Papers by Keyword: Barium Aluminate

Abstract: Photoluminescent (PL) materials are commonly utilized in applications such as leakage test, crack monitoring, banknote forgery detection, and fingerprint detection. Doping, chemical compositions and microstructure, are generally accepted as factors that influence luminescent intensity of spinel-structure phosphors such as SrAl₂O₄, CaAl₂O₄, and BaAl₂O₄. This study aimed at synthesizing BaAl₂O₄ photoluminescent powders by solution combustion technique. Effects of Eu doping and calcination temperatures on chemical compositions, microstructure and luminescent intensity of the materials were also examined. Experimental results indicated that Eu concentrations did not exhibit a significant effect on chemical composition and particle morphology. Higher calcination temperatures, on the contrary, resulted in reduction of secondary phase formation, and in alteration of morphology of particles and pores. The greatest luminescent intensity was achieved in the BaAl₂O₄ sample with 3 mol% Eu subjected to calcination at 900°C. Enhancement of the luminescent intensity in this sample might be attributed to minimal secondary phase and pore content.

Abstract: Barium aluminates have been obtained by the method of continuous precipitation at different values of pH. The method of thermal analysis showed that the main mass losses which are connected with dehydration processes occur in the temperature interval from 50 °C to 100 °C and from 150 °C to 200 °C. In addition, mass loss occurs in the temperature interval from 780 °C to 1000 °C which can indicate barium aluminate formation. XRD analysis was applied to determine phase composition of obtained substance and showed formation of Ba_1.17Al_10.67O_17.17 and BaAl₂O₄ at pH 6.5; 7.0 and 7.5 respectively. Significant influence of pH on precipitation composition has not been detected.

Abstract: Synthesizing barium aluminate using barium carbonate and aluminium hydroxide, the optimum conditions in reaction process of synthesizing barium aluminate were discussed. The phase of the products was characterized by XRD. The results indicate that the optimal synthesizing conditions are established with the yield of 88.43% when the roasting time is 80min, the roasting temperature is 1350°C and molecular proportion of Al₂O₃/BaO is 1.1. The bulk density of barium aluminate is 1.5g/cm³; average particle size is 89.808μm; surface mean size is 65.915μm; and the specific surface area is 0.0246016m²/g.

Abstract: Eu²⁺, Dy³⁺ co-doped alkaline earth aluminates MAl₂O₄: Eu²⁺, Dy³⁺ (M = Ba, Sr) have been prepared by in situ self-propagating high temperature synthesis (SHS) method. The influence of co-doping rare earth ions (Eu²⁺, Dy³⁺) on the luminescence of MAl₂O₄:Eu²⁺, Dy³⁺ were described in this study. The particles morphology, photoluminescence and afterglow properties of the phosphors were studied. Broad band UV excited luminescence was observed for BaAl₂O₄:Eu²⁺, Dy³⁺ and SrAl₂O₄:Eu²⁺, Dy³⁺ in the green region peak at _max = 503 nm and 523 nm, respectively. The dopant (Eu²⁺) and co-dopant (Dy³⁺) concentrations affect the crystallinity and luminescence properties of the materials.

Abstract: The Eu²⁺ doped barium aluminate (BaAl2O4:Eu²⁺) and strontium aluminate (SrAl2O4:Eu²⁺) with high brightness were synthesized by self-propagating high temperature synthesis (SHS) method. The influence of doping rare earth ions (Eu²⁺) on the luminescence of MAl2O4:Eu²⁺ were described in this study. The reactions were carried out in a SHS reactor under static argon gas at a pressure of 0.5 MPa. The morphologies and the phase structures of the products have been characterized by X-ray diffraction (XRD) and scanning electron microscope technique (SEM). The emission spectra of the products have been measured by an Ocean optics spectrometer at room temperature. Broad band UV excited luminescence was observed for BaAl2O4:Eu²⁺ and SrAl2O4:Eu²⁺ in the green region peak at λmax = 501 nm and 523 nm, respectively. The optimum Eu²⁺ doping ratio were 10.5 mol% and 6 mol% for BaAl2O4:Eu²⁺ and SrAl2O4:Eu²⁺, respectively

Abstract: Crystal structures of SrAl2O4, BaAl2O4 and their solid solutions have been reviewed in terms of the linkage pattern of [AlO4] tetrahedra. With SrAl2O4 the hexagonal-to-monoclinic phase transformation occurs at 950K during cooling. The space group change from P63 to its subgroup P21 eliminates the triad axis of the former phase, which involves a reduction in the symmetry of the trigonally distorted rings. The hexagonal structures of SrAl2O4 and BaAl2O4 differ distinctly in the linkage pattern of the [AlO4] tetrahedra. In the former structure, all of the tetrahedral rings are equivalent. In the latter, there are two types of tetrahedral rings; trigonal rings and asymmetrical ones. The trigonal rings, comprising 25% of the total number of rings, contain in their centers the Ba atoms with the special position. This implies that the triad axes exist in the centers of the rings, and hence they are distorted trigonally as in the hexagonal SrAl2O4. On the other hand, the Ba atoms in the asymmetrical rings are located at the general position site. The structural disorder in Ba0.6Sr0.4Al2O4 (space group P6322) was investigated by the combined use of Rietveld method and maximum-entropy method. The electron density distribution was satisfactorily expressed by the split-atom model, in which the strontium/barium and oxygen atoms were split to occupy the lower symmetry sites.