Hydratable Alumina-Bonded Suspensions: Evolution of Microstructure and Physical Properties During First Heating

Salomão, R.; Kawamura, Mirian A.; Souza, A. D. V.; Sakihama, J.

doi:10.1007/bf03401226

Cited by 18 publications

(28 citation statements)

References 40 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…Although the morphology of the pores remained irregular, it was possible to observe a significant reduction in the particles' packing efficiency. Such behaviors are typical from cast systems containing hydraulic binders such as hydratable alumina [6,7,10,29]. On the other hand, further increasing or decreasing in the water content beyond or below this range, respectively, resulted in the opposite behavior, with significant deviations of linearity.…”

Section: Conventional Processing: Suspensions Homogenized Inmentioning

confidence: 96%

Porogenic Behavior of Water in High‐Alumina Castable Structures

Salomão

2018

Advances in Materials Science and Engineering

View full text Add to dashboard Cite

Direct casting is a processing method that can produce large parts of complex geometry. It uses dispersions of ceramic particles in water and a hydraulic binder for consolidation. Studies on castable structures have reported the generation of a significant fraction of pores due to the presence of water. This effect occurs because drying preserves part of the interparticle pores originally occupied by water. The fraction of pores obtained in these cases can reach levels higher than 50%, affecting the properties of the structure. However, the porogenic behavior of water in these materials was not investigated in depth. In this work, aqueous suspensions of calcined alumina and hydratable alumina (hydraulic binder) of different water contents (40–60 vol.%) were prepared in a paddler mixer. For compositions of lower (5–35 vol.%) or higher (66–80 vol.%) water amounts, casting and curing steps were assisted by external pressure and a rotating device, respectively, to produce homogeneous microstructures. The total porosity after drying was similar to the initial volumetric content of water in the compositions when side effects, such as sedimentation and air entrapment, were prevented. Below water content of 25 vol.%, particles packing flaws became the main pore generator and the hydroxylation reaction of the binder no longer occurred effectively.

show abstract

Section: Conventional Processing: Suspensions Homogenized Inmentioning

confidence: 96%

Porogenic Behavior of Water in High‐Alumina Castable Structures

Salomão

2018

Advances in Materials Science and Engineering

View full text Add to dashboard Cite

show abstract

“…The hydrates of HA can be formed through dissolution and concentration reactions (see Equations 1 and 2). 9,10,[16][17][18][19] The hydration products of HA could confer sufficient bonding strength for demolding after curing procedure of HA-bonded castables.…”

Section: Introductionmentioning

confidence: 99%

“…6,9,28 Decomposition of β-AlOOH and β-Al(OH) 3 normally starts at approximately 270°C and lasts up to 350°C-400°C, depending on the different treated conditions. 9,28 It has been believed that the strength drops of HA-bonded castables during intermediate temperatures are ascribed to the decomposition of these hydrates. 6,9,20 However, this hypothesis has not been clarified from the perspective of phase evolution and microstructural change in the HA-bonded castables.…”

Section: Introductionmentioning

confidence: 99%

Microstructure evolution of hydration products and strength change of hydratable alumina‐bonded castables below 1250°C

Zhou

et al. 2020

J. Am. Ceram. Soc.

View full text Add to dashboard Cite

There have been reports that strength of hydratable alumina (HA)-bonded castables without silica fume drops significantly at 600°C and decreases substantially again at 1000°C. But the strength variation of the HA-bonded castables during the intermediate temperature range has not been investigated and elaborated from the perspective of phase evolution and microstructural change in the castables. In this work, the relationship between the change in the strength of castables and the microstructural characteristics of the HA-bonded castables was investigated. The phase and microstructure evolution of HA-bonded castables between 110°C and 1250°C were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and thermogravimetric analysis (TG). It has been found that strength drops of the HAbonded castables during heating process do not mainly happen at the temperature at which HA hydrates decompose, but at the temperature at which the structure of dehydrated HA hydrates disintegrates.

show abstract

“…Amostras moldadas contendo alumina hidratável como ligante, tipicamente apresentam uma queda nas propriedades mecânicas a 1100 °C [67]. No entanto, isso não aconteceu com as amostras CFAF-Pren, CFAF-Mold, CFAG-Pren e CFAG-Mold, onde ambos, a resistência e o módulo elástico aumentam de maneira continua.…”

Section: Amostras Verdes E Sinterizadas a 1100 °Cunclassified

“…No caso das amostras moldadas, é possível observar a presença de partículas de aluminas de transição (marcadas com uma seta). Estas partículas provêm da boehmita precipitada após a secagem do ligante hidráulico, e sua subsequente transformação a temperaturas acima de 900 °C[67,122].…”

unclassified

Porogênese em hexaluminato de cálcio (CaAl>sub<12>/sub<O>sub<19>/sub<): processamento, microestrutura e propriedades termomecânicas

Uehara¹,

Hideki²

View full text Add to dashboard Cite

O hexaluminato de cálcio (CaAl12O19 ou CA6) poroso é um material promissor para aplicações de isolamento térmico pois combina baixa condutividade térmica (~0,33 Wm-1 K-1 a 1400 °C), resistência mecânica razoável (2-8 MPa), inércia química, boa refratariedade (Tf ~1830 °C) e alta resistência ao choque térmico. Existem várias rotas para se obter o CA6 por meio de reações em temperaturas acima de 1300 °C, usando diversas fontes de Al2O3 e CaO, assim como diferentes métodos de processamento. No entanto, embora suas propriedades físicas tenham sido avaliadas, dois pontos principais ainda requerem investigação: o impacto das características das matérias-primas no desenvolvimento da microestrutura de sistemas porosos formados in situ, e a evolução da microestrutura e propriedades de sistemas obtidos a partir de CA6 pré-formado. Neste trabalho, foram produzidas peças de CA6 in situ a partir de diferentes fontes de Al2O3 (alumina calcinada e hidróxido de alumínio) e carbonato de cálcio (CaCO3) de diferentes granulometrias, processados por prensagem uniaxial e moldagem direta de suspensões e submetidas a diferentes tratamentos térmicos. As amostras (verdes e secas e após tratamento térmico) foram submetidas à análise microestrutural (MEV e DRX) e dilatométrica, ensaios para determinação das propriedades físicas (porosidade total, distribuição de tamanho de poros e condutividade térmica) e propriedades mecânicas (resistência à ruptura por compressão e módulo elástico). Estruturas à base de CA6 formado in situ obtidas por prensagem e moldagem direta apresentaram elevada porosidade (até 71 %) e uma resistência à compressão acima de 10 MPa. Verificou-se que o processo de conformação determinou a porosidade à verde inicial da peça, enquanto o tamanho de partícula de alumina induziu a um crescimento de grão assimétrico (partícula grossa) ou à densificação da peça (partícula fina). Dois mecanismos antagonistas acontecem ao mesmo tempo na reação in situ: a reação expansiva da formação de aluminatos intermediários (efeito porogênico) e a densificação das partículas de Al2O3. As partículas de carbonato tiveram uma grande influência no tamanho final dos poros. O efeito porogênico do hidróxido de alumínio foi efetivo até um conteúdo máximo de 50 %vol. Palavras-chave: hexaluminato de cálcio, reação in situ, alumina, carbonato de cálcio, isolante térmico, cerâmica porosa, granulometria ABSTRACT SAKIHAMA, J. Calcium hexaluminate (CaAl12O19) porogenesis: Processing, microstructure and thermomechanical properties. 110p. Tese (Doutorado)

show abstract

Hydratable Alumina-Bonded Suspensions: Evolution of Microstructure and Physical Properties During First Heating

Cited by 18 publications

References 40 publications

Porogenic Behavior of Water in High‐Alumina Castable Structures

Porogenic Behavior of Water in High‐Alumina Castable Structures

Microstructure evolution of hydration products and strength change of hydratable alumina‐bonded castables below 1250°C

Porogênese em hexaluminato de cálcio (CaAl>sub<12>/sub<O>sub<19>/sub<): processamento, microestrutura e propriedades termomecânicas

Contact Info

Product

Resources

About