Low-cost solid FeS lubricant as a possible alternative to MoS2 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, micro-structures, 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°C. 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 fric-tion (COF) in all of the samples.     

Low-cost solid FeS lubricant as a possible alternative to MoS_2 for producing Fe-based friction materials

Three reaction systems of MoS_2–Fe, FeS –Fe, and Fe S–Fe–Mo were designed to investigate the use of FeS as an alternative to MoS_2 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 MoS_2 reacts with the matrix to produce iron-sulfides and Mo when sintered at 1050°C. Iron-sulfides produced in the MoS_2–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 Fe S–Fe–Mo system showed a phase composition, porosity, and density similar to those of the MoS_2–Fe system, but an uneven distribution of iron-sulfides and Mo in this system resulted in less-optimal mechanical properties. Finally, the Fe S–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.     

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.     

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.     

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.     

镁基固态储氢材料研究进展

 镁基储氢材料具有储氢量高、镁资源丰富以及成本低廉等优点,被认为是极具应用前景的一类固态储氢材料。利用镁基储氢材料供氢主要有热分解放氢和水解产氢2种途径。MgH₂的热分解放氢焓值高（75 kJ/mol H₂）,造成其放氢温度较高、动力学差; MgH₂的水解过程中,由于常温水解产物Mg（OH）₂逐渐包裹在MgH₂表面,阻隔了MgH₂与水的接触,从而导致水解产氢效率较低。近年来,大量研究工作聚焦于改善MgH₂的热解/水解供氢性能及实际应用,已经取得了大量成果。针对目前国内外镁基固态储氢材料的研发,总结了材料/结构改性、反应条件对镁基储氢材料的热解/水解性能的影响,重点阐述了固态镁基储氢材料组成成分-微观结构-储放氢性能之间的关系,并对镁基储氢系统及实际应用场景进行了归纳。未来通过镁基固态储运氢技术的发展,将实现氢气的高安全、高效及大规模储运,助力中国氢能产业的发展。     

纳米Al2O3改性酚醛树脂在汽车制动摩擦材料上的应用

用偶联剂KH570对纳米Al2O3进行表面处理,经透射电镜检测,发现纳米Al2O3能够均匀有效地分散在酚醛树脂中,并确定了纳米Al2O3质量为树脂质量的6%时分散性最好.运用共混的方法,对酚醛树脂进行纳米Al2O3改性处理,分析了纳米Al2O3的质量为树脂质量的2%,4%,6%,8%和10%时,改性酚醛树脂对汽车制动摩擦材料性能的影响.结果表明:经过表面处理的纳米Al2O3改性醛醛树脂,当纳米Al2O3质量为树脂质量的6%时,酚醛树脂的性能提升最明显,酚醛树脂的热分解温度提高了41℃,且降低失重率,纳米Al2O3改性酚醛树脂制备的摩擦材料的摩擦系数最稳定,具有较低的磨损率.     

李群方法在寻找一类二次Hamilton系统平衡点中的运用

对一类二次Hamilton系统,假设它有一个平衡点,运用李群方法,得到了一种线性不变群.在该群的作用下,由Hamilton系统的已知平衡点而得到的新点,仍为Hamilton系统的平衡点。