Research On Solidify Characteristic Of Colloidal Process And Its Application Technology

Colloidal process is a novel technology in ceramic molding. The ceramic slurry which is consisted of ceramic powder and other media (water, organic matter, etc.) is solidified by either the chemical reaction and evaporation of medium in the solvent, or the acting force between particles. The near-net dimension and homogeneous green body can be obtained by colloidal process. This paper is aimed to study the composition of colloidal systems, improve the mechanical properties of green body and make this technology operating friendly. Moreover, the paper also presents the preparation of electronic ceramics with utmost scales and complex shapes using colloidal technology. Finally a new technology named direct writing based on two colloidal systems is discussed, 2-dimensional thick films and 3-dimensional materials is prepared by direct writing.In this paper, the effects of different particle size and distribution on the rheological characteristics of Ba_0.7Sr_0.3TiO₃ suspensions have been studied. The effects of pH value, the amount of dispersant and solid loading on the viscosity of slurry have been discussed. The high solidloading, low viscosity slurry is prepared.Gel-casting is introduced as one of the most classic colloidal in-situ technologies. Based on the dynamics of free radical polymerization, the paper discusses the affection of various parameters on both polymerization process and related 3-dimension net structure. Relationships among polymerization process, internal structure of gel and mechanical properties of green body are presented separately. By optimizing fabricating parameters, the mechanical properties of green body are improved, so as to make gel-casting process more reliable. The paper gives detailed description on the principle of pores generation during gel-casting process for slurry preparation. Then, a new method called (vacuum+stirred+ultrasonic) is presented to remove pores in slurry, not only by floating the pores, but also making the pores expand to explode. The proposed method improves the properties of both green body and sintered body significantly. Below the vitrification point, polymers can be reshaped by colding drawing, so as to make green body contract itself. With this principle, green body can be pre-processed using cold isopressing to increase its density. The bending strength reaches 32.8MPa and the density is 98.2%.A drying apparatus with net-shaped jig is designed for large-scaled flaky body preparation. With this method, deformation rate is largely reduced, from 50% to 3%. Large-scaled PZT piezoelectric ceramic which has diameter up to 16cm is obtained by gel-casting. The uniformity coefficient of dielectric constant is 5.6%. This paper also presents the preparation of 1-3 type BST/PMMA compound ceramics by gel-casting. Because of the different hear expansion coefficient between PMMA and BST, the composite subjects tensile strength as the applied electric field parallel to voids and subjects compressive stress as the field normal to voids. The composite thus exhibits anisotropic properties in ferroelectric-paraelectric phase transition point and filed induced phase transition. Compared to bulk ceramic, the dielectric constant of composite is sharply reduced and the dielectric tunability decrease slightly, which shows that this composite is a good candidate for tunable devices. During the preparation of ZnO thick film using aqueous gel tape casting, the brittleness of thick film can be improved by doping glycerol. The ratio between tensile strength and elastic modulus increase from 0.004 to 0.022, and the solid loading of ZnO thick film is up to 75.5wt% compared to 60wt% of custom water-based tape casting, both of which show the improved operability of gel tape casting. The varistor voltage of multilayer ZnO varistor is 153V, the leakage current is 2μA, and the nonlinear coefficient is 21.The PZT thick films have been prepared by direct writing. When the penpoint height is 30μm, the line is smooth. Different thickness from 30μm to 250μm canbe obtained by controlling writing velocity. By adjusting the distance between lines, the surface roughness of thick film is 0.73μm which is smaller than 1.22μm of screen printing. The 70μm thick film is sintered at 1160℃for 1h. The dielectric constant is 750, dielectric loss is 0.012. The electric property of thick film whith is prepared by direct writing is very similar to screen printing. Compared to screen printing, the random 2-dimensional pattern can be prepared without mask.Single phase composite solution is prepared by oppositely charged polyelectrolyte PAA-PEI-water compound system with concentration 50wt% and ratio 12:1 of PAA and PEI. Using direct writing technology, this single phase composite solution is deposited in isopropanol solution with concentration 80wt%, and it is solidified instantaneously. In this case, the relative viscosity of polyelectrolyte gel can reach 5*10⁴. Materials with 3-dimension structure can be obtained by this method.