| 摘要: | 本研究以檸檬酸先驅物法來製得磁性鐵酸鋇粉體。硝酸鋇與硝酸鐵依化學計量比溶解於去離子水中後，加入過量檸檬酸以鏊合溶液裡的金屬離子。溶液之酸鹼值藉由添加氨水來調整。起始溶液共有6種不同之酸鹼值，分別為0.8 (未加氨水)、3、5、7、8及10。之後提升溶液溫度至90℃並加入回流裝置，促使鏊合反應完全。經200℃乾燥24小時及不同熱處理溫度後，以XRD、FT-IR、TEM、SEM、TG-DSC、和SQUID做性質分析。本文將探討溶液酸鹼值及熱處理溫度對鐵酸鋇之影響。從XRD之分析，可得有添加氨水於起溶液中，則增加檸檬酸之解離，促使鋇離子與鐵離子鏊合反應更均勻；而未添加氨水(pH=0.8)，反應不完全，在高溫熱處理後還有中間相態存在。在溶液酸鹼值大於8以上，鏊合反應完全且均勻，使得在650℃時便可得到單一相態鐵酸鋇。在pH值為3時，反應過程中得到中間相態γ-Fe2O3，γ-Fe2O3易與BaCO3形成鐵酸鋇粉體，且在700℃時磁性質表現也較其他pH值高。
Magnetic BaFe12O19 powder with crystallite sizes in nanometers was produced via citric acid precursor method. Citric acid was added into an aqueous solution, containing nitrates of iron and barium in stoichimetric ratios to form the required barium ferrite, to chelate the metallic ions. The pH value of starting aqueous solutions was adjusted using NH4OH. The solutions with six different pH values were prepared; they were the solutions of pH = 0.8 (without NH4OH additions), 3, 5, 7, 8, and 10, respectively. After drying, the solid citrate precursors were obtained. The solid citrate precursors were then calcined in air at different temperature. Effects of pH of the starting solution and calcination temperatures of the solid precursors on characteristics of resultant particles were investigated using XRD, FT-IR, TEM, SEM, TG-DSC and SQUID. The XRD analysis indicates that adding NH4OH into the starting solution will increase the ionization of citric acid and provide more carboxyl groups to chelate Ba2+ and Fe3+. Without NH4OH additions, no sufficient carboxyl groups, ionized from citric acid, were available to completely and simultaneously chelate iron and barium ions. The starting solutions at pH≧8 contained enough number of carboxyl groups to have both Fe3+ and Ba2+ be completely and homogeneously chelated, resulting in the direct formation of single crystalline phase of BaFe12O19 at calcinations temperatures as low as 650℃. At pH=3, resulting in the formation of crystalline γ-Fe2O3 intermediate. γ-Fe2O3 easily reacts with BaCO3 to form BaFe12O19. The results of magnetic measurements show that the calcined sample at 700℃ gives the highest Ms, Mr and Hc than those using other pH values. |
