Initial Formaldehyde Concentration Research Articles

Detailed surface and gas-phase chemical kinetics of diamond deposition.

A chemical kinetic model is developed that includes detailed descriptions of both gas-phase and surface processes occurring in gas-activated deposition of diamond films on diamond (111) surface. The model was tested by simulating diamond film deposition in a hot-filament reactor using methane-hydrogen, methane-argon, and methane-oxygen-hydrogen gas mixtures. The gas-phase part of the model includes transport phenomena and predicts correctly the measured concentrations of major gaseous species. The surface part of the model reproduces the general experimental trends--the effects of temperature, pressure, initial methane concentration, and the addition of oxygen--for the growth rate and film quality. Analysis of the computational results revealed the factors controlling the growth phenomena. Among several reaction pathways describing deposition of diamond initiated by different gaseous species, including ${\mathrm{CH}}_{3}$ and several ${\mathrm{C}}_{2}$${\mathrm{H}}_{\mathit{x}}$ species, the H-abstraction--${\mathrm{C}}_{2}$${\mathrm{H}}_{2}$-addition mechanism appears to dominate. The key role of hydrogen and oxygen is identified to be the suppression of the formation of aromatic species in the gas phase, which prevents their condensation on the deposition surface. Activation of the growing surface by H atoms and gasification of ${\mathit{sp}}^{2}$ carbon by OH radicals are other important factors. The developed model does not support the theory of preferential etching by H atoms advanced to explain the kinetic competition between diamond and nondiamond phases. Instead, it establishes the critical role of aromatics condensation and interconversion of ${\mathit{sp}}^{2}$ and ${\mathit{sp}}^{3}$ carbon phases mediated by hydrogen atoms.

Numerical modeling of the filament-assisted diamond growth environment

A numerical model of the filament-assisted diamond growth environment has been developed and used to calculate temperature, velocity, and species concentration profiles, accounting both for transport and detailed chemical kinetics. The computed hydrocarbon concentrations agree well with previously measured values, when allowance is made for 3D effects not included in our model. Upper-bound, diffusion-limited film growth rates for various assumed growth species have been computed, and it has been found no hydrocarbon species other than CH3, C2H2, or CH4 can account for measured diamond growth rates. The effect of thermal diffusion on H-atom profiles has been examined, and found to be only 10%. Although the environment is far from thermodynamic equilibrium, several reactions are close to partial equilibrium throughout the region from the filament to the substrate. It is also shown that homogeneous H-atom recombination is too slow to explain the experimentally observed decrease in the concentration of H with increasing initial methane concentration.

Toxicity of 1,1,1-Trichloroethane and Trichloroethene on a Mixed Culture of Methane-Oxidizing Bacteria

The influence of trichloroethene (TCE; 0 to 65 mg/liter) and 1,1,1-trichloroethane (1,1,1-TCA; 0 to 103 mg/liter) on methane consumption of a mixed culture of methane-oxidizing bacteria was studied in laboratory batch experiments. Increasing concentrations of TCE or 1,1,1-TCA resulted in decreasing methane consumption. Methane consumption was totally inhibited at a concentration of 13 mg of TCE per liter, while methane consumption was still observed at the upper studied concentration of 103 mg of 1,1,1-TCA per liter. The inhibition of methane consumption by TCE depended on the initial concentration of methane. A model accounting for competitive inhibition between methane and TCE or 1,1,1-TCA was used to simulate methane consumption at various concentrations of TCE or 1,1,1-TCA. The simulations indicated that competitive inhibition may be the mechanism causing the inhibitory effect of TCE on methane consumption, while this does not seem to be the case for 1,1,1-TCA.

ESR spectroscopic detection of methoxyl radicals formed in the photochemical gas-phase reaction of methane and water

During the photolysis of methane-water gas mixtures, a radical has been trapped by both {alpha}-phenyl-N-tert-butylnitrone and 5,5-dimethyl-l-pyrroline 1-oxide. The analysis of the ESR parameters along with the control experiments and the determination of reaction products strongly suggests the detection of methoxyl radical. It is revealed that the yield of methanol and methoxyl radical depends on the initial concentration of methane and the reaction temperature, and the observed difference between their yields is mainly ascribed to the reaction CH{sub 3}O{sup {sm bullet}} + CH{sub 4} {yields} CH{sub 3}OH + {sup {sm bullet}}CH{sub 3}, which is favorable at higher concentration of initial methane and at higher reaction temperature. Furthermore, the preferential trapping of the methoxyl radical by the spin traps is discussed.

Selective formose reactions initiated by γ-irradiation

Formose reactions initiated by γ-irradiation in the presence of inorganic bases selectively produce ethylene glycol and pentaerythritol as major products at room temperature in the presence of calcium hydroxide. The yield ratio of ethylene glycol to pentaerythritol depends on the initial concentration of formaldehyde. At low concentration, the main product is ethylene glycol, whereas pentaerythritol increases at high concentration. The decomposition of formaldehyde is inhibited by ethanol, a hydroxyl-radical scavenger. These results suggest that radical reactions play an important role in radiation-initiated formose synthesis, in contrast to thermal formose reactions.

Determination of free formaldehyde in nail varnish by HPLC

Free formaldehyde in cosmetic samples can be determined by HPLC and post-column derivatisation as a lutidine derivative. Applying this method to nail varnishes results in poor reproducibility. It is demonstrated that most of the formaldehyde determined is generated by hydrolysis of the resin in aqueous solution during sample clean-up, extraction and determination procedures. The hydrolysis is slowest in acidic solution at low temperature. The formaldehyde concentration is thus a function of the method of determination. Kinetic evaluation of its formation by hydrolysis shows that the initial concentration of free formaldehyde in the resin is below 100 ppm.

Reaction rates for the formation of deuterium tritide from deuterium and tritium

The rates of formation of DT in a mixture of D2 and T2 have been measured as a function of initial T2 concentration, pressure, temperature,and methane concentration in a stainless steel reaction container which had been treated to inhibit protium ingrowth. An attempt has been made to explain the experimental resuts on the basis of ion-molecule chain reactions. Some of the observations are consistent with a gas-phase ion, ground-state molecule reaction, but some of the more interesting observations require more complicated models. The addition of excited state molecules or heterogeneous catalytic effects are possibilities that will need further experiments for confirmation.

Active transport of formaldehyde in methanol-utilizing bacteria

Formaldehyde transport experiments were carried out with Pseudomonas C in batch cell-suspension systems in the absence of a growth-supporting carbon source. Direct measurements of extracellular formaldehyde concentrations and indirect measurements of intracellular formaldehyde concentrations were made. Initial transport rates were estimated for different initial formaldehyde concentrations. Adenosine triphosphate (ATP) consumption during formaldehyde transport was noted. Observed was the transport of formaldehyde against its own concentration gradient, along with the depletion of intracellular ATP. A proposed active transport model involving substrate inhibition was shown to be in agreement with the transport rate data. A stoichiometric relationship of three formaldehyde molecules transported per ATP molecule dephosphorylated was calculated from formaldehyde and ATP mass balances.

Glyoxal and malonaldehyde formation by ultraviolet irradiation of aqueous formaldehyde

Irradiation of dilute aqueous formaldehyde (5 × 10 −2–10 −3M) in the absence of oxygen by ultaviolet light from high- or low-pressure mercury lamps resulted in the formation of glyoxal and of malonaldehyde. The concentration of malonaldehyde reached a maximum after several hours and then declined. This maximal malonaldehyde concentration was proportional to the initial formaldehyde concentration. At initially 0.05 M formaldehyde (pH 9.4 and 36°C) malonaldehyde reached maximally 3.4 × 10 −5 M. In the range of pH 8.0–11.6, the maximal malonaldehyde concentration was reached at pH 9.4. Quantum yields of glyoxal and malonaldehyde after irradiation of 0.01 M formaldehyde (in 0.01 M NaHCO 3, 27°C, at 254 nm, under argon, for 195 min) were 7 × 10 −3 and 1.5 × 10 −3, respectively. In the presence of acetone (0.01 M), the chemical and quantum yields of glyoxal were enhanced, while those of malonaldehyde decreased. The known reaction of malonaldehyde with urea to form pyrimidines may be a model of a prebiotic synthesis of pyrimidines.

The oxidation of methane by nitrous oxide

The reaction of methane and nitrous oxide in a static system at 873°K has been examined at a range of nitrous oxide pressures from 15 to 50 Torr and methane pressures from 7.5 to 120 Torr. The main products initially observed are nitrogen, ethane, carbon monoxide, and water, and a mechanism accounting for these has been advanced. At very low conversion the products and mechanism begin to change significantly. Even at the lowest conversions investigated, ethylene is observed in the products. From experiments with added ethane and ethylene, their stationary concentrations were found to be less than one percent of the initial methane concentration. Ethylene is produced from ethane, and the main product of the reaction of ethylene is carbon monoxide. From the mechanism and the data, a value of k = 1.4 ± 0.3 × 107 cm3 mole−1 sec−1 may be derived for the reaction C H 3 + N 2 O → C H 3 O + N 2 .

Carbon formation from methane in combustion products

The rates of deposition of carbon on alumina surfaces and on soot particles, have been measured in a pilot scale tubular reactor in which cold methane was mixed with combustion products at 1920°K. A hard grey metallic film of carbon, quite free of soot, was deposited on alumina surfaces for initial methane concentrations between 12 and 24 per cent. An induction period of slow growth rate, before a film covered the surface completely, was followed by a constant growth rate. Measured growth rates were from 0·06 × 10 −6 to 1·43 × 10 −6 g/cm 2 sec of carbon on alumina at 1270°K to 1450°K, and from 0·1 × 10 −4 to 1·14 × 10 −4 g/cm 2 sec on soot particles at 1370°K to 1700°K. Methane decomposition rates were much higher than predicted by the unimolecular mechanism indicating a predominance of radical reactions. Carbon deposition rates were related to the mole fraction, χ, of hydrocarbons in the gas which bear more than three carbon atoms per molecule, by, m ̇ f = 1·0 × 10 2 n.χ . exp (−42,300/ RT f ), g/cm 2sec for carbon film, m ̇ s = 4·6 × 10 3 nχ exp (− 46,100/ RT g ), g/cm 2 sec for soot. A precoat of soot increased the growth rate of film carbon by 1·8 to 7·8 times yielding a hard adherent dull brown film

Effect of formaldehyde on the cationic polymerization of styrene

AbstractPolymerization of styrene has been carried out in the presence of formaldehyde at 30°C in benzene solution by using boron trifluoride etherate as a catalyst. The rate of polymerization in the initial stage was accelerated with addition of formaldehyde, while the steady‐state rate of polymerization was retarded in the presence of formaldehyde. The acceleration for the rate of polymerization was found only in a short time from the beginning. The steady‐state rate of polymerization followed the equation: where [C]0 and [F]0 are initial concentrations of catalyst and formaldehyde, [M] is the monomer concentration, and k1, k2, and k3 are constants. It has been assumed that the chain‐transfer reaction does not involve formaldehyde itself but rather the reaction products of formaldehyde, such as polystyrene having ethoxy or hydroxymethyl ends. The apparent chain‐transfer constant for the added formaldehyde has been determined to be 1.63.

Effect of equilibrium in aqueous formaldehyde solutions on its condensation reaction kinetics

1. The effect of the equilibrium which establishes itself in an aqueous solution of formaldehyde and an anionic catalyst on the kinetics of the formaldehyde condensation reaction has been studied. 2. The kinetics of the Cannizzaro reaction have been studied. The reaction rate as a function of the initial formaldehyde concentration is represented by a curve with a maximum. The experimental data have been interpreted on the assumption that the reaction is based on the interaction of monomeric formaldehyde with the free form of the catalyst, which are in equilibrium with their polymeric compounds.

The water-formaldehyde-hydrogen sulfide system. I. Solubility of hydrogen sulfide in aqueous solutions of formaldehyde and first solid product of the system

We have ascertained that aqueous solutions of formaldehyde absorb hydrogen sulfide proportionally to the formaldehyde present in solution. The highest molar ratio obtainable in solution is equivalent to the value CH2O/H2S = 2. When this ratio is reached, regardless of the initial concentration of formaldehyde, if the solutions are maintained constantly under pressure of hydrogen sulfide, separation of a solid product begins. Various chemical and physical studies indicate that the first solid separated from this system is HSCH2SCH2SCH2OCH2OH. A possible mechanism of formation of this compound from the liquid phase is discussed.

Induction Periods in the Ignition of Formaldehyde‐Oxygen‐Mixtures

AbstractOn the basis of the Frank‐Kamenetzkii criterion for thermal explosion a theoretical expression of the induction period in autocatalytic reactions with consumption of the catalyst is derived. Measurements on formaldehyde‐oxygen‐mixtures by Vanpee are in satisfactory agreement with the prediction that the induction period is inversely proportional to the initial concentration of formaldehyde.