FINE-TUNING OF CERAMIC-BASED CHEMICAL SENSOR
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Date Published: 24 Feb 2006 FINE-TUNING OF CERAMIC-BASED CHEMICAL SENSOR The vital need to develop fast responding sensors for toxic gases before their concentration reaches lethal levels is driven by events like the Sago coal mine disaster which took place on Jan 2, 2006 in Tallmansville, West Virginia where 12 miners died. Key interests of Dr. Abdul-Majeed Azad, Chemical and Environmental Engineering, University of Toledo, in this area have led to the development of a novel technique for detecting low levels of CO using tungsten oxide (WO3) and molybdenum oxide (MoO3). Challenges such as high selectivity, enhanced sensitivity and short response time which are highly dependant on the nano-features of materials used in solid-state ceramic-based chemical sensors are some of the aspects that have been addressed in this research. This has been augmented by the reason that nanofeatures such as dimensionality and size give us a better understanding of the material behavior such as their chemical, mechanical and optical properties. This technique is based on rigorous thermodynamic considerations of the metal/metal oxide coexistence and has resulted in a novel redox technique to enhance sensor behavior. By modulating the oxygen partial pressure across the equilibrium metal/metal oxide (M/MO) proximity line, formation and growth of new oxide surface on an atomic/submolecular level under conditions of ‘oxygen deprivation’ has been achieved in potential sensor materials. Speaking to Sensor Technology Abdul told “We believe that we have identified a technique based on sound thermodynamic principles whereby morphological and micro-structural modifications can be brought out in a semi-conducting oxide by using a novel gas phase redox scheme. We are not aware of such attempts in the published literature. By precisely modulating the oxygen potential slightly lower or slightly higher than that existing in the vicinity of a given oxide, we can cause atomic/molecular level reduction or oxidation of the given ceramic oxide. The concept and technique of ‘oxygen deprivation’ for such changes on the atomic/molecular level is new and novel and has not been exploited hitherto”. Some of the specific potential applications of the latest sensors developed are largely due to the innovative modifications done at the sensor material level. Such sensors become very valuable in situations where sensing of noxious gases such as carbon monoxide, methane, nitrogen oxides and hydrogen sulfide in shortest period of time and with the maximum sensitivity is crucial. The sensitivity of sensors made with these systems is much higher than the same oxides prepared by conventional techniques because of the innovative modification done to the sensor material as well as to the presence of unique micro-structural features such as large surface area, high aspect ratio and, textured and oriented grains. This is one of the major drivers of this technology in the area of effective and timely hazardous gas detection. Complementing this are the results obtained in the case of tungsten oxide-based carbon monoxide sensors (in the range of 14–100 ppm CO) with enhanced sensing characteristics. Abdul added “We have shown by ample research that sensors with extraordinary functional features can be developed by incorporating in them nano-fibrillar structures. Thus, sensors with such attributes would find applications in the areas of air quality control and monitoring, furnace environment, carburization processes, environmental detection of Nitrogen Oxide (NOx) and H2S in coal power plants, Methane (CH4) and CO in coal mines (Sago coalmine disaster is an example, where fast responding sensors could have saved lives) and, CH4 and H2S in solid oxide fuel cell anodes”. Currently, Abdul is collaborating with Prof. Sheikh Akbar at the Ohio State University on the research aspects and on the commercialization endeavors he is working with ER Microsensor, the production arm of Essential Research, Inc. a small business in Cleveland, OH. Details: Dr. Abdul-Majeed Azad, Associate Professor, Chemical and Environmental Engineering, 3052 Nitschke Hall, University of Toledo, 2801 W. Bancroft St., Toledo, OH 43606-3390. Phone: (419) 530-8103. Fax: (419) 530-8086. Email: Abdul-Majeed.Azad@utoledo.edu. URL: http://www.eng.utoledo.edu/~aazad; http://www.che.utoledo.edu/
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