Oxidation of zirconium between 400° and 800°C

The vacuum microbalance method is used to study the oxidation reaction for two surface preparations over the temperature range of 400° to 800°C. The results fit in well with the authors previous work at temperatures of 200° to 425°C and with the work of other groups at higher temperatures. An analysis of the rate data shows that the cubic rate law fits the experimental data best for the abraded specimens. However, the parabolic rate law can be fitted to the data if an initial deviation is disregarded. With chemically polished specimens, a good fit is obtained with the parabolic rate law. The parabolic rate law constant A gives two straight lines when plotted as log A vs 1/T. For the temperature range of 200° to 525°C an energy of activation of 18,200 cal per mol is calculated while a value of 28,600 cal per mol is calculated for the temperature range of 525° to 750°C. The results of this work bring together the previously determined high-temperature oxidation studies of Cubicciotti with the early low-temperature studies of Gulbransen and Andrew.     

Equilibrium Pressure Measurements Above ZnS from 680° to 825°C

The pressure of the gas in equilibrium with sphalerite has been determined in the temperature range of 680° to 825°C, using the Knudsen orifice method. A comparison of these experimental pressures with those calculated from thermal data and from other equilibrium measurements shows that the vapor above sphalerite is predominantly dissociated ZnS. Equations have been given for correctly calculating dissociation pressures using the Knudsen orifice method. It has been shown that the experimentally determined pressure is the same, whether the zinc sulphide is sphalerite or not, or a mixture of wurtzite and sphalerite.     

475°C (885°F) embrittlement in stainless steels

Changes in hardness, tensile properties, microstructure, electrical resistance, and X-ray diffraction effects indicate that lattice strains are necessary for the embrittlement of ferritic stainless steels when heated for relatively short times at 475°C (885°F). It is suggested that 475°C (885°F) embrittlement is due to the accelerated formation of an intermediate stage in the formation of σ under the influence of these strains.     

在850C°和925C°的烃—氮混合物中的渗碳与气体反应

1.前言钢的气相渗碳工艺主要包括吸热型气体法和近来出现的几种氮基法。决定这些系统渗碳功能的气氛组成是CO、CO_2、H_2、H_2O和碳氢化合物。在吸热型气体法中,碳氢化合物(常用     

哈氏C-2000合金在800°C和1000°C的氧化行为(英文)

研究哈氏C-2000合金在(800°C,1000 h)和(1000°C,100 h)时的氧化行为。分别利用增重法、SEM、XRD和XPS表征氧化动力学和氧化膜的形貌特征。合金在800°C和1000°C时均基本满足抛物线速率规律。此外,由于退火孪晶提高了合金化元素及氧原子的扩散速率,因此,降低了合金的高温抗氧化性能。在800°C时,氧化膜微观结构主要是由NiO和Cr1.3Fe0.7O6组成。此外,初始退火孪晶结构在氧化后依然可见,且临近氧化膜附近出现了富Mo相。然而,在1000°C时,氧化膜的微观结构由细小的铬氧化物和粗大的镍氧化物颗粒通过相互镶嵌而构成,同时,在临近氧化膜处几乎无富Mo相出现。     

Thermal oxidation of single-crystal aluminum at 550°C

Oxygen transport during oxide growth on (110), (111), and (100) Al crystals at 550°C is investigated by¹⁸O/SIMS combined with kinetic measurements and SEM and TEM observations. Starting with an electropolished surface, the experimental evidence suggests oxide growth by oxygen anion transport via local pathways through an outer amorphous Al₂O₃ layer and oxygen incorporation at the periphery of the underlying laterally growing -Al₂O₃ islands. The kinetics, island morphology and epitaxy are sensitive to substrate orientation. This oxide growth behavior is compared with oxide formation on a sputter-cleaned and annealed (111) Al surface.     

The oxidation of Iron-Chromium-Manganese alloys at 900°C

The oxidation of nine ternary iron-chromium-manganese alloys was studied at 900°C in an oxygen partial pressure of 26.7 kPa. The manganese concentration was set at 2, 6, and 10 wt. %, and chromium at 5, 12, and 20 wt. %. The scales formed on the low-chromium alloys consisted of (Mn,Fe)₂O₃, -Fe₂O₃, and Fe₃O₄. These alloys all exhibited internal oxidation and scale detachment upon cooling. The scales formed on the higher-chromium alloys were complicated by nodule formation. Initially, these scales had an outer layer of MnCr₂O₄ with Cr₂O₃ underneath, adjacent to the alloy. With the passage of time, however, nodules formed, and the overall reaction rate increased. This tendency was more marked at higher manganese contents. Although these alloys contained a high chromium content, the product chromia scale usually contained manganese. It was concluded that the presence of manganese in iron-chromium alloys had an adverse effect on the oxidation resistance over a wide range of chromium levels.     

Raman Spectroscopy Analysis of Oxide Film of NZ8 Alloy Corroded in 360 °C Li Water and 400 °C Steam

通过拉曼光谱法研究NZ8合金在360℃锂水和400℃蒸汽的静态高压釜中腐蚀后氧化膜的晶体结构。结果表明,NZ8合金的氧化膜主要由单斜氧化锆组成,其中包括少量畸变的四方氧化锆。随着腐蚀时间的延长,氧化膜中平均四方氧化锆含量不断减少,单斜氧化锆含量不断增加,四方氧化锆在向单斜氧化锆转变。从氧化膜/基体界面到氧化膜外表面,四方氧化锆含量不断减少,界面处四方氧化锆含量最高。NZ8合金在360℃锂水中腐蚀98d后所得氧化膜/金属界面处四方氧化锆含量较其在400℃蒸汽中腐蚀70d所得氧化膜/金属界面处四方氧化锆含量高,而且在400℃蒸汽中腐蚀后氧化膜外表面没有四方氧化锆形成。四方氧化锆向单斜氧化锆的转变决定了NZ8合金的耐腐蚀性能。氧化膜中四方氧化锆含量越高,则锆合金的耐腐蚀性能越好。     

Chloridation-oxidation of Fe-Cr and Ni-Cr alloys at 800°C

The chloridation-oxidation behavior of Fe-Cr (0–25 wt. %Cr) and Ni-Cr (0–20 wt.%Cr) alloys was studied at 800°C in three different H₂-HCl-H₂O() environments. In a low-HCI and low-H₂O() environment, where Cr₂O₃ is thermodynamically stable, the corrosion resistance of the Fe-Cr alloys increased with increasing Cr content in the alloys. In a high-HCl and high-H₂O() environment, where FeCr₂O₄ is stable and CrCl₂ is metastable, the corrosion resistance of the Fe-Cr alloys depended similarly on the Cr content. Low-Cr-Fe-Cr alloys exhibited large weight losses, while Fe-Cr alloys with higher than 19 wt. %Cr showed good corrosion resistance. In an environment of high-HCl in the absence of H₂O(), the evaporative corrosion rate was fast and limited by gas phase diffusion, and independent of the Cr content in the Fe-Cr alloys. Ni and Ni-Cr alloys generally showed good corrosion resistance in the environments of high H₂O() because of the low NiCl₂ vapor pressure and formation of a protective Cr₂O₃ scale. However, in the environment of high HCl in the absence of H₂O(), selective formation and evaporation of CrCl₂ occur, which results in Cr depletion and networks of voids for even a high-Cr Ni-Cr alloy.     

350°C - Thermal Stability of Austempered Ductile Iron

AUSTEMPERED DUCTILE IRON(ADI)is gettingincreasing interest because of the excellent mechanicalproperties,resulting from the peculiar ausferriticmicrostructure.The combination of high strength andhigh toughness makes ADI a cost effective alternativeto steel in several applications.In the recent past at theUniversity of Trento a lot of work was devoted to theapplication of ADI's to the production of automobile'sendothermic piston rings.A preliminary research hasbeen carried out to e…     

Partial phase relationships of Mg-Zn-Ce system at 350 °C

The alloys were prepared in Mg-rich corner of Mg-Zn-Ce system. Partial phase equilibrium relationships of these alloys at 350 °Cwere identified by using scanning electron microscopy(SEM), electron probe microanalysis(EPMA), X-ray diffraction(XRD) analysis and selected area electron diffraction(SAED) pattern analysis of transmission electron microscopy(TEM). Partial isothermal section of Mg-Zn-Ce system in Mg-rich corner was identified. The results show that there is one ternary compound (T-phase) in Mg-Zn-Ce system. The T-phase is a linear ternary compound in which the content of Ce is about 7.7% (molar fraction); while the content of Zn is changed from 19.3% to 43.6% (molar fraction). The crystal structure of T-phase is C-centered orthorhombic. In addition, one two-phase region of Mg+T-phase and one three-phase region of Mg+T-phase+MgZn(Ce) exist in the Mg-rich corner of Mg-Zn-Ce system at 350 °C.     

Chloridation-oxidation of nine commercial high-temperature alloys at 800°C

Chloridation-oxidation studies of nine commercial high-temperature alloys were carried out at 800°C in three different H₂-HCl-H₂O() environments: (A) both low HCl and H₂O() partial pressures, where either Cr₂O₃ or FeCr₂O₄ is stable, (B) both high HCl and H₂O() partial pressures, where FeCrO₄ is stable and CrCl₂ is metastable, and (C) high HCl partial pressure in the absence of H₂O(), where either CrCl₂ or Cr₂O₃ is stable. Although alloy 600 has the lowest Cr content of these nine alloys, it showed excellent corrosion resistance in all three environments because of its high Ni content. Alloy 304, with the lowest Ni content of the nine alloys, exhibited poor corrosion resistance in the environment C, fair resistance in the environment B and good resistance in the environment A. Alloy 800 showed very good resistance in Environment A, and fair corrosion resistance in Environment B; however, it suffered linear weight-loss kinetics when exposed to Environment C The alloys 617, 214, HR-160, X, 230 and 86 have good corrosion resistance in Environments A and B because of their relatively high contents of oxide-scale-forming elements Cr and/or Al. In Environment C, chlorine dramatically decreased the adhesion of the scale on the surface, and aluminum in alloys 617 and 214 hardly showed its usual beneficial effect in combating corrosion, nor does silicon in alloy HR-160. Different corrosion mechanisms are proposed for the alloys in the different environments.     

Cu-state evolution during leaching of bornite at 50 °C

The bioleaching of bornite with mixed moderately thermophilic culture at 50 °C was investigated. The intermediary species formed during the leaching of bornite were characterized by XRD and XPS. In addition, the evolution of Cu-state during leaching of bornite was further studied by applying φ_h-pH diagram and cyclic voltammetry. The results showed that the bornite was more likely to be leached at high redox potential. Furthermore, the intermediary sulfides, such as isocubanite, covellite, chalcopyrite, disulfide, and polysulfide, were formed in the course of bornite dissolution. The Cu 2p photoelectron spectrum revealed that the valence of copper in bornite and intermediary sulfide formed in the dissolution of bornite is +1. The bornite and chalcopyrite can be converted into each other, and both can be further converted to covellite and/or chalcocite.     

Corrosion of titanium in phosphoric acid at 250 °C

Corrosion studies of a commercially pure titanium in phosphoric acid solutions at 250 °C were carried out by immersion test in an autoclave. At lower phosphoric acid concentration (0.1 mol/L), the corrosion was mild. At higher phosphoric concentration (1.0 mol/L) corrosion, a 25 μm-thick white corrosion products layer was formed on the samples after 24 h immersion. XRD analysis shows that the white layer consists mainly of titanium oxide phosphate hydrate (π-Ti₂O(PO₄)₂·2H₂O). The corrosion product shows the morphology of fiber bundles. A thermodynamic analysis of the formation of the corrosion product is presented.     

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.     

Effect of nitrogen on sigma formation in Cr-Ni steels at 1200°F (650°C)

The addition of nitrogen (0.10 to 0.20 pct) to Fe-Cr-Ni alloys of simulated commercial purity results in a real displacement of the σ phase boundaries to higher chromium contents. The effect is small for the (γ + σ)/γ boundary, but is pronounced for the (γ + α + σ)/(γ + α) boundary. Although there is an indication of an exceptionally large shift of the σ boundaries to higher chromium contents, especially in steels with nitrogen over 0.2 pct, the major portion of this apparent shift results from the fact that carbide and nitride precipitation cause “chromium impoverishment” of the matrices. The effect of combined additions of nitrogen and silicon to the Fe-Cr-Ni phase diagram is demonstrated also. Nitrogen can nullify the effect of about 1 pct Si in shifting the (γ + σ)/γ phase boundary to lower values of chromium at all nickel levels from 8 to 20 pct. Nitrogen can nullify this σ-forming effect of about 2 pct Si at the 8 pct Ni level, but not at the 20 pct Ni level. The alloys studied were in both the cast and the wrought conditions. There are indications that the σ phase forms more slowly in the cast alloys than in the wrought alloys if both are in the completely austenitic state. The presence of δ ferrite in the cast alloys accelerates the formation of σ. Cold working increases the rate of σ formation in both cast and wrought alloys.     

Solubility of hemimorphite in ammonium sulfate solution at 25 °C

The solubility of natural hemimorphite in ammonium sulfate solution was measured by isothermal solution method at 25 °C and the dissolved residue of hemimorphite was investigated by X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) methods. The results show that zinc and silica in hemimorphite simultaneously dissolve in ammonium sulfate solution. The solubility of zinc in solution increases rapidly from 4.5381 mmol/kg in 0.5469 mol/kg ammonium sulfate solution to 11.5083 mmol/kg in 3.7038 mol/kg ammonium sulfate solution. The solubility of silica in solution increases slowly from 2.5509 mmol/kg in 0.5469 mol/kg ammonium sulfate solution to 7.2891 mmol/kg in 3.7038 mol/kg ammonium sulfate solution. The dissolved residue is the characteristic of hemimorphite Zn₄Si₂O₇(OH)₂·H₂O based on the results of the XRD, SEM and FTIR. Thus, no phase transition occurs in the dissolution process of hemimorphite in ammonium sulfate solution.