Availableonlineatwww.sciencedirect.com Science Direct E噩≈RS ELSEVIER Joumal of the European Ceramic Society 30(2010)1195-1202 www.elsevier.comlocate/jeurceramsoc Fabrication of textured alumina by orienting template particles during electrophoretic deposition Li Zhang, Jef vleugels, Omer Van der biest K ULeunen, Department of Metallurgy and Materials Engineering, Kasteelpark Arenberg 44, B-3001 Heverlee, belgium Available online 16 July 2009 orientation during EPD was examined with respect to the impact of the electric field force, gravity and hydrodynamic force in two different deposition cells with vertically or horizontally positioned deposition electrodes. A sharp(00 1)fbre texture'was obtained after templated grain growth during sintering of a deposit formed from a stirred 5 vol% platelet containing suspension in a vertical deposition cell. The texture was characterized by means of the Lotgering factor, texture index and electron backscattering diffraction(EBSD) 2009 Elsevier Ltd. All rights reserved. Keywords: Suspensions; Platelets; Al2 O3: Texture Introduction This work shows the possibility to align platelet template dur- ing electrophoretic deposition(EPD). EPD is a colloidal proces Textured materials have been investigated extensively in the wherein particles suspended in a stable suspension are deposited past few years due to their improved electronic and structural on one of the electrodes by applying an electric field. The sim- properties. If polycrystalline particles could be aligned, they plicity in experimental set-up leads to low equipment cost. EPD may be able to exhibit the anisotropic characteristics typical is also a fast compacting technique and the deposit thickness of single crystals. For instance, as an important engineer- can be easily controlled. EPD has the capability to form com- ing ceramic, textured a-alumina is widely investigated and the plex shapes and patterns. Moreover, EPD can be applied on a property of this textured a-alumina was reported to be signif- wide range of substrates such as porous ceramics, conductive icantly enhanced 24 Textured materials can be produced by a polymers or metals. 0. I variety of techniques including magnetic orientation and tem- In this study, hexagonal a-alumina platelet templates were growth(TGG). -6Templated grain growth is widely aligned in a fine matrix alumina powder by EPD. After tem- investigated. 4-6 Large and anisotropically shaped template par- plated grain growth, a highly textured material was developed ticles are homogeneously aligned in a fine matrix powder during The mechanism of platelet alignment during deposition was compacting. During sintering, textured material was obtained by investigated considering the impact of orientation forces grain growth in the anisotropic direction of the aligned template particles. The template alignment in the green compact is a crit ical factor in TGG since it determines the final texturisation. 2. Experimental procedure Templates could be aligned by various powder consolidation techniques including uniaxial pressing, slip casting, tape cast- High purity fine a-alumina powder(0.3 um, Baikowski ing, gel casting, centrifugal casting and extrusion. - In those grade SM8, France)was used as matrix powder, whilst hexag- cases, the active forces orientate the template grains during the onal alumina platelets(10-15 um in diameter, -0.5 um thick, powder consolidation process ELF Atochem, France)were used as templates. The morphology of the alumina matrix powder and platelet template is shown in milled for 24 h on a multi-directional mixer(type Turbula, WAB Corresponding author. Tel: +32 16 321777: fax: +32 16 321992 Switzerland) at 70rpm in absolute ethanol(99.9% Merck Bel E-mail address: LiZhang@mtm kuleuven. be(L. Zhang gium) with 0.5 vol% de-ionised water. Zirconia milling balls 0955-2219 front matter@ 2009 Elsevier Ltd. All rights reserved. doi: 10. 1016/j-jeurceramsoc. 2009.06.026Available online at www.sciencedirect.com Journal of the European Ceramic Society 30 (2010) 1195–1202 Fabrication of textured alumina by orienting template particles during electrophoretic deposition Li Zhang ∗, Jef Vleugels, Omer Van der Biest K.U.Leuven, Department of Metallurgy and Materials Engineering, Kasteelpark Arenberg 44, B-3001 Heverlee, Belgium Available online 16 July 2009 Abstract (0 0 1)-Textured -alumina has been processed by electrophoretic deposition (EPD) and templated grain growth. The mechanism of platelet template orientation during EPD was examined with respect to the impact of the electric field force, gravity and hydrodynamic force in two different deposition cells with vertically or horizontally positioned deposition electrodes. A sharp (0 0 1) ‘fibre texture’ was obtained after templated grain growth during sintering of a deposit formed from a stirred 5 vol% platelet containing suspension in a vertical deposition cell. The texture was characterized by means of the Lotgering factor, texture index and electron backscattering diffraction (EBSD). © 2009 Elsevier Ltd. All rights reserved. Keywords: Suspensions; Platelets; Al2O3; Texture 1. Introduction Textured materials have been investigated extensively in the past few years due to their improved electronic and structural properties. If polycrystalline particles could be aligned, they may be able to exhibit the anisotropic characteristics typical of single crystals.1 For instance, as an important engineer￾ing ceramic, textured -alumina is widely investigated and the property of this textured -alumina was reported to be signif￾icantly enhanced.2–4 Textured materials can be produced by a variety of techniques including magnetic orientation and tem￾plated grain growth (TGG).3–6 Templated grain growth is widely investigated.4–6 Large and anisotropically shaped template par￾ticles are homogeneously aligned in a fine matrix powder during compacting. During sintering, textured material was obtained by grain growth in the anisotropic direction of the aligned template particles. The template alignment in the green compact is a crit￾ical factor in TGG since it determines the final texturisation. Templates could be aligned by various powder consolidation techniques including uniaxial pressing, slip casting, tape cast￾ing, gel casting, centrifugal casting and extrusion.5–9 In those cases, the active forces orientate the template grains during the powder consolidation process. ∗ Corresponding author. Tel.: +32 16 321777; fax: +32 16 321992. E-mail address: Li.Zhang@mtm.kuleuven.be (L. Zhang). This work shows the possibility to align platelet template dur￾ing electrophoretic deposition (EPD). EPD is a colloidal process wherein particles suspended in a stable suspension are deposited on one of the electrodes by applying an electric field. The sim￾plicity in experimental set-up leads to low equipment cost. EPD is also a fast compacting technique and the deposit thickness can be easily controlled. EPD has the capability to form com￾plex shapes and patterns. Moreover, EPD can be applied on a wide range of substrates such as porous ceramics, conductive polymers or metals.10,11 In this study, hexagonal -alumina platelet templates were aligned in a fine matrix alumina powder by EPD. After tem￾plated grain growth, a highly textured material was developed. The mechanism of platelet alignment during deposition was investigated considering the impact of orientation forces. 2. Experimental procedure High purity fine -alumina powder (∼0.3m, Baikowski grade SM8, France) was used as matrix powder, whilst hexag￾onal alumina platelets (10–15m in diameter, ∼0.5m thick, ELF Atochem, France) were used as templates. The morphology of the alumina matrix powder and platelet template is shown in Fig. 1. Fine alumina matrix powder suspensions were initially milled for 24 h on a multi-directional mixer (type Turbula, WAB, Switzerland) at 70 rpm in absolute ethanol (99.9% Merck Bel￾gium) with 0.5 vol% de-ionised water. Zirconia milling balls 0955-2219/$ – see front matter © 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.jeurceramsoc.2009.06.026