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Nandi P.,Bhabha Atomic Research Center | Patil A.S.,Bhabha Atomic Research Center | Paul B.,Materials Processing Division | Sarkar A.,Bhabha Atomic Research Center | And 2 more authors.
Transactions of the Indian Ceramic Society

Glasses with nominal composition (mol%) 34BaO-10Al2O3-17B2O3-34SiO2-(5-x)La2O3-xTiO2 (x = 0, 1, 2, 3, 4) were prepared by melt quenching technique. Activation energy of crystallization (Ea) was calculated by Kissinger's model considering the shift in peak crystallization temperature (Tc) at three different heating rates (10°, 15° and 20°C.min-1) in differential thermal analysis. Among the glasses studied, composition with x = 1 had the maximum Ea as a result of its slower crystallization rate. Thermal expansion coefficients of as prepared bulk glasses matched with that of Crofer 22APU alloy. Sandwich type seals were made with two Crofer plates at 990°C and their vacuum integrity was tested at room temperature. Cross-sectional interface of the seals was studied under scanning electron microscope with energy dispersive X-ray analysis. Very different morphology at metal to glass-ceramics interface was observed with varying TiO2 concentration. Microstructure at the interface of the seal with x = 1 glass had less porosity and less chromium enrichment at the interface than the other compositions which was probably due to slower rate of crystallization during the heat treatment. © 2012 Copyright The Indian Ceramic Society. Source

Majumdar S.,Materials Processing Division | Kishor J.,Materials Processing Division | Paul B.,Materials Processing Division | Hubli R.C.,Materials Processing Division | Chakravartty J.K.,Bhabha Atomic Research Center
Corrosion Science

Isothermal oxidation behavior of the single layer NbSi2 and the double layered (NbSi2+Nb5Si3) silicide coated Nb-1Zr-0.1C (wt.%) alloys has been studied between 800 and 1300°C in static laboratory air. The single layer coated alloy shows a lower weight gain as compared to the double layer coatings at all temperatures. The formation of amorphous silica scale embedded with Nb2O5 oxide particles is observed beyond 1100°C, and a superior oxidation resistance is detected between 1100 and 1300°C. A kinetic equation relating the thickness of the coating layer with the various process parameters for pack siliconizing of Nb-alloy has been established. © 2015 Elsevier Ltd. Source

Paul B.,Materials Processing Division | Kishor J.,Materials Processing Division | Chakraborty S.P.,Materials Processing Division | Suri A.K.,Materials Processing Division
Journal of Thermal Analysis and Calorimetry

The present paper deals with differential thermal analysis studies conducted to find out the onset temperature for silicothermic reduction of MoO2 to Mo. The reaction kinetics of Si-MoO2 system has been analyzed by a model-free Kissinger method. X-ray diffraction analysis has confirmed the formation of Mo metal and SiO2 as the slag phase after silicothermic reduction of MoO2. The activation energy for silicothermic reduction of MoO2 to Mo was evaluated to be 309 kJ mol-1. © 2012 Akadémiai Kiadó, Budapest, Hungary. Source

Paul B.,Materials Processing Division | Limaye P.K.,Materials Processing Division | Hubli R.C.,Materials Processing Division | Suri A.K.,Materials Processing Division
International Journal of Refractory Metals and Hard Materials

The paper deals with the microstructure and wear properties of the Mo-30W alloy, coated with silicide based oxidation resistant coatings using pack cementation technique. The microstructure of the coating revealed that the coating was free of cracks or pores, adherent to the substrate and comprised of either single layer or double layer depending the coating temperature. Scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS) was used to determine diffusion profiles for Mo, W and Si. Reciprocating sliding wear and friction experiments were performed on the uncoated and coated alloy. Double layer coating showed an improved friction coefficient as compared to base alloy as well as a single layer coated alloy. The wear tests also showed a marked improvement of wear resistance of coated alloy as compared to uncoated alloy. The coating was found to be wear resistant at 7 N. © 2014 Elsevier Ltd. Source

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