Study On Better Conditions For Mg₂B₂O₅ Whisker Growth And The Growth Process

In order to solve the problems met in industry test of High-Temperature flux method preparation of Mg₂B₂O₅ whisker, the main work has been done in this dissertation was as follows:General methods and mechanisms for whisker growth, different growth methods of Mg₂B₂O₅ whisker, separating, purifying and dispersing techniques have been comprehensively reviewed. Then we did some modifying work to abandoned whiskers with impurity by using ultrasonic dispersing and resintering with raw materials. We optimized the growth conditions for fine Mg₂B₂O₅w and analyzed the growth process for Mg₂B₂O₅w in the system of MgCl₂·6H₂O-Na₂B₄O₇·10H₂O-KCl. Finally, we find out the reason for impurity forming and the resource of non-free Cl in industry-grade products. Main conclusions are as follows:1. Ultrasonic dispersing has some effects on whiskers with impurity; and resintering with raw materials can not work effectively.2. High boron portion can assure the deep growth of whisker. When the ratio of B and Mg is B:Mg(mol)=3:1 and the temperature was kept between 750-850℃, good whiskers with uniform morphology and large L/D ration can fully and moderately be grown.3. When preparing Mg₂B₂O₅ whiskers, if conditions are not controlled carefully, there inevitably occurs an undesired phase-boracite Mg₃B₇O₁₃Cl, which undoubtedlybrings impurities into final products. And it just finds out why abundant Cl appeared when there was no free Cl in industry-grade whisker products. 4. SLS(solid-liquid-solid)mechanism based on dissolving-depositing process has been proposed, which can explain clearly how Mg₂B₂O₅ whiskers are formed.