Investigations on the Effect of Tungsten Carbide and Graphite Reinforcements during Spark Erosion Machining of Aluminium Alloy (AA 5052) Hybrid Composite

Silicon - Reinforcements introduced to metal matrix composites are known for their inherent properties like corrosion resistance, wear resistance and machinability. This study deals with the...     

Impression creep behavior of different zones in friction stir welded Mg–Zn–Mn wrought alloy

The friction stir welded joint of wrought ZM21 alloy was divided into five parts, and their localized creep behavior was studied via the impression method. The tests were carried out in the stress range of 300–450 MPa (σ_imp/G ≈ 0.02–0.03) and in the temperature range of 448–523 K. Optical and SEM micrographs and EDS taken before and after the impression tests were used to study the microstructure of various zones of the FS welded joint. Power law was found to satisfactorily relate the stress and strain rates. The steady-state impression velocity was found to vary significantly between the advancing and retreating sides of TMAZ and HAZ. For TMAZ, the creep exponent on the AS was 4.8, and on the RS, it was 7.8. The activation energy on the AS was ~?133 kJ/mol, and on the RS, it was ~?101 kJ/mol. Similarly, for HAZ, the creep exponent on the AS was found to be 5.5 and on the RS, it was 4.9. The activation energy on the AS was ~?86 kJ/mol and on the RS, it was ~?232 kJ/mol. The cross-over of steady-state impression velocity of different zones indicates that the weak zone was temperature and stress dependent. Within the stresses and temperatures studied, the weld zone's creep resistance (i.e., lower minimum impression velocity) was found to be better than the base material. As it is with most magnesium alloys, dislocation climb was found to be the operative mechanism in the FS weldments of ZM21 alloy. The rate-controlling mechanism remains to be identified because the wide variation in n and Q values suggests that different creep mechanisms are in operation in different zones.

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Dark fermentative biohydrogen production by Acinetobacter junii-AH4 utilizing various industry wastewaters

Hydrogen (H₂) is one of the most promising renewable energy sources, anaerobic bacterial H₂ fermentation is considered as one of the most environmentally sustainable alternatives to meet the potential fossil fuel demand. Bio-H₂ is the cleanest and most effective source of energy provided by the dark fermentation utilizing organic substrates and different wastewaters. In this study, the bio-H₂ production was achieved by using the bacteria Acinetobacter junii-AH4. Further, optimization was carried out at different pH (5.0–8.0) in the presence of wastewaters as substrates (Rice mill wastewater (RMWW), Food wastewater (FWW) and Sugar wastewater (SWW). In this way, the optimized experiments excelled with the maximum cumulative H₂ production of 566.44 ± 3.5 mL/L (100% FWW at pH 7.5) in the presence of Acinetobacter junii-AH4. To achieve this, a bioreactor (3 L) was employed for the effective production of H₂ and Acinetobacter junii-AH4 has shown the highest cumulative H₂ of 613.2 ± 3.0 mL/L, HPR of 8.5 ± 0.4 mL/L/h, HY of 1.8 ± 0.09 mol H₂/mol glucose. Altogether, the present study showed a COD removal efficiency of 79.9 ± 3.5% by utilizing 100% food wastewater at pH 7.5. The modeled data established a batch fermentation system for sustainable H₂ production. This study has aided to achieve an ecofriendly approach using specific wastewaters for the production of bio-H₂.     

Impression Creep Behavior of an Mg–Zn–RE Alloy at Elevated Temperatures

Mg–Zn–RE alloys are promising candidates for automotive and aerospace applications as, among magnesium alloys, they have better corrosion and creep resistance abilities at elevated temperatures. This study evaluates the high-temperature creep behavior of ZE41 magnesium alloy, belonging to the Mg–Zn–RE family, using impression test. Impression tests were performed under a constant temperature and stress with a flat-ended cylindrical punch. Power law and Eyring relationships were used to analyze the creep mechanism. By applying the power-law relationship, it was found that the creep exponent decreased from 7.5 to 4 in the temperature range of 493 K to 593 K. Activation energy increased from 78.5 to 107.1 kJ/mol in the applied stress range of 350 to 500 MPa (normalized stress: 0.024 ≤ σ_imp/G ≥ 0.034). Using the Eyring relationship, a single activation energy of 25 kJ/mol for the entire stress and temperature range was obtained. Based on the creep exponent and activation energy, it is proposed that pipe-diffusion-controlled dislocation climb is the dominant mechanism, but grain boundary sliding also contributes at higher stresses.

     

Study and Analysis of the Effect of Harmonics on the Hot Spot Temperature of a Distribution Transformer Using Finite-Volume Method

Transformers are critical components in power systems and their failure can cause long interruption of power supply. The condition of a transformer can be monitored by performing thermal analysis. The use of non-linear devices, such as rectifiers and converters, draws harmonic currents that increase losses in transformers, thereby increasing their operating temperature. In this article, a new numerical approach is presented for determining the rise in hot spot temperature in a 5-kVA, 400/400-V dry-type three-phase transformer laboratory prototype. The key novelty is that the additional winding eddy current loss due to non-linear loads is considered in the numerical modeling. The winding eddy current loss corresponding to harmonic distortion is estimated by conducting experiments and calculations. Numerical simulations are carried out for a wide range of non-linear loads using a commercial computational fluid dynamics package, FLUENT 6.3. The proposed numerical methodology is validated by performing experiments on the transformer for possible non-linear loads and comparing the measured hot spot temperature with the simulated values. Correlation equations for rise in hot spot temperature as a function of total harmonic distortion are presented, which can be used for estimating the life of transformers when connected to different types of loads.     

Carbon Nanotubes and Nanohorn Hybrid Composite Buckypaper as Microporous Layer for Proton Exchange Membrane Fuel Cell

In the present work, carbon nanotubes (CNT) and CNT‐carbon nanohorns (CNH) (0, 30, 50, 70 and 100 wt.% CNH) composite Buckypapers (BPs) were fabricated using vacuum filtration technique. Structure and property relation of composite BPs were studied using scanning electron microscope, four probe technique, BET surface area and contact angle measurements. Properties such as electrical conductivity, hydrophobic nature and microstructure of CNT‐30 wt.% CNH composite BP are superior to other composite BP. Hence, CNT‐30 wt.% CNH composite BP is chosen as a microporous layer (MPL) for PEMFCs and tested in fuel cell testing fixture. Polarization studies reveal that the cells performance with composite BPs is comparable with SGL‐MPL based cell. Hydrogen pumping and polarization studies of the cells confirms that composite BPs act as a good MPL at anode as well as cathode at 0.4 to 0.8 V. Hence, CNT‐CNH composite BPs are potential candidates for PEMFC applications.     

The Effect of Nickel Electroplating on Corrosion Behavior of Metal Matrix Composites

Nickel electroplating was applied to A356.2 aluminum alloy and its composites for improving its corrosion resistance. The corrosion resistance of the A356.2 and composites reinforced with rice husk ash particulates was evaluated by potentio-dynamic polarization tests in aerated 3.5% NaCl solution. Composites were fabricated by using the liquid state processing technique. Scanning electron microscopy, energy dispersive spectroscopy, techniques were used for surface analysis of the coatings before the corrosion tests and optical microscope was used to study the surface morphology of the uncoated and coated specimens after polarization tests. Results demonstrated that the nickel coated specimens exhibited higher corrosion resistance than the uncoated specimens. However, it was noticed that there was no significant change in the corrosion resistance for the nickel plated composites.     

Investigation on the flexural behaviour of reinforced concrete beams using phyllite aggregates from mining waste

This paper investigated the flexural behaviour of 12 reinforced concrete (RC) beams made of phyllite coarse aggregates produced as by-product of underground gold mining activity. The beams were tested to failure under four point test. Collapse of the beams which were adequately designed against shear failure occurred mostly through either flexural-shear failure and/or diagonal tension failure. The experimental failure loads averaged approximately 115% of the theoretical failure loads. It was observed that the beams developed early shear cracks and higher flexural crack widths than allowable at service loads. Deflections compared reasonably well with the design code requirement but displacement ductility was low. It is recommended that British Standard (BS) 8110 design concrete shear stress values be multiplied by 0.8 to assure that the predicted shear capacity of phyllite concrete would be low and reasonable as compared to flexural capacity. In that case, BS 8110 can be used to provide adequate load factor against flexural failure for under-reinforced RC beams made of phyllite coarse aggregates.     

Stackable nonvolatile memory with ultra thin polysilicon film and low-leakage (Ti, Dy)xOy for low processing temperature and low operating voltages

We report the fabrication process as well as material and electrical characterization of ultra thin body (UTB) thin film transistors (TFTs) for stackable nonvolatile memories by using in situ phosphorous doped low-temperature polysilicon followed by the chemical mechanical polishing (CMP) process. The resulting polysilicon film is about 13 nm thick with approximately 10¹⁹ cm⁻³ doping. Root mean square surface roughness below 1 nm is achieved. Metal nanocrystals and high-k dielectric are selected for storage nodes and tunneling barriers to achieve low operating voltages. The number density and average diameter of nanocrystals embedded in the gate stack are 7.5 × 10¹¹ cm⁻² and 5.8 nm, respectively. Furthermore, scanning transmission electron microscopy (STEM), convergent beam electron diffraction (CBED) and electron energy loss spectroscopy (EELS) are performed for material characterization. The dielectric constant of the (Ti, Dy)_xO_y film is 35, and the off-state leakage current at −1 V bias and 2.8 nm equivalent oxide thickness is 5 × 10⁻⁷ A/cm². We obtain a memory window of about 0.95 V with ±6 V program/erase voltages. Our results show that UTB TFT is a promising candidate for the three-dimensional integration in high-density nonvolatile memory applications.     

Housing and urban poor

Research Officer, Kwasi Owusu‐Adade, at the Building and Road Research Institute at Kumasi, highlights the role housing plays in the life of the rural migrant and concludes that a greater commitment by government could be demonstrated in practical terms. Low‐income housing requires a supply of land on a rolling basis with the encouragement of locally produced materials, material depots and the provision of basic amenities for illegal settlements which do not seriously inhibit future overall development.