Jean-Paul Clech has inquired about the primary literature reporting on tin transformation. I was recently sent a copy (my thanks to Jay Brusse of NASA's tin whisker web site) of an article (published over fifty years ago in a magazine for museum curators) that reviews that literature (going back to 1913). The authors were with the research laboratory of the British Museum. They conclude 

[I]t should be emphasised that the occuurence of true tin pest is a rarity both in Europe and the U.S.A.; the literature indicates how difficult it has been found to initiate the transformation, and of the many cases of so-called tin pest reported to the Tin Research Institute, the overwhelming majority have been clearly cases of ordinary corrosion. It has not, in fact, been found possible to obtain a single illustration known with certainty to represent authentic tin pest of natural occurrence.

I have typed up the relevant part (one page) including citations, and (since the listserve doesn't accept attachments) have copied it below. It looks fine formatted as html, but I know that many people don't receive these postings with html formatting. Those who have a compelling desire to get this in a more readable format can send a request DIRECT TO MY EMAIL ADDRESS, PLEASE DON'T BE A PEST TO THE FORUM, and I will send a .pdf version, along with the a .pdf of the original article.

Gordon Davy
Baltimore, MD
[log in to unmask]
410-993-7399



  _____  

Excerpt from H.J. Plenderleith and R.M. Organ, "The Decay and Conservation of Museum Objects of Tin", Conservation, 1, no. 2 (1953), pp. 63-72.

 

The cause of tin pest lies in the fact that near a room-temperature of 20°C tin can exist in either of two modifications: either as a powdery grey tin of density equal to 5.8466 at 18°C <outbind://181/#_ftn1> [1], or as a tetragonal white tin of density equal to 7.28 at 25°C: equilibrium exists at 13.2°C, according to E. Cohen <outbind://181/#_ftn2> [2] who measured the emf between half-cells of grey tin and white tin, in aqueous solutions of "pink salt," (NH4)2SnCl6 of the same concentration.

Other workers by other methods have found different values for the equilibrium temperature: thus Cohen and Dekker <outbind://181/#_ftn3> [3] by a dilatometric method found a value between 12 and 14.3 °C (probably very nearly 13°C), and a value of 20°C has also been given by a much earlier emf determination <outbind://181/#_ftn4> [4]. The currently accepted value due to Cohen is 13.2 °C...

The factors affecting the initiation of the change at a temperature below equilibrium are many: most investigators have found it necessary to cool white tin strongly; inoculation with grey tin in the presence of an electrolyte such as aqueous solution of pink-salt hastens initiation. Thus Murphy <outbind://181/#_ftn5> [5] cooled his specimens to -78°C in the absence of both electrolyte and the grey form, and found initiation required 10-11 days in cast unworked tin; Tamman and Dreyer <outbind://181/#_ftn6> [6] cooled their specimens to between 0°C and-20°C in the presence of both electrolyte and tin. The initiation required 10 days. Cohen and De Meester <outbind://181/#_ftn7> [7] worked their specimens at -80°C and kept them at -50°C, photographing them hourly, until the form appeared, but it is not clear from their paper how many hours initiation required. The constitution of the tin is
also of importance, most workers having used "Chempur" or tin of similar (99.98%) purity, but, for example, Murphy <outbind://181/#_ftn8> [8] found that 0.2% silver prevented initiation, even after cold working and in the presence of grey tin, for at least 6 weeks at -78°C.

The most important single factor in initiating the change is probably inoculation with ?-nuclei; indeed it is suggested that the difficulty found by one laboratory in repeating the later work on ?-tin by another laboratory is due to the latter having been "infected" with particles of grey tin. These may take so long to transform back to white tin at a room temperature so little above 13.2°C that they may vitiate subsequent experiments.

The clearest work on the rate of transformation of ? to ? after initiation has been done by Tamman and Dreyer <outbind://181/#_ftn9> [9] who used plates of Kahlbaum-tin and of Banka-tin, 0.6 mm thick. "Warts" of grey tin (due to the 25% greater volume of ?-tin compared with ?-tin) were produced by inoculation under the above-mentioned conditions, and the diameters of six selected "warts" were measured in a given direction every 20 hours at a temperature of -10°C ± 2°. They ascertained that the surface velocity of growth was independent of the thickness of the plate. This velocity was greater than the rate of penetration, which was of the order of 0.2 mm in several days, and 1.0 mm in several months. Table II... summarizes these results... A curve derived from the data contained in the accompanying Table II... indicates a maximum rate of transformation at about -30°C.

[Table II gives the velocity (in mm/10 hrs) at the following temperatures: 10, 8, 5, 0, -5, -10, -20, -30, -40, and -50°C. The corresponding velocities (in mm/hr) are 0.25, 0.3, 0.4, 0.9, 1.3, 1.95, 3.25, 4.05, 2.5, and 0.15. These are in the presence of "pink salt" (see above). Values without pink salt are also given: -10°C (1.3) and -20°C (1.8).]


  _____  

 <outbind://181/#_ftnref1> [1] E. Cohen and J. Olie in Zeitschrift für physikalische Chemie, LXXI (1910), p. 385.

 <outbind://181/#_ftnref2> [2] E. Cohen in the Transactions of the Faraday Society, VII (1911), p. 126.

 <outbind://181/#_ftnref3> [3] E. Cohen and K.D. Dekker in Zeitschrift für physicalische Chemie, CXXVII (1927), pp. 178-82. Abstracted in the Journal of the Institute of Metals, XXXVIII (1927), p. 383.

 <outbind://181/#_ftnref4> [4] E. Cohen quoted in G. Tamman and K.L. Dreyer, Zeitschrift für anorganische und Allgemeine Chemie, CIC (1931), pp. 97-108.

 <outbind://181/#_ftnref5> [5] A.J. Murphy in the Journal of the Institute of Metals, XXXV (1926), p. 118.

 <outbind://181/#_ftnref6> [6] G. Tamman and K.L. Dreyer, op. cit.

 <outbind://181/#_ftnref7> [7] E. Cohen and W.A.T. Cohen de Meester in Verslag Koninklijke Nederlandsche Akademie von Wetenschappen; Amseterdam XC (1938), p. 5; op.cit. XCI (1938), p. 9; op. cit. XCI (1938), p. 8. (Work done in Van't Hoff Laboratory, Utrecht.)

 <outbind://181/#_ftnref8> [8] op. cit.

 <outbind://181/#_ftnref9> [9] op. cit.


-------------------------------------------------------------------------------Leadfee Mail List provided as a service by IPC using LISTSERV 1.8d
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Leadfree
To temporarily stop delivery of Leadree for vacation breaks send: SET Leadfree NOMAIL
Search previous postings at: http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315
-------------------------------------------------------------------------------