Preparation of ceramic piezoelectric effect of dispersants
The institute with PMN-PZT piezoelectric ceramic powders were prepared by solid-phase method, dispersant ammonium citrate (TAC) and polymethyl methacrylate ammonium (PMAA-NH4). Settlement experiment 25ml graduated cylinder preparation solid content 4% (volume fraction), the different types and amount of dispersant suspension each 20ml, ultrasonic dispersion 0.5h, then put it aside stale 48h, measuring sedimentation volume. Using NDJ-1 rotary viscometer viscosity; PH meter PH value was measured by PHS-25-type number; micro structure and morphology before and after the powder dispersed with Phlips SEM.
1 dispersants affect the stability of the slurry
Ceramic powders with large specific surface area due, in liquid medium prone reunion. Especially when a high amount of solid phase content, the average distance between the particles decreased, the probability of particle collision and agglomeration substantially increases so that the dispersibility of the ceramic paste affect the stability and uniformity. In order to improve the performance of the ceramic slurry to obtain a slurry suitable for molding an injection molded, the main addition of a suitable dispersing agent, but because the inorganic dispersant such as ion Na +, PO4 ^ 3, etc. will have properties such as electrical conductivity of ceramic, the dielectric constant and other adverse effects, such an inorganic dispersant is restricted within a certain field. And an inorganic dispersant as compared to small organic molecules and the polymer dispersing agent volatile at high temperature calcination, the ceramic performance will not be adversely affected. Therefore, this experiment, the ammonium citrate (TAC) and polymethacrylic acid amine (PMAA-NH4) Effect of two polyelectrolyte dispersing agent, a dispersing agent, the stability of the slurry as shown in Fig.
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As apparent from Table 1, except that the dispersant in the slurry influence of sedimentation volume is the same, i.e. with the increase of the amount of dispersant, the sedimentation volume increase after the first reduction Seoul, there is a minimum value. TAC terms of dispersants, when an amount of about 7.5% (volume fraction) around, get a minimum sedimentation volume 1.8ml; while PMAA-NH4 amount at 5.6% (volume fraction), the smallest settlement. The reason why the dispersant slurry sedimentation volume will have such influence is mainly due to the low amount of the dispersant, the dispersant is not effective particle surface covered by the Brownian motion of the particles due to collision, so that the dispersant not adsorbed on the particle surfaces occurred paste , agglomeration, so dispersion stability is poor; increasing the amount of dispersant, help to increase the coverage of the particle surface thereof, so that the dispersion stability of the system increases; but the dispersant added is too large, the particle surface has been adsorbed amount reached saturation, because excess free molecule of the dispersant and would lead to crosslinking between the particles in the flocculation, so that the dispersion stability deteriorates.
2 dispersant impact on the viscosity
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Figure 2 is a dispersant and the PMAA-NH4 TAC slurry viscosity curves, and the influence of the dispersant on the stability of the slurry is substantially the same, within a certain range increase in the amount of the dispersing agent, the viscosity of the slurry continues to decrease, and the lowest value. However, when the amount of dispersant is too much or too small, the viscosity of the slurry will increase, indicating that there is an amount of the dispersing agent is the optimum range. Adding an appropriate amount of dispersant, when the surface just covered with a layer of solid particles form a monolayer adsorption electrolyte lowest viscosity. When the amount of dispersant is low, its surface coverage at a lower powder, powder surface and some parts of the positively charged, negatively charged, some parts of the two neighboring particles with different charges attract each region, resulting in bridging effect, will lead slurry flocculation. When too much dispersant added, the ionic strength of the excessive compression of electric double layer, reduces the electrostatic repulsion between the particles, while an excess of free molecular chain is prone to bridging gaps or flocculation, so that the stability decreased, the viscosity of the slurry increase. Two dispersants reach the required minimum viscosity value added in different amounts, TAC of approximately 7.5% -8.0% (volume fraction), and PMAA-NH4 amount is 5.2% - 5.8% (volume fraction).
