Search Results
Abstract
A homogeneous TiO2 gel was obtained by hydrolysing titanium(IV) isopropoxide that was previously modified by reaction with acetic acid. The so stabilized precursor was hydrolysed under strong acidic medium (pH=0 by HCl). Dried TiO2 powders were characterized by FT-IR, XRD, N2 adsorption analyses, coupled thermogravimetric (TG) gas chromatographic (GC) and `mass spectrometric (MS) analyses. A semiquantitative analysis of the main evolved chemical species allowed to depict both the chemical rearrangements occurring in the TiO2 matrix during pyrolysis and the chemical composition of the initial gel.
Abstract
A homogeneous TiO2 gel sample was prepared, via sol-gel method, hydrolysing titanium(IV) isopropoxide, previously modified by reaction with formic acid. The amorphous TiO2 gel was characterized using various techniques such as FT-IR, XRD and N2 adsorption analysis. Thermoanalyses (TG, DTA) coupled with gas chromatographic (GC) and mass spectrometric measurements (MS), by means of a home-assembled instrumental interfaces, were performed in order to quantify the organic component still present in the titania gel and its release during pyrolysis. Several chemical species were evolved and detected in gas phase for temperatures up to 350C, before crystallization of TiO2-anatase.
Abstract
An amorphous TiO2 gel was obtained by hydrolysing titanium(IV) isopropoxide with a stoichiometric amount of water using SnCl2 as catalyst. In these operative conditions, a TiO2 gel matrix containing a lower fraction of organic residual was obtained with respect to samples prepared by previously modifying the titanium alkoxide precursor with chelating ligands. Dried gel powders were characterized by N2 adsorption analyses, FT-IR and XRD measurements. Thermogravimetric (TG) and differential thermal analysis (DTA) coupled with mass spectrometric (MS) and gas chromatographic (GC) measurements were performed in order to identify the organic products released from TiO2 gel pyrolysis. The Tg-MS semiquantitative analysis of the main evolved species allowed to describe both the chemical composition of the initial TiO2 gel and the chemical rearrangements occurring in the matrix during heating up to its crystallisation to anatase form at 420°C.
Abstract
A simple method for preparing F-doped anatase TiO2 nanoparticles with high visible light photocatalytic activity was developed using TiCl4 and HF as TiO2 and fluorine precursors in HCl solution by a one-step hydrothermal treatment without any organic species. The presence of HF plays an important role in the formation of the F-doped shuttle-like anatase TiO2 nanostructures. XRD analysis showed that the F− could prevent the transformation of anatase to rutile in HCl solution. Compared with ordinary TiO2, the F-doped TiO2 nanoparticles synthesized at 180 °C exhibited better photocatalytic activity for the degradation of rhodamine B under visible light irradiation. Possible formation mechanism of F-doped anatase TiO2 under hydrothermal conditions was discussed.
Abstract
Homogeneous TiO2 powders were obtained, via sol-gel method, hydrolysing titanium(IV) isopropoxide, previously reacted with oxalic acid in order to better control the gelling process. The characterization of the amorphous TiO2 powders was carried out by using different techniques such as FT-IR, XRD and N2 adsorption analysis. Coupled thermogravimetric (TG) gas chromatographic (GC) and mass spectrometric (MS) analyses were performed to quantify the organic content present in the titania gel and its release during pyrolysis. A detailed semiquantitative analysis of the evolved chemical species from TG-MS data allowed to describe the chemical composition of the TiO2 gel and the chemical rearrangements occurring in matrix during pyrolysis up to its crystallization to anatase form at 530C.
Abstract
The thermal decomposition of ammonium perchlorate (AP) is considered to be the first step in the combustion of AP-based composite propellants. In this report, the effect of the specific surface area of titanium oxide (TiO2) catalysts on the thermal decomposition characteristics of AP was examined with a series of thermal analysis experiments. It was clear that the thermal decomposition temperature of AP decreased when the specific surface area of TiO2 increased. It was also possible that TiO2 influences the frequency factor of AP decomposition because there was no observable effect on the activation energy.
Abstract
Preliminary examinations regarding formation of bismuth titanates in a part of Bi2O3—TiO2 system rich with TiO2 have been carried out. Bismuth titanates have been synthesized from mixtures of Bi2O3 and TiO2 (anatase) by the conventional solid-state method at the temperatures ranged from 1273 to 1473 K. Differential thermal analysis (DTA), powder X-ray diffraction (XRD) and scanning electron microscopy (SEM) have been used to study the formation of bismuth titanates. The following compounds have been achieved: Bi4Ti3O12, Bi2Ti2O7 and Bi2Ti4O11. Existence of controversial bismuth titanate of formula Bi2Ti3O9 in the Bi2O3—TiO2 system has not been confirmed.
Summary Thermal decomposition of dried TiO2 gel, obtained by hydrolysing acetylacetonate-modified titanium(IV) isopropoxide, was monitored by simultaneous TG/DTA/EGA-FTIR measurements in dynamic air up to 900°C. XRD and FTIR were employed to identify the solid reaction products. Thermal degradation of the TiO2 gel consists of five distinct mass loss steps, the total mass loss being 43.8&. EGA by FTIR revealed the release of H2O below 120°C; followed by acetone, isopropyl acetate and 1-propanol around 200-300°C, and finally CO and CO2 up to 550°C. Highly exothermic reaction at 410-550°C is caused by the combustion of carbon residues. Crystalline TiO2-anatase is formed around 500°C and TiO2-rutile close to 800°C.
Abstract
TiO2(0–20 mol%)-8 mol% YSZ (8YSZ) ceramics were synthesized by a traditional solid-state reaction method. A cubic single phase was observed for 8YSZ, 4 mol% TiO2-8YSZ and 8 mol% TiO2-8YSZ. Tetragonal and cubic mixed phases were observed for 12–20 mol% TiO2-8YSZ ceramics. The sintering temperature was 1,700 °C for 8YSZ and 4 mol% TiO2-8YSZ ceramics, whereas it was 1,500 °C for 8–20 mol% TiO2-8YSZ. The thermal conductivity at room temperature decreased in proportion to increasing TiO2 content, from 3.0 to 2.3 W/m K. The specific heat of TiO2-8YSZ ceramics was unaltered as the TiO2 content changed.
Abstract
The formation of TiO2 prepared by hydrolysis method was presented. Thermodynamics and kinetics of anatase crystallization reaction were investigated. Differential method of kinetic data evaluation in non-isothermal conditions according toKissinger, Ozawa and Kazeev-Yerofeev was applied. Starting, crystallized and thermally treated powders were determined using X-ray powder diffraction analysis. The characteristic parameters (the activation energy, constant rate and formal kinetic order of reaction) of TiO2 formation were calculated using DSC data.
