Drop‐and‐catch (DnC) calorimetry using aerodynamic levitation and laser heating

Abstract

Design, calibration, and operation of a system for drop‐and‐catch (DnC) calorimetry on oxides from temperature above 1500°C are described. This system allows the measurement of heat contents and heats of fusion by drop calorimetry of small (100 mg or less) samples held by containerless levitation at high temperature and dropped in a calorimeter at room temperature. The spheroids, 2‐3 mm in diameter, prepared by laser melting of powders, are aerodynamically levitated in a splittable nozzle levitator and laser heated to the desired temperature monitored by radiation thermometry. The sample is dropped by splitting the nozzle and caught by splittable water‐cooled calorimetric plates at 25°C, which provide complete enclosure of the sample to avoid heat loss by radiation. The drop time is ~0.1 seconds, calorimeter equilibration time after the drop is ~15 minute. DnC experiments are automated with software‐controlled laser power and programmable delay between splitting the nozzle and catching the sample. The fusion enthalpy of Al2O3 measured by DnC calorimeter, 120 ± 10 kJ/mol, agrees well with previously reported values. The system can be used for measurements of fusion enthalpies of refractory oxides amenable to laser heating as well as for splat quenching of oxide melts.

In‐situ determination of the HfO2–Ta2O5‐temperature phase diagram up to 3000°C

“…Selected beads were levitated and rotated in a conical nozzle levitator (CNL) in air, while being heated with a laser. This method has been described in more detail by McMurray et al and Ushakov . Temperatures on laser melting and cooling traces during quenching from the liquid state were simultaneously monitored using two pyrometers.…”

Thermodynamics of reaction between gas‐turbine ceramic coatings and ingested CMAS corrodents

“…Rock Thermochemistry Laboratory at UC Davis. Detailed description of the laser heating system for operation at temperatures up to 4273 K has been described previously in detail . Weighed 7YSZ beads were aerodynamically levitated in a splittable nozzle levitator in argon flow, laser heated from ~2973 to 3673 K and dropped into a calorimeter at 298 K, thus measuring enthalpy as a function of temperature.…”

“…In this study, we have used high‐temperature solution calorimetry (HT solution calorimetry) at 1723 K to directly measure the enthalpies of reaction between some selected ceramic coatings and molten CMAS. This technique was complemented in selected samples with drop‐and‐catch (DnC) calorimetry and differential thermal analysis (DTA) above 1773 K to measure the enthalpy of fusion required for the calculation of their enthalpy of mixing with molten CMAS. We have selected the TBC compositions 7YSZ, 31YSZ, and 16RESZ; EBC compositions Y 2 Si 2 O 7 and Yb 2 Si 2 O 7 ; and the apatites CaY 4 Si 3 O 13 and CaYb 4 Si 3 O 13 for the HT solution calorimetric measurements.…”

Thermochemistry of BaSm2O4 and thermodynamic assessment of the BaO–Sm2O3 system

“…Crystallization temperatures of the samples were also studied in oxygen by analysis of cooling traces on laser melted aerodynamically levitated samples. The experimental setup was described in detail elsewhere . The temperature was measured with FAR spectropyrometer operating in the 500‐1000 nm range.…”

“…The experimental setup was described in detail elsewhere. 21 The temperature was measured with FAR spectropyrometer 22,23 operating in the 500-1000 nm range. Figure 1C).…”