颗粒粒度分布对高固相含量氧化铝浆料流变性能的影响

EFFECT OF PARTICLE SIZE DISTRIBUTION ON THE RHEOLOGICAL BEHAVIOR OF DENSE ALUMINA SUSPENSIONS

制备了低粘度、高固相含量氧化铝悬浮浆料,并将其有效地应用于原位凝固胶态成型工艺中。将中位粒径尺寸分别为0.3μm和2.2μm的2种氧化铝以不同级配混合后制得的粉体配制浆料。研究了氧化铝粉体颗粒度分布对高固含量氧化铝悬浮浆料流变性的影响。实验结果表明:混合粉体制成的悬浮液表现出不同的流变性。由细颗粒粉体制备的浆料表现出剪切稀化行为,但随着粗颗粒含量的增加,浆料逐渐向剪切厚化转变,依次呈现出Casson型、Bingham型、Herschel-Bulkey型3种不同的流变学特征,并得出了各自相应的流变学模型方程。讨论了流变模型转变的原因及其对胶态成型工艺的影响。粉体经级配后,当中位径d50<1μm时,浆料呈现出触变性,并且触变性随着颗粒度的减小而增大。体积分数(下同)为58%固相含量的级配浆料的粘度较50%固含量的未级配浆料下降了7至10倍,明显改善了浆料的流变性,适合于原位凝固胶态成型工艺。

The less viscous dense alumina suspensions were obtained for the effective application in the in-situ colloidal forming process. The effects of the particle size distribution （PSD） of alumina on the rheological behavior of dense alumina suspensions were investigated. Two alumina powders with different particle sizes （d50 ≈ 0.3 and 2.2 μm） were mixed to obtain suspensions with various bimodal PSDs. The results show that the suspensions of the mixtures demonstrated different rheological behaviors. The suspension made from fine particles show a shear-thinning characteristic, and as the fraction of the coarse particles in the mixtures is increased, the suspensions show a transition from shear-thinning to shear-thickening and the rheological characteristic varies, following the Casson, the Bingham, and then the Herschel-Bulkey model in sequence. Three rheological model formulae for the above characteris- tics are obtained. The reasons of the transition of rheological curve forms and its effect on colloidal forming are also investigated. The suspensions of the mixture with a median particle size below 1 μm has a thixotropic property and the thixotropy increases as the particle size decrease. It is also found that the viscosity of the mixed suspension with the bimodal PSDs at 58% （in volume fraction, the same below） is 7 to 10 times less than that of the suspensions with the monomodal PSDs at 50 %, and it is suitable for the in-situ colloidal forming process.