A fully temperature controlled test chamber for the application of gas sensor characterization

Research and development on gas sensors design and fabrication demands the needs for test chambers as the characterizing and testing of gas sensor are based on its detection of the concentration of different type of gas under the influence of temperature and also humidity. This project, a Fully Temperature Controlled Test Chamber is about the design and development of a system to provide an artificial environment for gas sensor characterization. The main part of the designed system is the temperature feed back loop control system. Its function is to monitor and regulate the environment temperature to the desired value for characterization of gas sensor under test. While the LM35DZ temperature sensor is used for this purpose, the intended chamber system to be designed is able to communicate with control switches from outside of the chambers using keypad and LCD. The user can set the desired temperature in the chamber, and then the PIC16F877A microcontroller which acts the "brain" of this system will analyze and process the input signal from the sensor and keypad to give the corresponding output to control the heater and display on the LCD screen. When the steady state condition has been reached, the chamber will be ready for the testing of gas sensors under test. The inlet valve, vacuum pump and fan integrated in the chamber are also fully controlled by the microcontroller. Beside, the control system can also be controlled manually by using the manual switches. When tested using the sensor under test, the test chamber and the regulation system of the temperature are working successfully as programmed and give the desired outputs

Alcohol sensing properties of nanosized thick film WO3 doped with Y2O3

In this paper the response of printed thick-film of WO3 doped by Y2O3 to organic solvent was studied. Different ratio of doping was prepared and changes of film resistance at different temperature in present of vaporized types of alcohol were observed. The results showed a high sensitivity of the film of 80.1%WO3-18.8%Y2O3 to Toluene, Xylene, Methanol, and 2-Propanone (Acetone) at 250, 450, and 550 °C, and higher sensitivity of 94.3%WO3-4.7%Y2O 3 at 350 °C. Microscopic images of the samples including SEM and TEM were observed. EDX and XRD analysis onto the samples also were done

Development of nanocrystalline laser ablated thick film array gas sensor

A multi-layer thick film array sensor for gas sensing application including heater element, insulator layer, and interdigitated electrodes was designed and fabricated on alumina substrate. Tin dioxide and platinum nanopowder were used in the pellet form as the active and catalyst layers, respectively. Pulse laser ablation deposition (PLAD) technique was used to deposit the sensitive layer onto the electrode part of each sensor. Microstructural and morphological properties of the sensor surface were determined. Sensors were exposed to wood smoke and their sensitivity were measured and compared with the results of the sensors without catalyst layer

Development of nanocrystalline thick film gas sensors

In the last three decades along with growing industries and development of cities,many pollutants have entered into the environment cycle. Some resultants of these contaminations can be felt as air pollution. Now, many cities across the world have been equipped with the databases to collect and analyze the information related to air quality and to give the index of air pollution known as API. In order to record and monitor the pollution, some of those databases use advanced equipment and instrument which are very expensive and need regular overhaul and maintenance. However, some databases are equipped with simpler gas detectors, so-called solid state gas sensors. Nowadays, many types of solid state gas sensors, employed different techniques of fabrication, are released in the market. One of those techniques is known as Thick Film Technology which has proved to be very promising and low cost option to fabricate gas sensors for gas analyzers, but some problems still are associated to their efficiency such as deficient of selectivity, influence of humidity, cross sensitivity, response time, and power consumption. The main goal of this doctoral thesis is to develop a nanocrystalline metal oxide thick film gas sensor using print screen technology having fast response time and highly sensitive to air contaminants. The fabricated gas sensor consists of a heater, an electrode, and a sensitive film onto an alumina substrate, which can stand up to high firing temperature during fabrication and operation. To fabricate the sensitive paste, tin dioxide (SnO2) and tungsten trioxide (WO3) were used as the base powders. Meanwhile, platinum,silver, and yttria (Y2O3) were used as additives and dopings. Finally, types of alcohol (ethyl alcohol, isopropanol, and methanol), hydrocarbon (xylene,isobutane), ketones (acetone), mixture of inorganic gases (exhaust fumes), and wood smoke were applied to the sensors for measurement. Fabrication of the sensitive paste has brought the development of a novel vehicle binder in the organic phase of the paste. The novel binder fulfills the screen printing criteria in which can be prepared very fast, having less additional material with at least one month shelf life. Crystallite size of sensitive powder of the sensors was measured using XRD analysis, showing sizes less than 30 nm and 20 nm for metal oxide phase and metal additives, respectively. Low dependency of WO3 sensors doped with Y2O3 to humidity was observed. Sensitivity of fabricated sensors in the presence of applied gases was compared to some commercial sensors and higher sensitivity was observed. The 0.9WO30.1Y2O3 sensor (WY-90) shows to be very sensitive to organic solvents compared with sensitivity of TGS2620 (Alcohol Sensor). The 0.98SnO20.02Pt sensor (SnPt-980) shows to be more sensitive with faster response time to organic solvents and truck exhaust gas than the commercial sensors of TGS2602 (Air Quality Taguchi Sensor), TGS3870 (Methane and Carbon Monoxide), and TGS4160 (Carbon Dioxide). It shows a response time as low as 15 seconds in the presence of 500 ppm exhaust gas compared to 28 seconds response time of TGS2602. Since the sensor is equipped with a heater element, it can operate at different working temperatures and produce different sensing signal in the presence of different gases or solvents, lead to have a selective gas sensor. Also, the approach of screen printing fabrication eases the fabrication of an array of four individual gas sensors with a very thin metal oxide and catalyst layer, using pulse laser ablation deposition (PLAD) technique. The results show that the response time of the array is significantly decreased to as low as 5 seconds in the presence of 200 ppm acetone

Film paste and its preparation thereof

The present invention relates to an organic thick film paste which includes organic binder and active powder which provides conductive, semiconductive, resistive or insulative properties of the film paste. The thick film paste further includes glass powder. The organic binder is based-on linseed stand oil. The organic binder is mixed with finely ground active powder to form a conductive, semiconductive, resistive or insulative paste. The film paste is used to print a pattern or meander in form of thick–film structure on alumina, aluminum nitrate, ceramic or polymer substrates. The present invention also includes method of producing the organic thick film paste and also a method of producing organic thick film paste printed on alumina, aluminum nitrate or polymer substrates

SnO2/Pt thin film laser ablated gas sensor array

A gas sensor array was developed in a 10 × 10 mm2 space using Screen Printing and Pulse Laser Ablation Deposition (PLAD) techniques. Heater, electrode, and an insulator interlayer were printed using the screen printing method on an alumina substrate, while tin oxide and platinum films, as sensing and catalyst layers, were deposited on the electrode at room temperature using the PLAD method, respectively. To ablate SnO2 and Pt targets, depositions were achieved by using a 1,064 nm Nd-YAG laser, with a power of 0.7 J/s, at different deposition times of 2, 5 and 10 min, in an atmosphere containing 0.04 mbar (4 kPa) of O2. A range of spectroscopic diffraction and real space imaging techniques, SEM, EDX, XRD, and AFM were used in order to characterize the surface morphology, structure, and composition of the films. Measurement on the array shows sensitivity to some solvent and wood smoke can be achieved with short response and recovery times