ISIJ International
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ONLINE ISSN: 1347-5460
PRINT ISSN: 0915-1559

ISIJ International Vol. 29 (1989), No. 7

  • Surface and Grain Boundary Segregation on and in Iron and Steels

    pp. 529-538

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    DOI:10.2355/isijinternational.29.529

    The equilibrium segregation of the elements A=C, Si, Sn, N, P, O, and S was studied for binary systems Fe-A in the stability range of the α-solid solution using surface analytical methods. On the surfaces ordered structures were observed by LEED and surface concentrations were determined by AES in dependence on bulk concentration and temperature. The chemical binding state was characterized by XPS. In grain boundaries the segregation of P and Sn was determined by AES on intergranular fracture faces after equilibration at elevated temperatures and fracture in UHV. Effects of alloying elements, especially C, on grain boundary segregation are described. Correlations of surface and grain boundary segregation with the chemical and mechanical behavior of steels are shortly discussed.
  • Amorphous Alloy Surface

    pp. 539-549

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    DOI:10.2355/isijinternational.29.539

    Amorphous alloy surfaces and their surface-related properties including surface compositions of as-processed alloys, effects of surface treatments on the surface compositions, corrosion behavior, catalytic properties for electrochemical reactions, and methods for preparation of amorphous alloys for utilization of superior characteristics of amorphous alloy surfaces are reviewed. The majority of the surface-related superior characteristics of amorphous alloys is based on the homogeneous single phase nature capable of forming a solid solution even if it is supersaturated with various elements. This characteristic enables us to tailor novel materials having new, attractive, unique and useful properties by additions of sufficient amounts of necessary elements.
  • Composition and Properties of Platinum–Rhodium Alloy Surfaces

    pp. 550-559

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    DOI:10.2355/isijinternational.29.550

    The use of Pt–Rh based three-way catalysts for automotive exhaust gas control stimulated us to study the surface composition and surface properties of various Pt–Rh alloy samples. In this paper we shall review our results concerning the relation of the surface structure and surface composition with the physical and chemical properties.
    The surface composition was studied under various experimental conditions, both in vacuum and in the presence of an atmosphere of NO, O2, CO and H2. The effect of the temperature on the surface composition will be described and discussed on the basis of thermodynamics. We shall discuss the relation of surface composition with the physical properties (Debye Temperature) and with the chemical properties of Pt–Rh alloys, in particular towards NO, CO, O2 and H2 and their reactions.
    Another part of the paper deals with the effect of the surface structure on the chemical properties of Pt–Rh alloys. NO dissociation, the first step in the NO reduction with CO or H2, is extremely sensitive to both the structure and the composition of the surface.
  • Surface Segregation of Impurities and Hydrogen Transport Kinetics of First Wall Candidate Metals

    pp. 560-567

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    DOI:10.2355/isijinternational.29.560

    Surface segregation behaviors of several important metals which are proposed to be used as first wall material of the fusion reactor are briefly reviewed. Examples of such phenomena are presented for nickel, vanadium and stainless steel as were experimentally observed by the present authors. As experimental results showed, the surface phenomena of these metals were characterized initially by the segregation of impurity sulfur. But, in the case of nickel, as sulfur was depleted in the course of experiments due to ion bombardment, the surface was predominated by oxygen which was believed to have been adsorbed from the gas phase. This impurity segregation and adsorption also played an important role on the surface of stainless steel.
    The presence of surface impurities due to segregation and/or adsorption is shown here to affect the hydrogen isotope permeation behaviors of these metals. Especially sulfur and oxygen seem to have significant influence on the permeation rate. Strictly speaking, the presence of these impurities are considered to inhibit ''hydrogen recombination'' process at the surface. And with their strong electronegative properties, some kind of electronic effects must be responsible for lowering recombination coefficient kR, where it is demonstrated that accumulation of these impurities decreased kR by orders of magnitude.
  • Effects of Alloying on the Wettability of Copper to Carbon Fibers

    pp. 568-575

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    DOI:10.2355/isijinternational.29.568

    Various dilute binary copper alloys were coated onto the surface of carbon filbers. The wetting behavior of these alloys was examined by scanning electron microscope after heating the coated fibers at 1403 K. Tensile strength of the coated fibers was measured prior to and after the heat treatment. The measured results of the tensile strength were then analyzed by Weibull distribution theory. Alloying additions of Mo, Cr, V, Fe, and Co at one atomic fraction were found to be effective on the improvement of the wettability of copper to carbon fibers. Wetting mechanism was then discussed to conclude that such transition metals can be expected to cause wetting: those forming miscibility gaps in liquid state and having rather small solid solubility in copper in the binary system, and those being able to cause interface reactions. Interface reactions can be controlled by the rather small alloying additions so that the least degradation in the strength of carbon fibers could be resulted.
  • RHEED and AES Study of Si(111)√3×√3–R30° Structure Induced by Adsorption of Impurity Gases

    pp. 576-579

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    DOI:10.2355/isijinternational.29.576

    A √3×√3 RHEED pattern was first observed for a Si(111) surface annealed at about 900 K after exposure of hydrogen gas with a very small amount of impurity gases. A profile of C-KLL Auger electron spectrum is similar to that of SiC state. Annealing the surface at about 1100 K, SiC pattern was observed in the RHEED pattern. Rocking curves of RHEED intensities from the √3×√3 surface was similar to that from clean Si(111) 1×1 with diffuse √3×√3 surface at high temperature. Since the amount of carbon atoms were very small, it is considered that the √3×√3 structure is similar to that at high temperature and pinned by carbon atoms.
  • An Experimental Study of Making Magnetite Superconcentrate Blocks and Their Reduction by Solid Reductants

    pp. 580-588

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    DOI:10.2355/isijinternational.29.580

    A new solid state processing route for making steel strip has been proposed which basically consists of making sponge iron block directly from magnetite superconcentrate powder, followed by its hot and cold rolling. Preliminary experiments on the making of sponge iron block direct from magnetite superconcentrate powder have been made. They consist of mixing magnetite superconcentrate powder with a naturally occurring water soluble Babul gum binder. The mixture is compacted into a block shape which is subsequently reduced at high temperatures in a vertical shaft furnace with a variety of solid reductants to produce a sponge iron block. The effect of binder content and superconcentrate/water ratio on the crushing strength of green superconcentrate block has been studied. It has been shown that Acacia Arabica binder could produce a sufficiently strong block of magnetite superconcentrate at a low concentration. The reduction behaviour of the green superconcentrate blocks has been investigated using lignite char, charcoal and saw dust charcoal. Lignite char has been found to be a better reducing agent in comparison to other two. The structural changes occurring in the magnetite superconcentrate block during reduction is also discussed. It was observed that at 1 427 K, the block as a whole reduced in a topochemical manner, and the reaction interface was diffuse. At 1 273 K, the reaction interface was spread over the entire cross-section of the block. The carbon content of the sponge iron block was not same at all the areas of the block, and was a function of time at a given reduction temperature.
    It has been shown that it is possible to obtain crack free sponge iron blocks from magnetite superconcentrate blocks by reduction in a bed of solid reductant.
  • Numerical Analysis of Molten Steel Flow in Ladle of RH Process

    pp. 589-595

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    DOI:10.2355/isijinternational.29.589

    As the result of the analysis of molten steel flow in a ladle during 310 t RH treatment by the use of a three-dimensional fluid analysis program, the following facts have been found:
    (1) In the actual ordinary operational conditions of the flow velocity of molten steel discharged out of a down snorkel, by-pass flow does not take place between the down snorkel and up snorkel, and also the effect of a center-to-center distance of the snorkels on the generation of such by-pass flow is little.
    (2) When the sectional area of the snorkel is small, a stagnating phenomenon occurs over the whole surface of ladle bath. Whilst, when a circulation rate is increased by enlarging the sectional area of the snorkel, the mixing of the bath in the ladle is improved.
    (3) As for the equipment characteristics, it is more advantageous to increase RH decarburization rate when the snorkel sectional area is large.
    x

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  • Morphology of Iron Reduced from Wustite with H2–H2O–H2S Mixtures

    pp. 596-604

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    DOI:10.2355/isijinternational.29.596

    The reduction of pure wustite plates with H2–H2O–H2S mixtures has shown that the overall reaction rates are varied over several orders of magnitude in response to the product morphology, which are Type A (porous iron), Type B (porous wustite covered with dense iron), and Type C (dense wustite covered with dense iron), depending on its temperature, the oxygen and sulphur potentials in reducing gas, and cation defect concentration in wustite.
    The reduction of wustite doped by traces of sulphur and the reduction experiment of changing from initial gas composition into different one were also conducted on the emphasis of the action of sulphur.
    The results indicated together with the result of Auger electron spectroscopy that sulphur segregates more strongly on the surface of metallic iron rather than wustite and at the same time into the interface between them during reduction.
    On the basis of these knowledge, the iron morphologies were interpreted by a mechanism composed of several experimental conditions and factors affecting the nucleation and growth of iron.
    x

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  • A Theoretical Study on Nozzle Design for Gas–Particle Mixture Flow

    pp. 605-613

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    DOI:10.2355/isijinternational.29.605

    The theoretical equations governing the nozzle flows of a gas–particle mixture was extended to the complicated case where a continuous distribution of particle sizes is present and some calculation examples were demonstrated in the previous paper. But, the governing equations were applicable only to the case where the gas–phase velocity is subsonic. Then, we have, here, rewritten an equation to obtain the gas–phase velocity in the form different from the previous case so that the governing equations are valid to the whole gas velocity region including the supersonic flow. Thereby, a few sample calculations have been illustrated for supersonic mist flows composed of air and water–particles, which are commonly applied to the secondary cooling zone of continuously cast slabs. The results so obtained have been discussed from a numerical point of view. Also, it has been shown that the nozzle geometry can be designed in accord with the pressure profile given along a nozzle axis in advance.
  • Progress in Materials for Can Stock and Future Trends

    pp. 614-624

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    DOI:10.2355/isijinternational.29.614

    Developments in electrolytic tin plate, tin-free steel and more recent low tin materials are described with emphasis on their corrosion performance and their applicability to the newer can manufacturing processes. The significance of tinplate special property tests and their relative importance are discussed as related to corrosion performance in cans for moderate to high corrosivity food products. Information regarding pitting corrosion of aluminum killed continuous cast tinplate in cans for light colored fruits is also reviewed. Tin-free and low tin materials are being used in drawn and welded cans, but better enamel coverage is required than for tinplate cans. Long term trends show that aluminum has taken over most of the beer and soft drink market but its use in food cans remains very limited. New processable multilayer plastic barrier materials have been introduced as cans, bowls and trays for single serving microwaveable foods, which could have a significant impact on metal cans. The solid waste issue and recyclability of the various materials is discussed. A new process for improving the quality of shelf stable processed foods is also described.

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