常压环境下铅笔芯的质谱放电行为研究

Study on Discharge Behavior of Pencil Lead at Ambient Pressure by Mass Spectrometry

铅笔芯内所含石墨和黏土的混合比例如果不符合国家标准,将不利于计算机读卡设备正确识读和非专业人士鉴定。本文采用常压质谱法对不同黑度(石墨含量)、硬度的铅笔芯进行分析,为实现铅笔品质的快速鉴别提供了一种有效的技术手段。该方法直接将铅笔芯作为电离装置,在高电压作用下以空气(相对湿度40%)为介质,铅笔芯产生电晕放电,其放电行为能够对质谱信号产生直接影响。实验优化了工作条件,分析了6种型号铅笔芯(4B、3B、2B、HB、H和2H)中石墨含量与其质谱信号之间的关系,并结合主成分分析(PCA)对不同型号铅笔芯进行区分。结果表明,不同型号铅笔芯的放电行为对质谱信号产生较大影响,质谱信号随铅笔芯中石墨含量的增多而增强;6种型号铅笔芯区分正确率高达99%以上。此方法操作简单且可重复性强,可用于市场上不同品质铅笔芯的快速鉴定。

Graphite and clay mixed in pencil lead, with non-standard proportions will be read correctly by computer card reading equipment and identified by non-specialists. In this paper, a rapid and effective method based on atmospheric mass spectrometry utilizes quality evaluation for the pencil lead by the analysis of different degrees of blackness （graphite content） and hardness. At ambient pressure, with about 40% relative humidity, pencil lead was directly used as an ionization device to produce coronal discharge and impact the mass spectrum signals in air at high voltage. Here, experimental conditions were optimized, the relationship between the graphite content in pencil leads （e. g. 4B, 3B, 2B, HB, H and 2H） and their mass spectrum signals were analyzed, and six kinds of pencil leads were discriminated by principal component analysis （PCA）. The results showed that the discharge behaviors of the different types of pencil lead have an influence on the signal intensity, which increases with the increasing graphite content in pencil lead. On the basis of the mass spectra raw data, six kinds of pencil lead were correctly identified to more than 99%. The method is available with a good reproducibility and straightforward operation, providing a rapid tool for the quality evaluation for commercially available pencil lead.