Preparation of Multi-layered Ceramic Particles

陶瓷颗粒的微观结构或表面形态取决于制备工艺和条件，因此其性能也因此而不同。利用这种柔性，可以控制颗粒的微观结构，制备具有多层或定制微结构的陶瓷颗粒。本研究旨在阐明超声喷雾热解陶瓷颗粒的微观结构对实验条件的依赖关系。首先采用超声喷雾法制备了赤铁矿颗粒。没有添加添加剂(甘油)的溶液中的颗粒表面光滑。较大的颗粒是中空的，外壳较厚，而中等大小的颗粒是致密的。以乙二胺四乙酸二钠为络合剂，乳酸钙、醋酸钙、正磷酸二氢铵水溶液为原料，采用超声喷雾热解法制备了羟基磷灰石颗粒。颗粒的表面形貌取决于实验条件，而焙烧良好的颗粒表面比较粗糙。采用超声喷雾热解法制备了羟基磷灰石/赤铁矿摩尔比为1/0.5~1/9的羟基磷灰石-赤铁矿复合粒子，平均粒径为0.2~0.6um。当HAP含量较大时，表面起皱或充满韧窝，而赤铁矿含量较高的粒子表面光滑。对于较大的颗粒(直径0.8微米)，确定了壳-核型双层结构。这种层状结构是由于Ca-EDTA螯合键的断裂而在液滴表面引发HAP沉淀而形成的。

The microstructures or surface morphology of ceramic particles depend on the preparation procedure and conditions, and thus their properties vary, accordingly. With utilizing such flexibility one can control the microstructure of the particulate and prepare ceramic particles which have a multi-layered or tailored microstructure. This study aims to clarify the dependence of the microstructure of of the ceramic particles through ultrasonic-spray pyrolysis on the experimental conditions.Hematite particles were first prepared by ultrasonic spraying aqueous solutions ferric nitrate. The surface was smooth for the particles out of the solutions without additives (glycerol). Larger particles were hollow with a thick shell, while medium sized particles were dense. The solutions with the additive yielded hollow particles with a thin shell, and dimples were observed on the shell which were caused by the release of decomposed gas out of the particles.Hydroxyapatite (HAP) Particles were prepared by ultrasonic spray-pyrolysis of aqueous solutions of calcium lactate or acetate, ammonium dihydrogen orthophosphate with EDTA as the chelating agent. The surface morphology of the particles depended on the experimental conditions while the rough surface was observed for the well-calcined particles. The particles were about 0.5mum in diameter.With those aqueous solutions HAP-hematite composite particles were prepared through the ultrasonic spray pyrolysis where the molar ratio HAP/hematite was 1/0.5-1/9. The average diameter ranged from 0.2 to 0.6mum. With larger HAP content the surface was wrinkled or dimple-full, while the smooth surface was for the particles with greater hematite contents. A shell-nuclear type double layer structure was confirmed for larger particles (>O. 8mum in diameter). Such layered structure was built by initiating the HAP precipitation on the surface of the droplets due to breakage of Ca-EDTA chelate bonding.