No abstract

In this work porous silicon samples obtained by electrochemical etching were investigated. Using scanning probe microscope the morphology of porous silicon samples was studied. To determine the thickness of the porous layer and the pore diameter, micrographs were obtained using a scanning electron microscope. The dimensions of the nanocrystallites were determined from the Raman spectra. For the detection of vapors of organic compounds, planar structures were used. The results of the study confirmed the possibility of using nanoporous silicon as a sensitive material for the determination of acetonitrile and chloroform vapors. It is shown that the adsorption phenomena in porous silicon depend on its structure and morphology. It is established that the humidity of the air when detecting the vapors of organic compounds under investigation has a significant effect on the sensitivity. It is also shown that such structures can be used as instruments for measuring air humidity.

This paper presents an experimental study on the performance of shielding concrete with additives of magnetite nanoparticles. Two concretes with magnetite additives as well as one based concrete were tested. In order to achieve the high-performance concrete, all concrete mixes had a constant water/cement ratio of 0.45. In order to measure the mechanical properties, concrete samples were made in accordance with dimension such as 40 × 40 × 160 mm. But, for measurement of protective properties the concrete was made in accordance with dimension of rotary antennas such as 400 × 400 mm with a thickness of 10 mm. The nanoparticles Fe 3 O 4 were synthesized by chemical condensation method. XRD have shown the presence of cubic structure of Fe 3 O 4 spinel with crystallite size is equal to 130.0 Å. The TEM microphotograph shows that the Fe 3 O 4 nanoparticles are spherical, the range of sizes is 12-30 nm. The magnetic retardation suggests that the magnetite nanoparticles have superparamagnetic properties. This is explained by the fact that under the influence of external magnetic field, they are single-domain, in other words, they become uniformly magnetized throughout the volume. The additives of magnetite nanoparticles at a concentration of 0.5% mass have not a negative effect on flexural strength. The samples with additives of magnetite nanoparticles showed better shielding of microwave radiation in the frequency range from 0.7 GHz to 13 GHz. The maximum efficiency of suppression of electromagnetic disturbance is equal to 19.9 dB at a frequency of 1.5 GHz with a thickness of 10 mm.

No abstract

No abstract