Quartz Window Research Articles

Band-approximated radiative heat transfer analysis of a solar chemical reactor for the thermal dissociation of zinc oxide

A solar chemical reactor for the thermal dissociation of ZnO is modeled by means of a detailed heat transfer analysis that couples radiative transport to the reaction kinetics. An extended band-approximated radiosity method enables the analysis of directional and wavelength depended radiation exchange. Boundary conditions included the incident concentrated solar radiation, determined by the Monte Carlo ray-tracing technique, and the hemispherical and band-approximated optical properties derived for the quartz window. Validation was accomplished by comparing the numerically modeled and experimentally measured window temperatures, reaction rates, and energy conversion efficiencies. The experimentally measured solar-to-chemical energy conversion efficiency increased with temperature, peaked at 14% for a reactor temperature of 1900 K and ZnO dissociation rate of 12 g/min, and decreased as the reactor approached its stagnation temperature. The conditions for which this efficiency can be augmented are discussed.

First Observation of RF-Induced Visible Light Fluctuations

In order to detect rf modulation of visible light emitted from plasma, a high-speed photodiode measurement system was developed. The system is located outside the vacuum vessel of the TST-2 spherical tokamak and measures visible light emissions through a quartz window. A dedicated amplifier for the photodiode was made. Care was taken to reduce the rf pickup noise. The frequency spectrum of the light signal detected during high harmonic fast wave (HHFW) heating showed modulation by HHFW. This is the first measurement of visible light modulation induced by HHFW, and shows promise for measurement of the rf electric field in the plasma core.

Effect of oxygen vacancies on nonlinear dielectric properties of SrTiO3 thin films

Ferroelectrics (FE) are a class of nonlinear dielectrics which exhibit an electric field dependent dielectric constant. High temperature superconductors (HTSC) offer lower microwave surface resistance than conventional materials. There have been significant interest and effort in combining the low microwave losses of HTSC with the voltage control of FE dielectric constant er to implement high quality voltage tunable microwave devices, such as phase shifters, filters, delay lines, and tunable oscillators [1–4]. In such devices, it is desirable to have a large capacitance change ratio [tunability = (Cmax–Cmin)/Cmax] under a certain electric field range accompanied by a small dielectric loss. SrTiO3 (STO) thin films which posses a transition peak located at 60–70 K is one of the most interesting FE materials due to its high nonlinearity and reasonably low dielectric loss. A main focus on research for effective utilization of STO thin films is the development of materials with simultaneously optimized permittivity (absolute magnitude as well as its electric field dependence.) and low dielectric loss (tand). However, the tunability and dielectric loss in STO thin films have not been comparable to that of bulk materials. Comparing with STO single crystal, most STO thin films showed low dielectric constant, low tunability and large dielectric loss. Many reasons have been suggested to the degradation in dielectric properties of STO thin films. The tetragonal distortion (ratio of in-plane and surface normal lattice parameters, D = a/c), the dead layer near interface, and the local polar regions near charged defects like oxygen vacancies are expected to degrade the dielectric properties of STO thin films [5–7]. Several researchers have investigated the effect of oxygen vacancies on dielectric properties of heteroepitaxially grown STO thin films [8, 9]. It is worthwhile to note that the study of oxygen vacancies on dielectric properties of hetero-epitaxial STO thin films is complicated because of the additional effect of film stress due to film-substrate crystal lattice mismatch and difference in thermal expansion coefficients. There have been no systematic studies on the influence of oxygen vacancies on dielectric properties of STO thin films. In this study, STO thin films were homoepitaxially grown on Nb doped STO (Nb:STO) substrate. No additional stress is caused by lattice constant mismatch and thermal expansion coefficient differences between films and substrate in the homo-epitaxial STO thin films. The effect of oxygen vacancies on dielectric properties of STO thin films are presented. STO thin films were deposited on Nb:STO substrates by pulsed laser deposition (PLD). KrF excimer laser radiation (Lamda Physik Compex 201) with repetition rate of 5 Hz was focused on a rotating target set in the chamber through a quartz window. The incident angle of laser beam to the target surface was fixed to be 45 . The output laser pulse energy was kept as 150 mJ which yielded a growth rate of 0.02 nm per pulse. The laser energy density was about 2 J/cm. X. Z. Liu B. W. Tao (&) Y. R. Li The National Key Laboratory of Electronic Thin Films and Integrated Devices, University of Electronic Science & Technology of China, Jianshe Road, Chengdu 610054, China e-mail: bwtao@uestc.edu.cn

Plasma parameters in the vicinity of the quartz window of a low pressure surface wave discharge produced in O 2

Plasma parameters in the vicinity of the dielectric window of a low density, microwave discharge produced in O 2 at 915 MHz are investigated by a spherical probe and optical emission spectroscopy while the microwave field distribution is measured by a spectrum analyzer. The electron energy distribution function is found to be strongly dependent on the position with respect to the slot antenna, exhibiting a group of energetic electrons at locations where the electric field and the optical intensity exhibit maximum values. The density of energetic electrons decreases sharply just a few cm away from the dielectric.

Effect of furnace atmosphere on E-glass foaming

The effect of furnace atmosphere on E-glass foaming has been studied with the specific goal of understanding the impact of increased water content on foaming in oxy-fired furnaces. E-glass foams were generated in a fused-quartz crucible located in a quartz window furnace equipped with video recording. The present study showed that humidity in the furnace atmosphere destabilizes foam, while other gases have little effect on foam stability. These findings do not contradict the generally accepted ‘dilution model’, suggesting that foaming is more severe in oxy-fired furnaces than in air-fired furnaces because the higher concentration of water in the furnace atmosphere ultimately enhances sulfate decomposition resulting in stronger foaming. The failure to reproduce this effect in laboratory experiments may be attributed to water incorporation into the glass melt occurring during ablation melting in industrial furnaces.

High-pressure operation of a xenon-GPSC/MSGC hybrid detector for hard X-ray spectrometry

The performance of a high-pressure xenon gas proportional scintillation counter/microstrip gas chamber (GPSC/MSGC) hybrid detector has been investigated for filling pressures from 1 up to 10 bar, for 22-, 30- and 60-keV photons. GPSC/MSGC hybrid detectors are based on a xenon-GPSC instrumented with a CsI-coated microstrip plate photosensor placed directly within the xenon envelope, as a substitute for the photomultiplier tube. This design avoids the constraints due to the use of a quartz scintillation window for GPSC–photosensor coupling, which absorbs a significant amount of scintillation and is a drawback for applications where large detection areas and high filling pressures are needed. The lowest energy resolutions are achieved for 2 bar (5.5% and 3.4%, FWHM, for 22- and 60-keV photons, respectively). Increasing the pressure to the 5–6 bar range, competitive energy resolutions of 7% and 4.5% are still achieved for 22- and 60-keV photons, respectively. This detector could be a compelling alternative in applications where compactness, large detection area, insensitivity to strong magnetic fields, room temperature operation, large signal-to-noise ratio and good energy resolution are important requirements.

Nitrogen-Implanted Silicon Oxynitride: A Coating for Suppressing Field Emission From Stainless Steel Used in High-Voltage Applications

In this paper, the authors examine the field emission performance of stainless steel polished to varying degrees, both before and after being coated with a nitrogen-implanted silicon oxynitride layer. The deposition procedure utilizes the simultaneous sputtering of silicon dioxide from a dielectric quartz window and ion implantation of nitrogen from an RF inductively coupled plasma. Here, the scanning field emission microscopy results indicate that prior to being coated, the number of emission sites increased drastically from 12 to more than 300 as the surface roughness increased from 4 to 64 nm, corresponding to polishing with 1-mum diamond paste to 15-mum (600 grit) silicon carbide paper. However, after being coated with nitrogen-implanted silicon oxynitride, all the samples displayed zero to five emission sites at electric field strengths at least three times higher than the uncoated stainless samples. Thus, neither the roughness of the underlying stainless steel nor that of the top surface of the coating had an effect on suppressing field emission. Depth profiling using Auger electron spectroscopy determined that the 0.24-mum-thick silicon oxynitride coating contained approximately 15% nitrogen. Fourier transform infrared spectroscopy of a coated silicon wafer confirmed this stoichiometry and bonding. The technical impact of this work is that coating the large contoured stainless steel surfaces with a nitrogen-implanted silicon oxynitride layer may eliminate the need for expensive labor-intensive polishing procedures currently used in high-voltage electrode structures, such as those found in electron injectors

Optically accessible channel reactor for the kinetic investigation of hydrocarbon reforming reactions

A new experimental reactor concept for studying heterogeneously catalyzed gas phase reactions was developed, which allows true surface temperature measurements along the reactor through a quartz window without affecting the flow in the reactor using IR thermography. The catalyst is coated as a thin layer onto a metal plate. The laminar flow field is similar to the one in a monolith channel. A small stream of gas can be withdrawn with a moveable capillary to measure the concentration profile in the reactor. The spatial resolution of the gas sampling is ≤0.1 mm. Two- and three-dimensional fluid dynamic modeling of the channel reactor was performed to check the velocity field in the channel for different operating conditions. Buoyancy forces were insignificant at the conditions studied; the parabolic inlet flow profile was maintained along the reactor channel. The heat loss by radiation from the quartz glass top surface was found to be three times larger than the heat loss by free convection. The methanation of carbon monoxide and carbon dioxide was studied at 550 and 500 °C, respectively. For these reactions nearly isothermal conditions were observed. The partial oxidation of methane, performed without diluting the feed, was also studied at 500 and 550 °C. The measured hot spots correlated well with the concentration profile measurements. Film diffusional limitations were found only significant for the oxidation reaction.

Lens-coupled liquid core waveguide for ultraviolet-visible absorption spectroscopy

We have developed and characterized a modular liquid core waveguide (LCW) assembly for use in a commercial spectrophotometer to measure very low light absorbance values for dilute aqueous solutions in both the ultraviolet and visible wavelengths. The sample cell in this assembly is composed of a ∼1m, pure Teflon® AF 2400 tube that is coupled to the spectrophotometer light path with a quartz lens and windows. Spectrophotometric absorbance measurements of test solutions (e.g., dilute sodium nitrate and hydrogen peroxide) produce clear and distinct spectra that exhibit a lower limit of detection of 3mAU between 240 and 640nm. At absorbances above 10mAU our LCW system produces spectra from multiple independent injections that have a relative standard deviation of less than 10% and average absorbances within 5% of calculated values based on published molar absorptivities.

Development and use of a TG-DTA-microscope for evaluation of pharmaceutical materials

The successful combination of microscopy with thermogravimetry-differential thermal analysis is reported. Simultaneous use of all three techniques is made possible by custom fitting a quartz glass window into the furnace of a commercially available TG-DTA. The quartz window enabled direct observations from a microscope mounted above the furnace throughout the entirety of the thermal analytical experiments. Several examples are provided for the use of this combined system for evaluating dehydrations, degradation and phase conversions in pharmaceutical materials. In some examples, microscopy provided information not accessible from the thermal analytical data alone. In others, the thermal analytical data was more informative than the microscopy.

Properties of the C-terminal Domain of Enzyme I of the Escherichia coli Phosphotransferase System

The bacterial phosphoenolpyruvate (PEP):glycose phosphotransferase system (PTS) mediates uptake/phosphorylation of sugars. The transport of all PTS sugars requires Enzyme I (EI) and a phosphocarrier histidine protein of the PTS (HPr). The PTS is stringently regulated, and a potential mechanism is the monomer/dimer transition of EI, because only the dimer accepts the phosphoryl group from PEP. EI monomer consists of two major domains, at the N and C termini (EI-N and EI-C, respectively). EI-N accepts the phosphoryl group from phospho-HPr but not PEP. However, it is phosphorylated by PEP(Mg(2+)) when complemented with EI-C. Here we report that the phosphotransfer rate increases approximately 25-fold when HPr is added to a mixture of EI-N, EI-C, and PEP(Mg(2+)). A model to explain this effect is offered. Sedimentation equilibrium results show that the association constant for dimerization of EI-C monomers is 260-fold greater than the K(a) for native EI. The ligands have no detectable effect on the secondary structure of the dimer (far UV CD) but have profound effects on the tertiary structure as determined by near UV CD spectroscopy, thermal denaturation, sedimentation equilibrium and velocity, and intrinsic fluorescence of the 2 Trp residues. The binding of PEP requires Mg(2+). For example, there is no effect of PEP on the T(m), an increase of 7 degrees C in the presence of Mg(2+), and approximately 14 degrees C when both are present. Interestingly, the dissociation constants for each of the ligands from EI-C are approximately the same as the kinetic (K(m)) constants for the ligands in the complete PTS sugar phosphorylation assays.

A system to irradiate and measure luminescence at low temperatures

We have developed a system to irradiate samples and record radioluminescence (RL), optically stimulated luminescence (OSL), and thermoluminescence (TL) at temperatures ranging from -150 degrees C to 200 degrees C. The system consists of a cryostat, an irradiation/stimulation unit fitted with an X-ray tube (40 kV Moxtek) and a quartz window for optical stimulation, and a detection unit that utilises a photomultiplier tube and an interchangeable filter pack. Experiments have been conducted with quartz and albite (a feldspar). TL and OSL experiments show that several optically sensitive trapping states are stable below -50 degrees C. In addition, an increase in OSL is seen as the OSL stimulation temperature is lowered below -50 degrees C, and an increase in RL is apparent as the temperature is lowered during irradiation. This indicates that not only are optically sensitive low temperature traps present but that luminescence becomes more efficient at low temperatures.

The near Infrared Window—Glass or Quartz? A Study in Precision

All near infrared instruments are equipped with a “window” to protect the detectors from the atmosphere. Many types of sample cells are also fitted with a window between the sample surface and the detector. These windows may be composed of special optical glass or quartz. This paper describes variability of wheat flour spectra when using a series of glass and quartz windows. Differences among the windows of both glass and quartz exhibited differences of up to respectively 40% and 14% in the spectral data when they were used in the development of calibration models for the prediction of protein content in wheat flour. The differences among the windows did not affect the precision of spectral data when the same window was used for replicate testing, but induced absolute biases of up to over 3% (glass) and 1% (quartz) to the predicted protein results. Biases could be countered by use of derivatives or by combining spectral data from flours by using the different windows in the development of the calibration models. An anomaly was noted in the flour spectra obtained using quartz window number 4. The anomaly was found to cause significant biases in the prediction of protein content. The biases could be removed if the calibration model was developed using a wavelength range that avoided the anomaly.

Multiple Air-Jet Window Cooling for High-Temperature Pressurized Volumetric Receivers: Testing, Evaluation, and Modeling

High air outlet temperatures increase the solar share of pressurized solar receivers for gas turbines, operated in solar-fossil hybrid mode. However, an increase in outlet temperature over 800°C leads to excessive heating of the receiver window, unless it is actively cooled. This paper describes modeling, testing, and evaluation of a high-temperature receiver with external multiple air-jet window cooling. An asymmetric window-cooling design with pulsating air mass flow rates achieves suitable cooling of the concave fused-silica window. A thermodynamic receiver model, comprising nongray radiative heat transfer, convection, and conduction is the basis of the external window cooling design. In addition to high-temperature testing with window cooling in operation, solar tests at lower temperatures with no window cooling were conducted to verify the thermodynamic receiver model. Temperature distributions on the quartz window and the absorber were determined by an infrared scanner which was specially developed for temperature measurement on the high-temperature module. Comparisons of simulations and measurements show good agreement. With multiple air-jet window cooling, receiver air outlet temperatures over 1000°C could be reached, while window temperatures are kept below 800°C.

Self-association and Chaperone Activity of Hsp27 Are Thermally Activated

The small heat shock protein 27 (Hsp27) is an oligomeric, molecular chaperone in vitro. This chaperone activity and other physiological roles attributed to Hsp27 have been reported to depend on the state of self-association. In the present work, we have used sedimentation velocity experiments to demonstrate that the self-association of Hsp27 is independent of pH and ionic strength but increases significantly as the temperature is increased from 10 to 40 degrees C. The largest oligomers formed at 10 degrees C are approximately 8-12 mer, whereas at 40 degrees C oligomers as large as 22-30 mer are observed. Similarly, the chaperone activity of Hsp27 as indicated by its ability to inhibit dithiothreitol-induced insulin aggregation also increases with increased temperature, with a particularly sharp increase in activity as temperature is increased from 34 to 43 degrees C. Similar studies of an Hsp27 triple variant that mimics the behavior of the phosphorylated protein establish that this protein has greatly diminished chaperone activity that responds minimally to increased temperature. We conclude that Hsp27 can exploit a large number of oligomerization states and that the range of oligomer size and the magnitude of chaperone activity increase significantly as temperature is increased over the range that is relevant to the physiological heat shock response.

Laminar-burning velocities of hydrogen–air and hydrogen–methane–air mixtures: An experimental study

The laminar burning velocities of hydrogen–air and hydrogen–methane–air mixtures are very important in designing and predicting the progress of combustion and performance of combustion systems where hydrogen is used as fuel. In this work, laminar flame velocities of hydrogen–air and different composition of hydrogen–methane–air mixtures (from 100% hydrogen to 100% methane) have been measured at ambient temperatures for variable equivalence ratios ( ER = 0.8 – 3.2 ). A modified test rig has been developed from the former Cardiff University ‘Cloud Chamber’ for this experimental study. The rig comprises of a 250 mm length cylindrical stainless steel explosion bomb enclosed at one end with a stainless steel plug which houses an internal stirrer to allow mixing. The other end is sealed with a 120 mm diameter round quartz window. Optical access for filming flame propagation is afforded via two diametrically opposed quartz windows in both sides. Flame speeds are determined within the bomb using a high-speed Schlieren photographic technique. This method is an accurate way to determine the flame–speed and the burning velocities were then derived using a CHEMKIN computer model to provide the expansion ratio. The design of the test facility ensures the flame is laminar which results in a spherical flame which is not affected by buoyancy. The experimental study demonstrated that increasing the hydrogen percentage in the hydrogen–methane mixture brought about an increase in the resultant burning velocity and caused a widening of the flammability limits. This experiments also suggest that a hydrogen–methane mixture (i.e. 30% hydrogen+70% methane) could be a competitive alternative fuel for existing combustion plants.

Diamond-like carbon thin films grown by large-area surface-wave mode microwave plasma CVD: Effects of stage distance to microwave window

Diamond-like carbon (DLC) thin films were grown on silicon and quartz substrates by using large-area surface-wave mode microwave plasma chemical vapor deposition at different distances from microwave quartz window. The chemical, optical, bonding and structural properties of the films were characterized by X-ray photoelectron spectroscopy, UV/VIS/NIR spectroscopy, Fourier transform infrared spectroscopy and Raman spectroscopy. Nitrogen atomic concentration (%) of the films increased with decreasing the distance of substrate to microwave quartz window. Optical band gap of the films decreased from 2.7 to 2.4 eV when the substrate to microwave quartz window decreased from 12 to 3 cm. The FT-IR absorbance peaks of the DLC films in the region 2800–3000 cm − 1 became more and more prominent as the distance of substrate to the microwave quartz window increased from 3 to 12 cm, suggesting the formation of crystalline structure in the films. The increase of sp 2 fraction with decreasing the distance of substrate to the microwave quartz window (i.e. increasing the electron density of the plasma) was conformed by Raman spectra of the films.

Instantaneous determination of crude proteins, fat and fibre in animal feeds using near infrared reflectance spectroscopy technology and a remote reflectance fibre-optic probe

In the present study we address the development of a rapid technique – near infrared reflectance spectroscopy (NIRS) technology and the use of a remote reflectance crude fibre (CF)-optic probe (fitted with a 5 cm × 5 cm quartz window) – to perform instantaneous analysis of quantitative parameters such as the ether extract (DM), crude protein (CP) and crude fibre in animal feed and fodder. The technique does not involve the destruction or treatment of the sample because it is based on direct application of a fibre-optic probe on the feed (with different physical characteristics, such as commercialisation in the form of meal, tablets and granules) given to cattle, swine, sheep, birds and rabbits that is used in different stages of animal development—juvenile development, growth, fattening, etc. The regression method employed was modified partial least squares (MPLS). The calibration results using 72 samples permitted the determination of crude protein, the ether extract and crude fibre. This calibration is applicable within the ranges for crude protein of 5–495 g kg −1; the ether extract, 16–66 g kg −1; crude fibre, 23–111 g kg −1, with multiple correlation coefficients (RSQ) for crude protein, the ether extract and crude fibre of 0.991, 0.932 and 0.848, respectively. The standard errors of prediction corrected (SEPC) for the above parameters in g kg −1 were 12.5, 2.09 and 6.05, respectively. The robustness of the analytical method was confirmed by applying it to 10 samples for external validation. The results obtained indicate that NIRS with a fibre-optic probe can be used as a quality control method in animal feeds and fodder for the determination of crude protein, the ether extract and crude fibre.

マイクロ波矩形プラズマを用いた高分子表面親水化の研究

A microwave rectangular plasma was generated over 450 mm long using a sectorial horn antenna with the aperture of 400×10 mm2 and permanent magnets. High density plasma was efficiently produced due to the electron cyclotron resonance (ECR) heating. Ion saturation current density of 5-10 mA/cm2 for Ar plasma was attained in the vicinity of the ECR zone which is close to the quartz window. The spatial plasma uniformity of ±7% was obtained over 300 mm long at 400 W, 1.0 Pa at the position of 160 mm away from the quartz window. This plasma source was applied to the surface modification of the high density poly(ethylene) (HDPE) and poly(tetrafluoroethylene) (PTFE) sheets. After Ar plasma irradiation at 400 W, 10 Pa and 150 s, the contact angles on the HDPE and PTFE surfaces decreased from 82° to 31° and from 90° to 49°, respectively. In addition, the uniformity on the plasma treatment was ±7% for HDPE and ±5% for PTFE over 420 mm long. X-ray photoelectron spectroscopy (XPS) analysis showed that defluorination and the formation of C=O groups appeared on the plasma treated surfaces.

FlhB Regulates Ordered Export of Flagellar Components via Autocleavage Mechanism

The bacterial flagellum is a predominantly cell-external super-macromolecular construction whose structural components are exported by a flagellum-specific export apparatus. One of the export apparatus proteins, FlhB, regulates the substrate specificity of the entire apparatus; i.e. it has a role in the ordered export of the two main groups of flagellar structural proteins such that the cell-proximal components (rod-/hook-type proteins) are exported before the cell-distal components (filament-type proteins). The controlled switch between these two export states is believed to be mediated by conformational changes in the structure of the C-terminal cytoplasmic domain of FlhB (FlhB(C)), which is consistently and specifically cleaved into two subdomains (FlhB(CN) and FlhB(CC)) that remain tightly associated with each other. The cleavage event has been shown to be physiologically significant for the switch. In this study, the mechanism of FlhB cleavage has been more directly analyzed. We demonstrate that cleavage occurs in a heterologous host, Saccharomyces cerevisiae, deficient in vacuolar proteinases A and B. In addition, we find that cleavage of a slow-cleaving variant, FlhB(C)(P270A), is stimulated in vitro at alkaline pH. We also show by analytical gel-filtration chromatography and analytical ultracentrifugation experiments that both FlhB(C) and FlhB(C)(P270A) are monomeric in solution, and therefore self-proteolysis is unlikely. Finally, we provide evidence via peptide analysis and FlhB cleavage variants that the tertiary structure of FlhB plays a significant role in cleavage. Based on these results, we propose that FlhB cleavage is an autocatalytic process.