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Mechanical characterization of diesel soot nanoparticles: in situ compression in a transmission electron microscope and simulations

机译：柴油烟灰纳米粒子的机械表征：透射电子显微镜和模拟中的原位压缩

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Incomplete fuel burning inside an internal combustion engine results in the creation of soot in the form of nanoparticles. Some of these soot nanoparticles (SNP) become adsorbed into the lubricating oil film present on the cylinder walls, which adversely affects the tribological performance of the lubricant. In order to better understand the mechanisms underlying the wear caused by SNPs, it is important to understand the behavior of SNPs and to characterize potential changes in their mechanical properties (e.g. hardness) caused by (or during) mechanical stress. In this study, the behavior of individual SNPs originating from diesel engines was studied under compression. The experiments were performed in a transmission electron microscope using a nanoindentation device. The nanoparticles exhibited elasto-plastic behavior in response to consecutive compression cycles. From the experimental data, the Young's modulus and hardness of the SNPs were calculated. The Young's modulus and hardness of the nanoparticles increased with the number of compression cycles. Using an electron energy loss spectroscopy technique, it was shown that the sp(2)/sp(3) ratio within the compressed nanoparticle decreases, which is suggested to be the cause of the increase in elasticity and hardness. In order to corroborate the experimental findings, molecular dynamics simulations of a model SNP were performed. The SNP model was constructed using carbon and hydrogen atoms with morphology and composition comparable to those observed in the experiment. The model SNP was subjected to repeated compressions between two virtual rigid walls. During the simulation, the nanoparticle exhibited elasto-plastic behavior like that in the experiments. The results of the simulations confirm that the increase in the elastic modulus and hardness is associated with a decrease in the sp(2/)sp(3) ratio.
机译：内燃机内部燃烧的不完全燃料导致纳米颗粒的形式产生烟灰。这些烟灰纳米颗粒（SNP）中的一些被吸附在气缸壁上存在的润滑油薄膜中，这对润滑剂的摩擦学性能产生不利影响。为了更好地理解由SNP引起的磨损的潜水机制，了解SNP的行为并表征由（或期间）机械应力引起的机械性能（例如硬度）的潜在变化。在这项研究中，在压缩下研究了来自柴油发动机的单个SNP的行为。使用纳米狭窄装置在透射电子显微镜中进行实验。纳米颗粒响应于连续的压缩循环而表现出弹性塑性行为。从实验数据中，计算杨氏模量和SNP的硬度。少年的纳米颗粒的模量和硬度随压缩循环的数量而增加。使用电子能量损失光谱技术，示出了压缩纳米颗粒内的SP（2）/ SP（3）比率降低，这表明是弹性和硬度增加的原因。为了证实实验结果，进行了模型SNP的分子动力学模拟。使用碳和氢原子构建SNP模型，其形态和组成与实验中观察到的形态学和组成。在两个虚拟刚性墙壁之间进行模型SNP反复压缩。在模拟期间，纳米粒子表现出这样的弹性塑料行为在实验中。仿真的结果证实，弹性模量和硬度的增加与SP（2 /）SP（3）比的减少相关。

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