Gas-metal Interface Research Articles

Laser Burnthrough Time Reduction Due to Tangential Airflow- An Interpolation Formula

This paper contains an investigation of the influence of a tangential gas flow on the time required for a laser beam of given intensity to burn through a metal sheet. From a consideration of the hydrodynamics of the liquid metal-gas interface and the time required for an entrained liquid droplet to vaporize, an interpolation formula is derived relating the time required for burnthrough at a given freestream Mach number to that required in the absence of tangential flow, or for flow rates less than the critical velocity at which melt droplets are entrained. The interpolation formula so derived depends only on the thermodynamic properties of the melt, the hydrodynamic properties of the boundary layer and the size of the spot irradiated by the laser beam. The formula predicts an intermediate velocity for which the time for burnthrough is a minimum. Physical explanation of the minimum is given in the text. For limiting cases of very large laser spot size, the reduction in burnthrough time disappears.

C-O反応を伴う溶鉄の窒素吸収について

The effect of carbon-oxygen reactions on the rate of nitrogen absorption in liquid iron were studied under N2-O2 and N2-CO2 gas mixtures.It was confirmed that the experimental results on the decarburization of liquid iron agreed well with those obtained by several investigators.On the other hand, the simultaneous absorption of nitrogen in liquid iron shows a peculiar behavior as compared with the absorption without carbon -oxygen reaction at the interface. Namely, it was observed that the nitrogen concentration in liquid iron does not reach to equilibrium with nitrog en partial pressure in bulk gas phase, although the rate of nitrogen absorption in the initial period is rather rapid. This may be resulted from the decrease of nitrogen partial pressure at g as-metal interface due to the evolution of carbon monoxide from liquid iron. In this case, the nitrogen absorption may be controlled mainly by the transfer of nitrogen in liquid iron and also in gas phase.When the oxygen concentration of gas phase becomes nearly 30 percent, the effect of the absorbed oxygen at the gas-metal interface becomes more predominant in nitrogen absorption than that of d ecrease of nitrogen partial pressure at interface. When liquid iron contains sulphur, the effect of the adsorbed sulphur at the interface may also be predominant similarly to the case of 30% O2-N2 gasmixture.

Effect of sulphur on the rate of decarburization of molten iron

AbstractIron melts, containing 1–3% C and up to 3% S, were decarburized by gaseous argon-oxygen, principally at 1450°C. Sulphur itself was not removed from the melt but its presence decreased the rate of decarburization. The retarding effect of sulphur was greatest in the range 0–0.3% S, and became less noticeable at higher contents. The main rate-determining step was mass transport of oxidant (principally CO2 near the gas-metal interface) in the gas phase, with a second step becoming important and observable as sulphur was added. The reaction which is retarded, due to occupation by sulphur of surface sites, may be the activated adsorption of CO2.The rate may level out at contents of S above 1% due to the direct adsorption of oxygen. Resume Des bains de fer contenant jusqu’a 3% S et de 1 a 3% C ont ete decarbures a 1,450°C par des melanges argon-oxygene. Le soufre, tout en demeurant intouche, abaissait par sa presence le taux de decarburation. L'effet du soufre etait le plus marque pour des teneurs compri...

Superheating in the Zirconium-Oxygen Combustion System

WHEN a clean metal surface is exposed to the attack of a gas such as oxygen in low temperature conditions, reaction begins at the gas-metal interface, so that if the reaction products are nonvolatile an intermediate layer between the gas and metal will be formed. If, however, the rate at which the oxidation occurs is sufficiently high and the amount of energy supplied by the oxidation is sufficiently large, the oxidation mode, in most cases, changes into a different sustained rapid combustion mode. This initial rapid rise in temperature of the metal is called an “autoignition” period when it is followed by a sustained period of rapid combustion.

A practical application of infrared reflection spectroscopy to the study of the gas-metal interface

Description is given of a versatile cell for obtaining infrared spectra of a gas-metal interface by multiple specular reflection off the metal surface. The cell will fit into the optical assembly of a commercially available reflectance spectrometer and can be used under ultrahigh vacuum or high pressure flow conditions. The metal reflecting plates are clamped onto a central block containing an external well which can be accommodated with a cartridge heater or a suitable liquid coolant—thereby giving a total temperature range of ca. 80–800 °K. Provisions are included for variations in the total number of reflections and for an angle of incidence fixed between 45 and 70 °. The experimental conditions necessary for obtaining spectra of surface species are outlined, and results are given for an application of the technique to carbon monoxide interaction with electropolished copper at 40–175 °C.

New explanation of the polarity effect in current collection

The phenomenon of unequal contact voltages at the positive and negative brushes of a sliding current-collection system has previously been explained as being ohmic in nature. Measurements are now presented which suggest that it is due instead to a change in surface potential difference at the metal-gas interface, which occurs even without sliding.

Fe-O-J系およびFe-S-J系溶鉄の窒素吸収速度

The rates of nitrogen absorption in the ternary liquid iron, Fe-O-J, at several oxygen levels were measured at 1600°C. The results show that chromium and vanadium clearly increase the apparent mass transfer coefficient in any oxygen levels, as chromium and vanadium increase up to about 2%. Manganese and nickel have virtually no effect on the apparent mass transfer coefficient. The deoxidizing elements, such as chromium and vanadium, act as counter-poison for surface active oxygen. However, it is reasonable to consider that oxygen at the gas-metal interface mostly remains near interface, andacts as a resistant substance, even if the deoxidizing elements are present.It is further observed that carbon, manganese and silicon in the ternary liquid iron, Fe-S-J, have virtually no effect on the apparent mass transfer coefficient, probably because of the lower affinities of these elements to sulphur and the weaker effect of sulphur on the rate of nitrogen absorption than oxygen.

Models for electron emission from metals with adsorbed monolayers

The need for employing chemical rather than particle models to describe the electronic properties of a metal-gas interface has been investigated theoretically. Using the Thomas-Fermi-Dirac theory, both the microscopic charge distribution and the total electronic energy of the interface have been evaluated in such a way that one can distinguish between the coulombic and quantum mechanical contributions. It has been shown that the quantum mechanical corrections are a significant part of the total energy and may not be neglected. The differences between various macroscopic models are discussed, and it is concluded that a particle model, using only the concepts of electrostatics and statistical mechanics, does not represent adequately the electronic properties of alkali-refractory metal or alkaline earth-refractory metal interfaces. Detailed results for both cesium and barium adsorption on (100) and (110) faces of tungsten are presented.

Thermoelectric Power and Chemisorbed Hydrogen

CHEMISORPTION and catalysis on palladium have been attributed to holes in the d band of the metal1. Earlier work has shown that ambient gases change the thermoelectric power of silver2 and copper3. The present communication demonstrates how simultaneous measurements of thermoelectric power and resistance show how chemisorbed hydrogen affects the Fermi-level of palladium at the metal–gas interface.

Control of Texture in Magnetic Material by Surface Energy

Different crystallographic planes, at a gas-metal interface, have different surface energies. Although the energy difference is small (less than 100 erg/cm2), it is sufficient to cause migration of boundaries between grains of different (hkl) surfaces provided there is a sufficiently small restraint to boundary migration. Since the (110) plane is the plane of lowest surface energy γ in 3% silicon-iron, grains with (110) planes at the gas-metal interface are favored to grow at the expense of other (hkl) grains (γ110<γhkl) when the material and annealing atmosphere are free of impurities. In the presence of certain impurities, however, γ100 may be lower than γhkl and grains with (100) planes are favored to grow at the expense of all others. With proper processing, sharp (110)[001] or (100)[001] textures may be obtained in sheets of high-purity silicon-iron. Grain size and texture can be altered by deliberate additions of oxide film to the surface, by the amount of silicon in the alloy, and by the choice of annealing atmosphere. The effect of improved texture and low impurity concentration on magnetic properties is discussed.

The Determination of Transient Temperatures and Heat Transfer at a Gas-Metal Interface Applied to a 40-mm Gun Barrel

The problem of measuring very rapidly changing temperature and heat transfer at a gas-solid interface is becoming of increasing importance. This paper presents a method of doing this under the conditions of unidirectional heat flow in a semi-infinite solid. Temperatures are measured very near the metal surface by means of a special type of thermocouple. Equations are derived in which resulting thermocouple measurements are used to calculate the heat transfer through the surface. The method is illustrated by application to a 40-mm gun barrel. Experimental temperature records from four thermocouples installed along the barrel are shown. The ballistic heat transfer a t these locations is determined from these records. The experimental temperature curves are also compared with theoretical results.

熔融鐵炭素合金の脱炭反應に關する研究(II)

In order to study the effect of the oxygen pressure on the decarburization reaction, Fe-C alloys containining about 1-4% carbon were melted and decarburized with the oxygen gas stream, which had previously been prepared to show a partial pressure between 20 and 760mm Hg by mixing pure oxygen gas (or pure nitrogen) into air, the rate of the carbon removal being measured by flow method. In this case the equation of the rection rate was simplified as follows:The carbon contents measured at every time interval into this equation being introduced, the values of the specific constant, k0, were estimated for various oxygen pressures with the result of which the relation between k0 and po2 was found asBesides this, in case of lower carbon contents up to 1%, each value was found to be constant at higher oxygen pressures above 300mm Hg, where the oxygen contents on the surface of molten iron, could be presumed as predominant over those of carbon. In order to determine where the reaction occurred, the reaction rate was measured by varying the area of interface between gaseous and liquid phases. In consequence, it was found linearly proportional to that area, the reaction being shown to take place on the interface. The oxygen contents, dissoved in molten iron during the process of this reaction, were analysed in the samples killed with aluminum and were found to have no proportionality to the partial pressure of oxygen in gaseous phase, and to show the characteristic values corresponding to carbon contents. According to the results stated above, the reaction mechanism of this sort was presumed as follows:(1) The oxygen molecule dissociated on being adsorbed at the gas-metal interface, and then its atom was dissolved into the surface layer to participate in the reaction.(2) The oxygen which participated in this reaction must be in equilibrium with that in the gaseous phase at a given pressure.When the pressure of carbon monoxide produced in the reaction became considerable as compared with the oxygen pressure, this reaction was found to be retarded by the former gas.