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Title: Barocaloric effects in barium-dicalcium propionate salts
Author: Avramenko, Alexander
ISNI:       0000 0004 9354 3353
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2020
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Fluid refrigerants used in vapour-compression cooling systems such as air conditioners and fridges contribute to environmental damage. Should barium dicalcium organic salts show persistent entropy changes under pressure that are reversible, they may serve as environmentally friendly solid-state barocaloric cooling materials. In this thesis, I synthesised barium dicalcium propionate and barium dicalcium butyrate and investigated their refrigerant properties. Using differential scanning calorimetry, I found the thermally driven entropy changes associated with the phase transition as ~39.6 J K-1 kg-1, for barium dicalcium propionate, and as ~12.4 J K-1 kg-1 for barium dicalcium butyrate. Through variable-pressure differential thermal analysis, I confirmed the persistence of the phase transition entropy changes under pressure and characterised the shift of the phase transition upon application of pressure for both salts. From these calorimetric measurements, I found giant barocaloric effects of the propionate salt and butyrate salt comparable to the largest reported barocaloric effects. I identified the minimum pressure to drive the phase transition in the propionate salt as ~9 MPa, and as ~16 MPa in the butyrate salt. Via temperature-controlled powder x-ray diffraction, I calculated the volume change across these phase transition as ~2.2 % for the propionate salt, and as ~0.9 % for the butyrate salt. These values agree with the measured phase transition entropy changes and the measured shift of the phase transition under application of pressure, as per the Clausius-Clapeyron relation. Using variable-pressure x-ray diffraction measurements in a diamond anvil cell with synchrotron radiation, I confirmed reversible pressure-driven phase transitions at room temperature for the propionate salt and at ~373 K in the butyrate salt. Together, my findings suggest that barium dicalcium propionate and barium dicalcium butyrate, organic salts that are made of cheap naturally abundant elements, may be promising solid-state barocaloric refrigerants.
Supervisor: Moya, Xavier Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
Keywords: Barocaloric ; Refrigeration ; Solid-state cooling ; Caloric ; solids-to-solid phase-transition