Gas Evolution Rate Research Articles

The entrapment and thermal evolution of low energy inert gas ions injected into borosilicate glass

Low energy (100–1750 eV) A+ and Kr+ ions were injected into borosilicate glass targets from a monoenergetic ion source contained within an ultra-high vacuum system. The entrapped gas was released from the glass target by heating in a controlled manner so that target temperature varied as a prescribed time function and the evolved gas was recorded with a small mass spectrometer. Observations of the integrated rate of gas release allowed deduction of the probability of ion entrapment as a function of ion fluence and energy and measurements of the instantaneous gas evolution rate as a function of temperature allowed deduction of the energies required for gas atom mobility in the glass. The results of these studies are compared with earlier measurements using more poorly defined ion and target parameters and the depth and nature of trapping centres for ion retention in the glass is discussed.

Effect of gas evolution on the rate of mass transfer at vertical electrodes

The effect of H 2 evolution on the mass-transfer rate of the reduction of K 3Fe(CN) 6 at vertical nickel electrodes was studied. A similar study was carried out on the effect of O 2 evolution on the mass transfer rate of the oxidation of K 4Fe(CN) 6. The variables studied were: rate of gas evolution, electrode height and electrode—diaphragm separation. Calculations were conducted to test the feasibility of using gas evolution as a means for stirring instead of the forced flow method. It was found that gas stirring is an economical way of stirring within the range of current density studied.

Rotating two-ring electrodes as a tool for electrochemical investigations of gas-evolving reactions

Summary It is shown that two concentric ring electrodes located on a rotating disc surface can be used as an instrument for chemical and electrochemical analysis of gas-evolving reactions up to rates of gas evolution from the inner ring of 140 ml h −1 cm −2 for a rotation speed of 2950 rev. min −1 . A linear dependence between the inner ring current generating a certain species, and outer ring current of detection of that species, is found with a collecting effeciency of 17% up to a gas evolution rate of 27 ml h −1 cm −2 . The same value is obtained without gas generation in the ferrocyanide-ferricyanide redox system. After a transition period from 27 to 40 ml h −1 cm −2 , the collecting efficiency coefficient attains another constant value of 11%. It is suggested that the two linear parts of the plot pertain to a laminar mass transfer regime (17%) and a turbulent regime (11%) for the collecting of reaction products. However, in view of the results reported earlier 1 , which indicate that there is no change in the hydrodynamic situation on the inner ring electrode for gas generation rates up to 250 ml h −1 cm −2 , this method is recommended for electrochemical analysis even under conditions of extremely high rates of generation of gaseous bubbles from the electrode surface, the turbulence affecting the operation of the detecting electrode, but only in a well deffned and reproducible, manner.

Ring electrode on rotating disc as a tool for investigations of gas-evolving electrochemical reactions

Summary Gas evolution is known to interfere with rotating disc measurements because of the tendency of the bubbles to block the center of the disc. It is shown that a ring-shaped electrode of small thickness, placed on a rotating insulator disc surface, can be used for electrochemical investigations. Under such conditions, gas evolution is shown to be without any effect on hydrodynamic and diffusional parameters, which are defined by disc rotation, disc geometry, viscosity of the electrolytic solution and diffusion of electroactive species, similar to that on conventional rotating disc electrodes. At a rotation speed of 2950 rev. min −1 , a change in the rate of gas evolution from the ring electrode from 2.5×10 −2 to 2.5×10 2 cm 3 h −1 cm −2 , was found not to affect the diffusion layer thickness, which remained the same as that without gas evolution. An original method for plating platinum on the platinum ring electrode is developed.

Ring electrode on rotating disc as a tool for investigations of gas-evolving electrochemical reactions

Gas evolution is known to interfere with rotating disc measurements because of the tendency of the bubbles to block the center of the disc. It is shown that a ring-shaped electrode of small thickness, placed on a rotating insulator disc surface, can be used for electrochemical investigations. Under such conditions, gas evolution is shown to be without any effect on hydrodynamic and diffusional parameters, which are defined by disc rotation, disc geometry, viscosity of the electrolytic solution and diffusion of electroactive species, similar to that on conventional rotating disc electrodes. At a rotation speed of 2950 rev. min−1, a change in the rate of gas evolution from the ring electrode from 2.5×10−2 to 2.5×102 cm3 h−1 cm−2, was found not to affect the diffusion layer thickness, which remained the same as that without gas evolution. An original method for plating platinum on the platinum ring electrode is developed.

Poly(ethylene sulfide). II. Thermal degradation and stabilization

AbstractHigh molecular weight poly(ethylene sulfide) undergoes severe thermal degradation at the high temperatures (220–260°C) required for processing in injection‐molding equipment. Thermal degradation of the polymer is accompanied by gas evolution and a decrease in melt viscosity. Stabilization of poly(ethylene sulfide) can be effectively accomplished by addition of small concentrations of certain 1,2‐polyamines, preferably together with certain zinc salts as coadditives. Use of this stabilizer system inhibits thermal degradation to a remarkable extent, making it possible to mold the polymer at these high temperatures and obtain excellent physical and mechanical properties. Investigation of the thermal degradation process was carried out. The rate at which gases evolved from unstabilized poly(ethylene sulfide) resins of various molecular weights and preparative histories and from model compounds of the same organic backbone structure was measured at temperatures ranging from 220 to 260°C. Rate of gas evolution from the resins, irrespective of chain length or preparation, was found to be constant at 230°C. The evolved gases, analyzed by infrared spectroscopy and gas chromatography, contained ethylene. Nearly identical apparent activation energies were found for the gas evolution reaction from the resin and model compounds. The ΔE* values were in good agreement with ΔE* determined by other techniques, 58 ± 2 kcal/mole. This is about the energy requirement expected for the homolytic cleavage of a carbon–sulfur bond of the type present in a poly(ethylene sulfide) structure. The rate and analytical data indicate that the degradative mechanism at processing (molding) temperatures is primarily due to the organic structure of the polymer. A mechanism of thermal stabilization is proposed in which the polyamine and zinc salt, in presence of molten polymer at processing temperatures, form a two‐centered electron transfer complex, capable of reacting with both radicals of the homolytically cleaved bond, “healing” the scission, so to speak.

Gasification of Coal with Laser Light Irradiation, Plasma Jet and Discharge-generated Excited Species

The laser light, plasma jet and electro discharge-generated excited species bring the new methods of coal gasification. Coal irradiated with laser light can produce gases rich in acetylene. The acetylene to methane ratio is relating to the light flux at the surface temperature of the decomposing coal. The high temperature and rapid quenching by use of plasma jet make also production of gases rich in acetylene. The acetylene content of gas was increased with the presence of hydrogen-argon.Pyrolysis of coal in microwave discharge yields gaseous products containing hydrogen, carbon oxides, and hydrocarbons, with acetylene as the main hydrocarbon. The rate of gas evolution and the distribution of fragments depend on the initial presence of argon, water vapour and hydrogen. An interaction of glow-discharge generated excited hydrogen species with coal delivers methane and carbon mono-oxide as major products. Minor products of saturated hydrocarbons come through the reaction between excited hydrogen species and non-aromatic precursor structures in coal.

Vacuum Maintenance in Image Tubes

The conflict between the vacuum requirements for electron-beam tubes and the physical characteristics of piezoelectric conversion materials has restricted most ultrasonic image converters in current use to continuous pumping, or if sealed, to limited beam currents. This paper reviews some of these conflicts encountered during the development of a sealed high-conductance quartz image converter. The vacuum problem is described in terms of the pressure level allowable, the gas sources within a tube, and the gas evolution produced by temperature changes and electron bombardment. Measurements disclose gas evolution rates proportional to the 37th power of the absolute temperature, and similar effects for electron bombardment. Consequently, unbaked tubes must be continuously pumped at high rates, and the potential life of a sealed tube is extended as the bakeout temperature during vacuum processing is raised. However, the properties of some piezoelectric materials may prelude high bakeout temperature. The anisotropic thermal expansion characteristics of crystalline quartz was an initial problem, but has been overcome through the use of a compliant seal. Barium titanate is susceptible to reduction when heated in vacuum at high temperatures. Any new ultrasonic material considered for a sealed image tube is suspect until its reaction to the rigors of vacuum processing is fully known.

A Contribution to the Theory of Electrolytic Chlorate Formation

Analysis of literature data indicates that anodic discharge of hypochlorite in relatively concentrated salt solutions approximately fits the Ibl‐Venczel correlation for mass transport at gas evolving electrodes. In this correlation, the mass transfer coefficient varies as the one‐half power of the gas evolution rate. Equations are derived for a model system employing a separate electrolyzer and reactor with circulating flow between them, considering the Foerster mechanism for homogeneous formation of chlorate in solution and the mass transport limited anodic discharge. Efficiency of chlorate formation is related to appropriate dimensionless groups containing the important system parameters. It is proposed that the model provides a basis for economic optimization of an electrolyzer‐reactor flow system.

Thermal and thermal oxidative degradation of polycarbamides

DATA is given in t h e literature by many authors studying thermal degradation mechanisms of polymers obtained by polymerization and polycondensation [~, 2], but little information is available regarding the thermal and thermal oxidative degradation of polycarbamides. This paper gives the results of a s tudy of the thermal and thermal oxidative degradation of polycarBamides, differing as to their heat resistance and melting points, in relation to the structure of the main unit. We at tempted to s tudy the behaviour of the polycarbamides at elevated temperatures by investigating the kinetics of thermal degradation in relation to the rate of gas evolution and the weight loss, and also the thermal oxidative degradation in relation to the rate of oxygen absorption and changes in the viscosity of polycarbamide solutions before and after degradation.

The properties of Viton “A” elastomers—IV. The influence of solid-gas interaction at Viton “A” and stainless steel surfaces on gas evolution rates in high vacuum : L. de Csernatony, Vacuum16, No. 8, p. 427.

The properties of Viton “A” elastomers—IV. The influence of solid-gas interaction at Viton “A” and stainless steel surfaces on gas evolution rates in high vacuum : L. de Csernatony, Vacuum16, No. 8, p. 427.

Gas evolution rate of black-epoxy painted surface

Gas evolution rate of black-epoxy painted surface

Reduction kinetics in titaniferous slags

The work described in this paper is part of a wider investigation into the reduction behaviour of titaniferous slags, particularly in blast-furnace smelting. It is generally agreed that if the reduction of titania (TiO2) could be slowed or stopped, the problems of smelting titaniferous ores could be minimized or eliminated. The reduction kinetics are important for a clear understanding of the process.Several iron oxide-bearing slags of the system CaO- F eO-Al2O3- TiO2-SiO2 of varying CaO/SiO2 ratio (0.6 to 1.2) and TiO2 content (0 to 30%) were reduced in contact with a metallic iron phase in graphite crucibles. The progress of reduction was observed by measuring the rate of gas evolution and by analyzing samples taken after measured time intervals, for iron in the slag and titanium in the metal.It was shown that the effect of titania on the activity of iron oxide in slag, particularly acid slags, was qualitatively similar to that of lime but less effective. It was found that titanium was reduced and approached saturation in the metal faster from basic slags than with acid slags and that acid slags permit a higher titanium content. For successful smelting of titaniferous ores the CaO/SiO2 ratio of the slag should vary between 0.8 and 1.0, decreasing in value as the titania content of the slag increases. Résumé Cet article s'inscrit dans le plan d'un ouvrage de plus grande envergure, concernant l'étude de la réductibilité des scories titanifères de haut fourneau. Il est couramment admis que, si la réduction de l'oxyde de titane (TiO2) peut être amoindrie ou annihilée, les problèmes propres au smeltage des minerais titaniféres seront minimisés ou éliminés. L'étude des mécanismes de réduction est, de ce fait, importante pour une compréhension claire et nette du procédé.Plusieurs scories, à base d'oxyde de fer, du type CaO-FeO-Al2O3-TiO2-SiO2, avec un rapport CaO/SiO2 variant de 0.6 à 1.2 et un contenu en TiO2 vari ant de 0 à 30%, furent réduites, en présence d'une phase de fer métallique, dans des creusets de graphite. L'évolution de la réduction fut suivie en mesurant le taux du dégagement gazeux et en analysant la teneur en fer de la scorie et la teneur en titane, dans la phase métallique à partir de certains échantillons, prélevés de la scorie et de la phase métallique à des intervalles précis de temps.Il put être montré que l'effet du TiO2 sur L'activité de l'oxyde de fer dans la scorie, particulierement pour les scories acides, était qualitativement semblable à celui de la chaux mais moins effectif. Il fut rouvé: 1) que le titane est plus vite réduit, et sa teneur de saturation plus vite atteinte, dans la phase métallique, à partir de scqries basiques, plutôt qu'à partir de scories acide; et 2) que dans les scories acides, une teneur en titane plus élevée est permi se. Les conditions optimal es de smeltage de minerais titanifères sont fixées par le rapport CaO/SiO2 qui devrait varier entre 0.8 et 1.0, la valeur du rapport allant en diminuant au fur et à mesure que la teneur en oxyde de titane dans la scorie va en croissant.

Adsorption and Occlusion of Gases by the Low-Temperature Forms of Ice

Water vapor condensed on a surface at −196°C in the presence of O2, N2, Ar, or CH4, forms a condensate which, on warming, evolves gas in three temperature ranges. The rate of gas evolution first goes through a maximum between −196° and −125°C probably from release of adsorbed gas due to decrease in surface area of the amorphous ice. A second peak in the gas evolution rate appears in the same temperature range as the formation of cubic ice between −120° and −110°C. The remainder of the occluded gas comes out between −70° and −40° (at 15° rise/min) where cubic ice transforms to the hexagonal form. Nitrogen adsorption isotherms indicate surface areas as high as 241 m2/g for amorphous ice prepared at −196°C, and annealing measurements suggest areas as high as 500 m2/g for lower-temperature preparations. Water—oxygen mixtures subjected to a microwave discharge, then condensed at −196° and allowed to warm, evolve as much as 97% of the product oxygen between −70° and −40°C.

Gas Evolution Rate of Black-Epoxy Painted Surfaces

It is the purpose of this paper to present the data of gas evolution from the surfaces coated with a black-epoxy paint which is widely used in space simulation chambers. The data have been taken by measuring the pressures in the test dome pumped through a pipe of known conductance. In the first evacuation, the remarkably high rate of gas evolution has been observed for the epoxy painted surfaces ; their rate decreases with time by degassing in vacuum even at a room temperature. It is supposed that organic solvent or unreacted substances in addition to water vapor could increase the amount of evolution gas at the initial stage. For all samples exposed to gases or air after degassing in vacuum, the rate of gas evolution is inversely proportional to the pumping time. The evolution rate at a room temperature for the epoxy painted surfaces after exposure to atmospheric, humid air is higher by a factor of 6 to 10 than that after exposure to nitrogen, oxygen, and argon for the same time. This is probably due to sorption of water vapor in air. The results are compared with available data obtained by different workers for similar materials.

The properties of Viton “A” elastomers IV. The influence of solid-gas interaction at Viton “A” and stainless steel surfaces on gas evolution rates in high vacuum

Solid-gas interactions are investigated by observing the change in gas evolution rates after conditioned samples are exposed to different gases. The effect of reactivity and molecular weight of the gas is evaluated by selecting as test gases helium, argon and air. Gas interdiffusion and surface exchange effects are examined by comparing data for samples retained in the chamber with those fully exposed to air. Elastomer baking temperature range extends from ambient to 350°C. Stainless steel (EN58F) data refers to ambient temperature only. Results indicate a definite saying in pump-down time, ranging from 80 to 20 per cent depending on baking temperature, after sample is exposed to dried argon. A further advantage after argon exposure is the attainment of lower ultimate pressures. Improvement after exposure to helium is intermediate between argon and air. This is due to the ease with which helium exchange takes place with active constituents of air.

Some Effects of Surface Layers on the Degassing Properties of Copper

The effects of pretreatment and surface layers on the degassing properties of OFHC copper were investigated. With the use of a radiofrequency mass spectrometer, the throughput method of analysis was employed to measure the evolution characteristics of H2, H2O, N2, CO, and CO2. Pretreatments such as hydrogen and vacuum firing, as well as surface layers on the metal, influence the quantity and rate of gas evolution at elevated temperatures. Surface layers of copper oxide, nickel, gold, and titanium accelerate degassing. A layer of vapor-deposited titanium on the copper greatly reduces the quantity of evolved gases.

The properties of Viton “A” elastomers II. The influence of permeation, diffusion and solubility of gases on the gas emission rate from an O-ring used as an atmospheric seal or high vacuum immersed

Gas emission rates were measured for a Viton “A” O-ring at ambient temperature, with the O-ring compressed in a trapezium groove, as is common practice for atmospheric seals, and for an O-ring completely immersed in vacuum. The effect of a 16 hour 100°C bake on the gas emission rates under the above conditions was determined after the O-ring had returned to ambient temperature. Results indicate that gas emission rates depend both on surface effects, eg adsorption, bulk effects and solubility and diffusion. For atmospheric seals permeation is a major factor, and because of this the use of guard vacuum is advocated. It is important that this is maintained during the baking period, when permeation rates are particularly high. The mechanism of diffusion-controlled degassing is discussed and numerical results of the solution of the appropriate mathematical functions are presented. The gas evolution rate from an unbaked O-ring used as an atmospheric seal in a trapezium groove was found to be 40 per cent of that from the fully immersed ring. In the case of baked rings, however, the gas evolution rate from the atmospheric seal was over 30 times greater than that from the fully immersed ring; the use of a guard vacuum reduced the evolution rate from the atmospheric seal to about the same values as that from the fully immersed ring.

Gas evolution from a solid rocket propellant during depressurizationto produce a quench.

Mass flow rate of gas evolution from burning solid rocket propellant during transient depressurization of combustion chamber

Breakdown of Simple Hydrocarbons subjected to a Silent Electric Discharge

THE gassing tendencies of insulating oils used in the electrical industry are assessed by measuring the rate of gas evolution or absorption when they are exposed under an atmosphere of hydrogen in an electrodeless discharge tube of the Siemens Evers-type. Previous investigations1–4 have been confined to the investigation of a wide variety of commercial oils and the effect of additions of aromatic rich oil fractions and other additives chosen for their ability to impart a desirable hydrogen gas absorbing characteristic to the mixture. The different hydrocarbon types present in the oils, paraffins, naphthenes, olefines and aromatics cause the discharge reaction to be a complex competitive process in which the gas evolved by the paraffins and naphthenes is partially or completely absorbed by the olefinic and aromatic fractions. To avoid this complexity and enable a clearer understanding of the reaction processes to be reached, certain pure saturated and unsaturated hydrocarbons representative of the types found in oils have been selected for investigation. The experiments have shown that the discharge reaction is closely related to the corresponding radiolytic breakdown of simple hydrocarbons5.