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Transition alumina phases can be produced also using high temperature melting followed by solidification [9, 10].To avoid formation of the thermodynamically most stable α phase in the final material, quenching rate must be sufficiently high [11, 12].The γ forms predominantly in rapid cooling of melted alumina, being the path of least resistance among the alumina phases [11,
Crystal phase transitions are often irreversible and thus deterministic processes. For example, alumina (Al 2 O 3) undergoes a series of irreversible first-order phase transitions with increasing temperature as it transforms from hydrated alumina [bayerite, α-Al(OH) 3] into the metastable η phase, the θ phase, and finally the most stable α phase previously reported
Therefore, the properties of the expected alumina depend on the method and form it is derived from. Appropriay selected parameters significantly affect the characteristics of the final material obtained by the sol-gel method. Alumina during thermal treatment occurs in different phase
The result of crystalline phase analysis showed the diffraction peaks that are indexed at (311), (222), (400) and (440) associated with γ-alumina which become wider from curve a to f (Fig.
alumina Phase transformation Densification Microstructure a b s t r a c t In this work, we studied the aptitude to sintering green bodies usingAl 2O 3 transition alu-mina as raw powder. We focused on the influence of the heating rate on densification and microstructural evolution. Phase transformations from transition alumina → → →
The η-to-θ phase transition of alumina is unidirectional in bulk and retains the crystal lattice orientation. We report a rare example of a statistical kinetics study showing that for nanoparticles on a bulk Al(OH) 3 surface, this phase transition occurs nondeterministically through an ergodic equilibrium through the molten state, and the
The phase transformation studies ,have shown that syntheticaluminas produced in,the laboratory have not transformed to:.a;lphaalumina at 400 to C in the presence o\'f nittric acid and water vapor.; Amorphous alumina produced in the pilot plant is- transformed to alpha. alumina.
This type of alumina has less thermal conductivity (thermal insulation) compared to the alpha-alumina particles. Gamma alumina is a white powder with very small particles. As semi-stable alumina, it is normally made by thermal mineral dehydration. This type of alumina phase has various properties and features. These properties are as
Alumina is extensively used as a catalyst support in a wide range of heterogeneous catalyst systems, where its phase structure significantly influences catalytic properties. Herein, Na-promoted Fe catalysts were impregnated on four different phases of alumina (γ-, δ-, θ-, and α-Al2O3) and evaluated for CO2 hydrogenation to produce hydrocarbons. Among all the alumina tested, the α-Al2O3
The alumina is transformed to α-alumina after calcinations at 1200 °C. The results of the XRD analysis show that the α-alumina (α-Al 2 O 3) phase existed after the sample had been calcined at 1200 °C or and above. The increase of calcination temperature causes the increase in weight
Transition alumina phases can be produced also using high temperature melting followed by solidification [9, 10].To avoid formation of the thermodynamically most stable α phase in the final material, quenching rate must be sufficiently high [11, 12].The γ forms predominantly in rapid cooling of melted alumina, being the path of least resistance among the alumina phases [11,
Crystal phase transitions are often irreversible and thus deterministic processes. For example, alumina (Al 2 O 3) undergoes a series of irreversible first-order phase transitions with increasing temperature as it transforms from hydrated alumina [bayerite, α-Al(OH) 3] into the metastable η phase, the θ phase, and finally the most stable α phase previously reported
In this work, physical phenomena related to the growth and phase formation of alumina, Al 2O 3, are investigated by experiments and computer calculations. Alumina finds applications in a wide variety of areas, due to many beneficial properties and several existing crystalline phases. For example, the α and κ phases are widely used as wear
Alumina is extensively used as a catalyst support in a wide range of heterogeneous catalyst systems, where its phase structure significantly influences catalytic properties. Herein, Na-promoted Fe catalysts were impregnated on four different phases of alumina (γ-, δ-, θ-, and α-Al2O3) and evaluated for CO2 hydrogenation to produce hydrocarbons. Among all the alumina tested, the α-Al2O3
alumina Phase transformation Densification Microstructure a b s t r a c t In this work, we studied the aptitude to sintering green bodies usingAl 2O 3 transition alu-mina as raw powder. We focused on the influence of the heating rate on densification and microstructural evolution. Phase transformations from transition alumina → → →
The η-to-θ phase transition of alumina is unidirectional in bulk and retains the crystal lattice orientation. We report a rare example of a statistical kinetics study showing that for nanoparticles on a bulk Al(OH) 3 surface, this phase transition occurs nondeterministically through an ergodic equilibrium through the molten state, and the
The phase transformation studies ,have shown that syntheticaluminas produced in,the laboratory have not transformed to:.a;lphaalumina at 400 to C in the presence o\'f nittric acid and water vapor.; Amorphous alumina produced in the pilot plant is- transformed to alpha. alumina.
The phase composition of alumina hydrate powders and calcined products was examined by x-ray diffraction analysis in the range 2θ = 10°-90° with CuKα radiation. Content of α phase in the calcined products was calculated according to the formula . Fourier transform infrared spectra (FTIR) were measured on a NICOLET 6700 spectrophotometer
The alumina is transformed to α-alumina after calcinations at 1200 °C. The results of the XRD analysis show that the α-alumina (α-Al 2 O 3) phase existed after the sample had been calcined at 1200 °C or and above. The increase of calcination temperature causes the increase in weight
ABSTRACT. Alumina nanoparticles were synthesized by thermal dehydration of Al(OH) 3 (gibbsite), which shows the sequential formation of AlOOH (bohemite), γ, δ, θ, and α-alumina phases upon heat treatment in the temperature range: 150-1150°C. Alumina nanoparticles were characterized by X-ray diffraction and 27 Al MAS-NMR studies to investigate the structural transitions, in particular
Crystal phase transitions are often irreversible and thus deterministic processes. For example, alumina (Al 2 O 3) undergoes a series of irreversible first-order phase transitions with increasing temperature as it transforms from hydrated alumina [bayerite, α-Al(OH) 3] into the metastable η phase, the θ phase, and finally the most stable α phase previously reported
Current transition alumina catalysts require the presence of significant amounts of toxic, environmentally deleterious dopants for their stabilization. Herein, we report a simple and novel strategy to engineer transition aluminas to withstand aging temperatures up to 1200 °C without inducing the transformation to low-surface-area α-Al 2 O 3
Transition alumina phases can be produced also using high temperature melting followed by solidification [9, 10].To avoid formation of the thermodynamically most stable α phase in the final material, quenching rate must be sufficiently high [11, 12].The γ forms predominantly in rapid cooling of melted alumina, being the path of least resistance among the alumina phases [11,
The phase transformation studies ,have shown that syntheticaluminas produced in,the laboratory have not transformed to:.a;lphaalumina at 400 to C in the presence o\'f nittric acid and water vapor.; Amorphous alumina produced in the pilot plant is- transformed to alpha. alumina.
Aluminium oxide (or aluminium(III) oxide) is a chemical compound of aluminium and oxygen with the chemical formula Al 2 O 3.It is the most commonly occurring of several aluminium oxides, and specifically identified as aluminium oxide.It is commonly called alumina and may also be called aloxide, aloxite, ALOX or alundum in various forms and applications and alumina is refined from bauxite.
Otherwise, the presence of impurities in the starting alumina powder could be at the origin of liquid silicates formation. Generally, this glassy phase is located in grain boundaries and triple points. The formation of the amorphous phase facilitates alumina densification during sintering (Fig.
The alumina silica phase diagram is of great importance in materials science and engineering, particularly in the field of ceramics. This diagram provides crucial information about the behavior and properties of the alumina silica system at various temperatures and compositions. Understanding this phase diagram is essential for designing and
This type of alumina has less thermal conductivity (thermal insulation) compared to the alpha-alumina particles. Gamma alumina is a white powder with very small particles. As semi-stable alumina, it is normally made by thermal mineral dehydration. This type of alumina phase has various properties and features. These properties are as
Then the phase diagram is particularly simple, as shown in Fig. 16.6. There is a compound, mullite, with the composition (Si02)2 (Al203)3, which is slightly more stable than the simple solid solution, so the alloys break up into mixtures of mullite and alumina, or mullite and silica. The phase diagram has two eutectics, but is otherwise
The result of crystalline phase analysis showed the diffraction peaks that are indexed at (311), (222), (400) and (440) associated with γ-alumina which become wider from curve a to f (Fig.
