Measuring and testing – Gas analysis – Detector detail
Reexamination Certificate
1998-05-07
2001-03-20
Raevis, Robert (Department: 2856)
Measuring and testing
Gas analysis
Detector detail
Reexamination Certificate
active
06202471
ABSTRACT:
BACKGROUND OF THE INVENTION
The ability to detect the presence and composition of chemical species has been an important goal for several reasons. For example, the detrimental environmental effects of toxic species such as formaldehyde, carbon monoxide, ozone, hydrocarbons, chlorocarbons, nitrogen oxides, aromatics and heavy metals has led to the need to develop efficient, sensitive, and affordable ways of detecting the composition and presence of such toxic substances. Additionally, the efficiency of chemical processes, in terms of energy and raw material used per unit product or service delivered, relies on the ability of the overall system to reliably sense deviations from the optimal processing conditions. Since process efficiencies directly determine the overall costs of the process and indirectly determine the wastes generated by the process, it is critically important that a method be available that can provide the necessary feedback about the process (sensors) and initiate actions to evolve the system parameters to the optimal levels (actuators).
The temperature, pressure and flow monitoring and control of chemical, environmental, biochemical, biomedical, geological, metallurgical, and physical processes have been extensively researched and the state-of-the-art technologies quite effectively enable real-time evolution of the monitored process. However, compositional monitoring and control of these processes leaves much to be desired. Crude methods for process monitoring and control are based upon batch analysis, i.e., a statistical set of samples are obtained (“grab sample” approach) and then analyzed for composition. These data are then interpreted and actions are initiated to control the process to desired levels. The response time for such a strategy often is in days, if not weeks. This strategy has serious deficiencies since it inherently accepts inefficient operation between the time the samples were obtained and the actions are initiated to correct deviations from the optimal. Yet another deficiency in such a strategy is that it overlooks the possibility that the process conditions may have changed during the response and analysis lag time.
Alternatively, sophisticated monitors (such as gas chromatographs with suitable sampling and transport systems) have been integrated into the processes. These systems are expensive, bulky, not suited for extreme temperatures and pressures, and have response times that are more than a few minutes. Real-time composition monitoring and control of the chemical and combustion processes require sensors that overcome these limitations. Specifically, sensor technology for gas sensing applications should ideally be selective, sensitive to trace species, fast (short response time), small, accurate, reproducible, stable in extreme environments, durable (long life), and affordable.
Prior art methods for producing gas sensors include those of U.S. Pat. No. 4,631,952 which teaches a method of preparing a sensor by the formation of a dispersion of conducting particles with a material capable of swelling in the presence of the liquid, gas or vapor to be sensed. Furthermore, U.S. Pat. No. 4,984,446 teaches the preparation of a gas detecting device by a layer by layer build up process, and U.S. Pat. No. 4,988,539 teaches an evaporation-deposition method and process for manufacturing a gas detection sensor. Finally, U.S. Pat. No. 5,387,462 teaches a method of making a sensor for gas, vapor, and liquid from a composite article with an electrically conductive surface having an array of whisker-like microstructures with an aspect ratio of 3:1 to 100:1.
Although these prior methods provide improved methods for producing sensors, there is still a need to develop sensors which are selective, sensitive to trace species, fast, small, accurate, reproducible, stable in extreme environments, durable, and finally affordable.
SUMMARY OF THE INVENTION
In one aspect, the invention includes a method of making a chemical composition sensor. This method comprises selecting a sensing material which interacts with an analyte species of interest, and forming a laminated structure of this sensing material and at least one electrode layer. The laminated structure is then cut crosswise to expose alternating layers of the sensing and electrode materials. Finally, terminal leads are attached to the slices.
The laminated structure may include multiple sensing and/or electrode layers, each of which may be of the same or different compositions. The structure may have 3-500 layers, or in other embodiments 10-100 layers, or in still other embodiments 20-50 layers. The slices may be calcined and sintered before they are cut. The sensor may be partially or completely coated, for example to protect the electrodes from environmental damage. The sensing layers may be prepared using powders or composites, e.g., nanostructured powders and nanocomposites. The termination step may be accomplished before the cutting step. The interaction between the sensor and the analyte may be physical, chemical, electronic, electrical, magnetic, structural, thermal, optical, surface, or some combination. The sensor may include layers other than the sensing and electrode layers, for example, heating or insulating layers.
In a related aspect, the invention comprises a method of manufacturing a sensor, including selecting a sensing material, providing that material in a nanostructured form (e.g., a nanostructured powder or a nanocomposite), forming a laminated structure comprising an electrode layer and a sensing layer which includes the nanostructured material, and terminating the layers by providing, for example, electrical leads.
In other aspects, the invention includes methods of determining a change in state of an environment, such as a chemical composition change. In one set of such methods, a laminated sensor comprising 10-500 layers is inserted into the environment, and a property change in the sensor is used to determine the change in the environment. In another set of such methods, a nanostructured laminated sensor is inserted into the environment, and a property change in the sensor is used to determine the change in the environment. In these methods, the nanostructured sensor may have, for example 3-500 layers.
In some embodiments of the methods described above, the laminated sensor may have 10-100 layers. In other embodiments, the sensor may have 20-50 layers. The property change may be chemical, physical, electronic, electrical, magnetic, structural, thermal, optical, surface, or some combination.
Yet another aspect of the invention comprises chemical composition sensors comprising laminated structures. In one group of embodiments of this aspect, the sensors may have 10-500 layers, where at least one layer is a sensing layer and at least one layer is an electrode layer. In another group of embodiments, the sensors may have 3-500 layers, where at least one layer is a sensing layer and at least one layer is an electrode layer, and where the sensors respond to environmental changes by changing their capacitance, inductance, permittivity, permeability, dielectric constant, resonance frequency, refractive index, transparency to light, reflection characteristics, and/or coercivity.
In either of these groups of embodiments, the laminated structure may contain multiple sensing layers or multiple electrode layers, which may have the same or differing compositions. The structures may have 10-100 layers, or 20-50 layers. Some layers may be nanostructured. Layers other than the sensing and electrode layers, such as insulating or heating layers, may also be included in the structure. The sensors may also be terminated with at least one terminal lead connected to an electrode layer.
Definitions
“Sensitivity,” as that term is used herein, is a dimensionless measure equal to the ratio of the change in a measured property to the original value of that property. For example, the sensitivity of a chemical sensor whose resistance is a function of chemical environment is defined as ((R
a
−R
s
)/R
a
),
Kostlecky Clayton
Leigh William
Vigilotti Anthony
Xu Chuanjing
Yadav Tapesh
Hogan & Hartson L.L.P.
Langley Stuart T.
Nanomaterials Research Corporation
Raevis Robert
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