The beneficial influence of ultrasound in the polymerization of ε-caprolactam to polyamide-6 (Nylon 6). Part I: Primary experimental results

Epsilon-caprolactam (CL) polymerization to polyamide-6 (Nylon 6) was studied at different contents of water in CL (0.01-2 wt%), with or without epsilon-amino-caproic acid (ACA) as an activator, applying to the mixture an initial treatment of Ultrasound (US) (17.5-20 kHz) at low temperatures (70-110 degrees C) and for short times (max 10 min). It was verified that polymerization at 260 degrees C produces a polymer having a much higher molecular weight (MW) when US is applied with respect to silent (SIL) conditions i.e. without the use of ultrasound. This constitutes a "pre-sonication effect". The ratio (MW)(US)/(MW)(SIL) is inversely proportional to the initial content of water in CL. The action of US converts CL at very low temperatures (70-110 degrees C) and water content, in comparison with silent conditions where CL was unconverted. Optimized conditions are studied with respect to nature and pressure of gas inside the reactor, temperature, time and frequency of US irradiation, energy consumption and nature of activator

The beneficial influence of ultrasound in the polymerization of ε-caprolactam to polyamide-6 (Nylon 6). Part II: Additional experiment to understand the "pre-sonication effect"

Ultrasound (US) "pre-sonication effect" is the beneficial effect of US in the hydrolytic polymerization of epsilon-caprolactam (CL) mixtures with very low water concentrations (about 0.1-1 wt%). It appears after a mild initial treatment of the mixtures with US [17.5-20 kHz, short times (5-15 min), low temperatures (70-110 degrees C)] followed by heating at 220-260 degrees C. An explanation is proposed on the basis of the formation in mild conditions (100 degrees C) of low concentrations of cyclic oligomers never detected in the literature at those conditions. These, under US irradiation, produce linear amino acid oligomers, which are strong activators of polymerization when the mixture of CL and water, after US irradiation, is heated at the suitable polymerization temperature indicated above

Photodegradation of Pollutants in Air: Enhanced Properties of Nano-TiO2Prepared by Ultrasound

Nanocrystalline TiO2samples were prepared by promoting the growth of a sol–gel precursor, in the presence of water, under continuous (CW), or pulsed (PW) ultrasound. All the samples turned out to be made of both anatase and brookite polymorphs. Pulsed US treatments determine an increase in the sample surface area and a decrease of the crystallite size, that is also accompanied by a more ordered crystalline structure and the samples appear to be more regular and can be considered to contain a relatively low concentration of lattice defects. These features result in a lower recombination rate between electrons and holes and, therefore, in a good photocatalytic performance toward the degradation of NOxin air. The continuous mode induces, instead, the formation of surface defects (two components are present in XPS Ti 2p3/2region) and consequently yields the best photocatalyst. The analysis of all the characterization data seems to suggest that the relevant parameter imposing the final features of the oxides is the ultrasound total energypervolume (Etot/V) and not the acoustic intensity or the pulsed/continuous mode

The Gaia spectrophotometric standard stars survey - III. Short-term variability monitoring

We present the results of the short-term constancy monitoring of candidate Gaia Spectrophotometric Standard Stars (SPSS). We obtained time series of typically 1.24 h - with sampling periods from 1-3 min to a few hours, depending on the case - to monitor the constancy of our candidate SPSS down to 10 mmag, as required for the calibration of Gaia photometric data. We monitored 162 out of a total of 212 SPSS candidates. The observing campaign started in 2006 and finished in 2015, using 143 observing nights on nine different instruments covering both hemispheres. Using differential photometry techniques, we built light curves with a typical precision of 4 mmag, depending on the data quality. As a result of our constancy assessment, 150 SPSS candidates were validated against short-term variability, and only 12 were rejected because of variability including some widely used flux standards such as BD+174708, SA 105-448, 1740346, and HD 37725

Method for activation of chemical or chemical-physical processes by a simultaneous use of microwaves and ultrasonic pulses and chemical reactor that carries out this method

An apparatus (1) for activation of chemical-physical processes comprising a microwave source (40), for example a magnetron or a klystron or a solid state oscillator (FET transistor), operatively connected at one end of a microwave antenna, for example a co-axial antenna (3), at a connector (13). The apparatus, furthermore, comprises a generator of electric current (45) at high frequency connected to an ultrasonic transducer (2) for example by a shielded cable, not shown in the FIG. In operative conditions, the antenna (3) and the ultrasonic transducer (2) are arranged substantially at right angles and at direct contact with a reacting mass (15) contained container (10) in order to activate it and then to complete a desired chemical and/or physical process. More in detail, the reacting mass (15) is subject contemporaneously, or alternatively, to an electromagnetic field generated by the antenna (3), diagrammatically indicated (30), and from the ultrasonic field (20) generated by the ultrasonic transducer (2). By arranging the microwave antenna (3) and the ultrasonic transducer (2) in the reacting mass (15) the efficiency of the process is optimized achieving a synergistic effect thanks to the combination of the electromagnetic field and the ultrasonic field