Crystal growth of LiF/LiYF4 eutectic crystals and their luminescent properties

Undoped and 0.5 mol% Ce-doped LiF–LiYF₄ eutectic crystals were grown by the micro-pulling-down method at different growth rates. The SEM images of all the eutectic crystals showed LiF with rod-like structure in the LiYF₄ matrix. The diameter of the rod phase systematically decreased with the increase of the growth rate. The radioluminescence spectra of cerium doped crystal under alpha-ray excitation showed emission peak at 325 nm related to Ce³⁺ 5d-4f transition. The white part in the cathodoluminescence image is considered to be due to Ce³⁺ ion in LiYF₄ phase, according to the scanning electron microscopy (SEM) image in the same region.     

Growth and optical properties of LiF/LaF3 eutectic crystals

Neutron imaging devices employing a scintillator can be used in various fields, and eutectic crystals can be suitable for the imaging with a fine position resolution of a few hundred micrometers. Since LiF and LaF₃ have different refractive indexes of 1.41 and 1.64 at 300 nm, respectively, the eutectic crystal is expected to behave as a scintillator with light guiding properties. Thus, the optical properties of Ce-doped LiF/LaF₃ eutectic crystal grown by micro-pulling down method were investigated. The light output of LiF/Ce:LaF₃ eutectic crystal was relatively small. The emission peaks at 300 nm originating from Ce³⁺ of 5d–4f transition were observed under excitation by UV photons and 5.5 MeV alpha rays. Moreover, the photo-luminescence decay time of Ce-doped LiF/LaF₃ eutectic crystal was estimated to be 17 ± 1 ns.     

Growth of MgAl2O4/MgO eutectic crystals by the micro-pulling-down method and its characterization

MgAl₂O₄/MgO eutectic fibers and rods have been grown successfully by the micro-pulling-down method, and the microstructures and optical characterizations of grown crystals were performed. MgAl₂O₄/MgO eutectic fibers of 0.3–1 mm in diameter and about 500 mm in length, and the rods having 5 mm in diameter with approximately 60 mm in length have been grown with the 6–120 mm/h of growth speed. The eutectic fibers showed homogeneous microstructure in which MgO fiber/whisker aligned to the growth direction in the MgAl₂O₄ (spinel) matrix. The grown crystals looked semitransparence under naked eyes. Optical and orientational characterizations were performed. The second phase of MgO was easily removed by selective etching with hydrochloric acid, and then porous single crystalline bodies were obtained.     

Preparation and thermal-insulating properties of Ce-doped ZrO2 hollow fibers derived from a metaplexis template

ZrO₂ is an attractive thermal-insulating material for high-temperature applications owing to its low heat conductivity and corrosion resistance. The seed hair in metaplexis is a natural fiber with a hollow structure that endows it with outstanding thermal-insulating properties. In this paper, we describe a procedure for preparing CeO₂-stabilized tetragonal ZrO₂ hollow fibers obtained by imitating a metaplexis template. The metaplexis fibers were first immersed in a mixed solution of ZrOCl₂ and Ce(NO₃)₃ to prepare the precursor fibers. The fibers thus produced were subsequently dried in vacuum and sintered under the standard atmospheric pressure in aerobic atmosphere at temperature values of 900, 1100, and 1300°C. The microstructures, phase composition, pore size distribution, and thermal conductivities of the fibers were investigated. Results showed that the Ce-stabilized ZrO₂ fiber inherited the hollow structure of the metaplexis, consequently exerting a significant effect on its thermal-insulating properties. Compared to conventional ZrO₂ fibers, the thermal conductivities of Ce-stabilized ZrO₂ fibers can decrease by approximately 12%-24.3%.     

Orientation relationships of unidirectionally aligned GdAlO3/Al2O3 eutectic fibers

Unidirectionally solidified rare-earth activated GdAlO₃(GAP)/Al₂O₃ eutectic crystal with well-aligned fibrous structure exhibits excellent light guiding property and can be used as a scintillator plate for high-resolution X-ray imaging. In this paper, the microstructures and orientation relationships of the GAP/Al₂O₃ eutectic fibers were investigated. The regular GAP single crystal fibers with a hexagonally close-packed arrangement grew straight in the same direction along the solidification direction, and were embedded in a c-axis oriented Al₂O₃ single crystal matrix. The majority of GAP fibers had the orientation relationships of [0 1 0]GAP//[0 0 0 1]Al₂O₃ to the growth direction and $(100)\text{GAP}//(11\overline{2}0){\text{Al}}_2{\text{O}}_3$ to the interface plane, while slight misorientation angle of both [0 1 0]GAP axis and (1 0 0)GAP plane were observed. In the GAP/Al₂O₃ interface boundary, the lattice misfit between the two phases was relieved by insertion of extra half-planes on the Al₂O₃ side.     

Growth of YAG:Ce3+-Al2O3 eutectic ceramic by HDS method and its application for white LEDs

The resin-free YAG:Ce³⁺-Al₂O₃ eutectic ceramic phosphor for white light emitting diodes (WLEDs) was successfully grown in vacuum by Horizontal Directional Solidification method (HDS). X-ray diffraction and scanning electron microscopy indicate that this material has a typical eutectic structure of interpenetrating sapphire and garnet phases. The excitation spectra, emission spectra and temperature characteristics of the eutectic show that it is characterized by a wide excitation band and it has good stability in high temperature. In X-ray photoelectron spectroscopy, annealing in an air atmosphere could eliminate the oxygen vacancies and didn’t change the Ce³⁺ valence in the eutectic. The YAG:Ce³⁺-Al₂O₃ eutectic ceramic with different thickness was fixed in COB (chip on board) element for researching the performance of the WLEDs with the phosphor. The electroluminescence characterization of the WLEDs show that the WLEDs with the eutectic ceramic are more excellent than the common commercial WLEDs.     

Preparation and properties of polyamide 6 fibers prepared by the gel spinning method

Polyamide 6 (PA6) fibers were prepared by CaCl₂ complexation and the gel spinning technique. PA6 was partially complexed with CaCl₂ for the purpose of suppressing interchain amide group hydrogen bonding. The fibers were characterized with scanning electron microscopy, X‐ray diffraction (XRD), differential scanning calorimetry (DSC), and Fourier transform infrared (FTIR) spectroscopy. In the gel spinning process, a mixed tetrachloroethane and chloroform solution was chosen as the coagulation bath after a comparison of different types of solutions. From our investigation of the morphology, structure, and mechanical properties of gel‐spun and hot‐drawn fibers, it was indicated that the modulus and tensile strength increased with increasing draw ratio, the orientation of the fibers was improved, and the cross section of the PA6 gel fibers became more smooth and tight. The results from the XRD, DSC, and FTIR tests indicated that calcium metal cations complexed with the carbonyl oxygen atoms of PA6. The maximum modulus and tensile strength values obtained in this study were 28.8 GPa and 413 MPa, respectively, at a draw ratio of 8. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Microstructure and hardness scaling in laser-processed B4C-TiB2 eutectic ceramics

Surface layers of the pseudo-binary eutectic comprised of boron carbide (B₄C) and titanium diboride (TiB₂) were directionally solidified via direct laser irradiation in an argon atmosphere. The resulting surface eutectic layers had highly oriented lamellar microstructures, whose scale (i.e. interlamellar spacing) was controlled directly by the laser scan rate, following an inverse square root dependence for lower solidification velocities. Higher velocities (>∼4.2 mm/s) departed from this relationship, although well-ordered microstructures were still achieved. A concomitant increase in the Vickers hardness with decreasing interlamellar spacing was observed, although the trend did not correspond to traditional Hall-Petch behavior. The hardness of the eutectic composites became load-independent at indenter loads greater than 9.81 N, indicating a potential transition from plastic to fractural deformation during indentation. A Vickers hardness of 32 GPa was achieved in the highest solidification velocity samples (42 mm/s) which had interlamellar spacings of 180 nm.     

Microstructure of the directionally solidified ternary eutectic ceramic Al2O3/MgAl2O4/ZrO2

The directionally solidified Al₂O₃/MgAl₂O₄/ZrO₂ ternary eutectic ceramic was prepared via induction heating zone melting. Smooth Al₂O₃/MgAl₂O₄/ZrO₂ eutectic ceramic rods with diameters of 10 mm were successfully obtained. The results demonstrate that the eutectic rods consist of Al₂O₃, MgAl₂O₄ and ZrO₂ phases. In the eutectic microstructure, the MgAl₂O₄ and Al₂O₃ phases form the matrix, the ZrO₂ phase with a fibre or shuttle shape is embedded in the matrix, and a quasi-regular eutectic microstructure formed, presenting a typical in situ composite pattern. During the eutectic growth, the ZrO₂ phase grew on non-faceted phases ahead of the matrix growing on the faceted phase. The hardness and fracture toughness of the eutectic ceramics reached 12 GPa and 6.1 MPa·m ^1/2, respectively, i.e., two times and 1.7 times the values of the pre-sintered ceramic, respectively. In addition, the ZrO₂ phase in the matrix reinforced the matrix, acting as crystal whiskers to reinforce the sintered ceramic.     

Mechanical properties of directionally solidified Al2O3/Y3Al5O12 eutectic ceramic prepared by optical floating zone technique

Al₂O₃/Y₃Al₅O₁₂(YAG) directionally solidified eutectic (DSE) crystal was prepared by optical floating zone technique. Al₂O₃/YAG DSE consists of continuous entangled Al₂O₃ and the YAG forming a three-dimensional networks structure. The volume fraction of porosity is ultra-low (0.013%) and the average equivalent diameters of most pores (>84%) are smaller than 4?μm. The Al₂O₃/YAG DSE shows excellent high-temperature elastic stiffness. The Young’s modulus at 1500?°C maintains more than 85% of the value at room temperature. Bending strength exhibits excellent retention up to high temperature as well. High-temperature ball indentation testing shows plastic deformation involving dislocations and twinning, which predominantly occur in Al₂O₃ phase, while the YAG phase is stable. Evaluation on H_v/E index predicts Al₂O₃/YAG DSE with moderate capability to accommodate damages. Our results highlight Al₂O₃/YAG DSE as excellent high-temperature structural materials.     

对位芳纶染色方法研究进展

综述了对位芳纶结构是影响其染色性能的原因,总结了近年来对位芳纶的染色方法和工艺.表明由于对位芳纶分子结构紧密,结晶度高,小分子染料很难进入到纤维大分子内部,而导致其染色困难,阻碍了对位芳纶在防护服等应用领域方面的进一步应用拓展.指出开展对对位芳纶染色理论的研究,对提高其染色性能及染品的色牢度有着重要的意义.     

Mechanical and electromechanical properties of piezoelectric ceramic fibers drawn by the alginate gelation method

Piezoelectric ceramic fibers are widely used in piezocomposite devices. The various methods that are used to draw ceramic fibers differ in the way the fiber form is obtained, which in return closely affects the density, uniformity and the properties of the fibers that are obtained at the end. In this study, the processing-property relationship in the piezoceramic fibers drawn using the alginate gelation method is investigated, with a focus on the mechanical and electrical properties of individual fibers. Fibers with a Weibull strength of 65.3 MPa, remanent polarization of 22 μC/cm² and a total bipolar field induced strain of 0.25% under an electric field of 2.5 kV/mm, piezoelectric coefficient of 300 pm/V and dielectric constant of 3323 were produced. 1-3 piezocomposite devices prepared from these fibers had a 6 dB higher free-field voltage sensitivity and a 50% wider bandwidth compared to a solid disk transducer of the same dimensions.     

Electrochemical properties of nano- and micro-sized LiNi0.5Mn1.5O4 synthesized via thermal decomposition of a ternary eutectic Li-Ni-Mn acetate

Nano- and micro-sized LiNi_0.5Mn_1.5O₄ particles are prepared via the thermal decomposition of a ternary eutectic Li-Ni-Mn acetate. Lithium acetate, nickel acetate and manganese acetate can form a ternary eutectic Li-Ni-Mn acetate below 80 °C. After further calcination, nano-sized LiNi_0.5Mn_1.5O₄ particles can be obtained at an extremely low temperature (500 °C). When the sintering temperature goes above 700 °C, the particle size increases, and at 900 °C micro-sized LiNi_0.5Mn_1.5O₄ particles (with a diameter of about 4 μm) are obtained. Electrochemical tests show that the micro-sized LiNi_0.5Mn_1.5O₄ powders (sintered at 900 °C) exhibit the best capacity retention at 25 °C, and after 100 cycles, 97% of initial discharge capacity can still be reached. Nano-sized LiNi_0.5Mn_1.5O₄ powders (sintered at 700 °C) perform the best at low temperatures; when cycled at −10 °C and charged and discharged at a rate of 1 C, nano-sized LiNi_0.5Mn_1.5O₄ powders can deliver a capacity as high as 110 mAh g⁻¹.     

Recovery of Na2SO4·10H2O from a reverse osmosis retentate by eutectic freeze crystallisation technology

The increasing amount of waste water and effluent from South Africa's mining industry forms a growing problem, which processing requires sustainable solutions in which both the water and the dissolved component can be re-used. Eutectic freeze crystallisation (EFC) has been identified as a key technology that is not only energy efficient, but also produces ice and salt products of high quality. Unlike reverse osmosis membrane systems, EFC can treat both dilute and concentrated systems minimising waste water volumes. In this paper it is shown that freeze and eutectic freeze crystallisation can be used for the processing of a reverse osmosis retentate stream containing 4% NaSO₄ and a number of impurities (F, Cl, K, Li, Mg, Ca, NO₃ and NH₄), producing both pure water and NaSO₄·10H₂O crystals. The influence of the impurities on the eutectic point and on the crystal structure of mirabilite was investigated using EFC technology investigated for a pure binary system, for a synthetic reverse osmosis retentate as well as for a concentrated NaCl system. In addition, investigations into the recovery and purity of mirabilite for these streams were conducted.     

Rheological properties of cellulose/chitin xanthate blend solutions and properties of the prepared fibers

The focus of this article is the rheological properties of cellulose xanthate, chitin xanthate, and their blend solutions with cellulose/chitin blend weight ratios of 9.5 : 0.5, 9 : 1, 8 : 2, and 5 : 5 (mostly 9 : 1 blend solutions). The preparation and properties of fibers from 9 : 1 blend solutions and cellulose xanthate solutions are also discussed. The non‐Newtonian index of the investigated solutions was found to vary in the following order: chitin < cellulose < 9.5 : 0.5 blend < 9 : 1 blend < 8 : 2 blend < 5 : 5 blend. Showing a tendency contrary to that of the non‐Newtonian index, the structure viscosity index varies in the following order: chitin > cellulose > 9.5 : 0.5 blend > 9 : 1 blend > 8 : 2 blend > 5 : 5 blend. For 5–9 wt % 9 : 1 blend solutions, increasing the solution temperature aids the improvement of the fluidity of 9 : 1 blend solutions in the temperature range of 10–40°C. The zero shear viscosity decreases in an index manner with the solution temperature increasing. The 7–8 wt % 9 : 1 blend solutions have good filtering and rheological properties and are ideal for spinning fibers. The mechanical properties of blend fibers spun from 7% 9 : 1 blend solutions are lower than those of pure cellulose and are much higher than those of Crabyon fiber, and they still reach the national criteria and fit the need for further processing. This proves that the viscose method which we have developed here is an efficient way of preparing cellulose/chitin blend fibers with satisfactory mechanical properties and processing properties. Scanning electron microscopy photographs show that the surface of 9 : 1 blend fibers is coarser than that of pure cellulose fibers. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Investigation of a postprocessing method to tailor the mechanical properties of carbon nanotube/polyamide fibers

The incorporation of carbon nanotubes to thermoplastic fibers can potentially improve mechanical, thermal and electrical properties. In this article, a methodology to tailor the mechanical properties of carbon nanotube/nylon fibers is presented. Multiwalled nanotubes (MWNT) were combined to polyamide 12 through melt compounding and twin‐screw extrusion. Pellets containing between 0 and 5.0 wt % MWNT were extruded and subsequently melt spun with a capillary rheometer to produce filaments. To further promote the alignment of the polymer chains and MWNTs, postdrawing parameters were systematically investigated: temperature, drawing speed and elongation. The best improvements in terms of elastic modulus and yield strength were measured at 140°C and 500% elongation, whereas drawing speed was shown to have a negligible effect. It was confirmed through electron microscopy and X‐ray diffraction that these enhancements were mainly induced by the alignment of the polymer chains along the fibers' axis. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 4375–4382, 2013     

Rheological properties of UHMWPE/HDPE blend gels and morphology and mechanical properties of gel-spun fibers

To produce polyethylene (PE) fibers with relatively high tensile strength but low cost, ultra-high-molecular-weight polyethylene (UHMWPE)/high-density polyethylene (HDPE) (UH) blend gels were prepared from paraffin oil and further fabricated into UH blend fibers by gel spinning. This research focused on the rheological properties of UH blend gels with high solid contents (SCs) ranging from 25 to 100 g/L, as well as morphology and mechanical properties of resultant gel-spun UH blend fibers. The rheological measurements indicated that the apparent viscosity, shear storage, and loss moduli of the UH blend gels were not markedly increased compared with those of the UHMWPE gel with much less SC. No obvious solid–liquid phase separation occurred in UH blend gels at a temperature above the sol–gel transition temperature. UH blend fibers were prepared by drawing as-spun fibers (draw ratio [λ] = 3) at 110°C to λ = 15, 45, 60, and 80, respectively. The orientation degree of fibril structure in UH blend fibers increased with increasing λ but the length of fibrils (L_fibril) showed a complex change. The L_fibril of UH blend fibers became larger due to chain arrangement in company with the transformation of the kebab structure to the extended shish structure when the λ was less than 45 but decreased during further elongation (λ = 60 and 80) because of fibril breakage and recrystallization. The change in morphological behavior led to the corresponding change in mechanical properties of resultant gel-spun UH blend fibers. The tensile strength of gel-spun UH55-45 blend fiber (UHMWPE/HDPE = 5/5 and λ = 45) reached 15.6 cN/dtex, which could fulfill the requirement of mechanical properties in common application.     

Mode-II fracture properties of CFRP/steel composite structure reinforced by short aramid fibers

Abstract

To obtain a good bonding strength of steel/CFRP adhesive joint, the steel surface was machined by grooving process. Short aramid fibers were mixed into the adhesive layer to achieve the further adhesion strength. In the pressing process of steel/CFRP specimen preparation, short aramid fibers with the diameter of several micrometers could be embedded in the grooved gap and the rough surface of CFRP. The higher strength aramid fibers had been not only improved interfacial strength of steel/epoxy and CFRP/epoxy, but also reinforced the adhesive layer due to the bridging activities of aramid fibers. In this study, Mode II fracture strength of grooved-steel/CFRP adhesive joints was investigated by end-notch bending test. The ultimate load and fracture energy of specimens have been improved by 15.7 and 6.8%, in comparison to specimens with smooth steel surface, respectively. The reinforcing mechanisms of CFRP/steel bonding joint as a result of short aramid fibers were discussed according to the failure modes of specimens, and scanning electron microscopy observation and experimental results were carried out.     

Effect of silane coupling agents on the properties of pine fibers/polypropylene composites

In the present work, PP‐based composites, reinforced with surface modified pine fibers, have been prepared. The surface of the fibers has been treated with several silane derivatives bearing specific functionalities. ? NH₂, ? SH, long aliphatic chain, and methacrylic group were chosen as functionalities of the silane derivatives for evaluating the compatibility with the polymer matrix. Mechanical analysis, contact angle and XPS spectra, SEM microscopy, and water uptake measurements were used as characterization techniques for evaluating the nature of composites. XPS as well as contact angle measurements demonstrated that pine fibers and silane derivatives were effectively coupled. The mechanical analysis showed an increase in Young's and flexural moduli, by 12% and 130% respectively, and nonsignificant changes in the ultimate tensile strength were noted after surface modification. Water uptake measurements revealed a low water absorption by the materials, always lower than 2 wt %. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3706–3717, 2007     

Preparation of grafted cationic polymer/silver chloride modified cellulose fibers and their antibacterial properties

In this article, we present a simple method for synthesizing antibacterial cellulose fibers that were modified with a cationic polymer and immobilized silver chloride (AgCl) particles. Relatively simple techniques of graft polymerization and onsite precipitation were used to fabricate the composites. Scanning electron microscopy images, Fourier transform infrared spectroscopy, X‐ray diffraction, thermogravimetric analysis, and energy‐dispersive X‐ray spectroscopy confirmed the immobilization of the AgCl particles. The observed inhibition zone of the immobilized AgCl particle composites indicated that the biocidal silver ions were released from the composites in aqueous solution. Compared with cationic‐polymer‐grafted cellulose fibers or AgCl alone, the cationic polymer/AgCl composites showed excellent antibacterial activity against Gram‐negative Escherichia coli and Gram‐positive Staphylococcus aureus. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42092.