通过sol-gel法制备出Ni颗粒表面均匀包覆尿素掺杂二氧化钛的纳米核壳颗粒Ni/(TiO_2+Urea),研究尿素的加入对颗粒的电流变行为、磁流变行为及在电场、磁场同向耦合场作用下的电磁流变行为的影响.结果表明:尿素的加入有效改善颗粒的电流变性能,剪切强度达到40 kPa(4 kV/mm直流电场),是无尿素时的10倍;尿素的加入对颗粒的磁流变性能无影响;然而尿素的加入有效改善了颗粒的电磁流变性能,在2 kV/mm直流电场与148 kA/m磁场的同向耦合场作用下,颗粒电磁流变液的剪切强度达到55 kPa,而无尿素的Ni/TiO_2颗粒的电磁流变液的剪切强度仅为45 kPa.尿素中极性基团是提高电磁流变效应的主要因素.对颗粒在电磁耦合场作用下的颗粒形貌进行观察发现,在耦合场作用下,颗粒形成更加粗而致密的柱状结构,因此导致耦合场下电磁流变液强度的提高.
The core/shell particles of Ni coated by TiO_2 and urea,Ni/(TiO_2+Urea),were obtained by the sol-gel method,and the effect of the urea on the electrorheological(ER)behavior,magnetorheological(MR)behavior,and electromagnetic theological(EMR)behavior was investigated.The results indicate that the addition of urea effectively improve the ER activities of the particle and the shear stress reaches to 40 kPa under an electric field of 4 kV/mm,which is 10 times more than that of no urea particles.The addition of urea has no effect on the MR activities;However,the addition of urea effectively improves the EMR activities of the particles,and the shear strength of EMR can reach 55 kPa under an electric field of 2 kV/mm and magnetic field of 148 kA/m.In contrast,the shear strength of the EMR of the Ni/TiO_2 particles(no urea)is only 45 kPa.Polar groups in urea are important for the EMR effect.The micmstructure observation of the particles under the electromagnetic coupling field showes that particles have thick and dense cylindrical structure,so the addition of urea can increase the strength of the EMR under electromagnetic coupling field.
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