Horng-Huey Ko

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.

Thermal Behavior and Phase Transformation of TiO2 Nanocrystallites Prepared by a Coprecipitation Route

TiO2 freeze-dried precursor powders were synthesized using a coprecipitation route that includes titanium tetrachloride (TiCl4) as initial material prepared at 348xa0K (75xa0°C) and pH 7. Differential scanning calorimetry/thermogravimetry (DSC/TG), X-ray diffraction (XRD), transmission electron microscopy (TEM), and selected area electron diffraction (SAED) and high resolution TEM were utilized to characterize the thermal behavior and phase transformation of the TiO2 freeze-dried precursor powders after calcination. The main compound of the TiO2 freeze-dried precursor powders was TiO2·H2O based on a TG analysis conducted at a heating rate of 20xa0K (20xa0°C)/min. The anatase TiO2 (a-TiO2) first appeared at 473xa0K (200xa0°C), then from a-TiO2 transformed to rutile TiO2 (r-TiO2) at 773xa0K (500xa0°C). The activation energy of a-TiO2 formation from TiO2 freeze-dried precursor powders was 242.4xa0±xa033.9xa0kJ/mol, whereas, the activation energy of phase transformation from a-TiO2 to r-TiO2 was 267.5xa0±xa019.1xa0kJ/mol. The crystallite size of a-TiO2 grew from 3.5 to 23.2xa0nm when raising the calcination temperature from 473xa0K to 873xa0K (200xa0°C to 600xa0°C). In addition, the crystallite size of r-TiO2 increased from 17.4 to 48.1xa0nm when calcination temperature increased from 773xa0K to 1073xa0K (500xa0°C to 800xa0°C).

Process Parameters on the Crystallization and Morphology of Hydroxyapatite Powders Prepared by a Hydrolysis Method

The effects of process parameters on the crystallization and morphology of hydroxyapatite (Ca10(PO4)6(OH)2, HA) powders synthesized from dicalcium phosphate dihydrate (CaHPO4·2H2O, DCPD) using a hydrolysis method have been investigated. X-ray diffraction (XRD), Fourier-transform infrared (FT-IR) spectra, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and selected area electron diffraction (SAED) were used to characterize the synthesized powders. When DCPD underwent hydrolysis in 2.5 NaOH solution (Na(aq)) at 303xa0K to 348xa0K (30xa0°C to 75xa0°C) for 1xa0hour, the XRD results revealed that HA was obtained for all the as-dried samples. The SEM morphology of the HA powders for DCPD hydrolysis produced at 348xa0K (75xa0°C) shows regular alignment and a short rod shape with a size of 200xa0nm in length and 50xa0nm in width. With DCPD hydrolysis in 2.5xa0M NaOH(aq) holding at 348xa0K (75xa0°C) for 1 to 24xa0hours, XRD results demonstrated that all samples were HA and no other phases could be detected. Moreover, the XRD results also show that all the as-dried powders still maintained the HA structure when DCPD underwent hydrolysis in 0.1 to 5xa0M NaOH(aq) at 348xa0K (75xa0°C) for 1xa0hour. Otherwise, the full transformation from HA to octa-calcium phosphate (OCP, Ca8H2(PO4)6·5H2O) occurred when hydrolysis happened in 10xa0M NaOH(aq). FT-IR spectra analysis revealed that some carbonated HA (Ca10(PO4)6(CO3), CHA) had formed. The SEM morphology results show that the 60 to 65xa0nm width of the uniformly long rods with regular alignment formed in the HA powder aggregates when DCPD underwent hydrolysis in 2.5xa0M NaOH(aq) at 348xa0K (75xa0°C) for 1xa0hour.

Effects of Solute and Surfactant Addition on the Crystallization and Morphology of Hydroxyapatite Powders Synthesized by Hydrolysis of Calcium Hydrogen Phosphate Dehydrate (DCPD)

The effects of the addition of alcohol and cetyltrimethylammonium bromide (CTAB) on the crystallization and the morphology of hydroxyapatite (HA) powders synthesized by hydrolysis of calcium hydrogen phosphate dehydrate (DCPD) in the 2.5xa0M NaOH solutions at 348xa0K (75xa0°C) for 1xa0hour have been studied. The values of zeta potential have large differences between the sums of DCPD with CTAB (ZDCPD+CTAB) minus the sum of DCPD and CTAB (ZDCPDxa0+xa0ZCTAB), and of HA with CTAB (ZHA+CTAB) minus the sum of HA and CTAB (ZHAxa0+xa0ZCTAB), respectively. When the hydrolysis of DCPD occurred in the 2.5xa0M NaOH solutions at 348xa0K (75xa0°C) for 1xa0hour both with and without alcohol and CTAB, XRD results show the only one phase of HA in the as-dried powders. When the NaOH solution does not contain CTAB, the crystallite size of HA powders decreased from 23xa0±xa01 to 16xa0±xa01xa0nm as the alcohol content was more than 50xa0pct. The crystallite size of HA powders obtained from DCPD synthesized in the 2.5xa0M NaOH solution with 1.0xa0×xa010−3xa0M CTAB decreased when the alcohol content was increased to 70xa0pct, whereas the crystallite size increased when the alcohol concentration was greater than that of 70xa0pct. SEM images show that the HA powders have a rod-like shape when DCPD was synthesized in the 2.5xa0M NaOH solution without CTAB or alcohol. When the NaOH solution had 1.0xa0×xa010−3xa0M CTAB and various alcohol concentrations, the morphology of HA powder still maintained a rod-like or needle-like shape. The HA powder had a maximum specific surface area of 180.25xa0m2/g when the hydrolysis of DCPD occurred in a 2.5xa0M NaOH solution containing 1.0xa0×xa010−3xa0M CTAB and 70xa0pct alcohol at 348xa0K (75xa0°C) for 1xa0hour.