(749d) Using Quenched Glass Particles to Recover Thermal Histories of Pyrotechnical Events

A typical pyrotechnical event generates environment temperatures exceeding 2000 K, and lasts from a few microseconds to seconds.   To obtain the thermal histories of these pyrotechnical events, traditional temperature measuring techniques are either too fragile or sluggish to describe the event with good accuracy.

This study explores the possibility to use glass particles as thermosensors.  The structures of glasses are strongly dependent on the quench rate during glass formation. In addition, silicate and borate glasses have unique Raman signatures corresponding to the connectedness of their respective network forming units [SiO₄] and [BO₃].  These signatures therefore change depending on quench rate.  This effect is well understood and quantified considering cooling times that measure in minutes to years.

Glass particles that are injected into the combustion environment will experience a cooling rate that depends on both, the environment temperature as it cools down, and the particle size.  On this time scale, cooling takes place in less than a second.  Recovering particles after the event, analyzing the Raman signature on a per-particle basis, and correlating this signature with the fictive temperature of the glass will allow to determine the cooling rate of the combustion environment in the range of the observed fictive temperatures. Different glasses can potentially be used to extend the temperature range from which cooling rate information can be recovered.

An experimental setup has been built where aerosolized silicate and borate glass particles are heated to temperatures in excess of their melting points (max. 1600 K).  The particles are then propelled through a ~100 µm orifice into an adjustable low-pressure environment, where they cool at rates corresponding to the pressure and their size, generally in the range 10³ - 10⁴ K/s.  Particles are collected on a filter and analyzed by Raman microscopy.  The extent to which the Raman signature and therefore the fictive temperature is sensitive to cooling rate changes on this time scale will be quantified.