Eco-friendly alumina suspensions for tape-casting process
Introduction
Tape casting process is widely used in the ceramic industry in order to produce thin and flat ceramic tapes for microelectronics [1], [2] or membranes for gas separation [3], [4]. The suspensions used in the tape casting process are basically composed of a ceramic powder, a solvent, a dispersant, a binder and a plasticizer. The binder and plasticizer are usually polymers coming from the petrochemical sector and they may present risks for the operator health or the environment (in particular with organic solvents).
Due to the REACH regulation in Europe (Registration, Evaluation, Authorisation & restriction of Chemicals), the use of some of these products could be forbidden in the near future. In this respect, the preparation of aqueous suspensions formulated with a binder based on a methylcellulose compound was previously described by A. Kristoffersson et al. [5], T. Chartier and A. Bruneau [6] or D. Hotza and P. Greil [7].
The aim of this work is to go further in the sustainable approach in order to substitute all the additives coming from petrochemicals by biosourced additives which do not present risks for the operator’s health. However, the rheological properties of the ceramic suspension must be adapted to the tape casting process. The green tapes must be easily handled without cracks or bubbles, and the sintered tapes must be dense.
This work focuses on the preparation of alumina suspensions with some biosourced additives for the tape casting process. First, the selection of dispersants has been performed by a sedimentation test of alumina suspensions. Pectin, which is widely used in the food-processing industry [8] has been used as binder. Pectin presents interesting gelation properties and has not yet been used in the ceramic processes. Finally the glycerol has been used as a plasticizer [7]. The influence of each organic additive on the rheological behavior of ceramic suspension has already been studied by Moreno [9], [10] or Hotza and Greil [7]. In a similar way, a particular attention is given in the first part of this paper on the role of the introduction order of the different organic additives on the physicochemical properties of the suspensions. Curiously, the influence of the introduction order of the different organic additives are scarcely studied in the literature. The second part of the paper presents the rheological behavior of the suspensions elaborated from the bio-polymer additives and the characterization of the green and sintered tapes obtained with these suspensions.
Section snippets
Physicochemical study of aqueous ceramic suspensions
This first part focuses on the role of binder and dispersant on the physicochemical characteristics of the aqueous alumina suspensions.
Green and sintered tapes
This second part is dedicated to the preparation of green and sintered tapes by tape casting. The aqueous alumina suspensions were formulated with the protocol 1 and with the ammonium lignosulfonate as a dispersant and the pectin as a binder.
Conclusion and perspectives
This work shows that dense ceramic tapes could be obtained via a water-based tape casting process using eco-friendly additives. The green tapes can be easily handled and carried. The sintered tapes have a good general aspect and the relative densities of the sintered tapes shaped with biosourced additives are close to the relative densities of tapes shaped with conventional additives [21], [22].
The ammonium lignosulfonate extracted from the maritime pine of Landes (France) seems to be a
Acknowledgements
The authors wish to thank Stephane Laurent and Valentina Rousseau, respectively from the Rettenmaier society and the Tembec society for their availability and for having provide samples of different products, Marguerite Biena for her expertise in rheology measurements and, Yann Launay and Patrice Duport for their SEM experiments.
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