Oxyhydrogen Research Articles

Heterogeneous chain propagation in a rarefied oxyhydrogen flame

In the 1950s and 1960s, Semenov’s theory of branched chain processes had become capable of quantitatively describing hydrogen combustion [1, 2], but the theory fit the experimental data only in the depth of the ignition peninsula. As reported in [3], Semenov and colleagues observed [1] a hydrogen combustion rate exceeding the theoretical expectations, and Azatyan and Aleksandrov detected [4] finite “anomalously deep burnups” near the ignition limit, which were tens of times those calculated. In his Nobel lecture in 1956, Semenov formulated the concept of heterogeneous chain propagation [5]. Therefore, Semenov and Azatyan proposed [3] to seek the cause of the discrepancy between the theory and the experimental data among possible heterogeneous reactions. A figure in Semenov and Azatyan’s report [3] shows that the additional contribution of the hypothetical heterogeneous chain propagation to the gas-phase component of the process in terms of finite burnups was only 10‐12%. To explain the discrepancy, a mechanism was put forward in which HO 2 radicals form on the surface and react with hydrogen atoms to produce hydroxyl radicals leaving the surface for the gas phase. However, the case in which the reaction H + HO 2 yields not hydroxyl radicals but a hydrogen peroxide molecule leaving the surface for the gas phase is apparently more advantageous from an energy standpoint; therefore, the assumed processes of heterogeneous branching or noticeable propagation of chains are unlikely. The purpose of this study was to reveal and refine the contributions of various heterogeneous chain propagation mechanisms to the gas-phase component of the process using analysis and targeted experiments. Heterogeneous chain propagation can be experimentally studied only by highly sensitive methods. We used resonance fluorescence spectroscopy of rarefied flames, whose sensitivity threshold ( 10 8 cm —3 ) was suf

Heterogeneous chain propagation in a rarefied oxyhydrogen flame

Heterogeneous chain propagation in a rarefied oxyhydrogen flame

Modeling of Generation and Growth of Non-Spherical Nanoparticles in a Co-Flow Flame

Generation and growth of polydisperse non-spherical silica nanoparticles in an oxy-hydrogen co-flow diffusion flame have been simulated for the first time. A complete set of Navier–Stokes equations describing multi-component chemically-reacting fluid flows was first solved considering the detailed H2/O2 chemistry and oxidation/hydrolysis reactions of SiCl4. A recently developed aggregate sectional model (Jeong & Choi, 2001) was employed to solve the dynamics of particles undergoing generation, convection, diffusion, coagulation and coalescence in a spatially two-dimensional flame system. Non-uniform spatial distributions of flame temperatures and non-spherical particle sizes were successfully simulated. Comparison on flame temperature and particle size between the numerical simulation and the experimental data has also been done. Performance of a simple monodisperse model was also studied by comparing with the detailed sectional model.

Evaluation of thermal shock resistance of cordierite honeycombs

A comparative study on thermal shock resistance (TSR) of extruded cordierite honeycombs is presented. TSR is an important property that predicts the life of these products in thermal environments used for automobile pollution control as catalytic converter or as diesel particulate filter. TSR was experimentally studied by quenching (descending test) the heated samples to water or by heating (ascending test) with an oxyhydrogen flame along with crack detection by acoustic emission (AE) method. TSR was also calculated by using coefficient of thermal expansion (CTE), modulus of elasticity (MOE) and modulus of rupture (MOR) of the honeycomb samples. Cordierite honeycombs of 200 and 400 cpsi were used for the above study. It was observed that the trends of TSR were same for both the experimental methods as well as by calculation. The ascending test method showed lower TSR values compared to water quench method due to early detection of cracks by AE. Finite element method (FEM) was also used to evaluate the thermal stress distribution in solid cordierite using thermal shock test data. It was observed that the maximum thermal stress calculated by FEM was lower than the strength of the material; therefore, the solid cordierite did not fail during such tests.

Thermal shock and thermal fatigue study of alumina

Preliminary results on the thermal shock and thermal fatigue behaviour of alumina studied in a newly designed novel and simple test equipment are reported. The top surface of a test sample was heated by an oxy-hydrogen flame while the opposite surface was cooled to generate temperature and thermal stress gradients. The maximum stressed zone and the effect of the thickness of the sample on critical temperature difference (TC) were studied by conducting actual experiments on plain and indented alumina specimens and also by modelling temperature and thermal stress distribution in the sample using a finite element (FE) software. It was observed that the maximum stress was experienced near the periphery of the top surface and TC was more for thicker samples. Thermal fatigue study was conducted by varying temperature difference of the fatigue cycles and also by inducing different crack lengths in the sample. It was observed that the fatigue life sharply decreased with increase in initial crack length or by increasing the temperature difference of the fatigue cycles. The acoustic emission (AE) signals corresponding to formation and growth of large number of micro-cracks were observed. # 2002 Elsevier Science Ltd. All rights reserved.

Preparation and characterization of SiO2–B2O3–P2O5 particles and films generated by flame hydrolysis deposition for planar light-wave circuits

Boron-phosphosilicate glass particles were deposited on Si wafer by flame hydrolysis deposition under controlled conditions. A few ten nanometer sized and spherical glass particles were synthesized in an oxy-hydrogen flame. The wafer surface temperature of 500 °C proved sufficient to form the Si–O–B framework while a higher temperature (approximately 730 °C) was required to produce Si–O–P formation. Gaussian bands at 3242 cm−1 provided evidence that the dissolved B2O3 concentration increased with the substrate temperature. In as-deposited porous films, a certain quantity of crystalline B2O3 remained, which was completely transformed into the noncrystalline phase after post deposition annealings. Film density measurements indicated that the B2O3 content in the doped silica films would be substantially lower than that in the precursor mixture.

Thermal shock and thermal fatigue study of ceramic materials on a newly developed ascending thermal shock test equipment

A test equipment was designed to study thermal shock and thermal fatigue of ceramic materials subjected to fast heating (ascending). The equipment was designed to generate thermal stress in a test specimen by heating one surface of it by an oxy-hydrogen flame while cooling the opposite surface. The sample cracked when thermal stress exceeded its mechanical strength. The in situ crack formation was detected by an acoustic emission system coupled to the set up. The hot zone temperature was measured by an infra red pyrometer. The equipment was also designed to run thermal fatigue test cycles in automatic mode between two selected temperatures. The temperature and thermal stress distribution in the test specimen were modelled using finite element software. The effect of temperature distribution of the top and bottom surfaces on thermal stresses was studied. It was observed that the thermal stress is very sensitive to the temperature distribution on the top surface and maximum near the periphery of the top surface. This was in agreement with the experimental results in which the cracks were originated from the periphery of top surface. It was also observed that the failure temperature was higher for thicker samples.

Measurement of Heat Flux and Heat Transfer Coefficient of an Oxy-Hydrogen Flame Used for Thermal Shock Test

Heat flux and heat transfer coefficient profiles of an oxy-hydrogen flame used for thermal shock and thermal fatigue tests of ceramic materials were generated experimentally by measuring the heat lost by the flame through the small annular zones of copper block over which the flame was impinged. The copper block in the form of a hollow cylinder with water inlet and outlet facility was fabricated. In order to impinge the flame over a selected area, pyrophylite rings of varying internal diameters (dia.=3–11 mm) were used. A constant flow of water through the copper block was maintained and the temperatures of the inlet and outlet water were measured to calculate the heat flow parameters. The experiments were repeated by replacing the pyrophylite discs from smaller to bigger holes, thereby, measuring heat input over gradually increasing areas. From the experimental data, the heat flux and heat transfer coefficient profiles were generated by employing standard heat loss equations.

CONTROL OF SIZE AND MORPHOLOGY OF NANO PARTICLES USING CO 2 LASER DURING FLAME SYNTHESIS

An attempt has been made to control size and morphology of nanoparticles generating and growing in a co-flow oxy-hydrogen flame combining CO 2 laser irradiation. The coalescence characteristic time could be controlled nearly independent of the collision characteristic time of particles by raising particle temperature rapidly with laser beam irradiation during flame synthesis. Silica aggregates generated by hydrolysis of SiCl 4 in a flame are irradiated by a high-power CO 2 laser beam, and rapidly heated up to temperatures that are high enough to enhance sintering, but lower than evaporation temperature. Sintering of aggregates is rapidly enhanced to change aggregates into more spherical particles. Since spherical particles have much smaller collision cross sections than volume-equivalent aggregates, much slower growth of particles is observed when the flame is irradiated by CO 2 laser beam and as a result, the diameter of resulting spherical particles decreases to about 60% of the size observed without CO 2 laser beam as the laser power increases. A higher precursor flow rate even resulted in the change of non-spherical particles into smaller spherical particles as CO 2 laser power increased. Light-scattering measurement with an Ar-ion laser and TEM observation through a localized thermophoretic sampling were used to confirm the above effects of CO 2 laser irradiation in a flame. Depending on the irradiation height of CO 2 laser beam in a flame, significantly different mechanisms were found. The radial distributions of scattering intensity and morphological change were also studied. The proposed method controlling the sintering characteristic time of particles using CO 2 laser irradiation in a flame seems to be promising to produce smaller and, at the same time, spherical nanoparticles even for high carrier gas flow rate.

Wavelet structural analysis of silica glasses manufactured by different methods

Wavelet analysis of X-ray diffraction patterns was made for structures of silica glasses manufactured by electrical fusion, oxy-hydrogen flame fusion of quartz powder, and flame hydrolysis of SiCl 4. The analysis indicates that their structures were not affected by the manufacture methods. It is believed that there is a thermodynamically most favoured or unique structure for glass in an intermediate range up to a few nm. It is expected that amorphography (in analogy to crystallography for crystal) for glass will emerge as a new branch of science. According to our statistical crystallite model, glass structure could be determined by the crystallography of corresponding crystals and the damping with interatomic distance for the crystalline regularity.

Quality assurance system for a decomposition method as demonstrated for the Wickbold combustion technique

A five-step model for a quality assurance system is developed for an internal quality control check. It includes the quality control of the decomposition method and the detection method as steps belonging together. The Wickbold combustion technique as decomposition method in combination with atomic absorption spectrometry was chosen. The vaporization of the elements mercury, arsenic, lead, antimony and selenium is based on combustion in an oxyhydrogen flame. To check the efficiency of the analytical system, the uncertainty of results was calculated on the basis of the "Guide to the Expression of Uncertainty in Measurement".

New Universal Quartz Burner for Decomposition of Samples by the Wickbold Combustion Technique in Determination of Arsenic, Antimony, Selenium, Mercury, and Lead

Abstract A new universal quartz burner for the Wickbold decomposition method is investigated with respect to its fast and efficient decomposition of solid samples for determining volatile trace elements like arsenic, antimony, selenium, mercury, and lead. Decomposition is based on burning samples in an oxyhydrogen flame. The samples are transported into the flame in gaseous form by pyrolyzing the material in an oven heated to 1100C. During this decomposition step, a nitrogen stream loaded with carbon tetrachloride mobilizes the volatile elements, causing separation from the sample matrix. An effective precombustion in oxygen and a large turbulent flame improve decomposition conditions. Different certified inorganic and organic reference materials are pyrolyzed and combusted, and the combustion products are absorbed in water. Metals found in the absorption solutions are analyzed by flow injection/hydride generation/atomic absorption spectrometry. Data were analyzed by several statistical tests recommended for quality control purposes. The combination of a decomposition and detection method resulted in very low detection limits: 1.4 μg arsenic/kg, 0.8 pig antimony/kg, 1.8 μg mercury/kg, 1.4 μg lead/kg, and 1.6 μg selenium/ g can be detected without an extra enrichment step.

Investigation of the functionality of different burner types used for the Wickbold decomposition method

The functionality of different burner types used for the Wickbold decomposition method was investigated to understand the low recovery rate problem. The elements chlorine and sulphur were the subject of recovery experiments. The influence of the amount of sample transported into the oxyhydrogen flame on the efficiency of combustion is presented. The difference between the manner of transportation into the flame, direct nebulisation of liquids or previous evaporation are investigated. A new nebuliser for introducing liquids into the oxyhydrogen flame with an evaporation step was developed to reduce decomposition problems.

Flame pyrolysis – a preparation route for ultrafine pure γ-Fe2O3 powders and the control of their particle size and properties

Highly dispersed γ-Fe2O3 powders with particle sizes down to 5 nm were directly synthesized by combustion of solutions of iron pentacarbonyl or iron(III) acetylacetonate in toluene in an oxyhydrogen flame. The particle size as well as other properties of the obtained powders can be controlled simply by varying the iron concentration in the starting solutions. Phase composition, morphological and magnetic properties of the powders were studied. The reasons for the formation of γ-Fe2O3 are discussed by means of structure–chemical/kinetic considerations. The materials are interesting as recording materials, or ferrofluids, or for colour imaging and bioprocessing.

Flame sample introduction system for inductively coupled plasma atomic emission spectrometry

An oxygen–hydrogen flame sample introduction system for inductively coupled plasma (ICP) atomic emission spectrometry is discussed. Linking two dissimilar sources was found to be a non-trivial exercise. A total consumption burner oxyhydrogen flame–ICP tandem source was used for the analysis of slurries of marine sediment Certified Reference Materials with particle diameters of less than 2 µm. Significant memory effects were observed. Detection limits were 0.3 ppm for Cu, 1 ppm for Mn and 1 ppm for Zn and the precision ranged between 1% and 3%(both determined using aqueous standards).

Degradation of Transmission of Silica Glass on Excimer Laser Irradiation

The effects of prolonged irradiation of KrF (248nm) and ArF (193nm) lasers on the optical properties of silica glass were studied, with a glass made from a high purity silicon tetrachloride by the oxy-hydrogen flame hydrolysis method for sample. Experiments were conducted as an acceleration test for services in excimer laser apparatuses, and the results were examined in terms of solarization, i.e., degradation in transmission, T, or increase in the absorption coefficient at 5.8eV, k2, as a function of the per pulse laser energy density, e. It was found that k2 was related to e as in: for KrF excimer laser: k2=2.38×10-7⋅e3.15(e⋅p)1.31, and for ArF excimer laser: k2=8.71×10-8⋅e1.42(e⋅p)1.45, where p is the number of shots. It was demonstrated that these formulas were precise enough to make reasonable estimates of the service lifetime for silica glass in industrial excimer laser apparatus, where the intensity of the laser would be much smaller.

Property Modification of Silica Glass by Ultrahigh Pressure Heating

A high purity silica glass containing a large amount of OH-group was synthesized from high purity silicon tetrachloride by the oxy-hydrogen flame direct hydrolysis method, and the effects of heat-treatment at 900°C under ultrahigh pressure of 10kbar or 20kbar were examined. The glass so treated was optically isotropic and macroscopically amorphous because no birefringence was observed, but a substantial increase in the refractive index was noted. Structural analysis of the 10kbar-treated glass by the laser Raman scattering spectrometry revealed the occurrence of the Raman spectral shifts, indicating a decrease in the Si-O-Si bond angle even though it is basically of the amorphous silica structure. For the 20kbar-treated glass, on the other hand, the analysis revealed the presence of the Raman spectra that are characteristic of α-quartz in addition to those that are characteristic of silica glass.

Hydroxyl Formation in Silica Tubes and Layers due to Oxy–Hydrogen Flames

ABSTRACTA novel kind of hydroxyl formation during the processing of quartz glass tubes with oxy-hydrogen burners was found and studied in detail by high-resolution laser spectroscopy. The formation mechanism involving hydrogen penetration from the flame and following reactions is discussed.

Experiments on REM and SREM using a Tem/Stem Microscope with a Configurable Angle-Resolving Detector

A Philips EM 420 electron microscope equipped with a field emission gun and an external STEM unit was used to compare images of single crystal surfaces taken by conventional reflection electron microscopy (REM) and scanning reflection electron microscopy (SREM). In addition an angle-resolving detector system developed by Daberkow and Herrmann was used to record SREM images with the detector shape adjusted to different details of the convergent beam reflection high energy electron diffraction (CBRHEED) pattern.Platinum single crystal spheres with smooth facets, prepared by melting a thin Pt wire in an oxyhydrogen flame, served as objects. Fig. 1 gives a conventional REM image of a (111)Pt single crystal surface, while Fig. 2 shows a SREM record of the same area. Both images were taken with the (555) reflection near the azimuth. A comparison shows that the contrast effects of atomic steps are similar for both techniques, although the depth of focus of the SREM image is reduced as a result of the large illuminating aperture. But differences are observed at the lengthened images of small depressions and protrusions formed by atomic steps, which give a symmetrical contrast profile in the REM image, while an asymmetric black-white contrast is observed in the SREM micrograph. Furthermore the irregular structures which may be seen in the middle of Fig. 2 are not visible in the REM image, although it was taken after the SREM record.

Superconducting YBa 2Cu 3O x particulate produced by total consumption burner processing

This paper summarizes the results on the characterization of fine particulates of YBa 2Cu 3O x superconducting oxide produced by reacting an atomized nitrate solution containing yttrium:barium:copper in the atomic ratio 1:2:3 respectively, in an oxyhydrogen flame. The characterization of the resulting oxide compound includes microstructural analysis by optical microscopy and scanning electron microscopy (SEM), X-ray diffraction and magnetic susceptibility measurements. SEM reveals the primary particle size (about 0.1−0.3 μm) and morphology of a substrate deposit, produced from solution concentrations ranging from 5 to 33 g l −1. X-ray diffraction measurements of oxygen-annealed particulate reveal a crystal structure identical with that of the conventionally produced superconducting oxide. Magnetic susceptibility measurements using a superconducting quantum interference device magnetometer demonstrate that the material is superconducting with a T c of about 93 K.