メタル粉分散系の非線形レオロジー特性 Nonlinear Rheological Properties of Metal Powder Suspension
本研究では分散剤L-95を用い, 鉱油中にメタル粉を分散させた試料について, そのレオロジー的性質を検討した。定常流粘度測定においては, Shear-thinning挙動が見られたが, せん断速度の中間域で一時的に平坦部が現れた。動的粘弾性測定では, 定常せん断との重畳により, ひずみとひずみ速度が大きく影響することが分かった。これらのレオロジー的挙動は, フロックモデルを用いて説明可能であることが示された。
Rheological properties of disperse system of magnetic metal powder treated by dispersant (L-95) in mineral oil were studied. In a steady shear measurement, shear -thinning behavior was observed, however, a plateau region appeared in the region of middle shear rate. In a stress growth measurement, the times when the maximum value of stress appeared are almost the same for all samples. The longer the rest period, the larger the maximum value of stress is. In dynamic viscoelastic measurements, the values of storage modulus were almost constant irrespective of frequency at small strain amplitude up to 5%. However, with increasing strain amplitude, the value of storage modulus decreased and a minimum in the frequency dependence of storage modulus was observed in lower frequency region. These phenomena are associated with breaking down and formation of the flocculated network structure formed by metal powder in shear field. Viscoelastic values decreased with increasing strain and the strain amplitude at which the value began to decrease reduced with the concentration. The effects of steady shear flow on dynamic measurements for the suspensions having flocculated structure were studied by transient unidirectional shear flow experiment such as the parallel superposition of steady shear flow and small amplitude oscillatory shear. Storage modulus decreased with increasing strain amplitude in high strain region. The higher the concentration, the smaller was the strain region in which the non-linear behavior was observed. The dynamic viscosity took a maximum tentatively prior to decrease, because the rupture of the flocculated network structure caused an increase in the internal friction. The recovery of the network structure after cessation of steady shear was examined by time dependence of storage modulus. In the initial time region the value of storage modulus increased, however the value decreased rapidly after reaching a maximum and attained an equilibrium for larger strain amplitude. This result can be explained by alteration of network structure formed by metal powder.
色材協會誌 71(9), 548-554, 1998-09-20