High-efficiently doping nitrogen in kapok fiber-derived hard carbon used as anode materials for boosting rate performance of sodium-ion batteries

The engineering of plant-based precursor for nitrogen doping has become one of the most promising strategies to enhance rate capability of hard carbon materials for sodium-ion batteries;however,the poor rate performance is mainly caused by lack of pyridine nitrogen,which often tends to escape because of high temperature in preparation process of hard carbon.In this paper,a high-rate kapok fiber-derived hard carbon is fabricated by cross-linking carboxyl group in 2,6-pyridinedicarboxylic acid with the exposed hydroxyl group on alkalized kapok with assistance of zinc chloride.Specially,a high nitrogen doping content of 4.24%is achieved,most of which are pyridine nitrogen;this is crucial for improving the defect sites and electronic conductivity of hard carbon.The optimized carbon with feature of high nitrogen content,abundant functional groups,degree of disorder,and large layer spacing exhibits high capacity of 401.7 mAh g^(−1)at a current density of 0.05 A g^(−1),and more importantly,good rate performance,for example,even at the current density of 2 A g^(−1),a specific capacity of 159.5 mAh g^(−1)can be obtained.These findings make plant-based hard carbon a promising candidate for commercial application of sodium-ion batteries,achieving high-rate performance with the enhanced pre-cross-linking interaction between plant precursors and dopants to optimize aromatization process by auxiliary pyrolysis.

Recent Progress in Improving Rate Performance of Cellulose-Derived Carbon Materials for Sodium-Ion Batteries

Cellulose-derived carbon is regarded as one of the most promising candidates for high-performance anode materials in sodium-ion batteries;however,its poor rate performance at higher current density remains a challenge to achieve high power density sodium-ion batteries.The present review comprehensively elucidates the structural characteristics of cellulose-based materials and cellulose-derived carbon materials,explores the limitations in enhancing rate performance arising from ion diffusion and electronic transfer at the level of cellulose-derived carbon materials,and proposes corresponding strategies to improve rate performance targeted at various precursors of cellulose-based materials.This review also presents an update on recent progress in cellulose-based materials and cellulose-derived carbon materials,with particular focuses on their molecular,crystalline,and aggregation structures.Furthermore,the relationship between storage sodium and rate performance the carbon materials is elucidated through theoretical calculations and characterization analyses.Finally,future perspectives regarding challenges and opportunities in the research field of cellulose-derived carbon anodes are briefly highlighted.

Experimental study on the influences of cutter geometry and material on scraper wear during shield TBM tunnelling in abrasive sandy ground

When shield TBM tunnelling in abrasive sandy ground,the rational design of cutter parameters is critical to reduce tool wear and improve tunnelling efficiency.However,the influence mechanism of cutter parameters on scraper wear remains unclear due to the lack of a reliable test method.Geometry and material optimisation are often based on subjective experience,which is unfavourable for improving scraper geological adaptability.In the present study,the newly developed WHU-SAT soil abrasion test was used to evaluate the variation in scraper wear with cutter geometry,material and hardness.The influence mechanism of cutter parameters on scraper wear has been revealed according to the scratch characteristics of the scraper surface.Cutter geometry and material parameters have been optimised to reduce scraper wear.The results indicate that the variation in scraper wear with cutter geometry is related to the cutting resistance,frictional resistance and stress distribution.An appropriate increase in the front angle(or back angle)reduces the cutting resistance(or frictional resistance),while an excessive increase in the front angle(or back angle)reduces the edge angle and causes stress concentration.The optimal front angle,back angle and edge angle for quartz sand samples areα=25°,β=10°andγ=55°,respectively.The wear resistance of the modelled scrapers made of different metal materials is related to the chemical elements and microstructure.The wear resistances of the modelled scrapers made of 45#,06Cr19Ni10,42CrMo4 and 40CrNiMoA are 0.569,0.661,0.691 and 0.728 times those made of WC-Co,respectively.When the alloy hardness is less than 47 HRC(or greater than 58 HRC),scraper wear decreases slowly with increasing alloy hardness as the scratch depth of the particle asperity on the metal surface stabilizes at a high(or low)level.However,when the alloy hardness is between 47 HRC and 58 HRC,scraper wear decreases rapidly with increasing alloy hardness as the scratch depth transitions from high to low levels.The sensitive hardness interval and recommended hardness interval for quartz sand are[47,58]and[58,62],respectively.The present study provides a reference for optimising scraper parameters and improving cutterhead adaptability in abrasive sandy ground tunnelling.

APPLICATION OF DIAMOND TWIST DRILL FOR DRILLING HARD-BRITTLE MATERIALS

提出了硬脆材料孔加工新方法，介绍了金刚石麻花钻的电沉积制造工艺，将研制出的钻头应用于玻璃、大理石、花岗石以及氧化铝陶瓷等硬脆材料的孔加工实验。结果表明，使用该钻头不仅可以有较高的钻削效率，而且可以获得较好的孔进口与出口精度。最后对该技术的应用前景进行了讨论。

Research on Ultrasonic Vibration Grinding of the Hard and Brittle Materials

It is well known that grinding techniques are main methods to machine hard and brittle materials such as engineering ceramics. But the conventional grinding has many shortcomings such as poorer surface finish, quicker wear and tear of grinding tools, lower efficiency and so on. Ultrasonic vibration grinding （UVG） which combines ultrasonic machining and grinding emerged as a developing and promising technique in recent years. In this paper, experimental studies on UVG were conducted on several kinds of hard and brittle material by altering processing parameters such as vibration frequency and its amplitude, diamond abrasive grit size, cutting depth, feeding speed and rotary speed of tools. The experimental results show that alteration in any of above mentioned parameters will bring effects on the processed surface finish of these materials. Of them, the diamond abrasive grit size has the greatest. Moreover, conventional grinding experiments were also carried out on these materials. By comparison, it was found that the UVG is superior to the conventional method in terms of the ground surface quality, the working efficiency and the wear rate of tools.

Etching‐assisted femtosecond laser modification of hard materials

With high hardness, high thermal and chemical stability and excellent optical performance, hard materials exhibit great potential applications in various fields, especially in harsh conditions. Femtosecond laser ablation has the capability to fabricate three-dimensional micro/nanostructures in hard materials. However, the low efficiency, low precision and high surface roughness are the main stumbling blocks for femtosecond laser processing of hard materials. So far, etching- assisted femtosecond laser modification has demonstrated to be the efficient strategy to solve the above problems when processing hard materials, including wet etching and dry etching. In this review, femtosecond laser modification that would influence the etching selectivity is introduced. The fundamental and recent applications of the two kinds of etching assisted femtosecond laser modification technologies are summarized. In addition, the challenges and application prospects of these technologies are discussed.

A general synthesis of inorganic nanotubes as high-rate anode materials of sodium ion batteries

Ino rganic tubular materials have an exceptionally wide range of applications,yet developing a simple and universal method to controllably synthesize them remains challenging.In this work,we report a vaporphase-etching hard-template method that can directly fabricate tubes on various thermally stable oxide and sulfide materials.This synthesis method features the introduction of a vapor-phase-etching process to greatly simplify the steps involved in preparing tubular materials and avoids complicated postprocessing procedures.Furthermore,the in-situ heating transmission electron microscopy(TEM)technique is used to observe the dynamic formation process of TiO_(2-x) tubes,indicating that the removal process of the Sb2S3 templates first experienced the Rayleigh instability,then vapor-phase-etching process.When used as an anode for sodium ion batteries,the TiO_(2-x) tube exhibits excellent rate performance of134.6 mA h g^(-1) at the high current density of 10 A g^(-1) and long-term cycling over 7000 cycles.Moreover,the full cell demonstrates excellent cycling performance with capacity retention of 98%after 1000 cycles,indicating that it is a promising anode material for batteries.This method can be expanded to the design and synthesis of other thermally-stable tubular materials such as ZnS,MoS_(2),and SiO_(2).

Physical and numerical investigations of target stratum selection for ground hydraulic fracturing of multiple hard roofs

Ground hydraulic fracturing plays a crucial role in controlling the far-field hard roof,making it imperative to identify the most suitable target stratum for effective control.Physical experiments are conducted based on engineering properties to simulate the gradual collapse of the roof during longwall top coal caving(LTCC).A numerical model is established using the material point method(MPM)and the strain-softening damage constitutive model according to the structure of the physical model.Numerical simulations are conducted to analyze the LTCC process under different hard roofs for ground hydraulic fracturing.The results show that ground hydraulic fracturing releases the energy and stress of the target stratum,resulting in a substantial lag in the fracturing of the overburden before collapse occurs in the hydraulic fracturing stratum.Ground hydraulic fracturing of a low hard roof reduces the lag effect of hydraulic fractures,dissipates the energy consumed by the fracture of the hard roof,and reduces the abutment stress.Therefore,it is advisable to prioritize the selection of the lower hard roof as the target stratum.

QUANTITATIVE ANALYTIC TECHNOLOGY OF ULTRA-HARDNESS AND WEAR RESISTENT SURFACING MATERIAL

Mathematical models between surfacing welding properties of C, Cr, Mo, V, W alloy system and encode factors of alloy additives are established by test methods of advanced trial optimizing technology and computer assistant design (CAD). They help to draw unitary functions and binary isoclines diagrams through which the influence of encode factorial linearity, nonlinear effect and factors interaction of alloy additives on the performances of surfacing welding can be analyzed directly and quantitatively. Meanwhile, the performances of deposited metal can also be predicted according to the content of alloy additives.

Hardness Measurement of (TiB_2-TiAl)/TiAl Symmetrically Function Gradient Materials

( TiB2-TiAl)/TiAl symmetrically function gradient materials ( FGM) were prepared by spark plasma sintering ( SPS). Owing to the difference, of the thermal expansion coefficients between TiB2 and TiAl, a compressive surface stress was introduced to the FGM fry the thermal expansion mismatch. The hardness values of the uniform materials and the FGM were tested, respectively. For the FGM with a compressive surface stress, hardness is obviously superior to that of the uniform material. When the FGM was subjected to heat treatment, the hardness decreased due to a partial relaxation of the compressive surface stress.

Formation of L1_(0)-FeNi hard magnetic material from FeNi-based amorphous alloys

L1_(0)-FeNi hard magnetic alloy with coercivity reaching 861 Oe was synthesized through annealing Fe_(42)Ni_(41.3)Si_8 B_(4)P_(4)Cu_(0.7)amorphous alloy,and the L1_(0)-FeNi formation mechanism has been studied.It is found the L1_(0)-FeNi in annealed samples at 400℃mainly originated from the residual amorphous phase during the second stage of crystallization which could take place over 600 C lower than the measured onset temperature of the second stage with a50 C/min heating rate.Annealing at 4000 C after fully crystallization still caused a slight increase of coercivity,which was probably contributed by the limited transformation from other high temperature crystalline phases towards L1_(0)phase,or the removal of B from L1_(0)lattice and improvement of the ordering quality of L1_(0)phase due to the reduced temperature from520℃to 400℃.The first stage of crystallization has hardly direct contribution to L1_(0)-FeNi formation.Ab initio simulations show that the addition of Si or Co in L1_(0)-FeNi has the effect of enhancing the thermal stability of L1_(0)phase without seriously deteriorating its magnetic hardness.The non-monotonic feature of direction dependent coercivity in ribbon segments resulted from the combination of domain wall pinning and demagnetization effects.The approaches of synthesizing L1_(0)-FeNi magnets by adding Si or Co and decreasing the onset crystallization temperature have been discussed in detail.

Abrasion test of flexible protective materials on hydraulic structures

In this study, several kinds of flexible protective materials sprayed with polyurea elastomers （hereinafter referred to as polyurea elastomer protective material） were adopted to meet the abrasion resistance requirement of hydraulic structures, and their abrasion resistances against the water flow with suspended load or bed load were studied systematically through tests. Natural basalt stones were adopted as the abrasive for simulation of the abrasion effect of the water flow with bed load, and test results indicate that the basalt stone is suitable for use in the abrasion resistance test of the flexible protective material. The wear process of the polyurea elastomer protective material is stable, and the wear loss is linear with the time of abrasion. If the wear thickness is regarded as the abrasion resistance evaluation factor, the abrasion resistance of the 351 pure polyurea is about twice those of pure polyurea with a high level of hardness and aliphatic polyurea, and over five times that of high-performance abrasion-resistant concrete under the abrasion of the water flow with suspended load. It is also about 50 times that of high-performance abrasion-resistant concrete under the abrasion of the water flow with bed load. Overall, the abrasion resistance of pure polyurea presented a decreasing trend with increasing hardness. Pure polyurea with a Shore hardness of D30 has the best abrasion resistance, which is 60 to 70 times that of high-performance abrasion-resistant concrete under the abrasion of the water flow with bed load, and has been recommended, among the five kinds of pure polyurea materials with different hardness, in anti-abrasion protection of hydraulic structures.

Femtosecond laser-induced periodic surface structures on hard and brittle materials

Hard and brittle materials have high hardness,excellent optical stability,chemical stability,and high thermal stability.Hence,they have huge application potential in various fields,such as optical components,substrate materials,and quantum information,especially under harsh conditions,such as high temperatures and high pressures.Femtosecond laser direct writing technology has greatly promoted the development of femtosecond laser-induced periodic surface structure(Fs-LIPSS or LIPSS by a femtosecond laser)applications of hard and brittle materials due to its high precision,controllability,and three-dimensional processing ability.Thus far,LIPSSs have been widely used in material surface treatment,optoelectronic devices,and micromechanics.However,a consensus has not been reached regarding the formation mechanism of LIPSSs on hard and brittle materials.In this paper,three widely accepted LIPSS formation mechanisms are introduced,and the characteristics and applications of LIPSSs on diamonds,silicon,silicon carbide,and fused silica surfaces in recent years are summarized.In addition,the application prospects and challenges of LIPSSs on hard and brittle materials by a femtosecond laser are discussed.

Research progress on carbon materials as negative electrodes in sodium-and potassium-ion batteries

Carbon materials,including graphite,hard carbon,soft carbon,graphene,and carbon nanotubes,are widely used as high-performance negative electrodes for sodium-ion and potassium-ion batteries(SIBs and PIBs).Compared with other materials,carbon materials are abundant,low-cost,and environmentally friendly,and have excellent electrochemical properties,which make them especially suitable for negative electrode materials of SIBs and PIBs.Compared with traditional carbon materials,modifications of the morphology and size of nanomaterials represent effective strategies to improve the quality of electrode materials.Different nanostructures make different contributions toward improving the electrochemical performance of electrode materials,so the synthesis of nanomaterials is promising for controlling the morphology and size of electrode materials.This paper reviews the progress made and challenges in the use of carbon materials as negative electrode materials for SIBs and PIBs in recent years.The differences in Na+and K+storage mechanisms among different types of carbon materials are emphasized.

Study on the fatigue and wear characteristics of four wheel materials

The fatigue and wear characteristics of four different steel wheel materials are investigated in detail by using rolling contact fatigue and wear bench tests on a JD-1 apparatus, analyzing chemical composition and hardness, and performing profile analysis and micro-morphology analysis. The wear and fatigue behavior of one of the materials under different operation speeds is also investigated. The results show that the wear resistance of the materials has a positive correlation with their carbon content, while fatigue resistance has a negative correlation. Based on hardness analysis as a function of depth into the specimen, the thickness of layers with a steep hardness gradient has a negative correlation with the initial surface hardness in the tests using different materials. The hardness increments, however, have a positive correlation with initial surface hardness. The rolling tests on one material using different rotation speeds show that the hardness increments and the thickness of layers with a steep hardness gradient increase with the rotation speed. The analyses and experimental results demonstrate that two of the four materials exhibit good wear resistance and rolling contact fatigue resistance, making them suitable for either highspeed or heavy axle railroad operations.

Vanadium-modified hard carbon spheres with sufficient pseudographitic domains as high-performance anode for sodium-ion batteries

Hard carbons are promising anode materials for sodium-ion batteries.To meet practical requirements,searching for durable and conductive carbon with a stable interface is of great importance.Here,we prepare a series of vanadiummodified hard carbon submicrospheres by using hydrothermal carbonization followed by high-temperature pyrolysis.Significantly,the introduction of vanadium can facilitate the nucleation and uniform growth of carbon spheres and generate abundant V-O-C interface bonds,thus optimizing the reaction kinetic.Meanwhile,the optimized hard carbon spheres modified by vanadium carbide,with sufficient pseudographitic domains,provide more active sites for Na ion migration and storage.As a result,the HC/VC-1300 electrode exhibits excellent Na storage performance,including a high capacity of 420 mAh g^(-1) at 50mA g^(-1) and good rate capability at 1 A g^(-1).This study proposes a new strategy for the synthesis of hard carbon spheres with high tap density and emphasizes the key role of pseudographitic structure for Na storage and interface stabilization.

Body armour-New materials, new systems

This is a very timely review of body armour materials and systems since new test standards are currently being written, or reviewed, and new, innovative products released. Of greatest importance, however, is the recent evolution, and maturity, of the Ultra High Molecular Weight Polyethylene fibres enabling a completely new style of system to evolve e a stackable system of Hard Armour Plates. The science of body armour materials is quickly reviewed with emphasis upon current understanding of relevant energy-absorbing mechanisms in fibres, fabrics, polymeric laminates and ceramics. The trend in ongoing developments in ballistic fibres is then reviewed, analysed and future projections offered. Weaknesses in some of the ceramic grades are highlighted as is the value of using cladding materials to improve the robustness, and multi-strike performance, of Hard Armour Plates. Finally, with the drive for lighter, and therefore smaller, soft armour systems for military personnel the challenges for armour designers are reported, and the importance of the relative size of the Hard Armour Plate to the Soft Armour Insert is strongly emphasised.

Effect of Media Material on Biogas Production

The paper investigates the effects of the quantity of media materials with simple appraisal on biogas yields between hard and soft wood subjected to the same atmospheric condition in the Ado-Ekiti, Nigeria, between October 2009 and June 2010. Sixteen digesters were used and the mechanical grinding of cassava peels was done in a clean mortar and pestle. Specific grammes of cow dung and cassava peels (200 g, 150 g, 100 g and 50 g) were seeded with four substrates (woods) mixed up with 1200 cm3 of distilled water respectively. The appropriate ratios of the prepared slurries were transferred into different digesters for bio-degradation process which is third-fourth full with the aid of a funnel, and the tubes were passed into a measuring cylinder as a gas collector?inverted over acidified water in a plastic vessels. The volume of biogas produced ranged from 6964 cm3 to 13,185 cm3 by Mahogany, and Iroko ranged from 5340 cm3 to 10,250 cm3 were obtained for both hard woods used. Likewise, the volumes of gas produced by soft woods were from 2465 cm3 to 6445 cm3 by?Obeche and 3430 cm3 to 6990cm3 by Araba. The results showed that, the highest percentage of the seedling media materials (33% each) on the substrates (cassava peel and cow dung) produced the highest biogas with 2800 cm3 of Mahogany, 2400 cm3 of Iroko, 1200 cm3 of Araba and 1130 cm3 of Obeche woods respectively. It was established that, the rate of biogas yields is directly proportional to the quantity of the seedling materials to obtain a reliable results as an alternative renewable energy.

透明硬脆材料激光剥离关键问题研究(特邀)

透明硬脆材料由于其优异的力学性能、热稳定性、耐腐蚀性以及光电性能,广泛应用于半导体与电子领域。传统透明硬脆材料切片方法效率低、材料损耗大,制约了硬脆材料的推广应用。激光剥离技术是近年来新兴的一种透明硬脆材料切片新方法,较传统金刚线切割方法大幅提升硬脆材料的切片效率和材料利用率,目前已发展成为硬脆材料激光加工领域学术研究与产业应用的焦点。文中深入分析透明硬脆材料激光剥离物理过程,归纳激光剥离过程关键科学问题:透明硬脆材料对激光的非线性吸收、激光作用下材料内部微观结构演化与缺陷扩展规律,以及激光光场调控对材料改质影响机制等。基于这些科学问题,综述了近年来激光剥离不同类型透明硬脆材料的研究进展,目前用于激光剥离的材料已涵盖了SiC、Si、GaN、金刚石等半导体材料,蓝宝石、多晶Al_(2)O_(3)、氧化锆等陶瓷材料,激光剥离技术已发展出超快激光双脉冲诱导剥离、超快激光-化学辅助剥离、多激光复合剥离等。激光剥离物理过程是一个典型的激光-材料-热学-力学多学科交叉问题,尽管在实验结果方面获得了显著突破和迅猛发展,但目前对于工艺机理仍缺乏深入的理论与数值建模研究。未来透明硬脆材料激光剥离技术将会朝着百微米以下超薄厚度剥离、改质层低损伤、工艺自适应等方向发展,将为半导体与电子等领域快速发展提供更大的技术支撑。