The Cry of Tin

Editor’s Note

Tin has been long known to release a “shriek” or “cry” when bent. Here Bruce Chalmers of University College London attempts to move beyond the vague notion that the sound is caused by the grinding of crystals against one another during deformation. He proposes that it stems from the phenomenon of twinning, in which two crystals share some of the same crystal lattice points, typically with one crystal being a mirror image of the other. Chalmers, who became a celebrated crystallographer, was then working with E. N. da C. Andrade, a pioneer in the study of the crystal structures of metals. Andrade endorses Chalmer’s work here, saying that it may be important for understanding the general phenomenon of twinning.　　中文

IT is an observation of respectable antiquity that when a bar of tin is bent it emits a characteristic creaking, known as the “cry of tin”. According to Mellor1, who is one of the few authorities to refer to the subject, the cry “is supposed to be produced by the grinding of the crystals against one another during the bending of the metal”, and I have been unable to find in the literature any more definite explanation of its origin. In the course of some experiments which I have been carrying out with Prof. E. N. da C. Andrade on single crystal wires I have made observations which, I think, make possible a rather more precise attribution of the sound.　　中文

I have obtained the cry with cadmium as well as with tin. When single crystal wires of these metals are stretched, the deformation takes place in two stages, a slip on the glide planes, which constitute in both cases a unique system, being succeeded by a mechanical twinning on a specified plane. The twinning does not take place until after a definite amount of glide extension has occurred, which enables the two phenomena to be studied separately.　　中文

With single crystal wires no sound is produced during the glide stage of extension, but with both metals twinning is accompanied by the characteristic creaking or tearing sound. The same sound also occurs when such wires are violently bent or twisted, a process which gives rise to the surface marking characteristic of twinning, although it does not allow the separation of twinning from other effects in the way that simple extension does.　　中文

The tin with which the phenomenon is normally observed is in a polycrystalline state. Although the cry occurs when polycrystalline cast rods of both tin and cadmium are bent, drawn wires of small diameter do not give it unless they are annealed, or, in other words, the production of the sound depends on the size of the crystallites being greater than a certain minimum—larger crystals, of course, being subjected to more severe strain when the metal is bent. It is reasonable to suppose that the cry is an accompaniment of twinning in the case of the polycrystalline state as well as in the single crystal state.　　中文

Preliminary measurements on cadmium indicate that whereas the heat evolved in the twinning is of the order of 0.1 calories per gram, less than one-tenth of this amount is produced during the whole extension accompanying gliding, although this extension is considerably greater than that due to the twinning. The measurements, which are being followed up with more accurate methods, give, at present, only rough approximations, but suffice to establish clearly this very much greater heating which accompanies twinning. This observation suggests that some of the mechanical energy that is supplied to the lattice to cause twinning is afterwards liberated as heat energy and, in particular cases, as sound energy, the cry of tin and cadmium being a manifestation of the latter.　　中文

It may be added that while a cry can be produced from zinc, which crystallises in the hexagonal system and twins readily, I have not been able to produce a cry with any metal crystallising in a cubic system, for which twinning does not take place.　　中文

Bruce Chalmers

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The observations of Dr. Chalmers described in the above letter, which are being followed up, seem to me likely to prove of considerable importance for elucidating the problem of twinning. The generation of heat agrees with the view that, in twinning, the molecules, when sufficient energy is applied, slip from one equilibrium position to another, about which they then execute heavily damped vibrations, the energy of vibration dissipating itself in heat and probably in radiation of a frequency of the Reststrahlen order. The sound indicates that the twinning does not take place over the whole region of twinning simultaneously, for the sound frequency is much too low to be connected with the vibration of molecules or molecular units, but is propagated from layer to layer with a velocity or velocities of the order of sound velocity. It is possible that in the case of substances where sudden twinning is unaccompanied by audible sound, the sound exists, but is of too high a frequency to be heard.　　中文

E. N. da C. Andrade

(129, 650-651; 1932)

Bruce Chalmers: Physics Laboratory, University College, London, April 6.

Reference:

1. Complete Treatise of Inorganic Chemistry, 7, 296.