Materials2014, 7(10), 7157-7172; doi:10.3390/ma7107157 - published 23 October 2014 Show/Hide Abstract
Abstract: This study aims to analyze contamination with the use of soil reclaimed with ferronickel slag (FNS). In order to investigate any contamination due to FNS disposal, soils were collected from three sites. The contamination analysis was done on these samples through a series of laboratory tests. Furthermore, laboratory tests simulating field conditions were performed in a soil chamber. In the lab test, three leaching agents, namely fresh water, acidic water and seawater, were used. The soil samples used were sand and silt with a relative density of 40% and a compaction ratio of 90%, respectively. The pH of the effluent discharged from the experimental soil chamber was also analyzed. After leaching, soil samples were subjected to analysis. The results showed that pH was higher in the silt than in the sand. The results of the laboratory tests exhibited that leaching of hazardous elements from FNS is limited, so that it can be used as a substitute for natural aggregate in the cement industry or construction applications.
Materials2014, 7(10), 7145-7156; doi:10.3390/ma7107145 - published 22 October 2014 Show/Hide Abstract
Abstract: The fabrication of transparent polycrystalline Y3Al5O12 (YAG) is still a challenge, requiring the achievement of highly pure and fully dense, homogeneous materials. An important role is played by the powder characteristics: pure, fine and unagglomerated powders are essential for achieving full density and the required microstructural features. Keeping in mind these requirements, the aim of this work was to investigate the role of different synthesis parameters during co-precipitation, which is widely used to prepare YAG powders for transparent devices. The key role of the precipitant solution is here illustrated, by comparing the effect of aqueous ammonia (AA) versus ammonium hydrogen carbonate (AHC). This latter allowed the preparation of softly agglomerated powders, characterized by a very good sinterability. However, when AHC is used, attention should be paid to its concentration. By comparing the effect of two AHC precipitant solutions (at 0.5 M and 1.5 M, respectively), only the former one allowed the preparation of pure YAG powders, free from secondary phases. In this last condition, by using both chlorides and nitrates as YAG precursors, pressureless sintering at 1500–1600 °C/3 h gave rise to pure materials, highly dense and characterized by a fine and homogeneous microstructure.
Materials2014, 7(10), 7130-7144; doi:10.3390/ma7107130 - published 22 October 2014 Show/Hide Abstract
Abstract: The reuse system proposed by the authors is an overall business system for realizing a cyclic reuse flow through the processes of design, fabrication, construction, maintenance, demolition and storage. The reuse system is one of the methods to reduce the environmental burden in the field of building steel structures. These buildings are assumed to be demolished within approximately 30 years or more for physical, architectural, economic and social reasons in Japan. In this paper, focusing on building steel structures used for plants, warehouses and offices without fire protection, the performance of steel structural members for reuse is evaluated by a non-destructive test. First, performance evaluation procedures for a non-destructive test, such as mechanical properties, chemical compositions, dimension and degradation, are shown. Tensile strengths are estimated using Vickers hardness measured by a portable ultrasonic hardness tester, and chemical compositions are measured by a portable optical emission spectrometer. The weldability of steel structural members is estimated by carbon equivalent and weld crack sensitivity composition using chemical compositions. Finally, the material grade of structural members of the building steel structure for reuse is estimated based on the proposed procedures.
Materials2014, 7(10), 7118-7129; doi:10.3390/ma7107118 - published 21 October 2014 Show/Hide Abstract
Abstract: In this paper, the corrosion residual strength of the AZ91D magnesium alloy in the presence of sulfate-reducing bacteria is studied. In the experiments, the chemical composition of corrosion film was analyzed by a scanning electron microscope with energy dispersive X-ray spectroscopy. In addition, a series of instruments, such as scanning electronic microscope, pH-meter and an AG-10TA materials test machine, were applied to test and record the morphology of the corrosion product, fracture texture and mechanical properties of the AZ91D magnesium alloy. The experiments show that the sulfate-reducing bacteria (SRB) play an important role in the corrosion process of the AZ91D magnesium alloy. Pitting corrosion was enhanced by sulfate-reducing bacteria. Corrosion pits are important defects that could lead to a significant stress concentration in the tensile process. As a result, sulfate-reducing bacteria influence the corrosion residual strength of the AZ91D magnesium alloy by accelerating pitting corrosion.
Materials2014, 7(10), 7105-7117; doi:10.3390/ma7107105 - published 21 October 2014 Show/Hide Abstract
Abstract: The densification behavior, microstructure and mechanical properties of bulk TiB2-based ceramic composites, fabricated using the spark plasma sintering (SPS) technique with elements of (Fe–Ni–Ti–Al) sinter-aid were investigated. Comparing the change of shrinkage displacement of pure TiB2 and TiB2–5 wt% (Fe–Ni–Ti–Al), the addition of elements Fe–Ni–Ti–Al into TiB2 can facilitate sintering of the TiB2 ceramics. As the sintering temperature exceeds 1300 °C, the relative density does not significantly change. Alumina particles and austenite (Fe–Ni–Ti) metallic binder distributed homogeneously in the grain boundary of TiB2 can inhibit the growth of the TiB2 grains when the sintering temperature is below 1300 °C. The density and particle size of TiB2 greatly influence the mechanical behavior of TiB2–5 wt% (Fe–Ni–Ti–Al) composites. The specimen sintered at 1300 has the highest microhardness of 21.1 ± 0.1 GPa with an elastic modulus of 461.4 GPa. The content of secondary borides (M2B, being M = Fe, Ni), which are more brittle than TiB2 particles, can also influence the fracture toughness. The specimen sintered at 1500 °C has the highest fracture toughness of 6.16 ± 0.30 MPa·m1/2 with the smallest M2B phase. The results obtained provide insight into fabrication of ceramic composites with improved mechanical property.
Materials2014, 7(10), 7093-7104; doi:10.3390/ma7107093 - published 20 October 2014 Show/Hide Abstract
Abstract: XNiSn (X = Ti, Zr and Hf) half-Heusler alloys have promising thermoelectric properties and are attracting enormous interest for use in waste heat recovery. In particular, multiphase behaviour has been linked to reduced lattice thermal conductivities, which enables improved energy conversion efficiencies. This manuscript describes the impact of spark plasma sintering (SPS) on the phase distributions and thermoelectric properties of Ti0.5Zr0.5NiSn based half-Heuslers. Rietveld analysis reveals small changes in composition, while measurement of the Seebeck coefficient and electrical resistivities reveals that all SPS treated samples are electron doped compared to the as-prepared samples. The lattice thermal conductivities fall between 4 W·m−1·K−1 at 350 K and 3 W·m−1·K−1 at 740 K. A maximum ZT = 0.7 at 740 K is observed in a sample with nominal Ti0.5Zr0.5NiSn composition.