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In 1937 Dr H. Wilman and I (Finch and Wilman 1937) first drew attention to a new effect consisting in the occurrence of broad bands or areas of blackening in electron diffraction transmission ...patterns obtained from crystals of organic compounds such as long-chain hydrocarbons and poly- cyclic aromatic compounds. We found that the position of these diffuse areas corresponded to the arrangement and separation of the carbon atoms in the molecules. Subsequently, in collaboration with Dr A. Charlesby (1939), we were able to show that this diffuse-area pattern appeared to be due to molecules which, though orientated with respect to the beam in accordance with the crystal orientation, nevertheless bore no definite phase relationship to each other, and this pattern thus resembled that of a gaseous stream of orientated molecules. We found that this lack of phase relationship could be explained on the assumption that, due to thermal agitation, the individual molecules were displaced from their mean position in a random fashion, there being no connexion between the displacement of adjacent molecules.
A discussion on friction - Surface changes due to sliding Finch, George Ingle; Spurr, R. T.
Proceedings of the Royal Society of London. Series A, Mathematical and physical sciences,
05/1952, Volume:
212, Issue:
1111
Journal Article
Metallic bearing surfaces on sliding become coated with an amorphous Beilby layer formed by the smearing out of molten projections. The heating has been held to be due to the overcoming of friction ...between the metals themselves. However, there are many examples of the formation of Beilby layers where there is no evidence of the occurrence of direct intermetallic contact and where the frictional forces must have been other than between metals. In practice a metallic bearing surface is invariably covered with an amorphous oxide layer. The load-carrying capacity of this layer depends largely on the rigidity of the underlying metal. It is, therefore, a particular virtue of the Beilby layer that in addition to its smoothness it is, in general, much harder than the underlying metal. The bearing metals in general use are more fusible than their oxides. The heat generated in the sliding of the oxide-covered metal pair leads first to the softening of the more fusible metal and the consequent rupturing of its oxide film. Intermetallic contact is, however, still prevented by the oxide film which remains intact on the more refractory, and consequently still rigid surface. It is well known that Beilby layers are formed on both surfaces of a sliding element, even when the metals have widely different melting-points. This is due to the high temperature developed at the asperities of the rougher surface as these slide in long tracks over the smoother surface.
The fact that hydrogen is formed during the cathodic combustion of moist “detonating gas” (VI) suggests that carbonic oxide can be burnt by steam in the discharge. To test this view, systematic ...investigations along the following three lines were undertaken:—A study of (i) the effect of hydrogen on the cathodic combustion of carbonic oxide, (ii) the cathodic equilibrium between steam and carbonic oxide, and (iii) the cathodic combustion of mixtures of hydrogen and oxygen in various proportions. In what follows is given an account of the investigation of the effect of dilution with hydrogen on the cathodic combustion of “detonating gas.” The experimental results have shown, inter alia, that hydrogen is, in the absence of sputtered metal atoms, a more powerful promoter of the cathodic combustion of carbonic oxide than steam, and that more carbon dioxide than steam is formed when a mixture of carbonic oxide, hydrogen and oxygen in equal proportions is burnt cathodically. These and the further facts set forth below, considered in conjunction with those previously established in the course of the preceding investigations of this series, have enabled us to put forward in what follows a view of the mechanism of the cathodic combustion of carbonic oxide and of the rôle played therein by hydrogen, steam and metal particles, which is not only in accordance with the said facts, but also appears to us to afford a satisfactory basis for a reasonable explanation of the known facts relating to the combustion of carbonic oxide in flames in general.
A spectrographic examination of the cathodic combustion of carbonic oxide “detonating gas” has shown that carbonic oxide ions are not formed in either the cathode or interelectrode zones under the ...conditions of our experiments (V). This fact proves that carbonic oxide molecules can be burnt cathodically without being ionised. The observed acceleration of the rate of cathodic combustion of “detonating gas” by steam and/or metal particles cannot, therefore, be attributed to the overcoming of the electrostatic forces of repulsion existing between similarly charged ions (III and IV). The present investigation was originally undertaken with the object of submitting certain of our earlier views to the test of experiment. During its prosecution, however, Prof. S. Chapman, F. R. S., suggested to us that considerations arising out of the three-body collision theory might lead to a satisfactory explanation of the mechanism of the combustion of “detonating gas”; and since then the investigation has been considerably extended in order to enquire more closely into the precise nature of the rôle or rôle played by such promoters of cathodic combustion as metal atoms and steam molecules.
The experimental results on the electrical charging of gold, silver and nickel surfaces, as set fourth in Parts I and II of the present series, have led to the conclusion that there are at least five ...different types of adsorption of a gas on a hot metallic surface, each of which can be clearly defined in terms of the nature of the charge on, and the tenacity with which such charge is retained by, the surface. In three such cases the adsorbed gaseous molecules are in an active, electrically charged condition. Before the full significance of these observations in their bearing upon the nature and mechanism of heterogeneous catalysis can be properly appreciated it will be necessary to accumulate systematically further facts relating to the electrical condition of hot surfaces; and with this object the investigation is being extended to a variety of different surfaces. An account is given below of the experimental results obtained with a platinum surface at temperatures up to 850° C. Experimental. The apparatus used and the experimental procedure followed was as previously described. Platinum specially supplied by Messrs. Johnson and Matthey, and stated by them to contain over 99·5 per cent. Pt and to be free from non-platinum metals, in the form of a 22 S. W. G., 6 by 10 cm. sheet, to which was fused a 25 S. W. G. similar platinum wire, was employed and will be referred to in what follows for the sake of brevity as the surface. The charges were measured by means of a Lindemann quadrant electrometer.
In Parts I and II of the present series an account was given of an investigation of the ignition and slow non-self-propellant combustion of electrolytic gas in direct current discharges. In those ...experiments a smooth direct current discharge was maintained between cooled platinum or copper electrodes in pure electrolytic gas, confined over sulphuric acid, at pressures between 30 and 180 mm. in such a manner as to eliminate, as far as possible, any chemical combination other that that caused only by the ionisation of the gases. The proportionality between the rate of chemical change and the current was then studied. It was shown that (i) an electric discharge can be passed through electrolytic gas in such a manner that combination takes place at a rate which is determined only by the discharge; (ii) up to a certain limiting current, which depends upon (a) the nature of the cathode material, (b) the gas pressure, and (c) the gap width, combustion is confined to the cathode zone, its rate being directly proportional to the current, i. e., to the number of ions arriving at the cathode in a given time; (iii) after a certain limiting current has been exceeded, combustion commences abruply in the inter-electrode zone and is thereafter superposed upon the cathodic combustion, the two then continuing as independent simultaneous effects; (iv) this inter-electodic combustion, like the cathodic, is also proportional to the current passing; unlike the cathodic, however, it is independent of the material of the electodes, but dependent upon (a) the gas pressure, and (b) the gap width.
It was shown in part I of the present series of researches that a gold or silver surface becomes charged when heated in vacuo or in contact with various gases, and that the charge on the surface ...depends, in the main, upon the temperature and the nature of the gas, and also to some extent upon the previous history of heating of the surface; but is independent, within wide limits, of the gas pressure. In view of the close bearing which these results undoubtedly heave upon the nature and mechanism of heterogeneous catalysis, the investigation is being extended to an examination of the electrical conditions of a variety of other surfaces. In what follows an account is given of the experimental results obtained with a nickel surface at temperatures up to 850° C. The apparatus previously described and illustrated in Part I was employed in all experiments to be described below, a rolled-up nicked 20 S. W. G. Sheet, 7 cm. by 12 cm., being suspended in the vertical quartz vessel by means of a narrow nickel tape cut from the sheet itself. The sheet had been previously washed with petroleum ether, no attempt having been made to remove the thin oxide film. The surface charge was measured by means of a Lindemann electrometer. The experimental procedure was essentially that followed and described in Part I.
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