Nanoporous zirconia microspheres prepared by salt-assisted spray drying
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Nanoporous zirconia microspheres prepared by salt‑assisted spray drying M. Skovgaard1 · M. Gudik‑Sørensen2 · K. Almdal3 · A. Ahniyaz4 Received: 11 November 2019 / Accepted: 20 March 2020 © The Author(s) 2020 OPEN
Abstract Nanoporous zirconia with high surface area and crystallinity has a wide range of industrial applications, such as in inorganic exchangers for ion exchange columns, catalyst substrates, and packing material for HPLC. Spherical particles of crystalline nanoporous zirconia are highly desired in various industries due to easy handling of the materials in a fluidized bed. Here, spray drying was adopted to produce spherical nanoporous zirconia powders in both laboratory scale and pilot plant scale. Effect of salts on spray-dried Z rO2 powders and their crystallization behavior was studied. It was found that addition of salts to the zirconia precursors has a huge effect on the crystallization of nanoporous zirconia powders. These results have a great impact on the development of microspheres of nanocrystalline ZrO2 and potentially open up a new opportunity to the low-cost production of porous ceramic microspheres with the salt templating method, in general. Keywords Nanoporous materials · ZrO2 · Salt-assisted spray drying · Nanomaterials · Ceramics · Dental materials
1 Introduction In the last couple of decades, zirconia has gained increasing interest, due to its mechanical properties, ability to catalyze chemical reactions and ionic conductivity at high temperature. For this reason, zirconia and zirconia doped with varies metal oxides, such as yttria, ceria, and magnesia, have been widely studied [1]. Zirconia exhibits three crystallographic phases with increasing temperature at atmospheric pressure: monoclinic below 1175 °C, tetragonal between 1175 and 2370 °C and cubic above 2370 °C. Furthermore, a metastable tetragonal phase exists at room temperature. However, the metastable tetragonal zirconia phase transforms to the stable monoclinic phase due to a range of external factors: applied shear stresses [2], aging in humid atmosphere [3] or annealing [4]. The tetragonalto-monoclinic phase transformation is associated with a volume expansion of ~ 4 vol%. This volume expansion is
the cause of the excellent mechanical properties of doped zirconia ceramics, as the stress-induced phase transformation of metastable tetragonal zirconia grains at the crack tips is the basis of transformation toughening in zirconia ceramics [5]. Porous zirconia with high surface area is of interest for various functional applications. Spherical micron sizedporous zirconia is of particular interest due to the reduced particle aggregation and free-flowing properties. Both alcohol drying [6] and spray drying [7] are known from the literature, and spray drying is furthermore widely used in various industries due to the easy operation and high reproducibility of the process. Another way to obtain small zirconia particles is by modifying of the precursor blend. Salt-assisted spray drying was tested as a possible route. It is
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