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[en] Ceramic filters specially SiC filters are used in advanced coal combustion and gasification processes to remove fine dust particles from the fuel gas at high temperatures and high pressure for protection of turbine blades and other downstream components from corrosion and erosion and to meet the environmental regulations. Processing of corrosion resistant porous SiC ceramics at low temperature using a simple technique is still challenging. In this study oxide bonded porous SiC ceramics were synthesized by cost effective method. The corrosion behaviour of SiC ceramic filter materials in presence of steam, coal ash and both coal ash and steam was investigated at 1000 °C for 96–240 h. The apparent changes in mass, porosity and density with corrosion duration and environment were recorded. Finally SEM, XRD and mechanical tests of the corroded samples were carried out. The corrosion test results indicated water vapour is the perpetrator for strength degradation.
[es]Los filtros cerámicos, especialmente los filtros de SiC, se utilizan en procesos avanzados de combustión y gasificación de carbón para eliminar las de polvo fino partículas en suspensión del gas combustible, a altas temperaturas y altas presiones, para proteger los álabes de las turbinas, y otros componentes aguas abajo, de la corrosión y la erosión y para cumplir con las regulaciones ambientales. El procesamiento de cerámicas porosas de SiC resistentes a la corrosión a baja temperatura utilizando una técnica simple sigue siendo un desafío. En este estudio, las cerámicas porosas de SiC ligadas mediante óxidos se sintetizaron mediante un método rentable. El comportamiento a la corrosión de los filtros cerámicos de SiC en presencia de vapor de agua, ceniza de carbón y ceniza de carbón y vaporde agua se investigó a 1000° C durante 96-240 horas. Se registraron los cambios aparentes en masa, porosidad y densidad con la duración de la corrosión y el medio ambiente. Finalmente se llevaron a cabo estudios de MEB, DRX, XRD y propiedades mecánicas de las muestras corroídas. Los resultados del ensayo de corrosión indicaron que el vapor de agua es el responsable de la degradación de la resistencia mecánica.
[en] Boron lined proportional counters of standard cylindrical geometry were developed and characterized for reactor applications. It is observed that the life of boron lined proportional counters is significantly lower if irradiated in high neutron flux keeping the HV bias “ON” compared to the irradiation with HV bias “OFF”. When operated in gamma radiation, the boron lined proportional counters suffer count rate loss and underestimate the neutron flux. The loss in the count rate in gamma radiation is attributed to the space charge effect. The space charge effect is theoretically calculated for a known gamma radiation. The estimated values compared well with the experimentally observed values. Neutron sensitivity is estimated by modeling the boron lined proportional counters in FLUKA Monte-Carlo simulation code. The estimated neutron sensitivity values are comparable to the experimental and theoretical values. - Highlights: • Life tests of boron lined proportional counters with HV bias “ON” and “OFF” conditions. • Estimation of space charge effect in boron lined proportional counters due to gamma radiation. • Neutron sensitivity estimation of boron lined proportional counters
[en] An annular shape silver lined proportional counter is developed to measure pulsed neutron radiation. The detector has 314 mm overall length and 235 mm overall diameter. The central cavity of 150 mm diameter and 200 mm length is used for placing the neutron source. Because of annular shape the detector covers >3π solid angle of the source. The detector has all welded construction. The detector is developed in two halves for easy mounting and demounting. Each half is an independent detector. Both the halves together give single neutron pulse calibration constant of 4.5×10"4 neutrons/shot count. The detector operates in proportional mode which gives enhanced working conditions in terms of dead time and operating range compared to Geiger Muller based neutron detectors
[en] Zinc oxide-silica (ZnO/SiO2=20:80, molar ratio) nanocomposites consisting of ZnO nanoparticles embedded in a dielectric matrix were prepared by a sol-gel technique (spin coating). Optical transmittance, Raman effect and photoluminescence measurements of the composites indicated effective capping of the ZnO nanoparticles (radii 1.4-1.5 nm) in the host showing practically no variation of particle size with the post-deposition-annealing treatments. The blue shift of the band gap (4.23-4.29 eV) from that of bulk ZnO (3.3 eV) indicated strong carrier confinement for samples annealed at T≤773 K. Highly intense UV emission (approx. 4.2 eV) at room temperature could be obtained by annealing the composites in static oxygen atmosphere, while the visible defect-related luminescence (approx. 2.62 and 2.43 eV) could be reduced, resulting in a high intensity ratio (approx. 27) of the two
[en] Exchange of zeolite X with La3+ and Pr3+ has been studied. Almost complete exchange (98.6% La and 99.4% Pr) is possible by repeated exchange at 100deg C with activation in between. Thermal stability and surface acidity increase with the degree of exchange. PrX shows higher surface acidity and better thermal stability than LaX. These observations have been explained taking into consideration the charge densities, ionic sizes, electronic configurations, electronegativities and oxidation states of the exchanging cations. (author)
[en] The nuclear instrumentation scheme deployed to measure the reactor core neutron flux shall be capable of monitoring the status in all states of reactor operation viz. Start-up, intermediate and power ranges. The instrumentation is also required to serve the monitoring of the core during fuel loading, refuelling including anticipated accidental conditions. The operational range of nuclear instrumentation starts from the subcritical state (typically Keff.=0.95) upto beyond full power (typically 125%FP). This demands use of multiple types of neutron detectors in different sets in order to meet the wide measurement range (over ten decades) and redundancy for safety class IA requirements
[en] There has been an increased interest in utilizing thorium as nuclear fuel primarily because this potential actinide is three times more abundant in the earth's crust, as compared to the widely used uranium. Th utilization gives considerable savings in uranium ore and in 235U isotope enrichment units. India alone accounting one fourth of the world's thorium reserve (∼1.2 megaton) is working on a new reactor concept, advanced heavy water reactor, that will generate 60% of its total power from thorium. AHWR will be configured with fuels containing 2-4 % fissile isotopes of uranium (233U) and plutonium (239Pu) in the thoria based matrices: Th1-yUyO2, and Th1-yPuyO2. Workability with the fuels rests on their performance in high burnup (50 GWD ton-1 or higher) situation they will be subjected to because of their reprocessing difficulties by the presence of hard gamma emitting daughters (212Bi, 0.7-1.8 MeV, and 208Tl, 2.6 MeV). In order to understand the physico-chemical evolution of the fuel at high burnup one needs the input of basic data of physics and chemistry of the fuel in the presence of the fission products (fps). By concerted effort of chemists in Trombay laboratories, relevant thermophysical properties like thermal expansion, thermal conductivity and heat capacity, and thermodynamic and transport properties of the fuel and fission products were carried out. In this talk, the consolidated data of the different properties of the thoria-urania fuel and the anticipated behavior of the fuel at high burnup situation will be presented. (author)
[en] The in-phase and anti-phase motions of antiferroelectric liquid crystals were changed due to the influence of charge density associated with the layer modulation modifying the elastic behaviour. The elastic constant was changed because of the coupling between charge density variation and variation of azimuthal angle (ϕ). We obtained theoretically a modified elastic constant depending on the variation of charge density in both in-phase and anti-phase motions. The theoretically elastic constant decreases with the increase of the coupling coefficient between charge density and in-phase azimuthal angle (ϕa). We theoretically accounted the dependence of dielectric strength for both relaxations depending on the effective elastic constant influenced by the presence of charge density and discussed the results with experimental observations
[en] Thermochemistry in the decomposition of lanthanum dioxycarbonate, La2O2CO3(s), was studied over the temperature region of 773-1190K. The decomposition reaction can be written asLa2O2CO3(s)=La2O3(s)+CO2(g)The equilibrium property of the above reaction was then studied by tensimetric measurement of the CO2(g) pressure over the biphasic mixture of La2O2CO3(s) and La2O3(s) at different temperatures. The temperature dependence of the equilibrium pressure of CO2 thus measured could be given bylnpCO2(Pa)(+/-0.22)=-17502.2T+25.87(773=< T(K)=<1190)From the above vapor pressure expression, the median enthalpy and entropy of the decomposition of the oxycarbonate from the second law analysis worked out to be 145.5+/-5.0kJmol-1 and 119.2+/-5.0Jmol-1K-1, respectively. The results are discussed in the light of available thermochemical data of the compound
[en] A large body of experimental observations has evolved with particular reference to deuterated palladium, a mechanism of fusion unique to condensed matter. The mechanism brings to focus the relevance of the electronic structure of the host lattice, indicating the features that are desired. Direct interaction of electronegative elements such as oxygen (as happens in electrolysis experiments) creates, through modification of the electronics structure, situations under which heavy electrons are manifested. In cases where an oxide interface is present, an analogous situation is created at the onset of an insulator-metal transition caused by the induced migration of deuterons through the layer. Screened by the heavy fermions, deuterons in such situations undergo transition to a more stable quasi-molecular state, (D+D+)2e-, with substantially reduced nuclear separation. Through quantum mechanical tunneling, fusion takes place in such a cluster with a yield of 10-1.5s-1, a value consistent with observed excess heat production and near-surface occurrence of the phenomenon. 45 refs., 1 fig