Solid FeS lubricant:a possible alternative to MoS2 for Cu-Fe-based friction materials

Molybdenum disulfide (MoS₂) is one of the most commonly used solid lubricants for Cu-Fe-based friction materials. Nevertheless, MoS₂ reacts with metal matrices to produce metal sulfides (e.g., FeS) and Mo during sintering, and the lubricity of the composite may be related to the generation of FeS. Herein, the use of FeS as an alternative to MoS₂ for producing Cu-Fe-based friction materials was investigated. According to the reaction principle of thermodynamics, two composites-one with MoS₂ (Fe-Cu-MoS₂ sample) and the other with FeS (FeS-Cu₂S-Cu-Fe-Mo sample), were prepared and their friction behaviors and mechanical properties were compared. The results showed that MoS₂ reacted with the Cu-Fe matrix to produce FeS, metallic ternary sulfides, and Mo when sintered at 1050℃. The MoS₂-Cu-Fe and FeS-Cu₂S-Cu-Fe-Mo samples thereby exhibited similar characteristics with respect to phase composition, density, hardness, and tribological behaviors. Micrographs of the worn surfaces revealed that the stable friction regime for both composites stemmed from the iron sulfides friction layers rather than from the molybdenum sulfides layers.     

第一性原理研究MoS2的电子结构及光学性质

为了系统深入地研究MoS_2的电子能带结构和光电性质,基于密度泛函理论的第一性原理平面波赝势方法,计算和分析了材料MoS_2的电子结构及其光学性质,给出了MoS_2的能带结构、光吸收谱、电子态密度、能量损失谱、反射谱、介电函数谱等光学性质。计算结果表明:体材料MoS_2的电子跃迁形式是非垂直跃迁,具有间接带隙的半导体材料,带隙宽为1.126 eV;价带和导带的形成是由Mo和S的价电子起作用产生的。通过分析其光学性质,发现MoS_2的介电函数的实部和虚部的峰值都出现在低能区,当光子能量的升高,介电函数值会缓慢降低;材料MoS_2对可见紫外区域的光子具有很强的吸收,最大吸收系数为3.17×105cm~(-1);MoS_2在能量为18.33eV位置出现了共振现象,其它区域内能量的损失值都趋于为0,说明电子之间共振非常微弱。这些光学性质奠定了该材料在制作微电子和光电子器件方面的作用,尤其是在紫外探测器应用方面有着潜在的应用前景,为未来对MoS_2材料的进一步研究提供理论参考。     

Flexible photodetector based on large-area few-layer MoS2

Developing flexible photodetectors is crucial for both military and civil fields. Large-area MoS_2 films from several to dozens of layers are controllably synthesized via a facile atmospheric-pressure sulfurization route of predeposited Mo films and transferred onto other substrates(e.g. SiO_2/Si wafers, quartz slides, polymers). The flexible photodetectors were fabricated by transferring as-synthesized MoS_2 films onto interdigital electrodes patterned on polyethylene terephthalate(PET) substrates. No additional complex lithography positioning techniques were needed during the device fabrication process due to the large area of as-grown atomic thin MoS_2 films. As-obtained flexible photodetectors showed responsibilities of ～ 20 mA/W and response time of several seconds. This demonstrates the possibility of employing large-area two-dimensional semiconductors to meet the increasing demands for wearable and portable electronics.     

MoSe_2电子结构和光学性质的理论研究

基于密度泛函理论第一性原理,计算了MoSe_2的能带结构、态密度和光学性质,再根据相关参数分析了该材料的半导体特性和光学性质。能带结构结果表明MoSe2具有间接带隙宽度为0.853 eV的半导体材料,从态密度图可看出价带由Mo的5s4d价电子和Se的4s4p价电子起主要作用,其它价电子作用较少导带主要是Mo的4d和Se的4s4p价电子作用。通过计算得到的复介电函数,根据其它光学参数与其之间的关系,分析获得复折射率、反射和吸收谱、能量损失函数和光电导率等光学性质。由光学性质可知复介电函数的峰值都出现在低能区;介于可见到紫外区域的光子具有最大的吸收系数2.99×10~5cm~(-1);在光子能量17.93 eV处,Mo的4s4d和Se的4p电子发生共振,其它区域能量损失值都趋于0,说明电子之间共振非常微弱。这些光学性质在制作微电子、光电子器件和紫外探测器方面有着广泛的应用前景。     

Low-cost solid FeS lubricant as a possible alternative to MoS<Subscript>2</Subscript> for producing Fe-based friction materials

Three reaction systems of MoS₂-Fe, FeS-Fe, and FeS-Fe-Mo were designed to investigate the use of FeS as an alternative to MoS₂ for producing Fe-based friction materials. Samples were prepared by powder metallurgy, and their phase compositions, microstructures, mechanical properties, and friction performance were characterized. The results showed that MoS₂ reacts with the matrix to produce iron-sulfides and Mo when sintered at 1050℃. Iron-sulfides produced in the MoS₂-Fe system were distributed uniformly and continuously in the matrix, leading to optimal mechanical properties and the lowest coefficient of friction among the systems studied. The lubricity observed was hypothesized to originate from the iron-sulfides produced. The FeS-Fe-Mo system showed a phase composition, porosity, and density similar to those of the MoS₂-Fe system, but an uneven distribution of iron-sulfides and Mo in this system resulted in less-optimal mechanical properties. Finally, the FeS-Fe system showed the poorest mechanical properties among the systems studied because of the lack of Mo reinforcement. In friction tests, the formation of a sulfide layer contributed to a decrease in coefficient of friction (COF) in all of the samples.     

基于Pt-Au-MoS2-ITO传感器对于H2O2的还原检测

实验探究了二硫化钼（MoS₂）作为一种新型材料与贵金属纳米粒子金（Au）、铂（Pt）的复合基底对于过氧化氢（H₂O₂）的还原性检测,采用氧化铟锡导电玻璃（ITO）作为电极,制备出了基于Pt-Au-MoS₂-ITO的生物传感器,为H₂O₂还原性检测的便携性操作打下了基础.实验采用电化学沉积的方法制备材料,同时使用循环伏安（CV）法、计时电流法等传统电化学手段表征了传感器电化学性能,采用场发射扫描电子显微镜（FE-SEM）来表征传感器表面形貌.建立了用于H₂O₂还原检测的、具有高检测限、高灵敏度和宽检测范围的传感器.     

A fluid dynamics route for producing graphene and its analogues

A novel fluid dynamics route for scalable and efficient production of graphene and its analogues is demonstrated. Atomic force microscopy and transmission electron microscopy analyses strongly suggest that the bulk layered materials （graphite, BN, MoS2, and WS2） are efficiently exfoliated into individual layers containing mono-and few-layer nanosheets. Computational fluid dynamics analysis indicates that multiple fluid dynamics events are responsible for efficient exfoliation. Cavitation and pressure release can generate normal force for exfoli- ation. The velocity gradient-induced viscous shear stress, the turbulence-induced Reynolds shear stress, and shear effects stemmed from turbulence and flow channel-induced collisions can generate lateral force for exfoliation, resulting in theses bulk layered materials self-exfoliation down to single or few layers through their intrinsically lateral self-lubricating ability.     

Preparation and photocatalytic activity of Cu-doped TiO2/SiO2

Cu²⁺-doped nanostructured TiO₂-coated SiO₂ (TiO₂/SiO₂) particles were prepared by the layer-by-layer assembly technique and their photocatalytic property was studied. TiO₂ colloids were synthesized by the sol-gel method using TiOSO₄ as a precursor. The experimental results showed that TiO₂ nanopowders on the surface of SiO₂ particles were well distributed and compact. The amount of TiO₂ increased with the increase in coating layers. The shell structure appeared to be composed of anatase titania nanocrystals at 550°C. The 2-layer coated TiO₂ particles on the surface showed a higher degradation rate compared with all the different-layer samples. The photocatalytic activity of Cu²⁺-doped TiO₂/SiO₂ was higher than that of undoped TiO₂/SiO₂. The optimum dopant content was about 0.10wt%.     

Noble-metal-free MoS2/Ta3N5 heterostructure photocatalyst for hydrogen generation

A noble-metal-free heterostructure composed of Ta_3N_5 nanosheets and MoS_2 co-catalyst was developed as an efficient photocatalyst for hydrogen production. In special, the MoS_2/Ta_3N_5 heterostructure with 5.2 wt% of MoS_2 exhibits a H_2 generation rate of 119.4 μmol h~(-1) g-1, which is comparable to that of Ta_3N_5 nanosheets with Pt as co-catalyst. The efficient H2 generation for MoS_2/Ta3N5 heterostructure is resulted from the short diffusion distance of photo-excited charge carriers in Ta3 N5 nanosheets, efficient transfer of electrons from Ta3 N5 nanosheets to MoS_2 surface, and reduced overpotential for water reduction. Furthermore, the stability of the MoS_2/Ta_3N_5 heterostructured photocatalysts are evaluated for the photocatalytic H_2 generation.     

Critical electronic structures controlling phase transitions induced by lithium ion intercalation in molybdenum disulphide

We report on first-principles studies of lithium-intercalation-induced structural phase transitions in molybdenum disulphide (MoS2 ), a promising material for energy storage in lithium ion batteries. It is demonstrated that the inversion-symmetry-related Mo-S p-d covalence interaction and the anisotropy of d-band hybridization are the critical factors influencing the structural phase transitions upon Li ion intercalation. Li ion intercalation in 2H-MoS2 leads to two competing effects, i.e. the 2H-to-1T transition due to the weakening of Mo-S p-d interaction and the D 6h crystal field, and the charge-density-wave transition due to the Peierls instability in Li-intercalated 2H phase. The stabilization of charge density wave in Li-intercalated MoS2 originates from the enhanced electron correlation due to nearest-neighbor Mo-Mo d-d covalence interaction, conforming to the extended Hubbard model. The magnitude of charge density wave is affected by Mo-S p-d covalence interaction and the anisotropy of d-band hybridization. In 1T phase of Li-intercalated MoS2 , the strong anisotropy of d-band hybridization contributes to the strong Fermi surface nesting while the d-band nonbonding with S-p facilities effective electron injection.     

Al,K和Si对钼粉还原及烧结过程的影响

采用液固掺杂技术将不同含量的KOH,H₂SiO₃和Al（NO₃）₃·9H₂O溶液加入到MoO₂粉末中,并通过还原、压制和烧结工艺制备成钼棒。研究了掺杂钼粉的平均费氏粒度、松装密度与掺杂量的关系,采用扫描电子显微镜（SEM）对掺杂钼粉的表面形貌及烧结钼棒的断口形貌进行了分析。研究结果表明,随着K,Al和Si掺杂量的提高,钼粉的粒度及松装密度均呈先减小后增大的变化趋势,且钼棒晶粒中的气孔呈增多趋势。通过SEM分析发现,由于K,Al和Si的掺杂,烧结钼棒的断裂形貌由沿晶断裂逐渐向穿晶断裂转变。综合比较后认为,Mo-0.005Al-0.27K-0.098Si和Mo-0.005Al-0.36K-0.1305Si为最优配方。     

钼精矿焙烧处理过程中典型杂质元素的热力学行为及分析

通过模拟实验结合X射线荧光光谱仪(X-ray fluorescence spectrometer,XRF)、电感耦合等离子光谱发生仪(inductively coupled plasma spectrometer,ICP)及矿物解离分析仪(mineral liberation analyser,MLA)等研究了钼精矿焙烧处理流程中多种杂质元素间的相互作用,在MLA对物相定量分析的基础上,采用Factsage7.0软件分析了钼精矿焙烧过程中不同杂质元素反应进行的热力学条件。结果表明：杂质元素在钼精矿及后续处理流程中的分布存在明显的粒度偏析,主要表现为K、Si等杂质更多以大分子量的矿物形式赋存在较粗粒度的钼精矿中,而Fe、Ca、Cu等杂质则更多以FeS₂、CaSO₄、CuFeS₂等小分子量的化合物形式赋存在较细粒度的钼精矿中。FeS₂、CaSO₄和SiO₂等杂质会在高温焙烧过程中与MoO₃形成致密度较高的混合物,降低Mo的浸出率。云母在钼...     

SrGa2S4:Ce blue TFEL in new structure

SrGa₂S₄: Ce blue TFEL device with a novel structure was prepared by electron beam evaporation. The dielectric constant of insulator layer in this structure is far less than that in the conventional structure, so the hot-electrons can be accelerated in SiO₂ layers. The stable TFEL with good chromaticity was achieved and the basic characteristics were investigated.     

Study on antireflection SiO2 coatings fabricated by layer-by-layer deposition

Multifunctional (poly(diallyldimethyl ammonium chloride)/ sodium poly(4-styrene sulfonate)) _n ((PDDA/PSS) _n ) thin films were fabricated by layer-by-layer assembled on the glass substrate. The monolayer silica nanoparticles were prepared on the (PDDA/PSS) _n films. The SiO₂-polyelectrolyte coatings exhibit antireflection properties with low refractive index (as low as 1.22). Interestingly, wavelengths of maximum transmittance could be well tailored by simply changing the particle size of SiO₂. A maximum transmittance of 97.03% in the visible spectral range is achieved for the particle size of 100 nm SiO₂ films. The coatings also show excellent mechanical stability and good adhesion to substrates. The easy availability of the raw materials and simplicity of the fabrication method for such films might make them be potentially useful for various applications.     

Morphological evolution and kinetic enhancement of Li2FexMn1-xSiO4/C cathodes for Li-ion battery

Li_2MnSiO_4-based cathode materials possess reasonable work potentials and high theoretical capacities,while the practical energy/power densities are constrained by their inferior kinetics of Li~+ diffusion.In this work,the Pmn2_1-structure Li_2Fe_xMn_(1-x)SiO_4/C materials were synthesized via a solvothermal method and evaluated as Liion cathode materials,with notable morphological evolutions and tunable crystallographic habits observed after solvothermal process.The Li_2Fe_(0.33)Mn_(0.67)SiO_4/C material delivers an initial reversible capacity of 250.2mAh g~(-1)at 0.1 C(～1.51 Li~+insertion/extraction,1 C=166 mA g~(-1)),excellent high-rate capability(52.2 mAh g~(-1)at 5 C),and good long-term cyclability(64.6%after 196 cycles at 2 C).The enhanced electrochemical properties are attributed to the boosted ion/electron transports induced by preferred morphological and structural characteristics of Li_2Fe_(0.33)Mn_(0.67)SiO_4/C.     

二氧化硅胶体聚合体吸附铀的研究

采用自制的二氧化硅胶体聚合体,进行了pH值、接触时间和铀初始浓度对二氧化硅胶体聚合体吸附铀效果影响试验,结果表明,溶液的pH对二氧化硅胶体聚合体吸附铀的效果影响较大,并且在pH为4时吸附铀的效果达到最佳;二氧化硅胶体聚合体吸附铀的速度快,30 min即可达到吸附平衡;该材料去除铀的效率高,当溶液中铀初始浓度低于10 mg/L时,该材料对铀的去除率大于98%;随着初始铀浓度增加,吸附容量增加,铀的去除率降低;扫描电镜分析结果表明,二氧化硅胶体聚合体表面形貌吸附铀前后变化不大;能谱分析结果表明,1 g吸附剂所吸附铀的质量分数为4.32%,与二氧化硅胶体聚合体从溶液中吸附铀43.0 mg相吻合.     

Influence of sulfides on the tribological properties of composites produced by pulse electric current sintering

Self-lubricating Al₂O₃-15wt% ZrO₂ composites with sulfides, such as molybdenum disulfide (MoS₂) and tungsten disulfide (WS₂) serving as solid lubricants, were fabricated by using the pulse electric current sintering (PECS) technique. The coefficient of friction (COF) of the Al₂O₃-15wt% ZrO₂ composite without/with sulfides was in the range of 0.37–0.48 and 0.27–0.49, respectively. As the amount of sulfides increased, the COF and the wear rate decreased. The reduction in COF and wear rate of the sulfide-containing composite is caused by a reduction in shear stresses between the specimen and the tribological medium due to the formation of a lubricating film resulting from the lamellar structure of sulfides located on the worn surface.     

CaCl2的水解反应对固态SiO2显微特征的影响

利用扫描电镜(SEM)和能谱仪(EDS)等手段,并结合热力学理论计算,研究了浸泡在1173 K温度下脱水不完全的CaCl2熔盐中的固态SiO2圆柱样显微特征变化及其原因,初步分析了CaCl2盐的水解反应对固态SiO2电解特性的影响.结果表明,未严格脱水操作的CaCl2盐很容易高温水解,生成的CaO在熔体中的活度只要不低于0.001,即可与SiO2逐级形成CaO·SiO2(CS)、3CaO·2SiO2(C3 S2)和2CaO·SiO2(C2 S)等多种硅酸盐,导致圆柱体外表面的形貌、结构发生较大变化;圆柱体内部渗透进入的熔盐中CaO含量低,形貌变化较小.外表面硅酸盐层的存在使仅内置阴极集流体的固态Si O 2圆柱体电解还原速度减慢和难度增加.     

Sintering behavior of Cr in different atmospheres and its effect on the microstructure and properties of copper-based composite materials

Copper matrix composites consisting of chromium (Cr) or ferrochrome (Cr-Fe) as strengthening elements and molybdenum disulfide as a lubricant had been sintered in nitrogen and hydrogen atmosphere, respectively. Their morphology and energy-dispersive X-ray spectrometry (EDS) analysis showed that serious interaction occurred between MoS₂ and Cr (or Cr-Fe) particles when the samples were sintered in hydrogen atmosphere. Chromium sulfide compound (Cr_xS_y) was formed as a reaction product, which decreased the density and strength of the composites remarkably. This interaction was inhibited when the samples were sintered in nitrogen atmosphere; thus, the mechanical properties of the composites were improved.     

CoFe2O4/SiO2纳米复合材料的制备及其磁性

采用溶胶-凝胶法制备（CoFe₂O₄）_x/（SiO₂）_1-x纳米复合材料. 利用X射线衍射（XRD）和振动样品磁强计（VSM）研究样品结构、 晶粒尺寸及磁性. 结果表明, 随SiO₂含量增加, 样品的晶粒尺寸减小, 比饱和磁化强度和矫顽力降低. 