Preparation of dense and phase‐pure Ba2Ti9O20 is generally difficult using solid‐state reaction, since there are several thermodynamically stable compounds in the vicinity of the desired composition and a curvature of Ba2Ti9O20 equilibrium phase boundary in the BaO–TiO2 system at high temperatures. In this study, the effects of B2O3 on the densification, microstructural evolution, and phase stability of Ba2Ti9O20 were investigated. It was found that the densification of Ba2Ti9O20 sintered with B2O3 was promoted by the transient liquid phase formed at 840°C. At sintering temperatures higher than 1100°C, the solid‐state sintering became dominant because of the evaporation of B2O3. With the addition of 5 wt% B2O3, the ceramic yielded a pure Ba2Ti9O20 phase at sintering temperatures as low as 900°C, without any solid solution additive such as SnO2 or ZrO2. The facilities of B2O3 addition to the stability of Ba2Ti9O20 are apparently due to the eutectic liquid phase which accelerates the migration of reactant species.

Functional nanocrystalline metallic iron powder is produced by the method of electro-discharge in the low oxygen environment of water. In order to obtain superparamagnetic iron oxide Fe 3 O 4, the manufacturing Fe particles were oxidized in the oxygen-rich water to continue oxidation process. Besides, the nanocrystalline Fe particle will be oxidized at temperatures of 200° C , 250° C , 300° C , 350° C , 400° C , 500° C and 600° C for 1 h in air to produce iron oxide α- Fe 2 O 3. The X-ray diffraction, SEM and transmission electron microscope (TEM) were used to analyze the crystal structure and the powder morphologies. The results showed that pure Fe and FeO with a pretty narrow particle size distribution ranges from 1 nm to 10 nm were obtained by the method of electro-discharge. After oxygen-rich oxidation treatment the γ- Fe 2 O 3 and Fe 3 O 4 were obtained at room temperature in 10 days. Thereafter, no more transformation was found in water environment. This result proves that Fe 3 O 4 can be a stable superparamagnetic iron oxide. However, for the Fe particles heat-treated at temperatures of 200 to 600° C , α- Fe 2O3 was formed at temperatures above 300° C for 1 h treating time. Further application studies of this material will be presented in our future research works.