A confined jet reactor (mixer) is presented as a novel solution for the scalable continuous hydrothermal flow synthesis (CHFS) of nanoceramics. In CHFS, nanoceramics are formed upon mixing of two streams consisting of an aqueous metal salt solution at room temperature with a flow of less dense supercritical water (at 240 bar and 450 °C). Upon mixing, hydrolysis and dehydration occurs, resulting in the particles being formed in a continuous manner. The confined jet mixer used herein overcomes previous designs of mixers that can accumulate material internally and block. A method for scaling up the jet mixer (reactor) is described, to determine the size of jet mixer (internal mixer diameter 13.5 mm) prior to its use in a newly commissioned pilot plant designed to process flow rates 40 times greater than the equivalent laboratory-scale process (internal mixer diameter 4.6 mm). It was confirmed that the pilot plant scale mixer allowed safe and continuous operation with no blockages at much higher concentrations (i.e., higher molarity) of metal salt precursor than laboratory scale because of the higher velocities and larger physical dimensions of the mixer. Consequently, the pilot plant was used to manufacture nanoparticles at a rate >400 times that of the laboratory-scale process. The synthesis of zinc oxide nanoparticles was used as a model to compare the properties of particles produced on different production scales. The same model system was also used to assess the limitations of a scale-up strategy based on mass (i.e., increasing the molarity of the metal salt).

A new continuous supercritical water pilot plant was used for the large-scale production of nanomaterials in the Zn–Ce oxide system. Similar to an existing laboratory continuous process, the pilot plant mixes aqueous solutions of the metal salts at room temperature with a flow of supercritical water (450 °C and 24.1 MPa) in a confined jet mixer, resulting in the formation of nanoparticles in a continuous manner. The Zn–Ce oxide system, as synthesized here under identical concentration conditions than those used in our laboratory scale process (but 17.5 times total flow rate), has been used as a model system to identify differences in particle properties due to the physical enlargement of the mixer. The data collected for the nanoparticles from the pilot plant was compared to previous work using a laboratory scale continuous reactor. In the Ce–Zn binary oxide series, it was shown that Zn had an apparent solubility of about 20 mol% in the CeO2 (fluorite) lattice, whereafter a composite of the two phases was obtained, consistent with the high solubility observed in previous studies using a continuous hydrothermal process. Because of the inherent scalability of the continuous process and excellent mixing characteristics of the confined jet mixer, it was found that the pilot plant nanoparticles were almost indistinguishable from those made on the laboratory scale.

Continuous hydrothermal flow synthesis of crystalline ZnO nanorods and prisms is reported via a new pilot-scale continuous hydrothermal reactor (at nominal production rates of up to 1.2 g/h). Different size and shape particles of ZnO (wurtsite structure) were obtained via altering reaction conditions such as the concentration of either additive H2O2 or metal salt. Selected ZnO samples (used as prepared) were evaluated as solid oxide gas sensors, showing excellent sensitivity toward NO2 gas. It was found that both the working temperature and gas concentration significantly affected the NO2 gas response at concentrations as low as 1 ppm.

A dense composite of silver and Ce0.8Sm0.2O2−δ (Ag-CSO) was manufactured from ceramic nanoparticles coated by electroless deposition of silver. At 700 °C, a 1-mm-thick membrane of the composite delivered an excellent oxygen permeation rate from air with a value of 0.04 μmol cm–2 s–1, using argon as the sweep gas and 0.17 μmol cm–2 s–1 using hydrogen. The low sintering temperature of the CSO nanoparticles allows the use of Ag rather than Pt or Pd and reduces the amount of metal needed for electronic conductivity to just 5.6 vol %, which is lower than any value reported in the literature. Oxygen diffusivity measurements confirmed that the oxygen migration remained high in the composite, with an increase in surface exchange coefficient of three orders of magnitude over Gd-doped ceria. The ease of membrane fabrication, combined with encouraging oxygen permeation rates, demonstrate the promise of the material for high-purity oxygen separation below 700 °C.

A high performance vanadium-doped LiFePO4 (LFP) electrode is synthesized using a continuous hydrothermal method at a rate of 6 kg per day. The supercritical water solvent rapidly generates core/shell nanoparticles with a thin, continuous carbon coating on the surface of LFP, which aids electron transport dynamics across the particle surface. Vanadium dopant concentration has a profound effect on the performance of LFP, where the composition LiFe0.95V0.05PO4 achieves a specific discharge capacity which is among the highest in the literature (119 mA h g-1 at a discharge rate of 1500 mA g-1). Additionally, a combination of Xray absorption spectroscopy analysis and hybrid-exchange density functional theory suggest that vanadium ions replace both phosphorous and iron in the structure, thereby facilitating Li + diffusion due to Li + vacancy generation and changes in the crystal structure.