• A K Das

      Articles written in Bulletin of Materials Science

    • Some studies on the reaction between fly ash and lime

      A Basumajumdar A K Das N Bandyopadhyay S Maitra

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      The reaction between fly ash (FA) and lime is extensively exploited for the manufacture of building bricks, blocks and aggregates. To get a better idea of this reaction, FA from different sources were mixed in different ratios with lime and compacted. The compacts were treated both by ordinary water and hydrothermal curing to promote lime bearing hydrate bond formation e.g. CaO–SiO2–H2O (C–S–H), CaO–Al2O3–H2O (C–A–H) etc. The decrease in free lime content in these compacts was measured as a function of curing time and curing process. This drop in this content was correlated to the chemical composition of the fly ashes. The mathematical relationships between free lime remaining in the compacts after its maximum decrease in concentration and lime binding modulus (a ratio between the amount of added lime and the total amount of lime binding constituents present in FA) for both types of curing were developed. Further, the rate of decrease in free CaO content under both types of curing conditions was compared from kinetic study. From this study the orders of the reactions and rate constants were found out.

    • Effect of heat treatment on properties of steam cured fly ash–lime compacts

      S Maitra S Das A K Das A Basumajumdar

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      Four different varieties of class F fly ashes, collected from different sources from the state of West Bengal (India) were mixed with lime in 9 : 1 wt ratio, followed by compaction of the mixes. The compacts were subjected to steam curing to develop an optimum strength by the reaction between fly ash and lime. The steam cured compacts were heated at different elevated temperatures and free lime content, compressive strength, bulk density and water absorption tendency of these compacts were measured and FTIR spectral changes were studied as a function of the heating temperatures. Kinetics of thermal dehydration of the compacts was also studied from thermogravimetric measurements under non-isothermal condition to ascertain the order of dehydration process and the associated activation energy.

    • Studies on nonvolatile resistance memory switching in ZnO thin films

      L M Kukreja A K Das P Misra

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      Six decades of research on ZnO has recently sprouted a new branch in the domain of resistive random access memories. Highly resistive and c-axis oriented ZnO thin films were grown by us using d.c. discharge assisted pulsed laser deposition on Pt/Ti/SiO2/Si substrates at room temperature. The resistive switching characteristics of these films were studied in the top-bottom configuration using current–voltage measurements at room temperature. Reliable and repeated switching of the resistance of ZnO thin films was obtained between two well defined states of high and low resistance with a narrow dispersion and small switching voltages. Resistance ratios of the high resistance state to low resistance state were found to be in the range of 2–5 orders of magnitude up to 20 test cycles. The conduction mechanism was found to be dominated by the Ohmic behaviour in low resistance states, while Poole–Frenkel emission was found to dominate in high resistance state. The achieved characteristics of the resistive switching in ZnO thin films seem to be promising for nonvolatile memory applications.

© 2017 Indian Academy of Sciences, Bengaluru.