Synthetic Air Atmosphere Research Articles

Temperature-dependent rate coefficients for the reactions of Cl atoms with methyl methacrylate, methyl acrylate and butyl methacrylate at atmospheric pressure

Rate coefficients for the gas-phase reactions of Cl atoms with a series of unsaturated esters CH 2 C(CH 3)C(O)OCH 3 (MMA), CH 2 CHC(O)OCH 3 (MAC) and CH 2 C(CH 3)C(O)O(CH 2) 3CH 3 (BMA) have been measured as a function of temperature by the relative technique in an environmental chamber with in situ FTIR detection of reactants. The rate coefficients obtained at 298 K in one atmosphere of nitrogen or synthetic air using propene, isobutene and 1,3-butadiene as reference hydrocarbons were (in units of 10 −10 cm 3 molecule −1 s −1) as follows: k (Cl+MMA) = 2.82 ± 0.93, k (Cl+MAC) = 2.04 ± 0.54 and k (Cl+BMA) = 3.60 ± 0.87. The kinetic data obtained over the temperature range 287–313 K were used to derive the following Arrhenius expressions (in units of cm 3 molecule −1 s −1): k (Cl+MMA) = (13.9 ± 7.8) × 10 −15 exp[(2904 ± 420)/ T], k (Cl+MAC) = (0.4 ± 0.2) × 10 −15 exp[(3884 ± 879)/ T], k (Cl+BMA) = (0.98 ± 0.42) × 10 −15 exp[(3779 ± 850)/ T]. All the rate coefficients display a slight negative temperature dependence which points to the importance of the reversibility of the addition mechanism for these reactions. This work constitutes the first kinetic and temperature dependence study of the reactions cited above. An analysis of the available rates of addition of Cl atoms and OH radicals to the double bond of alkenes and unsaturated and oxygenated volatile organic compounds (VOCs) at 298 K has shown that they can be related by the expression: log k OH = 1.09 log k Cl − 0.10. In addition, a correlation between the reactivity of unsaturated VOCs toward OH radicals and Cl atoms and the HOMO of the unsaturated VOC is presented. Tropospheric implications of the results are also discussed.

Relative kinetic measurements of rate coefficients for the gas-phase reactions of Cl atoms and OH radicals with a series of methyl alkyl esters

Abstract Relative kinetic studies have been performed on the reactions of Cl atoms with a series of methyl alkyl esters in a 405-liter borosilicate glass chamber at (298 ± 3) K and one atmosphere of synthetic air using in situ FTIR spectroscopy to monitor the reactants. Rate coefficients (in units of cm3 molecule−1 s−1) were determined for the following compounds: methyl acetate (2.48 ± 0.58) × 10−12; methyl propanoate (1.68 ± 0.36) × 10−11; methyl butanoate (4.77 ± 0.87) × 10−11; methyl pentanoate (7.84 ± 1.15) × 10−11; methyl hexanoate (1.09 ± 0.31) × 10−10; methyl heptanoate (1.56 ± 0.37) × 10−10; methyl cyclohexane carboxylate (3.32 ± 0.76) × 10−10; methyl-2-methyl butanoate (9.41 ± 1.39) × 10−11. In addition rate coefficients (in units of 10−11 cm3 molecule−1 s−1) have been obtained for the reactions of OH radicals with the following compounds: methyl butanoate (3.55 ± 0.71), methyl pentanoate (5.41 ± 1.08), and methyl-2-methyl butanoate (4.08 ± 0.82). Using the kinetic rate data tropospheric lifetimes for the methyl alkyl esters with respect to their reactions with OH, and Cl have been estimated for typical ambient air concentrations of these oxidants.

SYNTHESIS AND CHARACTERIZATION OF LANTANIUM, NEODYMIUM AND ERBIUM MALEATES

The lanthanium, neodymium and erbium maleates, were prepared starting from the oxides with hydrochloric acid for the formation of the salts, both in aqueous suspension, and after recrystallizade and dry, acid maleic was added. The obtained compositions were studied through the with EDTA complexometry, molar conductance thermogravimetry (TG), infrared spectroscopy, rays-X difratometry for the method of the powder and molecular modelling. The curves TG were obtained in atmosphere of synthetic air. The results made possible to establish the stochiometry and the degree of hydration of the compositions, that presented general formula: M(Mal)x.nH2O. The curves TG also allowed to verify the thermal stability, as well as the process of thermal decomposition, of these composed. The rays-X diffraction, for the method powder, showed that all the compositions possess crystalline structure, however, without formation of series isomorphous.

Rate Coefficients for the Gas-Phase Reactions of OH and NO3Radicals and O3with Ethyleneglycol Monovinyl Ether, Ethyleneglycol Divinyl Ether, and Diethyleneglycol Divinyl Ether

Kinetic studies have been performed on the reactions of OH and NO(3) radicals and ozone with three ethyleneglycol vinyl ethers (EGVEs), that is, ethyleneglycol monovinyl ether (EGMVE, HOCH(2)CH(2)OCH=CH(2)), ethyleneglycol divinyl ether (EGDVE, H(2)C=CHOCH(2)CH(2)OCH=CH(2)), and diethyleneglycol divinyl ether (DEGDVE, H(2)C=CHOCH(2)CH(2)OCH(2)CH(2)OCH=CH(2)). Using a relative rate technique, rate coefficients have been determined for the reactions in a 405 L borosilicate glass chamber at (298 +/- 3) K in one atmosphere of synthetic air using in situ FTIR spectroscopy to monitor the reactants. The following rate coefficients (in units of cm(3) molecule(-1) s(-1)) were obtained: (1.04 +/- 0.22) x 10(-10), (1.23 +/- 0.33) x 10(-10), and (1.42 +/- 0.30) x 10(-10) for the reaction of OH with EGMVE, EGDVE, and DEGDVE, respectively; (2.23 +/- 0.46) x 10(-12), (1.95 +/- 0.50) x 10(-12), and (6.14 +/- 1.38) x 10(-12) for the reaction of NO(3) with EGMVE, EGDVE, and DEGDVE, respectively; and (2.02 +/- 0.41) x 10(-16), (1.69 +/- 0.41) x 10(-16), and (2.70 +/- 0.56) x 10(-16) for ozonolysis of EGMVE, EGDVE, and DEGDVE, respectively. Using the kinetic rate data, tropospheric lifetimes for EGMVE, EGDVE, and DEGDVE with respect to their reactions with OH, NO(3), and ozone have been estimated for typical ambient air concentrations of these oxidants.

Real-time analysis of soot emissions from bituminous coal pyrolysis and combustion with a vacuum ultraviolet photoionization aerosol time-of-flight mass spectrometer

This paper reports on-line analyses of the soot emissions from the Inner Mongolia bituminous coal combustion and pyrolysis processes with a vacuum ultraviolet photoionization aerosol time-of-flight mass spectrometer (VUV-ATOFMS). The soot particles are generated by heating a small amount of screened coal powder in synthetic air and nitrogen atmosphere in a tubular oven. The vacuum ultraviolet photoionization time-of-flight (VUV-TOF) mass spectra of the soot particles emitted from combustion and pyrolysis at different oven temperatures and different stages are obtained. The VUV-TOF mass spectra are assigned with the references of the results of the off-line GC/MS analysis.

Morphological Evolution of Tin Oxide Nanobelts after Phase Transition

This article reports a study of the thermal stability and morphological changes in tin oxide nanobelts grown in the orthorhombic SnO phase. The nanobelts were heat-treated in a differential scanning calorimetry (DSC) furnace at 800 ° Cf or 1hi n argon, oxygen, or synthetic air atmospheres. The samples were then characterized by DSC, X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), and high resolution field emission scanning electron microscopy (FE-SEM). The results confirmed that the orthorhombic SnO phase is thermodynamically unstable, causing the belts to transform into the SnO2 phase when heat-treated. During the phase transition, if oxygen is available in the furnace atmosphere, nanofibers grow at the edge of nanobelts at about 50° of the belts' growth direction, while particles grow on the belt surface in the absence of oxygen. Although the decomposition process reduces the nanobelt cell volume by 22%, most belts remain monocrystalline after the heat treatment. The results confirm that phase transition is a decomposition process, which explains the morphological changes in the belts based on metallic tin generated in the process.

Interactions of the Polyaniline and Nafion bilayer sensor structure with ammonia in a dry and wet air atmosphere

Presented here are the preliminary results concerning an interactions of a novel bilayer sensor structure of polyaniline and Nafion as an ammonia gas sensors in a Surface Acoustic Wave and electric planar systems. The investigations were performed with a 50 and 100 ppm concentrations of the ammonia (NH3) in a synthetic dry (relative humidity RH∼4–5%) and wet air (RH∼50–54%) atmosphere. The prototype polyaniline and nafion bilayer structure has been manufactured by two deposition technologies: 72 nm of PANI by PVD technology and Nafion film ( $\sim\kern-3pt 300$ nm) by spin coating technology and specific process of annealing. A good interactions with ammonia for the bilayer structure (PANI film with Nafion) has been observed especially at higher relative humidity of the atmosphere.

A thermogravimetric analysis of the combustion of a Brazilian mineral coal

Knowledge of coal combustion kinetics is crucial for burner design. This work aims to contribute on this issue by determining the kinetics of a particular Brazilian bituminous coal. Non-isothermal thermogravimetry was applied for determining both the pre-exponential factor and the activation energy. Coal samples of 10 mg and 775 mm mean size were used in synthetic air atmospheres (21 % O2). Heating rates from 10 to 50 oC/min were applied until the temperature reached 850 oC, which was kept constant until burnout. The activation energy for the primary and the secondary combustion resulted, respectively, in 135.1 kJ/mol and 85.1 kJ/mol.

Selection criteria for recycled polyolefins from urban wastes by using TG analysis

The thermal behavior of a mixture of recycled polyolefins (PE/PP mix), variously colored recycled polyolefins, recycled polyolefin blends and recycled polyolefin/PET blends was analyzed by thermogravimetry. Atmospheres of nitrogen and synthetic air were used to compare the effects of inert and oxidative medium. Four characteristic temperatures, T1, T2, T3 and T4, related to oxidative processes and atmospheric conditions, were defined. Relationships between T1, T2, T3 and T4 and comparing pigmented and transparent material allow assessing the effect of different pigments on volatilization, oxidation and onset temperatures of decomposition processes. These analyses provide preliminary parameters for selecting acceptable processing temperature conditions of recycled household and engineering plastics, and provide a few criteria to select colored recycled polyolefins.

TOF-SIMS investigations on weathered silver surfaces

Silver-coated quartz crystal microbalance (QCM) disks were treated under different environmental conditions (including changes in parameters such as relative humidity (%RH) and SO(2)/H(2)S content) in atmospheres of synthetic air and pure N(2) for 24 h in a weathering chamber. The corroded surfaces were subjected to depth profiling by a time of flight (TOF) secondary ion mass spectrometry (SIMS) instrument, equipped with a Bi(+) analysis gun and Cs(+) sputter gun. The evaluation of the in-depth distribution of several elements and species provides evidence for the formation of a corrosion layer containing Ag(2)SO(3), even in the absence of oxidizing agents, such as H(2)O(2) or NO(2). Furthermore it could be elucidated that the thickness of the formed Ag(2)SO(3) layer does not depend on the SO(2) concentration but rather on the humidity and oxygen content of the ambient atmosphere. In weathering experiments in atmospheres composed of synthetic air, humidity, and H(2)S, the presence of different oxygen species (surface and bulk) and silver sulfide could be detected by TOF-SIMS depth profiling experiments. The obtained results for both acidifying gases are in good correlation with the corresponding tapping mode atomic force microscopy (TM-AFM) investigations and in situ QCM measurements.

Kinetic Study of the Oxidative Degradation of Brazilian Fuel Oils

Complex materials as fuel oils are characterized by physical and chemical parameters. This paper deals with the determination of the activation energy of three kinds of Brazilian fuel oils. As it is possible to establish a direct relation between ignition delay and activation energy, these kinetic parameters can be used to characterize these oils regarding the combustion quality of the fuel. Activation energies were determined as a function of conversion degree (α) and temperature by model-free kinetics. The samples, here named A, B, and C, were supplied by Petrobras-Cenpes, and they were characterized by thermogravimetry (TG) and differential thermal analysis (DTA). Transient experiments were performed from room temperature up to 600 °C at five heating rates (2.5, 5.0, 10.0, 15.0, and 20.0 °C min−1) in an atmosphere of synthetic air and samples of about 20.0 mg were used. In all experiments, three distinct decomposition regions were observed and identified as low-temperature oxidation (LTO), fuel deposition (FD), and high-temperature oxidation (HTO). In order to compare these oils, we considered the medium value of the activation energy obtained between conversions of 1% and 90% only for the LTO region. The results are as follows: sample A = 43.8 kJ mol−1, sample B = 57.2 kJ mol−1, and sample C = 61.8 kJ mol−1, showing that the sample A is the best option among the samples studied in this work and that the activation energy is a suitable parameter for this purpose.

Study of the aluminothermic reduction of niobium pentoxide through thermal analysis experiments and high energy milling processing

Aluminothermic reduction of niobium pentoxide was studied through thermal analysis techniques such as differential thermal analysis (DTA) and thermogravimetry (TG) as well as through high energy milling processing. Reactants mixtures were composed by powders of Nb2O5 and Al. In the case of DTA-TG experiments, different molar ratios Nb2O5:Al were heated in a dynamic atmosphere of synthetic air under controlled conditions. The high energy milling runs were carried out via SPEX vibratory mill under argon atmosphere and with milling power equal to 7:1 (ratio of mass of balls to mass of mixture) with 10 pct excess of Al over the stoichiometric mass of aluminum necessary. In both kinds of experiments, X ray diffraction was used in order to identify the products of reaction. From DTA-TG experiments, it was possible to determine the experimental value of the enthalpy change (-595.9 kJ.mol-1), which is near to the theoretical one. From the milling experiments, it was possible to verify the possibility of the occurance of aluminothermic reducion of niobium pentoxide via this kind of processing.

Thermal analysis of brazilian tropical soils originating from different sources

Brazilian tropical Latosol soil samples were thermally analyzed associating thermogravimetric (TG) and differential scanning calorimetric (DSC) techniques under synthetic air or argon atmospheres. Rhodic eutrudox soils with forest vegetation, from unburnt and burnt cane plantations and that of a sandy phase having cerrado vegetation were investigated. From the organic soil fraction humic acids were extracted that decompose similarly to the commercial product, following the steps: i) adsorbed water, dehydrations, decarboxylations and release of organic molecules, ii) thermolabile decomposition fraction, iii) macromolecular organic matter and iv) residues. The DSC curves gave the corresponding peak for water release near 100 ºC and exothermic peaks at temperatures higher than 300 ºC, attributed to the combustion of thermolabile organic matter. The TG curves for all soil samples are more complex than those of the humic acids due to the inorganic components, being characterized by stages i) dehydration process, ii) thermolabile organic matter, iii) macromolecular organic domain and iv) oxide residues. These steps of decomposition correspond to three endothermic DSC peaks and one exothermic peak clearly shown under a synthetic air atmosphere, being attributed to the combustion of the macromolecular organic fraction near 300 ºC. The DSC curves from burnt and unburnt red Latosol soils from sugar cane cultivation showed more intense endothermic peaks than those of the forest. These thermal results show the influence of both the type and the organic matter contents on curve profiles, which are highly influenced by the soil mineral compositions and land-use activities, as well as the burning processes.

Highly Mixed Phases in Ball-milled Cu/ZnO Catalysts: An EXAFS and XANES Study

New highly mixed phases have been identified in Cu/ZnO systems by EXAFS and XANES at both the Cu and Zn K-edge. The phases were generated by ball-milling Cu(2)O/ZnO mixtures under three different atmospheres of synthetic air (SA), SA + CO(2) and CO(2). The system milled in CO(2) shows disproportionation of Cu(2)O into Cu(0), Cu(1+) (cuprite Cu(2)O-type phase) and Cu(2+) (tenorite CuO-type phase), while most of the Zn(2+) is transformed into a nanocrystalline/amorphous ZnO-type zincite that forms a superficial mixture of oxide and carbonate phases. When synthetic air is added to the CO(2) atmosphere, ball milling results in the oxidation of nearly half the Cu(1+) into Cu(2+) with no Cu metal formed. The copper phase in this material is almost entirely amorphous. In SA, a significant amount of Cu(2+)- and Zn(2+)-based phases appears to react to form a nanocrystalline/amorphous Cu(1-x)Zn(x)O (x approximately 0.3) solid solution. This distorted rock saltlike solid solution, in which Zn and Cu feature different octahedral environments, was never reported before. It is thought to be formed by incorporation of Zn(2+) in the Cu fcc sublattice of the cuprite Cu(2)O matrix and the concomitant oxidation of Cu(1+) into Cu(2+). The formation of such a highly mixed Cu(1-x)Zn(x)O phase indicates strong Cu/Zn interaction in the Cu/ZnO system, which also suggests the presence of highly mixed phases in conventionally prepared activated catalysts.

Kinetics of isothermal thermooxidative degradation of poly(vinyl chloride)/chlorinated polyethylene blends

The thermooxidative degradation of poly(vinyl chloride)/chlorinated polyethylene blends of different compositions was investigated by means of isothermal thermogravimetry in flowing atmosphere of synthetic air at temperatures 240–270 °C. The main degradation processes are dehydrochlorination of PVC and CPE. For calculation of the apparent activation energy and apparent pre-exponential factor two kinetic methods were used: isoconversional method and Prout–Tompkins method. True compensation dependency between Arrhenius parameters, obtained using Prout–Tompkins model, was found. Calculated kinetic parameters of isothermal thermooxidative degradation are close to those from non-isothermal degradation and confirm the assumption of the main degradation process in PVC/CPE blends.

Influence of alkaline extraction on the characteristics of humic substances in Brazilian soils

An investigation was made of the influence of alkaline extraction on the characteristics of humic substances extracted from Brazilian soil samples. Humic substances (HS) from seven different soils samples collected in Brazil were extracted using the procedure recommended by the International Humic Substances Society (IHSS). Soils, HS and humins were characterized by thermogravimetry and differential thermal analysis. About 8 mg of each material (soil, HS and humin) were placed in a platinum crucible and heated continuously from 20 to 750 °C at a heating rate of 10 °C min −1 in an atmosphere of synthetic air (100 ml min −1). A thermal analysis revealed a difference between the content and structural characteristics of organic matter present in HS and humin fractions in relation to their soils. The results indicated that alkaline extraction alters the characteristics of humic substances during the extraction process, underlining the importance of developing methodologies and analytical procedures that allow organic matter in soils to be studied without extracting it.

Kinetics of thermooxidative degradation of poly(vinyl chloride)/chlorinated polyethylene blends

The thermooxidative degradation of poly(vinyl chloride)/chlorinated polyethylene blends of different compositions was investigated by means of dynamic thermogravimetry in flowing atmosphere of synthetic air in temperature range 50–650 °C. Kinetic analysis was applied to the first basic degradation step (up to 400 °C) where the main degradation processes were the dehydrochlorination of PVC and CPE. For calculation of the apparent activation energy and apparent preexponential factor three kinetic methods were compared: integral Kissinger method, integral isoconversional Kissinger–Akahira–Sunose method and differential isoconversional Friedman method. The existence of the true or false compensation effect is discussed.

Thermal stability and decomposition of nafion® membranes with different cations

The thermal decomposition of Nafion has been studied by means of high-resolution and constant heating rate thermogravimetry (TG), under nitrogen and synthetic air atmospheres. Nafion membranes have been studied in acid and salt (alkali chlorides) forms. The TG curves of Nafion with alkali countercations show similar profiles, whichever the atmosphere employed. The kinetics of thermal decomposition of the Nafion-Cs+ has also been studied. The method employed to calculate the kinetic parameters and to estimate the polymer lifetime from the data was based on Kissinger's method.

Oxidation kinetics of an Fe–31.8Mn–6.09Al–1.60Si–0.40C alloy at temperatures from 600 to 900 °C

An Fe–31.8Mn–6.09Al–1.60Si–0.40C alloy was subjected to thermogravimetric tests, in atmospheres of pure oxygen and synthetic air. The alloy showed good oxidation resistance, especially at 600 and 700 °C in air and at 600 °C in oxygen. Owing to autocorrelation identified in the results, kinetic data were analyzed by the statistical method of Cochrane and Orcutt. Parabolic kinetic behaviour was observed for the Fe–Mn–Al–Si–C alloy oxidation process in air at 600, 700 and 800 °C and in pure oxygen at 900 °C.

A study on combustion of Chinese coals by TA/MS

Thermal behavior and evolution characterization under designed combustion conditions of 13 Chinese coals of different ranks were investigated by means of thermal analysis/mass spectrometry (TA/MS). The experiments were carried out in a synthetic air atmosphere (20% oxygen+80% nitrogen) with a flow rate of 150 ml min −1 and the samples were heated from 40 up to 1200 °C at a constant heating rate of 10 K min −1. The volatile products and their evolution profiles against the temperature during the combustion were identified through the on-line recorded mass spectra. The results revealed that the whole combustion procedure could be broadly divided into 4 phases and the temperature of the maximum weight loss rate shifted to lower temperatures as the coal rank decreased. In addition to the primary combustion products water and carbon dioxide, fragments with the masses m/ z 15, 55–60, 66, 67 and sulphur dioxide ( m/ z 64) were also found in the mass spectra.