Thermal, Viscoelastic and Surface Properties of Oxidized Field’s Metal for Additive Microfabrication

Field’s metal, a low-melting-point eutectic alloy composed of 51% In, 32.5 Bi% and 16.5% Sn by weight and with a melting temperature of 333 K, is widely used as liquid metal coolant in advanced nuclear reactors and in electro–magneto–hydrodynamic two-phase flow loops. However, its rheological and wetting properties in liquid state make this metal suitable for the formation of droplets and other structures for application in microfabrication. As with other low-melting-point metal alloys, in the presence of air, Field’s metal has an oxide film on its surface, which provides a degree of malleability and stability. In this paper, the viscoelastic properties of Field’s metal oxide skin were studied in a parallel-plate rheometer, while surface tension and solidification and contact angles were determined using drop shape analysis techniques.

A Robust Recovery of Ni From Laterite Ore Promoted by Sodium Thiosulfate Through Hydrogen-Thermal Reduction

Laterite ore is one of the important sources of nickel (Ni). However, it is difficult to liberate Ni from ore structure during reduction roasting. This paper provided an effective way for a robust recovery of Ni from laterite ore by H2 reduction using sodium thiosulfate (Na2S2O3) as a promoter. . It was found that a Ni content of 9.97% and a Ni recovery of 99.24% were achieved with 20 wt% Na2S2O3 at 1,100°C. The promoting mechanism of Na2S2O3 in laterite ore reduction by H2 was also investigated. The thermogravimetric results suggested the formation of Na2Mg2SiO7, Na2SO3, Na2SO4, and S during the pyrolysis of laterite with Na2S2O3, among which the alkali metal salts could destroy the structures of nickel-bearing silicate minerals and hence release Ni, while S could participate in the formation of the low-melting-point eutectic phase of FeS-Fe. The formation of low-melting-point phases were further verified by the morphology analysis, which could improve the aggregation of Ni-Fe particles due to the capillary forces of FeS-Fe as well as the enhanced element migration by the liquid phase of sodium silicates during reduction.

Deposits in Gas-fired Rotary Kiln for Limonite Magnetization-Reduction Roasting: Characteristics and Formation Mechanism

The formation mechanism of deposits in commercial gas-fired magnetization-reduction roasting rotary kiln was studied. The deposits ring adhered on the kiln wall based on the bonding of low melting point eutectic liquid phase, and the deposit adhered on the air duct head by impact deposition. The chemical composition and microstructure of the deposits sampled at different locations varied slightly. Besides a small amount of quartz and limonite, main phases in the deposits are fayalite, glass phase and magnetite. The formation of the deposits can be attributed to the derivation of low melting point eutectic of fine limonite and coal ash, and the solid state reaction between them. Coal ash, originated from the reduction coal, combining together with fine limonite particles, results in the accumulation of deposits on the kiln wall and air duct. Fayalite, the binder phase, was a key factor for deposit formation. The residual carbon in limonite may cause an over-reduction of limonite and produce FeO. Amid the roasting process, SiO2, originated from limonite and coal ash, may combine with FeO and reduce the liquefaction temperature, therewith liquid phase generates at high temperature zone, which can significantly promote the growth of deposits.

The Microstructure Evolution of AA7050 in the Process of Homogenization

This paper used the metallographic analysis, X-ray diffraction analysis (XRD), differential scanning thermal analysis (DSC), scanning electron microscope (SEM) and electron probe analysis (EPMA) system to research the evolution law of the microstructure and properties of AA7050 under different homogenization system. And analyzes the cause of this evolution combined with the test results put forward. The research shows that high melting point eutectic phase S (Al2CuMg) can be fully re-dissolution through two-stage homogenization, at the same time avoid the overburning of low melting eutectic phase. We optimized the AA7050 homogenization heat treatment system and the optimal homogenization scheme is 430°C/18h+467°C/12h.

Study on the Corrosion Resistance Behavior of Multi-Elements Alloy CoCrFeNiTi0.5

Multi-elements alloy with good thermal stability is expected to serve as the superheater tube material of ultra-supercritical boiler and may suffer from hot corrosion under the coal-fired atmosphere. In this study, the corrosion resistance behavior of multi-elements alloy CoCrFeNiTi0.5 coated with alkali metal sulfates at 750°C is investigated systematically. The results showed the corrosion kinetics curves of the alloy followed a parabolic growth rate. The corrosion products, which consisted of volatile Na (CrO4) (SO4), (Fe,Ni) xSy, Cr/Ti oxide as well as compound oxides with spinel structure AB2O4, were found in the oxide scale and internal attack zone of the alloy. The oxide layer had good adhesion with the matrix at the beginning of corrosion. Prolonging corrosion time, the oxide layer in thickness increased and became loose as well as porous. The micro-pores generated in the interface between the oxide scale and matrix with the occurrence of the internal oxidation and internal sulfidation. In a word, the corrosion resistance behavior of multi-elements alloy CoCrFeNiTi0.5 at 750°C can be attributed to the formation of the protective oxide layers and to the basic fluxing in molten Na4SO4 induced by low melting point eutectic.

A Failure Criterion of Friction Pair under Boundary Lubrication

The formation and lubrication mechanism of boundary lubricating film were discussed. The boundary lubricating film includes adsorption film and chemical reaction film, and has respective temperature operating range. The adsorption film adsorbed in metal surface by Van-der Wads, and the parenchyma is the external friction between adsorption molecule layers. The chemical reaction film is made by the reaction between metal and extreme pressure additive in base oil, and the anti-wear capability is realized by the low-melting point eutectic alloy. The temperature is regarded as a judge criterion for failure of boundary lubrication. The failure model for boundary lubricating film is established. According to the failure model, the failure criterion proposed is effective by analysis of the spiral bevel gear using the finite element method. These results provide a basis for the application of boundary lubrication.

Development of Diffusion Barrier Coatings for Mitigation of Fuel-Cladding Chemical Interactions

Fuel Cladding Chemical Interactions (FCCI) in a nuclear reactor occur due to thermal and radiation enhanced inter-diffusion between the cladding and fuel materials, and can have the detrimental effects of reducing the effective cladding wall thickness and the formation of low melting point eutectic compounds. Deposition of diffusion barrier coatings of a thin oxide on the inner surface of the cladding can potentially reduce or delay the onset of FCCI. This study examines the feasibility of using nanofluid-based electrophoretic deposition (EPD) process to deposit coatings of titanium oxide, yttria-stabilized zirconia (YSZ) and vanadium oxide. The deposition parameters, including the nanofluid composition, current, and voltage were optimized for each coating material using test flat substrates of T91 ferritic-martensitic steel. Diffusion characteristics of the coatings were investigated by diffusion couple experiments using the fuel surrogate cerium. These diffusion couple studies performed in the temperature range of 560°C and 585°C showed that the oxide coatings significantly reduce the solid state inter-diffusion between cerium to steel.