Equilibrium in the reaction of carbon dioxide with liquid copper from 1090° to 1300°C

A study has been made of the equilibrium in the reaction of carbon dioxide with liquid copper. The equation for the reaction may be written as follows: \(2\;\text{Cu}\;(\text{liq})\;+\;\text{CO}_2\;(\text{g})\;=\;\underline{\text{Cu}_2\;\text{O}}\;+\;\text{CO}\;(\text{g})\)The equilibrium constant for this reaction was determined from 1090° to 1300° C.     

Thermophysical properties of TiB2SiC ceramics from 300 °C to 1700 °C

In the present work, high-frequency induction heating is used to fabricate TiB₂SiC ceramics and the relative density was more than 97%, and then the thermophysical properties of TiB₂SiC ceramics were investigated in detail. The specific heat showed the weak dependence on the test temperature due to the presence of the interface gap because the relative density was not 100%. As the sintering temperature increased, the thermal diffusivity of TiB₂SiC ceramics increased, which was due to the increase of relative density and grain growth. The thermal conductivity of TiB₂SiC ceramics showed a marked increase with increasing grain size and relative density. This could be attributed to a reduction in the number of grain boundaries that interrupt the heat flow path, resulting in an increase in the mean free path of the phonons. Larger grains led to an increase of mean free path of the phonons and thus contributed to a further increase in thermal conductivity.     

High-Temperature Oxidation of Ni–20 wt.% Cu from 700 to 1100°C

Ni–20 wt.% Cu was oxidized in different oxygen pressures from 1×10^–5 to 1 atm at 700–1100°C. The oxidation consisted of an initial transient period in which a composite scale of NiO and Cu oxides formed, and a subsequent quasi steady-state regime during which parabolic growth of NiO determined the overall oxidation rate. Based on the oxide composition and the oxygen- pressure dependence of the parabolic rate constant, it is concluded that outward transport of Ni via vacancies determines the growth rate of the oxide during the steady-state period, either in the grain boundaries or in the lattice. The influence of Cu dissolved in NiO on the oxidation rate and the oxygen-pressure dependence of the parabolic rate constants is discussed.     

Corrosion behaviour of X52 pipeline steel in high H2S concentration solutions at temperatures ranging from 25°C to 140°C

Abstract

High temperature and high pressure immersion tests in an autoclave were employed to study the corrosion behaviour of X52 pipeline steel in aqueous solutions containing high concentrations of H₂S. The corrosion products generated were characterised using scanning electron microscope, energy dispersive spectroscopy and X-ray diffraction. It was seen that at a constant H₂S concentration of 22 g/l, the corrosion rate increased with increasing temperature up to 90°C, thereafter decreased at 120°C and slightly increased again at 140°C while the corrosion rate increased with H₂S concentration at a temperature of 90°C. When the temperature and H₂S concentration increased, the corrosion product converted from iron rich to sulphur rich products in the following sequence: mackinawite→troilite→pyrrhotite, where the microstructure and stability of the corrosion products had an important effect on the corrosion rate. The corrosion film was formed through the combination of the outward diffusion of Fe²⁺ ions and the inward diffusion of H₂S and HS^? species.     

Adaptive VN/Ag nanocomposite coatings with lubricious behavior from 25 to 1000 °C

A two-phase nanocomposite coating that consists of inclusions of silver in a vanadium nitride matrix (VN/Ag) was investigated as a potential adaptive coating with a reduced friction coefficient from 25 to 1000 °C. This nanocomposite structure was selected based on the premise that silver and silver vanadate phases would form on the surface of these coatings, reducing their friction coefficient in the (i) room to mid-range and (ii) mid-range to high temperatures, respectively. Silver and vanadium were expected to react with oxygen at high temperatures and create a lubricious silver vanadate film on the coating. The VN/Ag coatings were deposited using unbalanced magnetron sputtering and their elemental composition was evaluated using X-ray photoelectron spectroscopy. The tribological properties of the materials against Si₃N₄ balls were investigated at different temperatures. The lowest friction coefficients recorded for samples with identical compositions were 0.35, 0.30, 0.10 and 0.20 at 25, 350, 700 and 1000 °C, respectively. Post-wear testing Raman spectroscopy and X-ray diffraction (XRD) measurements revealed the formation of silver vanadate compounds on the surface of these coatings. In addition, real time Raman spectroscopy and high temperature XRD revealed that silver vanadate, vanadium oxide and elemental silver formed on the surface of these coatings upon heating to 1000 °C. Upon cooling, silver and vanadium oxide were found to combine at about 400 °C, leading predominantly to the formation of silver vanadate phases on the surface of these materials.     

Study of the tensile behaviour of tungsten wires from ambient temperature to 320 °C in relation to their microstructure

The tensile test results have been interpreted in terms of the microstructure typical of drawn tungsten wires; the influence of test temperature between 25 °C and 320 °C is significant and is linked to the dependence of the mechanical behaviour of tungsten versus temperature and to the development with increasing temperature of a necking zone in which damage and rupture take place in two stages, a localized damage controlled first by the hoop stress associated to the notch effect linked to necking and rupture under the axial stress and the notch effect just mentioned.     

Tensile properties of zone refined iron in the temperature range from 298° to 4.2°K

The tensile properties of zone refined iron have been evaluated in the temperature range from 298° to 4.2°K. It has been found that the higher the purity, the lower the flow stresses and the better the low temperature ductility. Yield stresses as low as 3,800 psi have been observed at room temperature and elongations of 10 pct have been observed at 4.2°K. The major portion of the ductility at 4.2°K arises from twinning. Deformation by twinning at 4.2°K is not suppressed by prestraining at room temperature and the twins occur all through the test. Slip traces were observed to initiate at the ends of previously formed twin traces.     

Microstructures of a Ni-9.6 at.% Ta-16.6 at.% Cr alloy after aging up to 1000 hours from 600 to 1,000°C

The effects of aging of a Ni-rich Ni-Ta-Cr alloy on the microstructure (using optical and scanning electron microscopy) and hardness are presented. In the solution-annealed condition (1280°C, 4 h) the microstructure consisted of a face-centered cubic matrix and about 10% of a Ni₃Ta type phase, which contained some Cr; the hardness was about 530 DPH. No change in the microstructure nor significant change in hardness occurred upon aging at 600°C for 1,000 h. Aging from 700 to 1000°C produced a significant decrease in hardness, to about 330 DPH after 1000 h. A lamellar product formed, usually initiating at the secondary particles present in the solution-annealed condition. At longer times and higher temperatures, a coarser lamellar product formed. The results of qualitative EDS analysis of the phases are reported.     

Erosion resistance of arc-sprayed coatings to iron ore at 25 and 315 °C

Iron ore pellets are sintered and reduced in large continuous industrial oil-fired furnaces. From the furnace, powerful fans extract large volumes of hot gas. Being exposed to gas-borne iron ore particles and temperatures ranging between 125 and 328 °C, fan components are rapidly eroded. Extensive part repair or replacement is required for maintaining a profitable operation. The arc spraying technique has been suggested for repair provided it could produce erosion-resistant coatings. Conventional and cored wires (1.6 mm diameter) were arc sprayed using various spray parameters to produce 250 to 300 μm thick coatings. Arc-sprayed coatings and reference specimens were erosion tested at 25 and 315 °C and impact angles of 25 and 90° in a laboratory gas-blast erosion rig. This device was designed to impact materials with coarse (32 to 300 μm) iron ore particles at a speed of 100 m/s. The coating volume loss due to erosion was measured with a laser profilometer built by National Research Council Canada several years ago. Few arc-sprayed coatings exhibited erosion resistance comparable with structural steel at low impact angles. Erosion of arc-sprayed coatings and reference specimens dramatically increases at 315 °C for both 25° and 90° impact angles. Erosion-enhanced oxidation was found to be responsible for the increase in volume loss above room temperature. Though arc spraying can be appropriate for on-site repair, the development of more erosion-resistant coatings is required for intermediate temperatures.     

Oxidation Mechanism of Cu2O to CuO at 600–1050°C

To clarify the oxidation mechanism of Cu₂O to CuO, Cu₂O oxidation was studied at 600–1050 °C under 1atm O ₂. The Cu₂O specimens were prepared through completely oxidizing 99.99999 and 99.5 pure copper at 1000°C in an Ar + 1 O ₂ atmosphere. The oxidation kinetics of Cu₂O specimens prepared from both purity levels followed the logarithmic law, not the parabolic law or the cubic law as reported in the literature. The activation energy for Cu₂O oxidation is relatively high in the lower-temperature range, but becomes very small or even negative at higher temperatures. The logarithmic oxidation rate law can be explained by Davies et al.s model related to grain-boundary diffusion in the oxide layers. The very small or negative activation energies in the higher-temperature range can be attributed to the very small thermodynamic driving force and the fast lateral growth of CuO grains related to a sintering effect. The influence of small amount of impurities is also discussed.     

A Novel Method to Calculate the Carbides Fraction from Dilatometric Measurements During Cooling in Hot-Work Tool Steel

Dilatometry is a useful technique to obtain experimental data concerning transformation. In this paper, a dilation conversional model was established to calculate carbides fraction in AISI H13 hot-work tool steel based on the measured length changes. After carbides precipitation, the alloy contents in the matrix changed. In the usual models, the content of carbon atoms after precipitation is considered as the only element that affects the lattice constant and the content of the alloy elements such as Cr, Mo, Mn, V are often ignored. In the model introduced in this paper, the alloying elements (Cr, Mo, Mn, V) changes caused by carbides precipitation are incorporated. The carbides were identified using scanning electron microscope and transmission electron microscope. The relationship between lattice constant of carbides and temperature are measured by high-temperature X-ray diffraction. The results indicate that the carbides observed in all specimens cooled at different rates are V-rich MC and Cr-rich M₂₃C₆, and most of them are V-rich MC, only very few are Cr-rich M₂₃C₆. The model including the effects of substitutional alloying elements shows a good improvement on carbides fraction predictions. In addition, lower cooling rate advances the carbides precipitation for AISI H13 specimens. The results between experiments and mathematical model agree well.     

Application of a counter-current gaseous diffusion model to the oxidation of hafnium carbide at 1200 to 1530°C

A counter-current gaseous diffusion model is presented to describe the oxidation of hafnium carbide between 1200 and 1530°C. The model separates the porous hafnia scale into two gas diffusion regions separated by a flame front, where O ₂ and CO react to form CO ₂.In the outer region, O ₂ and CO ₂ counter-diffuse; in the inner region, CO ₂ and CO counter-diffuse. The concentration gradients of each gaseous specie in the pores of the hafnia are determined and the rate of oxidation is calculated. A porosity of 2% and a pore radius of 0.01 m are representative of the values observed in hafnia during the early stages of HfC oxidation. These values lead to predictions of parabolic rate constants that are close to those measured by thermogravimetric analysis. In addition, the predicted and measured parabolic rate constants are shown to have the same dependence upon temperature and oxygen partial pressure.     

Mechanical properties of as-fabricated and 2300 °C annealed tungsten wire tested up to 600 °C

Recent efforts dedicated to the mitigation of tungsten brittleness have demonstrated that tungsten fiber-reinforced composites acquire pseudo ductility even at room temperature. Crack extension and fracture process is basically defined by the strength of tungsten fibers. Here, we move forward and report the results of mechanical and microstructural investigation of different grades of W wire with a diameter of 150 μm at elevated temperature up to 600 °C. The results demonstrated that potassium doping to the wire in the as-fabricated state does not principally change the mechanical response, and the fracture occurs by grain elongation and delamination. Both fracture stress and fracture strain decrease with increasing test temperature. Contrary to the as-fabricated wire, the potassium-doped wire annealed at 2300 °C exhibits much lower fracture stress. The fracture mechanism also differs, namely: cleavage below 300 °C and ductile necking above. The change in the fracture mechanism is accompanied with a significant increase of the elongation to fracture being ~ 5% around 300 °C.     

Observation of Oxide Development from Room Temperature (RT) to 700 °C Demonstrated by In Situ XPS of Crofer 22 APU Alloy

Oxidation of Metals - The planar-type solid oxide fuel cell (SOFC) owes its design to the interconnector section which enables units of fuel cells to be stacked together. High operating temperature...     

Inhibitor Protection of Steels in Solutions of Sulfuric Acid under High-Temperature Corrosion (up to 200°C)

Protection of Metals and Physical Chemistry of Surfaces - This article analyzes corrosion of 08Kh18N10T chrome nickel steel in 2 M H2SO4 in wide temperature range t = 0–200°C. Under such...     

Coordination of Pre-oxidation Time and Temperature for a Better Corrosion Resistance to CO2 at 550 °C

Oxidation of Metals - Influence of pre-oxidation treatment on the oxidation resistance of F91 to CO2 at 550 °C was investigated. The formation of the thin scale of (Fe, Cr)2O3...     

RE-W cathode discharge properties in N2 and CO2 atmosphere at high temperature up to 1000 °C

Rare earth-tungsten (RE-W) cathode discharge properties in N₂ and CO₂ atmosphere at high temperatures were studied experimentally. The effect of temperature, atmosphere, cathode material and diameter on discharge current and corona inception voltage were investigated. The results show that the discharge current is larger and the corona inception voltage is lower in N₂ atmosphere than in CO₂ atmosphere. The range of the corona discharge voltage is narrower in CO₂ atmosphere. When the temperature is above 900 °C, the corona discharge becomes very unstable. As the temperature increases, the discharge current increases obviously and the corona inception voltage decreases significantly. Besides, the discharge current increases and the corona inception voltage decreases with the decrease of cathode diameter. The corona inception voltage also decreases significantly with the decrease of work function of different cathodes.