No abstract available

[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

No abstract available

[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] Beaches are the main sources for economic heavy minerals (HM) like ilmenite rutile, monazite, zircon, garnet and sillimanite. The seasonal HM accumulations, colloquially called 'beach washings' are mined by IREL and KMML in Kerala and by IREL and several private enterprises in Tamil Nadu. These sediments are found to contain 85-90% THM. It is presumed that during the monsoon, the sea is agitated and the churning and spiralling action of water lifts HM-bearing sediments from the sea floor and transports in suspension and deposits on the beach berm, the backwash taking the relatively lighter part of the sediment load back into the sea. This process is thought to give rise to HM-enriched sand on the beach face and the swash plain. It is pertinent to understand the controls on these economically important and scientifically interesting processes. Beachface is the seaward section of a beach exposed to and shaped by the action of waves. The beach face is the zone of most active change. Berm is the terrace of a beach that has formed in the backshore, above the water level at high tide. Berms are commonly found on beaches that have fairly coarse sand and are the result of the deposition of material by low energy waves. On broad beaches there may be three or more sub-parallel berms, each formed under different wave conditions. Swash zone is defined as that part of the beach extending from a nearshore shallow depth to the limit of maximum inundation; is a relatively narrow region of great importance for the exchange of sediment between land and sea. Morphological processes such as storm-induced erosion, post-storm recovery, seasonal variation in foreshore shape, and evolution of rhythmic

[en] The Archean granite-greenstone terrane exposed around Atkur-Guntipally and Madanapally area in Mahabubnagar District of Telangana is comprised of granitoids of Peninsular Gneissic Complex (PGC) and 2.7 Ga metavolcanics belonging to Gadwal schist belt, in Eastern Dharwar Craton (EDC). The granite-greenstone sequence of the study area is located around the northern part of Neoarchean Gadwal schist belt. The present study pertains to the coarse grained, mesocratic granitic rocks that occur on either side of narrow N-S trending metabasalt (0.8 to 1.6 km width) in the area. Petrographically the granitoids exhibit hypidiomorphic texture and are essentially composed of K-feldspar, quartz, plagioclase, biotite + hornblende and zircon, epidote, apatite and opaques are noticed as accessory minerals. Mafic rich microgranitoid enclaves (MME's) are widely noticed indicating magma mingiling phenomenon. These granitic rocks are peraluminous in nature and exhibit a cal-alkaline trend. Major oxide geochemistry indicates high SiO₂ (71.22 to 72–84%) and high Na₂O +K₂O (8.19 to 9.0%) content. Positive correlation between SiO vs alkalis (Na₂O, K₂O) and alumina (Al₂O₃) indicate normal differentiation trend characteristic of calc-alkaline plutonic felsic magmatism. Chondrite normalised REE plot of these granitoids exhibits conspicuous LREE enrichment, negative Eu anomaly and depleted HREE patterns indicating a crustal source. (author)

[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.