Growth Reactions of Potassium Titanate Fibers by Slow-cooling Calcination Method

Abstract

The growth of potassium titanate fibers was studied by a new growth technique called “slow-cooling calcination method”. By this method, a specific composition is incongruently melted into a solid phase and liquid phase, and then is slowly cooled to a temperature region below the incongruent-melting temperature. Fibrous crystals are grown by a incongruent melt-association reaction between the solid and liquid phases during the cooling precess. In the system K₂Ti₂O₅-K₂Ti₆O₁₃, a stating material having the n value between 2<n<6 in the K₂O⋅nTiO₂ formula was incongruently melted into a liquid phase and K₂Ti₆O₁₃ solid phase at above the incongruent-melting temperature (1114°C±15°C) of K₂Ti₄O₉, and then was slowly cooled to a temperature region below 1114°C. During the slow-cooling process, the incongruently melted K₂Ti₆O₁₃ solid phase and liquid phase again reacted to associate. This association reaction plays a very important role to grow potassium titanate fibers, especially K₂Ti₄O₉ fibers. Relatively long fibers were grown in the mixed fibers of K₂Ti₄O₉ and K₂Ti₂O₅ when a starting material of K₂O⋅2.8TiO₂ composition was calcined at 1150°C for 4h, and then was slowly cooled to 950°C with a rate of 16°C/h, and was followed by quenching to room temperature. Consequently, the K₂Ti₄O₉ fibers in them were grown by an incongruent melt-association reaction, and the K₂Ti₂O₅ fibers were crystallized from the liquid phase during the quenching process. The growth of K₂Ti₄O₉ fibers was mainly depended upon three factors of starting composition, calcination temperature and cooling rate, and furthermore was also promoted by repeating the incongruent melt-association reaction.