Synthesis Of Strontium Aluminate Via Polymeric Precursor

Strontium aluminate phosphors are a kind of photoluminescent materials with stable performance and high efficiency. They are widely used in the display of visible light. In this thesis, strontium aluminate powders were prepared via polymeric precursor method and the effects of the molar ratio of citric acid (CA) to total metal cations concentration (CA/M) and the pH of the starting solutions on the formation of strontium aluminate were investigated. Differential thermal analysis and thermogravimetric (DTA/TG), X-ray diffractometry (XRD) and Fourier transform infared spectroscopy (FT-IR) were used to characterize the precursors and the derived oxide powders. Sr3Al2O6 was synthesized via citric acid precursor and single phase Sr₃Al₂O₆ was derived from CA/M=1 and CA/M=2 precursor at 1200℃and 1100℃for 2h, respectively. SrAl₂O₄, SrAl₄O₇ and SrAl₁₂O₁₉ were prepared via CA and EDTA route. Phase pure SrAl2O4 was synthesized from CA/M=2 precursors at a temperature of 900℃for 2 h, without the formation of any intermediate phase. SrAl₂O₄ was obtained from EDTA precursor at 1200℃for 2h. Increasing the pH of the starting solutions and CA/M promoted the formation of SrAl₄O₇. When CA/M was 2, well crystallized, single-phase SrAl₄O₇ was synthesized at 900℃for 2h for the precursor with pH=7, but it could not be obtained for the precursor with pH=1. Increasing CA/M up to 4, single-phase SrAl₄O₇ was also synthesized at 900℃for 2h for the precursors with pH=7, but it was obtained at 1100℃for 2h for the precursors with pH=1. SrAl₄O₇ can be stable up to 1400℃for 2h and it shows decomposition at 1500℃for 2h. Most of SrAl₄O₇ decomposes to SrAl₁₂O₁₉ as the major phase and an unidentified phase (main reflection at d=3.0149) at 1600℃for 2h. Single-phase SrAl₄O₇ was obtained from EDTA precursor at 1050℃for 2 h. Increasing the pH of the starting solutions retarded the formation of SrAl₁₂O₁₉. Single-phase SrAl₁₂O₁₉ was derived from CA precursor with unadjusted pH at 1200℃for 2h. Increasing the pH of the starting solutions to 7, the formation temperature of single-phase SrAl₁₂O₁₉ increased to 1300℃. On the other hand, SrAl₁₂O₁₉ was obtained from EDTA precursor at 1400℃for 2 h.