Phase transitions and dimensional and morphological changes in an ?Aluminum Hydroxide-Alumina? system under a shock-wave action

Abstract

A method is proposed to study the sequence of phase transitions in powdered materials under a shock-wave action. It is shown that the "aluminum hydroxide-alumina" system has the following sequence of phase transformations under a shock-wave action: bayerite → boehmite → γ-Al 2 O 3 → α-Al 2 O 3 . It is found that there are no transitional high-temperature modifications of alumina. A method is developed for obtaining a submicron alumina powder, which allows obtaining materials with a controlled phase composition, including a thermodynamically stable α-modification of Al 2 O 3 . The specific features of the morphological structure and the phase and structural characteristics of powders after a shock-wave action are considered.

Development of AMZ composites via mutual attraction of particles in wet processing

“…Investigation of the phase transformation of aluminum alkoxide shows that around 24.7% weight loss has occurred during heating from room temperature up to 1000°C 33 . Therefore, it can be concluded that use of aluminum alkoxide leads to diminished density and enhanced porosity.…”

“…Meanwhile, the conversion of aluminum trihydroxide to aluminum monohydroxide was completed as well. Also, the conversion of aluminum monohydroxide to γ‐Al 2 O 3 was expected to occur and completed 33 . Notably, the resulting composites did not contain any detectable defect.…”

“…Aluminum alkoxide changes to AlO(OH) and then to Al(OH) 3 after hydrolysis and it will transform to α-alumina while being heated. 25,26,33 In order to confirm that the utilized aluminum alkoxide would take part in the formation of mullite, coated zircon was sintered at 1630°C for 3 hours. The XRD analysis of the sintered sample has been shown in Figure 2.…”

Microstructure, oxidation behaviour and mechanical properties of Fe2O3 doped yttria-partially-stabilized zirconia coatings produced on metallic substrates by electrophoretic deposition

“…These microstructural changes were expected and occurred due to the phase transformation from θ-to α-Al 2 O 3 phase during the oxidation of aluminium alloy [31][32][33][34]. Generally, the morphologies of EPD coatings are similar to APS coatings [11,31,32], which produce compressive stress favouring α-Al 2 O 3 phase transformation [33][34][35][36]. Consequently, TGO scales under the EPD coatings consisting of more α-Al 2 O 3 phase have lower growth rate.…”

“…2), the TGO scales were retarded in the Fe 2 O 3 doped 3Y-PSZ coatings. The factors affecting the growth of TGO scale are still under debate [30][31][32][33]. It has been established that the oxidation of alumina scale usually follows the parabolic kinetics, indicating the diffusion-controlled growth [37].…”