Argonne National Laboratory scientists have collaborated with Superior Graphite to develop a non-intrusive, real-time sensor that measures temperatures up to 3000°C with 2-3% accuracy.
The sensor uses two ultrasonic transducers to convert speed-of-sound measurements to temperature readings and is being used in Superior Graphite’s Electroconsolidation process, which can be used to manufacture parts from powders of 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 3000ºC.
The company needed a non-intrusive 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.
Argonne’s technique reportedly 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 are said to 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 non-intrusively measure process temperatures as high as 3000ºC to an accuracy of 2-3 percent.