資 源 と素材(Shigen-to-Sozai) Vol.109 p.593-600(1993) 論文 The Role of Compaction in Agglomeration in Liquid and Formulation of Scale-up Equation* by Tsuyoshi HIRAJIMA1, Winston GUINTO2 Masami TSUNEKAWA3 and Masayoshi NAKAMURA4 The effects of agitation intensity and amount of bridging liquid on agglomerate formation in agglomeration in liquid were experimentally investigated. An increase in agitation intensity advanced the compaction of agglomerates, reduced the porosity and changed the saturation degree which is the ratio by volume of the bridging liquid to the pores of an agglomerate. It was observed that the process of agglomerate growth depended on the changes in porosity. Based on this observation, the effects of agitation intensity on the process of compaction and changes in porosity were quantitatively elucidated and a scale-up equation was formulated. In addition, model agglomerates of the zirconia powder were cold isostatically pressed to investigate the influence of green agglomerate porosity on the density of sintered agglomerates. The results showed that the agglomerates produced by agglomeration in liquid must have porosi- ties less than 0.51 in order to achieve high density and strength after sintering. To achieve this objective, the formulated scale-up equation was utilized to design a batch-type horizontal agglomerator that can provide the agitation energy required to produce agglomerates with porosities below 0.51. The newly designed agglomerator was successfully tested in the production of highly dense microspherical agglomerates of zirconia. KEY WORDS: Compaction, Scale-up, Agglomeration in Liquid, Zirconia Microspheres 1.Introduction High performance micro-spheres offer a number of indus- trial applications. Mixing, dispersing and ultrafine grinding of fine ceramics, super conducting materials, etc. are some applications that necessitate the use of micro-balls. However, conventional methods are hardly capable of producing micro- spheres with diameters less than 500ƒÊm. The authors previ- ously reported that it is possible to produce high performance dense micro-spheres of zirconia by the methods of agglomera- tion in liquid1)2). In the production of microagglomerates, understanding the mechanism of agglomerate formation is very important. This knowledge is a key to the development of a scale-up equation that can be utilized to design large capacity agglomerators. Until now, scale-up of agglomerators have been based mainly on the experience of engineers and references are seldomly available. It is known that compaction is important for agglomerate formation as reported by Hira- jima et al.3), Kawashima et al.4) and Capes et al.5). However, the effects of bridging liquid and the agitation intensity on agglomerate formation based on the compaction process have never been quantified which prevented their application in the development of a scale-up equation. In this paper, agglomeration tests are conducted to elucidate the effects of agitation intensity and the amount of bridging liquid on the process of agglomeration in liquid. The results are theoretical- ly discussed based on the compaction process. The results from the agglomeration experiments are used in the derivation of a scale-up equation and agglomerate porosity equation. The formulated equation is applied in the scaling-up of agglom- erator. The final porosity of the green agglomerates affects the density and strength of sintered agglomerates. The porosity of a green agglomerate needed to ensure high density and strength after sintering is quantified by sintering model ag- glomerates shaped as disks. The result is used to determine the required agitation intensity and amount of bridging liquid to produce highly dense agglomerates. The calculated amount of bridging liquid and impeller rotational speed are used during the testing of the newly designed agglomerator. 2. Experimental 2.1 Agglomeration test The starting material used was a commercially available zirconia stabilized with 2.6 mole % of Y203. A typical lot analysis (weight percent) of this material was 4.58 Y2O3, 0.02 CaO, 0.03 Na20, and the balance was ZrO2. The equi- librium moisture content of this material was approximately 0.3%. The specific surface area was 6.76m2/g and the average particle size was 0.45ƒÊm. The size distribution of this powder fits the Rosin-Rammler distribution with absolute size con- stant De=0.635 and the distribution constant n=1.075. The suspending liquid used was an aliphatic hydrocarbon *Received Noveml)er 11 ,1992:accepted for publication March 2, 1993 1～3.Faculty of Engineering,Hokkaido Univelsity,Kita-ku,Sapporo 060,Japan 1.Instructor, Dr. 2.Graduate Student 3.Associate Profbssor, Dr. 4.Showa Shell Sekiyu, K.K., 3-2-25, Kasumigaseki, Chiyoda-ku, Tokyo,100 資源 と素 材 109(1993) No.8 593 <19>