Volume 109, Issue 3

Some published experimental results on the thermodynamic data of pure solid CaO and MgO significantly contradict the widely used data in review books or tables, such as JANAF data. We scrutinized all the original experimental data forming the basis in review books and tables in order to establish a more realistic uncertainty range. The two Gibbs energy functions of CaO and MgO are combined with those of all other relevant phases to develop a thermodynamic database for the Mg–Ca–O system. The first systematic study of the calculated Mg–Ca–O phase diagram is presented. This phase diagram is validated by recently obtained dedicated experimental data using in-situ synchrotron radiation diffraction to study phase formation and reactions during melting and solidification of Mg and Mg–Ca alloys with CaO-additions below 1050 K. Intricacies in the solidification path of Mg-rich ternary alloys are revealed by the present thermodynamic calculations. Mg-rich alloys are categorized in four groups according to their participation in different invariant four-phase reactions. The development of non-equilibrium constitution of four phases, (Mg) + Mg 2 Ca + MgO + CaO, in the fully solidified sample is explained.

The thermodynamic optimisation of the Cu–S–Sn system was carried out using the CALPHAD technique. For the liquid phase, an associated solution model, (Cu, Cu 2 S, S, SnS, Sn), was used by assuming the existence of two associates: Cu 2 S and SnS. Ternary compounds Cu 5 Sn 2 S 7 and Cu 10 Sn 2 S 13 were treated as stoichiometric compounds. Ternary compounds Cu 4 SnS 4 , Cu 2 SnS 3 , and Cu 4 Sn 3 S 8 were located on the Cu 2 S–SnS 2 joint and described using the model (Cu 2 S) p (SnS 2 ) q . The Cu 2 Sn 3 S 7 compound was also located on the Cu 2 S–SnS 2 joint and was described as (Cu 2 S, SnS 2 ) considering the range of its homogeneity. With the present thermodynamic parameters, the projection of the liquidus surfaces and invariant reactions of the Cu–S–Sn system were predicted. A set of self-consistent thermodynamic parameters of the Cu–S–Sn system could be obtained.

A horizontal linear heat flow apparatus connected to an optical microscope was used to directly observe the grain boundary groove shapes of solid neopentylglycol solution equilibrated with neopentylglycol-succinonitrile eutectic liquid at a constant temperature gradient. The thermal conductivity variations with temperaure for solid neopentylglycol solution and neopentylglycol-succinonitrile eutectic solid were measured with a radial heat flow apparatus. By using the observed grain boundary groove shapes and measured values of temperature gradients and thermal conductivity of solid phase and liquid phase, the values of the Gibbs–Thomson coefficient, solid–liquid interfacial energy and grain boundary energy were determined for the solid neopentylglycol solution equilibrated with the neopentylglycol-succinonitrile eutectic liquid.

Magnetic characterization of amorphous–nanocrystalline Fe–Cr–B–Si–Ni–Nb alloys was the goal of this study. In this regard, three different amorphous Fe 40 Cr 20 Si 15 B 15 M 10 (Nb, Ni, Ni 0.5 Nb 0.5 ) alloys were prepared using the mechanical alloying technique for up to 20 h and subsequent annealing. The prepared samples were characterized using X-ray diffraction, scanning and transmission electron microscopy, differential scanning calorimetry and vibrating scanning magnetometry. According to the results, amorphous phase can successfully form in Fe 40 Cr 20 Si 15 B 15 M 10 (Nb, Ni, Ni 0.5 Nb 0.5 ) alloys. The coercivity and saturation magnetization values of the amorphous Fe 40 Cr 20 Si 15 B 15 Ni 10 sample were about 100 Oe and 65.9 emu · g –1 . By replacement of Ni with Nb, the coercivity and saturation magnetization values were slightly increased (to about 142 Oe) and decreased (to about 14 emu · g –1 ), respectively. Regardless of the annealing condition, amorphous–nanocrystalline Fe 40 Cr 20 Si 15 B 15 Ni 10 alloy showed higher saturation magnetization and lower coercivity values in comparison with the samples containing Nb.

This paper aims to evaluate the dry sliding wear of AISI 304 austenitic stainless steel as a function of the applied load. Samples of AISI 304 were heat treated (sensitized) to precipitate Cr 23 C 6 carbides in the grain boundaries, and the resulting microstructure was compared to that of the non-sensitized samples. Wear testing was carried out at room temperature of 25°C and a relative humidity of about 60% using a pin-on-disk apparatus. The load applied was varied from 10 to 30 N at a constant sliding velocity of 0.5 m s –1 . Wear particles were analyzed by means of scanning electron microscopy and X-ray diffraction. The results showed that the dynamic friction coefficient remained effectively constant with increasing applied load. The surface hardness measured after the wear process generally increased at higher loads due to subsurface strain-hardening, and deformation-induced martensitic transformation occurred during the wear process. Surface roughness and weight losses were found to increase with increasing the load for both sensitized and non-sensitized samples. In addition, a great amount of Cr 23 C 6 carbides in the grain boundaries favored a size reduction of the debris generated due to wear.

The microstructure and wear properties of AZ91C alloy were studied by performing solution annealing and then aging heat treatment, friction stir processing, and friction stir processing followed by solution annealing and aging. The heat-treated microstructure included fine dendritic grains (50 ± 14.2 μm) with a considerable dissolution and dispersion of continuous network-like β-Mg 17 Al 12 precipitates at grain boundaries. Friction stir processing significantly refined the microstructure and grains (9 ± 2.3 μm); followed by the breaking-up and dissolution of dendrites and continuous β-Mg 17 Al 12 precipitates. Heat treatment of the friction stir processed area resulted in excessive grain growth (175 ± 71.4 μm) and dispersion of fine β precipitates. Under a range of applied stresses (0.78 MPa, 2.44 MPa and 3.66 MPa) for the wear tests, only friction stir processed samples showed improvement in wear behavior at low stress, while at the higher stresses, along with the effectiveness of other processes it was the most effective process on improving the wear resistance. Heat treatment had the most effect on improving the wear resistance at the intermediate stress; moreover, applying it to the friction stir processed area remarkably enhanced the wear resistance at all stresses. Heat treatment of the friction stir processed area also resulted in the lowest friction coefficient values during the wear test, indicating the convenience of this process for wear performance of cast AZ91C alloy. Abrasion was shown as the dominant wear mechanism.

Simple, economic, and scalable production of 2D molybdenite (MoS 2 ) nanosheets is necessary for practical applications, as in next generation anodes for Li-ion batteries. One currently developing route for production of MoS 2 nanosheets is exfoliation of bulk molybdenite using a ball milling technique. In this research, the morphological evolution of molybdenite in the milling process of MoS 2 and MoS 2 –Al 2 O 3 systems is studied. Structural changes in molybdenite were investigated using transmission electron microscopy and X-ray diffraction. Results showed that when MoS 2 was milled alone, 2D nanosheets, nanobars, and nanotubes were formed in the first step of the process and then structural destruction occurred when milling was prolonged. However, when alumina was included, destruction initiated from the beginning of the milling process leading to a highly activated structure.

Bredigite has been recently evaluated as a biodegradable ceramic with high mechanical strength, biocompatibility, bioactivity and excellent cell behavior. The objective of this research was to fabricate a nanostructured bredigite scaffold for bone repair and restoration via the space holder technique. The crystallite size, phase composition, particle size, pore morphology and pore size distribution of the scaffold were characterized using X-ray diffraction, as well as transmission and scanning electron microscopy. The results showed the fabrication of a highly interconnected porous scaffold, with a total porosity of about 86%, a pore size of about 400–600 μm, and the compressive strength of about 1.1 MPa. The prepared scaffold with nanosized structure and high porosity level leading to a high specific surface area could be used as an ideal scaffold for bone regeneration in bone tissue engineering applications.

It has been recognized that a simple and economic preparation of superhydrophobic films is the prerequisite for their industrial and commercial applications. In this work, superhydrophobic films were successfully achieved on insulating materials. For such films, the contact angle can reach a maximum of 151.8° (sliding angle about 8°) with a surface roughness of 10.88 μm. If surface roughness was less than 10.88 μm, the contact angle increased with roughness, but for roughness greater than 10.88 μm, the contact angle decreased with roughness. It was further revealed that the surface hierarchical structures of the films were responsible for such a high contact angle and a low sliding angle. Moreover, the wetting ability of the rough films was different and can be interpreted using the different wetting state models. In addition, sandstorm tests and hydrophobicity experiments showed that such films could resist the external force well and exhibit a durable superhydrophobicity.

Here we report, for the first time, a modified arc-discharge method for synthesis of Cu/Ag core/shell particles with an Ag shell thickness of about 5 nm, based on the difference in the melting points and the evaporating pressures of the elements Cu and Ag. The present approach can as well provide wider application to synthesis of other core/shell structures with high melting-point metal elements as core and low melting-point metals as shell.