Solute segregation at grain boundaries in superplastic SiO2-doped TZP

Grain boundary structure, chemical composition, and bonding state in superplastic SiO₂-doped TZP and undoped TZP were investigated by high resolution electron microscopy (HREM), energy dispersive X-ray spectroscopy (EDS) and electron energy loss spectroscopy (EELS) using a field emission type transmission electron microscope (FE-TEM). No amorphous phase was observed at any grain boundaries in either SiO₂-doped TZP or undoped TZP. Yttrium ions segregated over a width of 4–6 nm at grain boundaries in both materials, and silicon ions segregated over a width of 5–8 nm at grain boundaries in SiO₂-doped TZP. The average dihedral angle between grain boundaries in SiO₂-doped TZP was as high as 80°, which agreed well with the fact that no grain boundary had glass phase. The strain energy is accumulated by the dissolution of silicon ions into the tetragonal zirconia lattice. However, the grain boundary energy of SiO₂-doped TZP is likely to be low enough to compensate the increase of strain energy near grain boundaries. OK-edge EELS spectra taken from grain boundaries in SiO₂-doped TZP were shifted 3–4 eV to the higher energy side in comparison with those from the grain interior. This may suggest that the chemical bonding is strengthened at grain boundaries by the presence of solute silicon. The strengthening may be responsible for the enhanced superplasticity in SiO₂-doped TZP.     

Microwave synthesis of wollastonite powder from eggshells

Wollastonite powder was synthesized by microwave assisted solid-state reaction in a 2.45 GHz microwave furnace with a maximum power output of 2.4 kW. Bio-solid waste eggshell and SiO₂ were used as starting materials for the synthesis. α-Wollastonite formation started at 800 °C. The single phase was obtained after 10 min heating at 1100 °C. The use of microwave heating lowered the processing temperature and time for wollastonite synthesis.     

Microstructural Characterization of Superplastic SiO2-doped TZP with a Small Amount of Oxide Addition

The microstructures of 5 wt% SiO₂-doped TZP, 5 wt% (SiO₂+ 2 wt% MgO)-doped TZP, and 5 wt% (SiO₂+ 2 wt% Al₂O₃)-doped TZP are characterized by high-resolution electron microscopy, energy-dispersive X-ray spectroscopy, and electron energy loss spectroscopy. An amorphous phase is formed at multiple grain junctions but not along the grain-boundary faces in these three materials. A small addition of MgO and Al₂O₃ into the SiO₂ phase results in a marked reduction in tensile ductility of SiO₂-doped TZP. This reduction seems to correlate with segregation of magnesium or aluminum ions at grain boundaries and a resultant change in the chemical bonding state.     

Effect of synthesis condition on morphology and yield of hydrothermally grown SnO2 nanorod clusters

In this present work, we report the synthesis of SnO₂ nanorod clusters by means of hydrothermal treatment of colloidal hydrous tin oxide at 200 °C. Effect of synthesis parameters including concentrations of Na₂SnO₃·3H₂O and NaOH, and hydrothermal time on morphology and yield of the products is investigated. At optimum synthesis condition, nanorod clusters consisting of single crystalline, tetragonal-shaped rutile SnO₂ nanorod with uniform shape and size of 190 ± 6 nm in diameter and 1.4 ± 0.2 μm in length were obtained. The influence of precursor concentration on yield and morphology development was discussed. Grown mechanism is described based on aggregation of nanocrystals and their subsequent growth homocentrically.