ABSTRACT
Neutron and high-energy x-ray diffraction measurements have been performed on multi-component 55SiO(2)·10B(2)O(3)·25Na(2)O·5BaO·ZrO(2) borosilicate host glass loaded with 30 wt% UO(3). Both the traditional Fourier transformation technique and the reverse Monte Carlo simulation of the experimental data have been applied to get structural information. It was established that the basic network structure consists of tetrahedral SiO(4) units and of mixed tetrahedral BO(4) and trigonal BO(3) units, similar to the corresponding host glass. Slight changes have been observed in the oxygen surroundings of the Na and Zr modifier cations; both the Na-O and Zr-O distances decrease and a more compact short-range structure has been obtained compared to the host glass. For the U-O correlations two distinct peaks were resolved at 1.84 and 2.24 Å, and for higher distances intermediate-range correlations were observed. Significant correlations have been revealed between U and the network former Si and B atoms. Uranium ions take part in the network forming, which may be the reason for the observed good glassy stability and hydrolytic properties.
Subject(s)
Boron Compounds/chemistry , Glass/chemistry , Models, Molecular , Monte Carlo Method , Neutron Diffraction , Silicates/chemistry , Uranium/chemistry , X-Ray Diffraction , Computer SimulationABSTRACT
The structure of 0.7SiO(2)-0.3Na(2)O glass was investigated by means of neutron and high-energy x-ray diffraction. The maximum momentum transfer was 35 and 23.5 Å(-1) for the two experiments. The two datasets were modelled simultaneously by the reverse Monte Carlo simulation technique. By using reasonable constraints it was possible to separate the six partial pair correlation functions. Nearest neighbour distances, coordination numbers and bond angle distributions have been revealed. It was found that 63% of the O atoms are in the bridging position. The Na-O distance is 2.29 Å and the coordination number is 2.5. The Na-Na nearest neighbour distance is 2.6 Å, a value significantly smaller than previously reported. Neighbouring sodium ions tend to be located at the same oxygen atom. The average Si-O ring size is 7.6.
ABSTRACT
The possibility of improving the aspect of the glaucomatous excavation under the influence of the postoperative ocular hypotonization is shown on 12 eyes (11 patients) observed during the past 13 years. All patients suffered from very advanced chronic simple glaucoma--8 had a C/D 0.9 (postoperatively 0.6 in 3 eyes, 0.4 in 4 eyes and 0.1 in 1 eye), 3 a C/D 0.8 (postoperatively 0.4 in 1 eye and 0.2 in 2 eyes) and 1 a C/D 0.7 (which diminished postoperatively to 0.4). Of the 12 eyes, only one showed an improvement of the visual field, 5 a lowering of the visual acuity (progression of the cataract) and 3 a decrease of the visual field after a new increase of the intraocular pressure.
