Final Product Analysis Research Articles

Research and development on porous components for MCFC applications

A fuel cell is a complex system in which every single part must have optimal and long lasting characteristics to assure a good performance. Our research group has focused on a specific section of a cell, the porous components, the elements that directly come into play and more strongly influence the working and performance. Attention has been focused on matrix, in particular trying to improve it by intervening in the first step of raw powder choice. α-LiAlO 2 has been considered a new interesting and promising material to test. The purpose of this work is the study of the possibility of producing an α-LiAlO 2-based matrix with suitable properties for a MCFC cell. The subsequent steps of powder characterisation, tape preparation and final product analysis are presented as well as the various application techniques.

Kinetics and mechanism of hydroxyl radical and OH-adduct radical reactions with nitroxides and with their hydroxylamines.

Stable nitroxide radicals are potent antioxidants and are among the most effective non-thiol radioprotectants, although they react with hydroxyl radicals more slowly than typical phenolic antioxidants or thiols. Surprisingly, the reduced forms of cyclic nitroxides, cyclic hydroxylamines, are better reductants yet have no radioprotective activity. To clarify the reason for this difference, we studied the kinetics and mechanisms of the reactions of nitroxides and their hydroxylamines with (*)OH radicals and with OH-adducts by using pulse radiolysis, fluorimetric determination of phenolic radiation products, and electron paramagnetic resonance spectrometric determination of nitroxide concentrations following radiolysis. Competition kinetics with phenylalanine as a reference compound in pulse radiolysis experiments yielded rate constants of (4.5 +/- 0.4) x 10(9) M(-1) s(-1) for the reaction of (*)OH radical with 2,2,6,6-tetramethylpiperidine-N-oxyl (TPO), 4-hydroxy-TPO (4-OH-TPO), and 4-oxo-TPO (4-O-TPO), (3.0 +/- 0.3) x 10(9) M(-1) s(-1) for deuterated 4-O-TPO, and (1.0 +/- 0.1) x 10(9) M(-1) s(-1) for the hydroxylamine 4-OH-TPO-H. The kinetic isotope effect suggests the occurrence of both (*)OH addition to the aminoxyl moiety of 4-O-TPO and H-atom abstraction from the 2- or 6-methyl groups or from the 3- and 5-methylene positions. This conclusion was further supported by final product analysis, which demonstrated that (*)OH partially oxidizes 4-O-TPO to the corresponding oxoammonium cation. The rate constants for the reactions of the nitroxides with the OH-adducts of phenylalanine and terephthalate have been determined to be near 4 x 10(6) M(-1) s(-1), whereas the hydroxylamine reacted at least 50 times slower, if at all. These findings indicate that the reactivity toward (*)OH does not explain the differences between the radioprotective activities of nitroxides and hydroxylamines. Instead, the radioprotective activity of nitroxides, but not of hydroxylamines, can be partially attributed to their ability to detoxify OH-derived secondary radicals.

The atmospheric chemistry of the HC(O)CO radical

The chemistry of the HC(O)CO radical, produced in the oxidation of glyoxal, has been studied under conditions relevant to the lower atmosphere using an environmental chamber/Fourier Transform infrared spectrometric system. The chemistry of HC(O)CO was studied over the range 224–317 K at 700 Torr total pressure and was found to be governed by competition between unimolecular decomposition [to HCO and CO, reaction (5)] and reaction with O2 [to form HO2 and 2CO, reaction (6a), or HC(O)C(O)O2, reaction (6b)]. The rate coefficient for decomposition relative to that of reaction with O2 increases with increasing temperature. Assuming a value for k6 of 10−11 cm3 molecule−1 s−1, the following expression for the unimolecular decomposition is obtained at 700 Torr, k5 = 1.4+9/−1.1 × 1012 exp(−3160 ± 500/T). The rate coefficients for reactions (6a) and (6b) are about equal, with no strong dependence on temperature. The reaction of HC(O)C(O)O2 with NO2 was also studied. Final product analysis was consistent with the formation of HCO, CO2, and NO3 as the major products in this reaction; no evidence for the PAN-type species, HC(O)C(O)O2NO2, was found even at the lowest temperature studied (224 K). The UV-visible absorption spectrum of glyoxal is also reported; results are in substantive agreement with previous studies. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 149–156, 2001

The significance of monoisotopic and carbon-13 isobars for the identification of a 19-component dodecapeptide library by positive ion electrospray Fourier transform ion cyclotron resonance mass spectrometry

Harnessing the ultra high resolution capabilities of Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) and positive ion electrospray, we have demonstrated the significance and utility of cumulative mass defect high resolution mass separation stable isotope distribution, exact mass measurement and elemental formula as a means of simultaneously identifying 19 components of the dodecapeptide library Ac-ANKISYQS[X]STE-NH(2). With an instrument resolution of 275 000 (average), isobaric multiplets attributed to monoisotopic and carbon-13 components of peptides: Ac approximately SLS approximately NH(2); Ac approximately SNS approximately NH(2); Ac approximately SOS approximately NH(2); Ac approximately SDS approximately NH(2); within the mass window of 1380-1385 Da, and Ac approximately SQS approximately NH(2); Ac approximately SKS approximately NH(2); Ac approximately SES approximately NH(2); Ac approximately SMS approximately NH(2), within the mass window 1395-1400 Da, were mass resolved, accurately mass measured and identified from the computed molecular formulas. This experimental procedure enabled the separation of monoisotopic and carbon-13 isobars yielding enhanced selectivity and specificity and serves to illustrate the significance of monoisotopic and carbon-13 isobars in final product analysis. Chromatographic separation (HPLC) was of limited utility except for monitoring the overall extent of reaction and apparent product distribution. Positive ion electrospray-FTICR-MS and fast atom bombardment (FAB) MS were used to assess final product quality and apparent component distribution.

State resolved detection of Cl, Br, CIO and BrO

Nascent CIO and BrO products in photodissociation or reaction processes were observed in a state resolved manner by applying the two-photon laser-induced fluorescence technique, where two simultaneously absorbed laser photons excite the products to the C-state. CI and Br atoms can be observed by means of three-photon excitation with subsequent recording of the VUV fluorescence light. The advantage of this detection technique, other than the simpler laser system, is the use of low energy photons which don't interfere with other processes. State resolved detection of BrO products has been performed in the reactions 0(1D)+CF3Br and Br+03.The photodissociation of OCl0(2A2v1,v2,v3)→Cl0(X2πω, v,J,λ)+0(3P) in the 356–371 nm region is clearly a function of the initial type of motion of OC10(2A2vl,v2,v3). The population of the fragment rotational levels is observed to resemble Boltzmann distributions of around 1000 K. When high vibrationally excited states of the symmetric stretch mode of OC10(2A2v1>17,v2,v3) are excited, then most of the available energy is transferred to CIO vibration. Those extremely vibrationally excited CIO products carry sufficient energy to react with ambient nitrogen in the atmosphere, which is confirmed in a final end product analysis where the formation of N20 is observed.The Cl quantum yield of the minor OCIO(2A2 v1,v2,v3) → CI(2PJ) + 02 channel depends on the state of the parent molecule and is of the order of 4%.

Surface Wave Plasma Abatement of CHF3 and CF4 Containing Semiconductor Process Emissions

Projected exponential growth in semiconductor device manufacture over the next few years demands technology to reduce the corresponding increase in etchants such as perfluorocompounds (PFCs), CHF3, and SF6 that would be emitted into the atmosphere. These compounds are a cause for concern because of their large global warming potentials relative to CO2 and of their long lifetimes in the atmosphere, often tens of thousands of years. We demonstrate that a plasma-based technology can yield effective (up to 99.9%) destruction and removal efficiencies (DREs) for CF4 and CHF3 present in etch recipes widely used in the semiconductor industry. Specifically, we report application of surface wave plasmas at 2.45 GHz for this purpose. Post-plasma effluent analysis included the determination of DREs and product distributions, simultaneously by gas-phase FTIR and QMS. Application of microwave powers from 500 to 1950 W were investigated and DREs for CF4 and CHF3 reported. Final product analysis indicated that PFC conversion was limited to low molecular weight gases such as CO2, CO, COF2, H2O, and HF. These investigations demonstrate that surface wave plasma destruction of the referenced PFCs at the output of semiconductor etch tools is a viable nonintrusive point of use abatement technology.

A pulse radiolysis study on energy transfer mechanism in trioctylphosphineoxide–cyclohexane and tributylphosphate–cyclohexane systems by using benzophenone as a probe

Abstract Measuring the G values of ketyl radicals, benzophenone has been used as a probe to study the energy transfer mechanism in trioctylphosphineoxide(TOPO)–cyclohexane(CH) and tributylphosphate(TBP)–CH systems under pulse radiolysis. Results showed that there was a process of energy transfer between the excited CH and TBP or TOPO, which coincided with our previous experiments on final product analysis. Rate constants (k) of energy transfer and GCH∗ (G value of singlet cyclohexane), which are k=4.8×109 dm3 mol−1. S−1, GCH∗=1.3×0.1 for TBP and k=8.3×1012 dm3 mol−1 s−1, GCH∗=1.4±0.1 for TOPO, were obtained by Stern–Volmer method. The abnormality of the rate constant for TOPO is discussed. Another process fitted with WAS equation was assumed to be geminate ions scavenging, and the α=7.3, Ggi=3.8±0.1 for TBP, α=649, Ggi=3.7±0.1 for TOPO, were gained. Meanwhile the mechanism of the latter process were also discussed.

Selectivity in dehydrodimerisation of amides: Final product analysis from radiolysis in the liquid phase

N, N-Dimethylformamide (DMF) and N, N-dimethylacetamide (DMA) were irradiated with γ-rays and accelerated electrons (linac) in the liquid phase at different temperatures. Qualitative and quantitative analysis of the radiolysis products have been made by capillary GC. Effects of irradiation temperature and dose rate have revealed secondary mechanisms for the formation of the parent radicals. Irradiation in presence of N 2O tends to reveal tonic reactions for the immediate formation of parent radicals.

Pulse radiolytic studies on the oxidation of 1,3 dithiolane 2-thione (ETTC) by OH radicals in aqueous media

The reaction between 1,3 dithiolane 2-thione or ethylene trithiocarbonate (ETTC) and pulse radiolytically generated OH . radicals have been investigated in aqueous solution. An absorption spectrum of the transient species with an absorption maximum at 390 nm was obtained. The spectrum was assigned to the radical cation ETTC .+ formed by the electron transfer reaction, as supported by transient conductivity measurements. The G-value of the radical cation was obtained as 4.2±0.2. The bimolecular formation rate constant of ETTC .+ was determined as 1.8±0.2 × 10 10 dm 3 mol -1 s -1 and its molar absorbance value at 390 nm was estimated to be 237 ± 20 m 2 mol -1. The second-order decay rate constant of ETTC .+ ( k = 6.5±0.9 × 10 8 dm 3 mol -1s -1) was attributed to the formation of a dimer dication (ETTC) 2+ 2, as confirmed by a final product analysis by gas chromatography.

Laser assisted synthesis of ultrafine silicon powder

Ultrafine Si powder has been produced by means of laser assisted decomposition of SiH4. Optical on-line diagnostics and final product analysis have been employed in order to establish both gas-phase precursor dissociation and particle growth mechanism. Morphologic and crystallographic characterizations of the powder have been performed. Nitridation of Si powders and compacts have been accomplished. Results are compared with those obtained by direct laser induced photosynthesis of Si3N4 powder.

Radical production evidenced by dimer analysis in γ-irradiated amides in aqueous solutions and in the solid state

A study of the nature and distribution of radicals produced by the radiolysis of amides in the solid state has been made by two complementary methods: (i) final product analysis by capillary gas chromatography and (ii) the direct observation of radicals by electron spin resonance spectroscopy. The dimer isomer distribution for N-methylformamide (NMF), N-methylacetamide (NMA) and N,N-dimethylformamide (DMF) allows one to estimate the parent radical distribution by using a statistical rule for dimer formation. In the solid state the radiolytic formation of radicals is selective. Final product analysis by capillary gas chromatography and the direct study of radicals by pulse radiolysis are also complementary methods for studying the nature of radicals produced from the radiolysis of amides in aqueous solutions. The selective production of one parent radical is characteristic of dilute solutions.

ChemInform Abstract: STOICHIOMETRY AND RATE OF REACTION OF HYDROGEN ATOMS WITH OXYGEN

AbstractDie Reaktion von H‐Atomen (10‐6‐10‐5 mol dm‐3) mit O2 (0‐10‐5 mol dm‐3) in überschüssigem Ar wird in einem fast flow‐Entladungsrohr bei Gesamtdrücken zwischen 2 und 10 Torr sowie Temp. von 231 bis 512 K untersucht (massenspektrometrischer und gaschromatographischer Nachweis der Produkte).

Study on charge transfer reaction of several organic molecules with accelerated rare gas ions.

Observing the charge transfer mass spectra of ethylbenzene, cyclobutane and methanol in Ar and Xe ion impacts, we investigated the dependence of the secondary ion peak intensities (normalized to primary ion current and target pressure) on the translational energy of primary ions (0-3500 eV). In the case of ethylbenzene, several maxima of the secondary ion peak intensities were observed in Ar and Xe ion impacts. The correlation between the maxima and the primary ion energy was examined in terms of near adiabatic theory of Massey. Supplementary studies on the energy distribution of primary ion, charge transfer cross section between methanol and Xe ion, and final product analysis in rare gas ion irradiation on cyclobutane were described.

Stoichiometry and rate of reaction of hydrogen atoms with oxygen

The reaction of hydrogen atoms (10–6–10–5 mol dm–3) with oxygen (0–10–5 mol dm–3) in excess argon has been studied in a fast flow—discharge tube at total pressures from 2 to 10 Torr and temperatures from 231 to 512 K using mass spectrometry and gas chromatography for final-product analysis. A method of measuring small concentrations of water (ca. 10–7 mol dm–3) has been developed which enabled the relative rates of reactions (2) and (3) to be determined, reaction (4) being negligible: H + O2+ Ar → HO2+ Ar (1), H + HO2→ H2+ O2(2), H + HO2→ 2OH (3), H + HO2→ H2O + O. (4). Over the range 231 < T/K < 464, log10(k3/k2)=(1.44 ± 0.39)–(320 ± 120/T)(errors throughout are standard deviations).

Formation and characterization of platinum(III)-ammonia complex ions using pulse radiolysis

The reactions of hydroxyl radical with tetraammineplatinum(II) perchlorate and of the hydrated electron with trans-dihydroxotetraammineplatinum(IV) perchlorate have been investigated in aqueous media with the fast-reaction technique of pulse radiolysis in conjunction with conductivity and UV-visible absorption detection. The kinetic studies have been supplemented by final-product analysis on pulse-irradiated solutions for the formation of free ammonia and for changes in the concentration of platinum(II). The hydroxyl radical reaction proceeds by an addition proces to the platinum(II) center, with a rate constant of (6.6 +/- 0.4) x 10/sup 9/ M/sup -1/ s/sup -1/. The hydrated electron reduces the platinum(IV) complex with a rate constant of (4.9 +/- 0.3) x 10/sup 10/ M/sup -1/ s/sup -1/. The nascent products of these reactions are transitory species in which the metal has a formal oxidation state of III, and evidence is presented to support their formulation as Pt(NH/sub 3/)/sub 4/(H/sub 2/O)(OH)/sup 2 +/ and Pt(NH/sub 3/)/sub 4/(OH)/sub 2//sup +/, respectively. Both species exhibit intense absorption bands with peaks near 270 nm, and they undergo reactions to yield three further transients, one of these being Pt(NH/sub 3/)/sub 4/(H/sub 2/O)/sub 2//sup 3 +/ absorbing in the region of 250 nm. The two additional transients, arising at amore » secondary level, exhibit absorption bands of lesser intensity with peaks in the region of 340 and 530 nm. The nature of these species and their long-term reactions are discussed. A mechanism is proposed whereby the foregoing intermediates are interrelated by acid-base, ammonia substitution, and water elimination processes.« less