PdO/Pd system equilibrium phase diagram under a gas mixture of oxygen and nitrogen

The thermal equilibrium decomposition properties of the PdO-Pd system under oxygen partial pressures ranging from 0.1 to 1.0 atm in a total combined pressure of oxygen and nitrogen of 1.0 atm were investigated by means of thermal-gravimetric analyses. The phase diagram of Pd-PdO over the range of oxygen/nitrogen gas concentration was established. The decomposition temperature of PdO to Pd was found to increase with the partial pressure of oxygen.     

The electrical conductivity of NiO at 1000°C

Specimens of NiO for conductivity measurements were made from Ni foil, containing less than 25ppm total impurities, by spot welding platinum leads to the foil which was then oxidized to compact NiO at 1300°C. Four point d.c. conductivity measurements were carried out at oxygen partial pressures between 1 atm and 10^?10 atm provided by gas mixtures and monitored using a zirconia-based solid state cell sensitive to oxygen. The results indicate a predominance of doubly charged cation vacancies below 10^?5 atm oxygen partial pressure and of singly charged cation vacancies above this value.     

Thermodynamic considerations of pore formation and hydrostatic pressure during underwater wet welding

The pore and crack formations in the weld bead during underwater wet welding are the main cause of failure to reach the required mechanical properties of the weld metal. These defects are closely associated with the decomposition of the water molecule under electric arc conditions. In this paper, the thermodynamic calculations of the complex process of the water decomposition under the conditions of high electric arc temperatures at a pressure of 1 atm of steam are discussed. The values of the partial pressures of the five main products of the vaporizations and decomposition of the water (H₂O_(g), H₂, O₂, H and O) are calculated for temperatures between 1870 and 4000 K. Due to the fact that atomic hydrogen is mainly responsible for pore formation in the weld metal, its partial pressure as a function of partial pressures of atomic oxygen and steam (water vapour) is expressed. Hydrogen solubility values in the liquid metal under the conditions of underwater wet welding at depths of 50 and 100 m, and a comparison between the thermodynamic calculation and porosity measurement results at depths of 50 and 100 m, are presented.     

Gaseous equilibria in the C-H-O ternary system at 500–2000 K, 0.1–10 atm

The complex gaseous equilibria of approximately 10,000 different compositions in the C-H-O ternary system containing up to 40 gaseous species have been calculated at temperatures of 500, 1000, 1500, and 2000 K for total pressures of 0.1, 1.0, and 10.0 atm. The results are represented by selected isoactivity curves of carbon and isobars of hydrogen and oxygen plotted on C-H-O Gibbs composition triangles. The effects of changing composition, temperature, and pressure upon the chemical equilibria in this system are analyzed. In addition, the role of the C-H-O system in selected industrial applications is briefly discussed, including the choice of gas mixtures for the carburization of metals; the extent of carbon deposition at various temperatures, pressures, and compositions in reforming and gasification processes; the free hydrogen partial pressure in the anode compartment of fuel cells and influence of water addition; the oxygen potential in the products of combustion engines; and chemically buffered gas mixtures in controlled atmospheres.     

Effect of the oxygen partial pressure on the kinetics of decomposition of the Ba<Subscript>2</Subscript>YCu<Subscript>3</Subscript>O<Subscript>7−δ</Subscript> phase at temperatures <400°C

The effect of the oxygen partial pressure on the spinodal decomposition in the Ba₂YCu₃O₆—Ba₂YCu₃O₇ system has been studied. A decrease in the oxygen partial pressure was found to increase the decomposition rate. The most probable cause of the effect consists in the decrease of oxygen concentration in the near-boundary regions of grains.     

The corrosion of chromium and nickel-chromium alloys in oxygen-sulfur-carbon gases at 800°C

The simultaneous oxidation and sulfidation of Cr, Ni-10Cr, Ni-20Cr, and Ni-30Cr was studied at 800°C in three gases falling within the Cr₂O₃ stability field of the Cr-S-O system. The sulfur partial pressure remained constant at 1×10^?6 atm, whereas the oxygen partial pressure varied from 5×10²¹ to 5×10^?20 atm, and the carbon activity varied from 0.108 to 0.416. Reaction kinetics were measured, and the reaction products were characterized by X-ray diffraction, metallography, scanning electron microscopy, and X-ray energy dispersive analysis. Reaction rates decreased with increasing oxygen partial pressure and decreased with increasing chromium content of the alloys. Sulfides always formed along with Cr₂O₃, even though the gases fell within the oxide stability field. No carburization was observed even though carbon activities were sufficiently high to form carbides. The reaction mechanisms are discussed, and the absence of carburization is analyzed on the basis of a three-dimensional stability diagram.     

XPS and AES studies of the high temperature corrosion mechanism of Fe-30Cr alloy

Fe-30Cr alloy specimens were pre-oxidized at two different oxygen partial pressures (10^?16 and 10^?19 atm) at 900°C and subsequently exposed to environments containing both oxygen and sulfur. The sulfur and oxygen partial pressures were maintained such that Cr₂O₃ was the stable phase. The Cr₂O₃ scales formed during pre-oxidation became rapidly unstable when exposed to an environment whose composition approached the chromium sulfide-chromium oxide phase boundary; but when exposed to a higher oxygen partial pressure with the same sulfur partial pressure, the preformed scales remained intact. For elucidating the sulfidation mechanisms, the reaction products on the surface were analyzed at different stages of sulfidation by X-ray photo-electron spectroscopy and Auger electron spectroscopy. Correlation of the reaction mechanisms with thermodynamic and transport parameters are discussed.     

Oxidation of tantalum in oxygen-nitrogen and oxygen-inert gas mixtures

The oxidation of tantalum in oxygen-nitrogen and oxygen-inert gas mixtures at925°C has been studied. The oxygen pressure was close to 0.5 atm in all experiments, and partial pressures of the second component of from 0 to 180 Torr were employed. Spherical specimens were used to provide quantitatively significant kinetic data. A model has been proposed which suggests that the oxygen pressure at the reaction interface close to the metal surface is lower than the external pressure because of the finite permeability of the porous outer oxide layer, and that the inert gas effectively reduces the permeability. The model gives good quantitative agreement with the experimental results.     

The influence of an intermediate annealing treatment on the oxidation of copper and nickel

A study has been made of the effects of an intermediate, isothermal annealing treatment in argon on the oxidation kinetics of copper and nickel in 1 atm oxygen at 800 and 1100°C, respectively, using a semiautomatic microbalance. Changes in scale morphology and composition have been investigated using various physical techniques. The outer CuO layer formed on copper during oxidation dissociates very rapidly on annealing to give CU₂O and oxygen since the partial pressure of oxygen in the gas is below the dissociation pressure of CuO but above that of Cu₂O at 800°C. The CuO layer is quickly re-formed on reoxidation in oxygen. There are relatively few other changes in the oxide morphologies of either metal during annealing, although the small grains present in the scale adjacent to the metal after oxidation are able to grow. During reoxidation both metals show a reduction in oxidation rate constant because of the decrease in total cation vacancy concentration in the scale and the reduced cation vacancy gradient across the scale brought about by the reduction in oxygen partial pressure at the oxide-gas interface during annealing. The reoxidation rate constants following annealing approach those recorded prior to annealing as the equilibrium cation vacancy levels in the scales are reestablished in the oxidizing environment. Rosenberg's method for analysis of the kinetics of reoxidation has enabled the equilibrium concentrations and diffusion coefficients of cation vacancies in CU₂O and NiO during oxidation in 1 atm oxygen at the appropriate temperatures to be estimated approximately. These show reasonable agreement with literature values.     

An Ultralow Oxygen Partial Pressure-Controlling System and Its Application to Oxidation Studies

An ultralow oxygen partial pressure-controlling system, based on solid-stateelectrochemical principles, has been developed. This system consists of anoxygen sensor and an oxygen pump and is controlled by a PC computer. Theoxygen sensor is used to measure the oxygen partial pressure in an enclosedsystem, while the oxygen pump is used to transport oxygen from the ambientair into the enclosed system or from the enclosed system to the ambientair. The operating conditions of this system have been studied. The resultsshowed that it can be used to establish a stable oxygen partial pressure inthe range of 10–185×105 Pa (1×10–235 atm)in the enclosed system. This system has been used to investigate theselective oxidation of the Cr and the oxide formation on the surface of aNi–Cr alloy under three different low oxygen partial pressures. Theoxide morphology was studied using atomic force microscopy (AFM). The resultsagreed well with those in the literature and also confirm the reliability of this system.     

Formation of oxynitride layers on titanium alloys by gas diffusion treatment

Titanium alloys were oxynitrided in controlled nitrogen-oxygen gas atmospheres between 650 °C and 950 °C for 5 h to 10 h with two different techniques of gas diffusion treatment. One technique was performed in an oxygen-containing (oxygen amount ≥ 0.4 %) nitrogen environment. The other technique was performed in a deoxygenated (oxygen amount < 0.01 % to 0.0005 %) nitrogen environment with subsequent cooling in an oxygen-containing nitrogen environment (with an oxygen pressure of 1 Pa). The surface microhardness of oxynitrided samples increased due to the strengthening effect of titanium oxynitrides (TiN_xO_y). The maximum microhardness of the titanium oxynitrides was obtained with a near-equiatomic composition of nitrogen and oxygen in TiN_xO_y under optimal oxygen partial pressure and temperature-time conditions.     

纯铬和镍铬合金高温硫化、氧化腐蚀所产生的针状结构

在T=800℃,Ps_2=10~(-6)大气压,Po_2=5×10~(-21)～5×10~(-20)大气压(即靠近Cr_3S_4—Cr_2O_3热力学边界的Cr_2O_3稳定区中)的条件下,对纯铬和镍铬合金进行了高温腐蚀试验。在腐蚀的最初阶段,Cr_8S_4与Cr_2O_3同时生成,而且腐蚀层呈针状结构。当反应温度及硫分压不定时,合金成份及氧分压的改变对于针状结构的发育有明显的影响。作者对反应的机理进行了讨论。     

Synthesis and superconductivity of Y2Ba1Cu1O5 and Pt added Nd1Ba2Cu3O7?y bulk superconductor

Nd₁Ba₂Cu₃O_7−y (Ndl23) bulk superconductor with T_c>77K was prepared by a melt process under 1 atm pure oxygen and reduced oxygen partial pressures. The addition of Y₂Ba₁Cu₁O₅ (Y211) particles suppressed the generation of microcracks during oxygenation in resulting in the dispersion of Y211 fine particles. The addition of a small amount of Pt resulted in the reduction of the size of Y211 particles. The oxygen partial pressure (Po₂) of 0.01 atm was the optimum atmosphere for the synthesis of Ndl23 in which Y211 particles were dispersed finely and homogeneously. The addition of Y211 and Pt enhanced the flux pinning force in a melt-processed Ndl23 specimen because the presence of Y atoms in a melt phase suppressed, to some extent, the substitution of Nd on Ba site in an Ndl23 crystal prepared by a melt process.     

Active Oxidation of Liquid Silicon: Experimental Investigation of Kinetics

Small scale laboratory experiments on the oxidation of liquid silicon have reproduced important features of the industrial refining of liquid silicon: active oxidation led to the formation of amorphous silica spheres as a reaction product. The boundary condition for active oxidation in terms of maximum oxygen partial pressure in the bulk gas was found to lie between 2·10^?3 and 5·10^?3?atm at T?=?1,500?°C. The active oxidation of liquid silicon had linear kinetics, and the rate was proportional to bulk oxygen partial pressure and the square root of the linear gas flow rate, consistent with viscous flow mass transfer theory. Classical theory for unconstrained flow over a flat plate led to mass transfer rates for SiO_(g) which were 2–3 times slower than observed. However, computational fluid dynamic modeling to take into account the effects of reactor tube walls on flow patterns yielded satisfactory agreement with measured volatilization rates.     

Fabricating TiO2 Photocatalysts by rf Reactive Magnetron Sputtering at Varied Oxygen Partial Pressures

Titanium dioxide (TiO₂) thin films were fabricated onto non-alkali glass substrates by rf reactive magnetron sputtering at room temperature using Ti-metal target at varied oxygen partial pressure [O₂/(Ar + O₂)]. The sputtering deposition was performed under an rf power of 200 W. The target to substrate distance was kept at 80 mm, and the total gas pressure was 10 mTorr after 2 h of deposition. It was found that the crystalline structure, surface morphology, and photocatalytic activities of the TiO₂ thin films were affected by the oxygen partial pressure during deposition. The XRD patterns exhibited a broad-hump shape indicating the amorphous structure of TiO₂ thin films. The thin films deposited at a relatively high value of oxygen partial pressure (70%) had a good photo-induced decomposition of methylene blue (MB), photo-induced hydrophilicity, and had a small grain size.     

低氧压预氧化对FeCrAlSiY合金耐LBE熔液腐蚀性能的影响

为进一步提高核反应堆系统的结构材料 Fe-Cr 基合金抗 LBE 腐蚀的性能,对其进行成分优化和表面处理十分重要。 对 Fe-12Cr-xAl-2Si-0.6Y 合金进行低氧压预氧化试验,分析并讨论氧分压和 Al 含量对合金预氧化产物的影响,并研究预氧化前后的合金在 LBE 合金熔液中的耐腐蚀性能。结果表明,Fe-12Cr-2Al-2Si-0.6Y 合金在不同氧分压下进行预氧化后生成的表面氧化物均以 Al2O3 为主,氧分压越大,合金表面发生选择性氧化速度越快。不同 Al 含量的 Fe-12Cr-xAl-2Si-0.6Y 合金在 10^?15 atm(1 atm=0.101 3 MPa)氧分压下进行预氧化,随着 Al 含量的增加,合金表面氧化物由以 Cr₂O₃为主逐渐变为以 Al₂O₃ 为主,还混合有少量复合氧化物。进行低氧压预氧化处理能有效提高合金在 450 o C 的 LBE 合金熔液中的耐腐蚀性能。研究成果可为设计和开发耐 LBE 熔液腐蚀的 FeCrAlSiY 合金提供参考,促进该体系合金在核电工业领域的运用。     

在600-800℃低氧压下Co-Nb合金的氧化

研究了含15与30wt%Nb的两种Co-Nb合金在600-800℃低氧压F的氧化性能选择的氧压低于相应温度的氧化钴分解压,由H2-CO2混合气获得,在600℃为10-24atm,而700与800℃为10-20atm.两种合金在600与700℃氧化结果仅产生由α-CO与氧化铌(NbO2与Nb2O5)混合物组成的内氧化带在700℃尚可能生成双元氧化物CONb2O6在内氧化带界而无贫Nb层可见.两会金,尤其是Co-30Nb在800℃时发生了由内氧化向外氧化的转变,伴随有贫Nb的单相区出现于合金的表层.从Co中N     

SrCo0.7Fe0.2Nb0.1O3-δ perovskite stabilized by niobium for oxygen permeation

The effect of Nb doping on the oxygen permeation and stability of SrCo0.8Fe0.2O3-δ(SCFO)was investigated comprehensively.Cubic perovskite phase was formed in SrCo0.7Fe0.2Nb0.1O3-δ(SCFNO).The SCFNO with a thickness of 1 mm had a high level of oxygen permeation flux of 1.4 ml·min-1·cm-2 at 850 ℃ under air/He gradient.The bulk diffusion is the rate-limiting step in overall oxygen permeation mechanism for SCFNO when the thickness is higher than 1.0 mm.The partial substitution of Nb for Co suppresses the transition of oxygen vacancies order/disorder proven by DSC measurement and enhances the phase stability under low oxygen partial pressure.During long-term tests under low oxygen pressure,the SCFNO extibites structural stability and stable oxygen permeation.It is proved that substitution of Nb for Co is an effective way to improve the properties of SCFO.     

基于热力学计算的水工况对耐热钢高温氧化行为影响

基于热力学计算方法,对6种不同的水工况条件下的高温氧分压进行了计算和对比。计算结果显示,TP347H和T91两种材料在570℃时高温氧化产物类型转变的临界氧分压约为1.0×10^-15,而常规的加氧工况OT(1)、纯水工况、还原性全挥发处理工况AVT(R1)在此条件下的氧分压均高于1.0×10^-10,因此认为常规的加氧工况和还原性全挥发处理工况对TP347H、T91的高温氧化产物的热力学控制效果相差无几。通过改变材料中的合金元素含量,材料高温氧化产物的种类会发生变化。当提高Cr含量时,表层致密氧化层Cr₂O₃的体积分数提高。而对于新型的Fe-18Ni-25Cr-xAl材料,随着Al含量的增加,(Fe, Cr, Al)₂O₃的质量分数一定程度增加。当Al质量分数高于3%时,表层会出现致密的Al₂O₃相,能够提高高温氧化保护的效果。     

Surface tension of molten tin investigated with sessile drop method

1INTRODUCTIONSurface tension is one of the most i mportantthermophysical parameters of molten metals,which greatly influences the processes of crystalli-zation,phase transition and crystal growth of mol-ten metals,and plays a key roleinthe processes ofmetallurgy,casting and welding.Measurement ofsurface tension and its temperature coefficient isi mportant to the research of metal thermophysicalproperties[13].Tin andits alloys are applied widelyin the solder industries and the manufacture o…