Polymeric Precursor Synthesis of Alumina Containing Manganese Oxide

Gouvêa, Douglas; Villalobos, Rafael; Capocchi, José Deodoro Trani

doi:10.4028/www.scientific.net/msf.299-300.91

Cited by 12 publications

(9 citation statements)

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“…Accordingly, several attempts have been made to control the characteristics of the resulting alumina powders and sintered alumina ceramics, including the addition of a fraction of ultrafine alumina crystallites as seed material 9 and the introduction of certain dopants to promote densification. 10 Benjamin 11 pioneered efforts to establish mechanical alloying for the synthesis of metallic alloys and intermetallics. Such procedures have been recently exploited for several other types of materials, although the degree of success varies considerably from one material to another.…”

Section: Introductionmentioning

confidence: 99%

Mechanical‐Activation‐Triggered Gibbsite‐to‐Boehmite Transition and Activation‐Derived Alumina Powders

Yong

Wang

2001

Journal of the American Ceramic Society

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Mechanical activation of monoclinic gibbsite (Al(OH) 3 ) in nitrogen led to the formation of nanocrystalline orthorhombic boehmite (AlOOH) at room temperature. The boehmite phase formed after merely 3 h of mechanical activation and developed steadily as the mechanical-activation time increased. Forty hours of mechanical activation resulted in essentially single-phase boehmite, together with ␣-alumina (␣-Al 2 O 3 ) nanocrystallites 2-3 nm in size. The sequence of phase transitions in the activation-derived boehmite was as follows: boehmite to ␥-Al 2 O 3 and then to ␣-Al 2 O 3 when flash-calcined at a heating rate of 10°C/min in air. ␥-Al 2 O 3 formed at 520°C, and flash calcination to 1100°C led to the formation of an ␣-Al 2 O 3 phase, which exhibited a refined particle size in the range of 100 -200 nm. In contrast, the gibbsite-to-boehmite transition in the unactivated gibbsite occurred over the temperature range of 220°-330°C. A flash-calcination temperature of 1400°C was required to complete the conversion to ␣-Al 2 O 3 phase, with both ␦-Al 2 O 3 and -Al 2 O 3 as the transitional phases. The resulting alumina powder consisted of irregularly shaped particles 0.4 -0.8 m in size, together with an extensive degree of particle agglomeration.

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Section: Introductionmentioning

confidence: 99%

Mechanical‐Activation‐Triggered Gibbsite‐to‐Boehmite Transition and Activation‐Derived Alumina Powders

Yong

Wang

2001

Journal of the American Ceramic Society

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“…Supondo a hipótese de segregação do aditivo na superfície da γ-alumina [16], o valor da energia livre por volume da rede não seria alterado, pois as ligações não são rompidas ou distorcidas, mantendo-se a simetria da rede. Assim, a energia livre de rede do material puro e contendo o aditivo seria a mesma.…”

Section: Resultsunclassified

“…Para produção da alumina foi utilizado método baseado na patente de Pechini [16], que propõe uma via de preparação química de óxidos que limita a adição de contra íons inorgânicos e permite a cristalização lenta das partículas. O precursor polimérico foi preparado pela adição de Al(NO 3 …”

Section: Materiais E Métodosunclassified

“…Centrando o estudo no íon Mn, a literatura reporta a temperatura de início de cristalização da α-alumina sendo decrescida à 900 o C com a adição de 7% em mol de óxido de manganês [16]. Este trabalho aponta por análises de difração de raios X que não há formação de fase secundária do manganês durante a calcinação da alumina dopada com Mn e tampouco solubilização do íon na rede do óxido matriz, o que se opõe a resultados previamente estabelecidos [13] e desacredita uma teoria de nucleação heterogênea por fases secundárias assim como formação de fase líquida.…”

Section: Introductionunclassified

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Efeito do íon Mn como aditivo na transição de fase <FONT FACE=Symbol>g ®a</FONT> da alumina

Castro

Gouvêa

2003

Cerâmica

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“…This gives a wide range of opportunities for future investigation [12,13]. Furthermore, different manganese oxides (MnO 2 , MnO) were employed in order to accelerate the sintering process and grain growth of alumina, and it was established that Mn 2+ shifts the temperature of reaction to lower values [14][15][16][17]. These investigations were mostly performed on α-alumina as the starting material.…”

Section: Introductionmentioning

confidence: 99%

Physical properties of sintered alumina doped with different oxides

et al. 2018

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Corundum (α-alumina) is a suiTab. material for usage in various industry fields owing to its chemical stability, electrical and mechanical features. It is known that properties of ceramics could be modified by addition of different oxides, as well as by changing the consolidation parameters. In this respect, alumina was doped with 1 wt.% of Cr 2 O 3 , Mn 2 O 3 and NiO, followed by 1 hour of mechanical activation in a high-energy planetary ball mill. A sensitive dilatometer was used for sintering of powder mixtures up to 1400 o C and recording the obtained dilatation. The final density varied between cca. 1.9 and 3.3 g/cm 3. Microstructural changes were detected by SEM measurements. Changes in electrical permittivity and loss tangent were associated with the preparation conditions (types of additives, duration of mechanical activation). For a given mixture, the sintering increases the relative permittivity and decreases losses, exhibiting the optimal values of 8.32 and 0.027, respectively, for the sample activated 60 minutes and sintered, with the addition of MnO 2. Mechanical measurements indicate significant differences in strength with the addition of different transition metal oxides. Samples with Mn and Ni, activated and sintered, with strength of 121 and 86 MPa, respectively, have a significantly higher tensile strength than the other tested samples, due to their more compact microstructures.

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Polymeric Precursor Synthesis of Alumina Containing Manganese Oxide

Cited by 12 publications

References 0 publications

Mechanical‐Activation‐Triggered Gibbsite‐to‐Boehmite Transition and Activation‐Derived Alumina Powders

Mechanical‐Activation‐Triggered Gibbsite‐to‐Boehmite Transition and Activation‐Derived Alumina Powders

Efeito do íon Mn como aditivo na transição de fase <FONT FACE=Symbol>g ®a</FONT> da alumina

Physical properties of sintered alumina doped with different oxides

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