The urethane forming cure reactions of hydroxyl terminated polybutadiene (HTPB) binder with three different isocyanate curatives,
viz., toluene diisocyanate (TDI), isophorone diisocyanate (IPDI) and 4,4'-methylene bis(cyclohexyl isocyanate) (MCHI), were
investigated by differential scanning calorimetry (DSC). The effect of two cure catalysts, viz., dibutyl tin dilaurate (DBTDL)
and ferrric tris-acetylacetonate (FeAA) on the cure reactions was also studied. Cure kinetics was evaluated using the multiple
heating rate Ozawa method. The reactivities of the three isocyanates and catalytic efficiencies were compared based on the
DSC reaction temperatures, activation energies and rate constants. Viscosity build-up in these systems at isothermal temperature
was also studied and compared with the results from DSC.
Authors:K. Muraleedharan, M. Kannan, and T. Gangadevi
The effect of additives (CuO, MnO2 and TiO2) on the thermal decomposition kinetics of potassium metaperiodate (KIO4) to potassium iodate (KIO3) has been studied in air by thermogravimetry under isothermal conditions. Irrespective of whether p- or n-type, the metal
oxides show only a little or no influence on the rate of the decomposition except for the small decrease when the oxide concentration
is as high as 10 wt%. The rate law for the decomposition of KIO4 (Prout–Tompkins model) remained unaffected by the additives.
Authors:K. Muraleedharan, M. P. Kannan, and Devi T. Ganga
The thermal decomposition of potassium iodate (KIO3) has been studied by both non-isothermal and isothermal thermogravimetry (TG). The non-isothermal simultaneous TG–differential thermal analysis (DTA) of the thermal decomposition of KIO3 was carried out in nitrogen atmosphere at different heating rates. The isothermal decomposition of KIO3 was studied using TG at different temperatures in the range 790–805 K in nitrogen atmosphere. The theoretical and experimental mass loss data are in good agreement for the thermal decomposition of KIO3. The non-isothermal decomposition of KIO3 was subjected to kinetic analyses by model-free approach, which is based on the isoconversional principle. The isothermal decomposition of KIO3 was subjected to both conventional (model fitting) and model-free (isoconversional) methods. It has been observed that the activation energy values obtained from all these methods agree well. Isothermal model fitting analysis shows that the thermal decomposition kinetics of KIO3 can be best described by the contracting cube equation.
Authors:K.G. Mandal, K. Kannan, A.K. Thakur, D.K. Kundu, P.S. Brahmanand, and A. Kumar
Three-year (2007/2008–2009/2010) field experiment was conducted at the Directorate of Water Management Research Farm under Deras command in Odisha, India to assess the crop yield, irrigation water use efficiency (WUE), sustainable yield index (SYI), land utilization index (LUI) and changes in soil organic carbon (SOC) for dominant rice systems, viz. rice-maize-rice, rice-cowpea-rice, rice-sunflower-rice, rice-tomato-okra and rice-fallow-rice. Results revealed that crop yield, in terms of total system productivity (TSP) increased by 273, 113, 106 and 58% in rice-tomato-okra, rice-sunflower-rice, rice-maize-rice and rice-cowpea-rice, respectively, when compared to rice-fallow-rice. Irrigation WUE was 49–414% greater in rice-based diversified systems than the existing rice-fallow-rice (2.98 kg ha−1 mm−1). The SYI ranged from 0.65 to 0.75 indicating greater sustainability of the systems. Three crops in a sequence resulted in greater LUI and production efficiency compared to rice-fallow-rice. The gross economic return and benefit-cost ratio was in the order: rice-tomato-okra > rice-maize-rice > rice-sunflower-rice > rice-cowpea-rice > rice-fallow-rice. The SOC storage ranged from 40.55 Mg ha−1 in rice-fallow-rice to 46.23 Mg ha−1 in rice-maize-rice system. The other systems had also very close values of SOC storage with the rice-maize-rice system; there was a positive change of SOC (7.20 to 12.52 Mg ha−1) for every system, with highest in rice-maize-rice system and the lowest in rice-fallow-rice. It is concluded that the appropriate rice-based system would be rice-tomato-okra followed by rice-maize-rice, rice-sunflower-rice and rice-cowpea-rice. Rice-fallow-rice is not advisable because of its lower productivity, lower LUI and economic return.
Authors:V. M. Abdul Mujeeb, M. H. Aneesh, K. Muraleedharan, T. G. Devi, and M. P. Kannan
Pure and doped samples of potassium bromate (KBrO3) were subjected to precompression and their thermal decomposition kinetics was studied by thermogravimetry at 668 K. The samples decomposed in two stages governed by the same rate law (contracting square equation), but with different rate constants, k1 (for a α ≤ 0.45) and k2 (for α ≥ 0.45), as in the case of uncompressed samples. The rate constants k1 and k2 decreased dramatically on precompression, the decrease being higher for doped samples. Cation dopants (Ba2+, Al3+) caused more desensitization effect than the anion dopants (, PO43−) of the same magnitude of charge and concentration. The results favor ionic diffusion mechanism proposed earlier on the basis of doping studies.
Authors:V. M. Abdul Mujeeb, K. Muraleedharan, M. P. Kannan, and T. Ganga Devi
The thermal decomposition of potassium bromate (KBrO3) has been studied as a function of particle size, in the range 53–150 μm, by isothermal thermogravimetry at different temperatures, viz. 668, 673, 678, and 683 K in static air atmosphere. The theoretical and experimental mass loss data are in good agreement for the thermal decomposition of all samples of KBrO3 at all temperatures studied. The isothermal decomposition of all samples of KBrO3 was subjected to both model fitting and model-free (isoconversional) kinetic methods of analysis. Isothermal model fitting analysis shows that the thermal decomposition kinetics of all the samples of KBrO3 studied can be best described by the contracting square equation. Contrary to the expected increase in rate followed by a decrease with decrease in particle size, KBrO3 shows a regular increase in rate with reduction in particle size, which, we suggest, is an impact of melting of this solid during decomposition.
Authors:A. Ramanujam, P. Achuthan, P. Dhami, R. Kannan, V. Gopalakrishnan, V. Kansra, R. Iyer, and K. Balu
A generator system has been developed for the preparation of carrier-free 90Y from 90Sr present in the high level waste (HLW) of the Purex process by employing a supported liquid membrane (SLM) using 2-ethylhexyl-2-ethylhexyl phosphonic acid (KSM-17 equivalent to PC 88A) supported on a polytetrafluoro ethylene (PTFE) membrane. When uranium depleted Purex HLW at appropriate acidity is passed sequentially through octyl (phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide (CMPO) sorbed on chromosorb-102 (abbreviated as CAC) and Zeolite AR1 (synthetic mordenite) columns, all the trivalent, tetravalent and hexavalent metal ions and monovalent 137Cs ions are sorbed. After adjusting to pH 2 with NaOH the resulting effluent is used as feed in a single stage membrane cell partitioned with a PTFE membrane impregnated with KSM-17 and having a feed and receiver compartment with 5.0 ml capacity each. The receiver compartment was filled with a 0.5M HNO3 or 0.5M HCl stripping solution. 90Y alone is preferentially transported across the membrane leaving behind all the impurities viz. 90Sr, 125Sb, 106Ru, 106Rh, etc. in the feed compartment. This technique can yield 90Y in mCi levels in a pure and carrier-free form for medical applications. The feed can be reused repeatedly after allowing for 90Y buildup.
Authors:M. Jose John, K. Muraleedharan, V. M. Abdul Mujeeb, M. P. Kannan, and T. Ganga Devi
Pure and doped samples of sodium oxalate (Na2C2O4) were subjected to pre-compression and their thermal decomposition kinetics was studied at five different temperatures in the range 783–803 K under isothermal conditions by thermogravimetry. The pre-compressed samples decomposed in two stages governed by different rate laws; the Prout–Tompkins model best describes the acceleratory stage of the decomposition while the decay region is best fitted with the contracting cylinder model as in the case of uncompressed sodium oxalate samples. The rate constants k1 and k2 of the acceleratory and deceleratory stages of the thermal decomposition were dramatically decreased on pre-compression. However, the activation energies, evaluated by model fitting kinetic method, E1 and E2 for the respective stages of decomposition remained unaltered by pre-compression. The results favor ionic diffusion mechanism proposed earlier on the basis of doping studies.