Electrophoretic deposition (EPD) is attracting increasing interest as a materials processing technique for a wide range of technical applications. This technique enables the production of unique microstructures and nanostructures as well as novel and complex material combinations in a variety of macroscopic shapes, dimensions and arrangements starting from micron-sized or nanosized particles. This review presents a comprehensive summary of relevant recent work on EPD describing the application of the technique in the processing of several traditional and advanced materials (functional and structural ceramic coatings, composite and porous materials, laminated ceramics, functionally graded materials, thin films and nanostructured materials), with the intention to highlight how EPD evolved from being a technique restricted only to traditional ceramics to become an important tool in advanced materials processing and nanotechnology. Moreover the fundamental EPD mechanisms and novel theories proposed to clarify the processes involved are explained.

Electrophoretic deposition: From traditional ceramics to nanotechnology

Ceramic nanocomposites are attracting growing interest, thanks to new processing methods enabling these materials to go from the research laboratory scale to the commercial level. Today, many different types of nanocomposite structures are proposed in the literature; however, to fully exploit their exceptional properties, a deep understanding of the materials’ behavior across length scales is necessary. In fact, knowing how the nanoscale structure influences the bulk properties enables the design of increasingly performing composite materials. A further key point is the ability of tailoring the desired nanostructured features in the sintered composites, a challenging issue requiring a careful control of all stages of manufacturing, from powder synthesis to sintering. This review is divided into four parts. In the first, classification and general issues of nanostructured ceramics are reported. The second provides basic structure–property relations, highlighting the grain-size dependence of the materials properties. The third describes the role of nanocrystalline second-phases on the mechanical properties of ordinary grain sized ceramics. Finally, the fourth part revises the mainly used synthesis routes to produce nanocomposite ceramic powders, underlining when possible the critical role of the synthesis method on the control of microstructure and properties of the sintered ceramics.

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Structural Ceramic Nanocomposites: A Review of Properties and Powders' Synthesis Methods.

Synthesis of an alumina–YAG nanopowder via sol–gel method

In this paper, we are reporting an extensive characterization, by means of open circuit voltage measurements, of Ce0.8Gd0.2O2, La0.9Sr0.1Ga0.8Mg0.2O3, and La2Mo0.6W1.4O9 oxide-ions and BaCe0.8Y0.2O3 and BaCe0.55Zr0.3Y0.15O3 proton-conducting electrolyte materials for solid oxide fuel cell (SOFC) applications. This simple and common technique, well known for a long time in the electrochemical study of solid oxide fuel cells, has been here proposed for the electrical characterization of these ceramic materials, in order to define their ionic transport numbers, the maximum voltage performances, the thermal and chemical stability, and also to suggest the ideal temperature range for different applications, as in the electrochemical devices, sensors, and SOFC field. In the paper, controlled and reproducible working conditions have been applied in a wide range of temperature, by means of ultrapure gas (H2 and O2), under operational conditions found in real SOFC devices and, mainly, without the usual problems related to the chemical compatibility, the depolarization efficiency, and the high current density required to the electrode materials in the design of a more efficient SOFC device.

Electrochemical open circuit voltage (OCV) characterization of SOFC materials

EPD is a technique where charged particles in a stable colloidal suspension are moved through the liquid due to electric field and deposited on an oppositely charged conductive substrate, forming the intended material or device EPD enables fabrication of a wide range of structures from traditional to advanced materials, from nanometric thin films to a fraction of 1 mm thick films, and from porous scaffolds to highly compact coatings These structures include different compositions with complex shapes and structures which can be formed in a relatively short experimentation time by simple apparatus This review presents the fundamentals, mechanisms, and characteristics of EPD along with its past and recent applications

Electrophoretic Deposition (EPD): Fundamentals and Applications from Nano- to Micro-Scale Structures

Al2O3-YAG (50 vol.%) nanocomposite powders were prepared by wet-chemical synthesis and characterized by DTA-TG, XRD and TEM analyses. Amorphous powders were pre-heated at different temperatures (namely 600 °C, 800 °C, 900 °C and 1215 °C) and the influence of this thermal treatment on sintering behavior, final microstructure and density was investigated. The best performing sample was that pre-calcined at 900 °C, which yields dense bodies with a micronic/slightly sub-micronic microstructure after sintering at 1600 °C. A pre-treatment step to induce controlled crystallisation of the amorphous powder as well as a fast sintering procedure for green compacts, were also performed as a comparison. Finally, the previously stated thermal pre-treatment of the amorphous product was coupled to an extensive mechanical activation performed by wet planetary/ball milling. This procedure was highly effective in lowering the densification temperature, so that fully dense Al2O3-YAG composites, with a mean grain size smaller than 200 nm, were obtained by sintering in the temperature range 1370–1420 °C.

Comparison among different sintering routes for preparing alumina-YAG nanocomposites

Characterization of LSGM films obtained by electrophoretic deposition (EPD)

Influence of some processing parameters on the production of fully dense nanocomposite materials

Alumina-yttrium aluminum garnet (YAG) 50 vol % nanocomposite powders were prepared by a wet-chemical synthesis and characterized by simultaneous DTA-TG, XRD, and TEM analyses. Amorphous powders were preheated at four different temperatures (namely, 600, 800, 900, and 1215°C) on the basis of the previous characterization, and the influence of this thermal treatment on sintering behavior, final microstructure, and density was investigated. The best-performing sample was that precalcined at 900°C; however, dense bodies were just yielded by sintering at 1600°C, resulting in a micronic/slightly submicronic microstructure. A preseeding step by a fast thermal treatment of the amorphous powder as well as a fast sintering procedure of green compacts, following some literature indications, were also performed as a comparison. Finally, the previously stated thermal pretreatment of the amorphous product was coupled to its extensive mechanical activation performed by wet planetary/ball milling. This procedure was strongly effective in lowering the densification temperature, so that fully dense alumina/YAG composites, with a mean grain size smaller than 200 nm, were obtained by sintering in the temperature range 1370–1420°C.

Antonia Simone

Papers

Comparison among different sintering routes for preparing alumina-YAG nanocomposites

Characterization of LSGM films obtained by electrophoretic deposition (EPD)

Influence of some processing parameters on the production of fully dense nanocomposite materials

Different Sintering Routes for Preparing Alumina-Yttrium Aluminum Garnet Nanocomposites