Slip-Jump Model for Carbon Combustion Synthesis of Complex Oxide Nanoparticles

Carbon Combustion Synthesis of Oxides (CCSO) is a promising method to produce submicron- and nano- sized complex oxides. The CCSO was successfully utilized for producing several complex oxides, a complete theoretical model including the sample porosity, fl ow parameters and reaction energetics is needed to predict the combustion parameters for CCSO. In this work, we studied the ignition temperature and combustion wave axial temperature distribution, activation energy, combustion heat and thermal losses for a typical CCSO synthesis for cylindrical samples of Ni-Zn ferrites with high (\u3e85%) porosity. We developed a two level combustion model of chemically active nano-dispersed mixture, using the experimentally measured ignition temperature and combustion parameter values utilizing the slipjump method for high Knudsen numbers. The theoretical predictions of highly porous samples when the flow resistivity is small and the gas can easily fl ow through the cylindrical sample are in good agreement with the experimental data. The calculation of combustion characteristics for the lower porosity values demonstrated that the surface combustion was dominated due to high gas flow resistivity of the sample. Finger combustion features were observed at this combustion mode

Study of dynamic features of highly energetic reactions by DSC and High-Speed Temperature Scanner (HSTS)

The dynamic features of Al2O3 - polytetrafluoroethylene (PTFE) and Al - PTFE reactions in non-isothermal conditions are presented. The Differential Scanning Calorimetry (DSC) and High-Speed Temperature Scanner (HSTS) were used to characterize the Al2O3/Al – PTFE reactions at different heating rates. The study shows that the HSTS instrument can give more information about the reaction mechanism and kinetics than the conventional DSC measurements. In this work we show that high heating rates may reveal exothermic reaction between Al2O3 and PTFE that were previously unidentified. The PTFE can potentially remove the oxide layer from aluminum in the initial period of the reaction and increase the direct contact area between oxygen and aluminum, which increases the reaction velocity and improves the energy release abilities of the system

Fabrication of Yttrium Ferrite Nanoparticles by Solution Combustion Synthesis

The ternary oxide system Y-Fe-O presents fascinating magnetic properties that are sensitive to the crystalline size of particles. There is a major challenge to fabricate these materials in nano-crystalline forms due to particle conglomeration during nucleation and synthesis. In this paper we report the fabrication of nano sized crystalline yttrium ferrite by solution combustion synthesis (SCS) where yttrium and iron nitrates were used as metal precursors with glycine as a fuel. The magnetic properties of the product can be selectively controlled by adjusting the ratio of glycine to metal nitrates. Yttrium ferrite nano-powder was obtained by using three concentration of glycine (3, 6 and 10 wt.%) in the initial exothermic mixture. Increasing glycine content was found to increase the reaction temperature of the system. The structural and magnetic properties of yttrium ferrite before and after annealing at temperature of 1000 °C were investigated by X-ray diffractometry, Differential Scanning Calorimetry (DSC) and cryogenic magnetometry (PPMS, Quantum Design). X-ray diffraction showed that, a broad diffraction peak was found for all samples indicating the amorphous nature of the product. Particle size and product morphology analysis identified that, Nitrate/ glycine combustion caused considerable gas evolution, mainly carbon dioxide, N2 and H2O vapor, which caused the synthesized powders to become friable and loosely agglomerated for glycine concentration from 3 wt.% up to 10 wt.%. The study of the magnetic properties of produced materials in a metastable state was performed by measuring dependencies of Magnetization (M) on temperature, and magnetization on magnetic field strength between 5 K and 300 K. Magnetization measurements on temperature zero-fieldcooled and field-cooled show different patterns when the fraction of glycine is increased. The analysis of zero-field-cooled (ZFC), field-cooled (FC) and magnetization curves of annealed samples confirmed that nanoparticles exhibit superparamagnetic behavior. The increasing concentration of glycine leads to an increased blocking temperature

Charge and Discharge Behaviour of Li-Ion Batteries at Various Temperatures Containing LiCoO2 Nanostructured Cathode Produced by CCSO

There are technical barriers for penetration market requesting rechargeable lithium-ion battery packs for portable devices that operate in extreme hot and cold environments. Many portable electronics are used in very cold (-40 °C) environments, and many medical devices need batteries that operate at high temperatures. Conventional Li-ion batteries start to suffer as the temperature drops below 0 °C and the internal impedance of the battery increases. Battery capacity also reduced during the higher/lower temperatures. The present work describes the laboratory made lithium ion battery behaviour features at different operation temperatures. The pouch-type battery was prepared by exploiting LiCoO2 cathode material synthesized by novel synthetic approach referred as Carbon Combustion Synthesis of Oxides (CCSO). The main goal of this paper focuses on evaluation of the efficiency of positive electrode produced by CCSO method. Performance studies of battery showed that the capacity fade of pouch type battery increases with increase in temperature. The experimental results demonstrate the dramatic effects on cell self-heating upon electrochemical performance. The study involves an extensive analysis of discharge and charge characteristics of battery at each temperature following 30 cycles. After 10 cycles, the battery cycled at RT and 45 °C showed, the capacity fade of 20% and 25% respectively. The discharge capacity for the battery cycled at 25 °C was found to be higher when compared with the battery cycled at 0 °C and 45 °C. The capacity of the battery also decreases when cycling at low temperatures. It was important time to charge the battery was only 2.5 hours to obtain identical nominal capacity under the charging protocol. The decrease capability of battery cycled at high temperature can be explained with secondary active material loss dominating the other losses

Low-cost carbon-silicon nanocomposite anodes for lithium ion batteries

The specific energy of the existing lithium ion battery cells is limited because intercalation electrodes made of activated carbon (AC) materials have limited lithium ion storage capacities. Carbon nanotubes, graphene, and carbon nanofibers are the most sought alternatives to replace AC materials but their synthesis cost makes them highly prohibitive. Silicon has recently emerged as a strong candidate to replace existing graphite anodes due to its inherently large specific capacity and low working potential. However, pure silicon electrodes have shown poor mechanical integrity due to the dramatic expansion of the material during battery operation. This results in high irreversible capacity and short cycle life. We report on the synthesis and use of carbon and hybrid carbon-silicon nanostructures made by a simplified thermo-mechanical milling process to produce low-cost high-energy lithium ion battery anodes. Our work is based on an abundant, cost-effective, and easy-to-launch source of carbon soot having amorphous nature in combination with scrap silicon with crystalline nature. The carbon soot is transformed in situ into graphene and graphitic carbon during mechanical milling leading to superior elastic properties. Micro-Raman mapping shows a well-dispersed microstructure for both carbon and silicon. The fabricated composites are used for battery anodes, and the results are compared with commercial anodes from MTI Corporation. The anodes are integrated in batteries and tested; the results are compared to those seen in commercial batteries. For quick laboratory assessment, all electrochemical cells were fabricated under available environment conditions and they were tested at room temperature. Initial electrochemical analysis results on specific capacity, efficiency, and cyclability in comparison to currently available AC counterpart are promising to advance cost-effective commercial lithium ion battery technology. The electrochemical performance observed for carbon soot material is very interesting given the fact that its production cost is away cheaper than activated carbon. The cost of activated carbon is about $15/kg whereas the cost to manufacture carbon soot as a by-product from large-scale milling of abundant graphite is about$1/kg. Additionally, here, we propose a method that is environmentally friendly with strong potential for industrialization. © 2014 Badi et al.; licensee Springer

Computational and Experimental Study on Undoped and Er-Doped Lithium Tantalate Nanofluorescent Probes

We present a combined density functional theory (DFT) and experimental work on lithium tantalate LiTaO3 (LT) and its Er-doped counterparts. We calculate the electronic and optical properties for both LT and LT:Er+3, with Er occupying either Li or Ta sites, at 4.167 mol%. The generalized gradient approximation (GGA) calculations show that the Er-4 f bands appear closer to the conduction band bottom and to the valance band top, for the first and second doped configurations, respectively. This agrees with changes in the imaginary part of the frequency dependent dielectric function between the doped configurations. There are striking differences between the GGA and the hybrid functional HSE06 calculations for the band structures of the doped configurations. HSE06 accurately predicts the location in energy for all Er-4 f orbitals: These are now spread in energy and appear above and below the Fermi energy. We synthesized LT:Er+3 nanoparticles, validated through X-ray diffraction and Scanning Electron Microscopy. Differential scanning calorimetry and thermogravimetric analysis confirmed increases in the activation energy and lowering of the reaction temperature due to Er+3 doping. The LT:Er+3photoluminescence showed strong f–f emission in the visible and near-infrared regions, in an excellent agreement with the HSE06 electronic information

Carbon combustion synthesis of Janus-like particles of magnetoelectric cobalt ferrite and barium titanate

Carbon combustion synthesis of oxides was applied for quick and energy efficient production of multiferroic composite of cobalt ferrite and barium titanate to form Janus-like particles matrix structure. The exothermic oxidation of carbon nanoparticles with an average size of 5 nm and a specific surface area of 110 m2/g generates a self-propagating thermal wave with peak temperature of up to 1000 °C. The thermal front rapidly propagates through the mixture of solid reactants (magnetic- CoFe2O4 and ferroelectric-BaTiO3) and results in localized hot-spot sintering of magneto-electric phases to form a nanocomposite structure. Carbon is not incorporated in the product and is emitted as a gaseous CO2. Existence of discrete CoFe2O4 and BaTiO3phases in the composites nanostructures was confirmed using X-ray powder diffraction along with SEM and TEM analysis. We estimated the activation energy for the combustion synthesis of Janus-like particles to be 112 ± 3.3 kJ/mol, indicating that the barium titanate and cobalt ferrite presence decrease the activation energy barrier of carbon oxidation and facilitate the ignition process of the combustion synthesis. We observe that the as-synthesized samples show magnetoelectric coupling on multiferroic cobalt ferrite–barium titanate ceramic composites

Nanoenergetic composite based on I2O5/Al for biological agent defeat

The risk of bioterrorism events involving the intentional airborne release of contagious agents has led to development of new approaches for bio agent defeat technologies both indoors and outdoors. This report describes nanoenergetic gas generators (NGG) system that exhibit long term stability and superior release of biocidal substances for destruction of pathogenic bacteria. The effect of iodine vaporization on destroying of Escherichia coli (E-coli, HB101 K-12 strain) by using expressing Green Fluorescent Protein (GFP) was investigated. HB101 K-12 has been genetically modified to prevent its growth unless grown on an enriched medium. To obtain quantitative data we used pGLO transformation of bacteria with a gene that codes for GFP. Following the transformation procedure, the bacteria express their newly acquired jellyfish gene and produce the fluorescent protein which causes them to glow a bright green color under ultraviolet light. The experimental results revealed that increasing concentration of deposited iodine up to 20 ug/m2 the iodine totally destroyed the entire E-coli colonies. These behavioral features of the Al/I2O5 nanothermite mixture offer both a thermal event and release of biocidal agent (atomic iodine) useful in destroying detrimental biological materials. The study has shown that I2O5/Al nanosystem is extremely effective to sterilize harmful biological agents such (E-coli) bacteria in seconds

Electrochemical features of combustion-synthesized lithium cobaltate as cathode material for lithium ion battery

Lithium cobaltate (LiCoO2) was produced by carbon combustion synthesis of oxide (CCSO) using carbon nanoparticles as a fuel. In this method, the exothermic oxidation of carbon nanoparticles with an average size of 5 nm (specific surface 80 m2/g) gives rise to a self-propagating thermal wave with maximum temperatures of up to 900°C. The thermal front rapidly propagates through the mixture of solid reactants converting it to lithium cobaltate. XRD data suggest that the as-synthesized products were single phase. Carbon is not incorporated in the product and is evolved from the reaction zone as gaseous CO2. Thermogravimetric analysis was used to identify the features of interaction in the LiNO3-Co3O4-C system. The key features affecting the process-carbon pre-concentration in the reacting mixture and oxygen infiltration to the reaction zone-led to the formation of layered structure of LiCoO2 and affected the particle sizes. The synthesized crystalline nanoparticles were nearly spherical, and their average particle diameters ranged between 60 and 200 nm

PTFE–Al2O3 reactive interaction at high heating rates

Differential scanning calorimetry and a high-speed temperature scanner were used to characterize dynamic features of the reaction between polytetrafluoroethylene (PTFE) and Al2O3 under heating rates ranging between 20 and 780 °C min−1. Exothermic reaction behavior between PTFE and Al2O3 was observed at heating rates of 150 °C min−1 and higher. Thermodynamic calculations predicted an adiabatic temperature of 1,425 K for the PTFE/Al2O3 stoichiometric ratio. At lower heating rates, endothermic decomposition of PTFE dominated the interaction, where PTFE decomposes into gaseous products that escape the system without interacting with alumina. The enthalpy of the PTFE–Al2O3 exothermic reaction was estimated to be −103 kJ mol−1 with activation energy of 21 kJ mol−1. This study shows that, for energetic formulation of Al–PTFE, the Al2O3 layer on the aluminum particles can exothermically react with PTFE, producing AlF3 and carbon monoxide