Degree Of Crystal Orientation Research Articles

A novel fast fabrication of crystal-oriented hydroxyapatite ceramics via gel-casting in high magnetic field

Hydroxyapatite ceramics with oriented crystal structures are successfully fabricated via a novel and fast gel-casting process in high magnetic field for the first time. Experimental conditions as direction and duration of gel-casting in magnetic field were altered for selective crystal orientation of a,b-/c-plane of hydroxyapatites. The effect of slurry preparation process as ball-milling and freeze-drying on orientation degree and grain growth behavior of hydroxyapatite particles is elucidated with detailed analysis of the size distribution of particles, viscosity of slurry, microstructure and crystal structure of sintered bodies with assistance of SEM, XRD and advanced mapping observation of EBSD patterns. In addition, the influence of sintering temperature on the crystal phase transformation of the oriented outermost surface is also clarified through Raman spectroscopy in depth. It was found that the freeze-drying processed slurry shows potential in enhancing the crystal orientation degree than the ball-milling case, during where a suppressed grain growth phenomenon and inhibition of crystal phase transformation on highly oriented hydroxyapatite was also observed.

Temperature-stable Characteristics of Textured (Bi,Sm)ScO3-PbTiO3 Ceramics for High-temperature Piezoelectric Device Applications

In this study, textured 0.38(Bi<sub>0.97</sub>Sm<sub>0.03</sub>)ScO<sub>3</sub>-0.62PbTiO<sub>3</sub> (0.38BSS-0.62PT) ceramics with high Curie temperature were evaluated to assess temperature stable characteristics for high-temperature piezoelectric device applications. The 4 vol% BaTiO<sub>3</sub> incorporated 0.38BSS-0.62PT ceramic was fabricated by conventional tape casting. Textured 0.38BSS-0.62PT ceramic was successfully produced at sintering temperature of 1150°C by textured grain growth (TGG). Textured 0.38BSS-0.62PT ceramic exhibited a high degree of crystal orientation of 94% in the [001]-direction. It also showed excellent dielectric and piezoelectric properties, (<i>ε</i><sup>T</sup><sub>33</sub>/<i>ε</i><sub>0</sub> of 1746, <i>d</i><sub>33</sub> of 719 pC/N, <i>k</i><sub>p</sub> of 61.8% and <i>g</i><sub>33</sub> of 45×10<sup>-3</sup>Vm/N, respectively). In addition, it also exhibited relaxor-like ferroelectric characteristics with a large relaxation coefficient (γ) of 1.77 along with high Curie temperature of approximately 373℃. Its temperature stability was satisfactory, resulting from in-situ <i>d</i><sub>33</sub> and <i>k</i><sub>p</sub>, which were lower than 10% below Curie temperature. The electro-strain also showed thermally stable characteristics. Therefore, it is considered that the textured 0.38BSS-0.62PT ceramic has potential for high-temperature piezoelectric device applications.

Implication of Freeze-Thaw Erosion and Mechanism Analysis of High-Performance Aromatic Liquid Crystal Fibers.

According to the demand for high-performance fibers for high-latitude ocean exploration and development, this paper selects representative products of high-performance liquid crystal fibers: thermotropic liquid crystal polymer fibers (TLCP) and poly p-phenylene terephthalamide (PPTA) fibers. Through a series of freeze-thaw (F-T) experiments for simulating a real, cold marine environment, we then measure the retention of mechanical properties of these two kinds of fibers. Before that, due to the difference in their chemical structures, we tested their Yang-Laplace contact angle (YLCA) and water absorption; the results suggested that PPTA fibers would absorb more moisture. Surprisingly, then, compared with thermotropic liquid crystal polymer (TLCP) fibers, the retention of the mechanical properties of poly p-phenylene terephthalamide (PPTA) fibers decreased by around 25% after the F-T experiments. The Fourier-transformed infrared (FT-IR) analysis, the attenuated total reflection (ATR) accessory analysis and the degree of crystal orientation measured by two-dimensional wide-angle X-ray diffraction (2D-WAXD) confirm that no changes in the chemical and the orientation structure of the crystal region of the fibers occurred after they underwent the F-T cycles. However, as observed by scanning electron microscopy (SEM), there are microcracks of various extents on the surface of the PPTA fibers, but they do not appear on the surface of TLCP fibers. It is obvious that these microcracks will lead to the loss of mechanical properties; we infer that the moisture absorbed by the PPTA fibers freezes below the freezing point, and the volume expansion of the ice causes the collapse of the microfibrillar structure. The two sorts of fibers subjected to the F-T experiments are immersed in a sodium chloride solution, and the amount of water infiltrated into the PPTA microfibrillar structure is evaluated according to the content of sodium ions in the fiber surface and subsurface layers through X-ray spectroscopy (EDS) elemental analysis. From the above analysis, we found that TLCP fibers can more effectively meet the operating standards of the severe and cold marine environment.

Low-Temperature Phase-Transition for Compositional-Pure α-FAPbI3 Solar Cells with Low Residual-Stress and High Crystal-Orientation.

Transition of δ-phase formamidinium lead triiodide (δ-FAPbI3 ) to pure α-phase FAPbI3 (α-FAPbI3 ) typically requires high processing temperature (150 °C), which often results in unavoidable residual stress. Besides, using methylammonium chloride (MACl) as additive in fabrication will cause MA residue in the film, compromising the compositional purity. Here, a stress-released and compositional-pure α-FAPbI3 thin-film is fabricated using 3-chloropropylammonium chloride (Cl-PACl) by two-step annealing. The 2D template of n = 2 can preferentially form in perovskite with the introduction of Cl-PACl at a temperature as low as 80 °C. Such a 2D template can guide the free components to form ordered α-FAPbI3 and promote the transition of the formed δ-FAPbI3 to α-FAPbI3 by reducing the phase transition energy. As a result, the obtained perovskite films via low-temperature phase-transition have a high degree of crystal orientation and reduced residual stress. More importantly, most of the Cl-PACl is volatilized during the subsequent high-temperature annealing process accompanied by the disintegration of the 2D templates. The residual trace of Cl-PA+ is mainly concentrated at the grain boundary near the perovskite surface layer, stabilizing α-FAPbI3 and passivating defects. Perovskite solar cell based on pure α-FAPbI3 achieves a power conversion efficiency of 23.03% with excellent phase stability and photo-stability.

Toughening Wet-Spun Silk Fibers by Silk Nanofiber Templating.

Regenerated silk fibers typically fall short of silkworm cocoon fibers in mechanical properties due to reduced fiber crystal structure and alignment. One approach to address this has been to employ inorganic materials as reinforcing agents. The present study avoids the need for synthetic additives, demonstrating the first use of exfoliated silk nanofibers to control silk solution crystallization, resulting in all-silk pseudocomposite fibers with remarkable mechanical properties. Incorporating only 0.06wt% silk nanofibers led to a ≈44% increase in tensile strength (over 600MPa) and ≈33% increase in toughness (over 200kJkg-1 ) compared with fibers without silk nanofibers. These remarkable properties can be attributed to nanofiber crystal seeding in conjunction with fiber draw. The crystallinity nearly doubled from ≈17% for fiber spun from pure silk solution to ≈30% for the silk nanofiber reinforced sample. The latter fiber also shows a high degree of crystal orientation with a Herman's orientation factor of 0.93, a value which approaches that of natural degummed B. mori silk cocoon fiber (0.96). This study provides a strong foundation to guide the development of simple, eco-friendly methods to spin regenerated silk with excellent properties and a hierarchical structure that mimics natural silk.

Stress-strain behavior and corresponding crystalline structures of four types of polyethylene under a wide range of strain rates

Stress-strain behavior of four types of polyethylene (PE), i.e. low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), medium-density polyethylene (MDPE) and high-density polyethylene (HDPE), under a wide strain rate ranging from 0.001 to 1000 s−1, and the crystalline structures of corresponding fractured PEs were investigated. Results demonstrated that when the strain rate was less than 1 s−1, PE exhibited ductile fracture with a rougher section. While at strain rates larger than 1 s−1, the damage was manifested as brittle fracture with a smooth fracture surface. For all PE specimens, the yield strength increased with strain rate, but the increasing dependency of yield stress on strain rate was diverse in various strain rate ranges. Under the same strain rate, due to the largest molecular weight and lowest branching degree, HDPE showed the highest values in yield strength, crystallinity, crystal orientation degree, and crystallite size. At the appropriate stain rate, i.e. 10 s−1, HDPE with less branched structure is more likely to obtain higher crystallinity and molecular chain orientation degree.

Quantitative analysis of Protective Role of salivary protein on demineralization of enamel

Objective: The aim of this study was to analyze the effect of salivary proteins (statherin and histatin-1) on demineralized enamel surface and to study changes in texture, magnitude and direction of crystallites and changes in prismatic structure of enamel respectively. Material & Methods: Synchrotron x-ray diffraction technique to determine the variation in degree of crystal orientation (texture). Incisors were demineralized and sectioned to 300-500 microns, rinsed with salivary protein solutions of statherin and histatin separately and in combination with short and full-lengths. A beam spot size of 20μm × 20μm was used to obtain 2D diffraction patterns to distinguish orientation of crystallites. Results: The contour maps as well as the SEM analysis present similar surface properties of the sample treated with STN-21 and the controlled PBS sample. Therefore, STN-21 was found potent in preventing demineralization and restoring surface enamel texture followed by STN-21+HTN-21 and STN43+HTN38. HTN-21 and HTN-38 showed similar demineralization pattern as the controlled demineralized sample. Conclusion: Ranking of demineralization among samples was found to be controlled demineralized > HTN-21 = HTN-38 > STN-43+HTN-38 > STN-21+HTN-21 > STN-21. Developing STN-21 as a therapeutic against dental caries and erosion. Keywords: Enamel, Demineralization, salivary proteins.

Analysis of process parameters affecting the crystal orientation of Na+-β″-Al2O3 solid electrolyte in one-step synthesis cum sintering process

Na+-ion conducting Na+-β"-Al2O3 solid electrolyte has been prepared by a one-step synthesis cum sintering process as an alternative to the conventional solid-state reaction process, and the degree of crystal orientation was evaluated by the Lotgering factor with XRD Cu-Kα radiation source. In order to analyze the process parameters which affect the value of Lotgering factor, two experiments were carried out separately, i.e. on dwelling at various temperatures before sintering and different granule sizes selected in the press-forming. The Na+-β"-Al2O3 fabricated by one-step synthesis cum sintering process fully crystalized without any secondary phase. As a result, lower values of Lotgering factor indicated a higher ionic conductivity of Na+-β"-Al2O3. Among the processes including the heat treatment step, the smallest Lotgering factor was observed in the dwelling temperature of 1000 °C for 2 h. In terms of granule size, the smaller grain size showed the lower Lotgering factor.

Comparative analysis of the morphology, chemistry and structure of the tibiotarsus, humerus and keel bones in laying hens

ABSTRACT Bone properties are adapted to their specific functions in the animal, so various types of bones develop different characteristics depending on their location in the skeleton. The aim of this research was to compare the chemical composition, crystalline characteristics and structural organisation in tibiotarsus, humerus and keel bones as representatives of hen skeletal mineralisation. Complementary analytical techniques, such as X-ray radiography, optical and electron microscopy, thermogravimetry and 2D X-ray diffraction, were used for characterisation. The humerus had a thinner cortex and cortical bone mineral had higher crystallinity and a greater degree of crystal orientation than the tibiotarsus. The humerus generally lacks medullary bone although, when present, it has a more mineral content than seen in the tibiotarsus. These differences were attributed to the different forces that stimulate bone formation and remodelling. The keel cortical bone had a lower degree of mineralisation than the tibiotarsus or humerus. Its degree of mineralisation decreased from the cranial to the distal end of the bone. This gradient may affect keel mechanical properties, making it more prone to deformation and fractures. Data from studying different bones in laying hens can help to understand mineralisation as well as finding solutions to prevent osteoporosis-related fractures.

Production of crystal-oriented lanthanum silicate oxyapatite ceramics with anisotropic electrical conductivity and thermal expansion

Lanthanum silicate oxyapatite (LSO) has a very high oxide-ion conductivity along the c-axis of its hexagonal crystal. The effect of the crystal orientation in LSO ceramics on the anisotropy of their electrical and mechanical properties has not been studied systematically because centimeter-scale ceramics with different degrees of crystal orientation are difficult to produce. We produced crystal-oriented LSO ceramics by slip casting under a strong magnetic field and subsequent sintering. Using LSO ceramics with different degrees of crystal orientation, the electrical conductivity (σ) and linear thermal expansion coefficient (α) were measured. σ parallel to the c-axis (σ||c) increased as the degree of crystal orientation increased, whereas σ perpendicular to the c-axis (σ⊥c) was relatively insensitive to this parameter. The σ||c and σ⊥c values of our samples were almost the same as those of LSO single crystals. α also exhibited anisotropy originating from the asymmetry of the crystal structure.

Oriented surface nucleation in diopside glass

Oriented surface crystallization on polished diopside glass surfaces has been studied with scanning electron microscopy, electron backscatter diffraction, transmission electron microscopy and laser scanning microscopy. An orientation preference of [001] parallel to the glass surface was detected for separately growing diopside crystals even as small as 700 nm in size. This finding shows that crystal orientation occurs in the outermost surface layer without crystal-crystal interaction and indicates that the crystal orientation is a result of oriented nucleation. Depending on surface preparation, monomodal crystal orientation distributions with [100] perpendicular to the surface or bimodal distributions with [100] and [010] perpendicular to the glass surface were detected. It was also shown that the degree of crystal orientation increases with decreasing surface roughness. The observed orientation of diopside crystals could be explained in terms of the interfacial energies of different crystal faces.

Production of Crystal Oriented Neodymium Silicate Oxyapatite Ceramics and Their Conductivity

Production of oxide ion conductor ceramics having high conductivity is important for applications of solid oxide fuel cells (SOFC) and chemical sensors. Particularly, the ceramics with high ionic conductivity around 873 K have attracted attention for development of SOFC and sensors operated at middle-temperature.Neodymium silicate oxyapatite, denoted by NSO hereafter, was known to show very high oxide ion conductivity along to the c-axis below 873 K [1]. To utilize this property, production of the crystal-oriented ceramics is necessary. In this research, we produced crystal-oriented NSO green bodies by a slip casting under a magnetic field less than 1 T. Dense and crystal-oriented NSO ceramics were obtained by subsequent conventional sintering under an ambient atmosphere. In addition, NSO ceramics having different degree of crystalline orientation were successfully produced. Using these ceramics, the degree of the crystal orientation and its dependence on conductivity were discussed on the basis of experimental data.Composition of NSO was Nd9.43(SiO4)6O2, which was confirmed to be close to the oxyapatite single phase (NSO has a wide composition range [2], [3]). The raw materials were Nd2O3 and SiO2. NSO was synthesized by solid state reaction method at 1473 K or 1773 K.For production of crystal-oriented NSO green body, controlling the distribution of particle size was important to prepare a slurry used for slip casting. Therefore, the synthesized NSO powder was grinded by planetary ball mill. The slurry was prepared by mixing of the grinded NSO powder and polyethyleneimine in distilled water. The c-axis oriented NSO green body was prepared by slip casting under a magnetic field of 1 T and 0.5 T. These green bodies were denoted by NSO-1T and NSO-0.5T, hereafter. The green body produced without magnetic field was denoted as NSO-0T. The green bodies were sintered at 1873 K for 6 h in air in order to obtain the dense ceramics.X-ray diffraction (XRD) patterns on surfaces of (a) NSO-0T, (b) NSO-0.5T and (c) NSO-1T are shown in the Figure. XRD profile of (a) NSO-0T is good agreement with that of the oxyapatite single phase (standard data (d), ICSD No. 01-075-7767). Regarding to the patterns of (b) NSO-0.5T and (c) NSO-1T, intensities of (00l) peaks were very high, compared to those of (a) NSO-0T and standard data. The degree of crystal orientation was evaluated by Lotgering factor [4] calculated from these XRD patterns. Lotgering factors of the densified NSO-1T and NSO-0.5T were 0.93 and 0.95, respectively. In the case of perfect crystal-orientation, Lotgering factor is unity. Contrary, the factor is zero for random crystalline orientation. The factor values of 0.93 and 0.95 indicate that the degrees of the c-axis orientation are very high.Conductivity was measured by electrochemical impedance method between 773 K and 1273 K under air. The conductivity was found to be depended on the Lotgering factor values. Conductivities at 773 K of the samples sintered from NSO-1T, NSO-0.5T, and NSO-0T were 3.97×10-3, 3.04×10-3, and 3.88×10-4 S cm-1, respectively. The conductivities of the samples with highly c-axis orientation was about 10 times higher compared to that of randomly oriented samples. The conductivities of sintered NSO-0.5T and NSO-1T along to the c-axis at 773 K are confirmed to be close to that of a single crystal (6.4×10-3 S cm-1) [5].Considering into high magnetic susceptibility of neodymium, the crystal-oriented NSO ceramics can be fabricated under magnetic fields less than 1 T and high conductivity was achieved comparable to that of single crystal.Reference[1] S. Nakayama, et al, Journal of the European Ceramic Society, 19, 507-510, (1999).[2] R. O. Miller, et al, J. Am. Ceram. Soc., 47, 653-654, (1964).[3] G. J. McCathy, et al, J. Inorg. Nucl. Chem., 29, 253-254, (1967).[4] F. K. Lotgering, J Inorg. Nucl. Chem., 9, 113-123 (1959).[5] S. Nakayama, et al, Journal of materials science letters, 20, 913-915, (2001). Figure 1

Self‐assembled fibrillar polyethylene crystals with tunable properties

AbstractDue to its simple linear chain structure, crystal morphology of linear low‐density polyethylene (LLDPE) fibers can be controlled to fulfill the needs of diverse advanced applications. This study presents a simple two‐step method to produce LLDPE fibers with self‐assembled fibrillar crystals and highly oriented amorphous phase. Rather than conventional melt spinning, fibers were treated in a two‐step eco‐friendly bath without drawing after extruded fibers emerge from the spinneret. Treated fibers through the baths demonstrated lower crystallinity, but significantly higher degree of crystal orientation when compared to control fibers of traditional melt spinning. Morphological analysis revealed that a unique microstructure was formed after spinning through a two‐step eco‐friendly bath. As‐spun fibers demonstrated spherulitic morphology which can be transformed into a fibrillar structure followed by post‐drawing process. Cross sectional images of the treated LLDPE fibers produced at 400 m/min showed fibrillar PE crystals which can be more dominant upon post‐drawing. After two‐step bath treatment, produced fibers need low draw ratios to exhibit high performance. Our novel modification followed by hot drawing process can manipulate internal structure with performance of PE fibers to an outstanding level of 0.35 GPa strength and 3 GPa modulus at a production speed of 400 m/min.

In Situ Formation of Hexagon-like Column Array Hydroxyapatite on 3D-Plotted Hydroxyapatite Scaffolds by Hydrothermal Method and Its Effect on Osteogenic Differentiation.

In the preparation of bioactive bone graft materials, surface topography is essential for the ultimate stem cell response. However, the tunable fabrication of surface topography for 3D bioceramic scaffolds is still a technical problem because of the low processability and high brittleness of bioceramics. In this study, an evenly spaced hexagon-like column array surface was fabricated in situ via a hydrothermal method on 3D plotted hydroxyapatite scaffolds. Compared with the Control scaffolds, hydroxyapatite scaffolds with a hexagon-like column array topography possessed a higher crystal orientation degree and specific surface area, which further enhanced fibronectin adsorption. The array topography on the hydroxyapatite scaffolds also showed good biocompatibility with human adipose-derived stem cells (ADSCs). More importantly, the Array scaffolds significantly promoted the expression levels of osteogenic-related genes and proteins compared with the Control scaffolds. The results suggested that the construction of hexagon-like column array topography might be critical for the design of bone regeneration scaffolds with spontaneous stimulation capacity.

Accelerating shear-induced crystallization and enhancing crystal orientation of isotactic-polypropylene via nucleating agent self-assembly

Accelerating shear-induced crystallization and enhancing crystal orientation of isotactic-polypropylene (iPP) via controlling the morphology of N,N′-dicyclohexyl-2,6-naphthalene dicarboxamide (NJS) is reported here. By adjusting the final heating temperature, NJS crystallizes into dotlike, needlelike, and treelike morphologies. Due to the selective absorption, longer polymer chains are anchored on the surface of NJS, leading to a lower viscosity of the composite than pure iPP. Since that anchoring points will inhibit the relaxation of oriented polymer chains after shear ceases, the shear-induced crystallization kinetics of the composite is greatly accelerated compared with pure iPP. As the morphology of NJS changes from dotlike to treelike, the crystallization induction time decreases further from 620 s to 250 s. Additionally, the branches of the treelike NJS will be detached from the tree upon the shear flow and orient themselves in the shear direction, which endows a highest degree of crystal orientation of the composites with treelike NJS.

Conversion of silicate glass to highly oriented divalent ion substituted hydroxyapatite nanorod arrays in alkaline phosphate solutions

This study presents a new strategy for preparing highly oriented nanorod array of divalent ion substituted hydroxyapatite (HAp) and factors controlling the rate of glass conversion. HAp nanorod arrays were prepared on a series of alkali/alkaline-earth silicate glasses in the Na2O–CaO–SrO–SiO2 system in phosphate aqueous solutions with different pH values via a glass conversion process. The effects of the substitution of Sr2+ for Ca2+ and the network connectivity (NC) of the silicate glasses on the degree of crystal orientation of the nanorod array of HAp crystals, the crystallite size, and the partial substitution of Sr2+ for Ca2+ in the HAp crystal lattice were investigated using X-ray diffraction, 29Si magic angle spinning nuclear magnetic resonance (NMR) spectroscopy, and field-emission scanning electron microscopy. Sr-free Na2O–CaO–SiO2 glass was converted into HAp nanorod arrays highly-oriented toward the c-axis, whereas the increase in the NC of the glass led to a decrease in the rate of the conversion process from glass to HAp, which resulted in the reduction of the degree of c-axis orientation of the nanorod array of the HAp crystals. However, the rate of the conversion process was remarkably promoted in alkaline phosphate solutions, resulting in an increase of the degree of c-axis orientation of the nanorod array. The Sr/(Sr + Ca) molar fraction of silicate glasses determined the molar fraction of substituted Sr2+ in HAp crystal lattice.

Structural transformation from shish‐kebab crystals to micro‐fibrils through hot stretching process of gel‐spun ultra‐high molecular weight polyethylene fibers with high concentration solution

ABSTRACTStructural evolution of gel‐spun ultra‐high molecular weight polyethylene fibers with high concentration solution via hot stretching process was investigated by in situ small‐angle X‐ray scattering, in situ wide‐angle X‐ray diffraction measurements, scanning electron microscopy, and differential scanning calorimetry. With the increase of stretching strain, the long period continuously increases at relative lower stretching temperature, while it first increases and then decreases rapidly at relative higher stretching temperature. The kebab thickness almost keeps constant during the whole hot‐stretching process and the kebab diameter continually decreases for all stretching temperatures. Moreover, the length of shish decreases slightly and the shish quantity increases although there is almost no change in the diameter of shish crystals during the hot stretching process. The degree of crystal orientation at different temperatures is as high as above 0.9 during the whole stretching process. These results indicate that the shish‐kebab crystals in ultra‐high molecular weight polyethylene fibers can transform continuously into the micro‐fibril structure composed mostly of shish crystals through the hot stretching process. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018, 56, 225–238

Structural evolution from shish-kebab to fibrillar crystals during hot-stretching process of gel spinning ultra-high molecular weight polyethylene fibers obtained from low concentration solution

The pre-stretched gel-spinning ultra-high molecular weight polyethylene fibers with low concentration solution obtained from industrial production line were used to study the structural transition from shish-kebab to fibrillar crystals during hot-stretching process via in-situ small-angle X-ray scattering, wide-angle X-ray diffraction measurements, and scanning electron microscopy. With the increase of hot-stretching strain, the kebab crystals (lamellae) undergo stress-induced fragmentation and recrystallization at 90, 100, and 110 °C and melting and recrystallization at 120 °C to transform to fibrillar crystals. Furthermore, the shish length of pre-stretched fibers at all stretching temperatures first increase and then gradually decrease with the strain, but the number of shish continuously increase and the shish diameter increase firstly and finally keep almost constant. The degree of crystal orientation for all stretching temperatures is as high as above 0.9 during the whole stretching process. These results indicate that the shish-kebab crystals of ultra-high molecular weight polyethylene fibers prepared from low concentration solution can smoothly transform to fibrillar crystals through the hot stretching process.

The structure evolution of polyamide 1212 after stretched at different temperatures and its correlation with mechanical properties

The development of polyamide fibers with excellent mechanical performance is always a hot research topic. In this paper, the structure evolution of polyamide 1212 (PA1212) after stretching at different temperatures was characterized by Wide-Angle X-ray Diffraction (WAXD) and Small-Angle X-ray Scattering (SAXS) techniques. Experimentally, it was found that there existed a maximum tensile strength of PA1212 after pre-stretching at 140 °C according to the subsequent mechanical measurements. The formation mechanism of this mechanical property variation was investigated from the different aspects of aggregation structure, such as crystal forms, degree of crystal orientation, crystallinities, density of micro cavity and lamellar long spacing. The related characterization results showed that the α−from crystals, the highest degree of crystal orientation and crystallinities, and a lower density of micro cavity were formed when PA1212 was pre−stretched at 140 °C, which were crucial in improving mechanical properties of PA1212. The structure evolution from spherulites to oriented fibrils was observed directly from the images of scanning electron microscopy (SEM), and was also evidenced by 2D-SAXS and 2D-WAXD patterns. These findings expounded the structure evolution and formation mechanism of PA1212 fibers with excellent mechanical performance.

Orientation control of barium titanate films using metal oxide nanosheet layer

In the present work, we aim to achieve the preferred crystal orientation of chemical solution deposition (CSD)-derived BaTiO3 films on ubiquitous Si wafers with the assistance of Ca2Nb3O10 nanosheet (ns-CN) template layers. The ns-CN on platinized Si (Pt/Si) substrates aligned the BaTiO3(100) plane to the substrate surface, because of the favorable lattice matching of the ns-CN (001) plane. The CSD process in air required a high crystallization temperature of 900 °C for the preferred crystal orientation of BaTiO3(100) because of the BaCO3 byproduct generated during the combustion reaction of the precursor gel. The processing in vacuum to remove CO2 species enhanced the crystal orientation even at the crystallization temperature of 800 °C, although it can generate oxygen vacancies () that cause distorted polarization behavior under an applied field higher than approximately 150 kV/cm. The relative dielectric constant (εr) of the (100)-oriented BaTiO3 film on the ns-CN-supported Pt/Si substrate (ns-CN/Pt/Si) was generally larger than that of the randomly oriented film on Pt/Si, depending on the degree of crystal orientation.