Sintering behavior and thermal conductivity of nickel-coated graphite flake/copper composites fabricated by spark plasma sintering

Nickel-coated graphite flakes/copper（GN/Cu） composites were fabricated by spark plasma sintering with the surface of graphite flakes（GFs） being modified by Ni–P electroless plating. The effects of the phase transition of the amorphous Ni–P plating and of Ni diffusion into the Cu matrix on the densification behavior, interfacial microstructure, and thermal conductivity（TC） of the GN/Cu composites were systematically investigated. The introduction of Ni–P electroless plating efficiently reduced the densification temperature of uncoated GF/Cu composites from 850 to 650℃ and slightly increased the TC of the X–Y basal plane of the GF/Cu composites with 20 vol%–30 vol% graphite flakes. However, when the graphite flake content was greater than 30 vol%, the TC of the GF/Cu composites decreased with the introduction of Ni–P plating as a result of the combined effect of the improved heat-transfer interface with the transition layer, P generated at the interface, and the diffusion of Ni into the matrix. Given the effect of the Ni content on the TC of the Cu matrix and on the interface thermal resistance, a modified effective medium approximation model was used to predict the TC of the prepared GF/Cu composites.

Development of Cu-Exfoliated Graphite Nanoplatelets (xGnP) Metal Matrix Composite by Powder Metallurgy Route

In the present investigation the possibility of using exfoliated graphite nanoplatelets (xGnP) as reinforcement in order to enhance the mechanical properties of Cu-based metal matrix composites is explored. Cu-based metal matrix composites reinforced with different amounts of xGnP were fabricated by powder metallurgy route. The microstructure, sliding wear behaviour and mechanical properties of the Cu-xGnP composites were investigated. xGnP has been synthesized from the graphite intercalation compounds (GIC) through rapid evaporation of the intercalant at an elevated temperature. The thermally exfoliated graphite was later sonicated for a period of 5 h in acetone in order to achieve further exfoliation. The xGnP synthesized was characterized using SEM, HRTEM, X-ray diffraction, Raman spectroscopy and Fourier transform infrared spectroscopy. The Cu and xGnP powder mixtures were consolidated under a load of 565 MPa followed by sintering at 850°C for 2 h in inert atmosphere. Cu-1, 2, 3 and 5 wt% xGnP composites were developed. Results of the wear test show that there is a significant improvement in the wear resistance of the composites up to addition of 2 wt% of xGnP. Hardness, tensile strength and strain at failure of the various Cu-xGnP composites also show improvement upto the addition of 2 wt% xGnP beyond which there is a decrease in these properties. The density of the composites decreases with the addition of higher wt% of xGnP although addition of higher wt% of xGnP leads to higher sinterability and densification of the composites, resulting in higher relative density values. The nature of fracture in the pure Cu as well as the various Cu-xGnP composites was found to be ductile. Nanoplatelets of graphite were found firmly embedded in the Cu matrix in case of Cu-xGnP composites containing low wt% of xGnP.

Electroless nickel plated graphite fibers and surface behavior in G_(r(Ni))/6061Al composite

The electroless nickel plated graphite fibers reinforced aluminum matrix composites (Gr(Ni))/Al) were produced by squeeze casting, and the microstructure of Gr(Ni)/Al composite and surface behavior of Ni-P coating were studied. The optimum process of electroless Ni-P plating included: burning to get rid of glue→degreasing→neutralization→acidulating→sensitizing→activation→electroless plating. The surface analysis results show that the electroless nickel plating can diffuse into the graphite fiber surface during the squeeze casting, and the Ni-P coating and aluminum alloys can produce brittle phase NiAl3 or NiAl. The X-ray diffraction(XRD) results indicate that Al4C3 is so little that no Al4C3 peaks are found, and the harmful Al4C3 can be decreased by the electroless plating Ni-P coating. The coating improves the interfacial bonding of continuous graphite fibers reinforced aluminum matrix composites.

Effect of graphite contents on friction and wear properties of Ni-Cr-W composites

Ni-based alloy/W/graphite self-lubricating composites with different graphite addition amounts were prepared using PM （powder metallurgy） method. It is found that the addtion of graphite can increase the tensile strength and hardness, while the bending strength decreases. The tribological properties of the composites when rubbing with Al2O3 ceramic disc were investigated in the temperature range of 20600℃. The results show that the tribological properties of the alloy are improved by adding graphite. When the graphite content is up to 9%, the friction coefficient at 600℃ is about 0.2, which is one third of that with no graphite. At elevated temperature, the friction coefficients change a little with velocity and load. At room temperature, graphite extruded from the composite plays the the role of lubrication. The synergistic effect of oxide films and graphite are responsible for the reduction of friction coefficient at high temperature.

Field-assisted tunneling enabled pressure-sensitive composites/sensors for smart concrete structures

Spiky spherical nickel powder with sharp nano-tips on its surface is a kind of excellent fillers for developing pressure-sensitive cement-based composites/sensors for traffic detection,structural health monitoring,and border and military security.The sharp nano-tips on the surface of spiky spherical nickel particles can induce field emission and tunneling effects,which leads to the ultrahigh pressure-sensitive responses of the cement-based composites.In this paper,we systematically introduce research on nanotip-induced ultrahigh pressure-sensitive cement-based composites/sensors,with attentions to their pressure-sensitive property and sensing mechanism,pressure-sensitive characteristic model,and smart structure system for traffic detection.

梯度层对铜基复合材料摩擦学性能的影响

采用粉末冶金方法制备均质石墨−铜复合材料(10%C/Cu,质量分数)和2层梯度石墨−铜复合材料(7%C/Cu-10%C/Cu),研究梯度层对石墨−铜复合材料物理性能和摩擦学性能的影响,并对其摩擦磨损机制进行分析。研究结果表明:梯度复合材料的致密度和导电性相比于均质复合材料都得到了显著提升。在法向载荷为24、26和30 N时,梯度复合材料的磨损率相比于均质复合材料分别降低了8.24%、12.10%和11.30%;梯度材料和均质材料的平均摩擦因数和磨损率均随载荷的增加而升高;梯度复合材料的磨痕深度、宽度和材料挤出高度都比均质复合材料的小,且均随载荷的增加而增大。2种复合材料的磨损机制主要以磨粒磨损为主,氧化磨损和黏着磨损为辅。

涂层层数对镍粉/石墨基复合材料介电性能和吸波性能的影响

为了解制备工艺对涂覆型吸波材料性能的影响,实验研究涂层层数对镍粉/石墨基复合材料的介电性能及吸波性能的影响机制。选用PU2540型聚氨酯为黏结剂,镍粉、石墨为功能粒子,涤/棉平纹织物为基布,采用纺织涂层(刮涂法)工艺制备了涂层层数不同的镍粉/石墨基涂层复合材料。测试该复合材料的介电常数(实部、虚部、损耗角正切值)和反射损耗,分析涂层层数对复合材料介电性能和吸波性能的影响。结果表明:在测试频率1^(1)000 MHz范围内,3层的镍粉/石墨基复合材料对电磁波的极化能力、损耗能力及耦合能力最强;在测试频率10~3000 MHz范围内,涂层层数2层的复合材料的吸波性能最好,反射损耗最小峰值为-26.460 dB;3种涂层层数不同的复合材料在不同频段表现出不同的吸波特性。所得结果可为开发经济实用的吸波材料提供理论参考。

Effect of activators on the properties of nickel coated diamond composite powders

Nickel coated diamond composite powders were fabricated via a newly developed direct electrodeposition technique. The effects of activators on the coating of diamond were firstly investigated and diamond grinding wheels were then prepared from Ni-coated diamond composite powders with different activators. The microstructural characterizations of this composite powders were finally conducted by scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffraction, and the mechanical and tribological properties of as-prepared diamond grinding wheels were also measured. There are changes in microstructures and properties of the composite powders with activators. The activator concentration also has an influence on the morphologies and phase structures of the Ni coating on diamond particles.The composite powders with more compact coating of nickel can be prepared by adding 1 g dm^（-3） or more AgNO_3 as an activator to electrodeposit nickel on diamond. The mechanical and tribological properties of diamond grinding wheels were significantly improved when the coating phase structure of Ni crystal grew with（111） plane orientation on the surface of diamond particles. The wheels made from nickel coated diamond composite powders possessed the advantages of easy preparation and outstanding tribological properties. Therefore, Ni coated diamond composite powders exhibit a great potential to be extensively applied in diamond cutting and grinding tools.

Spray pyrolysis synthesis of nickel-rich layered cathodes LiNi_(1-2x)Co_xMn_xO_2(x = 0.075, 0.05, 0.025) for lithium-ion batteries

In this study we report a series of nickel-rich layered cathodes LiNi1-2xCoxMnxO2（x = 0.075, 0.05,0.025） prepared from chlorides solution via ultrasonic spray pyrolysis. SEM images illustrate that the samples are submicron-sized particles and the particle sizes increase with the increase of Ni content.LiNi0.85Co0.075Mn0.075O2 delivers a discharge capacity of 174.9 mAh g-1 with holding 93% reversible capacity at 1 C after 80 cycles, and can maintain a discharge capacity of 175.3 mAh g-1 at 5 C rate. With increasing Ni content, the initial specific capacity increases while the cycling and rate performance degrades in some extent. These satisfying results demonstrate that spray pyrolysis is a powerful and efficient synthesis technology for producing Ni-rich layered cathode（Ni content 〉 80%）.

预置工艺参数对铜基自润滑复合材料熔覆层的影响

道岔滑床板是轨道交通线路的重要部件之一,其正常工作是列车运行安全的基本保证。目前我国的滑床板采用Q235钢,需要人工定期涂油养护,该方法受服役环境影响明显,成本大,同时存在污染环境、操作安全等隐患。拟选用具有耐磨耐蚀性能良好的铜基自润滑材料,使用不同的预置法工艺进行试样制备与熔覆实验,对床板进行表面强化。对比预置法制备的试样情况与熔覆性能,最终获得适合的预置法工艺以及相应的工艺参数。

Recent progress in synthesis of composite powders and their applications in low-carbon refractories

The development of low-carbon refractories is of great significance,but it is limited by the deteriorated properties that resulted from the decreased graphite content.Incorporating composite powders has proved to be effective in improving the properties of low-carbon refractories.The recent progress in the synthesis of composite powders including modified graphite,nanocarbon-containing composite powders,oxide/non-oxide and non-oxide composite powders and their applications in low-carbon refractories were reviewed,and the future development of composite powder technology was prospected.

镍粉/石墨粉/NBR复合电磁屏蔽材料的研制及性能

采用镍粉、石墨粉填充丁腈橡胶,制备了镍粉/石墨粉/NBR复合电磁屏蔽材料,对比了不同镍粉/石墨粉比例复合电磁屏蔽橡胶的各项性能。采用扫描电子显微镜、发泡硫化仪、热常数分析仪和矢量网络分析仪等,对材料进行测试和表征。结果表明,石墨粉可提高橡胶交联程度,对NBR具有补强作用,表现为韧性断裂;随石墨粉用量增加,复合材料导热性能和导电性能提高;当镍粉/石墨粉比例为1︰4时,复合材料在10.5 GHz屏蔽效能达18.7 dB。

镀镍石墨粉对铜基石墨复合材料力学性能的影响

采用粉末冶金工艺制备铜基石墨复合材料，考察烧结工艺、石墨粉颗粒表面镀镍及强化相对铜基石墨复合材料的力学性能和组织结构的影响，并对材料的组分、显微组织形态结构及断口形貌等进行系统的观察和分析，测试材料的硬度、冲击韧性和在室温、300℃、500℃各温度的压溃强度。结果表明：采用镀镍石墨粉改善了石墨和铜合金基体界面结合状态，界面结合更加牢固紧密，明显提高铜基石墨复合材料的力学性能，室温压溃强度和冲击韧性提高了30％～50％，高温强度提高了35％～60％，而对复合材料的硬度影响不大，复压复烧工艺更有利于发挥镀镍石墨粉的优越性。

制备细镍包石墨粉末的动力学

控制反应速度是采用水热方法制备包覆粉末的关键技术之一。以细镍包石墨粉末为研究对象 ,探讨了制备过程中的一系列反应参数 :温度、表面活性剂、硫酸铵浓度、氨水浓度、氢分压以及初始溶液镍浓度等因素对反应诱导期、还原速度的影响 ,证明了这些参数控制着反应速度。

镀镍石墨/硅橡胶导电复合材料的性能研究

以镀镍石墨为导电填料制备镀镍石墨/甲基乙烯基硅橡胶(MVQ)导电复合材料,并对其性能进行研究。结果表明,采用密炼工艺、硫化温度为110℃、偶联剂A-151和硫化剂双24用量分别为6和8份时,所制备的镀镍石墨/MVQ复合材料的导电性能和拉伸性能较好。

镀铜石墨粉含量对铜-镀铜石墨复合材料组织与性能的影响

比较了用粉末冶金法制备的铜 -镀铜石墨复合材料的显微组织与部分性能。结果表明 ,随镀铜石墨含量的增加 ,铜 -镀铜石墨复合材料的密度和导电性降低 ,但其组织中石墨分布更均匀 ,并且铜有利于构成三维网状 ,使该复合材料具有更好的导电性。

石墨粉末上化学镀镍研究

对石墨粉末进行了表面化学镀镍研究，经表面处理后，再在碱性溶液中进行化学镀镍处理。

镀镍石墨粉与铜基自润滑材料摩擦磨损特性研究

采用粉末冶金复压复烧工艺制备铜基石墨复合材料，考察了不同载荷条件下铜基石墨复合材料的摩擦磨损性能．结果表明：在载荷20～60N条件下，含6％（质量分数）石墨的铜基复合材料经历了轻微磨损、中等磨损到严重磨损3个过程；石墨颗粒表面镀镍可以提高石墨与铜合金基体的界面结合强度以及磨损过程中所形成的转移层与基体问的粘附性能，含6％镀镍石墨的铜基复合材料的自润滑性能得到改善，只经历了轻微磨损和中等磨损2个过程．

金属Ni/石墨/BaTiO_3基复合PTC材料的研究

探讨了降低BaTiO3 基的PTC陶瓷室温电阻率的新途径 ,即在BaTiO3 基的PTC陶瓷配方中加入石墨或金属Ni。目的是将石墨或金属Ni优良的导电性和BaTiO3 陶瓷的PTC效应相结合 ,制备出具有较低室温电阻率又有较好PTC效应的复合材料。通过对大量实验和数据分析 ,优化了实验配方和工艺条件 。

镀镍石墨粉的电化学性质

利用化学镀方法在石墨粉表面镀覆了一层均匀、完整的金属镍 ,研究了镀镍石墨粉电极及镀镍石墨粉作为MH/Ni电池镍电极导电剂时的电化学性质。实验表明 ,石墨粉表面镀覆金属镍可增加其电化学活性 ;用镀镍石墨粉作为电极导电剂时 ,可以改善镍电极的导电性能 ,降低电池内阻 ,提高正极活性物质的利用率 ,且电池的循环稳定性好 ,以 1C倍率充放电循环 12 0次不衰减。