Evolution Of Carbon Monoxide Research Articles

Microstructural Stability and Creep Behavior of Si‐C‐O (Nicalon) Fibers in Carbon Monoxide and Argon Environments

Constant‐load creep‐rupture tests were performed on single Si‐C‐O fibers (Nicalon). Test environments included pure carbon monoxide (CO), pure argon gas, and a mixture of CO and argon gas with a CO partial pressure of 40 kPa. Fibers were tested at temperatures of 1200°‐1400°C and at nominal applied stresses of 0.15–0.7 GPa. The as‐received and crept specimens were characterized by means of scanning electron microscopy, transmission electron microscopy, X‐ray photoemission spectroscopy, electron‐probe microanalysis, Auger electron spectroscopy, and thermo‐gravimetric analysis. In pure argon, the microstructure of the Nicalon fiber was unstable, which was attributed to the decomposition of the silicon oxycarbide phase, which resulted in CO and silicon monoxide gas evolution and silicon carbide grain growth. Fiber shrinkage was observed at temperatures <1300°C at low applied stresses. At high stresses, fibers exhibited only primary creep. In the CO/ argon‐gas environment, very limited grain growth and a smooth carbon coating were observed at the fiber surface at temperatures <1350°C. At all applied stresses, fibers exhibited steady‐state creep whose rates, strains, and times to failure were higher than those observed in argon. The apparent activation energy for creep of Nicalon fibers in the CO/argon‐gas environment was 435 kj/mol. At temperatures >1350°C in the CO/argon‐gas environment, however, the fiber behaved as in pure argon. Tests in pure CO only resulted in lower strains to failure and thicker carbon layers on the fiber surface. A rheological model based on the viscous flow of a concentrated suspension was proposed to describe the fiber deformation. The continuously decreasing creep rate in argon was suggested to be related to the continuous increase of the total solid volume fraction, which affects the fiber viscosity. On the other hand, the steady‐state creep of Nicalon with a stable microstructure in the CO/ argon‐gas environment was characterized by a Newtonian‐type viscous flow, which supports the predictions of the model.

Reduction of FeO in smelting slags by solid carbon: Experimental results

The reduction of CaO-SiO2-Al2O3-FeO slags containing less than 10 wt pct FeO by solid carbonaceous materials such as graphite, coke, and coal char was investigated at reaction temperatures of 1400 °C to 1450 °C. The carbon monoxide evolution rate from the system was measured using stationary and rotating carbon rods, stationary horizontal carbon surfaces, and pinned stationary spheres as the reductants. The measured reaction rate ranged from 3.25 × 10−7 mol cm−2 s−1 at 2.1 pct FeO under static conditions to 3.6 × 10−6 mol cm−2 s−1 at 9.5 pct FeO for a rotating rod experiment. Visualization of the experiment using X-ray fluoroscopy showed that gas evolution from the reduction reaction caused the slag to foam during the experiment and that a gas film formed between the carbon surface and the slag at all times during experimentation. The reaction rate increased with increased slag FeO contents under all experimental conditions; however, this variation was not linear with FeO content. The reaction rate also increased with the rotation speed of the carbon rod at a given FeO content. A small increase in the reaction rate, at a given FeO content, was found when horizontal coke surfaces and coke spheres were used as the reductant as compared to graphite and coal char. The results of these experiments do not fit the traditional mass transfer correlations due to the evolution of gas during the experiment. The experimental results are consistent, however, with the hypothesis that liquid phase mass transfer of iron oxide is a major factor in the rate of reduction of iron oxide from slags by carbonaceous materials. In a second article, the individual rates of the possible limiting steps will be compared and a mixed control model will be used to explain the measured reaction rates.

A Czochralski Silicon Growth Technique which Reduces Carbon to the Order of 1014 per Cubic Centimeter

Graphite hot components were improved in a Czochralski‐type puller and carbon concentrations were reduced in silicon crystals to at a solidified fraction of 5% and to at 80%. The improvements include a means to exhaust carbon monoxide gas generated from the graphite heat shield, silicon carbide coatings on the graphite heater, crucible, suscepter, and purge tube. It was found that the graphite heat shield is an important source of carbon, and that carbon monoxide evolution from the melt surface is an important purification mechanism in the Czochralski silicon growth process in addition to the segregation phenomenon of carbon.

Fire‐hazard assessment of extended‐chain polyethylene and aramid composites by cone calorimetry

AbstractA cone calorimeter is used to determine the fire performance of polymer composite materials containing combustible reinforcing fibres in addition to combustible matrix resins. Extended‐chain polyethylene and aramid fibre‐reinforced composites containing epoxy, vinylester and phenolic matrix resins are examined at various cone irradiances. Values for time to ignition, rate of heat release, effective heat of combustion, smoke density and evolved carbon monoxide and carbon dioxide are reported for the reinforcements, matrix resins and composites. The reinforcements have a significant effect on the fire‐hazard properties of the composite materials. For the epoxy and vinylester composites, times to ignition reflect those of the component of higher ignitability. This was not the case for the aramid‐reinforced phenolic composite, in which the resin surface layer hinders combustion of the fabric reinforcement. Resin and reinforcement contributions to the composite rate of heat release behaviour as a function of time are generally discernible.

The effect of mechanical degradation on the pyrolysis of poly(methyl methacrylate) and its copolymers

The effect of mechanical degradation in air on the thermal degradation of poly(methyl methacrylate) and its copolymers with methacrylamide and hydroxymethyl methacrylamide has been studied by pyrolysis—evolved gas—infrared analysis. It has been shown that degradation results in reduced zip length, decreased yield of monomer, and evolution of carbon dioxide, carbon monoxide, methanol and methane. These latter gaseous products can lead to erroneous interpretation and to postulation of incorrect degradation mechanisms. The results demonstrate that the effects of mechanical degradation must be considered when preparing samples for thermal degradation studies.

Photochemistry of iron pentacarbonyl adsorbed on titanium dioxide

AbstractThe photolysis of iron carbonyl (Fe(CO)5) adsorbed on titanium dioxide (TiO2, anatase) was studied by FT‐IR spectroscopy. When adsorbed Fe(CO)5 is illuminated by visible and near‐UV light, the IR spectrum of its photolysis products is hardly observed, indicating that most of the Fe(CO)5 is photodecomposed to iron(0) or iron oxides on TiO2. The carbon monoxide (CO) evolution rate upon illumination depends on the wavelength of light; 433 nm light is more effective for CO evolution than 366 nm light. This result implies that the band‐gap excitation of TiO2 has little effect on the photolysis of adsorbed Fe(CO)5, since the absorption edge of TiO2 (anatase) lies at around 400 nm. The effects of substrates on the photolysis of adsorbed Fe(CO)5 are discussed with reference to previous results obtained for aluminium oxide (Al2O3) and silicon dioxide (SiO2), on which the photolysis leads to the formation of Fe2(CO)9 or Fe3(CO)12.

Thermal desorption measurement technique

Practical thermal desorption measurements require an ultrahigh vacuum (UHV) system with a simple method of calibrating the residual gas analyzer for a number of gases. The calibration system should be easy to move between systems. We describe how the gas injection method of Kendall has been used to calibrate an UHV system and present example measurements of the carbon dioxide and carbon monoxide evolution during the decomposition of a commercial triple carbonate used in cathode ray tube manufacture. The activation energy of the BaCO3 component of the triple carbonate was found to be 94.7 kcal/mol.

A comparison of the fire-retardant properties of zinc hydroxystannate and antimony trioxide in brominated polyester resins containing inorganic fillers

Studies have been carried out to evaluate the fire-retardant properties of zinc hydroxystannate, relative to those of antimony trioxide, in resins based on the bromine source, DBNPG, containing various inorganic fillers. The effectiveness of ZnSn(OH) 6 and Sb 2O 3 as flame retardants depends on several factors including incorporation level of the additives and fillers, and bromine content of the resin. CaCO 3 is a poor filler in these resins, talc and Al 2O 3 are reasonably effective and ATH is good, particularly at high loadings (> 50 phr). In general, Sb 2O 3 gives optimum performance in ATH-filled resins, whereas ZnSn(OH) 6 exhibits a marked flame-retardant synergism with anhydrous Al 2O 3. Although Sb 2O 3 increases smoke emission from unfilled and alumina-filled resins, ZnSn(OH) 6 significantly reduces both the rate of production, and the maximum level, of smoke generated from these materials. In addition, the ZnSn(OH) 6-Al 2O 3 combination markedly inhibits the evolution of carbon monoxide from burning resins and is clearly an excellent overall fire-retardant system for this type of polymer. Thermoanalytical studies provide evidence for a combined condensed/vapour phase mode of action, in which the ZnSn(OH) 6-Al 2O 3 system catalytically promotes the dehydrobromination of the resin and leads to the subsequent formation of volatile metal halides or oxyhalides. These processes lead to an increase in the yield of thermally-stable char, at the expense of flammable products, and result in the introduction of combustion-inhibiting species into the flame.

Influence of the sample mass and the presence of the reaction products on the thermoanalytical results

It has been known from the very beginning of the thermal analysis that the transport processes can significantly influence the thermoanalytical results. In this paper, three characteristic examples are given to show that this problem is more complex and arises more frequently than it is generally believed. The studied reactions are the carbon monoxide evolution from calcium oxalate, the thermal degradation of polytetrafluoroethylene, and the thermal decomposition of azodicarbonamide. TG and DSC experiments were carried out with sample masses varying between 0.05 and 8 mg. The necessity of the development of new kinetic models is concluded.

Production of trace levels of carbon monoxide during methanogenesis on acetate and methanol

Production of trace levels of carbon monoxide was consistently observed in the off-gas of a laboratory anaerobic digester fed Waste Activated Sludge. Inocula from this digester was enriched for acetate and methanol utilizing methanogenic populations. These enriched inocula were then monitored in batch assays for carbon monoxide and hydrogen production. Results demonstrated that carbon monoxide is produced during methanogenesis on both substrates. Subsequent utilization of CO was observed to occur after methane production was essentially complete for the assays conducted with methanol. Carbon monoxide evolution during methanogenesis on acetate displayed a markedly different trend from that observed from methanol.

N, N-disubstituted lithium bis(carbamoyl)cuprate. A convenient complex for one-pot conversions of amines to formamides, oxamides, carbamates, and oxamic acids

Lithium bis(carbamoyl)cuprates ( 2) were readily derived from secondary amines such as N-methylaniline, N-methylbenzylamine, and diethylamine, under mild carbonylation conditions (0°C, 1 atm of carbon monoxide), but diphenylamine and benzylphenylamine were unsuitable as the starting materials. The carbamoylcopper complexes 2 formed in ether were readily converted to the corresponding formamides, oxamides, carbamates, and oxamic acids by the appropriate treatment. The formation and stability of 2 depended much on the solvent used. The higher polarity effect of the solvent (DME, THF, and HMPA) made 2 less stable and caused concomitant evolution of carbon monoxide in further reactions. A palladium catalyst was found to be effective for cross-coupling reactions of 2 with iodobenzene or ( E)-β-bromostyrene.

Kinetics and equilibrium of Co 2(CO) 6(η 4-norbornadiene) formation from Co 2(CO) 8 and norbornadiene under CO

The formation of Co 2(CO) 6(η 4-NBD) from Co 2(CO) 8 and NBD is a reversible endothermic reaction: Co 2(CO) 8 + NBD ▪ Co 2(CO) 6(η 4-NBD) + 2CO; Δ H 0 14.9 ± 0.7 kcal mol −1 In the forward reaction the carbon monoxide evolution is of first order in both Co 2(CO) 8 and NBD and of minus first order in CO. The carbon monoxide uptake in the reverse reaction is first order in both Co 2(CO) 6(η 4-NBD) and CO. The temperature dependence of the equilibrium constant K, and of the rate constant for the forward reaction k CO between 25 and 45°C is represented by log 10 K = (7.41 ± 0.48) − (3259 ± 147)/ T ( K in M) and log 10 k CO = (18.30 ± 1.75) − (7054 ± 540)/ T ( k CO in s −1).

Dye-sensitized photo-oxygenation of 1,2-cyclohexanediones

The dye-sensitized photo-oxygenation of the enols of 1,2-cyclohexanedione ( 1) has been carried out in various solvents at -70°-40°. Singlet oxygen is involved in the reaction as evidenced by quenching and rate enhancement observed in deuterated methanol. The reaction proceeds by an ene reaction with singlet oxygen to afford the hydroperoxide, 4, which closes to a five-membered endoperoxide, 5, as a major path or to dioxetane ( 6) as a minor one. The endoperoxide, 5, decomposed to 5-oxoalkanoic acid ( 2) with evolution of carbon monoxide or was trapped by the solvent (MeOH or EtOH) to give methyl or ethyl 5-carboxy-2-hydroxypentanoate ( 3). Competition between the enol of 3-methyl-1,2-cyclohexanedione ( 1a) and 2,3-dimethyl-2-butene (TME) has shown that the enol is as reactive as TME toward singlet oxygen.

Toxic Hazards of Acrolein and Carbon Monoxide During Combustion

Low molecular weight flammable liquid materials and sucrose, in place of polymeric materials such as polyethylene, polypropylene, cellulose, etc., were combusted in a tube furnace under different burning conditions. Evolution of acrolein and carbon monoxide were determined using gas chromatographic analysis. It was found that acrolein may have a greater lethal role than carbon monoxide under certain burning conditions.

Toxicity of smoke during chair smoldering tests and small scale tests using the same materials

Toxicological evaluation of smoke produced during smoldering chair tests was undertaken by exposing mice to smoke emitted prior to, as well as following, flaming ignition of the chairs. By exposing several groups of mice, using undiluted smoke from the room containing the chairs, as well as various dilutions of the smoke, different levels of acute lethality were obtained. From these experiments, chairs constructed with polyurethane foam were found to create higher toxic atmospheres than chairs constructed with polyester or cotton fiber cushions. The same materials (polyurethane foam, polyester and cotton fibers) were also thermally decomposed in a small scale system and mice were exposed to the smoke to evaluate acute toxicity. Again polyurethane foam was found to produce smoke more toxic than smoke produced by polyester and cotton fibers. Sensory irritation monitored in mice during the smoldering tests indicated that an intense level of irritation was present long before large amounts of smoke were generated and long before flaming ignition occurred. The phenomenon of eye, nose and throat irritation would therefore be the first effect impeding escape attempts of individuals in a fire situation. Sensory irritation was followed by asphyxiation as evolution of carbon monoxide or hydrogen cyanide, or both, occurred. The same pattern of responses was observed with smoke generated with the small scale decomposition system.

The reaction of 1,3,2-dioxastannolans with diacyl chlorides: decarbonylation in the reaction with oxalyl chloride

Abstract 2,2-Dibutyl-1,3,2-dioxastannolans react with carbonyl chloride to give the corresponding ethylene carbonates, and with malonyl chloride or succinyl chloride to give the oligomeric malonates or succinates. The reaction of oxalyl chloride, however, depends of the number of methyl substituents carried by the carbon atoms of the ring; with none, ethylene oxalate is essentially the only product, but increasing methylation induces the evolution of carbon monoxide and the formation of the ethylene carbonate until, with four methyl substituents, only the carbonate of pinacol, and no oxalate is formed, providing a striking example of the Thorpe-Ingold effect. The mechanism of this decarbonylation is discussed.

The preparation of a ferrofluid by decomposition of dicobalt octacarbonyl: II. Nucleation and growth of particles

The formation of a ferrofluid by thermal decomposition of a toluene solution of dicobalt octacarbonyl , in the presence of ethyl (2 hexyl) sodium sulfosuccinate, has been studied. The carbon monoxide evolution, the diameters of the particles, and the number of growing particles have been measured using also small-angle X-ray scattering and magnetic methods. The different sequences of CO evolution are explained. At least two factors are responsible for the formation of particles of very narrow size distribution: the presence of microreactors in the reaction medium and a diffusion controlled growth mechanism.

Catalytic gasification of char from hydrocracked pitch

Gasification of hydrocracked pitch (vacuum residuum) was performed non-catalytically and with K 2CO 3 and V 2O 5 catalysts. In agreement with studies of many other workers, K 2CO 3 was found to enhance the gasification rate. In contrast, V 2O 5 was found to inhibit gasification when compared to the non-catalytic rate. X-ray photoelectron spectra were obtained on both catalysts and on catalyst-pitch residues. They indicated that K 2CO 3 does not exist under reaction conditions. This experimental finding suggests that some of the catalytic gasification mechanisms recently reported in the literatúre may be incorrect. In this work, both catalysis and inhibition during gasification have been explained in terms of three effects, reaction at carbon edge planes, intercalation of the catalyst or inhibitor, and electron transfer. Potassium donates its outer electron to the π-electron clouds associated with the carbon layers. Extra electrons facilitate the formation of an unstable reaction intermediate which leads to the evolution of carbon monoxide. The vacant d-orbitals in vanadium stabilize π-electrons in the carbon layers, thereby making carbon monoxide evolution less likely. Thus, opposite extremes of a single effect account for both catalysis and inhibition.

Carbon Monoxide Evolution from Natural and Synthetic Materials

Carbon monoxide evolution was determined for a wide variety of natural and synthetic materials pyrolyzed under rising temperature conditions and at selected fixed temperatures. The yield of carbon monoxide was strongly influenced by the chemical composition of the material, by temperature, and by sample weight.

Carbon Monoxide Evolution From Elastomers

Carbon monoxide evolution was determined for a wide variety of solid and cellular elastomers, pyrolyzed at rising temperature from 200 to 800°C and at a fixed temperature of 800°C. The yield of carbon monoxide was influenced by chemi cal composition and heating rate.