Biomass-derived bamboo charcoal has received significant research attention as electrode material for supercapacitors due to its abundant re-sources,low cost,excellent electrical conductivity,and tunable surface architecture.In this study,bamboo sawdust was employed as the precursor,potassium bicarbonate(KHCO3)was used as a porogen,and a hot-pressing technique was applied to densify the raw material,resul-ting in bamboo-derived carbon with a high specific surface area.The results indicated that the bamboo biochar treated by physicochemical syner-gistic activation had a well-developed porous structure(specific surface area of 1 205 m2/g,pore volume of 0.639 cm3/g).It exhibited a high specific capacitance of 372 F·g-1 at 0.5 A·g-1 and maintained 70.4％capacitance retention after 3 000 cycles at a high current density of 10 A·g-1,which showed good electrochemical stability.Therefore,the synergistic hot-pressing and KHCO3 activation is an effective strategy for enhancing the electrochemical performance of biochar.
The mechanical properties of polypropylene(PP)and polycaprolactam(PA6)were analyzed after they were immersed in three common automobile stain solutions,namely,No.95 gasoline,glass water and car wash liquid,respectively.The common machine learning methods such as grey correlation degree and technique for order preference by similarity to ideality were used to analyze and process the mechanical property data of the material after immersion,and the comprehensive evaluation was carried out,and the reliability of machine learning in the application of material property exploration was verified by material mechanism analysis and tensile fracture morphology analysis.The results showed that glass water and car washing liquid had little effect on the mechanical properties of polypropylene and great effect on the mechanical properties of polycaprolactam,95 gasoline had little effect on the mechanical properties of polycaprolactam and great effect on the mechanical properties of polypropylene.The comprehensive anti-aging value of polycaprolactam soaked in 95 gasoline was the highest in all six groups of tests,and the anti-aging performance was the best.The comprehensive anti-aging value of polypropylene soaked in No.95 gasoline is the lowest among all the six groups of tests,and the anti-aging performance is the worst.
Displacement-controlled cyclic compressive responses of polycrystalline superelastic NiTi shape memory alloys (SMAs) are investigated at a maximum strain epsilon(max) of 4.2 % and over frequencies ranging from 0.0007 Hz to 50 Hz in stagnant air. Our focus was on understanding the interactions among phase transition (PT), heat transfer and plastic flow of austenite phase during cyclic operation. We monitored temperature oscillations along with stress-strain relations and observed a critical frequency f(cri)(AY), below which the responses were primarily influenced by the frequency-dependent coupling between PT and heat transfer, and above which macroscopic plastic deformation of the austenite phase played an important role in the cycling process, interacting with PT and heat transfer. Such interactions at high frequencies (f>f(cri)(AY)) led to reductions in temperature magnitude, transition strain, latent heat, and hysteresis heat in subsequent cycles, eventually leading to stabilized responses without plastic deformation. Theoretical analysis considering the interactions among PT, heat transfer, and plastic deformation was conducted to interpret and quantify the experimental findings. We find that the initiation and saturation of macroscopic plastic deformation of SMAs due to heat accumulation acted as a negative feedback mechanism in the cyclic responses, preventing the materials from overheating and potential damage in applications.
To clarify the mechanical behavior and deformation mechanism of rare earth magnesium(Mg)alloy WE43 under extreme service loads,high-speed impact tests under various deformation temperatures and loading paths were conducted using a split Hopkinson pressure bar.The flow stress along extrusion direction(ED)and extrusion radial direction(ERD)decreases apparently with deformation temperature.Compared with conventional Mg alloys,it exhibits a slight anisotropy and an unusual C-shaped char-acteristic.Cellular dislocation,mechanical twin and fine grain that occur after high-speed impact deformation are insensitive to the loading direction,but strongly dependent on the deformation tem-perature,especially superimposed with adiabatic temperature rise.As a result,dynamic recrystallization(DRX)occurs even at an ambient temperature of 25 ℃.Double twinning and prismatic slip or pyramidal slip are the dominant deformation mechanisms at 25 ℃.These twins induce mechanical cutting refinement to form some fine-grained structures,accompanied by a small number of fine grains by twinning induced DRX.In contrast,the deformation at 250 ℃ is mainly controlled by prismatic slip and pyramidal slip,accompanied by various types of twinning in early deformation stage.Compared with 25 ℃,more fine-grained microstructures are formed at 150 and 250 ℃ through a synergy mechanism of twinning induced mechanical cutting and twinning induced DRX.
Currently,uranium molybdenum alloy(U-Mo)is a very popular fuel used in research reactors,space reactors,and small reactors for special purposes.During the irradiation process,the microstructure of the U-Mo fuel will undergo a series of changes,which may affect the fuel performance during reactor operation.These changes mainly include:the formation of the interaction layer between the U-Mo fuel core and the matrix,the release of fission products(mainly the release of fission gas),and the refinement of the grain size for U-Mo fuel with high burnup.This article summarizes the main characteristics of the above changes and the latest research progress for them.At the same time,it also proposed the development trends in the study of microstructural changes after fuel irradiation in today's world where advanced detection technology has made significant progress.
Supersulfated cement (SSC) is a kind of environment-friendly cement with less or even no clinker, which could consume a lot of phosphogypsum (PG). In order to improve the property of original PG, two modification methods have been taken to study the hydration properties of SSC containing PG with or without modification. The results show that the compressive strength of SSC with modified PG improves at some extent. The pore structure of SSC with modified PG at 90 days also can be optimized, especially for SSC with burnt PG, its porosity, average pore size, threshold aperture, the most probable pore size and the pore volume fraction of microscopic pore all perform best. For early hydration, SSC with burnt PG delays the early hydration and prolongs its induction period, while SSC with neutralized PG accelerates its early hydration. The final hydration products of all SSCs are mainly ettringite and C-S-H gels, while the quantity of ettringite of the control is relative low. Modification treatments can make ettringite more stable especially for SSC with burnt PG. (C) 2019 Elsevier Ltd. All rights reserved.
Because of the insufficient calcium hydroxide content required for the pozzolanic reaction in ultra-high per-formance concrete (UHPC) incorporating high-volume mineral admixtures, hydrated lime was intentionally added to the mortar used for UHPC to investigate its influence on the compressive strength and splitting tensile strength of mortar. The mechanism of the effect of hydrated lime on the mechanical properties of mortar was analysed by microstructural tests, including X-ray diffraction (XRD), thermogravimetric analysis (TGA), envi-ronmental scanning electron microscopy (E-SEM), and mercury intrusion porosimetry (MIP). The results showed that supplementary hydrated lime at various proportions was conducive to the improvement in the mechanical properties of mortar under the combined curing of hot water at 90 degrees C and subsequent dry-air heating at 250 degrees C. The improvement in mechanical properties was due to the transformation of calcium-(aluminium)-silicate -hy-drate (C-(A)-S-H) gels generated by the pozzolanic reaction into crystalline tobermorite and xonotlite and the subsequent refinement of the microstructure. Furthermore, a denser microstructure and better mechanical properties were achieved when the pozzolanic reaction and cement hydration reached an optimal balance, accompanied by a relatively high content of crystallised phases, including tobermorite and xonotlite.
Lead smelting slag (LSS) is a hazardous waste containing heavy metals (Cr, Ni, Cu, Zn, As, and Pb) and its improper disposal may cause irreparable damage to the ecosystem. Cementitious materials prepared with LSS can be used in construction fields and hazardous heavy metals are also solidified in prepared cementitious materials. In this study, the effects of particle sizes of LSS (8.30, 12.54, and 19.04 mu m) on the compressive strength of prepared with high-volume LSS multiple coupling excitation cementitious materials were explored. According to the composition of LSS, activators were set as 6% MgO, 6% bischofite, 7% CaO, 1% CaCl2, and 8% cement, respectively. Decreasing the particle size of LSS could significantly improve the compressive strength of cementitious materials, especially in the early stage. The sample containing LSS with the particle size of 8.30 mu m showed the highest compressive strength (47.1 MPa) and activity index (78.2%) among the samples containing LSS with different particle sizes. LSS with three particle sizes was analyzed with Fourier transform infrared spectroscope (FTIR) and X-ray diffractometer (XRD). The analysis results indicated that decreasing the particle size of LSS increased the specific surface areas (SSAs) and decreased the degree of crystallinity. Moreover, the microscopic analysis of cementitious materials implied that decreasing the particle size enhanced the degree of reaction and gelation, thus resulting in the denser structure of blocks. The results confirmed the compressive strength of LSS-based cementitious materials.
Severe plastic deformation (SPD) with high strain rate can increase the material dislocation density, reduce the grain size, and improve the mechanical properties. In this article, ultrasonic compound cutting (UCC) was proposed to improve the efficiency of preparing ultra-fine grain (UFG) pure copper by SPD methods. The motion characteristics and strain rate model of UCC were analyzed, and it was concluded that the maximum strain rate in the primary shear zone can be increased by ultrasonic vibration. According to the 3D FEM equivalent model of UCC, the UCC and traditional compound cutting (TCC) were compared and analyzed from the perspective of strain rate. The simulation results showed that the strain rate in the shear zone of UCC was significantly larger than that of TCC. The microstructure and mechanical properties of pure copper chip were studied by using a self-developed machining device. The experiment results showed that the grain refinement, dislocation density, and microhardness of pure copper chip were significantly improved in UCC. When the ultrasonic amplitude was 3 μm, the UCC chip grains were about 2.66 μm and the hardness reached 124 HV, which was about 8% higher than the TCC chip. The findings of this research provide an important reference for machining UFG pure copper with enhanced mechanical properties.
The preparation of complex porous materials using a small molecular surfactant as the stabilizer of a high internal phase emulsion can result in harm to the environment. In this study, porous composites based on soy protein isolate with poly(acrylic acid) were prepared by in situ polymerization of a high internal phase monomer emulsion with an internal phase volume fraction of 80%. The material was prepared from acrylic acid and an N,N-methyl diacrylic acid monomer solution as the continuous phase, peanut oil as the dispersed phase, and soy protein isolate as the composite stabilizer. Scanning electron microscopy showed that porous composites exhibited a concave/convex three-dimensional interpenetrating pore structure. Fourier-transform infrared spectra revealed the existence of many active groups such as carboxyl, amino, hydroxyl, and sulfhydryl. The composite had a high adsorption capacity for lead ions, even at low concentration, with a removal rate of up to 95.7%. The adsorption process conformed to a two-stage model involving internal diffusion and Langmuir isothermal adsorption. The maximum saturated adsorption capacity was 36.71 mg/g when the initial solution concentration was 150 mg/L, the adsorbent concentration was 7.0 g/L, and the adsorption mechanism involved chemical interactions between the lead ions and the composite groups -COOH, -OH, and -SH.
In recent years, new materials and protection technologies have rapidly developed with the rising worldwide terrorism. This article studied the antiexplosion performance of reinforced concrete (RC) slabs strengthened with polyisocyanate oxazolidine (POZD) coated steel plate through contact blast tests and numerical simulations. The damage mode and damage mechanism of RC slab reinforced by POZD coated steel plate were analyzed by numerical simulation. The results showed that the antiexplosion performance of steel plate-RC slab was enhanced with the increase of the coating thickness. Based on the above analysis, the empirical expressions of normalized crater diameter, back damage area diameter and POZD bulging diameter were obtained.
为改善素混凝土管易开裂、延性差等缺陷,基于纤维混凝土良好的抗裂性和耐久性,选用聚丙烯粗纤维和玄武岩纤维,设计了无纤维、单掺玄武岩纤维、单掺聚丙烯粗纤维及混掺玄武岩-聚丙烯粗纤维的四组混凝土管节,通过三点试验对比分析管节的开裂破坏形态、荷载-位移曲线和承载力,并建立纤维混凝土管节三点试验的数值模型,进一步探究聚丙烯粗纤维与玄武岩纤维对素混凝土管破坏形态和承载力的影响.结果表明,聚丙烯粗纤维可有效地改善混凝土管的破坏形态,提高混凝土管节的抗裂性能与承载能力,相比于无纤维管节,混掺玄武岩-聚丙烯粗纤维管B2P4的承载力提升了46.26％,效果最佳.此外,各组管节数值模拟结果与试验结果较为一致,承载力误差控制在5％以内,表明模拟合理.通过试验和数值模拟,获得提升混凝土管节抗裂性能和承载力的玄武岩-聚丙烯粗纤维的最佳掺量.
聚醚醚酮(PEEK)具有良好的化学稳定性和优异的力学性能,有望替代传统的金属和陶瓷材料,成为骨科、整形以及牙科植入物的新选择,但目前PEEK材料的表面生物惰性在一定程度上限制了其临床应用.相比于将活性材料与PEEK进行混合来提高材料的骨整合能力,表面改性不仅能够保持PEEK基体材料本身良好的力学性能,而且可以有效改善材料表面与周围组织的相互作用,是提高其生物活性的一种行之有效的途径.本文将综述PEEK材料表面改性策略的最新研究进展,基于改性方法的原理以及过程的不同,分别从表面直接物理处理、表面物理沉积以及湿化学法三个方面对各自的技术原理和研究进展进行总结,并分析各类方法的优缺点.最后,系统分析各类表面改性策略有待解决的主要问题,并对今后的发展方向进行了展望.
本工作对手机超薄盖板玻璃表面裂纹萌生及扩展过程进行了实验比较和数值模拟.结果表明:对于未经化学钢化处理的玻璃,在载荷为9.80 N的情况下,裂纹萌生时间为压痕出现后30 s;而对于化学钢化玻璃,即便在严苛环境条件下,在9.80 N的载荷作用下,缺陷压痕处未发现裂纹.ABAQUS数值模拟结果表明:(1)最大主张应力位于压印缺陷的四角,并沿径向向外扩展;(2)化学钢化玻璃的最大主张应力比未经化学钢化的玻璃低465 MPa.数值模拟得到的最大主张应力位置与实际裂纹萌生位置一致.对玻璃表面裂纹扩展行为的认识有助于高强度超薄盖板玻璃的研发.
本工作研究了经青稞秸秆灰(HBSA)改性的氯氧镁水泥砂浆(MOCM)作为普通混凝土(NC)的防护层,来抵御西部盐湖地区卤水侵蚀的过程,本工作以普通混凝土作为粘结基层,分别研究了MOCM中掺入HBSA、混凝土基层涂刷界面剂以及不同MOCM厚度等因素对其粘结强度的影响.通过粘结拉拔试验确定最优的设计参数,进一步分析了盐卤侵蚀环境下HBSA改性MOCM粘结强度的损伤劣化规律.采用微观测试技术分析了MOCM的物相组成、官能团结构、微观形貌特征,揭示了HBSA对MOCM粘结性能的影响机理.结果表明,厚度为18 mm、掺入HBSA且涂刷界面剂的MOCM粘结强度最高,抵抗盐卤侵蚀的能力也最强.HBSA中有较多的活性SiO2,活性SiO2 能够与MOCM的水化产物发生二次水化反应,生成水化硅酸镁(M-S-H)凝胶,填充MOCM内部孔隙,增强其密实性,提高其粘结强度.
为响应节能减排号召,新能源成为能源发展的主要研究方向,而锂离子电池作为新能源的一种,被广泛研究和应用.金属极薄带材是锂离子电池中的关键性材料,也是锂离子电池集流体的主要载体材料,将其他活性物质涂敷于金属极薄带上,可作为负极或正极.高品质金属极薄带可以更好地提高锂离子电池的充放电效率,使锂离子电池的性能得到提升.本文综述了铜箔、铝箔、镍箔、不锈钢箔以及表面处理铜箔、铝箔复合集流体在锂离子电池中的研究进展,重点分析了极薄带材的厚度、表面处理及力学性能等对锂离子电池的影响,指出超薄、超延展、高强度的高性能金属极薄带在锂离子电池中的未来发展方向.
尾砂是矿山选厂将矿石磨细提取有价元素后排放的固体废弃物,选矿回收率的提高导致选厂产生的尾砂粒度越来越细.利用细尾砂作为骨料与胶凝材料混合回填采空区,是矿山实现其大宗量消纳处置的重要途径.然而,细尾砂自身粒度细、渗透性差的特点导致矿山充填中存在浆体沉降浓缩困难、采场脱水效率低以及充填体强度发展缓慢的问题.近年来,超级絮凝理论、高效絮凝剂的研究与开发,以及深锥浓密机的推广应用,实现了细尾砂高效浓缩脱水;柱塞泵、减阻剂的使用从工艺和材料方面推动了细尾砂膏体物料长距离输送技术问题的解决;细尾砂胶凝材料的开发在提高充填体强度、降低充填成本方面的潜力巨大.本文从细尾砂物化性质分析出发,梳理了细尾砂在矿山充填中存在的问题,总结了国内外细尾砂充填关键技术与材料的研究进展,并对细尾砂充填的发展趋势进行了展望.
为了增强泡沫铝的抗侵彻性能,本工作将聚脲涂覆于三种相对密度的泡沫铝试件端面制备了聚脲涂覆泡沫铝复合件,研究了聚脲涂覆方式对复合件准静态和动态压缩力学行为及吸能特性的影响规律,讨论了聚脲涂覆泡沫铝的变形失效特征.结果表明:聚脲涂覆泡沫铝应力-应变曲线的线弹性段和初始屈服平台段应变率敏感性较弱,致密化段具有显著应变率敏感性;在动态加载下,泡沫铝试件端面涂覆聚脲有助于缓解应力-应变曲线屈服平台段锯齿振荡现象,可以提升其致密应变对应的理想吸能效率值,尤其在背压面涂覆聚脲的泡沫铝试件的理想吸能效率值提升效果最明显;在准静态加载下,背压面涂覆聚脲的泡沫铝试件加载密实后仍呈"圆柱"状,变形较为均匀;在动态加载下,聚脲的涂覆可有效防止冲击荷载下泡沫铝碎片飞溅造成的危害.该研究可为聚脲涂覆泡沫铝复合板在军用方舱结构中的应用提供理论参考依据.
为了研究不同原材料对相似材料单轴抗压强度的影响规律,以lSO标准砂、细河沙为骨料,水泥、石膏、腻子粉为胶结材料,制备了砂水石体系、沙水石体系、沙粉石体系的相似材料,通过正交实验法、力学性能测试法、回归分析法、最小二乘曲线拟合法等实验手段,研究了三种相似材料配合比及不同配合比下的力学性能表征.结果表明,不同原材料的属性直接决定了相似材料的力学性能,胶结材料会对相似材料单轴抗压强度产生正相关影响,骨料会对相似材料单轴抗压强度产生负相关影响;沙水石体系的单轴抗压强度与砂水石体系的单轴抗压强度相差约 42%,沙粉石体系的单轴抗压强度与沙水石体系的单轴抗压强度相差约344%.通过多元回归性分析得到了适用于砂水石体系、沙水石体系、沙粉石体系的单轴抗压强度经验公式,在此基础上,定义了一种影响相似材料单轴抗压强度的强度影响系数,实现了原材料与相似材料单轴抗压强度之间的量化表征,最终明确沙粉石体系为三种体系中最优体系.
