Ceramic Embedded Junction Thermocouple for In Situ Transient Temperature Measurement in Confined Extreme Thermal...

Transient temperature measurement under confined extreme thermal environments requires sensors with rapid response and structural stability. Conventional thermocouples often suffer from delayed response or insufficient junction protection, leading to inaccurate characterization of local thermal loads. In this work, a ceramic embedded junction thermocouple was developed for in situ transient temperature measurement. The sensor structure was optimized by finite element simulation, and a NiCr/NiSi junction was embedded into an Al₂O₃ ceramic substrate through inorganic bonding, thermal treatment, and surface grinding. The fabricated sensor was evaluated through thermoelectric characterization, high-temperature stability testing, dynamic response measurement, and calibration. The sensor exhibited a Seebeck coefficient of 41.26 μV/°C from 300 to 1200 °C, maintained continuous output at 1200 °C for 8 h, and achieved a response time of approximately 187 μs. The maximum relative deviation was below 0.47% within 300-1000 °C. During a confined thermal nose explosion test, the sensor successfully captured transient temperature evolution and recorded a peak temperature of approximately 1289 °C. Conventional thermocouples recorded peak temperatures below 800 °C, which were approximately 40% lower than the developed sensor. The proposed sensor provides a reliable approach for localized transient temperature measurement under confined extreme thermal environments.