Primary Crystal Size Research Articles

Changing Template/Al2O3 Ratio in Reaction Gel-An Effective Way to Regulate Nature of Intermediate Phases and Properties of SAPO-11 Molecular Sieves during Crystallization.

A study has been conducted to investigate the formation of intermediate phases during the crystallization of SAPO-11 molecular sieves from reaction mixtures with a varying template (di-n-propylamine) DPA/Al2O3 ratio. It was found that changing the DPA/Al2O3 ratio from 1.0 to 1.8 in the initial reaction gels leads to the formation of different intermediate phases during crystallization into a SAPO-11 molecular sieve. It is shown that at the ratio template/Al2O3 = 1.0, an intermediate amorphous silicoaluminophosphate is formed; at 1.4, a mixture consisting of amorphous and layered phases forms; and at 1.8, a layered phase is present. A simple and innovative approach for controlling the morphology, size, and characteristics of primary crystals and the secondary porous structure in hierarchical SAPO-11 is proposed. The method is based on regulating the DPA/Al2O3 ratio in the reaction gel. The synthesized SAPO-11 molecular sieves with a hierarchical porous structure exhibited high selectivity in the hydroisomerization of n-hexadecane.

Effect of Material Properties and Variability of Mannitol on Tablet Formulation Development.

Using a high level of mannitol as adiluent in oral formulations can potentially result in tablet defects (e.g., chipping, cracking) during compression. This work aims to scrutinize the linkage between the mechanical properties and material attributes of mannitol and also uncover how variations between vendors and lots can lead to significant changes in the compaction performance of tablet formulations containing mannitol. The mechanical properties (Poisson's ratio, fracture energy) and mechanical performance (ejection force, pressure transmission ratio, residual radial die-wall stress, and tensile strength) of mannitol compacts were assessed on a compaction simulator for four lots of mannitol from two different vendors. The variation of material attributes of each lot, including particle size distribution (PSD), crystal form, primary crystal size and morphology, specific surface area (SSA), powder flow, and moisture absorption were investigated. The variability of material attributes in mannitol lots, especially primary crystal size and SSA, can result in significant changes in mechanical properties and mechanical performance such as ejection force and residual radial die-wall stresses, which potentially led to chipping during compression. The study elucidated the linkage between fundamental material attributes and mechanical properties of mannitol, highlighting their impact on tablet defects and compaction performance in compression. A comprehensive understanding of the variability in mannitol properties between vendors and lots is crucial for successful formulation development, particularly when high percentages of mannitol are included as a brittle excipient.

INVESTIGATION OF THE STRUCTURE OF ALSI25CU4CR AND ALSI25CU5CR ALLOYS

The hypereutectic aluminium-silicon alloys AlSi25Cu4Cr and AlSi25Cu5Cr are heat treated T5, T6 and T7. The quenching of the alloys was carried out under the same conditions. Artificial aging at T5 was carried out at a temperature of 180º C for 2, 4 and 6h, and at T6 at 180º C for 8, 10, 12 and 14h. The artificial aging of the studied compositions at T7 was carried out at a temperature of 370º C for 20, 40 and 60 min. The influence of heat treatment on the size, shape and distribution of primary and eutectic silicon crystals in the alloy structure was investigated. It was established that the proposed heat treatment regimes do not lead to a significant change in the shape and size of the primary silicon crystals, but contribute to their uniform distribution in the structure of the studied alloys. Rounding of the silicon crystals in the composition of the eutectic of the investigated alloys was observed.

Features of the formation of crystalline hydrosulfoaluminates during hydration of stoichiometric mixtures of calcium aluminates with calcium sulfate

Calcium aluminates as mineral binders allow to produce cements and concretes with high early strength, low porosity, increased heat resistance, frost resistance and corrosion resistance compared to materials based on Portland cement. An important structure-forming process in aluminate cements is formation of hydrosulfoaluminate phases (ettringite, monosulfoaluminate). Finding out the parameters that allow to control this process is of exceptional importance for construction practice. Hydration of various calcium aluminates C3A, C12A7, CA, and CA2 in the presence of stoichiometric amounts of various forms of calcium sulfate (CaSO4⋅2H2O, α-CaSO4⋅0.5H2O, anhydrite) was studied in order to determine the comparative ratio and the peculiarities of nucleation and growth of the hydrosulfoaluminate phase crystals. It was found that the highest yield of ettringite (∼100 wt% by 28 days) is achieved during hydration hardening of the composition C3A + 3CS¯H2, the yield is reduced in the series C12A7–CA–CA2. Monosulfoaluminate is not formed as the predominant product, its yield reaches 25 wt% during hydration of low-base aluminates. Ettringite crystals can form as a highly dispersed mass (from C3A) or prismatic (fibrous) crystals (from other aluminates). It was clearly shown for the first time that the origin and growth of ettringite crystals occurs in the matrix of aluminum hydroxide gel formed during hydration of calcium aluminates. Varying the pH of aluminate-sulfate mixtures changes the morphology, size and number of primary ettringite crystals. Lamellar hexagonal crystals of monosulfoaluminate are formed from hydroaluminates of type C4AH13-19 at low availability of calcium sulfate. The explanation of the experimental data was carried out using thermodynamic calculations. The results obtained can be used in practice to control the content, ratio and morphology of hydrosulfoaluminate phases in cement stone.

Polyphenol‐Mediated Synthesis of Superparamagnetic Magnetite Nanoclusters for Highly Stable Magnetically Responsive Photonic Crystals

AbstractAchieving high stability and excellent optical performance in complex environments is crucial for practical applications of magnetically responsive photonic crystals (MRPCs). It, however, remains a great challenge. This study demonstrates a polyphenol‐mediated strategy for synthesizing size‐controllable superparamagnetic magnetite (Fe3O4) colloid nanocrystal clusters (CNCs) that can be stably dispersed in various polar solvents to form MRPCs with brilliant structural colors for a long term. As tannic acid (TA) functions as a linker to robustly bind polyvinylpyrrolidone (PVP) chains to Fe3O4 surfaces, the MRPCs can maintain nearly constant diffraction wavelength and high reflectance for up to 4 years. The strong coordination between TA and Fe3+ inhibits crystal growth, ensuring the small primary crystal size and superparamagnetism of Fe3O4@TA‐PVP CNCs. Partial oxidation of TA accelerates the crystal nucleation and growth, reducing the overall CNC particle size, which can be utilized for controlling the particle size. Additionally, enhancing the dissolution of PVP before the solvothermal reaction improves the size monodispersity of the products, making the as‐constructed MRPCs ideal for practical applications in color display, sensors, anti‐counterfeiting, and camouflage. The Fe3O4@TA‐PVP CNCs with high stability and versatility for surface‐functionalization are also promising for magnetic resonance imaging, targeting drug delivery, recyclable catalysis, and magnetic nanomotors.

Assessment of the effect of small additions of some rare earth elements on the structure and mechanical properties of castings from hypereutectic chromium white irons

<abstract> <p>Article considers the influence of additions of rare earth elements such as Sm, La, Ce, Nd, and Y on the structure and properties of hypereutectic high-chromium white cast iron of grade G-X300CrMo27-2. To obtain an increased content of carbides in the studied cast iron samples, the carbon content was 3.75–3.9 and 4.1–4.2 wt%. The amount of rare earth elements additives added to the melt is 0.2% by weight. Data were obtained on the effect of overheating and cooling rate in the crystallization interval on the effect of rare earth additives, the structure and properties of white cast iron castings are given. According to the results of the microprobe analysis, it was shown that, under the chosen crystallization conditions, Sm, La, and Ce can form solid solutions with primary and eutectic carbides (FeCr)<sub>7</sub>C<sub>3</sub>. La and Ce form solid solutions with austenite. Nd and Y do not dissolve in iron chromium phases. All listed rare earth elements form phosphides and oxyphosphides. Experimental data are presented on the effect of rare earth elements on the size of primary (FeCr)<sub>7</sub>C<sub>3</sub> carbides and a hypothesis is proposed on the effect of rare earth elements on the crystallization process of hypereutectic chromium white cast irons. Experimental data are presented on the effect of REE additives on the microhardness of phases, hardness, strength, and resistance to abrasive wear of cast iron castings. It was found that the introduction of these additives into hypereutectic chromium white cast iron does not contribute to the modification of the structure and leads to an increase in the size of primary crystals, as well as a decrease in their mechanical properties. However, the addition of Y increases the abrasive wear resistance, but reduces the strength of castings made from such white cast iron.</p> </abstract>

Quantification of surface orientation effect on the thermal stability of γ-Al2O3 with different morphologies

Three types of γ-Al2O3materials with morphologies as cluster, nanorod, and nanoplate, respectively, were prepared by hydrothermal synthesis of the corresponding boehmites as the precursors and subsequent calcination at 600 °C. The surface orientations of the γ-Al2O3materials were identified using the characterization techniques of XRD, TEM and SAEDto quantify the morphologies. To assess the thermal stability of different Al2O3materials, the phase compositions and the specific surface areas changing with temperature in 600–1200 °C were analyzed. The results show that the transformation of Al2O3from γ- to δ-, θ-, and finally to α-phase is remarkably diverse for different Al2O3, which is more dependent on the surface orientation rather than the primary crystal size of the material. The variation of total surface energy of each surface-oriented Al2O3with the temperature demonstrates its own regularity when taking the phase composition and the crystal plane proportion into account. The Nanorod Al2O3benefits from its large proportion of (100)δ||(001)θplanes featured with low surface energies, giving rise to large surface area (92.5 m2/g) at 1000 °C. In contrast, the Cluster sample contains the least α-Al2O3 at 1200 °C, suggesting its high thermal stability, but concomitant with significant loss in surface area.

Designed nanostructures created via physicochemical switching of the growth mode between single crystals and mesocrystals.

Most biominerals are composed of mesocrystals, in which individual nanoparticle building units have a defined long-range order on the atomic scale in at least one direction. Although the crystal size and orientation of the mesostructures are spatially designed in biological architectures, it has been difficult to achieve adequate control of the crystal growth to produce modulated mesostructures in artificial aqueous systems. Here, we propose a simple physicochemical approach for the spatial design of nanostructures using an aqueous solution system. The ordered arrays of oriented fluorapatite (FA) rods similar to tooth enamel are produced on a polymer substrate in a supersaturated solution. We succeeded in reversible switching of the growth mode of FA between single-crystalline rods and mesocrystalline grains through the disturbance of the solution. The primary crystal size was tuned between micrometric rods ∼0.5 μm wide and >5 μm long and nanoscale grains ∼10 nm wide and 50 nm long without a drastic change in the c direction. Hierarchical architectures consisting of iso-oriented FA microrods and nanograins were constructed via temporal control of the crystal growth mode by switching a physicochemical parameter, such as the degree of supersaturation at the growth front.

Comparative analysis of the effect of Ni, Mn, Fe and Si additives on the microstructure and phase composition of hypereutectic aluminum-calcium alloys

A comparative analysis of the phase composition and morphology of primary crystals in hypereutectic alloys of the Al–Ca–Ni–X system (where X is Fe, Si, Mn) was carried out by calculation and experimental methods, including the construction of liquidus surfaces. Additional alloying of the base Al–6%Ca–3%Ni alloy with iron and silicon leads to the formation of coarse elongated primary crystals up to 100 μm in length. It was found that the addition of manganese, on the contrary, leads to the formation of relatively small (average size about 20 μm) compact primary crystals of two four-component phases. Presumably, they are phases based on ternary compounds Al9CaNi and Al10CaMn2. The composition of eutectics in quaternary alloys has been determined. All aluminum-calcium eutectics are characterized by a higher proportion of the second phases, a thinner structure compared to the aluminum-silicon eutectic in AK18 silumin, and are also capable of spheroidization upon heating, starting from 500 °C. The combination of compact and spherical particle morphology after annealing in the 63-2Mn alloy appears to be favorable for deformation. Comparison of the manufacturability of the experimental alloy Al–8%Ca–1%Ni–2%Mn and the grade silumin AK18 showed the advantage of the former. In terms of the totality of its characteristics, the experimental alloy can be considered as the basis for the development of hypereutectic alloys of a new generation as an alternative to piston silumins of the AK18 type. The experimental alloy, the microstructure of which is characterized by a compact morphology and small size of primary crystals and a fine structure of the eutectic, in contrast to hypereutectic silumins, does not require special modification.

Analysis of piston microstructure in the most critical zones

This paper presents the results of testing the microstructure in the most critical zones of pistons made of aluminum piston alloys. The paper analyzes the shape, size and distribution of primary Si crystals and other phases in three most important piston zones (the edge of the combustion chamber, the area of rings groove and piston pin boss). The phase stoichiometry was identified by comparing the results of EDS analysis with the results reported in the studied literature. The results show that the necessary size, shape and distribution may be obtained in specific zones if appropriate solidification conditions are provided that are necessary for the formation of specific phases.

Photocatalytic Oxidation of Propane Using Hydrothermally Prepared Anatase-Brookite-Rutile TiO2 Samples. An In Situ DRIFTS Study.

Photocatalytic oxidation of propane using hydrothermally synthesized TiO2 samples with similar primary crystal size containing different ratios of anatase, brookite and rutile phases has been studied by measuring light-induced propane conversion and in situ DRIFTS (diffuse reflectance Fourier transform infrared spectroscopy). Propane was found to adsorb on the photocatalysts, both in the absence and presence of light. The extent of adsorption depends on the phase composition of synthesized titania powders and, in general, it decreases with increasing rutile and brookite content. Still, the intrinsic activity for photocatalytic decomposition of propane is higher for photocatalysts with lower ability for propane adsorption, suggesting this is not the rate-limiting step. In situ DRIFTS analysis shows that bands related to adsorbed acetone, formate and bicarbonate species appear on the surface of the photocatalysts during illumination. Correlation of propane conversion and infrared (IR) data shows that the presence of formate and bicarbonate species, in excess with respect to acetone, is composition dependent, and results in relatively low activity of the respective TiO2. This study highlights the need for precise control of the phase composition to optimize rates in the photocatalytic oxidation of propane and a high rutile content seems to be favorable.

Mathematical Modeling of Emulsion Solvent Diffusion for Spherical Crystallization: How To Deconvolute Primary Crystal Size Distribution from Agglomerate Size Distribution?

Spherical crystallization (SC) is a novel process intensification strategy, which can substantially reduce the manufacturing cost for solid oral dosage forms. However, although the manufacturabilit...

Microstructures and pharmaceutical properties of ferulic acid agglomerates prepared by different spherical crystallization methods.

Spherical agglomerates of an active pharmaceutical ingredient, ferulic acid (FA), were prepared using four different spherical crystallization methods, i.e., quasi-emulsion solvent diffusion (QESD), anti-solvent, pH shift, and the direct method. Both the as-received FA and spherical agglomerates were characterized in terms of specific surface area (SSA), primary crystal shape and size, granule morphology and size, powder flowability, tabletability at two distinct speeds, and dissolution (both powder and tablet). Results showed that the microstructure, which is affected by size, shape, and packing of primary crystals, was the key that determined the flowability, tabletability and dissolution. The QESD powder exhibited the best flowability and tabletability. Both powder and tablet dissolution of FA followed the order of as-received>QESD>anti-solvent>pH shift, which was consistent with the order of the surface area exposed to the dissolution medium and not SSA. Moreover, compression reduced differences in the rates of dissolution of FA powders due to the size reduction of agglomerates by fragmentation.

The modification of hypereutectic high-alloy silumins — prospects for the development of technology for producing materials with a low linear expansion coefficient

This article discusses the possibilities of using hypereutectic silumins and the problems that impede their wider distribution. The known methods of manufacturing products from hypereutectic silumins of high quality are shown. A method for producing casting blocks from hypereutectic silumins by direct chill casting is considered. The possibility of milling primary silicon crystals by introducing modifiers and master alloys of Al-Si-P, Al-Cu-P systems, inorganic carbon and phosphorus compounds is shown. The tendency of copper-doped silumins to hot shortness is shown. The technology of impact on the melt of ultrasonic cavitation is considered together with the introduction of additional active modifiers made of master alloy rods to obtain casting blocks from hypereutectic high-alloy silumins using the method of direct chill casting with a primary silicon crystal size of no more than 10 µm. Technological principles for reducing the grain size of α-solid solution, uniformly distributed over the ingot cross-section, are proposed.

Synthesis of MOR Zeolite/Magnetite Composite via Seed Assisted Method.

MOR zeolite is an effective adsorbent for separating organic molecules from various solutions owing to its large windows of 0)65 × 0)70 nm and its relatively high silica-alumina ratio which provides higher hydrophobicity. Fine powdery MOR zeolite is desirable for adsorption of organic molecules considering its larger surface area; however, fine particles are difficult to remove from solutions after treatment. Intensification of magnetic susceptibility through combination with magnetic particles ensure quick and easy removal of fine adsorbents by magnetic force. Meanwhile, seed assisted method is a powerful technique to direct and accelerate zeolite synthesis by adding seed crystals into the precursor sol prior to hydrothermal synthesis. In this work, we selected magnetite as the magnetic particle and propose the hydrothermal synthesis of MOR zeolite/magnetite composite via seed assisted method for the first time. MOR zeolite/magnetite composite with high MOR zeolite crystallinity was obtained by synthesizing for only 6 hours at 463 K when adding seed crystals, while no sign of crystallization was observed even after 24 hours in their absence. In addition, pre-milling of seed crystals together with magnetite was found to be effective to incorporate magnetite into MOR zeolite during crystallization and to decrease the primary crystal size of the crystallized MOR zeolite.

Synthesis of hierarchical ZSM-5 aggregates by an alkali-treated seeds method with cetyltrimethylammonium bromide for the methanol to gasoline reaction

A series of hierarchical ZSM-5 aggregates with a relatively low SiO2/Al2O3 ratio (~ 50) were successfully synthesized using alkali-treated commercial ZSM-5 as seeds and cetyltrimethylammonium bromide (CTAB) as mesogenous template. The effect of the amounts of CTAB on the physicochemical and catalytic properties of the synthesized catalysts was characterized by XRD, FE-SEM, FE-TEM, N2 physical adsorption, ICP-OES, NH3-TPD, Py-IR and TGA. Moreover, the possible formation mechanism of the hierarchical ZSM-5 aggregates was studied. The results indicated that the mesoporosity of the hierarchical ZSM-5 aggregates was greatly enhanced with the addition of CTAB. The primary crystal size of the ZSM-5 aggregates significantly decreased owing to the protective effect of CTAB, which inhibits the further crystal growth. The hierarchical ZSM-5 aggregates prepared with addition of a suitable amount of CTAB showed large specific surface areas and large external surface areas, abundant intercrystalline mesopores and appropriate concentration of acid sites, which resulted in excellent catalytic performance in the methanol to gasoline reaction. The stability of the catalyst was remarkably improved and the gasoline yield was given a rise of 10% compared with the catalyst prepared in the absence of CTAB.

Enabling High-Rate Mn Oxide Pseudocapacitors Using Highly Dispersed Mn3O4 Nanocrystallites

Mn oxides are promising electrode materials for supercapacitors applications. They provide the advantages of high specific areal capacitance and densities, which are beneficial to achieving high device energy density. Nevertheless, they have so far demonstrated insufficient current rate performance, which is related to their poor electronic conductivities. Indeed, the establishment of a conductive network that is capable of efficiently connecting the nano-sized oxide particles within the electrode is essential to giving high current rate capability. In this work, we investigated the interplay between the Mn oxide particle properties and those of carbon conductive additives on the rate performance of the Mn oxide pseudocapacitor electrodes. The investigation adopts Mn3O4 as an example. Mn3O4 nano-crystallite powders having the same primary crystal size but varied agglomeration at the nano-meter scale were synthesized by a novel controlled solution oxidation process. The oxide powders were matched with carbon additives of different morphologies and dimensionalities for constructing electrodes having various electric networking configurations. The correlation between the rate performance of the oxide electrodes and the powder properties of both the oxide and the carbon additives is addressed. In particular, it is demonstrated that remarkable rate performance, along with superb cycle stability, is achieved with highly dispersed oxide nano-crystallites with zero-dimension carbon black additive. The results are important to the architecture design for oxide-based pseudocapacitors. Figure 1

Hydrothermal Synthesis of Rare-Earth Modified Titania: Influence on Phase Composition, Optical Properties, and Photocatalytic Activity.

In order to expand the use of titania indoor as well as to increase its overall performance, narrowing the band gap is one of the possibilities to achieve this. Modifying with rare earths (REs) has been relatively unexplored, especially the modification of rutile with rare earth cations. The aim of this study was to find the influence of the modification of TiO2 with rare earths on its structural, optical, morphological, and photocatalytic properties. Titania was synthesized using TiOSO4 as the source of titanium via hydrothermal synthesis procedure at low temperature (200 °C) and modified with selected rare earth elements, namely, Ce, La, and Gd. Structural properties of samples were determined by X-ray powder diffraction (XRD), and the phase ratio was calculated using the Rietveld method. Optical properties were analyzed by ultraviolet and visible light (UV-Vis) spectroscopy. Field emission scanning electron microscope (FE-SEM) was used to determine the morphological properties of samples and to estimate the size of primary crystals. X-ray photoelectron spectroscopy (XPS) was used to determine the chemical bonding properties of samples. Photocatalytic activity of the prepared photocatalysts as well as the titania available on the market (P25) was measured in three different setups, assessing volatile organic compound (VOC) degradation, NOx abatement, and water purification. It was found out that modification with rare earth elements slows down the transformation of anatase and brookite to rutile. Whereas the unmodified sample was composed of only rutile, La- and Gd-modified samples contained anatase and rutile, and Ce-modified samples consisted of anatase, brookite, and rutile. Modification with rare earth metals has turned out to be detrimental to photocatalytic activity. In all cases, pure TiO2 outperformed the modified samples. Cerium-modified TiO2 was the least active sample, despite having a light absorption tail up to 585 nm wavelength. La- and Gd-modified samples did not show a significant shift in light absorption when compared to the pure TiO2 sample. The reason for the lower activity of modified samples was attributed to a greater Ti3+/Ti4+ ratio and a large amount of hydroxyl oxygen found in pure TiO2. All the modified samples had a smaller Ti3+/Ti4+ ratio and less hydroxyl oxygen.

Carbon/Li4Ti5O12 Composite Spheres Prepared Using Chinese Yam as Carbon Source with Ultrahigh Capacity as Anode Materials for Lithium Ion Batteries

AbstractSpinel structured Li4Ti5O12 (LTO) spheres modified with carbon (Carbon/LTO composites) using Chinese yam (CY) as carbon source have been obtained by a hydrothermal method combining with a calcining at 700 °C in N2 atmosphere. The influences of the additions of CY on the morphology, structure, carbon content and also the electrochemical properties of the resulted carbon/LTO composite spheres have been investigated in details. SEM and TEM investigations show that all the composites possess spherical morphology and consist of nanosized Li4Ti5O12 crystals modified with carbon. With the increase of CY additions, the size of Li4Ti5O12 primary crystals decrease gradually, and reach to a turn over point and then the crystal size turn to large ones when the CY content increased further. It has been demonstrated that carbon modification of Li4Ti5O12 with Chinese yam as carbon source could efficiently improve the electrochemical performance of Li4Ti5O12. One of the composite sample named as C/LTO‐10 shows an ultrahigh initial specific capacity of about 211.9 mAh ⋅ g−1 at a current density of 1 C. It shows excellent cycle performance and maintains a specific capacity of 184.5 mAh ⋅ g−1 even after 300 cycles. A specific capacity of 123.5 mAh ⋅ g−1 still could be delivered at a high current density of 30 C, exhibiting also superior rate capability.

Influence of Ni on the refinement and twinning of primary Cu6Sn5 in Sn-0.7Cu-0.05Ni

The influence of Ni on the size and twinning of primary Cu6Sn5 crystals in Sn-0.7Cu-0.05Ni and Sn-xCu (x = 0.7, 0.9, 1.1) (mass%) solder joints is studied using synchrotron radiography and SEM-based EBSD. It is shown that the Ni addition does not cause significant refinement of primary Cu6Sn5 if the alloy is fully melted. However, for peak temperatures ≤250 °C relevant to industrial soldering, primary Cu6Sn5 are not completely melted in Sn-0.7Cu-0.05Ni and there are 10–100 times more numerous and smaller crystals than in Sn-0.7Cu. X-shaped Cu6Sn5 crystals with an angle of ∼70° commonly formed in Sn-0.7Cu-0.05Ni/Cu joints and are shown to be penetration twins. This type of growth twinning was only found in partially melted samples, both in Sn-0.7Cu-0.05Ni/Cu joints and binary Sn-1.1Cu alloy. The frequency of twinned crystals was significantly higher in Ni-containing solders. The results are discussed in terms of the influence of Ni on the Cu6Sn5 liquidus slope and on the lattice parameters of (Cu,Ni)6Sn5.