Conformation-Changing Aggregation in Hydroxyacetone: A Combined Low-Temperature FTIR, Jet, and Crystallographic Study

Aggregation in hydroxyacetone (HA) is studied using low-temperature FTIR, supersonic jet expansion, and X-ray crystallographic (in situ cryocrystallization) techniques. Along with quantum chemical methods (MP2 and DFT), the experiments unravel the conformational preferences of HA upon aggregation to dinners and oligomers. The O-H center dot center dot center dot O=C intramolecular hydrogen bond present in the gas-phase monomer partially opens upon aggregation in supersonic expansions, giving rise to intermolecular cooperatively enhanced O-H center dot center dot center dot O-H hydrogen bonds in competition with isolated O-H center dot center dot center dot O=C hydrogen bonds. On the other hand, low-temperature IR studies on the neat solid and X-ray crystallographic data reveal that HA undergoes profound conformational changes upon crystallization, with the HOCC dihedral angle changing from similar to 0 degrees in the gas phase to similar to 180 degrees in the crystalline phase, hence giving rise to a completely new conformation. These conclusions are supported by theoretical calculations performed on the geometry derived from the crystalline phase.

Low temperature synthesis of layered NaxCoO2 and KxCoO2 from NaOH/KOH fluxes and their ion exchange properties

We report a low temperature synthesis of layered Na0×20CoO2 and K0×44CoO2 phases from NaOH and KOH fluxes at 400°C. These layered oxides are employed to prepare hexagonal HCoO2, LixCoO2 and Delafossite AgCoO2 phases by ion exchange method. The resulting oxides were characterised by powder X-ray diffraction, X-ray photoelectron spectroscopy, SEM and EDX analysis. Final compositions of all these oxides are obtained from chemical analysis of elements present. Na0×20CoO2 oxide exhibits insulating to metal like behaviour, whereas AgCoO2 is semiconducting.

Shape Transformation of ZnO Nanorods/Nanotubes at Low Temperature

We report the shape transformation of ZnO nanorods/nanotubes at temperatures (similar to 700 degrees C) much lower than the bulk melting temperature (1975 degrees C). With increasing annealing temperature, not only does shape transformation take place but the luminescence characteristics of ZnO are also modified. It is proposed that the observed shape transformation is due to surface diffusion, contradicting the previously reported notion of melting and its link to luminescence. Luminescence in the green-to-red region is observed when excited with a blue laser, indicating the conversion of blue to white light.

Pulsed plasma treatment of polluted gas using wet/low temperature corona reactors

pplication of pulsed plasma for gas cleaning is gaining prominence in recent years mainly from the energy consideration point of view. Normally, gas treatment is carried out, at or above room temperature, by a conventional dry type corona reactor. However, this treatment is still inadequate in the removal of certain stable gases present in the exhaust/flue gas mixture. The authors report some interesting results of the treatment of such stable gases with pulsed plasma at very low ambient temperature. Also reported in the paper is an improvement in DeNO/DeNOx efficiency using unconventional wet-type reactors, designed and fabricated by the authors, operating at different ambient temperatures. Apart from laboratory tests on simulated gas mixtures, field tests were also carried out on the exhaust gas of a 8 kW diesel engine. Further, an attempt was made to test the feasibility of a helical wire as a corona electrode in place of the conventional straight wire electrode. A comparative analysis of the various tests is presented together with a note on the energy consideration

Non-Thermal Plasma Applications at Very Low Temperature

Application of non-thermal plasma for gas cleaning is gaining prominence in the recent years. Normally, the gas treatment was carried out at or above room temperature, by the dry type plasma reactor. However, this treatment is still inadequate in the removal of certain stable gases present in the flue gas mixture. We propose the non-thermal plasma process at very low temperature, and report here some interesting results of treatment of NO or N2O with pulsed plasma below — 100°C ambient temperature. Direct methanol synthesis from CH4 and CO2 at very low temperature is also reported. A comparative analysis of the various tests are presented together with a note on the energy consideration

Pulsed plasma treatment of polluted gas using wet/low temperature corona reactors

Application of pulsed plasma for gas cleaning is gaining prominence in recent years mainly from the energy consideration point of view. Normally, gas treatment is carried out, at or above room temperature, by a conventional dry type corona reactor. However, this treatment is still inadequate in the removal of certain stable gases present in the exhaust/flue gas mixture. The authors report some interesting results of the treatment of such stable gases with pulsed plasma at very low ambient temperature. Also reported in the paper is an improvement in DeNO/DeNOx efficiency using unconventional wet-type reactors, designed and fabricated by the authors, operating at different ambient temperatures. Apart from laboratory tests on simulated gas mixtures, field tests were also carried out on the exhaust gas of a 8 kW diesel engine. Further, an attempt was made to test the feasibility of a helical wire as a corona electrode in place of the conventional straight wire electrode. A comparative analysis of the various tests is presented together with a note on the energy consideration

Non-thermal plasma applications at Very Low Temperature

Application of non-thermal plasma for gas cleaning is gaining prominence in the recent years. Normally, the gas treatment was carried out at or above room temperature, by the dry type plasma reactor. However, this treatment is still inadequate in the removal of certain stable gases present in the flue gas mixture. We propose the non-thermal plasma process at very low temperature, and report here some interesting results of treatment of NO or N2O with pulsed plasma below — 100°C ambient temperature. Direct methanol synthesis from CH4 and CO2 at very low temperature is also reported. A comparative analysis of the various tests are presented together with a note on the energy consideration

Evidence for low temperature glassy behavior in La0.5Sr0.5CoO3

We report the observed low temperature spin glass like feature in the optimally doped La0.5Sr0.5CoO3 ferromagnetic system. The characteristic of glassy behavior has been identified by noting (i) the frequency-dependent shift of the low temperature hump position in the out of phase ac susceptibility component; (ii) evolution of freezing temperature with dc biasing field that adheres to de Almeida-Thouless relation; (iii) memory effect; and (iv) sluggish magnetic relaxation. The results of magnetic measurements demonstrate that neither the inter-cluster interaction nor the spin disorder at the interface between ferromagnetic clusters is responsible for the manifestation of such collective glassy behavior. Rather, it is believed to arise from a distinct cluster glass like phase that possibly coexists with the dominant ferromagnetic phase. (C) 2012 American Institute of Physics. [doi:10.1063/1.3684610]

Study of Low Temperature Magnetic Properties of a Single Chain Magnet with Alternate Isotropic and Non-collinear Anisotropic Units

Here we study thermodynamic properties of an important class of single-chain magnets (SCMs), where alternate units are isotropic and anisotropic with anisotropy axes being non-collinear. This class of SCMs shows slow relaxation at low temperatures which results from the interplay of two different relaxation mechanisms, namely dynamical and thermal. Here anisotropy is assumed to be large and negative, as a result, anisotropic units behave like canted spins at low temperatures; but even then simple Ising-type model does not capture the essential physics of the system due to quantum mechanical nature of the isotropic units. We here show how statistical behavior of this class of SCMs can be studied using a transfer matrix (TM) method. We also, for the first time, discuss in detail how weak inter-chain interactions can be treated by a TM method. The finite size effect is also discussed which becomes important for low temperature dynamics. At the end of this paper, we apply this technique to study a real helical chain magnet.

Anomalous low-temperature magnetic and magnetotransport properties in Ru-deficient SrRuO3

SrRuO3 is a well-known itinerant ferromagnet with many intriguing characteristics. The Ru deficiency in this system is believed to play a pivotal role in influencing many of its magnetic and transport properties. The present study involves the magnetic and transport properties of the Ru-deficient SrRu0.93O3 sample to gain more insight into the unusual low-temperature behavior. The ac susceptibility study reveals a sharp ferromagnetic transition at 150 K followed by a hump at T-h similar to 50 K, which has anomalous frequency dependence. Besides, the T-h shifts to lower temperatures with an increase in the superposed dc-biasing field and adheres to H-2 dependence, in accordance with the Gabay and Toulouse line for the Heisenberg spin glass systems. We also observe a pronounced memory effect toward the low-temperature side, signifying the characteristic of glassy behavior. The temperature-dependent magnetoresistance indicates the signature of an additional ordering toward the low-temperature side. All of the interesting findings combined unveil the existence of low-temperature cryptic magnetic phase in SrRu0.93O3. (C) 2012 American Institute of Physics. doi:10.1063/1.3673427]

Low temperature charge transport and microwave absorption of carbon coated iron nanoparticles-polymer composite films

In this paper, the low temperature electrical conductivity and microwave absorption properties of carbon coated iron nanoparticles-polyvinyl chloride composite films are investigated for different filler fractions. The filler particles are prepared by the pyrolysis of ferrocene at 980 degrees C and embedded in polyvinyl chloride matrix. The high resolution transmission electron micrographs of the filler material have shown a 5 nm thin layer graphitic carbon covering over iron particles. The room temperature electrical conductivity of the composite film changes by 10 orders of magnitude with the increase of filler concentration. A percolation threshold of 2.2 and an electromagnetic interference shielding efficiency (EMI SE) of similar to 18.6 dB in 26.5-40 GHz range are observed for 50 wt% loading. The charge transport follows three dimensional variable range hopping conduction. (C) 2012 Elsevier Ltd. All rights reserved.

Structural-modulation-driven low-temperature glassy behavior in SrRuO3

We present a critical investigation on the structural, magnetic, and magnetotransport properties of two sets of polycrystalline SrRuO3 samples with uniquely defined ferromagnetic transition temperatures. The ac magnetic susceptibility study exhibits the remarkable memory effect, a distinct characteristic of glassy behavior, at low temperatures. The transport study suggests a crossover from Fermi-liquid to non-Fermi-liquid behavior. Most strikingly, the temperature-dependent magnetoresistance exhibits two distinct dips (one around ferromagnetic ordering temperature and the other around 50 K), resembling a double-well potential in appearance. In addition, the temperature-dependent coercive field shows a plateau around 50 K. An attempt has been made to employ neutron diffraction to understand the genesis of such unusual low-temperature magnetic features. From the neutron-diffraction study, we find the evidence for changes in the unit-cell lattice parameters around 60 K and, thus, believe that the low-temperature anomalous magnetic response is closely intertwined to lattice-parameter change.

Activation of Lattice Oxygen of TiO2 by Pd2+ Ion: Correlation of Low-Temperature CO and Hydrocarbon Oxidation with Structure of Ti1-xPdxO2-x (x=0.01-0.03)

Lattice oxygen of TiO2 is activated by the substitution of Pd ion in its lattice. Ti1-xPdxO2-x (x = 0.01-0.03) have been synthesized by solution combustion method crystallizing in anatase TiO2 structure. Pd is in +2 oxidation state and Ti is in +4 oxidation state in the catalyst. Pd is more ionic in TiO2 lattice compared to Pd in PdO. Oxygen storage capacity defined by ``amount of oxygen that is used reversibly to oxidize CO'' is as high as 5100 mu mol/g of Ti0.97Pd0.03O1.97. Oxygen is extracted by CO to CO2 in absence of feed oxygen even at room temperature which is more than 20 times compared to pure TiO2. Rate of CO oxidation is 2.75 mu mol g(-1) s(-1) at 60 degrees C over Ti0.97Pd0.03O1.97 and C2H2 gets oxidized to CO2 and H2O at room temperature. Catalyst is not poisoned on long time operation of the reactor. Such high catalytic activity is due to activated lattice oxygen created by the substitution of Pd ion as seen from first-principles density functional theory (DFT) calculations with 96 atom supercells of Ti32O64, Ti31Pd1O63, Ti30Pd2O62, and Ti29Pd3O61. The compounds crystallize in anatase TiO2 structure with Pd2+ ion in nearly square planar geometry and TiO6 octahedra are distorted by the creation of weakly bound oxygens. Structural analysis of Ti31Pd1O63 which is close to 3% Pd ion substituted TiO2 shows that oxygens associated with both Ti and Pd ions in the lattice show bond valence sum of 1.87, a low value characteristic of weak oxygen in the lattice compared to oxygens with valence 2 and above in the same lattice. Exact positions of activated oxygens have been identified in the lattice from DFT calculations.

Synthesis and characterization of nano CoFe2O4 by low‐temperature combustion synthesis using different fuels

The combustion synthesis has been utilized to prepare nanophased powders of cobalt spinel ferrite using ODH and glycine fuels. The product was characterized by X‐ray diffraction; Fourier transformed spectroscopy, scanning electron microscopy, UV‐Vis absorption etc. The XRD patterns reveal spinal cubic structure. SEM profiles show the product is porous, agglomeration, irregular in shape. The crystallite size was estimated using Scherer’s formula and W‐H plots and show nano in size (13 nm: ODH & 36 nm: Glycine). The UV‐Vis absorption shows at ∼430 nm in both the samples.