Kinetics of disilicide layer growth at the interface of tungsten with molten copper, silver, and tin saturated with silicon

The kinetics of WS₂ layer growth at the interface of tungsten with molten metals saturated with silicon is studied. Research is performed at 1200°C using melts based on copper, silver, and tin. It was established that WSi₂ layer growth in these melts obeys a “parabolic” rule but the corresponding growth rate constants differ markedly, i.e., from 3.4·10^?11 m²/sec (melt based on copper) to 1.5·10^?13 m²/sec (melts based on silver and tin). The reasons for this difference are discussed.     

Evaluation of Thermal Stability of Multilayered Nanostructured Coatings Based on Analysis of Diffusion Mobility of Components of the Layers

The thermal stability of multilayered nanostructured coatings is evaluated by analyzing the diffusion mobility of layer components. The possibility of increasing the thermal stability of multilayered coatings based on mutually soluble Ti–Al–N and Cr–N layers due to the introduction of an additional barrier layer based on Zr–N into a multilayered nanostructure is investigated in detail. Calculated diffusivities of basic metallic elements of the coating into corresponding nitride layers upon heating in a temperature range of 800–1000°C evidence the absence of noticeable diffusion spread of layer boundaries in the presence of the Zr–N-based barrier layer. For example, their values lower upon its introduction (it is found at t = 1000°C, cm²/s: D_Cr/TiN = 5 × 10^–17, D_cr/ZrN = 2 × 10¹⁸, \({D_{Ti/C{r_2}N}}\) = 9 × 10^–18, and D_Ti/ZrN = 3 × 10^–18). The physicomechanical properties of coatings do not vary upon their vacuum annealing at t < 900°C; however, they noticeably lower with a further increase in temperature due to the degradation of a multilayered coating structure during annealing.     

Assembling Tunable Time-Resolved Fluorescence Layer onto Nano-Gold

The assembling of a coating of time-resolved fluorescent chelator BSPDA （ abbreviated for 4, 7-bis （ sulfhydrylphenyl）-1, 10-phenanthroline-2, 9-dicarboxylic acid） onto a nano-gold layer was demonstrated. First, BSPDA was synthesized by simple procedures, and then an approach was developed to immobilize BSPDA onto the nano-gold layer deposited on a silane modified glass substrate, whereby europium ion （Ⅲ, Eu^3＋ ） was captured and released owing to the interactive process of complexation and dissociation between BSPDA functionalized coating and Eu^3＋ solution. The fluorescence spectra and related lifetimes were determined. Also, the BSPDA functionalized coating＇s specific complexation with Eu^3＋ on the BSPDA assembly layer and the nonspecific adsorption of Eu^3＋ on the nano-gold layer were compared. These results allowed a selective complexation of Eu^3＋ by assembling a BSPDA chelating layer on the nano-gold layer; thus, a tunable time-resolved fluorescent layer was covalently attached, The results of the nanoparticle assembling and probing （or labeling） processes to specific bio-systems were very interesting and had significant implications to time-resolved-fluorescence-based detection on biosensor surfaces such as DNA chip and to arrayed light display devices.     

Solar spectral conversion based on plastic films of lanthanide-doped ionosilicas for photovoltaics:Down-shifting layers and luminescent solar concentrators

The mismatch between the photovoltaic(PV) cells absorption and the solar irradiance on earth is one of the major limitations towards more efficient PV energy conversion.This aspect was addressed by downshifting the solar irradiance on Earth through luminescent down-shifting layers based on lanthanidedoped surface-functionalized ionosilicas(ISs) embedded in poly(methyl methacrylate)(PMMA) coated on the surface of commercial Si-based PV cells.The IS-PMMA hybrid materials exhibit efficient solar radiation harvesting(spectral overlap of ～9.5 × 10~(19) photons/(s·m~2)) and conversion(quantum yield～52%).The direct solar radiation and the down-shifted radiation are partially guided and lost through total internal reflection to the layer edges being unavailable for PV conversion of the coated PV cell.By tuning the down-shifting layer thickness,it also acts as luminescent solar concentrator enabling the collection of the guided radiation by flexible PV cells applied on the borders of the down-shifting layer leading to an enhancement of the PV energy conversion from ～5%(in the case of the single-use of the luminescent down-shifting layer) to～13% comparing with the bare PV cell.The overall electrical output of the device resulted in an absolute external quantum efficiency increase of～32% for the optimized Eu~(3+)-based films in the UV spectral region(compared with the bare PV device,which is among the best values reported so far).     

Leaching of lead sulphate in sodium carbonate solution

The recovery of lead from scrap lead acid batteries by pyrometallurgical processes is generally accompanied by emissions of sulphur dioxide and lead-containing particulates into the atmosphere. The latter two products are undesirable as they lead to serious environmental problems. In an effort to overcome these difficulties, a sodium carbonate leaching process was investigated. In the present contribution, the leaching reactions of pure lead sulphate in sodium carbonate solutions are discussed from both a thermodynamic and kinetic aspect based on the experimental results obtained on leaching rates, stoichiometry of the reaction and X-ray diffraction analysis of the reaction products. A mass transfer model based on the diffusion of CO₃^2? ions through a solution boundary layer is proposed to account for the leaching rates.     

The effect of electrolyte composition on the cathodic reduction of CuFeS2

The electrochemical reduction of CuFeS₂ mineral electrodes has been investigated by performing cathodic polarization curves, constant potential experiments, and cyclic polarization curves in various electrolytes. The effects of H₂SO₄, Fe²⁺ and Cu²⁺ concentrations have been examined as well as the effects of various dissolved gases, air, O₂, H₂S and N₂. Decreasing H₂SO₄ only shifts the curve to more negative potentials but initial concentrations of 0.36 M Fe²⁺ cause up to a ten-fold enhancement in the observed current. The presence of oxygen or Cu²⁺ also leads to an increase in the reduction current but in either case further increases in current are observed when Fe²⁺ is added to the electrolyte. Chalcocite (Cu₂S) or djurleite (Cu_1.96S) have been identified as products of reaction, although it is possible that a thin layer of a different copper-iron sulfide may form as an intermediate based on the color changes which appear after cathodic excursions. In addition, scanning Auger microprobe analyses of these surfaces show an increasing Cu:Fe ratio as the time at potential is increased. The results also indicate that the solid product layer is porous. A mechanism which accounts for the observed current increase in the presence of Fe²⁺ is proposed which involves a redox reaction between dissolved Fe²⁺ and cupric ion in the copper sulfide product layer.     

Effect of the electrospark alloying regime on the durability of high-speed steel R6M5K5 cutters

The effect of electrospark alloying with refractory compounds based on WC, TiC, TiN, and TiB₂ on the mechanical and service properties of high-speed steel R6M5K5 cutters was investigated. Increasing the electrospark discharge energy by increasing the current strength to 3 A, and the specific alloying time to 1.2–1.8 Msec/m², increased the alloyed layer depth, but decreased the microhardness. Further increase of alloying time did not produce further increase in layer depth. The optimal regimes of electrospark alloying were determined from durability tests of the hardened cutting tool. The greatest increase in durability (by 1.3–1.4 times) was obtained at I=1.5–2 A, τ=0.9–1.5 Msec/m², at which values the optimal combination of hardness and coating depth was attained.     

The anomalous behavior of Schottky barrier diodes made on lightly doped GaAs

When Schottky barrier diodes are used to evaluate lightly dopedn type (n～10¹⁵ per cu cm) epitaxial GaAs onn ⁺ substrates, the diodes do not always have the expected varactor characteristics. The capacitance variation with bias is sometimes too small, and the voltage intercept on the 1/C ² vsV plot too high. This behavior has been attributed either to a thin intrinsic semiinsulating layer between substrate and epi layer,¹ or to deep trap impurities in the epi layer.² The effects seen in this work are shown to be due to traps by the dependence of diode characteristics on heat, light, and frequency. These diodes also have conductances which decrease with reverse bias. The model of Sah and Reddi³ leads to a reduction in high frequency junction capacity and capacitance-bias variation range. The large, bias dependence conductance observed in our diodes must also be explained, however. A schematic model is proposed in which a series resistancer, due to the resistance of the undepleted epi layer at high frequency, is shunted by a capacitanceC _u, also due to the undepleted layer. A junction conductance 1/R is in parallel with the junction capacitanceC. The equivalent circuit seen by the capacitance bridge, used for obtaining data, is a measured capacitanceC _m in parallel with the measured shunt resistanceR _m. Much of the observed diminution of capacity and varactor action can be accounted for in terms of this model. The series resistancer seems to be large only at high frequencies, and is associated with the traps in the epi layer.     

Electrowinning copper at high current densities

Agitation of the electrolyte by gas sparging was studied as a means of intensifying the electrowinning of copper. Diffusion layer profiles at the cathode were quantitatively measured using a new technique based on the mass transfer controlled codeposition of a tracer metal ion. Smooth, good quality cathodes were produced in a prototype cell at current densities up to 30 A/dm² (270 asf). B. V. TILAK, formerly also with the J. Roy Gordon Research Laboratory is now with the Hooker Research Center, Niagara Falls, N.Y. 14302. This paper is based on the presentation made at the 102nd Annual Meeting of AIME, Chicago, 1973.     

The microstructures and properties of an al- 12 wt pct

A new process for producing rapidly solidified bulk alloys was developed based on the hammer- and-anvil concept. In the process, an A1-12 wt pct Si alloy slab was built up layer by layer and then hot worked to get a solid and integral sheet. The oxygen content of the layer-deposited alloy is less than the typical value of powder metallurgy (PM) alloys by one order, and the cooling rate can reach 10⁴ K/s, which is higher than that of the spray deposition process. In comparison with the ingot-processed Al-12 wt pct Si alloy, layer-deposited alloy exhibits su- perior mechanical properties. This is attributable to the fine and uniform silicon-particle distri- bution which not only brings on dispersion hardening effect but also raises the elongation and fracture strain. The mechanisms responsible for this enhancement were discussed in terms of particle size and effective volume fraction.     

Development of Functionally Graded Sintered Hard Materials

Abstract

Functionally graded materials consisting of two different materials with a graded interlayer have attracted much interest for their ability to exhibit the characteristics of the individual materials plus new functionality. This concept was applied to the field of hard materials. The developed material consists of a titanium based ceramic surface layer, a tough cemented carbonitride core containing Bl type and WC phases, and an intermediate layer with graded composition. The surface region is characterised by a high compressive residual stress of 0·8 GN m^?2. When applied in the form of cutting tools, the material was found to have an abrasion resistance and fracture toughness much higher than those of a conventional cermet of uniform composition. Because of the graded composition, the ceramic surface layer has high adhesive strength, providing longer life than coated tools when spalling of the film can occur easily. The new material is produced by controlled sintering of a green compact of uniform composition. PM/0743     

Modeling the heat flow to an operating sirosmelt lance

A mathematical model of the heat flow to a Sirosmelt lance is presented, which predicts lance wall and air temperatures and the thickness of the slag layer on the lance. By measuring the distribution of wall temperature and slag thickness on an operating Sirosmelt lance, the model was used to determine both the heat-transfer coefficient between the vessel contents and the lance and the thermal conductivity of the slag layer. The slag layer thermal conductivity was found to be within the range of 0.5 to 1.1 W m⁻¹ K⁻¹, while the outside heat-transfer coefficient varied from 80 to 150 W m⁻² K⁻¹, both of which are smaller than quoted in the literature for metal/slag systems. The discrepancy was attributed primarily to the large quantities of combustion gases that envelop the lance and reduce convection and conduction from the melt to the lance. Other factors causing low thermal conductivity and a low heat-transfer coefficient include the thermal resistance at the slag/lance interface and the mushy region on the outside of the slag layer.     

Growth of a layer of W6Co7 phase in systems with participation of phases containing cobalt

Growth kinetics for a layer of W₆Co₇ at the interfaces tungsten-cobalt and tungsten-melts based on copper and tin containing cobalt at 1200 °C are studied. It is established that rate constant for growth of this layer in the system with participation of tin (k_Sn) is much greater than in the system with copper (k_Cu). Dependences are determined for these constants on cobalt activity in the melt (a_Co): k_Cu(m²/sec) = = 1.72 · 10^?15(a_Co ? 0.221) + 2.99 · 10^?14 (a_Co ? 0.221)²; k_Sn(m²/sec) = 1.8 · 10^?14 (a_Co ? 0.221) + + 9.077 · 10^?12 (a_Co ? 0.221)³.     

Uranium sorption from phosphoric acid solutions using selective ion exchange resins: Part II. Kinetic studies

Experiments have shown that the sorption of uranium from strong phosphoric acid solutions onto four D2EHPA/TOPO based ion exchange resins and one aminophosphonic acid resin is particle diffusion controlled in the uranium concentration range 42–780 μM. Interdiffusion coefficients of about 10^?12 m²s^?1 were obtained for D2EHPA/TOPO resins and 0.14 × 10^?12 m²s^?1 with the aminophosphonic acid exchanger at 20°C in 3 M H₃PO₄. Both homogeneous particle diffusion, based on Fick's Law, and the ash layer diffusion model fitted the kinetic measurements.     

Vibration damping characteristics of laminated steel sheet

The use of laminated steel sheets as vibration damping materials was studied. The laminate consisted of a viscoelastic layer which was sandwiched between two steel sheets. The study sought to identify parameters affecting the damping efficiency of the laminate. Two viscoelastic materials, a copolymer based on ethylene and acrylic acid (PEAA) and polyvinyl butyral (PVB), were used. A frequency analyzer was used to measure the loss factor of the laminates. A theoretical analysis of damping efficiency based on a model described by Ungar^[2] was also carried out. The results showed that the loss factor of the PEAA-based laminates increased monotonically with increasing thickness of the viscoelastic layer and leveled off at 25.9 pct of total thickness. Ungar’s theory predicted a higher loss factor than the experimental data. This might have resulted from interfacial adhesive bonding, a nonuniform viscoelastic layer thickness, and the extrapolation of the rheological data from low to high frequencies. The loss factor of the laminate increased with increasing temperature, reached a maximum value, and then decreased. An optimum temperature for maximum damping was found for each laminate configuration. The PEAA-based laminates possessed higher damping efficiency than the PVB-based laminates at room temperature. The symmetric laminate (with the same steel sheet thickness) possessed a better damping efficiency than asymmetric laminates. The maximum damping peak of the laminates using a polymer blend, when compared to the laminates using unblended resin, exhibited a lower loss factor value, became broader, and occurred at a temperature between theT _g’s of the individual components of the polymer blend. This paper is based on a presentation made in the symposium “Acoustic/Vibration Damping Materials” presented during the TMS Fall Meeting, Indianapolis, IN, October 1–5, 1989, under the auspices of the TMS Physical Metallurgy Committee.     

Dynamic reactive wetting and its role in hot dip coating of steel sheet with an Al-Zn-Si alloy

The effect of substrate preheat temperature on the dynamic wetting of 55Al-43.4Zn-1.6Si hot dip coating melts on low-carbon steel substrates has been investigated. An experimental apparatus based on the sessile drop technique was developed, which allowed the substrate to be preheated to a different temperature than that of the droplet. The initial wetting and spreading of the molten metal droplet on the substrate was recorded at 1000 frames per second using a high-speed digital camera. Wetting was improved (ϑ decreased from 120 to 25 deg) as the substrate preheat temperature was increased from room temperature and approached the droplet temperature, beyond which the improvement in wetting was negligible. Immersion experiments using a thermocouple instrumented substrate dipped into a coating bath were performed for various substrate preheat temperatures. Interfacial heat fluxes and interfacial resistances were calculated from the temperature responses. The “minimum” interfacial resistance was decreased by an order of magnitude (1 × 10⁻⁴ to 2 × 10⁻⁵ m² K/W) as the substrate preheat temperature was increased from room to bath temperature. The reduction in interfacial resistance was related to the improvement of the initial wetting and the increase in mass transfer of iron atoms from the substrate across the interface. There was an apparent increase in the minimum interfacial resistance for substrate temperatures greater than the bath temperature. This was due to the increased rate of alloy layer formation and the exothermic nature of the Fe-Al interfacial reactions. The significance of these findings was discussed with respect to the mechanism of alloy layer formation at the interface during the initial stages of solid-liquid contact. This article is based on a presentation made in the “Geoffrey Belton Memorial Symposium,” held in January 2000, in Sydney, Australia, under the joint sponsorship of ISS and TMS.     

Fatigue crack growth behavior of 2124/SiC/10p functionally graded materials

Powder metallurgy processing involving cold pressing and hot extrusion has been used to fabricate bulk functionally graded materials (FGMs) based on the 2124/SiC/10p composite system. Two forms of single-core bulk FGMs with circular cross section were fabricated. One form (designated 10SiC-2124) had a central core of unreinforced Al-2124 alloy that was surrounded by a 2124/SiC/10p reinforced surface layer: the other (designated 2124-10SiC) had a composite core and an alloy surface layer. These forms enabled the effect of the radial graded core on fatigue to be investigated with fatigue crack propagation from either (1) a ductile core to a more brittle region or (2) a brittle core to a ductile region of the FGM. The fatigue crack growth rate was measured using a constant applied stress intensity factor range (δK=7 MPa ) technique. Two main fatigue crack growth rates were distinguished corresponding to growth in the core and in the surface layer. The results show that FGMs may exhibit good fatigue crack propagation resistance. For example, when the crack propagated from the brittle core to the tough surface layer, the average fatigue crack growth rate in the Al-2124 core (3.9×10⁻⁶ mm/cycle) was significantly lower than for the Al-2124 alloy (1.5×10⁻⁵ mm/cycle) at a similar δK value (7 MPa ), due to the highly tortuous crack path in the 2124/SiC/10p brittle layer. The 2124/SiC/10p brittle layer had a lower fatigue crack growth rate (6.6×10⁻⁶ mm/cycle) than the 2124/SiC/10p conventional composite (7.5×10⁻⁶ mm/cycle) because of the compressive residual stresses in the surface layer. Thus, FGMs could be more acceptable for critical applications than their conventional composite counterparts.     

The electrochemical oxidation of chalcopyrite in ammoniacal solutions

The anodic dissolution of chalcopyrite in ammoniacal solutions was investigated using electrochemical methods. At low overvoltages, the formation of a copper deficient sulfide layer, Cu_1-xFeS₂ through a charge transfer reaction is proposed based upon the dependence of the rest or open circuit potential on solution composition and the presence of a Tafel region of appropriate slope. In addition, a current peak that occurs at 10⁻⁴ A/cm² is a function of the square root of the voltage scanning speed and is explained in terms of a charge transfer reaction. At larger overvoltages, constant potential experiments and mass balances performed at various anodic potentials indicate that the dissolution is consistent with the overall reaction, CuFeS₂ + 4NH₃ + 9OH^- = Cu(NH₃) ₄ ⁺² + Fe(OH)₃ + S₂O ₃ ⁼ + 3H₂O +9e ^-, although some copper may be released to solution in the cuprous state and some ferrous iron has been identified in the product film. Currentvs time data taken during constant potential experiments were found to obey a linear rate relationship. This was interpreted in terms of the formation of a layer of constant thickness which is corroded at the outer interface at the same rate it is formed at the inner interface.. The model proposed is typical of the corrosion of some metals. An examination of the polarization curves shows the dissolution reaction to be first order with respect to [OH^-]. The lack of dependence on [Cu²⁺] indicates that the catalytic effect of cupric ion during oxygen pressure leaching is related only to the cathodic reduction of O₂ in agreement with the results of previous investigations.     

Experimental study on inclusion absorbed by the absorption bar in liquid steel

The refractory absorption bar is inserted into the submersed nozzle by a stopper to absorb the inclusion flowing through the nozzle and increase the cleanness of liquid steel during the continuous casting process. Based on the high-temperature hot-state experiment, the influence of the groove structure of the absorption bar on the inclusion absorption rate in liquid steel is analysed. Experimental result shows that when the groove direction of the absorption bar is perpendicular to the rotating direction, the optimal groove depth is 3?mm, the maximum thickness of the absorption layer is 362.9?μm and the maximum absorption velocity is 0.19?μm?s^?1; when the groove direction of the absorption bar is parallel to the rotating direction, the optimal groove depth is 2?mm, the maximum thickness of absorption layer is 404.3?μm and the maximum absorption velocity is 0.22?μm?s^?1. When the groove depth is determined, the absorption rate when the groove direction of the absorption bar is parallel to the rotating direction is higher than that when the groove direction of the absorption bar is perpendicular to the rotating direction. In addition, the number of grooves on the absorption bar is positively proportional to the absorption capability. An inclusion absorption capability model is established based on the multiple regression method and the absorption capabilities of different absorption bars are evaluated. This experiment has provided significant data supporting smelting of clean steel.     

Improving tantalum's oxidation resistance by Al+ ion implantation

Tantalum was implanted with 180 keV Al⁺ ions to fluences up to 3×10¹⁸ Al⁺/cm². Subsequent microchemical and microstructural observations showed that an amorphous layer covered the surface and extended to depths near 3000 Å for fluences above 2.4×10¹⁸ Al⁺/cm². The layer, comprised of ～70 at. pet Al and ～30 at. pet Ta, crystallized at temperatures above 500°C. Oxidation measurements, performed in one atmosphere of air and at temperatures below 600°C, showed that the layer stopped oxidation of the implanted tantalum, while unimplanted tantalum oxidized rapidly. The protection provided by the implantation deteriorated somewhat by temperatures near 735°C but still reduced the oxidation rate by a factor of 5. The deterioration is caused by localized rupturing of the implanted layer and the resulting oxidation of the underlying tantalum. At 910°C, the implanted tantalum oxidized almost as rapidly as unimplanted tantalum.