scholarly journals Extreme high temperature redox kinetics in ceria: exploration of the transition from gas-phase to material-kinetic limitations

2016 ◽  
Vol 18 (31) ◽  
pp. 21554-21561 ◽  
Author(s):  
Ho-Il Ji ◽  
Timothy C. Davenport ◽  
Chirranjeevi Balaji Gopal ◽  
Sossina M. Haile
Keyword(s):  
High Temperature ◽  
Thermodynamic Properties ◽  
Gas Phase ◽  
Gas Flow ◽  
Solid Phase ◽  
Oxygen Release ◽  
Flow Rates ◽  
Redox Kinetics ◽  
Extreme High Temperature ◽  
Relaxation Experiments

Overcoming influences of oxygen release or uptake from the solid phase in relaxation experiments requires large gas flow rates, as dictated by the thermodynamic properties of the solid.

Comparative Study of GaN Growth Process by MOVPE

1999 ◽  
Vol 572 ◽  
Author(s):  
Jingxi Sun ◽  
J. M. Redwing ◽  
T. F. Kuech
Keyword(s):  
High Temperature ◽  
Comparative Study ◽  
Gas Phase ◽  
Residence Time ◽  
Gas Flow ◽  
Flow Sheet ◽  
Flow Zone ◽  
High Quality ◽  
Phase Temperature ◽  
High Temperature Gas

ABSTRACTA comparative study of two different MOVPE reactors used for GaN growth is presented. Computational fluid dynamics (CFD) was used to determine common gas phase and fluid flow behaviors within these reactors. This paper focuses on the common thermal fluid features of these two MOVPE reactors with different geometries and operating pressures that can grow device-quality GaN-based materials. Our study clearly shows that several growth conditions must be achieved in order to grow high quality GaN materials. The high-temperature gas flow zone must be limited to a very thin flow sheet above the susceptor, while the bulk gas phase temperature must be very low to prevent extensive pre-deposition reactions. These conditions lead to higher growth rates and improved material quality. A certain range of gas flow velocity inside the high-temperature gas flow zone is also required in order to minimize the residence time and improve the growth uniformity. These conditions can be achieved by the use of either a novel reactor structure such as a two-flow approach or by specific flow conditions. The quantitative ranges of flow velocities, gas phase temperature, and residence time required in these reactors to achieve high quality material and uniform growth are given.

Experimental Study on Oxidation of Graphite for HTR

2013 ◽  
Author(s):  
Yang Liu ◽  
Ximing Sun ◽  
Yujie Dong
Keyword(s):  
Electron Microscopy ◽  
High Temperature ◽  
Gas Flow ◽  
Normal Operation ◽  
Flow Rates ◽  
Water Ingress ◽  
Oxidized Graphite ◽  
Helium Coolant ◽  
Scanning Electron ◽  
High Temperature Gas

In the high temperature gas-cooled reactor, the oxidation of graphite is inevitable as a result of impurities in helium coolant. As an air or water ingress accident would cause graphite components to oxidize more seriously, thereby it would affect the reactor normal operation and safety. Oxidation velocity and oxidation product of a selected graphite (excess material from 10MW High Temperature Gas-cooled Reactor) were studied, samples are oxidized between 400°C to 1200 °C with gas flow rates ranging from 125 to 500 ml/min. Relationship between oxidation conditions and surface properties of oxidized graphite is also elaborated by means of gas chromatography and scanning electron microscopy for scanning of graphite surface.

Testing of Ceramics for Production of Heating Elements for Usage in High Temperature Helium Loop

2014 ◽  
Author(s):  
Jan Berka ◽  
Antonín Rotek ◽  
Jan Vit ◽  
Jaroslav Kutzendorfer
Keyword(s):  
High Temperature ◽  
Ceramic Material ◽  
Test Section ◽  
Gas Flow ◽  
Electric Resistance ◽  
Flow Rates ◽  
Cordierite Ceramics

Heating elements are one of the important components of High Temperature Helium Loop. By means of heating elements the heating of test section of the loop to required temperature is provided even in high gas flow rates in the loop. The insulation of heating elements was manufactured of cordierite ceramics. With these elements the maximum projected temperature 900 °C could not be reached because of decreasing of electric resistance among the spirals. Therefore several tests were done in order to discover the reason of the problem. Consequently properties of new ceramic material based on corundum for manufacturing of the new heating elements were verified.

Numerical Investigation of Pulsed Chemical Vapor Deposition of Aluminum Nitride to Reduce Particle Formation

2011 ◽  
Author(s):  
Derek Endres ◽  
Sandip Mazumder
Keyword(s):  
Gas Phase ◽  
Direct Contact ◽  
Gas Flow ◽  
Film Growth ◽  
Chemical Vapor ◽  
Particle Formation ◽  
Group V ◽  
Flow Rates ◽  
Group Iii ◽  
Reactor Pressure

Particles of aluminum nitride (AlN) have been observed to form during epitaxial growth of AlN films by metal organic chemical vapor deposition (MOCVD). Particle formation is undesirable because particles do not contribute to the film growth, and are detrimental to the hydraulic system of the reactor. It is believed that particle formation is triggered by adducts that are formed when the group-III precursor, namely tri-methyl-aluminum (TMAl), and the group-V precursor, namely ammonia (NH3), come in direct contact in the gas-phase. Thus, one way to eliminate particle formation is to prevent the group-III and the group-V precursors from coming in direct contact at all in the gas-phase. In this article, pulsing of TMAl and NH3 is numerically investigated as a means to reduce AlN particle formation. The investigations are conducted using computational fluid dynamics (CFD) analysis with the inclusion of detailed chemical reaction mechanisms both in the gas-phase and at the surface. The CFD code is first validated for steady-state (non-pulsed) MOCVD of AlN against published data. Subsequently, it is exercised for pulsed MOCVD with various pulse widths, precursor gas flow rates, wafer temperature, and reactor pressure. It is found that in order to significantly reduce particle formation, the group-III and group-V precursors need to be separated by a carrier gas pulse, and the carrier gas pulse should be at least 5–6 times as long as the precursor gas pulses. The studies also reveal that with the same time-averaged precursor gas flow rates as steady injection (non-pulsed) conditions, pulsed MOCVD can result in higher film growth rates because the precursors are incorporated into the film, rather than being wasted as particles. The improvement in growth rate was noted for both horizontal and vertical reactors, and was found to be most pronounced for intermediate wafer temperature and intermediate reactor pressure.

scholarly journals A preliminary examination of fluid inclusions in nepheline, sorensenite, tugtupite and chkalovite from the Ilímaussaq alkaline intrusion, South Greenland

1970 ◽  
Vol 81 ◽  
pp. 1-41
Author(s):  
V.S Sobolev ◽  
T.Y Bazarova ◽  
N.A Shugurova ◽  
N.Sh Bazarov ◽  
Y.A Dolgov ◽  
...  
Keyword(s):  
High Temperature ◽  
Liquid Phase ◽  
Gas Phase ◽  
Fluid Inclusions ◽  
Solid Phase ◽  
Inert Gases ◽  
Preliminary Examination ◽  
Alkaline Intrusion ◽  
Primary Inclusion ◽  
Academy Of Sciences

A preliminary examination has been undertaken of fluid inclusions in four minerals from the Ilímaussaq alkaline intrusion. The apparatus used in the study has been developed in the Institute of Geology and Geophysics of the Siberian Branch of the Academy of Sciences, Novosibirsk. Primary three-phase inclusions (liquid-gas-crystals) in nepheline from naujaite homogenize in the liquid phase at 850-1040° C. The gas phase in one analysed inclusion is dominated by CO2. Primary gas-liquid inclusions in nepheline from green lujavrite homogenize at 910-970° C in the liquid phase. These temperatures are in agreement with temperatures obtained on nephelines from Lovozero, Miask and Synnur and with data from fusion experiments on the rocks in question. Primary gas-liquid inclusions in sorensenite and tugtupite from late analcimealbite veins homogenize at 400-460° C. The liquid phase of fluid inclusions in tugtupite contains 21 weight per cent of salts -sodium chloride is assumed to be predominant. The gas phase in one primary inclusion in tugtupite is dominated by CO2. Secondary fluid inclusions in the two minerals homogenize at 350-100° C. The temperatures obtained are in agreement with those estimated from mineralogical evidence. A big crystal of chkalovite from an ussingite-analcime vein contains several generations of fluid inclusions. The primary liquid-gas-crystal inclusions homogenize at 860-980° C. The solid phase is dissolved at 330-360° C, two immiscible liquids appear at 700-800° C. Half of the ca. 250 fluid inclusions examined belong to this category. The several generations of secondary inclusions which embrace liquid-gascrystal inclusions, gas-liquid inclusions and gas inclusions homogenize in several groups between 760°C and 100°C. The liquid phase of the high temperature inclusions contains 40-44 weight per cent NaCI. The pressure at the temperature of homogenization is estimated to be higher than 1000 atm. The gas phase is dominated by CO2 and N2 + inert gases. The unexpectedly high temperature of homogenization of the primary inclusions of the chkalovite is difficult to explain. A detailed study of this problem is in preparation.

scholarly journals Modeling of InGaN MOVPE in AIX 200 Reactor and AIX 2000 HT Planetary Reactor

1999 ◽  
Vol 4 (1) ◽  
Author(s):  
R. A. Talalaev ◽  
E. V. Yakovlev ◽  
S. Yu. Karpov ◽  
Yu. N. Makarov ◽  
O. Schoen ◽  
...  
Keyword(s):  
Gas Phase ◽  
Large Scale ◽  
Gas Flow ◽  
Solid Phase ◽  
Process Analysis ◽  
Scale Production ◽  
Modeling Analysis ◽  
Large Scale Production ◽  
Flow Heat ◽  
Insight Into

Multiwafer Planetary Reactor is a promising system for large-scale production of heterostructures for LED's based on III-group nitrides. Analysis of chemical processes occurring in the reactor allows one to get insight into specific mechanisms governing growth of nitride based heterostructures. In the present paper results of modeling analysis of MOVPE of InxGa1−xN layers in AIX-200 Reactor and AIX 2000 HT Planetary Reactor are reported. The model used for MOVPE process analysis accounts for gas flow, heat transfer, and multicomponent mass transport along with gas phase and surface chemical reactions. Results of the modeling analysis of In transport and incorporation into the solid phase are compared with experimental data. It is shown that the model predicts reasonably well the In incorporation during MOVPE of InGaN under In/(In+Ga) ratio in the gas phase less than 20%.

Synthesis of Al-B system nanostructures by interaction of disperse aluminium with boron and diborane in arc discharge plasma

2020 ◽  
pp. 11-18
Author(s):  
A.G. Astashov ◽  
◽  
A.V. Samokhin ◽  
N.V. Alekseev ◽  
V.A. Sinayskiy ◽  
...  
Keyword(s):  
High Temperature ◽  
Gas Phase ◽  
Thermal Plasma ◽  
Gas Flow ◽  
Arc Discharge ◽  
Experimental Studies ◽  
Plasma Chemical ◽  
Aluminum Boride ◽  
Disperse Aluminum ◽  
Boride Phases

Experimental studies of aluminium boride synthesis as a result of interaction of disperse aluminum with diborane B2H6 and disperse boron in a flow of thermal plasma of different composition generated in electric arc plasma torch have been carried out. Experimental work on the synthesis of aluminium boride nanoparticles from elements (a mixture of disperse aluminum and boron) has shown the possibility of obtaining in thermal plasma arc discharge of such phases of the boride as AlB12 and AlB31. The specific surface of the powders obtained is from 3 to 27 m2/g. According to X-ray phase analysis, the powders obtained, except for aluminum boride phases, also contain boron, aluminum, aluminum nitride and boric acid phases. The greatest yield of aluminum boride phases is provided by using the nitrogen plasma with hydrogen and enthalpy 4.5 kWt∙h/m3 in the reactor with increased high-temperature zone. The use of gaseous diborane made it possible to eliminate restrictions on the evaporation of boron particles but did not provide an opportunity to obtain aluminum borides in the plasma-chemical process. It was concluded that it is necessary to perform quenching of high-temperature gas flow containing boron and aluminum vapor to form aluminum borides from the gas phase in plasma-chemical synthesis. Such an approach should ensure that the temperature is reduced to the values at which aluminum borides are stable and that the formation of aluminum boride nanoparticles will occur as a result of condensation from the gas phase under these conditions.

Activity of Lead in Copper Matte at Very Low Lead Concentration

2013 ◽  
Vol 32 (3) ◽  
pp. 197-206 ◽  
Author(s):  
Ty Tran ◽  
Steven Wright ◽  
Shouyi Sun
Keyword(s):  
Activity Coefficient ◽  
Gas Phase ◽  
Gas Flow ◽  
Matte Grade ◽  
Copper Matte ◽  
Lead Removal ◽  
Calculated Concentration ◽  
Flow Rates ◽  
Concentration Changes ◽  
Lead Species

AbstractThe thermodynamic behavior of lead in Cu-Fe matte was investigated using a transportation technique where argon gas was bubbled into a bath of copper matte containing approximately 100 ppm lead at temperatures between 1300 and 1400 °C. The effect of flow rate, temperature and matte grade were investigated on the lead transport from a bath containing 100 grams of synthetic copper matte to the gas phase. The concentration of lead in the bath was followed with time. At argon flow rates between 3 l h1 and 18 l h−1, it was observed that the concentration change of lead in the matte was found to follow a first order relationship where the calculated concentration at time t, is of the form [Pb] = a.e−b.t, where a is equal to the initial lead content in ppm, [Pb]i, and b is an exponential term and t is time in minutes. The partial pressure of lead species in the gas phase was calculated from the concentration changes in the matte and from the bubbling gas rate. At gas flow rates between 3 and 9 l h−1, the lead removal appeared to be under equilibrium conditions. At higher gas flow rates, the apparent rate decreased, mainly due to splashing of matte into the cold zone of the furnace. In these experiments with Ar as the carrier gas, the sulphur and oxygen partial pressures of the melt were not controlled. Chemical analysis of the major components in the matte showed only random variation with bubbling time, and so a thermodynamic solution model for copper matte was used to calculate the equilibrium sulphur pressure expected. From this approach the proportion of Pb, PbS and Pb2 species in the gas could be calculated knowing the relevant reaction constants, e.g., PbS(g) = Pb(g) + ½S2(g). From the proportions of the lead species in the gas, the value of the lead activity coefficient with respect to the gas state could be determined. For a 50% copper matte, it was found that the activity coefficient increased with temperature, from a value of 0.8 at 1300 °C to 1.4 at 1400 °C. At the white metal composition, this value was 0.28 at 1300 °C. These results are compared with other relevant studies in the literature.

DISPERSED PHASE VELOCITY IN A HIGH-TEMPERATURE GAS FLOW

2019 ◽  
Vol 23 (4) ◽  
pp. 319-328
Author(s):  
Dmitry V. Nesterovich ◽  
Oleg G. Penyazkov ◽  
Yu. A. Stankevich ◽  
M. S. Tretyak ◽  
Vladimir V. Chuprasov ◽  
...  
Keyword(s):  
High Temperature ◽  
Phase Velocity ◽  
Gas Flow ◽  
Dispersed Phase ◽  
High Temperature Gas

Passive Auto-Focus Algorithm for Correcting Image Distortions Caused by Gas Flow in High-Temperature Measurements of Surface Phenomena

2012 ◽  
Vol 17 (4) ◽  
pp. 379-384 ◽  
Author(s):  
Krzysztof Strzecha ◽  
Tomasz Koszmider ◽  
Damian Zarębski ◽  
Wojciech Łobodziński
Keyword(s):  
High Temperature ◽  
Gas Flow ◽  
Temperature Measurements ◽  
Surface Phenomena ◽  
Auto Focus ◽  
High Temperature Measurements

Abstract In this paper, a case-study of the auto-focus algorithm for correcting image distortions caused by gas flow in high-temperature measurements of surface phenomena is presented. This article shows results of proposed algorithm and methods for increasing its accuracy.

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