A Study On The Preparation Of Potassium Titanate Whiskers Using Wet-chemical Route

Whiskers of potassium titanate,often expressed as K₂O.nTiO₂(whereinn=1,2,4,6,8),are artificial fibers with good mechanical performance.They arecommercially produced by solid-state calcination methods. The calcination methodsare often complicated and energy-consuming processes,and the quality of theirproduct whiskers are usually not easy to be controlled. However, using hydrothermalmethod can not synthesize the K₂Ti₆O₁₃ whiskers in one step. For the presenthydrothermal methods, the major disadvantage is their high reaction pressure inpreparation of potassium titanate whiskers.A new wet-chemical route was employed to prepare the potassium titanatewhiskers under atmospheric and morderate hydrothermal pressures in this work. Theas-synthesized products were characterized and the hydrothermal reaction mechanismwas discussed.The results show that K₂Ti₆O₁₃ whiskers can be obtained in two steps, firstly theirprecursors were synthesized in a concentrated KOH solution under atmosphericpressure and then calcining the precursors convert them into the whiskers.Comparedwith the direct calcination methods, the calcinations of the precursors was conductedin a rather low temperature(550℃).The results demonstrate that the synthesisconditions greatly influenced the type, crystallinity and morphology of precursors.Therefore,adjusting the synthesis conditions can improve the morphology andproductivity of K₂Ti₆O₁₃. The effects of the titanium source and reaction conditions on the hydrothermalreaction rate, product phase, and whiskers morphology were investigated. Hydratedtitania, anatase TiO₂ and rutile TiO₂ were used as the titanium sources in this workand their activity with KOH decreased in turn.The results show that using hydratedtitania as titanium source can not obtain K₂Ti₆O₁₃ whiskers with good morphology. Incontrast, using anatase TiO₂ produced uniform K₂Ti₆O₁₃ whiskers with a length of10～20um and a diameter of 200～700nm.Initial KOH concentration, molar ratio of K₂O/TiO₂, annealling parameters, andcooling mode significantly affected morphology of the as-synthesized whiskers.Using anatase,an optimal synthesis condition is:10%(wt.%)KOH solution;K₂O/TiO₂molar ratio of 5;annealing temperature and time of 300℃and 5 hours, respectively;natural cooling with the furnace, etc.. The reaction pressures varied from 70 to 80 atmduring these tests.A rhombic potassium hexatitanate with formula ofK₂Ti₆O₁₃·0.85H₂O was prepared under the optimum conditon and the whiskers grewalong the [110] direction.The formation mechanism of K₂Ti₆O₁₃ under the optimized synthesis conditionwas discussed. It was suggested that anatase TiO₂ particles disolved during the initialstage from ambient temperature to 250℃,and then, at 250℃-300℃,crystallization ofK₂Ti₆O₁₃ ocurred accompanying with the dissolution of TiO₂. During the annealingperiod at 300℃, a simultaneous crystallization and re-crystallization process ofK₂Ti₆O₁₃ took place,and the disslved K₂Ti₆O₁₃ continueously crystallized during thefollowing cooling stage.The hydrothermal method presented in this study is a simple process,it can beoperated at a more moderate condition.The morphology of the as-prepared whiskerswas good controlled.