The oxidation of aluminum at high temperature studied by Thermogravimetric Analysis and Differential Scanning Calorimetry.

Abstract

The oxidation in air of high-purity Al foil was studied as a function of temperature using Thermogravimetric Analysis with Differential Scanning Calorimetry (TGA/DSC). The rate and/or extent of oxidation was found to be a non-linear function of the temperature. Between 650 and 750 °C very little oxidation took place; at 850 °C oxidation occurred after an induction period, while at 950 °C oxidation occurred without an induction period. At oxidation temperatures between 1050 and 1150 °C rapid passivation of the surface of the aluminum foil occurred, while at 1250 °C and above, an initial rapid mass increase was observed, followed by a more gradual increase in mass. The initial rapid increase was accompanied by a significant exotherm. Cross-sections of oxidized specimens were characterized by scanning electron microscopy (SEM); the observed alumina skin thicknesses correlated qualitatively with the observed mass increases. 5 ACKNOWLEDGMENTSThe work described herein was sponsored by the Sandia National Laboratories Weapons Systems Engineering Assessment Technology (WSEAT) Program. The SEM work was carried out by Richard Grant and Amy Allen, and specimens were prepared for SEM by Alice Kilgo. 6

Effects of temperature on the surface and subsurface of Al-Mg-Si welded joints

“…However, the oxide tended to agglomerate and thus exfoliate when being exposed for longer times and at higher temperatures. It is in agreement with [30][31][32] that raising the temperature further resulted in rapid oxidation degradation and instead of surface texture, the rates of mass increase changed proportionally with temperature. Meanwhile, the growth of oxide is a spontaneous process and it is accepted that as the temperature increases, the movement of atoms becomes violent as the oxidation temperature is higher.…”

“…As the temperature increased, internal diffusion of oxygen ions become more dominant and the subsequent of oxidation reaction took place leading to the formation of internal oxidation. It is emphasised that an internal oxidation resulted when alloy element was selectively oxidised and in other words, the diffused metal cannot reach the surface quickly to develop external scale [30]. When oxygen penetrates the metal subsurface, dissolves in an alloy, and reacts to solute metal, dispersed precipitates of metal oxides were formed as shown in Figures 4 (a-c) and 5 (a-c) [35].…”

Irreversible Thermal Expansion of Replicated Aluminium Foam

“…Compression will take place under air cooling but not to the initial size. The entire metal foam inner surface is coated by oxide film which is amorphous aluminium oxide within 300ºС [9,10]. In the process of thermal expansion due to deformation cracks will occur [11][12][13][14][15]20] in the amorphous alumina film (Fig.…”

Desarrollo y optimización de recubrimientos de aleación MCrAlY con dispersión de cargas cerámicas obtenidos por proyección térmica sostenible para aplicaciones de resistencia a oxidación a altas temperaturas

“…La capa de alúmina amorfa inicial que cubre una partícula de Al (presente incluso a temperatura ambiente) inicialmente crece muy lentamente durante la etapa de oxidación a baja temperatura (etapa I de la Figura 2.15) que se extiende hasta aproximadamente 550 °C. La velocidad de este proceso pasa a ser controlado por la difusión de cationes de Al (Jeurgens, Sloof, Tichelaar, & Mittemeijer, 2002 (Coker, 2013).…”

“…Una vez que la mayor parte de la capa de óxido se transforma en cristales gruesos y densos de α-alúmina se obtiene una cobertura continua policristalina, la difusión del límite de grano se ralentiza y la velocidad de oxidación disminuye rápidamente. (Coker, 2013) (Coker, 2013).…”