Chromium Content Of Alloy Research Articles

Amorphous alloy catalysts for decomposition of CCl 2F 2 by hydrolysis

Catalytic decomposition by hydrolysis of CCl 2F 2 (CFC-12) to HF, HCl and CO 2 was studied for the amorphous binary NiZr and ternary NiZrCr alloy catalysts. The activity and durability for each catalyst were measured and compared. The amorphous Ni40at.%Zr alloy maintained its high activity for 70 h at 723 K, after which it decreased drastically. The amorphous NiZrCr alloy, activated at 823 K for several hours, showed a high activity and gave much longer durability at 723 K. The increase in the alloy chromium content enhanced the activity and elongated the life time. Among the NiZr15at.%Cr alloys, the specimen containing 40 at.% Zr showed the highest activity for the decomposition of CFC-12 but the specimen with 70 at.% Zr could not even be activated. The characterization of the reacted specimens was carried out using X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray analysis and X-ray photoelectron spectroscopy. Their structures were significantly changed by the reaction, because they were exposed to corrosive HCl and HF, formed by the decomposition reaction of CFC-12.

The corrosion behavior of sputter-deposited amorphous chromium-zirconium alloys in 6 M HCl solution

Amorphous binary CrZr alloys containing 11–66 at% Zr were successfully prepared by a magnetron sputtering method. Amorphous CrZr alloys thus prepared were spontaneously passive in 6 M HCl solution. Their corrosion rates were four orders of magnitude lower than chromium metal and one-third of zirconium metal and decreased with alloy chromium content. XPS analysis revealed that airformed films and passive films on the amorphous CrZr alloys were composed of double oxyhydroxides of chromium and zirconium. This appears to be responsible for the high corrosion resistance of the amorphous CrZr alloys in comparison with their constituent elements; the formation of chromium-containing passive film is more protective than the film on zirconium metal, despite the fact that chromium metal dissolves actively in 6 M HCl solution.

Electrochemical and XPS studies of the effects of alloying elements on the corrosion behavior of amorphous FeCrMetalloid alloys in 9 M H 2SO 4

The corrosion behavior of amorphous FeCr13P7C, FeCr13P7B and FeCr20B alloys in 9 M H 2SO 4 solution at 30°C was investigated. An increase in the alloy chromium content improved the corrosion resistance of the amorphous FeCr13P7C and FeCr13P7B alloys. When only B is contained as a metalloid, alloying with chromium up to 15 at% is ineffective in increasing the corrosion resistance. The addition of phosphorus accelerates the cathodic reaction of hydrogen evolution on the amorphous FeCr alloys. This leads to sharp ennoblement in the corrosion potential of amorphous Fe8Cr13P7M (M  C,B) alloys from the active state to the passive state with immersion time, while the corrosion potential of Fe8Cr20B alloy is unchanged. Chromium is concentrated in the passive film on the amorphous Fe8Cr13P7M (M  C,B) alloys formed by immersion in 9 M H 2SO 4 solution, and is further concentrated by prolonged immersion. In particular, the concentration of chromic ions in the passive film on the Fe8Cr13P7C alloy is higher than that in the film on the Fe8Cr13P7B alloy.

The corrosion behavior of amorphous Ni-Cr-19p alloys in hydrochloric acid

The corrosion behavior of the amorphous Ni-Cr-19P alloys in 1, 6 and 12 M HCl solutions at 30°C was investigated. The amorphous Ni-19P alloy shows an almost constant corrosion rate of about 0.05 mm y−1 regardless of the concentration of hydrochloric acid. This is attributed to the formation of an elemental phosphorus layer acting as a diffusion barrier against active dissolution of the alloy. The corrosion rate of the amorphous Ni-Cr-19P alloys decreases with increase in alloy chromium content, but increases in 12 M HCl when 15 at% or more chromium is added. The formation of the elemental phosphorus layer on Ni-P and low chromium alloys is effective in decreasing the corrosion rate and in ennobling the corrosion potential with a consequent passivation. By contrast, when the content of active chromium is very high such as 15 at% or more, active dissolution of chromium in 12 M HCl solution prevents the formation of an elemental phosphorus layer, and hence no passivation by the formation of chromium enriched passive film occurs. Pitting corrosion occurred only in 12 M HCl but the pitting corrosion resistance can be improved effectively by the addition of chromium.

The Effect of Chromium Content (0 to 35%) in Fe-Cr Alloys on Corrosion Rates and Mechanisms in 1.0 N Sulfuric Acid

Abstract The effect of chromium content (0 to 35 percent) in Fe-Cr alloys on their dissolution in 1.0 N sulfuric acid was investigated. Corrosion rates increase with increasing chromium content. Corrosion rates were determined by three electrochemical techniques (Tafel extrapolation, three-point, and polarization resistance methods) and were compared with the rates determined by weight-loss measurements. The cathodic hydrogen evolution reaction is independent of the chromium content; that is, the exchange current density (i0) and the Tafel slope (βc) are essentially constant with changes in chromium content. The anodic Tafel constant (βa) for alloy dissolution is also independent of the chromium content. The increase in corrosion rates observed with increasing chromium content is directly proportional to the change in the active direction of anodic open-circuit potential and, therefore, also the corrosion potential in this case. Some effects of this phenomenon on pitting and crevice corrosion in chloride ...

Anodic polarization behaviour of Ni 60Nb 40 and Ni 55Cr 5Nb 40 glasses

The corrosion behaviour of Ni 60Nb 40 and Ni 55Cr 5Nb 40 metallic glass alloys in a 0.1 M H 2SO 4 solution has been investigated. Anodic polarization curves of these alloys suggest that a protective film is always present on the surface of the alloys. The thickness of this passive film was found to increase with increasing time. The open-circuit potential shifts in the noble direction on the replacement of 5 at.% Ni in the Ni 60Nb 40 glass by chromium and the transpassive stage is reached at +1500 mV with respect to a saturated calomel electrode for both the metallic glasses. This transpassivity of amorphous NiNb alloys was not expected in view of the stable nature of the niobium film. Auger electron spectroscopy of the passive film on these metallic glasses was carried out to obtain information about the thickness and composition of the passive film at various polarization potentials. The improved corrosion resistance of Ni 55Cr 5Nb 40 glass is due to the formation of hydrated chromium oxyhydroxide film, which contains chromium in excess of the alloy chromium content.

Effect of yttrium on the sulfidation behavior of Ni-Cr-Al alloys at 700�C

The sulfidation of Ni-10Cr-5Al, Ni-20Cr-5Al, and Ni-50Cr-5Al, and of the same alloys containing 1% Y, was studied in 0.1 atm sulfur vapor at 700°C. The sulfidation process followed linear kinetics for all the alloys except Ni-50Cr-5Al-1Y, and possibly Ni-50Cr-5Al, which followed the parabolic law. The reaction rates decreased with increasing chromium content in alloys without yttrium, and the addition of yttrium reduced the rates by at least a factor of two for the alloys containing 10 and 20% Cr and by an order of magnitude for Ni-50Cr-5Al. Alloys containing 10 and 20% Cr (with and without yttrium) formed duplex scales consisting of an outer layer of NiS1.03 and an inner lamellar layer of a very fine mixture of Cr2S3 and A12O3 in a matrix of NiS1.03. The two alloys containing 50% Cr formed only a compact layer of Cr2S3, which was brittle and spalled during cooling. The lamellae in the duplex scales were parallel to the specimen surface and bent around corners. The lamellae were thicker than those on Ni-Al binary alloys. The lamellae were also thicker in scales on the 20% Cr alloy than on the 10% Cr alloy. The presence of yttrium refined the lamellae and increased the lamellae density near the scale/metal interface in the 10% alloy, but in the 20% Cr alloy the lammellae were thicker and more closely spaced. Platinum markers were found in the inner portion of the exterior NiS1.03 layer close to the lamellar zone. A counter-current diffusion mechanism is proposed involving outward cation diffusion and inward sulfur diffusion, although diffusion was not rate controlling for alloys containing 10 and 20% Cr. Auger analysis of scales formed on Ni-50Cr-1Y showed an even distribution of yttrium throughout the layer of Cr2S3, suggesting that some yttrium dissolved in the sulfide. The reduced sulfidation rate of samples containing yttrium is explained by the possible dissolution of yttrium as a donor. The presence of Y4+ would then decrease the concentration of interstitial chromium ions in the N-type layer of Cr2S3, which would decrease the reaction rate.

Sulfidation properties of Fe-Cr alloys at 1073 K in H2S-H2 atmospheres of sulfur pressures 10?2 and 10?5 Pa

An investigation is reported on the sulfidation properties of Fe-Cr alloys over their complete compositional range in H2S -H2atmospheres at 1073 K. Sulfidation of alloys containing less than 60 at. % Cr obeyed parabolic kinetics and alloys of larger chromium content and chromium followed linear kinetics. Scales were composed of two distinct layers: an outer columnar grained sulfide and an inner equiaxed grained sulfide layer of increased relative thickness and porosity at larger alloy chromium contents. The scales on quenched specimens were composed of either (CrFe)5S6or (FeCr)S plus small amounts of (FeCr)3S4at\(P_{S_2 }\) =10−2Pa and of (CrFe)5S6at\(P_{S_2 }\) =10−5Pa. Internal sulfidation was most pronounced in the high chromium content alloys and at the low sulfur pressure. The parabolic sulfidation rate at\(P_{S_2 }\) =10−2Pa was large and of practically constant value irrespective of alloy composition. These kinetics at\(P_{S_2 }\) =10−5Pa, however, increased from a very low value by three orders of magnitude as the alloy chromium content was increased from 5–60 at.%.

高温濃厚苛性ソーダ溶液中におけるFe-Cr合金の腐食

A series of polarization and immersion tests on iron-chromium alloys with varing chromium contents were carried out in 48%-NaOH solution at various temperatures and the results obtained are summarized as follows.(1) The dissolution at acitive state decreases with increasing chromium content in alloys and does not occur when the chromium content is over 13% at 100°C and 24% at 140°C. (2) On increasing chromium content, the dissolution as FeO2− ion decreases. (3) At higher potentials, chromium in alloys easily dissolves as CrO42− ion and have no effect to inhibit the dissolution of iron in alloys. (4) Natural electrode potential of alloys containing up to 13%Cr are about Eh=−0.9 V. At 140°C, the natural electrode potential of a 18%Cr-Fe alloy shows a low potential of active state. (5) The corrosion rate logarithmically increases with increasing temperature. (6) The corrosion resistance severly increases with increasing Cr content over 25%. Especially, a 30%Cr-Fe alloy shows excellent resistance.

The isothermal oxidation of Co-Cr alloys in 760 Torr oxygen at 1000�C

The isothermal oxidation of Co-Cr alloys containing 0–30% Cr in 760 Torr oxygen at 1000° C has been studied kinetically and by appropriate physical techniques. Chromium additions to cobalt increase the parabolic oxidation rate to an almost constant level from 2 to 15% Cr, while further additions to 20–30% Cr decrease the rate. All the alloys produce a virtually pure CoO layer outside a layer containing Co-Cr spinel particles in a Cr3+ -doped CoO matrix. The variation of oxidation rate with alloy chromium content is explained in terms of the complex interplay of doping, blocking of cation transport by voids and spinel particles and short circuiting by transport of dissociative oxygen across these voids and other processes, internal oxidation making a negligible direct contribution to weight gain. Complete spinel layers are never quite developed under the conditions studied, although formation of spinel does slow the oxidation rate. The improved protection eventually obtained at higher chromium levels is produced by the tendency to form a Cr2O3 healing layer.

Nickel Oxide Scales and Sodium Sulfate-Induced Hot Corrosion of Nickel

Abstract The protection that a nickel oxide scale gives nickel metal against sodium sulfate induced hot corrosion is investigated in this research. The failure of a scale to protect the metal is attributed to infiltration, rather than dissolution, of the by molten salt along cracks and pores. The addition of chromium, chromium sesquioxide, or chromate ions to the sodium sulfate could not be shown to inhibit corrosion in spite of the fact that the chromium content of nickel base alloys is known to enhance their hot corrosion resistance. These results are consistent with a pseudo scale model of sodium sulfate induced hot corrosion for nickel base alloys rather than an acid base model. The addition of molybdenum, tungsten, or their oxidation products to sodium sulfate was found to increase the rate of corrosion. This increase is ascribed to an increase in the rate of infiltration of the scale by the molten salt as the result of an increase in the size or number of defects, which is also consistent with the p...

An ESCA study of the Fe 2+/Fe 3+ ratio in passive films on iron-chromium alloys

X-ray photoelectron spectra of Fe 2p 3 2 electrons are measured for passive films on iron and FeCr alloys passivated for 1 h in 1M H 2SO 4 at + 100 and + 500 mV (s.c.e.). When chromium content of FeCr alloys increased to ca. 12 at.%, binding energy of Fe 2p 3 2 electrons from oxidized state shifted abruptly from ca. 710·3 to ca. 709·6 eV and no more change in binding energy was observed at high chromium content. This abrupt shift of binding energy is in accord with the fact that the Fe 2+/Fe 3+ ratio showed sharp increase at ca. 12 at.% chromium. This phenomenon can be attributed to the inhibition of oxidation of iron due to the change in film structure and properties.

有機酸溶液中におけるステンレス鋼の腐食に関する研究 (第6報)

Polarization and weight loss tests on iron-chromium alloys were conducted in saturated monocarboxylic acid solutions. The results obtained were as follows:(1) The critical current density and passive current density decreased as increasing the chromium content in alloys.(2) Alloys of high chromium content began to dissolve in the hexavalent condition of chromium at a potential of about Eh=1.2V in the same manner as in inorganic acid solutions.(3) The corrosion rate of alloys containing up to 18% Cr was greater than that of pure iron in formic and acetic acid solutions. But, in propionic and butyric acid solutions, the corrosion rate decreased gradually as chromium content increased.(4) The corrosion rate decreased as increasing the carbon content in saturated monocarboxylic acids.

The sulfidation of dilute Co-Cr alloys at low sulfur partial pressures $$(p_{{\text{S}}_{\text{2}} } = {\text{5x10}}^{{\text{ - 4}}} {\text{Torr)}}$$

The sulfidation of pure chromium and Co-Cr alloys containing 1, 5, 10, 17, and 25 wt. % Cr in H 2-1%H2S at 1000°C has been studied in detail by thermogravimetric methods, metallography, and electron probe microanalysis. In this gas mixture, which has an effective sulfur partial pressure of 5×10−4 Torr, only CrS is formed, on all the alloys containing greater than 1 wt. % Cr, although there is some evidence that it may contain a little dissolved cobalt. The Co-1 Cr alloy is unattached. The sulfidation rate increases with increasing chromium content, the 25 wt. % Cr alloy corroding 100 times slower than pure chromium. Internal precipitation of CrS also occurs, the depth of the affected zone increasing with alloy chromium content. The rate-controlling mechanism appears to be the diffusion of chromium from the interior of the alloy to the alloy-scale interface, there being virtually no chromium remaining there. There is good qualitative agreement between the measured rate constants and values calculated from the rate of supply of chromium from the interior of the alloy.

The Transient Oxidation of Fe‐Cr and Ni‐Cr Alloys

The early stages of oxidation of Fe‐Cr and Ni‐Cr alloys, containing respectively nominally 5, 10, 15, and 30 a/o Cr, in 1 atm oxygen at 600°C have been studied by transmission electron microscopy of stripped films and by electron diffraction. Substantial amounts of iron and nickel oxides, respectively, are produced on all alloys before steady‐state, healing, chromium‐containing oxide layers are developed. This occurs more rapidly and more completely as the alloy chromium content is increased. For dilute Fe‐Cr and very dilute Ni‐Cr alloys, grain and subgrain boundaries and other substructural defects of the alloy are covered by thicker oxide. This is due either to their efficiency as cation vacancy sinks or to more local diffusional paths in the oxide above them. Conversely, for alloys richer in chromium (up to 30%), healing is most rapid in these locations due to rapid chromium diffusion to the alloy/oxide interface, leading to thin oxide above the defects. The tendency of rapidly growing iron oxides to overgrow the chromium‐containing oxides, and also to undermine them by encroaching on the alloy, is countered by the rapid development of a general healing layer of for the dilute Fe‐Cr alloys and for the concentrated alloys. probably does not form a healing layer for dilute Ni‐Cr alloys and the completion of a healing layer is slower than for Fe‐Cr alloys. This is largely due to the lower alloy interdiffusion coefficient. However, the slow growth of limits overgrowth and scale encroachment. healing is eventually approached by dense internal oxide formation, resulting partly from the relatively high solubility of oxygen in Ni‐Cr alloys.

Conditions of preparation of iron-chromium powders by the diffusion-impregnation technique

1. Data are presented on the effects of the amount of chromium in the starting charge on the chromium content of iron-chromium alloy powders of various compositions, obtained under different conditions of diffusion impregnation from point sources. It was established that the maximum chromium content of alloys of various compositions and maximum coefficients of chromium recovery from the starting charge correspond to a temperature of 1100°C. In addition, only a relatively small amount of chlorides remains in sponge after diffusion impregnation at this temperature. 2. The coefficient of chromium recovery from the starting charge in diffusion impregnation from point sources is higher than for impregnation from solid packing materials.

Chromium Oxide Scale Growth on Iron‐Chromium Alloys: II . Influence of Alloy Composition

, containing small quantities of dissolved iron, is the only oxide formed in the oxidation of iron‐chromium alloys in the range 22–68% Cr in oxygen at 800°–1200°C; it is also formed, at least initially, on alloys containing 14 and 18% Cr. The oxide growth is diffusion‐controlled, with an apparent activation energy of 36 kcal mole−1. The increase in oxidation rate with alloy chromium content is slight up to 37% Cr, but becomes more marked with the chromium‐rich alloys. Iron only enters the scale during the very early stages of oxidation, so the weight fraction of iron in the oxide decreases with time. Alloy interdiffusion coefficients have been determined from chromium concentration profiles in the underlying alloy. The activation energies for inter‐ diffusion are 51 and 59 kcal mole−1 for Fe‐27% Cr and Fe‐59% Cr, respectively, but interdiffusion is much slower for the chromium‐rich alloy. The chromium concentration at the alloy/oxide interface, which is determined largely by the ratio of oxidation rate to alloy interdiffusion rate, governs the type of oxide formed if lifting and cracking of the stressed scale occurs. Factors affecting the tendency for scale failure in this way are discussed.

Cr濃度を異にする高Cr-Fe合金の窒素中における窒素吸収について

Studies were made on the influence of the chromium content of high Cr-Fe alloys in the range from 15 to 25% of chromium on the nitrogen absorption at 1250°C in pure nitrogen. The results obtained were as follows:(1) When the chromium content was increased in high Cr-Fe alloys which had not been -added with both carbon and nitrogen, the nitrogen abrosption was promoted remarkably. While, the single austenite zone formed by the nitrogen absorption was not widened with increase of the chromium content.(2) High Cr-Fe alloys containing 0. 1% of carbon absorbed nitrogen more readily than those without carbon. The addition of 0. 1% of carbon formed a considerable amount of austenite in 15% Cr-Fe alloy before the nitrogen absorption, and the austenite accelerated The nitrogen absorption. The promoting effect of carbon on the nitrogen absorption was found to be more remarkable in this alloy than in alloys of higher chromium contents and with the same carbon content, in which almost all the structural constituents were consisted of ferrite.(3) Nitrogen pre-alloyed in high Cr-Fe alloys was found to retard the nitrogen absorplion though the austenite forming tendency of nitrogen was very similar to that of carbon. The effect of 0.1% of nitrogen in preventing the nitrogen absorption of high Cr-Fe alloys was not so marked in 15% Cr-Fe alloy as in alloys with higher chromium contents because of the formation of an appreciable amount of austenite in 15% Cr-Fe alloy by the prealloying of 0. 1% of nitrogen.(4) It was not always true that the higher the nitrogen content of high Cr-Fe alloys before the nitrogen absorption, the less the absorption rate. The nitrogen c3ntent of 25% Cr-Fe alloy containing 0.3% of nitrogen before the nitrogen absorption was found to have a high level of about 1. 0% in the single austenite zone by the nitrogen absorption at 1250°C for 4 hours. The strong absorption was presumably caused by the high chromium content and the fact that the pre-alloyed nitrogen was much enough to produce an appreci-able amount of austenite.(5) The single austenite zone of 15% Cr-Fe alloys consisted wholly of martensite when quenched in water immediately after the nitrogen absorption, while a considerable amount of austenite was retained in 20% Cr-Fe alloys. The austenite thus retained, however, was fully hardened by the subzero-treatment using liquid oxygen. In 25% Cr-Fe alloys martensite was no longer formed even by the subzero-treatment.(6) The retained austenite by the quenching in the single austenite zone which was formed by the nitrogen absorption was fairly stable against the heating at temperatures below about 600°C the nitrogen-containing austenite decomposed, however, rather readily by the tempering at above 600°C. in even 25% Cr-Fe alloy. The transformation from ferrite toaustenite on heating occurred at higher temperatures as the chromium content of alloys were raised, the change being found at about 1050°C in 25% Cr-Fe alloys.

マグネシウム合金の腐蝕(第8報)

An addition of chromium to magnesium alloys containing aluminium was tried by preparing a mother alloy with aluminium, and corrosion test was carried out in N/10 NaCl solution. It is shown that the addition of chromium for magnesium alloys containing aluminium, but not manganese, is markedly effective as that of manganese to reduce the rate of corrosion (Mg-Al-Zn-Cr alloys prepared with mother alloy Al-Zn-Cr containing 10-25% Cr, Table 2 and Fig. 2), but for magnesium alloys containing both aluminium and manganese it has no effect (Mg-Al-Mn-Cr alloys prepared with mother alloy Al-Mn-Cr containing 5-15% Cr, Table 1 and Fig. 1), or it is slightly effective (Mg-Al-Zn-Mn-Cr alloys containing more than 0.2% Mn which were prepared with mother alloy Al-Zn-Mn-Cr containing 5-25% Cr, Table 3 and Fig. 3). All alloys thus prepared, however, lost a large amount of chromium in melting, and found to contain only 0.01-0.03% Cr by analysis, irrespective of chromium content in mother alloys used and hence whether the beneficial effect is brought about by chromium addition or not is somewhat obscure. The effect of Sn, Cd, Pb, Ca, Sb, Bi, Si, Ce, Se, Ba, Mo, V or Zr added to Electron AZG alloy, containing small amount of chromium as above, has also been studied. The results obtained are shown in Fig. 4 and in Table 5 and 6.