无取向电工钢冶炼过程氧含量控制

无取向硅钢的磁性能与钢的洁净度水平密切相关。为实现对无取向电工钢冶炼过程氧含量的合理控制,分析了无取向电工钢冶炼过程碳氧含量变化数据,热力学计算转炉终点临界碳含量与炉渣α_FeO。结果表明:随着转炉终点碳含量的降低,终点氧含量升高且波动范围大,合理出钢碳含量应控制为0.03%～0.05%;为满足炉渣中T.Fe≤24%的现场生产要求,终点碳含量应高于0.031%;钢包底吹氩气可有效降低钢液中过剩氧,降低钢液的平均碳氧积;据现场生产数据,RH精炼前理想碳、氧含量应控制为0.025%～0.035%和500×10^-6～650×10^-6,相应转炉终点碳含量控制为0.03%～0.04%。     

Corrosion resistance of Mg(OH)_2/Mg-Al-layered double hydroxide coatings on magnesium alloy AZ31:influence of hydrolysis degree of silane

Mg(OH)_2/Mg-Al-layered double hydroxide(LDH)coatings were modified with methyltrimethoxysilane(MTMS)on magnesium alloys.Effect of hydrolysis degree of silane solution on coating formation was investigated.Chemical compositions and surface morphologies of the coatings were examined using X-ray diffraction(XRD),Fourier transform infrared spectroscopy(FTIR),X-ray photoelectron spectroscopy(XPS)and field-emission scanning electronic microscopy(FESEM).Results indicated that the composite coatings consisted of polymethyltrimethoxysilane(PMTMS),LDH and Mg(OH)_2.Electrochemical and hydrogen evolution measurements revealed that the composite coatings possessed good corrosion resistance,especially the ones prepared in a high hydrolysis degree of silane.The optimum corrosion resistance of the composite coating was LDH/PMTMS-3 coating,which had the lowest value of corrosion current density(5.537 × 10~(-9) A·cm~(-2))and a dense surface.Plausible mechanism for coating formation and corrosion process of MTMS-modified Mg(OH)_2/Mg-Al-LDH coatings were discussed.     

Low dielectric constant polyimide mixtures fabricated by polyimide matrix and polyimide microsphere fillers

Polyimide microspheres were prepared via non‐aqueous emulsion polymerization by using pyromellitic dianhydride (PMDA) as anhydride monomer and 2,2‐bis(4‐(4‐aminophenoxy)phenyl)propane as amine monomer. The polyimide microspheres were well characterized by Fourier transform infrared spectroscopy, SEM and laser particle size analyzer. They were spherical in shape and monodisperse and their size was 31–33 μm. Polyimide mixtures formed by polyimide microspheres as fillers and polyimide composed of pyromellitic and dianhydride 4,4′‐oxydianiline (ODA) as matrix were investigated with regard to thermal properties, dielectric properties and mechanical properties. With 10%–50% polyimide microspheres in the polyimide mixtures, the dielectric constants were 2.26–2.48 (1 MHz) and the loss tangents were 0.00663–0.00857 (1 MHz), which were both significantly lower than the values for ODA‐PMDA polyimide. The decomposition temperature and glass transition temperature were above 440 and 290 °C. The polyimide mixtures possessed excellent thermal resistance. When the percentage of polyimide microsphere addition was 30%, the polyimide mixtures had the largest tensile strength (128.50 MPa) and elongation at break (9.01%). These results indicate that the polyimide microspheres were used as both low dielectric fillers and reinforcing fillers. © 2020 Society of Chemical Industry     

白炭黑表面改性研究现状及进展

白炭黑是橡胶工业中非常重要的补强剂,目前市场上主要是采用沉淀法进行生产。但沉淀法生产的白炭黑直接应用时效果较差,在工业应用前大多需要进行改性处理。通过分析国内外白炭黑改性技术研究现状,归纳总结出了表面接枝改性、偶联剂改性、离子液改性、大分子界面改性及并用改性5种白炭黑改性技术的特点,其中偶联剂改性为目前工业应用上的主要改性工艺,而其他改性工艺由于生产成本、改性效果、产品稳定性等因素暂未实现大规模工业应用。     

Ultrafine porous boron nitride nanofiber-toughened WC composites

Porous fibers are widely used in catalysis chemistry and hydrogen storage but are rarely used in structural ceramics. In this study, spark plasma sintering was used to prepare an ultrafine porous boron nitride nanofiber-toughened WC composite for the first time. The obtained WC-0.05 wt% ultrafine porous boron nitride nanofiber composites exhibited better properties (ie, a 2.3% increase in hardness and a 19.6% increase in fracture toughness) compared to those of the pure WC specimen. The fiber porosity improved the second phase-WC matrix microstructural combination. The described approach is a novel preparation method for the WC composites. Furthermore, a new toughening mechanism, which is based on “pinning and stretching”, was determined. These findings suggest that porous boron nitride fibers can be considered to be second phases for toughening the WC composites.     

氯化铵蒸发器结垢成分鉴别及原因分析

多效蒸发器结垢的问题常常发生,影响热效率和装置的正常运行。为明确导致蒸发器结垢的原因和成分,利用X射线衍射（XRD）、等离子发射光谱（ICP）、扫描电镜能谱（SEM-EDS）、偏光显微镜、拉曼光谱和离子色谱等分析测试技术,对浙江大洋生物科技集团股份有限公司的氯化铵多效蒸发器上的不明结垢物做了表征和分析。结果表明,该结垢物的主要成分为磷酸铁、氧化铝和有机物的混合物。探讨了发生上述结垢的原因,并提出相应的解决方案,减少了公司氯化铵蒸发器的结垢。     

A tunable dynamic vibration absorber for unbalanced rotor system

A tunable dynamic vibration absorber for unbalanced rotor system which is made up of coil springs and magnetic spring is presented. The structure of the absorber is introduced and the stiffness tuning mechanism of the magnetic spring is explained. A finite element model of the rotor-absorber system was built and the influencing factors to the appearance of the absorber were studied numerically. Finally, experiments were carried out to verify the numerical results, and PID control strategy was tested. The numerical and experimental results show that the present absorber is effective for vibration suppression of an unbalanced rotor system, and the control strategy is effective.     

Layered-Perovskite Nanowires with Long-Range Orientational Order for Ultrasensitive Photodetectors

2D layered metal-halide perovskites combine efficient exciton radiative recombination in crystal interior with long-distance free-carrier conduction at layer edges, which are promising candidates for realizing high-performance photovoltaic, light-emission and photodetection devices. The anisotropic electrical conductivity in layered perovskites imposes an additional requirement of orientational control for enabling favorable charge transport. However, rational fabrication of single-crystalline nanostructures with pure crystallographic orientation is still elusive. Herein, large-scale pure (101)-orientated 2D-perovskite single-crystalline nanowire arrays are realized by combining solvent engineering with the capillary-bridge lithography technique. Ordered nucleation at liquid–air interface and unidirectional growth along the dewetting direction are demonstrated by fluorescence microscopy and grazing-incidence X-ray scattering in discrete capillary bridges. In consideration of crystal interior exhibiting high resistance arising from the serial insulating organic barriers and ultrafast dissociation of excitons to generate long-lived free carriers at layer edges, ultrasensitive photodetectors are demonstrated with average responsivity exceeding 1.1 × 10⁴ A W⁻¹ and detectivity exceeding 9.1 × 10¹⁵ Jones.