Biochemistry of water-logged soils. Part IV. Carbon and nitrogen transformations

1. During the fermentation of water-logged soil containing added substances with different carbon-nitrogen ratios, the reaction first turns slightly acid, but soon returns to the original hydrogen-ion concentration (pH 7·6). 2. The quantities of ammonia present in the medium increase up to a point, after which there is steady decrease. 3. There is nitrification only in the case of substances with narrow C/N ratios. The production of nitrate generally commences only after about a month, when the vigour of the initial fermentation has subsided and fairly large quantities of ammonia have accumulated in the medium. 4. The extent of mineralisation of nitrogen is determined chiefly by the C/N ratio, though in the cases of substances like mahua and lantana the presence of other constituents may also influence the processes. The quantities of mineralised nitrogen present in the soil system generally tend to decrease after about two months.

Tailoring of Structural Morphology of Silver Nanowires in Electrochemical Growth

Noble metal such as Ag normally exists in an fcc crystal structure. However as the size of the material is decreased to nanometer lengthscales, a structural transformation from that of its bulk state can be expected with new atomic arrangements due to competition between internal packing and minimization of surface energy. In many previous studies, it has been shown that silver nanowires (AGNWs) grown inside anodic alumina (AAO) templates by ac or dc electrochemical deposition from silver salts or complexes, adopt fcc structure and below some critical diameter ∼ 20 nm they may acquire hcp structure at low temperature. This is, however, critically dependant on the nature of confinement, as AgNWs grown inside nanotube confinement with subnanometer diameter have been reported to have fcc structure. Hence the question of the crystal structure of metal nanowires under combined influence of confinement, temperature and deposition condition remains open. In this abstract we show that the alternative crystal structures of AGNWs at room temperature can be achieved with electrochemical growth processes under specific conditions determined by the deposition parameters and nature of confinement. We fabricated AgNWs of 4H hexagonal structure with diameters 30 – 80 nm inside polycarbonate (PC) templates with a modified dc electrodeposition technique, where the nanowires were grown at deposition potentials as low as 10 mV in 2 M silver nitrate solution[1]. We call this low-potential electrodeposition (LPED) since the electrodeposition process occurs at potential much less than the standard Nernst potential (770 mV) of silver. Two types of electrodes were used – stainless steel and sputtered thin Pt film, neither of which had any influence on the crystal structure of the nanowires. EDS elemental analysis showed the nanowires to consist only of silver. Although the precise atomic dynamics during the LPED process is unclear at present, we investigated this with HRTEM (high-resolution transmission electron microscopy) characterization of nanowires grown over various deposition times, as well as electrical conductivity measurements. These experiments indicate that nanowire growth does not occur through a three-dimensional diffusion controlled process, as proposed for conventional over-potential deposition, but follow a novel instantaneous linear growth mechanism. Further experiments showed that, (a) conventional electrochemical growth at a small over-potential in a 2 mM AgNO3 solution yields nanowires with expected fcc structure inside the same PC templates, and (2) no nanowire was observed under the LPED conditions inside hard AAO templates, indicating that LPED-growth process, and hcp structure of the corresponding nanowires depend on deposition parameters, as well as nature of confinement.

Synthesis of nanocrystalline alpha-Al2O3 by ultrasonic flame pyrolysis

Nanocrystalline alpha-alumina was synthesized in an indigenously built ultrasonic flame pyrolysis (UFP) setup. This paper describes the technical aspects of the apparatus and particle formation in the flame. Ultrasonically atomized aluminium nitrate dissolved in methanol-water mixture was pyrolyzed in an oxy-propane flame for yielding nanocrystalline alpha-alumina. The formation of nanophase alumina was confirmed by powder XRD analysis. Scanning electron microscopy (SEM) analysis was carried out to study particulate morphology. (C) 2003 Elsevier Science Ltd. All rights reserved.

Nitrogen and carbon flows through Belandur lake - Role of Bellandur lake as a natural wetland treating Bangalore wastewater

Much of the Bangalore sewage is treated in three streams namely Bellandur (K&C Valley),Vrishabhavati and Hebbal-Nagavara stream systems. Among these it is estimated that out of a total of about 500MLD of partially treated sewage is let into the Bellandur tank. We estimate that a total of about 77t N non-industrial anthropogenic nitrogen efflux (mainly urine and excreta) in Bangalore city. This is distributed between that handled by the three sewage streams, soak-pits and land deposition. About 17-24.5t N enters the Bellandur tank daily. This has been happening over few decades and our observations suggest that this approximately 380ha tank is functioning as a C and N removal system with reasonable efficiency. The ammoniacal and nitrate nitrogen content of the water at the discharge points were estimated and found that over 80% of the nitrogen influx and over 75% of the C influx is removed by this tank system. We observed that there are three nitrogen sinks namely bacterial, micro-algal and macrophytes. The micro-algal fraction is dominated by Microcystis and Euglenophyceae members and they appear to constitute a significant fraction. Water hyacinth represents the single largest representative of the macrophytes. This tank has been functioning in this manner for over three decades. We attempt to study this phenomenon from a material balance approach and show that it is functioning with a reasonable degree of satisfaction as a natural wetland. As the population served and concomitant influx into this wetland increases, there is a potential for the system to be overloaded and to collapse. Therefore a better understanding of its function and the need for maintenance is discussed in the paper.

Synthesis from zinc oxalate, growth mechanism and optical properties of ZnO nano/micro structures

We report the synthesis of various morphological micro to nano structured zinc oxide crystals via simple precipitation technique. The growth mechanisms of the zinc oxide nanostructures such as snowflake, rose, platelets, porous pyramid and rectangular shapes were studied in detail under various growth conditions. The precursor powders were prepared using several zinc counter ions such as chloride, nitrate and sulphate along with oxalic acid as a precipitating agent. The precursors were decomposed by heating in air resulting in the formation of different shapes of zinc oxide crystals. Variations in ZnO nanostructural shapes were possibly due to the counter ion effect. Sulphate counter ion led to unusual rose-shape morphology. Strong ultrasonic treatment on ZnO rose shows that it was formed by irregular arrangement of micro to nano size hexagonal zinc oxide platelets. The X-ray diffraction studies confirmed the wurzite structure of all zinc oxide samples synthesized using different zinc counter ions. Functional groups of the zinc oxalate precursor and zinc oxide were identified using micro Raman studies. The blue light emission spectra of the various morphologies were recorded using luminescence spectrometer. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Thermodynamic properties of Ln-O (Ln = La, Pr, Nd) solid solutions and their deoxidation by molten salt electrolysis

The lanthanide metals lanthanum, praseodymium and neodymium containing 2,200, 2,600, 1,850 mass ppm oxygen, respectively, were deoxidized to 20-30 ppm level at 1,073 K by an electrochemical method. The metal to be deoxidized was used as the cathode in an electrolysis cell which consisted of a graphite anode and molten CaCl2 electrolyte. The calcium metal produced at the cathode by electrolysis effectively deoxidized the lanthanide metal. Calcium oxide produced by deoxidation, dissolved in the melt. The liberation of carbon monoxide/dioxide at the anode was found to prevent accumulation of oxygen in the melt. For a quantitative discussion of the limits of deoxidation achievable by this technique, a thermodynamic investigation of the lanthanide-oxygen (Ln-O ; Ln = La, Pr, Nd) solid solutions was conducted. The lanthanide metal, yttrium and titanium samples were immersed in calcium-saturated CaCl2 melt, containing a small quantity of dissolved CaO, at 1,093 K. The oxygen potential of the melt and the Ln-O solid solutions were obtained from the oxygen content of yttrium samples at equilibrium, and the known thermodynamic properties of yttrium-oxygen solid solution. The results were confirmed by using Y/Y2O3 equilibrium to control the oxygen potential of the molten salt reservoir. The oxygen affinity of the metals was found to decrease in the order : Y > Ti > Nd > Pr > La. The deoxidation results are consistent with the thermodynamic properties of the RE-O solid solutions.

Enhancement of charge and energy storage in sol-gel derived pure and La-modified PbZrO3 thin films

Antiferroelectric lanthanum-modified PbZrO3 thin films with La contents between 0 and 6 at. % have been deposited on Pt(111)/Ti/SiO2/Si substrate by sol-gel route. On the extent of La-modification, maximum polarization (Pmax) and recoverable energy density (W) have been enhanced followed by their subsequent reduction. A maximum Pmax ( ∼ 0.54 C/m2 at ∼ 60 MV/m) as well as a maximum W ( ∼ 14.9 J/cc at ∼ 60 MV/m) have been achieved on 5% La modification. Both Pmax and W have been found to be strongly dependent on La-induced crystallographic orientations.

Relaxor characteristics of layered Ba1-(3/2)xLaxBi2Nb2O9 ceramics

Barium lanthanum bismuth niobate Ba1−(3/2)xLaxBi2Nb2O9 (x = 0, 0.05, 0.1, and 0.15) powders have been prepared via solid state reaction route. The monophasic layered perovskite nature of each composition of these was confirmed by x-ray diffraction studies. A continuous decrease in the lattice parameter c of parent BaBi2Nb2O9 with increase in La3+ doping level was noteworthy. A decrease in dielectric constant maximum (εm), a shift in dielectric anomaly to lower temperatures (from 488 to 382 K), and an increase in the diffuseness (γ) (from 1.58 to 1.84) of dielectric anomaly were encountered on increasing x from 0 to 0.15. Vogel-Fulcher analyses showed a decrease in freezing temperature (Tf) (from 157 to 40 K) and an increase in the activation energy (0.53 to 1.12 eV) for frequency dispersion with increase in La3+ content. A downward shift in the peak position of the pyroelectric coefficient with increasing La3+ doping level was observed. The observed changes in the above physical properties were attributed to the increase in A-site chemical heterogeneity as a result of aliovalent La3+ doping on Ba2+ sites and associated A-site vacancy formation.

Effect of Adiabatic Flame Temperature on Nano Alumina Powders during Solution Combustion Process

Nano ceramic alumina powders are synthesized by solution combustion synthesis using aluminium nitrate as oxidizer and urea as fuel with different fuel to oxidizer ratio. The variation of adiabatic flame temperatures are calculated theoretically for different fuel/oxidizer ratio according to thermodynamic concept and correlated with the observed flame (reaction) temperatures. A ``multi channel thermocouple setup connected to computer interfaced Keithley multi meter 2700'' is used to monitor the thermal events occurring during the process. The combustion products, characterized by XRD, show that the powders are composed of polycrystalline oxides with crystallite size of 32 to 52 nm. An interpretation based on maximum combustion temperature and the amount of gases produced during reaction for various fuel to oxide ratio has been proposed for the nature of combustion and its correlation with the characteristics of as-synthesized powder.

Effect of AC&DC field on the dielectric response of (Pb,La)TiO3 thin films

Lanthanum doped lead titanate thin films are the potential candidates for the capacitors, actuators and pyroelectric sensor applications due to their excellent dielectric, and ferroelectric properties. Lanthanum doped lead titanate thin films are grown on platinum coated Si substrates by excimer laser ablation technique. A broad diffused phase transition with the maximum dielectric permittivity (ϵmax) shifting to higher temperatures with the increase of frequency, along with frequency dispersion below Tc, which are the signatures of the relaxor like characteristics were observed. The dielectric properties are investigated from −60°C to 200°C with an application of different dc fields. With increasing dc field, the dielectric constant is observed to reduce and phase transition temperature shifted to higher temperature. With the increased ac signal amplitude of the applied frequency, the magnitude of the dielectric constant is increasing and the frequency dispersion is observed in ferroelectric phase, whereas in paraelectric phase, there is no dispersion has been observed. The results are correlated with the existing theories.

Synthesis, Structure, and Magnetic Properties of a New Eight-Connected Metal-Organic Framework (MOF) based on Co-4 Clusters

A hydrothermal reaction of cobalt nitrate, 4,4'-oxybis(benzoic acid) (OBA), 1,2,4-triazole, and NaOH gave rise to a deep purple colored compound Co-4(triazolate)(2)(OBA)(3)], I, possessing Co-4 clusters. The Co-4 clusters are connected together through the tirazolate moieties forming a two-dimensional layer that closely resembles the TiS2 layer. The layers are pillared by the OBA units forming the three-dimensional structure. To the best of our knowledge, this is the first observation of a pillared TiS2 layer in a metal-organic framework compound. Magnetic studies in the temperature range 1.8-300 K indicate strong antiferromagetic interactions for Co-4 clusters. The structure as well as the magnetic behavior of the present compound has been compared with the previously reported related compound Co-2(mu 3-OH)(mu(2)-H2O)(pyrazine)(OBA)(OBAH)] prepared using pyrazine as the linker between the Co-4 clusters.

Synthesis of BiFeO by carbonate precipitation

Magnetoelectric multiferroic BiFeO3 (BFO) was synthesized by a simple carbonate precipitation technique of metal nitrate solutions. X-ray powder diffraction and thermo-gravimetric analysis (TGA) revealed that the precipitate consists of an intimate mixture of crystalline bismuth carbonate and an amorphous hydroxide of iron. The precipitate yielded BiFeO3 at an optimal calcination temperature of similar to 560A degrees C. Energy dispersive X-ray (EDX) analysis showed 1:1 ratio between Bi and Fe in the oxide. X-ray photoelectron spectroscopy (XPS) studies confirmed that Fe to be in +3 oxidation states both in the precipitated powder and BiFeO3. The synthesized BFO exhibits a very weak ferromagnetic correlation at room temperature and the degree of which increases slightly on cooling down to 10 K suggesting alteration in the long range spatial modulation of the spins arrangement as compared to the bulk BiFeO3.

Nitrates-melt synthesized LiNi0.8Co0.2O2 and its performance as cathode in Li-ion cells

Layered LiNi0.8Co0.2O2 crystallizing in R (3) over barm space group is synthesized by decomposing the constituent metal-nitrate precursors. Oxidizing nature of metal nitrates stabilizes nickel in +3 oxidation state, enabling a high degree of cation ordering in the layered LiNi0.8Co0.2O2. The powder sample characterized by XRD Rietveld refinement reveals <2% Li-Ni site exchange in the layers. Scanning electron microscopic studies on the as-synthesized LiNi0.8Co0.2O2 sample reflect well defined particles of cubic morphology with particle size ranging between 200 and 250 nm. Cyclic voltammograms suggest that LiNi0.8Co0.2O2 undergoes phase transformation on first charge with resultant phase being completely reversible in subsequent cycles. The first-charge-cycle phase transition is further supported by impedance spectroscopy that shows substantial reduction in resistance during initial de-intercalation. Galvanostatic charge-discharge cycles reflect a first-discharge capacity of 184 mAh g(-1) which is stabilized at 170 mAh g(-1) over 50 cycles.

Preparation and characterization chemistry of nano-crystalline Ni-Cu-Zn ferrite

In submitted research; nanocrystalline powders having elements Ni0.5Cu0.25Zn0.25Fe2 xInxO4 with varied amounts of indium ( x = 0.0, 0.1, 0.2, 0.3 and 0.4) were grown-up by modified citrate to nitrate alchemy. The realism of single phase cubic spinel creation of the synthesized ferrite samples was studied by the DTA-TGA, XRD, SEM, EDX, FT-IR, VSM and dielectric measurements. SEM was applied to inspect the morphological variations and EDX was used to determine the compositional mass ratios. The studies on the dielectric constant (epsilon'), dielectric loss (epsilon `'), loss tangent (tan delta), ac conductivity (sigma(ac)), resistive and reactive parts of the impedance analysis (Z' and Z `') at room temperature were also carried out. The saturation magnetizations (Ms) were determined using the vibrating sample magnetometer (VSM). Ms. decreased with the increase In3+ doping content, as Fe3+ of 5(mu B) ions are replaced by In3+ of 5 mu(B) ions. (C) 2012 Elsevier B. V. All rights reserved.

Rapid synthesis and characterization of an oxygen-deficient defect perovskite La4BaCu5O13+d phase

Oxygen-deficient defect perovskite La4BaCu5O13+d phase has been synthesized by the nitrate-citrate gel combustion method at 950 C for 2 h. Structural parameters were refined by the Rietveld refinement method using room-temperature powder XRD data. The La4BaCu5O13+d crystallizes in the tetragonal structure with space group P4/m (no. 83) and having the lattice parameters a=8.6508 c=3.8606 (1) Å and (2) Å, respectively. Oxygen content was determined by the iodometric titration. Low-temperature resistivity result reveals that La4BaCu5O13+d compound exhibit metallic behavior up to 15 K.