Results 1 - 10 of 4940
Results 1 - 10 of 4940. Search took: 0.025 seconds
|Sort by: date | relevance|
[en] It was found that thermoluminescence (TL) in zircons fades anomalously. Several factors that could affect the rate of anomalous fading were also studies. It was determined that grain size, dose rate and total dose received by the sample did not have any significant effect on the rate of anomalous fading. However annealing of the sample (approx 900deg C for 1 hr in air) or its storage at different temperature (well below the peak temperature) seems to affect, at least, the fast component part of the anomalous fading TL. This component can also be removed by infra-red light
[en] Reactions of natural zircon with Na2CO3 with mole ratios ranging from 1:1 to 1:2.6 were studied at 800 and 900 degC for periods up to 48 hours. The products of the reaction were Na2ZrO3, Na2SiO3 and Na2ZrSiO5. A reaction mechanism, valid within the range of temperature of this study, has been proposed on the basis of the relative proportions of the co-existing phases as a function of composition, temperature and time. The reaction was initiated with the formation of Na2ZrSiO5 which later reacted with any excess Na2CO3 present resulting in the formation of Na2ZrO3 and Na2SiO3. When treated with water, Na2ZrSiO5 remained unaffected while Na2ZrO3 was converted to amorphous hydrated zirconia. (author)
[en] In order to characterize inhomogeneities in monolithic ceramics, signal characterization of backscattered 25 MHz focussed, pulsed ultrasound has been applied in a step by step approach. The first step was to examine voids in glass. These were optically characterized as spheres with diameters of 30 to 120 μm. Correlations were made with the ultrasonic signals returned. A mathematical model for ultrasound scattering from spheres in an elastic medium based on Ying and Truell's work was used to predict the frequency response characteristics for voids. The next step involved the manufacture of spherical particles of zirconia in the size range of 20 to 200 μm diameter which were also imbedded in glass. The model was modified to calculate the backscattering of ultrasound from inhomogeneities of known elastic constants. The most recent step was the introduction of spherical inclusions into crystallizable glass. Optical characterization was made, then the glass was crystallized to introduce a host matrix structure similar to that of a ceramic. Using appropriate values for elastic constants, experimental and theoretical results are found to be well correlated. This presentation review the work down on inhomogeneities in glasses and its application to defect characterization in ceramics
[en] This paper presents the results of U–Pb (LA-ICP-MS) and Lu–Hf isotope studies of detrital zircons from the presumably Permian meta sedimentary rocks of the Tokur terrane. It has been established that the grains of detrital zircons from the meta sedimentary rocks of the Tokur and Ekimchan formations have a similar age distribution, which indicates the similar (or equal) age of these formations. The youngest zircons in these rocks has a U–Pb age of 326–323 Ma, which determines the lower age limit of the protolith of the rocks. The upper age limit of the formations corresponds to 254–251 Ma, which is the age of the Late Permian granitoids intruded into these formations. The main sources of zircon in the meta sedimentary rocks of the Tokur terrane are the igneous and metamorphic massifs of the southeast framing of the North Asian Craton. The Tokur terrane can be considered as a fragment of the Paleozoic accretionary complex, formed near the southeastern margin of the North Asian Craton.
[en] In order to resolve the age of Navysh volcanics (NV), which is usually attributed to the Lower Riphean of the Ai Formation, we have used geochronological, petrologic, and mineralogical methods of zirconology, apart from the SHRIMP isotopic data of single zircon grains. Moreover, TIMS isotope age analyses have been conducted, the results of which can be regarded as both controlling and providing the most correct information. The TIMS and SHRIMP data make it possible to suggest a polychronous character of the NV, which include not only Riphean, but also Paleozoic groups of volcanics. In this situation, an assessment of the scales of such polychroneity of NV and, correspondingly, of the Ai Formation as a whole becomes urgent.
[en] The results of U–Th–Pb geochronological study indicate that the youngest peaks on the relative probability curves of the age obtained for the Un’ya-Bom terrane correspond to ages of 207 and 212 Ma. These values were obtained for zircons from the meta-aleurolite samples from the Kurnal and Amkan formations, respectively. Similar age estimates for the youngest peaks were also obtained in the case of detrital zircons from the metasedimentary rocks of the Tukuringra terrane in the eastern part of the Mongol–Okhotsk fold belt, which indicates that, within the belt, Lower Mesozoic flyshoid complexes are much more widespread than was assumed. Based on the geochronological and Sm–Nd isotopic data obtained, it was shown that the material was carried to the sedimentation basin mainly from the continental massifs of the Amur superterrane.
[en] U–Pb dating on inherited detrital zircons has been applied to obtain the probable maximum age of deposition of the detrital protolith of the Nevado–Filábride complex (Betic Cordillera, Spain). Five of eight samples correspond to the lower part of the lithologic sequence of this complex, where radiometric dating of metasediments has not been presented till the present. The youngest age populations in the majority of samples are Carboniferous. The estimation of the maximum age of deposition in the lower and upper units is 349.1 ± 1.6 and 334.6 ± 2.9 Ma, respectively. In addition, samples show common age populations at ca. 490–630 and ca. 910–1010 Ma. Observations agree with the Carboniferous to early Permian U–Pb ages previously obtained in orthogneisses levels which are situated in the upper part of the complex. Combination of the minimum age of deposition deducible from the orthogneisses studies and the maximum ages of deposition obtained from the detrital zircons of this work, allow establishing the deposition of de studied lithological succession comprised between ca. 282 and 349 Ma or a shorter period.
[en] Highlights: • Zircon up to 10 g/100 g metakaolin improved microstructure and mechanical properties. • No new phases were formed upon the addition of zircon. • Zircon didn't participate in geopolymerization reaction. • Zircon entered between polysialate networks and formed a rigid microstructure. • Higher content of zircon (15 g/100 g kaolin) lowered the compressive strength.