Metallurgical Analysis on a Cracked Super Duplex Stainless Steel Flange

A flange-to-pipe weldment in a seawater-intake-return-line suffered from cracking on its flange portion after in service for 4 months. The flange was fabricated from S32750 super duplex stainless steel. The cracked flange was investigated by visual inspection and fractographic examination on the crack surface, metallographic examination, hardness measurement, and chemical composition analysis of the flange-to-pipe weldment. The results of laboratory analysis showed that the flange had cracked in a brittle manner resulting from the presence of large amount of sigma phase in the flange material. Formation of such brittle second phase precipitates in the flange material was due to improper heat treatment.     

Conjugate Symmetric Sequency-Ordered Complex Hadamard Transform

A new transform known as conjugate symmetric sequency-ordered complex Hadamard transform (CS-SCHT) is presented in this paper. The transform matrix of this transform possesses sequency ordering and the spectrum obtained by the CS-SCHT is conjugate symmetric. Some of its important properties are discussed and analyzed. Sequency defined in the CS-SCHT is interpreted as compared to frequency in the discrete Fourier transform. The exponential form of the CS-SCHT is derived, and the proof of the dyadic shift invariant property of the CS-SCHT is also given. The fast and efficient algorithm to compute the CS-SCHT is developed using the sparse matrix factorization method and its computational load is examined as compared to that of the SCHT. The applications of the CS-SCHT in spectrum estimation and image compression are discussed. The simulation results reveal that the CS-SCHT is promising to be employed in such applications.     

Studies on the influence of chloride ion and pH on the corrosion and electrochemical behaviour of AZ91D magnesium alloy

The influence of chloride ion concentration and pH on the corrosion and electrochemical behaviour of die-cast and ingot-cast AZ91D alloy have been studied with a focus on the stability of microconstituents in these environments. The experimental techniques used include immersion studies, potentiodynamic polarization, X-ray diffraction and optical and scanning electron microscopy. The corrosion rate for the ingot and die-cast was very high in highly acidic solutions (pH 1–2) as compared to that in neutral and highly alkaline solutions (pH 4.5–12.0), and the rate increased with chloride ion concentration at all pH levels. In general, the die-cast showed a lower corrosion rate at all pH values and chloride ion concentrations. The open circuit corrosion potential shifted to more negative (more active) values with increase in concentration of chloride ions. Corrosion morphologies revealed more attack on primary and eutectic with increasing chloride concentration. In highly acidic conditions, corrosion attack was found on (Mg₁₇Al₁₂) and eutectic phase ( regions with higher Al content) while at pH 12.0 the ingot exhibited a pitting type of morphology. The corrosion product consisted of magnesium hydroxide, fallen particles and magnesium–aluminium oxide; the amount of each component was found to be a function of chloride ion concentration and pH.     

Synthesis of Yb:YAG Ceramics Without Sintering Additives and their Performance

High‐quality 10%Yb:YAG ceramics was successfully synthesized without sintering additives such as SiO₂ for the first time. Optical scattering loss of the Yb:YAG ceramics was 0.1%/cm and its transmitted wavefront distortion was λ/19.5 (t = 4.7 mm), which was very comparable to single crystal laser materials. Laser performance of thin disk made of this material (φ11 × t0.15 mm) was 74.1% of slope efficiency (optical‐to‐optical conversion efficiency: 68.1%) and the maximum output power reached 1.8 kW. Synthesis of high‐purity and high‐quality YAG ceramics without using sintering additives was demonstrated for the first time to our knowledge and we can discuss the technological meaning of high‐purity materials for the future.     

Environmental study of the impact of greenery in an institutional campus in the tropics

Urban environment quality is worsening every year. It is a fact that the urban air temperature is gradually rising in all cities and some effective measures are needed to mitigate it. Planting of vegetation is one of the main strategies to mitigate the urban heat island (UHI) effect. Large urban parks can extend positive effects to the surrounding built environment. National University of Singapore (NUS) complex can be considered as a “city” on a smaller scale. The greenery along Kent Ridge Road seems like a “rural” area, with a cooler ambient temperature. Some methodologies were employed in this study, such as satellite image, field measurement and computer simulations. The satellite image was used to identify the “hot” and “cool” spots in NUS environment. Field measurement was used to get the real temperature distribution across the campus and finally, computer simulation was used to predict some scenarios of different conditions. The result shows that buildings near or surrounded by greenery have lower ambient temperature than the ones away from the greenery and it is an effective way to lower the ambient temperature. The TAS simulation results also show that a rooftop garden has the potential of cooling energy savings for NUS buildings.     

Correction to: Improving the Summer Power Generation of a Hydropower Reservoir Using the Modified Multi‑Step Ahead Time‑Varying Hedging Rule

Water Resources Management -     

Novel corrosion experiments using the wire beam electrode. (IV) Studying localised anodic dissolution of aluminium

An electrochemically integrated multi-electrode array namely the wire beam electrode (WBE) has been applied in novel experiments to study the anodic dissolution behaviour of aluminium (AA1100), which was exposed to corrosive media with and without the presence of corrosion inhibitor potassium dichromate. The objective of this work is to demonstrate the applicability of the WBE for investigating corrosion processes under anodic polarisation. Anodic current measurements and mapping have been made, for the first time, with the WBE surface being anodically polarised. Pitting potential as well as anodic dissolution profile has been successfully determined by mapping anodic dissolution currents over the anodically polarised WBE surface. The pitting potential determined using the WBE method was found to correlate well with that determined using the conventional pitting scan method; and the anodic dissolution profile determined using the WBE method was found to correlate with maps obtained using the scanning reference electrode technique (SRET). Potassium dichromate was found to significantly affect the pitting potential, anodic dissolution profile and pitting initiation characteristics of aluminium. Two mechanisms of localised corrosion initiation have been identified. For WBE surface under free corrosion or low anodic polarisation conditions, the initiation of localised corrosion was found to be due to the disappearance of minor anodes, which lead to accelerated dissolution of a few major anodes. For WBE surface under large anodic polarisation, the initiation of localised corrosion was found to be due to the formation of active new anodic sites. This work suggests that the WBE method is useful for understanding the electrochemical behaviour of localised anodic processes, and their dependence on externally controllable variables.     

Use of Machining to Increase the Recovery of Scandium from Refractory Silicate Raw Material

The effect of machining conditions on the scandium leaching effectiveness from the wastes of wet magnetic separation of iron–titanium magnetites in sulfuric acid solution has been studied. It has been shown that the degree of recovery of scandium into sulfuric acid solution linearly increases with an increase in the degree of amorphization of specimens of wastes of wet magnetic separation.

     

Effect of heat treatment on corrosion behaviour of magnesium alloy AZ91D in simulated body fluid

The research explored ways of improving corrosion behaviour of AZ91D magnesium alloy through heat treatment for degradable biocompatible implant application. Corrosion resistance of heat-treated samples is studied in simulated body fluid at 37 °C using immersion and electrochemical testing. Heat treatment significantly affected microgalvanic corrosion behaviour between cathodic β-Mg₁₇Al₁₂ phase and anodic α-Mg matrix. In T4 microstructure, dissolution of the β-Mg₁₇Al₁₂ phase decreased the cathode-to-anode area ratio, leading to accelerated corrosion of α-Mg matrix. Fine β-Mg₁₇Al₁₂ precipitates in T6 microstructure facilitated intergranular corrosion and pitting, but the rate of corrosion was less than those of as-cast and T4 microstructures.