Vol.2 No.2 2009

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Research paper : A strategy to reduce energy usage in ceramic fabrication (K. Watari et al.)−136−Synthesiology - English edition Vol.2 No.2 (2009) absorbs microwave, and generates heat. On the other hand, the carbodiimide (-N=C=N-) of the reactive segment firmly bonds the segments present on other particle surfaces[10].While the UV reactive binder was effective for forming ceramic sheets, ultraviolet rays did not readily reach the interior in large samples since they have short wavelengths. Because microwave possesses longer wavelengths compared to UV, the microwave reactive binder was effective for the fabrication of a large green body. The ceramic green body fabricated using these binders contained only 0.5 wt% of organic substance, and the shape could be maintained with significantly lower amount of organic substance compared to the conventional method. This is an application of surface coating and reactive trigger technologies that we nurtured as elemental technologies to realize the energy-saving process.5.3 Inorganic binder technologyNext, we investigated the inorganic binder technology using inorganic substances, for the total elimination of organic binders that express a “plasticity” function (Fig. 3). First we focused our attention to the fact that clay minerals possess plasticity. Although the expression mechanism of plasticity in clay minerals has not been clarified, it is thought to be related to: (1) effect of water film formed on the particle surface, and (2) slippage caused by the intercalation compound of clay. We focused on (1) and studied the inorganic materials that can retain water. Assuming that the mechanism whereby a new inorganic binder provides shape retention and fluidity is the same as in clay minerals where it is “the effect of water film formed on the particle surface” that does so, we looked for materials in which there was interaction between the particle surface and water, and which could retain sufficient amount of water. Hydrates chemically contain large quantities of water, and take multiple forms in accordance to the chemical bonds of the component elements. Therefore, we thought hydrates could be applied widely to various ceramics. Also, the advantages of hydrates were that most of them were of low cost and had high purity compared to clay minerals. Hence, our research started with the technology for hydration material with fluidity and shape retention properties.There is a saying that “one who controls binders controls ceramics,” and the importance of binder technology is extremely high in the ceramic manufacturing process. Therefore, the guideline for binder development is almost never publicized. Also, since the binder function involves complex factors, it is difficult to express it in physical quantities. Therefore, at the sites of research and production, for example, in investigation of extrusion technology, it is “ultimately determined by actually extruding the product on the machine.” In the first phase of the research, the definitions of binder functions (shape retention and fluidity) were set originally, and these were evaluated from the behavior of the samples formed by the extruder. Since this method was based on the observation of the extruded sample and on the relative assessment of shape retention and fluidity, it was far from an absolute assessment of physical quantities. However, it was extremely useful in narrowing down the material and seeking optimal conditions since assessment could be done easily with a small amount of material[12].For the development of inorganic binder technology, we decided to look for inorganic material that showed the same plasticity behavior as the existing organic binders and clay minerals based on the assessment of binder functions. As a result, for the expression of plasticity of alumina ceramics, we found that the addition of hydraulic alumina (-alumina) was useful. Hydraulic alumina separated out onto the surface of alumina particle as hydrate particles by hydration. It was found that the particles contained large amounts of water and had high binder functions. As a result, we succeeded in the extrusion of alumina ceramic tubes without using organic binders depending on the added amount, as shown in Fig. 5[13]. Moreover, a similar effect was seen in other hydrates, and we confirmed an expression of plasticity in various ceramics.5.4 Assessment of inorganic binder particle surfaceThe development of the inorganic binder mentioned in the previous section succeeded by hypothesizing that the shape retention and fluidity properties were due to the water film existing on the binder surface. We considered the mechanism of plasticity expression in inorganic binders as follows. Shape is retained since the ceramic particles obtain mild bonding force through the surface tension of water that accompanies the inorganic binder. On the other hand, fluidity is gained because the water film works like a bearing and lubricity occurs between the surfaces of the inorganic binder. While the effect of surface tension could be understood readily, experimental demonstration was necessary for the expression of lubricity. Therefore, our group established the measurement technology for surface-surface interactive force using the atomic force microscope (AFM) to make actual measurements of the interactive force that act between the Fig. 5 Alumina ceramics fabricated using inorganic binder technology.

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