Thermal performance of multi-walled carbon nanotubes (MWCNTs) in aqueous suspensions with surfactants SDBS and SDS

The surfactants of sodium dodecylbenzene sulfonate (SDBS) and sodium dodecyl sulfate (SDS) are used in multi-walled carbon nanotubes (MWCNT) aqueous solution respectively due to the hydrophobic nature of MWCNT. Thermal conductivities of nanofluid solutions are measured via the LAMBDA measuring system by transient hot wire method and compared as function of dispersing two different surfactants. MWCNT (hereinafter sometime referred to as CNTs) nanofluid gets a good dispersion and long time stability with both surfactants within 3/1 relative ratio mixture. However, the thermal conductivity of nanofluid decreases with increasing the concentration of both surfactants, and CNT nanofluid with SDBS exhibits better thermal conductivity than that with SDS dispersant. Finally the proper mixture ratio of CNT nanofluid with SDBS and pH value is examined and results show that 0.5 wt.% CNT nanofluids with 0.25 wt.% SDBS, at pH ≈ 9.0 condition display the best thermal performance which increases by 2.8% totally on thermal conductivity compared with that of base fluid distilled water (DW).     

Sulfur dioxide leaching of spent zinc–carbon-battery scrap

Zinc–carbon batteries, which contain around 20% zinc, 35% manganese oxides and 10% steel, are currently disposed after use as land fill or reprocessed to recover metals or oxides. Crushed material is subjected to magnetic separation followed by hydrometallurgical treatment of the non-magnetic material to recover zinc metal and manganese oxides. The leaching with 2 M sulfuric acid in the presence of hydrogen peroxide recovers 93% Zn and 82% Mn at 25 °C. Alkaline leaching with 6 M NaOH recovers 80% zinc. The present study shows that over 90% zinc and manganese can be leached in 20–30 min at 30 °C using 0.1–1.0 M sulfuric acid in the presence of sulfur dioxide. The iron extraction is sensitive to both acid concentration and sulfur dioxide flow rate. The effect of reagent concentration and particle size on the extraction of zinc, manganese and iron are reported. It is shown that the iron and manganese leaching follow a shrinking core kinetic model due to the formation of insoluble metal salts/oxides on the solid surface. This is supported by (i) the decrease in iron and manganese extraction from synthetic Fe(III)–Mn(IV)–Zn(II) oxide mixtures with increase in acid concentration from 1 M to 2 M, and (ii) the low iron dissolution and re-precipitation of dissolved manganese and zinc during prolonged leaching of battery scrap with low sulfur dioxide.     

The effects of different additives in electrolyte of AGM batteries on self-discharge

Hydrogen and oxygen evolution at the negative and positive electrodes in AGM batteries are the main reasons of self-discharging. The self-discharge of five AGM batteries was investigated by measuring different potential between two electrodes during 48 days. Five different battery electrolytes were used including 35% (w/w) H₂SO₄ without additives and the remaining contain 7.1, 9.94, and 21.3 g l⁻¹ sodium sulfate, 4 g l⁻¹ boric acid, 3 g l⁻¹ citric acid, and finally 0.7 and 1 g l⁻¹ stearic acid except one containing boric acid that the concentration of H₂SO₄ was 36% (w/w). The results revealed that the rate of self-discharge for battery without additive was 0.01 V day⁻¹. The battery with boric acid showed the lowest rate of self-discharge with 0.0025 V day⁻¹. It was also found that stearic and citric acids are comparatively appropriate additives for decreasing the self-discharge. They caused a decrease of the self-discharge rate to 0.005 and 0.0075 V day⁻¹ on appropriate concentration, respectively. In compared to other additives, sodium sulfate showed to be not an appropriate additive for decreasing battery self-discharging. The rate of 0.03 V day⁻¹ of self-discharging was obtained for the battery containing all selected concentration of sodium sulfate during first 4 days of measuring.     

Novel electrochemical behavior of zinc anodes in zinc/air batteries in the presence of additives

In our continued efforts to find an electrically rechargeable zn/air secondary battery, we report the unique behavior of a zinc oxide anode in the presence of additives such as phosphoric acid, tartaric acid, succinic acid and citric acid. These additives were added to the electrolyte, which is an 8.5 M KOH solution containing 25 g of ZnO and 3000 ppm of polyethylene glycol in 1 l of water. In zn/air systems there are two main problems namely the hydrogen overpotential and dendrite formation during recharging. Investigations have studied in detail both of the problems in order to overcome them. The results obtained in presence of additives are compared with the behavior of the electrolyte 8.5 M KOH in the absence of additives. It has been concluded that the hydrogen overpotential is raised enormously while dendrite formation is reduced to some extent. Out of the four acids studied, the order of increase in hydrogen overpotential is: tartaric acid > succinic acid > phosphoric acid > citric acid. The prevention of dendrite formation follows the order: citric acid > succinic acid > tartaric acid > phosphoric acid.     

Investigation on fuel-rich premixed flames of monocyclic aromatic hydrocarbons: Part I. Intermediate identification and mass spectrometric analysis

Fuel-rich premixed flames of seven monocyclic aromatic hydrocarbons (MAHs) including benzene, toluene, styrene, ethylbenzene, ortho-xylene, meta-xylene, and para-xylene were studied at the pressure of 30 Torr and comparable flame conditions (C/O = 0.68). The measurement of photoionization efficiency (PIE) spectra facilitated the comprehensive identification of combustion intermediates from m/z = 15 to 240, while mass spectrometric analysis was performed to gain insight into the flame chemistry. Features of the sidechain structure in fuel molecule affect the primary decomposition and aromatics growth processes, resulting in different isomeric structures or compositions of some primary products. This effect becomes weaker and weaker as both processes proceed. The results indicate that most intermediates are identical in all flames, leading to similar intermediate pools of these fuels. Consequently the chemical structures of flames fueled by different MAHs are almost identical, subsequent to the initial fuel-specific decomposition and oxidation that produce the primary intermediates. On the other hand, special features of the sidechain structure can affect the concentration levels of PAHs by increasing the concentrations of the key intermediates including the benzyl radical and phenylacetylene. Therefore, the total ion intensities of the PAH intermediates in the flames were observed to increase in the order of: benzene < toluene and styrene < four C₈H₁₀, which implies the same order of the sooting tendency.     

Selective hydrogen generation from real biomass through hydrothermal reaction at relatively low temperatures

The effect of additives, such as an inorganic alkali and a nickel catalyst, on the hydrothermal process was examined to generate hydrogen from biomass with high selectivity at relatively low temperatures around 400 °C. At first, a cellulose sample as model biomass was subjected to the hydrothermal process at 400 °C under 25 MPa in the presence of an alkali (Na₂CO₃) and a nickel catalyst (Ni/SiO₂). The combination of these two additives led not only to highly efficient generation of hydrogen but also to effective dissolution of CO₂ into an alkaline liquid layer. Here the molar yields of gas products from the cellulose sample were compared with the equilibrium quantities obtained using a thermodynamics calculation software. Furthermore, the hydrothermal process of real biomass, such as wood chips, organic fertilizer and food waste, in the presence of both the two additives resulted in highly selective production of hydrogen even at 400 °C.     

Improving the interfacial resistance in lithium cells with additives

Improved interfacial resistance was observed in lithium cells by the use of new additives. The additives, nitrile sucrose and nitrile cellulose and their lithium salts, were evaluated in polyvinylidene difluoride (PVDF) thin-film gelled electrolytes containing a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC). The electrochemical properties of the films with and without the additives were measured as a function of temperature and compared. The interfacial resistance (R_in) of the films with the additives was significantly lower than that without the additives, especially at sub-ambient temperatures. For example, the R_in at −20°C for the films with additives was around 7000 Ω cm² and that for the films without the additives was >20,000 Ω cm². Results obtained from using the additives in lithium-ion (Li-ion) cells show significant improvements in the low frequency resistance of the cells.     

Role of TiB2 and Bi2O3 additives on the rechargeability of MnO2 in alkaline cells

With an aim to understand the role of recently reported Ti-containing additives like TiB₂ on the rechargeability of manganese oxide cathodes in alkaline cells, a redox reaction involving the chemical oxidation of Mn(OH)₂ with H₂O₂ in KOH solution and a non-redox reaction involving the reaction of Mn(III) acetate with KOH have been carried out in the presence and absence of 1 wt% TiB₂ and 0.5 wt% TiB₂ + 4.5 wt% Bi₂O₃ additives. The solid products formed during the reactions have been analyzed by X-ray diffraction and a redox titration to determine the oxidation state of manganese while the filtrate has been analyzed to determine the amount of dissolved manganese with reaction time. The results suggest that irreversible reactions that follow the disproportionation reaction of dissolved Mn³⁺, which leads to the formation of electrochemically inactive phases like birnessite (δ-MnO₂) and hausmannite (Mn₃O₄) and a consequent decline in capacity retention, are suppressed in the presence of the TiB₂ additive, with the suppression being more effective when Bi₂O₃ is present along with TiB₂.     

On the influence of additives in electrolyte solutions on the electrochemical behavior of carbon/LiCoO2 cells at elevated temperatures

In this paper, we studied the influence of some organic additives in electrolyte solutions based on alkyl carbonate mixtures and LiPF₆ on the charge–discharge cycling characteristics of Li-ion cells at elevated temperatures (up to 60 °C). These additives were tested in relation to their impact on the electrochemical responses of both lithium–carbon and lithiated cobalt oxide electrodes. The additives chosen belong to organic compounds such as siloxanes, strained olefins, alkoxysilanes, and vinyl ethers. The main findings are as follows: the impedance of carbon and LiCoO₂ electrodes is smaller in solutions containing additive AD1 (hexamethyldisiloxane) from the siloxane family. Both Li/LiCoO₂ and carbon/LiCoO₂ cells exhibited much more stable charge–discharge cycling at 60 °C in the siloxane-containing solutions than in additive-free solutions. XPS analysis of LiCoO₂ electrodes cycled in the solution containing the additives indicated that their surface chemistry is strongly modified by the presence of siloxanes, even at low concentration.     

The effect of temperature on the condensed phases formed in fuel-rich premixed benzene flames

The sooting structure of premixed fuel-rich atmospheric pressure benzene flames burning at the same C/O molar ratio = 0.8 was studied in different temperature conditions (T_max = 1720 K and 1810 K) by changing the cold gas velocity. Compositional profiles of gaseous and condensed phases, measured by probe sampling and chemical analysis, indicated that pyrolytic routes leading to higher soot formation are more favoured in the lower temperature conditions.The structural analysis of condensed phases, including condensed species and soot, has been carried out by using FT-IR and UV–Visible spectroscopy sensitive to the hydrogen bonding and carbon network, respectively.The very low hydrogenated character, as evaluated by FT-IR and elemental analysis, and the high aromatic/graphitic nature of the benzene soot, as shown by a detailed examination of UV–Visible spectral parameters, confirmed the effect of benzene fuel on the internal structure of soot particles already in the early stages of particle inception.     

Cu–Ga–Se thin films prepared by a combination of electrodeposition and evaporation techniques

Cu–Ga–Se thin films were prepared using a combination of electrodeposition and evaporation techniques. A Cu–Se/Mo/glass precursor thin film was first prepared by galvanostatic electrodeposition. On top of this film three different thicknesses of Ga were deposited by evaporation. The Cu–Ga–Se thin films were formed by annealing the Ga/Cu–Se/Mo/glass thin film configuration in a tubular chamber with Se powder, at different temperatures. Thin films were characterized by X-ray diffraction (XRD), photocurrent spectroscopy (PS), inductively coupled plasma (ICP) analysis, and scanning electron microscopy (SEM). The detailed analysis from X-ray reveals that after annealing at 550 °C the CuGaSe₂ phase is formed when the thickness of Ga is 0.25 μm, however at 0.5 μm and 1.0 μm Ga the formation of CuGa₃Se₅ and CuGa₅Se₈ phases is observed respectively. Band gap values were obtained using photocurrent spectroscopy.     

Comparison of novel composite anodes with different proportions of α/β-PbO2 and the application in long-period zinc electrowinning

Zinc is an important non-ferrous metal material, of which the hydrometallurgy process has requirements for anode materials. In the present work, Pb-0.6%Sb/α-PbO₂/β-PbO₂-MnO₂(CNTs) composite electrodes with different proportions of α/β-PbO₂ were obtained and compared before and after zinc electrolytic simulation process. The optimal one was contrasted with traditional Pb-0.8 wt%Ag anode in long-period zinc electrowinning application. It was found that α-PbO₂ transition layer could effectively improve the electrodeposition distortion of β-PbO₂ surface and make the corrosion resistance better. Novel composite anode with more β-PbO₂ proportion showed weaker internal resistance and greater OER electrocatalytic activity. The anode obtained by controlling the electrodeposition time of α&β-PbO₂ phases at 1.5 h & 1 h had the best physical and chemical properties. Its cell voltage value (2.833 V) was 299 mV lower than that of traditional Pb-0.8 wt%Ag anode (3.132 V) in zinc electrodeposition. In addition, the compactness of the composite anode was improved under the function of active particles. The energy-saving effect of novel composite anode in long-period zinc electrowinning application was obvious.     

Manganese dioxide as a cathode catalyst for a direct alcohol or sodium borohydride fuel cell with a flowing alkaline electrolyte

The oxygen reduction reaction at a manganese dioxide cathode in alkaline medium is studied using cyclic voltammetry and by measuring volume of oxygen consumed at the cathode. The performance of the manganese dioxide cathode is also determined in the presence of fuel and an alkali mixture with a standard Pt/Ni anode in a flowing alkaline-electrolyte fuel cell. The fuels tested are methanol, ethanol and sodium borohydride (1 M), while 3 M KOH is used as the electrolyte. The performance of the fuel cell is measured in terms of open-circuit voltage and current–potential characteristics. A single peak in the cyclic voltammogram suggests that a four-electron pathway mechanism prevails during oxygen reduction. This is substantiated by calculating the number of electrons involved per molecule of oxygen that are reacted at the MnO₂ cathode from the oxygen consumption data for different fuels. The results show that the power density of the fuel cell increases with increase in MnO₂ loading to a certain limit but then decreases with further loading. The maximum power density is obtained at 3 mg cm⁻² of MnO₂ for each of the three different fuels.     

Catalytic activity of oxides and halides on hydrogen storage of MgH2

Hydrogen sorption kinetics of ball milled MgH₂ with and without chemical additives were studied. We observed kinetics and capacity improvement with increasing the number of sorption cycles that contributed to the micro/nano cracking of MgH₂ particles, shown by XRD and SEM studies. In addition, to investigate the proposed specific role of O²⁻-based additives on the sorption kinetics of MgH₂, we have undertaken a comparative study evaluating the performances of MgH₂ containing the NbCl₅, CaF₂ or Nb₂O₅ additives. At 300 °C, addition of NbCl₅ and CaF₂ improved the sorption capacity to 5.2 and 5.6 wt% within 50 min, respectively, in comparison to the required 80 min in the case of Nb₂O₅. This suggests the importance of the chemical nature of the catalyst for hydrogen sorption in MgH₂. In addition, the catalyst specific surface area was shown to be very critical. High surface area Nb₂O₅ (200 m² g⁻¹), prepared by novel precipitation method, exhibits an excellent catalytic activity and helped to desorb 4.5 wt% of hydrogen from MgH₂ within 80 min at a temperature as low as 200 °C.     

Two-phase flow patterns of nitrogen and nanofluids in a vertically capillary tube

Two-phase flow patterns of nitrogen gas and aqueous CuO nanofluids in a vertically capillary tube were investigated experimentally. The capillary tube had an inner diameter of 1.6 mm and a length of 500 mm. Water-based CuO nanofluid was a suspension consisted of water, CuO nanoparticles and sodium dodecyl benzol sulphate solution (SDBS). The mass concentration of CuO nanoparticles varied from 0.2 wt% to 2 wt%, while the volume concentration of SDBS varied from 0.5% to 2%. The gas superficial velocity varied from 0.1 m/s to 40 m/s, while the liquid superficial velocity varied from 0.04 m/s to 4 m/s. Experiments were carried out under atmospheric pressure and at a set temperature of 30 °C. Compared with conventional tubes, flow pattern transition lines occur at relatively lower water and gas flow velocities for gas–water flow in the capillary tube. While, flow pattern transition lines for gas–nanofluid flow occur at lower liquid and gas flow velocities than those for gas–water in the capillary tube. The effect of nanofluids on the two-phase flow patterns results mainly from the change of the gas–liquid surface tension. Concentrations of nanoparticles and SDBS have no effects on the flow patterns in the present concentration ranges.     

An experimental and theoretical study of toluene pyrolysis with tunable synchrotron VUV photoionization and molecular-beam mass spectrometry

An experimental study of toluene pyrolysis (1.24 vol.% toluene in argon) was performed at low pressure (1.33 kPa) in the temperature range of 1200–1800 K. The pyrolysis process was detected with the tunable synchrotron vacuum ultraviolet (VUV) photoionization and molecular-beam mass spectrometry (MBMS). Species up to m/z = 202 (C₁₆H₁₀), containing many radicals (CH₃, C₃H₃, C₅H₃, C₅H₅, C₇H₅, C₇H₇, C₉H₇, C₁₁H₇ and C₁₃H₉) and isomers, such as C₃H₄ (propyne and allene), C₄H₄ (vinylacetylene and 1,2,3-butatriene), C₅H₅ (cyclopentadienyl radical and pent-1-en-4-yn-3-yl radical), C₆H₄ (3-hexene-1,5-diyne and benzyne), C₆H₆ (benzene and fulvene), C₇H₈ (toluene and 5-methylene-1,3-cyclohexadiene) and so on, were identified from near-threshold measurements of photoionization mass spectra, and the mole fraction profiles of the pyrolysis products were evaluated from measurements of temperature scan. Experimental results indicate that the reaction C₇H₈ → C₇H₇ and the subsequent reactions are dominant at comparatively low temperature (<1440 K), while the reaction C₇H₈ → C₆H₅ and subsequent reactions gradually become competitive and important with increasing temperature. Furthermore the barriers of the decomposition pathways of toluene and benzyl radical determined by quantum mechanical calculation are in good agreement with the initial formation temperatures of the species. Based on the mole fractions and formation temperatures of the detected pyrolysis species, a simple reaction network is deduced. At relatively high temperatures, H-abstraction is prevalent and the mole fraction of C₂H₂ is so high that many aromatics are formed through the hydrogen-abstraction/C₂H₂-addition (HACA) mechanism. Moreover the reactions of benzyl with toluene/benzyl/phenyl/propargyl radicals to directly produce larger aromatics should play an influential role in PAH formation. Meanwhile the five-member-ring recombination mechanism also plays an indispensable role in the aromatics growth, as cyclopentadienyl radical (C₅H₅) was determined to be a major product of the decomposition of toluene.     

Effect of heat-treatment temperature on carbon corrosion in polymer electrolyte membrane fuel cells

This study examines the effect of heat-treatment temperature on the electrochemical corrosion of carbon nanofibers (CNFs) in polymer electrolyte membrane (PEM) fuel cells. Corrosion is investigated by monitoring the generation of CO₂ using an on-line mass spectrometer at a constant potential of 1.4 V for 30 min. The experimental results show that the generation of CO₂ decreases with increasing heat-treatment temperature, indicating that less electrochemical carbon corrosion occurs. In particular, when the heat-treatment temperature is 2400 °C, the change intensifies. X-ray photoelectron spectroscopic analysis shows that oxygen functional groups on the carbon surface decrease with increasing heat-treatment temperature. A reduction in oxygen functional groups increases the hydrophobic nature of the carbon surface, which is responsible for the increased corrosion resistance of CNFs.     

Kinetic model for the esterification of oleic acid catalyzed by zinc acetate in subcritical methanol

The esterification of oleic acid in subcritical methanol catalyzed by zinc acetate was investigated in a batch-type autoclave. The effect of reaction conditions such as temperature, pressure, reaction time and molar ratio of oleic acid to methanol on the esterification was examined. The oleic acid conversion reached 95.0% under 220 °C and 6.0 MPa with the molar ratio of methanol to oleic acid being 4 and 1.0 wt% zinc acetate as catalyst. A kinetic model for the esterification was established. By fitting the kinetic model with the experimental results, the reaction order n = 2.2 and activation energy E_a = 32.62 KJ/mol were obtained.     

An experimental and kinetic modeling study of cyclohexane pyrolysis at low pressure

The pyrolysis of cyclohexane at low pressure (40 mbar) was studied in a plug flow reactor from 950 to 1520 K by synchrotron VUV photoionization mass spectrometry. More than 30 species were identified by measurement of photoionization efficiency (PIE) spectra, including some radicals like methyl, propargyl, allyl and cyclopentadienyl radicals, and stable products (e.g., 1-hexene, benzene and some aromatics). Among all the products, 1-hexene is formed at the lowest temperature, indicating that the isomerization of cyclohexane to 1-hexene is the dominant initial decomposition channel under the condition of our experiment. We built a kinetic model including 148 species and 557 reactions to simulate the experimental results. The model satisfactorily reproduced the mole fraction profiles of most pyrolysis products. The rate of production (ROP) analysis at 1360 and 1520 K shows that cyclohexane is consumed mainly through two reaction sequences: cyclohexane → 1-hexene → allyl radical + n-propyl radical, and cyclohexane → cyclohexyl radical → hex-5-en-1-yl radical that further decomposes to 1,3-butadiene via hex-1-en-3-yl and but-3-en-1-yl radicals. Besides the stepwise dehydrogenation of cyclohexane, C3 + C3 channels, i.e. C₃H₃ + C₃H₃ and C₃H₃ + aC₃H₅ also have important contribution to benzene formation. The simulation reveals that C₃H₃ + C₃H₃ = phenyl + H reaction is the key step for other aromatics formation, i.e. toluene, phenylacetylene, styrene, ethylbenzene and indene in this work.     

Electrodeposition synthesis and electrochemical properties of nanostructured γ-MnO2 films

The thin films of carambola-like γ-MnO₂ nanoflakes with about 20 nm in thickness and at least 200 nm in width were prepared on nickel sheets by combination of potentiostatic and cyclic voltammetric electrodeposition techniques. The as-prepared MnO₂ nanomaterials, which were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS), were used as the active material of the positive electrode for primary alkaline Zn/MnO₂ batteries and electrochemical supercapacitors. Electrochemical measurements showed that the MnO₂ nanoflake films displayed high potential plateau (around 1.0 V versus Zn) in primary Zn/MnO₂ batteries at the discharge current density of 500 mA g⁻¹ and high specific capacitance of 240 F g⁻¹ at the current density of 1 mA cm⁻². This indicated the potential application of carambola-like γ-MnO₂ nanoflakes in high-power batteries and electrochemical supercapacitors. The growth process for the one- and three-dimensional nanostructured MnO₂ was discussed on the basis of potentiostatic and cyclic voltammetric techniques. The present synthesis method can be extended to the preparation of other nanostructured metal-oxide films.