Effect Of Crystallization Temperature Research Articles

Mechanical property—processing relations for SiC foams synthesized via polymer particle templating of polycarbosilane

AbstractSilicon carbide foams with an average pore diameter of 650 nm and an inter‐pore ligament thickness of 150 nm have been synthesized using spherical polymethylmethacrylate (PMMA) particle templating of a β‐SiC nanoparticle‐loaded polycarbosilane (PCS) preceramic polymer and the effect of crystallization temperature upon their microstructure and mechanical properties investigated. Differential scanning calorimetry and thermogravimetric analysis were used to investigate both the kinetics of PMMA decomposition and the influence of β‐SiC nanoparticles upon the mechanisms of PCS cure, pyrolysis, and partial crystallization. As the crystallization temperature was systematically increased, the inter‐pore ligament structure coarsened and nanopores developed within the ligaments between the β‐SiC nanoparticles. The foam's Young's modulus and compressive strength at first increased with crystallization temperature, reaching a maximum after processing at 1300˚C. However, further increases in temperature resulted in a rapid fall in both foam modulus and compressive strength. To gain insight into the fundamental processes responsible for the overall (macroscale) mechanical properties, models for open/closed cell foams were inverted and used in conjunction with the measured foam density, Young's modulus, and compressive strength to estimate the mechanical properties of the inter‐pore ligaments. This procedure indicated that changes to the ligament properties were responsible for the observed dependence of the foam mechanical properties upon crystallization temperature.

Accurate derivation of THG conversion efficiency in periodically poled nonlinear medium and optimizing conversion parameters

We have derived a novel equation to accurately predict the third harmonic generation (THG) conversion efficiency in hybrid periodically poled nonlinear medium. Our equation considers the general case that takes both depleted pump regime and phase mismatching cases, resulting in more precise predictions of efficiency. This level of accuracy is crucial for certain applications like high-power THG lasers. Moreover, accurate calculation of THG power density is essential to prevent exceeding the crystal damage threshold. We applied our equation on hybrid MgO:PPLN crystal to determine the optimal SHG region length corresponding to two different power densities, namely, 0.25 and 0.5MW/cm2. The effect of crystal temperature on efficiency was also studies. Furthermore, a comparison between the derived equation and the commonly used nondepleted pump regime equation was performed. We found that the latter equation is significantly less accurate, particularly at high power densities, with the efficiency of the depleted pump regime being 50.6% less than nondepleted one. To demonstrate the effectiveness of the equation, our results were compared with experimental data, and we observed a good agreement between them.

Effect of Crystallization Temperature on the Mechanical and Physical Properties of Solution Cast Polybutylene adipate co-terephthalate/Thermoplastic Starch Films

Starch-based biodegradable films of polybutylene adipate co-terephthalate (PBAT) have been prepared by the solution casting method. The effect of heating at two different temperatures (80 and 110°C) on the mechanical, optical and morphological properties of these films has been evaluated. The two temperatures were selected based on the crystallization and melting temperatures of PBAT. The blend of PBAT with thermoplastic starch has been prepared by melt mixing technique using two roll mills and then the solution casting method has been followed to prepare the films. Apart from curing at room temperature, the films have been cured at 80°C and 110°C. The tensile strength of the films increased by 110% and 252% for films heated to 80°C and 110°C, respectively. As revealed from spectroscopic analysis, the heating of films has no significant effect on the absorption of light by the films in the UV-visible region. The bonding characteristics of the films have been evaluated using Fourier transform infrared (FTIR) spectroscopy. The lowest water absorption and vapour permeability have been obtained in films cured at 80°C.

Fabrication of hesperetin/hydroxypropyl-β-cyclodextrin complex nanoparticles for enhancement of bioactivity using supercritical antisolvent technology

Hesperetin (HST) is a bioflavonoid from citrus fruits and its clinical application is still markedly limited by its poor water solubility (1.27 µg/mL). Herein, a complex nanoparticle containing HST and hydroxypropyl-β-cyclodextrin (HP-β-CD) was prepared through supercritical antisolvent (SAS) technology to improve HST solubility, dissolution rate and bioactivity. The effects of crystallization temperature, crystallization pressure, mass flow rate, and drug concentration were systematically investigated using single-factor experiment and orthogonal experiment. The physicochemical properties and structure of the complex were examined using SEM, FTIR, DSC, BET, XPS and XRD analyses. After processing through SAS technology, the in vitro performance of HST was significantly improved such as solubility, dissolution rate and antineoplastic activity. HST as a potential antiproliferative and antioxidant compound appear to have anti-tumor effect on A549 cells. The above results proved that supercritical antisolvents crystallization was a feasible method to fabricate polymer-pharmaceutical complex nanoparticles for drug delivery system.

Preparation of Pickering emulsion stabilized by lauroyl lysine

Abstract In this paper, the effect of Nε-lauroyl lysine (LL) on stabilizing W/O Pickering emulsions was investigated, and the effect of crystallization temperature on the particle size of LL was explored. The Pickering emulsion was prepared with LL as particle emulsifier, and the effects of homogenization rate, emulsification temperature, particle concentration, oil-water volume ratio and other factors on the preparation of emulsion were discussed. The results showed that the LL particles were the smallest for a crystallization temperature of 30 °C with a size of (1.3 ± 0.2) µm. The oil-water-LL contact angle was 142.9° ± 1.6°, and the prepared emulsion was of W/O type. The most stable emulsions were obtained under the following conditions: homogenization rate = 11,000 r min−1, emulsification temperature = 20 °C, particle concentration = 2 wt%, oil-water volume ratio = 1:1. In addition, LL showed good tolerance to the aqueous phases with different pH values. The LL-stabilized emulsion system proved to be stable over the long term in the stand tests.

Na1.5Y2.5F9: Ce3+, Tb3+, Eu3+ glass-ceramics for white light

A simply encapsulated, long-range excitation method for white light generation was proposed. Na1.5Y2.5F9: Ce3+, Tb3+, Eu3+ (NYFCTE) glass-ceramics (GCs) were synthesized by the melt-quenching method. The effect of crystallization temperature on the formation of crystallites was analyzed by X-ray diffraction (XRD). The morphology and size of nanocrystals were investigated by transmission electron microscope (TEM). The unit cell diagram of Na1.5Y2.5F9 nanocrystals was drawn. In addition, the luminescence properties of Ce3+, Tb3+, Eu3+ ions-doped Na1.5Y2.5F9 GCs were tested and analyzed. The sample NYFCTE2 emits bright white light when excited by a 320 nm light source at a distance from the light source. The NYFCTE2 sample obtained white light with Commission Internationale de L'Eclairage (CIE) coordinate of (0.3110, 0.3472), Correlated Color Temperature (CCT) of 6467.72 K, and reliable thermal stability. The above results indicate that the proposed white light generation method and NYFCTE GCs have immense application prospects for illumination.

Effects of crystallization temperature and cooling rate on the polymorphism of trans‐1,4‐polyisoprene vulcanizate

AbstractThe effects of crystallization temperature and cooling rate on the polymorphism of trans‐1,4‐polyisoprene vulcanizate (TPI‐V) with different sulfur dosages were monitored by WAXD in real time. The results showed that both the crystallization temperature and the cooling rate play decisive roles in determining the polymorphism and their relative amounts, whereas their effects are interfered by the crosslinking density which restrains the crystallization kinetics. Only α crystal is formed when crystallization is conducted at 40°C or greater and mixed α/β crystals are obtained in the temperature range of 10–30°C. β crystal is predominate when crystallized at 10°C while α crystal is limited at 30°C. Both the lower temperature and increased crosslinking density are beneficial to β crystal formation. A high crosslinking density causes a prolonged time is needed for pure α crystal formation, and hinders the TPI‐Vs from forming pure α crystal even if crystallization is conducted at 45°C. A lower cooling rate favors the formation of α crystal while a higher cooling rate favors β crystal formation. The β spherulites are much brighter than α spherulites under the observation of polarized microscopy.

Improved Rotational Foam Molding Properties of Tailored Polyethylene Blends with Higher Crystallization Temperature and Viscosity-Temperature Sensitivity.

Rotational foam molding has attracted more and more attention due to the inexpensive machines required, low residual stresses, and flexible design for special and high-value-added applications. However, it is a great challenge to control cell sizes and morphology because of its coalesce and collapse during prolonged heating or at different temperatures. A novel tailored polyethylene blend with a unique chain structure for rotational foam molding was creatively proposed and demonstrated, and the effects of crystallization temperature and viscosity–temperature sensitivity on foaming were also investigated. The polyethylene blends with few chain branches in the low-molecular-weight part and many chain branches in the high-molecular-weight part effectively improved the crystallization temperature and the viscosity–temperature sensitivity for better prevention of coalesce and collapse during the foam-shaping stage.

Transparent MgO-Al2O3-SiO2 glass-ceramics prepared with ZrO2 and SnO2 as nucleating agents

Transparent spinel glass-ceramics in MgO-Al2O3-SiO2 (MAS) system have been prepared by choosing tin dioxide and zirconia as nucleating agents. The effect of crystallization temperature on the crystallization properties, microstructure, and mechanical properties of the glass-ceramics were investigated. The results revealed that spinel, gahnite, and zirconia were observed in the glass-ceramics. The Kissinger method was used to calculate the crystallization kinetics of spinel glass-ceramics, and the crystallization activation energy was 381 kJ/mol. The grain size and content of the crystalline phase become higher with the rising crystallization temperature, and the transparency of glass-ceramics decreased. In terms of mechanical properties, raising the crystallization temperature induced higher microhardness and hence the bending strength first increased and then decreased. In the optimal preparation condition (810 °C/2 h + 1000 °C/2 h), the colorless and transparent glass-ceramics had excellent overall properties, with a microhardness of 9.3 GPa and bending strength of 170 MPa.

Effects of crystallization temperature on the characteristics of sugar crystals in date fruit syrup as measured by differential scanning calorimetry (DSC), polarized microscopy (PLM), and X-ray diffraction (XRD).

Characteristics of sugar crystals are important for developing set-syrup due to their contribution to the desired mouth feel when consumed. Two types of set-syrup (i.e. seeds with and without) were developed by storing the syrup at -20, 4 and 15°C. The melting temperatures (onset and peak), and enthalpy of set-syrup without seeds (SN) were 30.2°C, 74.6°C and 42.2kJ/kg respectively. In the case of SN, enthalpy decreased with the decrease of crystallization temperature (P < 0.05), while there was insignificant change in the case of set-syrup with seeds (SW) (P > 0.05). Polarized Light Microscopy (PLM) images showed that finer crystals were formed in the cases of set-syrups (i.e. SN and SW) as the storage temperature was decreased. X-ray diffraction (XRD) analysis showed the formation of different polymorphic sugar crystals. Crystallization temperatures at 4 and -20°C can be used to produce finer crystals with varied polymorphic characteristics.

Sustainable synthesis of highly water-selective ZSM-5 membrane by wet gel conversion

High-performance zeolite socony mobil five (ZSM-5) membranes were successfully prepared on a cheap, tubular α-Al2O3 support via a proposed wet gel conversion (WGC), aiming at avoiding the competitive zeolite crystals growth in the solution and ensuring the formation of polycrystalline zeolite layer onto the support surface. A small amount of gel was loaded on seeded tubes via dip-coating and then converted to ZSM-5 membranes via direct crystallization without using any additional synthesis solution for membrane growth. By using this method, the amount of synthetic gel was largely reduced as compared with the traditional hydrothermal synthesis. The effects of crystallization temperature, crystallization duration, and synthetic gel silica source dissolution duration on the morphologies, microstructures, and pervaporation performances of ZSM-5 membranes were investigated. Under optimized synthesis conditions, the as-synthesized ZSM-5 membrane showed high separation performance and stability in isopropanol dehydration. During the 104-h pervaporation test, the permeation flux was stable at 2.96 kg m−2 h−1 with a separation coefficient exceeding 10,000. The synthetic route exhibited excellent reproducibility for the fabrication of highly water-selective ZSM-5 membrane. This work provides a novel, feasible method for the preparation of zeolite membranes with high performance, high atom economy, low cost, and reduced waste solution.

Facile Hydrothermal Synthesis of EAB‐Type Zeolite under Static Synthesis Conditions

AbstractConventionally, EAB‐type zeolites are crystallized by hydrothermal synthesis for many days under agitational synthesis conditions such as rotation or stirring. In the present study, EAB‐type zeolite is obtained by hydrothermal synthesis within 12 h under static synthesis conditions for the first time. The effects of crystallization temperature, aging of the precursor sol, and addition of seed crystals are investigated. The results reveal that EAB‐type zeolite can be obtained when using a precursor sol with short aging time followed by hydrothermal synthesis in a very narrow temperature range 110 °C−120 °C under static synthesis condition. Addition of seed crystals is found to suppress the formation of SOD‐type zeolite, the primary phase at high hydrothermal synthesis temperatures, while it does not increase the crystallization rate of EAB‐type zeolite. Furthermore, the crystallization behavior at 120 °C is examined by varying the synthesis time. EAB‐type zeolite with invariably twinned plate‐like morphology starts to crystallize between synthesis time of 3 to 6 h at 120 °C under the static synthesis condition.

Template-free method for the synthesis of high-pore-volume γ-Al2O3 nanofibers in a membrane dispersion microreactor

Mesoporous γ-Al2O3 nanofibers with high pore volume and uniform pore size distributions were successfully synthesized via a template-free method in a membrane dispersion microreactor followed by calcination. The effects of crystal temperature, pH values, continuous phase concentration and washing solvent on the γ-Al2O3 nanofibers were carefully studied. The results showed that the as-obtained γ-Al2O3 nanofibers showed a length of 40–60 nm and a width of 3.2–3.4 nm, which were attributed to the high microscopic mixing rate in the membrane dispersion microreactor. Moreover, the precursors of γ-Al2O3 nanofibers treated with deionized water and mixed deionized water/alcohol solution had high pore volumes, reaching to 1.60 ml g−1 and 2.00 ml g−1, respectively. Furthermore, the adsorption performance of γ-Al2O3 nanofibers with high pore volumes was also investigated. These fibers showed an excellent adsorption capacity of 1323.68 mg g−1 for the removal of Congo red from aqueous solution, thereby indicating their potential for applications in adsorption and other related areas.

Solution-grown composite single crystals of poly(L-lactic acid)-b-polystyrene block copolymers and poly(L-lactic acid) homopolymers

In the present work, composite single crystals (CSCs) composed of poly (L-lactic acid) (PLLA) homopolymer and poly (L-lactic acid)-b-polystyrene (PLLA-b-PS) block copolymers (BCPs) were prepared by solution co-crystallization. The effects of crystallization temperature (Tc), mass ratio of BCP/homopolymer and PS block length on the morphology and growth habit of the CSCs were investigated. Particularly, parallelogram CSCs with four {110} crystal planes as edges tend to be formed at a low Tc and a small BCP/homopolymer mass ratio for the BCP with a short PS block. The parallelogram shape of the crystals indicates the growth rates along four {110} crystal planes are different in two directions. It is proposed that the folded surface free energy is reduced after incorporation of PLLA-b-PS BCP into the crystals, leading to accelerated growth and concave surface structure along the long side direction. The chain folding of the PLLA block in the CSCs was also discussed. It is found that, in order to match the chain folding of PLLA homopolymer, the PLLA block in the BCPs adopts more chain folds in the CSCs than that in the single crystals formed by neat BCPs.

Effect of crystallization temperature on glass-ceramics derived from tailings waste

Abstract Sintered glass-ceramics containing CaO–Al2O3–SiO2 were successfully fabricated by application of sinter-crystallization process, with tungsten tailings waste (TTW) as main raw materials. Crystallization kinetics analysis showed that surface crystallization dominated the overall crystallization process and the ingredient of TTW was beneficial to the crystallization process. The effects of crystallization temperature on crystallization behavior and properties of glass-ceramics demonstrated that it played an important role in controlling the crystal growth and crystalline phase transition. With the increasing crystallization temperature to 1050 °C, part of the crystalline phase was transformed from wollastonite to anorthite. Also, the glass-ceramic fired at 950 °C for 2 h presented higher volumetric density (2.82 g/cm3), lower water absorption (0.09%), higher flexural strength (97.56 MPa), superior Vickers hardness (6.3 GPa), moderate acid resistance (0.18%), and lower alkali resistance (0.19%). Leaching tests performed on as-prepared glass-ceramics demonstrated that heavy metals were stabilized well in the newly formed phase. Overall, the glass-ceramics derived from TTW are promising for exploring high value-added products and vitrifying hazardous elements, as well as promoting their application in construction and environmental protection.

Fabrication and orientation of Ni-LAB membranes by linker salt approach

Abstract Metal-organic framework (MOF) materials have exhibited exponential growth over the last two decades and MOF membranes already show great potential in separation application. Herein the linker salt method was firstly applied to the preparation of MOF membranes using Ni-LAB [Ni2(L-asp)2(bipy)] membranes as a model. This method is based on the utilization of organic linker salts instead of its protonated forms, thus their solubility and deprotonation step could be greatly enhanced, leading to a higher supersaturation that is beneficial for the formation of MOF membranes. This method was effective and led to the greener and milder synthesis for Ni-LAB membranes. In this work, all of the Ni-LAB membranes were fabricated on α-Al2O3 tubes by secondary growth method using ball-milled Ni-LAB seeds. By using the linker salt potassium l -aspartate hydrate and soluble metal source nickel nitrate hexahydrate, continuous and compact Ni-LAB membrane can be prepared by crystallizing at 150 °C for only 1 h, in which both the soluble metal precursor and the organic linker salt played important roles in the rapid preparation of Ni-LAB membrane. Effect of crystallization temperature on membrane preparation was investigated, it was found that Ni-LAB membrane can be synthesized even at 70 °C and the membranes prepared at different temperatures showed different morphologies. The Ni-LAB membrane could also be prepared in a dilute solution and the concentration of synthetic solution greatly affected the orientation of Ni-LAB membrane. Ni-LAB membrane exhibited preferential (200) orientation when prepared with a low concentration of synthetic solution whereas it showed preferential (101) & (002) orientation when prepared with a relative high concentration. The generation of corrosive nitric acid during the preparation process can be greatly reduced and replaced by eco-friendly potassium nitrate. Single gas permeation tests were carried out to evaluate the quality of the as-synthesized Ni-LAB membranes.

Promising high-conductivity Li1.5Al0.5Ge1.5(PO4)3 solid electrolytes: the effect of crystallization temperature on the microstructure and transport properties

High-conductivity NASICON-type solid electrolytes of Li1.5Al0.5Ge1.5(PO4)3 composition have been obtained through glass crystallization. Thermal behavior of the precursor glass has been investigated; glass transition and crystallization temperatures have been determined by DSC. The influence of glass crystallization temperature (750, 800, 820, and 850 °C) on the phase composition, microstructure, molecular structure, and ionic conductivity of Li1.5Al0.5Ge1.5(PO4)3 glass-ceramics has been studied. It was found that the optimum crystallization temperature for obtaining an electrolyte with the highest conductivity (0.39 mS cm−1 at 25 °C) is 820 °C.

Thermal process and mechanism of phase transition and detoxification of glass-ceramics from asbestos tailings

Based on the chemical and mineral composition of asbestos tailings, the asbestos tailings powder was pre-fired, formed into green body and finally heat-treated to prepare glass-ceramics through the processes of crystallization and sintering. The main crystal phases of the sample were forsterite and enstatite, and the minor crystal phases were magnesioferrite and diopside. The effects of crystallization temperature (787–867 °C) and sintering temperature (1150–1250 °C) on crystallization and phase change, micromorphology and physical-chemical properties of glass ceramics were investigated by means of thermogravimetry-differential scanning calorimetry analysis (TG-DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM-EDS) and mechanical properties tests. The results showed that the toxic phase chrysotile was almost converted into forsterite when the asbestos tailings powder was pre-fired at 700 °C for 1 h. During the sintering process of the green body, with the increase in the crystallization temperature, the content of the forsterite firstly increased and then decreased, and the enstatite increased gradually. After crystallizing at 850 °C for 1 h and holding at different sintering temperatures for 1 h, the glass-ceramics samples were obtained. With the increase in sintering temperature, the content of diopside in the samples gradually decreased, the hematite gradually disappeared and magnesioferrite precipitated at the same time. The crystal morphology was transformed from aggregates of spherulites and ellipse into intertwined bodies of spherulites, ellipse and round bar-like shape. The glass-ceramics achieved optimum compactness at the sintering temperature of 1200 °C with the water absorption rate being 0.026%, the bulk density being 3.164 g/cm3, and the flexural strength being 88 MPa, which reached the standard of glass ceramics for construction. In the process of preparing glass-ceramics from asbestos tailings, the phase transition and detoxification in asbestos tailings were realized, which had certain practical value for the utilization of asbestos tailings and the preparation of high value-added materials.

Effect of crystallization temperature on energy-storage density and efficiency of lead-free Bi0.5(Na0.8K0.2)0.5TiO3 thin films prepared by sol–gel method

Abstract Lead-free Bi0.5(Na0.80K0.20)0.5TiO3 (BNKT) ferroelectric films were synthesized on Pt/Ti/SiO2/Si substrates via the chemical solution deposition. The influence of the crystallization temperature on the microstructures, the ferroelectric and energy-storage properties of the films was investigated in detail. The results showed that the BNKT films have reached the well crystallized state in the single-phase perovskite structure at 700 °C. Ferroelectric and energy-storage properties of the films were significantly enhanced by increasing the crystallization temperature. The remnant polarization (2Pr) and maximum polarization (2Pm) reached the highest values of 18.4 μC/cm2 and 61.2 μC/cm2, respectively, under an applied electric field of 300 kV/cm. Thanks to the strong enhancement in 2Pm and the large Pmax - Pr value, the highest energy-storage density (Jreco) and efficiency of 2.3 J/cm3 and 58.2%, respectively, were obtained. These results indicate that the BNKT films have application potentials in advanced capacitors.

Dielectric characterization of a novel Bi2O3-Nb2O5-SiO2-Al2O3 glass-ceramic with excellent charge-discharge properties

A newly designed glass-ceramic system consisting of 15Bi2O3-15Nb2O5-40SiO2-30Al2O3 was successfully prepared, which was followed by its controlled crystallization at different heating temperatures. The effects of crystallization temperature on the microstructure, phase evolution and the energy storage behaviors of the novel material were systematically investigated. A maximum theoretical energy storage density of up to 15.3 J/cm3 was found in the samples heated at 800 °C. The polarization-electric (PE) hysteresis loops of this material exhibited very good linear character and high energy efficiency. In addition, an approximate value of 25 ns for discharged period T has been obtained, which demonstrated that most of the energy stored in dielectric was released over a very short time. The maximum powder density exceeds a high value of 90 MW/cc in a 390 kV/cm electric field. Therefore, the new developed Bi2O3-Nb2O5-SiO2-Al2O3 glass-ceramic can be used as an alternative, promising high-performance electrostatic capacitor material.