Quartz Wall Research Articles

An operando optical fiber UV–vis spectroscopic study of the catalytic decomposition of NO and N 2O over Cu-ZSM-5

The role of the bis( μ-oxo)dicopper core, i.e., [Cu 2( μ-O) 2] 2+, in the decomposition of NO and N 2O by the Cu-ZSM-5 zeolite has been studied with combined operando UV–vis monitoring of the catalyst and on-line GC analysis. An optical fiber was mounted on the outer surface of the quartz wall of the plug-flow reactor and collected the UV–vis diffuse reflectance spectra under true catalytic conditions. Measurement under transient reaction conditions indicated that [Cu 2( μ-O) 2] 2+ is formed by O abstraction of N 2O, which is an intermediate in the NO decomposition. This conversion of N 2O to N 2 and O 2 is strongly retarded below 673 K. Above 673 K, the produced [Cu 2( μ-O) 2] 2+ fulfills the role of O 2 release, guaranteeing the self-reduction of the catalytic site. Studying the NO decomposition as a function of the O 2 content in the feed strongly suggested that O 2 release from [Cu 2( μ-O) 2] 2+ is rate limiting in the NO decomposition at 773 K.

Economic performance evaluation method for hydroelectric generating units : Liu, Y. et al. Energy Conversion and Management, 2003, 44, (6), 797–808

A novel, compact mesoscale thermophotovoltaic (TPV) power generating system using a combination of porous media combustion and a simple band-pass filtering method has been proposed and experimentally studied. The novelty in this work is the idea of harvesting the heat produced in the microcombustor via the silicon carbide (SiC) porous media which becomes an effective radiator owing to its high emissivity. This is then combined with wafers that have a high optical transmissivity in the part of the spectrum that is useful for power conversion using the TPV system. In this work, we utilised two combustor wafers (silicon and quartz) with suitable thermal and optical properties. Quartz having a high transmissivity of 0.9 compared to silicon (<0.6) proved to be superior in performance when combined with the porous media combustion for TPV power generation. To further illustrate the combination of effects, we also performed experiments in which porous media was not inserted in the combustor and the radiation was effectively from the hot combustor walls. In this case, silicon which has a higher emissivity than the quartz performs better. Overall the TPV power generation was SiC + quartz > SiC + Si > pure Si walls > pure quartz walls.

Fourier transform infrared analysis of gas composition in low-volume light bulbs.

Fourier transform infrared spectroscopy has been used for in situ analysis of HBr, CH3Br, and CO within light bulbs at different stages of burning time. The interference fringes originated in the quartz walls of the bulbs have been eliminated by different methods. The NIPALS procedure yielded higher S/N ratio than the fringe-elimination method applied. The CO and HBr showed time-dependent concentration changes during the burning period. The maximum CO concentration (approximately 6 ppm) was detected after 30-50 s of burning time, and then it practically burned out after 5 h. The HBr concentration increased in the first 3 min of burning, and then its concentration stabilized at a 10-15 ppm level. After 5 s of illumination, the CH3Br concentration became undetectable.

Mineralogy of Ni-Cu-Platinum-Group Element Sulfide Ore in the 800 and 810 Orebodies, Copper Cliff South Mine, and P-T-X Conditions during the Formation of Platinum-Group Minerals

The 800 and 810 orebodies are two major deposits in the Copper Cliff South mine, located at opposite contacts between the quartz diorite of the Copper Cliff offset dike and metapelite of the McKim Formation. The Copper Cliff South mine is one of the richest Cu-Ni- platinum-group elements (PGE) deposits in the Copper Cliff offset dike. The ore is composed of variable proportions of pyrrhotite, chalcopyrite, and pentlandite and occurs as massive sulfides, semimassive sulfides with inclusions of quartz diorite and wall rocks, net-textured sulfides, disseminated sulfides, and veins. Sphalerite and magnetite are also present in minor amounts. The primary magmatic minerals in the quartz diorite are plagioclase, quartz, amphibole, and biotite. The most common platinum-group mineral (PGM) in the Copper Cliff South mine is sperrylite (PtAs 2 ). It occurs in every textural type of ore, typically enclosed by chalcopyrite, pyrrhotite, pentlandite, cobaltite, and hydrous silicates such as chlorite, amphibole, and epidote. Sperrylite may be homogeneous, zoned (with Sb-rich cores and Sb-poor rims), associated with hollingworthite (RhAsS) and cobaltite, or it may contain inclusions. The Pd-bearing minerals are froodite (PdBi 2 ) and michenerite (PdBiTe), which are most commonly enclosed by silicates (chlorite, biotite, quartz) or chalcopyrite. Hollingworthite invariably occurs in the center of zoned cobaltite in veins or in disseminated sulfides. Argentian gold (Au 0.56 Ag 0.44 ) occurs as small grains in chalcopyrite and in a veinlet with parkerite (Ni 2 Bi 3 S 2 ). The most abundant Ag mineral is hessite (Ag 2 Te), which is present in almost every sample with galena, gersdorffite, and locally PGM. Volynskite (AgBiTe 2 ) occurs as a zoned grain with tsumoite (BiTe) in the center. The most common trace minerals spatially and genetically associated with PGM are tsumoite, galena, gersdorffite, cobaltite, hessite, melonite, and native Te. The Copper Cliff South mine area was affected by more than one hydrothermal event, deformation, and metamorphism, all of which affected the primary igneous textures and mineralogy of the rocks. The first hydrothermal event was responsible for the extensive remobilization of metals, including some PGE. This is revealed by the presence of PGM in large veins in quartz diorite and metapelite and by chlorite, amphibole, epidote, biotite, and quartz that often enclose PGM. The temperature at the time of this event was estimated in samples containing garnet and biotite in equilibrium to be 327° to 540°C. Pressure, estimated using amphibole chemistry, may have been as high as 3 to 4 kbars. The fluid responsible for the transport of metals was very rich in Cl and oxidizing. The fluid composition, temperature, and/or pressure changed with time, suggested by the presence of zoned minerals, including sperrylite, gersdorffite, and cobaltite. Based on the textural relationships, sperrylite precipitated before tellurides and galena, and after or at the same time as michenerite. A second hydrothermal event produced calcite-bearing veinlets that cut larger veins.

FTIR study of adsorption and photodegradation of L-α-alanine on TiO2 powder

An infrared study of the adsorption of L-α-alanine (L-Ala) on TiO2 powder in aqueous suspension was carried out. When the amino acid is in the zwitterionic form and the TiO2 surface is positively charged, experimental results indicated that L-Ala molecules are adsorbed on titania through the carboxylated group, which gives rise to a bridged structure with the positive centers (protonated hydroxyls) of the TiO2 surface. Adsorbed amino acid was photodegradated in model conditions by exposing the sample to UV light through the quartz walls of the IR cell. The amine function was found to be preferentially removed from the adsorbed L-Ala molecules during the initial period of UV irradiation, and then the complete mineralization of the rest of the molecular structure occurred. This surface process agrees with the results of the analysis of the species that diffuse from the surface of the photocatalyst into the bulk of the liquid medium in the actual photodegradation carried out with TiO2 suspended in aqueous solutions of L-Ala.

WS2 Nanotube Bundles and Foils

WS2 nanotubes were synthesized in large amounts by reaction of H2S with WO3 nanopowder using a fluidized-bed reactor. The nanotubes come often in a few centimeter long bundles or alternatively as a few centimeters large foil deposited on the quartz wall of the reactor. Transmission electron microscopy revealed that the open-ended nanotubes are quite uniform in shape: up to 0.5-mm long and 15−20 nm in diameter, and they are chiral.

Electron Energy Distributions in Inductively Coupled Plasma of Argon

The effects of gas pressure, electron density and coil current on the electron energy distribution functions (EEDFs) in inductively coupled discharges of argon are studied numerically. The EEDF for low gas pressure is close to the Maxwellian, whereas the EEDF for high gas pressure is lower than the Maxwellian in the high energy tail due to inelastic collisions. Since the energy loss due to inelastic collisions is compensated by the energy deposition due to the induced electric field, the EEDF near the quartz wall becomes close to the Maxwellian. However, this EEDF is not the real Maxwellian because the velocity distribution of electrons near the wall is anisotropic in velocity space and hence in nonequilibrium. We proposed the factor ξ which represents the magnitude of the effect of Coulomb collisions. The factor is the ratio of electron–electron collision frequency to electron-atom inelastic collision frequency. The effect of Coulomb collisions on the EEDF is negligibly small for ξ< 0.01. The distribution function for the azimuthal component of electron velocity varies significantly as the radial position changes, whereas the distribution functions for the other components do not vary so much.

Transient convection of Te doped GaSb induced by g-jitter

Gallium antimonide (GaSb) is commercially used for solar cells and thermophotovoltaic devices. It is also used as a substrate material for the epitaxial growth of heterostructures, which are used for optoelectronic applications. The semiconducting properties of the material are governed by an antisite defect that requires compensation by a donor dopant such as tellurium to provide n-type conductivity. The electronic and optical properties of Te doped GaSb are greatly influenced by the degree of Te segregation in the crystal. The latter is strongly affected by buoyancy and thermocapillary (Marangoni) driven convections. Both types of convections are associated with a temperature-induced density and surface tension gradients along the sample. During 1996 and 1997, nine microgravity experiments were conducted on the MIR space station to determine the segregation of dopants during microgravity crystal growth using the QUELD furnace on the microgravity isolation mount. The space-grown samples displayed fluctuations in [p] and hence in [Te] attributed to g-jitters events and not to Marangoni convection during crystal growth (J. Vac. Sci. Technol. A 18(2) 2000). On the numerical side, attempts were made to study the effect of convection and the g-jitter on the segregation of Te in terrestrial and in microgravity conditions. Since no data of the g-jitter were available during the experiment attempt is made to study the transient convection due to the two different types of g-jitters. In the first case, the time dependent gravity was introduced in the momentum equations. In the second case, the time dependent velocity was implemented at the boundary of the quartz sample. The full Navier–Stokes equation combined with heat and mass transfer equations were solved numerically using the finite element techniques. The results show that g-jitter and time dependent velocity applied at the quartz wall play an important role in segregation of tellurium in the melt. A detailed parametric study was performed in order to reveal the convection pattern under various conditions.

Influence of the partial pressure of GaCl 3 in the growth process of GaN by HVPE under nitrogen

This study presents the results of experiments performed in a conventional atmospheric horizontal HVPE reactor. The growth results are analysed with a model based on two desorption mechanisms of chlorine. The kinetic of the epitaxial film growth of GaN on sapphire by hydride vapour phase epitaxy is investigated under a variety of experimental conditions. The growth rate and the parasitical deposit on the quartz walls of the reactor upstream and above the substrate depend on the reactor geometry and on the composition of the vapour phase. The result of the experiment for a zero supersaturation over the substrate is discussed. Theoretical calculations compared with experimental results show the non-homogeneity of the gaseous species and the non-equilibrium of the GaCl 3 in the vapour phase.

Chemical zoning of muscovite from the Ervedosa granite, northern Portugal

AbstractThe tin-bearing muscovite granite from Ervedosa contains unzoned primary muscovite. This Hercynian S-type granite was hydrothermally altered at the stanniferous quartz vein walls and contains three types of muscovite: (1) very small unzoned muscovite replacing albite; (2) small unzoned hydrothermal muscovite replacing K-feldspar and quartz; and (3) zoned subhedral muscovite.In the zoned muscovite, the core has a composition similar to that of magmatic muscovite from the unaltered granite, while the rim has a composition similar to that of hydrothermal muscovite replacing K-feldspar and quartz in the altered granite. The rim corresponds to a late overgrowth richer in the celadonitic component than the core. Infiltrated mineralizing fluids reacted with biotite and K-feldspar of the unaltered granite. We interpret the rim of muscovite to have precipitated from these solutions.

Heterogeneous quenching of O2(1g) molecules in H2:O2 mixtures

Quenching of O2(1g) molecules both in the gas phase and on a reactor surface has been investigated in binary mixtures of hydrogen and oxygen by using the fast-flow quartz reactor and infrared emission spectroscopy. Rate constants of the O2(1g) deactivation by H2 and O2 at room temperature have been determined to be (1.5±0.5) 10-18 cm3 s-1 and (1.6±0.2) 10-18 cm3 s-1, respectively. Heterogeneous quenching of O2(1g) on quartz walls has been studied both in pure oxygen and in H2:O2 mixtures. A model of O2(1g) heterogeneous quenching in binary mixtures has been developed and has allowed us to describe all observed features of singlet oxygen kinetics. Active surface complexes formed by `chemisorbed' atomic oxygen and `physadsorbed' molecules of O2 and H2 are assumed to be responsible for the O2(1g) heterogeneous deactivation. It has been shown that the higher rate of O2(1g) quenching in pure oxygen is connected with a quasi-resonant transfer of the O2(1g) electronic excitation to physadsorbed oxygen molecules. The observed effect of the wall passivation by hydrogen is conditioned both by the absence of the similar resonance in the hydrogen surface complex and by the higher bond energy of H2 in this complex. Bond energies of O2 (3750±450 K) and H2 (4050±450 K) in the surface complexes have been determined from the model parameters by fitting calculations to experimental results.

Effects of Photochemical Formation of Mercuric Oxide

The photochemistry of elemental mercury and oxygen was examined using quartz flow reactors. Germicidal bulbs were used as the source of 253.7-nm ultraviolet radiation. The formation of mercuric oxide, as visually detected by yellow-brown stains on the quartz walls, was confirmed by both ICP-AES and SEM-EDX analyses. In addition, a high surface area calcium silicate sorbent was used to capture the mercuric oxide in one of the experiments. The implications of mercuric oxide formation with respect to analysis of gases for mercury content, atmospheric reactions, and direct ultraviolet irradiation of flue gas for mercury sequestration are discussed.

Experimental and Theoretical Study of the Growth of GaN on Sapphire by HVPE

We study the influence of the reactor geometry and the control of the parasitic deposits on the growth of GaN by HVPE. Growth rates around 100 μm/h have been obtained with gas outlets close to the substrate and 16 μm/h with homogeneous vapour. The quality of the epitaxial layer deteriorates while the growth rate increases with decreasing distance between gas outlets and substrate, and the increase of the parasitic deposit. We predict by a model that in a homogeneous vapour and for a deposited mass on the quartz wall up to 0.86 g/h, the growth rate decreases drastically at high temperature down to etching. Adding HCl to the main nitrogen flow, the parasitic deposit decreases and the growth rate stays constant.

The behavior of flame front with heating mechanisms in two entrained-bed coal reactors

An experimental study was carried out in two laboratory-scale coal reactors to investigate the effect of heating rate on a pulverized coal flame. Each reactors had different heating mechanisms. For reactor A losing large heat through transparent quartz wall, pulverized coal particles were ignited by secondary air of 1050 K. Flame front could be visualized through the transparent wall. Reactor B was insulated with castable refractory to minimize the heat loss through the reactor wall and accompanied with secondary air of 573 K. Flame front was estimated from the gas temperature and species concentration measured using R-type thermocouple(Pt–Pt/Rh 13%) and gas chromatograph at various coal–air ratios and swirls. The flame front position was closely related with heating rate. The heating rate for lifted flame was of the order of 10 4–10 5 K/s and for ignition at least over 10 4 K/s. The heating mechanism had little impact on the extinction limits. The swirl forced the flame front to move toward the upstream by the rapid mixing of coal and air. However, it slightly increased the carbon conversion and the cold gas efficiency only below immediately fuel-rich conditions due to relatively low reactor temperature and a little increased residence time.

Detection by emission spectroscopy of active species in plasma–surface processes

The present paper is a review of recent works relating to the optical emission spectroscopy applied to the determination of the ground state densities of N, O and B atoms in Ar–N 2, Ar–O 2 and Ar–BCl 3 flowing post-discharges. New results on the B-atom destruction probability ( γ=0.4–0.5) on quartz walls are presented. The effect of small quantities of H 2 into Ar–N 2 and Ar–O 2 discharge on N and O atoms densities within the respective post-discharge has been analysed. Then, the authors demonstrate that the optical emission of Na in impurity may be applied to the determination of the vibrational temperature of N 2 ( X,v) states at the usual temperatures for nitriding of metals in Ar-N 2 post-discharges. From the diagnostic of Ar-N 2 post-discharges, it is clearly specified that the nitriding of iron base alloys in a flowing post-discharge reactor is coming from N atoms, especially as a few H 2 is admixed into the Ar–N 2 discharge. Finally, correlation between N-atom density and the thickness of iron nitrided layers are given as H 2 is introduced into the Ar–N 2 discharge.

Image charge effects on colloidal crystal ordering

We theoretically investigated the effect of the container wall on the structural ordering of aqueous dispersions of negatively charged electrostatically stabilized colloidal spherical particles. The colloidal crystal contained between two quartz plates is modeled as a set of crystal planes oriented parallel to the quartz walls. We consider the electrostatic interactions between the particles and the container wall, and the particles and their induced image charges. The position-dependent interaction energies of a plane with its neighbors and the induced image charges are calculated under the Debye–Hückel approximation. We also theoretically investigate the effect of charged container walls on the ordering of the colloidal particle dispersion. For zero wall surface charge, the colloidal sphere plane nearest to the container wall is held in a deeper potential well than are interior colloidal planes. A negative wall surface charge creates a shallower well for the nearest colloidal sphere plane, which is still deeper than that of the interior planes. A positive wall surface charge creates the deepest potential well. These results rationalize our recent observations of the initial nucleation of crystalline colloidal array by formation of 2D hexagonal colloidal layers near the container wall. We calculate the root-mean-square displacement of the planes at various distances from the wall and use the Lindermann-type melting criteria to examine ordering.

Ignition phase of a pulsed microwave-excited oxygen plasma

A pure oxygen plasma has been investigated for continuous mode as well as for pulsed power operation. Microwave power is fed to the plasma by an annular waveguide with 10 slotted line radiators on the inner side (SLAN principle). Plasma diagnostics were performed using (i) electrostatic probe methods for electron diagnostics, (ii) two-dimensional optical emission spectroscopy for excited oxygen mapping, and (iii) two-photon laser-induced fluorescence LIF for the quantitative measurement of atomic oxygen. Time-resolved emission spectroscopy was possible with a fast gated CCD camera system equipped with suitable optical filters. Of special interest was the ignition phase of the discharge. The temporal and spatial density variation of excited atomic oxygen was monitored. A first signal is visible after 7 μs after power application followed by an emission burst localized at a position nearby the quartz wall at about 15 μs after gas breakdown. End-on images from the camera prove that the plasma then expands mainly in the azimuthal direction. After 150 μs a symmetrical excitation zone with 10 emission maxima has formed and a homogeneous power coupling from all slot antennae is achieved. Electron densities measured by probes and atomic oxygen ground state densities determined by LIF show much slower temporal changes than the emission intensity. The experimental results are interpreted by considering the relevant channels leading to the production of atomic oxygen.

Nature, origin and evolution of the granitoid-hosted early Proterozoic copper-molybdenum mineralization at Malanjkhand, Central India - a reply

At Malanjkhand, Central India, lode-type copper (-molybdenum) mineralization occurs within calcalkaline tonalite-granodiorite plutonic rocks of early Proterozoic age. The bulk of the mineralization occurs in sheeted quartz-sulfide veins, and K-silicate alteration assemblages, defined by alkali feldspar (K-feldspar ≫ albite) + dusty hematite in feldspar ± biotite ± muscovite, are prominent within the ore zone and the adjacent host rock. Weak propylitic alteration, defined by albite + biotite + epidote/zoisite, surrounds the K-silicate alteration zone. The mineralized zone is approximately 2 km in strike length, has a maximum thickness of 200 m and dips 65°–75°, along which low-grade mineralization has been traced up to a depth of about 1 km. The ore reserve has been conservatively estimated to be 92 million tonnes with an average Cu-content of 1.30%. Supergene oxidation, accompanied by limited copper enrichment, is observed down to a depth of 100m or more from the surface. Primary ores consist essentially of chalcopyrite and pyrite with minor magnetite and molybdenite. δ34S (‰) values in pyrite and chalcopyrite (−0.38 to +2.90) fall within the range characteristic of granitoid-hosted copper deposits. δ18O (‰) values for vein quartz (+ 6.99 to +8.80) suggest exclusive involvement of juvenile water. Annealed fabrics are common in the ore. The sequence of events that led to the present state of hypogene mineralization is suggested to be as follows: fracturing of the host rock, emplacement of barren vein quartz, pronounced wall-rock alteration accompanied by disseminated mineralization and the ultimate stage of intense silicification accompanied by copper mineralization. Fragments of vein quartz and altered wall rocks and striae in the ore suggest post-mineralization deformation. The recrystallization fabric, particularly in chalcopyrite and sphalerite, is a product of dynamic recrystallization associated with the post-mineralization shearing. The petrology of the host rocks, hydrothermal alteration assemblages, ore mineral associations, fluid inclusions and the sulfur and oxygen isotopes of ores are comparable to those in Phanerozoic (and reported Precambrian) porphyry-copper systems, and the Malanjkhand deposit has important implications for both metallogenic models for, and mineral exploration in, Precambrian terrains.

High-density conversion of light energy via direct illumination of catalyst

Steam reforming of methane was studied under direct illumination of a catalyst by concentrated light in the energy receiver/reactor with a transparent wall. In such a reactor, both the specific rate of hydrogen production and the specific power loading of the light-to-chemical energy conversion appear to increase considerably with respect to a conventional stainless steel reactor, reaching 130 Ndm 3/h per 1 g of the catalyst and 50–100 W/cm 3, respectively. No considerable photochemical enhancement of the reaction rate was observed. The increase in the reaction rate is supposed to be caused by a significant intensification of energy supply into the catalyst bed due to absorption of light directly by granules of the catalyst used. Moreover, the transparent reactor also showed a higher efficiency of energy conversion because the temperature of the illuminated quartz wall appears to be lower than that for a steel wall which results in lower heat losses. This evidences in clear potentialities of a new generation of “volumetric” solar energy receivers/reactors.

Mode identification of surface waves excited in a planar microwave discharge

A planar high-density plasma, 22 cm in diameter and 9 cm in length, is produced by a 2.45 GHz microwave radiation of 500 W through small slot antennas in argon at 20 - 350 Pa without a magnetic field. Several types of azimuthal and radial standing wave mode pattern are observed in the optical emission from the plasma depending on the discharge conditions. The microwave field in the plasma measured by a movable antenna decreases exponentially in the axial direction from the quartz wall adjacent to the slot antennas, thus suggesting the propagation of surface waves in the r, directions. The measured azimuthal microwave field distributions and the optical emission pattern clearly show a mode transition of the standing surface wave from a mode to a mode when the pressure is decreased from 140 to 44 Pa at the constant power of 400 W. Here denotes the transverse magnetic mode of azimuthal mode number m and radial mode number n. A wave dispersion analysis based on a one-interface uniform-density model predicts these modes in a range of electron densities corresponding to those measured by a Langmuir probe in the experiment.