Monitoring of ethylene for agro-alimentary applications and compensation of humidity effects

We used SnO2 gas sensors for monitoring ethylene in the range of interest for fruit ripening. The effect of atmospheric humidity on the sensor conductance and response towards ethylene was quantitatively measured. An algorithm for humidity compensation of the sensor’s response was developed and applied to experimental data. The results of our analysis proved useful for the application of chemoresistive sensors for agro-alimentary monitoring

Semiconductor gas sensors for environmental monitoring

Atmospheric pollution is still a topical problem in most European cities; it injures human health and greatly damages monuments and historical buildings. Atmospheric pollution control is today performed by means of traditional analytical techniques, which are expensive and require cumbersome devices. Thereby, low cost, portable and versatile equipment is an issue. Recently developments in the European legislation have caused a general change in the management of air quality assessment, making proposable the use of reliable solid state gas sensors. This work aims to analyze the most important semiconductor oxides for gas sensing. Aspects, such as the role of nanostructures to improve gas sensor performance, addition of catalysts and/or dopants to obtain a better selectivity, theoretical models to justify the size-dependent behaviour of the gas response of nanocrystalline oxides will be described. Array of these sensors, assembled in small remotely controlled monitoring units, have been used for on-field tests. The results of a long term field trial, performed locating several units closely to conventional monitoring stations, will be reported, as well as the experiments aimed to evaluate the concentrations of the same pollutants at different heights. These experiments are crucial to investigate air quality inside buildings, since the pollution of the outdoor air is one of the main factors affecting the indoor atmosphere

Secondary amenorrhea in severe Asherman's syndrome: Step by step fertility retrieval by Bettocchi's hysteroscope: Some considerations.

Abstract The aim of this report was to define the best diagnostic and therapeutic approach when secondary amenorrhea is related to undiagnosed Asherman syndrome. We present a single case of secondary amenorrhea with a previous diagnosis of alterated hypothalamic-hypophysary regulation, with a component of ovarian function in probable reduction, which was evaluated in our department and resulted affected by Asherman's syndrome IV stage. We describe step by step the diagnosis and treatment of a previously misdiagnosed case of severe Asherman's syndrome. An appropriate diagnosis and adequate treatment are mandatory to allow menses and fertility to be restored when severe Asherman's syndrome occurs

Vanadium and Tantalum doped Titanium oxide (TiTaV): a novel material for gas sensing

A new material based on titanium dioxide modified by tantalum and vanadium has been synthesized. The prepared powders have been deposited to produce gas sensors in the form of thick films through screen-printing technology. The crystalline phase and morphology were examined by XRD and SEM analyses. The results showed that Ta addition inhibited the anatase-to-rutile phase transformation and hindered grain growth during heating, whilst vanadium did the opposite. The sensors have been tested with different gases showing good selectivity; in particular, the samples with greatest content of Ta showed good response to benzene, only slightly influenced by presence of carbon monoxide

Aqueous and alcoholic syntheses of tungsten trioxide powders for NO2 detection

Different synthetical routes involving several solvents for obtaining WO3powders, suitable for gas sensing have been studied. Aqueous and alcoholic solvents proved to be the most promising media to grow nanometric particles. Among these, a modified sol-gel route that involves ethanol and a di-chetone, highlighted a more homogeneous grain-size distribution. The structure and morphology evolution of pure WO3powders with time and annealing temperature have been studied. The study of the energy barrier and conductance versus temperature allows to understand the reason for the high response of WO3to oxidising gases and its lack of sensitivity to reducing agents. Films of WO3responded to NO2, sensing as low a gas concentration as 200ppb. © 2003 Elsevier B.V. All rights reserved

(Ti, Sn)O2 binary solid solutions for gas sensing: Spectroscopic, optical and transport properties

Titania films were obtained through two synthetic processes, a traditional sol–gel method and a hydrothermal route. In SG synthesis, thermal decomposition of the precursor in oven at 400 °C for 2 h led to pure anatase TiO2; in HY synthesis, instead, crystalline anatase grains were obtained in autoclave at 200 °C for 1 h. To investigate the microstructural evolution of SG and HY titania with temperature, each powder was annealed at 650, 750, 850 °C for 1 h and subjected to XRD analysis. Surprisingly, HY titania, contrary to SG, maintained the anatase phase, up to 850 °C, without any introduction of foreign elements. The sensing layers, obtained from as grown powders, were fired at 650, 750 or 850 °C and tested vs. methane and carbon monoxide. Both types of films fired at 850 °C yield insignificant responses to both CO and CH4, demonstrating the lack of influence of the crystalline phase on the gas response. Moreover, as regards the films fired at 650 and 750 °C, the gas responses are higher for SG than for HY samples, despite larger particle size

(Ti, Sn)O2 solid solutions for gas sensing: A systematic approach by different techniques for different calcination temperature and molar composition

Tin–titanium solid solutions at increasing Ti molar fraction, x = 0.1, 0.3, 0.5, 0.7 and 0.9, were prepared by symplectic gel co-precipitation (SGC) method from stoichiometric hydroalcoholic solutions of Ti and Sn metalalkoxides. Structural, spectroscopic and electrical analyses were performed and the results have been correlated. The peaks of the XRD patterns change from the positions of SnO2 cassiterite to those of TiO2 rutile,whenincreasing the Ti content in the solid solution. Photoluminescence (PL), FT-IR and UV–vis- NIR characterizations are in agreement with the formation of solid solutions: PL peak falls either in the visible or IR region, depending on the Ti content in the solid solution; FT-IR spectra reveal a progressive upward shift of the high-frequency absorption edge of the skeletal vibration modes from the value of SnO2 to one of TiO2 on increasing the Ti content; UV–vis-NIR spectra reveal a progressive downward shift of the VB–CB absorption edge on increasing Ti content. The changes induced by CO interaction at increasing temperature in the FT-IR and UV–vis-NIR spectra revealed a different behaviour of the materials following the Ti content: for the lowest Ti molar fraction (x = 0.1) as well as for SnO2 the reduction gives rise to mono-ionized oxygen vacancies, for the other solid solution the loss of reticular oxygen gives rise to doubly ionized oxygen vacancies and to Ti3+ ions. From the electrical-conductance point of view, two groups of films can be identified: pure SnO2 and the solid solution with x = 0.1, and all the other solutions including pure titania, in agreement with the results of FT-IR investigations. The best response to carbon monoxide was achieved by the solutions with x = 0.3 and x = 0.5. Opposite to electrical properties, exhibiting good responses to reducing gases, these agents did not appreciably modify the PL yield of the solid solutions. Conversely, PL emissions were sensitive to NO2, particularly for Ti0.5Sn0.5O2