Fuel Rich Research Articles

Influence of fuels in the sol-gel combustion synthesis of Li2MnO3 positive electrode material for Li-ion battery

The capacities of Li2MnO3 depend on the method of synthesis and synthesis conditions. The influence of the nature of fuel and fuel compositions on the sol-gel combustion synthesis (SCS) of Li2MnO3 and the concomitant effect on their electrochemical performance are reported. The use of glycine, citric acid fuels and their mixtures in the fuel stoichiometric compositions resulted in a violent reaction leading to loss of powders. Therefore, the fuel-rich (FR) composition that allows for better complexation of the metals in solution and doesn't result in any violent reaction is recommended in the SCS of Li2MnO3 and other ceramic oxides. The glycine FR composition produced Li2MnO3 with the poorest electrochemical performance that was ascribed to its rough morphology. The citric acid FR Li2MnO3 sample (C-FR) delivered the most comprehensive electrochemical performance considering its increasing discharge capacities with an increase in the current density, its suppression of the charge transfer resistance after the rate capability test, and good rate performance. The improved electrochemical performances of C-FR were attributed mainly to its large particle size and well-developed crystallites. The results show that the SCS of C-FR Li2MnO3 sample could be further optimized to exploit better electrochemical properties of this material.

High temperature oxidation of C 2Cl 4/CH 4 mixtures

Experiments on high temperature oxidation of multi-chlorinated hydrocarbons, tetrachloroethylene (C 2Cl 4), with hydrocarbon fuels, CH 4, were performed in a 15 mm i.d. tubular flow reactor. Temperatures ranged from 700 to 850 °C, with the average residence time in the range from 0.3 to 1.5 s. Three equivalence ratios, φ=0.87 (fuel-lean (FL)), φ=1 (stoichiometry (S)), and φ=1.3 (fuel-rich (FR)), were studied. The global Arrhenius equations for the decomposition of C 2Cl 4 for each reactant set ratio are: k lean =5.77×10 15 exp(−30447/RT) , k stoi =5.15×10 15 exp(−30421/RT) , and k rich =6.32×10 14 exp(−28879/RT) . The important reactions for destruction of parent C 2Cl 4 include: C 2Cl 4→C 2Cl 3+Cl, C 2Cl 4+H→C 2Cl 3+HCl and C 2Cl 4+H→C 2HCl 3+Cl. The resulting reactant loss, and intermediate and final product profiles were determined. C 2HCl 3, C 2Cl 2, CO, CO 2 and HCl are the major products for the reaction of C 2Cl 4/CH 4/O 2 mixtures for these three reaction systems. Minor intermediates include C 2H 3Cl, C 2HCl, COCl 2, CH 3CHCl 2, C 2H 4, C 2H 6, CCl 2CHCH 3, trans-CHClCHCl, cis-CHClCHCl, trans-ClHCCClCH 3, C 6H 6, and Cl 2. The experimental data showed that as the oxygen concentration increased, the temperature needed to detect the resulting products decreased.

Flame-ion chemistry of the lanthanide metals Ce, Pr and Nd

A pair of premixed, H 2O 2Ar flames of fuel-rich (FR) and fuel-lean (FL) composition, both at atmospheric pressure and 2425 K, were doped with about 10 −6 mol fraction of the lanthanide metals La, Ce, Pr and Nd; from a previous study, La was used as a benchmark. The metals produce solid particles in the flames and gaseous metallic species. The latter include metallic atoms A near the flame reaction zone, but only the monoxide AO, the oxide hydroxide OAOH and, in some cases, the dioxide AO 2 further downstream at equilibrium. Metallic ions (< 1% of the total metal) were observed by sampling the flames through a nozzle into a mass spectrometer. All of the observed ions can be represented by four hydrate series: (a) major signals of AO +· nH 2O ( n = 0–3) for La, Ce, Pr and Nd; (b) small signals of AO 2H +· nH 2O ( n = 0–2) for Ce, Pr and Nd; (c) still smaller signals of AO 2 +· nH 2O ( n = 0, 1) for Ce, Pr and Nd in the FL flame only; and (d) tiny signals of AOH +· nH 2O ( n = 0, 1) for Pr and Nd in the FR flame only. The actual structures of some of these ions may not correspond to simple hydrates: e.g. AO +·H 2O = A(OH) 2 + = protonated OAOH; AO 2H +·H 2O = A(OH) 3 +, etc. Since hydrogen flames contain essentially no natural ionization, a major objective was to consider probable ionization mechanisms for the metals. The primary reactions include both chemi-ionization, and thermal (collisional) ionization of AO whose ionization energy is low (about 5 eV). Some of the ions are formed by secondary ion/molecule reactions including three-body hydration, proton transfer, electron (charge) transfer, H atom abstraction by radicals and oxidation. In addition, the chemical ionization of the metallic species by H 3O + was investigated. The flame-ion chemistry of these metals is discussed in detail.

Ion chemistry of second-row transition metals in hydrocarbon flames: cations and anions of Y, Zr, Nb, and Mo

A pair of laminar, premixed, CH4–O2 flames above 2000 K at atmospheric pressure, one fuel-rich (FR) and the other fuel-lean (FL), were doped with ~10−6 mol fraction of the second-row transition metals Y, Zr, Nb, and Mo. Since these hydrocarbon flames contain natural ionization, metallic ions were produced in the flames by the chemical ionization (CI) of metallic neutral species, primarily by H3O+ and OH− as CI sources. Both positive and negative ions of the metals were observed as profiles of ion concentration versus distance along the flame axis by sampling the flames through a nozzle into a mass spectrometer. For yttrium, the observed ions include the YO+•nH2O (n = 0–3) series, and Y(OH)4−. With zirconium, they include the ZrO(OH)+•nH2O (n = 0–2) series, and ZrO(OH)3−. Those observed with niobium were the cations Nb(OH)3+ and Nb(OH)4+, and the single anion NbO2(OH)2−. For molybdenum, they include the cations MoO(OH)2+ and MoO(OH)3+, and the anions MoO3− and MoO3(OH)−. Not every ion was observed in each flame; the FL flame tended to favour the ions in higher oxidation states. Also, flame ions in higher oxidation states were emphasized for these second-row transition metals compared with their first-row counterparts. Some ions written as members of hydrate series may have structures different from those of simple hydrates; e.g., YO+•H2O = Y(OH)2+ and ZrO(OH)+•H2O = Zr(OH)3+, etc. The ion chemistry for the production of these ions by CI in flames is discussed in detail. Keywords: transition metals, ions, flame, gas phase, negative ions.

Ion chemistry of phosphorus in hydrocarbon flames: Part 1. electron scavenging by negative ion formation

Premixed methane—oxygen flames at atmospheric pressure of both fuel-rich (FR) and fuel-lean (FL; i.e. oxygen-rich) composition were doped with small amounts ( < 0.1 mol %) of volatile phosphorus alkyl triesters. It was demonstrated that these organo phosphorus compounds lead to efficient scavenging of the free electrons, normally present in the burnt gas of hydrocarbon flames, by negative ion formation. The anions produced by chemical ionization reactions were observed by sampling the flame gas through a nozzle into a mass spectrometer. Under both FR and FL conditions, the mass spectrum of phosphorus anions was dominated by PO − 3, with a lesser contribution from PO − 2. Also, H 2PO − 4 and PO − were observed below 100 u, as well as HPO − 4 and PO − 4 in the FL flame, and H 2CPO − 2 in the FR case. Above 100 u, the identity of the additive survivedin the FR flame to give anions of the type (RO) x PO y (OH) − z , where R is the alkyl group. However, these were replaced in the FL flame by anions of the type PO − n ( n = 5–8) below 160 u. The formation chemistry of this considerable variety of phosphorus anions is discussed in detail, involving mainly three-body association, nucleophilic displacement (S N2) and proton abstraction reactions.

Ion chemistry of phosphorus in hydrocarbon flames: Part II. Positive Ion Formation

Premixed methane/oxygen flames at atmospheric pressure of both fuel-rich (FR) and fuel-lean (FL; i.e. oxygen-rich) composition were doped with small amounts (< 0.1 mol%) of volatile phosphorus alkyl triesters. The phosphorus positive ions (cations) produced by chemical ionization reactions were observed by sampling the flame through a nozzle into a mass spectrometer. This study follows on from Part I in which the phosphorus negative ions (anions) were similarly investigated. About a dozen phosphorus cations were observed in each flame below 160 u, many of them common to both flames. The cations can be represented by five series. The first involves ions of the type (RO) 4- n P(OH) + n with n = 0–4 (FR, R = CH 3) or n = 2–4(FL, R = CH 2H 5). Evidence was obtained for a methyl cation transfer reaction. The remaining four series amount to the hydrates PO + n · xH 2O with n = 1–4; x has various values for each series in each flame in the range 0–3. However, many of these “hydrates” have the general form PO a (OH) b (O 2) c (H 2O) + d involving coordinate bond formation of O 2 and H 2O with the central P atom. Virtually all the high-mass ions appear to have four-coordinate tetrahedral structures. The phosphorus cation formation chemistry is discussed in detail involving three-body association, nucleophilic displacement (S N2) and proton transfer reactions. Finally, some points of comparison are made between the cations and the phosphorus anions presented in Part I.