Non-Isothermal Oxidation Behaviors and Mechanisms of Ti-Al Intermetallic Compounds

Non-isothermal oxidation is one of the important issues for the safe application of Ti-Al alloys, so this study aimed to illustrate the non-isothermal oxidation behaviors and the corresponding mechanisms of a TiAl-based alloy in comparison with a Ti3Al-based alloy. The non-isothermal oxidation behaviors of Ti-46Al-2Cr-5Nb and Ti-24Al-15Nb-1.5Mo alloys in pure oxygen were comparatively investigated with a thermogravimetry-differential scanning calorimetry (TGA/DSC) simultaneous thermal analyzer heating from room temperature to 1450 °C with a heating rate of 40 °C/min. When the temperature rose above 1280 °C, the oxidation rate of the Ti-46Al-2Cr-5Nb alloy sharply increased and exceeded that of the Ti-24Al-15Nb-1.5Mo alloy owing to the occurrence of internal oxidation. When the temperature was higher than 1350 °C, the oxidation rate of the Ti-46Al-2Cr-5Nb alloy decreased obviously due to the generation of an oxygen-barrier β-Al2TiO5-rich layer by a chemical reaction between Al2O3 and TiO2 in the oxide scale. Based on Wagner’s theory of internal oxidation, the reason for the occurrence of internal oxidation in the Ti-46Al-2Cr-5Nb alloy is the formation of the α phase in the subsurface, while no internal oxidation occurred in the Ti-24Al-15Nb-1.5Mo alloy due to the existence of the β phase in the subsurface with the enrichment of Nb and Mo.

Effects of oxygen concentration on the passivation of Si-containing steel during high-temperature oxidation

The relationship between the passivation period of Si-containing steel and oxygen concentrations was investigated by conducting the oxidizing experiments employing four different oxygen concentrations on a simultaneous thermal analyzer (STA) at a heating temperature of 1260°C. The results show that the duration of passivation period increased with the increasing oxygen concentration. Moreover, the passivation period occurred at the oxygen concentrations ranging from 2.0 vol.% to 3.0 vol.%, whereas no visible passivation period was observed at the oxygen concentrations ≤1.5 vol.%. In addition, the oxidation mass gain versus time followed a linear relationship before the passivation period, which lasted for about 20 min when the mixed binary atmosphere was introduced into the sample chamber right from the beginning of the heating process.

Phase transformation and microstructure study of the as-cast Cu-rich Cu-Al-Mn ternary alloys

Four Cu-rich alloys from the ternary Cu-Al-Mn system were prepared in the electric-arc furnace and casted in cylindrical moulds with dimensions: f=8 mm and length 12 mm. Microstructural investigations of the prepared samples were performed by using optical microscopy (OM) and scanning electron microscopy, equipped by energy dispersive spectroscopy (SEM-EDS). Assignation of crystalline phases was confirmed by XRD analysis. Phase transition temperatures were determined using simultaneous thermal analyzer STA DSC/TG. Phase equilibria calculation of the ternary Cu-Al-Mn system was performed using optimized thermodynamic parameters from literature. Microstructure and phase transitions of the prepared as-cast alloys were investigated and experimental results were compared with the results of thermodynamic calculations.

Preparation of Aluminum Nanoparticles and Oxidation Mechanism of Nano- and Micro-Particles

Aluminum nanoparticles were prepared by laser and inducting heating methods, then the phase, structure and thermal properties of them were characterized by X-ray diffraction, electron microscope and simultaneous thermal analyzer, respectively. The results showed that there was great difference between micro- and nanoparticles in oxidation behavior. Aluminum micron particles had a very strong endothermic peak at the temperature of about 660°C and the absorption heat enthalpy is 328J/g.The release heat enthalpies of aluminum nanoparticles oxidized by oxygen are 4.219 kJ/g and 3.584 kJ/g. Because of the size decreases to nano-size, the aluminum nanoparticles can be oxidized directly by oxygen and release a large amount of heat, which is beneficial to the propellants when it been burn. However, the micro-particles should absorb heat which other components released, and release heat slowly after melted, which are not as good as the nano-ones.

Fabrication of Ca(OH)2 Nanostructures by Facile Solution – Based Synthesis at Various Reaction Temperatures as CO2 Adsorbent

Calcium hydroxides (Ca(OH)2) nanostructures have been fabricated through simple facile solution based synthesis at different temperatures 35,45 and 55°C repectively.Ethanol was utilized as a medium for reaction. The synthesized powder was characterized by Field Emission Scanning Electron Microscope (FESEM SUPRA 35VP ZEISS), Fourier transform infrared (FTIR Perkin Elmer Spectrum One Spectrophotometer) and X-raydiffraction (XRD). Based on XRD analysis, the synthesis samples exhibited crystal hexagonal phase of Ca(OH)2.The crystallite size for powders prepared was between 17 nm to 31 nm. Short nanorod like structures was successfully obtained in 80 ml ethanol solution for entire temperatures. However, the length and diameter decreased with increased the reaction temperatures. Short nanorod synthesized at 55°C has small diameters and length compared at 35°C. Carbon dioxide (CO2) adsorption for synthesized powders was studied by simultaneous thermal analyzer (STA). Ca(OH)2 prepared at 35°C and45°C in 80 ml ethanol showed CO2 adsorption capacity about 9.3 mmol/g and 9.7 mmol/g respectively.