玄武岩连续纤维的制备

利用坩埚法制备玄武岩连续纤维。研究了玄武岩纤维的熔融过程和拉丝工艺以及玄武岩纤维的基本特性。结果表明:选择陕西略阳辉绿岩矿作为玄武岩连续纤维的原矿,采用分体式氧化铝氧化铬坩埚,高度为13 mm,孔径为4 mm,台阶式漏嘴纺制玄武岩连续纤维,最长能成形15 m,纤维直径为12．2μm。     

热处理工艺对GH33A合金高温低周疲劳寿命的影响

本文研究了不同热处理工艺对GH33A高温合金在550℃时的低周疲劳寿命和循环变形行为的影响。结果表明,当应变范围△ε_l<1.2％时,采用双级时效工艺(B工艺)可获得最长的疲劳寿命;当应变范围△ε_l>1.2％时,采用标准热处理工艺可获得较长的疲劳寿命。热处埋工艺不同,合金的循环变形行为也不同。应根据具体构件的受力条件来制定合理的热处理工艺。以发挥合金的潜力.     

大口径抛物反射面天线的准光理论分析

文中用准光理论分析了大口径抛物反射面天线的波束变换特性，讨论了天线性能与辐射波束尺寸、馈源波束尺寸的关系，探讨了用准光理论设计天线的可能性，给出了若干有实用价值的计算公式。     

一类n维Lotka—Volterra模型的稳定性特征

本文给出n维Lotka-Volterra合作系统局部渐近稳定性和全局稳定性的判别条件,并证明该系统正平衡位置的稳定性特征:局部渐近稳定性和全局稳定性是等价的.     

煤直接液化反应中分散相催化剂研究进展

煤直接液化工艺中催化剂作用十分重要,粒径小、分散性高的催化剂能够有效提升煤转化效率。将流动反应介质中小颗粒的固体催化剂命名为分散相催化剂,综述煤直接液化中常用的几种分散相催化剂,包括金属卤化物催化剂、过渡金属氧化物催化剂和铁系催化剂,提出可能的催化机理。     

Synthesis of highly concentrated suspension of chemically converted graphene in organic solvents: Effect of temperature on the extent of reduction and dispersibility

We report the effect of temperature on the extent of graphene oxide reduction by hydrazine and the dispersibility of the resulting chemically converted graphene (CCG) in polar organic solvents. The extent of graphene oxide reduction at high temperatures was only slightly higher than at low temperatures (30–50 °C), while the dispersibility of the resulting CCG in organic solvents decreased markedly with increasing temperature. The low dispersibility of CCGs prepared at high temperatures was greatly affected by reduction and influenced by the formation of an irreversible agglomerate of CCG at high temperatures. The reduction of graphene oxide at low temperatures is necessary to prepare highly dispersible CCG in organic solvents. CCG prepared at 30 °C is dispersible in N-methyl-2-pyrrolidone concentrations as high as 0.71 mg/mL. The free-standing paper made of this CCG possessed an electrical conductivity of more than 22,000 S/m, one of the highest values ever reported.     

Synthesis of single-crystal SnO2 nanowires for NOx gas sensors application

Single-crystal SnO₂ nanowires (NWs) were successfully synthesized and characterized as sensing materials for long-term NO_x stability detection in environmental monitoring. Reproducible and selective growths of the SnO₂ NWs on a patterned, 5 nm-thick gold catalyst coated on a SiO₂/Si wafer as substrate were conducted by evaporating SnO powder source at 960 °C in a mixture of argon/oxygen ambient gas (Ar: 50 sccm/O₂: 0.5 sccm). The as-obtained products were characterized by field-emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), Raman scattering, and photoluminescence (PL). The SEM and HRTEM images revealed that the products are single-crystal SnO₂ NWs with diameter and length ranges of 70 nm–150 nm and 10 μm–100 μm, respectively. The three observed Raman peaks at 476, 633, and 774 cm⁻¹ indicated the typical rutile phase, which is in agreement with the XRD results. The NWs showed stable PL with an emission peak centered at around 620 nm at room-temperature, indicating the existence of oxygen vacancies in the NW samples. The electrical properties of synthesized SnO₂ NWs sensor were also investigated and it exhibited a negative temperature coefficient of resistance in the measured range (300–525 K). The calculated activation energy E_c of SnO₂ NWs was 0.186 eV. Moreover, the SnO₂ NW sensors exhibited good response to NO_x gas. The response of the sensors to 5 ppm NO_x reached 105% at an operating temperature of 200 °C.     

Improved stability of volume resistivity in carbon black/ethylene-vinyl acetate copolymer composites by employing multi-walled carbon nanotubes as second filler

Semiconductive polymer shielding layers of power cable require stable volume resistivity to protect the insulation layer from stress enhancements when carbon black (CB)/polymer composite undergoes thermal cycles. For the CB-filled polymer composites, CB would often re-aggregate when temperature is close to the melting point of polymer matrix, so that the conductive network would be destroyed. Re-distribution of CB and re-formation of conductive CB network under thermal cycles might be the main reason for the instability of volume resistivity. In this work, the re-aggregation of CB in the CB/polymer composites was disclosed. Besides, a small amount of multi-walled carbon nanotubes (MWNTs) was employed as cofiller with CB to improve the stability of volume resistivity of the polymer composites under thermal cycles. The total weight fraction of conductive fillers (CB or CB cofilled with MWNTs) was set as 35 wt%. Compared with the polymer composites loaded with CB solely, the volume resistivity of the composites filled with CB-MWNTs was much more stable with changing temperature. This can be attributed to the enhancement of conductive networks when the MWNTs are employed as second conductive filler.     

Photocatalytic degradation and heat reflectance recovery of waterborne acrylic polymer/ZnO nanocomposite coating

This work aims to clarify the photocatalytic degradation mechanism and heat reflectance recovery performance of waterborne acrylic polymer/ZnO nanocomposite coating. To fabricate the nanocomposite coating, ZnO nanoparticles (nano-ZnO) were dispersed into acrylic polymer matrix at the various concentrations from 1 to 6% (by total weight of resin solids). The photocatalytic degradation of nanocomposite coating under ultraviolet (UV) light irradiation has been investigated by monitoring its weight loss and chemical/microstructural/morphological changes. As the topcoat layer, its heat reflectance recovery has been evaluated under UV/condensation exposure by using an artificial dirty mixture of 85 wt% nanoclay, 10 wt% silica particles (1–5 μm), 1 wt% carbon black, and 2 wt% engine oil. After 108-cycle UV/condensation exposure, infrared spectra and weight loss analysis indicated that the maximal degradation for nanocomposite coating is observed at 1 wt% nano-ZnO. On the other hand, after 96 hr of UV light exposure, the nanocomposite coating with1 wt% nano-ZnO could restore effectively the reflective index of solar-heat reflectance coating (from 58.45 to 80.78%). Finally, the photodegradation mechanism of this waterborne acrylic polymer coating has been proposed as the UV-induced formation of CC CO conjugated double bonds. As a result, its self-cleaning phenomenon can be achieved as the recovery of heat reflectance.