Characteristics of indirect laser-induced plasma from a thin film of oil on a metallic substrate

Optical emissions from the major and trace elements embodied in a transparent gel prepared from cooking oil were detected after the gel was spread in a thin film on a metallic substrate. Such emissions are due to the indirect breakdown of the coating layer. The generated plasma, a mixture of substances from the substrate, the layer, and the ambient gas, was characterized using emission spectroscopy. The characteristics of the plasma formed on the metal with and without the coating layer were investigated. The results showed that Al emission induced from the aluminum substrates coated with oil films extends away from the target surface to ablate the oil film. This finally formed a bifurcating circulation of aluminum vapor against a spherical confinement wall in the front of the plume, which differed from the evolution of the plasma induced from the uncoated aluminum target. The strongest emissions of elements from the oil films can be observed at 2 mm above the target after a detection delay of 1.0 μs. A high temperature zone has been observed in the plasma after the delay of 1.0 μs for the plasma induced from the coated metal. This higher temperature determined in the plasma allows the consideration of the sensitive detection of trace elements in liquids, gels, biological samples, or thin films.     

机油中痕量磨损金属元素的间接烧蚀LIBS探测研究

机油在发动机的运转过程中具有非常重要的作用。发动机的运转,会使机油的成分和元素含量发生变化,导致机油变质,进而加剧发动机的磨损,探寻一种快速有效的机油性能检测手段,则是防止发生事故的重要前提。间接烧蚀激光诱导击穿光谱技术(IA-LIBS)是针对机油样品提出的一种全新检测方法,其核心是基于金属基底产生的高温等离子体间接烧蚀样品,在保持了LIBS基本特点的基础上,提高了样品检测灵敏度和稳定性。在前期研究基础上,以机油中Mg、Fe和Ni为目标元素,分析了不同类型机油中的基体效应对其定量分析结果的影响,表明不同油种之间的基体效应对目标元素的定标曲线影响甚小,可忽略;同时建立了目标分析元素的综合定标曲线,拟合线性系数达到了0.99以上。通过对现场机油中添加的已知浓度的目标元素的检测,IA-LIBS分析结果与实际值吻合较好,准确度均低于5%。该研究完善了IA-LIBS的方法研究,为以后评价机油的性能提供了依据,对于诊断发动机的磨损状况具有重要的科学意义。