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Single crystalline barium hexaferrite crystals form very firm and relatively large particle agglomerates. The fabrication of composites and coatings require isolated crystals. For it is necessary to know their deagglomeration behaviour. In this paper we present the zeta potential in dependence on the pH -value of three several modified barium hexaferrite powders which dispersed in aqueous media. The zeta potential describes the extension of the electrical layer and the surface barrier of suspended particles and gives information to prepare singularized barium hexaferrite particles in aqueous media.Keywords

Electrophoretic deposition (EPD) is a very attractive technique for fabrication of a variety of light-weight ceramic composite materials combining high temperature strength with improved fracture toughness, damage tolerance, thermal shock and oxidation resistance. [1][2][3] The interest in this process is based not only on its high versatility to be used with different materials and combinations of materials but also because it is a cost-effective technique which usually requires simple equipment. [4,5] The successful application of the EPD technique requires a stable suspension of charged ceramic particles. In the EPD procedure, charged particles in suspension are subjected to an electric field, which drives the particles towards the deposition electrode where the reinforcing fibre is placed. [1] The EPD infiltration process is especially complex when non-conductive fibres (e.g. Nextel TM 720) are used. The non conductive fibres must be held in contact with the deposition electrode to allow for infiltration of the particles. Moreover, in order to optimize the deposition process, the basic parameters which determine the stability of the suspension and the mobility of the particles must be known and controlled. [3,4] The present paper describes the mechanical characterization of continuous oxide fibre reinforced ceramic matrix composites fabricated by EPD technique. To increase the size and the thickness of the materials, six 2D fibre mats were placed in the EPD cell and infiltrated simultaneously under optimum conditions for suspension stability. A rapid sintering process at a maximal temperature of 1300°C was used in order to densify and reduce porosity of the deposit (ceramic matrix).Results and discussion: Figure 1 shows the flow chart of the method used in this investigation to fabricate oxide-oxide ceramic matrix composite with higher level of fibre mats content as reinforcement (> 45 vol.%). The first step in the EPD process is the preparation of a stable, agglomerate-free colloidal suspension, as mentioned above. According to previous investigations of the electrophoretic behaviour of a-Al 2 O 3 particles and Nextel TM 720 fibre mats in ethanol, [6] it was determined that both components show a positive electrical surface charge. This fact is favourable for the electrophoretic deposition (infiltration) of particles into the fibre mat, as also discussed elsewhere. [6] In the second step the non-conductive fibre mats were attached to the deposition electrode, in order to obtain a tight fixing of the mats to it, as schematically shown in Figure 2(a). The composite samples were fabricated by using a newly developed electrophoretic deposition cell, shown schematically in Figure 2(b) and described in detail elsewhere. [6] It is a very suitable cell for conducting model EPD experiments allowing the manipulation of the relevant EPD parameters. The cell is used to improve the infiltration of large surfaces with circular area of up to 78 cm 2 . To our knowledge this represents the largest CMC fabricated to date by t...

The electrophoretic deposition (infiltration) method represents a convenient alternative technique to fabricate ceramic matrix composites (CMCs) with improved high matrix density. The focal point of the present work is to describe the basic principle of the EPD technique applied to fabricate CMCs with oxide matrix and oxide fibres. Optimisation of the suspension stability is emphasised as well as the operational determination of the parameters for EPD and the designed of a new EPD cell to warrant the improved infiltration of the particles into fibre mats used as reinforcement. The electrophoretic deposition (infiltration) technique was applied to fabricate composites with alumina matrix (α-Al2O3) reinforced with NextelTM 720 fibres. The fabricated composites demonstrate that EPD permits to achieve a high matrix density with an excellent high intra-tow infiltration of the matrix particles. Moreover a mechanism of the EPD infiltration of oxide fibres is proposed and consequently progress in understanding the fundamentals of the technique applied to oxide-oxide systems has been made.