Trinitrotoluene Detection by Semiconductor Gas Sensors
Development of Fundamentals and Engineering Solutions of Detection of Explosives (Group of Nitrocyclohydrocarbons) by Micromachined Semiconductor Gas Sensors Using Gas Pre-Concentration System
Tech Area / Field
- ENV-MIN/Monitoring and Instrumentation/Environment
- INS-DET/Detection Devices/Instrumentation
3 Approved without Funding
Kurchatov Research Center, Russia, Moscow
- Scientific and Technical Center of Measuring Gas Sensors, Russia, Moscow reg., Lyubertsy\nMoscow State University / Department of Chemistry, Russia, Moscow\nInstitute of General and Inorganic Chemistry (IONKh), Russia, Moscow
- Kyushu University / Advanced Science and Technology Center for Cooperative Research, Japan, Fukuoka\nCentro per la Ricerca Scientifica e Tecnologia / Institute for Scientific and Technology Research, Italy, Trento
Project summaryThe Project objective is the development of methods and means for trinitrotoluene (TNT) detection by semiconductor gas sensors to assist the governmental structures in the antiterrorist activity.
Cyclic nitrocompounds and their derivatives are the base of explosives widely used in the economical activity and for military purposes. Although the control of illegal use of explosives is very important, the problem of TNT detection by semiconductor gas sensors has not been solved by now, first of all, because of low concentration of saturated TNT vapours (10-7 – 10-8 g/m3 under normal conditions) and complex chemistry of cyclic nitrocompounds. The main requirement for the gas sensors is the exceptionally high sensitivity in a range of 10-9 – 10-11 g/m3. Nowadays, to detect explosives very expensive stationary systems based on liquid and gas-chromatography, chromatography-mass spectrometry, mass-spectrometry, chemiluminescence, and colorimetry on the basis of selective color reactions are used. Some of these methods allow to detect picogram (10–12 g/m3) concentrations of TNT in air. The combination of chromatography and mass-spectrometry methods is also used to determine the impurity content of TNT. At the same time, it is possible to determine the source of toluene, the methods of its nitriding and purification. As a rule, all techniques mentioned above are applicable in special laboratories to analyze the residual products of explosion or to test suspect objects. These methods are time consuming (30–60 min) and generally include the stages of preliminary sampling and concentrating. None of these methods enables continuous environmental monitoring, and therefore they can not prevent the acts of terrorism performed by kamikaze.
The novelty and technical features. Within the frame of the Project for the first time a highly sensitive microelectronic chip coupled with the systems of pre-concentrating and pulsed heating of cyclic nitrocompounds is proposed for TNT detection. The distinctive feature of the work is the integrated approach to TNT detection, that involves combining in a single system the achievements in both semiconductor gas sensors and selective systems of gas pre-concentrating.
The basic element of the sensor system is a microelectronic chip with a thin layer of sensitive material deposited onto the membrane. The microelectronic chip will be manufactured using a proprietary technology, developed by the Authors of the Project. It is supposed to compare the possibilities of two types of microelectronic chips. The first one is based on the combination of micromashining technique with the technology of thick-film deposition of gas-sensitive layer. A semiconductor layer on the basis of nanocomposite is applied to a thin (1.2 m) dielectric membrane with a surface area of 2ґ2 mm2. The size of the heated area coated by the sensitive layer is 200 ґ 200 m. Such a design allows to manufacture the sensors with extremely low energy consumption of about 20 mW. This new development has better parameters as compared with all others available commercially now. We believe that the application of thin aluminium oxide membranes as carriers for the sensitive layer is very promising. Now, the Al2O3 membranes with a thickness of 10-40 m and diameter of 3-4 mm have been obtained. Thermal properties of these membranes are a little worse than those of silicon oxide / silicon nitride membranes, but the technology of their fabrication is simpler and does not require expensive microelectronics equipment. The heaters of such elements will be made of platinum by magnetron sputtering technique.
The sensitive layer will be produced from heterogeneous nanocrystalline porous systems (nanocomposites) with a specific surface area of about 150–200 m2/g. The nanocomposites include superdispersed metal oxides Fe2O3, NiO, CuO, MoO3, V2O5 that exhibit catalytic activity toward organic molecules. In such systems an extremely high sensitivity of electronic state of interfaces to the gas phase composition is observed. In contrast to traditional gas sensitive materials like SnO2, and ZnO, for which the gas adsorption is of primary importance for sensor signal, in nanocomposites the deep reconstruction of electronic state of interfaces has the predominant effect allowing to improve the gas sensitivity to 10–100 ppb level. The specificity of catalytic reactions as distinct from adsorption will allow to improve the selectivity of materials toward cyclic nitrocompounds and their derivatives.
Because of low vapour pressure of TNT its detection in air under normal conditions is very complicated. Generally, the stage of preliminary concentrating is required, when from a large volume of air passed through the adsorbent a nitrocompound is recovered by pulse heating. The study carried out by the Authors of the Project demonstrated that TNT retention is the best when 3-[9'-(10'-methylanthril)]propylsilan (MAPS) deposited onto silica gel (10 m) is used. МAPS interacts as a donor with nitrocompounds and forms the complexes which decompose on heating.
During the Project realization there will be developed the methods and found an optimal engineering solution for a system detecting 10-100 ppb of TNT in air. The analysis of the possibility of semiconductor gas sensor application in the systems of TNT-based explosives detection will be made on the basis of the following activities within the Project:
- The designs of microelectronic chip with low energy consumption (< 20 mW) and high stability will be developed using micromashining technique.
- The porous nanocrystalline heterogeneous systems with specific surface area of about 200 m2/g and sensitivity to TNT of up to 10-100 ppb will be produced. The relationships between the composition, microstructure, electrophysical and sensitive properties of nanocomposites with respect to cyclic nitrocompounds will be established.
- The system of cyclic nitrocompounds concentrating will be developed and the mechanisms of their retention in pulse heating conditions will be determined.
- An electronic system combining chips and signal converter, and a software for the primary data conversion and processing and their analysis results transfer through information networks will be developed.
- The prototypes of gas sensor systems will be produced and tested in laboratory. The influence of temperature, humidity and gas interference will be studied.
After completion of the Project the stage of sensor systems development with the participation of the Authors is planned. The obtained results can be communicated to industrial enterprises or design organizations.
Role of Foreign Collaborators/Partners
All Foreign Collaborators are eminently qualified specialists in the problem to be solved within the Project. Their role in the Project realization is very important. The close contacts with Foreign Collaborators will be maintained during realization of all tasks of the Project so as to exchange ideas, discuss the results obtained, and search for optimal solutions. The testing of a sensor prototype at the final stage of the Project can be realized with participation of Foreign Collaborators.
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