Near-Net Shape Forming of Advanced Ceramics

Wang, L.; Aldinger, Fritz

doi:10.1002/(sici)1527-2648(200003)2:3<110::aid-adem110>3.0.co;2-4

Cited by 28 publications

(18 citation statements)

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“…Over the last few years, significant effort has been devoted to developing new forming methods for manufacturing complex-shaped ceramic products with minimal number of detrimental defects [8][9][10] This work aims to study the preparation and rheological characterisation of concentrated aqueous suspensions of commercial nanosized powders of barium titanate (nanoBT) for shape forming by slip and gel casting, the latter using thermogelling polysaccharides. The performance of these consolidation techniques for obtaining dense green bodies from the BT nanopowder is discussed.…”

Section: Introductionmentioning

confidence: 99%

“…Over the last few years, significant effort has been devoted to developing new forming methods for manufacturing complex-shaped ceramic products with minimal number of detrimental defects [8][9][10]. Slip casting is a well known technique for consolidating ceramic suspensions into complex shapes [11], although long times can be required, especially for nanosuspensions where the water filtration occurs with more difficulty.…”

Section: Introductionmentioning

confidence: 99%

“…In colloidal systems the interfaces play a key role in the surface properties, such as adsorption, surface charge, electric double layer, etc [6,7]. In the case of 3 nanosized particles, their massive surface areas and hence substantial interaction forces between the particles make it more difficult to prepare stable nano-particle suspensions and study their colloidal properties.Over the last few years, significant effort has been devoted to developing new forming methods for manufacturing complex-shaped ceramic products with minimal number of detrimental defects [8][9][10] This work aims to study the preparation and rheological characterisation of concentrated aqueous suspensions of commercial nanosized powders of barium titanate (nanoBT) for shape forming by slip and gel casting, the latter using thermogelling polysaccharides. The performance of these consolidation techniques for obtaining dense green bodies from the BT nanopowder is discussed.…”

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confidence: 99%

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Gel casting of aqueous suspensions of BaTiO3 nanopowders

Santacruz¹,

Nieto²,

Binner³

et al. 2009

Ceramics International

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Commercial nano BaTiO 3 powders have been formed into green bodies using colloidal forming routes. A study of the rheological behaviour of the suspensions as a function of dispersant concentration and homogenisation time was made in order to prepare stable concentrated suspensions of the nanopowders. Bulk components were then manufactured using aqueous slip and gel casting involving polysaccharides that gel on cooling, i.e. agar. The performance of theses consolidation techniques for obtaining dense green bodies from the BaTiO 3 nanopowders was studied. It was possible to prepare relatively big gel cast samples with a similar density and microstructure and in a shorter time compared to those obtained by slip casting. Another difficulty found in nanoceramics manufacturing is the shaping of homogeneous green bodies. In general, colloidal processing allows the production of complex-shaped parts with a decreased number and size of pores and hence higher reliability 6 . In colloidal systems the interfaces play a key role in the surface properties, such as adsorption, surface charge, electric double layer, etc [6,7]. In the case of 3 nanosized particles, their massive surface areas and hence substantial interaction forces between the particles make it more difficult to prepare stable nano-particle suspensions and study their colloidal properties.Over the last few years, significant effort has been devoted to developing new forming methods for manufacturing complex-shaped ceramic products with minimal number of detrimental defects [8][9][10] This work aims to study the preparation and rheological characterisation of concentrated aqueous suspensions of commercial nanosized powders of barium titanate (nanoBT) for shape forming by slip and gel casting, the latter using thermogelling polysaccharides. The performance of these consolidation techniques for obtaining dense green bodies from the BT nanopowder is discussed. ExperimentalThe starting material was a commercial nanoBT powder (HPB-1000, TPL Inc., was added as a deflocculant to the solution [20,27] prior to the addition of sufficient of the nanoBT powder to generate suspensions with solids loadings of 70, 75 and 80 wt% (28, 33 and 40 vol%, respectively). The suspensions were mixed using by mechanical agitation with helices and further homogenised using ultrasound (a 400 W sonication probe, UP400S, Hielscher Ultrasonics GmbH, Stuttgart, Germany) for up to 10 min.Suspensions were cooled in an ice-water bath during ultrasonication in order to avoid heating.A commercially available agar (Grand Agar, Hispanagar S.A., Burgos, Spain) was used as the gelling agent. Solutions of agar were prepared at concentrations of 6 wt% by heating in a pressure vessel [14,15] in order to achieve the 110ºC required for its full dissolution without the water boiling.The rheological behaviour of the suspensions was studied using a rheometer (Haake RS50, Karlsruhe, Germany) with a double-cone and plate measuring system, provided with a solvent trap to reduce evaporation. Flow curves...

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Section: Introductionmentioning

confidence: 99%

“…Over the last few years, significant effort has been devoted to developing new forming methods for manufacturing complex-shaped ceramic products with minimal number of detrimental defects [8][9][10]. Slip casting is a well known technique for consolidating ceramic suspensions into complex shapes [11], although long times can be required, especially for nanosuspensions where the water filtration occurs with more difficulty.…”

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

See 1 more Smart Citation

Gel casting of aqueous suspensions of BaTiO3 nanopowders

Santacruz¹,

Nieto²,

Binner³

et al. 2009

Ceramics International

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“…Por estas razones, se está realizando un gran esfuerzo en el desarrollo de nuevos métodos de conformado coloidal más versátiles y rentables (2,3). Una vía importante en este aspecto, es la fabricación de piezas con forma casi final, como es el caso de los procesos de tecnología del producto semifinal o procesamiento inteligente (Near Net Shaping, NNS), en los que el mecanizado que se requiere es mínimo (4). La mayoría de estos métodos se basa en la rápida consolidación de un fluido, transformando una suspensión bien dispersa en un cuerpo rígido, como es el caso de la coagulación directa (DCC) (5), la gelificación (6,7), el conformado por vibración (8), el conformado por capas o fabricación directa de cerámicas (solid free-form, SFF) (9), el conformado inducido por la temperatura (temperatura induced forming, TIF) (10), etc.…”

Section: Introductionunclassified

Nuevas aplicaciones de los alginatos en el conformado cerámico

Santacruz¹,

Nieto²,

Moreno³

2005

Bol. Soc. Esp. Ceram. Vidr.

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Los alginatos son polisacáridos naturales empleados a menudo en el procesamiento cerámico como ligantes temporales. Sin embargo, además de su función espesante, los alginatos presentan interesantes propiedades como agente gelificante. Esta función ha sido menos explotada en cerámica pero está empezando a recibir gran atención por su versatilidad de cara a nuevas rutas de conformado de piezas y, sobre todo, de láminas y recubrimientos. En este trabajo se revisan los procesos de conformado neto (near-net shaping, NNS) por formación de geles químicos, entre los que se pueden distinguir dos grupos de técnicas, las que emplean monómeros que polimerizan en presencia de un activador y/o catalizador y las que emplean polisacáridos de elevado peso molecular que forman estructuras a través de cationes presentes en el medio. Este trabajo se centra en el último caso y, en particular, se revisa la química de los alginatos, haciendo énfasis en su estructura y en los mecanismos de gelificación y, por último, se evalúan las posibilidades de aplicación de la gelificación química con alginatos en la producción de láminas por la técnica de colaje en cinta, con especial atención a los parámetros que gobiernan el proceso. Palabras clave: Procesamiento, Conformado, Suspensiones, Aditivos de procesamiento, Gelificación química, Alginatos New applications of alginates in the shape forming of ceramicsAlginates are naturally occurring polysaccharides frequently used as temporary binders in ceramic processing. However, behind their thickenning behaviour, alginates have interesting gelling properties. This function has not been exploited in ceramics, although it is receiving increased attention because of the versatility facing new shaping routes for manufacturing bulk pieces and, in particular, films and coatings. This work reviews the near-net shaping of ceramics through chemical gelation, among which two groups of techniques can be distinguished: those using monomers that polymerize by means of initiators/catalysts, and those using high molecular weight polysaccharides that develop a network structure by means of cations present in the medium. The last case is reviewed in this work, which presents the basis of the chemistry of alginates, focusing their structure and the gelation mechanism, and explores the viability of alginate gelation in the manufacture of thick films by tape casting on the basis of the processing parameters. Key words: Processing, Shaping, Suspensions, Processing additives, Chemical gelation, Alginates INTRODUCCIÓNLos costes totales de producción y el impacto medioambiental son aspectos determinantes para la implantación de un proceso de conformado. El procesamiento coloidal permite obtener piezas de forma compleja con un elevado control del número y tamaño de defectos, así como una alta reproducibilidad y fiabilidad (1,2,3). Por estas razones, se está realizando un gran esfuerzo en el desarrollo de nuevos métodos de conformado coloidal más versátiles y rentables (2,3). Una vía importante en este aspecto, es la fabri...

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“…14 Direct coagulation casting (DCC) [27][28][29][30][31][32] has been investigated and patented as a method for the production of complex-shaped, high strength, high reliability ceramic components. This procedure is based on the destabilization of a high solids loading, electrostatically stabilized suspension, produced mainly by any one of the following methods: 31 (a) changing the pH of the suspensions from a pH regime with high surface potential towards the IEP of the powder through the addition of urea with catalyzers or lactones; [33][34][35] or (b) increasing the ionic strength in order to compress the electrostatic double layer of the powder particles.…”

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confidence: 99%

Rheological Characterization and Coagulation Casting of Al₂O₃–Nano Zirconia Suspensions

Santacruz

Binner

2007

Journal of the American Ceramic Society

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The rheological behavior of electrosterically dispersed aqueous suspensions composed of submicron alumina and nano zirconia particles in different ratios and solids contents has been studied during in-situ coagulation casting. Glucono-δ-lactone was used as the coagulant to achieve destabilization of the ceramic suspensions by acidifying the suspension so that the pH became close to the isoelectric point (IEP) for both powders. The effect of the lactone content and the solids loading were studied on the rheological parameters during the coagulation process and the conditions optimized to yield homogeneous green samples with a uniform nano zirconia distribution and densities between 58 and 60% of theoretical. These were subsequently sintered to yield composites with a final density of 97%.

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Near-Net Shape Forming of Advanced Ceramics

Cited by 28 publications

References 3 publications

Gel casting of aqueous suspensions of BaTiO3 nanopowders

Gel casting of aqueous suspensions of BaTiO3 nanopowders

Nuevas aplicaciones de los alginatos en el conformado cerámico

Rheological Characterization and Coagulation Casting of Al₂O₃–Nano Zirconia Suspensions

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Near-Net Shape Forming of Advanced Ceramics

Cited by 28 publications

References 3 publications

Gel casting of aqueous suspensions of BaTiO3 nanopowders

Gel casting of aqueous suspensions of BaTiO3 nanopowders

Nuevas aplicaciones de los alginatos en el conformado cerámico

Rheological Characterization and Coagulation Casting of Al2O3–Nano Zirconia Suspensions

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Rheological Characterization and Coagulation Casting of Al₂O₃–Nano Zirconia Suspensions