Studied Temperature Range Research Articles

Ab Initio Molecular Dynamics Investigation of CH4/CO2 Adsorption on Calcite: Improving the Enhanced Gas Recovery Process.

Ab initio molecular dynamics simulations of CH4 and CO2 on the calcite (104) surface have been carried out for the molecular level analysis of CO2-enhanced gas recovery process (EGR). This process takes advantage of the stronger interaction of CO2 with the reservoir walls compared to CH4, therefore can improve the extraction of the latter, while at the same time sequestering the former underground. Pure and mixed gases were considered and the temperature effect on the systems behavior was analyzed. For pure gases, carbon dioxide shows great stability on the surface in the studied temperature range, while methane molecules start leaving the surface at 298 K. For gas mixtures, the reported results confirm that for low to medium concentrations, a temperature of 373 K could determine the best methane extraction efficiency, as CH4 interaction with the surface is quite weak and carbon dioxide binds strongly on the surface. On the other hand, when full coverage is achieved, the best efficiency is reached for the highest temperature. Finally, when considered a 2:2 gas layer, carbon dioxide tends to adsorb preferentially to the surface while methane keeps floating above it, thereby reducing its chance to be adsorbed back. These results reveal nanoscopic details for the design of suitable EGR processes.

Structure and diffuse dielectric study of CCT1-xBixO thin film for x=0.02 synthesized via untraditional sol-gel route

Using modified sol-gel route the prepared bismuth doped CaCu3Ti4O12 (CCTO) ceramic thin film is subjected to X-Ray diffraction followed by reitveld refinement using Maud (2.92) for structural analysis. The structural data are presented in the text. The micrographs of Scanning Electron Microscope (SEM) show randomly oriented and dense rod like microstructure. This type of microstructure is not yet reported and hence here it is presented for the first time in this material. The dielectric constant of the film is measured in the frequency range 100 Hz- 1 MHz with variation in temperature from 100 to 600 K. The observed typical relaxor behaviour of the material is confirmed by peaks broadening at low frequency with increasing temperature and the peaks shift to low frequency region with decreasing temperature. This relaxation behaviour arises due to space charge polarization. The broad band spectrum of high dielectric constant is seen over the studied temperature range.

Dielectric Relaxation and Impedance Spectroscopy of 30V2O5 · 20Bi2O3 · 50P2O5 Glass

Dielectric properties of traditionally quenched 30V2O5 · 20Bi2O3 · 50P2O5 glass been investigated at different frequencies in temperature range of 298–573 K. X-ray diffraction (XRD) was used to confirm the amorphous nature of the formed glass and for ion. The thermal analysis was investigated by differential scanning calorimetry (DSC) technique where the temperature stability i.e. Tc–Tg of the glass sample was 207.5 K. This means that the present glass has a high thermal stability. Dielectric constant, dielectric loss, loss tangent, ac conductivity and electric modulus were calculated for the formed glass in the studied temperature range. The prepared glass has a large dielectric constant increase with temperature. The activation energy calculated from dc conductivity Edc, dielectric loss Etan δ and $${{E}_{{{{M}^{{'{\kern 1pt} '}}}}}}$$ modulus frequency relaxation time was 0.180, 0.209 and 0.185 eV, respectively. Activation energy values of Edc and $${{E}_{{{{M}^{{'{\kern 1pt} '}}}}}}$$ are nearly identical, indicate that the ions overcome same energy barrier in conducting and relaxing process. The small value of stretched exponent parameter (β) of 0.061 suggests good correlated motion between the ions of non-Debye-type relaxation. The semicircles formed with Nyquist diagram indicate a single-phase material with electronic type of conduction mechanism.

Influence of Temperature and Temperature Prehistory on Frictional Characteristics of Metal Friction Pairs

The temperature effect on the frictional characteristics of a silver-silver friction pair was experimentally studied. These characteristics are as follows: Amontons’ and Coulomb’s friction coefficients and specific friction force parameters. The applicability of the Coulomb’s friction law to the description of the friction force dependence on the normal load in the studied temperature range is substantiated. In addition, the experiments showed that the contact frictional characteristics are significantly affected by its temperature prehistory and the temperature variation direction during the experiment—from room to maximum or from maximum to room.

Caloric properties of Cs60Bi40 alloy in the temperature range of 293-1125 K

The results of the enthalpy measurements of the Cs60Bi40 alloy in the range of 431–1127 K of the solid and liquid states are presented. The experiments were carried out by the mixing method on a massive isoperibolic calorimeter. The estimated errors for enthalpy and heat capacity of the melt were 0.4 and 1.4%, respectively. It was shown that the heat capacity of the melt decreases linearly with increasing temperature, and its absolute value in the studied temperature range is 1.25–1.45 times higher than the additive value. Table of recommended values of caloric properties over the range from 298.15 K to 1175 K was developed.

Isothermal thermogravimetric method using a fast scanning calorimeter and its application in the isothermal oxidation of nanogram-weight polypropylene

Conventional thermogravimetry (TG) is a common method for studying thermal degradation and/or thermal oxidation of polymers. However, the temperature range for isothermal TG studies is limited to regions close to the melting temperature, where thermal degradation and/or thermal oxidation proceed slowly. Higher temperatures cannot be reached because thermal degradation and/or thermal oxidation start upon heating, even using the highest possible heating rate of the conventional TG. The method of fast scanning calorimetry (FSC) to obtain a quasi-real-time isothermal TG curve via a nanogram-weight sample (nano-TG method) was reported. During the 50 cycles of FSC measurements of polypropylene (PP) between room temperature and 300 °C, regardless of air flow, all FSC traces were consistent with each other (i.e., thermal oxidation of PP was fully suppressed during the fast scanning). On the other hand, when the sample was annealed for a few seconds at 300 °C during the cyclic FSC runs, the apparent heat capacity (which can be converted into relative weight) decreased with increasing total annealing time. The decrease in apparent heat capacity is explained by the progression of thermal oxidation. The nano-TG method was applied to determine the thermal oxidation kinetics of PP using the Avrami-Erofeev model. The non-isothermal TG curve calculated from the kinetic parameters of the nano-TG analysis was in good agreement with the experimental data obtained from the conventional TG measurements for the early stage of weight loss. The present method is applicable for the thermal degradation/oxidation analysis of microplastics in the environment or small impurity analysis of polymers.

Enhanced magnetocaloric effect and magnetic phase diagrams of single-crystal GdCrO3

The crystalline structure, magnetism, and magnetocaloric effect of a GdCrO$_3$ single crystal grown with the laser-diode-heated floating-zone technique have been studied. The GdCrO$_3$ single crystal crystallizes into an orthorhombic structure with the space group $Pmnb$ at room temperature. Upon cooling, under a magnetic field of 0.1 T, it undergoes a magnetic phase transition at $T_{\textrm{N-Cr}} =$ 169.28(2) K with Cr$^{3+}$ ions forming a canted antiferromagnetic (AFM) structure, accompanied by a weak ferromagnetism. Subsequently, a spin reorientation takes place at $T_{\textrm{SR}} =$ 5.18(2) K due to Gd$^{3+}$-Cr$^{3+}$ magnetic couplings. Finally, the long-range AFM order of Gd$^{3+}$ ions establishes at $T_{\textrm{N-Gd}} =$ 2.10(2) K. Taking into account the temperature-(in)dependent components of Cr$^{3+}$ moments, we obtained an ideal model for describing the paramagnetic behavior of Gd$^{3+}$ ions within 30--140 K. We observed a magnetic reversal (positive $\rightarrow$ negative $\rightarrow$ positive) at 50 Oe with a minimum centering around 162 K. In the studied temperature range of 1.8-300 K, there exists a strong competition between magnetic susceptibilities of Gd$^{3+}$ and Cr$^{3+}$ ions, leading to puzzling magnetic phenomena. We have built the magnetic-field-dependent phase diagrams of $T_{\textrm{N-Gd}}$, $T_{\textrm{SR}}$, and $T_{\textrm{N-Cr}}$, shedding light on the nature of the intriguing magnetism. Moreover, we calculated the magnetic entropy change and obtained a maximum value at 6 K and ${\Delta}{\mu}_0H$ = 14 T, i.e., -${\Delta}S_{\textrm{M}} \approx$ 57.5 J/kg K. Among all RCrO$_3$ (R = $4f^n$ rare earths, $n =$ 7-14) compounds, the single-crystal GdCrO$_3$ compound exhibits the highest magnetic entropy change, as well as an enhanced adiabatic temperature, creating a prominent magnetocaloric effect for potential application in magnetic refrigeration.

Reaction kinetics of a series of alkenes with ClO and BrO radicals: A theoretical study

AbstractQuantum chemical calculations were used to investigate the mechanism and kinetics of the reaction of XO (X = Cl, Br) radicals with linear C2 to C4 alkenes. Two reaction routes, namely, addition and H‐abstraction, were investigated as part of the XO‐radical initiated degradation of these alkenes. Energies and structural parameters were obtained at the CCSD(T)/CBS//M062x/cc‐pVTZ level of theory, and the canonical variational transition state theory with small‐curvature tunneling corrections was used to calculate rate constants at temperatures spanning 200‐3000 K. The addition of the electron‐deficient XO radical onto the olefinic moiety was the major degradation channel, owing to its low barrier heights. Moreover, the H‐abstraction route also played a key role in governing the fate of the alkene in the high‐temperature regime, when compared to the addition routes. The computed branching ratios for various reaction routes further ascertained the relative dominance of the addition and H‐abstraction routes over the studied temperature range. The computed kinetic and thermodynamic parameters can be beneficial towards designing a better chemical kinetic model, relevant for both atmospheric as well as combustion systems. In addition to this, the formed HOCl (or HOBr) can damage the ozone layer and cause ecological imbalance.

Triethylene Glycol Dehydration by Thermopervaporation

A wide range of membranes (hydrophobic and hydrophilic) for the task of triethylene glycol dehydration by thermopervaporation was studied. The transport characteristics of the membranes using individual liquids (water, triethylene glycol) were determined in the thermopervaporation process with varying temperature of the feed flux (40-). The maximum water flux (3.7 kg/m2∙h) in all the studied temperature ranges was demonstrated by the commercial pervaporation hydrophobic PolyAn membrane. For the commercial hydrophilic membrane MDK-I water flux at 80 °С was 2.8 kg/m2∙h. During thermopervaporation of triethylene glycol in the studied temperature range, TEG flux through the membranes was not observed, which shows the advantage of this process for TEG dehydration. For the first time, experiments were provided using PolyAn membranes to removal water from TEG by thermopervaporation with porous condenser. The maximum permeate flux (1.9 kg/m2∙h) was achieved for the PolyAn membrane at a concentration of 70 % wt. TEG in water

Mg-substitution effect on microstructure, dielectric relaxation and conduction phenomenon of Fe based perovskite nanomaterials

In this work, we have investigated the electrical and dielectric properties of the Mg doped perovskite (La0.8Ca0.1Pb0.1Fe1-xMgxO3 (x = 0.0, x = 0.1 and x = 0.2)) using the electrical impedance spectroscopy in the temperature range of (200–320 K). The crystal structure evaluated by X-Ray diffraction proved an orthorhombic structure of all the studied compounds with a Pbnm space group. Impedance fitting based on an equivalent circuit and the M″ fitting confirmed the existence of two relaxation phenomena attributed to grains and grain boundaries contributions. The study of the dc electrical conductivity proved that all compounds followed the variable range hopping (VRH) model at low temperature and the Arrhenius model at high temperature range. From conductivity analysis and the temperature dependence of the Jonscher’s power low exponent, we noted an alternation of correlated barrier hopping (CBH) and non-overlap small polaron tunneling model (NSPT) conduction processes at the studied temperature range. The relaxation phenomenon for both contributions and the deduced activation energies were found to be sensitive to the Mg composition; for the grain contribution, a minimum activation energy value was recorded for x = 0.1 compound and increased for suplementary Mg content. While, for grain contribution the activation decreases with the increase in Mg ion concentration. Concerning the evolution of the magnetization versus temperature, it was measured to investigate the effect of the Mg amount on the magnetic behavior of the prepared compounds under the studied temperature range.

Features of the electrical resistivity as a function of temperature in GdxPb1−xMo6S8 (x = 0.5, 0.7, and 0.9) superconductors

For the first time, the temperature ρ(T) and magnetic field ρ(H) dependences of the electrical resistivity have been studied in compounds GdxPb1−xMo6S8 (x = 0.5, 0.7, 0.9), in the temperature range 2–300 K and magnetic fields up to 9 T. In the absence of a magnetic field, the compounds Gd0.9Pb0.1Mo6S8 and Gd0.7Pb0.3Mo6S8 exhibit features along ρ(T) (maximum and minimum for Gd0.9Pb0.1Mo6S8, and an inflection for Gd0.7Pb0.3Mo6S8), in some temperature ranges. The ρ(T) dependence of Gd0.5Pb0.5Mo6S8 is monotonic over the entire investigated temperature range. The presence of a small positive magnetoresistance (up to 2%) is established, which peaks at temperatures where there are features. It is shown that the dependence of the magnetization M(T) in the studied temperature range does not have features associated with long-range magnetic transformations. It is suggested that the features along the ρ(T) of Gd0.9Pb0.1Mo6S8 and Gd0.7Pb0.3Mo6S8 can be caused by band structure rearrangement, and the appearance of two charge carrier channels that are responsible for the semiconductor and metallic behavior of the temperature dependences of the electrical resistivity.

Comparative investigation of electrophysical characteristics of ceramic and single crystal LiNbO3

Electrophysical characteristics have been studied in ceramic and single crystal LiNbO3 of congruent and near-congruent composition. The comparative study has been carried out in a wide temperature range (290-800 K). Dispersion of the real part of the dielectric constant ε′ has been considered. Temperature dependences ε′(T) and σ(T) have been obtained and value of static conductivity has been determined in ceramic and single crystal LiNbO3 in the given temperature range. Temperature dependences of specific static conductivity σ dc have been obtained due to impedance spectroscopy data analysis. Ceramic LN conductivity has been shown to be much higher in the whole studied temperature range. Charge carriers activation enthalpy in high-temperature area (above 420 K) is H a = 0.88 eV for ceramic LN and H a = 1.24 eV for single crystal LN.

Electrical and Photoelectric Properties of α-Si/SiO2 and α-Ge/SiO2 Multilayer Nanostructures on p-Si Substrates Annealed at Various Temperatures

The properties of multilayer α-Si(Ge)/SiO2 nanostructures deposited onto p-Si substrates and annealed at various temperatures are investigated. The total nanolayer thickness is no larger than 300–350 nm. It is found that despite the formation of crystals in a nanolayer, the quantum-size effect does not manifest itself in the photoelectric properties of the nanolayer–substrate heterojunction in the studied temperature range of 300–900 nm. At the same time, the photocurrent efficiency (A/W) in this range becomes constant. The found results are explained by a small nanolayer thickness. When applying a sufficiently large lock bias, the electric field of the nanolayer–substrate junction reaches the outer nanolayer boundary, which abruptly decreases the surface carrier recombination. Just this recombination usually suppresses the photodetector sensitivity in the short-wavelength spectral region. The constant efficiency of the studied heterostructures in a broad spectral range makes them attractive for use in various photoelectric devices.

Eutectic ionic liquids as potential electrolytes in dye-sensitized solar cells: Physicochemical and conductivity studies

Ionic liquids (ILs) have been introduced as the electrolyte in dye-sensitized solar cells (DSSC) to replace organic solvents due to their non-flammability, chemical, and thermal stability, as well as less prone to evaporation and leakage. A series of eutectic ILs mixtures composed of 1-ethyl-3-methylimidazolium iodide, [C2C1im]I, 1-ethylpyridinium iodide [C2py]I, 1-propylpyridinium iodide, [C3py]I and 1-butylpyridinium iodide, [C4py]I was developed. The structures and purity of the compounds were validated by nuclear magnetic resonance and Karl Fischer Titration. Their physicochemical properties, such as viscosities and ionic conductivities were evaluated for their potential use as electrolytes in DSSCs. The melting temperature of pure ionic liquids and the mixtures were determined using differential scanning calorimetry in the temperature range of 123.15 K to 393.15 K. It is found that eutectic mixtures were formed at the molar ratios of {0.75[C2py]I:0.25[C2C1im], {0.25[C2py]I:0.75[C2C1im]I}, {0.50[C2py]I:0.50[C2C1im]I}, {0.25[C2C1im]I:0.75 [C4py]I}, {0.75[C2C1im]I:0.25[C4py]I}, and {0.50[C2C1im]I:0.50[C4py]I} with the latter forming a highly stable liquid with no apparent melting peak in the studied temperature range. To understand the formation of eutectic composition, a correlation between molecular structures and the interaction energies of the cations and anions of ILs was performed using the Conductor-like Screening Model for Real Solvents (COSMO-RS). Dynamic viscosities of the binary mixtures were evaluated in the temperature range of 283.15 K to 353.15 K with 10 K increment. The highest ionic conductivity was exhibited by the eutectic ILs electrolyte {0.50[C2C1im]I:0.50[C4py]I:I2(50 wt%)} at 9.67 mS·cm−1 showing its potential for electrolyte application in DSSC.

Reaction kinetics of a series of alkanes with ClO and BrO radicals: A theoretical study

AbstractReactive halogen species (ClO and BrO) play a critical role in the stratospheric ozone depletion. However, the reactivity of these radical moieties with volatile organic compounds is also important in determining the composition of the Earth's atmosphere. In this study, the reactions of BrO and ClO radicals with a series of smaller linear alkanes (CnH2n+2, n = 1,2,3, and 4) were studied using the CCSD(T)/CBS//B3LYP/cc‐pVTZ level of theory. The kinetics of the title reactions were evaluated using the Canonical Variational Transition (CVT)/Small Curvature Tunneling (SCT)/Interpolated Single Point Energy (ISPE) methodology over the studied temperature range of 200‐3000 K. H‐abstraction from the nonterminal carbon was found to be thermodynamically and kinetically favorable in comparison to abstraction of H atom from the primary carbon. On a per‐hydrogen basis at 298 K, BrO and ClO are focused to abstract the secondary hydrogens of C3H8 faster than the primary hydrogens by factors of 40 and 110, respectively. On the other hand, for n‐C4H10 at the same temperature, the per‐hydrogen preferences for secondary H atoms are found to be factors of 220 and 270 for BrO and ClO, respectively. To aid in modeling the stratospheric environment and combustion regime, three parameter fits to the computed rate constants between 200 and 3000 K are provided. The branching ratios and thermochemical parameters for the various reaction channels are also discussed in this paper.

Novel cadmium substituted barium zinc niobate perovskites: Phase formation, structural and impedance studies

Herein we report the structural and impedance properties of the novel Cd-substituted perovskites, Ba(Zn1/3-xCdx)Nb2/3O3 (BZCN), 0 ≤ x ≤ 0.333, prepared by solid-state reaction at 1000 °C for 17 h. The doping mechanism of this complete substitutional solid solution was proposed to be a one-to-one replacement of Zn2+ by Cd2+ as to maintain the overall electroneutrality of the system. BZCN perovskites crystallised in a cubic symmetry, space group Pm3m, Z = 1 and their refined lattice constants, a = b = c were found to be in the range 4.0917(3)-4.1693(13) Å. A moderate unit cell expansion was discernible with increasing CdO concentration, thus portraying a linear correlation between lattice constant and composition that obeyed the Vegard's law. The surface microstructures of these BZCN perovskites were composed of irregular polyhedral grains and their determined crystallite sizes by both Scherrer and Williamson-Hall methods were found to be in the range 21.0–44.8 nm. Both TGA and DTA analyses also confirmed that these materials were thermally stable as neither phase transition nor weight loss was discernible within the studied temperature range 30–1000 °C. BZCN perovskites were highly insulating with high activation energies in the range ~ 2.51–3.19 eV. At 1 MHz and 30 °C, the recorded dielectric constants and losses were found to be ~ 24–29 and ~ 0.24–0.38, respectively.

Effect of preparation method on NH3-SCR activity of Cu-LTA catalysts

The preparation method effect on the catalytic properties and hydrothermal stability of copper-loaded LTA (Cu-LTA) zeolites for the selective catalytic reduction of NOx with NH3 (NH3-SCR) has been investigated. Copper nitrate and liquid-state ion exchange (IE) was found to be the best for maximizing the SCR performance of Cu-LTA among the Cu sources and loading methods studied here. When fresh, the low-temperature (≤ 400 °C) activity of Cu-LTA prepared in this way, denoted Cu-LTA(n)IE, is lower than that of the catalyst prepared using copper acetate via ion exchange. After hydrothermal aging at 900 °C for 24 h, however, Cu-LTA(n)IE shows a higher deNOx activity in the studied temperature range than any other catalysts. The overall characterization results show that the excellent hydrothermal durability of Cu-LTA(n)IE resulted from the stability of [2Z-Cu] species generated by locating Cu2+ ions onto Al pairs in the LTA framework.

Removal of AV 90 dye using ordered mesoporous carbon materials prepared via nanocasting of KIT-6: Adsorption isotherms, kinetics and thermodynamic analysis

CMK-8 type ordered mesoporous carbon (OMC) materials were prepared by hard-templating method using KIT-6 as a mesoporous silica template. The influence of synthesis parameters on the structural properties of KIT-6 and OMC samples was investigated. In the studied temperature range (60–150 °C), suitable hydrothermal treatment temperature to obtain well-ordered mesoporous KIT-6 sample was determined as 120 °C. Mesoporous carbons were prepared by using KIT-120 sample as a hard-template. NaOH solution was used to remove silica from the silica–carbon matrix and at the end of two leaching cycles, the pore volume and the surface area decreased by 1/3 with the change in NaOH concentration from 1 M to 4 M. Finally, 2 M NaOH concentration and one leaching number were determined as the best conditions to obtain mesoporous carbon (C2M1) with a high uniformity, high surface area (1020 m2/g), high pore volume (0.98 cm3/g), and relatively high wall thickness (6.25 nm). In the adsorption studies, the optimum pH value was determined as 2 for anionic Acid Violet 90 (AV 90) dye adsorption on C2M1 sorbent. The highest dye removal was achieved as 1311.5 mg/g at 298 K, pH 2 and 360 mg/L dye concentration. Langmuir, Freundlich, Temkin, and Henry adsorption isotherm models were used to examine the adsorption mechanism, and Freundlich isotherm model with a relatively higher correlation factor (R2 > 0.94) was found to be the best-fitted model to the experimental data. Pseudo second order kinetic model was determined as suitable to explain kinetic behavior of the adsorption process. Thermodynamic analysis of the experimental data revealed that the adsorption process of AV 90 dye on C2M1 sorbent was exothermic with an enthalpy change of –22.82 kJ/mol and the activation energy was found to be 45.8 kJ/mol. The N2 adsorption–desorption and FTIR analysis of the used sorbent revealed that the mesopore structure was preserved and there was no significant change in structural bonds after AV 90 adsorption. Results show that CMK-8 type mesoporous carbon material is a promising sorbent for the removal of AV 90 dye from aqueous solution.

Computational Study Investigating the Atmospheric Oxidation Mechanism and Kinetics of Dipropyl Thiosulfinate Initiated by OH Radicals and the Fate of Propanethiyl Radical.

The OH radical-initiated atmospheric oxidation mechanism of dipropyl thiosulfinate (CH3CH2CH2-S(O)S-CH2CH2CH3, DPTS), a volatile released by Allium genus plants, has been investigated using ab initio/DFT electronic structure calculations. The DPTS + •OH reaction can proceed through (1) abstraction and (2) substitution pathways. The present calculations show that addition of •OH to the sulfur atom of the sulfinyl (-S(═O)) group, followed by simultaneous cleavage of the S-S single bond, leading to the formation of propanethiyl radical (PTR) and propanesulfinic acid, is the major pathway when compared to the other possible abstraction and substitution reactions. The barrier height for this reaction was computed to be -5.4 kcal mol-1 relative to that of the separated DPTS + •OH reactants. The rate coefficients for all the possible pathways for DPTS + •OH were explored by RRKM-ME calculations using the MESMER kinetic code in the atmospherically relevant temperatures T = 200-300 K and the pressure range of 0.1-10 atm. The calculated total rate coefficient for the DPTS + •OH reaction was found to be 1.7 × 10-10 cm3 molecule-1 s-1 at T = 300 K and P = 1 atm. The branching ratios and atmospheric lifetime of DPTS + •OH were also determined in the studied temperature range. In addition, electronic structure calculations on the multichannel reactions of PTR with atmospheric oxygen (3O2) were investigated using the same level of theory. The calculations showed that unimolecular elimination of hydroperoxyl radical (HO2) from the RO2 adduct through formation of propanethial is a major reaction under atmospherically relevant conditions. The overall results suggest that the atmospheric removal of DPTS is mainly due to reactions with •OH and 3O2, resulting in formation of propanesulfinic acid, propanethial, HO2, and sulfur dioxide (SO2) as the major products. The atmospheric lifetime of DPTS was estimated to be less than 2 h in the studied temperature range. Estimations of the global warming potential of DPTS and the products of its reaction with •OH reveal that while the contribution made by DPTS to global warming is negligible, the various products formed as a consequence of its interaction with OH radical may make substantial contributions to global warming, acid rain, and formation of secondary organic aerosols.

Influence of Carbon Cap on Self-Diffusion in Silicon Carbide

Self-diffusion of carbon (12C and 13C) and silicon (28Si and 30Si) in 4H silicon carbide has been investigated by utilizing a structure containing an isotope purified 4H-28Si12C epitaxial layer grown on an n-type (0001) 4H-SiC substrate, and finally covered by a carbon capping layer (C-cap). The 13C and 30Si isotope profiles were monitored using secondary ion mass spectrometry (SIMS) following successive heat treatments performed at 2300–2450∘C in Ar atmosphere using an inductively heated furnace. The 30Si profiles show little redistribution within the studied temperature range, with the extracted diffusion lengths for Si being within the error bar for surface roughening during annealing, as determined by profilometer measurements. On the other hand, a significant diffusion of 13C was observed into the isotope purified layer from both the substrate and the C-cap. A diffusivity of D=8.3×106e−10.4/kBT cm2/s for 13C was extracted, in contrast to previous findings that yielded lower both pre-factors and activation energies for C self-diffusion in SiC. The discrepancy between the present measurements and previous theoretical and experimental works is ascribed to the presence of the C-cap, which is responsible for continuous injection of C interstitials during annealing, and thereby suppressing the vacancy mediated diffusion.