Spectroscopy in separated flames-V The argon- or nitrogen-sheathed nitrous oxide-acetylene flame in flame emission spectroscopy

The separation of the premixed nitrous oxide-acetylene flame by sheathing with argon or nitrogen is described. The interconal zone of the hot, slightly fuel-rich flame exhibits low background and noise levels and an extended reducing atmosphere, providing better conditions for the excitation of atoms of elements which form refractory oxides. The limits of detection found for nine such elements are greatly superior to those obtainable in the conventional unsheathed flame under similar conditions.     

spectroscopy in separated flames-VI The argon or nitrogen-sheathed nitrous oxide-acetylene flame in atomic-absorption spectroscopy

The separation of the premixed nitrous oxide-acetylene flame at a 50-mm slot burner by sheathing with argon or nitrogen is described. In comparison with the conventional flame, the interconal zone of the hot, slightly fuel-rich separated flames provides better conditions for the maintenance of free atoms of elements which form refractory oxides. Optimum conditions for the determination by atomic-absorption spectroscopy of the elements Al, Be, Ge, Mo, Si, Ti, V and Zr in both separated and conventional flames at the same burner have been established. Significant improvement in detection limits and sensitivities is obtained in the separated flames.     

Emission spectra of nitrous oxide supported acetylene flames at atmospheric pressure

The emission spectra of a premixed flame of acetylene supported by nitrous oxide have been recorded under different fuel-gas mixture conditions. The emission spectra in these flames of a series of metals, for which it is difficult to obtain a significant population of ground state atoms for atomic absorption spectroscopy in more conventional flames, have also been studied. The red secondary zone which is present in the fuel-rich flames shows emission attributable to long-lived CN and NH species which form a strongly reducing atmosphere to inhibit refractory oxide formation from elements such as molybdenum, titanium and aluminium introduced into the flame. An attempt has also been made to explain some of the reactions which may occur between the flame species above the primary reaction zone.     

Experimental estimation of fluorescence power efficiencies of several atoms in three turbulent flames used in atomic fluorescence flame spectrometry

An experimental system for the measurement of approximate atomic fluorescence power efficiencies of atoms in turbulent flames used in atomic fluorescence flame spectrometry is described. An expression is derived for the power efficiency as a function of instrumental parameters. Experimentally measured power efficiencies for eleven elements in fuel-rich oxyhydrogen, fuel-rich oxyacetylene, and fuel-rich hydrogen/argon/entrained air flames are given. The power efficiencies vary considerably from one spectral line to another, but as a result of the entrainment of ambient air into the turbulent flames, the values obtained in different flames are approximately equal. It is also shown that fluorescence radiation should rarely produce a significant error in atomic absorption spectrometry.     

Application of an oxygen-shielded air-acetylene flame to atomic spectroscopy

A burner has been designed which provides an oxygen-shielded air-acetylene flame for atomic-absorption work. The chemical reducing properties of the oxygen-shielded flame operated under fuel-rich conditions are enhanced by the higher C: O ratio obtainable in the flame and by the higher flame temperature just above the reaction zone. The flame is inherently essentially free from the risk of flashback, and is offered as an alternative to the nitrous oxide-acetylene flame for use with certain types of equipment and for particular applications.     

Free-atom formation processes in premixed fuel-rich and stoichiometric oxygen-acetylene flames employed in atomic emission and absorption spectroscopy

Detailed observations on the atomic and molecular absorption and emission spectra of the various zones of premixed oxyacetylene flames are presented. Spatial flame profile data for both the natural flame species and those formed when solutions of metallic salts are nebulized into the flame are interpreted in terms of: (a) the relative concentrations of reactive intermediate and stable species in the various zones; (b) the mechanism of free-atom formation from aerosol droplets; and (c) free-atom depopulation processes. The results of this study clearly show that the striking enhancement in atomic spectra observed in either absorption or emission for many elements in the fuel-rich oxyacetylene flame originate in the favorable chemical environment provided by the interconal zone for the formation and existence of free-atoms.     

Spectroscopy in separated flames-II The use of the separated air-acetylene flame in long path atomic absorption spectroscopy

The application of a separated air-acetylene flame to the determination of several elements by long-path atomic-absorption spectroscopy is described. The factors which govern the stability and reproducibility of the separated flame have been investigated. High sensitivity and stability and low background absorption are obtained in the the determination of zinc, iron, copper, mercury, magnesium and silver by the method described.     

Atomization efficiencies in halocarbon-loaded acetylene-air flames—I. Monochlorides of readily volatilized elements

Carbon tetrachloride vapour was introduced with a carrier air stream into the mixing chamber of an acetylene-air flame while nebulizing aqueous solutions of several metal salts. The atomic absorption signal was measured under increasing flow rate of the halocarbon vapour at constant fuel-to-oxidant ratio, and the latter parameter was also varied in separate experiments. By applying the theory developed by Sugden and Bulewicz, the exclusive formation of monochlorides in the gaseous phase (presented here, in Part I) and the additional formation of hydroxychlorides and dichlorides (presented in Part II) could be elucidated. From the decrease of the signal measured for the alkali elements of known monochloride dissociation constants and dissociation energies, the temperature and the chlorine concentration present in the observed flame zone could be calculated. It is inferred that only 19% of the total halogen introduced is converted to HCl and Cl species in a slightly fuel-rich flame. The signal depression is stronger in a fuel-lean flame of higher monoatomic chlorine concentration for those elements which have a relatively efficient atomization under these flame conditions. An increase of the electron concentration resulting from the introduction of the halocarbon in an alkali-containing flame was deduced from the experimental findings, in agreement with earlier observations.     

Determination of chromium in low-alloy steels by atomic-absorption spectrophotometry

Iron causes severe depression of the signal in determination of chromium by atomic-absorption spectrophotometry in an air-acetylene flame. This effect can be eliminated by addition of hydroxylamine hydrochloride and use of a fuel-rich flame. Addition of iron to the standard solutions is not necessary for up to 300 ppm of iron in the test solution.     

Effect of soot microstructure on its ozonization reactivity

Large uncertainty among the measured uptake coefficients of O(3) on soot highlights the importance of the sources and chemical structures of soot samples in this reaction. Soot samples with different microstructures were prepared by combusting n-hexane under controlled conditions. Their reactivities to O(3) were further investigated using in situ Raman spectroscopy. The fuel∕oxygen ratio in the combustion experiments not only affected the diameter of the primary particles, but also influenced the micro-chemical structure of soot. Average diameters of soot particles decreased with the decreasing fuel∕oxygen ratio. Compared to the "fuel-rich" flame soot, the "fuel-lean" flame soot showed lower structural uniformity with higher disordered carbon content at the graphene layer edges (D1 band) and the surface graphene layers (D2 band) and the amorphous carbon content (D3 band). This disordered carbon was identified as the reactive component for the ozonization of both the "fuel-rich" and "fuel-lean" flame soot samples. The kinetics study demonstrated that the disordered carbon at the surface graphene layers was more active than that at the graphene layer edges in one sample, and the reactivity of these two microstructures types to O(3) in the "fuel-rich" flame soot was higher than that in the "fuel-lean" flame soot.     

Effects of gas composition and flame sheathing on the spatial velocity profiles of laminar analytical acetylene flames

A recently developed technique has been employed to spatially map the rise velocity pronies (horizontal and vertical) of commonly used laminar analytical flames and to determine the influence on the profiles of fuel-to-oxidant ratio and the presence of a flame sheath. The rise velocities for fuel-rich, lean, and stoichiometric flames were found to differ substantially, the entire profile being greatest for the fuel-rich condition and lowest for the fuel-lean flame. In addition, the change in rise velocity with the addition of a solid (quartz tube) or gas (N₂) sheath was studied. The flowing sheath, at several different flow rates, affected each rise velocity profile principally by altering atmospheric entrainment and thereby changing secondary combustion in the flame. In contrast, a solid quartz tube used as a sheath produces an additional increase in the entire velocity profile of each flame, since it constrains gas expansion to the direction of flame propagation. The degree to which the velocity of each flame is affected by either a flowing N₂ and quartz sheath is strongly influenced by fuel-to-oxidant ratio.     

Spectroscopy in separated flames-I. The use of the separated air-acetylene flame in thermal emission spectroscopy

The separation of a premixed air-acetylene flame is described. The interconal zone of this flame exhibits very low radiative background, and is only slightly cooler than that of a normal air-acetylene flame. The use of the separated flame in flame photometry, for which it has several pronounced advantages, has been investigated.     

Determination of silicon in organo-silicon compounds by flame emission spectrometry

Abstract

Optimum conditions for the determination of silicon by flame emission spectrometry were ascertained. The maximum signal emanates from a region immediately above the tip of the inner cone of a fuel-rich oxygen-acetylene flame. The organosilicon compound is aspirated as a solution in ethanol and the emission intensity at 2516.1 Å is measured. Quantitative determinations were made using a working curve and by the method of standard addition. Detection limit is 3.5 μg/ml.     

Spectroscopic study of atomization processes and inter-element effects on the flame emission of chromium and iron in an air—acetylene flame

Emission spectroscopy is applied for characterization of reactions occurring in air—acetylene flames normally used for atomic absorption spectrometry. Inter-element effects on the emissions of chromium and iron are discussed. Two atomic emission lines with different upper energies and a molecular emission line of the diatomic oxide MO are compared for determination of the excitation temperature and the degree of atomization in fuel-rich and lean flames. The reductive power of the fuel-rich flame is essential for atomization of chromium salts. Inter-element effects by iron can be attributed to the formation of refractory oxides, and to mutual catalytic oxidation.     

Determination of silicone fluid surfactants in polyurethane/polyether blends by atomic-absorption spectroscopy

A method for the atomic-absorption determination of silicone fluid surfactants present in some polyurethane/polyether blends is described. The silicone fluid in the pure state, or in the presence of polyurethane blend, is diluted with a solvent and sprayed into the nitrous oxide/acetylene flame. The effects of solvent, instrumental conditions, time and presence of the polyurethane blends were investigated. Polyurethane/polyether blends do not interfere with the silicon absorption when the samples are dissolved in aqueous ethanol (1:1) and sprayed into a fuel-rich flame.     

Indirect method for the determination of aluminium by atomic-absorption spectrometry using an air-acetylene flame

The enhancement of the atomic-absorption signals of iron, cobalt, nickel and chromium in a fuel-rich air-acetylene flame by small amounts of aluminium makes possible the indirect determination of aluminium in the concentration range 0.01-10 ppm. The optimization of working conditions and the occurrence of interferences are reported.     

A Sensitive Indirect Method for the Determination of Titanium by Atomic Absorption Spectrophotometry Using an Air-Acetylene Flame

Abstract

The enhancement of the atomic absorption signal of iron in a fuel-rich air-acetylene flame by small amounts of titanium makes possible the determination of titanium at concentrations of 0.01 to l0ppm. The optimisation of working conditions for the determination of titanium by this indirect method are reported.     

Flame Emission Spectromethic Method POH Determinanoh of Rhehium in Molybdenite Flue Dust

Abstract

Optimum conditions for the determination of rhenium by flame emission speetronetry vere ascertained. The mart mim signal emanates from a region immediately above the tip of the inner cone of fuel-rich oxygen-acetylene flame. The sample was introduced as a solution in cyclohexanone by a sprayer-burner. Emission intensity at 3460 Å vas measured. In molybdenite flue dust, after normal dissolution steps, rhenium(VTl) vas extracted from 1.8–3.6 N H₂SO₄ vita cyclohexanone and the organic phase, vas. sprayed directly into the flame. Detection limit is 2.5 μg/al.     

Evolved-gas zeeman flame atomic absorption spectrometry for the determination of arsenic compounds

An evolved-gas separation/flame Zeeman atomic absorption spectrometric approach is demonstrated for the speciation and determination of arsenic in oyster tissue. No digestion is needed and separation of inorganic arsenic compounds having similar boiling points is achieved. A stoichiometric or air-rich acetylene/air flame for atomic absorption spectrometry is not generally suitable for arsenic determination because of severe ultraviolet absorption interference at 193.7 nm and low sensitivity; polarized flame Zeeman atomic absorption spectrophotometry with a fuel-rich flame is suitable for the detection of traces of arsenic. The evolved-gas separation/Zeeman atomic absorption approach is simple, based on commercially available instrumentation, and useful for the selective determination of major arsenic compounds. Data are given to demonstrate optimal conditions and to show application to oyster tissue.     

Soot Formation in Premixed Hydrocarbon Flames

The critical fuel-oxygen ratio for soot formation and its dependence on temperature and pressure are discussed for various hydrocarbons. It is shown in the case of the Bunsen flame that the shape and structure of the flame front also have a decisive effect on soot formation. In the reaction zone of fuel-rich hydrocarbon flames, unsaturated compounds are formed, and the concentration profiles of these products can provide quantitative information about their importance in soot formation. The “mechanism” of soot formation is discussed on the basis of the concentrations of higher hydrocarbons and the variation of the number and size of the soot particles. The effects of electric fields and foreign additives on soot formation have been given consideration.