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A multi‐stage fiber spreading process for the preparation of high‐performance continuous aramid fiber reinforced nylon 12 (CAF/PA12) composites was proposed in this paper. The effects of spreading rod crown radius, spreading rod axis height and traction speed on fiber impregnation effect and filaments properties were investigated. The fiber volume fraction of the prepared filament was approximately 30%. And the maximum tensile strength and modulus of the filaments were 839.89 MPa and 41.35 GPa, which were 34.36% and 34.30% higher than unspreading filaments, respectively. The influences of printing process parameters such as printing temperature, the combination of layer thickness and printing spacing on the transverse tensile properties of the specimens were studied. Printed specimens reached a transverse tensile strength and tensile modulus of 13.988 MPa and 1.293 GPa, respectively. The influences on low velocity impact properties of the specimens were also investigated in terms of impact energy and printing stacking sequences. Results revealed that the impact threshold energy of orthotropic ([0/90/0/90]2) specimens was 50 J. Quasi‐isotropic ([0/45/90/−45]2) specimens exhibited the superior impact resistance with an impact load of 4.939 kN. Macro‐ and micro‐matrix crack, surface buckling, fiber fracture and delamination were the main failure modes of the specimens. Highlights: A novel thermoplastic composite filament forming process was proposed, and the filament forming equipment was designed and manufactured.Continuous aramid fiber‐reinforced PA12 filaments with about 30% fiber content were prepared by orthogonal tests under different forming process conditions, which showed maximum tensile properties of 839.89 MPa and 41.35 GPa, respectively.Spreading multiplication was positively related to filament tensile properties, which was major affected by the axial height of the spreading rod.Transverse tensile strength (13.988 MPa tensile strength and 1.293 GPa tensile modulus) of printed specimens was investigated under different printing parameters.Fiber orientation had a significant effect on the low‐velocity impact properties. Micro‐ and macro‐matrix crack, surface buckling, fiber fracture and delamination were the main failure modes of the low‐velocity impact specimens. [ABSTRACT FROM AUTHOR]

Continuous fiber reinforced thermoplastic composites (CFRTP) have been increasingly used in aerospace and rail transport in recent years because of their high strength and light weight. In this paper, the effects of nozzle temperature, printing speed, substrate temperature and layer thickness on the tensile properties and macro/microscopic damage modes of CAF/PA12 printed specimens was systematically investigated. The fiber volume fraction(FVF) of CAF/PA12 filaments was 25.62%. The maximum average tensile strength and tensile modulus of CAF/PA12 printed specimens reached 572.60 MPa and 18.49 GPa, respectively. The results of the cross-sectional analysis indicated that filament toothed fractures and transverse cracks were the main macroscopic failure modes of CAF/PA12 composites. In SEM images, the main microscopic failure modes of CAF/PA12 composite are fiber fracture, fiber pull-out pores and unimpregnated fibers. [ABSTRACT FROM AUTHOR]

KBaPO4:Eu2+/Sm3+ phosphor was synthesized via the high-temperature solid-phase reaction method. The structural properties, surface morphology, and optical properties of the synthesized samples were obtained by the X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), and fluorescence measurements. The XRD patterns indicate that the crystal structure of KBaPO4 has not been changed by co-doped with two rare-earth ions. Under the excitation of 400 nm, the Eu2+ and Sm3+ co-doped KBaPO4 phosphors showed typical emission peaks at 430 (blue), 562 (yellow), and 600 nm (red). Meanwhile, with the increase of the Sm3+ content, the photoluminescent (PL) emission intensity of Sm3+ increased until the content reaches 0.12. However, the PL intensity of Eu2+ ions gradually decreased, which indicated that there was a possible energy transfer between the two ions. Therefore, the obtained results indicated that Eu2+/Sm3+ co-doped KBaPO4 is a promising phosphor for the use in white light-emitting diodes with near ultraviolet chips.

Dy3+ -doped and Dy3+/Eu3+ co-doped KZnPO4 phosphors have been successfully synthesized by solid-state method. X-ray diffraction (XRD), photoluminescence spectra and fluorescence lifetime are employed to characterize these samples. It can be indicated from XRD results that KZnPO4 phosphors exhibit pure phase with high crystallinity. Under excitation of 391 nm, Dy3+-doped KZnPO4 phosphors showed two typical emission bands at 485 nm (blue) and 577 nm (yellow). In the case of Dy3+ and Eu3+ co-doped KZnPO4 phosphors, it can be found that color coordinates are sensitive to the Eu3+ concentration due to the red emission from Eu3+ ions. The emission color changes from blue to warm white by increasing the Eu3+ contents. The color coordinates and color temperature were also adjusted by changing the contents of Eu3+ ions. Furthermore, the mechanism of energy transfer from Dy3+ to Eu3+ ions is demonstrated to be quadrupole–quadrupole interaction for the co-doped samples. [ABSTRACT FROM AUTHOR]