Hydrogen Gas Flow Rate Research Articles

From Nanoparticles to Nanowires of GaN with Different Hydrogen Gas Flow Rates by PDC-PECVD

III-V family semiconductors have received considerable attention for microelectronic and optoelectronic applications. In particular, GaN nanostructures have a huge number of applications due to its wide and direct band gap, high melting point and high electrical breakdown field. Wurtzite structure of GaN nanoparticles and nanowires were synthesized using different hydrogen gas flow rate of 0, 3 and 7sccm (standard cubic centimetres per minute) via pulsed direct current plasma enhanced chemical vapor deposition (PDC-PECVD) at low temperature, 650°C. GaN nanostructures including nanowires and nanoparticles were grown using gallium atoms and nitrogen plasma on Si (111) substrates. Characterizations of GaN nanostructures were carried out using X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS) and field emission electron microscopy (FE-SEM). Morphology of the grown GaN nanostructures changed from nanoparticles to nanowires with increasing the hydrogen gas flow rates. XRD results demonstrate that lattice constants ratio of a/c of hexagonal structure and gallium/nitrogen ratio in the synthesized GaN nanostructures decreased with increasing hydrogen flow rates. GaN nanoparticles and nanowires were grown on Si (111) with average diameters of 45nm and 25nm, respectively. The results show that the hydrogen plasma can significantly affects on morphology and lattice parameters of GaN nanostructures by low temperature PECVD method.

Reduction of Ammonium Paratungstate Generated during Hydrometallurgical Processing of Tungsten-Copper Borings

Tungsten-copper(W-Cu) alloy is employed for manufacturing heavy duty contactors, relays,switches etc. During production of such components, W-Cu turnings/borings aregenerated. At CSIR-NML, a process for recovering tungsten and copper fromtungsten-copper borings containing 46.01% W, 53.78% Cu, 0.13% Fe and otherminor metals as high purity tungsten powder and copper powder has beendeveloped. In the present work, a detailed investigation on reduction ofammonium paratungstate (APT) having purity 99.95% by hydrogen gas to produce highpurity tungsten powder is presented. The various process parameters such astemperature, time and flow rate of hydrogen gas have been optimized. At the temperatureof 800°C and 0.1 lpm flow rate a reduction of 77.78% was observed upto 2h time. At 900°C, with increase in flow rate from 0.1 lpm to 0.3lpm the increase in reduction was found to be from 63.88% to 99.99% at 1h time.At still high temperature of 1000°C, almost complete reduction was obtainedat 0.1 lpm flow rate in 1h time. The effect of bed-depth was also carried out. Atall temperatures chemical reaction was the rate determining step.

Performance of sanitary sewer collection system odour control devices operating in diverse conditions

Controlling odours from sanitary sewer systems is challenging as a result of the expansive nature of these systems. Addition of oxidizing chemicals is often practiced as a mitigation strategy. One alternative is to remove odorous compounds in the gases vented from manholes using adsorptive media. In this study, odour control devices located at manholes were observed to determine the ability of these systems to reduce hydrogen sulphide from vented gases. The odour control devices incorporated pressure regulation to control gas flow out of manhole covers and adsorptive media to remove hydrogen sulphide in the vented gases prior to release. Pressure regulation was accomplished using a variable volume bladder and two pressure relief valves that permitted gas flow when pressures exceeded 1.3 to 2.5 cm water column. The reduction in gas flow vented from manholes was intended to extend the service life of the adsorptive media, as compared with odour control devices that do not incorporate pressure modulation. Devices were deployed at four locations and three adsorptive media were tested. Although measured collection system hydrogen sulphide concentrations varied from zero to over 1,000 ppm, the removal rates observed using odour control devices were typically above 90%. The lower removal rates observed at one of the sites (50.5 ± 36.1%) appeared related to high gas flow rates being emitted at this location. Activated carbon was used in most of the tests, although use of iron media resulted in the highest removal observed: 97.8 ± 3.6%. The expected service life of the adsorptive media contained within the odour control devices is a function of site-specific hydrogen sulphide concentrations and gas flow rates. The units used in this study were in service for more than 8 to 12 months prior to requiring media replacement.

구리기판을 이용한 그래핀 박막 특성 및 그래핀을 이용한 트랜지스터의 특성 분석

화학적 증착방법으로 구리기판 위에 그래핀을 형성하고 일반적인 전사방법을 이용하여 그래핀 박막을 제작하였다. 메탄과 수소 가스의 유량비에 따른 특성에 대하여 라만 분석법을 이용하여 조사하였다. 메탄의 유량이 많을수록 그래핀의 형성이 잘 이루어지는 것을 확인하였다. 수소의 양이 증가할수록 D (<TEX>$1350cm^{-1}$</TEX>), G (<TEX>$1580cm^{-1}$</TEX>) 대역이 증가하였으며, 상대적으로 메탄의 유량비가 증가할수록 2D (<TEX>$2700cm^{-1}$</TEX>)의 픽이 강도가 증하였다. D (<TEX>$1350cm^{-1}$</TEX>)은 결함과 관련되어 있는 픽이다. 그래핀의 단층확인은 G/2D의 비율이 작을수록 그래핀이 단일박막임을 알 수 있고, 200도에서 열처리 후 0.55의 값을 나타내는 것을 확인하였다. 그래핀 채널 트랜지스터를 제작한 결과 p 형 반도체로서의 전달특성이 나타나는 것을 확인하였다. Graphene thin film was prepared on the copper foils by chemical deposition, and the characteristic of graphene depending on <TEX>$H_2$</TEX> and CH4 gas flow rates was analyzed by the Raman spectra. The graphene formation was improved with increment of methan gas flow rates. The increment of hydrogen gas flow rate made high intensity of D(<TEX>$1350cm^{-1}$</TEX>) and G(<TEX>$1580cm^{-1}$</TEX>). The peak of D(<TEX>$1350cm^{-1}$</TEX>) is related with the defects, and the 2D(<TEX>$2700cm^{-1}$</TEX>) increased depending on the increment of amount of methan gas flow rate. The rate of G/2D indicates the quality of garphene to like a monolayer, and the small value of G/2D means better grapheme. The G/2D of graphene after annealed at <TEX>$200^{\circ}C$</TEX> was 0.55 and improved the characteristic of graphene than the deposited-grapnene. Thin film transistor with graphene as an active channel was p-type semiconductor.

Effects of hydrogen in the cooling step of chemical vapor deposition of graphene

We investigated the effects of hydrogen gas flow rate in the cooling step of CVD on graphene film. We discovered that hydrogen gas in the cooling step influences the quality of graphene. The D peak (defects of graphene) intensity of the Raman spectrum tends to increase with an increasing hydrogen flow rate. Whether methane gas as a hydrocarbon source is maintained during the cooling step or not, the hydrogen flow rate during the cooling step strongly affects the quality of CVD-grown graphene.

Effect of H2 Flow Rate on High-Rate Etching of Si by Narrow-Gap Microwave Hydrogen Plasma

For the purpose of realizing a low-cost production process of silane (SiH4) gas, we have proposed the high-rate etching of metallurgical-grade Si by narrow-gap microwave hydrogen plasma. In this paper, effect of hydrogen gas flow rate (0–10 L/min) on the etch rate has been investigated and correlated with the relative variation of hydrogen-atom density estimated by actinometry. By decreasing hydrogen gas flow rate, the etch rate gradually increases up to the maximum value of 11 μm/min at 2 L/min. This increase is well correlated with the increase of hydrogen-atom density due to the longer residence time of hydrogen molecules in the plasma. On the other hand, when the gas flow rate is lower than 2 L/min, the etch rate abruptly decreases with decreasing gas flow rate in spite of the increase of hydrogen-atom density. From the surface observations and Raman measurements, it is found that the decrease in etch rate in the lower flow rate range is attributed to the formation of microcrystalline Si particles due to the decomposition of generated-SiH4 molecules in the plasma.

Effects of Enthalpy-Enhancing Gas on Ionic Conductivity of Atmospheric Plasma-Sprayed 3.9YSZ Electrolyte for 45-75 μm Particles

Enthalpy-enhancing gas is used to optimize the ionic conductivity of atmospheric plasma-sprayed 3.9 mol% yttria-stabilized zirconia (3.9YSZ) electrolyte. In the experiment, three hydrogen gas-flow rates were used to control the plasma energy. The size of the 3.9YSZ feedstock powder was sieved to be set in the range of 45-75 μm. When the hydrogen gas-flow rate was increased, the electrolyte became harder, and the sprayed surfaces became smoother. However, the lowest apparent porosity and the highest bulk density of the electrolyte were obtained at a hydrogen gas-flow rate of 7 L/min. A 3.9YSZ electrolyte with an ionic conductivity of 2860 µ(S/cm) and the lowest dissociation energy was obtained at 800 °C with a hydrogen gas-flow rate of 12 L/min. It was controlled by the intragrain conductivities. A higher hydrogen gas-flow rate enhanced the growth of columnar grains and suppressed the appearance of the monoclinic phase, which led to the greater intragrain conductivities. The increase in grain-boundary conductivities is closely related to the decrease in grain size.

Construction and Evaluation of the Calibration Facility for High-Pressure Hydrogen Gas Flow Meters

The calibration facility was newly constructed for high-pressure hydrogen gas flow meters. This facility can supply hydrogen gas of 350 Nm3/h at 35 MPa continuously for about 10 min. The calibration facility has the multi-nozzle calibrator, in which five critical nozzles calibrated by the NMIJ standards, are equipped, and can measure hydrogen gas flow rate within the relative standard uncertainty of 0.18 %. Also, the Coriolis flow meter for high pressure hydrogen were calibrated and evaluated by this calibration facility, and its output was scattered within about ±1.5 %. The present results show that the calibration facility constructed is useful for the evaluation of the high-pressure hydrogen gas flow meters, as well as the calibration.

Raman Spectroscopy of Amorphous Carbon Prepared by Pulsed Arc Discharge in Various Gas Mixtures

To meet various application requirements, it is important to enable an improvement of a-C structure and properties, such as hardness, adhesion, and wear resistance. In this study, we used the Raman spectroscopy to investigate the a-C thin films structure dependence on the different deposition parameters. The effect of nitrogen, argon, and hydrogen gas flow rate was analyzed to determine the influence on the film properties. The change in the gas type, combination, and flow had a significant influence on the D and G bands of the a-C Raman spectra. The addition of N2into the chamber promoted the sp2creation, while with adding hydrogen the layer contained more sp3bonds. The depositions of a-C thin films were carried out in pulsed arc discharge vacuum installation. Micro-Raman measurements of the deposited materials were performed using an ISA Dilor-Jobin Yvon-Spex Labram confocal system with 632.8 nm radiation from a He-Ne laser using a back-scattering geometry.

Role of hydrogen in Sb film deposition and characterization of Sb and GexSby films deposited by cyclic plasma enhanced chemical vapor deposition using metal-organic precursors

To meet increasing demands for chemical vapor deposition methods for high performance phase-change memory, cyclic plasma enhanced chemical vapor deposition of Sb and GexSby phase-change films and characterization of their properties were performed. Two cycle sequences were designed to investigate the role of hydrogen gas as a reduction gas during Sb film deposition. Hydrogen gas was not introduced into the reaction chamber during the purge step in cycle sequence A and was introduced during the purge step for cycle sequence B. The role of hydrogen gas was investigated by comparing the results obtained from these two cycle sequences and was concluded to exert an effect by a combination of precursor decomposition, surface maintenance as a hydrogen termination agent, and surface etching. These roles of hydrogen gas are discussed through consideration of changes in deposition rates, the oxygen concentration on the surface of the Sb film, and observations of film surface morphology. Based on these results, GexSby phase-change films were deposited with an adequate flow rate of hydrogen gas. The Ge and Sb composition of the film was controlled with the designed cycle sequences. A strong oxygen affinity for Ge was observed during the X-ray photoelectron spectroscopy analysis of Sb 3d, Sb 4d, and Ge 3d orbitals. Based on the XPS results, the ratios of Ge to Sb were calculated to be Ge0.32Sb0.68, Ge0.38Sb0.62, Ge0.44Sb0.56, Ge0.51Sb0.49 and Ge0.67Sb0.33 for the G1S7, G1S3, G1S2, G1S1, and G2S1 cycles, respectively. Crystal structures of Sb, Ge, and the GeSb metastable phase were observed with various GexSby film compositions. Sb crystallinity decreased with respect to Ge crystallinity by increasing the Ge fraction. A current–voltage curve was introduced, and an electro-switching phenomenon was clearly generated at a typical voltage, Vth. Vth values increased in conjunction with an increased proportion of Ge. The Sb crystallinity decrease and Vth increase were explained via the bonding characteristics of each element.

Mo Powders Fabricated from MoO3 by Reduction in Hydrogen Gas

We studied the effect of temperature and reaction time by investigating the various temperatures and reaction times in the reduction of molybdenum oxide (MoO3) to molybdenum (Mo) powder in hydrogen gas. We also studied the effect of the reaction of reduction according to the various hydrogen gas flow rates. We surveyed the reduction from molybdenum oxide to molybdenum powder in hydrogen gas and checked two temperature ranges, one from 400℃ to 600℃ and the other from 700℃ to 900℃. We found that the reaction ratio of molybdenum oxide increased with an increasing temperature and also increased with an increasing reaction time, but hydrogen gas did not influence the reduction ratio of molybdenum oxide. We examined molybdenum powders fabricated by ball milling for two hours, using with X-ray diffraction (XRD) and a scanning electron microscopy (SEM).

Effects of Enthalpy‐Enhancing Gas on Ionic Conductivity of Atmospheric Plasma‐Sprayed 3.9YSZ Electrolyte for 20–45 μm Particles

Enthalpy‐enhancing gas is used to optimize the ionic conductivity of atmospheric plasma‐sprayed 3.9 mol% yttria‐stabilized zirconia (3.9YSZ) electrolyte. In the experiment, three hydrogen gas flow rates were used to control the plasma energy. The size of the 3.9YSZ feedstock powder was sieved to be in the range of 20–45 μm. When the hydrogen gas flow rate increased, the sprayed surfaces became rougher. Nevertheless, the lowest apparent porosity, the highest bulk density, and the hardest electrolyte were obtained at the hydrogen gas flow rate at 7 L/min. A 3.9YSZ electrolyte with an ionic conductivity of 1480 μ (Ω cm)‐1 was obtained at 800°C, when the hydrogen gas flow rate was at 12 L/min. It was controlled by the grain‐boundary conductivity, which was closely related to the lowest migration energy, the highest density of the columnar grains, and the closest bonding between lamellar layers. The increase in the hydrogen gas could diminish the amount of the migration energy and increase the grain‐boundary conductivity. On the other hand, a larger cubic lattice constant and a less amount of the monoclinic phase in the as‐sprayed electrolyte helped obtain greater intragrain conductivity.

Measurement of Specific Enthalpy Under Very Low Pressure Plasma Spray Condition

VLPPS has attracted much attention in recent years, especially concerning its potential applications but not so much concerning the properties of the plasma jet. Operating parameters such as the chamber pressure and the secondary gas flow rate have a strong influence on specific enthalpy and temperature of the plasma jet, and then on the efficient use of the system. In this work, thermodynamic properties measurements under very low pressure (i.e., around 1 mbar) were performed using a modified enthalpy probe (increase of the internal diameter and thermal insulation of the head). Several parameters such as arc current intensity, hydrogen gas flow rate and working distance were considered in order to check their effect on the characteristics of the plasma jet and to determine the variation of the specific enthalpy, temperature, and heat flux versus these parameters.

Effects of enthalpy-enhancing gas on ionic conductivity of atmospheric plasma-sprayed 3.9 mol % yttria-stabilized zirconia electrolyte for 75–106 micron particles

Enthalpy-enhancing gas is used to optimize the ionic conductivity of atmospheric plasma-sprayed 3.9 mol % yttria-stabilized zirconia (3.9YSZ) electrolyte. In the experiment, three hydrogen gas flow rates are used to control the plasma energy. The 3.9YSZ feedstock powder is sieved to obtain particles with sizes in the range of 75–106 µm. The electrolyte has the highest hardness and lowest roughness when sprayed at hydrogen gas flow rates of 12 and 7 Lmin−1, respectively. The electrolyte bulk density increases and the apparent porosity decreases with increasing hydrogen gas flow rate. A 3.9YSZ electrolyte with an ionic conductivity of 1789 µ(Ω cm)−1 is obtained at 800°C with a hydrogen gas flow rate of 12 Lmin−1. It is controlled by the grain-boundary conductivity. The increase in grain-boundary conductivity is closely related to a low apparent porosity, low migration energy, and a decrease in grain size. Hydrogen gas enhances the growth of columnar grains and suppresses the formation of the monoclinic phase, which is attributed to increased intragrain conductivity.

Hydrogen-Tritium Isotope Separation by CECE Process with a Randomly Packed LPCE Column

Experimental and analytical studies on hydrogen-tritium isotope separation by a CECE process with a LPCE column have been carried out in order to apply it to the water detritiation system for fusion reactors. Kogel catalysts and Dixon gauze rings were mixed at a certain ratio and packed in the column in a random manner. Performance tests of tritium separation by the column of 1 m length and 2.5 cm I.D. were performed at 101 kPa and 343 K. The maximum value of the separation factor was 19200 when the flow rate of hydrogen gas was 5 L/min. The optimum value of catalyst packing ratio was obtained as 35 % by the analysis using the channeling stage model. The values of separation factors predicted by the model corresponded with measured ones very well.

On the Response of Different Particle State Sensors to Deliberate Process Variations

Deliberate particle state variations were performed using atmospheric plasma spray (APS) and high-velocity oxy-fuel flame spraying (HVOF) to create a set of first-order process maps. Particle states were measured simultaneously using five in-flight particle sensors: DPV-2000, Accuraspray, SprayWatch, TDS, and SprayCam. While the sensors use similar methods for calculating particle characteristics, absolute values of temperature and velocity were considerably different. Process map trends among sensors are in agreement for the HVOF process, but differ when using plasma spray at high total gas flow conditions. After understanding the stochastic nature of particle detection, an open loop feedback control algorithm was implemented to achieve similar particle states with different hydrogen gas flow rates. The resulting particle state window measured by three different sensors under select fixed hydrogen flow rates was significantly narrowed.

Deposition of BN interphase coatings from B-trichloroborazine and its effects on the mechanical properties of SiC/SiC composites

Boron nitride thin films were deposited on silicon carbide fibers by chemical vapor deposition at atmospheric pressure from the single source precursor B-trichloroborazine (Cl 3B 3N 3H 3, TCB). The film growth and structure, as a function of deposition temperature, hydrogen gas flow rate, and deposition time, were discussed. The deposition rate reaches a maximum at 1000 °C, then decreases with the increasing of temperature, and the apparent activation energy of the reaction is 127 kJ/mol. Above 1000 °C, gas-phase nucleation determines the deposition process. The deposited BN films were characterized by Raman spectroscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM). The effect of BN interphase on the mechanical properties of the unidirectional SiC fiber-reinforced SiC matrix (SiC/SiC) composites was also investigated. The results show that the flexural strength of SiC/SiC composites with and without coating is 276 MPa and 70 MPa, respectively, which indicates that BN interphase coating deposited from B-trichloroborazine precursor can effectively adjust the fiber/matrix interface, thus causing a dramatic increase in the mechanical properties of the composites.

The effect of plasma spray parameters on the cavitation erosion of Al2O3–TiO2 coatings

This paper reports a study of how the choice of plasma spray parameters, used during deposition of Al2O3–13%TiO2 coatings on carbon steel, influences the cavitation erosion properties of such coatings. The parameters studied are the power feeding rate and hydrogen flow rate. The surface and cross section of coatings before and after cavitation were also observed by scanning electron microscopy (SEM). The phases present in the coatings were characterized by X-ray diffraction method (XRD). The microscopic observations were used to study the inter-lamellar connection, porosity, unmelted particles and so on inside the coating. We also measured the roughness, microhardness, adhesion strength and cavitation erosion of the coatings. The XRD results showed that the coating includes different allotropes of Al2O3 such as α and γ. The cavitation erosion studies of the coatings were conducted by ultrasonic cavitation testing on the basis of ASTM G32 standard. It was found that cavitation erosion is accelerated around the unmelted particles and porosities. The results reveal that the cavitation resistance of the coating is determined by its microstructure and that increasing discontinuities (inside the coating) reduce its cavitation resistance. We have found that the coating obtained at hydrogen gas flow rate of 16L/min and powder feeding rate of 20g/min has the best cavitation resistance.

Behaviour of arsenic and selenium in an ICP-QMS with collision and reaction interface

The performance of a collision reaction interface (CRI) for minimization of spectral interferences on analytical signals of 75As+ and 76Se+, 77Se+, 78Se+, 80Se+ and 82Se+ isotopes was evaluated by using H2 and He gases introduced through the sampler or skimmer cones of an inductively coupled plasma quadrupole mass spectrometer (ICP-QMS). Different gas flow rates were tested employing reference solutions prepared either in hydrochloric acid or in water soluble tertiary amines (CFA-C) media as carbon source. A hydrogen gas flow rate at 60 mL min−1 introduced through skimmer cone was effective for minimizing polyatomic interferences on 75As+ and Se isotopes, except for 80Se+. The use of He introduced through sampler or skimmer cones had a minor effect on the minimization of interferences when compared to the use of H2 gas. Moreover, it was observed that the gas introduction through the sampler cone had no effect on interferences when using gas flow rates up to 80 mL min−1 for both gases evaluated. Based on these results, it can be recommended to use H2 gas introduced through skimmer cone of the CRI for correcting polyatomic interferences on 75As+ and Se isotopes in matrixes containing up to 2% v v−1 chloride.

Oxidation and crystallization mechanisms in plasma-sprayed Cu-based bulk metallic glass coatings

Cu-based bulk metallic glass (BMG) coatings were built-up by the atmospheric plasma spraying (APS) process at different hydrogen flow rates. As the hydrogen flow rate increased, thermal energy in the plasma jet increased the melting state of the Cu-based BMG particles. Although it was expected that the difference in melting states would quantitatively affect the amorphous fractions in the coatings, both the amorphous fraction and the oxide content of the layers were independent of hydrogen flow rate. However, different melting states resulting from different hydrogen gas flow rates, and the subsequent oxidation which inevitably occurred during spraying, generated different crystallization processes in the coating. In this paper, crystallization mechanisms in plasma-sprayed BMG were studied using their microstructures. Specific analyses of the particles deposited at high travel speed and quenched in cold water also served for further understanding of the melting state and change in composition of the particles undergo during deposition.