Rapid, Direct Fabrication of Thermochromic Ceramic Composite Sensors via Flash Lamp Annealing

Abstract

An inorganic, high‐temperature (≈600 °C) thermochromic sensor is synthesized from a chemically bonded ceramic composite. The ceramic composite is composed of thermochromic 10 wt% chromium‐doped alumina (Cr:Al2O3) powder blended with a low‐reacting temperature (around 250 °C) phosphate binder, Al(H2PO4)3, (aluminum dihydrogen phosphate [ADP]). Cr‐doped alumina exhibits thermochromism at high temperatures, typically around 500–600 °C. Previously, infrared (IR) irradiation has been used to successfully convert ADP to an aluminum phosphate (AlPO4) ceramic phase that can bind ceramic components together. Here, an ultrahigh‐power (tens of kilowatts per square centimeter) flash lamp annealing (FLA) system is evaluated as an alternative photonic heating process to rapidly transform ADP to this ceramic. While IR lamps require 30 min to fully transform the ADP binder, FLA processes require less than 1 min and provide more dense microstructures, opening opportunities to additively manufacture ceramic components without the need for a post‐processing heating step. Final ceramics exhibit reversible thermochromic behavior, transitioning from pink to dark gray as the temperature increases from 25 to 600 °C. Here, the ability to use this technology to fabricate a temperature warning system for heated objects that are not yet emitting significant visible black‐body radiation is demonstrated.