Preparation and Electrorheological Properties of Anhydrous Aluminum Orthophosphate

We have studied the process and products of thermal dehydration of highly dispersed monoclinic AlРO4⋅2Н2О prepared by crystallization from an aluminum phosphate solution at 95–97°C and demonstrated the influence of isothermal or polythermal heat treatment on the formation of AlPO4 polymorphs similar in structure to α-quartz or tridymite. The formation of these phases has been shown to be related to changes in the oxygen coordination of aluminum as a result of the detachment of highly polarized molecules of water of crystallization in the composition of AlРO4⋅2Н2О. We have assessed the electrorheological (ER) activity of AlPO4 as a disperse phase of electrorheological fluids, with a weight fraction from 10 to 20%, and found out how AlPO4 preparation conditions influence the shear stress of the electrorheological fluids in electric fields from 3.5 to 4.0 kV/mm. Suspensions containing tridymite AlPO4 particles prepared under isothermal conditions have been shown to exhibit a stronger ER effect, at a level from 420 to 620 Pa. The ER activity of AlPO4 has been shown to increase with increasing heat treatment temperature and time, which is attributable to the formation of a more defect-rich particle surface due to intrinsic thermal disorder.