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过程和条件，因此它们的性质也相应变化。利用这种灵活性，可以控制颗粒的微观结构，并制备具有多层或定制微观结构的陶瓷颗粒。本研究旨在阐明超声-喷雾热解陶瓷颗粒的微观结构与实验条件的关系。采用超声波喷涂硝酸铁水溶液制备了赤铁矿颗粒。无添加剂（甘油）的溶液中颗粒表面光滑。较大的颗粒是中空的，外壳很厚，而中等大小的颗粒是致密的。添加了添加剂的溶液产生了空心颗粒，其壳薄，在壳上观察到由颗粒释放出的分解气体造成的凹痕。以EDTA为螯合剂，以乳酸钙或乙酸钙、正磷酸二氢铵水溶液为溶剂，采用超声喷雾热解法制备羟基磷灰石（HAP）颗粒。颗粒的表面形貌与实验条件有关，而煅烧良好的颗粒表面粗糙。颗粒直径约0.5 μ m。采用超声喷雾热解法制备HAP-赤铁矿复合颗粒，HAP/赤铁矿的摩尔比为1/0.5 ~ 1/9。平均直径为0.2 ~ 0.6 μ m。磷灰石含量高的颗粒表面呈褶皱或凹痕状，赤铁矿含量高的颗粒表面呈光滑状。大颗粒（>）为壳核型双层结构。直径8mm)。这种层状结构的形成是由于Ca-EDTA螯合键的断裂引发了液滴表面HAP的沉淀。

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.