Showing papers on "Chromium published in 1972"
TL;DR: In this paper, it was shown that the scale-forming reaction of Ni-20 wt. % Cr2O3 scales on dispersion-free systems must involve shortcircuit diffusion of chromium through the scale, and that it seems probable that an effect of the dispersion must be to retard or eliminate this short-circuit process.
Abstract: Alloys of Ni-20 wt. % Cr containing 3 vol. % of a dispersed oxide phase have been prepared by a mechanical alloying method and oxidized in oxygen at 100 Torr in the temperature range of 900 to 1200°C. It appears that the dispersed oxide has four distinct effects on the oxidation: (1) the selective oxidation of chromium to form a continuous protective Cr2O3scale is promoted; (2) the rate of growth of Cr2O3is reduced compared with particle-free alloys; (3) the adhesion of the Cr2O3is greatly improved; and (4)the scale-forming reaction appears to be at the scale-metal interface in alloys containing a dispersion, but at the scale-oxygen interface in alloys without a dispersion. It appears that the nature of the dispersed oxide is not important, since very similar effects can be obtained with ThO2,Y2O3,and CeO2dispersions. It is demonstrated that a logical deduction from this evidence is that the growth of Cr2O3scales on dispersion-free systems must involve short-circuit diffusion of chromium through the scale, and that it seems probable that an effect of the dispersion must be to retard or eliminate this short-circuit process. It is suggested that the oxide particles act as nucleation centers for the oxide, thus reducing the oxide grain size; and it is shown that this simple hypothesis is sufficient to explain a number of the experimental observations.
266 citations
TL;DR: In this article, the two phase diffusion between chromium and tungsten, forming b.c. solid solutions, has been followed right from the beginning by means of a special X-ray diffraction technique, light microscopy and electron microprobe analysis.
150 citations
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148 citations
TL;DR: In this paper, the authors examined the basis of intergranular corrosion in austenitic stainless steels by relating the grain boundary composition to the corrosion properties and found that the chromium depleted zones exist and that the depletion theory was valid for tests in weakly oxidizing solutions, however, the impurity segregation and not chromium depletion best explains the deterioration of corrosion properties.
Abstract: The basis of intergranular corrosion in austenitic stainless steels is examined by relating the grain boundary composition to the corrosion properties. The technique of Auger electron spectroscopy has been used to obtain the chemistry of intergranular fracture surfaces. It was found that the chromium depleted zones exist and that the depletion theory was valid for tests in weakly oxidizing solutions. In highly oxidizing solutions, however, the impurity segregation and not chromium depletion best explains the deterioration of corrosion properties. Impurity elements such as sulfur, silicon, nitrogen, and phosphorous were observed in the various steels examined. An attempt is made to explain the observed corrosion properties on the basis of chromium depletion and solute segregation theories combined with an electrochemical mechanism.
116 citations
115 citations
TL;DR: In this article, the scale-forming reaction is probably at the scalemetal interface in the alloys containing the dispersoid, whereas it is at scale-oxygen interface in dispersoid-free alloys.
Abstract: Alloys of Co-21 wt. % Cr-3 vol. % Y2O3have been prepared by a mechanical alloying method, and oxidized in oxygen at 100 Torr in the temperature range 900–1200°C. The general effects of the dispersed oxide phase are similar to those reported for nickel-base alloys: the selective oxidation of chromium to form a continuous protective Cr2O3scale is promoted; the rate of growth of Cr2O3is reduced compared to dispersoid-free alloys; the adhesion of the Cr2O3is greatly improved; and the scale-forming reaction is probably at the scale-metal interface in the alloys containing the dispersoid, whereas it is at the scale-oxygen interface in dispersoid-free alloys. This last point has not been positively demonstrated. The improvement in adhesion is of particular significance, since the scales on cobalt-base alloys are prone to spallation, and it has been possible to study the mechanism of adhesion in more detail. It appears that in dispersoid-free material the metal recedes from the scale-metal interface, leaving the scale supported on the tops of metal “peaks” but this does not happen in the alloy containing the dispersoid, either because the growth direction of the scale has been changed, or because of changes in the substrate grain size. In general, the observations support the model proposed in an early study for the oxidation of Ni-20 wt.% Cr alloys containing oxide dispersions.
80 citations
TL;DR: In this article, the interaction of chlorides of V, Cr, Mo, and W with the lithium or Grignard reagents derived from chloromethyltrimethylsilane produces thermally stable alkyls of formula V(CH2SiMe3)4, VO(CH 2SiMe 3)3, Cr(Ch2SiMo3) 4, and M2(M = Mo or W).
Abstract: The interaction of chlorides of V, Cr, Mo, and W with the lithium or Grignard reagents derived from chloromethyltrimethylsilane produces thermally stable alkyls of formula V(CH2SiMe3)4, VO(CH2SiMe3)3, Cr(CH2SiMe3)4, and M2(CH2SiMe3)6(M = Mo or W). The compounds have been investigated, where feasible, by i.r., Raman, electronic, e.s.r., and n.m.r. spectroscopy and the various spectral assignments are discussed in terms of proposed structures for the compounds.
78 citations
75 citations
72 citations
TL;DR: In this article, absolute secondary ion yields from cleaned and oxidized metal surfaces (Mg, Al, V, Cr, Fe, Ni, Cu) and from silver surfaces covered with different anions (Cl, -CN, -NO 3, -SO 4 ) were measured.
TL;DR: In this paper, a trigonally co-ordinated transition metal series has been characterized by analysis, molecular weight determination, and mass spectra, and the compounds M[N(SiMe3)2]3, where M = Sc, Ti, V, Cr, and Fe, have been prepared by reactions involving metal chloride complexes and the lithium derivative of hexamethyldisilazane.
Abstract: The compounds M[N(SiMe3)2]3, where M = Sc, Ti, V, Cr, and Fe, have been prepared by reactions involving metal chloride complexes and the lithium derivative of hexamethyldisilazane. The compounds have been characterized by analysis, molecular weight determination, i.r., and mass spectra. They are members of a trigonally co-ordinated transition metal series.
01 Apr 1972-Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science
TL;DR: In this paper, the compositional ranges for the σ phase in the Cr-Ni, Cr-Fe, and Cr-Co systems are from low chromium to 68, 63.4, and 62.1 wt pct Cr, respectively.
Abstract: Structural analyses were performed on alloy particles of chromium-rich Cr-Ni, Cr-Fe, Cr-Co, and Cr-Ni-Fe systems. Fine alloy particles (100 to 1000A in diameter) were prepared by evaporation of parent alloys in argon at 20 torr. In addition, alloy structures of bulk specimens of the Cr-Ni system were investigated using X-ray diffraction techniques to confirm the results obtained from the particulate alloys. In these binary systems, δ phase with W3O structure (A-15) and a phase withβ-uranium structure (D
8
) were identified in addition to the α (bcc) and γ (fcc) terminal solid solutions. The compositional ranges for the σ phase in the Cr-Ni, Cr-Fe, and Cr-Co systems are from low chromium to 68, 63.4, and 62.1 wt pct Cr, respectively. The δ phase exists in the range from pure chromium to 68, 58, and 54 wt pct Cr in the respective Cr-Ni, Cr-Fe, and Cr-Co alloy systems. Similarly, in the Cr-Ni-Fe system, it was found that δ phase occurs in the chromium corner while σ phase exists in the region bridging the two binary σ phases of the Cr-Ni and Cr-Fe systems. Possible modification of phase diagrams of these systems is discussed in view of these results.
TL;DR: In this article, the preparation and several reactions of tricarbonyl(phenylacetylene)chromium and tricarbonel(styrene) chromium are described.
TL;DR: In this paper, the initial stages in the oxidation of (100 and (110) chromium surfaces have been studied using reflection high energy electron diffraction under ultra high vacuum conditions.
TL;DR: The strength of metal-ceramic bonds with base metals containing chromium with respect to each other has been studied in detail for the first time in a preliminary report.
Abstract: The strength of metal-ceramic bonds with base metals containing chromium. A preliminary report
TL;DR: The pitting of pure iron and its alloys with chromium and copper, in neutral chloride solutions, has been studied using microscopy and time-lapse photography, and measurements have been made of local variations of pH value and electrode potential using micro-electrodes as mentioned in this paper.
Abstract: The pitting of pure iron, and its alloys with chromium and copper, in neutral chloride solutions, has been studied using microscopy and time-lapse photography, and measurements have been made of local variations of pH value and electrode potential using micro-electrodes. Primary pitting at a few discrete points is followed by secondary pitting at a large number of points. On pure iron the pits are generally polygonal in shape, while with chromium-iron alloys the shape is less regular and attack is confined to grain boundaries. Facetting of the metal surface within the pits is commonly observed.The initial growth of pits corresponds to a current density of up to 1 A/cm2 but this rapidly decreases and, following accumulation of corrosion product, the corrosion rate settles down to a relatively low figure. The long-term penetration rate is reduced significantly by small alloying additions of copper.pH differences of up to 8 units have been measured between the pitted area (acid) and the surrounding u...
TL;DR: Both selenides and tellurides can be used for potentiometric determination, but the manganese(II) electrode serves as an analytical tool only when the disc consists of manganized telluride and silver sulphide.
TL;DR: In this paper, it was shown that porosity is mainly controlled by the concentration of particles in suspension rather than the current density, and the best method of controlling the dendritic growth at present depends on mechanical methods such as rotating cathodes with sponge covered scrapers.
Abstract: SummaryThe wellknown high speed nickel sulphamate bath has been used to codeposit chromium particles to give high rates of electrodeposition required in forming. Electrodeposition in the presence of conducting particles generally leads to a dendritic-like growth and porous deposits. Our investigations have shown that Cr content is mainly controlled by the concentration of particles in suspension rather than the current density. The factors affecting porosity have been studied; the best method of controlling the dendritic growth at present depends on mechanical methods such as rotating cathodes with sponge covered scrapers. Several experiments have been carried out in order to elucidate the mechanism and the results suggest that low porosity in electrodeposits would be obtained if sub-micron particles were used for codeposition.
TL;DR: In this paper, the authors investigated the correlation between the kinetics of oxidation and the morphologies and compositions of the chromic oxide scales produced and found that the formation of chromic oxides is associated with the maximum oxidation resistance of alloys with greater than 20% chromium.
Abstract: The oxidation behavior of iron-chromium-nickel alloys containing 0–30% chromium has been determined for oxidation at 1000°C in static pure oxygen atmospheres. Particular emphasis has been placed on the correlation between the kinetics of oxidation and the morphologies and compositions of the scales produced. Maximum oxidation resistance was associated with the formation of chromic oxide scales on alloys containing greater than 20% chromium. The loss of an oxide species from these scales by volatilization may limit the usefulness of alloys protected by chromic oxide scales to a temperature less than 1000°C.
01 Sep 1972
TL;DR: In this paper, a torsion-effusion technique was used to measure the pressure of carbon monoxide in equilibrium with a Cr23C6-Cr2O3-Cr mixture and a Cr7C3-C2O 3-Cr 23C6 mixture at temperatures between 1100 and 1300 K.
Abstract: The pressures of carbon monoxide in equilibrium with a Cr23C6-Cr2O3-Cr mixture and with a Cr7C3-Cr2O3-Cr23C6 mixture have been measured in the temperature range 1100 to 1300 K using the torsion-effusion technique. From the equilibrium data, the following equation for ΔGof of Cr23C6 (in cal per mole) has been calculated: ΔGf° (±1200) = −77,000 - 18.3T (1150 to 1300 K) Combining the results of this study at temperatures between 1100 and 1300 K with those of Kelleyet al.,3 at temperatures between 1500 and 1720 K, the following equation for ΔGof of Cr7C3 (in cal per mole) has been determined: ΔGf° (±400) = −35,200 - 8.7T (1100 to 1720 K) ) The above equation for ΔGof of Cr7C3 has been used to re-evaluate the equilibrium data of Kelleyet al.,3 and the following equation for ΔGof of Cr3C2 (in cal per mole) has been obtained: ΔGf° (±400) = −16,400 - 4.4T (1300 to 1500 K) CHROMIUM reacts with carbon to form three carbides:1,2 Cr23C6, Cr7C3, and Cr3C2. The chromium carbides are of considerable technical importance because of their precipitation behavior in certain high-chromium steels and superalloys. A precise knowledge of their thermodynamic properties is essential for the understanding and the prediction of their chemical behavior in various environments.
TL;DR: Tetra-t-butylchromium was prepared from CrCl 3 ·3THF and t-butyllithium in pentane by a disproportionation reaction.
01 Jan 1972-Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science
TL;DR: In this paper, the authors investigated the self-sustaining mechanism of chromium sulfide formation in the absence of Na2SO4-ash deposits and found that the total amount of sulfur was conserved in the sample even up to 300 hr of oxidation.
Abstract: It has been proposed in the literature that sulfidation of nickel-base alloys in the presence of Na2SO4-ash deposits, is a self-sustaining reaction, in that once chromium sulfides are formed in the metal, subsequent oxidation of the sulfides can liberate the sulfur and nucleate new chromium sulfide particles along an advancing front. The applicability of this mechanism to sulfidation reactions occurring in the absence of Na2SO4-ash deposits was investigated by exposing samples of an 85 Ni-15 Cr alloy which had been presulfidized in a SO2-N2 mixture, to an O2-N2 mixture for 30, 200, and 300 hr at 1600∮F. A progressive inward migration of chromium sulfides was revealed by metallographic measurements. By chemical analysis the total amount of sulfur was found to be conserved in the sample even up to 300 hr of oxidation. These results are consistent with the following self-sustaining model. 2Cr3S4+ 9O 3Cr2O3+ 8S 8S+ 6Cr 2Cr3S4
TL;DR: The morphology of the oxide has been studied using stereo scanning electron microscopy, coupled with backscattered electron photographs to locate the thoria particles in the surface of the chromium oxide as discussed by the authors.
Patent•
18 Oct 1972
TL;DR: A powder metallurgy product comprising iron and chromium, and/or aluminum and characterized by elongated grains that are stable at elevated temperatures was described in this article, where a method of producing such a product, including mechanically alloying a suitable powder charge, consolidating the mechanically alloyed powder, working the consolidated product so as to achieve therein a reduction of at least about 10%.
Abstract: A powder metallurgy product comprising iron and chromium, and/or aluminum and characterized by elongated grains that are stable at elevated temperatures. A method of producing such a product, including mechanically alloying a suitable powder charge, consolidating the mechanically alloyed powder, working the consolidated product so as to achieve therein a reduction of at least about 10%; and, then, heating the worked product to produce coarse elongated grains therein. The product produced according to the present invention exhibits good oxidation resistance and good room temperature and elevated temperature strength and ductility.
TL;DR: In this article, the authors measured the impedance of a chromium electrode over the frequency range 20 kHz − 10−2 Hz through the active-passive transition in sulphuric acid and showed that there is a coupling between the dissolution reaction and the relaxation of adsorbed O species on the electrode surface.
TL;DR: In this paper, the room temperature adsorption of nitrous oxide on α-chromia has been studied by means of IR spectroscopy and two different processes occur: (i) a rapid decomposition leading to a selective coverage of surface chromium sites with oxygen adsorbed through a quasi-double bond.