Vol.2 No.2 2009

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Research paper : A strategy to reduce energy usage in ceramic fabrication (K. Watari et al.)−135−Synthesiology - English edition Vol.2 No.2 (2009) defeated. Therefore, it is important for the developed binder to have almost the same function as the conventional binder. Therefore, we considered a binder technology using a material with high binder function but which can be used at fewer amounts.5 Development technology and research result5.1 Extraction of key technologyFigure 3 summarizes the functions of the binder. The functions can be roughly categorized into two types. First is to firmly bond the particles and to stably maintain the shape (shape retention). The ceramic green body must have a certain level of strength. One of the important functions of the binder is to maintain the given shape against the weight of the green body itself as well as against the strain of handling at the site of production. The binder with such function is used in the fabrication of ceramic films, sheets, and large products. Second is for the binder to give both fluidity and shape retention to the particles assembly (plasticity). That is, when the raw powder and the binder are mixed, the particles are bonded together weakly through the binder and retain shape (shape retention). Moreover, the shape is changed by simply applying certain amount of force (fluidity), and the shape must be maintained when the force is removed (shape retention). Plasticity is a function required in the production of complexly shaped products such as in extrusion and injection molding.We investigated the materials with high binding functions such as shape retention and plasticity, while aiming to reduce the amount of organic material. Moreover, other than the binder function, we considered properties that are sought in binders in general, such as: (1) low cost, (2) no reaction to raw powder, (3) being soluble in water and solvent, (4) ashes not remaining after decomposition and evaporation, and (4) decomposition gas not being harmful or corrosive.5.2 Reactive binder technologyWe selected the method of reducing the amount of organic binder by adding the same function as the existing organic binder used in the manufacturing line to very small amounts of organic substances. First, we developed a new binder technology where the “shape retention” function (Fig. 3) is expressed with minimum amount of organic material. Highly reactive organic molecules that would be binders were anchored onto the surface of the ceramic raw particle in a form of a film. The whole partilcle assemblies were formed into desired shapes, the reaction trigger (external stimulus) that excites chemical reaction was applied, and the molecules of the organic film layer were chemically bonded, to create the ceramic green body in which the particles were bonded together firmly. Figure 4 shows the concept of the technology to reduce the amount of organic binders. Unlike in the conventional forming method, the shape of the green body could be maintained efficiently with only a small amount of binders, because of the structure in which the binder molecules linked the ceramic particles with strong chemical bond. Also, partial aggregation of the binder could be prevented since the binder molecules were fixed on the particle surface in film form, and therefore the amount of the organic binder could be reduced.In this forming method, it was not desirable for the particles to bond before the particle assembly formed the desired shape. Therefore, the chemical bond was introduced at an arbitrary moment by using external stimulus as a reaction trigger. Irradiation of electromagnetic waves (ultraviolet rays[9], microwave[10]) and heating at 100 °C[11] were used as reaction triggers. When ultraviolet rays were used as reaction triggers, we succeeded in fabricating a solid body, as strong interparticle bond occurred by coating the ceramic particles with amino groups and phenyl azide groups[9]. For organic materials that react with microwave, we conducted experiments by referring to past reports, but were unable to reproduce them. Therefore, we looked at water, a high dielectric loss substance that absorbs microwave, and used water-soluble carbodiimide with water as a microwave reactive binder. The oxyethylene (-C2H4O-) that composes the water-soluble carbodiimide becomes the hydrophilic segment, Fig. 3 Functions of binder. Fig. 4 Fixing of organic molecule and application of reaction trigger to reduce the amount of organic binder.Shape maintenance(1)Strong bond(1) Weak bond (shape retention)(2) Bond breaking (fluidity)(3) Rebonding (shape retention)Plasticity (fluidity, shape retention)CreepForceForceCeramic particleReactive binder moleculeInterparticle bond is formedHighly reactive organicmolecules are fixed onto the ceramic particle surface.Reaction trigger (external stimulus) that excites chemical reaction is applied.

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