M. Hassan

Nano- and Microsized Phases in the WO3-ZnO-Nd2O3-Al2O3 System for Applications

WO3 and WO3-based materials in the form of thin films, either as bulk or as nanostructures, have been widely used for the detection of a variety of gases, such as NO2, H2, NH3 and Cl2. The purpose of this study was to prepare materials from the WO3-ZnO-Nd2O3-Al2O3 system containing high amount of WO3 for applications in environmental monitoring by applying the melt quenching method. Homogenized batches of the starting oxides were melted for 20 min at 1,240 °C in platinum crucibles in air atmosphere. The melts were quenched by pouring and pressing between two copper plates (cooling rates 101–102 K/s). Glassy-crystalline samples containing the monophase AlW12O37.5 was produced by quenching a melt with the composition of 80WO3⋅10Nd2O3⋅10Al2O3. Glassy-crystalline sample containing nanosized W18O49 (~60 nm) was obtained after cooling of a melt with the composition 76WO3⋅9.5ZnO⋅9.5Nd2O3-5Al2O3. A mixture of WO3 and AlW12O37.5 in the amorphous matrix was prepared by crystallization of a quenched sample with the composition 75WO3⋅10Nd2O3⋅5ZnO⋅10Al2O3. Samples were prepared by the screen printing technique as gas sensor s; thereafter dc resistance measurements were performed in the presence of relative humidity and ammonia. It was established that the glassy-crystalline sample containing the monophase AlW12O37.5 exhibits a significant sensitivity towards ammonia and relative humidity, while other phases show a good sensitivity only towards relative humidity.

Preparation of Nanoporous Hybrid Materials with Bridged Tetra Sulfide Functional Groups and Determination of Their Sensing Characteristics Towards Relative Humidity

Nano porous hybrid materials were synthesized by co-condensation of organically bridged tetra sulfide bis [3-(triethoxysilyl) propyl] tetra sulfide (BTPTS) and tetra ethoxylsilane (TEOS) in the presence of the non-ionic surfactant triblock copolymer poly(ethylene glycol)-block-poly (propylene glycol)-block-poly (ethylene glycol) (EO20PO70EO20) in acidic media as revealed by the measurement of nitrogen adsorption. The structure and chemical state of the materials were characterized by chemical analysis, Fourier–transform infrared spectroscopy (FTIR), 29Si MAS NMR, and thermo-gravimetric analysis (DTA/TG), revealing the integrity of organic groups inside the framework. The synthesized powders were prepared as sensors using the screen-printing technique and then evaluated on view of their sensing characteristics in the range from 0.0% to 96% relative humidity (RH) at room temperature. Sensors with a higher content of BTPTS show a better response towards RH.

Synthesis of RGO/SiO 2 and Ag/RGO/SiO 2 Nanocomposites and Study of Their Sensitivity Towards Humidity

In recent years, many interesting researches published on the study of new nanocomposite materials involves active components such as reduced graphene oxide (RGO), silver nanoparticles (Ag-NPs), and silica, which indicated very interesting properties and applications. The present work demonstrates the preparation of nanocomposite powders with the participation of Ag-NPs, RGO and tetraethyl-orthosilicate (TEOS) using the sol-gel technique. The phase formations are verified by X-ray diffraction analysis. The thermal behavior was studied using differential thermal analysis (DTA/TG) in air. The sensitivity against humidity was tested in a laboratory apparatus made of a thermostatic chamber operating at 25 °C, in which the RH could be varied between 0% and 96%.

Humidity Sensing Properties of Tungsten Based Glass Crystalline Materials in the WO 3 -ZnO-La 2 O 3 -Al 2 O 3 System

Glass crystalline materials from the WO3-ZnO-La2O3-Al2O3 system containing high WO3 concentrations (60–76 mol%) were prepared by controlling the glass crystallization and were then employed as humidity based sensors. According toX-ray analysis, WO3 separates as a crystalline phase from the amorphous structures with the nominal compositions 76WO3·9.5ZnO·9.5La2O3·5Al2O3 and 60WO3·7.5ZnO·7.5La2O3·25Al2O3 after the heat treatment. Samples were characterized by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) for elemental analysis. Using the screen printing technique, the synthesized crystalline glass samples were deposited onto interdigidated Pt electrodes; then the sensors were tested in the range from 0.0% to 96% relative humidity (RH) at room temperature. It was observed that the increase in the content of WO3 leads to improve sensor sensitivity towards RH.

New ZnO-Based Glass Ceramic Sensor for H2 and NO2 Detection

In this study, a glass ceramic with a nominal composition 58ZnO:4Bi2O3:4WO3:33.3B2O3 was synthesized by melt quenching technique. A gas sensor was then manufactured using a ZnO sol-gel phase as a permanent binder of the glass–ceramic to an alumina substrate having interdigitated electrodes. The film sensitivity towards humidity, NH3, H2 and NO2 was studied at different temperatures. X-ray diffraction technique (XRD), field emission- scanning electron microscopy (FE-SEM) and differential thermal analysis (DTA) were used to characterize the prepared material. Though the response in the sub-ppm NO2 concentration range was not explored, the observed results are comparable with the latest found in the literature.