Dou Zhang

Morphology control and piezoelectric response of Na0.5Bi0.5TiO3 synthesized via a hydrothermal method

In this study, lead-free sodium bismuth titanate (Na0.5Bi0.5TiO3, NBT) was synthesized using a hydrothermal method with processing temperatures of 100–180 °C and NaOH concentrations of 2–14 M. NBT spherical agglomerates of primary nanocubes, NBT nanowires and NBT microcubes were obtained and their morphologies exhibited a strong correlation with the synthesis conditions. NBT nanowires with a high aspect ratio were proven to be single-crystalline with a [110] growth direction by high-resolution TEM analysis. The in situ transformation process and dissolution–recrystallization mechanism were successfully used to explain the formation of different NBT morphologies. Domain structures and piezoelectric characteristics were systematically studied for NBT by piezoresponse force microscopy (PFM). Clear ferroelectric domain structures and obvious polarization switching behaviors were observed in all types of NBT. The NBT microcubes possessed a larger piezoresponse compared with the NBT spherical agglomerates and nanowires.

Hollow and porous hydroxyapatite microspheres prepared with an O/W emulsion by spray freezing method

Microspheres with hollow and/or porous structures have been widely used in various applications. A new method of spraying and freezing emulsions was developed to prepare hollow HA (hydroxyapatite) microspheres with interconnected pores by using PVA (polyvinyl alcohol) as emulsifiers and binders. The relationships between viscosity and shear time or rates were tested and the dispersing stability of oil in water (O/W) emulsions was characterized with comparison to suspensions without the addition of oil phase. The effects of solid loadings of HA and the volume ratio between oil and water on the morphologies of microspheres were investigated. Hollow HA microspheres with particle diameter of ~20μm and pore size of ~0.6μm were successfully obtained by spray freezing method. Besides, drying and sintering processes were crucial to the formation of hollow and porous structures, respectively. The gentamicin loading and releasing of HA porous microspheres with different hollow volumes were tested.

Direct ink writing of zirconia three-dimensional structures

Tailoring the rheological properties of colloidal inks is critical for the direct ink writing of three-dimensional structures. The rheological properties of zirconia colloidal inks are extremely sensitive to the concentration of ammonium polyacrylate (NH4PAA). The colloidal ink containing 47 vol% ZrO2, 0.005 g ml−1 cellulose and 0.8 wt% NH4PAA dispersant showed a low viscosity of 3 Pa s at a characteristic shear rate of 50 s−1 and maintained an equilibrium elastic modulus of 8 × 104 Pa when the stress amplitude was up to 200 Pa. Three-dimensional structures with a feature size of 200 μm were successfully assembled with fine integrity.