Primary Decomposition Products Research Articles

Phase transitions and phase decomposition of La 1− xSr xCoO 3− δ in low oxygen partial pressures

High-temperature X-ray diffraction has been used to investigate the phase stability of lanthanum strontium cobalt oxide (LSC) for a range of materials with the formula La 1− x Sr x CoO 3− δ ( x = 0.7, 0.4, and 0.2). The stability of LSC increases with La content in low oxygen partial pressures at high temperature. Oxygen vacancy ordering has been observed for all three compositions in either low oxygen pressure or under reducing gas, as evidenced by the formation of the brownmillerite phase. The crystal structure of the vacancy-ordered phase was determined using Rietveld analysis of synchrotron X-ray diffraction data. The decomposition products under low oxygen pressure and in reducing conditions have been identified and characterized, including the phase transition and thermal expansion of the primary decomposition products, LaSrCoO 4 and LaSrCoO 3.5.

Photochemical cleavage of a tattoo pigment by UVB radiation or natural sunlight

Millions of people have at least one tattoo. Complex and light absorbing molecules are implanted in the skin. When tattooed skin receives UV radiation or natural sunlight, photochemical cleavage of the pigments may occur. As a first step, we dissolved pigments in a suitable solvent and analyzed them after light irradiation. The widespread Pigment Red 22 was dissolved in different solvents. The solutions were irradiated with either UVB radiation (up to 8 h) or with natural sunlight (110 days). After irradiation, the solutions were analyzed by means of liquid chromatography and mass spectrometry. A clear cleavage of the pigment was detected in all solvents and the primary decomposition products were identified. In tetrahydrofuran and dioxane, the pigment concentration decreased significantly during UVB irradiation, whereas the pigment was completely destroyed during sunlight exposure. In chloroform and dichloromethane, the pigment concentration decreased slightly during UVB irradiation, whereas the pigment was almost completely destroyed during sunlight exposure. Since chloroform and dichloromethane do not affect the cleavage process, these solvents are optimal for such in vitro experiments. We have shown the cleavage of the tattoo pigment Red 22 when exposed to UVB radiation or natural sunlight. The decomposition products are hazardous showing a potential risk of being toxic or even carcinogenic. At present, a risk assessment is not feasible since the concentration of pigments and their decomposition products in skin are unknown.

TG/DTA/MS/IR study on decomposition of cadmium malonate hydrates in inert and oxidative atmosphere

Thermal decomposition of cadmium malonate hydrates was studied in dynamic helium and air atmospheres. It was found that content of hydration water in the initial sample strongly influences the way of decomposition reaction. The dehydration of cadmium malonate hydrate takes place in the temperature range 80–170 °C. The anhydrous cadmium malonate decomposes at about 250 °C. It was stated that the primary solid product of cadmium malonate decomposition is metallic cadmium. The gaseous products of cadmium malonate decomposition are CO 2, acetone, isobutylene and propyne and traces of water, acetic acid and oxygen. In helium majority of cadmium evaporates and the residue consists of small amount of elementary carbon formed in result of pyrolysis of malonate. The residue after decomposition of cadmium malonate with low amount of crystallization water molecules contains additionally CdO. The secondary reactions between decomposition products occur: oxidation of cadmium by oxygen in statu nascendi and formation of CdCO 3 in reaction between cadmium oxide and CO 2. In air cadmium instantaneously oxidizes and the final solid product of decomposition is CdO.

Composition of the gaseous products of pyrolysis of tobacco under inert and oxidative conditions

Theoretical and modeling work on the process of cigarette combustion showed that in the puffing stage of the burning cycle thermal decomposition of cigarette components in the pre-heat zone of the cigarette may take place under oxygen-starving (in the inner part of the cigarette) versus oxygen-rich conditions (at the cigarette periphery). A companion paper [O. Senneca, R. Chirone, P. Salatino, L. Nappi, A. Nunziata, J. Anal. Appl. Pyrolysis, submitted for publication. [1]] addressed the pattern and the kinetics of pyrolysis under inert versus oxidative conditions of several tobaccos and reported profound differences as regards the number of reaction steps, the rate, the temperature ranges and the yield in solid and gaseous products. The present paper investigates the effects of inert versus oxidative conditions on the composition of the gas produced. The experimental work consists of non-isothermal thermogravimetric experiments in connection with MS analysis. Experiments have been carried out in a Netzsch TG Skimmer apparatus that minimizes secondary reactions of primary decomposition products in the gas phase. MS profiles have been analyzed to underline the differences in the evolution of gaseous products under inert versus oxidizing conditions. Three different tobaccos have been tested, including omogenized and Kentucky tobaccos. A first analysis regarded the temperature at which chemical species are released. Results showed that most species of interest in tobacco smoke, in particular nitrogen containing species, are produced over quite broad temperature ranges under inert conditions and over much more limited ranges under oxidizing conditions. A second comparison regarded the cumulative amount of the species released. Also with this respect large differences have been observed when tobaccos are heated under inert or oxidative conditions. Some species, like CO, CO 2, NO x and H 2O, appear to be strongly favoured by oxidative conditions. Other species such as amines, H 2, aldehydes, aromatics and poliaromatics are instead favoured by inert conditions. Acrolein, HCN, butanone and nicotine are favoured by inert conditions for omogenized tobaccos and by oxidative conditions for Kentucky tobacco.

Dehydration of solids in different modes as a proof of their primary congruent dissociative vaporization

The main purpose of this paper is to prove the applicability of the mechanism of congruent dissociative vaporization (CDV) to the solid-state decomposition kinetics through the comparison of the fundamental theoretical relationship Ei/Ee=(a+b)/a resulted from this mechanism with experiment. It has been shown that the ratios of Ei and Ee parameters of the Arrhenius equation measured in the isobaric and equimolar modes (in the presence and absence of H2O vapour) for 22 reactants with the general formula aSalt⋅bH2O or aOxide⋅bH2O are in agreement with the values of (a+b)/a. The relative standard deviation is only 17% and the correlation coefficient is close to 0.99. A probability of accidental correlation for all set of the E parameters taken from the literature is lower than 4⋅10–16 . This strongly supports the validity of the CDV mechanism. The problem of stability of polyatomic molecules of inorganic salts in the gaseous state, which are the primary decomposition products of crystalline hydrates, was also discussed on the basis of recent mass spectroscopy studies. It was concluded that any doubts in the applicability of the CDV mechanism as a general mechanism of solid-state decomposition reactions are unsound.

Acute and Chronic Toxicity of Chlorine Dioxide (ClO2) and Chlorite (ClO2ˉ) to Rainbow Trout (Oncorhynchus mykiss) (4 pp)

Chlorite (ClO2-) is a primary decomposition product when chlorine dioxide (ClO2) is added during water treatment; therefore the toxic effects of both compounds on aquatic organisms are possible. Limited data are available concerning their toxicity to fish. The aim of this study was to investigate sensitivity of rainbow trout to acute and chronic toxicity of chlorine dioxide and chlorite, and to estimate the Maximum-Acceptable-Toxicant-Concentration (MATC) of those compounds in fish. The acute and chronic toxicity of chlorine dioxide and chlorite to larval and adult rainbow trout was investigated in 96-hour to 20-day laboratory exposures evaluating the wide range spectrum of biological indices under semi-static conditions. Median lethal concentration (96-hour LC50) values derived from the tests were: 2.2 mg/l for larvae; 8.3 mg/l for adult fish and 20-day LC50 for larvae was 1.6 mg/l of chlorine dioxide, respectively. Chlorite was found to be from 48 to 18 times less acutely toxic to larvae and adult fish, correspondingly. Both chemical compounds induced similar toxic effects in rainbow trout larvae during chronic tests (they affected cardio-respiratory and growth parameters), but chlorine dioxide had a higher toxic potency than chlorite. A significant decrease in the heart rate and respiration frequency of larvae was established. However, within an increase in exposure duration recovery of cardio-respiratory responses was seen to have occurred in larvae exposed to chlorite. Meanwhile, in larvae exposed to chlorine dioxide, a significant decrease in cardio-respiratory responses remained during all 20-day chronic bioassays. Chlorine dioxide also more strongly affected growth parameters of rainbow trout larvae at much lower test concentrations. Decreased rate of yolk-sack resorption occurred only in the tests with chlorine dioxide. Maximum-Acceptable-Toxicant-Concentration (MATC) of 0.21 mg/l for chlorine dioxide and of 3.3 mg/l for chlorite to fish was derived from chronic tests based on the most sensitive parameter of rainbow trout larvae (growth rate). According to substance toxicity classification accepted for Lithuanian inland waters, chlorine dioxide and chlorite can be referred to substances of 'moderate' toxicity to fish. Due to its very reactive nature, chlorine dioxide is rapidly (in a few hours) reduced to chlorite, which is persistent also as a biocide but 16 times less toxic to fish, according to MATC. Therefore, it is much more likely that fish will be exposed to chlorite than to chlorine dioxide in natural waters. Presently accepted, the Maximum-Permitted-Concentration of total residual chlorine (TRC) in waste-water discharging into receiving waters is 0.6 mg/l. If this requirement will not be exceeded, it is unlikely that fish would be exposed to lethal or even to sublethal concentrations of chlorine dioxide or chlorite. Furthermore, chlorine dioxide does not generate toxic nitrogenous (chloramines) or carcinogenic organic residuals (trihalomethanes). All these properties make chlorine dioxide a more promising biocide than chlorine.

Synthesis and thermal decomposition of freeze-dried copper–iron formates

The thermal decomposition of freeze-dried formate precursors for copper–iron oxides was investigated by means of DTA, TG, mass spectroscopy and X-ray powder diffractometry. The freeze-dried copper formate is crystalline. Its decomposition at about 200 °C releases formic acid (HCOOH) and carbon dioxide (CO 2) as main primary gaseous decomposition products beside metallic copper as a solid product. However, the decomposition of the amorphous freeze-dried iron formate starts with a dehydration process which ends up at about 200 °C. Further decomposition in several superimposed steps, between 220 °C and 330 °C, results in the delivery of: (a) HCOOH and CO 2 (with reduction of Fe(III) to Fe(II)), (b) HCOOH and CO or H 2CO and CO 2 (without reduction). Meanwhile, several secondary decomposition products are characterized by mass spectroscopy. Regarding the complex copper–iron formate, its decomposition does not reflect only some aspects of the single formates, but also an interaction between the components which lows down the decomposition temperature. Because of the intermediate formation of metallic copper, properties of the reactive homogeneous precursor are lost and the formation of the single-phase copper iron oxides requires an annealing temperature close to that of a mixed oxide technique.

The effects of sulfur and oxygen on the catalytic activity of molybdenum carbide during dry methane reforming

The sulfur tolerance of bulk Mo 2C catalyst has been evaluated for dry methane reforming (DMR) at 1050 °C, in the presence of dimethethylsulfide (DMS) at sulfur concentrations as high as 500 ppm. In addition, the effect of coupling the exothermic partial oxidation of methane with the highly endothermic reforming reaction was also investigated. It was determined that both DMS decomposition and partial oxidation take place in the gas phase, upstream of the catalyst bed, with CS 2 as the primary DMS decomposition product. The CS 2 was found to reversibly adsorbs on the catalyst surface, resulting in a stable but decreased activity. This conclusion was corroborated by examining the effects of DMS concentration, temperature, and in situ regeneration, and all are consistent with the occurrence of reversible sulfur chemisorption. Evidence is also presented to show that sulfur adsorption during DMR changes the redox chemistry of the catalyst, resulting in a slow oxidation of the surface. On the other hand, stable activity was maintained with oxygen in the feed and is attributed to lower CO 2 concentrations under these conditions. Comparison experiments with a supported Rh catalyst gave superior results with respect to sulfur tolerance during DMR, suggesting that sulfur poisoning of noble metal catalysts may not be a serious problem at the high temperatures used in methane reforming.

Catalytic decomposition of HCN on heated W surfaces to produce CN radicals

The catalytic decomposition processes of HCN on heated W surfaces were examined using laser spectroscopic and mass-spectrometric techniques. H atoms and CN radicals were identified as primary decomposition products on the catalyzer surfaces. The effective enthalpy for the production of CN was determined to be 370 kJ mol −1. The decomposition efficiency of HCN approaches 30% when the catalyzer temperature is over 2000 K. This efficiency is around half of that for H 2. If CN radicals produced in this manner can be doped in a-Si:H to terminate the dangling bonds, this could be a new technique to suppress the photodegradation of a-Si:H.

Thermal decomposition of Cd(CH3COO)2·2H2O studied by a coupled TG-DTA-MS method

The thermal decomposition of cadmium acetate dihydrate in helium and in air atmosphere has been investigated by means of a coupled TG-DTA-MS method combined with X-ray diffraction analysis. Dehydration of Cd(CH3COO)2·2H2O is a two-stage process with Cd(CH3COO)2·H2O as intermediate. The way of Cd(CH3COO)2 decomposition strongly depends on the surrounding gas atmosphere and the rate of heating. CdO, acetone and CO2 are the primary products of decomposition in air. In helium decomposition goes by two parallel and consecutive reactions in which intermediates, Cd and CdCO3, are formed. Metallic cadmium oxidizes and cadmium carbonate decomposes giving CdO. Some of the metallic cadmium, depending on the heating rate and the concentration of oxygen, evaporates. Acetone is partially oxidized in secondary reactions with oxygen.

Kinetics and mechanism of free-surface vaporization of zinc, cadmium and mercury oxides analyzed by the third-law method

On the basis of critical comparison of experimental and theoretical values of the E parameter and investigation of the retardation effect of oxygen on the evaporation rate of ZnO, CdO and HgO, it was concluded that the dissociative evaporation of ZnO and HgO proceeds with releasing of atomic oxygen (O) as a primary product of decomposition. By contrast, the mechanism of dissociative evaporation of CdO corresponds to the equilibrium reaction with releasing of molecular oxygen (O 2) as a primary product of decomposition. As was shown, this difference in mechanisms is not related with interatomic OO distances in these oxides. From the analysis of crystal structure for 12 different oxides, which evaporate with releasing of atomic oxygen, and for 13 compounds, which evaporate with releasing of molecular oxygen, it was revealed that the first mechanism is observed for all oxides with the cubic crystal structure. It was proposed that a decisive role in this difference belongs to a local symmetry in the position of O atoms.

Endo/exo isomerism in norcarane and 2-norcaranol hydrotrioxides (ROOOH).

Ozonation of norcarane (1) yielded endo and exo norcarane hydrotrioxides (2a, 2b), as characterized by (1)H and (13)C NMR spectroscopy. Further ozonation of the primary decomposition products of these hydrotrioxides, i.e., 2-norcaranols (3), produced the corresponding isomeric 2-norcaranol hydrotrioxides (4a, 4b), and hydrogen trioxide (HOOOH).

Radical Species Formed by the Catalytic Decomposition of NH3 on Heated W Surfaces

The catalytic decomposition processes of NH3 on heated W surfaces were examined by employing laser spectroscopic techniques. H atoms and NH2 radicals were identified as primary decomposition products on the catalyzer surfaces. The effective enthalpies for the production of these species were both determined to be 150 kJ/mol. NH radicals were also identified, but the production of this species is ascribed to secondary processes. N atoms are minor products in both the primary and secondary processes. The absolute density measurements show that the decomposition efficiency of NH3 is comparable to that of H2. The steady-state densities of NH3 and the stable products, H2 and N2, were also measured by mass spectrometry. When the catalyzer temperature is over 2000 K, the H2 density is comparable to that of residual NH3. H atoms are produced not only by the direct decomposition of NH3 but also by the decomposition of H2.

The Decomposition of the Sulfonate Additive Sulfopropyl Sulfonate in Acid Copper Electroplating Chemistries

The decomposition of sulfopropyl sulfonate (SPS, 4,5-dithiaoctane-1,8-disulfonic acid) in acid copper electroplating chemistries was studied using scanning electrochemical microscopy (SECM), UV-visible spectroscopy, high pressure liquid chromatography, liquid chromatography mass spectrometry, and electron spin resonance. The primary decomposition product is proposed to be the thiolsulfonate of SPS. Although this oxidation product can be formed by reaction with hydrogen peroxide, SECM studies of oxygen reduction on copper showed that there is not a peroxide intermediate and the product of oxygen reduction on copper in dilute sulfuric acid is water. The data suggests that SPS stabilizes Cu(I) and this complex is the intermediate. For this scheme, oxygen reacts with the SPS/Cu(I) complex in solution to form the thiolsulfonate of SPS and Cu(II). © 2003 The Electrochemical Society. All rights reserved.

Interactions of photo-excited zinc phthalocyanine with (hydro)peroxides: triplet vs. singlet state pathways

Photo-excited Zn-phthalocyanine (ZnPc) interactions with four (hydro)peroxides (ROOR ′) were studied by T–T absorption decay and fluorescence quenching. Triplet state interactions are weak (log k q∼4) and independent from the quencher used, while singlet quenching is variable (log k q 4.5–9.4). EPR and spin-trapping show that at low ZnPc concentrations the primary decomposition products are alkoxyl radicals. At high ZnPc concentrations, photosensitization of ROOH gives rise to peroxyl radicals. The (hydro)peroxide reducing potentials were estimated following AM1 MO-computations. Our experimental data and theoretical predictions (Marcus–Savéant theory) are consistent with a charge transfer mechanism to account for the alkoxyl radical formation.

The Yields of Radical Products in Water Decomposition under Discharges with Electrolytic Electrodes

The features of generation, combination, and scavenging of primary radicals under the action of an atmospheric-pressure glow discharge and microdischarges on electrolytic electrodes were compared. A profound difference in chemical effects was revealed at different polarities of the electrolytic electrode. The identity of water decomposition mechanisms was demonstrated for the electrolytic cathode in the case of a stationary discharge over the surface and for the arrays of quasi-stationary microdischarges at the valve anode immersed in the solution. The assumption that the generation of primary water decomposition products in a discharge system with an electrolytic cathode is predominantly due to ionization in the liquid phase at the expense of the kinetic energy of accelerated particles arriving from the discharge to the solution was confirmed.

Anaerobic microbial biogeochemistry in a northern bog: Acetate as a dominant metabolic end product

Field measurements and incubation techniques were used to determine the dynamics of acetate formation, iron reduction, and methanogenesis in surficial peat of an Alaskan bog. Acetate concentrations were ∼100 μM early in the season and decreased to ∼20 μM in July when the water table decreased. Acetate levels increased rapidly to ∼1000 μM when the water table rose to the surface in August. Acetate production in anaerobic slurries occurred at rates of 2.8–420 nmol carbon mL−1 day−1, which was 7–120 times more rapid than CH4 production. Experiments utilizing 14C‐acetate confirmed that methanogenesis was not acetoclastic although acetate was converted very slowly to CO2. Peat incubated anaerobically for 4.5 months at 24°C never produced methane from acetate, suggesting that anaerobic acetate accumulation would have occurred all season if the water table had remained high. CO2 production was the most rapid process measured in laboratory incubations (up to 750 nmol mL−1 day−1) and appeared to be due primarily to fermentation. Acetate was the primary organic terminal product of anaerobic decomposition in the bog, and acetate was ultimately oxidized to CO2 via aerobic respiration and to a much lesser extent anaerobically by Fe reduction.

Degradation of MTBE and Related Gasoline Oxygenates in Aqueous Media by Ultrasound Irradiation

Gasoline oxygenates [methyl \Itert\N-butyl ether (MTBE), di-isopropyl ether, ethyl \Itert\N-butyl ether, and \Itert\N-amyl methyl ether] in aqueous media are readily decompose upon ultrasonic irradiation (665 kHz). The optimal instrumental settings for the production of reactive radical species employing a specific reactor were determined using dosimetry. Since hydroxyl radical is generally believed to be the predominant reactive species leading to ultrasonically induced degradation of organic substrates in aqueous media, a terephthalate dosimeter was employed to selectively determine the yields of hydroxyl radicals. The decomposition of the gasolinie oxygenates and the primary decomposition products of MTBE were compared in the presence of different saturating gases (O\d2, N\d2, and Ar). The observed decomposition rates for the oxygenates were similar under Ar and O\d2 saturated conditions, but significantly slower under nitrogen saturated conditions. The observed decomposition rates for a number of the primary decomposition products of MTBE are significantly slower under N\d2 and O\d2 saturation relative to Ar saturation. All the gasoline oxygenates in this study were degraded by more than 98% within 3 h of ultrasonic irradiation under O\d2 saturationwith half-lives of 21–25 min.

Thermal decomposition behavior of 1,2-bis-(2,4,6-tribromophenoxy)ethane

The thermal decomposition behavior of 1,2-bis-(2,4,6-tribromophenoxy)ethane (BTBPE) widely used as flame retardant plastics additive was studied by HRTG and differential scanning calorimetries. It was pyrolysed in inert atmosphere at 240 and 340 °C in isothermal conditions, the decomposition products were collected and investigated by means of IR and GC-MS, most of them are identified. It was found that BTBPE mostly evaporates at 240 °C. The decomposition products at 340 °C depend on rate of their removal from the hot reaction zone. Main primary decomposition products found in case of rapid removal are tribromophenol and vinyl tribromophenyl ether. Whereas, prolonged contact with heating zone also produces hydrogen bromide, ethylene bromide, polybrominated vinyl phenyl ethers and diphenyl ethers, and dibenzodioxins. The nature of the identified compounds are in accordance with a molecular and radical pyrolysis reaction pathway.

Photochemical study of hexahydroquinoline derivatives--a new group of calcium antagonists.

The photochemical stability of 2,6,6-trimethyl-3-carbmethoxy-4-phenyl-5-oxo-1,4,5,6,7,8-hexahydroquinoline (HHQ) derivatives with different substituents on the phenyl ring (-Cl, -NO2, -CF3, -CH3, -OCH3) has been studied. The process of photodegradation was studied by UV spectrophotometry. The rate of photodegradation was found to depend on the type and position of the substituent in the phenyl ring. The compounds most susceptible to the damaging effect of light proved to be those containing the nitro group, in particular with the substituent in the ortho position of the aromatic ring. Derivatives with alkyl (-CH3) and halo-alkyl (-CF3) substituents showed the greatest photochemical stability. The compounds with substituents in the ortho position were found to be much less photostable than the meta isomers. The quantum yield values obtained ranged from 10(-4) to 10(-3), indicating the occurrence of secondary photochemical processes initiated by the primary products of decomposition.