Fabrication and properties of silver-based composites reinforced with carbon-coated Ti_3AlC_2

Ti_3AlC_2-reinforced Ag-based composites, which are used as sliding current collectors, electrical contacts, and electrode materials,exhibit remarkable performances. However, the interfacial reactions between Ag and Ti_3AlC_2 significantly degrade the electrical and thermal properties of these composites. To diminish these interfacial reactions, we fabricated carbon-coated Ti_3AlC_2 particles(C@Ti_3AlC_2) as reinforcement and prepared Ag–10 wt%C@Ti_3AlC_2 composites with carbon-layer thicknesses ranging from 50–200 nm. Compared with the uncoated Ag–Ti_3AlC_2 composite, Ag–C@Ti_3AlC_2 was found to have a better distribution of Ti_3AlC_2 particles. With increases in the carbon-layer thickness, the Vickers hardness value and relative density of Ag–C@Ti_3AlC_2 gradually decreases. With a carbon-layer thickness of 150 nm, we obtained the lowest resistivity of Ag–C@Ti_3AlC_2 of 29.4 135.5×10~(-9) Ω·m, which is half that of Ag–Ti_3AlC_2(66.7 × 10~(-9) Ω·m). The thermal conductivity of Ag–C@Ti_3AlC_2 reached a maximum value of 135.5 W·m~(-1)·K~(-1) with a 200-nm carbon coating(～1.8 times that of Ag–Ti_3AlC_2). These results indicate that the carbon-coating method is a feasible strategy for improving the performance of Ag–C@Ti_3AlC_2 composites.     

Microstructure and properties of Ag–Ti3SiC2 contact materials prepared by pressureless sintering

Ti₃SiC₂-reinforced Ag-matrix composites are expected to serve as electrical contacts. In this study, the wettability of Ag on a Ti₃SiC₂ substrate was measured by the sessile drop method. The Ag–Ti₃SiC₂ composites were prepared from Ag and Ti₃SiC₂ powder mixtures by pressureless sintering. The effects of compacting pressure (100–800 MPa), sintering temperature (850–950℃), and soaking time (0.5–2 h) on the microstructure and properties of the Ag–Ti₃SiC₂ composites were investigated. The experimental results indicated that Ti₃SiC₂ particulates were uniformly distributed in the Ag matrix, without reactions at the interfaces between the two phases. The prepared Ag–10wt%Ti₃SiC₂ had a relative density of 95% and an electrical resistivity of 2.76×10-3 mΩ·cm when compacted at 800 MPa and sintered at 950℃ for 1 h. The incorporation of Ti₃SiC₂ into Ag was found to improve its hardness without substantially compromising its electrical conductivity; this behavior was attributed to the combination of ceramic and metallic properties of the Ti₃SiC₂ reinforcement, suggesting its potential application in electrical contacts.     

Fabrication of Fe–TiC–Al2O3 composites on the surface of steel using a TiO2–Al–C–Fe combustion reaction induced by gas tungsten arc cladding

The aim of the present study was to fabricate Fe–TiC–Al₂O₃ composites on the surface of medium carbon steel. For this purpose, TiO₂–3C and 3TiO₂–4Al–3C–xFe (0 ≤ x ≤ 4.6 by mole) mixtures were pre-placed on the surface of a medium carbon steel plate. The mixtures and substrate were then melted using a gas tungsten arc cladding process. The results show that the martensite forms in the layer produced by the TiO₂–3C mixture. However, ferrite–Fe₃C–TiC phases are the main phases in the microstructure of the clad layer produced by the 3TiO₂–4Al–3C mixture. The addition of Fe to the TiO₂–4Al–3C reactants with the content from 0 to 20wt% increases the volume fraction of particles, and a composite containing approximately 9vol% TiC and Al₂O₃ particles forms. This composite substantially improves the substrate hardness. The mechanism by which Fe particles enhance the TiC + Al₂O₃ volume fraction in the composite is determined.     

Microstructure and properties of Ag–Ti_3SiC_2 contact materials prepared by pressureless sintering

Ti_3SiC_2-reinforced Ag-matrix composites are expected to serve as electrical contacts. In this study, the wettability of Ag on a Ti_3SiC_2 substrate was measured by the sessile drop method. The Ag–Ti_3SiC_2 composites were prepared from Ag and Ti_3SiC_2 powder mixtures by pressureless sintering. The effects of compacting pressure(100–800 MPa), sintering temperature(850–950°C), and soaking time(0.5–2 h) on the microstructure and properties of the Ag–Ti_3SiC_2 composites were investigated. The experimental results indicated that Ti_3SiC_2 particulates were uniformly distributed in the Ag matrix, without reactions at the interfaces between the two phases. The prepared Ag–10 wt%Ti_3SiC_2 had a relative density of 95% and an electrical resistivity of 2.76 × 10-3 mΩ?cm when compacted at 800 MPa and sintered at 950°C for 1 h. The incorporation of Ti_3SiC_2 into Ag was found to improve its hardness without substantially compromising its electrical conductivity; this behavior was attributed to the combination of ceramic and metallic properties of the Ti_3SiC_2 reinforcement, suggesting its potential application in electrical contacts.     

Effect of NaCl on synthesis of ZrB2 by a borothermal reduction reaction of ZrO2

ZrB₂ powders were synthesized via a borothermal reduction reaction of ZrO₂ with the assistance of NaCl under a flowing Ar atmosphere. The optimal temperature and reaction time were 1223 K and 3 h, respectively. Compared with the reactions conducted without the addition of NaCl, those performed with the addition of an appropriate amount of NaCl finished at substantially lower temperatures. However, the addition of too much NaCl suppressed this effect. With the assistance of NaCl, a special morphology of polyhedral ZrB₂ particles covered with ZrB₂ nanosheets was obtained. Moreover, the experimental results revealed that the special morphology was the result of the combined effects of B₂O₃ and NaCl. The formation of the special microstructure is explained on the basis of the "dissolution-recrystallization" mechanism.     

Enhanced electrochemical properties of LaFeO3 with Ni modification for MH-Ni batteries

In this work, we synthesized LaFeO₃-xwt%Ni (x=0, 5, 10, 15) composites via a solid-state reaction method by adding Ni to the reactants, La₂O₃ and Fe₂O₃. Field-emission scanning electron microscopy (FE-SEM) and energy-dispersive X-ray spectroscopy (EDS) results revealed that Ni powders evenly dispersed among the LaFeO₃ particles and apparently reduced their aggregation, which imparted the composites with a loose structure. Moreover, the Ni formed a conductive network, thus improving the conductivity of the composites. The maximum discharge capacity of the LaFeO₃ electrodes remarkably increased from 266.8 mAh·g-1 (x=0) to 339.7 mAh·g-1 (x=10). In particular, the high-rate dischargeability of the LaFeO₃-10wt%Ni electrode at a discharge current density of 1500 mA·g-1 reached 54.6%, which was approximately 1.5 times higher than that of the pure LaFeO₃. Such a Ni-modified loose structure not only increased the charge transfer rate on the surface of the LaFeO₃ particles but also enhanced the hydrogen diffusion rate in the bulk LaFeO₃.     

Effect of reinforcement content on the adhesive wear behavior of Cu10Sn5Ni/Si3N4 composites produced by stir casting

The main objective of this paper was to fabricate Cu10Sn5Ni alloy and its composites reinforced with various contents of Si₃N₄ particles (5wt%, 10wt%, and 15wt%) and to investigate their dry sliding wear behavior using a pin-on-disk tribometer. Microstructural examinations of the specimens revealed a uniform dispersion of Si₃N₄ particles in the copper matrix. Wear experiments were performed for all combinations of parameters, such as load (10, 20, and 30 N), sliding distance (500, 1000, and 1500 m), and sliding velocity (1, 2, and 3 m/s), for the alloy and the composites. The results revealed that wear rate increased with increasing load and increasing sliding distance, whereas the wear rate decreased and then increased with increasing sliding velocity. The primary wear mechanism encountered at low loads was mild adhesive wear, whereas that at high loads was severe delamination wear. An oxide layer was formed at low velocities, whereas a combination of shear and plastic deformation occurred at high velocities. The mechanism at short sliding distances was ploughing action of Si₃N₄ particles, which act as protrusions; by contrast, at long sliding distances, direct metal-metal contact occurred. Among the investigated samples, the Cu/10wt% Si₃N₄ composite exhibited the best wear resistance at a load of 10 N, a velocity of 2 m/s, and a sliding distance of 500 m.     

Preparation of nano-TiO2/diatomite-based porous ceramics and their photocatalytic kinetics for formaldehyde degradation

Diatomite-based porous ceramics were adopted as carriers to immobilize nano-TiO₂ via a hydrolysis-deposition technique. The thermal degradation of as-prepared composites was investigated using thermogravimetric-differential thermal analysis, and the phase and microstructure were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, and transmission electron microscopy. The results indicated that the carriers were encapsulated by nano-TiO₂ with a thickness of 300-450 nm. The main crystalline phase of TiO₂ calcined at 650℃ was anatase, and the average grain size was 8.3 nm. The FT-IR absorption bands at 955.38 cm-1 suggested that new chemical bonds among Ti, O, and Si had formed in the composites. The photocatalytic (PC) activity of the composites was investigated under UV irradiation. Furthermore, the photodegradation kinetics of formaldehyde was investigated using the composites as the cores of an air cleaner. A kinetics study showed that the reaction rate constants of the gas-phase PC reaction of formaldehyde were κ=0.576 mg·m-3·min-1 and K=0.048 m3.     

Microstructure and mechanical properties of Nb–Mo–ZrB2 composites prepared by hot-pressing sintering

Nb–Mo–ZrB₂ composites (V(Nb)/V(Mo)=1) with 15vol% or 30vol% of ZrB₂ were fabricated by hot-pressing sintering at 2000℃. The phases, microstructure, and mechanical properties were then investigated. The composites contain Nb-Mo solid solution (denoted as (Nb, Mo)ss hereafter), ZrB, MoB, and NbB phases. Compressive strength test results suggest that the strength of Nb–Mo–ZrB₂ composites increases with increasing ZrB₂ content; Nb–Mo–30vol%ZrB₂ had the highest compressive strength (1905.1 MPa). The improvement in the compressive strength of the Nb–Mo–ZrB₂ composites is mainly attributed to the secondary phase strengthening of the stiffer ZrB phase, solid-solution strengthening of the (Nb, Mo)ss matrix as well as fine-grain strengthening. The fracture toughness decreases with increasing ZrB₂ content. Finally, the fracture modes of the Nb–Mo–ZrB₂ composites are also discussed in detail.     

Reaction mechanism for in-situ β-SiAlON formation in Fe3Si-Si3N4-Al2O3 composites

In this work, Fe₃Si-Si₃N₄-Al₂O₃ composites were prepared at 1300℃ in an N₂ atmosphere using fused corundum and tabular alumina particles, Al₂O₃ fine powder, and ferrosilicon nitride (Fe₃Si-Si₃N₄) as raw materials and thermosetting phenolic resin as a binder. The effect of ferrosilicon nitride with different concentrations (0wt%, 5wt%, 10wt%, 15wt%, 20wt%, and 25wt%) on the properties of Fe₃Si-Si₃N₄-Al₂O₃ composites was investigated. The results show that the apparent porosity varies between 10.3% and 17.3%, the bulk density varies from 2.94 g/cm3 and 3.30 g/cm3, and the cold crushing strength ranges from 67 MPa to 93 MPa. Under the experimental conditions, ferrosilicon nitride, whose content decreases substantially, is unstable; part of the ferrosilicon nitride is converted into Fe₂C, whereas the remainder is retained, eventually forming the ferrosilicon alloy. Thermodynamic assessment of the Si₅AlON₇ indicated that the ferrosilicon alloy accelerated the reactions between Si₃N₄ and α-Al₂O₃ fine powder and that Si in the ferrosilicon alloy was nitrided directly, forming β-SiAlON simultaneously. In addition, fused corundum did not react directly with Si₃N₄ because of its low reactivity.     

高性能铜铝复合排的制备及界面研究

采用固-液法浇注和铸轧工艺制备铝/铜复合材料.研究不同工艺对铜/铝复合排界面结合强度的影响,并对铜/铝复合排界面结构和复合机理进行分析.结果表明:当进行300°C×1h热处理时,所得复合排的结合强度最高,多次热循环后复合排界面结合强度有所增加.电子探针能谱扫描分析(EDS)和X射线衍射分析(XRD)表明铜/铝复合界面上生成金属间化合物Al2Cu,Al4Cu9和AlCu相,从而使得界面层硬度增大.采用该方法制备的铜/铝复合排,整体拉伸强度达98MPa,电阻率为0.021 6×10-6Ω.m.     

基于八羧基酞菁铝近红外荧光检测铜（Ⅱ）离子

探讨了八羧基酞菁铝的分子光谱性质,利用八羧基酞菁铝的荧光光谱（最大激发波长620nm,最大发射波长698nm）近红外特性,建立了一种荧光猝灭法检测Cu2＋的新方法。考察了各种因素的影响,实验表明：在优化条件下,（pH 4.5、八羧基酞菁铝浓度5.0×10^-6mol.L^-1、反应时间5min、反应温度为室温）该方法的线性范围2.5×10^-6mol.L^-1～3.0×10^-5mol.L^-1（R=0.9974）,检出限8.3×10^-7mol.L^-1.利用该方法测定了实际水样中Cu^2＋的含量。     

[Ag／CoPt]n／Ag薄膜的结构和磁性

采用磁控溅射方法在玻璃基片上制备了[Ag／CoPt]n／Ag薄膜,并在600℃退火30min．结果表明,Ag掺杂厚度（x）对CoPt薄膜的结构和磁性影响很大．当Ag层厚度为0．5nm时,薄膜的垂直取向程度最高,其垂直矫顽力高达8．68×10^5A·m^-1而平行矫顽力仅为0．54×10^5A·m^-1．适当厚度的Ag不仅有利于薄膜的垂直取向,而且能降低晶粒间的交换耦合作用．     

微纳米ZrB2p/Al复合材料的原位合成机制和组织特征

采用Al--KBF4--K2ZrF6组元通过熔体直接反应法制备了ZrB2颗粒增强铝基复合材料,优化的初始合成温度范围为850～870℃,反应时间为25～30 min.扫描电镜观察结果显示：ZrB2颗粒尺寸为300～400 nm,颗粒间距200 nm左右,有团簇现象,团簇体尺寸为30～40μm.当颗粒理论体积分数为3%时,单位熔体体积内ZrB2颗粒形核数量为6.68×1017 m-3,平均线长大速率为47.3nm.s-1.分析团簇原因认为：大量细小高熔点ZrB2增加了熔体黏度,颗粒扩散阻力大,限制了颗粒迁移位移;ZrB2颗粒因密度大具有较高的沉降速率.原位反应过程分析表明：通过Al3Zr--AlB2间的分子化合及[Zr]--[B]间的原子化合得到ZrB2颗粒,是高温稳定相.     

SOFCs阴极材料La0.6Sr0.4Co1-x Fex O3-δ溶胶凝胶自燃烧法的制备

以分析纯La（NO₃）₃·6H₂为O、Sr（NO₃）₂、Co（NO₃）₂·6H₂O和Fe（NO₃）₁·9H₂O为原料,采用溶胶凝胶-自燃烧法制备了不同组成的La_0.6Sr_0.4Co_1-xFe_xO_3-δ（LSCF）超细粉体。采用X线衍射（XRD）和透射电子显微镜（TEM）对合成超细粉体的结构和形貌进行测定和表征。结果表明:溶胶凝胶-自燃烧法可一步合成粒径为30～70 nm的LSCF超细粉体,且随着Fe³⁺含量的增加,衍射峰值向低角度方向略有偏移。对超细粉体的烧结性能、热膨胀性能及电性能进行测试,结果表明:该粉体在1 100℃下烧结2 h,其相对密度达到97%。热膨胀系数随x(Fe³⁺含量)增加而增大,由x=0.1时的8.42×10^-6K^-1增大至x=0.5时的9.56×10^-6K^-1。直流四端子法电导测试表明:电导率随温度的升高（200～800℃）出现极大值,最大值可达950 S/cm,在500～700℃范围内,电导率均在200 S/cm以上,能够很好地满足中低温固体氧化物燃料电池对阴极材料的要求。     

室温下金属铝膜的霍尔效应初步研究

采用真空蒸发镀膜法制备了金属铝薄膜,在室温下,用四探针法测量了样品的电阻率和霍尔系数。结果表明,制成的金属铝膜,电阻率由块体材料的10^-8Ω·m 增大到薄膜样品的10^-5Ω·m;霍尔系数由块体材料的10^-11m³/C数量级左右增大到10^-4m³/C数量级;电阻率和霍尔系数随着金属铝膜厚度的减小而逐渐增大。     

Synthesis and characterization of Cr2AlC with nanolaminated particles

In this work, we reported the large-scale and low cost synthesis of high purity Cr2 AlC powders with nanolaminated particles by pressureless sintering. The chemical reactions involved in synthesizing Cr2 AlC had been studied and discussed. The results showed that the Al contents in the starting materials and sintering temperatures had significant effects on the synthesis and purity of Cr2 AlC. The obtained high purity Cr2 AlC powders were stable up to at least 1400 °C. The Cr2 AlC powders consisted of nanolaminated particles, the size of which was tunable by adjusting sintering time. The present synthesized nanolaminated Cr2 AlC powders would be an excellent reinforcement material for metal matrix composites.     

In situ (α-Al2O3+ZrB2)/Al composites with network distribution fabricated by reaction hot pressing

In situ (α-Al2O3+ZrB2)/Al composites with network distribution were fabricated using low-energy ball milling and reaction hot pressing. Differential thermal analysis (DTA) was used to study the reaction mechanisms in the Al–ZrO2–B system. X-ray diffraction (XRD) and scanning electron microscopy (SEM) in conjunction with energy-dispersive X-ray spectroscopy (EDX) were used to investigate the composite phases, morphology, and microstructure of the composites. The effect of matrix network size on the microstructure and mechani-cal properties was investigated.The results show that the optimum sintering parameters to complete reactions in the Al–ZrO2–B system are 850℃ and 60 min.In situ-synthesizedα-Al2O3 and ZrB2 particles are dispersed uniformly around Al particles, forming a network micro-structure; the diameters of theα-Al2O3 and ZrB2 particles are approximately 1–3μm. When the size of Al powder increases from 60–110μm to 150–300μm, the overall surface contact between Al powders and reactants decreases, thereby increasing the local volume fraction of re-inforcements from 12% to 21%. This increase of the local volume leads to a significant increase in microhardness of thein situ (α-Al2O3–ZrB2)/Al composites from Hv 163 to Hv 251.