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Abstract (Ra,Ba)SO4 solid solutions are commonly encountered as problematic scales in subsurface energy-related applications, e.g., geothermal systems, hydraulic fracturing, conventional oil and gas, etc. Despite its relevance, its crystallization kinetics were never determined because of radium (226), high radioactivity (3.7 × 1010 Bq g−1), and utilization in contemporary research, therefore constrained to trace amounts ( 0.99. What if lab-on-a-chip technology could create new opportunities, enabling the study of highly radioactive radium beyond traces to access new information? In this work, we developed a lab-on-a-chip experiment paired with computer vision to evaluate the crystal growth rate of (Ba,Ra)SO4 solid solutions. The computer vision algorithm enhances experimental throughput, yielding robust statistical insights and further advancing the efficiency of such experiments. The 3D analysis results of the precipitated crystals using confocal Raman spectroscopy suggested that {210} faces grew twice as fast as {001} faces, mirroring a common observation reported for pure barite. The crystal growth rate of (Ba0.5Ra0.5)SO4 follows a second-order reaction with a kinetic constant equal to (1.23 ± 0.09) × 10−10 mol m−2 s−1.

A combination of simultaneous thermal analysis, evolved gas analysis and non-ambient XRD techniques was used to characterise and investigate the conversion reactions of ammonium uranates into uranium oxides. Two solid phases of the ternary system NH3−UO3−H2O were synthesised under specified conditions. Microspheres prepared by the sol-gel method via internal gelation were identified as 3UO3⋅2NH3⋅4H2O, whereas the product of a typical ammonium diuranate precipitation reaction was associated to the composition 3UO3⋅NH3⋅5H2O. The thermal decomposition profile of both compounds in air feature distinct reaction steps towards the conversion to U3O8, owing to the successive release of water and ammonia molecules. Both compounds are converted into α-U3O8 above 550 °C, but the crystallographic transition occurs differently. In compound 3UO3⋅NH3⋅5H2O (ADU) the transformation occurs via the crystalline β-UO3 phase, whereas in compound 3UO3⋅2NH3⋅4H2O (microspheres) an amorphous UO3 intermediate was observed. The new insights obtained on these uranate systems improve the information base for designing and synthesising minor actinide-containing target materials in future applications. Keywords: Nuclear fuel fabrication, Co-conversion, Internal gelation, ADU, UO3, U3O8