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

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.