Sinterability of Forsterite Prepared via Solid‐State Reaction

In this work, the sinterability of forsterite powder synthesized via solid‐state reaction was investigated. X‐ray diffraction (XRD) analyses indicate that the synthesized powder possessed peaks that correspond to stoichiometric forsterite. Scanning electron micrographs revealed that the powders were formed agglomerates, which were made up of loosely packed fine particles. Subsequently, the forsterite powders were cold isostatically pressed into a disk shape under 200 MPa and sintered in air at temperature ranging from 1200°C to 1500°C (interval of 50°C) with ramp rate of 10°C/min and dwelling time of 2 h. The sinterability of each sintered samples was examined in terms of phase stability, relative density, Vickers hardness, fracture toughness, and microstructural examination. XRD examination on all the sintered samples exhibited pure forsterite, in which the generated peaks were found to be in a good agreement with JCPDS card no. 34‐0189. The densification of forsterite progressed to reach a maximum relative density of ~91% at 1500°C. This study also revealed that high‐strength forsterite ceramic can be synthesized via solid‐state reaction as forsterite attained favorable mechanical properties, having fracture toughness of 4.88 MPam^1/2 and hardness of 7.11 GPa at 1400°C.     

Synergistic Effects of Carbon Fillers of Phenolic Resin Based Composite Bipolar Plates on the Performance of PEM Fuel Cell

The most essential and costly component of polymer electrolyte membrane fuel cells is the bipolar plate. The production of suitable composite bipolar plates for polymer electrolyte membrane fuel cell with good mechanical properties and high electrical conductivity is scientifically and technically very challenging. This paper reports the development of composite bipolar plates using exfoliated graphite, carbon black, and graphite powder in resole‐typed phenol formaldehyde. The exfoliated graphite with maximum exfoliated volume of 570 ± 10 mL g⁻¹ used in this study was prepared by microwave irradiation of chemically intercalated natural flake graphite in a few minutes. The composite plates were prepared by varying exfoliated graphite content from 10 to 35 wt.% in phenolic resin along with fixed weight percentage of carbon black (5 wt.%) and graphite powder (3 wt.%) by compression molding. The composite plates with filler weight percentage of 35/5/3/exfoliated graphite/carbon black/graphite powder offer in‐plane and trough‐plane electrical conductivities of 374.42 and 97.32 S cm⁻¹, bulk density 1.58 g cm⁻³, compressive strength 70.43 MPa, flexural strength 61.82 MPa, storage modulus 10.25 GPa, microhardness 73.23 HV and water absorption 0.22%. Further, I–V characteristics notify that exfoliated graphite/carbon black/graphite powder/resin composite bipolar plates in unit fuel cell shows better cell performance compared exfoliated graphite/resin composite bipolar plates. The composite plates own desired mechanical properties with low bulk density, high electrical conductivity, and good thermal stability as per the U.S. department of energy targets at low filler concentration and can be used as bipolar plates for proton exchange membrane fuel cells.     

Development of Joints Between Two Parallel SS-Laminated BSCCO/Ag HTS Tapes

Stainless-steel (SS)-laminated high-strength high-temperature superconductor (HTS) BSCCO tapes are now commercially available for different practical applications. These SS-laminated HTS tapes are tolerant to smaller winding diameters, and the pancake winding becomes much easier due to higher tensile strength. However, the joining of two parallel SS-laminated HTS tapes is more complicated because of their limitation in maximum temperature exposure. The joining between the pancakes however becomes resistive due to the SS-laminated layer. We have experimentally studied the performance of the bridge joint between two parallel SS-laminated BSCCO tapes with different numbers of cross bridges of two different types of BSCCO tape. The splices of both SS-laminated BSCCO tape and silver (Ag)-sheathed BSCCO tape have been used as cross bridges at the joint. The current–voltage $I$–$V$ characteristic curves of the joints were investigated at 77 K, which is liquid nitrogen temperature. Joint resistance has been estimated from the $I$– $V$ characteristic curve. The lowest joint resistance achieved at 77 K at self-field, with six bridges made of SS-laminated HTS tape, is 0.78 $mu Omega$, and the lowest joint resistance of six Ag-sheathed HTS bridges is 0.54 $muOmega$. The corresponding contact resistances are 0.402 and 0.27 $muOmegacdothbox{cm}^{2}$ for both types of joints.      

Effect of coefficient of thermal expansion on positive temperature coefficient of resistivity behavior of HDPE–Cu composites

Positive temperature coefficient of resistivity (PTCR) characteristics of (high density polyethylene) HDPE–Cu composites has been investigated with reference to the conventional HDPE–CB (carbon black) composites. Plot of resistivity against temperature of HDPE–CB composites showed a sudden rise in resistivity (PTC trip) at 127°C, close to the melting temperature of HDPE. However, the PTC trip temperature (98°C) for HDPE–Cu composites was appeared well below the melting temperature of HDPE. Addition of 1 phr nanoclay in the composites resulted in an increase in PTC trip temperature of HDPE–Cu composites, whereas no significant effect of nanoclay on PTC trip temperature was evident in case of HDPE–CB–clay composites. We proposed that the PTC trip temperature in HDPE–Cu composites was governed by the difference in coefficient of thermal expansion (CTE) of HDPE and Cu. The room temperature resistivity and PTC trip temperature of HDPE–Cu composites were very much stable upon thermal cycling. DMA results showed higher storage modulus of HDPE–Cu composites than the HDPE–CB composites. Thermal stability of HDPE–Cu composites was also improved compared to that of HDPE–CB composites. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Pomegranate (Punica granatum) juices: chemical composition, micronutrient cations, and antioxidant capacity

Abstract: Phenolics, flavonoids, anthocyanins, and tannins of pomegranate juices, obtained from 9 Tunisian ecotypes were quantified. Phenolics and flavonoids in the variety Tounsi (TN) (3299 mg gallic acid equivalents [GAE]/L and 636 mg quercetin equivalents [QE]/L of juice, respectively) were higher than in the variety Gabsi (GB) (1570 mg GAE/L and 135 mg QE/L of juice, respectively). The highest anthocyanins quantity was found in GB 2 with 156 mg cyanidin‐3‐glucoside equivalents (CGE)/L. TN 3 ecotype showed the highest tannins quantity with 2550 mg catechin equivalents (CE)/L of juice. TN 1 presented the highest radical‐scavenging activity (2, 2′‐azinobis‐3‐ethylbenzothiazoline‐6‐sulphonate [ABTS], IC₅₀ [50% inhibition concentration] = 525 mg/L), as well as the highest concentration of micronutrient cations (potassium and sodium). A high correlation (R²= 0.80) between antioxidant capacity and proanthocyanin contents was found, this suggests that proanthocyanins are the principal contributor in the antioxidant capacity of pomegranate. Our data suggest also that the high concentrations of K⁺ and Na⁺ may play a role in the adaptation of pomegranate to arid environments.     

Price elasticity and the growth of computer spending

The price of computers is a key factor in explaining the growth of computer spending. However, it remains unclear whether the price elasticity of the demand for computers is constant over time. Findings on the pattern of price elasticity will have important implications in the study of information technology (IT) innovation diffusion. To test the hypothesis of dynamic price elasticity, we extend existing growth models to include a price factor with different elasticity specifications. Nested specifications of three growth models were tested using spending data from 1955 to 1984 adjusted by a quality price index for computers. The results indicate that three out of four competing models depict dynamic price elasticity over the investigated period. A similar pattern is also observed when the models are estimated using more recent data on mainframe computer spending. Our results underscore the dynamic behavior of price sensitivity in computer spending over time. They offer a new perspective to study innovation attributes and to examine their impacts empirically over time. Implications for information systems (IS) management and IT suppliers are also discussed     

Performance Analysis of Aluminum- and Copper-Rotor Induction Generators Considering Skin and Thermal Effects

Recent progress in wind-power generation has led to the use of grid-connected and self-excited induction generators (SEIGs). Aluminum has been the common conductor material for squirrel-cage induction machines for a long time, largely because of low cost and ease of manufacturing. Recent developments in materials engineering have brought forth copper-rotor induction machines with promising results. In these machines, skin effect as well as temperature effect on the machine equivalent-circuit parameters during operation are expected to play an important role in the evaluation of induction-machine performance. In this paper, a qualitative performance analysis of aluminum- and copper-rotor SEIGs considering the skin and thermal effects has been presented theoretically and experimentally.     

The Temperature Uniformity During Air Drying of a Colloidal Liquid Droplet

ABSTRACT

The mathematical analysis for drying of individual droplets containing dissolved or suspended solids has been given significant importance due to the increasing popularity of the spray drying operation in the production of various chemicals, ceramics, drugs, food, and dairy powders as well as nanoparticles. The physical and biological qualities of the final products primarily depend on the history experienced by the droplet within the dryer. It is, therefore, desirable to ‘estimate’ the droplet's behavior and various characteristics such as moisture content and temperature profiles accurately. In the literature, several models have been presented to estimate moisture and temperature profiles inside a particle considering various assumptions. One common assumption is the uniform temperature distribution within the droplets being dried. The present article has presented an estimation procedure to evaluate the temperature distribution within a porous skim milk droplet to determine whether the uniform temperature distribution assumption is reasonable. Here, the surface-center temperature differences were estimated by considering the one-dimensional, unsteady-state heat conduction equation for a spherical droplet. Shrinkage of droplets was taken into consideration during modeling. A new concept of the Biot number has also been applied in the current article to assist in the determination of the rate-limiting process.