LAMINATIONS
Lamination errors occur on copper alloy cents, but not on copper plated zinc cents. They occur because of a planchet defect caused by impurities or internal stresses in the alloy which causes metal to separate along horizontal planes of weakness. Lamination flaws occur when impurities or foreign materials or gas become trapped within the planchet metals as they are being formed or are the result of an inadequately mixed alloy. (1) Copper alloy cents are 95% copper and 5% tin and zinc (until 1962 when the cent's tin content, which was quite small, was removed). Thus the amount of the minority metal was sufficient to create separation along horizontal planes if the alloy was not mixed properly.
Copper plated Zinc Cents are composed of Zinc Alloy 190 electroplated with 8 microns of copper. Zinc Alloy 190 contains 0.005% max Lead; 0.010% max Iron; 0.005% max Cadmium; 0.7% to 0.9% Copper; and 99.08% Zinc. I think that the supply of minor metals is insufficient to be reflected as an inadequate alloy mix capable of producing a lamination. In addition, Zinc strip - as it is being processed for rolling into coils - has lubrication applied to it which leads to improved surface finish, as well as distributing a corrosion-protective barrier on the strip. (2) This added protection serves to further prevent corrosion induced laminations from developing.
In addition the hardness of Zinc Cents is a bit less than the hardness of copper cents which also serves to prevent lamination in Zinc Cents. The Hardness of copper cents = ~76 on the Rockwell 15-T scale and a range of "Hardness between 62 and 72 Rockwell 15T are [sic] considered nominal (standard) for RTS planchets [note: planchets for all denominations] at the United States Mint." (RTS= Ready to Strike). (3) I have had hardness tests run with these results: "The actual 15T Rockwell Hardness on this 1976D was measured at 75.2" and "The actual value on this 2000-D was measured at 59.1." (4)
I think that the primary reason, however, we do not see lamination on Zinc Cents is that the Interfacial Free Energy for Zinc is significantly less than for Copper, which would explain why Copper after being rolled is more subject to delamination than is Zinc.
"The surface energy defined as the surface excess free energy per unit area of a particular crystal facet is one of the basic quantities in surface physics. It determines the equilibrium shape of mezoscopic crystals, it plays an important role in faceting, roughening, and crystal growth phenomena, and may be used to estimate surface segregation in binary alloys." (5)
This can also be seen when examining the Metallic Crystalline Structure. The Metallic Crystalline Structure of Copper is face centered cubic (FCC) structure and The Metallic Crystalline Structure of Zinc is hexagonal close packed (HCP) structure. Both have a packing factor of 0.74, consist of closely packed planes of atoms, and have a coordination number of 12. The difference between the FCC and HCP is the stacking sequence. The HCP layers cycle among the two equivalent shifted positions whereas the FCC layers cycle between three positions. Cubic lattice structures allow slippage to occur more easily than non-cubic lattices, so HCP metals are not as ductile as the FCC metals. The impact on the slip system (slip planes and slip direction) of Copper is to increase the likelihood of consequent deformation mechanisms and delamination. (6)
A lamination can occur on clad coins, but such occurrence is rare. It can be recognized because it occurs in the clad layer itself and does not expose the copper core.
Footnotes:
(1)
http://www.error-ref.com/(2) Jarden Zinc - Technical Brief: Lubrication of Solid Zinc Strip
(3) ALTERNATIVE METALS STUDY Contract Number: TM-HQ-11-C-0049 FINAL REPORT August 31, 2012 by Concurrent Technologies Corporation, Submitted to: United States Mint, Page 42.
(4)
https://conecaonline.org/rockwell-h...jnIRxzZ0gh2s(5) Surface Science 411 (1998) 186-202: The surface energy of metals by L. Vitos, A.V. Ruban, H.L. Skriver, J. Kolla´r
---Center for Atomic-scale Materials Physics and Department of Physics, Technical University of Denmark, DK-2800 Lyngby, Denmark, Research Institute for Solid State Physics, H-1525 Budapest, P.O. Box 49, Hungary
Received 3 November 1997; accepted for publication 2 May 1998
(6) "Primary Metallic Crystalline Structures - Similarities and Difference Between the FCC and HCP Structure"
https://www.nde-ed.org/EducationRes.../fcc_hcp.htm
Posted 01/12/2019 10:25 am
Does it have a different name?
