Novel Powder‐Processing Methods for Advanced Ceramics

Sigmund, Wolfgang M.; Bell, Nelson S.; Bergström, Lennart

doi:10.1111/j.1151-2916.2000.tb01432.x

Cited by 444 publications

(279 citation statements)

References 86 publications

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“…In above two cases, with low solid loading, the mag-nitude of the average Van der Waals forces could be small due to the relatively large distance between suspended particles, so a small addition of dispersant could lead to repulsion forces with enough magnitude to counterbalance Van der Waals forces [50], and the frequency of the collisions between separated particles is lower. This explains why the rheological properties of the suspensions are almost unaffected by the amount of dispersant at low solids loading.…”

Section: ) Effects Of Solid Loadingmentioning

confidence: 99%

Formation characterization and rheological properties of zirconia and ceria-stabilized zirconia

Nikumbh¹,

Adhyapak²

2010

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Zirconia and ceria-stabilized zirconia (12Ce-TZP) were synthesized by the dicarboxylate coprecipitation technique such as fumarate, succinate, tartarate and adipate. The formation of these dicarboxylate precursors was studied by elemental analysis, thermal analysis and infrared spectroscopy. The precursors were further decomposed at 650 o C for 2 hours to form respective zirconia and ceria-stabilized zirconia. The composition of these oxides was checked by Atomic absorption spectrometer and Energy dispersive X-ray analysis. The structural and morphological characterization of these oxides was done by using X-ray diffraction analysis, surface area, scanning electron micrographs and particle size distribution analysis. These properties were found depending to great extent on the nature of the precursors. The zirconia and ceria-stabilized zirconia obtained from adipate precursor were found to be good for slipcasting. The slips (i.e., suspensions) of these oxides with different solid contents were prepared at different pH with distilled water and ethanol as dispersing agents, with and without deflocculant. The suspension rheological flow (i.e., variation of shear stress and viscosity with shear rate) was determined. The minimum viscosities were observed at pH = 10.16 for ZrO 2 -water and pH = 10.26 for 12Ce-TZP-water system. The slip, green and sedimentation bulk density were measured.

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Section: ) Effects Of Solid Loadingmentioning

confidence: 99%

Formation characterization and rheological properties of zirconia and ceria-stabilized zirconia

Nikumbh¹,

Adhyapak²

2010

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“…Diversos processos de preparação de cerâmicas porosas estão sendo pesquisadas na busca de novos materiais com estruturas com diferentes tamanhos de poros, geometria complexa, microestrutura definida e sem a necessidade da etapa de usinagem [2]. Dentre estes, destaca-se o processamento por gelcasting [3], associado à aeração de uma suspensão cerâmica com um agente espumante [4].…”

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Processamento e caracterização de espumas vitrocerâmicas do sistema Li2O-ZrO2-SiO2-Al2O3 (LZSA) produzidas por gelcasting

et al. 2014

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RESUMONeste trabalho, a técnica de viscosimetria foi utilizada para avaliar as características reológicas de suspensões preparadas com precursor vitrocerâmico do sistema LZSA (Li 2 O-ZrO 2 -SiO 2 -Al 2 O 3 ). A partir da caracterização reológica, foi possível estabelecer condições composicionais adequadas de fração de sólidos, dispersante e monômeros orgânicos. A quantidade de agente espumante para produção de espumas vitrocerâmicas por gelcasting foi determinada pela variação volumétrica após agitação. As espumas resultantes foram submetidas a tratamentos térmicos no intervalo de temperatura compreendido entre 200 e 500°C/60 min, para degradação da matéria orgânica e a 950°C/60 min para sinterização e cristalização. Com os corpos cerâmicos porosos foram realizadas medidas de retração térmica, densidade aparente, análise microestrutural e resistência mecânica. A adequação das características reológicas do precursor LZSA por gelcasting permitiu a produção de espumas com elevada porosidade (> 90%) aberta e interconectada com boa estabilidade térmica e com resistência mecânica compatível com cerâmicas porosas. Palavras-chave: reologia, gelcasting, espumas vitrocerâmicas. ABSTRACTIn this work the viscosimetry technique was used to evaluate the rheological characteristics of ceramic suspensions prepared with a LZSA (Li 2 O-ZrO 2 -SiO 2 -Al 2 O 3 ) glass. From the rheological characterization it was possible to establish optimized conditions of solid fraction, dispersant, organic monomers and foaming agent for the production of glass-ceramic foams by gelcasting. The resulting foams were subjected to heattreatments at 200-500°C/60 min, for degradation of organics and at 950°C/60 min for sintering and crystallization. With the obtained porous ceramic bodies linear thermal shrinkage, apparent density and mechanical strength measurements as well as microstructural analysis were performed. The adaptation of the rheological characteristics of the LZSA parent glass powder with the gelcasting processing technique allowed the production of ceramic foams with high open and interconnected porosity (>90%) with good thermal stability and with mechanical strength suitable for the production of porous ceramics.

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“…Colloidal processing of ceramic materials has led to the development of several novel forming methods for casting bulk ceramic preforms (1). These processes can be superior to conventional forming methods when structural uniformity is a key issue and in situations where loss of material from post-sintering machining and finishing processes has a significant cost impact.…”

Section: Introductionmentioning

confidence: 99%

Near net shape forming processes for chemically prepared zinc oxide varistors.

Lockwood¹,

Voigt²,

Tuttle³

et al. 2005

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Chemically prepared zinc oxide powders are fabricated for the production of high aspect ratio varistor components. Colloidal processing in water was performed to reduce agglomerates to primary particles, form a high solids loading slurry, and prevent dopant migration. The milled and dispersed powder exhibited a viscoelastic to elastic behavioral transition at a volume loading of 43-46%. The origin of this transition was studied using acoustic spectroscopy, zeta potential measurements and oscillatory rheology. The phenomenon occurs due to a volume fraction solids dependent reduction in the zeta potential of the solid phase. It is postulated to result from divalent ion binding within the polyelectrolyte dispersant chain, and was mitigated using a polyethylene glycol plasticizing additive.Chemically prepared zinc oxide powders were processed for the production of high aspect ratio varistor components. Near net shape casting methods including slip casting and agarose gelcasting were evaluated for effectiveness in achieving a uniform green microstructure achieving density values near the theoretical maximum during sintering. The structure of the green parts was examined by mercury porisimetry. Agarose gelcasting produced green parts with low solids loading values and did not achieve high fired density. Isopressing the agarose cast parts after drying raised the fired density to greater than 95%, but the parts exhibited catastrophic shorting during electrical testing. Slip casting produced high green density parts, which exhibited high fired density values. The electrical characteristics of slip cast parts are comparable with dry pressed powder compacts. investigated for use with the chemically prepared ZnO material. Recommendations for further investigation to achieve a viable production process are presented.Alternative methods for near net shape forming of ceramic dispersions were 4

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Novel Powder‐Processing Methods for Advanced Ceramics

Cited by 444 publications

References 86 publications

Formation characterization and rheological properties of zirconia and ceria-stabilized zirconia

Formation characterization and rheological properties of zirconia and ceria-stabilized zirconia

Processamento e caracterização de espumas vitrocerâmicas do sistema Li2O-ZrO2-SiO2-Al2O3 (LZSA) produzidas por gelcasting

Near net shape forming processes for chemically prepared zinc oxide varistors.

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