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Sensor measures temperatures nonintrusively in hostile environmentsSuperior Graphite Company
Solving the ProblemSuperior Graphite Company (Chicago, Ill.) was selected by the U.S. Department of Commerce, Advanced Technology Program (ATP), for a research award aimed at the development and commercialization of the company's Electroconsolidation® process, which can be used to manufacture parts from powders of many different materials, including metals, ceramics, and polymeric composite materials. High-tech components often start out as particles of advanced materials that are mixed with binders before being formed into desired shapes. The preforms are then densified to their final microstructural state using high temperatures and pressures. In Superior Graphite's process, preformed parts are immersed in a bed of graphite powder lying inside a cylindrical die chamber. Heat is generated resistively within the graphite powder by means of an electrical current. Because the electrical properties of the graphite medium vary with pressure, temperature, and proximity to the preformed parts, temperatures fluctuate significantly within the die chamber, and can be as high as 3000°C. The company needed a nonintrusive sensor for temperature control during sintering and to avoid over- or under-heating the preforms. Thermocouples were not practical because they are intrusive and not suitable above 2000°C. Superior Graphite thought the answer might lie with Argonne National Laboratory, and so enlisted Argonne's aid. The result was a sensor that converts speed-of-sound measurements to temperature readings, nonintrusively, at temperatures up to 3000°C, with 2-3% accuracy. According to Dr. William Goldberger, Superior Graphite's Vice President of Research,"With the completion of this work, the technology is ready to be commercialized. The ATP project--including Argonne's research--resolved many of the obstacles we faced." "This collaboration is a good example of how national-laboratory expertise can complement a company's R&D. Sometimes it's a bit like finding just the right piece of a puzzle to complete the picture," says Dr. Nachappa Gopalsami, the Argonne scientist who developed the sensor. How the Sensor WorksArgonne's technique measures the speed of pulsed ultrasonic waves as they traverse any portion of the granular medium lying directly between two ultrasonic transducers. The transmitting and receiving transducers are placed on either side of the process die so that they won't affect the sintering/densification procedure. Speed-of-sound measurements accurately reflect the real-time temperature of a part in thermal contact with the granular medium once the sensor has been calibrated in terms of the pressure sequence used by the process. The sensor technology is rugged enough for use in hostile environments and can nonintrusively measure process temperatures as high as 3000°C to an accuracy of 2-3 percent. The sensor was developed by Argonne's Sensors, Instrumentation and Nondestructive Evaluation Section in the Energy Technology Division. Members of the sensor development tea. were co-inventors Nachappa Gopalsami (team leader) and Hual-Te Chien, and William Lawrence working with Superior Graphite's Brian Merkle and Joshua Borton.. Argonne's research was funded by Superior Graphite Company under an award from the U.S. Department of Commerce, Advanced Technology Program. Argonne's Sensor ResearchIn recent years, Argonne has developed various sensors for on-line and off-line system diagnostics, process monitoring, defect detecting, and material evaluation. The sensors are based on advanced techniques such as millimeter-wave and microwave, acoustics and ultrasonics, mass spectroscopy, nuclear magnetic resonance, and optics. Sensors recently developed or being developed include an ultrasonic viscometer, a speed-of-sound gas leak detector, a microwave dielectric sensor, a millimeter-wave remote effluent sensor, and an ion-mobility gas sensor. Working with ArgonneArgonne has many types of contractual agreements to meet the needs and interests of industry, state and local governments, federal agencies and other organizations. Based on material prepared by Vic Comello, Technical Services Division. For More InformationFor more information, contact Argonne's Office of Technology Transfer (800-627-2596, partners@anl.gov). |
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