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Although XLPE cables are widely used in power transmission and distribution systems, their insulating properties are susceptible to degradation due to thermal aging. In order to clarify the influence law of the thermal aging process on the structural and dielectric properties of XLPE cables, this paper investigates the thermal aging characteristics of XLPE cables by using polarization and depolarization current measurement. Results show that when the XLPE cable is aged at 140 °C, the crystallinity of the insulation layer appears to increase and then decrease. With the increase in aging time, micron-sized microvoids appear on the surface of the XLPE. At the same time, the DC conductivity and 0.1 Hz dielectric loss factor of the insulating layer increase with the aging time. The average DC conductivity increased from 2.26 × 10−16 S/m for new cables to 4.47 × 10−16 S/m after aging for 432 h, while the dielectric loss increased from 0.11% to 0.42%. The polarization characteristics of thermal-aged cables were further analyzed using the extended Debye model. Results indicate that the time constant of the third branch of the model increased significantly with increasing aging time. A correspondence between this parameter and the thermal aging time of the cable was established. Thermal aging can damage the crystalline structure of XLPE, so that the number of interfaces between the crystalline and amorphous regions of the material increases, resulting in structural damages and a decline in the dielectric properties of the cable insulation. [ABSTRACT FROM AUTHOR]

Nanofibrillated cellulose (NFC) consists of ultrafine cellulose structures in which the fibrils can have widths in the range from about 5 to 100 nm. NFC has been studied and developed in the paper industry, using bleached pulp from wood as the raw material. One of the issues in the application of NFC is their heat resistance to thermal degradation. The production process of NFC results in a decrease in their pyrolysis temperature during the nanofibrillation of bleached pulp; however, the details behind the reason and mechanisms are still unclear. In this study, NFC was prepared from bleached hardwood and softwood pulp by mechanical nanofibrillation using a grinder, and the pyrolysis behavior was investigated. For both bleached pulps, a decrease in the pyrolysis temperature was observed after nanofibrillation. The results suggest that the decrease in the pyrolysis temperature from nanofibrillation is not due to damage of the crystalline cellulose by nano fibrillation, but the damage of the hemicellulose components in the surface of the cellulose microfibrils or the interface between the crystalline cellulose and hemicellulose. If the hemicellulose on the surface of crystalline cellulose could be removed from the NFC, then the decrease in the pyrolysis temperature could be suppressed. [ABSTRACT FROM AUTHOR]

[Display omitted] • Crystalline Ni(OH) 2 /Amorphous NiMoS electrocatalyst were designed and synthesized by two-step hydrothermal process. • The as-obtained material shows excellent hydrogen evolution over all pH ranges. • The synergistic mechanism and the role of crystalline Ni(OH) 2 and amorphous NiMoS was elucidated. Designing and fabricating efficient electrocatalysts is a practical step toward the commercial application of the efficient hydrogen evolution reaction (HER) over all pH ranges. Herein, novel Ti@Ni(OH) 2 -NiMoS heterostructure with interface between crystalline Ni(OH) 2 and amorphous NiMoS was rationally designed and fabricated on Ti mesh (denoted as Ti@Ni(OH) 2 -NiMoS). Acid etching and calcination experiments helped in accurate elucidation of the synergistic mechanism as well as the vital role on crystalline Ni(OH) 2 and amorphous NiMoS. In acidic solutions, the HER performance of Ti@Ni(OH) 2 -NiMoS was mainly attributed to the amorphous NiMoS. In neutral, alkaline, and natural seawater solutions, the HER performance was mainly determined by the synergistic interface behaviors between the Ni(OH) 2 and NiMoS. The crystalline Ni(OH) 2 accelerated water dissociation kinetics, while the amorphous NiMoS provided abundant active sites and allowed for fast electron transfer rates. To deliver current densities of 10 mA·cm−2 in acidic, neutral, alkaline, and natural seawater solutions, the Ti@Ni(OH) 2 -NiMoS required overpotentials of 138, 198, 180 and 371 mV, respectively. This paper provides general guidelines for designing efficient electrocatalyst with crystalline/amorphous interfaces for efficient hydrogen evolution over all-pH ranges. [ABSTRACT FROM AUTHOR]

[Display omitted] • The crystallization process of amorphous YAG oxide is investigated from an atomic point of view. • The crystallization proceeds on the surface and interior of the amorphous YAG separately, and which show the preferential crystallization of the surface atoms. • Some atoms in the amorphous phase were controlled by the periodic potential field of the crystal atoms and produced dynamically changing semi-ordered structures at the amorphous/crystalline interface with mainly concentrated within 1–2 nm from the interface. The transformation from amorphous materials to crystals and the corresponding microscopic mechanism have become a research focus in materials science, condensed matter physics, and biophysics etc. In this paper, taking Y 3 Al 5 O 12 (YAG) as an example, the crystallization process of amorphous YAG oxide is investigated from an atomic point of view through the combination of spherical aberration-corrected transmission electron microscopy (SCTEM) with an in situ heating method, and the morphology and structural evolution of the surface and interface are explored. It is observed that the crystallization proceeds on the surface and interior of the amorphous YAG separately. Through atomic-scale imaging, it is determined that semi-ordered structures are formed in a few atomic layers at the amorphous/crystalline interface and that the structural transformation process from the amorphous to the semi-ordered state and then to the crystal structure may be the main reason for the multiple stages of the crystallization of amorphous oxides. This study demonstrates the mechanism of the amorphous-to-crystal transformation on the atomic scale and contributes to gaining a better understanding of the crystallization process of bulk oxides, especially complex metal oxides. [ABSTRACT FROM AUTHOR]

Microstructures and mechanical properties of Ni matrix composites reinforced with amorphous SiO 2 particles by in-situ pyrolysis of polycarbosilane (PCS) coated on Ni powders were studied in this paper. The submicron spherical amorphous SiO 2 particles instead of traditional SiC uniformly distributing in the composites result from the generated silicon source by PCS pyrolysis combined with oxygen impurity in the preparation. The prepared composites achieve high yield strength, 172 MPa, and ultimate tensile strength, 494 MPa, as well as outstanding ductility, total elongation 28.4 %, which is improved 13.9 %, 50.6 % and 160.6 % compared with those for pure Ni samples, respectively. The effects of solid solution strengthening, grain refinement strengthening, reinforcement particle strengthening and dislocations behavior of at amorphous/crystalline interface on the combination of high strength and ductility of the composites were discussed. [Display omitted] • Amorphous SiO 2 reinforced Ni matrix composites were fabricated by in-situ pyrolysis of polycarbosilane coated on Ni powders. • Amorphous SiO 2 instead of crystalline SiC formed by the combination of silicon generated in the pyrolysis with oxygen. • The composites exhibit a combination of excellent tensile strength and ductility. [ABSTRACT FROM AUTHOR]

• • The large-sized 4H-SiC single crystals were grown via sublimation technique. • • Impact of crucible structure on growth behavior was systematically investigated. • • SiC crystal grown in specific crucible exhibits superior characteristics. Silicon carbide (SiC), as the wide bandgap semiconductor, has gradually attracted attention from investigators due to the excellent integrated performance, widely recognized as a revolution in the electronic devices. For these applications, it is crucial to prepare the high-quality SiC crystal ingot by optimizing growth parameters and crucible structures. In this study, the effect of TaC coating and graphite paper on the growth process of SiC ingot were investigated compared to the growth in conventional graphite crucible through modeling and experiment. We demonstrated that the grown crystal using TaC-coated graphite relay ring and graphite paper surrounded the inner wall of powder container shows the superior characteristics in terms of the crystalline perfection and interface shape. In addition, the new crucible structure can provide a low-cost solution to prepare SiC crystal ingot using PVT method. [ABSTRACT FROM AUTHOR]

[Display omitted] The CSL/DSCL model for interfaces in crystalline materials offers a unified framework to study interface dislocations in phase boundaries and disconnections in grain boundaries. The model relies on the existence of a coincidence relation between the two lattices that meet at an interface. The model's ability to quantitatively predict the thermodynamics and kinetics of interfaces has been demonstrated for a limited set of symmetric tilt grain boundaries (STGBs) in cubic materials and twin boundaries. However, the lack of a general framework of interface defects prevents its applicability to arbitrary rational boundaries. In this paper, we present a mathematical framework based on the Smith normal form (SNF) for integer matrices to study the bicrystallography of rational phase and grain boundaries. One of the main results of the paper is a constructive proof of the invariance of the coincident site lattice (CSL) under discrete relative displacements of the parent lattices (of possibly different kind) by a displacement shift complete lattice (DSCL) vector. In addition, we obtain necessary and sufficient conditions on two lattices, related by not only rotations but also lattice distortions, for the existence of a coincidence relation. We first apply these results to explore coincidence relations in arbitrary phase boundaries, and study interface dislocations. In particular, we demonstrate the framework for a phase boundary formed by a strained hexagonal lattice and a square lattice. As a second application, we show how to enumerate all possible (geometric) disconnection modes in arbitrary rational grain boundaries, including glide and non-glide modes in both STGBs and asymmetric-tilt grain boundaries (ATGBs). The constructive nature of the framework lends itself to an algorithmic implementation based exclusively on integer matrix algebra to construct all interfaces that admit CSLs up to a prescribed size, and determine disconnection modes in grain boundaries. We demonstrate the use of SNF bicrystallography on selected bicrystal misorientation axes/angles in face-centered cubic (fcc), body-centered cubic (bcc), and hexagonal (hex) lattices. [ABSTRACT FROM AUTHOR]

ZSR-P loaded nano-TiO 2 composite photocatalysts (TiO 2 /ZSR-P) have been prepared by the sol–gel method using the by-product Zr-containing silica residue (ZSR) as precursors during the production process of zirconium oxychloride, the structure and properties of TiO 2 /ZSR-P were characterized in this paper. The results showed that the TiO 2 /ZSR-P composite photocatalysts were characterized by the uniform loading of nano-TiO 2 on the surface of amorphous SiO 2 particles in ZSR-P. TiO 2 and SiO 2 were combined by forming -Ti-O-Si- bonds at the interface and the crystalline structure of TiO 2 powders was identified a mixed phase of anatase and rutile, its loading amount was 17.14%, the particle size raged from 7 to 12 nm. The degradation rate of TiO 2 /ZSR-P to the concentration of 5 ppm and 10 ppm methyl orange solution reached 99.52% and 100% respectively after 140 min of ultraviolet irradiation, and it still maintained stable performance after repetitive-use of the catalyst for 4 times. [ABSTRACT FROM AUTHOR]