Karol Nitsch

Improvement in corrosion resistance of the 316l stainless steel by means of Al2O3 coatings deposited by the sol-gel method

Abstract Two-, four- and six-layer Al2O3 coatings of the AISI 316 type stainless steel have been prepared by means of the Sol-Gel method. As a precursor substance aluminium isopropoxide was used. The coatings were approx. 2–3 μm thick and had amorphous structures. The higher sintering temperature (within the range 500–850°C), the lower cathode current density values, however also the lower breakdown potentials. Basing on results of EIS measurements it has been determined that the stainless steel/Al2O3 coating system may be substituted by an electrical model comprising three constant phase elements. The aluminium oxide coating heated at temperature of 500°C remains stable within the period of 1000 hours exposition in the Ringers solution.

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.

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.

Thick-film resistive temperature sensors

This paper discusses thick-film resistive temperature sensors investigated at the Technical University of Wroclaw. The technology and electrical properties of resistance temperature detectors, thermistors, low-temperature thermometers and heating elements are presented. The R(T) curve of chosen air-fireable Ni - P based films agrees with Ni wire. The initially aged thermistors from the system can operate in the range from room temperature up to 673 K. The commercial thick-film resistors modified by the negative TCR drivers (e.g. powder) are fully suitable for low-temperature measurements in the range from 20 to 100 K. The integrated gas sensors need heaters because temperature influences their sensitivity, selectivity and response time. The thick-film compatible system based on commercially available resistive and conductive inks allows continuous long-term electrical heating of the sensor up to 673 K. The admissible operating temperature is much higher for the heaters made from conductive inks; for example fritless platinum heaters are satisfactory up to 1073 K.

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.

Description of the frequency behaviour of metal–SiO2–GaAs structure characteristics by electrical equivalent circuit with constant phase element

Abstract Measurements of the capacitance and conductance of Au/Pd/Ti–SiO 2 –GaAs structures with different treatments of GaAs surface as a function of frequency (100 Hz–1.6 MHz) at fixed gate voltages have been performed and large dispersion has been observed. The analysis of these characteristics using the impedance spectroscopy method has allowed for the construction of the electrical equivalent circuit for the investigated structures which contains: the insulator capacitance, the series resistance, the space charge capacitance and the constant phase element (CPE) connected in series with resistance. The values of the parameters of the circuit elements have been determined by the broad range of the gate voltage. These elements are attributed to the physical phenomena in different regions of the analysed systems. The CPE (with parameter n ∼0.53–0.57) connected in series with resistance describes the complex electron processes in the GaAs–SiO 2 region resulting in the large frequency dispersion of electrical characteristics of the investigated structures.

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.

Application of sensor dynamic response analysis to improve the accuracy of odour-measuring systems

A system consisting of a matrix of three semiconductor gas sensors was applied to the classification of different orange juices. The sensor matrix responses were sampled in short time intervals. Such responses were processed by discrete wavelet transform (DWT) together with the k-nearest neighbour (kNN) classification algorithm or by the probabilistic neural network (PNN). The obtained results show that both types of signal processing (DWT + kNN and PNN) applied provide very good class separation for time response analysis, while in the case of the static response analysis the correct classification coefficients are much lower. It is shown that the analysis of the sensors time response can be an efficient way of increasing both the accuracy level and the immunity to external noise in e-nose systems. The possibility of reducing the number of sensors without decreasing the system performance is also demonstrated. Additional experiments have shown that for both processing methods, the results obtained with the dynamic response of a single sensor were better than those reached with the three-sensor array measured in static conditions.

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 conductive microstructures containing nano sized silver particles

The properties of the structures made by ink-jet printing with the use of the ink containing nano silver sized particles are presented. After structures printing on substrate, to obtain good electrical conductivity, sintering process is necessary. It is shown, that thermal process influences strongly the resistance, and after the process the resistivity of printed structures can be only a little bit higher than the value of the bulk material. Also different electrical test proved similarity between printed and bulk silver. It was stated that the adding some polymer materials for mechanical parameters improving of printed materials up to 1.5% of total mass of the ink do not influence significantly electrical parameters of the printed layers.