Reducing air interference is one of the most important steps in achieving direct determination of nitrogen element in water by laser-induced breakdown spectroscopy (LIBS). In this work, plasma amplification LIBS assisted with spatially resolved spectroscopy was used to reduce air interference in LIBS. The longitudinal spatially resolved spectrum of N I 746.831 nm at different breakdown position was obtained and optimized by imaging the plasma on the spectrometer entrance slit. By selecting the pixel range of plasma from 1-256 to 25-80, the background equivalent concentration (BEC) was reduced from 34.29 ppm to 9.58 ppm. Furthermore, the limit of detection (LoD), R2, the average relative error (REAV), and the root mean square error of cross validation (RMSECV) were improved from 2.01 to 0.53 ppm, 0.7779 to 0.9554, 24.76% to 15.22%, and 11.03 to 3.63 ppm, respectively. The results shown that the weak air interference and higher quantitative analysis performance of plasma amplification LIBS could be obtained by spatially resolved spectroscopy.
Flame propagation characteristics of wood dust deflagration and suppression mechanism of ultrafine powders are investigated systematically. The deflagration reaction intensity of wood dust increases firstly and then decreases with the increase in dust cloud concentration. This is due to factors such as oxygen supply, positive feedback among flame characteristic parameters. Thus, there is an equivalent dust concentration for greatest deflagration intensity. Nano-sized ultrafine zirconium hydroxide (Zr(OH) 4 ) and silicon dioxide (SiO 2 ) powder are introduced to suppress wood dust deflagration at the equivalent concentration. It is found that Zr(OH) 4 has a suppression effect of endothermic decomposition to generate zirconia (ZrO 2 ), dilution of oxygen and absorption of free radicals; while SiO 2 exerts suppression effect due to its high melting point and heat absorption. The suppression performance of Zr(OH) 4 is better than that of SiO 2 . This is because that Zr(OH) 4 and ZrO 2 have a catalytic carbonization effect. It can not only improve thermal stability of wood particles by catalyzing production of high-temperature resistant residuals, but also promote the formation of catalytic sites to reduce crystallite size of carbon layer on wood particles surface, weakening heat and mass transfer between particles.
危险品化学品经营许可证（带存储）