Estudo do desempenho de um analisador de mobilidade elétrica de nanopartículas

Abstract

Electrical Mobility Analyzer is a device used to produce aerosol nanoparticles in narrow size ranges previously set as a function of the electrical charges of the particles in order to produce desirable monodisperse chains. The polydisperse particles entering this equipment make a trajectory that is a function of the electric field strength and its electrical mobility, and this trend is a function of the aerosol particle diameter. The importance of producing monodisperse aerosols is linked to its application in the calibration of high-precision equipment in this era of nanotechnology. Another relevant factor is directly related to the issue of occupational health, in which nanoparticles may pose a risk to human health as present in the breathing air at a concentration higher than that allowed by the environmental legislation. The electric mobility separation process involves four main stages: (i) generating polydisperse nanoparticles; (ii) the stability of the particles loads; (iii) separation by electric mobility, and (iv) counting the particles produced to calculate efficiency. Commercial analyzers (Differential Mobility Analyzer) are devices with very high prices in the market due to the latest technology concerning them, therefore, the present study sought to develop and optimize an analyzer with its own technology and low cost. For this purpose, starting from a polydisperse aerosol (broad size range) produced with nanoparticles at different NaCl concentrations yielded a monodisperse aerosol (narrow size range) via electric mobility rating. The system used was basically concentric cylinders of stainless steel with polydisperse nanoparticles being fed into the annular region, while ultrapure air was fed to the system. The electrically charged particles were attracted or repelled the central electrode according to their acquired loads. Design calculations led to the disposal of a collection hole in the system that allowed the classification of patículas by size ranges in the nanometer scale. After the experiments conducted in FEQUI / UFU, it was found that the amount of nanoparticles produced in the system was a function of concentration of NaCl used in solution as well as the average size of the particles produced. In addition, tests were performed in the Department of Chemical Engineering, Federal University of São Carlos (DEQ / UFSCar), using a commercial analyzer (SMPS) TSI brand. These tests helped the comparison of experimental results with theoretical, showing that this Electric Mobility Analyzer was quite efficient in the production of monodisperse nanoaerossóis, priced less than 10% of the value of commercial equipment. A mobility swing nanoparticle classification, based on the load distribution has been proposed to estimate size distributions produced, which is representative for balance and excessive monodisperse aerosol.