scholarly journals The influence of pressure on the boiling points of metals

1910 ◽  
Vol 83 (565) ◽  
pp. 483-491 ◽  
Keyword(s):  
Atmospheric Pressure ◽  
Boiling Point ◽  
High Vacuum ◽  
Similar Type ◽  
Exact Relation ◽  
Reduced Pressure ◽  
Boiling Points ◽  
Experimental Values ◽  
Low Pressures ◽  
Very High

Part I. — Pressures below 760 mm . In a previous communication (‘Proc.’, A, vol. 82, 1909, p. 396) the approximate boiling points of a number of metals were determined at atmospheric pressure. Apart from the question of finding the exact relation between the boiling point and pressure, it is an important criterion of any method for fixing the temperatures of ebullition to demonstrate that the experimental values obtained are dependent on the pressure. It is specially desirable when dealing with substances boiling at temperatures above 2000° to have some evidence that the points indicated are true boiling points. Previous work on the vaporisation of metals at different pressures has been confined to experiments in a very high vacuum except for metals like bismuth, cadmium, and zinc, which boil at relatively low temperatures under atmospheric pressure. The observations were limited to very low pressures on account of the difficulty of obtaining any material capable of withstanding a vacuum at temperatures over 1400° and the consequent necessity for keeping the boiling point below this limit by using very low pressures. Moreover in the case of the majority of the metals, e. g. , copper, tin, ebullition under reduced pressure has never been observed. The difficulties indicated above were avoided by using a similar type of apparatus to that previously described, and arranging the whole furnace inside a vacuum enclosure, thus permitting of the use of graphite crucibles to contain the metal.

scholarly journals II. On the critical state of gases

1880 ◽  
Vol 30 (200-205) ◽  
pp. 323-329 ◽  
Keyword(s):  
Critical Point ◽  
Critical Points ◽  
Critical State ◽  
Atmospheric Pressure ◽  
Boiling Point ◽  
Chemical Society ◽  
Boiling Points ◽  
Intermediate Condition ◽  
Specific Volumes

In a paper read before the Chemical Society, in May, 1879, I gave an account of a method of determining what is termed by Kopp the “specific volumes” of liquids; that was shown to be the volume of liquid at its boiling-point, at ordinary atmospheric pressure, obtainable from 22,326 volumes of its gas, supposed to exist at 0°. Being desirous of extending these researches, with the view of ascertaining such relations at higher temperatures, since April, 1879, I have made numerous experiments, the results of, and deductions from which I hope to publish before long. The temperatures observed vary from the boiling-points of the liquids examined, to about 50° above their critical points; and in course of these experiments I have noticed some curious facts, which may not be unworthy of the attention of the Society. It is well known that at temperatures above that which produces what is termed by Dr. Andrews the “critical point” of a liquid, the substance is supposed to exist in a peculiar condition, and Dr Andrews purposely abstained from speculating on the nature of the matter, whether it be liquid or gaseous, or in an intermediate condition, to which no name has been given. As my observations bear directly on this point, it may be advisable first to describe the experiments I have made, and then to draw the deductions which appear to follow from them.

RESPIRATORY MOVEMENTS AND ENDURANCE OF FROGS AT LOW PRESSURES

1957 ◽  
Vol 35 (5) ◽  
pp. 593-601
Author(s):  
James C. Hall ◽  
Helen I. Battle
Keyword(s):  
Atmospheric Pressure ◽  
Prolonged Exposure ◽  
Low Pressure ◽  
Reduced Pressure ◽  
Lung Inflation ◽  
Initial Effect ◽  
Advanced Stages ◽  
Normal Atmospheric Pressure ◽  
Low Pressures ◽  
Respiratory Movements

Exposure of three species of frogs (Rana pipiens, R. clamitans, and R. sylvatica) to pressures of 1.5, 3.0, and 5.0 cm. Hg induces characteristic changes in the frequency and type of breathing. The immediate initial effect is that of increasing both mouth and lung oscillations for a brief period, prior to a gradual decline in rate. Lung oscillations persist longer than mouth oscillations, and on return to normal atmospheric pressure, are initiated earlier and at a rapid rate. During advanced stages of decompression, excess lung inflation is resultant from several consecutive inhalations, prior to a deep exhalation. R. pipiens is most resistant to low pressure, and R. sylvatica least resistant. Large individuals of a species survive longer than small. Survival is better with little oxygen in an atmosphere of nitrogen at normal atmospheric pressure than with a comparable oxygen supply at a reduced pressure. A brief acclimatization to pressures of 1.5 and 3.0 cm. Hg can be produced by prolonged exposure to 15 cm. Hg but not by intermittent exposures to low pressure.

The Corona breakdown of aerials in air at low pressures

1963 ◽  
Vol 271 (1347) ◽  
pp. 551-564 ◽  
Keyword(s):  
Field Strength ◽  
Electric Field ◽  
Radio Frequency ◽  
Critical Field ◽  
Diffusion Theory ◽  
Reduced Pressure ◽  
Radiated Power ◽  
Diffusion Controlled ◽  
Experimental Values ◽  
Low Pressures

Radio-frequency corona breakdown of the air surrounding a transmitting aerial operating under conditions of reduced pressure occurs for a comparatively low radiated power. In this paper the theory of diffusion-controlled breakdown is discussed and used to deduce the critical field strength for breakdown at the tip of a prolate spheroidal unipole aerial. Two independent methods are used to determine the electric field strength at the tip of the unipole. In one of these the voltage on the coaxial transmission line feeding the unipole is measured at a distance of three-quarters of a wavelength from the base of the unipole. In this way the current entering the base of the unipole can be found, and hence the electric field at the tip can be calculated. The other method makes use of a small microphone actuated by the attractive force of the electric field. When this method is used, the radio-frequency oscillator is square-wave modulated. The two methods give satisfactory agreement. In the breakdown experiments two unipoles of different base diameter were used. For each of these experimental values of the critical field strengths for onset of corona are compared with the values deduced from the diffusion theory of breakdown.

scholarly journals 592 Water Flux from Lettuce Plants at Reduced Atmospheric Pressure

HortScience ◽  
2000 ◽  
Vol 35 (3) ◽  
pp. 499A-499
Author(s):  
Kenneth A. Corey ◽  
Phil A. Fowler ◽  
Raymond M. Wheeler
Keyword(s):  
Relative Humidity ◽  
Plant Growth ◽  
Vapor Pressure ◽  
Water Loss ◽  
Atmospheric Pressure ◽  
Ambient Pressure ◽  
High Vacuum ◽  
Thermal Control ◽  
Plant Responses ◽  
Reduced Pressure

Reduced atmospheric pressures may be used to minimize mass and engineering requirements for plant growth habitats used in some extraterrestrial applications. A chamber with high vacuum capability and thermal control at Kennedy Space Center was used to measure water loss of lettuce plants at reduced atmospheric pressures. A test stand with three, high-pressure sodium vapor lamps was used to determine short-term plant responses to reduced pressure. Initial experiments with lettuce showed that a pressure of 10 kPa (≈0.1 atm) resulted in a 6.1-fold increase in the rate of water loss compared to water loss at ambient pressure. However, due to low relative humidity, plants wilted after 30 minutes exposure to 10 kPa. A follow-up experiment in which relative humidity was controlled between 70% and 85%, demonstrated that water loss was directly proportional to the vapor pressure gradient, regardless of atmospheric pressure in the pressure range of 10 to 101 kPa. However, the response was curvilinear, suggesting effects on the pathway resistance. Results indicate that plant growth at atmospheric pressures of 5 to 10 kPa should be achievable. Further work will necessitate better relative humidity control and carbon dioxide control in order to separate vapor pressure deficit effects from diffusion effects.

XXVII.—A Common Thermometric Error in the Determination of Boiling-Points under Reduced Pressure

1910 ◽  
Vol 30 ◽  
pp. 436-436
Author(s):  
Alexander Smith ◽  
Alan W. C. Menzies
Keyword(s):  
Linear Function ◽  
Vapour Pressure ◽  
Boiling Point ◽  
Thermal Equilibrium ◽  
Reduced Pressure ◽  
Considerable Error ◽  
Boiling Points

When the bulb of a thermometer is enclosed in an evacuated vessel, the dilatation of the bulb introduces a considerable error in the temperature readings. This fact may be well known, but in the literature of boiling-point and vapour-pressure determinations we have observed no reference to it, and no corrections on account of it. Yet, except in the roughest work, this effect cannot be ignored. Thus, a test carried out with eleven thermometers showed that when the pressure round the bulb was lowered from 748 mm. to 20 mm. and thermal equilibrium with the bath had been recovered, the readings were from 0·10° to 0·17° lower. In all but one case, when there was a slight permanent dilatation, the change was constant and was a linear function of the change in pressure. The change bore no relation to the sizes of the bulbs. The thickness of the glass varied considerably, but could not, of course, be measured.

scholarly journals IV. Note on the atomicity of aluminium

1865 ◽  
Vol 14 ◽  
pp. 74-77 ◽  
Keyword(s):  
Atmospheric Pressure ◽  
Boiling Point ◽  
Good Deal ◽  
Preliminary Note ◽  
Reduced Pressure

In the “Preliminary Note on some Aluminium Compounds,” by Messrs. Buckton and Odling, published in the last Number of the Society’s ‘Proceedings,’ some questions of considerable theoretical importance are raised in connexion with the anomalous vapour-densities of aluminium ethyle and aluminium methyle. The authors have discovered that the vapour of aluminium methide (Al 2 Me 6 ) occupies rather more than two volumes (H = 1 vol.) at 163°, when examined by Gay-Lussac’s process, under less than atmospheric pressure. The boiling-point of the compound under atmospheric pressure is given at 130°, and the compound accordingly boiled a good deal below 130° at the reduced pressure at which the determination was made.

The metachor as a characteristic of the association of electrolytes in aqueous solutions

1984 ◽  
Vol 49 (5) ◽  
pp. 1061-1078 ◽  
Author(s):  
Jiří Čeleda ◽  
Stanislav Škramovský
Keyword(s):  
Aqueous Solutions ◽  
Apparent Volume ◽  
Solutions Of Electrolytes ◽  
Molal Volumes ◽  
The Difference ◽  
High Concentrations ◽  
Experimental Values ◽  
Suitable Characteristic ◽  
Association Of Ions ◽  
Very High

Based on the earlier paper introducing a concept of the apparent parachor of a solute in the solution, we have eliminated in the present work algebraically the effect which is introduced into this quantity by the additivity of the apparent molal volumes. The difference remaining from the apparent parachor after substracting the contribution corresponding to the apparent volume ( for which the present authors suggest the name metachor) was evaluated from the experimental values of the surface tension of aqueous solutions for a set of 1,1-, 1,2- and 2,1-valent electrolytes. This difference showed to be independent of concentration up to the very high values of the order of units mol dm-3 but it was directly proportional to the number of the free charges (with a proportionality factor 5 ± 1 cm3 mol-1 identical for all studied electrolytes). The metachor can be, for this reason, a suitable characteristic for detection of the association of ions and formation of complexes in the solutions of electrolytes, up to high concentrations where other methods are failing.

Epitaxial Silicon Layers Made by Reduced Pressure/Temperature CVD

1988 ◽  
Vol 129 ◽  
Author(s):  
J.L. Regolini ◽  
D. Bensahel ◽  
J. Mercier ◽  
C. D'Anterroches ◽  
A. Perio
Keyword(s):  
Thermal Processing ◽  
Atmospheric Pressure ◽  
Rapid Thermal Processing ◽  
Processing System ◽  
Epitaxial Silicon ◽  
Reduced Pressure ◽  
Selective Epitaxial Growth ◽  
Main Decomposition ◽  
Rate Limiting ◽  
Reactive Gas

ABSTRACTIn a rapid thermal processing system working at a total pressure of a few Torr, we have obtained selective epitaxial growth of silicon at temperatures as low as 650°C. When using SiH2Cl2 (DCS) as the reactive gas, no addition of HCl is needed. Nevertheless, using SiH4 below 950°C a small amount of HCl should be added.Some kinetic aspects of the two systems, DCS/HCI/H2 and SiH4/HCl/H2, are presented and discussed. For the DCS system, we show that the rate-limiting reactions are slightly different from those commonly accepted in the literature, where the results are from systems working at atmospheric pressure or in the 20-100 Torr range.Our model is based on the main decomposition of DCS, SiH2Cl→SiHCl + HCl, instead of the widely accepted reaction SiH2Cl2→SiCl2 + H2. This is the main reason why no extra HCl is required in the DCS/H2 system to obtain full selectivity from above 1000°C down to 650°C.

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