- Calorimetric and dielectric studies of phase transitions in ammonium nitrite
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The heat capacity of ammonium nitrite has been measured between 13 and 310 K with an adiabatic calorimeter.Two phase transitions were found at (181.3 +/- 0.2) K and (276.5 +/- 0.1) K.The molar enthalpy and molar entropy of the phase transition were determined as follows: (670 */- 30) J*mol-1 and (3.70 +/- 0.17) J*K-1*mol-1 for the former, and (1240 +/- 60) J*mol-1 and (4.84 +/- 0.23) J*K-1*mol-1 for the latter.Another phase transition was confirmed at 346 K for which the molar entropy of transition ca. 20 J*K-1*mol-1 was estimated from d.t.a.A strong peak in the dielectric permittivity occurred at 276 K second-order transition.The first-order transition at 181 K was dielectrically neutral.The intermediate phase stable between 181 and 276 K was supercooled to 13 K as a metastable phase for which a residual molar entropy (1.4 +/- 0.5) J*K-1*mol-1 was determined.
- Moriya, Keiichi,Matsuo, Takasuke,Suga, Hiroshi
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- CALORIMETRIC, THERMOANALYTICAL AND DIELECTRIC STUDIES OF PHASE TRANSITIONS IN AMMONIUM NITRITE.
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Ammonium nitrite NH//4NO//2 has been studied by differential thermal analysis, calorimetry and dielectric measurement. A higher order phase transition was found at 276. 5 K. The enthalpy and entropy of transition are 1. 2 kJ mol** minus **1 and 4. 6 J K** minus **1 mol** minus **1, respectively. A peak of the dielectric constant, reaching 12 at 200 Hz, occurred at the transition temperature. The temperature dependence of the dielectric constant suggests that the low temperature phase is ferroelectric. A first order transition occurred at 347 K, of which a detailed study has been hampered by the decompositon of the sample
- Moriya, K.,Matsuo, T.,Suga, H.
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- Direct synthesis of V-W-Ti nanoparticle catalysts for selective catalytic reduction of NO with NH3
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A series of V-W-Ti nanoparticle catalysts with variable V doping amounts were directly synthesized by the sol-gel method, and their catalytic performances were tested for the selective catalytic reduction of NO with ammonia. The catalysts were characterized by means of XRD, Raman, BET, TEM, SEM, NH3-TPD, H2-TPR and XPS. SCR kinetic studies were conducted to understand the mechanistic features of V-W-Ti catalysts. It was found that the V0.02W0.04Ti catalyst exhibited the highest NO conversion and the lowest apparent activation energy. The characterization results showed that V was incorporated into the TiO2 framework and the redox cycle of V4+ + Ti4+ → V5+ + Ti3+ existed over the V-W-Ti catalysts. A high concentration of reducible and distorted V species could account for the excellent NH3-SCR catalytic performance of the V0.02W0.04Ti catalyst. In situ FT-IR spectroscopy was performed to investigate the mechanism of the NH3-SCR reaction over the V0.02W0.04Ti catalyst. Experimental results showed that both Lewis and Bronsted acid sites over the V0.02W0.04Ti catalyst were involved in the NH3-SCR reaction. The adsorption of nitrate species was significantly limited and the adsorbed NO2 gaseous molecules were easily formed over the V0.02W0.04Ti catalyst, which resulted in the high catalytic activity at low temperature. This journal is
- Cheng, Kai,Liu, Jian,Zhao, Zhen,Wei, Yuechang,Jiang, Guiyuan,Duan, Aijun
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