Colloidal Filtration of Silicon Nitride Aqueous Slips, Part II: Slip Casting and Pressure Casting Performance

Moreno, Rodrigo; Salomoni, A.; Stamenkovic, I.; Mello-Castanho, Sonia Regina Homem de

doi:10.1016/s0955-2219(98)00137-x

Cited by 26 publications

(17 citation statements)

References 6 publications

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“…D ISPERSION of ceramic powders in a liquid phase is required in colloidal processing such as slip casting [1][2][3][4][5][6][7][8][9][10][11] and tape casting. [12][13][14][15] Colloidal processing has been shown to be superior to conventional dry pressing in terms of achieving higher density and sintered microstructure uniformity.…”

Section: Introductionmentioning

confidence: 99%

State of the Dispersant and Particle Surface During Wet‐Jet Milling for Preparation of a Stable Slurry

Hotta

Yılmaz

Shirai

et al. 2008

Journal of the American Ceramic Society

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Wet‐jet‐milled alumina slurries exhibited distinctly different stability behavior compared with ball‐milled ones in terms of reflocculent efficiency and rheological properties. The distinction was attributed to the different behavior of the same dispersant (NH4+ salt of poly(acrylic acid); PAA–NH4+) in ball milling and wet‐jet milling. Alumina particles after the wet‐jet milling retained the initial surface conditions, although ball‐milled alumina particles yielded more hydroxyl groups on the surface. Furthermore, degradation of dispersant on milling was investigated qualitatively. Infra‐red analysis and isoelectric point measurements suggested that degradation of the dispersant occurred during ball milling, indicating neutralization of the dispersant due to formation of monodentate COOX groups. On the other hand, in the case of wet‐jet milling, COO− groups of PAA–NH4+ were not degraded at all, indicating maintenance of the structures of dispersant with electrostatic repulsion. Change in the polymer size of the dispersant by different milling methods was confirmed using high performance liquid chromatography (HPLC) measurements. The HPLC results of the wet‐jet milled samples showed that a dispersant with a larger molecular size was generated. Force measurement on approach via the colloid probe method in the centrifuged supernatant of the milled slurries confirmed that the interaction distance between an α‐alumina colloid probe and c‐sapphire surface was about two times larger in the wet‐jet‐milled slurry supernatant compared with the ball milled one. Thus, it was found that wet‐jet milling process led to a stable slurry because of the maintenance of not only steric repulsion but also electrostatic repulsion.

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Section: Introductionmentioning

confidence: 99%

State of the Dispersant and Particle Surface During Wet‐Jet Milling for Preparation of a Stable Slurry

Hotta

Yılmaz

Shirai

et al. 2008

Journal of the American Ceramic Society

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“…The concept behind pressure casting (also referred to as pressure filtration or filter pressing ) is similar to slip casting. The main difference is that an external pressure (typically 2.5–10 MPa) is applied to speed up the casting process . Since gypsum molds are relatively weak and cannot withstand pressures greater than about 0.5 MPa, porous polymer (plastic resin) or metal molds are often used in pressure casting operation.…”

Section: Ceramic Forming Techniquesmentioning

confidence: 99%

Near‐Net‐Shaping Methods for Ceramic Elements of (Body) Armor Systems

et al. 2014

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Shape‐forming techniques which may be useful in producing components for body armor are reviewed. The techniques are classified in three general categories, dry, wet, and plastic. The different shaping techniques are compared based on key parameters including shape limitations, rate of production, cost, and safety. The techniques are evaluated as to their suitability to be used to produce different body armor components such as breast plates, deltoid, shin and knee protection, and helmets. Dry‐pressing is the current standard for producing “relatively flat” components such as breast plates, but performance is limited by the inherent problem associated with dry‐pressing, namely, the difficulty in producing homogeneous green bodies because of agglomerates in the powder. Plastic processing has the potential to be useful to produce more reliable “flat” components with improved performance due to high shear mixing breaking up agglomerates. Wet (colloidal) processing techniques such as gelcasting and freeze casting may be useful to produce components with high curvature and more complex shape such as helmets. Tiles or segments may be combined to produce shaped components with increased flexibility.

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“…En general, los materiales cerámicos avanzados parten de polvos submicrónicos, cuyo empaquetamiento requiere la aplicación de mayores presiones (del orden de varios MPa) (53,54). Esto implica necesariamente el rediseño de las máquinas de prensado de forma que permitan aumentar el rango de presiones, lo cual no constituye un problema técnico importante en sí mismo.…”

Section: Esquema De Las Técnicas De Conformadounclassified

Tendencias en el conformado de suspensiones cerámicas

Moreno¹

2000

Bol. Soc. Esp. Ceram. Vidr.

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El procesamiento coloidal de materiales cerámicos permite mejorar las propiedades finales de los productos, reduciendo el número y tamaño de los defectos, y aumentando la reproducibilidad del proceso. Esto exige, por una parte, el adecuado conocimiento de los parámetros coloidequímicos y reológicos que rigen la estabilidad de la suspensión y, por otra, el control de las variables específicas de cada proceso de conformado. La técnica de colaje se ha utilizado tradicionalmente en la industria, dada su gran versatilidad, su bajo costo y la elevada uniformidad de las piezas así obtenidas. Sin embargo, el desarrollo industrial impone la búsqueda de nuevas técnicas de conformado capaces de aunar las ventajas del colaje (como la posibilidad de obtener piezas de forma casi final, con el fin de reducir o eliminar la etapa de mecanización) con las propias de otros procesos (como los de prensado), como son la reducción del ciclo de fabricación y la automatización del proceso. Esto ha impulsado el desarrollo de nuevos procesos de conformado en los que la manipulación de las propiedades coloidales de una suspensión permiten obtener piezas de forma casi neta. En este trabajo se muestran las bases de dichas técnicas y se discuten las tendencias actuales en el conformado coloidal de materiales cerámicos. Palabras clave: Procesamiento, Conformado, Suspensiones Trends in slip forming of ceramicsColloidal processing of ceramics allows to improve the final properties of the products by reducing the number and size of defects, enhancing the reproducibility of the process. This needs on one hand an adequate knowledge of colloidal and rheological parameters that control the stability of the suspension and, on the other hand, the control of the specific parameters of each forming technique. Slip casting has been widely used in the industry due to its high versatility, the low cost and the high uniformity in the so cast bodies. However, the industrial development needs the search of new forming techniques capable to combine the advantages of casting processes (as the possibility to obtain near-net shaped parts where machining is reduced or even avoided) with those of other processes (such as pressing) mainly related to the reduction of the fabrication cycle and the possibility of automation. All this has favoured the development of new forming techniques where a proper manipulation of the colloidal properties of a slip makes possible to obtain near-net shaped parts. This work shows the basis of such processes and discusses the actual tendencies in colloidal forming of ceramics. Key words: Processing, Forming, Slips INTRODUCCIÓNEl procesamiento cerámico es el conjunto de operaciones por las que, a partir de uno o varios polvos de partida, se llega a obtener una pieza de la forma y estructura deseadas. La fabricación de un producto, pues, requiere el establecimiento de una sistemática que permita ejercer un adecuado control en cada una de las etapas del proceso, ya que las propiedades del sistema en cada etapa determinan todas las restant...

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Colloidal Filtration of Silicon Nitride Aqueous Slips, Part II: Slip Casting and Pressure Casting Performance

Cited by 26 publications

References 6 publications

State of the Dispersant and Particle Surface During Wet‐Jet Milling for Preparation of a Stable Slurry

State of the Dispersant and Particle Surface During Wet‐Jet Milling for Preparation of a Stable Slurry

Near‐Net‐Shaping Methods for Ceramic Elements of (Body) Armor Systems

Tendencias en el conformado de suspensiones cerámicas

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