Ramazan Kahraman

Anomalous Manganese Activation of a Pyrophosphate Cathode in Sodium Ion Batteries: A Combined Experimental and Theoretical Study

Sodium ion batteries (SIBs) have many advantages such as the low price and abundance of sodium raw materials that are suitable for large-scale energy storage applications. Herein, we report an Mn-based pyrophosphate, Na(2)MnP(2)O(7), as a new SIB cathode material. Unlike most Mn-based cathode materials, which suffer severely from sluggish kinetics, Na(2)MnP(2)O(7) exhibits good electrochemical activity at ~3.8 V vs Na/Na(+) with a reversible capacity of 90 mAh g(-1) at room temperature. It also shows an excellent cycling and rate performance: 96% capacity retention after 30 cycles and 70% capacity retention at a c-rate increase from 0.05C to 1C. These electrochemical activities of the Mn-containing cathode material even at room temperature with relatively large particle sizes are remarkable considering an almost complete inactivity of the Li counterpart, Li(2)MnP(2)O(7). Using first-principles calculations, we find that the significantly enhanced kinetics of Na(2)MnP(2)O(7) is mainly due to the locally flexible accommodation of Jahn-Teller distortions aided by the corner-sharing crystal structure in triclinic Na(2)MnP(2)O(7). By contrast, in monoclinic Li(2)MnP(2)O(7), the edge-sharing geometry causes multiple bonds to be broken and formed during charging reaction with a large degree of atomic rearrangements. We expect that the similar computational strategy to analyze the atomic rearrangements can be used to predict the kinetics behavior when exploring new cathode candidates.

Finite Element Modeling of Thermopiezomagnetic Smart Structures

Linearconstitutiveequationsofa thermopiezomagneticmedium involving mechanical, electrical, magnetic, and thermal e elds are presented with the aid of a thermodynamic potential. A thermopiezomagnetic medium can be formed by bonding together a piezoelectric and magnetostrictive composite. Two energy functionals are dee ned. It is shown via Hamilton’ s principle that these functionals yield the equations of motion for the mechanical e eld, Maxwell’ s equilibrium equations for the electrical and magnetic e elds, and the generalized heat equation for the thermal e eld. Finite element equations for the thermopiezomagnetic media are obtained by using the linear constitutive equations in Hamilton’ s principle together with the e nite element approximations. The e nite element equations are utilized on an example two-layer smartstructure, which consistsof a piezoceramic (barium titanate ) layer at the bottom and a magnetoceramic (cobalt ferrite ) layer at the top. An electrostatic e eld applied to the piezoceramic layer causes strain in the structure. This strain then produces magnetic e eld in the magnetoceramic layer.

Thermodynamic analysis of convective heat transfer in an annular packed bed

A combination of the first and second law of thermodynamics has been utilized in analyzing the convective heat transfer in an annular packed bed. The bed was heated asymmetrically by constant heat fluxes. Introduction of the packing enhances wall to fluid heat transfer considerably, hence reduces the entropy generation due to heat transfer across a finite temperature diAerence. However, the entropy generation due to fluid-flow friction increases. The net entropy generations resulting from the above eAects provide a new criterion in analysing the system. Using the modified Ergun equation for pressure drop estimation and a heat transfer coeAcient correlation for an annular packed bed, an expression for the volumetric entropy generation rate has been derived and displayed graphically. In the packed annulus, the fully developed temperature profile and the plug flow conditions have been assumed and verified with experimental data. The volumetric entropy generation map shows the regions with excessive entropy generation due to operating conditions or design parameters for a required task, and leads to a better understanding of the behavior of the system. ” 2000 Elsevier Science Inc. All rights reserved.

Entropy generation in a rectangular packed duct with wall heat flux

The entropy generation due to heat transfer and friction has been calculated for fully developed, forced convection flow in a large rectangular duct, packed with spherical particles, with constant heat fluxes applied to both the top (heated) and bottom (cooled) wall. An approximate analytical expression for the velocity profile developed for packed bed with H/dp > 5 has been used together with the energy equation of fully developed flow to calculate the non-isothermal temperature profiles along the flow passage. The velocity profile takes into account the increase in the velocity near the wall due to the higher voidage in this region of the bed. The effect of the asymmetric heating on the velocity profile is neglected under the thermal conditions considered. The volumetric entropy generation rate and the irreversibility distribution ratios have been calculated and displayed graphically for the values of H/dp = 5 and 20. It was found that the irreversibility distributions are not continuous through the wall and core regions, hence the optimality criterion of equipartition of entropy generations should be considered separately for these regions of the packed duct.

Effect of fouling on operational cost in pipe flow due to entropy generation

The effect of fouling on thermodynamic performance can be evaluated by studying the increase of entropy generation rate due to fouling as compared to that for clean surface tubes. In this study, an attempt has been made to correlate the effect of fouling with entropy generation and related operational cost. In the model developed, fouling thickness and tube surface temperature are considered to be the main parameters. Numerical results of entropy generation and related operational cost due to both heat transfer and viscous friction under fouling conditions are presented and discussed.

Influence of Epolene G-3003 as a Coupling Agent on the Mechanical Behavior of Palm Fiber-Polypropylene Composites

ABSTRACT Composites of palm fiber and polypropylene were compounded using a mixing equipment connected to an extruder. The composites were then injection molded into standard tensile specimens for mechanical characterization. The fracture morphology of the specimens was also analyzed by Scanning electron microscopy. It was observed that as the fiber content increases the composite modulus also increases, which is an indication for the existence of adhesion to some degree between polypropylene and the much stiffer palm fiber. However, the adhesion is not satisfactory, resulting in decrease in composite tensile strength with fiber addition. The compatibilizer Epolene G-3003 was used to minimize this incompatibility between the wood fibers and the polypropylene matrix. Utilizing Epolene G-3003 improved the fiber-matrix adhesion, resulting in a significant improvement in composite performance. The composite strength with 40 wt% fiber content and 6 wt% compatibilizer almost reached the strength of pure polypropylene.

An Auger spectroscopic investigation of the high temperature reduction of zirconium dioxide surfaces in vacuum

Abstract The vacuum reduction of the ZrO 2 surface layer formed on oxygen-saturated zirconium has been investigated by Auger spectroscopy. Sputter-depth-profiles of the ZrO 2 layer show that its outer surface is reduced after exposure to UHV at 900 and 1100 K. The AES spectrum of Zr also evidences an increasing extent of partially reduced Zr on ZrO 2 surfaces as the UHV annealing temperature is increased from 800 to 1200 K. Quantitative Auger analyses of ZrO 2 surfaces show that the O/Zr surface atomic ratio remains near its stoichiometric value of 2 after UHV anneals at temperatures up to about 700 K. The surface O/Zr atomic ratio is about 1.1 after UHV annealing at 1000 K, with intermediate extents of surface reduction after UHV annealing between 700 and 900 K. This surface reduction occurs very rapidly and is essentially unaffected by extending the high temperature UHV anneal time from fractions of a min to 1 h. These observations provide support for a previously proposed mechanism for the catalytic reduction of CO by H 2 on ZrO 2 .

Plastics recycling: insights into life cycle impact assessment methods

Abstract The increased consumption of plastics in day to day life has a significant impact on the environment. Life cycle assessment (LCA) is widely used to select a sustainable alternative in plastic waste management. The LCA studies on mechanical recycling and energy recovery scenarios showed that recycling resulted in lower emissions and provided benefits to the environment. These results are valid only if the performance of the recycled plastic is equivalent to those of the virgin materials. Many LCA studies have been focused on individual impact categories rather than aggregated single score. The decision making process becomes complex if individual impact categories are used. This research is focused on the comparison of LCA results between individual and aggregated impacts and integration of performance of recycled plastics in LCA. The results indicated that recycling was the preferred option if it could replace a minimum of 70–80% of virgin plastics.

Investigation by Auger spectroscopy of the composition and surface oxidation characteristics of oxygen saturated zirconium

Abstract The surface oxidation characteristics of oxygen saturated zirconium (Zr:O ss ) have been investigated between room temperature and 1190 K using Auger spectroscopy and sputter-depth-profiling techniques. Zr:O ss substrates were prepared by absorbing oxygen from surface oxide layers into Zr foils at high temperature. Quantitative Auger analysis confirms that the composition of Zr:O ss is approximately ZrO 0.44 .Zr:O ss oxidizes slightly faster at room temperature than pure Zr during initial O 2 exposure. The high temperature surface oxidation of Zr:O ss was studied in the absence of interference from the simultaneous bulk absorption of oxygen, which occurs with pure Zr substrates. The thickness of the ZrO 2 surface layer formed on Zr:O ss increases with the extent of O 2 exposure, exposure time and oxidation temperature up to 900 K. Above 900 K the surface oxidation is not complete to ZrO 2 .

A mixed iron–manganese based pyrophosphate cathode, Na2Fe0.5Mn0.5P2O7, for rechargeable sodium ion batteries

The development of secondary batteries based on abundant and cheap elements is vital. Among various alternatives to conventional lithium-ion batteries, sodium-ion batteries (SIBs) are promising due to the abundant resources and low cost of sodium. While there are many challenges associated with the SIB system, cathode is an important factor in determining the electrochemical performance of this battery system. Accordingly, ongoing research in the field of SIBs is inclined towards the development of safe, cost effective cathode materials having improved performance. In particular, pyrophosphate cathodes have recently demonstrated decent electrochemical performance and thermal stability. Herein, we report the synthesis, electrochemical properties, and thermal behavior of a novel Na2Fe0.5Mn0.5P2O7 cathode for SIBs. The material was synthesized through a solid state process. The structural analysis reveals that the mixed substitution of manganese and iron has resulted in a triclinic crystal structure (P1[combining macron] space group). Galvanostatic charge/discharge measurements indicate that Na2Fe0.5Mn0.5P2O7 is electrochemically active with a reversible capacity of ∼80 mA h g(-1) at a C/20 rate with an average redox potential of 3.2 V. (vs. Na/Na(+)). It is noticed that 84% of initial capacity is preserved over 90 cycles showing promising cyclability. It is also noticed that the rate capability of Na2Fe0.5Mn0.5P2O7 is better than Na2MnP2O7. Ex situ and CV analyses indicate that Na2Fe0.5Mn0.5P2O7 undergoes a single phase reaction rather than a biphasic reaction due to different Na coordination environment and different Na site occupancy when compared to other pyrophosphate materials (Na2FeP2O7 and Na2MnP2O7). Thermogravimetric analysis (25-550 °C) confirms good thermal stability of Na2Fe0.5Mn0.5P2O7 with only 2% weight loss. Owing to promising electrochemical properties and decent thermal stability, Na2Fe0.5Mn0.5P2O7, can be an attractive cathode for SIBs.