Bench- and pilot-scale continuous-flow hydrothermal production of barium strontium titanate nanopowders

• Continuous-flow hydrothermal synthesis of barium titanate nanopowders.
• Base is necessary for the generation of the crystalline perovskite.
• Barium strontium titanate nanoparticles produced across the targeted full stoichiometric range.
• Products are substoichiometric single phase crystalline nanoparticles.
• Pilot-scale production of perovskite nanoparticles.

Barium strontium titanate (Ba(1−x)SrxTiO3) nanopowders have been prepared at both bench- and pilot-scales using a fully hydrothermal continuous-flow system. A mixed solution of barium nitrate (and/or strontium nitrate) with titanium bis (ammonium lactato) dihydroxide was mixed in-flow with a sodium hydroxide stream before meeting a pre-heated flow of supercritical water at a counter-current mixing point which resulted in the crystallisation of Ba(1−x)SrxTiO3. The obtained nanopowders were characterised by ICP-MS, powder X-ray diffraction, transmission electron microscopy and Raman spectroscopy. All products were found to be sub-stoichiometric with the total M2+:Ti ratio varying between 0.8:1 and 0.96:1, attributed to the formation of divalent metal carbonates preventing full incorporation of the M2+ ions into the perovskite structure in the extremely short reaction times employed. The obtained products were found to adopt the expected perovskite structure, while increasing strontium content led to a decrease in both particle size and lattice parameter. Products with target compositions of Ba(1−x)SrxTiO3 (0 ⩽ x ⩽ 1) were produced for the first time by a fully hydrothermal route at both the bench-scale of ∼5 g h−1 and pilot-scale at ∼80 g h−1.

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