Helena Teterycz

New design of an SnO2 gas sensor on low temperature cofiring ceramics

Abstract A new design for thick film gas sensors was investigated. The sensors were made by the low temperature cofiring ceramics (LTCC) technique with a platinum heater buried inside the multilayer structure. SnO2 or SnO2 with Pd as catalyst thick films were used as gas sensitive materials. The properties of the gas sensors were measured with methane and carbon monoxide. The results of our study show that LTCC can be successfully applied in sensor technology as well as confirming the correctness of the sensor design.

The role of Lewis acidic centers in stabilized zirconium dioxide

Abstract The physico-chemical properties of ZrO 2 , MgO and admixtured (stabilized) zirconium dioxide are presented. The synthesis of stabilized ZrO 2 was conducted in a low-temperature process. The catalysts obtained on the basis of zirconium dioxide were monophase materials of a regular structure. The lattice parameter of the materials did not differ much from the standard value. The character of the surface active centers was being changed as a result of the admixturing. Synthesized monophase materials of catalytic properties, Zr-Mg-O and Zr-Mg-Y-O, have many strong Lewis centers at surfaces. There appeared not only the stabilization of the regular polymorphous structure of ZrO 2 , but also a modification of catalytic properties of the materials when the basic admixture (MgO and Y 2 O 3 ) was being introduced to basic zirconium dioxide. The authors present a mechanism of alcohol or aldehyde condensation to ketone at the surface of the materials with the participation of Lewis acidic centers.

Thick-film humidity sensors

The results of an investigation of thick-film humidity sensors based on ceramic materials are discussed in the paper. Thick-film technology is very promising for the production of low cost sensors based on ceramic materials. The technology gives the possibility for reproducible production of sensors with a defined microstructure, determined porosity and proper structure of grains and grain boundaries. Ceramic sensors have advantages over polymer sensors due to their better thermal stability and resistance to chemicals. Properties of thick-film planar humidity sensors based on - (ZCT) ceramics are presented. The influence of and Si additives, as well as firing temperature, on the sensor characteristics are discussed. Impedance spectroscopy measurements determined the correlation between the technological parameters and the electrical properties of humidity sensors. The role of each part of the sensitive material in the electrical conduction process is determined on the basis of measurements and calculated equivalent circuits. The proposed model describes the frequency characteristics at various relative humidities with very good fit to the experimental data. A new approach to the modelling of the impedance frequency dependence by means of an equivalent circuit yields very promising results for sensors.

The influence of Rh surface doping on anomalous properties of thick-film SnO2 gas sensors☆

Abstract Here there are presented new results from the investigations of SnO2 thick-film sensor. The effects of rhodium surface doping on dc and ac properties of SnO2 gas sensors were studied. The measurements reveal anomalous behaviour of the sensors. Below characteristic temperature, the resistance of the sensors increases in presence of reducting gases. The mechanism associated with the presence of rhodium can be connected with the increase of acceptor surface states concentration and causes the inversion of near-surface layers.

Anomalous behaviour of new thick film gas sensitive composition

Abstract Anomalous properties of gas sensitive film based on SnO2 are presented. The gas sensitive film was prepared by adding CeO2 and rhodium. The gas sensor was made on alumina substrate by the screen printing technique. The resistance characteristics of these gas sensors were investigated. It was found that resistance of the sensors increased in the presence of reducing gases. This behaviour was in contrast to typical properties of SnO2 sensors. Our sensors, based on the new composition, exhibited very short response time in CO and CH4.

Humidity insensitive thick film methane sensor based on SnO2/Pt

Abstract The influence of environment humidity on electrical parameters is one of the basic disadvantages of the described SnO2 sensors. Due to complex research, the authors have managed to work out cermet composition (SnO2–Pt-black) which eliminates humidity influence on methane detection. In this paper, the basic characteristics of this latest methane sensor are presented.

Properties of selective gas-sensitive SnO2/RuO2/Pt composition and detection mechanism

We present new gas-sensitive material that has been obtained by mixing the powders of tin dioxide (semiconductor) and ruthenium dioxide (metallic conduction). The powder mixture was doped with platinum by the impregnation method. The X-ray and scanning electron microscopy investigation has shown that this material is a three-phase composition. The resistance of (SnO 2 + RuO 2 + Pt) material is much higher than pure SnO 2 . Applied as a gas-sensitive layer in thick-film sensors, the material presents high selectivity to methane in the presence of carbon monoxide. The three-phase composition reacts in a way similar to SnO 2 when applied as a catalyst in a test reaction of n-butyl alcohol condensation. Considering the microstructure, numerous research studies, and literature, the authors suggest the following explanation of physicochemical effects appearing in this gas-sensitive material. The authors think that two potential barriers appear in this composition: the first barrier on the boundary of tin dioxide grains, the second one is Schottkys barrier on the boundary of SnO 2 grain and RuO 2 grain. The appearance of Schottkys barrier on SnO 2 /RuO 2 boundary causes an increase in resistance of studied composition. The definite improvement in sensor selectivity is caused by specific catalytic properties of RuO 2 . The catalyst reveals high activity in the heterogeneous reaction of carbon monoxide conversion by water vapor. Analyzing the results of conducted research, the authors think the selectivity of resistive gas sensors may be significantly improved by applying multiphase gas-sensitive material.

Catalytic properties of Sn-Ce-Rh-O in dehydrogenation and oxidative dehydrogenation reactions

A new, single-phase Sn0.925Ce0.07Rh0.005O2 gas sensitive material has up to now been used as a catalyst for the bimolecular condensation of aldehydes and C-alkylation of hydroxyarenes with alcohols. It was subjected to the isopropanol test, the oxidative dehydrogenation of cyclohexane test, and the cyclohexene + H2 test. A general physico-chemical analysis was done, and it included XRD, SEM, mercury porosimetry, TPD NH3, and IR (pyridine) spectroscopy. The tests results are compliant with the basic character of the catalyst; however, it reveals significant total acidity (0.274 mmol NH3/g) and the presence of Lewis strong acid centers (0.126 mmol Py/g). The presence of these centers in the dehydrogenating catalysts cause the ability to catalyze both the bimolecular condensation of aldehydes and C-alkylation of hydroxyarenes with alcohols.

The Relationship between the Mechanism of Zinc Oxide Crystallization and Its Antimicrobial Properties for the Surface Modification of Surgical Meshes

Surgical meshes were modified with zinc oxide (ZnO) using a chemical bath deposition method (CBD) at 50 °C, 70 °C, or 90 °C, in order to biologically activate them. Scanning electron microscopy (SEM), mass changes, and X-ray diffraction measurements revealed that at low temperatures Zn(OH)2 was formed, and that this was converted into ZnO with a temperature increase. The antimicrobial activity without light stimulation of the ZnO modified Mersilene™ meshes was related to the species of microorganism, the incubation time, and the conditions of the experiment. Generally, cocci (S. aureus, S. epidermidis) and yeast (C. albicans) were more sensitive than Gram-negative rods (E. coli). The differences in sensitivity of the studied microorganisms to ZnO were discussed. The most active sample was that obtained at 90 °C. The mechanism of antimicrobial action of ZnO was determined by various techniques, such as zeta potential analysis, electron paramagnetic resonance (EPR) spectroscopy, SEM studies, and measurements of Zn(II) and reactive oxygen species (ROS) concentration. Our results confirmed that the generation of free radicals was crucial, which occurs on the surface of crystalline ZnO.

Deposition of one-dimensional zinc oxide structures on polypropylene fabrics and their antibacterial properties

In this article, a new method of modification of polypropylene fabric surface is presented, in order to obtain a material with antibacterial properties. The surface of the fabric is modified by direct deposition of the hexagonal zinc oxide rods onto the surface. For this reason, the influence of temperature on the size and morphology of microstructures of ZnO was investigated. Deposition was carried out at two temperatures, 75 and 90℃. The surface of the fabrics was treated with oxygen plasma. The influence of oxygen plasma on the parameters of rods was examined. The microstructure and crystalline structure of ZnO rods were investigated by scanning electron microscopy and X-ray diffraction. In addition, the impact of morphology and size of obtained ZnO structures on the biological activity of modified materials was determined. The tests revealed that the modified fabric shows very good antibacterial activity.