Results 1 - 10 of 2550
Results 1 - 10 of 2550. Search took: 0.028 seconds
|Sort by: date | relevance|
[en] In this work, high temperature solid phase method was applied to prepare Sr2MgSi2O7:Eu, Dy blue light long-persistence materials with different contents of H3BO3. Under the condition of low H3BO3 content, it was difficult for Eu and Dy to enter Sr2MgSi2O7 lattice, impurity phase of Sr3MgSi2O8 was observed, and initial afterglow luminance of the sample was very low. With the increase of H3BO3, Sr3MgSi2O8 phase disappeared, Eu and Dy entered Sr2MgSi2O7 lattice smoothly, and the grain size as well as initial afterglow luminance of samples increased significantly. The initial afterglow luminance of the sample reached the maximum while the H3BO3 content was 10% (molar ratio). As H3BO3 content increased further, the initial afterglow luminance reduced rapidly. After detailed analysis, we consider that the key factors influencing the afterglow luminance of samples are the formation and the density of luminous unit, which is greatly determined by the Eu and Dy’s entering Sr2MgSi2O7 lattice as well as the grain size of Sr2MgSi2O7 crystal. (paper)
[en] Sr1.95TiO4:0.05Sm3+ phosphors with various fluxes were synthesized. The influence of these fluxes on the crystallization behavior, morphology, and luminescence properties of Sr1.95TiO4:0.05Sm3+ phosphor was systematically investigated. The results showed that the luminescence properties and morphology of the phosphor were improved by adding fluxes. The emission intensity of the phosphor was enhanced about 39–94% with the addition of single fluxes, while, it was enhanced about 200% when H3BO3+NH4HF2 was used as composite flux. The synthesis temperature of the Sr1.95TiO4:0.05Sm3+ phosphor was decreased but the emission intensity was increased when H3BO3+NH4HF2 was used as composite flux. The luminescence spectrum mainly showed three intense emission bands at 568, 603 and 649 nm. Its luminescence lifetime was 716.77 μs. All these indicated that the addition of H3BO3+NH4HF2 was greatly useful to lower the sintering temperature, improve the crystallization and morphology, and enhance the luminescence properties of layered perovskite Sr1.95TiO4:0.05Sm3+ phosphor.
[en] The REACH European directive aims at protecting man and nature from chemical products. REACH means Registration, Evaluation, Authorization and Restriction of chemicals and it was implemented in the European law in june 2007. Nuclear industry uses a large range of chemicals and among them we find boric acid. According to REACH boric acid needs an authorization to be used because of its toxic effect on reproduction and for some uses it must be replaced by another less toxic chemical. In nuclear industry, there is no substitute to boric acid whose role is to control nuclear reactions. The use of boric acid in the nuclear sector represents only 0.5% of all its uses in the European Union. The point is that if boric acid is no more allowed in other industrial sectors than nuclear sector, it would disappear and be no more available for operating reactors. (A.C.)
[en] Highlights: • Structural evolution during pyrolysis of novolac resin containing H3BO3 or B2O3. • The catalytic graphitization depends on BOC formation and cleavage. • Composition, bond strength and crystallization controlled the carbons' reactivity. • Better oxidation resistance can be attained without the carbon's crystallization.
[en] It was measured that the neutron radiation effect on the generated Li from 10B (n· α)7Li react ion, the loss of boron content and pH change in boric acid solution. With compensation for interference of excess boron 50∼2,000 μg/ ml, lithium 0.2∼1.0 μg/ml range was determined within RSD 6.4%. The amount of lithium generated from 10B (n· α)7Li reaction was proportionate to the concentration of boron and the time of irradiation, under our experimental condition. The pH value of irradiated boric acid was shifted to considerably low. It is estimated that boric acid would be transformed into the polyborate form, by radiolysis products of water, which has high dissociation constant