Acoustic absorption behaviour of a tall carbon nanotube forest

Previous investigations have shown that a 3-mm-high carbon nanotube (CNT) forest has an acoustic absorption coefficient of about 5-10% within the frequency range 125 Hz-4 kHz, which is above that of conventional acoustic materials on a per-mass basis. It was hypothesised that a CNT array of greater height, lower density, and with a non-uniform arrangement of the nanotubes could enhance the amount of acoustic absorption. In order to investigate this hypothesis, an impedance tube test was conducted to measure the acoustic absorption coefficient of a relatively tall 6-mm CNT forest. The results indicate that a greater length and lower density of CNTs may improve the absorption performance of CNT-based acoustic absorbers. Analyses of the results showed anomalies in the measured acoustic absorption coefficient compared with previous investigations. Theoretical analyses were performed based on classical models of acoustic absorption to explain the anomalies. This study describes the factors that may affect the acoustic absorption behaviour of nanomaterials.M. Ayub, A. C. Zander, C. Q. Howard, B. S. Cazzolato, D. M. Huang, N. T. Alvarez, and V. N. Shano

LCVD of aluminium stripes obtained by pyrolysis of TMAA and TMA

Maskless patterning of aluminium has been achieved by using visible light from a copper bromide vapor laser for pyrolytic decomposition of trimethylaluminium (TMA) and trimethylamine alane (TMAA). A silicon monocrystalline wafer was used as a substrate. The deposition was carried out at different process parameters (partial pressure of the precursors, laser power and scanning speed). The analysis of the resultant stripes included scanning electron microscopy, Auger electron spectroscopy, Talystep and electrical resistance measurements. The crystalline structure of the layers showed well-defined grains for both precursors. The Auger electron spectra indicated pure aluminium layers with small quantities of oxygen and carbon for stripes deposited from TMAA while those obtained from TMA were more contaminated. The difference in the layers composition for the used precursors resulted in their resistivity values. The low resistivities of aluminium stripes deposited from TMAA (up to 4.0 [MATH].cm) makes it promising precursor for metalization with aluminium and especially for chemical vapor deposition enhanced with pulsed visible laser

LASER INDUCED DIRECT WRITING OF ALUMINIUM

Maskless configuration of aluminium has been grown by using visible light of a copper laser for pyrolytic decomposition of trimethylaluminium (TMA). The process was carried out in vacuum or argon and hydrogen atmosphere at partial pressure of TMA 0,5 and 5 mbar. The crystalline structure of the coating shows well defined grains. This morphology was observed for the first time by using pulsed visible laser. The Auger electron spectra indicate the presence of bonded oxygen and carbon incorporated into the aluminium. These elements cannot be totally avoided but their concentration can be reduced at the established optimum conditions to obtain low resistivity of the layer

Mass spectrometric study of laser induced pyrolytic decomposition of TIBA and TMAA

The composition of the gaseous phases during pyrolytic laser-induced chemical vapor deposition (LCVD) of aluminium from triisobutylaluminium (TIBA) and trimethylamine alane (TMAA) (aluminium trihydride trimethylamine) was determined. The analysis was carried out by means of quadrupole mass spectrometer (QMS) in closed reaction cell. The developed arrangement for sampling allowed in situ analyses during the LCVD process. The decomposition of the aluminium precursors was induced by copper bromide vapor laser on the surface of (111) silicon monocrystalline wafer at different process parameters (partial pressure, laser power and scanning speed). The analyses showed usual gaseous products for the pyrolysis of TIBA and TMAA and additional species. The occurred pyrolysis products were probably dueto different ways of decomposition of the precursors caused by pulsed laser irradiation. The results from this study combined with surface analysis of the deposit could help for better understanding of LCVD and for obtaining of high purity aluminium layers

Blade Deterioration in a Gas Turbine Engine

A study has been conducted to predict blade erosion of gas turbine engines. The blade material erosion model is based on three dimensional particle trajectory simulation in the three-dimensional turbine flow field. The trajectories provide the special distribution of the particle impact parameters over the blade surface. A semi-empirical erosion model, derived from erosion tests of material samples at different particulate flow conditions, is used in the prediction of blade surface erosion based on the trajectory impact data. To improve the blade erosion resistance and to decrease the blade deterioration, the blades must be coated. For this purpose, an experimental study was conducted to investigate the behavior of rhodium platinum aluminide coating exposed to erosion by fly ash particles. New protective coatings are developed for erosion and thermal barrier. Chemical vapor deposition technique (CVD) was used to apply the ceramic TiC coatings on INCO 718 and stainless steel 410. The erosive wear of the coated samples was investigated experimentally by exposing them to particle laden flow at velocities from 180 to 305m/s and temperatures from ambient to 538°C in a specially designed erosion wind tunnel. Both materials (INCO 718 and stainless steel 410) coated with CVD TiC showed one order of magnitude less erosion rate compared to some commercial coatings on the same substrates