Esca-studies of the composition profile of low temperature oxide formed on chromium steels—I. Oxydation in dry oxygen

ESCA (Electron Spectroscopy for Chemical Analysis) has been used to analyse the composition of oxide films formed on chromium steels with 6–20%Cr at room temperature in pure oxygen at 0·2 atm. during different times from 2 min to 46 h. Ion etching was used to clean the surface before oxidation and to investigate the composition profile by successive stripping of the oxide layer.It is demonstrated that the total chromium content in the oxide is proportional to the concentration in the metal, but that it varies with depth inside the film. At the oxide-gas boundary the chromium concentration is less than in the metal, while chromium is enriched at the metal phase boundary. It is suggested that the oxide consists of (Fe,Cr)₂O₃ in the outermost zone and FeCr₂O₄ at the inside, with the reservation that the method is not sensitive to deviations from stoichiometry.The thickness of the layer has been determined as 25 Å from the intensity ratio of the deconvoluted ESCA peaks of the metallic and oxidized states. The thickness and the composition profile of the film do not vary noticeably with the oxidation time.     

Microstructural characteristics of the oxide scale formed on 304 stainless steel in oxygenated high temperature water

The microstructural characteristics of oxide scale formed on type 304 stainless steel in oxygenated high temperature water have been investigated. From outer to inner layer, the oxide scale consists of faceted spinel particles, irregularly shaped hematite particles and a compact layer of nano-sized spinels. Some outmost spinels formed on top of other particles are depleted in Cr, while the hematite particles tightly embedded into the inner layer contain more Cr in the inner than in the outer part. The inner nano-sized oxide grow inwards directly from the bottom of outer particles. The related oxidation mechanism is discussed.     

The mechanism of oxide film formation on Alloy 690 in oxygenated high temperature water

Oxide films formed on Alloy 690 exposed to 290 °C water containing 3 ppm O₂ were investigated. It was found that Cr rich oxides form initially through solid-state reactions. Ni–Fe spinels gradually develop on surface layer by precipitation with increasing immersion time. Initially formed Cr rich oxides react with outwards diffusing Ni and Fe to form small spinel particles which then vanish gradually. An inner layer develops from oxide/matrix interface through inward diffusion of oxidant. Cr is preferentially oxidized and tends to dissolve into solution. The resultant inner layer consists of predominant NiO which cannot serve as a protective barrier layer.     

An ESCA and Mössbauer study of the oxide layer formed on steel in water containing chromate and chloride ions

The formation of oxidic layers on steel in chromate solutions was studied by photo-electron and Mössbauer spectroscopy. To simulate more aggressive realistic systems, some chloride ions were added to the solution. The layers formed under these conditions were found to be thicker by an order of magnitude than those formed in the absence of chloride ions. They probably consist of ferric and chromic oxides of the corundum type (Fe_1?2Cr_x)₂O₃, with the Cr : Fe ratio being depth dependent. The oxide layer is subdivided into small regions behaving superparamagnetically. This heterogeneity of the layer is ascribed to the attack by the chloride ions. The structure of the oxides found differs from the spinel structure reported by other authors who used chloride-free solutions.     

高温含铅碱液中690TT合金氧化膜的耐蚀性能

利用静态高压釜,在330℃的10%NaOH+10 g/L PbO腐蚀介质中,对690TT合金进行5～60 d的浸泡实验,结果表明:690TT合金氧化膜由NiO、NiFe<,2>O<,4>和NiCr<,2>O<,4>构成.合金的氧化膜分层,靠近基体的腐蚀产物为混杂的富Cr和富Ni氧化物,是沿晶腐蚀和表面均匀腐蚀综合作用所致.中间层主要以NiCr<,2>O<,4>为主,外层是NiFe<,2>O<,4>以及NiO<,0>氧化膜同时具有n型和P型半导体特征,内层富Cr的氧化物为p型半导体,而外层富Fe的氧化物为n型半导体.     

Reflectance spectroscopy of oxide films. II. Oxide layers on chromium metal

Infrared reflectance spectra of oxidized chromium are presented as the first of a series of investigations of the reflectance spectra of oxidized materials. The spectra agree well with the behavior predicted in an earlier note, and confirm that simultaneous identification and thickness measurements of corrosion films are possible using this technique. The most prominent features for identification purposes are absorption bands at 610, 540, and 440 cm ^–1 for films 1.5- thick, and at 610 and 300 cm^–1 for thicker films. These bands are discernable despite the complicated effects introduced by interference fringes in the low-energy spectral region.     

Effect of hydrogen in Inconel Alloy 600 on corrosion in high temperature oxygenated water

Corrosion test on hydrogen charged and uncharged coupons of Inconel Alloy 600 in high temperature oxygenated water showed more weight loss of charged coupon. Observation of the oxide film by transmission electron microscopy (TEM) showed a defective, thicker oxide layer on charged coupon. Analyses of the oxide film by TEM-energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy indicated enrichment of Ni but depletion of Cr in the oxide film on charged coupon. The changes in corrosion behavior and microstructure of the oxide film were most likely due to the hydrogen enhanced preferential dissolution of Cr cations in the water.     

Corrosion in solar heating systems. II. Corrosion behaviour of AA 6351 in water/glycol solutions

A research was carried out in order to investigate the corrosion behaviour of the metals most commonly used as construction materials for solar absorber plates. With this view, an attempt was made to test the corrosion resistance of the aluminium alloy AA 6351 (nominal composition: 1% Si, 0.6% Mg, 0.3% Mn, the balance Al) towards common uninhibited heat transfer fluids, such as ethylene and propylene glycol/water mixtures. Long time gravimetric tests consisted in up to 60 day exposures of the aluminium specimens to pure, chloride-polluted, or degraded glycol/water solutions, at the temperature of 80°C. The degradation into acidic products, experienced by heat transfer liquids in service, was simulated by keeping the ethylene and propylene glycol/water solutions at their boiling temperature for 30 days, in contact with copper. In glycol/water solutions the presence of chlorides at low concentration (200 ppm) caused the aluminium corrosion rates to increase by more than one order of magnitude, while in degraded solutions, containing 143 or 86 ppm cupric ions, corrosion rates higher than two order of magnitude with respect to pure solutions were obtained. During the gravimetric tests, pitting corrosion was observed in some cases and its extent was rated by evaluating the deepest and the average metal penetration, the pit density and the average pit size. The influence of heat transfer on the alloy AA 6351 corrosion and on the couple copper/AA 6351 efficiency was evaluated by gravimetric and electrochemical tests. Heat transfer through aluminium was found to significantly increase the aluminium alloy pitting potential. On the contrary, it stimulated the aluminium galvanic corrosion, when applied on either aluminium or copper. Under galvanic coupling conditions, the aluminium corrosion rates calculated from the average galvanic currents were a very little contribution to the gravimetric corrosion rates. This demonstrates that in low conductive solutions the risk of matching such dissimilar metals as copper and aluminium does not reside in the galvanic contact itself, but mainly in the mere presence of the noblest metal in the same solution where aluminium is immersed.     

Effects of temperature on the Corrosion of copper in sea water at different hydrostatic pressures

An investigation has been made of the effect which an increasing hydrostatic pressure may have on copper corrosion at different temperatures in sea water at pH 7.8. The tests were carried out at a pressure of 1, 50, 100, 200 and 300 atm at a temperature of 5 °, 10 ° and 20 °C. The pressure set in which the tests were effected was pressurized by an hydropneumatic pump and it was fitted not only with a work electrode, but also with two Pt and one Ag-AgCl reference electrodes for electrochemical tests. It was found that copper corrosion is always stimulated by a pressure rise and that the increased corrosion rate is accelerated by increasing temperatures. The maximum increase (71%) was obtained at T = 20 °C; D.O = 7.0 ppm and pH = 7.8 at a pressure of 150 atm. But at a temperature of approx. 5 °C, the maximum increase did not exceed 30% always at a pressure of 150 atm. The test findings also evidenced that at a temperature ≤ of 10 °C, the pressure rise did not affect the anodic process but only the cathodic reduction, whereas the anodic process too was significantly accelerated at 20 °C and the influence of the pressure was found to be more accentuated.     

Fundamental studies of driven and self-propelled rotary tool cutting processes—II. Experimental investigation

An extensive experimental investigation has been carried out to verify the developed mechanics of cutting analyses for the fundamental driven and self-propelled rotary tool cutting processes. This involved testing the dynamic or perfect equivalence between the rotary tool and equivalent classical processes over a wide range of inclination angles, cut thickness and rake angles using statistical processing techniques. The collinearity conditions at the shear plane and rake face have also been tested as part of the model verification. It has been shown that all the force components, deformation and basic cutting parameter trends and quantities required for perfect equivalence have been satisfied as were the necessary collinearity conditions. The verified models provide a deeper understanding of the cutting mechanics and characteristics of these ingenious material removal operations and form the basis for the development of predictive cutting models for the fundamental and complex practical rotary tool operations.     

Effect of alternately changing the dissolved Ni ion concentration on the oxidation of 304 stainless steel in oxygenated high temperature water

Characteristics of oxide films formed on 304 stainless steel under alternately changing Ni²⁺ concentrations in oxygenated high temperature water were examined. Oxides preformed under low Ni²⁺ concentration evolve from hematite to spinel after subsequent immersion under high Ni²⁺ concentration. Meanwhile, Ni content in the surface layer of oxide rises up while Fe content drops. Oxide films preformed under high Ni²⁺ concentration show little change in phase composition after subsequent immersion under low Ni²⁺ concentration. Fe contents in surface layer rise up while the change of Ni contents depends on the original phase composition and whether residual Ni²⁺ is present.     

Analysis of oxide formed on Ti during exposure in bentonite clay. I. The oxide growth

Titanium is a candidate as a canister material for the encapsulation of spent nuclear fuel due to its excellent corrosion properties. The aim of this paper is to determine the corrosion rate of titanium in ground-water saturated bentonite clay at 95°C. The exposure times were ranging from 4 months to 6 years. The analysis tool was ESCA. The results show that the oxide consists mainly of TiO² and is 65–90 Å thick. A few monolayers of TiO and Ti₂O₃ exist close to the metal interface. It is found, that the oxide follows the same logarithmic growth law as in aqueous solutions: y = 71.7 + 3.65 In t (y in Å and t in years). This law applies irrespective of salt or oxygen content or if bentonite is present on the surface. No influence of the alloying clement Pd was found. Deviations from the logarithmic growth law was also found, which indicates that a change of growth can occur in a long term perspective. It is suggested that the increased growth rate is caused by crystallization of the oxide. The influence of bentonite is that the majority component montmorillonite is adsorbed in a 10–40 Å thick layer on the surface.     

Optimal process design in steady-state metal forming by finite element method—II. Application to die profile design in extrusion

A new approach to optimal process design in steady-state metal forming is presented. In the approach, optimal process design problems are mathematically formulated and solved using a penalty rigid-viscoplastic finite element method as a tool for carrying out necessary calculations for optimization. The basic formulation is presented and the solution procedure is described with the emphasis on the method of calculating the design sensitivities. The accuracy of the design sensitivities thus obtained is assessed by a series of numerical tests. An iterative scheme for optimizing the design variables based on the predicted design sensitivities is also given.     

Photoelectrochemical properties of oxide films formed by anode plasma electrolytic oxidation on titanium in water solutions

It is shown that films of titanium dioxide obtained by anodic plasma electrolytic processing of commercial titanium in an aqueous solution of ammonium chloride are photosensitive. Incident photon to charge carrier efficiency (IPCE) in the near ultraviolet (366 nm) reached 8.5%. Magnitude of the photocurrent generated by the films obtained under optimum processing conditions decreases no more than 20% at the transition from the ultraviolet to the mixed light.     

Corrosion rate of steel in concrete—Measurements beyond the Tafel law

The rapid galvanostatic pulse technique was applied on site on a large number of measuring points with reinforcement varying from severely corroding to passive state. The measurements provide reliable results on corrosion potential, ohmic resistance and polarization resistance in very short time. The overall scatter of the data is not bigger than with any other instrumentation used for corrosion rate determination in the field. For actively corroding zones the current from the counter electrode is self-confined, no guard-ring is needed and the corrosion rate can be calculated on the basis of the reinforcement area under the counter-electrode. For passive zones the calculated “corrosion rate” is overestimated (on a very low level). Corrosion rate calculated from polarization resistance data are always instantaneous values. For engineering application (residual service life) the daily and seasonal changes in corrosion rate have to be considered. In the frequent case of chloride induced localized corrosion the local penetration rates calculated from R_p data can vary up to a factor of 5–10 and local penetration rates of 1 mm/year may occur. This uncertainty on a very high level of corrosion rate is much more important than variations induced by using devices with or without guard ring.     

Characterization of oxide scales formed on low carbon steel between 1100 and 1250 °C in air

A low carbon steel was oxidized isothermally at temperatures of 1100–1250 °C for up to 2 h in air, and the oxide scales were examined. Several hundred micrometer-thick scales formed owing to poor oxidation resistance at high temperatures. Scales consisting mainly of Fe₂O₃, Fe₃O₄, and FeO spalled easily, owing to the formation of voids and cracks in the scales. All the alloying elements were also oxidized and incorporated in the iron oxide scales, depending on their local concentration in the matrix.     

Effects of the solution temperature and the pH on the electrochemical properties of the surface oxide films formed on Alloy 600

The surface oxide films on Alloy 600 have been investigated as a function of the solution temperature and the pH by using a cyclic voltammetry, potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and a depth profiling by Auger electron spectroscopy (AES). H₃BO₃, Na₂SO₄ and NaOH aqueous solutions with temperatures in the range of 30–300 °C were used as the test solutions. As the solution temperature of the 0.5 M H₃BO₃ increased, the thickness of the passive film increased but the resistance of the passive film was diminished, which is coincident with a solution temperature dependency of the passive current in the potentiodynamic curve. The inner oxide film on Alloy 600 was distinguishable from the Cr-rich outer oxide film above 100 °C. From the Mott–Schottky relation, the oxide formed in 0.5 M H₃BO₃ at 300 °C showed a p-type semiconductor property, accompanied by a Cr-rich oxide film throughout the whole oxide film unlike the n-type oxide films up to 250 °C. The oxide resistance of the passive film decreased in the order of 0.5 M H₃BO₃, 0.1 M NaOH and 0.5 M Na₂SO₄, which is consistent with the pH dependency of the passive current. Ni-rich oxide films of a p-type were formed in the 0.5 M Na₂SO₄ or 0.1 M NaOH.     

Effects of temperature on the protective property, structure and composition of the oxide film on Alloy 625

The paper mainly investigated the protective property, structure and composition of the oxide film on Alloy 625 in a lithium borate buffer solution (pH_300°C = 6.93) in the temperature range of 25–300 °C. The methods used were electrochemical measurements and XPS analysis. As temperature increased, the protective property of the oxide film degraded, and the structure varied from a singe-layer to double-layer. The oxide film consisted of Cr₂O₃ and Cr(OH)₃ at 25 and 150 °C, while it contained Ni(OH)₂, in addition to Cr₂O₃ and Cr(OH)₃ at 250 and 300 °C. This was mainly attributed to the temperature-induced variation of composition and protective property of the barrier layer.     

On the determination of thermal phenomena during drilling—Part II. Comparison of experimental and analytical twist drill temperature distributions

The analytical models, developed in Part I of this paper, for estimating the temperature distributions along the cutting edge and on the clearance face of a twist drill are evaluated using an experimental technique that measures average drill flank temperatures. While the transient model tends to overestimate the values of the average flank temperatures, especially during drilling to a one diameter hole depth, the temperatures predicted from the steady state model agree reasonably well with the experimental results. The difference between the analytical and experimental results varied with the physical and thermal properties of the powder metallurgy work materials used in this experiment. The analytical drill temperature distribution models are also compared with others found in the literature.