Nanocrystalline Si-Based Resistive Humidity Sensors Prepared via HWCVD at Various Filament Temperatures
The growth of nanocrystalline Si on glass substrates via hot-wire chemical vapor deposition (HWCVD) at various filament temperatures and the fabrication of nanocrystalline Si-based resistive humidity sensors are reported. Experimental results indicate that the average diameter of nanocrystalline Si particles increases with increasing filament temperature. Measurements of the resistivity change of samples with humidity at 25°C show that the sensor response of samples fabricated at high filament temperatures is lower than that of samples fabricated at low filament temperatures. The sensitivity of the sensor increases with relative humidity.
Raman spectral study of silicon nanowires
Raman spectra of silicon nanowires (Si NW's) have been analyzed, and the observed Raman peaks were assigned. The typical features of the first-order Raman peaks of the optical phonons were found matching those predicted by the quantum confinement effect. However, the sizes of Si NW's, derived from the microcrystal model (MCM) of Raman spectra do not fit the usual confined size, the diameter, of the nanowires from transmission electron microscope images. Abundant structure defects can be observed in Si NW's so that the Si NW's actually consist of many smaller Si grains. The size of such Si grains was found to give a better agreement with the size derived from the Raman spectra. This indicates that MCM can be used to interpret the Raman spectrum of Si NW's as long as one takes into account the influence of defect on the confined size.
Numerical and experimental investigation on air distributor design of fluidized bed reactor of sawdust pyrolysis
Abstract An improved biomass conversion in a lab-scale fluidized bed reactor (FBR) is achieved by optimizing the air distributor orifice size and number. Two approaches for introducing air were numerically and experimentally examined. These included perforated plate and downward orifice sparger. 3 mm and 5 mm orifice diameters, and 7, 9 and 13 holes were simulated at flow velocities of 2, 4, 6, and 8 times the minimum fluidization velocity, Umf. The simulation results revealed that increasing the orifice number has a positive effect on gas holdup, particularly for the perforated plate, which showed a uniform distribution of bubbles. The sparger configuration produced larger bubbles sizes, which could lead to better recirculation of solid flux, while stagnant particle zones were observed at the lower section of both distributors. A pyrolysis unit is also inserted at the top of freeboard of the FBR. For perforated plate with 6Umf, the pyrolysis process achieved thermal and cold gas efficiencies of 82.91% and 52.03%, respectively, while combustible gases with 41.6%mol CO, 8.7%mol CH 4 and 2.17%mol HC, were obtained. For sparger pipe and 6U mf _sp, 35.33 ppm NOx and 111 ppm SO 2 were measured in flue gas from combustion process at bed region.