Features of kinetic processes in the active medium of a pulsed chemical oxygen-iodine laser

Conclusion It can be concluded from our experiments and calculations that the product CF₃O₂ of the interaction between the CF₃ radical and the O₂ molecule quenches the oxygen O₂(¹) more strongly. At low chlorine admixture density in the singlet-oxygen stream this output energy of the oxygen-iodine laser with CF₃I as the atomic iodine donor is lower compared with CH₃I. The rate constant of quenching singlet oxygen by CF₃O₂ molecules is (3–5)·10^–11 cm³·sec^–1. It would be possible to decrease the influence of CF₃O₂ by adding to the initial O₂ ^*–O₂–CF₃I–Ar active mixture some other substance causing the CF₃ radicals to enter in a chemical reaction with a shorter characteristic time than that for CF₃O₂ formation. Of course, neither the initial substance nor the reaction products should quench O₂ ^* noticeably. This role can be possibly assumed by the NO molecule.The influence of the chlorine additive on the output energy of a laser with CH₃I and CF₃I differs greatly. The choice of the chlorine donor must therefore be determined by the amount of this additive. CH₃I is preferable if the chlorine is fully utilized in the singlet-oxygen laser, and CF₃I in the opposite case.Quantum Radiophysics Division, Lebdev Physics Institute. Translation of Preprint No. 21 of the Lebedev Physics Institute, Moscow, 1991.     

Specific features of the inhibition of the combustion of propane-air and hydrogen-air mixtures by trifluoromethane and pentafluoroethane

Experimental data on the flammability limits and combustion kinetics of propane-air mixtures at atmospheric pressure in the presence and absence of CF₃H, C₂F₅H, CF₄, N₂, and CO₂ additives are presented. It was found that CF₃H and C₂F₅H inhibit the process of combustion. At the same time, the effect of CF₄, N₂, and CO₂ is caused only by mixture dilution, with a marked contribution of heat capacity in the case of CF₄ and CO₂. The mechanisms of chain termination by the inhibitors and the reasons for their different efficiency in the inhibition of hydrogen and propane combustion are explained.     

Zur plasmachemischen Umsetzung von GaAs mit CCl4 und CF2Cl2 in Gegenwart von Sauerstoff

The halogen liberation and reaction with GaAs by a plasma discharge in a flow reactor, using CCl₄, CF₂Cl₂ and CCl₄/O₂, CF₂Cl₂/O₂ mixtures was measured. The yields were studied in dependence from the output of a 27 MHz radio-frequency generator and from the oxygen content of the etching gas. A simple model of the kinetics is introduced to discuss the experimental results.     

Investigation on the storage performance of LiMn2O4 at elevated temperature with the mixture of electrolyte stabilizer

In order to investigate the effect of different electrolytes of LiPF₆-based and LiPF₆-based with the mixed additives of ethanolamine and heptamethyldisilazane on the storage performance of LiMn₂O₄, the commercial LiMn₂O₄ are added into these different electrolytes for storing deliberately at 60 °C in air for 4 h. The results show that the electrolyte with additives can prevent LiMn₂O₄ from being eroded by HF to a certain extent, and improve the storage performance of the material. The initial discharge capacities are 97.7 and 88.4 mAh g^?1 at 0.1 and 1?C, respectively, which are much higher than that 84.4 and 63.6 mAh?g^?1 of LiMn₂O₄ stored in the electrolyte without additives. Moreover, the former LiMn₂O₄ retains 89.1 % of its initial discharge capacity at 1?C after 150 cycles, while this is not up to 84 % for the latter.     

Structural, electrical and gas-sensing properties of In2O3 : Ag composite nanoparticle layers

The central objective of this study is to investigate (i) size-dependent properties of In₂O₃ nanoparticles and (ii) the role of metal additives in enhancing the gas sensing response. For this purpose, In₂O₃ : Ag composite nanoparticle layers having welldefined individual nanoparticle size and composition have been grown by a two step synthesis method. Thermogravimetric analysis, X-ray diffraction and transmission electron microscopy have been used to study the effect of post-synthesis heat treatment on the size and structure of the nanoparticles. A first-time unambiguous observation of sizedependent lowering of transformation temperature has been explained in terms of lower cohesive energy of surface atoms and increase in surface-to-volume ratio with decrease in nanoparticle size. The gas sensing studies of In₂O₃ as well as the In₂O₃ : Ag composite nanoparticle layers have been studied as a function of size and composition. In₂O₃: Ag composite nanoparticle layers with 15% silver show a sensitivity of 436 and response time of 6 s for 1000 ppm of ethanol in air. Ag additives form a p-type Ag₂O, which interact with n-type In₂O₃ to produce an electron-deficient space-charge layer. In the presence of ethanol, interfacial Ag₂O reduces to Ag, creating an accumulation layer in In₂O₃ resulting in increased sensitivity     

Preparation, characterization and luminescence properties of porous Si3N4 ceramics with Eu2O3 as sintering additive

Porous Si₃N₄ ceramics with photoluminescence properties were prepared by pressureless sintering using α-Si₃N₄ powder as raw material and Eu₂O₃ as sintering additive. Chemical composition, phase formation, microstructure and photoluminescence properties of porous Si₃N₄ ceramics were studied by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence measurements (PL/PLE). The results show that single Eu₂O₃ additive promotes α→β transformation but not significant densification. A broad band emission center at 570 nm assigned to Eu²⁺ is observed, Eu³⁺ in Eu₂O₃ is (partially) converted to Eu²⁺ by reaction with Si₃N₄, which results in a lower β aspect ratio and β-content compared to the other Ln (Ln=lanthanide) oxide additives.     

Fuel additives and heat treatment effects on nanocrystalline zinc ferrite phase composition

Nanocrystalline ZnFe₂O₄ powder was prepared by the auto-combustion method using citric acid, acetic acid, carbamide and acrylic acid as fuel additives. Pure spinel zinc ferrite with the crystallite size of about 15 nm can be obtained by using acrylic acid as fuel additive. Samples prepared using other fuel additives contain ZnO impurities. In order to eliminate ZnO impurities, the sample prepared with citric acid as fuel additive was annealed at different temperatures up to 1000 °C in air and in argon. Annealed powders have pure ZnFe₂O₄ phase when annealing temperature is higher than 650 °C in air. Sample annealed at 650 °C in air is paramagnetic. However, annealed powders become a mixture of Fe₃O₄ and FeO after annealing at 1000 °C in argon atmosphere due to Zn volatility and the reduction reaction.     

ZnO-Bi2O3-Sb2O3-BaO系陶瓷的晶界相与抗退降性能

在通常的ＺｎＯ－Ｂｉ₂Ｏ₃－Ｓｂ₂Ｏ₃系电压敏陶瓷中，加入能构成压敏特性的钡添加剂，发现除已知的Ｂｉ₂Ｏ₃和Ｚｎ_2．３３Ｓｂ_０．６７Ｏ₄晶界相以外，还出现新的晶界相，分析表明是固溶有微量其它成分的偏锑酸钡（ＢａＳｂ₂Ｏ₆）晶相。同时还发现，ＢａＳｂ_{2关键词：}     

Quantum mechanical studies on the singlet and triplet potential energy surface of the reactions CF3O2 + I,CF3O + OI and CF3 + OIO

The singlet and triplet potential energy surfaces for the reactions CF₃O₂ + I (1), CF₃O + OI (2) and CF₃ + OIO (3) are investigated using ab initio quantum mechanical methods. Four important isomeric energy minima were found, three on the singlet surface, CF₃OOI, CF₃OIO and CF₃IO₂ and one on the triplet surface ³CF₃OIO. CF₂O + FOI are shown to be the most probable products for all reactions, CF₃O +I and CF₃O + O(³P) are possible for reactions (2) and (3) while the reaction pathway leading to CF₃O +OI is also possible for reaction (3).     

Influences of Bi2O3/V2O5 Additives on the Microstructure and Magnetic Properties of Lithium Ferrite

Lithium ferrite materials with different concentrations of Bi2O3 and V2O5 additives are prepared by the conventional ceramic technique. The x-ray diffraction analysis proves that the additives do not affect the final crystal phase of the lithium ferrite in our testing range. Both Bi2O3 and V2O5 additives could promote densification and lower sintering temperature of the lithium ferrite. The average grain size first increases, and then gradually decreases with the Bi2O3 content. The maximal grain size appears with 0.25 wt% Bi2O3. The average grain size first increases, and then is kept almost unchanged with the V2O5 content. The maximal average grain size of the samples with V2O5 additive is much smaller than that of the samples with Bi2O3 additive. Furthermore, the V2O5 additive more easily enters the crystal lattice of the lithium ferrite than the Bi2O3 additive. These characteristics evidently affect the magnetic properties, such as saturation flux density, ratio of remanence Br to saturation flux density Bs, and coercive force of the lithium ferrite. The mechanisms involved are discussed.     

Isotope-selective IR multiphoton dissociation of CHClF2 in the presence of NO2

2 to the CHClF₂/He mixture irradiated by a Q-switched CO₂ laser leads to oxidation of the dissociation product according to the reaction: CF₂+NO₂→COF₂+NO. The resulting COF₂ with a ¹³C content near 50% is easy to convert to CO₂ or CO for further enrichment by a nonlaser process. We measured the dependence of the fraction of dimerised CF₂ on NO₂ pressure p_NO2 and the amount of NO₂ required to suppress dimerisation on the dissociation yield. Both agree with a kinetic model using known rate constants. For the range of the dissociation parameters (¹³CF₂ yield of 10% per pulse, isotope selectivity of 130) of practical interest, 95% of the CF₂ produced is oxidized at p_NO2≈1/2p_CHClF2. In the absence of NO₂, major (20%–35%) losses of CF₂ at the metal walls of the irradiation system were observed. Addition of NO₂ suppresses them. For comparison, we also used O₂ as a scavenger in CHClF₂ dissociation. NO₂ is by orders of magnitude more efficient. Received: 21 January 1997/Revised version: 23 March 1997     

Effect of additives with extremely high specific heat on training of superconducting windings

Experiments on training of thin solenoids containing additives with an extremely high low-temperature heat capacity in an external magnetic field are described. The data obtained for the windings with and without the additives are compared. Gd₂O₂S ceramics is used as an additive (addition of this ceramics in an amount of 6.4 vol % raises the specific heat of the winding by a factor of 12.5). In the solenoid with the additive, the current at which training starts is 35% higher than in the solenoid without the additive, and the transitional current after 20 current feeds increases by 18%. Tensile stress σ reaches 300 MPa (in terms of a free-turn model).     

Theoretical investigation on kinetics and thermochemistry of reaction of CHF2CF2OCH2CF3 with OH radicals and global warming potentials

Theoretical investigation has been carried out on the mechanism, kinetics and thermochemistry of the gas-phase reactions between CHF₂CF₂OCH₂CF₃ and OH radical using a new hybrid density functional M06-2X/6-31+G(d,p) and G2(MP2)//M06-2X/6-31+G(d,p) methods. The most stable conformer of CHF₂CF₂OCH₂CF₃ is considered in our study and the possible H-abstraction reaction channels are identified. Each reaction channel shows an indirect H-abstraction reaction mechanism via the formation of pre-reactive complex. The rate coefficients are determined for the first time over a wide range of temperature 250–1000 K. At 298 K, the calculated total rate coefficient of k_OH = 1.01×10^?14 cm³ molecule^?1 s^?1 is in good agreement with the experimental results. The heats of formation for CHF₂CF₂OCH₂CF₃ and CF₂CF₂OCH₂CF₃ and CHF₂CF₂OCHCF₃ radicals are estimated to be -1739.25, -1512.93 and -1523.94 kJ mol^?1, respectively. The bond dissociation energies of the two C-H bonds are C(-H)F₂CF₂OCH₂CF₃: 423.34 kJ mol^?1 and CHF₂CF₂OC(-H)HCF₃: 411.87 kJ mol^?1. The atmospheric lifetime of CHF₂CF₂OCH₂CF₃ is estimated to be around 4.5 years and the 100-year time horizon global warming potentials of CHF₂CF₂OCH₂CF₃ relative to CO₂ is estimated to be 601.     

Sensitizing gaseous detonations for hydrogen/ethylene-air mixtures using ozone and H2O2 as dopants for application in rotating detonation engines

The effect of ozone and hydrogen peroxide as dopants on hydrogen-air and ethylene-air detonations was investigated with one-dimensional ZND calculations. Also, the effects of dopants were studied numerically with argon and helium as diluents with an aim to reduce the temperature of detonation products while maintaining a detonation wave of sufficient strength such that its propagation is stable near its propagation limits. The primary goal of the present investigation is to isolate the chemical kinetic effects from fluid and gas dynamic effects by altering the ignition chemistry of an unburned mixture without significantly changing its thermodynamic and physical properties. The ZND calculations demonstrate that the addition of O₃ and H₂O₂ in small quantities will substantially reduce the induction length (Δ_i) and time (τ_i), even with higher diluent percentages of argon and helium, making it a viable solution for reducing the operating temperatures of rotating detonation engines (RDEs). The effects of O₃ and H₂O₂ are also studied numerically at lower equivalence ratios for H₂/C₂H₄-air detonations with an aim to reduce the post-detonation temperatures below 2000 K for its application in practical engine cycles. Also, the efficacy of CF₃I, as an ignition promoter at small quantities, is studied numerically for hydrogen-air detonations, and its performance is compared with O₃ and H₂O₂.     

The kinetics of methane ignition in fuel-rich HCCI engines: DME replacement by ozone

Fuel-rich combustion of methane in a homogeneous-charge compression-ignition (HCCI) engine can be used as a polygeneration process producing work, heat, and useful chemicals like syngas. Due to the inertness of methane, additives such as dimethyl ether (DME) are needed to achieve ignition at moderate inlet temperatures and to control combustion phasing. Because significant concentrations of DME are then needed, a considerable part of the fuel energy comes from DME. An alternative ignition promotor known from fuel-lean HCCI is ozone (O₃). Here, a combined experimental and modelling study on the ignition of fuel-rich partial oxidation of methane/air mixtures at Φ = 1.9 with ozone and DME as additives in an HCCI engine is conducted. Experimental results show that ozone is a suitable additive for fuel-rich HCCI, with only 75 ppm ozone reducing the fuel-fraction of DME needed from 11.0% to 5.3%. Since ozone does not survive until the end of the compression stroke, the reaction paths are analyzed in a single-zone model. The simulation shows that different ignition precursors or buffer molecules are formed, depending on the additives. If only DME is added, hydrogen peroxide (H₂O₂) and formaldehyde (CH₂O) are the most important intermediates, leading to OH formation and ignition around top dead center (TDC). With ozone addition, methyl hydroperoxide (CH₃OOH) becomes very important earlier in the compression stroke under these fuel-rich conditions. It is then later converted to CH₂O and H₂O₂. Thus, ozone is a very effective additive not only for fuel-lean, but also for fuel-rich combustion. However, the mechanism differs between both regimes. Because less of the expensive additives are needed, ozone could help improving the economics of a polygeneration process with fuel-rich operated HCCI engines.     

The effect of fluorine-based plasma treatment on morphology and chemical surface composition of biocompatible silicone elastomer

X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) have been used to investigate the effect of reactive ion etching (RIE) on poly(methylhydrogensiloxane-co-dimethylsiloxane) surface in fluorine-based plasmas. Polysiloxane layers supported on the standard silicon wafers were etched using SF₆ + O₂ or CF₄ + O₂ plasmas. SEM studies show that the polysiloxane morphology depends on plasma chemical composition strongly. Presence of a columnar layer likely covered with a fluorine rich compound was found on the elastomer surface after the CF₄ + O₂ plasma exposure. After the SF₆ + O₂ or CF₄ + O₂ plasma treatment the polysiloxane surface enriches with fluorine or with fluorine and aluminum, respectively. Different morphologies and surface chemical compositions of the silicone elastomer etched in both plasmas indicate different etching mechanisms.     

The mechanism of formation of the hydroperoxyl radical in the CF<Subscript>3</Subscript>COOH + <Superscript>3</Superscript>O<Subscript>2</Subscript> system: a quantum-chemical study

Ab initio quantum-chemical calculations of the (CF₃CO₂H₂⁺…³O₂) and (CF₃CO₂⁻…³O₂) complexes were performed by the MP2 method. It was found that these complexes were characterized by low complex formation energies, of 2.97 and 1.72 kcal/mol, respectively. According to the MP2(full)/6-311++G(d, p) calculation data, the bridge stabilization of oxygen by linking with both the CF₃CO₂H₂⁺ cation and CF₃CO₂⁻ anion is much more favorable energetically. A study of the potential energy surface of the joint molecular system (CF₃CO₂H₂⁺…³O₂…CF₃CO₂⁻) shows that proton experiences activationless transfer from the cation to the ³O₂ molecule accompanied by electron transfer from the CF₃COO⁻ anion. An analysis of spin density distribution shows that two radicals are stabilized in the (CF₃CO₂….OOH….O=C(OH)CF₃) complex in the triplet state observed on the potential energy surface.     

Manifestation of resonance dipole-dipole interaction in spectra of low-temperature molecular mixtures of C2F6 in CF4 and CF4 in C2F6

We have measured IR absorption spectra of solutions C₂F₆ in CF₄ (T = 178 K) and CF₄ in C₂F₆ (T = 173 K) in the overtone range of the spectrum. We have studied how the resonance dipole-dipole interaction affects the formation of contours of bands that correspond to transitions to states involving the vibrations ν₁₀(C₂F₆) and ν₃(CF₄), which are strong in the dipole absorption. For the system C₂F₆ in liquid CF₄, the state ν₂ + ν₁₀(C₂F₆) resonantly interacts with the state ν₂(C₂F₆) + ν₃(CF₄), and, for the system CF₄ in liquid C₂F₆, the state ν₁ + ν₃(CF₄) resonantly interacts with the state ν₁(CF₄) + ν₁₀(C₂F₆). The contours of the bands ν₂ + ν₁₀ (C₂F₆) in the spectrum of the mixture with CF₄ and of the bands ν₁ + ν₃(CF₄) in the spectrum of the mixture with C₂F₆ have been calculated.     

Spectral properties of Nd<Superscript>3+</Superscript> ions in samples of transparent Y<Subscript>2</Subscript>O<Subscript>3</Subscript> ceramics

The spectral and luminescent characteristics of samples of Y₂O₃:Nd³⁺ ceramics obtained from different precursors under different preparation conditions (the concentration of an HfO₂ compacting additive, the temperature and time of synthesis) are studied at 300 and 77 K. It is shown that the spectral positions of absorption and luminescence lines of ceramics correspond to those of a Y₂O₃:Nd³⁺ single crystal. At the same time, the absorption and luminescence spectra show an inhomogeneous broadening, characteristic of disordered crystals and glass. The energies of the ⁴ I _9/2 and ⁴ F _3/2 Stark states of the Nd³⁺ ion are calculated. The calculation results nearly coincide with the data from the literature for the Y₂O₃:Nd³⁺ single crystal and transparent ceramics. Samples containing the compacting additive show additional lines, whose intensities correlate with its concentration and the method of preparation of Y₂O₃:Nd³⁺ ultradispersed powders. It is assumed that these lines are related to the fact that either Nd³⁺ ions enter the composition of the HfO₂ compacting additive or Hf⁴⁺ ions are present in the nearest environment of Nd³⁺ ions at the boundaries of granules enriched with HfO₂.     

Electrochemical sensing of H2O2 using cobalt oxide modified TiO2 nanotubes

Cobalt oxide (Co₃O₄) modified anatase titanium dioxide nanotubes (ATNTs) have been investigated for the electrochemical sensing of hydrogen peroxide (H₂O₂). ATNTs have been synthesized by a two-step anodization process. ATNTs were then modified with Co₃O₄ employing chemical bath deposition method. The structure and morphology of ATNTs and their modification with Co₃O₄ has been confirmed by X-ray diffraction by scanning electron microscopy. H₂O₂ sensing has been studied in 0.1 M PBS solution, by cyclic voltammetry and amperometry. Variation in the peak positions and current densities was observed with addition of H₂O₂ for Co₃O₄ modified ATNTs. Sensitivity and limit of detection improved with modification of ATNTs with Co₃O₄ with precursor concentration up to 0.8 M. However, at higher precursor concentrations sensitivity and limit of detection toward H₂O₂ deteriorated. Co₃O₄ Modified ATNTS using 0.8 M precursor concentration are comparatively more suitable for H₂O₂ sensing applications due to the optimum formation of Co₃O₄/ATNTs heterojunctions.