Two-step Crystallization Process Research Articles

Effects of C-S-H gel surface structure on sodium chloride evaporation crystallization in C-S-H gel nanopores with molecular dynamics analysis

The evaporation crystallization of salt solutions in cement-based material pores accelerates durability degradation. It is necessary to investigate the mechanisms and process of evaporation crystallization in the pore channel of C-S-H gels on a nanoscale level. With molecular dynamics simulation, this paper explored the influence of C-S-H gel surface structure on the evaporation crystallization process of NaCl solution based on a new solid–liquid model. NaCl crystallization in the channel space of the C-S-H gel nanopore followed a two-step crystallization mechanism (nucleation and crystallization). The adsorption of sodium and chloride ions on the C-S-H gel surface shows significant differences. The surface of C-S-H gel is electronegative, so the C-S-H gel surface adsorption capacity of cations is stronger than that of anions and the C-S-H gel surface adsorption of sodium ions is more stable. The difference of silica-oxygen tetrahedron density of C-S-H gel surfaces caused the difference of charge characteristic of C-S-H gel surfaces. The C-S-H gel surface structure has an effect on the sodium chloride crystallization position, but has not obvious impact on the two-step evaporation crystallization process. These findings provide a theoretical basis for addressing the nanoscale characteristics of C-S-H gel surface and the macroscale durability of cement-based materials.

Direct Observation of Two-Step, Stratified Crystallization and Morphology in Conjugated Polymer Thin Films

A two-step stratified crystallization process has been directly observed during cooling of poly(3-hexylthiophene) (P3HT) thin films of thickness h = 20–250 nm: a thin (<20 nm) layer at the free surface crystallizes ∼25 °C higher than the bulk crystallization temperature (TC,bulk), whereas the rest of the film (i.e., the underlayer) crystallizes near TC,bulk. In situ measurements of films with and without a free surface unequivocally ascribe the high-temperature crystallization to a surface-induced process, which correlates with the formation of large birefringent structures and highly oriented edge-on crystallites at the air–polymer interface. In contrast, crystallization of the bulk-like underlayer leads to mostly edge-on-oriented crystallites in thinner films and becomes increasingly isotropic in thicker films. For h < 20 nm, free-surface effects dominate and only high-temperature crystallization is observed. These results highlight the potential of melt crystallization to tailor morphology and orientation across thin film thickness for specific electronic applications.

Heat-induced local structural variation in porous-type amorphous alumina prepared by anodization

Porous-type anodic amorphous alumina is an important functional material in the current chemical industry and the future fields of nanotechnology and glass science. To identify their heat-induced local structural variations, anion-free, phosphate-, oxalate-, and sulfate-incorporated amorphous alumina were investigated. The glass transition temperature of the all amorphous alumina was determined to be ∼470 °C. In the phosphate-incorporated alumina, two-step crystallization process involving an anion-free inner layer and anion-incorporated outer layers were identified. In addition, the sensitive local structural variation in anion-free and -incorporated alumina was clarified. In the anion-free sample, the average coordination number (NAl–O) increases slightly just before the crystallization temperature due to nucleation. In the oxalate- and sulfate-incorporated samples, the average NAl–O gradually decreased and reached at value close to that of the anion-free sample due to gradual cleavage in the chemical bonds between the anions and aluminum ions. For the phosphate-incorporated sample, the average NAl–O decreased and exhibited a value substantially different from that of the anion-free sample because of the gradual formation of chemical bonds between phosphate and aluminum ions. These findings contribute to the development of an intrinsic understanding of the changes in physical and chemical properties with heat treatment for anodic alumina and the structural features of intermediate oxides that cannot be glass.

The effect of borate bioactive glass ceramics containing silver nanoparticles on removal physiognomies of methylene blue

Several studies have been carried out with several materials on the removal of methylene blue from water. Well-known bioactive glass 46S5.2 was prepared by complete replacement of the silicate partner with boron oxide via a two-step crystallization process, in particular its glass-ceramic derivative. The characterization techniques for ceramic sample were performed such as Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive X-ray (EDX). Transmission electron microscope (TEM) was employed to ensure that silver addition reaches to the nanoscale. UV/Vis. optical absorption spectroscopy was utilized in the retracing process of methylene blue adsorption from its contaminated water. The antimicrobial activity of the prepared sample was also studied extensively. Also for the prepared glass-ceramic samples, the reusability test was carried out to ensure that they could be used more than once in water treatment applications.

π-Pimer, π-Dimer, π-Trimer, and 1D π-Stacks in a Series of Benzene Triimide Radical Anions: Substituent-Modulated π Interactions and Physical Properties in Crystalline State

π-Pimer, π-Dimer, π-Trimer, and 1D π-Stacks in a Series of Benzene Triimide Radical Anions: Substituent-Modulated π Interactions and Physical Properties in Crystalline State

Nanoscale Crystallization Mechanisms in a GeSSbCsCl Glass Ceramic and Relationships with Mechanical and Optical Properties

Crystallization of 62.5GeS2–12.5Sb2S3–25CsCl glass ceramic was investigated using different techniques from the macro- to nanoscale. A two-step crystallization process was evidenced, allowing for a...

A Scandium MOF with an Unprecedented Inorganic Building Unit, Delimiting the Micropore Windows.

A new scandium metal-organic framework (Sc-MOF) with the composition of [Sc(OH)(OBA)], denoted as Sc-CAU-21, was prepared under solvothermal reaction conditions using 4,4'-oxidibenzoic acid (H2OBA) as the ligand. Single-crystal structure determination revealed the presence of the new inorganic building unit (IBU) {Sc8(μ-OH)8(O2C)16}. It is composed of cis-connected ScO6 polyhedra forming an eight-membered ring through bridging μ-OH groups. The connection of the IBUs leads to a 3D framework, containing 1D pores with a diameter between 4.2 and 5.6 Å. Pore access is limited by the size of the IBU, and in contrast to the isoreticular aluminum compound Al-CAU-21 [Al(OH)(OBA)], which is nonporous toward nitrogen at 77 K, Sc-CAU-21 exhibits a specific surface area of 610 m2 g-1. The title compound is thermally stable in air up to 350 °C and can be employed as a host for photoluminescent ions. Sc-CAU-21 exhibits a ligand-based blue emission, and (co)substituting Sc3+ ions with Ln3+ ions (Eu3+, Tb3+, and Dy3+) allows the tuning of the emitting color of the phosphor from red to green. Single-phase white-light emission with CIE color coordinates close to the ideal for white-light emission was also achieved. The luminescence property was utilized in combination with powder X-ray diffraction to study in situ the crystallization process of Sc-CAU-21:Tb and Sc-CAU-21:Eu. Both studies indicate a two-step crystallization process, with a crystalline intermediate, prior to the formation of Sc-CAU-21:Ln.

Two-Step Liquid Phase Crystallized Germanium-Based Photodetector for Near-Infrared Applications

This work presents a wafer-scale two-step liquid phase crystallization process to obtain polycrystalline but epitaxial germanium on 2”-silicon wafers (Ge-on-Si). The crystallinity is confirmed using Raman spectroscopy and X-ray diffraction, with an extracted dislocation density of 108cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> , an improvement of 10x over the previous report. The scanning electron imaging shows a uniform Ge film with a grain size of up to 12μm. Metal-semiconductor-metal (MSM) near-infrared (IR) photodiodes are fabricated on the epitaxial Ge with two different electrodes and two different surface passivation interlayers. Irrespectiveof the electrode/passivationcombination, all devices exhibit Ohmic characteristics. Contact resistivity varies from 3 mΩcm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> to 560 mΩ cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . This is contrary to virtually every previous report on MSM detector on n-type Ge. To probe further, kelvin probe force microscopy is used to characterize the surface potentials at grain boundaries and metal-Ge interfaces. The grain-to-grain band bending is very low, ~40 meV, hence, device characteristics are completely dominated by the metalGe band-bending which is 150-300 meV. The MSM devices using amorphous-Ge(30nm)/Al (100nm) and TiO2 (5nm)/Au (80nm) electrodes show an average spectral responsivity (SR) of 0.50 ± 0.16 A/W and 0.35 ± 0.09 A/W at 1550 nm and voltage bias of -3V, respectively. The maximum SR is 0.78 A/W and 0.48 A/W, respectively.

Fractionated crystallization and fractionated melting behaviors of poly(ethylene glycol) induced by poly(lactide) stereocomplex in their block copolymers and blends

Stereocomplexation has been an effective way to improve the physical properties of block copolymers or blends. However, the effect of stereocomplexation on the confined and fractionated crystallization of other crystallizable block has not been comprehensively investigated so far. In this work, we used poly(l-lactide) (PLLA) and poly(d-lactide) (PDLA) as stereocomplexable higher melting component and studied the confined crystallization and melting behaviors of poly(ethylene glycol) (PEG) in their block copolymers and blends. Unexpectedly, marked fractionated crystallization and fractionated melting behaviors of PEG component occurred during the two-step crystallization process, because of the constrained effect of the early formed stereocomplex (SC) crystals. The fractionated crystallization and melting behaviors were further facilitated with decreasing the isothermal crystallization temperatures of PLLA and PDLA (Tic,PLA). As revealed by polarized optical microscopy (POM), the increase of Tic,PLA favors the transformation of PEG component from the interlamellar to interspherulitic regions due to the reduced nucleation density of PLA. We proposed that fractionated crystallization and fractionated melting behaviors of PEG impacted by SC crystals were attributed to PEG component dispersed in and out interlamellar regions of PLA matrix. Moreover, small-angle X-ray scattering (SAXS) results indicated that two scattering peaks were identified for copolymers after two-step crystallization process, one consisted of mixed PEG and PLA lamellae and the other contained almost pure PEG lamellae originated from the crystallization of PEG dispersed in interfibriller/interspherulitic regions. This study has shed light on the unique fractionated crystallization and fractionated melting behaviors of the lower melting component in polymer systems with the higher melting component preferentially co-crystallized into SC crystals.

Si microalloying optimizes the thermal stability, crystallization behaviors and magnetic properties of Fe-rich Fe-B-Cu-Hf alloys

The new type Fe-rich Fe-B-Cu-Hf alloys show a great of potential applications as the energy-saving soft magnetic materials, due to its especial α-Fe/amorphous dual phases structure contributes to the high saturation magnetization (Ms), permeability (μe) and low loss cost (W), coercivity (Hc). However, these alloys are difficult to be used actually with the uniform α-Fe/amorphous dual phases structure, on account of the poor glass forming ability (GFA) and the difficulty of crystallizing α-Fe away from the Fe-B compounds precipitation. Therefore, the effects by Si substituting of minor B on GFA, thermal stability, crystallization behaviors and magnetic properties in Fe86B13−xSixCu0.4Hf0.6 alloys have been researched. The results show that Si microalloying is prominent and the ribbons with entire amorphous can still be easily fabricated as Si content is less than x = 1.0. As x = 0.75 and x = 1.0, the amorphous alloys have a two-step crystallization process and the uniform α-Fe/amorphous dual phases structure is easy to be fabricated. After annealing, the crystallized ribbons show a quick increasing trend of Ms values and reach to the maximum approximately 208 emu/g as the annealing temperature is near Tp1, and Hc values are effectively decreased by an auxiliary annealing process applied the magnetic field. The new developed Fe-B-Si-Cu-Hf system alloys with excellent soft magnetic properties show a great application prospect as the novel Fe-based soft magnetic materials.

Influence of plastic deformation by high-pressure torsion on the crystallization kinetics of a Pd40Ni40P20 bulk metallic glass

The influence of high-pressure torsion on the crystallization behavior of the pre-annealed Pd40Ni40P20 bulk metallic glass was investigated by differential scanning calorimetry and fluctuation electron microscopy. Calorimetry shows that deformation splits the single main crystallization peak into a two-step crystallization process including a primary and a main peak. This is in line with fluctuation electron microscopy, which shows a reduction of ordering upon deformation. The overall activation energy and the local activation energy of the crystallization were analyzed by the Kissinger and Kissinger-Akahira-Sunose methods, respectively. The primary crystallization peak occurs at a lower temperature but shows a higher activation energy due to the drastically accelerated atomic mobility. Deformation can accelerate the crystallization process by increasing the nucleation rate.

Melt Crystallization of Poly(butylene 2,6-naphthalate)

Poly(butylene 2,6-naphthalate) (PBN) is a crystallizable linear polyester containing a rigid naphthalene unit and flexible methylene spacer in the chemical repeat unit. Polymeric materials made of PBN exhibit excellent anti-abrasion and low friction properties, superior chemical resistance, and outstanding gas barrier characteristics. Many of the properties rely on the presence of crystals and the formation of a semicrystalline morphology. To develop specific crystal structures and morphologies during cooling the melt, precise information about the melt-crystallization process is required. This review article summarizes the current knowledge about the temperature-controlled crystal polymorphism of PBN. At rather low supercooling of the melt, with decreasing crystallization temperature, β’- and α-crystals grow directly from the melt and organize in largely different spherulitic superstructures. Formation of α-crystals at high supercooling may also proceed via intermediate formation of a transient monotropic liquid crystalline structure, then yielding a non-spherulitic semicrystalline morphology. Crystallization of PBN is rather fast since its suppression requires cooling the melt at a rate higher than 6000 K·s−1. For this reason, investigation of the two-step crystallization process at low temperatures requires application of sophisticated experimental tools. These include temperature-resolved X-ray scattering techniques using fast detectors and synchrotron-based X-rays and fast scanning chip calorimetry. Fast scanning chip calorimetry allows freezing the transient liquid-crystalline structure before its conversion into α-crystals, by fast cooling to below its glass transition temperature. Subsequent analysis using polarized-light optical microscopy reveals its texture and X-ray scattering confirms the smectic arrangement of the mesogens. The combination of a large variety of experimental techniques allows obtaining a complete picture about crystallization of PBN in the entire range of melt-supercoolings down to the glass transition, including quantitative data about the crystallization kinetics, semicrystalline morphologies at the micrometer length scale, as well as nanoscale X-ray structure information.

Improved phase-change properties of Sn–Zn–Sb alloys with a two-step crystallization process for multi-level data storage applications

Abstract We investigated Te-free ZnSb films for the potential applications in multi-level data storage. It was found that, the films could exhibit three phases during crystallization process, e.g., high amorphous phase, intermediate metastable ZnSb phase, and low stable ZnSb phase. However, the formation of the voids in the metastable ZnSb phase, high crystallization temperature and large amorphous resistance have an influence on the structure stability and SET power consumption during the repeated switching process. Interestingly, doping of Sn with a concentration of 11.1 at% into ZnSb can prevent the growth of metastable ZnSb grains, and different crystals like SnSb and ZnSnSb2 can be precipitated out during heat treatment, but the two-step crystallization process is kept unchanged. Moreover, the chemical environment of Sn in Zn–Sb studied by X-ray photoelectron spectroscopy indicates the formation of the large number of Sn–Sb and Sn–Zn bonds, which in turn reduces the crystallization temperature, lowers crystallization activation energy as well as decreases the amorphous resistance. The in situ transmission electron microscopy measurements on the optimized (ZnSb)88.9Sn11.1 composition confirms a two-step phase transition process from amorphous to rhombohedral SnSb crystals first, and then to the stable tetragonal ZnSb2Sn crystals. These excellent properties make Zn–Sb–Sn materials useful as a phase-change layer in low-power and high-density memory.

Self-Limited Growth of Nanocrystals in Structural Heterogeneous Phase-Change Materials during the Heating Process

Typical nanocomposite heterogeneous ZnSb-Al2O3 and ZnSb-ZnO phase-change materials were prepared. A direct comparison of the distinct structures in the amorphous, metastable, and stable states between two different materials was investigated systematically. Upon heating, ZnSb-Al2O3 films show a two-step crystallization process with the formation of the metastable orthorhombic ZnSb phase ahead of the stable trigonal ZnSb phase, while ZnSb-ZnO films could exhibit a one-step crystallization process with the formation of the stable trigonal ZnSb phase when the ZnO-doping concentration is more than 12.3 atom %. In the case of ZnSb-Al2O3, the structural transition to the metastable phase is accompanied by a pronounced increase in the grain size up to 100 nm. Such an increase in the crystal grain size is not found in ZnSb-ZnO films; i.e., the nanocrystals do not grow significantly when the crystallized film is precipitated with the metastable ZnSb phase. By the method of advanced scanning transmission electron m...

A Two-Step Crystallization Route for Hierarchical SAPO-34 Molecular Sieves: Unique Structural Features and Catalytic Property for DTO

The hierarchical structure can significantly improve the diffusion efficiency of the catalyst and regulate the product distribution. Therefore, the preparation of hierarchical SAPO-34 molecular sieve has been a hot research topic. With Cetyltrimethyl Ammonium Bromide (CTAB) and Diethylamine (DEA) as templates, a two-step crystallization process was employed to synthesize hierarchical SAPO-34 molecular sieves. We found that the aging process is vital for the formation of pure phase SAPO-34. It was investigated the relationship of crystallinity trend and mesoporous content with the crystallization time. The results showed that the prolongation of crystallization time was beneficial to enhance the crystallinity of the molecular sieve, but unfavourable to the retention of mesoporous structure. The formation process of hierarchical SAPO-34 molecular sieve involved agglomeration, disintegration, crystallization, re-agglomeration and growth. The hierarchical SAPO-34 molecular sieve with a satisfactory crystallinity and considerable mesoporous structure could be obtained after 36 hours of crystallization. Moreover, the sample had the most suitable acid strength as well as acid amount. The catalytic activity was investigated by catalytic dimethyl ether (DME) to olefin (DTO) reaction. It revealed that the conversion of DME and the selectivity to olefins over the hierarchical SAPO-34 molecular sieve were significantly enhanced with comparison to that over microporous SAPO-34 molecular sieve. The amount of coke deposition of the hierarchical SAPO-34 molecular sieve (14.2%) was lower than that over the microporous molecular sieve (16.5%). Meanwhile, the propylene selectivity of hierarchical SAPO-34 was higher than that of microporous SAPO-34 in the whole reaction. In a word, the hierarchical SAPO-34 molecular sieve synthesized in this study showed a longer catalytic life, higher coke deposition resistance and higher propylene selectivity.

Cold-crystallization of poly(butylene 2,6-naphthalate) following Ostwald’s rule of stages

Melt-crystallization of poly (butylene 2,6-naphthalate) (PBN) at temperatures lower than about 160 °C follows Ostwald’s rule of stages, leading first to formation of a transient smectic liquid crystalline phase (LC) which then may convert in a second step into crystals, controlled by kinetics. In the present work, the PBN melt was cooled at different rates in a fast scanning chip calorimeter to below the glass transition temperature, to obtain different structural states before analysis of the cold-crystallization behavior on heating. It was found that heating of fully amorphous PBN at 1000 K/s leads to a similar two-step crystallization process as on cooling the quiescent melt, with LC-formation occurring slightly above Tg and their transformation into crystals at their stability limit close to 200 °C. In-situ polarized-light optical microscopy provided information that the transition of the LC-phase into crystals on slow heating is not connected with a change of the micrometer-scale superstructure, as the recently found Schlieren texture remains unchanged.

Al-Sb-Ge phase change material: A candidate for multilevel data storage with high-data retention and fast speed

The phase change memory with Al-Sb-Ge alloy is investigated for the feasibility of embedded system and the potential possibility of multilevel data storage. The Al15Sb53Ge32 compound has a high crystallization temperature (333 °C) and outstanding data retention ability (260 °C). Ge atoms inhibit crystal growth to enhance thermal stability and Al15Sb53Ge32 contains sequential crystallization of Sb-rich and Ge regions in two-step crystallization process. Remarkably, the device presents a fast speed of 50 ns and endurance up to 2.3 × 104 cycles. At the same time, a reliable tripe-level resistance state of the phase change memory cell is observed.

High-Quality Single-Crystalline MFI-Type Nanozeolites: A Facile Synthetic Strategy and MTP Catalytic Studies

A facile strategy affording high-quality single-crystalline MFI-type nanozeolites (10–55 nm) with hexagonal prism morphology, good monodispersity, high crystallinity, and high product yield (above 97%) has been developed. This is achieved by synergistically using an l-lysine-assisted approach and a two-step crystallization process in a concentrated gel system (H2O/Si = 9). The morphological evolution of nanosized silicalite-1 is monitored by high-resolution transmission electron microscopy (HRTEM). In this process, metastable irregular nanoparticles are initially obtained at 80 °C as the first step. Consequently, a rearrangement in morphology toward equilibrium crystal shape and without excessive growth for the metastable nanoparticles occurs at 170 °C as the second step. Throughout the whole process, l-lysine acts as an inhibitor to effectively limit the crystal growth of zeolites. Thanks to the high-quality nanosized crystals, the as-prepared ZSM-5 catalysts exhibit superior performance in methanol-to-p...

A novel synthetic strategy of Fe-ZSM-35 with pure framework Fe species and its formation mechanism

A novel two-step crystallization process of Fe-ZSM-35 zeolite was designed, and analyzed by UV resonance Raman spectroscopy.

Synthesis and catalytic performance of ZSM-5/MCM-41 composite molecular sieve from palygorskite

ZSM-5/MCM-41 composite molecular sieve has been hydrothermally synthesized through a two-step crystallization process using palygorskite (PAL) as silicon and aluminum source. The products were characterized by various means and their catalytic properties for acetalization of cyclohexanone and esterification of acetic acid and n-butanol were also investigated. In the first step ZSM-5 zeolite could be formed from the acid-treated PAL after hydrothermal treatment using tetrapropylammonium bromide as template. XRD patterns, N2 adsorption and desorption data, and TEM images show that the composite obtained in the secondary step had a well-ordered mesoporous MCM-41 phase and a microporous ZSM-5 zeolite phase. Compared with ZSM-5, ZSM-5/MCM-41 composite possessed more total acid amount, weak acid sites and large pore structure due to the formation of MCM-41 and exhibited higher catalytic activity for the acetalization and esterification reaction.