| 1. |
- Bergström, L, et al.
(author)
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Colloidal processing of a very fine BaTiO3 powder-effect of particle interactions on the suspension properties, consolidation and sintering behavior
- 1997
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In: Journal of The American Ceramic Society. - 0002-7820 .- 1551-2916. ; 80, s. 291-300
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Journal article (peer-reviewed)abstract
- The relation between the suspension state and the rheological properties, the consolidation, and packing of a very fine (nanosized) BaTiO3 powder has been investigated. The BaTiO3 powder was suspended in a non-aqueous medium by adsorbing fatty acids and a polymeric dispersant, poly(12-hydroxy stearic acid), (PHS), at the BaTiO3/decane interface. Calculated interparticle energies implies that the suspension with PHS adsorbed is colloidally stable while the suspensions with oleic and octanoic acid can be characterised as weakly and strongly flocculated, respectively. Analysis of settling experiments and rheological measurements at high concentrations confirmed this characteristics. Pressure filtration resulted in nearly identical green body densities in spite of the differences in colloidal properties, but the preliminary sintering experiments and microstructural characterisation showed that the strongly flocculated suspension displays a significantly retarded sinterability compared to the colloidally stable and the weakly flocculated suspensions. The absence of a correlation between green density and sintering behavior was explained by considering both the volume taken by the adsorbed fatty acids and the PHS polymer-which can be substantial for nanosized powders- and the state of the suspension. While a decrease in the thickness of adsorbed surfactant or polymer layer will enable a higher particle packing density, such a thin adsorbed layer result in a more strongly flocculated suspension which will resist dense packing. Hence, it is suggested that the green bodies of the colloidally stable and the weakly flocculated suspensions correspond to a relatively homogeneous, but loosely packed, green body microstructure. The strongly flocculated suspension results in a green body with a more inhomogeneous microstructure.
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| 2. |
- Kondo, M, et al.
(author)
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Preparation of colloidal monolayers of alkoxylated silica particles at the air-liquid interface
- 1995
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In: Langmuir. - 0743-7463 .- 1520-5827. ; 11, s. 394-397
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Journal article (peer-reviewed)abstract
- A new concept of the formation of the monolayer of colloidal particles on the air-liquid interface based on a new simple model to consider the relation between the interparticle forces and the monolayer structures was proposed. Colloidal monolayers were formed by spreading monodisperse silica particles coated with alkyl chains of different length at the air-benzene interface and picking up the floating clusters or ordered domains with a mica substrate. Polycrystalline, two-dimensional monolayers was formed when the particles was coated with dodecane chains while coating with short alkane chains (butane, octane and decane) resulted in inhomogeneous, porous films. The difference in monolayer structure could be related to the interparticle forces and it was concluded that the formation of ordered colloidal monolayer required that the interparticle attraction is sufficiently weak allowing the formation of ordered domains which can deform during drying.
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