Weng-Sing Hwang

Formation and Morphology of Zn2Ti3O8 Powders Using Hydrothermal Process without Dispersant Agent or Mineralizer

Synthesis of Zn2Ti3O8 powders for attenuating UVA using TiCl4, Zn(NO3)2·6H2O and NH4OH as precursor materials by hydrothermal process has been investigated. The X-ray diffractometry (XRD) results show the phases of ZnO, anatase TiO2 and Zn2Ti3O8 coexisted when the zinc titanate powders were calcined at 600 °C for 1 h. When calcined at 900 °C for 1 h, the XRD results reveal the existence of ZnO, Zn2TiO4, rutile TiO2 and ZnTiO3. Scanning electron microscope (SEM) observations show extensive large agglomeration in the samples. Transmission electron microscope (TEM) and electron diffraction (ED) examination results indicate that ZnTiO3 crystallites formed with a size of about 5 nm on the matrix of plate-like ZnO when calcined at 700 °C for 1 h. The calcination samples have acceptable absorbance at a wavelength of 400 nm, indicating that the zinc titanate precursor powders calcined at 700 °C for 1 h can be used as an UVA-attenuating agent.

Phase Transformation and Microstructure of Zn2Ti3O8 Nanocrystallite Powders Prepared Using the Hydrothermal Process

This paper examines the phase transformation and microstructure of Zn2Ti3O8 nanocrystallite powders prepared using the hydrothermal process that includes TiCl4 and Zn(NO3)2·6H2O as the initial materials. Differential thermal analysis, X-ray diffraction, transmission electron microscopy (TEM), selected area electron diffraction, nanobeam electron diffraction, and high resolution TEM were utilized to characterize the transition behavior of zinc titanate precursor powders after calcination. Nanocrystalline Zn2Ti3O8 powders with a size range of about 5.0 to 8.0xa0nm were obtained when the precursor powders were calcined at 773xa0K (500xa0°C) for 1xa0hour. When the zinc titanate precursor powders were calcined at 1073xa0K (800xa0°C) for 1xa0hour, the cubic crystal of Zn2Ti3O8 with aoxa0=xa00.8399xa0±xa00.0003xa0nm still remained the predominant crystalline phase and the crystallite size increased to 20.0xa0nm. In addition, ZnTiO3 phase first appeared because of the 13.8 pct of Zn2Ti3O8 decomposition when the zinc titanate precursor powders were calcined at 1073xa0K (800xa0°C) for 1xa0hour. When the zinc titanate precursor powders were calcined at 1073xa0K (800xa0°C) for 9xa0hours, the Zn2Ti3O8 crystallites grew continuously to 80.0xa0nm and enhanced the crystallinity. When the precursor powders were calcined at 1273xa0K (1000xa0°C) for 1xa0hour, Zn2TiO4 crystallites with aoxa0=xa00.8461xa0±xa00.0002xa0nm were the predominant crystalline phase.

Effects of Heat Treatment on the Microstructure and Mechanical Properties of Low-Carbon Steel with Magnesium-Based Inclusions

The effects of heat treatment on the microstructure and mechanical properties of Mg-containing (7 ppm), low-carbon commercial steel (SS400) were investigated. Twenty different heat treatment paths were performed using a Gleeble 1500 thermomechanical simulator. It was observed by using an optical microscope that as the cooling rate increased and holding temperature decreased, the volume fractions of pearlite, Widmanstätten ferrite, and grain boundary allotriomorphs ferrite fell, whereas that of acicular ferrite (AF) increased. Quantifying the fractions of AF and other phases by using electron backscatter diffraction shows that the heat treatment path with a cooling rate of 20 K/s and holding temperature of 723 K (450xa0°C) induced the highest volume fraction (44 pct) of AF. As such, the toughness of the sample was increased 12.4 times compared with that observed in the sample containing 4 pct AF. Typical inclusions were analyzed using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy. The results showed that the magnesium-based complex inclusions could act as nucleation sites of AF. Inclusions with a size of about 5 μm can serve as heterogeneous nucleation sites for AF. Mg-containing SS400 steel also has excellent hot-ductility in the temperature range of 973 K to 1273 K (700xa0°C to 1000xa0°C), and the minimum percentage reduction in area (R.A pct) value of around 63 pct at 1073xa0K (800xa0°C).

In situ observation of growth behaviour of acicular ferrite in low-carbon steel containing 13 ppm magnesium

ABSTRACT SS400 steel with 13u2005ppm magnesium was prepared to study the effects of supercooling degree on the formation behaviour of acicular ferrite (AF) and microstructures of Mg-containing low-carbon steel. The inclusions characterised using an automated inclusion analyzer, ASPEX, were mostly MnS, MgAl2O4 and MgO with sizes of 1–2u2005μm. The growth behaviour of AF during the cooling process for austenite transformation to ferrite and continuous cooling temperature diagram was investigated using in situ observation with high-temperature confocal laser scanning microscopy. The initial formation temperature of AF decreased with increasing cooling rate. The temperature of AF transformation was in a narrow range of around 100–150u2005K. The probability of AF nucleation from inclusions and the average AF lath growth rate increased with increasing cooling rate due to the larger driving force and thermal strain energy around the inclusions during the cooling processes.