The Boudouard reaction, which is the reaction of carbon and carbon dioxide to produce carbon monoxide, represents a simple and straightforward method for the remediation of carbon dioxide in the ...environment through reduction: CO2(g) + C(s) ⇌ 2CO. However, due to the large positive enthalpy, typically reported to be 172 kJ/mol under standard conditions at 298 K, the equilibrium does not favor CO production until temperatures >700 °C, when the entropic term, −TΔS, begins to dominate and the free energy becomes negative. We have found that, under microwave irradiation to selectively heat the carbon, dramatically different thermodynamics for the reaction are observed. During kinetic studies of the reaction under conditions of flowing CO2, the apparent activation energy dropped from 118.4 kJ/mol under conventional convective heating to 38.5 kJ/mol under microwave irradiation. From measurement of the equilibrium constants as a function of temperature, the enthalpy of the reaction dropped from 183.3 kJ/mol at ∼1100 K to 33.4 kJ/mol at the same temperature under microwave irradiation. This changes the position of the equilibrium so that the temperature at which CO becomes the major product drops from 643 °C in the conventional thermal reaction to 213 °C in the microwave. The observed reduction in the apparent enthalpy of the microwave driven reaction, compared to what is determined for the thermal reaction from standard heats of formation, can be thought of as arising from additional energy being put into the carbon by the microwaves, effectively increasing its apparent standard enthalpy. Mechanistically, it is hypothesized that the enhanced reactivity arises from the interaction of CO2 with the steady-state concentration of electron–hole pairs that are present at the surface of the carbon due to the space-charge mechanism, by which microwaves are known to heat carbon. Such a mechanism is unique to microwave-induced heating and, given the effect it has on the thermodynamics of the Boudouard reaction, suggests that its use may yield energy savings in driving the general class of gas–carbon reactions.
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Polymers with crystallizable side chains have numerous applications, and their properties depend on their crystal morphologies and phase separation. Structural analysis on a wide spatial scale plays ...an important role in controlling the thermal properties and higher-order structures of these polymers. In this study, we elucidated the melting and crystallization processes of copolymers with varying crystallizable side-chain fractions over a wide spatial range. Differential scanning calorimetry revealed that the enthalpies of melting and crystallization increased linearly with increasing crystallizable side-chain fraction. The results of wide-angle X-ray scattering indicated that the crystal lattice was hexagonal. Conversely, spherulite-like higher-order architectures with linear structures and radial spreading were observed in the highly crystallizable components, but no micrometer-scale structures were observed in the less crystallizable components. In situ small-angle X-ray scattering was used to elucidate the phase separation and mixing processes. Lamellar crystallites were observed at crystallizable side-chain fractions of >55 wt.%, whereas small crystallites were observed at fractions of <45 wt.%. At temperatures above the order-disorder transition temperature, density fluctuations caused by correlation holes were observed. These properties have a strong effect on the crystallizable side-chain fraction.
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The problem of natural convective boundary-layer flow of a nanofluid past a vertical plate is revisited. The model, which includes the effects of Brownian motion and thermophoresis, is revised so ...that the nanofluid particle fraction on the boundary is passively rather than actively controlled. In this respect the model is more realistic physically than that employed by previous authors.
•The problem of natural convective boundary-layer flow of a nanofluid past a vertical plate is revisited.•The model is revised so that the nanofluid particle fraction on the boundary is passively rather than actively controlled.•The model is more realistic physically than that employed by previous authors.
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Heat transfer and fluid flow due to buoyancy forces in a partially heated enclosure using nanofluids is carried out using different types of nanoparticles. The flush mounted heater is located to the ...left vertical wall with a finite length. The temperature of the right vertical wall is lower than that of heater while other walls are insulated. The finite volume technique is used to solve the governing equations. Calculations were performed for Rayleigh number (10
3
⩽
Ra
⩽
5
×
10
5), height of heater (0.1
⩽
h
⩽
0.75), location of heater (0.25
⩽
y
p
⩽
0.75), aspect ratio (0.5
⩽
A
⩽
2) and volume fraction of nanoparticles (0
⩽
φ
⩽
0.2). Different types of nanoparticles were tested. An increase in mean Nusselt number was found with the volume fraction of nanoparticles for the whole range of Rayleigh number. Heat transfer also increases with increasing of height of heater. It was found that the heater location affects the flow and temperature fields when using nanofluids. It was found that the heat transfer enhancement, using nanofluids, is more pronounced at low aspect ratio than at high aspect ratio.
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The discovery of graphene has put the spotlight on other layered materials including transition metal dichalcogenites (TMD) as building blocks for novel heterostructures assembled from stacked atomic ...layers. Molybdenum disulfide, MoS2, a semiconductor in the TMD family, with its remarkable thermal and chemical stability and high mobility, has emerged as a promising candidate for postsilicon applications such as switching, photonics, and flexible electronics. Because these rely on controlling the position of the Fermi energy (E F), it is crucial to understand its dependence on doping and gating. To elucidate these questions we carried out gated scanning tunneling microscopy (STM) and spectroscopy (STS) measurements and compared them with transport measurements in a field effect transistor (FET) device configuration. This made it possible to measure the bandgap and the position of E F in MoS2 and to track its evolution with gate voltage. For bulk samples, the measured bandgap (∼1.3 eV) is comparable to the value obtained by photoluminescence, and the position of E F (∼0.35 eV) below the conduction band, is consistent with N-doping reported in this material. We show that the N-doping in bulk samples can be attributed to S vacancies. In contrast, the significantly higher N-doping observed in thin MoS2 films deposited on SiO2 is dominated by charge traps at the sample–substrate interface.
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The boundary layer flow induced in a nanofluid due to a linearly stretching sheet is studied numerically. The transport equations include the effects of Brownian motion and thermophoresis. Unlike the ...commonly employed thermal conditions of constant temperature or constant heat flux, the present study uses a convective heating boundary condition. The solutions for the temperature and nanoparticle concentration distributions depend on five parameters, Prandtl number
Pr, Lewis number
Le, the Brownian motion parameter
Nb, the thermophoresis parameter
Nt, and convection Biot number
Bi. Numerical results are presented both in tabular and graphical forms illustrating the effects of these parameters on thermal and concentration boundary layers. The thermal boundary layer thickens with a rise in the local temperature as the Brownian motion, thermophoresis, and convective heating each intensify. The effect of Lewis number on the temperature distribution is minimal. With the other parameters fixed, the local concentration of nanoparticles increases as the convection Biot number increases but decreases as the Lewis number increases. For fixed
Pr,
Le, and
Bi, the reduced Nusselt number decreases but the reduced Sherwood number increases as the Brownian motion and thermophoresis effects become stronger.
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Tremendous research works have been done to develop better cathode materials for a large scale battery to be used for electric vehicles (EVs). Spinel LiMn2O4 has been considered as the most promising ...cathode among the many candidates due to its advantages of high thermal stability, low cost, abundance, and environmental affinity. However, it still suffers from the surface dissolution of manganese in the electrolyte at elevated temperature, especially above 60 °C, which leads to a severe capacity fading. To overcome this barrier, we here report an imaginative material design; a novel heterostructure LiMn2O4 with epitaxially grown layered (R3̅m) surface phase. No defect was observed at the interface between the host spinel and layered surface phase, which provides an efficient path for the ionic and electronic mobility. In addition, the layered surface phase protects the host spinel from being directly exposed to the highly active electrolyte at 60 °C. The unique characteristics of the heterostructure LiMn2O4 phase exhibited a discharge capacity of 123 mAh g–1 and retained 85% of its initial capacity at the elevated temperature (60 °C) after 100 cycles.
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We report the measurement of the thermal conductivity of a suspended single-layer graphene. The room temperature values of the thermal conductivity in the range ∼(4.84 ± 0.44) × 103 to (5.30 ± 0.48) ...× 103 W/mK were extracted for a single-layer graphene from the dependence of the Raman G peak frequency on the excitation laser power and independently measured G peak temperature coefficient. The extremely high value of the thermal conductivity suggests that graphene can outperform carbon nanotubes in heat conduction. The superb thermal conduction property of graphene is beneficial for the proposed electronic applications and establishes graphene as an excellent material for thermal management.
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39.
Effects of Different Polypropylene Momeni, Vahid; Shahroodi, Zahra; Gonzalez-Gutierrez, Joamin ...
Polymers,
07/2023, Volume:
15, Issue:
14
Journal Article
Peer reviewed
The current study presents the effect of the backbone as an important binder component on the mechanical, rheological, and thermal properties of Aluminium (Al) alloy feedstocks. A thermoplastic ...elastomer (TPE) main binder component was blended with either polypropylene (PP), grafted-maleic anhydride-PP (PPMA), or grafted-maleic anhydride-PPwax (PPMAwax) plus PP, as the backbone. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) tests were performed to investigate the thermal properties of binder systems and feedstocks. Fourier-transform infrared (FTIR) spectroscopy was used to study the chemical interaction between the binder and the Al alloy. After making feedstock filaments, tensile tests, scanning electron microscopy (SEM), and fused filament fabrication (FFF) printing were done. The results showed that although the PP printability was acceptable, the best mechanical properties and printed quality can be achieved by PPMA. TGA test showed that all binder systems in the feedstocks could be removed completely around 500 °C. From FTIR, the possibility of chemical reactions between Al alloy particles and maleic anhydride groups on the grafted PP backbone could explain the better dispersion of the mixture and higher mechanical properties. Tensile strength in PP samples was 3.4 MPa which was improved 1.8 times using PPMA as the backbone.
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In this study, free convection heat transfer in a concentric annulus between a cold square and heated elliptic cylinders in presence of magnetic field is investigated. The square and elliptic ...cylinders are maintained at uniform temperatures and it is assumed that the walls are insulating magnetic field. Lattice Boltzmann method is applied to solve the governing equations. The effective thermal conductivity and viscosity of nanofluid are calculated by KKL (Koo–Kleinstreuer–Li) correlation. In this model effect of Brownian motion on the effective thermal conductivity is considered. The numerical investigation is carried out for different governing parameters namely; the Hartmann number, Rayleigh number and nanoparticle volume fraction. Also a correlation of Nusselt number corresponding to active parameters is presented. The results reveal that average Nusselt number is an increasing function of nanoparticle volume fraction and Rayleigh number, while it is a decreasing function of Hartmann number. Moreover it can be found that the enhancement in heat transfer increases as Hartmann number increases but it decreases with increase of Rayleigh number.
•MHD free convection of nanofluid in a semi annulus enclosure is studied.•LBM is applied to solve this problem.•KKL correlation is used to simulate knf and μnf.•Nuave is an increasing function of ϕ and Ra, while it is a decreasing function of Ha.
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