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1.
Carburization performance of Incoloy 800HT has been studied after cyclic and isothermal exposures to CH 4/H 2 carburizing gas mixtures at high temperatures for 500 h. At 800 °C in 2% CH 4/H 2, Incoloy 800HT suffered external oxidation and carburization, the external continuous layer of reaction products consists primarily of Cr 7C 3, Mn 1.5Cr 1.5O 4, and FeCr 2O 4 with Fe(Cr, Al) 2O 4 as a minor phase. At 1100 °C in 10% CH 4/H 2, external carburization did not occur likely due to high carbon dissolution in the alloy substrate at this temperature. A thermodynamic analysis indicated that 1000 °C was an approximate critical temperature, below which the environment should result in mixed oxidizing/carburizing behavior, while above this temperature reducing carburizing behavior should occur. The experimental results approximately agree with the thermodynamic analysis. Metal dusting was not observed under highly carburizing conditions ( aC>1). The size and morphology of Cr-rich phases (or Cr-carbides) are both temperature- and time-dependent, while the external continuity is more temperature-dependent rather than time-dependent. 相似文献
2.
Flow pattern observations and measurements of the heat transfer in a helical grooved micro fin tube are presented and compared with results for a smooth tube. The micro fin tube used (OD of 9.52 mm) was a Wieland Cuprofin EDX tube with 60 fins (height 0.25 mm) and a helix angle of 18°. The flow pattern observations at 39.7 bar ( Ts=+5 °C, pr=0.54) and 26.4 bar ( Ts=−10 °C, pr=0.36) show a wide range of the annular flow region. The transition from slug to annular flow does not occur, as expected, at constant vapour quality for all mass fluxes but there is an interdependence between transition vapour quality and mass flux. For the heat transfer in the micro fin tube, measurements at 39.7 bar are presented for heat fluxes up to 120 kW m −2, mass fluxes between 75 and 250 kg m −2 s −1 and vapour qualities between 0.1 and 0.9. 相似文献
3.
This article describes the results of an investigation concerning the failure of the back wall riser tube of a high pressure
boiler in a SWCC dual purpose power/water cogeneration plant. The failure occurred in one tube (facing furnace) which contained
eight ruptured openings covering a length of approximately 1.8 m. The tube material was carbon steel (SA 210A1). The cause
of the failure was determined by on-site visual inspection of the boiler and detailed macro and micro examinations of inner
and outer scales on the tube. The in situ non-destructive testing of selected boiler riser tubes was carried out using boroscope
and ultrasonic test (UT). The composition of the tube material and fire and water-side scale deposits were analyzed by energy
dispersive x-ray (EDX) and inductively coupled plasma (ICP) techniques. The cause of the failure of the riser boiler tube
appears to be caustic attack. The inside brown scale that developed during service resulted in overheating, wall thinning
due to caustic corrosion, and the associated ruptures of the tube in areas of high stress. The escaping steam eroded the outer
surface of the tube resulting in heavy loss of metal around the rupture points (punch). Recommendations are given to prevent/minimize
such failures. 相似文献
4.
Material properties of A106B low-carbon steels were developed for life prediction analyses of steam pipes operated at elevated temperatures but in the sub-creep temperature range. Tensile, fracture toughness, fatigue crack growth rate and low-cycle fatigue properties were obtained on the piping steel at 24°C (75°F) and 288°C (550°F). The latter temperature corresponded to the highest operating temperature of nuclear plant steam piping. Increasing the test temperature from 24°C (75°F) to 288°C (550°F) decreased the yield strength and fracture toughness of the steel. Fatigue crack propagation rate properties at 24°C (75°F) and 288°C (550°F) were found to be comparable. In the low-cycle fatigue tests, below a strain amplitude level of approximately 0.5%, cyclic softening was observed, while at higher strain levels, cyclic hardening was present. Based on the results of tensile and incremental-step fatigue testing, the strain-life curve was predicted. The predicted strain-life curve was found to be in agreement with the experimental result. The fracture surfaces of fracture toughness specimens showed ductile fracture, while striations were observed on those of fatigue crack growth specimens. Fatigue striations were also observed on the fracture surfaces of low-cycle fatigue specimens. Fatigue initiation was associated with inclusions. It was shown that plastic straining in A106B steel could be detected by acoustic emission and by monitoring the eddy current response. These nondestructive evaluation techniques exhibit possibilities for in-situ monitoring of fatigue deformation. While the development of material properties for the life prediction assessment of steam pipes is included in Part I of this paper, the establishment of a quantitative life prediction methodology and inspection criteria is contained in Part II. The developed life prediction methodology quantifies the effects of operating parameters on the remaining life of steam pipes using the material properties obtained in Part I. 相似文献
5.
An effective method is developed for low temperature metal oxide deposition through thermal decomposition of metal diketonates in supercritical carbon dioxide (scCO 2) solvent. The rates of Al(acac) 3 (Aluminum acetyl acetonate) and Ga(acac) 3 (Gallium acetyl acetonate) thermal decomposition in scCO 2 to form conformal Al 2O 3 and Ga 2O 3 thin films on planar surfaces were investigated. The thermal decomposition reaction of Al(acac) 3 and Ga(acac) 3 was found to be initialized at 150 °C and 160 °C respectively in scCO 2 solvent, compared to 250 °C and 360 °C in analogous vacuum-based processes. By measuring the temperature dependence of the growth rates of metal oxide thin films, the apparent activation energy for the thermal decomposition of Al(acac) 3 in scCO 2 is found to be 68 ± 6 kJ/mol, in comparison with 80–100 kJ/mol observed for the corresponding vacuum-based thermal decomposition reaction. The enhanced thermal decomposition rate in scCO 2 is ascribed to the high density solvent which effectively reduces the energy of the polar transition states in the reaction pathway. Preliminary results of thin film deposition of other metal oxides including ZrO x, FeO x, Co 2O 3, Cr 2O 3, HfO x from thermal decomposition of metal diketonates or fluorinated diketonates in scCO 2 are also presented. 相似文献
6.
A capillary tube based CO 2 heat pump is unique because of the transcritical nature of the system. The transcritical cycle has two independent parameters, pressure and temperature, unlike the subcritical cycle. In the present study, a steady state simulation model has been developed to evaluate the performance of a capillary tube based transcritical CO 2 heat pump system for simultaneous heating and cooling at 73 °C and 4 °C, respectively against optimized expansion valve systems. Capillary tubes of various configurations having diameters of 1.4, 1.5 and 1.6 mm along with internal surface roughness of 0.001–0.003 mm have been tested to obtain the optimum design and operating conditions. Subcritical and supercritical thermodynamic and transport properties of CO 2 are calculated employing a precision in-house property code. It is observed that the capillary tube system is quite flexible in response to changes in ambient temperature, almost behaving to offer an optimal pressure control. System performance is marginally better with a capillary tube at higher gas cooler exit temperature. Capillary tube length turns out to be the critical parameter that influences system optimum conditions. A novel nomogram has been developed that can be employed as a guideline to select the optimum capillary tube. 相似文献
7.
Structure/property studies were made on an experimental Al-3.18% Li-4.29% Cu-1.17% Mg-0.18% Zr powder alloy, which is of the low density/high modulus type. Alloy powder was made by the P&W/GPD rapid solidification rate (RSR) process, canned, and extruded to bar. The density was 2.458 × 10 6 g/m 3. The material was solution-treated, and aged at 149°C (300°F), 171°C (340°F), and 193°C (380°F), using hardness tests to determine the aging curves. Testpieces solution-treated at 516°C (961°F) showed an average yield strength (0.2% offset) of 43.3 ksi (299 MPa) and ultimate tensile strength of 50.0 ksi (345 MPa), with 1% elongation, which increased to 73.0 ksi (503 MPa) and 73.1 ksi (504 MPa), respectively, with only 0.2% elongation, on peak aging at 193°C (380°F), with a modulus of elasticity of 11.4 × 10 6 psi (78.3 GPa). Hardness values reached 90–92 R B on aging at 149–193°C (300–380°F). The as-extruded alloy showed superplastic behavior at 400–500°C (752–932°F) with elongations of 80–185% on 25.6 mm, peaking at 450°C (842°F). An RSR Al-2.53% Li-2.82% Mn-0.02% Zr extruded alloy showed only 18–23% elongation at 400–500°C (752–932°F). 相似文献
8.
BaTiO 3 thin films were prepared by using metal organic acid salts on MgO(100) substrates, which have large lattice-misfit with BaTiO 3. Amorphous films prefired at 470°C were crystallized to BaTiO 3 phase by heat treatment at higher temperature. Crystallinity and in-plane alignment of the prepared films were found to depend on the heat-treatment conditions. BaTiO 3 films with high crystallinity but poor (100)-orientation were obtained in air at higher than 1200°C. Whereas, (100)-oriented epitaxial BaTiO 3 film was fabricated by annealing at 900°C under low oxygen partial pressure ( p(O 2)). Low carbon dioxide partial pressure ( p(CO 2)) is also found to be essential for preparation of epitaxial BaTiO 3 films on MgO substrates by using metal organic acid salts. 相似文献
9.
The growth rate and chemical composition of thermally grown oxides on 111 InAs are presented. The oxide was found to grow very slowly at 350°C but the growth was rapid at 450 °C. The oxides grown at 350 °C contained approximately equal concentrations of As 2O 3 and In 2O 3 and no detectable elemental arsenic. The As 2O 3 concentration decreased and the elemental arsenic concentration increased with increasing growth temperature. The oxides were amorphous unless the growth temperature was 475 °C or above. 相似文献
10.
The purpose of this work is to investigate the influence of the preexistent oxide film on friction process between the forming tool and the tube, during the piercing in hot metal forming. A wear behavior of a low alloy steel (28NCDV10) is studied on a cylinder-ring tribometer. Two different atmospheres, which are air and steam, are employed for oxidizing the rings at 85O°C. The experimental results of rings without pre-oxidation exhibit a severe oxidation wear and metal transfer from the cylinder to the ring. While the oxidation of the rings, notably in the case of steam, shows a decrease in the wear rate. For a comparison with metallic materials, we considered some ceramic materials: A1 2O 3, Al 2O 3-TiO 2 We find that the metallic materials pre-oxidized in steam have a better behavior than all the other materials tested. 相似文献
11.
Carbon-enriched coal fly ash was evaluated in this work as a low-cost adsorbent for SO 2 removal from stack gases. The unburned carbon in coal fly ash was concentrated by mechanical sieving and vegetal oil agglomeration. The carbon concentrates were activated with steam at 900 °C in order to develop porosity onto the samples. The performance of these samples in the SO 2 abatement was tested in the following conditions: 100 °C, 1000 ppmv SO 2, 5% O 2, 6% water vapor. A good SO 2 removal capacity was shown by some of the studied samples that can be related to their textural properties. Cycles of SO 2 adsorption/regeneration were carried out in order to evaluate the possibility of thermal regeneration and re-use of these carbons. Regeneration of the exhausted carbons was carried out at 400 °C of temperature and a flow of 25 ml/min of Ar. After each cycle, the SO 2 removal capacity of the sample decreases. 相似文献
12.
Catalytic chemical vapor deposition (Cat-CVD) has been developed to deposit alumina (Al 2O 3) thin films on silicon (Si) crystals using N 2 bubbled tri-methyl aluminum [Al(CH 3) 3, TMA] and molecular oxygen (O 2) as source species and tungsten wires as a catalyzer. The catalyzer dissociated TMA at approximately 600 °C. The maximum deposition rate was 18 nm min −1 at a catalyzer temperature of 1000 °C and substrate temperature of 800 °C. Metal oxide semiconductor (MOS) diodes were fabricated using gates composed of 32.5-nm-thick alumina film deposited at a substrate temperature of 400 °C. The capacitance measurements resulted in a relative dielectric constant of 7.4, fixed charge density of 1.74×10 12 cm −2, small hysteresis voltage of 0.12 V, and very few interface trapping charges. The leakage current was 5.01×10 −7 A cm −2 at a gate bias of 1 V. 相似文献
13.
Ceramic foams were prepared by a self-blowing process of a poly(silsesquioxane) melt at 270 °C. The cell size, the interconnectivity density and the shape of the foam cells were adjusted by a thermal pre-curing procedure of the polymer at 200 °C. Inorganic fillers were used to modify processing behaviour and properties of the pyrolysed ceramic foam. After pyrolysis in inert atmosphere at 1200 °C ceramic composite foams with a total porosity up to 87% were obtained. The open cell ceramic foams had a mean cell diameter of 1.2 mm and a mean strut thickness of 0.2 mm. Interpenetrating phase composites (IPCs) were fabricated by infiltrating the open cellular ceramic preform with Mg alloy melt at 680 °C and a pressure of 86 MPa. The mechanical properties were found to depend on the reactions between the metal and the ceramic forming MgO, Mg 2Si and Al 12Mg 17 as the major reaction products. The IPCs showed a significantly higher creep resistance at 135 °C, compression strength and elastic modulus compared to the unreinforced magnesium alloys. 相似文献
14.
The objective of the present study was to generate submicrometer calcium hydroxide aerosols and to investigate the effectiveness of such aerosols in sulfur capture. The effectiveness of SO 2 removal by Ca(OH) 2 aerosol has been investigated in an isothermal reactor. Ca(OH) 2 aerosol was generated by a novel fluidizer system in which submicrometer-sized powders were entrained in gases. SO 2 was added to this aerosol to a concentration of 2000 ppm. The aerosol-SO 2 mixture was heated to 550°C-750°C in an isothermal tube reactor. The SO 2 removal efficiency, which varied from 20% to 70%, was determined to be a function of the aerosol concentration, reactor temperature and residence time. The fraction of aerosol reacted was not affected strongly by the aerosol concentration. The reaction kinetics were determined from the experimental data using a simple analytical model in which the rate is first order in both SO 2 and calcium hydroxide aerosol concentrations. 相似文献
15.
Sol–gel derived Bi 2Ti 2O 7 ceramic powders have been prepared from methoxyethoxides of bismuth and titanium (molar ratio of Ti/Bi = 1.23 and water/alkoxides = 1.31). The Bi 2Ti 2O 7 phase was stable at a low temperature (700 °C), but it then transformed into mixed phases of Bi 4Ti 3O 12 and Bi 2Ti 4O 11 at 850–1150 °C. The single phase of Bi 2Ti 2O 7 reoccurred at 1200 °C. Dielectric properties and ferroelectric behavior of samples sintered at 1150 and 1200 °C were examined. Under frequency of 1 MHz, samples sintered at 1150 and 1200 °C had a dielectric constant of 101.3 and 104.2, and a loss tangent of 0.0193 and 0.0145, respectively. Only the sample sintered at 1150 °C showed ferroelectric behavior, where remanent polarization is 3.77 μC cm −2 and coercive field is 24 kV cm −1. Thus, the Bi 2Ti 2O 7 did not exhibit ferroelectricity, but the mixed phase of Bi 4Ti 3O 12 and Bi 2Ti 4O 11 did. 相似文献
16.
Hydrogen-radical durability of TiO 2 thin films has been investigated under conditions for preparing Si thin film solar cells by catalytic chemical vapor deposition method. It is found that the composition and the optical transmittance of TiO 2 films are almost the same before and after hydrogen-radical exposures with a filament temperature at approximately 1700 °C and a H 2 pressure of approximately 133 Pa. The durability of TiO 2 film has also been observed even under the condition with higher hydrogen-radical density under a filament temperature at approximately 1900 °C, in which SnO 2 and ZnO are easily deoxidized. The application of TiO 2 film as a protecting material of transparent conducting oxide film for Si thin film solar cells are discussed by the hydrogen-radical durability and fundamental properties of TiO 2 thin film. 相似文献
17.
Co 3O 4 nanoparticles and cobalt (fcc-Co) powders were successfully synthesized by solvothermal process from a single precursor. The reaction of Co(Ac) 2 with sodium dodecylbenzenesulfonate (SDBS) shows evident-dependent temperature effect. At 180 °C, Co(Ac) 2 reacts with SDBS to produce precursor CoCO 3 plate structures, which are assembled by small nanoparticles. At the temperature of 250 °C, the precursor CoCO 3 can be gradually decomposed to form Co 3O 4 nanoparticles with diameter of ca. 70 nm. While, at 250 °C, the reaction of Co(Ac) 2 with SDBS also produce precursor CoCO 3 nanoparticles/plates, but the CoCO 3 nanoparticles/plates would only decompose to give metal Co. In this process, SDBS acts as not only a surfactant but also a reagent. Magnetic measurements reveal that the as-prepared Co 3O 4 nanoparticles exhibit weak ferromagnetic properties and Co powders show ferromagnetic properties. In addition, a possible formation mechanism was elaborately discussed. 相似文献
18.
MoSi 2-based intermetallics containing different volume fractions of MoB or Mo 5Si 3 were fabricated by hot-pressing MoSi 2, MoB, and Mo 5Si 3 powders in vacuum. Both classes of alloys contained approximately 5 vol.% of dispersed silica phase. Additions of MoB or Mo 5Si 3 caused the average grain size to decrease. The decrease in the grain size was typically accompanied by an increase in flexure strength, a decrease in the room temperature fracture toughness, and a decrease in the hot strength (compressive creep strength) measured around 1200 °C, except when the Mo 5Si 3 effectively became the major phase. Oxidation measurements on the two classes of alloys were carried out in air. Both classes of alloys were protected from oxidation by an in-situ adherent scale that formed on exposure to high temperature. The scale, although not analyzed in detail, is commonly recognized in MoSi 2 containing materials as consisting mostly of SiO 2. The MoB containing materials showed an increase in the scale thickness and the cyclic oxidation rate at 1400 °C when compared with pure MoSi 2. However, in contrast with the pure MoSi 2 material, oxidation at 1400 °C began with a weight loss followed by a weight gain and the formation of the protective silica layer. The Mo 5Si 3 containing materials experienced substantial initial weight losses followed by regions of small weight changes. Overall, the MoB and Mo 5Si 3 additions to MoSi 2 tended to be detrimental for the mechanical and oxidative properties. 相似文献
19.
The growth of CaF 2 films with a thickness of approximately 3–4 nm on well-oriented Si(1 1 1) substrates by molecular beam epitaxy at temperatures between 410 and 560 °C were investigated by ex vacuo atomic force microscopy. Layer-by-layer growth producing atomically flat CaF 2 surfaces has been observed in a very narrow growth temperature window between approximately 430 and 470 °C. Perfect triangular shaped islands of one CaF 2 layer height are found on the surface with all corners aligned with the Si
directions, indicating a pure B-stacking of the CaF 2 film. Surprisingly, also the substrate steps have been overgrown without visible defects. Below 410 °C, two different island orientations revealed a mixture of A- and B-stacking areas in the films. Above 520 °C non-wetting of the CaF interface layer leads to epitaxial films with a rough surface morphology. 相似文献
20.
The formation of CoSi 2 on strained epitaxial Si 0.8Ge 0.2/Si(100) films has been studied as a function of the deposition method and annealing temperature. Two types of deposition processes were used: a direct method, where 5 nm of pure Co metal were deposited at room temperature onto a strained 80 nm thick Si 0.8Ge 0.2 layer; and a co-deposition method, where 5 nm Co and 18.2 nm Si were simultaneously deposited in a 1:2 ratio onto a strained Si 0.8Ge 0.2 layer at 450°C. Samples were then annealed at temperatures ranging from 500 to 800°C. Extended X-ray absorbance fine structure spectroscopy (EXAFS) and X-ray diffraction (XRD) were used to characterize the structure of the resulting films. It was found that the samples prepared via the direct deposition method did not convert to CoSi 2 at any annealing temperature up to 800°C, while the co-deposited samples formed epitaxial CoSi 2 at even the lowest annealing temperature of 500°C. These results are discussed in terms of proposed reaction mechanisms of the different deposition methods, based on consideration of the Co–Si–Ge ternary phase diagram. 相似文献
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