Synthesis And Properties Of La-Ti-O ER Fluid And A Study On Evaporation Of ER Fluids

A new type of La-Ti-O electrorheological ?ER? materials with high ER performance were synthesized using a co-precipitation method, and they were able to meet the needs of practical applications. The particles were irregular particles with 100nm in diameter, and the La-Ti-O/silicone oil ER suspension exhibits extremely high ER effect in DC electric field. The yield stress of La-Ti-O/silicone oil ER sample with 60% particle volume fraction is over 150kPa in 5kV/mm DC electric field and the current density is about 6?A/cm2. The yield stress of La-Ti-O/silicone oil suspension is proportional to the electric filed strength, which fits the character of the polar molecule dominated electrorheological ?PM-ER? fluids. The ER effect fell when the particles were heated over 100?, and the yield stress of 120? heated sample in 5kV DC electric field is only one fourth of that of the 80? heated samples in same conditon.The TGA-FTIR analysis shows that La-Ti-O particles decompose and release CO₂ and H2O molecules after the heat temperature rises over 100?, which indicates the particles lost hydroxyl and carboxyl polar groups during the decomposition process. The polar groups on the particle surface make an important contribution to the high ER effect of La-Ti-O material.Ca-Ti-O/silicone oil ER fluids and TiO₂/silicone oil ER suspension were brought in to study the evaporation enhancement phenomenon of the PM-ER fluids, and the mechanism of evaporation enhancement, which provided theoretical basis for attenuating or eliminating evaporation enhancement effect and the effect, was analyzed.In experimenting the particles concentration, the area of gas-liquid interface, viscosity of silicone oil and environmental temperature were analyzed systematically. The evaporation enhancement is caused by the Kelvin effect. The silicone oil was absorbed on the surface of La-Ti-O particles which located at the gas-liquid interface to form nanometer size convex liquid surface, and the saturated vapor pressure of silicone oil on convex surface is raised up remarkably compared to the flat liquid surface, and lead to the evaporation enhancement effect in the PM-ER fluids. Increasing particle concentration or enlarging gas-liquid interface will increase the number of convex surface and speed up evaporation of silicone oil. The high viscosity silicone oil suspension loses less dispersant than low viscosity samples in the same time, but of the evaporation enhancement effect is much stronger in the former. The evaporation rate will rise with the increase of environmental temperature owing to the higher saturated vapor and lower viscosity of silicone oil at high temperature, but evaporation enhancement effect will reduce. Sealing the suspension during storage or transportation is the most effective measure to attenuate or eliminate evaporation enhancement effect.A novel pectinated electrodes plate was fabricated by integrating positive and negative electrodes parallelly and alternately on a single plate, and the edge electric field of the electric field was used to induce ER effect. The pectinated electrodes plates could applies external electric field with only a single plate and make a breakthrough at the limit that ER fluids require two plates to generate electric field which induces the ER effect, and enlarge the field of application of ER Fluids. The ER responding of Ca-Ti-O/silicone oil suspension under the edge electric field of the pectinated electrodes was studied, and the relationship of yield stress and structure of pectinated electrodes was obtained. According to the calculation of the electric potential distribution in the outside region of electrodes, the electric field near the plate varies periodically, and the strength and distribution of the electric field are determined by the electric potential between the positive and negative electrodes and the structure of the pectinated electrodes plate. The ER particles form chain structure along the electric field line under electric field. In the region near the insulating nylon, particle chains are nearly parallel to the plate, and the length of chain is short, also the interaction between adjacent particles is strong, thus the yield stress is high. With the increase of distance against the plate, particle chain is no longer in parallel with the plate and the length enlarges, also the interaction between adjacent particles becomes weakened comparatively, thus the yield stress decreases. In the region near the electrode, particle chains are approximately vertical to the plate, which cannot form effective chain between adjacent electrodes. In conclusion, the edge field between the electrodes makes a critical contribution to the ER effect.