and core liquid, respectively. The rheological studies indicated that NTs could be formed by a stable jet at a range of viscosities of the shell solution. Due to the shear thinning behavior of the shell solutions, their actual viscosity values at the time of jet formation will be lower than the viscosity of the core liquid. The morphology of the obtained NTs was strongly influenced by the viscosity of the shell solution. By increasing the concentration of BT precursor, the morphology of the BT NTs was changed from porous to more dense structure. XRD analysis revealed that the crystallization of BT NTs occurs at 550–630 °C calcination temperature range. Raman spectra confirmed the presence of tetragonal phase at early stage of crystallization.

Multi-scale development of a stratiform chromite ore body at the base of the dunitic mantle-crust transition zone (Maqsad diapir, Oman ophiolite): The role of repeated melt and fluid influxes

A stratiform chromite ore body crops out in the lower part of the dunitic mantle-crust transition zone (DTZ) that developed at the top of a mantle diapir in the Maqsad area in the Oman ophiolite. It is made of layers ranging in thickness from a few mm to a maximum of 3 m, and in modal composition from massive to antinodular and disseminated ore. The ore body is about 50 m thick and its lateral extent does not exceed several hundred meters. The layering dips gently to the southeast, parallel to that of the overlying gabbroic cumulates. The chromite composition is typical of a MORB kindred - moderate XCr (100 × Cr/(Cr + Al) atomic ratio), ranging from 48 to 60, and relatively high TiO2 content, ranging from about 0.3 to 0.5 wt% -, a characteristic shared by most lithologies issued from the igneous activity of the Maqsad diapir. The silicate matrix is essentially made of slightly serpentinized olivine with minor clinopyroxene and rare pargasitic amphibole, orthopyroxene and garnet. This strongly contrasts with the nature of the mineral inclusions mostly made of the assemblage amphibole-orthopyroxene-mica, enclosed in the chromite grains and represented in abundance all along the ore body whatever the ore grade. The inclusions demonstrate the involvement of a silica- and water-rich melt and/or fluid, in addition to MORB, in the early stages of chromite crystallization. The chemical composition of chromite, silicate matrix, together with the one of silicate inclusions display well-defined evolutions vertically along the stratiform chromitite. At the scale of the ore body, the compositional trends are independent of the ore concentration but the major kinks in these trends are well-correlated with levels of magmatic breccias. This shows that abrupt chemical changes can be attributed to sudden melt ± fluids injection events followed mainly by melt-fluid-rock interaction and in a lesser extent by quieter evolution by fractional crystallization. At the thin section scale, second order chemical variations, essentially in the Mg# (100 × Mg/(Mg + Fe2+) atomic ratio) of chromite and Fo of olivine, are clearly attributable to re-equilibration between these two solid phases, possibly in the presence of an interstitial melt/fluid.

Revealing the Effects of the Non-solvent on the Ligand Shell of Nanoparticles and Their Crystallization

When nanoparticles (NPs) are assembled from solution, a common assembly method of choice is either solution destabilization or solvent evaporation technique. The destabilization of the NP solution by non-solvents results in the formation of faceted supercrystals (SCs) while periodic film-like assemblies are typically formed by solvent evaporation. Here, we reveal the effect of non-solvents in washing, dispersing, and crystallizing NPs. Small angle neutron scattering (SANS) is employed for monitoring the ligand shell of NPs in solutions upon introduction of various non-solvents. The SC crystallization process is traced in situ with small-angle X-ray scattering (SAXS), and the structures of the resulting single-crystalline SCs are examined in detail by mapping the reciprocal space using SAXS and wide-angle X-ray scattering. Our study suggests that the relative miscibility of the non-solvent with solvents and ligands determines the solvation and thickness of the ligand shell and thereby the resulting structure of SCs. In the early stage of crystallization, truncated octahedral PbS NPs form SCs with face-centered cubic (fcc) symmetry. In the later stage, the fcc symmetry is preserved in the SC formed by larger (5.60 nm) NPs, but the SC assembled from smaller (4.14 nm) NPs undergoes a phase transition into body-centered cubic (bcc) lattice via Bain transformation, becoming a polycrystalline SC containing three structurally correlated bcc domains and one untransformed fcc domain. Our study provides the detailed understanding of the non-solvent effect that impacts beyond the formation of SCs, enabling the judicious selection of solvent/non-solvent mixtures for NP purification.

Surface crystallization behavior of calcium carbonate in the presence of SMPs secreted by SRB

Surface crystallization of insoluble carbonate poses a serious problem for marine equipment industries which can be seriously influenced by soluble microbial products (SMPs). In Here, the effects of SMPs secreted by sulfate-reducing bacteria on the formation of CaCO3 were investigated by monitoring the crystallization rates and crystal polymorphs and morphologies. When 8.95 mg/L of SMP was added, vaterite and calcite were formed at the initial stage. This could be partly attributed to the formation of SMP and Ca2+ complexes, which provided a nucleation site for calcite. Simultaneously, crystallization by particle attachment promoted the increase of the crystallization mass density in the early stage of crystallization. As the concentration increased to 17.90 mg/L, a larger proportion of vaterite was stabilized. However, a further increase of SMP concentration to 44.76 mg/L did not enhance the proportion of vaterite and a different morphology of elongated calcite was formed. All investigated concentrations of experiments indicate that lower concentrations of SMP promotes calcite nucleation, and higher concentrations inhibit the formation of vaterite. However, an inverse relationship still exists between the concentration of SMP and the amount of surface crystallization of calcium carbonate.

A novel liquid-mediated nucleation mechanism for explosive crystallization in amorphous germanium

We report a novel mechanism for explosive crystallization in amorphous germanium (a-Ge), which operates through liquid-mediated nucleation occurring under extreme thermal gradient conditions. The crystallization kinetics of sputter-deposited films with thicknesses ranging from 30 to 150 nm were characterized using in situ movie-mode dynamic transmission electron microscopy (MM-DTEM). After localized heating from a short laser pulse, explosive liquid phase nucleation (LPN) was observed to occur during the early stage (<2 μs) of crystallization in the thicker (>50 nm) films deposited on silicon nitride substrates. The crystallization front propagated at ∼12–15 m/s and produced nanocrystalline microstructure with ∼50 nm grains. A mechanism involving the existence of a relatively thick (>100 nm) transient liquid layer and a high nucleation rate is proposed to explain the behavior. The key thermodynamic and kinetic features as well as the feasibility of the mechanism are further explored by employing parametric and systematic phase-field modeling and simulations.

Mantle source to near-surface emplacement of enriched and intermediate poikilitic shergottites in Mars

Poikilitic shergottites make up >20% of the current martian meteorite collection, with a total of 27 samples. These meteorites are intrusive gabbroic to lherzolitic rocks and represent igneous materials recording important processes in the martian crust. To further constrain petrogenetic relationships amongst enriched and intermediate poikilitic shergottites, we studied a comprehensive suite of poikilitic shergottites — including four newly recovered samples (Northwest Africa [NWA] 11065, NWA 11043, NWA 10961, NWA 10618) — using bulk rock major- and trace-element compositions, mineral major-element compositions, oxygen fugacity (ƒO2) values, crystallization temperatures, phosphorus maps of olivine grains, and quantitative textural analyses. The characteristic bimodal textures (poikilitic and non-poikilitic textures) of poikilitic shergottites record evolving magmatic conditions at different stages of crystallization. Higher temperatures and more reducing conditions during early-stage crystallization are recorded in the poikilitic textures, while lower temperature and more oxidizing conditions are recorded in the non-poikilitic textures during late-stage crystallization. Oxygen fugacity estimates relative to the quartz-fayalite-magnetite (QFM) buffer for early-stage olivine-pyroxene-spinel assemblages of enriched and intermediate poikilitic shergottites suggest decoupling of ƒO2 and the degree of light rare earth element (LREE)-enrichment (i.e., [La/Yb]CI). An increase in ƒO2 exceeding 1 log unit from poikilitic to non-poikilitic textures implies degassing, with possible auto-oxidation, and/or crustal contamination. Quantitative textural analyses support the emplacement of both enriched and intermediate poikilitic shergottites as various shallow intrusive bodies, as well as a potentially widespread emplacement mechanism responsible for a major lithology of the martian crust. In addition, early assemblages (i.e., pyroxene oikocrysts) of all the poikilitic shergottites likely formed close to the crust-mantle boundary, implying a possible widespread presence of magma staging chambers at these depths. Fractional crystallization and magma storage in these chambers could have possibly resulted in all of the different enriched and intermediate shergottites that have been analyzed from Mars.

Petrology of the enriched poikilitic shergottite Northwest Africa 10169: Insight into the martian interior

The martian meteorite Northwest Africa (NWA) 10169 is classified as a member of the geochemically enriched poikilitic shergottites, based on mineral composition, Lu-Hf and Sm-Nd isotope systematics, and rare earth element (REE) concentrations. Similar to other enriched and intermediate poikilitic shergottites, NWA 10169 is a cumulate rock that exhibits a bimodal texture characterized by large pyroxene oikocrysts (poikilitic texture) surrounded by olivine-rich interstitial material (non-poikilitic texture). Olivine chadacrysts and pyroxene oikocrysts have higher Mg#s (molar Mg/Mg + Fe) than those in the interstitial areas, suggesting that the poikilitic texture represents early-stage crystallization and accumulation, as opposed to late-stage non-poikilitic (i.e., interstitial material) crystallization. Calculated oxygen fugacity values are more reduced (FMQ −2.3 ± 0.2) within the poikilitic regions, and more oxidized (FMQ −1.1 ± 0.1) within the interstitial areas, likely representing auto-oxidation and degassing during magma crystallization. Calculated parental melt compositions using olivine-hosted melt inclusions display a dichotomy between K-poor and K-rich melts, thus possibly indicating mixing of parental melt with K-rich melt. The 176Lu-176Hf crystallization age for NWA 10169 is 167 ± 31 Ma, consistent with the ages reported for other enriched shergottites. Based on the isochron initial 176Hf/177Hf value, the modeled source 176Lu/177Hf composition for NWA 10169 is 0.02748 ± 0.00037, identical within uncertainty to the source compositions of the enriched shergottites Shergotty, Zagami, LAR 06319, NWA 4468, and Roberts Massif (RBT) 04262, suggesting a shared, long-lived geochemical source, and distinct from the source of other enriched shergottites Los Angeles, NWA 856, and NWA 7320. This study reveals that at least two sources are responsible for the enriched shergottites, and that the martian mantle is more heterogeneous than previously thought. Additionally, the enriched shergottites, which share a source with NWA 10169, have consistent crystallization ages and magmatic histories, indicating that a common magmatic system on Mars is likely responsible for the formation of this group.

Geochemistry of Magmatic and Xenocrystic Spinel in the No.30 Kimberlite Pipe (Liaoning Province, North China Craton): Constraints on Diamond Potential

There are two genetic types of spinel (magmatic spinel crystallizing directly from kimberlite magma and xenocrystic spinel derived from mantle xenoliths) in the No.30 kimberlite pipe (Liaoning Province, North China Craton). Their geochemistry is investigated to reveal processes of diamond capture and resorption during kimberlite magmatism to constrain the diamond potential. Magmatic spinels are mostly euhedral to subhedral, 20 to 60 µm in size, and have compositional zones: the cores are classified as chromite with high Cr and Mg contents, and the rims are classified as magnetite with low Cr and high ferric Fe. The compositional trends suggest that magmatic spinel and olivine phenocrysts are crystallized contemporaneously during the early stages of kimberlite crystallization. During this period, temperature (T) and oxygen fugacity (fO2) values calculated at an assumed pressure of 1 GPa are in the range of 994–1274 °C and 1.6–2.4 log fO2 units below the nickel-nickel oxide (NNO) buffer, respectively. The high values of fO2 suggest heavy diamond resorption during kimberlite magmatism. Estimated temperatures of xenocrystic spinel range from 828 to 1394 °C, and their distributions indicate that only a small proportion of xenocrystic spinels are derived from the diamond stabilization field, which suggests a low potential of diamond capture. The low diamond capture and heavy diamond resorption during kimberlite magmatism contributed to the low diamond grade of the No.30 kimberlite.

Temporal and spatial variations in characteristics of fluid inclusions in epizonal magmatic-hydrothermal systems: Applications in exploration for porphyry copper deposits

Temporal and spatial variations in the room temperature phase relations of fluid inclusions serve as a proxy for the PTX properties of fluids associated with emplacement and crystallization of a shallow epizonal intrusion following the “Burnham Model”. Accordingly, during magma ascent, hydrous magmas approach and achieve volatile saturation in response to decreasing pressure (“first boiling”) and/or as a result of cooling and crystallization of anhydrous mineral phases (“second boiling”). In both cases, a magmatic aqueous fluid phase will exsolve from the volatile-saturated silicate melt. Fluid inclusions that trap the exsolved magmatic fluid show predictable room temperature phase relations, compositions, and microthermometric characteristics indicative of the pressure and temperature conditions of the trapping environment.We model aqueous phase equilibria as a function of temperature, pressure, and fluid composition. The composition and phase behavior of the magmatic aqueous fluid phase is adequately approximated by the system H2O-NaCl, and the PVTX characteristics of the magmatic fluids may be determined at any temperature and pressure using phase equilibrium data for this binary system. Then, PVTX data for the system H2O-NaCl are used to predict the room temperature phase relations and homogenization temperatures of fluid inclusions that trap the magmatic fluid at various times and locations in the magmatic-hydrothermal system. The temperature at any position in the system is based on established numerical models of conductive and convective cooling of shallow plutons, and the pressure at any depth is calculated assuming that hydrostatic conditions apply at temperatures <400 °C, and that lithostatic conditions are applicable at higher temperatures.We apply the model to four different stages during the crystallization of a shallow, intermediate composition magma, beginning in the early stages of crystallization and immediately following initial volatile saturation, and ending with complete crystallization of the melt. Mapping the stable fluid phase fields onto a cross-section of the pluton allows us to predict the characteristics of fluid inclusions trapped at various times and locations in the overall system. The fluid inclusion characteristics are predicted along five depth profiles that extend from the center of the pluton to the periphery. The results show good agreement with numerous studies that describe the distribution of halite-bearing, vapor-rich, and two-phase, liquid-rich inclusions in porphyry copper deposits.The results of this study may be applied in exploration for porphyry copper mineralization, as well as other magmatic-hydrothermal porphyry deposits in which the magmatic fluids can be approximated by the system H2O-NaCl. Importantly, halite-bearing fluid inclusions occur only within the pluton and in the immediately surrounding wallrocks, which represents the part of the system that often hosts mineralization. Similarly, fluid inclusion assemblages comprised of only vapor-rich inclusions occur in the near-surface, sub-volcanic part of the system, whereas coexisting halite-bearing and vapor-rich inclusions characterize the deeper parts of the system. The distribution of fluid inclusion types constrains the vertical and lateral position within the overall magmatic-hydrothermal system and, thus, develops vectors towards the magmatic center of the system that is most likely to host economic mineralization.

Effect of water on the phase relations of primitive K-basalts: Implications for high-pressure differentiation in the Phlegraean Volcanic District magmatic system

Phase relations, compositions, and modes of two natural primitive alkaline basalts were determined through experiments performed at 0.8 GPa, temperatures between 1000 and 1310 °C, and nominal water (H2Oi) contents varying from <1 (natural water rock content) to 6 wt%. The two natural samples used as starting material are high-Mg, moderate-K, alkaline basalt scoria clasts (Mg# = 0.68–0.66, Σalkalis = 4.4 wt%) dispersed within the hydromagmatic tuff of the Solchiaro eruption (Procida Island, southern Italy). These samples are considered representative of parental magmas feeding the Phlegraean Volcanic District, which includes the Campi Flegrei caldera and the Procida and Ischia islands. The composition of the experimental phases has been compared with that of natural rocks to constrain the early stages of crystallization of poorly differentiated magmas from the Phlegraean Volcanic District. Our study shows that the liquidus temperature at H2Oi < 1 wt% is ~1300 °C whereas with water contents between 1.5 and 3 wt%, and between 4 and 6 wt%, the apparent liquidus temperature decreases of about 50–100 °C, respectively. Under natural water conditions (<1 wt%), the liquidus phase is clinopyroxene, followed by olivine and Cr-spinel and, then, by plagioclase. The increase of H2O content in the system enhances olivine stability along with clinopyroxene at the liquidus temperature. The 4–6 wt% water bearing experiments show evidence of H2O saturation at 1100 °C, with olivine being replaced by orthopyroxene later joined by pargasitic amphibole and minor amounts of oxide starting from 1080 °C. The composition of glasses in the experiments with low H2Oi content is consistent with the trachybasaltic products of Procida; glasses obtained in the runs with 1.5–3 wt% water resemble the trend formed by the shoshonitic products of Campi Flegrei. The water-saturated experiments produced variably alkali-depleted residual glasses whose composition converges toward the subalkaline field. The compositions of the experimental clinopyroxenes match well those found in the Campi Flegrei products for which we have estimated crystallization conditions from 1140 to 1200 °C of temperature and from 0.6 to 0.9 GPa of pressure (22–33 km). Phase equilibria constraints and clinopyroxene compositions suggest that the parental magmas of Procida likely contained <2 wt% of H2O and were affected by an early stage of fractionation at a depth corresponding to the local Moho (~ 25 km corresponding to ~ 0.8 GPa assuming an average crustal density of 2.8 g/cm3). Based on our results, an early magmatic storage at this level could have caused a deep degassing process able to remove variable proportions of Na and K from the melt.

The Link between ZSM-5 Zeolite Crystallization and Mesopore Formation by Leaching.

Acid or base leaching are well-established tools in the synthesis of mesoporous zeolites. Previous studies suggest an inherent link between the structure-property relationship of mesoporous zeolites, that is, chemical resistance, pore diameter and distribution, with zeolite synthesis or crystallization conditions. The exact nature and/or origin of this link is currently however, poorly established. Here, we provide evidence how zeolite crystallization conditions influence the leaching behavior and thus structure of mesoporous zeolites. Electron microscopy and in situ small angle X-ray scattering both confirmed the crystallization of ZSM-5 to utilize both nanoparticles and oligomers as elemental building blocks. Utilization of these species is highly depended on supersaturation. The precursor solution of decreased water content favored a faster consumption of nanoparticles compared to its oligomers at the early stage of crystallization. Then the addition of oligomers can heal the surface imperfections and thus the resulting zeolite showed a higher resistance against acid leaching. In contrast, within the precursor solution of increased water content the slower consumption of nanoparticles led to crystals with a less robust rim. Defects existed in the rim due to limited healing by oligomers and, as such, mesopores can be created by the following post-treatment. Precise control over selected crystallization conditions can therefore further aid the design of optimized mesoporous zeolites.

Early stages of fat crystallisation evaluated by low-field NMR and small-angle X-ray scattering.

Low-field time-domain nuclear magnetic resonance (NMR; 20MHz) is commonly used in the studies of fats in the form of solid fat content (SFC) measurements. However, it has the disadvantage of low sensitivity to small amounts of crystalline material (0.5%), thus often incorrectly determining crystallisation induction times. From spin-lattice relaxation rate measurements (R1 ) during the isothermal crystallisation measurements of cocoa butter between 0.01 and 10MHz using fast field cycling NMR, we learnt previously that the most sensitive frequency region is below 1MHz. Thus, we focused on analysing our 10-kHz data in detail, by observing the time dependence of R1 and comparing it with standard SFCNMR and SFC determinations from small-angle X-ray scattering (SFCSAXS ). Although not reflecting directly the SFC, the R1 at this low frequency is very sensitive to changes in molecular aggregation and hence potentially serving as an alternative for determination of crystallisation induction times. Alongside R1 , we also show that SFCSAXS is more sensitive to early stages of crystallisation, that is, standard SFCNMR determinations become more relevant when crystal growth starts to dominate the crystallisation process but fail to pick up earlier crystallisation steps. This paper thus demonstrates the potential of studying triacylglycerols at frequencies below 1MHz for obtaining further understanding of the early crystallisation stages of fats and presents an alternative and complementary method to estimate SFC by SAXS.

Zircon chemistry and new laser ablation U–Pb ages for uraniferous granitoids in SW Cameroon

The Ekomedion two-mica granite, southwestern Cameroon, has potential for uranium and molybdenum mineralization. Here, we present LA-ICP-MS U–Pb ages, Lu–Hf isotope characteristics, trace element concentrations and Ti-geothermometry of zircon from this granite hosting U–Mo mineralization in pegmatitic pods. The majority of zircon are CL-dark though some CL-bright cores were also identified. U–Pb zircon age data range from 121 ± 3 to 743 ± 11 Ma with only 5 of 34 ages being near concordant. The concordant mean age of 603 ± 12 Ma is similar to ages of granitic intrusions along the Central African Shear Zone in Cameroon. Apparent ages with mean of 261 ± 6 Ma reveal open system behavior with respect to Pb and/or U. Zircon eHfi values range from − 20.3 to − 0.3. This implies that U–Mo was remobilized during partial melting of the surrounding gneiss. Zircon Th/U > 0.1 as well as an increasing Hf with decreasing Th/U indicates that fractional crystallization was the main factor that controlled U–Mo mineralization in pegmatitic pods. Y and Y/Ho ratios cluster from 29 to 33 close to the chondritic ratio of 28 and indicate fractionation of Y and Ho with low F contents during the earliest stages of crystallization. Late stage accumulation of F-rich magmatic-hydrothermal fluids impacted U–Mo mineralization as a ligand. Zircon contains a prominent negative Eu anomaly pointing to a fractionating system rich in plagioclase. Calculated Ti-in-zircon temperatures span 672 °C to 1232 °C with the temperatures at the high end reflecting interference from mineral inclusions in the zircon grains while the lower temperature values are linked to crystallization.