The effect of field emission traits of carbon-nanotubes on the generation of negative air ions
Date Issued
2009
Date
2009
Author(s)
Lu, Shan-Jen
Abstract
This study investigated the traits of field emission effect of carbon-nanotubes (CNTs) on generation of negative air ions (NAIs) by negative electric discharging, and the feasibility of developing a microscale air cleaner. The research evaluated the effect of the aspect ratio of CNTs, density of the CNTs, single-wall and multi-wall CNTs and double-wall CNTs, metal material, metal aspect ratio, and metal needle-point curvature on the discharging voltage of CNTs. It also evaluated the stability and the effective space of the generation of NAIs by using CNTs with negative electric discharging, and studied the possible generation of ozone. The results show that enhanced field emission gets bigger when the aspect ratio of CNTs increased, so that discharging voltage gets lower. The limited voltage value of multi-wall CNTs(aspect ratio ranged from 1666.66 to 5000) required only 0.5 kV when they used as discharging electrode. That was the first time the value lower than 1.0 kV. NTs array can reduce screening effect because of regular alignment and also reduce discharging voltage effectively. The field emission from CNTs array could be optimized with the inter-tube distance of 10th of the height(CNTs array with density of 1~2×109 CNTs/cm2). No matter the number of layers of CNTs, the CNTs with greater aspect ratio have lower discharging voltage. At same discharging voltage, the stability of NAIs by negative electric discharging gets higher when the aspect ratio of CNTs increases. nd we find out that the stability of generate NAIs by imitate pulsed corona is much better than continued discharging. If we close the electric field for 30sec and restart it for 1 minutes. We could keep the concentration of NAIs over than 4.0×105ions/cm3 for 30minutes. The NAIs concentration did not change with increasing space. CNTs on copper electrode can reach detecting limit range of NAIs at discharging voltage of 0.5kV without generation of ozone. At discharging voltage of 2.5 kV, CNTs on copper electrode begin to generate ozone at 0.2 ppb, this value is much lower than the Indoor Air Quality value (0.03 ppm), so we don’t have to worry about the problem of ozone pollution.
Subjects
negative air ions (NAIs)
field emission
carbon-0nanotubes
pulsed corona
Type
thesis
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