Optimization of room-temperature TCR of polycrystalline La0.9-xSrxK0.1MnO3 ceramics by Sr adjustment

High-density La_0.9-xSr_xK_0.1MnO₃ ceramics (LSKMO, A-site = La, Sr and K, 0 ≤ x ≤ 0.25) are successfully fabricated by using facile sol-gel method. Electrical properties are performed by using combination of phenomenological percolation (PP) model, double exchange (DE) mechanism, and Jahn-Teller (JT) effect. Moreover, X-ray diffraction and scanning electron microscopy are employed to analyze the structure and morphology of LSKMO ceramics. Valence states and ionic stoichiometry are assessed by using X-ray photoemission spectrometry. Results reveal that Sr²⁺ ions, substituting La³⁺ ions, significantly influenced DE mechanism and JT effect. In addition, Sr-doping plays essential role in improving electrical properties of LSKMO ceramics. At optimal doping content of x = 0.09, peak temperature coefficient of resistance (TCR) of the resistivity is found to be 11.56% K^?1 at 297.15 K, which is optimal TCR for A-site K-occupied perovskite manganese oxides. These results confirm that polycrystalline LSKMO ceramics render high room-temperature TCR values due to Sr-doping.     

One step method of structure engineering porous graphitic carbon nitride for efficient visible-light photocatalytic reduction of Cr(Ⅵ)

Porous g-C3N4 nanosheets (PCN) were prepared by the nickel-assisted one-step thermal polymerization method.Hydrogen (H2) which was produced by the reaction between nickel (Ni) foam and ammonia (NH3) defined the structure and properties of PCN.During the formation of PCN,the participation of H2 not only enhanced the spacing between layers but also boosted the specific surface area that more active sites were exposed.Additionally,H2 promoted pores formation in the nanosheets,which was beneficial to the transfer of photons through lamellar structure and improved the absorption efficiency of visible light.Remarkably,the obtained PCN possessed better Cr(Ⅵ) photocatalytic reduction efficiency than pure g-C3N4.The reaction rate constant (k) of PCN (0.013 min-1) was approximately twice that of bare g-C3N4 (0.007 min-1).Furthermore,the effects of original pH and concentration of Cr(Ⅵ)-containing solution on removal efficiency of Cr(Ⅵ) were explored.A possible photocatalytic mechanism was proposed based on the experiments of radical scavengers and photoelectrochemical characterizations.     

Investigating the effect of water-mixing nitrogen atmospheric pressure plasma jet on polyether-ether-ketone and time stability under different conditions

Possessing excellent properties including good biocompatibility, high strength, and stiffness, polyether-ether-ketone (PEEK) has significant application values in medical and industrial fields. However, the relatively poor wettability and low adhesion limit its further applications. Atmospheric pressure plasma jet (APPJ) has been utilized for adjusting PEEK properties, but better hydrophilization effect and time stability after treatment are still urgently needed. In this paper, we employ a water-mixing nitrogen (N₂ H₂O) APPJ to process PEEK, and surface wettability can be effectively improved (contact angle ~18° within 2 min, distance between sample and nozzle outlet: 10 mm) without inducing obvious microstructure damages. Additionally, after storing for 40 days, the sample treated by N₂ H₂O APPJ also possessed better wettability (~54°) compared with that treated by N₂ APPJ (~65°). On the basis of this low-damage and high-efficient modification method, we perform aging experiments under different conditions (different temperatures 25, −10°C; and low vacuum condition: 50 kPa) to determine a relatively optimum storing condition for this method. The experiment results indicate that low temperature and vacuum are conducive to retaining the plasma-induced wettability (~34°). The treatment method and storing conditions for PEEK presented here may facilitate the application of PEEK in various fields.     

LaCr0.7Fe0.3O3-NiMn2O4 supported NTC composite ceramics with a sandwich-like structure

A novel sandwich-like structure was first proposed to adjust the electrical properties of NTC thermistors. The LaCr_0.7Fe_0.3O₃-NiMn₂O₄ supported composite ceramics with sandwich-like structure were initially fabricated via traditional solid-state reaction and uniaxial pressing methods, which allowed for the advantages of each component to be integrated into one material. X-Ray diffraction analysis indicates the ceramics mainly consisting of orthorhombic perovskite LaCr_0.7Fe_0.3O₃ and cubic spinel NiMn₂O₄ phases. SEM images manifest that the three layers adhered well to each other and exhibited high density. For electrical properties, the ρ_25°C was expanded to a wide range of 1182–110,233 Ω?cm and could be adjusted to the desired values by tuning the volume ratio of two basic layers, the B value was enhanced from 3358 K to 4167 K by NiMn₂O₄, and the thermal stability was improved by LaCr_0.7Fe_0.3O₃ with a resistance shift less than 0.55 % after annealing at 150 °C for 1500 h.     

The effect of alkali metal oxide on the properties of borosilicate fireproof glass: Structure,thermal properties,viscosity, chemical stability

The purpose of the current work was to research the effect of alkali metal oxide on the structure, thermal properties, viscosity and chemical stability in the glass system (R₂O–CaO–B₂O₃–SiO₂) systematically. Because the glass would emulsify when Li₂O was added to the glass batch, this article did not discuss Li₂O. The results showed that when the amount of Na₂O was less than 4 mol.%, there was a higher interconnectivity of borate and silicate sub-networks in glass, as more mixed Si–O–B bonds were present in glass. The glass samples exhibited excellent thermal properties and chemical stabilities. As the amount of Na₂O exceeded 4 mol.%, the interconnectivity of borate and silicate sub-networks was weakened. The thermal properties and chemical stabilities of the glass samples were reduced. The connectivity of the silicate sub-network was weakened slightly as the Na/K ratio varied, and the coefficient of thermal expansion (CTE) of the glass samples gradually increased, and the resistance to thermal shock (RTS) value gradually decreased. Moreover, the viscosity of the glass samples decreased with the ratio of Na/Si and Na/K increased.     

Reinforced properties of polybenzoxazine-based nanocomposites with siloxane benzoxazine-modified halloysite nanotubes

Siloxane benzoxazine monomer (Ba-s) was synthesized using phenol, 3-aminopropyltriethoxysilane (KH-550), and paraformaldehyde, and then introduced onto halloysite nanotubes (HNTs) surface as a coupling agent to obtain functionalized HNTs (mHNTs). 1, 6-hexanediamine/phenol benzoxazine (Ba-h) was selected as a matrix to blend with mHNTs at the mass ratios of 1:0, 9:1, 7:1, 6:1, 4:1,7:3, and 3:2, respectively. The ring-opening copolymerization behaviors of the nanocomposites were investigated by differential scanning calorimetry. The results implied that the polymerization temperature of Ba-h was decreased by the grafted HNTs. The results of thermogravimetric analysis and dynamic mechanical analysis displayed that the obtained copolymers exhibit different degrees of improvement in the thermal stability and mechanical properties of Ba-h. These enhancements are attributed to the homogeneous dispersion of HNTs and the strong matrix-nanoparticle interactions based on SEM and TEM results. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47882.     

180 t转炉高废钢比冶炼工艺开发

通过对转炉炼钢过程的平衡计算结果进行分析,得出了提高废钢比的措施:减少渣量,减少冷却剂用量和添加升温材料等。结合理论计算和生产实践,减少1 kg/t炉渣可提高废钢比0.10%,减少1kg/t冷却剂可提高废钢比0.19%,增加1kg/t无烟煤可提高废钢比0.27%,增加1 kg/t清洁升温剂可提高废钢比0.41%,工艺优化后转炉废钢比可由17.0%提高到23.1%以上。