木材变磁铁创新趣味科研技能训练的探索与实践

高校是培养有见识、独立思考能力和创新意识专业人才的摇篮。通过木材变磁铁的科研技能训练课程实验,提升了学生综合运用所学知识开展科学研究的能力。本实验内容不但使学生了解木材的相关知识,而且锻炼了学生独立操作科研仪器和分析谱图的能力,打开了学生在科研领域的新视野,激发了学生热爱学习和科学研究的内在动力。

Effect of Ni content on the wear behavior of Al-Si-Cu-Mg-Ni/SiC particles composites

In recent years,the addition of Ni has been widely acknowledged to be capable of enhancing the mechanical properties of Al-Si alloys.However,the effect of Ni on the wear behaviors of Al-Si alloys and Al matrix composites,particularly at elevated temperat-ures,remains an understudied area.In this study,Al-Si-Cu-Mg-Ni/20wt%SiC particles(SiCp)composites with varying Ni contents were prepared by using a semisolid stir casting method.The effect of Ni content on the dry sliding wear behavior of the prepared compos-ites was investigated through sliding tests at 25 and 350℃.Results indicated that theθ-Al_(2)Cu phase gradually diminished and eventually disappeared as the Ni content increased from 0wt%to 3wt%.This change was accompanied by the formation and increase inδ-Al_(3)CuNi andε-Al_(3)Ni phases in microstructures.The hardness and ultimate tensile strength of the as-cast composites improved,and the wear rates of the composites decreased from 5.29×10^(−4)to 1.94×10^(−4)mm^(3)/(N∙m)at 25℃and from 20.2×10^(−4)to 7×10^(−4)mm^(3)/(N∙m)at 350℃with the increase in Ni content from 0wt%to 2wt%.The enhancement in performance was due to the presence of strengthening network structures and additional Ni-containing phases in the composites.However,the wear rate of the 3Ni composite was approximately two times higher than that of the 2Ni composite due to the fracture and debonding of theε-Al_(3)Ni phase.Abrasive wear,delamination wear,and oxidation wear were the predominant wear mechanisms of the investigated composites at 25℃,whereas delamination wear and oxid-ation wear were dominant during sliding at 350℃.

Elucidating the Role of Mass Transfer in Electrochemical Redox Reactions on Electrospun Fibers

Mass transfer can tune the surface concentration of reactants and products and subsequently infl uence the catalytic perfor-mance.The morphology of nanomaterials plays an important role in the mass transfer of reaction microdomains,but related studies are lacking.Herein,a facile electrospinning technique utilizing cellulose was employed to fabricate a series of carbon nanofi bers with diff erent diameters,which exhibited excellent electrochemical nitrate reduction reaction and oxygen evolu-tion reaction activities.Furthermore,the microstructure of electrocatalysts could infl uence the gas-liquid-solid interfacial mass transfer,resulting in diff erent electrochemical performances.

Long-Term Continuous Light Exposure Affects Body Weight and Blood Glucose Associated with Inflammation in Female Rats

Studies have indicated that night lights interfere with the circadian rhythm in the human body and threaten human health. Our previous studies indicated that continuous light exposure severely damages the reproductive endocrine system of female rats resembles polycystic ovary syndrome in women. In this study, we used the continuous measurement method to observe changes in the basal physiological indicators of female rats in an abnormal light exposure environment. Our study results indicated that in female rats: 1) the body temperature first continuously and gradually increased followed by a gradually decrease;2) the increase in body weight slowed down at the late stage of the experimental process;3) the random blood glucose level increased, and the fasting serum insulin level decreased;and 4) the serum C-reactive protein level increased. Our study investigated for the first time the correlation between the duration of continuous light exposure in female rats and the continuously measured basal physiological indicators and preliminarily discussed the effect of continuous light exposure on female basal metabolism and the possible inflammation mechanism. We propose that long-term continuous exposure to night lights in females severely damages their immune and metabolic systems.

“新农科”背景下农林高校化学类专业“九抓”课程建设

为培养具有国际竞争力的人才,“新农科”建设是我国振兴高等农林教育的重要举措。以东北林业大学化学类专业的课程建设为例,从课程内容选择和优化、教学设计、课程思政与示范引领、编著教材、教学评价、第二课堂、实验与实践、产教融合和国际化联合办学等九个方面的改革和收获进行探讨,为本科农林院校一流专业的课程建设提供参考。

Morphological Heredity of Intermetallic Nb_(5)Si_(3)Dendrites in Hypereutectic Nb-Si Based Alloys via Non-Equilibrium Solidification

For hypereutectic Nb-Si based alloys,primary Nb_(5)Si_(3)phases typically grow in a faceted mode during equilibrium or near-equilibrium solidification,which damages the ductility and toughness.To address this issue,here we artificially manipulate the growth morphology of Nb_(5)Si_(3)using electron beam surface melting(EBSM)and subsequent annealing treatments.Results show that such a non-equilibrium solidification pathway enables the transition from faceted growth to non-faceted dendritic growth of Nb_(5)Si_(3),along with evident microstructure refinement,generation of metastableβ-Nb_(5)Si_(3)phases and elimination of chemical segregation.The transformation fromβ-Nb_(5)Si_(3)toα-Nb_(5)Si_(3)and Nb solid solution(Nbss)particles is triggered by the annealing treatment at 1450°C for 5 h.Also,we find the annealing-mediated formation of inherited Nb_(5)Si_(3)dendrites that maintain the dendritic morphology of the original as-solidifiedβ-Nb_(5)Si_(3)dendrites.This work thus provides a feasible routine to obtain thermally stable and refinedα-Nb_(5)Si_(3)dendrites in hypereutectic Nb-Si based alloys.

Progress in Nb-Si ultra-high temperature structural materials:A review

Nb-Si based alloys have the greatest potential to replace nickel-based superalloys and become a new gen-eration ultra-high temperature structural material with service temperature of 1200-1400℃ due to their high melting point,high stiffness,low density,and attractive specific mechanical properties at elevated temperatures.This article reviewed the recent progress in the development of Nb-Si based refractory al-loys.Special attention was paid to the property characteristics,preparation techniques,alloying effects,oxidation resistance and fabrication of Nb-Si based alloy components.Thereafter,the trend of develop-ment in the future was forecasted,including:Optimization of the composition and microstructure of Nb-Si based alloys to achieve a balance of mechanical properties;Comprehensive properties evaluation for Nb-Si based alloys to accumulate sufficient data for engineering applications;Development of practical preparation technology for Nb-Si based alloy components with complex shapes;New multilayer compos-ite coatings for Nb-Si based alloy;Joining technology of Nb-Si alloy to itself and to superalloy.

Sulfur-deficient CoNi_(2)S_(4)nanoparticles-anchored porous carbon nanofibers as bifunctional electrocatalyst for overall water splitting

Water electrolysis technology is considered to be one of the most promising means to produce hydrogen.Herein,aiming at the problems of high overpotential and slow kinetics in water splitting,N-doped porous carbon nanofibers-coupled CoNi_(2)S_(4)nanoparticles are prepared as bifunctional electrocatalyst.In the strategy,NaCl is used as the template to prepare porous carbon nanofibers with a large surface area,and sulfur vacancies are created to modulate the electronic structure of CoNi_(2)S_(4).Electron spin resonance confirms the formation of abundant sulfur vacancies,which largely reduce the bandgap of CoNi_(2)S_(4)from 1.68 to 0.52 eV.The narrowed bandgap is conducive to the migration of valence electrons and decreases the charge transfer resistance for electrocatalytic reaction.Moreover,the uniform distribution of CoNi_(2)S_(4)nanoparticles on carbon nanofibers can prevent the aggregation and facilitate the exposure of electrochemical active sites.Therefore,the composite catalyst exhibits low overpotentials of 340 mV@100 mA·cm^(-2)for oxygen evolution reaction and 380 mV@100 mA·cm^(-2)for hydrogen evolution reaction.The assembled electrolyzer requires 1.64 V to achieve 10 mA·cm^(-2)for overall water-splitting with good long-term stability.The excellent performance results from the synergistic effect of porous structures,sulfur deficiency,nitrogen doping,and the well-dispersed active component.

Reconfigurable Vortex-like Paramagnetic Nanoparticle Swarm with Upstream Motility and High Body-length Ratio Velocity

Drug delivery systems with high-targeted doses can minimize excipients,reduce side effects,and improve efficacy.Human blood circulation is a complex circulatory system,and the motion control of microrobots in the static flow field in vitro is completely different from in vivo.How to achieve precise counterflow motion for targeted drug delivery without vascular blockage and immune rejection is the biggest challenge for micro-nano robots.Here,we propose a control method that enables vortex-like paramagnetic nanoparticle swarm(VPNS)to move upstream against the flow.By mimicking the clustering motion of wild herring schools and the rolling of leukocytes,VPNS are incredibly stable even when subjected to high-intensity jet impacts in the blood environment,can travel upstream,anchor at the target location,and dissipate when the magnetic field is withdrawn,which greatly reduces the risk of thrombosis.VPNS can also upstream along the vessel wall without an additional energy source and has a marked targeted therapeutic effect on subcutaneous tumors.

Precipitation behavior and properties of extruded 7136 aluminum alloy under different aging treatments

In this work, the mechanical properties and electrical conductivity of the extruded 7136 aluminum alloy treated by single-stage aging treatment(T6), retrogression and re-aging treatment(RRA), and multiple retrogression and re-aging treatment have been investigated by means of hardness measurements, electrical conductivity tests and tensile tests. The results have shown that the properties of the 7136 alloy such as hardness, tensile strength and electrical conductivity were sensitive to retrogression time(within 90 min). With prolonging the retrogression time, the tensile strength was enhanced first and then decreased, yet the electrical conductivity was continuously increased. The 60 min-treated alloy performed the highest tensile strength(716 MPa), whereas the 90 min-treated alloy possessed the highest electrical conductivity(33.95%IACS). Compared with the T6-treated alloy, the tensile strength and electrical conductivity were improved by 3.3%and 18.9%, respectively. The electrical conductivity showed an obvious increase with repetitious times of the RRA treatment. After 3 RRA60 treatment, a good combination of tensile strength(705 MPa) and electrical conductivity(33.20%IACS) can be obtained. Compared with the T6 condition, the tensile strength and electrical conductivity were improved by 1.7% and 16.3%, respectively. The mechanism of microstructure evolution under different aging treatments has been discussed in detail.

Single track and single layer formation in selective laser melting of niobium solid solution alloy

Selective laser melting（SLM） was employed to fabricate Nb-37 Ti-13 Cr-2 Al-1 Si（at%）alloy, using pre-alloyed powders prepared by plasma rotating electrode processing（PREP）. A series of single tracks and single layers under different processing parameters was manufactured to evaluate the processing feasibility by SLM, including laser power, scanning speed, and hatch distance.Results showed that continuous single tracks could be fabricated using proper laser powers and scanning velocities. Both the width of a single track and its penetration depth into a substrate increased with an increase of the linear laser beam energy density（LED）, i.e., an increase of the laser power and a decrease of the scanning speed. Nb, Ti, Si, Cr, and Al elements distributed heterogeneously over the melt pool in the form of swirl-like patterns. An excess of the hatch distance was not able to interconnect neighboring tracks. Under improper processing parameters, a balling phenomenon occurred, but could be eliminated with an increased LED. This work testified the SLMprocessing feasibility of Nb-based alloy and promoted the application of SLM to the manufacture of niobium-based alloys.

Pressure-driven mold filling model of aluminum alloy melt/semi-solid slurry based on rheological behavior

The pressure-driven mold filling ability of aluminum alloy melt/semi-solid slurry is of great significance in pressure casting processes,and the rheological behavior of the alloy has a crucial effect on the mold filling ability according to fluid dynamics.In this work,a pressure-driven mold filling model is first proposed based on the rheological behavior of the alloys.A356 alloy is employed as an example to clarify the rheological behavior of aluminum alloys,which obeys the power law model and is affected by temperature.The rheological behavior of the alloy in semi-solid state is modelled with the coupling of shear rate and temperature.The stop of mold filling attributes to the pressure loss which is caused by the viscosity during the flow of the melt/semi-solid slurry.Pressure loss caused by viscous flow and heat transfer between the alloy and the mold are calculated and coupled during the mold filling of the melt/semi-solid slurry.A pressure-driven mold filling model of aluminum alloy melt/semi-solid slurry is established based on steady-state rheological behavior.The model successfully predicts the filling length of melt/semi-solid slurry in pressure casting processes.Compared with the experimental results,the model can provide a quantitative approach to characterize the pressure-driven mold filling ability of aluminum alloy melt.The model is capable of describing the stop filling behavior of other aluminum alloys in pressure casting processes with corresponding rheological parameters and heat transfer coefficient.

低场MRI原位研究离子液体合成及相态变化

离子液体作为一个平台化合物已经在诸多领域得到广泛应用,但离子液体的生产成本仍然是限制其进一步工业化推广的瓶颈之一。深入研究反应动力学、反应传递耦合规律对优化离子液体合成工艺/关键设备,降低大规模离子液体制备成本至关重要。本研究用一个原位低场磁共振成像(MRI)设备实时监测ILs合成过程中的反应动力学和相态变化。通过建立双组分分析模型,即1H低场核磁共振(LF-NMR)弛豫法对反应体系中的各个组分进行定量分析,并采集MRI图像记录相位分离和倒置过程,系统考察了卤代烷烃的链长、卤素种类、搅拌速度、反应温度等对咪唑类离子液体反应动力学的影响规律。对溴丁烷、甲基咪唑合成溴代1-丁基-3-甲基咪唑类离子液体合成过程中相态变化进行了实时动态观测。本研究为检测离子液体反应过程及有机溶剂中离子液体的残余量提供一种快速、便利、无损的检测方法,有望利用低场MRI对离子液体系统中传质和反应动力学的结合研究做进一步探索。